The Bioavailability, Transport, and Bioactivity of Dietary Flavonoids: a Review from a Historical Perspective Gary Williamson, Colin D

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The Bioavailability, Transport, and Bioactivity of Dietary Flavonoids: A Review from a Historical Perspective Gary Williamson, Colin D. Kay, and Alan Crozier

Abstract: Flavonoids are plant-derived dietary components with a substantial impact on human health. Research has expanded massively since it began in the 1930s, and the complex pathways involved in bioavailability of flavonoids in the human body are now well understood. In recent years, it has been appreciated that the gut microbiome plays a major role in flavonoid action, but much progress still needs to be made in this area. Since the first publications on the health effects of flavonoids, their action is understood to protect against various stresses, but the mechanism of action has evolved from the now debunked simple direct antioxidant hypothesis into an understanding of the complex effects on molecular targets and enzymes in specific cell types. This review traces the development of the field over the past 8 decades, and indicates the current state of the art, and how it was reached. Future recommendations based on this historical analysis are (a) to focus on key areas of flavonoid action, (b) to perform human intervention studies focusing on bioavailability and protective effects, and (c) to carry out cellular in vitro experiments using appropriate cells together with the chemical form of the flavonoid found at the site of action; this could be the native form of compounds found in the food for studies on digestion and the intestine, the conjugated metabolites found in the blood after absorption in the small intestine for studies on cells, or the chemical forms found in the blood and tissues after catabolism by the gut microbiota. Keywords: bioactivity, bioavailability, dietary flavonoids, metabolism, transport

Introduction HPLC with absorbance detection at 370 nm (Hertog, Hollman, Although research on flavonoids spans over 80 yr, for many nu- & Venema, 1992). Two further papers followed in which the pro- tritionists the origins of their absorption, disposition, metabolism, cedure was used to quantify the flavonol and flavone contents of and excretion, commonly referred to as bioavailability, and their 28 vegetables and 9 fruits (Hertog, Hollman, & Katan, 1992) and protective role in the diet, began in the 1990s in the Nether- teas, wines, and fruit juices (Hertog, Hollman, & van de Putte, lands. At that time, routine HPLC-based quantitative analysis of 1993). Shortly thereafter, an assessment based on dietary history, flavonoid glycosides in fruits, vegetables, and their derived prod- of quercetin, kaempferol, myricetin, luteolin, and apigenin con- ucts was not straight-forward because of the number of com- sumption, principally from onions, tea, and apples, over a 5-yr pounds involved which were conjugated to varying degrees with period by 805 men aged 65 to 84 yr, associated flavonol and different sugars. A further complication was the limited num- flavone intake with reduced mortality from coronary heart disease ber of reference compounds that were available from commercial (CHD; Hertog, Feskens, Hollman, Katan, & Kromhout, 1993). sources. Initially, this was overcome by the use of an acid hy- OH OCH3 drolysis procedure, developed originally by Harborne (1965), that OH OH OH converted flavonol and flavone glycosides to their aglycones, such HO O HO O HO O as quercetin 1, kaempferol 2, isorhamnetin 3, myricetin 4, luteolin OH OH OH 5, and apigenin 6. Reference compounds were readily available for HO O HO O HO O the released aglycones, which were quantified using reverse-phase Quercetin 1 Kaempferol 2 Isorhamnetin 3

OH OH OH OH OH HO O HO O HO O CRF3-2018-0017 Submitted 1/28/2018, Accepted 3/14/2018. Author OH Williamson is with School of Food Science, Univ. of Leeds, Leeds LS2 9JT, U.K. OH Author Kay is with Food Bioprocessing and Nutrition Sciences, Plants for Human HO O HO O HO O Health Inst., North Carolina State Univ., North Carolina Research Campus, Kan- Myricetin 4 Luteolin 5 Apigenin 6 napolis, NC 28081, U.S.A. Author Crozier is with Dept. of Nutrition, Univ. of California, Davis, CA 95616, U.S.A. Author Crozier is also with School of In the ensuing years there was a growing interest in the pro- Medicine, Dentistry and Nursing, Univ. Glasgow, Glasgow, G12 8QQ, UK. Direct inquiries to author Crozier (E-mail: [email protected]). tective effects of ﬂavonoids and this review will focus on major developments with the principal dietary ﬂavonoids, namely

C 2018 Institute of Food Technologists® r 1054 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 doi: 10.1111/1541-4337.12351 Dietary flavonoids: a historical review . . . anthocyanins, flavan-3-ols, flavonols, and flavanones. There has The identity and concentration of metabolites that pass through been only limited research on flavones which are minor dietary the circulation provide important information for studies with components, and isoflavones have also been excluded as they have ex vivo and in vitro test systems designed to elucidate the modes their own unique history warranting separate review. of action underlying the protective effects of dietary flavonoids. A key to the advancement of research has been obtaining infor- It is these metabolites to which cells within the body are likely mation on the metabolism of flavonoids within the body following exposed, rather than their parent compounds that occur in fruits, ingestion and, in particular, the identification and quantification vegetables, and their derived products. of the phase II metabolites that enter the circulatory system from the upper gastrointestinal (GI) tract and the lower bowel. The Transport of flavonoids around the body substantial progress that has been made in this area can be linked Biological membranes surround mammalian cells and consist to the increasing availability of synthesized reference compounds of a lipid bilayer, through which hydrophilic molecules cannot (see Barron, Smarrito-Menozz, Fumeaux, & Viton, 2012), an pass. Cells control passage through this physical barrier using increasing number of which are now available from commercial transporters, which are proteins embedded in the membrane with sources, together with the use of HPLC/UPLC linked to an ion parts of the protein often exposed on both sides and protruding trap mass spectrometer, instruments which became available at rel- from it. As an example, glucose, which is a highly water-soluble atively affordable prices in the early 2000s. This facilitated identi- sugar, cannot pass through lipid bilayers, and requires various fication/partial identification, and quantification of trace amounts transporters to allow entry into the cell. Transporters can be of metabolites in biological samples. More recent advances in this considered as similar to enzymes, except they catalyze the spatial area can also be linked to the enhanced selectivity and sensitivity translocation of molecules rather than chemical transformation. of orbitrap and triple quadrupole mass spectrometers (Hird, Lau, The GLUT family of glucose transporters acts on the basis of Schuhmacher, & Krska, 2014). facilitated diffusion, and does not require energy (Augustin, 2010). Other types of transporters require either ATP hydrolysis directly, as is the case with the ABC transporters (Degorter, Xia, Interaction of Flavonoids with the Gastrointestinal Yang, & Kim, 2012), or indirectly, such as SGLT1 (Wright, Loo, Tract & Hirayama, 2011), and some require another molecule which After ingestion of food or a beverage, flavonoids in the ingested is transported in the same or opposing direction (Meredith, matrix must pass from the gut lumen into the circulatory system in & Christian, 2008). There are three organic anion transporter order to be absorbed. Since in planta almost all flavonoids are in the (OAT) families: the OAT family (SLC22A), the organic anion- form of glycosides, the attached sugar must be removed following transporting peptide (OATP) family (SLC21A), and the multidrug consumption before absorption can take place. This was a matter resistance-associated protein (MRP) family (ABC transporters), of some controversy before the discovery that flavonoid glucosides which carry out transepithelial transport of organic anions in the are hydrolyzed by lactase phlorizin hydrolase (LPH) in the brush- kidneys, liver, and brain. These transporters are responsible for border of the small intestine epithelial cells, thereby removing the most of the absorption and distribution of flavonoids around the attached sugar and releasing the aglycone. LPH exhibits broad body as well as their excretion in urine. An important part of substrate specificity for flavonoid-O-glycosides and the released bioavailability research on flavonoids are studies on the specificity aglycone may then enter the epithelial cells by passive diffusion as of these transporters that control the movement of flavonoids and a result of its increased lipophilicity and its proximity to the cellular their metabolites across the wall of the GI tract into the circulatory membrane (Day et al., 2000b). An alternative means of hydrolysis system, in and out of tissues and organs, and their excretion. is a cytosolic β-glucosidase (CBG) within the epithelial cells. In In earlier studies on flavonoid bioavailability, it was assumed order for CBG-mediated hydrolysis to occur, the polar glycosides that the ingested compound would be absorbed passively and ap- must be transported into the epithelial cells, possibly with the pear chemically unchanged in blood or urine, in the same way involvement of the active sodium-dependent glucose transporter as many drugs (Gugler & Dengler, 1973; Gugler, Leschik, & (SGLT1; Gee et al., 2000). Dengler, 1975). However, the ability of flavonoids to cross bi- Prior to passage into the blood stream the aglycones un- ological membranes depends on their size, hydrophobicity, and dergo metabolism forming sulfate, glucuronide and/or methy- any intracellular reactions that promote diffusion by maintaining a lated metabolites through the respective action of sulfotransferases, concentration gradient (Camenisch, Alsenz, van de Waterbeemd, uridine-5-diphosphate glucuronosyltransferases, and catechol-O- & Folkers, 1998). Once conjugated by phase II enzymes, the methyltransferases. There is also efflux of at least some of the ability of the flavonoid conjugates to cross membranes is greatly metabolites back into the lumen of the small intestine by specific reduced, and specific transporters are required (Williamson et al., transporters (see “Cellular Efflux of Flavonoids by ABC Trans- 2007). In addition, when using cultured cells as a model to assess porters”). Once in the bloodstream, metabolites can be subjected flavonoid actions, it is relevant that tumor and cultured cells often to further phase II metabolism with conversions occurring in the have higher levels of ABC transporters that rapidly remove conju- liver, prior to urinary excretion. Flavonoids not absorbed in the gates from the cell, limiting the action of flavonoids compared to small intestine pass into the distal GI tract where they are sub- the tissue in vivo. jected to the action of the intestinal microbiota which cleave conjugating moieties and the resultant aglycones are subject to ring Cellular efflux of flavonoids by ABC transporters fission, leading to the production of phenolic acids and aromatic One of the first papers to examine the interaction of flavonoids compounds. These too can be absorbed, subjected to phase II with ABC transporters was for the interaction of the flavonols, metabolism, and ultimately excreted in urine in substantial quan- quercetin 1, kaempferol 2, and galangin 7 with P-glycoprotein tities that, in most instances, are well in excess of metabolites that (ABCB1, MDR1; Critchfield, Welsh, Phang, & Yeh, 1994; Scam- enter the circulatory system via the small intestine without prior bia et al., 1994) followed by genistein 8 (Castro, & Altenberg, microbial catabolism. 1997) and grapefruit juice (Takanaga, Ohnishi, Matsuo, & Sawada,

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1055 Dietary ﬂavonoids: a historical review . . .

Figure 1–Illustration of the transporters and metabolizing enzymes involved in polyphenol metabolism throughout the body. (A) In the gut lumen, flavonoid glucosides are deconjugated by lactase phloridzin hydrolase (LPH) in the brush border of the enterocyte. The flavonoid aglycone can then enter the cell, and be conjugated by uridine diphosphate glucuronosyl transferase (UGT) or sulfotransferase (SULT), and the conjugates exported either back to the lumen or into the blood by various transporters. (B) Conjugated flavonoid metabolites in the blood can be imported into hepatocytes via various uptake transporters, and then returned to the circulatory system, alternatively they can be deconjugated intracellularly by enzymes such as β-glucuronidase (glcAase). Certain conjugates may be exported into the bile although this is probably a minor pathway for most metabolites. Intracellular deconjugation is enhanced under inflammatory conditions. (C) Ultimately, flavonoid conjugates can be excreted by the kidney, involving uptake into the proximal tubular cells by transporters and excretion into the urine. The presence of OAT4 on the basolateral side implies that conjugates could be reabsorbed into the kidney after excretion, but this has not been proven.

1998). Soon after, Walle, French, Walgren, and Walle (1999) HO HO O demonstrated that genistein-7-O-glucoside 9 could interact with O the ABC transporter MRP2 (ABCC2). Prenylation of the flavone OH HO O HO O OH chrysin 10 increased its interaction with ABCB1 (Comte et al., Galangin 7 Genistein 8 2001), and the structural requirements for binding of other flavonoids have been reported (Di Pietro et al., 2002). It is now HO clear that many flavonoid conjugates interact with ABC trans- HO O O O HO O HO porters, and that these transporters are crucial for determining their OH distribution around the body. For example, ABCC2 is situated on HO O OH HO O the brush border of small intestine enterocytes, and effluxes some Genistein-7-O-glucoside 9 Chrysin 10 conjugates back towards the gut lumen and, in effect, these compounds per se are no longer bioavailable to the body (Brand, van Cellular uptake of flavonoids by OATs der Wel, Williamson, van Bladeren, & Rietjens, 2007; Williamson One of the first papers to show that flavonoid could interact et al., 2007). ABCG2 also plays an important role in the efflux of with intake transporters reported that the (poly)phenol ellagic flavonoid conjugates from cells (Zhang, Yang, & Morris, 2004). acid 11 could inhibit OAT1 (Whitley, Sweet, & Walle, 2005). The specific roles of ABC transporters in flavonoid bioavailability In addition, genistein 8, but not genistein-7-O-glucoside 9 and are shown in Figure 1. (–)-epigallocatechin-3-O-gallate 12 interacted with the OATP

r 1056 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary flavonoids: a historical review . . . family of transporters (OATP1B1). Quercetin-3-O-rutinoside flavonoids, known to pass from the small to the large intestine, are 13 (rutin) appeared to stimulate uptake of an OATP1B1 sub- incubated under anaerobic conditions with feces and fecal bacteria. strate, whereas quercetin 1 had no effect (Wang, Wolkoff, & Morris, 2005). This was followed by further data showing that Flavonols the flavonoids morin 14 and silybin 15, but not quercetin 1, Pioneering research on flavonols by Hollman and colleagues naringenin 16, and narigenin-7-O-rutinoside 17 (narirutin) in the Netherlands produced a series of papers on the bioavailability of quercetin glycosides, in the form of quercetin-3,4- interacted with human OAT1, but only weakly with OAT3 (Hong, Seo, Lim, & Han, 2007). The first study to examine O-diglucoside 18 and quercetin-4 -O-glucoside 19, which occur in especially high concentrations in onions, along with small flavonoid conjugates such as sulfates and glucuronides, as found in the blood, was conducted by Wong et al. (2011b) who showed amounts of other flavonols such as isorhamnetin-4 -O-glucoside that flavonoid metabolites as present in plasma could be taken up 20.Quercetin1 itself enters the circulatory system, at best, in into cells via OAT transporters, and that the transporters were only trace amounts, and instead appears predominantly as phase quite specific for the class of flavonoid, its conjugated group and II glucuronide, sulfate, and methyl metabolites (Crozier, Del Rio, conjugation position. The specific roles of OAT transporters in & Clifford, 2010). At the time of the initial bioavailability inves- flavonoid bioavailability are shown in Figure 1. tigations, standards of quercetin metabolites were unavailable and so samples of biofluids were subjected to the acid hydrolysis pro- OH cedures developed by Hertog et al. (1992), in order to release the OH HO O quercetin aglycone. The levels found, compared to the amounts O OH found in most fruits and vegetables were extremely low, so to facil- O OH O O HO itate detection HPLC was used with post-column chelation with HO OH aluminum. This produced fluorescent derivatives which could be HO O HO OH O OH detected in 300-fold lower quantities than absorbance detection (Hollman, van Trijp, & Buysman, 1996). Ellagic acid 11 ( )-Epigallocatechin-3-O-gallate 12 OH OH OH OH HO OH HO OH OH O O O O OH OH OH HO O HO O HO O OH HO OH OH O O HO OH HO O HO O HO O O OH O HO O O 18 O 19 O HO O Quercetin-3,4'- -diglucoside Quercetin-4'- -glucoside HO OH HO HO OH OH HO O OCH Quercetin-3-O-rutinoside 13 Morin 14 3 OH HO OH O O HO O OH

O CH2OH OH OH HO O HO O O HO O Isorhamnetin-4'-O-glucoside 20 OH OH O HO OCH3 HO O The first study using this method of analysis involved feeding Silybin 15 Naringenin 16 fried onions, quercetin-3-O-rutinoside 13, and quercetin 1 to volunteers with an ileostomy (Hollman, de Vries, van Leeuwen, O OH O Mengelers, & Katan, 1995). In vitro incubation with gastrointesti- HO O HO O O HO HO nal fluids resulted in minimal breakdown. Absorption of quercetin, OH OH HO O defined by Hollman et al. (1995) as oral intake minus excretion in ileal fluid, was 52% for the onion quercetin glucosides, 17% for Naringenin-7-O-rutinoside 17 quercetin-3-O-rutinoside, and 24% for quercetin aglycone. It was concluded that humans absorb substantial amounts of quercetin and that absorption is enhanced by conjugation with glucose, but Bioavailability not the disaccharide rutinose. Attention will focus on key aspects of flavonoid bioavailability A further paper reported a study in which volunteers with a studies with humans. Investigations with animals can be helpful, functioning colon ingested fried onions containing 212 μmol but because of differences in endogenous metabolism and gut of quercetin glucosides after which plasma was collected. HPLC microflora, they can produce data that are difficult to apply to analysis of the acid hydrolyzed plasma revealed the presence of human studies (see Borges, van der Hooft, & Crozier, 2016). quercetin with a peak plasma concentration (Cmax) of 649 nmol/L Human studies are the gold standard and typically involve acute that was attained 2.9 hr (Tmax) after ingestion (Hollman et al., ingestion of food or a beverage by volunteers who have been on 1996). A number of other studies carried out over the intervening a low-(poly) phenol diet for approximately 2 days. Investigations years established that the sugar moiety was the major deter- have utilized individuals with an intact colon and ileostomists who mining factor influencing the absorption of flavonol glycosides. have had their colon removed surgically, supported by analysis of Conjugated quercetin appearing in the plasma after intake of plasma, urine and, ileal effluent. Studies with ileostomists have quercetin monoglucosides had a Cmax approximately 10-fold helped distinguish transformations occurring in the upper GI tract higher than after ingestion of quercetin-3-O-rutinoside (Hollman from those associated within the colon, and in this regard are et al., 1999), whereas the Tmax after quercetin-3-O-rutinoside especially useful when parallel studies are carried out in which ingestion was approximately 6 to 7 hr compared to ࣘ1hrfor

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1057 Dietary flavonoids: a historical review . . . the monoglucosides (Erlund et al., 2000; Graefe et al., 2001; Moon, Nakata, Oshima, Inakuma, & Terao, 2000; Olthof, A Hollman, Vree, & Katan, 2000). These findings suggested that the metabolites of quercetin monoglucosides are absorbed in the proximal GI tract, although those derived from the rutinoside are absorbed in the colon. At this juncture the identities of the quercetin conjugates in plasma were not known, although there was one report based on HPLC with diode array detection of the presence of 400 to 600 nmol/L concentrations of quercetin-3-O-rutinoside and several quercetin glycosides in the circulatory system of two non- supplemented volunteers (Paganga & Rice-Evans, 1997). In addition, Mauri et al. (1999) used HPLC-MS to identify and quantify seemingly high amounts of quercetin-3-O-rutinoside (up to 300 nmol/L) in plasma following the daily ingestion of tomato B puree for a period of 14 days. Neither of these early reports has been supported by subsequent investigations. The results of a more detailed feeding study were reported by Aziz, Edwards, Lean, and Crozier (1998) in which, following the ingestion of lightly fried onions, plasma, and urine samples were collected at a range of time points over a 24-hr period. The samples were analyzed, both before and after acid hydrolysis, by HPLC using the post-column chelation procedure of Hollman et al. (1996). Analysis of hydrolyzed samples showed a plasma Cmax of conjugated quercetin of 1.3 μmol/L and a Tmax of 1.9 hr, although 0 to 24 hr urinary excretion was equivalent to 0.8% of the ingestion quercetin glycosides. Analysis of samples prior to hydrolysis identified and quantified fluorescent HPLC peaks which co-chromatographed with quercetin-4 -O-glucoside Figure 2–Concentration of (A) quercetin-3-sulfate and and isorhamnetin-4-O-glucoside. However, subsequent research quercetin-3-O-glucuronide (B) isorhamnetin-3-O-glucuronide, a O O revealed these were misidentifications and that the compounds quercetin- -glucuronide and a quercetin- -diglucuronide in the plasma of volunteers collected 0 to 6 hr after the ingestion of lightly fried onions involved were almost certainly glucuronides for which reference containing 275 μmol of flavonol-O-glucosides. Data expressed in nmol/L compounds were not available at the time. ± standard error (n = 6). Note no quercetin metabolites were present in Using a mixture of undefined quercetin glucuronides as refer- plasma in detectable amounts 24 hr after supplementation (after Mullen ence compounds both Sesink, O’Leary, and Hollman (2001) and et al., 2006). Wittig, Herderich, Graefe, and Veit (2001) provided evidence for the accumulation of five quercetin-O-glucuronides in plasma after the ingestion of 270 g of lightly fried onions by four male the ingestion of quercetin-O-glucosides. The key breakthrough, and two female volunteers. The onion supplement containing however, came with the study of Day et al. (2001) which, with the quercetin-3,4-O-diglucoside 18 (107 μmol), quercetin-4-O- use of fully characterized quercetin and isorhamnetin metabolites, μ μ glucoside 19 (143 mol), and 275 mol of isorhamnetin-4 - identified quercetin-3-O-glucuronide 21, quercetin-3 -sulfate 22, O-glucoside 20 (11) μmol) which accounted for 95% of the and isorhamnetin-3-O-glucuronide 23 in plasma collected 1.5 hr 275 μmol flavonol intake. The plasma profiles of the five main after the ingestion of an onion supplement. metabolites, quercetin-3-O-glucuronide, quercetin-3-sulfate, and

- isorhamnetin-3-O-glucuronide along with two partially identified OH OSO3 OH OH metabolites, a quercetin-O-glucuronide-sulfate and a quercetin- 1 HO O HO O O-diglucuronide are illustrated in Figure 2. Table 1 contains de- OH HO OH tails of a pharmacokinetic analysis with information on Cmax, Tmax, O O OH O COOH HO O HO and the apparent elimination half-life (AT1/2). It should be noted that true T values can only be determined by intravenous dos- Quercetin-3-O-glucuronide 21 Quercetin-3'-sulphate 22 1/2 ing of metabolites. Estimates based on elimination after oral intake OH overestimate the true T1/2 because the metabolite is still entering HO OH O OCH COOH the circulatory systems when the elimination is being estimated. 3 O OH OH HO O HO O 1 OH The availability of reference compounds enables specific metabolites to be HO OH 2 3 O O OH identified by HPLC-MS and MS . In the absence of standards it is not possi- HO O COOH HO O ble to distinguish between isomers and to ascertain the position of conjugating groups on the flavonoid skeleton. Thus, the quercetin-O-diglucuronide and Isorhamnetin-3-O-glucuronide 23 Quercetin-3'-O-glucuronide 24 the quercetin-O-glucuronide-sulfate, along with other metabolites detected Later, having been given access to these reference com- in the onion study, could only be partially identified on the basis of their pounds along with quercetin-3-O-glucuronide 24, Mullen, Ed- MS fragmentation pattern. Nonetheless, the use of MS in this way represents 2 a useful HPLC detection system, as with low ng limits of detection it pro- wards, and Crozier (2006) used HPLC-MS to analyze flavonol vides structural information on analytes of interest that is not obtained with metabolites appearing in plasma and urine 0 to 24 hr after absorbance, fluorescence, or electrochemical detectors.

r 1058 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

OH OH HO OH OCH3 O O OH OH HO O HO O OH OH HO OH HO O O O HO O OH Quercetin-4'-O-glucoside Isorhamnetin-3-O-glucoside OH HO OH O COOH - OH OSO3 O OCH3 OH OH OH OH HO O HO O HO O HO O OH OH OH HO O HO O HO O OH HO O Quercetin-3'-O-glucuronide Quercetin Quercetin-3'-sulphate Isorhamnetin

OH OCH3 OCH3 OH OH OH O HO OH O COOH HO O HO O HO O OH OH HO OH HO OH O O O O OH HO O COOH HO O COOH HO O

Quercetin-3-O-glucuronide Isorhamnetin-3-O-glucuronide Isorhamnetin-4'-O-glucuronide

Figure 3–Potential routes for the metabolism of quercetin- and isorhamnetin-O-glucosides in in the proximal gastrointestinal tract. Fine curved red arrow indicates position of sugar cleavage (after Mullen et al., 2006).

Table 1–Pharmacokinetic analysis of quercetin metabolites detected in Table 2–Pharmacokinetic analysis of quercetin metabolites in the plasma plasma 0 to 24 hr after the consumption of 270 g of lightly fried onions of volunteers after the consumption of 250 mL of tomato juice containing containing 275 μmol of flavonol glucosides by six volunteers (after Mullen 176 μmol of quercetin-3-O-rutinoside (after Jaganath et al., 2006). et al., 2006). Cmax a T b AT c Cmax Metabolites (nmol/L) max (h) 1/2 (h) a T b AT c Metabolites (nmol/L) max (h) 1/2 (h) Quercetin-3-O-glucuronide 12 ± 24.7± 0.3 1.67 Quercetin-3’-sulfate 665 ± 82 0.8 ± 0.1 1.7 Isorhamnetin-3-O- 4.3 ± 1.5 5.4 ± 0.2 1.66 Quercetin-3-O-glucuronide 351 ± 27 0.6 ± 0.1 2.3 glucuronide O ± ± Isorhamnetin-3- - 112 18 0.6 0.1 5.3 Data presented as mean values ± standard error (n = 6). a glucuronide Cmax, post-ingestion peak plasma concentration. b O ± ± Tmax, time to reach Cmax. Quercetin-di- -glucuronide 62 12 0.8 0.1 1.8 cAT Quercetin-O-glucuronide- 123 ± 26 2.5 ± 0.2 4.5 1/2, apparent elimination half-life. sulfate Data expressed as mean values ± standard error (n = 6) a Cmax, post-ingestion peak plasma concentration. the plasma metabolite profile, it is evident that following the b Tmax, time to reach Cmax. c release of the aglycone, quercetin is subjected to sulfation, glu- AT1/2, apparent elimination half-life. curonidation, and possibly methylation. Arguably, the short Tmax times of quercetin-3-O-glucuronide, quercetin-3-sulfate, and the The two major metabolites, quercetin-3 -sulfate (Cmax – quercetin-O-diglucuronide are indicative of sulfation and glu- 665 nmol/L) and quercetin-3-O-glucuronide (Cmax – 351 curonidation taking place in enterocytes prior to passage of the nmol/L) appeared in plasma within 30 min of onion intake, both metabolites into the circulatory system. The longer plasma Tmax had Tmax values of under 1 hr and AT1/2 values of 1.7 and 2.3 of isorhamnetin-3-O-glucuronide, arguably, could reflect post- hr, respectively (Figure 2, Table 1; Mullen et al., 2006). The absorption 3-O-methylation of quercetin-3-O-glucuronide in quercetin-O-diglucuronide had a lower Cmax and similar Tmax the liver. Potential routes for the formation of the fully identi- and AT1/2 values. The pharmacokinetic profiles of isorhamnetin- fied metabolites are illustrated in Figure 3. 3-O-glucuronide and the quercetin-O-glucuronide-sulfate were Jaganath, Mullen, Lean, Edwards, and Crozier (2006) car- somewhat different in that both had a much longer AT1/2,whereas ried out a parallel feeding study in which volunteers ingested the sulfated glucuronide also had a much delayed ATmax (Table 1). 250 mL tomato juice containing 176 μmol of the rhamnose- However, the total contribution of these two compounds to the glucose conjugate, quercetin-3-O-rutinoside. In this instance, overall absorption profile was minimal, having no effect on the only two metabolites were detected in plasma, quercetin-3-O- overall Tmax and only extending the AT1/2 to 2.6 hr. This AT1/2 glucuronide and isorhamnetin-3-O-glucuronide (Figure 4). They is much shorter than values obtained in earlier flavonol absorption were present in approximately 25-fold lower quantities than in the studies which is almost certainly a consequence of the enhanced onion study with respective Cmax values of 12 and 4.3 nmol/L. 2 accuracy of analytical data obtained with HPLC-MS . The Tmax times were extended to approximately 5 h (Table 2), The data obtained by Mullen et al. (2006) indicated ab- indicating absorption in the lower bowel rather than the small in- sorption in the proximal part of the small intestine. How- testine. A total of nine methylated and glucuronidated quercetin ever, it provided no information on the mechanisms involved metabolites were detected in urine, but some volunteers excreted or the efficiency with which quercetin-3,4-O-diglucoside 18 only 3 to 4 metabolites. The overall 0 to 24 hr urinary excre- and quercetin-4-O-glucoside 19 are hydrolyzed and the resul- tion of metabolites ranged from 0.02% to 2.8% of quercetin-3- tant aglycone transported into the enterocyte. On the basis of O-rutinoside intake, which is probably a reflection of variations

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knowledge of the bioavailability of other dietary flavonoids including increasing information on microbiota-mediated events occurring in the GI tract. This recent research with other flavonoids suggests that the quercetin degradation pathways illustrated in Figure 5 are almost certainly an over-simplification of the potential conversions involved.

Flavan-3-ols Early research with (+)-catechin Early research into the bioavailability of the flavan-3-ol (+)- catechin 28 was reported in a series of papers originating from the Univ. of Singapore and the Univ. of Birmingham in the UK (see Das, 1971, 1974; Griffith, 1964; Hackett, & Griffith, 1981, Figure 4–Concentration of quercetin-3-O-glucuronide and 1981, 1983; Hacket, Griffith, Broillet, & Wermeille, 1983; Hack- isorhamnetin-3-O-glucuronide in plasma of volunteers collected 0 to 8 hr ett, Griffith, & Wermeille, 1985; Hackett, Shaw, & Griffith, 1982; μ after the ingestion of tomato juice containing 176 mol of Shaw,Hackett, & Griffith, 1982). Much of this research was funded quercetin-3-O-rutinoside. Data expressed in nmol/L ± standard error (n = 6). Note neither quercetin metabolite was present in plasma in by the Swiss pharmaceutical company Zyma SA, and it was not detectable amounts 24 hr after supplementation (after Jaganath, Mullen, related to nutrition but to the possible use of high doses of (+)- Lean, Edwards, and Crozier, 2006). catechin as a drug to protect against hepatitis. Despite the analyses being based mainly on paper chromatography and reagent color reactions, numerous (+)-catechin-derived products were identi- in the colonic microflora of the individual volunteers (Jaganath, fied. These identifications, as summarized by Das (1974), are pre- Mullen, Edwards, & Crozier, 2006). sented in Table 3. It would be more than 20 yr later before these Confirmation of large intestine absorption was obtained us- microbial-derived catabolites were identified in nutrition-based ing ileostomists in a study by Jaganath, Mullen, Lean, Edwards, bioavailability studies. and Crozier (2009). Unlike the volunteers with a functioning OH colon, neither plasma nor urinary metabolites were detected, OH OH and ileal fluid, collected after tomato juice consumption, con- HO O O tained 86% of the ingested quercetin-3-O-rutinoside. Urine col- OH lected from the ileostomy volunteers did not contain quercetin OH O metabolites and also lacked the phenolic acid catabolites 3,4- (+)-Catechin 28 5-(3'-Hydroxyphenyl)- -valerolactone 29 dihydroxyphenylacetic acid 25,3-hydroxyphenylacetic acid 26, OH OCH3 and 3 -methoxy-4 -hydroxyphenylacetic acid 27. OH OH O O O OH O OH OH 5-(3',4'-Dihydroxyphenyl)- -valerolactone 30 5-(3'-Methoxy-4'-hydroxyphenyl)- -valerolactone 31 HOOC HOOC

3',4'-Dihydroxyphenylacetic acid 25 4'-Hydroxyphenylacetic acid 26 OH OH H HOOC N HOOC OCH3 O OH 3-(3'-Hydroxyphenyl)propionic acid 32 3'-Hydroxyhippuric acid 33 HOOC

3'-Methoxy-4'-hydroxyphenylacetic acid 27 OH OH OH These catabolites were present in the urine of the volunteers HOOC HOOC with a functioning colon in quantities corresponding to 22% 3-Hydroxybenzoic acid 34 3,4-Dihydroxybenzoic acid 35 of quercetin-3-O-rutinoside intake, having probably originated OH from colonic bacteria-mediated deglycosylation of the rutinoside, OCH3 OH and ring fission of the released aglycone followed by the con- HOOC versions illustrated in Figure 5. In vitro fecal incubations with HOOC OH quercetin-3-O-rutinoside and [4-14C]quercetin revealed other 3-Methoxy-4-hydroxybenzoic acid 36 3-(3'-Hydroxyphenyl)hydracrylic acid 37 potential conversions, as shown in Figure 5, with the formation of hydroxybenzoic acids. Although excreted in urine after (–)-Epicatechin ingestion of tomato juice containing quercetin-3-O-rutinoside, (–)-Epicatechin 38 itself enters the circulatory system, at best, in 3-methoxy-4-hydroxyphenylacetic acid was not a product of trace amounts and, like quercetin, appears predominantly as phase fecal-mediated quercetin degradation. This implies that its forma- II glucuronide, sulfate, and methyl metabolites (Crozier, 2013; tion involves mammalian enzymes with 3-methylation of 3,4- Crozier et al., 2010; Ottaviani et al., 2016). At the time of the dihydroxyphenylacetic acid 25 potentially taking place in colono- initial bioavailability investigations reference compounds of (−)- cytes and/or the liver. epicatechin metabolites were unavailable, so human studies on the Despite it being almost 10 years since these HPLC-MS- post-ingestion fate of cocoa-based products treated plasma and based studies on the bioavailability of onion- and tomato-derived urine samples with mollusc β-glucuronidase/sulfatase prior to the flavonols were reported, there have been few subsequent new de- analysis of the released (−)-epicatechin by reverse-phase HPLC, velopments. However, there have been substantial advances in our typically with fluorescence (Richelle, Tavazzi, Enslen, & Offord,

r 1060 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

OH OH HO O

O HO O O O HO O HO HO HO OH OH Quercetin-3-O-rutinoside

OH OH HO O OH HO O Quercetin

OCH3 OH OH OH OH HOOC HOOC HOOC

3'-Methoxy-4'-hydroxyphenylacetic acid 3',4'-Dihydroxyphenylacetic acid 4'-Hydroxyphenylacetic acid

OH OH OH HOOC HOOC 3,4-Dihydroxybenzoic acid 4-Hydroxybenzoic acid

Figure 5–Proposed pathways for the catabolism of quercetin-3-O-rutinoside resulting in the production of hydroxyphenylacetic acids and benzoic acids based on feeds with tomato juice containing quercetin-3-O-rutinoside and fecal incubations with the rutinoside and quercetin. Curved ﬁne arrows indicate sugar cleavage and ring ﬁssion. Red arrows indication conversions catalysed by colonic microbiota, and blue arrow indicate a conversion mediated with mammalian enzymes (after Jaganath et al. (2006).

Table 3–Identiﬁcation of urinary metabolites of (+)-catechin in various species (based on Das, 1974).

Species tested 5C-Ring ﬁssion metabolites Phenolic acid metabolites Rat 5-(3-Hydroxyphenyl)-γ -valerolactone 29 3-(3-Hydroxyphenyl)propionic acid 32 5-(3,4-Dihydroxyphenyl)-γ -valerolactone 30 3-Hydroxyhippuric acid 33 5-(3-Methoxy-4-hydroxyphenyl)-γ -valerolactone 31 Guinea pig 5-(3-Hydroxyphenyl)-γ -valerolactone 29 3-Hydroxybenzoic acid 34 5-(3,4-Dihydroxyphenyl)-γ -valerolactone 30 3-Hydroxyhippuric acid 33 5-(3-Methoxy-4-hydroxyphenyl)-γ -valerolactone 31 Rabbit 5-(3-Hydroxyphenyl)-γ -valerolactone 29 3,4-Dihydroxybenzoic acid 35 5-(3,4-Dihydroxyphenyl)-γ -valerolactone 30 3-Methoxy-4-hydroxybenzoic acid 36 5-(3-Methoxy-4-hydroxyphenyl)-γ -valerolactone 31 3-Hydroxybenzoic acid 34 Man 5-(3-Hydroxyphenyl)-γ -valerolactone 29 3-(3-Hydroxyphenyl)hydracrylic acid 37 5-(3,4-Dihydroxyphenyl)-γ -valerolactone 30 3-(3-Hydroxyphenyl)propionic acid 32 5-(3-Methoxy-4-hydroxyphenyl)-γ -valerolactone 31 Monkey 5-(3-Hydroxyphenyl)-γ -valerolactone 29 3-(3-Hydroxyphenyl)hydracrylic acid 37 5-(3,4-Dihydroxyphenyl)-γ -valerolactone 30 3-(3-Hydroxyphenyl)propionic acid 32 5-(3-Methoxy-4-hydroxyphenyl)-γ -valerolactone 31 3-Hydroxybenzoic acid 34 3-Hydroxyhippuric acid 33

1999) or electrochemical detection (Rein et al., 2000; Wang et al., were converted to their aglycones by acid hydrolysis, relatively 2000). With this methodology, Richelle et al. (1999) showed that little is known about the individual metabolites present prior to following the consumption of 40 g of dark chocolate containing enzyme treatment. A further limitation that has become appar- 282 μmol of (–)-epicatechin, the epicatechin plasma levels rose ent is that β-glucuronidase/sulfatase preparations fail to fully hy- rapidly and reached a Cmax of 355 nmol/L after 2.0 hr with an drolyze most (−)-epicatechin-sulfates and methyl-(−)-epicatechin AT½ of 1.9 hr. sulfates and, as a consequence, (−)-epicatechin bioavailability is β-Glucuronidase/sulfatase treatment of samples in such stud- underestimated (Saha et al., 2012). This problem has been largely ies was convenient as a number of metabolites are converted overcome with the increasing use of HPLC-MS alongside the to a single product, (–)-epicatechin, thus simplifying the subse- development of methods for the synthesis of a range structurally quent quantitative analysis. However, as with ﬂavonols, which related (−)-epicatechin metabolites (SREMs; Mull et al., 2012;

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1061 Dietary ﬂavonoids: a historical review . . .

Zhang, Jagdmann, Van Zandt, Beckett, & Schroeter, 2013a, b) 500 as well as 5C-ring ﬁssion metabolites (5C-RFMs) such a 5- ( )-epicatechin (hydroxyphenyl)-γ -valerolactones and their phase II metabolites ) (+)-epicatechin

(Brindani et al., 2017; Curti et al., 2015; Lambert, Rice, Hong, 400 Hou, & Yang, 2005; Sanchez-Pat´ an´ et al., 2011). Although de- + tected earlier in the Singapore/Birmingham studies with ( )- * catechin (Table 3), 5C-RFMs were also identiﬁed, albeit almost metabolites in 300 three decades later, in blood and urine collected after green tea consumption (Li et al., 2000, 2001). 200 Identiﬁcation of (−)-epicatechin metabolites. Ottaviani, Momma, Kuhnle, Keen, and Schroeter (2012) fed volunteers a * cocoa-based drink which, when consumed by a 75-kg subject, 100

μ − μ Levels of epicatechin

contained 476 mol of ( )-epicatechin 38 and 66 mol of a plasma 2 h after consumption (nmol/L mixture of (+)-catechin 28 and (−)-catechin 39, and through * the use of reference compounds the investigators were able to 0 epicatechin- epicatechin- epicatechin- identify and quantify SREMs in human plasma, all of which 3'-O-glucuronide 5-sulfate 3'-sulfate attained Cmax 2 hr after cocoa intake, indicative of absorption in − the small intestine. The main metabolite was ( )-epicatchin-3 - Figure 6–Stereochemistry-dependent epicatechin metabolism. Levels of O-glucuronide 40 (Cmax 589 nmol/L). The main sulfated SREM individual epicatechin metabolites at peak plasma concentration 2 hr was (−)-epicatchin-3 -sulfate 41 (Cmax 331 nmol/L), together after the consumption of a cocoa drink containing 1.5 mg/kg body weight − of (−)-epicatchin or (+)-epicatechin. Data expressed in nmol/L as mean with lower amounts of ( )-epicatchin-5-sulfate 42 (Cmax 37 ∗ − values ± standard error (n = 7). , Signiﬁes statistically different from nmol/L) and ( )-epicatchin-7-sulfate 43 (Cmax 12 nmol/L). levels reached with the same metabolites after (−)-epicatechin Among the other SREMs detected in low concentrations were consumption, p < 0.05 (Ottaviani et al., 2012). With permission of The 4 -O-methyl-(−)-epicatchin-7-O-glucuronide 44, and a number Society of Free Radical Biology and Medicine. of methylated sulfates.

OH OH OH OH 24 hr after supplementation and the overall excretion of SREMs HO O HO O was 55.7 μmol, which is equivalent to 20.1% of the ingested − OH OH ( )-epicatechin which, when considering the different analytical OH OH strategies utilized, is broadly in line with urinary recoveries in ear- ( )-Epicatechin 38 ( )-Catechin 39 lier cocoa-based feeding studies (Baba et al., 2000; Mullen et al., 2009). OH Epicatechinstereochemistryandbioavailability. Ottaviani et al. HO OH O COOH OSO - (2012) also investigated the impact of flavan-3-ol stereochem- O 3 OH OH istry on the plasma SREM profile after volunteers ingested HO O HO O (−)-epicatechin 38 and (+)-epicatechin 45. This revealed OH OH that epicatechin-3 -O-glucuronide was the sole glucuronidated OH OH metabolite to be detected in plasma regardless of the enantiomer ( )-Epicatechin-3'-O-glucuronide 40 ( )-Epicatechin-3'-sulfate 41 consumed, but the Cmax was 336 nmol/L after (−)-epicatechin intake and only 13 nmol/L after ingestion of the (+) enantiomer. OH OH OH OH There was a similar trend with the Cmax of epicatechin-3 -sulfate - HO O O3SO O which was approximately 4-fold higher after (−)-epicatechin con- OH OH sumption. In contrast, epicatechin-5-sulfate reached a Cmax of - O3SO OH 50 nmol/L after (−)-epicatechin intake and 270 nmol/L following ( )-Epicatechin-5-sulfate 42 ( )-Epicatechin-7-sulfate 43 (+)-epicatechin ingestion, a 5-fold difference in favor of the (+) enantiomer (Figure 6). Thus, the concentrations and the relative amounts of individual glucuronide and sulfate metabolites were OH OH OCH HOOC 3 OH dependent on the stereochemical configuration of the epicatechin HO O O O HO O ingested. HO OH In an earlier study equal quantities of (–)-epicatechin (38), OH OH OH OH (+)-epicatechin (45), (+)-catechin (28), and (–)-catechin (39) 4'-O-Methyl-( )-epicatechin-7-O-glucuronide 44 (+)-Epicatechin 45 were consumed in a cocoa drink (Ottaviani et al., 2011). Based on plasma concentrations and urinary excretion obtained using Actis-Goreta et al. (2012) also identified and quantified an array enzyme hydrolysis, the bioavailability of the stereoisomers was of SREMs in plasma after the ingestion of 100 g dark chocolate ranked as (–)-epicatechin > (+)-epicatechin = (+)-catechin > containing 241 μmol of (−)-epicatechin and 90 μmol of (±)- (–)-catechin. There were also differences in the metabolic fate of catechin. Once again the main metabolites were (−)-epicatchin- the catechin and epicatechin epimers as reflected in the ratios of 3 -O-glucuronide (Cmax 290 nmol/L) and (−)-epicatechin-3 - their 3 -and4-O-methylated metabolites. Thus, stereochemistry sulfate (Cmax 233 nmol/L). The Cmax of the metabolites was ihas an effect on phase II methylation as well as sulfation and glu- reached after approximately 3 hr rather than 2 hr after intake, curonidation of flavan-3-ol monomers. As the individual flavan- presumably reflecting matrix differences between the cocoa drink 3-ol stereoisomers in cocoa products used in feeding studies are and the dark chocolate. In this study, urine was collected 0 to usually not fully determined, this finding raises the possibility that

r 1062 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary flavonoids: a historical review . . . varying stereochemical ratios could be a contributing factor in the differing metabolite profiles reported across research groups 2 (Actis-Goreta et al., 2012; Mullen et al., 2009; Ottaviani et al., 2012; Roura et al., 2005; Tomas-Barber´ an´ et al., 2007). 1.5 Use of the Loc-I-gut intestinal perfusion technique. Actis- Goretta et al. (2013) carried out a novel study on (−)-epicatechin bioavailability using a Loc-I-gut intestinal perfusion technique pre- 1 viously employed to study certain aspects of drug metabolism (% of intake) (Dahan, Lennernas,¨ & Amidon, 2012). A multilumen perfusion 0.5 catheter was introduced into the small intestine and three bal- Plasma radioactivity loons inflated to isolate two 20-cm sections of the jejunum. The upper balloon was positioned approximately 20 cm below the 0 0 2 4 6 8 10 12 14 16 18 20 22 24 ampulla of Vater. As a consequence, when (−)-epicatechin was introduced into the proximal and distal segments of the catheter, Time (h) this enabled biliary excretion of flavan-3-ols to be monitored by analysis of perfusates collected from the lumen above the upper Figure 7–Radioactivity detected in plasma collected 0 to 24 hr after the ingestion of 300 μCi (207 μmoles) of [2-14C](−)-epicatechin by balloon. ± n = μ − volunteers. Data presented as mean values standard error ( 8) and Utilizing six volunteers, 50 mg (172 mol) of ( )-epicatechin expressed as a percentage of the ingested radioactivity (Borges et al., was introduced into isolated jejunum sections, which were then 2017). perfused for 2.5 hr. An average of 23.4 mg of unchanged (−)- epicatechin was recovered along with 0.84 mg of metabolites, significant increase in flow-mediated vasodilation (FMD; Sansone indicative of low-level efflux of metabolites formed in the ente- et al., 2017). The mechanism by which theobromine mediates an rocytes back into the lumen of the jejunum. This implies that increased plasma concentration of SREMs remains to be deter- approximately 50% of the administered (−)-epicatechin was ab- mined. The study does, however, suggest that matrix effects with sorbed into the systemic circulation. (−)-Epicatechin metabolites other components may well have an impact on the absorption of reached sub-μmol/L peak plasma concentrations 1 hr after the not just flavan-3-ols, but also on other flavonoids and (poly) phe- initiation of perfusion. Urinary excretion of metabolites by the nols when they are consumed in foods as part of a regular, daily individual volunteers ranged from 2.4% to11.8% of the amount of diet. perfused (−)-epicatechin, which is somewhat lower than the urinary excretion of 20.1% of the ingested dose obtained when the O CH3 HN N same investigators fed chocolate to volunteers (Actis-Goreta et al., O N N

2012). Arguably, this reflects the fact that absorption in the perfu- CH3 sion model occurred in a 20-cm section of the jejunum compared Theobromine 46 to that occurring during passage through the full approximately 6 m length of the small intestine following ingestion. Bioavailability of [2-14C](−)-epicatechin Actis-Goretta et al. (2013) observed that the main metabolite There are reports of a feeding study that was carried out using effluxing back into the lumen of the jejunum was (–)-epicatechin- the radiolabeled flavan-3-ol, [2-14C](−)-epicatechin ([14C]EC) 3-sulfate, although (–)-epicatechin-3-O-glucuronide was present (Borges, Ottaviani, van der Hooft, Schroeter, & Crozier, 2017; in higher amounts in plasma and urine. This suggests that the sul- Ottaviani et al., 2016). Eight male volunteers each ingested a fate formed in enterocytes is preferentially effluxed back into the drink containing 300 μCi (207 μmol) of [14C]EC after which lumen of the jejunum, while (–)-epicatechin-3-glucuronide is ab- blood samples were obtained at intervals over a 48-hr period. sorbed into the circulatory system to a greater extent. This obser- All urine excreted and feces voided over a 72-hr period were vation is in line with studies in which ileostomists ingested either collected or until total excreted radioactivity was <1.0% of the green tea (Stalmach et al., 2010), Concord grape juice (Stalmach, administered dose over two consecutive 24-hr periods. The use of Edwards, Wightman, & Crozier, 2012), or a (poly) phenol-rich a radiolabeled substrate and analysis of samples in the first instance drink (Borges, Lean, Roberts, & Crozier, 2013) in the course of by liquid scintillation counting and, subsequently, by HPLC-MS2 which approximetly 90% of the (–)-epicatechin recovered in ileal in combination with an on-line radioactivity detector (RC) pro- fluid was sulfated. vided a wealth of novel data pertaining to the bioavailability of A further aspect of the study of Actis-Goretta et al. (2013) is (−)-epicatechin. that the use of the perfusion model enabled enterohepatic recircu- Recovery of radioactivity in urine, feces, and plasma. Analysis of lation of (–)-epicatechin to be directly determined in humans for blood revealed that radioactivity was associated almost exclusively the first time. Over the 2.5 hr-perfusion period, 2.6 to 18.4 μgof with plasma rather than red blood cells. The levels of radioactivity metabolites were excreted in the bile of individual volunteers. This in plasma, on the basis of each subject having a total volume of is equivalent to 0.005% to 0.04% of the perfused (–)-epicatechin, 3 L of plasma, were used to assess passage through the circulatory demonstrating that enterohepatic recirculation of metabolites of system, and this is illustrated in Figure 7. The profile is bipha- the flavan-3-ol is, at best, a minor event, assuming that the perfu- sic with maxima at 1 and 6 hr. The total radioactivity in plasma sion model is adequate for drawing conclusions in the context of never exceeded 2% of intake, although approximately 0.2% of in- dietary intake under life-like conditions. take, presumably derived from colonic absorption, was still present Impact of theobromine on (−)-epicatechin absorption. A recent 24 hr after ingestion. The 0 to 48 hr recovery of 14C in feces and 14 study with cocoa revealed that the Cmax of SREMs 2 hr after in- urine was 91.6% ± 1.3% of the ingested [ C]EC indicating that take of cocoa was enhanced significantly by co-ingestion of the tissue deposition of compounds derived from acute intake of the purine alkaloid, theobromine 46, in parallel with an accompanying flavan-3-ol was <10%.

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Pharmacokinetics of plasma metabolites. A total of 12 in the circulatory systems for longer than the SREMs with an (–)-epicatechin sulfate, glucuronide, and methyl metabo- AT1/2 of 5.7 hr, and they also had an area-under-the-curve con- lites were detected in plasma in nmol/L concentrations, centration approximately 3-fold higher than that of the SREMs namely: (–)-epicatechin-3-O-glucuronide 40, (–)-epicatechin-7- (Table 4). The main 5C-RFM, 5-(4–hydroxyphenyl)-γ - O-glucuronide 47, (–)-epicatechin-3-sulfate 41, (–)-epicatechin- valerolactone-3-sulfate, was still present in plasma, at a concen- 5-sulfate 42, (–)-epicatechin-7-sulfate 43,3-O-methyl-(–)- tration of approximately 50 nmol/L, 24 hr after (–)-epicatechin epicatechin-4-sulfate 48,3-O-methyl-(–)-epicatechin-5-sulfate ingestion (Figure 8C). 49,3-O-methyl-(–)-epicatechin-7-sulfate 50,4-O-methyl-(–)- - epicatechin-5-sulfate 51,4-O-methyl-(–)-epicatechin-7-sulfate OSO3 OH 52,3-O-methyl-(–)-epicatechin-5-O-glucuronide 53, and 3 -O- O methyl-(–)-epicatechin-7-O-glucuronide 54. O 5-(4'-Hydroxyphenyl)- -valerolactone-3'-sulfate 55

OH OCH3 OH OSO - HOOC 3 OH HO O O O HO O HO OH HO O COOH OH OH OH O OH OH OH O ( )-Epicatechin-7-O-glucuronide 47 3'-O-Methyl-( )-epicatechin-4'-sulfate 48 O 5-(4'-Hydroxyphenyl)- -valerolactone-3'-O-glucuronide 56

OCH3 OCH3 OH OH OH - OH HO O O3SO O HO OH O O O COOH OH OH - O O3SO OH 5-(3'-Hydroxyphenyl)- -valerolactone-4'-O-glucuronide 57 3'-O-Methyl-( )-epicatechin-5-sulfate 49 3'-O-Methyl-( )-epicatechin-7-sulfate 50

Urinary metabolites. The main urinary SREM, as in OH OH plasma, was (–)-epicatechin-3-O-glucuronide, along with OCH3 OCH3 - HO O O3SO O (–)-epicatechin-3 -sulfate, and 3 -O-methyl-(–)-epicatechin-5- sulfate. These compounds, together with related SREMs, were OH OH - O3SO OH excreted mainly in the initial 0 to 4 hr collection period with

4'-O-Methyl-( )-epicatechin-5-sulfate 51 4'-O-Methyl-( )-epicatechin-7-sulfate 52 relatively small amounts in urine collected over later time periods (Table 5), in keeping with the plasma pharmacokinetic proﬁles (Figure 8A and B). OCH3 OH The 5C-RFMs were excreted later, mainly over the 4 to 8 hr, 8 OCH HO 3 to 12 hr, and 12 to 24 hr collection periods (Table 5), which again O OH HOOC is in line with their plasma pharmacokinetic proﬁles (Figure 8C). HOOC OH HO O O O 14 HO O O HO As far as 2/3C-RFMs are concerned, excretion of C-labeled HO OH OH OH OH 3-(3 -hydroxyphenyl)hydracrylic acid 37 continued more than 24 hr after ingestion of [14C]EC, as did excretion of radiolabeled 3'-O-Methyl-( )-epicatechin-5-O-glucuronide 53 3'-O-Methyl-( )-epicatechin-7-O-glucuronide 54 hippuric acid 58 and 3-hydroxyhippuric acid 33 (Table 5).

As illustrated in Figure 8A and B, all the SREMs had a Tmax H of approximately 1.0 hr, indicative of absorption in the proximal HOOC N GI tract. Several of the metabolites were detected in plasma 30 O min after (–)-epicatechin ingestion with a mean concentration of Hippuric acid 58 854 nmol/L (Table 4). After attaining an overall Cmax, of 1223 nmol/L, 1.0 hr after [14C]EC intake the SREMs declined rapidly The mean total urinary excretion of SREMs, 5C-RFMs, two with an AT1/2 of 1.9 hr (Table 4), and in almost all instances had and three carbon ring-fission metabolites (2/3-RFMs), and hip- disappeared from the circulatory system within 8 hr (Figure 8A puric acids was 185 ± 16 μmol of the ingested radioactivity, a and B). recovery of 89%. The recovery of radioactivity as 5C-RFMs was 5C-RFMs were also detected in plasma but with different 42% of intake, that of 2/3-RFMs 7%, and hippuric acids 21%. pharmacokinetic profiles and Tmax times of approximately 6 hr, Thus, recovery of metabolites absorbed in the colon was 70% of which is characteristic of colon-derived products (Table 4 and the ingested radioactivity, whereas recovery of SREMs, absorbed Figure 8C). The main catabolites were 5-(4–hydroxyphenyl)- in the small intestine, was 20% (Table 5). γ -valerolactone-3 -sulfate 55 (Cmax 272 nmol/L) and 5- Fecal metabolites. Feces did not contain radiolabeled γ (4 –hydroxyphenyl)-γ -valerolactone-3 -O-glucuronide 56 (Cmax SREMs, but quantifiable amounts of three 5-(phenyl)- - 125 nmol/L). Lower concentrations of other 5C-RFMs were also valerolactones, five 5-(phenyl)-γ -hydroxyvaleric acids, 3-(3 - detected, namely 5-(3–hydroxyphenyl)-γ -valerolactone-4-O- hydroxyphenyl)propionic acid, and three unknown metabolites glucuronide 57 (52 nmol/L), two 5-(phenyl)-γ -valerolactone-O- were detected (Borges et al., 2017). The metabolite profiles of glucuronide-sulfates (39 nmol/L), and three 5-(hydroxyphenyl)- the 0 to 72 hr feces are presented in Table 6. Although there were γ -hydroxyvaleric acid derivatives, which had a combined Cmax of large variations in the individual profiles, on average the main γ 95 nmol/L (Figure 8C). The combined Cmax of the 5C-RFMs fecal metabolites were 5-(phenyl)- -hydroxyvaleric acids (12.3 μ γ μ was 588 nmol/L and their ATmax was 5.8 hr. They were retained mol) followed by 5-(phenyl)- -valerolactones (4.8 mol) and

r 1064 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

A ( )-Epicatechin Metabolites 350

300 EC-3'-GlcUA 250 EC-3'-S 200 EC-5-S EC-7-GlcUA

nmol/L nmol/L 150 EC-7-S 100

0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h)

B Methyl-( )-Epicatechin Metabolites 300

250 3'-Me-EC-5-S

3'-Me-EC-7-S 200 3'-Me-EC-4'-S

150 4'-Me-EC-5-S

nmol/L nmol/L 4'-Me-EC-7-S 100 3'-Me-EC-7-GlcUA

3'-Me-EC-5-GlcUA 50

0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h)

C -Valerolactone and Valeric acid Metabolites

350 4'-OH-VL-3'-S 300 3'-OH-VL-4'-GlcUA

250 4'-OH-VL-3'-GlcUA

OH-VA-S 200 3'-OH-VA-4'-GlcUA 150 nmol/L nmol/L

100

0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h)

Figure 8–Pharmacokinetic proﬁles of the concentration of the SREMs (A) (−)-epicatechin metabolites and (B) methyl-(–)-epicatechin metabolites and (C) the 5C-RFMs, μ-valerolactone and valeric acid metabolites detected in plasma 0 to 24 hr after the ingestion of 207 μmoles of [2-14C](−)-epicatechin by volunteers. Data expressed as mean values in μmol/L ± standard error (n = 8). EC-3-GlcUA, (–)-epicatechin-3-O-glucuronide; (–)-epicatechin-7-O-glucuronide (EC-7-GlcUA); (–)-epicatechin-3-sulfate (EC-3-S), (–)-epicatechin-5-sulfate (EC-5-S); (–)-epicatechin-7-sulfate (EC-7-S); 3-O-methyl-(–)-epicatechin-4-sulfate (3-Me-EC-4-S); 3-O-methyl-(–)-epicatechin-5-sulfate (3-Me-EC-7-S); 3-O-methyl-(–)-epicatechin-7-sulfate (3-Me-EC-7-S); 4-O-methyl-(–)-epicatechin-5-sulfate (4-Me-EC-5-S); 3-O-methyl-(–)-epicatechin-5-O-glucuronide (3-Me-EC-5-GlcUA); 3’-O-methyl-(–)-epicatechin-7-O-glucuronide (3-Me-EC-7-GlcUA); 5-(4-hydroxyphenyl)-γ -valerolactone-3-sulfate (4-OH-VL-3-S); 5-(3-hydroxyphenyl)-γ -valerolactone-4-O-glucuronide (3-OH-VL-4-GlcUA); 5-(4-hydroxyphenyl)-γ -valerolactone-3-O-glucuronide (4-OH-VL-3-GlcUA); 5-(hydroxyphenyl)-γ -hydroxyvaleric acid-sulfates (OH-VA-S) and 5-(3-hydroxyphenyl)-γ -hydroxyvaleric acid-4-O-glucuronide (3-OH-VA-γ -GlcUA). Based on the data of Ottaviani et al. (2016).

3-(3-hydroxyphenyl)propionic acid 32 (3.3 μmol), along with SREMs were gradually replaced, over a 24-h period, by 5C-RFMs lower amounts, 0.7 μmol, of three unknown metabolites. The and 3-(3-hydroxyphenyl)hydracrylic acid, absorbed at more dis- average total recovery of radioactivity was 10.1% of intake, with tal points in the GI tract, as well as by hippuric acids, which individual values ranging from 0% to 15.5%. are hepatic in origin. The presence of SREMs in plasma within Overview of [2-14C](−)-epicatechin bioavailability. The overall 30 min of [14C]EC ingestion (Table 4) points to their presence picture obtained is that 20% of the ingested [14C]EC was con- in the systemic circulatory system being associated with rapid en- verted to SREMs, which rapidly entered the circulatory system hancement of ﬂow-mediated dilatation induced by (–)-epicatechin via the small intestine. As they were excreted via the kidneys, the intake (Schroeter et al., 2006).

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Table 4–Pharmacokinetic analysis of SREMs and 5C-RFMs detected in human plasma 0 to 24 hr after ingestion of 300 μCi (207 μmol) of [14C] EC. Data expressed as mean values ± standard error (n = 8).a

Cmax (nmol/L) C30 min (nmol/L) Tmax (h) AUC(tf) (nmol/L/h) AT1/2 (h) Total SREMs 1223 ± 104 854 ± 76 1.0 ± 0.1 4,943 ± 471 1.9 ± 0.1 Total 5C-RFCs 588 ± 102 – 5.8 ± 0.4 14,352 ± 2264 5.7 ± 0.7

Based on the data of Ottaviani et al. (2016) and Borges et al. (2017). a SREMs, structurally-related (−)-epicatchin metabolites; 5C-RFMs, 5 carbon side-chain ring fission metabolites; Cmax, peak plasma concentration; C30 min, plasma concentration 30 min after ingestion; Tmax, time to reach peak plasma concentration; AUC(tf), area under the plasma concentration from time 0 hr to the time of final quantifiable sample; AT1/2, apparent elimination half-life; −, not detected.

Table 5–14C-Labelled SREMs, 5C-RFMs and 2/3C-RFMs detected in urine 0 to 48 hr after the ingestion of 300 μCi (207 moles) of [14C]EC by eight volunteers.

Metabolites 0to4hr 4to8hr 8to12hr 12to24hr 24to48hr 0-48hr Total SREMs 25.3 ± 3.1 9.2 ± 0.9 3.6 ± 0.8 2.5 ± 0.8 – 40 ± 4 (20%) Total 5C-RFMs 4.9 ± 1.6 43.3 ± 8.3 22.3 ± 4.1 16.4 ± 5.4 0.5 ± 0.5 87 ± 9 (42%) Hydroxyphenylacetic acid-sulfate – 0.9 ± 0.5 0.8 ± 0.6 1.2 ± 0.4 – 2.9 ± 1.1 3-(3-Hydroxyphenyl)hydracrylic acid – 0.7 ± 0.4 2.2 ± 0.5 5.3 ± 2.3 3.3 ± 1.7 11.5 ± 4.4 Total 2/3C-RFMS – 1.6 ± 0.6 3.0 ± 0.9 6.5 ± 2.4 3.3 ± 1.7 14 ± 4 (7%) Hippuric acid 0.6 ± 0.4 7.2 ± 3.9 5.6 ± 2.6 7.1 ± 2.1 5.9 ± 4.1 26.4 ± 7.1 3-Hydroxyhippuric acid – 1.6 ± 0.5 2.8 ± 0.7 7.0 ± 2.9 5.5 ± 2.3 16.9 ± 5.8 Total hippuric acids 0.6 ± 0.4 8.8 ± 4.1 8.4 ± 2.5 14.1 ± 4.1 11.4 ± 5.5 43 ± 7 (21%) Total metabolites 30.8 ± 3.7 62.9 ± 11.3 37.3 ± 5.8 39.5 ± 6.3 15.2 ± 5.6 185 ± 16 (89 %)

Data expressed as mean values in μmoles ± standard error (n = 8); italicised figures in parentheses represent urinary recoveries of metabolites as a percentage of -(–)-epicatechin intakea. Based on the data of Ottaviani et al. (2016) and Borges et al. (2017). aSREMs, structurally-related (−)-epicatchin metabolites; 5C-RFMs, 5 carbon side-chain ring fission metabolites; 2/3C-RFMs, 2 and 3 carbon side-chain ring fission metabolites.; −, not detected.

The potential main routes for the metabolism that occur in the valerolactone, which is further converted by the microflora to 5- proximal GI tract after ingestion of [2-14C]EC are illustrated in (3,4-dihydroxyphenyl)-γ -hydroxyvaleric acid. The 14C-labeled Figure 9. It is of note that an absence of methyl-(−)-epicatechin metabolites in the voided feces suggest that both these dihydroxy- metabolites which, arguably, indicates that methylation only oc- 5C-RFMs are dehydroxylated by the colonic microbiota (Table 6), curs after prior sulfation or glucuronidation. Most of the con- most, however, is absorbed and converted to sulfate and glu- versions probably take place in enterocytes to absorption into the curonide metabolites by colonoycte and/or hepatic enzymes as circulatory system with some post-absorption metabolism possibly illustrated in Figure 10. occurring in the liver. Feces, in addition to the 5C-RFMs also contained 3-(3- A portion of the SREMs formed in enterocytes, most notably hydroxyphenyl)propionic acid 32 (Table 6), a 3C-RFM produced (–)-epicatechin-3-sulfate, efflux back into the lumen of the small from (−)-epicatechin by in vitro fecal incubations (Roowi et al., intestine (see section “Urinary Metabolites”) and then along with 2010). Its likely immediate precursor is 5-(3-hydroxyphenyl)-γ - unabsorbed [14]EC pass along the GI tract to the colon in quan- hydroxyvaleric acid 59. The conversion could be carried out tities equivalent to approximately 70% of intake. The flavan-3-ols by microbial enzymes although an involvement of β-oxidation entering the colon are converted by the microbiota to 5C-RFMs, by mammalian enzymes catalyzing the removal of two carbons which remain in the circulatory system for an extended duration from the side chain is also feasible. In view of its accumula- compared to SREMs (Table 4), as sulfate and glucuronide, but not tion in fecal incubates with (−)-epicatechin, further metabolism as methylated metabolites. of 3-(3-hydroxyphenyl)propionic acid would appear to involve Unabsorbed radioactivity voided in 0 to 72 hr feces varied sub- mammalian enzymes with, potentially, a β-oxidation yielding stantially from volunteer to volunteer, but on average was equiva- 3-hydroxybenzoic acid, which glycination would convert to lent to 10.1% of intake (Table 6). With the exception of the 3C- 3-hydroxyhippuric acid, while dehydroxylation and glycination RFM, 3-(3-hydroxyphenyl)propionic acid, and minor amounts would yield hippuric acid (Figure 10). The glycination step in- of three unidentified metabolites, the radioactivity was associ- volves hepatic enzymes (Crozier, Clifford, & Del Rio, 2012) and ated exclusively with di-, mono-, and de-hydroxyvaleric acids and urinary excretion indicated there was a 21% conversion of the valerolactones, approximately 25% to 30% of which were sulfated ingested [14C]EC to hippuric acids (Table 5). (Table 6). The 3-sulfates potentially could originate from (−)- epicatechin-3-sulfate, which passed along the GI tract from the OH OCH3 OH small intestine to the colon, while, arguably, the two 5C-RFM HO O 4-sulfates may have been formed in coloncytes and effluxed back OH into the lumen of the colon. HOOC HO O 14 The possible metabolism of [2- C]EC and (–)-epicatechin-3 - 5-(3'-Hydroxyphenyl)- -hydroxyvaleric acid 59 Hesperetin 60 sulfate moving from the small to the large intestine, where ring fission is followed by phase II metabolism, is illustrated in Figure 10. Radiolabeled 3-(3-hydroyphenyl)hydracrylic acid 37 was ex- Although it is feasible that the sulfate moiety remains intact, for creted in urine after ingestion of [14C]EC (Table 5). The origins simplicity it is assumed that it is removed by the colonic bacteria of this 3C-RFM are unclear. It is not formed in vitro when (−)- releasing (–)-epicatechin. There is evidence that (–)-epicatechin is epicatechin is incubated with fecal bacteria (Roowi et al., 2010). subjected to microbiota-induced opening of the C-ring by break- (Phenyl)hydracrylic acids derived from the flavanone hesperetin 60 ing the O1-C2 bond, yielding a diaryl-propan-2-ol (Kutschera, are excreted in urine after orange juice consumption but they are Engst, Blaut, & Braune, 2011), followed by opening of the A- γ not in vitro fecal products of hesperetin (Pereira-Caro et al., 2014, ring, resulting in the formation of 5-(3 ,4 -dihydroxyphenyl)- - 2015a). 3-(3-Hydroxyphenyl)hydracrylic acid would, therefore,

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appear to be a microbial product that requires metabolism mol

μ by mammalian enzymes after absorption. 5C-RFMs are prod- (10.1%) 0.7 ucts of colon metabolism of ﬂavan-3-ols, but not hesperetin, which when subjected to ring ﬁssion yields 3C-RFMs (section 21.0 “Bioavailability”). This suggests that (−)-epicatechin-derived 3- (3-hydroxyphenyl)hydracrylic acid is produced by a pathway that does not involve a 5C-RFM intermediate (Figure 10). 14 − − The metabolism of [ C]EC in rats (Borges et al., 2016) is very (0.4%) different to that which occurs in humans (Ottaviani et al., 2016). 0.9 The main human plasma and urinary SREMs are (−)-epicatechin- 3-O-glucuronide and (−)-epicatechin-3-sulfate. Neither of these metabolites are detected in rats where the principal components in plasma and urine are unmetabolized (–)-epicatechin along with 3- (15.5%) 7.2 0.5 12.3 2.6 0.2 4.5 0.7 21.5 0.2O-methyl-( 3.3 −)-epicatechin 61,(−)-epicatechin-5-O-glucuronide − 32.0 62, and 3 -O-methyl-( )-epicatechin-5-O-glucuronide 53. Ci) by eight volunteers. Data expressed as in

μ OH OH OCH3 – – – – OH HO O (0.0%) mol] 300 – HO O HOOC OH μ HO O O OH HO OH OH

3'-O-Methyl-( )-epicatechin 61 ( )-Epicatechin-5-O-glucuronide 62 (8.9%) 0.3 These differences, especially the absence of (–)-epicatechin and

18.5 a 3 -O-methyl-(–)-epicatechin in the circulatory system of humans, are of importance in the context of in vivo and ex vivo studies investigating the potential protective effects and underlying modes Volunteers – (4.7%)

0.5 4.0 of action of dietary ﬂavan-3-ols. The current paradigm is that not only should appropriate physiological doses be used, but also that 9.7 C](–)-epicatechin (60 mg [207

14 metabolites to which the cells would be exposed in vivo should be utilized. This is in line with the complete lack of correlation between human and animal drug bioavailability, suggesting animal 15% of the mean values.

< models are not appropriate to make the types of assumptions we (35.5%) tend to be making these days (Musther, Olivares-Morales, Hatley,

73.5 Lui, & Hodjegan, 2014). The use of a radiolabeled substrate in both the rat and human studies enabled very comprehensive metabolomic proﬁles of (–)-epicatechin to be obtained. HPLC-RC-MS analysis produces (9.2%) data that are more reliably interpreted than those generated by

19.0 feeds with unlabelled substrates, irrespective of whether a targeted or an untargeted analytical strategy is employed. Now that an overall picture of (−)-epicatechin metabolism has been obtained, further elucidation of the complex pathways associated with in- –– – (7.0%) testinal microbial and subsequent phase II metabolism leading to the formation of 5C-RFMs, 3/2C-RFMs, hippuric acids, and other phenolics will necessitate the use of stable isotope-labelled intermediates and analysis with HPLC and high-resolution mass spectrometry. -sulfate 1.1 – 15.4 0.1 0.3 – – 0.1

-sulfate-sulfate – 1.3 4.3 – – 1.0Do (–)-epicatechin 0.8 – metabolites 1.6 – reach – – the brain? 0.2 0.9 0.2 – In the study by Borges et al. (2016), 1 × 103 dpm of radioac- -sulfate – – 1.5 – – – – – tivity, corresponding to 29 pmol of ﬂavan-3-ols, was detected in the saline-perfused brains of rats at 1, 3, 6, and 9 hr after [14C]EC

-valerolactone-hydroxyvaleric acid 0.6 – – –intake. 25.6 5.3The 0.2 mean fresh – weight – of – the – rat brain – was 1.5 1.9 g,so – the – γ γ

-valerolactone-4 -valerolactone-3 -hydroxyvaleric acid-hydroxyvaleric acid-4 – –concentration 5.9 of radiolabeled – compounds – was 15.2 pmol/g. – With – – γ γ γ γ the volume of each brain at approximately 1.5 mL, the concentration of radioactivity in the brain is approximately 19 nM. In -valerolactones 1.9 4.3 26.6 1.0 1.6 -hydroxyvaleric acids 11.8 12.6 45.7 8.2 12.6 γ

γ a study in which a mixture of (+)-catechin and (−)-epicatechin, -hydroxyvaleric acid 10.7 12.6 17.4 8.1 12.4 – 7.2 0.4 -hydroxyvaleric acid-3 γ γ derived from a grape extract, was fed to rats at 17 mg/kg,

-Dihydroxyphenyl)- -Dihydroxyphenyl)- − compared to the 1.21 mg ( )-epicatechin/kg in the Borges -Hydroxypheny)propionic acid 0.8 2.1 1.2 ,4 -Hydroxyphenyl)- -Hydroxyphenyl)- ,4 -Hydroxyphenyl)- -Hydroxyphenyl)- et al. (2016) study, low, unquantiﬁable amounts of metabolites –, not detected. and in italicised parentheses as a % of the ingested dose. Standard error of the individual values 5-(3 5-(Phenyl)- 5-(3 Unknowns Total phenyl- 3-(3 5-(Phenyl)- 5-(3 Table 6–Total and major individual ﬁssion metabolites voided in feces 0 to 72 hr after the ingestion of [2- Metabolites5-(3 Based on the dataa of Ottaviani et al. (2016) and Borges et al. (2017). 1 2 3 4 5 6 7 8 Mean 5-(4 Total phenyl)- 5-(3 Total metaboliteswere detected in the 14.5 brain after acute intake (Wang et al., 2012).

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OH OCH3 - O3SO O

OH OH 4'-O-Methyl-( )-epicatechin-7-sulfate

OCH3 OH OH OH HOOC HOOC O OH OCH3 HO O OO HO OO HO HO OH OH OH OH - - OH OH OSO3 O OSO3 O OH OH 3'-O-Methyl-( )-epicatechin-7-O-glucuronide ( )-Epicatechin-7-O-glucuronide OH OH OH OH ( )-Epicatechin-7-sulfate 3'-O-Methyl-( )-epicatechin-7-sulfate

OCH OH OH OCH3 3 OH - - OH OH OH OSO3 OSO3 HO O HO O HO O HO O HO O

HOOC OH HOOC OH OH OH OH HO O O HO O O OH OH OH HO HO [2-14C]( )-Epicatechin ( )-Epicatechin-4'-sulfate* 3'-O-Methyl-( )-epicatechin-4'-sulfate OH OH 3'-O-Methyl-( )-epicatechin-5-O-glucuronide ( )-Epicatechin-5-O-glucuronide*

OH OCH3 OH OH OH - OSO3 HO OH OH HO O HO O O COOH O HO O OH OH - OH - OSO3 OSO3 HO O OH O OH ( )-Epicatechin-5-sulfate 3'- -Methyl-( )-epicatechin-5-sulfate OH ( )-Epicatechin-3'-sulfate OH OH OCH3 ( )-Epicatechin-3'-O-glucuronide HO O

- OH OSO3 4'-O-Methyl-( )-epicatechin-5-sulfate

Figure 9–Proposed routes for the human metabolism of [2-14C](−)-epicatechin, potentially in enterocytes and hepatocytes, following its ingestion in the proximal gastrointestinal tract. Boxed metabolite names indicate the main products to accumulate in plasma and urine after (–)-epicatechin intake. Blue arrows indicate that the conversions are catalysed by mammalian enzymes. Asterisks indicate potential intermediates that do not accumulate in detectable quantities in either plasma or urine. The red circle indicates the position of 14C-label. Based on the data of Ottaviani et al. (2016) and Borges et al. (2017).

However, after 10 days of chronic supplementation, plasma through the use of plasma and/or urinary flavonoid metabolites as metabolite levels increased substantially and the brain con- more objective measures of flavonoid intake (Kuhnle, 2017). tained trace amounts of unmetabolized (−)-epicatechin and In this context it is of note that following (–)-epicatechin in- approximately 363 pmol/g of a mixture of an (−)-epicatechin- take, microbial-derived 5-(hydroxyphenyl)-γ -valerolactone and O-glucuronide, presumably (−)-epicatechin-5-O-glucuronide, hydroxyphenylvaleric acid sulfate and glucuronide metabolites be- and 3-O-methyl-(−)-epicatechin-5-O-glucuronide (Wang et al., gan to appear in the circulatory system after 2 hr and that 5-(4- 2012). This corresponds to a concentration of approximately hydroxyphenyl)-γ -valerolactone-3-sulfate was still present, albeit 484 nM and potentially could be higher, if 5C-RFCs, which in reduced amounts, 22 hr later as shown in Figure 8C. The sub- were not analyzed, were also present. Nonetheless, based on the stantial amounts of these 5C-RFMs that appear in urine over the very few studies that investigated this question, (−)-epicatechin same period (Table 5) indicate that the plasma pools are being metabolites seem to be present in the brain of rodents at levels that continually turned over, being replenished by absorption from offer the possibility of being of physiological relevance, such as in the colon which is counter balanced by removal via urinary ex- animal models of Alzheimer’s disease, where the grape flavan-3-ol cretion. Thus, regular consumption of products containing (–)- monomer extract has been shown to improve cognitive function epicatechin, such as cocoa, teas, red wine, apples, plums, and (Wang et al., 2012). berries, is likely to result, not just in the transient appearance of SREMs in the circulatory system, but in the more long-term pres- Biomarkers of flavan-3-ol consumption ence of 5C-RFMs, albeit at sub-μmol/L concentrations. Thus, in There currently exist several limitations with epidemiological epidemiological studies, 5-(4-hydroxyphenyl)-γ -valerolactone- studies into the potential health benefits of dietary flavonoids. In 3-sulfate 55 and 5-(4-hydroxyphenyl)-γ -valerolactone-3-O- most investigations intake is assessed by combining self-reported glucuronide 56, the principal 5C-RFMs in both plasma and information on diet with food composition flavonoid databases urine, could serve as key biomarkers of (–)-epicatechin intake in order to generate insights on intake. There is doubt about the (Ottaviani et al., 2016). In this regard it is of note that 5C- reliability of self-reported dietary assessments, as well as the mer- RFMs are also derived from catechins and gallocatechins, such its of food composition databases, with regard to the accuracy of as (−)-epigallocatechin-3-O-gallate 12, which occur in tea (van the flavonoid content of fruits, vegetables, and beverages, which der Hooft et al., 2012). Furthermore, 5C-RFMs also originate in practice can fluctuate enormously because of local growing to some degree from colonic catabolism of procyanidins (Ap- conditions, in addition to seasonal and varietal differences peldoorn, Vincken, Aura, Hollman, & Gruppen, 2009; Stoupi, (Rodriguez-Mateos et al., 2014c). As more is learnt about Williamson, Drynan, Barron, & Clifford, 2010), but they appear flavonoid bioavailability, these limitations can be overcome, result- not to be formed from theaflavins, and presumably thearubigins, ing in improvements in the interpretation of epidemiological data, after the ingestion of black tea (Pereira-Caro et al., 2017).

r 1068 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

OH OH OH

HO O HOOC OH OH OH 3-(3'-Hydroxyphenyl)hydracrylic acid ( )-Epicatechin OH OH

HO OH

OH OH 5-(3',4'-Dihydroxyphenyl)-3- (2'',4'',6''-trihydroxphenyl)propan-2-ol*

4 CO 2 OH OH 5-(4'-Hydroxyphenyl)- -valerolactone-3'-sulfate O 5-(4'-Hydroxyphenyl)- -valerolactone-3'-O-glucuronide O 5-(3',4'-Dihydroxyphenyl)- -valerolactone

5-(Phenyl)- -valerolactone-sulfate-O-glucuronides

OH OH OH OH OH 5-(3'-Hydroxyphenyl)- -hydroxyvaleric acid-4'-O-glucuronide HOOC 5-(3'-Hydroxyphenyl)- -hydroxyvaleric acid-4'-sulfate HOOC 5-(4'-Hydroxyphenyl)- -hydroxyvaleric acid-3'-sulfate 3',4'-Dihydroxyphenylacetic acid* 5-(3',4'-Dihydroxyphenyl)- -hydroxyvaleric acid

OH 3'- or 4'-sulfate OH

HOOC 5-(3'-Hydroxyphenyl)- -hydroxyvaleric acid H HOOC N

OH O Hippuric acid Benzoic acids* Liver HOOC OH 3-(3'-Hydroxyphenyl)propionic acid H HOOC N O 3'-Hydroxy-hippuric acid

Figure 10–Proposed routes for the metabolism by colonic microbiota of [2-14C](−)-epicatechin passing from the small to the large intestine (red arrows), and potential steps catalysed by mammalian enzymes in colonocytes and/or hepatocytes (blue arrows). Thin arrows indicate minor routes. Boxed metabolite names indicate the main products to accumulate in plasma after (–)-epicatechin intake. Asterisks indicate potential intermediates that do not accumulate in detectable quantities in either plasma or urine. The red circle indicates the position of 14C-label. Based on the data of Ottaviani et al. (2016) and Borges et al. (2017).

Anthocyanins Holub, & Wang, 2004; Kay, Pereira-Caro, Ludwig, Clifford, & Progress of research since 1997 Crozier, 2017; Sandhu et al., 2016; Wu, Cao, & Prior, 2002; Moderate to high anthocyanin intakes are reported in those who Zhong, Sandu, Edirisinghe, & Burton-Freeman, 2017). regularly consume berries and red grapes and their derived juices, OH red apples, plums, red cabbage, or red wine. Early reports identified OH HO O+ the presence of unmetabolized anthocyanins in plasma (Paganga, & OH OH O Rice-Evans, 1997) and urine (Lapidot, Harel, Granit, & Kanner, HO O+ HO HO O 1998); however, the HPLC profiles on which the identifications O HO were based now appear somewhat unconvincing in light of data HO HO HO O obtained with more modern analytical methodology. In contrast, HO O HO O HO HO the later identifications of unmetabolized cyanidin-3-O-glucoside OH OH 63 and cyanidin-3-O-sambubioside 64 in plasma and urine after Cyanidin-3-O-glucoside 63 Cyanidin-3-O-sambubioside 64 the consumption of an elderberry extract are more plausible (Cao & Prior, 1999; Cao, Muccitelli, Sanchez-Moreno,´ & Prior, 2001). OH Although many other early studies “identified” unmetabolized HO O+ precursor anthocyanins in biofluids using HPLC with absorbance O detection, with the increasing use of HPLC-MS, it has become HO apparent that, like other flavonoids, anthocyanins are absorbed HO HO O primarily as methyl, glucuronide, and sulfated phase II conjugates HO OH (Felgines et al., 2003, 2005; Kay, Mazza, Holub, & Wang, 2004; Kay, 2006; Kay, Mazza, & Holub, 2005; Kay, 2006; Kay, Mazza, Pelargonidin-3-O-glucoside 65

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Until recently, anthocyanins were widely believed to have low berries, blueberries, lingonberries, and grapes up to 40% of the in- bioavailability, with the majority of feeding studies, typically gested anthocyanins remained in the ileal fluid (Brown et al., 2014; with berries, reporting Cmax concentrations ranging from 1 to Gonzalez-Barrio,´ Borges; Mullen, & Crozier, 2010; Kahle et al., 120 nmol/L and urinary recoveries <1% of intake (Kay et al., 2006; Stalmach et al., 2013; McDougall et al., 2014). In volun- 2005; Prior, 2012; Sandhu et al., 2016; Stalmach et al., 2012), teers with a functioning colon this portion of anthocyanins would with one report of excretion as low as 0.005% (Wu et al., 2002). pass into the large intestine where it would be deglycosylated and Differences in reported recoveries are likely, in part, to be the the resulting aglycones broken down by fission of the C-ring, result of differing degree of hydroxylation of the B-ring of the with the A- and B-ring fragments being converted to a diversity anthocyanidin unit, with the excretion of metabolites of straw- of phenolic constituents (Feliciano et al., 2016; Gonzalez-Barrio´ berry pelargonidin-3-O-glucoside 65 being equivalent 1.8% of et al., 2011; Rodriguez-Mateos et al., 2014c), some of which intake (Felgines et al., 2003), whereas metabolites of blackberry are also produced by catabolism of other classes of flavonoids and cyanidin-3-O-glucoside 63 are reported at 10-fold lower concen- related dietary (poly)phenols, such as chlorogenic acids (Clifford, trations (Felgines et al., 2005). Alternatively, differences could be Jaganath, Ludwig, & Crozier, 2017; Williamson & Clifford, 2010, the result of differing methodology and quantification techniques. 2017). Acetylation of anthocyanins also appears to affect bioavailability, as >10-fold reductions in anthocyanin recovery in urine have been Bioavailability of raspberry anthocyanins reported relative to non-acylated structures (Kurlich, Clevidence, Plasma. In a recent study volunteers consumed 300 g Britz, Simon, & Novotny, 2005). raspberries, containing 292 μmol of mainly cyanidin-based Some recent publications have suggested anthocyanins exist as anthocyanins, in the form of cyanidin-3-O-sophoroside (66, hundreds of derivations of phase II conjugates and persist in the 175 μmol), cyanidin-3-O-(2-O-glucosyl)rutinoside (67, circulation almost indefinitely (Kalt, Lui, McDonald, Vinqvist- 56 μmol), cyanidin-3-O-glucoside (63,37μmol), and cyanidin- Tymchuk, & Fillmore, 2014; Kalt, MacDonald, Lui & Fillmore, 3-O-rutinoside (68,20μmol; Ludwig et al., 2015). Only 2017; Kalt, McDonald, Vinqvist-Tymchuk, Lui, & Fillmore, two anthocyanins, cyanidin-3-O-glucoside and a cyanidin- 2017). These inferences are based on an untargeted metabolomics O-glucuronide, were subsequently detected in plasma, with approach using single-ion monitoring and low-resolution triple- sub-nmol/L C values and T of 1 and 4 hr, respectively. quadrupole MS and are not supported by more suitable analyses max max None of the parent anthocyanins were detected in 0 to 24 based on high-resolution time-of-flight (TOF) or orbitrap MS hr urine, except for cyanidin-3-O-glucoside (19.9 nmol). In (Bajad & Shulaev, 2007; Pimpao˜ et al., 2014; van der Hooft et al., addition, 1.4 nmol of peonidin-3-O-glucoside 69,a3-methyoxy 2012; Zhou, Xiao, Tuli, & Ressom, 2012). In a review on the use analog of cyanidin-3-O-glucoside, was also detected in urine. of HPLC-MS for analyzing chemical contaminants in foods, Hird et al. (2014) emphasized that identification of unknowns using OH OH only multiple reaction monitoring/selective reaction monitoring OH OH + approaches has a high propensity for false positive identification, HO O+ HO O HO and additional scanning techniques within the MS/MS platform O O O O HO HO HO HO are required for further confirmation. These would include using HO O O OH HO multiple transitions and information-dependent acquisition (IDA) HO HO HO O approaches. MS/MS is well suited as the scanning speed is high, HO O HO O HO O and it can be highly accurate when multiple transitions, IDA, or HO HO MS3 approaches are used. However, it suffers from having poor OH OH '' mass accuracy. Therefore, single scanning techniques in untargeted Cyanidin-3-O-sophoroside 66 Cyanidin-3-O-(2 -O-glucosyl)rutinoside 67 analysis requires more high-resolution techniques such as TOF and orbitrap MS. In short, targeted approaches cannot be exchanged OH OCH3 OH OH for untargeted approaches as they require different platforms or HO O+ HO O+ highly optimized methodology using fragmentation-profiling. O O O HO O HO Metabolism and sites of absorption of anthocyanins HO O HO O HO O HO O HO HO Plasma pharmacokinetic data suggest the proximal GI tract is HO HO OH OH OH OH the site of the absorption of phase II metabolites of anthocyanins (de Ferrars et al., 2014b; Del Rio, Rodriguez-Mateus, Spencer, Cyanidin-3-O-rutinoside 68 Peonididin-3-O-rutinoside 69 Tognolini, Borges, & Crozier, 2013; Mullen, Edwards, Serafini, & Crozier, 2008b; Rodriguez-Mateos et al., 2014c). However, it is Thus, of the 292 μmol of anthocyanins ingested only 21.3 nmol now becoming apparent that the majority of ingested anthocyanins was excreted, indicating a 0.007% retrieval and corroborating pre- are absorbed as low-molecular-weight products of chemical and viously reported urinary recoveries. This very low bioavailability is microbial degradation (Czank et al., 2013, de Ferrars et al., 2014b, likely the result of raspberry anthocyanins consisting of primarily Ludwig et al., 2015; Rodriguez-Mateos et al., 2014c). The pres- di-and trisaccharides, and as LPH and/or CBG-mediated cleavage ence of anthocyanin-derived phenolic acids in the blood within 30 of the sugar moieties is unlikely to occur in the proximal GI tract, to 90 min after consumption suggests deglycosylation and chem- absorption in the small intestine would be restricted substantially ical degradation can occur in the upper small intestine (Czank (Prior, 2012). et al., 2013; de Ferrars et al., 2014b). None-the-less, ingested In the Ludwig et al. (2015) study, phenolic metabolites of anthocyanins appear to reach the colon where they are subject cyanidin appeared in plasma in more substantial nmol/L con- to microbial catabolism (Gonzalez-Barrio,´ Edwards, & Crozier, centrations following raspberry consumption (Figure 11). These 2011; McDougall et al., 2014). When ileostomists were fed rasp- included ferulic acid-4-sulfate 70, ferulic acid-4-O-glucuronide

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80 40 30 60 Ferulic Ferulic acid-4'-O-glucuronide 40 20 20 10 0 0 0 6 12 18 24 0 6 12 18 24

20 400 15 Isoferulic acid-3'-O-glucuronide 300 3',4'-Dihydroxyphenylacetic acid 10 200 5 100 0 0 0 6 12 18 24 0 6 12 18 24

Plasma concentration (nmol/L) 120 4000 3000 Hippuric acid 80 4'-Hydroxyhippuric acid 2000 40 1000 0 0 0 6 12 18 24 0 6 12 18 24 Time (h)

Figure 11–Pharmacokinetic proﬁles of phenolic catabolites in plasma following raspberry consumption. Data expressed as mean values ± standard error (n = 9; Ludwig et al., 2015).

71, isoferulic-3-O-glucuronide 72, and 4-hydroxyhippuric acid GI tract. In contrast, 3,4-dihydroxyphenylacetic acid 25 had a 73, all of which had 1.0 to 1.5 hr Tmax, indicating absorption Tmax of 6 hr, which is in line with absorption in the lower bowel in the upper GI tract. It is possible that pH-dependent transfor- (Ludwig et al., 2015). However, low concentrations were also mation of cyanidin to a retro-chalcone structure occurred in the found at earlier time points, indicating that the phenylacetic acid small intestine, followed by metabolism to caffeic acid (Clifford, is formed and also absorbed, to some extent, in the small intes- 2000). The findings of Stalmach et al. (2009) indicate that the tine (Figure 11). The major phenolic in plasma was hippuric acid conversion of caffeic acid to ferulic acid and isoferulic acid and 58, which had a relatively stable 1 to 2 μM concentration over their phase II metabolites can take place in enterocytes. However, 24 hr (Figure 11). These findings reflect those observed following 13 microbial-mediated ring fission of cyanidin in the upper bowel [ C5]cyanidin-3-O-glucoside consumption (Czank et al., 2013; is also plausible as significant bacterial populations ranging from de Ferrars et al., 2014b). 105 to 107 per mL exist between the duodenum and lower ileum Urine. Sixteen phenolic catabolites of anthocyanins were found (Mowat & Agace, 2014). in relatively high amounts in urine collected over 48 hr following raspberry consumption (Table 7; Ludwig et al., 2015). Once OH HO OH again, this finding is in agreement with studies involving other OCH3 OCH3 O COOH - OSO3 O berry sources such as blueberries and elderberries (de Ferrars,

HOOC HOOC Cassidy, Curtis, & Kay, 2014a; Rodriguez-Mateos et al., 2013; Zhong et al., 2017). The overall 0 to 48 hr increase in urinary Ferulic acid-4'-sulfate 70 Ferulic acid-4'-O-glucuronide 71 excretion of phenolic compounds after baseline subtraction was OH HO OH 43.9 ± 8.0 μmol, which is equivalent to 15% of the ingested rasp- O COOH O berry anthocyanins. The extent of hippuric acid formation result- OCH3 ing from cyanidin degradation is difﬁcult to quantify, because of HOOC high background levels originating from other dietary and endoge- Isoferulic acid-3'-O-glucuronide 72 nous sources and signiﬁcant person-to-person variation (Gruemer,

OH 1961; Self, Brown, & Price, 1960). Due to this uncertainty, hip- H OH HOOC N puric acid was not used in the estimated 15% recovery (Table 7; 13 O HOOC Ludwig et al., 2015). However, following consumption of [ C5] 4'-Hydroxyhippuric acid 73 4-Hydroxybenzoic acid 74 cyanidin-3-O-glucoside, the greatest proportion of the label was recovered as hippuric acid (de Ferrars et al., 2014b), confirming It is of interest that 4 -hydroxyhippuric acid 73, aproductof its significant contribution to the metabolic fate of anthocyanins. hepatic glycination of 4 -hydroxybenzoic acid 74,wasdetected In an earlier raspberry feeding study Gonzalez-Barrio´ et al. in plasma, with a Cmax of 78 nmol/L and a Tmax of 1.0 hr fol- (2010) identified urinary phenolic catabolites of cyanidin, using lowing the ingestion of the cyanidin-based raspberry anthocyanins GC-MS rather than HPLC-ion trap MS2,andtheyreporteda (Figure 11). This implies that caffeic acid, derived from cyanidin, significant increase in 4-hydroxymandelic acid 75, which was not underwent conversion to 4 -hydroxybenzoic acid in the upper detected in the later study by Ludwig et al. (2015). This is likely

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Table 7–Compounds excreted in urine in increased amounts 0 to 48 hr after ter ingestion of raspberries (Gonzalez-Barrio´ et al., 2010). Other ingestion of 300 g of raspberries containing 292 μmol of anthocyanins. urinary phenolics not produced by fecal incubations were 4- Increased 0 to 48 hr excretion hydroxymandelic acid, hippuric acid, and 4 -hydroxyhippuric Compounds after raspberry intakea,b acid, implying they are at least in part, products of mammalian Caffeic acid-3’-sulfate 1.0 ± 0.1c enzymes. None of the fecal metabolites that were detected were Dihydrocaffeic acid-3’-sulfate 1.1 ± 0.3d methylated products. It should be noted that ex vivo fecal culture Ferulic acid 5.9 ± 2.1d may not accurately reflect in vivo events, as not all GI tract micro- Ferulic acid-4 -sulfate 6.5 ± 2.6d biota are voided in feces and many which are cannot be cultured ± d Isoferulic acid-3 -sulfate 0.5 0.2 successfully in vitro (Stewart, 2012). Ferulic acid-4-O-glucuronide 1.8 ± 0.5d Potential pathways for the production of the various phenolic Isoferulic acid-3 -O-glucuronide 1.0 ± 0.4d Total hydroxycinnamate 17.8 ± 5.3d catabolites derived from cyanidin are illustrated in Figure 12. In derivatives the preparation of the proposed pathways the following points 3,4-Dihydroxyphenylacetic acid 2.9 ± 1.3d were considered: (homoprotocatechuic acid) r 3 -Methoxy-4 - 0.2 ± 0.2 The conversion of cyanidin to caffeic acid could involve pH- hydroxyphenylacetic acid (homovanillic acid) mediated degradation as well as microbial and mammalian ± d enzymes. Total phenylacetic acids 3.1 1.7 r 4-Hydroxybenzoic acid 6.4 ± 4.8d Subsequent methylation as well as glucuronide, sulfate, and 3,4-Dihydroxybenzoic acid Traces glycine conjugation are most probably mammalian in origin. (protocatechuic acid) r 3-Methoxy-4-hydroxybenzoic acid Traces Dehydroxylation and demethoxylation are almost certainly (vanillic acid) mediated by the gut microflora, whereas hydrogenation steps 4-Hydroxybenzoic acid-3-sulfate 0.3 ± 0.1d may be catalyzed by both microbial and mammalian enzymes. (protocatechuic acid-3-sulfate) d 3-Hydroxybenzoic acid-4-sulfate 0.2 ± 0.1 For convenience, the pathways in Figure 12 show C6−C3 (protocatechuic acid-4-sulfate) catabolites being converted by two α-oxidations to C6–C1 com- Total benzoic acid derivatives 6.9 ± 5.0d d pounds by microflora and/or mammalian enzymes. However, it 4 -Hydroxyhippuric acid 16.1 ± 1.9 − − ± d is plausible the C6 C3 catabolites progress directly to C6 C1 Hippuric acid 239 55 β − Total phenolic derivatives 43.9 ± 8.0d (15.0%)d structures via -oxidation and that C6 C2 catabolites arise inde- (excluding hippuric acid) pendently, possibly by α-oxidation. In reality, further complexity is Based on data of Ludwig et al. (2015). introduced as there are multiple points at which catabolites might aData expressed in μmol as mean values ± S.E. (n = 9). bContent of urine collected for 12 hr prior to supplementation and on an excretion per hour basis used be absorbed. For example, a percentage of some C6−C3 catabo- to subtract from 0 to 48 hr excretion values obtained after raspberry consumption to attain the values β cited. lites could be absorbed and undergo -oxidation and/or mam- cStatistically significant higher excretion 0 to 48 hr after raspberry intake (p ࣘ .05). dThe increased amount excreted expressed as a percentage of the dose of anthocyanins ingested malian phase II conjugation, whereas the balance is subjected to microbial hydrogenation and/β-oxidation prior to absorption and mammalian conjugation. Also, for some catabolites mammalian to be the consequence of differing analytical methodologies, as conjugation either does not occur or is incomplete. many small molecules with a benzene backbone are prone to sig- 13 nificant ion-suppression in HPLC-MS environments. Therefore, The bioavailability of [6,8,10,3 ,5’- C5]- GC-MS should be considered a more suitable method of analysis cyanidin-3-O-glucoside for some phenolic catabolites, although with orbitrap and TOF A notable anthocyanin feeding study is the previously men- mass spectrometry the limits of detection for these compounds are tioned investigation by Czank et al. (2013) and de Ferrars et al. 13 improved substantially. (2014b) who fed C5-labelled cyanidin-3-O-glucoside to human participants. Volunteers ingested 1114 μmol (500 mg) of the glu- OH OH coside and, after 48 hr, recovery was established as 44% of the HO OH HOOC OH 13C dose, with 6.9% in breath, 32% in feces, and 5.4% urine. OH 13 4'-Hydroxymandelic acid 75 Catechol 76 Resorcinol 77 The particular advantage of using [6,8,10,3 ,5 - C5]cyanidin-3- O-glucoside was that it had three 13C molecules incorporated OH into the A-ring and two into the B-ring (Figure 13). An array OH OH HO OH of phenolic products was detected in plasma and urine, and be- HOOC cause of the 13C-label, it was possible to ascertain whether they Pyrogallol 78 3-(3',4'-Dihydroxyphenyl)propionic acid 79 were derived from the A- or B-ring of cyanidin. The capacity to determine relatively low levels of incorporation of the 13C label Gonzalez-Barrio´ et al. (2011) also incubated raspberry antho- into the pools of phenolic compounds enabled cyanidin-derived cyanins, under anaerobic conditions, with human fecal slurries and catabolites to be identified and quantified in much more detail found the first catabolic step included cleavage of the sugar moi- than the above reported raspberry feeding study of Ludwig et al. ety, with subsequent degradation of cyanidin, resulting in the ac- (2015) where catabolites derived from cyanidin were reported only cumulation of catechol 76, (1,2-dihydroxybenzene), resorcinol 77 where there was a statistically significant increase in the urinary (1,5-dihydroxybenzene), pyrogallol 78 (1,2,3-trihydroxybenzene), pool after supplementation. The utility of the 13C labelling design 4-hydroxybenzoic acid 74, 3,4-dihydroxybenzoic acid 35 (proto- is emphasised with respect to the identification of urinary hippuric catechuic acid), 3-(3-hydroxyphenyl)propionic acid 32,and3- acid, as the incorporation of 13C label enabled the amounts de- 13 (3 ,4 -dihydroxyphenyl)propionic acid 79 (dihydrocaffeic acid). rived from [ C5]cyanidin-3-O-glucoside to be distinguished from Except for catechol, resorcinol, and pyrogallol, all these com- the unlabelled endogenous, or background diet-derived hippuric pounds were also detected in the urine of human volunteers af- acid, which in the raspberry study was not possible.

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OH HO OH

Pyrogallol HO OH OH + OH HO O OH Resorcinol OH OCH3 HO OH OH OCH O OH - 3 COOH OSO3 HO OH O - O COOH OH OSO3 Cyanidin OCH3 OCH3 OH HOOC O HOOC Ferulic acid-4'-sulfate HOOC HOOC HOOC 3-Methoxy-4-hydroxybenzoic acid O Isoferulic acid-3'- -glucuronide Caffeic acid-3'-sulfate Ferulic acid-4'-glucuronide

- OSO3 OH OCH OH 3 OCH3 OCH3 OCH OCH 3 3 OH OH OH OH

HOOC HOOC HOOC HOOC HOOC HOOC Isoferulic acid-3'-sulfate Isoferulic acid Caffeic acid* Ferulic acid 3'-Methoxy-4'-hydroxyphenylacetic acid Dihydroferulic acid

- OSO3 OH OH OH OH

HOOC HOOC HOOC 3-(4'-Hydroxyphenyl)propionic acid-3'-sulfate 3-(3',4'-Dihydroxyphenyl)propionic acid 3-(4'-Hydroxyphenyl)propionic acid

HOOC

- 3-(3'-Hydroxyphenyl)propionic acid OSO3 OH OH OH OH OH OH OH OH H HOOC N HOOC HOOC HOOC HOOC HOOC O 3',4'-Dihydroxyphenylacetic acid 4-Hydroxybenzoic acid-3-sulfate 3,4-Dihydroxybenzoic acid 4'-Hydroxyphenylacetic acid 4-Hydroxybenzoic acid 4'-Hydroxyhippuric acid

OH OH OSO - H 3 OH HOOC N HOOC OH HOOC HOOC O OH 3-Hydroxybenzoic acid-4-sulfate Benzoic acid Hippuric acid Catechol 4'-Hydroxymandelic acid

Figure 12–Proposed pathways for the conversion of cyanidin-based anthocyanins to phenolic acids and related compounds. Blue arrows indicate potential steps catalyzed by mammalian enzymes. Red arrows indicate steps that may be catalyzed by microbial enzymes. The formation of caffeic acid from cyanidin, as well as enzymatic steps, may also involved pH-mediated or microbiota-mediated degradation of the anthocyanidin (black arrows). Compounds with boxed names indicate main urinary components after raspberry consumption. Based on the data of Gonzalez-Barrio´ et al. (2011) and Ludwig et al. (2015). There is evidence for the formation of many additional products including 3-hydroxy-4-methoxybenzoic acid, other hydroxy-methoxy isomers of benzoic acid, and phase II metabolites of dihydroxyphenylacetic and hydroxy- and dihydroxycinnamic acids. Other catabolites of cyanidin include 4-hydroxybenzyldehyde and phloroglycinaldehyde (Czank et al., 2013, de Ferrars et al., 2014b). ∗, potential intermediates that did not accumulate in detectable amounts; GlcUA, glucuronide.

may be a consequence of matrix, anthocyanin glycosylation, and OH difference in dose. OH The investigations of Czank et al. (2013), de Ferrars et al. HO O+ 13C (2014b), and Ludwig et al. (2015) have provided novel details of the extensive metabolism and catabolism of cyanidin-3-O-glucoside O HO 63 following ingestion, and when these events are taken into con- HO sideration, anthocyanins appear much more bioavailable than pre- HO O HO viously reported. Other feeding studies with an elderberry extract OH (de Ferrars et al., 2014a) and cranberry juice (Feliciano et al., 2016; McKay, Chen, Zampariello, & Blumberg, 2015), which 13 O [6,8,10,3',5'- C5]Cyanidin-3- -glucoside have very different anthocyanin profiles to that of raspberries, have also shown the important role of phenolic and aromatic catabolites 13 Figure 13–Structure of [6,8,10,3 ,5’- C5]cyanidin-3-O-glucoside. in the bioavailability of anthocyanins. Having orders of magnitude higher plasma/serum Cmax and significantly longer half-lives, all evidence points towards the phenolic and aromatic catabolites as At present the effects of dose, matrix, age, genetics, background being the primary bioavailable products of anthocyanin consump- diet, and lifestyle on the metabolism and bioavailability of antho- tion and, therefore, as discussed in section “Bioactivity,” most cyanins are unknown, making it difficult to compare, in detail, likely are responsible for the reported bioactivity of not just an- findings of different feeding studies. With this in mind, the plasma thocyanins but also other dietary (poly)phenols and flavonoids. pharmacokinetic profiles (Figure 11) and the structural conversions illustrated in Figure 12 are based primarily on outputs from Anthocyanin bioavailability and matrix effects raspberry interventions, and are broadly in line with the array of Most investigations on the bioavailability of anthocyanins and 13C-labeled products detected by Czank et al. (2013) and de Fer- other flavonoids, with few exceptions, have focused on the acute rars et al. (2014b). Differences in findings between the two studies intake of a single product, such as a juice, fruit, or vegetable, after

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Flavanones All citrus fruits, orange, tangerine, lemon, lime, and grapefruit contain relatively high amounts of flavanones (Crozier, Jaganath, Marks, Saltmarsh, & Clifford, 2006). Most bioavailability studies have used orange juice, which is widely consumed and contains mainly hesperetin-7-O-rutinoside 80 (hesperidin) and naringenin-7-O-rutinoside 17, which occur alongside lower levels of other flavanone glycosides and the flavone apigenin-6, 8- C-diglucoside 81. Ferulic acid-4-O-glucoside 82 and coumaric acid-4-O-glucoside 83 have also been tentatively identified (Pereira-Caro et al., 2014, 2016).

HO HO HO O OH OH O OH OCH3 O HO O HO O HO O O HO HO HO O HO OH OH HO HO O Figure 14–Plasma pharmacokinetic profile of a HO O OH pelargonidin-O-glucuronide following the consumption of a strawberry Hesperetin-7-O-rutinoside 80 Apigenin-6,8-C-diglucoside 81 drink either with, 2 hr before, or 2 hr after a morning meal consisting of a croissant with butter and apple jelly, cereal, whole milk, and sausages by 2 OH overweight (BMI: 26 ± 2kg/m ) volunteers. Data expressed as mean OCH3 OH HO OH HO OH values ± standard error (n = 14). Based on the data of Sandhu et al., O O O O OH OH 2016). With permission of the American Chemical Society. HOOC HOOC Ferulic acid-4'-O-glucoside 82 Coumaric acid-4'-O-glucoside 83 volunteers had been on low-polyphenol diets for 2 to 3 days. OH OCH3 Information on matrix effects and the impact of other dietary HO constituents on anthocyanin bioavailability is therefore limited. HO O O O HO Strawberry anthocyanins. Mullen et al. (2008b) reported on OH HO O a feeding study in which strawberries, containing 222 μmol Hesperetin-7-O-glucoside 84 of the anthocyanin pelargonidin-3-O-glucoside 65, were consumed with and without 100 mL of double cream (48% fat). The cream reduced, but not significantly, the plasma Cmax of the main Progress of research since 1990s metabolite, a pelargonidin-O-glucuronide. It did, however, signif- Studies in the 1990s identified small amounts of glucuronide icantly extend the Tmax of the glucuronide, from 1.1 to 2.4 hr. The metabolites of flavanones in human urine, indicating flavonones 0 to 2 hr urinary excretion of the glucuronide and smaller quan- were bioavailable to some extent (Ameer, Weintraub, Johnson, tities of other metabolites was also significantly reduced when the & Rouseff, 1996; Fuhr, & Kummert, 1995). Subsequently, strawberries were eaten with cream but increased in the 5 to 8 hr more detailed studies, using HPLC with electrochemical de- excretion period, suggesting the addition of cream had no impact tection, further identified glucuronide and sulfate conjugates on absorption, only gastric emptying or metabolite kinetics. Over- post-hydrolysis with glucuronidase/sulfatase enzymes (Erlund, all, there was no significant difference in the 0 to 24 hr excretion Meririnne, Alfthan, & Aro, 2001; Manach, Morand, Gil- of the metabolites, which was equivalent to approximately 1% of Izquierdo, Bouteloup-Demange, & Rem´ esy,´ 2003). The study by anthocyanin intake. In keeping with these observations, measure- Manach et al. (2003) revealed the appearance of enzyme-released ment of plasma paracetamol and breath hydrogen established that aglycones in plasma at a sub μmol/L Cmax and approximately 5 cream delayed gastric emptying and extended mouth-to-cecum hr Tmax after drinking 500 mL orange juice containing 363 μmol transit time (Mullen et al., 2008b). of hesperetin-7-O-rutinoside and 83 μmol of naringenin-7-O- In a recent study by Sandhu et al. (2016), 14 overweight vol- rutinoside. Plasma elimination kinetics pointed to absorption in unteers ingested a strawberry beverage either with, or 2 hr before the distal GI tract. Urinary excretion over a 24-hr period after or 2 hr after, a morning meal consisting of a croissant with but- supplementation indicated a recovery of 4.5% of hesperetin and ter and apple jelly, cereal, whole milk, and sausages and providing 7.1% of narigenin. Increasing the intake of juice to 1 L doubled 838 kcal. Co-ingestion of the drink with the meal had a major im- the Cmax, but did not affect Tmax and only marginally increased pact on the plasma Cmax of the main anthocyanin, a pelargonidin- urinary recovery as a percentage of intake (Manach et al., O-glucuronide, which fell significantly to 12.8 ± 2.1 nmol/L 2003). compared to 38.0 ± 6.6 and 35.5 ± 2.1 nmol/L when the drink Studies comparing the bioavailability of hesperetin-7-O- was ingested, respectively, before and after the meal. Co-ingestion rutinoside 80 to orange juice treated with α-rhamnosidase, con- with the meal also extended the Tmax from approximately 1.8 to verting the rutinoside to hesperetin-7-O-glucoside 84, revealed 2.9 hr (Figure 14). Although urinary excretion was not reported, the importance of the conjugating sugar moiety to flavanone ab- preventing a quantitative assessment of change in the absorption sorption. The glucoside was much more bioavailable as indicated of anthocyanins, it is evident that the timing of consumption of a by significantly higher Cmax, area-under-the-curve and urinary multicomponent meal can have a marked impact on the profile and recovery of the flavanone metabolites. Elimination kinetics iden- kinetics of anthocyanin metabolites appearing in the circulatory tified the Tmax of metabolites of the glucoside at 0.6 ± 0.1 hr, system. whereas the Tmax of hesperetin-7-O-rutinoside metabolites was

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7.0 ± 3.0 hr (Nielsen et al., 2006). These differences in elim- a number of studies, with the recovery of naringenin typically ination kinetics suggested that CBG/LPH enzymes in the small higher than hesperetin (Silveira et al., 2014). intestine are able to hydrolyze hesperetin-7-O-glucoside, releasing Identification of hesperetin and naringenin phase II hesperetin prior to phase II metabolism. In contrast, only limited metabolites. Using HPLC-MS and authentic standards, Brett hydrolysis of hesperetin-7-O-rutinoside appears to take place in et al. (2009) identified hesperetin-3-O-glucuronide 85, the small intestine, allowing passage to the distal GI tract where hesperetin-7-O-glucuronide 86, naringenin-4-O-glucuronide microbial hydrolysis of the rutinoside occurs, releasing the agly- 87, and naringenin-7-O-glucuronide 88 in plasma and urine after cone for absorption and phase II metabolism. orange juice intake. In addition, two hesperetin diglucuronides and a hesperetin sulfo-glucuronide were detected. The identi- OH fied hesperetin metabolites were confirmed by Bredsdorff et al. HO OH O COOH (2010) who also identified hesperetin-3 ,7-O-diglucuronide 89, O OH 90 91 OCH3 HOOC OCH3 hesperetin-5,7-O-diglucuronide , and hesperetin-3 -sulfate . O HO O HO O O This study confirmed that hesperetin-7-O-glucoside was absorbed HO OH more readily than the 7-O-rutinoside, and, similarly, naringenin- HO O HO O 7-O-glucoside was also absorbed more rapidly, with metabolites Hesperetin-3'-O-glucuronide 85 Hesperetin-7-O-glucuronide 86 excreted in urine in approximately 7-fold higher amounts than those derived from naringenin-7-O-rutinoside (Bredsdorff et al.,

OH 2010). Potential routes for the formation of hesperetin metabolites O HO OH OH are illustrated in Figure 15. O COOH HOOC O HO O HO O O Absorption of flavanone-derived compounds in the proximal and HO OH distal GI tract. Borges et al. (2010) investigated the absorption HO O HO O and elimination of a (poly)phenol-rich drink containing a diverse Naringenin-4'-O-glucuronide 87 Naringenin-7-O-glucuronide 88 spectrum of (poly)phenolic and flavonoid compounds including 45 μmol of hesperetin-7-O-rutinoside. Hesperetin-7-O- OH glucuronide 84 and a second glucuronide, most proba- HO OH O COOH bly hesperetin-3 -O-glucuronide 85, together with a sulfated- O glucuronide, were excreted in human urine collected 0 to 24 hr OCH3 HOOC post-intake, with total recovery established as 12.0% of in- HO O O O HO gested hesperetin-7-O-rutinoside. In a subsequent study, where OH HO O ileostomists consumed the same beverage, the quantity of hesperetin metabolites detected in urine was 3.5% of intake (Borges O 89 Hesperetin-3',7- -diglucuronide et al., 2013). The differing levels of hesperetin metabolites excreted in urine by the ileostomists and volunteers with a function- OH ing colon indicates absorption of hesperetin is not exclusive to the OCH3 HOOC - large intestine but that around one-third is absorbed in the upper HO O O O OSO3 HO OCH3 GI tract and two-third in the lower bowel. The plasma pharma- OH HOOC O O HO O cokinetic profile of the hesperetin-O-glucuronides obtained when HO O HO the drink was consumed by volunteers with a colon is in line with OH HO O this observation, as although the Tmax was 3.7 hr, the profile Hesperetin-5,7-O-diglucuronide 90 Hesperetin-3'-O-sulfate 91 indicated that absorption began within 30 min of hesperetin-7- O-rutinoside ingestion (Figure 16).

OH O Interindividual variations in flavanone bioavailability. Brett OH et al. (2009) investigated the absorption, metabolism, and elimi- O O HO O HO O nation of flavanones in 20 volunteers after the ingestion of orange HO HO OH OH fruit and juice, and they reported no difference in plasma profiles HO O or urinary excretion between the treatments. A larger population Eriodictyol-7-O-rutinoside 92 study, feeding orange juice to 129 volunteers aged 18 to 80 yr, revealed that with increasing age there was a small but significant OH reduction in the excretion of hesperetin 60 but not naringenin OCH3 16. However, excretion was not affected by gender, body mass in- HOOC dex, or contraceptive pill use. Substantial inter-individual variation OH 93 was observed for excretion recovery, ranging from 1.6% to 59% 3-(3'-Hydroxy-4'-methoxyphenyl)hydracrylic acid of intake of naringenin (9.9% median recovery) and 0% to 25% for hesperetin (3.1% median). Possibly, the lack of effect of age Progress since 2014 and gender suggests the variability resulted from person-to-person Urinary excretion of hesperetin and naringenin metabolites differences in intestinal microbiota, although other factors could and their phenolic and aromatic acids was detailed in an orange contribute, including analytical methodology, dose, and juice pro- juice feeding study in which participants consumed 584 μmol of cessing method which affects soluble and precipitated flavanone (poly)phenolic compounds, including 348 μmol of hesperetin-O- levels (Tomas-Navarro,´ Vallejo, Sentandreu, Navarro, & Tomas-´ glycosides, 165 μmol of naringenin-O-glycosides, and 5 μmol of Barberan,´ 2014; Vallejo et al., 2010). Variable urinary excretion eriodictyol-7-O-rutinoside 92 (Pereira-Caro et al., 2014). A num- of orange juice flavanone metabolites has been reported across ber of flavanone metabolites were detected in 0 to 24 hr urine after

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OH O OCH3 O HO O HO O O HO HO OH OH HO O Hesperetin-7-O-rutinoside

- OSO3 OH OCH 3 OCH3 HO O HO O Hesperetin-sulfo-O-glucuronide

HO O HO O Hesperetin-3'-sulfate Hesperetin OH OH HO OH O COOH OCH3 O HO O OH HOOC OCH3 OCH3 O HO O O HO O HOOC O HO HO O O OH HO OH HO O HO O O Hesperetin-5-O-glucuronide Hesperetin-7-O-glucuronide Hesperetin-3'- -glucuronide

OH OH OH HO OH HO OH O COOH O HOOC OCH3 COOH O HO O O O O HO OCH OH 3 HOOC OCH3 O HOOC O HO O O O O HO HO O OH HO HOOC OH O HO O HO O O O HO O Hesperetin-5,7- -diglucuronide OH Hesperetin-3',7- -diglucuronide

Hesperetin-3',5-O-diglucuronide

Figure 15–Proposed pathways for the phase II metabolism and conversion of hesperetin metabolites. Compounds with boxed names indicate the main 0-24 hr urinary metabolites. juice consumption that were not present in the urine of the volunteers collected after drinking a flavanone-free placebo drink. This study reported an 83 μmol excretion of metabolites, principally the 3-O-and7-O-glucuronides of hesperetin, hesperetin- 3-sulfate, and the 4-O-and7-O-glucuronides of naringenin, which corresponds to 16% of the flavanone intake. Unlike the flavanone metabolites, baseline urine does contain phenolic and aromatic acids, as they are produced by endogenous pathways as well as being metabolic products of dietary flavanones and other (poly)phenolic compounds. However, eight phenolic catabolites were excreted in urine in significantly higher amounts 0 to 24 hr after orange juice consumption com- Figure 16–Hesperetin-O-glucuronide plasma pharmacokinetics after the pared with excretion after intake of the flavanone-free placebo ingestion of a (poly) phenol-rich drink containing 45 μmol of O drink (Table 8; Pereira-Caro et al., 2014). 3-(3-Hydroxy-4- hesperetin-7- -rutinoside by human volunteers. Data expressed as mean values ± standard error (n = 6). Based on the data of Borges et al. (2010). methoxyphenyl) hydracrylic acid 93 was excreted in substantial amounts after orange juice intake, yet was absent in placebo urine. 3-(3-Hydroxyphenyl)hydracrylic acid 37, although present in et al., 2014). Although post-intervention levels increased signif- trace amounts in the control urine, increased >10-fold after orange icantly by 378 μmol to 610 ± 48 μmol following orange juice juice consumption, whereas excretion of 4-hydroxhippuric acid intake, exactly how much of this increase in hippuric acid was increased approximately 100-fold from 0.2 to 19 μmol. The over- related to flavanone metabolism intake is difficult to ascertain be- all increase in phenolic catabolites, excluding hippuric acid, after cause of the contribution of endogenous sources. If increased hip- orange juice consumption was 134 μmol, which is 23% of the 584 puric acid was included in the calculation, the overall flavanone μmol intake of (poly)phenolic compounds (Table 8). Addition of recovery would be approximately 100%. It is, therefore, apparent 134 μmol to the 83 μmol excretion of flavanone glucuronide and that when both metabolites and catabolites are taken into con- sulfate metabolites indicates a recovery of 37% of intake. sideration, hesperetin- and naringenin-7-O-rutinosides are highly Excretion of hippuric acid 58 was not included in the reported bioavailable (Pereira-Caro et al., 2014). 37% recovery as the placebo 0 to 24 hr urine contained 232 ± Tofurther elucidate the metabolism pathways of flavanones, hes- 21 μmol of the glycinated benzoic acid derivative (Pereira-Caro peretin and naringenin were incubated in vitro with human fecal

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Table 8–Phenolic catabolites excreted in urine in signiﬁcantly increased amounts (p <.05) 0 to 24 hr after the ingestion of 250 mL of orange juice containing 584 μmol of (poly)phenolic compounds compared to a (poly) phenol-free placebo drink (based on Pereira-Caro et al., 2014).a

Phenolic catabolites Placebo drink Orange juice Increase with orange juice 3-(3-Hydroxy-4-methoxyphenyl)hydracrylic acid n.d 72 ± 10 72 3-(3-Hydroxyphenyl)hydracrylic acid 2.5 ± 0.8 31 ± 429 3-(3-Hydroxy-4-methoxyphenyl)propionic acid n.d. 4.7 ± 0.8 4.7 (dihydro-isoferulic acid) 3-(3-Methoxy-4-hydroxyphenyl)propionic acid n.d. 6.3 ± 1.0 6.3 (dihydroferulic acid) 3-Methoxy-4-hydroxyphenylacetic acid 4.7 ± 0.7 7.3 ± 0.8 2.6 3-Hydroxyhippuric acid n.d. 0.8 ± 0.3 0.8 4-Hydroxyhippuric acid 0.2 ± 0.1 19 ± 419 Hippuric acid 232 ± 21 610 ± 48 378 Total minus hippuric acid 7 141 134 (23%) Total with hippuric acid 239 751 512 (88%) aData expressed in μmol as mean values ± S.E. Figures in italicised parenthesis are excretion as a percentage of (poly)phenol intake. Not detected, n.d. slurries cultured under anaerobic conditions (Pereira-Caro, et al., hydroxycinnamate was converted principally to 3-methoxy-4- 2015a). Incubations were also carried out with ferulic acid 94,as hydroxyphenyl)propionic acid and its demethoxy-derivative 3- orange juice, as well as flavanones, also contains ferulic acid-4-O- (4-hydroxyphenyl)propionic acid, along with smaller amounts glucoside 82 (Pereira-Caro et al., 2014). Comparisons were made of their phenylacetic acid counterparts (Pereira-Caro et al., between fecal incubations and in vivo urinary excretion data to 2015a). Potential routes for these transformations are illustrated establish the potential involvement of microbial and mammalian in Figure 17, which again shows the possible conversion of 4- metabolism in the pathways illustrated in Figure 17 and 18. To hydroxyphenylacetic acid to 4-hydroxyhippuric acid. As with the summarize, naringenin is likely to undergo microbiota-mediated conversions depicted in Figure 12 in section “Do (−)-Epicatechin ring fission producing 3-(4-hydroxyphenyl)propionic acid which Metabolites Reach the Brain? Biomakers of Flavan-3-ol Con- is dehydroxylated and converted mainly to 3-(phenyl)propionic sumption.”, for convenience, the pathways in Figure 17 and 18 acid, which in vivo could potentially contribute to the uri- show C6−C3 catabolites being converted by two α-oxidations to nary pool of hippuric acid (Figure 17). Colonic ring fission C6–C1 compounds by microflora and/or mammalian enzymes. of hesperetin produces dihydroisoferulic acid [3-(3 -hydroxy-4 - However, the C6−C3 catabolites may progress directly to C6−C1 methoxyphenyl)propionic acid], which is demethylated produc- structures via β-oxidation and that C6−C2 catabolites arise inde- ing dihydrocaffeic acid [3-(3,4-dihydroxyphenyl)propionic acid]. pendently, possibly by α-oxidation. This, in turn, via successive dehydroxylations, is converted to 3- Orange juice intake was also characterized by urinary excre- (3-hydroxyphenyl)propionic acid and 3-(phenyl)propionic acid, tion of 3-(3-hydroxy-4-methoxyphenyl)hydracrylic acid and 3- which could be further converted to the respective urinary pools (3-hydroxyphenyl)hydracrylic acid (Table 8; Pereira-Caro et al., of 3-hydroxyhippuric acid and hippuric acid (Figure 18). In 2014), neither of which was reported to be produced from fla- vitro degradation of hesperetin also yields small quantities of vanones in fecal incubations (Pereira-Caro et al., 2015a, 2016). 3-(4-hydroxyphenyl)propionic acid and 4-hydroxyphenylacetic Because of their compatible B-ring substituent pattern, they acid, which, via the pathway illustrated in Figure 18, and like would appear to be catabolites of hesperetin and products of the naringenin catabolites, could be further converted to 4- a combination of gut flora transformations and colonocyte hydroxyhippuric acid. Previously reported colonic bacteria po- and/or hepatic conversions, possibly via the route shown in tentially involved in some of the proposed conversions illustrated, Figure 18. The involvement of the microbiota is supported in Figure 17 and 18, are Eubacterium limosum and members of the by a human study which showed urinary excretion of 3-(3- Enterobacter and Escherichia genera, which possess O-demethylase hydroxy-4-methoxyphenyl)hydracrylic acid following oral intake and hydrolase activity (DeWeerd et al., 1988; Grbic-Gali´ c,´ 1986; of hesperetin-7-O-rutinoside, but only trace amounts when ab- Hur & Rafii, 2000). sorption of the rutinoside was confined to a 20-cm segment of the

OCH3 OCH3 proximal jejunum using a Loc-I-gut intestinal perfusion catheter OH OH (Actis-Goretta et al., 2015), previously mentioned in the context − HOOC HOOC of ( )-epicatechin absorption in section “Urinary Metabolites.” Ferulic acid 94 3-(3'-Methoxy-4'-hydroxyphenyl)propionic acid 95 Flavanone bioavailability and matrix effects. Co-consumption of yogurt with flavanones had no impact on the plasma Cmax and OCH3 Tmax of hesperetin-O-glucuronides when volunteers drank orange OH μ HOOC juice containing 168 mol of hesperetin-7-O-rutinoside with and without a 150 mL yogurt (3.8% fat) (Mullen, Archeveque, Ed- 96 3'-Methoxy-4'-hydroxyphenylacetic acid wards, & Crozier, 2008a). The 0 to 5 hr urinary excretion of the Among the phenolic acids excreted in urine in increased flavanone metabolites was reduced significantly by the yogurt, but amounts after orange juice consumption (Table 8) are 3- the total quantity of metabolites in urine collected over 0 to 24 (3-methoxy-4-hydroxyphenyl)propionic acid 95 (dihydroferulic hr, corresponding to approximately 7.0% of intake, was not dif- acid) and 3-methoxy-4-hydroxyphenylacetic acid 96, which be- ferent. The yogurt had no effect on either gastric emptying or on cause of the 3-methoxy group are unlikely to be catabolites of the mouth-to-cecum transit time of the “head” of the meal, both hesperetin which has a 4-methoxy group. They could, how- of which were delayed by double cream when co-ingested with ever, be derived from ferulic acid-4-O-glucoside. In vitro,fe- strawberries (Mullen et al., 2008b). These incongruities could re- cal incubations with ferulic acid indicate this is feasible, as the flect the differences in fat content of the matrices as the double

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OGlcUA OH OCH3 - OSO3 HOOC HOOC Coumaric acid-4'-O-glucuronide 4'-Hydroxycinnamic acid HOOC Ferulic acid-4'-sulfate OH OCH OCH HO OH HO O 3 3 OH OGlcUA

OH OH O HOOC HOOC Phloroglucinol Naringenin Ferulic acid Ferulic acid-4'-O-glucuronide

OCH3 OCH3 OH OH OGlcUA

HOOC HOOC HOOC HOOC 3-(Phenyl)propionic acid 3-(4'-Hydroxyphenyl)propionic acid Dihydroferulic acid Dihydroferulic acid-4'-O-glucuronide

OCH3 - OSO3 OCH3 OH OH HOOC HOOC HOOC HOOC Dihydroferulic acid-4'-sulfate Phenylacetic acid 4'-Hydroxyphenylacetic acid 3'-Methoxy-4'-hydroxyphenylacetic acid

OCH3 OH OH

HOOC HOOC HOOC Benzoic acid 4-Hydroxybenzoic acid 3-Methoxy-4-hydroxybenzoic acid

- OSO3 OH H H HOOC N HOOC N HOOC Benzoic acid-4-sulfate O O Hippuric acid 4'-Hydroxyhippuric acid

Figure 17–Proposed pathways for the metabolism of naringenin and ferulic acid released by cleavage of hesperetin-7-O-rutinoside and ferulic acid-4-O-glucoside after the consumption of orange juice by humans. Compounds with boxed names indicate major components in 0 to 24 hr urine. Curved green arrow indicates ring fission. Red arrows are potential microbiota-mediated conversions and blue arrows indicate steps potentially catalysed by mammalian enzymes. GlcUA, glucuronide. Based on data of Pereira-Caro et al. (2014, 2015a,b, 2016). cream contained 48% fat compared to only 3.8% of the yogurt. the meal reaching the large intestine, thereby increasing upper in- Higher levels of fat are likely to stimulate both duodenal and ileal testinal absorption and limiting microbiota-mediated breakdown fat receptors and thereby delay both gastric emptying and the of the flavanones. mouth-to-cecum transit time of the head of the meal (Rao, Lu, Flavanone bioavailability and probiotics. Co-administration of & Schulze-Delrieu, 1996; Welch, Cunningham, & Read, 1988), a microencapsulated probiotic (Bifidobacterium longum R0175) and whereas the lower fat content of the yogurt would have a lesser orange juice flavanones (Pereira-Caro et al., 2015b), compris- impact. Therefore, the initial significant delay in urinary excretion ing a total of 196 μmol of (poly)phenols (56 μmol naringenin- of flavanone metabolites when orange juice was consumed with O-glycosides and 111 μmol hesperetin-O-glycosides), was ex- the yogurt may simply reflect the slower delivery of the bulk of plored in an acute study following a single oral bolus of orange the meal. juice with and without the probiotic. Subsequently, the same In the subsequent analysis of colon-derived urinary phenolic orange juice was consumed acutely after daily supplementation catabolites from the orange juice-yogurt study, 0 to 24 hr urine with the probiotic for a period of 4 wk. Bioavailability was as- contained a total of 62 ± 18 μmol of hydroxy- and methoxy- sessed by 0 to 24 hr urinary excretion, and it was similar when phenolic catabolites, equivalent to 37% of the ingested flavanones the orange juice was consumed with or without acute probi- (Roowi, Mullen, Edwards, & Crozier, 2009). However, urinary otic intake. Hesperetin-O-glucuronides, hesperetin-3-sulfate, and levels of microbial catabolites fell to 9.3 ± 4.4 μmol in the juice- naringenin-O-glucuronides were the main metabolites identified, plus-yogurt group. The reason for this substantial decline in mi- corresponding to 22% of intake, while excretion of key phenolic crobial catabolite excretion requires further investigation, but one and aromatic acids, excluding hippuric acid, was equivalent to 21% possible explanation is that yogurt potentially slowed the bulk of of the ingested (poly)phenols. Acute orange juice consumption

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OH OGlcUA HO OH OCH3

HOOC OH HOOC OH Phloroglucinol Isoferulic acid-3'-glucuronide 3-(3'-Hydroxyphenyl)hydracrylic acid OH OH OCH3 OH - OSO3 OCH3 HO O OCH3 OCH3

HOOC HOOC HOOC OH OH O Isoferulic acid Dihydro-isoferulic acid-3'-sulfate 3-(3'-Hydroxy-4'-methoxyphenyl)hydracrylic acid Hesperetin

OH OH OH OGlcUA OCH OCH 3 OCH3 OCH3 3 HOOC HOOC HOOC HOOC 3-Hydroxy-4-methoxybenzoic acid 3'-Hydroxy-4'-methoxyphenylacetic acid* Dihydro-isoferulic acid Dihydro-isoferulic acid-3'-O-glucuronide

OH OH OH 3-(3'-Hydroxyphenyl)propionic acid-4'-sulfate 3-(4'-Hydroxyphenyl)propionic acid-3'-sulfate HOOC HOOC HOOC 3-(3'-Hydroxyphenyl)propionic acid-4'-O-glucuronide O 3-(Phenyl)propionic acid 3-(3'-Hydroxyphenyl)propionic acid Dihydrocaffeic acid 3-(4'-Hydroxyphenyl)propionic acid-3'- -glucuronide

OH OH OH OH HOOC HOOC HOOC HOOC 3-(4'-Hydroxyphenyl)propionic acid Phenylacetic acid 3'-Hydroxyphenylacetic acid 3',4'-Dihydroxyphenylacetic acid OGlcUA

OH OH OH HOOC OH HOOC 3-(Phenyl)propionic acid-4'-O-glucuronide 4'-Hydroxyphenylacetic acid HOOC HOOC HOOC Benzoic acid 3-Hydroxybenzoic acid 3,4-Dihydroxybenzoic acid

OH - OSO3 OH HOOC H H HOOC HOOC N HOOC N 4-Hydroxybenzoic acid Benzoic acid-4-sulfate O O Hippuric acid 3'-Hydroxyhippuric acid OH H HOOC N

O 4'-Hydroxyhippuric acid

Figure 18–Proposed pathways for the colonic metabolism of hesperetin released by cleavage of hesperetin-7-O-rutinoside after the consumption of orange juice by humans. Based on urinary excretion in feeding studies and in vitro fecal incubations. Compounds with boxed names indicate major components in 0 to 24 hr urine. Curved green arrow indicates ring ﬁssion. Red arrows are potential microbiota-mediated conversions and blue arrows are steps potentially catalysed by mammalian enzymes. ∗, intermediate that did not accumulate in detectable amounts. GlcUA, glucuronide. Based on data of Pereira-Caro et al. (2014, 2015a,b, 2016, 2017).

after 4 wk of probiotic intake significantly increased excretion of with hesperetin-7-O-rutinoside and naringenin-7-O-rutinoside flavanone metabolites to 27% of intake, while excretion of the phe- did not result in the conversion of either rutinoside to a glu- nolic catabolites also increased significantly to 43% of (poly)phenol coside or glycoside to an aglycone (Pereira-Caro et al., 2015a). intake, giving an overall bioavailability of 70%. It is unclear as to Assuming the gut environment does not induce α-rhamnosidase how this increased bioavailability is mediated as neither the probi- and/or β-glucosidase expression in vivo, it is unlikely that cleavage otic bacterial profiles of stools, nor stool moisture, weight, pH, or of sugar residues represents a key mechanism by which chronic levels of short-chain fatty acids and phenols differed significantly intake of the probiotic enhances the bioavailability of the orange between treatments. However, as noted earlier in Bioavailability juice flavanones. Although the mechanism responsible for these of Raspberry Anthocyanins in vitro fecal bacterial profiles do not differences in bioavailability remains elusive, further investigation necessarily accurately represent the microbial population in the of the impact of long-term supplementation of probiotics on the colon as not all microbiota are voided in feces, and many that are, bioavailability and health-promoting benefits of flavanones, as well cannot be cultured successfully in vitro (Stewart, 2012). as other flavonoids and (poly)phenolics, is warranted. In vitro, the intestinal bacterium B. longum R0175 possessed- Biomarkers of flavanone intake. The main metabolites de- rhamnosidase activity when assayed by the method of Avila´ tected in urine after orange juice intake, which are absent et al. (2009) using p-nitrophenyl-α-L-rhamnopyranoside as a sub- in baseline urine, are the hesperetin metabolites, hesperetin- strate. However, in vitro anaerobic incubations of the bacterium 3-O-glucuronide 85 and hesperetin-3-sulfate 91. Hesperetin

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1079 Dietary flavonoids: a historical review . . . is a flavonoid with an unusual 3-hydroxy-4-methoxy B- Yet, the field persevered, as although many of the criticisms were ring structure so its phenolic catabolite 3-(3-hydroxy-4- appropriate, and flavonoids appeared non-essential for life, a sig- methoxyphenyl)hydracrylic acid 93, is likely to be a good marker nificant number of animal and in vitro studies identified biological of hesperetin intake as it is absent in baseline urine and unlikely activity. Despite these early criticisms, the number of publications to be derived from other dietary flavonoids (Pereira-Caro et al., on flavonoids continued to increase at an almost exponential rate 2014, 2016b). (Figure 19). In the 1960s, publications began emerging reporting that Bioactivity flavonoids from oats, sorghum, berries, and tea had significant This section describes in detail the perception of the flavonoid antioxidant activity, in addition to their previously reported action research field over time, as captured in previously published works, on capillary permeability (Harper, Morton, & Rolfe, 1968, 1969; often reviews, summarizing the expansion in diversity of ther- Lynn & Luh, 1964; Yasumatsu, Nakayama, & Chichester, 1965). apeutic targets and functional endpoints, with the goal of in- There was even an obscure report of feasibility studies into the forming and refining the focus of future investigations. Conse- effects of anthocyanins on night blindness (Borges, 1965). Against quently, where significant corroborating literature exists, suitable this background, interest in flavonoid research continued to diver- reviews were often referenced rather than the individual source, sify over the next decade. and, although the review may have extended beyond the ref- Mechanisms of action research in the 1970s extended into vari- erenced timeline/timeframe, the source publication did not. Fur- ous tissues, leveraging data from early observations on vascular per- thermore, we focus on modern theories, which have been brought meability and capillary function, including the eye (Varma, 1976), to the forefront of flavonoid research in recent years, and, perhaps renal and intestinal tissues (Robinson, L’Herminier, & Claudet, most significantly, special attention is centered on colonic metabo- 1979). Studies of vascular effects (vessel dilation) and blood pres- lites. Attention is given to beneficial health effects of monomeric sure (BP) reduction in animal models still predominated (Petkov & flavonoids, excluding medicinal plant sources, synthetic, pharma- Manlov, 1978), while emerging targets included membrane trans- cological, or topical treatments, or studies describing deleterious port (Robinson et al., 1979), enzyme inhibition (Borchardt & effects which primarily relate to cytotoxic activity at pharmaco- Huber, 1975), antimicrobial activity, and impact on metal chela- logical concentrations (Galati & O’Brien, 2004; Nijveldt et al., tion and antitumor activity (Brown, 1980; Fujita, Nagao, Varma, 2001; Skibola & Smith, 2000), phytoestrogenic effects (Cassidy, & Kinoshita, 1976). Early studies into the activity of flavonoids Bingham, & Setchell, 1994; D’Adamo & Sahin, 2014), or drug focused more on enzyme activity while later works concentrated interactions (Ameer & Weintraub, 1997). Isoflavones, as noted on antioxidant effects. in section “Introduction to Bioavailability and Transport,” have Clinical studies on flavonoid-rich foods, such as tea, focused been excluded as they have their own unique history warranting primarily on nutritive value (vitamin, mineral contents, and so a separate review. on), rather than flavonoid content, although some researchers were starting to propose that flavonoids also contributed to the reported Research 1930-to-1980 health effects. A review by Stagg and Millin (1975) highlighted In the 1930s, there were investigations on the activity of an the likely “contribution of flavonoids to the health effects” of tea. unknown plant constituent having “vitamin-like” qualities, which Interestingly, Kuhnau (1976) echoed the sentiments of many cur- was originally referred to as vitamin P. The evidence was initially rent flavonoid researchers, suggesting despite their non-essentiality, based on the clinical study of scurvy, where compounds in citrus flavonoids likely played a role in promoting “optimal health.” At were reported to act in association or synergy with ascorbic acid this time, the hypothesized mechanisms of action were still very on hemorrhagic symptoms associated with capillary fragility. A much linked to processes affecting capillary function. crystalline component, originally termed “citrin,” appeared to influence the biological activity of vitamin C on micro-vessel Research 1980-to-1990 permeability, and it was subsequently shown to be a mixture of The 1980s saw a further proliferation of mechanistic targets in hesperetin-7-O-rutinoside 80 (hesperidin) and an eriodictyol-O- animal and in vitro studies. In addition, there was increased focus on glucoside (Roger, 1988; Zilva, 1937). flavonoid subclasses beyond citrus-derived flavanones, including By the 1950s an extensive literature was accumulating on the flavonols, most notably quercetin 1 and flavan-3-ols. There was bioactivity of flavonoids/vitamins, and Clark (1949) and Clark, also a substantial number of publications on the bioactivity of MacKay, Mary, & Bryant (1950) noted, despite extensive clinical flavonoids from tea and traditional medicines, many of which and experimental studies into the biological activity of flavonoids, were published in Chinese, Japanese, and Russian and had never that there was a need for more studies to establish their bioavailabil- been translated into English. Reports of possible mechanisms of ity. This sentiment would become a common theme of the next action continued to grow, such as effects on membrane transport, half-century in flavonoid research. Shils and Good-Hart (2009) enzyme, and antioxidant activities, with research extending into published a review, citing nearly 300 publications, on vitamin- impact on prostaglandin synthesis and anticancer activities. P that questioned the “essential” nature of flavonoids. This was Flavonoids were still primarily considered drug or “drug-like” followed by harsh editorials directly criticizing the flavonoid liter- in the 1980s, and were studied following a pharmaceutical model, ature, stating that the evidence presented was confusing and con- by comparing the effects of aglycones and plant-derived glycosides flicting and that studies were poorly controlled, lacking statistical at high μmol/L concentrations and equating them with estab- power and reporting weak biological activity (Bean, 1956; Bryan, lished pharmaceutical agents in animal and cell culture models. 1956). The editorials went so far as to state, it was a “sad reflec- In addition, anticancer properties were most often attributed to tion of editorial judgment” to see these studies in press. Finally, in cytotoxicity. It would be some time before nutrition and food 1957 a review in JAMA by Pearson (1957) concluded there was scientists began studying the effects of flavonoids at levels more no convincing evidence of flavonoids being a “required” dietary relevant to the diet. Even in the 1980s, reviews were beginning nutrient, ending the pursuit of vitamin P as an essential nutrient. to note the apparent diversity of reported mechanisms of action

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Figure 19–Reported number of flavonoid publications in PubMed. MEDLINE R /PubMed R , The National Library of Medicine R (NLM R ). 10/10/2017; https://www.ncbi.nlm.nih.gov/pubmed. of flavonoids, as stated by Roger (1988) “the various effects of Mechanisms of action flavonoids suggest that numerous pharmacological mechanisms The 1980s would witness a drastic increase in the diversity are involved.” of mechanisms of action reported for flavonoids, particularly anti- inflammatory, enzyme, and membrane transport effects. There was an accumulation of studies reporting the ability of flavonols and Vascular activity flavanones to act as anti-inflammatory agents (Brasseur, 1989; Mid- The flavonol quercetin 1 is arguably the most investigated dleton & Kandaswami, 1992), including interfering with leukocyte flavonoid to date, and onions and apples are the most commonly migration, basophil histamine release (Middleton, 1986), arachi- consumed dietary sources, though most studies have used pure donic acid metabolism, and prostaglandin biosynthesis (Moore, quercetin (Toh, Tan, Lim, Lim, & Chong, 2013). The antithrom- Griffiths, & Lofts, 1983; Panthong, Tassaneeyakul, Kanjanapothi, botic action of quercetin and quercetin-3-O-rutinoside 13 was Tantiwachwuttikul, & Reutrakul, 1989; Welton, Hurley, & Will, commonly reported in vivo, in various culture models associated 1988). Other studies reported various actions on enzyme function with preventing platelet aggregation and inhibiting lipoxygenase (Nagai, Miyaichi, Tomimori, & Yamada, 1989) including: activity (LOX) activity (Gryglewski, Korbut, Robak, & Swies, 1987). In of flavonols on protein kinase inhibition (Cochet, Feige, Pirol- animal models, 3,3-O-dimethylquercetin 97 was also reported to let, Keramidas, & Chambaz, 1982; Ferriola, Cody, & Middleton, improve vascular tone in isolated vascular smooth muscle (Abdalla 1989; Rogers & Williams, 1989); flavone-induced liver monooxy- et al., 1989; Toh et al., 2013). genase activity (Siess, Guillermic, Le Bon, & Suschetet, 1989); the impact of flavonoids on xenobiotic metabolizing enzymes such

OCH3 as cyclooxygenase (COX) and lipoyxgenase (LOX; Roger, 1988; OH Wood, Smith, Chang, Huang, & Conney, 1986); the effects of HO O quercetin on enzyme secretory mechanisms, including interfer-

OCH3 ence of neutrophil enzyme transport (Long et al.,1981); and ef- O HO fects of quercetin and quercetin-3-O-rutinoside on lysosomal en- 97 3,3'-O-Dimethylquercetin zymes in fibroblasts (Vladutiu & Middleton, 1986). Flavonoids were also reported to have high affinities for membrane transport Reports of the vascular activity of anthocyanins from berries proteins (Kohrle, Spanka, Irmscher, & Hesch, 1988). Quercetin were also emerging, for example, anthocyanins from bilberry (Va c - was shown to affect ATP-driven pumps, including Na/K-ATPase cinium myrtillus) were shown to prevent an increase in vascular and calcium-ATPase, consequently affecting ion exchange flux permeability in animal models of hypertension (Detre, Jellinek, (Bakker-Grunwald, Andrew, & Neville, 1980; Breitbart, Stern, & Miskulin, & Robert, 1986). Rubinstein, 1983; Racker, 1986). There was continued pursuit of the redox behavior of flavonoids where many speculated electrochemical properties of flavonoids were driving their observed bio- Anticancer activity logical effects (Hodnick, Milosavljevic, Nelson, & Pardini, 1988). Interest in anticancer properties of flavonoids and flavonoid- rich foods was increasing, with studies reporting an impact of Research 1990-to-2000 flavonoids on phase II enzymes associated with chemo-protection Flavonoid-rich foods, supplements, and extracts became more (Talalay, 1989). Quercetin was reported to suppress phospholipid of a focus in the 1990s as opposed to the earlier more pharmacolog- metabolism by tumor promoters (Nishino, Nagao, Fujiki, & Sug- ical study designs. Particular attention was given to rich sources of imura, 1983) and to inhibit squamous cell carcinoma cell growth quercetin 1 and (−)-epicatechin 38/(+)-catechin 28 (Williamson (Castillo et al., 1989), whereas green tea flavonoids were shown to & Manach, 2005). A large number of reviews focused on tea possess anti-mutagenic activities (Wang et al., 1989). and its cardiovascular and anticancer activities, although studies

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1081 Dietary flavonoids: a historical review . . . exploring the impact of wine on cardiovascular disease (CVD) & Yokoyama, 2004; Tomasian, Keaney, & Vita, 2000). As NO is were also increasing, recognizing flavonoids as a contributory a free radical itself, and flavonoids were known to possess antiox- factor to the observed benefits of moderate wine consumption idant properties, protection of NO provided a logical avenue to (Rosenberg Zand, Jenkins, & Diamandis, 2002). explore the antioxidant properties of flavonoids. At the time, it A proliferation of human intervention studies was seen in the was believed that dietary antioxidants could preserve NO by pre- 1990s, whereas animal and in vitro studies had dominated the venting its reaction with superoxide and/or other oxygen-centered literature in previous decades. An expanding number of health radicals, maintaining vasodilatory response, and, subsequently, vas- outcomes was reported, with a focus on reduction of oxidative cular homeostasis. Most of this evidence came from studies using stress biomarkers, BP, lipids, lipoproteins, and various mechanisms tocopherols and vitamin C, however, investigations were already of vascular function (Williamson & Manach, 2005). The field was pursuing the impact of flavonoids on redox chemistry, and epi- also diversifying, exploring more novel flavonoid activities, includ- demiological studies reported associations between consumption ing impact on energy expenditure, body weight, mental perfor- and incidence of vascular disease, particularly for wine and tea; mance, antiviral activity, renal function, and oral disease (Nijveldt consequently, this avenue would become a significant focus of et al., 2001; Sakagami, Oi, & Satoh, 1999; Williamson & Manach, flavonoid research (Ursini et al., 1999). In opposition to the the- 2005). ory of preserved NO bioavailability, oxidative modification of LDL was also known to be an initiating factor in plaque formation, and The French Paradox and the mediterranean diet as flavonoids were observed to scavenge radicals in vitro, this would The introduction of the French Paradox (Dolnick, 1990; Re- also become a substantial area of flavonoid research (Chopra & nault & de Lorgeril, 1992), which arose from the observation that Thurnham, 1999; Ursini et al., 1999). These avenues of research the French population had a low incidence of CHD despite hav- were primarily explored using animal models, where flavonoids ing a high fat intake (Constant, 1997), led to a significant change were observed to reduce the severity of vascular disease (Duthie & of focus of research in the 1990s. The difference between the Bellizzi, 1999). For a detailed review of the role of flavonoids in French diet and that of other non-Mediterranean cultures was re- vascular health, describing the state of research in the 1990s, refer ported to be a higher consumption of red wine, and this sparked to Ursini et al. (1999). new interests in flavonoid research as red wine was recognized as a rich source of flavonoids (Formica & Regelson, 1995). This Anticancer activity would also lead to renewed interest in the Mediterranean Diet, A substantial increase in the number of studies into the an- which contains other flavonoid- and (poly) phenol-rich foods such ticancer effects of tea in both human cohort and animal stud- olive oil, fruits, coffee, and nuts (Davis, Bryan, Hodgson, & Mur- ies was reported, detailing reduced incidence of cancers of the phy, 2015; Trichopoulou, Vasilopoulou, & Lagiou, 1999). Meta- mouth, esophagus, stomach, pancreas, lung, prostate, bladder, analyses of studies published prior to 2000 reported beneficial ef- colon, and rectum (Isemura et al., 2000; Lamson & Brignall, 2000; fects of low-to-moderate red wine consumption on cardiovascular Trevisanato & Kim, 2000). events (Rotondo, Di Castelnuovo, & de Gaetano, 2001). Studies using red wine or red wine extracts reported numerous mech- Mechanisms of action anisms of action, including: attenuation of myocardial ischemic Despite the growing focus of studies exploring the radical- reperfusion injury, inhibition of platelet aggregation, promotion scavenging effects of flavonoids on LDL-cholesterol and NO of endothelial nitric oxide synthase (eNOS), inhibition of throm- bioavailability, effects on immune and inflammatory cell functions boxane synthesis, modulation of lipoprotein secretion, inhibition continued to be of interest, but they were largely overshadowed of carcinogenesis, low-density lipoprotein (LDL) oxidation, phos- by studies focusing on antioxidant, vascular, and anticancer effects. pholipase A2 (PLA2), COX and phosphodiesterase, increase in With respect to anti-inflammatory properties, studies continued cyclic nucleotide concentrations, and inhibition of protein kinases to report impacts on enzyme systems associated with immune involved in cell signaling (Das et al., 1999; Halpern et al., 1998; cell action and inhibition of prostaglandin synthesis (Manthey, Soleas, Diamandis, & Goldberg, 1997). For an extensive review 2000; Middleton, 1998). Other reported mechanisms included: of this evidence of wine flavonoids in health and disease refer to inhibition of cell proliferation and induced apoptosis; modula- Fernandes, Perez-Gregorio, Soares, Mateus, and de Freitas (2017). tion of phase I and II enzyme systems; inhibition of protein kinases; and inhibition of phosphorylation of c-jun and p44/42 Vascular activity mitogen-activated protein kinase (MAPK; Ahmad & Mukhtar, Tea was the focus of many cohort studies in the 1990s, most 1999; Brown, 1999; Lin & Liang, 2000; Yang et al., 2000; Yang, notably the Zutphen study, which reported that the incidence Lee, Chen, & Yang, 1997). of stroke was significantly decreased in those having the high- The radical-scavenging hypothesis. Reviews in the 1990s of- est intake of flavonols and flavones (Hertog et al., 1993). More- ten reported on antioxidant properties of flavonoids, citing direct over, cohort studies reported reduced risk of CVD, whereas ran- radical-scavenging activity, or action through inhibition of en- domized controlled trials (RCTs) focused on risk factors such dothelial eNOS or xanthine oxidase (Formica & Regelson, 1995; as LDL-cholesterol and homocysteine-lowering activity. Even Rice-Evans & Miller, 1996), and in much of the literature the in though most authors at that time agreed that the mechanisms vitro antioxidant capacity of foods was thought to translate to in of action of flavonoids were not fully understood, the vast con- vivo protection of free-radical damage (Catapano, 1997; Duthie sensus was that radical scavenging was somehow involved (Ursini, & Bellizzi, 1999; Eastwood, 1999; Rice-Evans & Miller, 1996; Tubaro, Rong, & Sevanian, 1999). In the 1980s, researchers rec- Wiseman, Balentine, & Frei, 1997). Numerous ex vivo and in vitro ognized the importance of nitric oxide (NO) in regulating vascular effects were observed, including increased plasma/serum antioxi- homeostasis, including regulating vascular tone, blood flow, leuko- dant capacity, and decreased phospholipid hydroperoxides, super- cyte adhesion, platelet reactivity, and smooth muscle cell prolif- oxide dismutase activity, DNA damage, plasma malondialdehyde, eration (Higashi, Noma, Yoshizumi, & Kihara, 2009; Kawashima and urinary 8-hydroxy-2-deoxyguanosine (Nijveldt et al., 2001;

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Sakagami et al., 1999; Williamson & Manach, 2005). There was protective effects included cocoa, tea, red wine, berries, and cit- growing interest in measuring the in vitro total antioxidant activ- rus. There was continued focus on the radical-scavenging effects ity of foods, using assays such as the Trolox equivalent antioxi- of flavonoids on NO bioavailability; however, some investiga- dant activity (TEAC) assay, which measured concentration of a tors were beginning to link flavonoids known enzyme activi- water-soluble vitamin E analog relative to the production of a sta- ties to numerous other CVD mechanisms, including inhibition ble radical cation chromophore, ABTS·+ (Rice-Evans, Miller, & of the superoxide anion-producing enzyme, NADPH oxidase Paganga, 1996; Williamson & Manach, 2005). (NOX; Schewe, Steffen, & Sies, 2008). Structure-activity rela- Despite near saturation of the literature with studies follow- tionship studies of (−)-epicatechin 38 and its metabolites in a ing the antioxidant hypothesis, some researchers were beginning human umbilical vein endothelial cell model of angiotensin II- to question its biological relevance. A review by Bors, Michel, stimulated superoxide production revealed methylation of the cat- and Stettmaier (1997) stated “despite the numerous reports of echol B-ring, or sole presence of a 4-OH group, resulted in flavonoids acting as specific scavengers for superoxide, few re- NOX inhibitory activity despite the absence of the reactive cat- port rate constants or utilize appropriate methodologies,” listing echol structure (Steffen, Gruber, Schewe, & Sies, 2008; Steffen, pulse radiolysis and electron paramagnetic resonance spectroscopy Schewe, & Sies, 2007). This finding not only identified an alter- as being required to prove direct radical-scavenging activity. They native mechanism to radical scavenging, but provided early proof concluded their review with, “flavonoids in vivo play a much wider that metabolism did not necessarily confer reduced activity. Fur- role than acting merely as antioxidants,” which has been the con- thermore, several animal models of vascular disease showed that sensus of most flavonoid researchers for decades and remains so quercetin 1 induced a dose-dependent reduction in BP, while a today. Many experts still ponder where the field would be today few others provided evidence of beneficial effects on vascular en- if the radical-scavenging theory of flavonoid activity had not been dothelial function and renal hypertrophy (Perez-Vizcaino, Duarte, not pursued for so long. Jimenez, Santos-Buelga, & Osuna, 2009). Interestingly, quercetin- 3-O-glucuronide 21 was shown to accumulate in foam cells within Research 2000 to 2010 human atherosclerotic lesions (Kawai et al., 2008a, b) revealing the Tea and red wine studies were at the forefront of flavonoid re- direct presence of quercetin metabolites at the site of tissue injury. search in the 2000s, flavan-3-ol-rich cocoa and chocolate studies The emerging role of flavonoid-rich cocoa and chocolate in car- were on the rise, and berry research was also gaining momentum. diovascular health was becoming more evident in the 2000s. Like Evidence continued to amount for the cardiovascular and anti- quercetin-3-O-glucuronide, epicatechin-3-O-gallate 98 was also cancer activity of flavonoids whereas the diversity of therapeutic shown to accumulate in foam cells within human atherosclerotic targets was also growing, which included an impact on cognitive lesions (Kawai et al., 2008a, b). decline, type-2 diabetes, and antiallergic properties. In addition, recognition of an obesity-induced metabolic imbalance referred OH OH to as “metabolic syndrome” provided new avenues for flavonoid HO O research, providing a mechanistic link between the obesity-related O O disorders, type-2 diabetes and CVD. The persistent focus on an- HO tioxidant activity of flavonoids was beginning to be questioned, HO OH despite its increased interest by industry as a marketing tool. Al- OH though there were considerable data describing the potential health )-Epicatechin-3-O-gallate 98 benefits of flavonoid intake, conclusive, and direct evidence of their disease prevention mechanisms remained unresolved, possibly as a result of mechanistic activity being primarily explored by us- There was an increase in studies exploring the impact of choco- ing unmetabolized aglycones, and their sugar conjugates of plant late and cocoa on human endothelium-dependent brachial artery origin, in cultured cells. Although it was not universally accepted vasodilation, where findings in previous decades relied on cell at the time, as discussed in section “Bioavailability,” bioavailability and animal models. Three separate meta-analyses published in the studies were accumulating, indicating that the principal flavonoid- 2000s concluded that RCTs feeding flavanol-3-ol-rich cocoa, for derived structures in the circulation, in addition to their phase II various durations, resulted in reduced biomarkers of CVD risk, in- metabolites, were phenolic acid and aromatic metabolites orig- cluding BP (Desch et al., 2010; Shrime et al., 2011), high-density inating from microbial catabolism in the lower intestine. The lipoprotein (HDL), LDL, insulin, mean arterial pressure, and en- first studies were starting to emerge focusing on the impact of dothelial function as measured by flow-FMD (Engler & Engler, this metabolism on flavonoid bioactivity, leading to an acknowl- 2006; Shrime et al., 2011). Acute/short-term feeding studies (2 edgement that radical-scavenging capacity may not be the “holy to 12 wk) with flavan-3-ol-rich-cocoa also significantly increased grail” of flavonoid action, as metabolism often abolished radical- FMD response in healthy, obese, hypercholesterolemic, and hyper- scavenging activity (Del Rio, Costa, Lean, & Crozier, 2010; Kay, tensive adults (Del Rio et al., 2013), whereas hypocholesterolemic 2010; Williamson & Clifford, 2010). effects and improvement in glycemic response were reported in humans and rodent models (Kim et al., 2014). Most clinical stud- Cardiovascular/cardio-metabolic disease ies focused on vascular endpoints such as BP and FMD, with a Epidemiological studies describing associations between long- few studies reporting significant activity on lipids, P-selectin, vas- term intake of flavonoid-rich foods and decreased incidence of cular cell adhesion molecule-1 (VCAM-1), and platelet activation CVD were accumulating in the 2000s, whereas animal mod- (Del Rio et al., 2013; Hooper et al., 2012; Kim et al., 2014). els following administration of flavonoids reported improvement Yet, the ex vivo antioxidant capacity of flavan-3-ols was still the in atherosclerotic endpoints such as reduction in oxidized LDL- focus of many publications, including reports of positive impact cholesterol, BP, and myocardial and cerebral infraction (Del Rio on oxidized biomarkers, such as oxidized-LDL and F2 isoprostanes et al., 2013). Foods most consistently reported as having cardio- (Engler & Engler, 2006).

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At this time, the perceived mechanism behind the impact of et al., 2010); however, in vivo studies with human volunteers cocoa on endothelial function was increased NO bioavailability, would not be conducted for some time. potentially through sacrificial radical scavenging by flavonoids (En- gler & Engler, 2006). However, some were beginning to report Cancer a more likely scenario where flavan-3-ols acted by regulat- A considerable number of animal and cell culture studies support ing cell-signaling cascades involving nuclear factor kappa-light- anticancer mechanisms of flavonoids, however, epidemiological β ĸβ chain-enhancer of activated -cells (NF- ) and nuclear factor studies provide inconsistent evidence, especially when consider- (erythroid-derived 2)-like 2 (Nrf2; Fraga & Oteiza, 2011). Fur- ing the results of prospective cohort studies. Inhibition of cancer thermore, new avenues in neuronal function and cognition were cell growth, angiogenesis, and migration has been reported in an- becoming more pronounced in chocolate research, where stud- imal studies for flavonoids, however, most mechanistic evidence ies reported improved special memory, memory and learning, and is derived from culture studies using unmetabolized flavonoids. peripheral and cerebral vascular blood flow, primarily using rodent For a detailed review of the available evidence for the anti-cancer models (Kim et al., 2014). activity of flavonoids refer to Zhou et al. (2016). Studies on black tea reported positive impacts on BP and FMD, with a few reporting effects on lipids, lipoproteins, and platelet aggregation, whereas studies on green tea most commonly re- Cognition ported beneficial effects on BP, FMD, body mass index (BMI), The 2000s would see new therapeutic targets emerge, particu- and insulin resistance (Del Rio et al., 2013; Gonzalez-Gallego,´ larly cognition, age-related neurodegeneration, and cognitive de- Garc´ıa-Mediavilla, Sanchez-Campos,´ & Tunõn,´ 2010). It should cline. Observational data suggested that regular moderate intake be noted that many other studies reported no effect of green or of flavonoid-rich foods, such as cocoa, berries, and red wine pro- black tea on CVD risk factors (Del Rio et al., 2013; Hodgson, vided cognitive benefit. Although evidence in humans was lack- 2006). ing, evidence from animal studies, primarily rodent, identified a Investigations involving moderate red wine consumption pro- positive impact of berries, cocoa, wine, apples, and citrus on cog- duced mixed results, particularly when comparing red wine to nitive outcomes. Researchers primarily observed improved learn- dealcoholized red wine. Investigations observing significant effects ing, working memory, special memory, and memory acquisition generally describe activity on FMD, BP,and heart rate (HR), with and retention, most often by feeding juice extracts. The reported a few studies reporting positive impacts on lipoproteins, insulin effects were linked to improvement in cerebrovascular blood flow sensitivity, and platelet aggregation (Del Rio et al., 2013). and inhibition on neuro-inflammation (Del Rio et al., 2013; Kim Research with berry and berry-derived juices found improve- et al., 2014; Vafeiadou, Vauzour, & Spencer, 2007). ments in BP, with a few studies detailing positive impact on lipids and lipoproteins, pulse wave velocity, and insulin sensitivity; yet Mechanism of action many others described a lack of efficacy of chronic intake of The therapeutic effect of flavonoids was observed in many anthocyanin-rich foods on BP (Del Rio et al., 2013). Animal stud- disease pathology models, including atherosclerosis, ischemia- ies noted endothelium-dependent relaxation of isolated porcine reperfusion, metabolic syndrome, inflammatory bowel disease coronary arterial rings, elicited by chokeberry and bilberry ex- (IBD), brain and skin inflammation, toxic shock and asthma. These tracts (Bell & Gochenaur, 2006). Publications most often have pathologies share common underlying processes or mechanisms, associated beneficial effects of berry consumption with their high most notably inflammation (Gonzalez´ et al., 2011). For exam- levels of anthocyanins (Bell & Gochenaur, 2006; Del Rio et al., ple, endothelial dysfunction is an early-stage pathology in the de- 2013). velopment of atherosclerosis, often considered a consequence of Despite the extensive consumption of oranges/orange juice in decreased NO bioavailability leading to a failure to maintain vascu- the USA and early focus with respect to “vitamin P-like” activ- lar endothelium homeostasis (Figure 20). However, the presence ity, citrus was an understudied dietary source of flavonoids in the of NO also aids in suppressing NF-ĸβ activation, consequently 2000s, although a few investigations observed beneficial effects inhibiting the release of proinflammatory and antithrombotic pro- on BP, HDL-cholesterol, and triacylglycerol levels. For an ex- teins (Montezano et al., 2011; Rajendran et al., 2013). In dis- tensive review of health-promoting effects of the citrus flavanone ease states a lack of homeostasis leads to increased expression of hesperetin-7-O-rutinoside 80 (hesperidin) see Li & Schluesener adhesion molecules, recruitment of leucocytes, and progression (2017). of the pathology (Granger, Vowinkel, & Petnehazy, 2004). Even though the most commonly reported activity of flavonoids is their Diabetes ability to alter cardiovascular function, in vitro studies often re- Flavonoids in multiple studies have been reported to (i) improve port mechanisms which have a shared role in anti-inflammatory glucose tolerance, (ii) enhance glucose uptake in peripheral tis- homeostasis, including: scavenging of free radicals, metal chela- sues, (iii) increase insulin resistance, (iv) directly impact glucose tion, impact on ion channel regulation, inhibition of xanthine transporters, (v) regulate rate-limiting enzymes involved in carbo- oxidase, NOX and lipoxygenase, regulation of inducible nitric hydrate metabolism, including α-glucosidase and aldose reductase, oxide synthase (iNOS), COX-2 expression, leukocyte activation, and (vi) improve platelet function (Cazarolli et al., 2008; Del Rio and platelet aggregation (Gilbert & Liu, 2010; Hidalgo et al., 2012; et al., 2013; Nicolle, Souard, Faure, & Boumendjel, 2011). Al- Lazze et al., 2006; Mladenka, Zatloukalova, Filipsky, & Hrdina, though the first papers on flavonoids and starch-digesting enzyme 2010; Scholz, Zitron, Katus, & Karle, 2010; Williamson, Barron, activity appeared in the 1980s (Moore, Griffiths, & Lofts, 1983), Shimoi, & Terao, 2005). Based on this evidence researchers postu- the action of flavonoids on glycemic control was not fully ex- lated flavonoids may prevent the development of atherosclerosis by plored until after 2000. Publications describing the inhibition of either restoring endothelial homeostasis or attenuating the initia- carbohydrate-digesting enzymes showed that flavonoids had the tion or progression of inflammation (Chen et al., 2011; Quintieri potential to inhibit postprandial glucose spikes (see Hanhineva et al., 2013; Romero et al., 2009; Sudano et al., 2012).

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A B Vasodilatory phenotype Pro-coagulant/-inﬂammatory phenotype

EPCs EMPs EPCs EMPs

CECs CECs PAI-1 CRP sICAM sICAM CRP PAI-1

P-selecn TNF-α E-selecn E-selecn TNF-α P-selecn

vWF IL6 sVCAM sVCAM IL6 vWF

Endothelial Homeostasis Endothelial dysfuncon

↓ Lipid ↑ Lipid ↓ Nitro- ↑ Nitro- peroxyl peroxyl tyrosine tyrosine radical radical NO NO

↓ ↑ ROS ROS

Figure 20–Dissimilarity between functional and dysfunctial endothelium. (A) Healthy responsive endothelium mediating endothelium-dependent vasodilation; (B) dysfunctional endothelium mediating impaired vasodilation and leading to increased expression of adhesion molecules and recruitment of leucocytes. CECs, circulating endothelial cells; CRP, C-reactive protein; EMPs, endothelial microparticles; EPCs, endothelial progenitor cells; IL-6, interleukin-6; NO nitric oxide; PAI-1, plasminogen activator inhibitor 1; PGI2, prostacyclin; ROS, reactive oxygen species; sICAM, soluble intercellular adhesion molecule; sVCAM, soluble vascular cell adhesion molecule; TNF-α, tumor necrosis factor alpha; vWF, von Willebrand factor. Based on the data of Arranz et al. (2013), Baptista et al. (2014), Bousova and Skalova (2012), Brown and Griendling (2015), Cuadrado et al. (2014), Day, Bao, Morgan, & Williamson G (2000a), Fraga and Oteiza (2011), Gonzalez-Gallego´ et al. (2010), Grassi et al. (2013), Joven et al. (2014), Kabirifar et al. (2017), Kawser Hossain et al. (2016), Kerimi & Williamson (2015), Khan et al. (2016), Li and Schluesener (2017), Li et al. (2008), Lodi et al. (2009), Matias, Buosim & Gomes (2016), Mladenka et al. (2010), Morais et al. (2016), Rendeiro et al. (2015), Romero et al. (2009), Ryter et al. (2002), Sanchez et al. (2006, 2007), Scholz et al. (2010), Sorrenti et al. (2007), Spencer et al. (2012), Steffen et al. (2008), Steffen et al. (2007), Stepkowski and Kruszewski (2011), Vauzour (2014), Wang et al. (2010), Xu et al. (2005).

Anti-inflammatory effects et al., 2013), suggesting a role in line with the attenuation of Although not fully understood, the health-promoting effects a low-level inflammatory insult over pharmacological treatment. of flavonoids were often speculated to involve the modula- Furthermore, the sheer number of activities reported suggests ei- tion of key enzymes and cell-signaling cascades involved in ther some unknown overlapping mechanisms of action or multi- antioxidant/xenobiotic metabolism and/or cytokine regulation ple mechanism are at play (Gomes et al., 2008; Kim et al. 2004; (Perez-Vizcaino et al., 2009). In human studies, reports of anti- Rajendran et al., 2013). For a detailed review presenting pathway inflammatory activity are somewhat limited; however, a few feed- diagrams which reflect the state of knowledge of mechanisms of ing studies observed reduced C-reactive protein (CRP), interaction at that time, see Gomes et al. (2008). In addition, Gonzalez´ leukins/chemotactic proteins, adhesion proteins/molecules, and et al. (2011) and Gonzalez-Gallego´ et al. (2010) provide notable oxidative biomarkers. Animal and cell culture studies reflected reviews of research summarizing 2000 to 2010 studies, defining the human investigations, but they reported additional activities, activity by flavonoid class and cell type. including inhibition of tumor necrosis factor-α (TNF-α), inter- γ feron gamma (IFN- ), iNOS, COX1/COX2, LOX, PLA2, se- Anticancer lectins, and upregulated expression of heme oxygenase (HO-1; New evidence has identified direct anticancer mechanisms of Bousova & Skalova, 2012; Del Rio et al., 2013; Gomes, Fernan- action of flavonoids, with flavonol and flavan-3-ol studies pointing des, Lima, Mira, & Corvo, 2008; Gonzalez-Gallego´ et al., 2010; to epigenetic modifications through histone or DNA methylation Hodgson, 2006; Romero et al., 2009; Ryter, Otterbein, Morse, or acetylation (Gilbert & Liu, 2010). Multiple molecular mecha- & Choi, 2002; Sanchez et al., 2006, 2007; Sorrenti et al., 2007). nisms of action were reported for many unmetabolized flavonoids, The anti-inflammatory evidence spanned many cell types, includ- such as quercetin 1,(−)-epigallocatechin-3-O-gallate 12,and ing macrophages, osteoblasts, dendritic cells, lymphocytes, masto- anthocyanins (Androutsopoulos, Papakyriakou, Vourloumis, cytes, neutrophils, endothelial cells, fibroblasts, and epithelial cells Tsatsakis, & Spandidos, 2010; Chen & Chen, 2013; Del Rio (Gonzalez´ et al., 2011; Gonzalez-Gallego´ et al., 2010). et al., 2013; Kandaswami et al., 2005; Moon, Wang, & Morris, Despite reports of anti-inflammatory activity, many studies 2006; Nishiumi et al., 2011; Singh & Agarwal, 2006; Spagnuolo demonstrate effects to be much lower than pharmacological et al., 2012), ranging from activities on cell cycle, apoptosis steroidal and nonsteroidal anti-inflammatory drugs (Rajendran and autophagy, and kinase and transcription factor regulation

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(Zhou et al., 2016). But again, authors were beginning to Studies reporting antioxidant activity over the decades of- question the physiological relevance of much of the in vitro culture ten focused on the structure-activity relationships of the various data, given the use of unmetabolized flavonoids which, at best, flavonoid classes and subclasses, where activity was related mainly have very limited occurrence in vivo (Androutsopoulos et al., to the impact of hydroxylated phenol rings, nucleophilic regions, 2010; Moon et al., 2006). Despite the vast amount of literature and Michael acceptor functionalities (Amic et al., 2007; Dinkova- reporting the anti-cancer actions of flavonoids, their impact on Kostova et al., 2007; Tsuji et al., 2013). The one nuance of this cancer incidence and mortality in longitudinal studies has not area of research was that studies were beginning to explore the been established (see Del Rio et al., 2013). impact of phase II metabolism on antioxidant activity. Much of this work focused on quercetin (Terao, 2009). Neuroprotection By 2010 researchers had started to to acknowledge that the Neuroprotection was beginning to be a prominent endpoint health effects of flavonoids were likely not only a result of direct in the landscape of flavonoid research, with reported mechanisms antioxidant activity, but also included inhibition of radical-forming of action continuing to grow during the 2000s. Effects in animal enzymes such as xanthine oxidase, NOX, and lipoxygenase, in ad- models included improvement in cerebrovascular blood flow and dition to impacts on platelet aggregation, leukocyte adhesion, and inhibition of neuroinflammation, which were potentially linked to vasodilatory properties. It was becoming apparent that flavonoids selective interactions with protein kinase and lipid kinase signaling had differential bioactivity across various cells, tissues, and disease cascades (Del Rio et al., 2013; Spencer, 2010). The majority of states (that is, healthy compared with disease models; Mladenka mechanistic evidence stemmed from studies using quercetin 1,lu- et al., 2010). Furthermore, radical-scavenging data were not sup- teolin 5,(−)-epigallocatechin-3-O-gallate 12,and(+)-catechin ported by the growing literature on flavonoid bioavailability. Ini- 28 in cultured cells, primarily microglial cells, and reporting tially this “missing link” was assumed to be activity of phase II activity on heme oxygenase-1 (HO1) and thioredoxin, inhibi- conjugates of aglycones, however, as early as 2000 the need to bet- tion of iNOS and NOX expression, reduction of prostaglandin ter assess the role of the colonic microflora in flavonoid bioactivity E2 (PGE2) and proinflammatory chemokines (TNF-α,IL-1β, was beginning to be discussed (Scalbert & Williamson, 2000). Re- IL-6, IL-8, IP-10, monocyte chemoattractant protein-1 [MCP- searchers soon established that gut metabolites of quercetin 1,such 1], RANTES,) inhibition of CCAAT/enhancer activator pro- as 3,4-dihydroxyphenylacetic acid 25 (Rechner et al., 2002), had tein delta, activator protein 1, cluster of differentiation 40 ligand comparable activity to quercetin in some assay systems, suggesting (CD40L), signal transducer and activator of transcription-1, p38, that metabolism, in this case microbial catabolism, did not neces- extracellular signal-regulated kinase (ERK), c-Jun N-terminal ki- sarily reduce biological activity (Glasser, Graefe, Struck, Veit, & nase (JNK), protein kinase B (Akt), Janus kinase and receptor Gebhardt, 2002). tyrosine-protein kinase 2, and stimulation of TRX1. For an extensive review of flavonoids, food sources, and neuro-cognitive Metabolism: impact on bioactivity effects refer to Spencer, Vafeiadou, Williams, and Vauzour (2012) In the early 2000s, a few research groups began to focus on phase and Rodriguez-Mateos et al. (2014c). II conjugation of flavonoid aglycones/glycosides post-absorption. Even though the microbial catabolism of flavonoids had been Antioxidants reported (Blaut, Schoefer, & Braune, 2003; Scalbert, Morand, Studies exploring the antioxidant hypothesis continued to grow Manach, & Remesy, 2002), it had yet to be accepted as play- in the 2000s, along with significant interest in endothelial dys- ing a significant role in the biological functionality of flavonoids. function and the use of FMD as a surrogate marker of vascu- The impact of phase II metabolism, principally glucuronidation lar health. At that time, the perceived mechanistic link between and methylation, on the biological activity of quercetin and var- flavonoid consumption and improved FMD response was the ac- ious flavan-3-ols was a major focus at that the time (Williamson tion of flavonoids as a “sacrificial” radical scavenger, preserving et al., 2005). Interestingly, in opposition to the previous antioxi- the bioactivity of NO. A large number of studies explored the dant research, which predicted that conjugation would result in a biological impact of wine, berries, olive oil, cocoa/chocolate, and reduced bioactivity, studies were reporting increased or differen- tea, the “so called” antioxidant-rich foods (Kay, Kris-Etherton, tial activity of flavonoid metabolites on multiple enzyme systems & West, 2006). This level of attention was no doubt perpetuated (Beekmann et al., 2012). For example, cultured lung cancer cells by scientists and industry relating the in vitro antioxidant capacity were shown to have reduced proliferation and increased apoptosis of various foods to health effects, and utilizing tests such as the when treated with an extract of quercetin glucuronides isolated TEAC, oxygen radical absorbance capacity (ORAC), and ferric from rabbits (Yang et al., 2006), whereas metabolites isolated from reducing antioxidant potential (FRAP) assays to promote the po- rats were shown to inhibit vascular endothelial cell hyperglycemic- tential health effects of foods. The fact that many reviews were induced apoptosis through a mechanism involving the inhibition being published at the time focusing on the antioxidant activity of of JNK and caspase-3 (Chao, Hou, Chao, Weng, & Ho, 2009). flavonoids indicates that this was still an area of substantial research Quercetin metabolites, both glucuronide and sulfate, were refocus. Furthermore, as ex vivo antioxidant assays were relatively ported to inhibit lipid peroxidation, COX-2, 15-lipoxygenase, simple to carry out and results were frequently positive, and as all xanthine oxidase, JNK, caspase-3, and vascular endothelial growth flavonoids are radical scavengers to some extent, it was relatively factor (VEGF), and to prevent endothelin-1-induced endothelial easy to publish these results. Statements such as “the pharmaco- cell dysfunction, as well as angiogenesis in various cell models logical effects of flavonoids are mainly due to their antioxidant (Beekmann et al., 2012; Day, Bao, Morgan, & Williamson, 2000a; activity” were commonplace in publications, although an almost Del Rio et al., 2013; Lodi et al., 2009). Pretreatment of en- equal weight was beginning to be given to the counterargument, dothelial cells with methylated (+)-catechin 28 metabolites was focusing on the apparent ability of flavonoids to modulate both also reported to decrease cell adhesion whereas the unmetabo- antioxidant and anti-inflammatory enzymes (Amic et al., 2007; lized precursors had no effect (Koga & Meydani, 2001). In addi- Tsuji, Stephenson, Wade, Liu, & Fahey, 2013). tion, (−)-epicatechin 28 and (−)-epigallocatechin 99 metabolites

r 1086 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary flavonoids: a historical review . . . isolated from human and rat urine inhibited tyrosine nitration and difficile,andBacteroides spp. Caffeic acid was reported to be the the release of arachidonic acid from colorectal adenocarcinoma strongest inhibitor, especially for scherichia coli, Salmonella, Pseu- cells (Lu et al., 2003; Williamson et al., 2005). Finally, the en- domonas, Clostridium,andBacteroides (Lee, 2006). zyme which converted flavonoid glucuronides back to their aglycone forms, β-glucuronidase, was activated during inflammation Mechanism of action of microbial metabolites in certain systems (Kawai et al., 2008a, b), potentially indicat- A mixture of flavan-3-ol metabolites from rats was reported ing that more active aglycones would also be present at sites of to reduce monocyte adhesion in human aortic endothelial cells inflammation. (Koga & Meydani, 2001). 3-O-Methyl-gallic acid and 2,4,6- OH OH trihydroxybenzaldehyde 104 were shown to induce apoptosis OH OH and inhibit cell proliferation in Caco-2 cells, although valerolac- HO O HO O OH OH tones, the microbial-derived catabolites of flavan-3-ols (see section OH OH OH OH “Flavan-3-ols”), were identified as inhibitors of cancer cell growth, matrix metalloproteinase, and NO production by macrophages ( )-Epigallocatechin 99 (+)-Gallocatechin 100 (Blaut et al., 2003; Grimm, Schafer, & Hogger, 2004; Lambert

OH OCH3 et al., 2005; Scalbert et al., 2002; Selma, Espin, & Tomas-Barberan, OH OH 2009). HOOC OH HOOC OH OH Gallic acid 101 3-O-Methylgallic acid 102 HO OH (3,4,5-trihydroxybenzoic acid) OH OHC OH HOOC OH OH 2,4,6-Trihydroxybenzaldehyde 104 Protocatechuic acid 105 (3,4-dihydroxybenzoic acid) HOOC Caffeic acid 103 Incubation of a phenolic extract containing primarily phenyl- propionic, phenylacetic, and benzoic acids, derived from the in Microbiome vitro microbial fermentation of blueberries, was reported to de- By the late 2000s it had become evident that intestinal micro- crease prostanoids in cultured colon cells, suggesting the actions of biota played a crucial role in the metabolism of phytochemicals. A berry flavonoids may exist in the colon even prior to absorption global focus had been spearheaded with the goal of understanding (Russell, Labat, Scobbie, & Duncan, 2007). In the case of antho- the relationships between the human epigenome, metabolome, cyanins, their in vitro instability had been established for decades, and microbiome. These initiatives included the: NIH Jumpstart however, their in vivo metabolism has only recently come to light, Program (launched in 2007) & NIH Human Microbiome Project with a large number of microbial catabolites recently identified (2008, USA); Irish ELDERMET initiative (2007); Metagenomics (Czank et al., 2013; Kay et al., 2017; see section “Early Research of the Human Intestinal Tract (MetaHIT, 2008) initiative; French with (+)-Catechin”). Probably the first catabolite of anthocyanins National Agency for Research project MicroObes (2008); Aus- to be studied was 3,4-dihydroxybenzoic acid 105 (protocatechuic tralian Jumpstart Human Microbiome project (CSIRO, 2009); acid). This phenolic acid exists in some traditional medicines and Canadian Human Microbiome Initiative (2009); Korean Micro- had known biological activity in cell and animal studies, which biome Diversity initiative (2010); European Commission on In- reported inhibition of monocyte adhesion, reduced VCAM-1, international Human Microbiome Standards (IHMS, 2011); and tracellulular adhesision molecule (ICAM)-1, TNF-α, and MCP-1 the French initiative MetaGenoPolis (France INRA 2012; Duda- expression, and activity towards iNOS and angiotensin-converting Chodak, Tarko, Satora, & Sroka, 2015; Lepage et al., 2013). With enzyme (ACE). 3,4-Dihydroxybenzoic acid is also of dietary ori- this new focus on intestinal microflora, publications exploring gin, occurring in cereals, dried fruit, juices, nuts, and so on. When flavonoid microbial activity began to emerge. studied as a pure compound, it has been reported to inhibit cell The earliest studies exploring the impact of flavonoids on the proliferation and induce apoptosis in cancer cells, and to stimu- intestinal microflora were primarily focused on either increasing late proliferation and increase stem cell viability of neuronal cells. the population of so-called “beneficial bacteria” (probiotic ef- Reported mechanisms of action include phosphorylation and ac- fects) or inhibiting the growth of perceived “deleterious species” tivation of JNK, p38MAPK, and p65/NF-ĸβ (Gonzalez-Sarr´ ´ıas, (antimicrobial activity). Some flavonoids appeared to be potent in- Larrosa, Tomas-Barberan,Dolara, & Espin, 2010; Wang, Wei, Yan, hibitors of microorganism growth, particularly the green and black Jin, & Ling, 2010a). tea flavan-3-ol monomers, (+)-catechin 28,(−)-epicatechin 38, The effect of 3-(3,4-dihydroxyphenyl)propionic acid 79 (dihy- (−)-epigallocatechin 99,and(+)-gallocatechin 100,whichwere drocaffeic acid), a colonic metabolite derived from multiple food reported to inhibit pathogenic microbial growth (Duda-Chodak sources, including cocoa, apples, and strawberries, was tested in a et al., 2015). For example, incubations with (−)-epicatechin and rat model of dextran sodium sulfate-induced colitis, and revealed (+)-catechin were observed to promote the growth of Eubac- that fecal water content and weight loss were less pronounced terium rectale/Clostridium coccoides, Lactobacillus spp., and Bifidobac- in treated rats relative to control animals (Larrosa et al., 2009). terium spp., and to decrease growth of Clostridium histolyticum.A It was also shown that distal colon mucosa homogenates from significant increase in the growth of Eubacterium rectale/Clostridium rats treated with the phenolic acid had diminished expression of coccoides was also reported with the inoculation of (+)-catechin TNF-α,IL-8,IL-1β, and reduced malonyldialdehyde and 8-oxo- (Tzounis et al., 2008). 2-deoxyguanosine concentrations. Alternatively, (−)-epicatechin, (+)-catechin, gallic acid 101, Considerable evidence was accumulating that highlighted the 3-O-methyl-gallic acid 102, and caffeic acid 103 all suppressed importance of the microbiome to human health, not only the the growth of pathogens like Clostridium perfrigens, Clostridium direct impact of phytochemical metabolites on tissues but also

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1087 Dietary flavonoids: a historical review . . . the impact of flavonoids on gut microbial populations themselves driver of uric acid synthesis. In line with these observations, the (Blaut et al., 2003; Scalbert et al., 2002; Selma, Esp´ın, & Tomas-´ USDA concluded there is no evidence to support the bioactivity Barberan,´ 2009). However, considerable obstacles still exist in es- of flavonoid-rich foods as it relates to their in vitro antioxidant ca- tablishing the impact of dietary flavonoids on the microbiome. pacity, as established by total antioxidant capacity assays. This led For example, there is a significant diversity of microbial species to a decision in 2012 to remove the ORAC Database for Selected in the gut and substantial inter-individual variability in bacterial Foods from the USDA’s Nutrient Data Laboratory (NDL). populations as a result of differing diet, lifestyle, ethnicity, and so on. Furthermore, only a small proportion of intestinal bacteria can be cultivated in vitro, making it difficult to explore mecha- The French Paradox nisms of action (Duda-Chodak et al., 2015; Lepage et al., 2013). Moderate red wine consumption has long been associated Despite these difficulties, it is clear that flavonoids can alter micro- with decreased CVD mortality in several epidemiological stud- biota ecology, as observed by reported bacteriostatic or bactericidal ies (Gaziano et al., 1993; Rimm et al., 1991), and may be partly actions (Etxeberria et al., 2013), suggesting the microbiome can credited to the anthocyanin content of wine (Dell’Agli, Busciala, become somewhat “normalize” to certain types of diet. For a com- & Bosisio, 2004; Erdman et al., 2007). However, after nearly prehensive review of the state of knowledge at this time, regarding 30 yr of publicity, the French Paradox appears to have lost momen- the interaction of flavonoids with the intestinal microbiota, see tum, leaving many questions still unresolved. The main criticisms Selma et al. (2009) and Duda-Chodak et al. (2015). of those opposing the theory relate to a lack of understanding of dose, what phytochemical components of wine are responsible Research 2010 to 2017 for the effect, the contribution of alcohol to the observed effects, The greatest changes in the direction of flavonoid research have and ethical issues associated with recommending consumption to probably occurred in the past decade. First and foremost, the ac- non-drinkers. It is clear that moderate alcohol intake alone can cumulation of information describing microbial metabolites as be- positively affect vascular mechanisms of action, and that excessive ing key to establishing the bioactivity of flavonoids. Furthermore, intake and binge drinking has many negative health consequences the realization that previous mechanistic findings, established by (Biagi & Bertelli, 2015; Mochly-Rosen & Zakhari, 2010; Tonelo, using aglycone/un-metabolized flavonoids at supraphysiological Providencia, & Goncalves, 2013). In recent years numerous mech- concentrations, require reconsideration. Finally, the appreciation anistic studies have been conducted using concentrations of the that the antioxidant hypothesis holds “little” physiological rele- C6-C2-C6 stilbene trans-resveratrol 106 greatly in excess of any- vance brought further motivation in the past decade to refine thing that would be reached systemically following moderate red previous theories. Although our understanding of the mechanism wine consumption. Most of these studies were conducted from of action of flavonoids is still evolving (Figure 21), the underlying a pharmacological perspective in view of resveratrol’s ability to ideology that flavonoids protect against various forms of biologi- enhance the longevity of a variety of organisms (Baur & Sinclair, cal stress remains valid. Unlike established micronutrients of which 2006; Baur et al., 2006; Pallauf, Rimbach, Rupp, Chin & Wolf dietary exclusion leads to nutritional deficiency disease, there is no 2016). officially recognized deficiency disease associated with suboptimal OH flavonoid consumption. However, flavonoids have been proposed OH to be “lifespan essential” (Holst & Williamson, 2008) as a diet de- HO O

ficient in flavonoids (that is, low in fruit and vegetables) is a strong OH HO OH risk factor for developing chronic degenerative diseases globally HO OH (Ezzati and Riboli (2013). Therefore, the concept that flavonoids OH HO O protect against the “stresses” of aging, including the associated OH OH chronic diseases, remains consistent in the literature. trans-Resveratrol 106 HO

Proanthocyanidin B2 dimer 107 Antioxidant/radical scavenging hypothesis By the end of the 2000s the antioxidant hypothesis as it relates The low amounts of resveratrol in red wines suggest it is ex- to direct radical-scavenging activity of phytochemicals was, for the tremely unlikely to be responsible for the reported beneficial ef- most part, considered a “debunked” theory. In the review titled fects following moderate red wine consumption (Corder, Crozier, “Unravelling of the health effects of polyphenols is a complex & Kroon, 2003). Despite the unconvincing mechanistic evidence puzzle complicated by metabolism,” Hollman (2014) concluded relative to moderate levels of red wine phytochemicals, such as that “although elegant, the antioxidant hypothesis must be re- resveratrol, catechins, or anthocyanins, an alternative possibility is jected,” the compelling argument being that, overall, flavonoid that the more abundant procyanidins are the key bioactives. In metabolites occur in the serum and tissues at more than 50-fold contrast to (−)-epicatechin 38 and (+)-catechin 28, procyani- lower concentrations than the pool of endogenous radical scav- dins have been shown to inhibit platelet aggregation in vitro and to engers/antioxidants, and as such their contribution to global re- suppress the synthesis of endothelin-1 by cultured endothelial cells dox status is likely to be extremely low, relative to other more (Corder, 2008). It is, however, unlikely that procyanidins, such as stable endogenous oxidizable substrates, including urate, bilirubin, proanthocyanidin B2 dimer 107, let alone oligomeric and poly- proteins/enzymes, unsaturated fatty acids, thiols, tocopherols, and meric forms, enter the circulatory system in sufficient quantity ascorbic acid. In addition, flavonoids’ known enzyme activity often to elicit bioactivity. However, the consumption of procyanidin- negates their contribution to the radical-scavenging “pool.” For rich red wine made from Tannat grapes has been associated with example, Shi and Williamson (2016) reported that quercetin re- increased male longevity in the department´ of Gers in the Midi- duced plasma urate, a recognized radical scavenger, in moderately Pyrenees region of Southwest France (Corder et al., 2006). If hyperuricemic men, through the partial inhibition of xanthine physiological concentrations of colonic catabolites of procyani- oxidoreductase, a major producer of intracellular superoxide and dins such as 5-(4-hydroxyphenyl)-γ -valerolactone-3-sulfate 55

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A B

Figure 21–Exponential proliferation of reported flavonoid activities. (A) Reported clinical pathologies; (B) reported clinical endpoints/biomarkers; (C) reported mechanisms of action. and 5-(4-hydroxyphenyl)-γ -valerolactone-3-O-glucuronide 56 to 45 yr of age after a follow-up of 18 yr (Cassidy et al., 2013). Fi- were implicated in cell culture or in vivo studies, the French nally, a meta-analysis of 14 prospective studies also found a reduced Paradox and the underlying mode of action would find renewed CVD risk associated with the consumption of flavonols, antho- interest. cyanins, flavones, flavan-3-ols, and flavanones (Wang, Ouyang, Liu, & Zhao, 2014). CVD Positive impacts of flavonoids on blood lipids, specifically LDL, Epidemiological evidence published over the past two decades HDL, and total cholesterol, are reported across numerous RCTs. indicates that consumption of flavonoid-rich food and beverages Improvements in lipid status are most often reported for quercetin, is inversely associated with the risk of CVD, although it should chocolate, green tea, grapes, wine, and berries (Hugel, Jackson, be noted that not all studies support this association (Curtis et al., May, Zhang, & Xue, 2016; Lilamand et al., 2014; Rodriguez- 2009; Geleijnse & Hollman, 2008; Wallace, 2011). Flavonoid in- Mateos, Heiss, Borges, & Crozier, 2014a). Intervention studies take was associated with lower CVD incidence and mortality in six of individuals with hypertension, metabolic syndrome, and di- of the 12 published cohort studies reviewed by Peterson, Dwyer, abetes mellitus report positive impact of foods rich in all five Jacques, and McCullough (2012), where the strongest associa- subclasses of flavonoids on BP (Clark, Zahradka, & Taylor, 2015; tions were found for reduced risk of mortality from CHD and Hugel et al., 2016). Other commonly reported biomarkers favor- flavonol/flavone intake (Peterson et al., 2012). Anthocyanin intake ably altered in flavonoid interventions include: CRP, VCAM-1, α has been reported to be associated with an 8% reduction in the risk ICAM-1, TNF- , interleukins (IL) IL-4, IL-6, IL-8, IL-13, and γ of hypertension during a 14-yr follow-up of 34,647 cases of hy- interferon- (Gonzalez-Gallego´ et al., 2010). It is important to pertension in individuals from the Nurses’ Health Study (NHS II) note that a number of studies have also reported no effect on many and Health Professionals’ Follow-up-Study (HPDS; Cassidy et al., of these biomarkers (Hooper et al., 2012; Rodriguez-Mateos et al., 2011). In a subsequent analysis, increased intake of flavanones in 2014a, c). women was associated with a reduction in risk of ischemic stroke Apples/flavan-3-ols. The European Prospective Investigation > in 1,800 incident strokes over a 14-yr period (Cassidy et al., 2012). into Cancer (EPIC; a cohort of 400,000 individuals and a 13-yr Jennings et al. (2012) reported higher anthocyanin intake associ- follow-up) reported a nearly 30% risk reduction in CVD mor- ated with lower arterial stiffness and central BP in 1,900 women tality associated with high flavonoid intake, with the greatest risk from the Twins UK registry cohort, and calculated that the incor- reduction (40%) for flavonols (Zamora-Ros et al., 2013). Ser- poration of 1 to 2 portions of berries daily would reduce overall ban et al. (2016) summarized several human RCTs, indicating atherosclerosis risk. An association between higher anthocyanin that quercetin intake greater than 500 mg/day is required to intake and a 32% decrease in the risk of myocardial infarction decrease systolic BP (SBP) and diastolic BP (DBP) in individ- (MI) was also reported in a cohort of nearly 100,000 women of 25 uals with metabolic syndrome or type 2 diabetes, although the

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1089 Dietary flavonoids: a historical review . . . clinical relevance is unclear given this level of quercetin is unlikely 74 yr, and reported a reduced relative risk of stroke when con- to be attained following “normal” dietary consumption. Both an- suming in excess of 1 cup per day. Additionally, a meta-analysis, imal studies and human RCTs have reported beneficial impact of including 11 trials, reported green tea was consistently associated quercetin on BP, particularly SBP, triacylglycerols (TAG), HDL- with decreased SBP and DBP by 3 mmHg (Hartley et al., 2013), cholesterol, and endothelin-1 (Marunaka et al., 2017; Rodriguez- whereas another meta-analysis, including 20 studies, concluded Mateos et al., 2014c). In addition, healthy subjects consuming that foods rich in flavan-3-ols lowered SBP and DBP by 2 to apple flesh for 4 wk were revealed to have enhanced FMD, and 3 mmHg in as little as 2 wk (Ried, Sullivan, Fakler, Frank, pulse pressure as well as increases in nitrite S-nitrosothiols. Even & Stocks, 2012). Finally, a systematic review and meta-analysis though there is extensive evidence of the BP- and cholesterol- summarizing 378 subjects from 11 RCTs also found daily con- lowering effects of quercetin in animal models, in humans such sumption of black tea for more than one week was associated evidence remains mixed (Larson, Symons, & Jalili, 2012; Toh et al., with significant reductions in BP (Greyling et al., 2014). Acute 2013). intervention studies have similarly reported beneficial effects on Hypertensive rodent models have shown quercetin to im- FMD, lipids, lipoproteins, and platelet aggregation, although oth- prove endothelial-dependent aortic dilatation, vascular relaxation, ers have reported no activity on these endpoints or mixed re- decreased body fluid volume, and modulation of the renin– sults (Grassi et al., 2013a; Hartley et al., 2013; Hodgson et al., angiotensin system (Marunaka et al., 2017). Some report that 2012). the vascular activity of quercetin is the result of its action on Berries, grapes/anthocyanins. Evidence from epidemiologi- angiotensin-converting enzymes, whereas quercetin glucuronide cal studies suggests that daily intake of anthocyanin-rich foods, and methyl metabolites have been reported to induce eNOS in such as berries, provides cardio-protective benefits. For example, aortic cells and to prevent endothelial dysfunction (Rodriguez- the Iowa Women’s Health Prospective Study reported a reduced Mateos et al., 2014c). risk of CHD and CVD-related mortality associated with elevated Cocoa,darkchocolate/flavan-3-ols. Cocoa and chocolate feed- anthocyanin-rich berry intake in a population of 35,000 post- ing sydies often report beneficial effects on multiple biomarkers in menopausal women followed for 16 yr. Anthocyanin intake was healthy volunteers and at risk groups, including: improved glucose associated with a lower risk of fatal CVD in the Cancer Pre- uptake, homeostatic model assessment of insulin resistance, quanti- vention Study II Nutrition Cohort (>100,000 men and women) tative insulin sensitivity check index, and insulin sensitivity indices, during 7 yr follow-up (McCullough et al., 2012) and inversely lipid metabolism (reduced LDL- and increased HDL-cholesterol), correlated with risk of myocardial infarction in 93,600 young- and antioxidant defence; reduced total cholesterol-to-HDL ra- and middle-aged women from the NHS II study over 18 yr of tio, plasma insulin and insulin resistance, BP (decreased overnight follow-up (Cassidy et al., 2013). Moreover, an inverse relationship ambulatory SBP, DBP, and HR), angiotensin-converting enzyme between anthocyanin intake and arterial stiffness (via pulse wave activity, platelet activity, P-selectin expression, endothelin-1, ad- velocity), peripheral systolic, central systolic, and mean arterial hesion molecules, plasma nitrite, oxidized LDL, and urinary iso- pressure was reported in a cross-sectional study of 1,898 women prostanes (Ellam & Williamson, 2013; Grassi et al., 2015). The drawn from the TwinsUK registry (Jennings et al., 2012). Another cumulative benefit of affecting such a diverse array of vascular large cross-sectional study with nearly 2,000 women showed in- biomarkers was observed in a recent human RCT reporting a sig- verse associations between higher anthocyanin intakes and arterial nificant lowering of 10-yr risk for CVD and CHD as established stiffness (Jennings et al., 2012). Despite these positive reports, sev- by the Framingham risk score (Sansone et al., 2015). Significant eral epidemiological studies have found no relationship between evidence exists for the contribution of (−)-epicatechin 38 to the berry intake and many of the above risk factors (Riso et al., 2013; benefits of cocoa consumption (Schroeter et al., 2006), yet inter- Rodriguez-Mateos et al., 2014a). estingly a recent human RCT revealed that beneficial changes to A systematic review of RCTs concluded that anthocyanins sig- FMD, pulse wave velocity (PWV), DBP, and circulating angio- nificantly improved LDL cholesterol, but not other markers of genic cells were more pronounced when cocoa flavan-3-ols were CVD risk (Wallace, Slavin, & Frankenfeld, 2016). Clinical in- ingested with methylxanthines, principally in the form of theo- tervention studies report lower BP, arterial stiffness, FMD, PWV, bromine 46, implicating the impact of multiple bioactives present lipids, lipoproteins, VCAM-1, CRP, IL-2, IL-1β, insulin sen- within cocoa (Sansone et al., 2017). For extensive reviews sum- sitivity, postprandial hyperglycemia, and platelet function fol- marizing cocoa intervention studies refer to Ellam and Williamson lowing berry intervention (blueberries, bilberries, strawberries, (2013), Heiss et al. (2015), Kuhnle, (2017), Sansone et al. (2015, or cranberries) in healthy individuals and volunteers at elevated 2017), and Schroeter et al. (2006). risk of CVD and metabolic syndrome (Giampieri et al., 2015; Tea/flavan-3-ols. Epidemiological evidence suggests daily Rodriguez-Mateos et al., 2014c; Toh et al., 2013). In a recent consumption of three cups of tea is associated with a reduced wild blueberry dose–response intervention study, feeding a bev- risk of CVD mortality whereas four cups significantly decreases erage containing 776 to 1,791 mg of total polyphenols, improve- body weight and BMI and lowers lipid peroxidation and markers ments in FMD were reported at 1, 2, and 6 hr post consump- of cardiometabolic disease risk (Vuong, 2014). Consistent with tion, which correlated with elimination kinetics of the phenolic these findings, de Koning et al. (2010), established black tea con- metabolites/catabolites. Similar observations were made using a sumption (3 to 6 cups daily) was inversely associated with CHD baked blueberry product, demonstrating that the efficacy of blue- in a large cohort of over 37,000 participants in The Netherlands berries is maintained following minimal processing (Rodriguez- involving a 13-yr follow-up. A study with over 75,000 Japanese Mateos et al., 2013, 2014b). Studies using diabetic apo-E-deficient green tea drinkers also reported the risk of CHD was decreased by mice, supplemented with cyanidin-3-O-glucoside, have reported more than 50% in women drinking as little as 1 to 2 cups per day reduced aortic lesion area and improved endothelium-dependent relative to those who consumed no tea (Mineharu et al., 2011). vaso-relaxation, supporting the human clinical and observational Kokubo et al. (2013) investigated the association between green findings (Rodriguez-Mateos et al., 2014c). Still, other RCTs tea intake and stroke incidence in > 80,000 Japanese, aged 45 to with berries have found no change in serum glucose or insulin

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(Rodriguez-Mateos et al., 2014a). Feeding studies using grapes Cancer have also observed effects which parallel those reported for berries, In vitro and animal mechanistic findings indicate flavonoids have such as reductions in SBP, DBP, TAG, and LDL-cholesterol, anticancer properties; however, clinical, epidemiological, and lon- and improvements in FMD, but, as reviewed by Wightman & gitudinal cohort studies are lacking and describe mixed results (Del Heuberger (2015), others have reported no effects. Rio et al., 2013; Zhou et al., 2016). Of the positive epidemio- Citrus flavanones. Epidemiological evidence suggests a higher logical studies, evidence suggests that foods and beverages rich in intake of citrus flavanones is associated with a 19% decreased risk flavonoids appear primarily protective against colon cancer de- of stroke (Cassidy et al., 2012). Studies exploring the vascular ef- velopment (Rodriguez-Mateos et al., 2014c). A recent Cochrane fects of citrus are more limited than other flavonoid-rich foods, but Review of the possible effects of flavonoids on colorectal can- have reported significant improvements in DBP,HDL-cholesterol, cer prevention identified a significant decrease in the incidence of triacylglycerol, FMD, and postprandial microvascular endothelial colorectal cancer from eight studies involving 390,769 participants reactivity. However, feeding pure hesperetin 60 and naringenin 16 spanning 3-to-13 yr, associated with (−)-epicatechin 38, flavonol, produced no cholesterol-lowering effects in hypercholesterolemic and total flavanone intake (Andrews, 2013). patients (Kurowska et al., 2000; Morand et al., 2011; Toh et al., Studies on quercetin using rodent and culture models report 2013). The citrus flavanones naringenin-7-O-rutinoside 17 and many anticancer mechanisms of action, including downregulating hesperetin-7-O-rutinoside 80 have been reported to have vari- cell survival, inhibition of proliferation, induced apoptosis, an- ous beneficial effects in rodent models including: hypoglycemic, giogenesis, and reduced breast cancer cell growth and migration, hypolipidemic, antihypertensive, and antithrombotic effects, im- whereas results with (−)-epigallocatechin-3-O-gallate 12 include provement in NO-mediated endothelial function, reduced fatty antiproliferative effects, suppression of prostate cancer growth, mi- livers, improved histological features in models of stroke (Hugel gration and invasion of lung cancer cells, estradiol-induced breast et al., 2016), and improved cognitive outcomes, including neu- cancer cell growth, and cancer stem cell growth (Zhou et al., rological score, locomotor activity, hanging wire latency, delayed 2016). Evidence of the anticancer effects of berries is primarily fall-off time, and increased memory retention (Li & Schluesener, derived from rodent studies where multiple models have been 2017). utilized, including oral, colon, lung, breast, bone, and skin cancer, reporting various effects, including reduction of premalignant lesions, number and size of metastases, tumor volume, and mi- Metabolic syndrome and obesity cro vessel density, and inhibition of tumor development and body Flavonoids positively affect many risk factors associated with weight loss (Giampieri et al., 2015). For a detailed review of an- metabolic syndrome (Kawser Hossain et al., 2016), including ticancer activity reported over the last 5 yr consult Zhou et al. hypertension, insulin resistance, hypercholesterolemia, and hy- (2016) and on mechanisms of action see Kerimi & Williamson pertriglyceridemia, but direct evidence of flavonoids preventing, (2017). attenuating, or reversing metabolic syndrome is limited. In agreement with the CVD data described above, and using mostly animal Cognition models of obesity, hypertension, dyslipidemia, diabetes and insulin Epidemiological studies report higher total flavonoid intake as- resistance, flavonoid studies have reported improved dyslipidemia sociated with slower rates of cognitive decline and reduction in and reduced BP,reduced lipid absorption, and obesity-induced in- dementia risk in healthy aging individuals (Rodriguez-Mateos flammation. Flavan-3-ols have shown promising activity on mech- et al., 2014c; Vauzour, 2014). Clinical studies have also shown anisms associated with obesity and metabolic syndrome, including elevated flavonoid intake to be associated with improved language the ability to decrease body weight and adipose tissue, improve glu- and episodic and verbal memory in healthy adults (Matias, Buosi, cose homeostasis, inhibit lipid accumulation in tissues, and increase & Gomes, 2016). the anti-inflammatory cytokine IL-10. Berry studies also report Quercetin has been reported to improve symptoms of cogni- reduced hepatic lipogenesis and prevention of body weight gain, tive decline and mental fatigue, increase posterior parietal activity, whereas studies with citrus flavanones and obese mouse models synaptic excitation, and neural information-processing speed (Vau- have observed increased adiponectin, improved dyslipidemia, and zour, 2014; Dajas et al., 2015). Diets high in cocoa flavan-3-ols reduced obesity, BP, and inflammatory cytokines such as TNA-α have been shown to improve cognitive abilities in healthy, older (Alam et al., 2014; Greyling et al., 2014). adults, and those at risk of early dementia. Cognitive outcomes A meta-analysis of 15 RCTs with green tea flavan-3-ols iden- that are significantly affected include: improved choice reaction tified significant improvements in body mass index, and waist time, working memory performance, verbal fluency,reaction time, circumference, but associations could not be disentangled from rapid visual information processing (RVIP), visual spatial working the known metabolic effects of caffeine (Phung et al., 2010). A memory, trail making task, serial 3s’ subtraction tasks, and re- further human study showed significant reduction in body weight duced mental fatigue (Bell, Lamport, Butler, & Williams, 2015; following 4 wk of apple juice consumption. Conversely, in a large Ellam & Williamson, 2013). Tea consumption has been shown study of African-American women (n = 46,906, over 12 yr), no to significantly affect mood (Bell et al., 2015). Associations be- association between tea consumption and reduced diabetes risk tween strawberry consumption and a reduced rate of cognitive was observed (Boggs, Rosenberg, Ruiz-Narvaez, & Palmer, 2010; decline was reported in older women in the Nurses’ Health Study Grassi et al., 2013a). It should be noted that the available evidence (Giampieri et al., 2015). Furthermore, consuming blueberry and is primarily derived from models exploring obesity or CVD rather Concord grape juice for 12 wk improved paired associate learning than metabolic syndrome directly; human clinical and animal ev- and word list recall in subjects with dementia (Vauzour, 2014). idence is required to establish the direct effect of flavonoids on Outcomes significantly affected by berry consumption in cogni- metabolic syndrome. For reviews of flavonoids and metabolic syn- tive performance trials include: rapid visual information processing drome refer to Galleano et al. (2012) and Kawser Hossain et al. task, task switching, flanker task (spatial selective attention), word (2016). recognition, image recognition, letter memory, and digit vigilance

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(Bell et al., 2015). Cognitive outcomes significantly affected by Many cardiovascular biomarkers are altered in flavonoid in- citrus include: digit symbol substitution task, continuous perfor- terventions, such as CRP, vascular cell adhesion molecules, and mance task, and finger tapping task (Bell et al., 2015). cytokines (Gonzalez-Gallego´ et al., 2010). These proteins are regulated by proinflammatory transcription factor NF-κβ.Al- Others ternatively, considerable evidence exists for direct activity on Two human epidemiological studies found positive associations NO-mediated endothelial function, suggesting activity on the between total dietary flavonoid intake and bone mineral density NO/cyclic guanosine monophosphate (cGMP) pathway, which (BMD) in women (Welch & Hardcastle, 2014) and cross-sectional modifies protein kinase-mediated signal transduction through studies also report positive associations between habitual tea con- Nrf2 activation (Brown & Griendling, 2015). As recent evi- sumption and BMD (Nash & Ward, 2017), although experimen- dence indicates, there is crosstalk between NF-κβ and Nfr2, tal evidence is limited. In rodent models quercetin 1 was shown which presents a logical target for future mechanistic investiga- to improve bone mineral density (Kawabata, Mukai, & Ishisaka, tions (Cuadrado, Martin-Moldes, Ye, & Lastres-Becker, 2014; Ho 2015), hesperetin-7-O-rutinoside inhibited bone resorption (Li et al., 2010; Kabirifar et al., 2017; Xu et al., 2005). & Schluesener, 2017) and, although limited mechanistic data are Supplementation with myricetin 4 in mice fed a high-fat, high- presently available, Nash and Ward (2017) proposed modulation sugar diet resulted in decreased body weight and improved hyperc- of osteoblastic and osteoclastic activity as a possible mechanism of holesterolemia and hypertriglyceridemia, suggesting that multiple action. mechanisms of action of flavonoids are at play (Fusi et al., 2017). Flavonoids such as quercetin 1, hesperitin-7-O-rutinoside Similarly, cocoa flavonoids have been reported to act on insulin 80,(−)-epigallocatechin-3-O-gallate 12, naringenin 16,and secretion, glucose transport, thromboxane A2, P-selectin, MAPK, cyanidin-3-O-glucoside 63 have shown promise as potential ther- and NOX (Arranz et al., 2013; Grassi, Desideri, & Ferri, 2013b; apeutics in many proinflammatory models of disease/disorder in- Kerimi & Williamson, 2015), thus supporting the “multiple mech- cluding experimental models of colitis (Vezza et al., 2016), arthritis anisms” theory, as no single mechanism is likely to regulate this (Li & Schluesener, 2017), asthma and acute respiratory distress syn- diversity of pathways. Although one consistency in flavonoid re- drome (Lago et al., 2014; Li & Schluesener, 2017), UV-exposed search is their ability to regulate various enzymes, and perhaps skin damage (Kawabata et al., 2015), glaucoma and ocular hyper- there is some unidentified mechanism involving universal enzyme tension (Patel, Mathan, Vaghefi, & Braakhuis, 2015), renal toxicity regulation. (Kawabata et al., 2015; Li & Schluesener, 2017), obesity-associated Catabolism of flavonoids by the gut microbiota leads to hepatic steatosis (Kawabata et al., 2015), and exercise-induced fa- a large number of compounds, including 4-hydroxybenzoic tigue (Kawabata et al., 2015). acid 74, 3,4-dihydroxybenzoic acid 105 (protocatechuic acid), 3-methoxy-4-hydroxybenzoic acid 108 (vanillic acid), 3,5,- Mechanisms of action dimethoxy-4-hydroxybenzoic acid 109 (syringic acid), and 3,4,5- A commonly repeated statement in flavonoid literature is that trihydroxybenzoic acid 101 (gallic acid) (Kay et al., 2017), and “mechanistic evidence is needed in support of the available ob- blood levels of many of these phenolics have been observed to servational data.” In this respect, the past decade has seen signif- correlate with improved endothelial function (Rodriguez-Mateos icant advances in mechanistic findings using human and animal et al., 2014c). models, whereas flavonoid conjugates/metabolites are beginning OCH3 OCH3 to be used in some in vitro cell culture models. Nevertheless, OH OH it is worth mentioning that certain transporters are required to HOOC HOOC OCH3 take up the flavonoid conjugates into cells (see section “Interac- Vanillic acid 108 Syringic acid 109 tion of Flavonoids with the Gastrointestinal Tract”), and some of (3-methoxy-4-hydroxybenzoic acid) (3,5-dimethoxy-4-hydroxybenzoic acid) these transporters are not present in cultured or immortalized cells. These aspects need to be considered in experimental design. Moreover, healthy volunteers fed blueberries showed increased Vascular mechanisms. The most recognized activity of FMD response, which correlated with plasma levels of microbial flavonoid-rich foods is their ability to maintain vascular homeosta- metabolites and decreased neutrophil NOX activity (Hugel et al., sis (Hugel et al., 2016; Rodriguez-Mateos et al., 2014c). Three 2016). An increase in serum cGMP in hypercholesterolemic in- recent meta-analyses support this observation, particularly with re- dividuals has also been noted after supplementation with purified spect to the effect of cocoa and tea flavan-3-ols on lowering both anthocyanins (Hugel et al., 2016). Finally, many additional mecha- SBP and DBP and improving endothelial dysfunction, as measured nisms have been reported for berry flavonoids in animal and in vitro mainly by FMD (Fusi, Spiga, Trezza, Sgaragli, & Saponara, 2017; studies and include: increase serum cGMP,up-regulation of super- Hooper et al., 2012); improvements in endothelial function are oxide dismutase (SOD), glutathione reductase (GSR), thioredoxin also often reported for quercetin, wine, berries, and grapes (Hugel reductase 1, and paraoxonase, decreased production of endothelin- et al., 2016; Lilamand et al., 2014). It is clear that meta-analyses 1, and inhibition of angiotensin-converting enzyme (Chalopin consistently show that flavonoid interventions have beneficial im- et al., 2010; Edirisinghe, Banaszewski, Cappozzo, McCarthy, & pact on BP and endothelial function, yet the direct mechanism Burton-Freeman, 2011; Hidalgo et al., 2012; Lazze et al., 2006; behind this activity remains elusive. One of the earliest reported Paixao,˜ Dinis, & Almeida, 2012; Persson, Persson, & Andersson, mechanisms linking BP and FMD is the activity of flavonoids on 2009; Rodriguez-Mateos et al., 2014a; Simoncini et al., 2011; Xu, calcium channel regulation, and these findings have been relatively Ikeda, & Yamori, 2004a, b). The diversity of such activities is par- consistent for 40 yr; however, this evidence is primarily derived alleled in a microarray analysis of aortic tissue from apo E-deficient from studies using flavonoid aglycones, and in light of the recent mice fed bilberry, indicating modulation of over 1,200 genes in- emphasis on the importance of testing flavonoid metabolites and volved in cellular and molecular pathways relating to cholesterol catabolites in vivo, it is difficult to discern the relevance of many metabolism, inflammatory process, oxidative stress, and angiogen- of these previous findings. esis (Mauray et al. 2012).

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Anti-inflammatory mechanisms. Based on the disease endpoints 3,4-Dihydroxybenzoic acid 105 (protocatechuic acid), a catabo- most commonly reported for flavonoid activity, namely, cardio- lite of several flavonoids, reduces monocyte adhesion to TNF- vascular and cardio-metabolic disorders, cancer, and cognitive de- α–activated mouse aortic endothelial cells (Li & Schluesener, cline, it is reasonable to consider an anti-inflammatory mecha- 2017; Wang et al., 2010b). In another study, 6 flavonoids nism of action of flavonoids, as inflammation is an overlapping and 14 flavonoid metabolites were screened individually, and mechanism responsible for the progression of these disease states. as 29 different mixtures, in a THP-1 monocyte model Unfortunately, proving this directly in human intervention studies of LPS-induced TNF-α secretion. Individually 3-hydroxy-4- is inherently difficult, considering the extreme variation in back- methoxy-benzoic acid 110 (isovanillic acid), 4-methoxybenzoic ground cytokine production between seemingly homogeneous acid-3-O-glucuronide 111 (isovanillic acid-3-O-glucuronide), individuals. Compounding this is the inadequacy of human nu- 3-methoxybenzoic acid-4-O-glucuronide 112 (vanillic acid-4- trition studies to detect subtle changes in inflammatory status in O-glucuronide), 4-hydroxybenzoic acid-3-sulfate 113 (proto- either healthy or at-risk individuals (Cesari et al., 2003; Smid- catechuic acid-3-sulfate), 3-hydroxybenzoic acid-4-sulfate 114 owicz & Regula, 2015). Despite a lack of clear evidence from (protocatechuic-sulfate), and benzoic acid-4-sulfate 115 all sig- human studies, anti-inflammatory mechanisms have consistently nificantly reduced TNF-α secretion. been reported in animal and in vitro studies, including the sup- ĸβ OH pression of the NF- and Janus kinase–STAT–signaling path- HO OH ways (Vezza et al., 2016). In addition, an increased number of O COOH publications report interference of pro-oxidant enzyme-signaling OH O cascades involving myeloperoxidase, NOX, lipoxygenase, cy- OCH3 OCH3 clooxygenase, phospholipase, NOS, and so on, or the expression HOOC HOOC of adhesion molecules such as ICAM, VCAM, E-selectin, and Isovanillic acid 110 Isovanillic acid-3-O-glucuronide 111 P-selectin (Tangney & Rasmussen, 2013). (3-hydroxy-4-methoxybenzoic acid) (4-methoxybenzoic acid-3-O-glucuronide) Anti-inflammatory action of quercetin has been reported in OH - humans, animals, and cell culture models, including reports on in- OCH3 OSO3 O HO OH OH hibition of cyclooxygenase and lipoxygenase activities (Marunaka O COOH et al., 2017). Evidence suggests that metabolites of quercetin 1, HOOC HOOC such as quercetin-3-O-glucuronide 21, could be deconjugated Vanillic acid-4-O-glucuronide 112 Protocatechuic acid-3-sulfate 113 by macrophages, which could theoretically lead to increasing (3-methoxybenzoic acid-4-O-glucuronide) (4-hydroxybenzoic acid-3-sulfate) availability of the quercetin aglycone in tissues (Kawabata et al., 2015), indicating that unmetabolized flavonoids could have bio- OH OSO - OSO - logical relevance in tissues. In addition, quercetin has been shown 3 3 to inhibit the activity of histone acetyl transferases in the pro- HOOC HOOC moter region of genes associated with inflammation, including Protocatechuic acid-4-sulfate 114 Benzoic acid-4-sulfate 115 the activation of sirtuins (Joven, Micol, Segura-Carretero, Alonso- (3-hydroxybenzoic acid-4-sulfate) Villaverde, & Menendez, 2014). Liang et al. (2011) demonstrated that (−)-epigallocatechin-3-O-gallate 12 treatment could signif- It is of note that four combinations of metabolites, which icantly reduce MCP-1, and hesperetin-7-O-rutinoside 80 was included 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3- shown to reduce circulating inflammatory markers in individu- methoxy-4-hydroxybenzoic acid, and the glucuronide and sulfate als with metabolic syndrome (Rodriguez-Mateos et al., 2014c). conjugates of 4-hydroxybenzoic acid and 3,4-dihydroxybenzoic α The physiological relevance of most cell culture studies ex- acid, exhibited synergy and significantly reduced TNF- se- ploring the mechanism of action of flavonoids is uncertain for a cretion to a greater extent than when tested individually (di number reasons: (a) use of unmetabolized precursor structures; (b) Gesso et al., 2015). In addition, Warner et al. (2017) investi- use of nonphysiologically relevant concentrations; and (c) models gated the activity of 1, 6, and 24 hr postprandial metabolite signa- explore the activity of single compounds in isolation, whereas in tures of cyanidin-3-O-glucoside 63 in stimulated endothelial cells. vivo flavonoid metabolites exist as complex mixtures, likely pro- Here both IL-6 and VCAM-1 were significantly reduced in re- viding additive or synergistic activity. Recently a few investiga- sponse to all mixtures/signatures tested. Interestingly, activity was tors have explored the activity of flavonoid metabolites of micro- observed at concentrations 10-fold lower than those occurring bial origin, at physiologically relevant concentrations in isolation in plasma after ingestion of the precursor anthocyanin (Warner and in combination. The colonic flavan-3-ol catabolite 5-(3,4- et al., 2017). dihydroxyphenyl)-γ -valerolactone 30 has been shown to inhibit Metabolic/diabetic mechanisms. Diabetic and obese rodent nitrite production and iNOS in macrophage models. Phenolic models have shown that quercetin 1 and quercetin glucosides re- catabolites of anthocyanins have also been reported to act on duce hyperglycemia and increase insulin secretion (Kawser Hos- TNF-α, VCAM-1, ICAM-1, IL-6, and MCP-1 (Amin et al., sain et al., 2016); naringenin 16 was shown to decrease hy- 2015; Rodriguez-Mateos et al., 2014c; Warner et al., 2016, 2017;). perglycemia and increase superoxide dismutase (Kawser Hossain Flavonoid catabolites from the serum of mice fed blueberries was et al., 2016); and kaempferol 2 to reduce fasting glucose and also shown to inhibit TNF-α and IL-6, by reducing phospho- body weight gain, improve insulin resistance, increase muscle α β rylation of MAPK, JNK, p38, and ERK1/2 in macrophage cell glucose uptake, reduce HbA1C, TNF- , IL-6, and IL-1 se- β lines (Rodriguez-Mateos et al., 2014a). Transcriptomic analysis cretion, increased -cell survival, antioxidant defense proteins, γ has also revealed that flavan-3-ol metabolites affect the expression peroxisome proliferator-activated receptor (PPAR)- , and sterol of genes involved in cell–cell junctions and focal adhesion involved regulatory-element-binding protein-1c. Effects were often rein monocyte migration and adhesion (Rodriguez-Mateos et al., ported to be associated with Akt, phosphatidylinositol-3-kinase, 2014c). and protein kinase C, and also with enhanced cyclic adenosine

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3,5’-monophosphate signaling (Li & Schluesener, 2017). Stud- 2015; Socci et al., 2017), trail making test (Desideri et al., 2012; ies with (−)-epigallocatechin-3-O-gallate 12 using animal models Mastroiacovo et al., 2015; Sorond, Hurwitz, Salat, Greve, & Fisher, also suggest improved insulin signaling and glucose homeostasis in 2013), and Benton task performance. Some of these findings were adipose tissue resulting from downregulation of the ERK/JNK- associated with increased cerebral blood volume (Brickman et al., p53 pathway or attenuation of inflammatory processes through 2014). However, it should be noted that not all studies have shown interference of toll-like receptor-4 (Legeay, Rodier, Fillon, Faure, positive effects; no benefits to cognitive performance were ob- & Clere, 2015). Studies on glycemic control by flavonoids have served in a study by Pase et al. (2013), although Decroix et al. been reviewed in detail (De Bock, Derraik, & Cutfield, 2012; (2016) showed increased cerebral blood oxygenation with no sig- Hanhineva et al., 2010; Williamson, 2013). nificant behavioral effect. Anticancer mechanisms. Although human data are lacking, an- The impact of cocoa on the brain is believed to be the re- imal and cell culture studies of breast, colon, lung, prostate, and sult of two underlying mechanisms, either via improvement in bone cancer are accumulating, reporting activities such as: im- blood-flow and angiogenesis in the brain or by direct interactions provement of mitochondrial dysfunction and decrease of mast with neuroprotective and neuromodulatory enzymes/proteins cell density; inhibition of basal and testosterone-induced acceler- (Sokolov, Pavlova, Klosterhalfen, & Enck, 2013). For example, ated proliferation; suppression of mesothelioma cell growth and cocoa flavan-3-ols have been reported to increase mean blood Wnt/β-catenin regulation (Li & Schluesener, 2017). Flavonoid flow velocity and cerebral blood flow (CBF) in RCTs (Bell et al., actions on Wnt regulation have led some to suggest they may have 2015; Rendeiro et al., 2015). Animal feeding studies with (−)- a therapeutic role in the treatment of colorectal cancer (Amado epicatechin 38 observed decreased neurologic deficit, brain infarcts et al., 2014). Various mechanisms have been reported based on cell in N-methyl-d-aspartate models, and anxiety, which were associ- culture studies (Fernando, Rupasinghe & Hoskins, 2015; George ated with increased Morris water maze (MWM), BDNF, pro- et al., 2016; George, Dellaire, & Rupasinghe, 2017; Giampieri BDNF, pAkt, pCREB, and pCaMKII, α-amino-3-hydroxy-5- et al., 2015; Joven et al., 2014; Khan et al., 2016; Li & Schlue- methyl-4-isoxazolepropionic acid receptor (AMAP)-GluR2, and sener, 2017; Zhou et al., 2016), however, many of these studies decreased monoamine oxidase-A (Matias et al., 2016; Rendeiro, are at high concentrations and use unmetabolized flavonoids. Rhodes, & Spencer, 2015). (−)-Epicatechin has also been reported Cognition and neuroprotective mechanism. Perhaps one the to have antiamyloidogenic effect on amyloid β peptide deposition most contemporary foci of flavonoid research is the study of (Kawabata et al., 2015). Animal studies feeding (+)-catechin 28 neurodegeneration and cognitive performance. Here, significant noted improvements in MWM performance associated with in- advances have been made in animal models, with more recent creased CBF, myogenic tone, and FMD in cerebral artery, and in- studies investigating translation to childhood development, aging, creased acetylcholine (ach) sensitivity to eNOS inhibition. Finally, and early cognitive decline in humans. Based on extensive ev- (−)-epigallocatechin-3-O-gallate 12 has been shown to provide idence of the vascular activity of flavonoids, many believe that AMP-activated protein kinase-medicated neuroprotection (Kawa- the impact of flavonoids on blood flow to the brain is the most bata et al., 2015). For a recent detailed review summarizing the probable cognitive mechanism of action. Indeed, rodent studies effects of cocoa on cognitive function refer to Grassi, Ferri, and investigating the effects of dietary flavonoids and flavonoid-rich Desideri (2016). foods have reported improvements in cognitive function associated Quercetin 1 supplementation has been reported to improve with improved cerebral vascular function and brain blood flow. MWM outcomes and to increase passive avoidance, where find- Many flavonoid interventions, particularly trials feeding berries ings were associated with increased CBF, nitrite, ATP, acetyl- and cocoa/chocolate, have observed beneficial effects on endothe- cholisterase, and glutathione levels (Bell et al., 2015). Quercetin, lial function, which could account for improved cognitive out- kaempferol, and myricetin were also reported to have anti- comes. However, these positive endothelial effects are reported to amyloidogenic effect on amyloid β peptide deposition (Kawabata co-occur with other vascular mechanisms such as increased vasodi- et al., 2015). Animal studies further indicated that improvement lation and cerebral blood flow, increased plasma NO, attenuation in “inhibition of the immobility time” may be associated with of blood glucose decline, monoamine oxidase inhibition, and in- increased serotonin and noradrenaline in the frontal cortex and creased synthesis of brain-derived neurotrophic factor (BDNF; hippocampus and also activation of the ERK pathway (Giampieri Bell et al., 2015). There is also substantial evidence to suggest et al., 2015; Rendeiro, Rhodes, & Spencer, 2015). a secondary or complementary mechanism of action involving Anthocyanin supplementation has been shown to improve modulation of neuro-inflammation. It is conceivable that these working memory and MWM outcomes (Rendeiro et al., 2015). distinct mechanisms have different effects in models of cognitive Enriched bilberry and blackcurrant extracts modulate amyloid performance in young humans/animals relative to attenuation of precursor protein processing and alleviate behavioral abnormali- age-related cognitive decline in older adults. Much of the available ties in the APP/PS1 mouse model of Alzheimer’s disease (Baptista, mechanistic evidence on neuroinflammation comes from studies Henriques, Silva, Wiltfang, & da Cruz e Silva, 2014; Vepsalainen with cultured glial cells (Matias et al., 2016), yet few studies are et al., 2013). Moreover, cyanidin-3-O-glucoside 63 rescued cogni- conducted using metabolized flavonoids. tive impairments, which were induced by amyloid β, via modula- Studies on cocoa in humans have revealed enhanced cognitive tion of glycogen synthase kinase (GSK)-3Beta/tau in rats (Baptista outcomes (Socci, Tempesta, Desideri, De Gennaro, & Ferrara, et al., 2014). 2017), including: increased global cognition scores (Neshatdoust Orange juice has been reported to increase human cerebral et al., 2016), working memory function (Camfield et al., 2012), blood flow (Bell et al., 2015). Hesperetin-7-O-rutinoside 80 has spatial working memory performance, choice reaction time (Field, shown activity in rodent models of Alzheimer’s disease, Hunting- Williams, & Butler, 2011), verbal fluency performance (Desideri ton’s disease, epilepsy, and neurotoxicity, where it is reported to et al., 2012; Mastroiacovo et al., 2015), serial 3s performance, have activity against amyloid β-induced neurotoxicity, attenuate visual information processing (Scholey et al., 2010), serial 7s sub- biochemical and mitochondrial alterations, and protect brain and traction performance, self-reported mental fatigue (Massee et al., sciatic nerve tissues against oxidative damage.

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Flavonols and their metabolites have been detected in ro- et al., 2016), inhibited TNF-α–stimulated expression of VCAM-1 dent brains (Bell et al., 2015; Kawabata et al., 2015), and even and ICAM-1, and decreased shear stress-induced platelet aggre- monomeric metabolites of proanthocyanidins were identified in gation in isolated human platelets (Wang et al., 2010b). Gallic mouse brains, and they correlated with improved cognitive func- acid decreased tumor size, proliferation, invasion, and angiogen- tion in an Alzheimer’s disease model where the beneficial effects esis, inhibited migration, induced apoptosis, and attenuated the were linked to improved synaptic plasticity (Wang et al., 2012). expression of NOX, cytokines, and receptor for advanced glyca- Despite metabolites being reported in abundance in rodent studies, tion end-products (Hugel et al., 2016; Zhou et al., 2016). The less most neuro/cognitive mechanisms of flavonoids have to date been often studied 3-methoxy-4-hydroxybenzoic acid has been shown reported in studies using neuronal cell lines and unmetabolized to inhibit angiotensin converting enzyme and to improve inflam- flavonoids. matory stress in animal and cell models (Amin et al., 2015; Hi- dalgo et al., 2012; Rodriguez-Mateos et al., 2014c; Warner et al., Microbiota: drivers of flavonoid bioactivity 2016). The realization of the importance of the microbiome to health In a proinflammatory screening study stimulating vascular en- has led to new theories and focus, including exploration of dothelial cells with oxidized LDL (oxLDL) or CD40L, cyanidin- metabotypes, the interactome, and epigenome (Kawser Hossain 3-O-glucoside 63 had no anti-inflammatory effects, although et al., 2016). The epigenome defines whether a gene will be active many of its catabolites significantly reduced IL-6 secretion, or silent under certain conditions, whereas a metabotype describes with glucuronide and sulfate conjugates of 3,4-dihydroxybenzoic an individual’s metabolic phenotype. It is believed that certain indi- acid (protocatechuic acid) eliciting the highest response. Sim- viduals, populations, ethnic origins, and so on, will cluster accord- ilarly, metabolites also reduced VCAM-1, with 4-hydroxy-3- ing to phenotypic characteristics associated with metabolism and methoxycinnamic acid (ferulic acid) inducing the greatest ef- microbiome. Accumulating evidence suggests dietary flavonoids fect (Amin et al., 2015). In another screening study of similar are able to modify epigenetic pathways (Joven et al., 2014), and it design, 14 phenolic metabolites and six flavonoids were evalu- is believed that understanding an individual’s metabolic phenotype ated for their ability to attenuate VCAM-1 secretion by human will bring us closer to establishing more personalized strategies for umbilical vein endothelial cells stimulated with TNF-α.Ofthe disease prevention. 20 compounds screened, 3,4-dihydroxybenzoic acid 105 (pro- Research involving metabolic phenotypes (or metabotypes) in- tocatechuic acid), 3-hydroxy-4-methoxybenzoic acid 110 (iso- volves using systems biology to explore complex relationships be- vanillic acid), 4-methoxybenzoic acid-3-O-glucuronide 111 (iso- tween the genome, transcriptome, proteome, and environment vanillic acid-3-O-glucuronide), 4-hydroxybenzoic acid-3-sulfate and it is a research direction many in the flavonoid field are begin- 113 (protocatechuic acid-3-sulfate), and 3-hydroxybenzoic acid- ning to explore (Ferrara & Seb´ edio,´ 2015). Linking these concepts 4-sulfate 114 (protecatechuic acid-4-sulfate) all significantly re- together requires a multitude of analytical, biological, and bioin- duced VCAM-1 secretion (Warner et al., 2016), indicating that formatics approaches. Jacobsen et al. (2013) stated “Despite the colonic catabolism and phase II metabolism of flavonoids increase recent advances in the biological principles that underlie microbial their anti-inflammatory efficacy (Figure 22). symbiosis in the gut of mammals, mechanistic understanding of the Ellagic acid 11 metabolism also warrants mention, as it is a contributions of the gut microbiome and how variations on the colonic metabolite of ellagitannins, found in flavonoid-rich foods metabotypes are linked to host health are obscure.” These investi- such as strawberries, raspberries, pomegranates, and some aged gators explored fecal samples of 124 Europeans who were healthy, wines. In experimental models, ellagic acid has been observed to obese, or had IBD, using metagenomics sequencing data, and they suppress tumor growth and angiogenesis, have antiproliferative and found only 33 metabolites which affected protein complexes as- proapoptotic effects, suppress cell invasion and motility, and cause sociated with disease responses that involved adaptive immune- G0/G1 cell-cycle arrest (Zhou et al., 2016). signaling pathways. Flavonoids were among these metabolites. It was noted that, independent of healthy or diseased samples, in- Influence of flavonoids on microbial growth dividuals were clustered having high, medium, or low metabolic The activity of flavonoids is unlikely to be exclusively the re- potential. In addition, quercetin was found to interact with dis- sult of reabsorbed microbial metabolites acting directly on target ease protein complexes associated with a large number of OMIM tissue, as an extensive literature exists describing the antimicrobial disease label identifiers, including obesity and IBD. Functionality activity of flavonoids, extending over 50 yr, where more recent ev- studies using meta-transcriptomic or meta-metabolomic analysis idence also indicates probiotic effects (Duda-Chodak et al., 2015). are required to identify the direct mechanistic links (Jacobsen et al., It is apparent that flavonoids and their microbial metabolites have 2013). direct activity in the gut, altering the microbiome, as well as the Accumulating evidence suggests that gut-derived pheno- immune status of the host (Duda-Chodak, 2012). However, the lic metabolites are responsible for much of the mechanis- gut microbiome does not always change measurably in studies tic activity of flavonoids. Possibly the most studied bacterial where flavonoids have been administered (Williamson & Clifford, catabolites of flavonoids are 4-hydroxy-3-methoxycinnamic acid 2017). In some intervention studies, feeding flavonoid-rich bever- 94 (ferulic acid), 3,4,5-trihydroxybenzoic acid 101 (gallic acid) ages produced both antimicrobial and probiotic effects on bacterial 3,4-dihydroxybenzoic acid 105 (protocatechuic acid), and 3- cell growth. It is clear there are inherently complex associations methoxy-4-hydroxybenzoic acid 108 (vanillic acid), which have between dietary flavonoids, microbial ecology, and human health all been consistently reported to have biological activity, and are (Figure 23), and disentangling these association will require signif- also found in the diet in their own right. Ferulic acid has been icant research focus over the coming years. reported to improve kidney structure and function in hypertensive In vitro cultures of flavanones and flavonols screened for ac- rats (Hugel et al., 2016), to reduce apoptosis and to cause cell-cycle tivity on intestinal bacterial growth of Bacteroides galacturonicus, arrest (Zhou et al., 2016). 3,4-Dihihydroxybenzoic acid inhibited Lactobacillus spp., Enterococcus caccae, Bifidobacetrium catenulatum, Ru- ACE and improved inflammatory stress in animal models (Hugel minococcus gauvreauii, and E. coli, revealed that naringenin 16 and

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Figure 22–OxLDL induced IL6 production. Data expressed as % relative to OxLDL treated endothelial cells. ∗Signiﬁcant relative to oxLDL-treated cells, p ࣘ 0.05, ANOVA with Tukey post-hoc t-test n = 3. Cyanidin-3-O-glucoside (C3G), 3,4-dihydroxybenzoic acid (protocatechuic acid; PCA), 3-methoxy-4-hydroxybenzoic acid (vanillic acid; VA), 4-hydroxybenzoic acid-3-sulfate (protocatechuic acid-3-sulfate; PCA-3-S), 4-hydroxybenzoic acid-3-O-glucuronide (protocatechuic acid-3-O-glucuronide; PCA-3-GlcUA).

growth, with the aglycones quercetin and naringenin displaying the greatest antibacterial activity (Duda-Chodak, 2012). O Animal studies using apple juice reported inhibition of Bac- teroides and promotion of Bifidobacterium, Lactobacillus,andBac- O teroidacae (Etxeberria et al., 2013). A cocoa drink reduced Flavonoid Bacteroides and Clostridium growth, while promoting growth of Eubacterium rectale, Lactobacillus spp., Enterococcus spp., and Bifi- dobacterium spp. (Cardona, Andres-Lacueva, Tulipani, Tinahones, & Queipo-Ortuno, 2013). Using an in vitro batch-culture model, Tzounis et al. (2008) found that flavan-3-ol monomers influenced bacterial populations even in the presence of other nutri- + HOOC ents. ( )-Catechin 28 significantly inhibited growth of Clostrid- ium coccoides-Eubacteriom rectale, whereas growth of Bifidobacterium Metabolism and Lactobacillus spp. remained unaffected (Tzounis et al., 2008). A cocoa intervention with rats showed a significant decrease in HOOC the proportion of Bacteroides, Clostridium,andStaphylococcus genera HOOC (Massot-Cladera, Perez-Berezo, Franch, Castell, & Perez-Cano, Gut Health 2012). Interestingly, reductions in Clostridium species correlated with weight loss and BMI. Finally, (−)-epicatechin 38 and (+)- catechin 28 were reported to stimulate the growth of beneficial Figure 23–Microbiota role in flavonoid bioavailability. bacterial groups, Eubacterium rectale, Clostridium coccoides, Lactobacil- lus spp., and Bifidobacterium spp. (Etxeberria et al., 2013; Kawabata, Sugiyama, Sakano, & Ohigashi, 2013). quercetin 1 exerted dose-dependent inhibitory effects on all the A black tea extract promoted proliferation of Klebsiella spp., bacterial species that were explored, whereas the flavanone glyco- and Enterococci Akkermansia, whereas green tea preparations inhib- sides were inactive (Duda-Chodak, 2012). Similarly, quercetin and ited Clostridium and Bacteroidaceae and promoted Lactobacillus and naringenin presented the highest antibacterial activities when the Bifidobacterium spp. (−)-Epicatechin, (+)-catechin, gallic acid, 3- viability of E. coli, Staphylococcus aureus, Salmonella typhimurium, O-methylgallic acid, and caffeic acid have also been reported to and Lactobacillus rhamnosus was assessed in culture. All tested suppress the growth of pathogens such as Clostridium perfringens, flavonoids induced a decrease in bacterial growth with the ex- Clostridium difficile,andBacteriodes spp. (Lee, 2006). ception of quercetin-3-O-rutinoside 13 (Parkar, Stevenson, & Consumption of a blueberry extract resulted in an increase in Skinner, 2008). In support of these findings, another study re- intestinal Bififobacterium (Vendrame et al., 2011), whereas animal ported that pure flavonoids influenced the viability of four bac- and in vitro studies using blueberry extracts observed the promo- terial species, E. coli, Staphylococcus aureus, Salmonella typhimurium, tion of Bifidobacterium breve, Lactobacillus rhamnosus,andLactobacil- and Lactobacillus rhamnosus. Again, all the tested compounds, ex- lus growth. Berry extracts, including strawberry, cranberry, black cept quercetin-3-O-rutinoside, induced a decrease in bacterial currant, lingonberry, and cloudberry, have also been reported to

r 1096 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary flavonoids: a historical review . . . inhibit the growth of Bacteroides, Clostridium perfringens, Clostridium It is clear that flavonoids can affect the microbiome, however, perrfingens, Staphylococcus, E. coli, Lactobacillus rhamnosus, Salmonella, the impact of the metabolome and microbiome on human health and Bifidobacterium lactis E-508 (Etxeberria et al., 2013). is inherently complex (Scalbert et al., 2014; van Duynhoven et al., The mechanism by which flavonoids modulate bacterial growth 2011) and unraveling the complex interplay between flavonoids is unknown, however, recent findings suggest flavonoids can up- and health will require deployment of complementary in vitro,ani- regulate defensive protein secretion and downregulate various mi- mal and human studies. One hurdle in moving forward is the large crobial metabolic and biosynthetic proteins, likely attributed to biological variation in the microbiome and human metabolism and their ability to bind bacterial cell membranes and to disturb nor- the relatively subtle effects of dietary interventions. Furthermore, mal membrane function (Kemperman, Bolca, Roger, & Vaughan, the links between flavonoid metabolism and the human gut micro- 2010). biome have yet to be captured by metabolomic and microbiomic approaches. It is clear that the field needs a unified focus in or- Microbiota: drivers of flavonoids impact on human health der to successfully characterize the associations between flavonoid The impact of flavonoids and/or their phenolic microbial consumption and disease risk (van Duynhoven et al., 2011, 2012). catabolites on microbial speciation can have a positive impact on host biochemistry and pathology. Although most of this research Further considerations is still in its infancy, a recent study of 122 subjects revealed an in- New theories brought new vigor, concepts, and approaches to hibitory role of flavonoid-rich fruits and vegetables on the growth the field of flavonoid research over the past two decades, including of potentially pathogenic clostridia in high- and low-flavonoid new concepts, such as metabolome, metabotype, microbiome, in- consumers (Klinder et al., 2016). Correlations were identified be- teractone, nutrikinetics, and nutradynamics (van Duynhoven et al., tween CVD risk factors and bacterial populations in those who 2012). The last decade has also seen significant progress in under- consumed fruits and vegetables containing high, medium, and standing the contribution of the epigenome to the development of low levels of flavonoids. Positive correlations were observed for: chronic diseases, including the potential impact of diet and lifestyle. body fat and Bacteroides/Prevotella; waist circumference and Atopo- Despite all this, based on the review of nearly 70 yr of flavonoid bium; cholesterol and Bifidobacterium;HDLandBacteroides;LDL research, one thing is clear: there is an almost linear prolifera- and Bifidobacterium, Lactobacillus/Enterococcus, Bacteroides/Prevotella, tion of reported activities and mechanism of action of flavonoids Clostridium leptum-Ruminococcus bromii/flavefaciens and Clostrid- (Figure 21). The question remains, why have so many different ac- ium histolyticum/perfringens; TNFα and Lactobacillus/Enterococcus, tivities been reported? With that in mind, perhaps it is now time Bacteroides/Prevotella, Atopobium, Eubacterium rectale/Clostridium to refocus efforts based on the accumulated breadth of knowl- coccoides,andClostridium histolyticum/perfringens;ICAMandEu- edge. Either flavonoid-rich foods, flavonoids, or their microbial bacterium rectale/Clostridium coccoides; and VCAM-1 and Lactobacil- metabolites have unique activities across a multitude of tissues and lus/Enterococcus (Klinder et al., 2016). Similarly, healthy mice fed biological pathways, which is unlikely, or they have shared activity flavonoid-enriched diets have shown increased Bifidobacterium spp. in a few key pathways, or they have a common mechanism of which was associated with decreased proinflammatory markers action involving a protein/enzyme or receptor which communi- TNF-α, PGE2, and leukotriene B4 (Espley et al., 2014). cates between signaling pathways (“crosstalk”), regulating multiple In an 8-wk feeding study with mice on a high-fat, high-glucose transcription factors. Based on the most commonly reported ac- diet, cranberries brought about an increased population of Akker- tions of flavonoids, that is, CVD, cardio-metabolic disorders, type mansia, a mucin-degrading bacterium within the intestine. There 2 diabetes, cancer, and neurodegeneration, and the established was also decreased intestinal triglycerides, intestinal and hepatic overlapping mechanism linking these disorders, namely inflam- inflammation, weight gain, visceral obesity, and liver weight rel- mation and redox regulation, significant evidence points towards ative to mice not receiving cranberry (Anhe et al., 2015). An- an overlapping mechanism which “lies at the crossroads” of a sig- other study feeding a blackcurrant extract to mice for 8 wk on naling pathway involving both inflammation and redox regulation. high- and low-fat diets with and without treatment with antibi- In this case, the most likely candidate would involve crosstalk be- otics also observed reduced weight gain and improved glucose tween NF-ĸβ and Nrf2. Alternatively, there is evidence to suggest homeostasis, but only in mice that did not receive the antibi- the involvement of VEGF or VEGF-receptor, or the PPAR nu- otic cocktail and hence had an intact microbiome. Interestingly, clear receptor family. However, any one of these mechanisms does the anthocyanin content of feces from the antibiotic-treated mice not account for the totality of activities reported across receptors, was 15-fold higher than the feces of the mice with an intact mi- transcription factors, and associated up- and down-stream signal- crobiome. This implies the microbiome is directly involved with ing proteins. It is also possible that flavonoids have multiple mech- anthocyanin catabolism/metabolism, and both gut metabolites and anism of action and could act on VEGF, PPARs, and a common microbiome likely contribute to the observed effects on weight crosstalk protein linking the NF-ĸβ and Nrf2 pathways. Finally, it and glucose-processing (Esposito et al., 2015). is just as possible that flavonoid activity is insufficient to produce In an 11-wk study with mice fed a high-fat diet supple- sizable health effects on their own, but in combination with their mented with or without a lingonberry extract, reduced weight apparent actions on nutrient regulation (absorption, metabolism), gain, inflammation, and endotoxemia were observed. 16s rRNA- such as fat, carbohydrate and protein metabolism, produce a com- sequencing identified a higher abundance of Akkermansia and bined measurable health effect. For example, flavonoids are re- Faecalibacterium, which are generally associated with promoting a ported to affect carbohydrate digestion and metabolism, and lipid healthy gut (Heyman-Linden et al., 2016). Furthermore, in rodent profiles, and these changes in combination with activity on tran- studies where the maternal diets were enriched with trans-fatty scription factors, as detailed above, would provide powerful health acids, anthocyanin-supplemented animals had restored expression effects. of Lactobacillus spp. and Bifidobacterium spp. DNA and reduced in- Vascular endothelial growth factor. VEGF and VEGF- flammatory markers associated with downregulation of NFĸβ in receptors are key players in the regulation of vascular cell offspring (Morais, de Rosso, Estadella, & Pisani, 2016). development and are also involved in monocyte regulation,

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RAC1 NADPH MAPK Oxidase PI3K

HO-1 IKK Keap1 Nrf2 IKβ P65 GST Chemokines HO-1 NQO1 iNOS GSK3B UGT ARE NF-ĸB COX GPx HDAC CYP

Figure 24–Reported activity of flavonoids on Nrf2 and NF-ĸB regulated enzymes, chemokines and “cross-talk” proteins. Figure adapted from reports identifying cross-talk between Nrf2 and NF-ĸB pathways (Arranz et al., 2013; Baptista et al., 2014; Bousova & Skalova, 2012; Brown & Griendling, 2015; Cuadrado et al., 2014; Day, Bao, Morgan, & Williamson, 2000a; Fraga & Oteiza, 2011; Gonzalez-Gallego´ et al., 2010; Gonzalez-Sarr´ ´ıas et al., 2010; Grassi et al., 2013; Joven et al., 2014; Kabirifar et al., 2017; Kawser Hossain et al., 2016; Kerimi & Williamson, 2015; Khan et al., 2016. Li & Schluesener, 2017; Li et al., 2008; Lodi et al., 2009; Matias et al., 2016; Mladenka et al., 2010; Morais et al., 2016; Rendeiro et al., 2015; Romero et al., 2009; Ryter et al., 2002; Sanchez et al., 2006, 2007; Scholz et al., 2010; Sorrenti et al., 2007; Spencer et al., 2012; Steffen et al., 2007, 2008; Stepowski & Kruszewski, 2011; Vauzour, 2014; Wang et al., 2010a; Xu et al., 2005). Enzymes, proteins and transcription factors identified have been previously reported to be affected by flavonoids or their metabolites (as referenced throughtout this review). macrophage migration, angiogenesis, and vascular permeability involvement of RAC1 is implicated in the activity of flavonoids (Alvarez-Aznar, Muhl, & Gaengel, 2017), nerve regeneration, and and their metabolites on NOX, HO-1, and the attenuation of attenuating vascular complications associated with diabetes (Sug- LPS-induced inflammatory stress (that is, activation of TLR4 in- anya, Bhakkiyalakshmi, Sarada, & Ramkumar, 2016). Interference ducing the release of proinflammatory cytokines; Cuadrado et al., with the VEGF-signaling pathway has been proposed as a mech- 2014; Ho et al., 2010; Kabirifar et al., 2017; Xu et al., 2005). anism behind flavonoids’ anticancer activity (Ci, Qiao, & Han, Flavonoids are also reported to be active on other notable crosstalk 2016) and VEGF is a suggested risk marker for coronary heart points linking these two pathways, including Keap1, GSK, Jun, disease (Wang et al., 2017). Quercetin and cocoa flavonoids have HDAC, p65, IKK, and HO-1, as well as having direct activity on also been reported to act on VEGF (Donnini, Finetti, Lusini, & NF-ĸβ and Nrf2 (Ahmad & Mukhtar, 1999; Baptista et al., 2014; Morbidelli, 2006; Kim et al., 2014), providing further evidence Bousova & Skalova, 2012; Brown, 1999; Gomes, Fernandes, Ho that VEGF is a reasonable mechanistic target. et al., 2010; Gonzalez-Sarr´ ´ıas et al., 2010; Kabirifar et al., 2017; Peroxisome proliferator-activated receptor-α. PPAR-α plays Gomes et al., 2008; Lin & Liang, 2000; Romero et al., 2009; Ry- a key role in glucose homeostasis and lipid metabolism (Yang, ter et al., 2002; Sanchez et al., 2006, 2007; Sorrenti et al., 2007; Xiao, & Wang, 2017), whereas PPAR-γ is involved in regulat- Wang et al., 2010a; Xu et al., 2005; Yang et al., 1997; Yang et al., ing endothelial function, BP, oxidative stress response (Kvandova, 2000; Zhou et al., 2016). Majzunova, & Dovinova, 2016), mitochondrial dysfunction, and neuro-inflammation (Agarwal, Yadav, & Chaturvedi, 2017). Al- Conclusions though controversial, PPAR polymorphisms have also been sug- Flavonoid research has recently undergone a transformation, and gested as being associated with coronary heart disease risk (Bal- with the demise of the radical-scavenging antioxidant hypothesis akumar, Rose, & Singh, 2007; Qian et al., 2016). The activity and the realization that the microbiome is inherently integrated of flavonoids on PPAR has been reported as a possible mecha- with flavonoid metabolism and bioactivity, the field is primed for nism of action in studies of cardio-metabolic and cognitive health. new discoveries. Researchers should be mindful of the past 80 yr of Flavonoids such as kaempferol have been reported to modulate flavonoid research, and some of the past highlights and low points PPAR-γ (Li & Schluesener, 2017). Based on the diverse roles of have been discussed in this paper to help new scientists to the field PPARs, they are logical targets for future investigation. avoid making some of the same mistakes. Moving forward, there Crosstalk. Evidence suggests a cycle or balance exists between are a number of key findings on bioavailability and bioefficacy NF-ĸβ and Nrf2 pathways (Cuadrado et al., 2014; Wardyn, Pons- which should be emphasized: ford, & Sanderson, 2015) in which RAC1 may be a coordinating r protein (Cuadrado et al., 2014) and could be an important target Parent flavonoids are deglycosylated during digestion, are ab- for flavonoid research (Figure 24). RAC1 can activate NF-ĸβ to sorbed in the small intestine, and appear in the blood as phase II metabolites. initiate an inflammatory response and also induce the Nrf2/ARE r pathway which in turn inhibits RAC1-dependent NF-ĸβ activa- Flavonoids can act on processes of digestion in the gut lumen tion. Therefore, RAC1 appears to have the ability to coordinate before absorption and affect the rate and extent of absorption ĸβ of macronutrients such as sugars. both the NF- and Nrf2 pathways, thus modulating inflamma- r tion, oxidative and metabolic pathways (Cuadrado et al., 2014; Flavonoid conjugates in the blood can act on the endothelial Wardyn et al., 2015). Quercetin 1, gallic acid 101, and caffeic acid cells lining the blood vessels, as well as the underlying smooth 103 have been reported to downregulate RAC1. Furthermore, the muscle cells, and regulate vascular tone, blood pressure, vascular health, and cognitive function.

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r The gut microbiome plays a major role in the metabolism and GSR glutathione reductase absorption of many flavonoids, but the products absorbed are GSK glycogen synthase kinase different chemical species to the ingested compounds, and HDL high-density lipoprotein they can exhibit their own biological activities, which may HO-1 heme oxygenase-1 perhaps even synergize with the parent flavonoid. HOMA-IR homeostatic model assessment of insulin resistance r Direct interactions between flavonoids and the gut micro- HR heart rate biome are likely to alter host immune and inflammatory sta- ICAM intracellular adhesion molecule tus, and also influence microbiome diversity. ICAM-1 intercellular adhesion molecule-1 r The activity of absorbed parent compounds and of microbial IDA information-dependent acquisition metabolites appears to involve action on key cell receptors or IL Interleukin (IL-1β, IL-4, IL-5, IL-6, IL-8, IL-13, crosstalk between cell signaling pathways, ultimately differen- IP-10) tially affecting various cells and tissues, depending on the cell iNOS inducible nitric oxide synthase phenotype and metabolic environment. JNK c-Jun N-terminal kinase LDL low-density lipoprotein Acknowledgments LOX lipoxygenase Gary Williamson acknowledges funding from the UK Biotech- LPH lactase phlorizin hydrolase nology and Biological Sciences Research Council (BBSRC), un- MAPK mitogen-activated protein kinase der the DRINC initiative (BB/M027406/1) and the European MCP-1 monocyte chemotactic protein-1 Research Council for an advanced grant (POLYTRUE? 322467). MI myocardial infarction Information on the catabolism and bioactivity of flavonoids de- MRP multi-drug-resistance-associated protein tailed in this review was funded by BBSRC grants to Colin Kay, MWM Morris water maze under the DRINC initiative (BB/H004963/1, BB/I006028/1). NF-ĸβ nuclear factor kappa-light-chain enhancer of acti- Colin Kay was also supported by the USDA National Institute of vatedBcells Food and Agriculture (Hatch/Kay-Colin; 1011757). Alan Crozier NO nitric oxide is a consultant for Mars Inc., and has received unrestricted research NOS nitric oxide synthase grants from Mars Inc. as well as funding from the US National Pro- NOX NADPH oxidase cessed Raspberry Council and the Coca-Cola Company, which Nrf2 nuclear factor (erythroid-derived 2)-like 2 supported some of the research mentioned in this review. OAT organic anion transporter Conflicts of Interest OATP organic anion transporting peptide OMIM Online Mendelian Inheritance in Man (catalog) The authors declare no conflicts of interest ORAC oxygen radical absorbing capacity Authors’ Contributions PGE2 prostaglandin E2 All three authors researched, wrote, and edited the review. Akt protein kinase B (PKB) PLA2 phospholipase A2 Nomenclature PPAR-γ peroxisome proliferator-activated receptor gamma ACE angiotensin-converting enzyme PWV pulse wave velocity AMAP α-amino-3-hydroxy-5-methyl-4- RC on-line radioactivity detector isoxazolepropionic acid receptor RCTs randomized controlled trials AT1/2 apparent elimination half-life 2/3-RFMs 2 and 3 carbon ring-fission metabolites BDNF brain-derived neurotrophic factor SBP systolic blood pressure BMD bone mineral density SGLT1 sodium-dependent glucose transporter 1 BMI body mass index SOD superoxide dismutase BP blood pressure SREM structurally related (−)-epicatechin metabolite 3/5C-RFMs 3/5-carbon ring fission metabolites TAG triacylglycerol [14C]EC [2-14C](−)-epicatechin TEAC Trolox-equivalent antioxidant activity CBF cerebral blood flow TLR4 Toll-like receptor 4 CBG cytosolic β-glucosidase Tmax time to reach peak plasma concentration CD40L cluster of differentiation 40 ligand TNF-α tumor necrosis factor-α CHD coronary heart disease TOF time-of-flight Cmax peak plasma concentration VCAM-1 vascular cell adhesion molecule-1 COX cyclooxygenase VEGF vascular endothelial growth factor CREB cAMP response element-binding protein CRP C-reactive protein References CVD cardiovascular disease Abdalla, S., Zarga, M. A., Afifi, F., al-Khalil, S., Mahasneh, A., & Sabri, S. DBP diastolic blood pressure (1989). Effects of 3,3 -di-O-methylquercetin on guinea-pig isolated smooth eNOS endothelial nitric oxide synthase muscle. Journal of Pharmaceutics and Pharmacology, 41, 138–141. Actis-Goreta, L., Lev´ eques,` A., Giuffrida, F., Romanov-Michailidis, F., EPIC European Prospective Investigation into Cancer Viton, D., Barron, D., . . . Dionisi, F. (2012). Elucidation of ERK extracellular signal-regulated kinase (−)-epicatechin metabolites after ingestion of chocolate by healthy humans. T1/2 elimination half-life Free Radical Biology and Medicine, 53, 787–795. FMD flow-mediated vasodilation https://doi.org/10.1016/jfreeradbiomed.2012.05.023. FRAP ferric-reducing antioxidant potential Actis-Goretta, L., Lev´ eques,` A., Rein, M., Teml, A., Schafer,¨ C., Hofmann, U., . . . Williamson, G. (2013). Intestinal absorption, metabolism and GI gastrointestinal

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excretion of (–)-epicatechin in healthy humans assessed by using an Aziz, A. A., Edwards, C. A., Lean, M. E. J., & Crozier, A. (1998). intestinal perfusion technique. American Journal of Clinical Nutrition, 98, Absorption and excretion of conjugated flavonols, including 924–933. https://doi.org/10.3945/ajcn.113.065789. quercetin-4-O-β-glucoside and isorhamnetin-4-O-β-glucoside by human Actis-Goretta, L., Dew, T. P., Lev´ esques,` A., Pereira-Caro, G., Rein, M., volunteers after the consumption of onions. Free Radical Research, 29, Teml, A., . . . Williamson, G. (2015). Gastrointestinal absorption and 257–269. metabolism of hesperetin-7-O-rutinoside and hesperetin-7-O-glucoside in Baba, S., Osakabe, N., Yasuda, A., Natsume, M., Takizawa, T., Takizawa, T., healthy humans. Molecular Nutrition and Food Research, 59, 1651–1662. . . . Terao, J. (2000). Bioavailability of (–)-epicatechin upon intake of https://doi.org/10.1002/mnfr.201500202. chocolate and cocoa in human volunteers. Free Radical Research, 33, Agarwal, S., Yadav, A., & Chaturvedi, R. K. (2017). Peroxisome 635–641. proliferator-activated receptors (PPARs) as therapeutic target in Bajad, S., & Shulaev, V. (2007). Highly-parallel metabolomics approaches neurodegenerative disorders. Biochemical and Biophysical Research using LC-MS2 for pharmaceutical and environmental analysis. Trends in Communications, 483, 1166–1177. Analytical Chemistry, 26, 625–636. https://doi.org/10.1016/j.trac.2007. https://doi.org/10.1016/j.bbrc.2016.08.043. 02.009. Ahmad, N., & Mukhtar, H. (1999). Green tea polyphenols and cancer: Bakker-Grunwald, T., Andrew, J. S., & Neville, M. C. (1980). K+ influx Biologic mechanisms and practical implications. Nutrition Reviews, 57, components in ascites cells: The effects of agents interacting with the (Na+ 78–83. + K+)-pump. Journal of Membrane Biology, 52, 141–146. Alam, M. A., Subhan, N., Rahman, M. M., Uddin, S. J., Reza, H. M., & Balakumar, P., Rose, M., & Singh, M. (2007). PPAR ligands: Are they Sarker, S. D. (2014). Effect of citrus flavonoids, naringin and naringenin, on potential agents for cardiovascular disorders? Pharmacology, 80, 1–10. metabolic syndrome and their mechanisms of action. Advances in Nutrition, https://doi.org/10.1159/000102594. 5, 404–417. https://doi.org/10.3945/an.113.005603. Baptista, F. I., Henriques, A. G., Silva, A. M., Wiltfang, J., & da Cruz e Silva, Alvarez-Aznar, A., Muhl, L., & Gaengel, K. (2017). VEGF receptor tyrosine O. A. (2014). Flavonoids as therapeutic compounds targeting key proteins kinases: Key regulators of vascular function. Current Topics Developmental involved in Alzheimer’s disease. ACS Chemical Neuroscience, 5, 83–92. Biology, 123, 433–482. https://doi.org/10.1016/bs.ctdb.2016.10.001. https://doi.org/10.1021/cn400213r Amado, N. G., Predes, D., Moreno, M. M., Carvalho, I. O., Mendes, F. A., Barron, D., Smarrito-Menozz, C., Fumeaux, & Viton, F. (2012). Synthesis of & Abreu, J. G. (2014). Flavonoids and Wnt/beta-catenin signaling: Potential dietary phenolic metabolites and isotopically-labeled dietary phenolics. In: role in colorectal cancer therapies. International Journal of Molecular Sciences, In J. P. E. Spencer & A. Crozier (Eds.), Flavonoids and related compounds: 15, 12094–12106. https://doi.org/10.3390/ijms150712094. Bioavailability and function (pp. 233–293). Boca Raton, FL: CRC Press. Ameer, B., & Weintraub, R. A. (1997). Drug interactions with grapefruit Baur, J. A., & Sinclair, D. A. (2006). Therapeutic potential of resveratrol. juice. Clinical Pharmacokinetics, 33, 103–121. Nature Reviews Drug Discovery, 5, 493–506. https://doi.org/10.2165/00003088-199733020-00003. https://doi.org/10.1038/nrd2060. Ameer, B., Weintraub, R. A., Johnson, J. V., & Rouseff, R. L. (1996). Baur, J. A., Pearson, K. J., Price, N. L., Jamieson, H. A., Lerin, C., Kaira, A., Flavanone absorption after naringin, hesperidin and citrus administration. . . . Sinclair, D. A. (2006). Resveratrol improves health and survival of mice Clinical Pharmacology and Therapeutics, 60, 34–40. on a high-calorie diet. Nature, 444, 337–342. https://doi.org/10.1016/S0009-9236(96)90164-2. https://doi.org/10.1038/nature05354. Amic, D., Davidovic-Amic, D., Beslo, D., Rastija, V., Lucic, B., & Trinajstic, Bean, W. B. (1956). The flavonoids in biology and medicine. A.M.A. archives N. (2007). SAR and QSAR of the antioxidant activity of flavonoids. Current of internal medicine, 98(4), 534–534. Medicinal Chemistry, 14, 827–845. https://doi.org/10.1001/archinte.1956.00250280136027. https://doi.org/10.2174/092986707780090954. Beekmann, K., Actis-Goretta, L., van Bladeren, P. J., Dionisi, F., Destaillats, Amin, H. P., Czank, C., Raheem, S., Zhang, Q., Botting, N. P., Cassidy, A., F., & Rietjens, I. M. (2012). A state-of-the-art overview of the effect of & Kay, C. D. (2015). Anthocyanins and their physiologically relevant metabolic conjugation on the biological activity of flavonoids. Food and metabolites alter the expression of IL-6 and VCAM-1 in CD40L and Function, 3, 1008–1018. https://doi.org/10.1039/c2fo30065f. oxidized LDL challenged vascular endothelial cells. Molecular Nutrition Food Bell, D. R., & Gochenaur, K. (2006). Direct vasoactive and vasoprotective Research, 59, 1095–1106. https://doi.org/10.1002/mnfr.201400803. properties of anthocyanin-rich extracts. Journal of Applied Physiology, 100, Andrews, L. (2013). Dietary flavonoids for the prevention of colorectal 1164–1170. https://doi.org/10.1152/japplphysiol.01105.2005.00626. cancer. Clinical Journal of Oncology and Nursing, 17, 671–672. Bell, L., Lamport, D. J., Butler, L. T., & Williams, C. M. (2015). A review of https://doi.org/10.1188/13.cjon.671-672. the cognitive effects observed in humans following acute supplementation Androutsopoulos, V. P., Papakyriakou, A., Vourloumis, D., Tsatsakis, A. M., with flavonoids, and their associated mechanisms of action. Nutrients, 7, & Spandidos, D. A. (2010). Dietary flavonoids in cancer therapy and 10290–10306. https://doi.org/10.3390/nu7125538. prevention: Substrates and inhibitors of cytochrome P450 CYP1 enzymes. Biagi, M., & Bertelli, A. A. (2015). Wine, alcohol and pills: What future for Pharmacology and Therapeutics, 126, 9–20. the French Paradox? Life Sciences, 131, 19–22. https://doi.org/10.1016/j.pharmthera.2010.01.009. https://doi.org/10.1016/j.lfs.2015.02.024. Anhe, F. F., Roy, D., Pilon, G., Dudonne, S., Matamoros, S., Varin, T. V., . . . Blaut, M., Schoefer, L., & Braune, A. (2003). Transformation of flavonoids Marette, A. (2015). A polyphenol-rich cranberry extract protects from by intestinal microorganisms. International Journal for Vitamin and Nutrition diet-induced obesity, insulin resistance and intestinal inflammation in Research, 73, 79–87. https://doi.org/10.1024/0300-9831.73.2.79. association with increased Akkermansia spp. population in the gut microbiota of mice. Gut, 64, 872–883. https://doi.org/10.1136/gutjnl-2014-307142. Boggs, D. A., Rosenberg, L., Ruiz-Narvaez, E. A., & Palmer, J. R. (2010). Coffee, tea, and alcohol intake in relation to risk of type 2 diabetes in Appeldoorn, M. M., Vincken, J. P., Aura, A.-M., Hollman, P. C., & African American women. American Journal of Clinical Nutrition, 92, Gruppen, H. (2009). Procyanidin dimers are metabolized by human 960–966. https://doi.org/10.3945/ajcn.2010.29598. microbiota with 2-(3,4-dihydroxyphenyl)acetic acid and 5-(3,4-dihydroxyphenyl)-γ -valerolactone as the major metabolites. Journal of Borchardt, R. T., & Huber, J. A. (1975). Catechol O-methyltransferase. 5. Agricultural and Food Chemistry, 57, 1084–1092. Structure-activity relationships for inhibition by flavonoids. Journal of https://doi.org/10.1021/jf803059z. Medicinal Chemistry, 18, 120–122. Arranz, S., Valderas-Martinez, P., Chiva-Blanch, G., Casas, R., Urpi-Sarda, Borges, J. (1965). Feasibility study on effects of anthocyanin in improving M., Lamuela-Raventos, R. M., & Estruch, R. (2013). Cardioprotective night vision - Final rept. 1 Aug-31 Dec 64. Technology Inc. San Antonio effects of cocoa: Clinical evidence from randomized clinical intervention Texas Division-Defense Technical Information Center, Ad0670982. trials in humans. Molecular Nutrition Food Research, 57, 936–947. Borges, G., Mullen, W., Mullan, A., Lean, M. E. J., Roberts, S. A., & https://doi.org/10.1002/mnfr.201200595. Crozier, A. (2010). Bioavailability of multiple components following acute Augustin, R. (2010). The protein family of glucose transport facilitators: It’s ingestion of a polyphenol-rich drink. Molecular Nutrition and Food Research, not only about glucose after all. IUBMB Life, 62, 315–333. 54(Suppl. 2), S268–S277. https://doi.org/10.1002/mnfr.200900611. https://doi.org/10.1002/iub.315. Borges, G., Lean, M. E. J., Roberts, S. A., & Crozier, A. (2013). Bioavailability of dietary (poly)phenols: A study with ileostomists to Avila,´ M., Jaquet, M., Moine, D., Requena, T., Pelaez,´ C., Arigoni, F., & discriminate between absorption in the small and large intestine. Food and Jankovic, I. (2009). Physiological and biochemical characterization of two Function, 4, 754–762. https://doi.org/10.1039/c3fo60024f. α-L-rhamnosidases in Lactobacillus plantarum NCC245. Microbiology, 155, 2739–2749. https://doi.org/10.1099/mic.0.027789-0. Borges, G., van der Hooft, J. J. J., & Crozier, A. (2016). A comprehensive evaluation of the [2-14C](–)-epicatechin metabolome in rats. Free Radical

r 1100 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

Biology and Medicine, 99, 128–138. and implications in human health. Journal of Nutritional Biochemistry, 24, https://doi.org/10.1016/j/freeradbiomed.2016.08.001. 1415–1422. https://doi.org/10.1016/j.jnutbio.2013.05.001. Borges, G., Ottaviani, J. I., van der Hooft, J. J. J., Schroeter, H., & Crozier, Cassidy, A., Bingham, S., & Setchell, K. D. (1994). Biological effects of a diet A. (2017). Absorption, metabolism, distribution and excretion of of soy protein rich in isoflavones on the menstrual cycle of premenopausal (−)-epicatechin: A review of recent findings. Molecular Aspects of Medicine, women. American Journal of Clinical Nutrition, 60, 333–340. E-pub ahead of print. https://doi.org/10.1016/j.mam.2017.11.002. Cassidy, A., O’Reilly, E.´ J., Kay, C. D., Sampson, L., Franz, M., Forman, J., Bors, W., Michel, C., & Stettmaier, K. (1997). Antioxidant effects of . . . Rimm, E. B. (2011). Habitual intake of flavonoid subclasses and flavonoids. Biofactors, 6, 399–402. incident hypertension in adults. American Journal of Clinical Nutrition, 93, Bousova, I., & Skalova, L. (2012). Inhibition and induction of glutathione 338–347. https://doi.org/10.3945/ajcn.110.006783. S-transferases by flavonoids: Possible pharmacological and toxicological Cassidy, A., Rimm, E. B., O’Reilly, E. J., Logroscino, G., Kay, C., Chiuve, consequences. Drug Metabolism Review, 44, 267–286. S. E., & Rexrode, K. M. (2012). Dietary flavonoids and risk of stroke in https://doi.org/10.3109/03602532.2012.713969. women. Stroke, 43, 946–951. https://doi.org/10.1161/strokeaha.111. Brand,W.,vanderWel,P.A.I.,Williamson,G.,vanBladeren,P.J.,& 637835. Rietjens, I. M. C. M. (2007). Modulating hesperetin bioavailability at the Cassidy,A.,Mukamal,K.J.,Liu,L.,Franz,M.,Eliassen,A.H.,&Rimm,E. level of its intestinal metabolism and ABC transporter mediated efflux B. (2013). High anthocyanin intake is associated with a reduced risk of studied in Caco-2 monolayers. Chemical-Biological Interactions, 169, 132–133. myocardial infarction in young and middle-aged women. Circulation, 127, https://doi.org/10.1124/dmd.107.019943. 188–196. https://doi.org/10.1161/circulationaha.112.122408. Brasseur, T. (1989). Anti-inflammatory properties of flavonoids. Journal de Castillo, M. H., Perkins, E., Campbell, J. H., Doerr, R., Hassett, J. M., Pharmacie de Belgique, 44(3), 235–241. Kandaswami, C., & Middleton, E., Jr. (1989). The effects of the Bredsdorff, L., Nielsen, I. L. F., Rasmussen, S. E., Cornett, C., Barron, D., bioflavonoid quercetin on squamous cell carcinoma of head and neck Bouisset, F., . . . Williamson, G. (2010). Absorption, conjugation and origin. American Journal of Surgery, 158, 351–355. excretion of the flavones naringenin and hesperetin from Castro, A. F., & Altenberg, G. A. (1997). Inhibition of drug transport by α-rhamnosidase-treated orange juice in human subjects. British Journal of genistein in multidrug-resistant cells expressing P-glycoprotein. Biochemical Nutrition, 103, 1602–1609. https://doi.org/10.1017/S0007114509993679. Pharmacology, 53, 89–93. Breitbart, H., Stern, B., & Rubinstein, S. (1983). Calcium transport and Catapano, A. L. (1997). Antioxidant effect of flavonoids. Angiology, 48, + Ca2 -ATPase activity in ram spermatozoa plasma membrane vesicles. 39–44. https://doi.org/10.1177/000331979704800107. Biochimica Biophysica Acta, 728, 349–355. Cazarolli, L. H., Zanatta, L., Alberton, E. H., Figueiredo, M. S., Folador, P., Brett, G. M., Hollands, W., Needs, P. W., Teucher, B., Dainty, J. R., Davis, Damazio, R. G., . . . Silva, F. R. M. B. (2008). Flavonoids: Cellular and B. D., . . . Kroon, P. A. (2009). Absorption, metabolism and excretion of molecular mechanism of action in glucose homeostasis. Mini Reviews in flavanones from single portions of orange fruit and juice and effects of Medicinal Chemistry, 8, 1032–1038. anthropometric variables and contraceptive pill use on flavanone excretion. https://doi.org/10.2174/138955708785740580. British Journal of Nutrition, 101, 664–675. Cesari, M., Penninx, B. W., Newman, A. B., Kritchevsky, S. B., Nicklas, B. https://doi.org/10.1017/S000711450803081X. J., Sutton-Tyrrell, K., . . . Pahor, M. (2003). Inflammatory markers and Brickman, A. M., Khan, U. A., Provenzano, F. A., Yeung, L. K., Suzuki, W., onset of cardiovascular events: Results from the Health ABC study. Schroeter, H., . . . Small, S. A. (2014). Enhancing dentate gyrus function Circulation, 108, 2317–2322. with dietary flavanols improves cognition in older adults. Nature Neuroscience, https://doi.org/10.1161/01.cir.0000097109.90783.fc. 17, 1798–1803. https://doi.org/10.1038/nn.3850. Chalopin, M., Tesse, A., Martinez, M. C., Rognan, D., Arnal, J. F., & Brindani, N., Mena, P., Benzie, I., Choi, S. W., Brighenti, F., Zanardi, F., . . . Andriantsitohaina, R. (2010). Estrogen receptor alpha as a key target of red Del Rio, D. (2017). Synthetic and analytical strategies for the quantification wine polyphenols action on the endothelium. PLoS One, 5, e8554. of phenyl-γ -valerolactone conjugated metabolites in human urine. https://doi.org/10.1371/journal.pone.0008554. Molecular Nutrition and Food Research, 61. https://doi.org/10.1002/mnfr. Chao, C. L., Hou, Y. C., Chao, P. D., Weng, C. S., & Ho, F. M. (2009). The 201700077. antioxidant effects of quercetin metabolites on the prevention of high Brown, J. P. (1980). A review of the genetic effects of naturally occurring glucose-induced apoptosis of human umbilical vein endothelial cells. British flavonoids, anthraquinones and related compounds. Mutation Research, 75, Journal of Nutrition, 101, 1165–1170. 243–277. https://doi.org/10.1017/s0007114508073637. Brown, M. D. (1999). Green tea (Camellia sinensis) extract and its possible role Chen, A. Y., & Chen, Y. C. (2013). A review of the dietary flavonoid, in the prevention of cancer. Alternative Medicine Review, 4, 360–370. kaempferol on human health and cancer chemoprevention. Food Chemistry, Brown, D. I., & Griendling, K. K. (2015). Regulation of signal transduction 138, 2099–2107. https://doi.org/10.1016/j.foodchem.2012.11.139. by reactive oxygen species in the cardiovascular system. Circulation Research, Chen, C. Y., Yi, L., Jin, X., Zhang, T., Fu, Y. J., Zhu, J. D., . . . Yu, B. 116, 531–549. https://doi.org/10.1161/circresaha.116.303584. (2011). Inhibitory effect of delphinidin on monocyte-endothelial cell Brown, E. M., Nitecki, S., Pereira-Caro, G., McDougall, G. J., Stewart, D., adhesion induced by oxidized low-density lipoprotein via ROS/p38MAPK/ Rowland, I., . . . Gill, C. I. R. (2014). The comparability of in vivo and in NF-kappaB pathway. Cell Biochemistry and Biophysics, 61, 337–348. vitro digestion of lignonberries: Impact on bioactivity. Biofactors, 40, https://doi.org/10.1007/s12013-011-9216-2. 611–623. https://doi.org/10.1002/biof.1173. Chopra, M., & Thurnham, D. I. (1999). Antioxidants and lipoprotein Bryan, A. H. (1956). The flavonoids in biology and medicine. A critical metabolism. Proceedings of the Nutrition Society, 58, 663–671. review. American Journal of Public Health and the Nations Health, 46, Ci, Y., Qiao, J., & Han, M. (2016). Molecular mechanisms and metabolomics 1468–1468. https://doi.org/10.2105/AJPH.46.11.1468-a. of natural polyphenols interfering with breast cancer metastasis. Molecules, Camenisch, G., Alsenz, J., van de Waterbeemd, H., & Folkers, G. (1998). 21(12). https://doi.org/10.3390/molecules21121634. Estimation of permeability by passive diffusion through Caco-2 cell Clark, W. G. (1949). Potentiation of effects of epinephrine by flavonoid monolayers using the drugs’ lipophilicity and molecular weight. European (vitamin P-like) compounds; relation of structure to activity. Journal of Journal of Pharmacological Sciences, 6, 317–324. Pharmacology Experimental Therapeutic, 95, 363–381. Camfield, D. A., Scholey, A., Pipingas, A., Silberstein, R., Kras, M., Clark, W., MacKay, E., Mary, J., & Bryant, E. F. (1950). The absorption and Nolidin, K., . . . Stough, C. (2012). Steady state visually evoked potential excretion of rutin and related flavonoid substances. A note on the (SSVEP) topography changes associated with cocoa flavanol consumption. differentiation between flavonoid glycosides and their aglucones. Journal of Physiology and Behaviour, 105, 948–957. the American Medical Association, 143, 1411–1415. https://doi.org/10.1016/j.physbeh.2011.11.013. Clark, J. L., Zahradka, P., & Taylor, C. G. (2015). Efficacy of flavonoids in Cao, G., & Prior, R. L. (1999). Anthocyanins are detected in human plasma the management of high blood pressure. Nutrition Reviews, 73, 799–822. after oral administration of an elderberry extract. Clinical Chemistry, 45, https://doi.org/10.1093/nutrit/nuv048. 574–576. Clifford, M. N. (2000). Anthocyanins – nature, occurrence and dietary Cao, G., Muccitelli, H. U., Sanchez-Moreno,´ C., & Prior, R. L. (2001). burden. Journal of the Science of Food and Agriculture, 80, 1063–1072. Anthocyanins are absorbed in glycated forms in elderly women: A https://doi.org/10.1002/(SICI)1097-0010(20000515)80:7<1044::AID- pharmacokinetic study. American Journal of Clinical Nutrition, 73, 929–926. JSFA605=3.0.CO;2-Q Cardona, F., Andres-Lacueva, C., Tulipani, S., Tinahones, F. J., & Clifford, M. N., Jaganath, I. B., Ludwig, I. A., & Crozier, A. (2017). Queipo-Ortuno, M. I. (2013). Benefits of polyphenols on gut microbiota Chlorogenic acids and the acyl-quinic acids: Discovery, biosynthesis,

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1101 Dietary ﬂavonoids: a historical review . . .

bioavailability and bioactivity. Natural Product Reports, 34, 1391–1421. Das,D.K.,Sato,M.,Ray,P.S.,Maulik,G.,Engelman,R.M.,Bertelli,A. https://doi.org/10.1039/c7np00030h. A., & Bertelli, A. (1999). Cardioprotection of red wine: Role of Cochet, C., Feige, J. J., Pirollet, F., Keramidas, M., & Chambaz, E. M. polyphenolic antioxidants. Drugs Under Experimental and Clinical Research, (1982). Selective inhibition of a cyclic nucleotide independent protein 25, 115–120. kinase (G type casein kinase) by quercetin and related polyphenols. Davis, C., Bryan, J., Hodgson, J., & Murphy, K. (2015). Definition of the Biochemical Pharmacology, 31, 1357–1361. Mediterranean diet; a literature review. Nutrients, 7, 9139–9153. Comte, G., Daskiewicz, J. B., Bayet, C., Conseil, G., Viornery-Vanier, A., https://doi.org/10.3390/nu7115459. Dumontet, C., . . . Barron, D. (2001). C-Isoprenylation of flavonoids Day, A. J., Bao, Y., Morgan, M. R., & Williamson, G. (2000a). Conjugation enhances binding affinity toward P-glycoprotein and modulation of cancer position of quercetin glucuronides and effect on biological activity. Free cell chemoresistance. Journal of Medicinal Chemistry, 44, 763–768. Radical Biology and Medicine, 29, 1234–1243. Constant, J. (1997). Alcohol, ischemic heart disease, and the French Paradox. Day, A. J., Canada, F. J., Diaz, J. C., Kroon, P. A., McLauchlan, R., Faulds, Clinical Cardiology, 20, 420–424. C. B., . . . Williamson, G. (2000b). Dietary flavonoid and isoflavones Corder, R. (2008). Red wine, chocolate and vascular health: Developing the glycosides are hydrolysed by the lactase sites of lactase phlorizin hydrolase. evidence base. Heart, 94, 821–823. https://doi.org/10.1136/hrt.2008. FEBS Letters, 468, 166–170. 143909. Day, A. J., Mellon, F., Barron, D., Sarrazin, G., Morgan, M. R. A., & Corder, R., Crozier, A., & Kroon, P. A. (2003). Drinking your health? It’s Williamson, G. (2001). Human metabolism of dietary flavonoids: too early to say. Nature, 426, 119. https://doi.org/10.1038/426119d. Identification of plasma metabolites of quercetin. Free Radical Research, 35, 941–952. Corder,R.,Mullen,W.,Khan,N.Q.,Marks,S.C.,Wood,E.G.,Carrier, M. J., & Crozier, A. (2006). Red wine procyanidins and vascular health. De Bock, M., Derraik, J. G., & Cutfield, W. S. (2012). Polyphenols and Nature, 444, 30. https://doi.org/10.1038/444566a. glucose homeostasis in humans. Journal of the Academy of Nutrition and Dietetics, 112, 808–815. https://doi.org/10.1016/j.jand.2012.01.018. Critchfield, J. W., Welsh, C. J., Phang, J. M., & Yeh, G. C. (1994). Modulation of adriamycin accumulation and efflux by flavonoids in Decroix, L., Tonoli, C., Soares, D. D., Tagougui, S., Heyman, E., & HCT-15 colon cells. Activation of P-glycoprotein as a putative mechanism. Meeusen, R. (2016). Acute cocoa flavanol improves cerebral oxygenation Biochemical Pharmacology, 48, 1437–1445. without enhancing executive function at rest or after exercise. Applied Physiology Nutrition and Metabolism, 41, 1225–1232. Crozier, A. (2013). Absorption, metabolism and excretion of (–)-epicatechin https://doi.org/10.1139/apnm-2016-0245. in humans: An evaluation of recent findings. American Journal of Clinical Nutrition, 98, 861–862. https://doi.org/10.3945/ajcn.113.072009. de Ferrars, R. M., Cassidy, A., Curtis, P., & Kay, C. D. (2014a). Phenolic metabolites of anthocyanins following a dietary intervention study in Crozier, A., Jaganath, I. B., Marks, S., Saltmarsh, M., & Clifford, M. N. post-menopausal women. Molecular Nutrition Food Research, 58, 490–502. (2006). Secondary metabolites as dietary components in plant-based foods https://doi.org/10.1002/mnfr.201300322 andbeverages.InA.Crozier,M.N.Clifford,&H.Ashihara(Eds.),Plant secondary metabolites: Occurrence, structure and role in the human diet (pp. 208– de Ferrars, R. M., Czank, C., Zhang, Q., Botting, N. P., Kroon, P. A., 302). Oxford: Blackwell Publishing. Cassidy, A., & Kay, C. D. (2014b). The pharmacokinetics of anthocyanins and their metabolites in humans. British Journal of Pharmacology, 171, Crozier, A., Del Rio, D., & Clifford, M. N. (2010). Bioavailability of dietary 3268–3282. https://doi.org/10.1111/bph.12676. flavonoids and phenolic compounds. Molecular Aspects of Medicine, 31, 446–467. https://doi.org/10.1016/j.mam.2010.09.007. Dejas, F., Abin-Carriquiry, J. A., Echeverry, C., Martinez, M. J. A., Arredondo, F., Blasina, F., . . . Vaamonde, L. (2015). Quercetin in brain Crozier, A., Clifford, M. N., & Del Rio, D. (2012). Bioavailability of dietary diseases: Potential and limites. Neurochemistry International, 89, 140–148. monomeric and polymeric flavan-3-ols. In J. P. E. Spencer & A. Crozier https://doi.org/10.1016/j.neuint.2015.07.002. (Eds.), Flavonoids and related compounds. Bioavailability and function (pp. 45–78). Boca Raton: CRC Press. de Koning Gans, J. M., Uiterwaal, C. S., van der Schouw, Y. T., Boer, J. M., Grobbee, D. E., Verschuren, W. M., & Beulens, J. W. (2010). Tea and coffee Cuadrado, A., Martin-Moldes, Z., Ye, J., & Lastres-Becker, I. (2014). consumption and cardiovascular morbidity and mortality. Arteriosclerosis, Transcription factors NRF2 and NF-kappaB are coordinated effectors of Thrombosi, and Vascular Biology, 30, 1665–1671. the Rho family, GTP-binding protein RAC1 during inflammation. Journal https://doi.org/10.1161/atvbaha.109.201939. of Biological Chemistry, 289, 15244–15258. https://doi.org/10.1074/ jbc.M113.540633. Dell’Agli, M., Busciala, A., & Bosisio, E. (2004). Vascular effects of wine polyphenols. Cardiovascular Research, 63, 593–602. Curti, C., Brindani, N., Battistini, L., Sartori, A., Pelosi, G., Mena, P., . . . https://doi.org/10.1016/j.cardiores.2004.03.019. Del Rio, D. (2015). Catalytic, enantioselective vinylogous mukaiyama aldol reaction of furan-based dienoxy silanes: A chemodivergent approach to Del Rio, D., Costa, L. G., Lean, M. E. J., & Crozier, A. (2010). Polyyphenols γ -valerolactone flavan-3-ol metabolites and δ–lactone analogs. Advanced and health: What compounds are involved? Nutrtion, Metabolism and Synthesis & Catalysis, 357, 4082–4092. https://doi.org/10.1002/ Cardiovascular Disease, 20,1–6.https://doi.org/10.1016/j.numecd. adsc.201500705. 2009.05.015. Curtis, P. J., Kroon, P. A., Hollands, W. J., Walls, R., Jenkins, G., Kay, C. D., Del Rio, D., Rodriguez-Mateos, A., Spencer, J. P., Tognolini, M., Borges, & Cassidy, A. (2009). Cardiovascular disease risk biomarkers and liver and G., & Crozier, A. (2013). Dietary (poly)phenolics in human health: kidney function are not altered in postmenopausal women after ingesting an Structures, bioavailability, and evidence of protective effects against chronic elderberry extract rich in anthocyanins for 12 weeks. Journal of Nutrition, diseases. Antioxidants and Redox Signaling, 18, 1818–1892. 139, 2266–2271. https://doi.org/jn.109.113126. https://doi.org/10.1089/ars.2012.4581. Czank, C., Cassidy, A., Zhang, Q., Morrison, D. J., Preston, T., Kroon, P. Desch, S., Schmidt, J., Kobler, D., Sonnabend, M., Eitel, I., Sareban, M., . . . A., . . . Kay, C. D. (2013). Human metabolism and elimination of the Thiele, H. (2010). Effect of cocoa products on blood pressure: Systematic anthocyanin, cyanidin-3-glucoside: A 13C-tracer study. American Journal of review and meta-analysis. American Journal of Hypertenions, 23, 97–103. Clinical Nutrition, 97, 995–1003. https://doi.org/10.3945/ajcn.112.049247. https://doi.org/1038/ajh2009.213. D’Adamo, C. R., & Sahin, A. (2014). Soy foods and supplementation: A Desideri, G., Kwik-Uribe, C., Grassi, D., Necozione, S., Ghiadoni, L., review of commonly perceived health benefits and risks. Alternative Theraties Mastroiacovo, D., . . . Ferri, C. (2012). Benefits in cognitive function, in Health and Medicine, 20(Suppl 1), 39–51. blood pressure, and insulin resistance through cocoa flavanol consumption in elderly subjects with mild cognitive impairment: The Cocoa, Cognition, Dahan, A., Lennernas,¨ H., & Amidon, G. L. (2012). The fraction dose and Aging (CoCoA) study. Hypertension, 60, 794–801. absorbed, in humans, and high jejunal human permeability relationship. https://doi.org/10.1161/hypertensionaha.112.193060 Molecular Pharmacology, 9, 1847–1851. https://doi.org/10.1021/mp300140h. Detre, Z., Jellinek, H., Miskulin, M., & Robert, A. M. (1986). Studies on Dajas, F., Abin-Carriquiry, J. A., Arredondo, F., Blasina, F., Echeverry, C., vascular permeability in hypertension: Action of anthocyanosides. Clinical Martinez, M., . . . Vaamonde, L. (2015). Quercetin in brain diseases. Physiology and Biochemistry, 4, 143–149. Neurochemistry International, 89, 140–148. https://doi.org/10.1016/j.neuint.2015.07.002. DeWeerd, K. A., Saxena, A., Nagle, D. P., Jr., & Suflita, J. M. (1988). Metabolism of the 18O-methoxy substituent of 3-methoxybenzoic acid and Das, N. P. (1971). Studdies on flavonoid metabolism. and metabolism of + other unlabeled methoxybenzoic acids by anaerobic bacteria. Applied and ( )-catechin in man. Biochemical Pharmacology, 20, 3435–3445. Enviromental Microbiology, 54, 1237–1242. Das, N. P. (1974). Excretion of m-hydroxyphenylhydracrylic acid from + Degorter, M. K., Xia, C. Q., Yang, J. J., & Kim, R. B. (2012). Drug ( )-catechin in the monkey (Macaca iris sp.). Drug Metabolism and Disposition, transporters in drug efficacy and toxicity. Annual Review of Pharmacology and 2, 209–213.

r 1102 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

Toxi co lo gy, 52, 249–273. https://doi.org/10.1146/annurev-pharmtox- urine as methylated and glucuronidated conjugates in humans. Journal of 010611-134529. Agricultural and Food Chemistry, 53, 7721–7727. di Gesso, J. L., Kerr, J. S., Zhang, Q., Raheem, K. S., Yalamanchili, S. K., https://doi.org/10.1021/jf051092k. O’Hagan, D., . . . O’Connell, M. A. (2015). Flavonoid metabolites reduce Feliciano, R., Boeres, A., Massacessi, L., Istas, G., Ventura, M. R., Nunes tumor necrosis factor-alpha secretion to a greater extent than their precursor Dos Santos, C., . . . Rodriguez-Mateos, A. (2016). Identification and compounds in human THP-1 monocytes. Molecular Nutrition and Food quantification of novel cranberry-derived plasma and urinary (poly) Research, 56, 1143–1154. https://doi.org/10.1002/mnfr.201400799. phenols. Archives of Biochemistry and Biophysics, 599, 31–41. Dinkova-Kostova, A. T., Cheah, J., Samouilov, A., Zweier, J. L., Bozak, R. https://doi.org/10.1016/j.abb.2016.01.014. E., Hicks, R. J., & Talalay, P. (2007). Phenolic Michael reaction acceptors: Fernandes, I., Perez-Gregorio, R., Soares, S., Mateus, N., & de Freitas, V. Combined direct and indirect antioxidant defenses against electrophiles and (2017). Wine flavonoids in health and disease prevention. Molecules, 22, 292. oxidants. Medicinal Chemistry, 3, 261–268. https://doi.org/10.2174/ https://doi.org/10.3390/molecules22020292. 157340607780620680 Fernando, W., Rupasinghe, H. P., & Hoskin, D. W. (2015)2015. Regulation Di Pietro, A., Conseil, G., Perez-Victoria, J. M., Dayan, G., Baubichon- of hypoxia-inducible factor-1α and vascular endothelial growth factor Cortay, H., Trompier, D., . . . Barron, D. (2002). Modulation by flavonoids signaling by plant flavonoids. Mini Reviews in Medicinal Chemistry, 15, of cell multidrug resistance mediated by P-glycoprotein and related ABC 479–489. https://doi.org/10.2174/1389557515666150414152933. transporters. Cellular and Molecular Life Sciences, 59, 307–322. Ferrara, M., & Seb´ edio,´ J. L. (2015). 1 - Challenges in nutritional Dolnick, E. (1990). “Le paradox francais.” Health, 41–47. metabolomics: From experimental design to interpretation of data sets. In Donnini, S., Finetti, F., Lusini, L., & Morbidelli, L. (2006). Divergent effects J.-L. Sebedio & L. Brennan (Eds.), Metabolomics as a tool in nutrition research of quercetin conjugates on angiogenesis. British Journal of Nutrition, 95, (pp. 3–16). Woodhead Publishing: Cambridge, U.K. 1016–1023. Ferriola, P. C., Cody, V., & Middleton, E., Jr. (1989). Protein kinase C Duda-Chodak, A. (2012). The inhibitory effect of polyphenols on human inhibition by plant flavonoids. Kinetic mechanisms and structure-activity gut microbiota. Journal of Physiology and Pharmacology, 63, 497–503. relationships. Biochemical Pharmacology, 38, 1617–1624. Duda-Chodak, A., Tarko, T., Satora, P., & Sroka, P. (2015). Interaction of Field, D. T., Williams, C. M., & Butler, L. T. (2011). Consumption of cocoa dietary compounds, especially polyphenols, with the intestinal microbiota: flavanols results in an acute improvement in visual and cognitive functions. A review. European Journal of Nutrition, 54, 325–341. Physiology and Behaviour, 103, 255–260. https://doi.org/10.1016/ https://doi.org/10.1007/s00394-015-0852-y. j.physbeh.2011.02.013. Duthie, G. G., & Bellizzi, M. C. (1999). Effects of antioxidants on vascular Formica, J. V., & Regelson, W. (1995). Review of the biology of quercetin health. British Medical Bulletin, 55, 568–577. and related bioflavonoids. Food and Chemical Toxicology, 33, 1061–1080. Eastwood, M. A. (1999). Interaction of dietary antioxidants in vivo: How Fraga, C. G., & Oteiza, P. I. (2011). Dietary flavonoids: Role of fruit and vegetables prevent disease? QJM, 92, 527–530. (–)-epicatechin and related procyanidins in cell signaling. Free Radical Biology and Medicine, 51, 813–823. https://doi.org/10.1016/j.freeradbiomed. Edirisinghe, I., Banaszewski, K., Cappozzo, J., McCarthy, D., & 2011.06.002. Burton-Freeman, B. M. (2011). Effect of black currant anthocyanins on the activation of endothelial nitric oxide synthase (eNOS) in vitro in human Fuhr, U., & Kummert, A. L. (1995). The fate of naringin in humans: A key endothelial Cells. Journal of Agricultural and Food Chemistry, 59, 8616–8624. to grapefruit juice-drug interactions? Clinical Pharmacology and Therapeutics, https://doi.org/10.1021/jf201116y. 58, 3655–373. https://doi.org/10.1016/0009-9236(95)90048-9. Ellam, S., & Williamson, G. (2013). Cocoa and human health. Annual Review Fujita, E., Nagao, Y., Varma, S. D., & Kinoshita, J. H. (1976). Tumor of Nutrition, 33, 105–128. https://doi.org/10.1146/annurev-nutr- inhibitors having potential for interaction with mercapto enzymes and/or 071811-150642. coenzymes: A review: Inhibition of lens aldose reductase by flavonoids - their possible role in the prevention of diabetic cataracts. Bioorganic Engler, M. B., & Engler, M. M. (2006). The emerging role of flavonoid-rich Chemistry, 6, 287–309. cocoa and chocolate in cardiovascular health and disease. Nutrition Review, 64, 109–118. https://doi.org/10.1111/j.1753-4887.2006.tb00194x Fusi, F., Spiga, O., Trezza, A., Sgaragli, G., & Saponara, S. (2017). The surge of flavonoids as novel, fine regulators of cardiovascular Cav channels. Erdman, J. W., Jr., Balentine, D., Arab, L., Beecher, G., Dwyer, J. T., Folts, European Journal of Pharmacology, 796, 158–174. J., . . . Burrowes, J. (2007). Flavonoids and heart health: Journal of Nutrition, https://doi.org/10.1016/j.ejphar.2016.12.033. 137 (Suppl 1), S S718–S737. Galati, G., & O’Brien, P. J. (2004). Potential toxicity of flavonoids and other Erlund, I., Kosonsen, T., Alfhan, G., Maenp¨ aä,¨ J., Perttunen, K., Kenraali, J., dietary phenolics: Significance for their chemopreventive and anticancer . . . Aro, A. (2000). Pharmacokinetics of quercetin from quercetin aglycone properties. Free Radical Biology and Medicine, 37, 287–303. and rutin in healthy volunteers. European Journal of Clinical Pharmacology, 56, https://doi.org/10.1016/j.freeradbiomed.2004.04.034. 545–553. Galleano, M., Calabro, V., Prince, P. D., Litterio, M. C., Piotrkowski, B., Erlund, I., Meririnne, E., Alfthan, G., & Aro, A. (2001). Plasma kinetics and Vazquez-Prieto, M. A., . . . Fraga, C. G. (2012). Flavonoids and metabolic urinary excretion of the flavanones naringenin and hesperetin in humans syndrome. Annals of the New York Academy Science, 1259, 87–94. after ingestion of orange juice and grapefruit juice. Journal of Nutrition, 131, https://doi.org/10.1111/j.1749-6632.2012.06511.x. 235–241. Gaziano, J. M., Buring, J. E., Breslow, J. L., Goldhaber, S. Z., Rosner, B., Espley, R. V., Butts, C. A., Laing, W. A., Martell, S., Smith, H., McGhie, T. VanDenburgh, M., . . . Hennekens, C. H. (1993). Moderate alcohol intake, K., . . . Hellens, R. P. (2014). Dietary flavonoids from modified apple increased levels of high-density lipoprotein and its subfractions, and reduce inflammation markers and modulate gut microbiota in mice. Journal decreased risk of myocardial infarction. New England Journal of Medicine, 329, of Nutrition, 144, 146–154. https://doi.org/10.3945/jn.113.182659. 1829–1834. https://doi.org/10.1056/NEJM199312163292501 Esposito, D., Damsud, T., Wilson, M., Grace, M. H., Strauch, R., Li, X., . . . Gee, J. M., DuPont, S. M., Day, A. J., Plumb, G. W., Williamson, G., & Komarnytsky, S. (2015). Black currant anthocyanins attenuate weight gain Johnson, I. T. (2000). Intestinal transport of quercetin glycosides in rats and improve glucose metabolism in diet-induced obese mice with intact, involves both deglycosylation and interation with the hexose transport but not disrupted, gut microbiome. Journal of Agricultural and Food Chemistry, pathway. Journal of Nutrition, 130, 2765–2771. 63, 6172–6180. https://doi.org/10.1021/acs.jafc.5b00963. Geleijnse, J. M., & Hollman, P. (2008). Flavonoids and cardiovascular health: Etxeberria, U., Fernandez-Quintela, A., Milagro, F. I., Aguirre, L., Martinez, Which compounds, what mechanisms? American Journal of Clinical Nutrition, J. A., & Portillo, M. P. (2013). Impact of polyphenols and polyphenol-rich 88, 12–13. dietary sources on gut microbiota composition. Journal of Agricultural and Food Chemistry, 61, 9517–9533. https://doi.org/10.1021/jf402506c. George, V. C., Dellaire, G., & Rupasinghe, H. P. V. (2017). Plant flavonoids in cancer chemoprevention: Role in genome stability. Journal of Nutritional Ezzati, M., & Riboli, E. (2013). Behavioral and dietary risk factors for Biochemistry, 45, 1–14. https://doi.org/10.1016/j.jnutbio.2016.11.007. noncommunicable disease. New England Jornal of Medicine, 369, 954–964. https://doi.org/10.1056/NEJMra1203528. George, V. C., Vijesh, V. V., Amararathna, D. I. M., Lakshmi, C. A., Anbarasu, K., Kumar, D. R. N., . . . Rupasinghe, H. P. V. (2016). Felgines, C., Talavera,´ S., Gonthier, M. P., Texier, O., Scalbert, A., Lamaison, Mechanism of action of flavonoids in prevention of inflammation-associated J.-L., & Rem´ esy,´ C. (2003). Strawberry anthocyanins are recovered in urine skin cancer. Current Medicinal Chemistry, 23, 3697–3716. as glucuronide and sulfo conjugates in humans. Journal of Nutrition, 133, https://doi.org/10.2174/0929867323666160627110342. 1296–1301. Giampieri, F., Forbes-Hernandez, T. Y., Gasparrini, M., Alvarez-Suarez, J. Felgines, C., Talavera,´ S., Texier, O., Gil-Izquierdo, A., Lamaison, J.-L., & M., Afrin, S., Bompadre, S., . . . Battino, M. (2015). Strawberry as a health Rem´ esy,´ C. (2005). Blackberry anthocyanins are mainly recovered from

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1103 Dietary ﬂavonoids: a historical review . . .

promoter: An evidence based review. Food and Function, 6, 1386–1398. Gruemer, H. D. (1961). Formation of hippuric acid from phenylalaine https://doi.org/10.1039/c5fo00147a. labelled with carbon-14 in phenylketonuric subjects. Nature, 189, 63–64. Gilbert, E. R., & Liu, D. (2010). Flavonoids influence epigenetic-modifying Gryglewski, R. J., Korbut, R., Robak, J., & Swies, J. (1987). On the enzyme activity: Structure - function relationships and the therapeutic mechanism of antithrombotic action of flavonoids. Biochemical Pharmacology, potential for cancer. Current Medicinal Chemistry, 17, 1756–1768. 36, 317–322. https://doi.org/10.2174/09298671-791111161. Gugler, R., & Dengler, H. J. (1973). Sensitive fluorometric method for Glasser, G., Graefe, E. U., Struck, F., Veit, M., & Gebhardt, R. (2002). determination of quercetin in plasma or urine. Clinical Chemistry, 19, 36–37. Comparison of antioxidative capacities and inhibitory effects on cholesterol Gugler, R., Leschik, M., & Dengler, H. J. (1975). Disposition of quercetin in biosynthesis of quercetin and potential metabolites. Phytomedicine, 9, 33–40. man after single oral and intravenous doses. European Journal of Clinical https://doi.org/10.1078/0944-7113-00080. Pharmacology, 9, 229–234. Gomes, A., Fernandes, E., Lima, J. L., Mira, L., & Corvo, M. L. (2008). Hackett, A. M., & Griffiths, L. A. (1981). The metabolism and excretion of Molecular mechanisms of anti-inflammatory activity mediated by 3-O-methyl-(+)-catechin in the rat, mouse, and marmoset. Drug Metabolism flavonoids. Current Medicinal Chemistry, 15, 1586–1605. and Disposition, 9, 54–59. https://doi.org/10.2174/09298670874911579. Hackett, A. M., & Griffiths, L. A. (1983). The effects of an experimental Gonzalez,´ R., Ballester, I., Lopez-Posadas, R., Suarez, M. D., Zarzuelo, A., hepatitis on the metabolic disposition of 3-O-(+)-[14C]methylcatechin in Martinez-Augustin, O., & Sanchez de Medina, F. (2011). Effects of the rat. Drug Metabolism and Disposition, 11, 602–606. flavonoids and other polyphenols on inflammation. Critical Reviews in Food Hackett, A. M., Griffiths, L. A., Broillet, A., & Wermeille, M. (1983). The Science and Nutrition, 51, 331–362. https://doi.org/10.1080/ + 14 10408390903584094. metabolism and excretion of ( )-[ C]cyanidanol-3 in man following oral administration. Xenobiotica, 13, 279–286. Gonzalez-Barrio,´ R., Borges, G., Mullen, W., & Crozier, A. (2010). https://doi.org/10.3109/00498258309052265 Bioavailability of anthocyanins and ellagitannins following consumption of Hackett, A. M., Griffiths, L. A., & Wermeille, M. (1985). The quantitative raspberries by healthy humans and subjects with an ileostomy. Journal of + 14 Agricultural and Food Chemistry, 58, 3933–3939. https://doi.org/10.102/ disposition of 3-O-methyl-( )-U- C) catechin in man following oral jf100315d. administration. Xenobiotica, 15, 907–914. + Gonzalez-Barrio,´ R., Edwards, C. A., & Crozier, A. (2011). Colonic Hackett, A. M., Shaw, J. C., & Griffiths, L. A. (1982). 3 -O-Methyl( )- catechin glucuronide and 3-O-methyl(+)-catechin sulphate: New urinary catabolism of ellagitannins, ellagic acid, and raspberry anthocyanins: In vivo + and in vitro studies. Drug Metabolism and Disposition, 39, 1680–1688. metabolites of ( )-catechin in the rat and the marmot. Experientia, 38, https://doi.org/10.1124/dmd.111.039651. 538–540. Gonzalez-Gallego,´ J., Garc´ıa-Mediavilla, M. V., Sanchez-Campos,´ S., & Halpern, M. J., Dahlgren, A. L., Laakso, I., Seppanen-Laakso, T., Dahlgren, Tunõn,´ M. J. (2010). Fruit polyphenols, immunity and inflammation. British J., & McAnulty, P. A. (1998). Red-wine polyphenols and inhibition of Journal of Nutrition, 104(Suppl 3), S15–S27. https://doi.org/10.1017/ platelet aggregation: Possible mechanisms, and potential use in health s0007114510003910. promotion and disease prevention. Journal of International Medical Research, 26, 171–180. https://doi.org/10.1177/030006059802600401. Gonzalez-Sarr´ ´ıas, A., Larrosa, M., Tomas-Barber´ an,F.A.,Dolara,P.,&´ Espin, J. C. (2010). NF-kappaB-dependent anti-inflammatory activity of Hanhineva, K., Torr¨ onen,¨ R., Bondia-Pons, I., Pekkinen, J., Kolehmainen, urolithins, gut microbiota ellagic acid-derived metabolites, in human M., Mykkanen,¨ H., & Poutanen, K. (2010). Impact of dietary polyphenols colonic fibroblasts. British Journal of Nutrition, 104, 503–512. on carbohydrate metabolism. International Journal of Molecular Science, 11, https://doi.org/10.1017/s0007114510000826. 1365–13402. https://doi.org/10.3390/ijms11041365. Graefe, E. U., Wittig, J., Mueller, S., Riethling, A.-K., Uehleke, B., Harborne, J. B. (1965). Plant polyphenols, XIV. Characterisation of flavonoid Drewelow, B., . . . Veit, M. (2001). Pharmacokinetics and bioavailability of glycosides by acidic and enzyme hydrolysis. Phytochemistry, 4, 107–120. quertin glycosides in humans. Journal of Clinical Pharmacology, 41, https://doi.org/10.1016/S0031-9422(00)86152-X. 492–499. Harper, K., Morton, A., & Rolfe, E. (1968). Antioxidants in oats: Glyceryl Granger, D. N., Vowinkel, T., & Petnehazy, T. (2004). Modulation of the esters of caffeic and ferulic acids. International Journal of Food Science & inflammatory response in cardiovascular disease. Hypertension, 43, 924–931. Te c h no lo gy, 4, 255–267. https://doi.org/10.1161/01.HYP.0000123070.31763.55. Harper, K., Morton, A., & Rolfe, E. (1969). The phenolic compounds of Grassi, D., Desideri, G., Di Giosia, P., De Feo, M., Fellini, E., Cheli, P., . . . blackcurrant juice and their protective effect on ascorbic acid. International Ferri, C. (2013a). Tea, flavonoids, and cardiovascular health: Endothelial Journal of Food Science & Technology, 4, 255–267. protection. American Journal of Clinical Nutition, 98, S1660–S1666. Hartley, L., Flowers, N., Holmes, J., Clarke, A., Stranges, S., Hooper, L., & https://doi.org/10.3945/ajcn.113.058313. Rees, K. (2013). Green and black tea for the primary prevention of Grassi, D., Desideri, G., & Ferri, C. (2013b). Protective effects of dark cardiovascular disease. Cochrane Database of Systematic Review, 6, Cd009934. chocolate on endothelial function and diabetes. Current Opinion in Clinical https://doi.org/10.1002/14651858.CD009934.pub2. Nutrition and Metabolic Care, 16, 662–668. https://doi.org/10.1097/ Heiss, C., Sansone, R., Karimi, H., Krabbe, M., Schuler, D., MCO.0b013e3283659a51. Rodriguez-Mateos, A., . . . Kelm, M. (2015). Impact of coca flavanol Grassi, D., Desideri, G., Mai, F., Martella, L., De Feo, M., Soddu, D., . . . intake on age-dependent vascualr stiffness in healthy mean: A randomized, Ferri, C. (2015). Cocoa, glucose tolerance, and insulin signaling: controlled, double-masked study. Age, 37, 56. https://doi.org/10.1007/ Cardiometabolic protection. Journal of Agricultural and Food Chemistry, 63, s11357-015-9794-9. 9919–9926. https://doi.org/10.1021/acs.jafc.5b00913. Herrmann, K. (1976). Flavonols and flavones in food plants: A review. Grassi, D., Ferri, C., & Desideri, G. (2016). Brain protection and cognitive International Journal of Food Science and Technology, 11, 433–448. function: Cocoa flavonoids as nutraceuticals. Current Pharmacceutical https://doi.org/10.1111/j.1365-2621.1976.tb00743.x. Design, 22, 145–151. https://doi.org/10.2174/13816128226661511121 Hertog, M. G. L., Hollman, P. C. H., & Katan, M. B. (1992). The content of 45730. potentially anticarcinogenic flavonoids of 28 vegetables and 9 fruits, Grbic-Gali´ c,´ D. (1986). O-Demethylation, dehydroxylation, ring-reduction commonly consumed in the Netherland. Journal of Agricultural and Food and cleavage of aromatic substrates by Enterobacteriaceae under anaerobic Chemistry, 40, 2379–2383. https://doi.org/10.1021/jf00024a011. conditions. Journal of Applied Bacteriology, 61, 491–497. Hertog, M. G. L., Hollman, P. C. H., & Venema, D. P. (1992). Optimization Greyling, A., Ras, R. T., Zock, P. L., Lorenz, M., Hopman, M. T., Thijssen, of a quantitative HPLC determination of potentially anticarcinogenic D. H., & Draijer, R. (2014). The effect of black tea on blood pressure: A flavonoids in fruits and vegetables. Journal of Agricultural and Food Chemistry, systematic review with meta-analysis of randomized controlled trials. PLoS 40, 1591–1598. https://doi.org/10.1021/jf00021a023. One, 9, e103247. https://doi.org/10.1371/journal.pone.0103247. Hertog, M. G. L., Feskens, E. J., Hollman, P. C. H., Katan, M. B., & Griffith, L. A. (1964). Studies on flavonoid metabolism. Identification Kromhout, D. (1993). Dietary antioxidant flavonoids and risk of coronary of the metabolites of (+)-catechin in rat urine. Biochemical Journal, 92, heart disease: The Zutphen Elderly Study. The Lancet, 342(8878), 173–179. 1007–1011. https://doi.org/10.1016/0140-736(93)92876-U. Grimm, T., Schafer, A., & Hogger, P. (2004). Antioxidant activity and Hertog, M. G. L., Hollman, P. C. H., & van de Putte, B. (1993). Content of inhibition of matrix metalloproteinases by metabolites of maritime pine bark potentially anticarcinogenic flavonoids in tea infusions, wines and fruit extract (pycnogenol). Free Radical Biology and Medicine, 36, 811–822. juices. Journal of Agricultural and Food Chemistry, 41, 1242–1426. https://doi.org/10.1016/j.freeradbiomed.2003.12.017. https://doi.org/10.1021/jf00032a015.

r 1104 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

Heyman-Linden, L., Kotowska, D., Sand, E., Bjursell, M., Plaza, M., Turner, Jacobsen, U. P., Nielsen, H. B., Hildebrand, F., Raes, J., Sicheritz-Ponten, T., C., . . . Berger, K. (2016). Lingonberries alter the gut microbiota and Kouskoumvekaki, I., & Panagiotou, G. (2013). The chemical interactome prevent low-grade inflammation in high-fat diet fed mice. Food and space between the human host and the genetically defined gut metabotypes. Nutrition Research, 60, 29993. https://doi.org/10.3402/fnr.v60.29993. The ISME Journal, 7, 730–742. https://doi.org/10.1038/ismej.2012.141. Hidalgo, M., Martin-Santamaria, S., Recio, I., Sanchez-Moreno, C., de Jaganath, I. B., Mullen, W., Edwards, C. A., & Crozier, A. (2006). The Pascual-Teresa, B., Rimbach, G., & de Pascual-Teresa, S. (2012). Potential relative contribution of the small and large intestine to the absorption anti-inflammatory, anti-adhesive, anti/estrogenic, and angiotensin- and metabolism of rutin in man. Free Radical Research, 40, converting enzyme inhibitory activities of anthocyanins and their gut 1035–1046. metabolites. Genes and Nutrition, 7, 295–306. Jaganath,I.B.,Mullen,W.,Lean,M.E.J.,Edwards,C.A.,&Crozier,A. https://doi.org/10.1007/s12263-011-0263-5. (2009). In vitro catabolism of rutin by human fecal bacteria and the Higashi, Y., Noma, K., Yoshizumi, M., & Kihara, Y. (2009). Endothelial antioxidant capacity of its catabolites. Free Radical Biology and Medicine, 47, function and oxidative stress in cardiovascular diseases. Circulation Journal, 73, 1189–1189. https://doi.org/10.1016/j.freeradbiomed.2009.07.031. 411–418. Retrieved from https://doi.org/JST.JSTAGE/circj/CJ-08-1102 Jennings, A., Welch, A. A., Fairweather-Tait, S. J., Kay, C., Minihane, A. M., Hird, S. J., Lau, B. P.-Y., Schuhmacher, R., & Krska, R. (2014). Liquid Chowienczyk, P., . . . Cassidy, A. (2012). Higher anthocyanin intake is chromatography-mass spectrometry for determination of chemical associated with lower arterial stiffness and central blood pressure in women. contaminants in foods. Trends in Analytical Chemistry, 59, 59–72. American Journal of Clinical Nutrition, 96, 781–788. https://doi.org/10.1016/jtrac.2014.04.005. https://doi.org/10.3945/ajcn.112.042036. Ho, H. H., Chang, C. S., Ho, W. C., Liao, S. Y., Wu, C. H., & Wang, C. J. Joven, J., Micol, V., Segura-Carretero, A., Alonso-Villaverde, C., & (2010). Anti-metastasis effects of gallic acid on gastric cancer cells involves Menendez, J. A. (2014). Polyphenols and the modulation of gene expression inhibition of NF-kappaB activity and downregulation of PI3K/AKT/small pathways: Can we eat our way out of the danger of chronic disease? Critical GTPase signals. Food and Chemical Toxicology, 48, 2508–2516. Reviews in Food Science and Nutrition, 54, 985–1001. https://doi.org/10.1016/j.fct.2010.06.024. https://doi.org/10.1080/10408398.2011.621772. Hodgson, J. M. (2006). Effects of tea and tea flavonoids on endothelial Kabirifar, R. Z. A., Ghoreshi, Z. A., Safari, F., Karimollah, A., Moradi, A., function and blood pressure: A brief review. Clinical and Experimental & Eskandari-Nasab, E. (2017). Quercetin protects liver injury induced by Pharmacology and Physiology, 33, 838–841. https://doi.org/10.1111/ bile duct ligation via attenuation of Rac1 and NADPH oxidase1 expression j.1440-1681.2006.04450.x. in rats. Hepatobiliary and Pancreat Diseases International, 16, 88–95. Hodgson, J. M., Puddey, I. B., Woodman, R. J., Mulder, T. P., Fuchs, D., Kahle, K., Kraus, M., Scheppach, W., Ackermann, M., Ridder, F., & Scott, K., & Croft, K. D. (2012). Effects of black tea on blood pressure: A Richling, E. (2006). Studies on apple and blueberry fruit constituents: Do randomized controlled trial. Archives of Internal Medicine, 172, 186–188. the polyphenols reach the colon after ingestion? Molecular Nutrition Food https://doi.org/10.1001/archinte.172.2.186. Research, 50, 418–423. https://doi.org/10.1002/mnfr.2005000132. Hodnick, W. F., Milosavljevic, E. B., Nelson, J. H., & Pardini, R. S. (1988). Kalt, W., Lui, Y., McDonald, J. E., Vinqvist-Tymchuk, M. R., & Fillmore, S. Electrochemistry of flavonoids. Relationships between redox potentials, A. E. (2014). Anthocyanin metabolites are abundant and persistent inhuman inhibition of mitochondrial respiration, and production of oxygen radicals urine. Journal of Agricultural and Food Chemistry, 62, 3926–3934. by flavonoids. Biochemical Pharmacology, 37, 2607–2611. https://doi.org/10.1021/jf500107. Hollman, P. C. (2014). Unravelling of the health effects of polyphenols is a Kalt, W., McDonald, J. E., Liu, Y., & Fillmore, S. A. E. (2017). Flavonoid complex puzzle complicated by metabolism. Archives of Biochemistry and metabolites in human urine during blueberry anthocyanin intake. Journal of Biophysics, 559, 100–105. https://doi.org/10.1016/j.abb.2014.04.013. Agricultural and Food Chemistry, 65, 1582–1591. https://doi.org/10.1021/ Hollman, P. C. H., de Vries, J. H. M., van Leeuwen, S. D., Mengelers, M. J. acs.jafc.6b05455. B., & Katan, M. (1995). Absorption of dietary quercetin glycosides and Kalt, W., McDonald, J. E., Vinqvist-Tymchuk, M. R., Lui, Y., & Fillmore, S. quercetin in healthy ileostomy volunteers. American Journal of Clinical A. E. (2017). Human anthocyanin bioavailability: Effect on intake duration Nutrition, 62, 1276–1282. and dosing. Food and Function, 8, 4563–4569. https://doi.org/10.1039/ Hollman,P.C.H.,Gaag,M.V.D.,Mengelers,M.J.B.,vanTrijp,J.M.P., C7FO01074E. de Vries, J. H. M., & Katan, M. B. (1996). Absorption and disposition Kandaswami, C., Lee, L. T., Lee, P. P., Hwang, J. J., Ke, F. C., Huang, Y. T., kinetics of the dietary antioxidant quercetin in man. Free Radical Biology and & Lee, M. T. (2005). The antitumor activities of flavonoids. In Vivo, 19, Medicine, 21, 703–707. 895–909. Hollman, P. C. H., van Trijp, J. M. P., & Buysman, M. N. C. P. (1996). Kawabata, K., Sugiyama, Y., Sakano, T., & Ohigashi, H. (2013). Flavonols Fluorescent detection of flavonols in HPLC by postcolumn chelation with enhanced production of anti-inflammatory substance(s) by Bifidobacterium aluminium. Analytical Chemistry, 68, 3511–3515. adolescentis: Prebiotic actions of galangin, quercetin, and fisetin. Biofactors, https://doi.org/10.1021/ac960461. 39, 422–429. https://doi.org/10.1002/biof.1081. Hollman, P. C. H., Bijsman, M. N. C. P., van Gameren, Y., Cnossen, E. P. J., Kawabata, K., Mukai, R., & Ishisaka, A. (2015). Quercetin and related de Vries, J. H. M., & Katan, M. B. (1999). The sugar moiety is a major polyphenols: New insights and implications for their bioactivity and determinant of the absorption of dietary flavonoids in man. Free Radical bioavailability. Food and Function, 6, 1399–1417. https://doi.org/10.1039/ Research, 31, 569–573. c4fo01178c. Holst, B., & Williamson, G. (2008). Nutirients and phytochemicals: From Kawai, Y., Nishikawa, T., Shiba, Y., Saito, S., Murota, K., Shibata, N., . . . bioavailabiity to bioefficacy beyond antioxidants. Current Opinions in Terao, J. (2008a). Macrophage as a target of quercetin glucuronides in Biotechnology, 19, 73–82. https://doi.org/10.1016/copbio.2008.03.003. human atherosclerotic arteries: Implication in the anti-atherosclerotic Hong, S. S., Seo, K., Lim, S. C., & Han, H. K. (2007). Interaction mechanism of dietary flavonoids. Journal of Biological Chemistry, 283, characteristics of flavonoids with human organic anion transporter 1 9424–9434. https://doi.org/10.1074/jbc.M706571200. (hOAT1) and 3 (hOAT3). Pharmacology Research, 56, 468–473. Kawai, Y., Tanaka, H., Murota, K., Naito, M., & Terao, J. (2008b). https://doi.org/10.1016/j.phrs.2007.08.007. (−)-Epicatechin gallate accumulates in foamy macrophages in human Hooper, L., Kay, C., Abdelhamid, A., Kroon, P. A., Cohn, J. S., Rimm, E. atherosclerotic aorta: Implication in the anti-atherosclerotic actions of tea B., & Cassidy, A. (2012). Effects of chocolate, cocoa, and flavan-3-ols on catechins. Biochemical and Biophysical Research Communications, 374, 527–532. cardiovascular health: A systematic review and meta-analysis of randomized https://doi.org/10.1016/j.bbrc.2008.07.086. trials. American Journal of Clinical Nutrition, 95, 740–751. Kawashima, S., & Yokoyama, M. (2004). Dysfunction of endothelial nitric https://doi.org/10.3945/ajcn.111.023457. oxide synthase and atherosclerosis. Arteriosclerosis, Thrombosis and Vascular Hur, H., & Rafii, F. (2000). Biotransformation of the isoflavonoids biochanin Bioliology, 24, 998–1005. https://doi.org/10.1161/01.ATV. A, formononetin, and glycitein by Eubacterium limosum. FEMS Microbiology 0000125114.88079.96. Letters, 192, 21–25. https://doi.org/10.1111/j.1574-6968.2000.tb09353.x. Kawser Hossain, M., Abdal Dayem, A., Han, J., Yin, Y., Kim, K., Kumar Hugel, H. M., Jackson, N., May, B., Zhang, A. L., & Xue, C. C. (2016). Saha, S., . . . Cho, S. G. (2016). Molecular mechanisms of the anti-obesity Polyphenol protection and treatment of hypertension. Phytomedicine, 23, and anti-diabetic properties of flavonoids. International Journal of Molecuar 220–231. https://doi.org/10.1016/j.phymed.2015.12.012. Sciences, 17, 569. https://doi.org/10.3390/ijms17040569. Isemura, M., Saeki, K., Kimura, T., Hayakawa, S., Minami, T., & Sazuka, M. Kay, C. D. (2006). Aspects of anthocyanin absorption, metabolism and (2000). Tea catechins and related polyphenols as anti-cancer agents. pharmacokinetics in humans. Nutritional Research Reviews, 19, 137–146. Biofactors, 13, 81–85. https://doi.org/10.1002/biof.5520130114. https://doi.org/10.1079/NRR2005116.

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1105 Dietary ﬂavonoids: a historical review . . .

Kay, C. D. (2010). The future of flavonoid research. British Journal of Lago, J. H., Toledo-Arruda, A. C., Mernak, M., Barrosa, K. H., Martins, M. Nutrition, 104(Suppl 3), S91–S95. https://doi.org/10.1017/s00071145 A., Tiberio, I. F., & Prado, C. M. (2014). Structure-activity association of 1000396x. flavonoids in lung diseases. Molecules, 19, 3570–3595. Kay, C. D., Mazza, G., Holub, B. J., & Wang, J. (2004). Anthocyanin https://doi.org/10.3390/molecules19033570. metabolites in human urine and serum. British Journal of Nutrition, 91, Lambert, J. D., Rice, J. E., Hong, J., Hou, Z., & Yang, C. S. (2005). 933–942. Synthesis and biological activity of tea catechin metabolites, M4 and M6 Kay, C. D., Mazza, G., & Holub, B. J. (2005). Anthocyanins exist in the and their methoxy derivatives. Bioorganic and Medicinal Chemistry Letters, 15, circulatory system primarily as metabolites in adult men. Journal of Nutrition, 873–876. https://doi.org/10.1016/j.bmci.2004.12.070. 135, 2582–2588. Lamson, D. W., & Brignall, M. S. (2000). Antioxidants and cancer. Alternative Kay, C. D., Kris-Etherton, P. M., & West, S. G. (2006). Effects of Medicine Review, 5, 196–208. antioxidant-rich foods on vascular reactivity: Review of the clinical Lapidot, T., Harel, S., Granit, R., & Kanner, J. (1998). Bioavailability of red evidence. Current Atherosclerosis Reports, 8, 510–522. wine anthocyanins as detected in human urine. Journal of Agricultural and Kay, C. D., Pereira-Caro, G., Ludwig, I. A., Clifford, M. N., & Crozier, A. Food Chemistry, 46, 4297–4302. https://doi.org/10.1021/jf980007o. (2017). Anthocyanins and flavanones are more bioavailable than previously Larrosa, M., Luceri, C., Vivoli, E., Pagliuca, C., Lodovici, M., Moneti, G., & perceived: A review of recent evidence. Annual Review of Food Science and Dolara, P. (2009). Polyphenol metabolites from colonic microbiota exert Te c h no lo gy, 8, 155–180. anti-inflammatory activity on different inflammation models. Molecular https://doi.org/10.1146/annurev-food-030216-025636. Nutrition and Food Research, 53, 1044–1054. Kemperman, R. A., Bolca, S., Roger, L. C., & Vaughan, E. E. (2010). Novel https://doi.org/10.1002/mnfr.200800446. approaches for analysing gut microbes and dietary polyphenols: Challenges Larson, A. J., Symons, J. D., & Jalili, T. (2012). Therapeutic potential of and opportunities. Microbiology, 156, 3224–3231. https://doi.org/10.1099/ quercetin to decrease blood pressure: Review of efficacy and mechanisms. mic.0.042127-0. Advances in Nutrition, 3, 39–46. https://doi.org/10.3945/an.111.001271. Kerimi, A., & Williamson, G. (2015). The cardiovascular benefits of dark Lazze, M. C., Pizzala, R., Perucca, P., Cazzalini, O., Savio, M., Forti, L., . . . chocolate. Vascular Pharmacology, 71, 11–15. https://doi.org/10.1016/ Bianchi, L. (2006). Anthocyanidins decrease endothelin-1 production and j.vph.2015.05.01.1. increase endothelial nitric oxide synthase in human endothelial cells. Kerimi, A., & Williamson, G. (2017). Differential impact of flavonoids on Molecular Nutrition and Food Research, 50, 44–51. redox modulation, bioenergetics, and cell signaling in normal and tumor https://doi.org/10.1002/mnfr.200500134. cells: A comprehensive review. Antioxidants and Redox Signaling [Epub ahead Lee, Y. K. (2006). Effects of antioxidant-rich foods on vascular reactivity: of print] https://doi.org/10.1089/ars.2017.7086. Review of the clinical evidence. Research in Microbiology, 8, 510–522. Khan, F., Niaz, K., Maqbool, F., Ismail Hassan, F., Abdollahi, M., Nagulapalli https://doi.org/10.1016/j.resmic.2006.07.004. Venkata, K. C., . . . Bishayee, A. (2016). Molecular targets underlying the Legeay, S., Rodier, M., Fillon, L., Faure, S., & Clere, N. (2015). anticancer effects of quercetin: An update. Nutrients, 29,8. epigallocatechin gallate: A review of its beneficial properties to prevent https://doi.org/10.3390/nu8090529. metabolic syndrome. Nutrients, 7, 5443–5468. Kim, J., Kim, J., Shim, J., Lee, C. Y., Lee, K. W., & Lee, H. J. (2014). Cocoa https://doi.org/10.3390/nu7075230. phytochemicals: Recent advances in molecular mechanisms on health. Lepage, P., Leclerc, M. C., Joossens, M., Mondot, S., Blottiere,` H. M., Raes, Critical Reviews in Food Science and Nutrition, 54, 1458–1472. J., . . . Dore, J. (2013). A metagenomic insight into our gut’s microbiome. https://doi.org/10.1080/10408398.2011.641041. Gut, 62, 146–158. https://doi.org/10.1136/gutjnl-2011-301805. Kim, H. P., Son, K. H., Chang, H. W., & Kang, S. S. (2004). Li, C., Lee, M. J., Sheng, S., Meng, X., Prabhu, S., Winnik, B., . . . Yang, C. Anti-inflammatory plant flavonoids and cellular action mechanisms. Journal S. (2000). Structural identification of two metabolites of catechins and their of Pharmaceutical Sciences, 96, 229–245. kinetics in human urine and blood after tea ingestion. Chemical Research in Klinder,A.,Shen,Q.,Heppel,S.,Lovegrove,J.A.,Rowland,I.,&Tuohy, Toxi co lo gy, 13, 177–184. https://doi.org/10.1021/tx9901837. K. M. (2016). Impact of increasing fruit and vegetables and flavonoid intake Li, C., Meng, X., Winnik, B., Lee, M. J., Lu, H., Buckley, B., & Yang, C. S. on the human gut microbiota. Food and Function, 7, 1788–1796. (2001). Analysis of urinary metabolites of tea catechins by liquid https://doi.org/10.1039/c5fo01096a. chromatography/electrospray ionization mass spectrometry. Chemical Koga, T., & Meydani, M. (2001). Effect of plasma metabolites of Research in Toxicology, 14, 702–707. https://doi.org/10.1021/tx0002536. (+)-catechin and quercetin on monocyte adhesion to human aortic Li, W., Khor, O. T., Xu, C., Shen, G., Jeong, W. S., Yu, S., & Kong, A. N. endothelial cells. American Journal of Clinical Nutrition, 73, 941–948. (2008). Activation of Nrf2-antioxidant signaling attenuates κ Kohrle, J., Spanka, M., Irmscher, K., & Hesch, R. D. (1988). Flavonoid NF B-inflammatory response and elicits apoptosis." Biochemical effects on transport, metabolism and action of thyroid hormones. Progress in Pharmacology, 76, 1485–1489. https://doi.org/10.1016/j.bcp.2008.07.017 Clinical and Biological Research, 280, 323–340. Li, C., & Schluesener, H. (2017). Health-promoting effects of the citrus Kokubo, Y., Iso, H., Saito, I., Yamagishi, K., Yatsuya, H., Ishihara, J., . . . flavanone hesperidin. Critical Reviews in Food Science and Nutrition, 57, Tsugane, S. (2013). The impact of green tea and coffee consumption on the 613–631. https://doi.org/10.1080/10408398.2014.906382. reduced risk of stroke incidence in Japanese population: The Japan public Liang, O. D., Kleibrink, B. E., Schuette-Nuetgen, K., Khatwa, U. U., health center-based study cohort. Stroke, 44, 1369–1374. Mfarrej, B., & Subramaniam, M. (2011). Green tea epigallo-catechin-gallate https://doi.org/10.1161/strokeaha.111.677500. ameliorates the development of obliterative airway disease. Experimental Lung Kuhnau, J. (1976). The flavonoids. A class of semi-essential food Research, 37, 435–444. https://doi.org/10.3109/01902148.2011.584359. components: Their role in human nutrition. World Review of Nutrition and Lilamand, M., Kelaiditi, E., Guyonnet, S., Antonelli Incalzi, R., Dietetics, 24, 117–191. Raynaud-Simon, A., Vellas, B., & Cesari, M. (2014). Flavonoids and arterial Kurlich, A. C., Clevidence, B. A., Britz, S. J., Simon, P. W., & Novotny, J. A. stiffness: Promising perspectives. Nutrition, Metabolism and Cardiovascular (2005). Plasma and urinary responses are lower for acylated vs nonacylated Disease, 24, 698–704. https://doi.org/10.1016/j.numecd.2014.01.015. anthocyanins from raw and cooked purple carrots. Journal of Agricultural and Lin, J. K., & Liang, Y. C. (2000). Cancer chemoprevention by tea Food Chemistry, 53, 6537–6542. https://doi.org/10.1021/jf050570o. polyphenols. Proceedings of the National Science Council of the Republic of China Kuhnle, G. G. C. (2017). Nutrtional epidemiology of flavan-3-ols: The B, 24, 1–13. known unknowns. Molecular Aspects of Medicine [Epub ahead of print]. Lodi, F., Jimenez, R., Moreno, L., Kroon, P. A., Needs, P. W., Hughes, D. https://doi.org/10.1016/j.mam.2017.10.003. A., . . . Perez-Vizcaino, F. (2009). Glucuronidated and sulfated metabolites Kurowska, E. M., Spence, J. D., Jordan, J., Wetmore, S., Freeman, D. J., of the flavonoid quercetin prevent endothelial dysfunction but lack direct Piche, L. A., & Serratore, P. (2000). HDL-cholesterol-raising effect of vasorelaxant effects in rat aorta. Atherosclerosis, 204, 34–39. orange juice in subjects with hypercholesterolemia. American Journal of https://doi.org/10.1016/j.atherosclerosis.2008.08.007. Clinical Nutrition, 72, 1095–1100. Long, G. D., DeChatelet, L. R., O’Flaherty, J. T., McCall, C. E., Bass, D. A., Kutschera, M., Engst, W., Blaut, M., & Braune, A. (2011). Isolation of a Shirley, P. S., & Parce, J. W. (1981). Effects of quercetin on magnesium- catechin-converting human intestinal bacteria. Journal of Applied Microbiology, dependent adenosine triphosphatase and the metabolism of human 111, 165–175. https://doi.org/10.111/j.1365-2672.2011.05025.x. polymorphonuclear leukocytes. Blood, 57, 561–566. Kvandova, M., Majzunova, M., & Dovinova, I. (2016). The role of Lu, H., Meng, X., Li, C., Sang, S., Patten, C., Sheng, S., . . . Yang, C. S. PPARgamma in cardiovascular diseases. Physiology Research, 65(Supple. 3), (2003). Glucuronides of tea catechins: Enzymology of biosynthesis and S343–S363. biological activities. Drug Metabolism and Disposition, 31, 452–461.

r 1106 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

Ludwig, I. A., Mena, P., Calani, L., Borges, G., Pereira-Caro, G., Bresciani, Mladenka, P., Zatloukalova, L., Filipsky, T., & Hrdina, R. (2010). L., . . . Crozier, A. (2015). New insights into the bioavailability of red Cardiovascular effects of flavonoids are not caused only by direct antioxidant raspberry anthocyanins and ellagitannins. Free Radical Biology and Medicine, activity. Free Radical Biology and Medicine, 49, 963–975. 89, 758–769. https://doi.org/10.1016/j.freeradbiomed.2015.10.400. https://doi.org/10.1016/j.freeradbiomed.2010.06.010. Lynn, D., & Luh, B. (1964). Anthocyanin pigments in Bing cherries. Journal Mochly-Rosen, D., & Zakhari, S. (2010). Focus on: The cardiovascular of Food Science, 29, 735–743. system: What did we learn from the French (Paradox)? Alcohol Research and Manach, C., Morand, C., Gil-Izquierdo, A., Bouteloup-Demange, C., & Health, 33, 76–86. Rem´ esy,´ C. (2003). Bioavailability in humans of the flavanones hesperidin Montezano, A. C., Burger, D., Ceravolo, G. S., Yusuf, H., Montero, M., & and narirutin after ingestion of two doses of orange juice. European Touyz, R. M. (2011). Novel Nox homologues in the vasculature: Focusing Journal of Clinical Nutrition, 57, 235–242. https://doi.org/10.1038/sj.ejcn. on Nox4 and Nox5. Clinical. Science (Lond), 120, 131–141. Retrieved from 1601547. https://doi.org/CS20100384. Manthey, J. A. (2000). Biological properties of flavonoids pertaining to Moon, J.-H., Nakata, R., Oshima, S., Inakuma, T., & Terao, J. (2000). inflammation. Microcirculation, 7, S29–S34. Accumulation of quercetin conjugates in blood plasma after short-term Marunaka, Y., Marunaka, R., Sun, H., Yamamoto, T., Kanamura, N., Inui, ingestion of onion by women. American Journal of Physiology, 279, T., & Taruno, A. (2017). Actions of quercetin, a polyphenol, on blood R461–467. https://doi.org/10.1152/ajpregu.2000.279.2.R461. pressure. Molecules, 22, https://doi.org/10.3390/molecules22020209. Moon, Y. J., Wang, X., & Morris, M. E. (2006). Dietary flavonoids: Effects Massee, L. A., Ried, K., Pase, M., Travica, N., Yoganathan, J., Scholey, A., on xenobiotic and carcinogen metabolism. Toxicology In Vitro, 20, 187–210. . . . Pipingas, A. (2015). The acute and sub-chronic effects of cocoa https://doi.org/10.1016/j.tiv.2005.06.048. flavanols on mood, cognitive and cardiovascular health in young healthy Moore, P. K., Griffiths, R. J., & Lofts, F. J. (1983). The effect of some flavone adults: A randomized, controlled trial. Frontiers in Pharmacology, 6, 93. drugs on the conversion of prostacyclin to 6-oxoprostaglandin E1. https://doi.org/10.3389/fphar.2015.00093. Biochemical Pharmacology, 32, 2813–2817. Massot-Cladera, M., Perez-Berezo, T., Franch, A., Castell, M., & Morais, C. A., de Rosso, V. V., Estadella, D., & Pisani, L. P. (2016). Perez-Cano, F. J. (2012). Cocoa modulatory effect on rat faecal microbiota Anthocyanins as inflammatory modulators and the role of the gut and colonic crosstalk. Archives of Biochemistry and Biophysics, 527, 105–112. microbiota. Journal of Nutrition Biochemistry, 33,1–7.https://doi.org/ https://doi.org/10.1016/j.abb.2012.05.015. 10.1016/j.jnutbio.2015.11.008. Mastroiacovo, D., Kwik-Uribe, C., Grassi, D., Necozione, S., Raffaele, A., Morand, C., Dubray, C., Milenkovic, D., Lioger, D., Martin, J. F., Scalbert, Pistacchio, L., . . . Desideri, G. (2015). Cocoa flavanol consumption A., & Mazur, A. (2011). Hesperidin contributes to the vascular protective improves cognitive function, blood pressure control, and metabolic profile effects of orange juice: A randomized crossover study in healthy volunteers. in elderly subjects: The Cocoa, Cognition, and Aging (CoCoA) Study - a American Journal of Clinical Nutrition, 93, 73–80. https://doi.org/10.3945/ randomized controlled trial. American Journal of Clinical Nutrition, 101, ajcn.110.004945. 538–548. https://doi.org/10.3945/ajcn.114.092189. Mowatt, A. M., & Agace, W. W. (2014). Regional specialization within the Matias, I., Buosi, A. S., & Gomes, F. C. (2016). Functions of flavonoids in the intestinal immune system. Nature Reviews Immunology, 14, 667–685. central nervous system: Astrocytes as targets for natural compounds. https://doi.org/10.1038/nri3738. Neurochemistry International, 95, 8591. https://doi.org/10.1016/j.neuint. Mull, E. S., van Zandt, M., Golebiowski, A., Beckett, R. P., Sharma, P. K., & 2016.01.009. Schroeter, H. (2012). A versatile approach to the regioselective synthesis of Mauray, A., Felgines, C., Morand, C., Mazur, A., Scalbert, A., & diverse (−)-epicatechin-β-D-glucuronides. Tetrahedron Letters, 53, 1501– Milenkovic, D. (2012). Bilberry anthocyanin-rich extract alters expression 1503. https://doi.org/10.1016/j.tetlet.2012.01.054. of genes related to atherosclerosis development in aorta of apo-E-deficient Mullen, W., Edwards, C. A., & Crozier, A. (2006). Absorption, excretion mice. Nutrition Metabolism and Cardiovascular Disease, 22, 72–80. and metabolite profiling of methyl-, glucuronyl-, glucosyl- and sulpho- https://doi.org/10.1016/j.numecd.2010.04.011. conjugates of quercetin in human plasma and urine after ingestion of Mauri, P. L., Iemoli, L., Gardana, C., Riso, P., Simonetti, P., Porrini, M., & onions. British Journal of Nutrition, 96, 107–116. Pietta, P. G. (1999). Liquid chromatography/electrospray ionization mass Mullen, W., Archeveque, M.-A., Edwards, C. A., & Crozier, A. (2008a). spectrometric characterization of flavonol glucosides in tomato extracts and Bioavailability and metabolism of orange juice flavanones in humans: Impact human plasma. Rapid Communications in Mass Spectrometry, 13, 924–931. of a full fat yogurt. Journal of Agricultural and Food Chemistry, 56, 11157– < https://doi.org/10.1002/(SICI)1097-0231(19990530)13:10 92. 11164. https://doi.org/10.1021/jf801974v. McCullough, M. L., Peterson, J. J., Patel, R., Jacques, P. F., Shah, R., & Mullen, W., Edwards, C. A., Serafini, M., & Crozier, A. (2008b). Dwyer, J. T. (2012). Flavonoid intake and cardiovascular disease mortality in Bioavailability of pelargonidin-3-O-glucoside and its metabolites in humans a prospective cohort of US adults. American Journal of Clinical Nutrition, 95, following the ingestion of strawberries with and without cream. Journal of 454–464. https://doi.org/10.3945/ajcn.111.016634. Agricultural and Food Chemistry, 56, 713–719. https://doi.org/10.1021/ McDougall, G. J., Conner, S., Pereira-Caro, G., Gonzalez-Barrio,´ R., jf072000p. Brown, E. M., Verrall, S., . . . Gill, C. I. R. (2014). Tracking (poly)phenol Mullen, W., Borges, G., Donovan, J. L., Edwards, C. A., Serafini, M., Lean, components from raspberries in ileal fluid. Journal of Agricultural and Food M. E. J., & Crozier, A. (2009). Milk decreases urinary excretion but not Chemistry, 62, 7631–7641. https://doi.org/10.021/jf502259j. plasma pharmacokinetics of cocoa flavan-3-ol metabolites in humans. McKay, D. L., Chen, O. C.-Y., Zampariello, C. A., & Blumberg, J. B. American Journal of Clinical Nutrition, 89, 1784–1791. https://doi.org/ (2015). Flavonoid and phenolic acids from cranberry juice are bioavailable 10.103945/ajcn.2008.217339. and bioactive in healthy older adults. Food Chemistry, 168, 233–240. doi Musther, H., Olivares-Morales, A., Hatley, O. J. D., Lui, B., & Hodjegan, A. https://doi.org/10.1016/j.foodchem.2014.07.062. R. (2014). Animal versus human oral drug bioavailability: Do they Meredith, D., & Christian, H. C. (2008). The SLC16 monocaboxylate correlate? European Journal of Pharmaceutical Sciences, 57, 280–291. transporter family. Xenobiotica, 38, 1072–1106. https://doi.org/10.1016/j.ejps.2013.08.018. https://doi.org/10.1080/00498250802010868. Nagai, T., Miyaichi, Y., Tomimori, T., & Yamada, H. (1989). Inhibition of Middleton, E., Jr. (1986). Effect of flavonoids on basophil histamine release mouse liver sialidase by plant flavonoids. Biochemical and Biophysical Research and other secretory systems. Progress in Clinical and Biological Research, 213, Communications, 163, 25–31. 493–506. Nash, L. A., & Ward, W. E. (2017). Tea and bone health: Findings from Middleton, E., Jr. (1998). Effect of plant flavonoids on immune and human studies, potential mechanisms, and identification of knowledge gaps. inflammatory cell function. Advances in Experimental Medicine and Biology, Critical Reviews in Food Science and Nutrition, 57, 1603–1617. 439, 175–182. https://doi.org/10.1080/10408398.2014.1001019. Middleton, E., Jr., & Kandaswami, C. (1992). Effects of flavonoids on Neshatdoust, S., Saunders, C., Castle, S. M., Vauzour, D., Williams, C., immune and inflammatory cell functions. Biochemical Pharmacology, 43, Butler, L., . . . Spencer, J. P. (2016). High-flavonoid intake induces 1167–1179. cognitive improvements linked to changes in serum brain-derived Mineharu, Y., Koizumi, A., Wada, Y., Iso, H., Watanabe, Y., Date, C., . . . neurotrophic factor: Two randomised, controlled trials. Nutrition Tamakoshi, A. & the JACC study Group (2011). Coffee, green tea, black tea and Healthy Aging, 4, 81–93. https://doi.org/10.3233/nha- and oolong tea consumption and risk of mortality from cardiovascular 1615. disease in Japanese men and women. Journal of Epidemiology and Community Neveu, V., Perez-Jimenez, J., Vos, F., Crespy, V., du Chaffaut, L., Mennen, Health, 65, 230–240. https://doi.org/10.1136/jech.2009.097311. L., . . . Scalbert, A. (2010). Phenol-Explorer: An online comprehensive

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1107 Dietary ﬂavonoids: a historical review . . .

database on polyphenol contents in foods. Database (Oxford), 2010, Pereira-Caro, G., Borges, G., van der Hooft, J. J. J., Clifford, M. N., Del Rio, bap024. https://doi.org/10.1093/database/bap024. D., Lean, M. E. J., . . . Crozier, A. (2014). Orange juice (poly)phenols are Nicolle, E., Souard, F., Faure, P., & Boumendjel, A. (2011). Flavonoids as highly bioavailable. American Journal of Clinical Nutrition, 100, 1385–1391. promising lead compounds in type 2 diabetes mellitus: Molecules of interest https://doi.org/10.3945/ajcn.114.090282. and structure-activity relationship. Current Medicinal Chemistry, 18, Pereira-Caro, G., Borges, G., Ky, I., Ribas, A., Del Rio, D., Clifford, M. N., 2661–2672. https://doi.org/10.2174/092986711795933777. . . . Crozier, A. (2015a). In vitro colonic catabolism of orange juice Nielsen, I. L. F., Chee, W. S. S., Poulsen, L., Offord-Cavin, E., Rasmussen, S. (poly)phenols. Molecular Nutrition & Food Research, 59, 465–475. E., Rasmussen, S. E., . . . Williamson, G. (2006). Bioavailability is improved https://doi.org/ by enzymatic modification of the citrus flavonoid hesperidin in humans: A 10.1002/mnfr.201400779. randomised, double-blind, crossover trial. Journal of Nutrition, 136, 404–408. Pereira-Caro, G., Oliver, C. M., Weerakkody, R., Singh, T., Conlon, M., Nijveldt, R. J., van Nood, E., van Hoorn, D. E., Boelens, P. G., van Norren, Borges, G., . . . Augustin, M. A. (2015b). Chronic administration of a K., & van Leeuwen, P. A. (2001). Flavonoids: A review of probable microencapsulated probiotic enhances the bioavailability of orange juice mechanisms of action and potential applications. American Journal of Clinical flavanones in humans. Free Radical Biology and Medicine, 84, 206–214. Nutrition, 74, 418–425. https://doi.org/10.1016/j.freeradbiomed.2015.03.010. Nishino, H., Nagao, M., Fujiki, H., & Sugimura, T. (1983). Role of Pereira-Caro, G., Fernandez-Quir´ os,´ B., Ludwig, I. A., Pradas, I., Crozier, flavonoids in suppressing the enhancement of phospholipid metabolism by A., & Moreno-Rojas, J. M. (2016a). Catabolism of citrus flavanones by the tumor promoters. Cancer Letters, 21,1–8. probiotics Bifidobacterium longum and Lactobacillus rhamnosus. European Journal of Nutrition, https://doi.org/10.1007/s00394-016-1312-z. Nishiumi, S., Miyamoto, S., Kawabata, K., Ohnishi, K., Mukai, R., Murakami, A., . . . Terao, J. (2011). Dietary flavonoids as cancer-preventive Pereira-Caro, G., Ludwig, I. A., Polyviou, T., Malkova, D., Garcia, A., and therapeutic biofactors. Frontiers in Bioscience (Scholar Edition), 3, Malkova, D., . . . Crozier, A. (2016b). Identification of plasma and urinary 1332–1362. metabolites and catabolites derived from orange juice (poly)phenols: Analysis by high performance liquid chromatography-high resolution mass O’Leary, K. A., Day, A. J., Needs, P. W., Mellon, F. A., O’Brien, N. M., & spectrometry. Journal of Agricultural and Food Chemistry, 64, 5724–5735. Williamson, G. (2003). Metabolism of quercetin-7- and quercetin-3- https://doi.org/10.1021/acs.jafc.6b02088. glucuronides by an in vitro hepatic model: The role of human beta-glucuronidase, sulfotransferase, catechol-O-methyltransferase and Pereira-Caro, G., Moreno-Rojas, J., Brindani, N., Del Rio, D., Lean, M. E. multi-resistant protein 2 (MRP2) in flavonoid metabolism. Biochemical J., Hara, Y., & Crozier, A. (2017). Bioavailability of black tea theaflavins: Pharmacology, 65, 479–491. https://doi.org/10.1016/S0006-2952(002) Absorption, metabolism and colonic catabolism. Journal of Agricultural 01510-1 and Food Chemistry, 65, 5365–5374. https://doi.org/10.1021/acs.jafc. 7b01707. Olthof, M. R. R., Hollman, P. C. H., Vree, T. B., & Katan, M. B. (2000). Bioavailability of quercetin-3-glucoside and quercetin-4-glucoside does not Perez-Vizcaino, F., Duarte, J., Jimenez, R., Santos-Buelga, C., & Osuna, A. differ in humans. Journal of Nutrition, 130, 1200–1203. (2009). Antihypertensive effects of the flavonoid quercetin. Pharmacology Reports, 61, 67–75. Ottaviani, J. I., Momma, T. Y., Heiss, C., Kwik-Uribe, C., Schroeter, H., & Keen, C. L. (2011). The stereochemical configuration of flavanols influences Persson, I. A. L., Persson, K., & Andersson, R. G. G. (2009). Effect of the level and metabolism of flavanols in humans and their biological activity Vaccinium myrtillus and Its polyphenols on angiotensin-converting enzyme in vivo. Free Radical Biology and Medicine, 50, 237–244. https://doi.org/ activity in human endothelial cells. Journal of Agricultural and Food Chemistry, 10.1016/freeradbiomed.2010.11.006. 57, 4626–4629. https://doi.org/10.1021/jf900128s. Ottaviani, J. I., Momma, T. Y., Kuhnle, G. K., Keen, C. L., & Schroeter, H. Peterson, J. J., Dwyer, J. T., Jacques, P. F., & McCullough, M. L. (2012). (2012). Structurally related (−)-epicatechin metabolites in humans: Associations between flavonoids and cardiovascular disease incidence or Assessment using de novo chemically synthesized authentic standards. Free mortality in European and US populations. Nutrition Reviews, 70, 491–508. Radical Biology and Medicine, 52, 1403–1412. https://doi.org/10.1016/ https://doi.org/10.1111/j.1753-4887.2012.00508.x. freeradbimed.2010.11.005. Petkov, V., & Manolov, P. (1978). Pharmacological studies on substances of Ottaviani, J. I., Borges, G., Momma, T., Spencer, J. P. E., Keen, C. L., plant origin with coronary dilatating and antiarrhythmic action. American Crozier, A., & Schroeter, H. (2016). The metabolome of [2-14C](–)- Journal of Chinese Medicine, 6, 123–130. https://doi.org/10.1142/ epicatechin in humans: Implications for the assessment of efficacy safety, and s0147291778000198. mechanisms of action of polyphenolic bioactives. Science Reports, 16, 29034. Phung, O. J., Baker, W. L., Matthews, L. J., Lanosa, M., Thorne, A., & https://doi.org/10.1038/srep29034. Coleman, C. I. (2010). Effect of green tea catechins with or without Paganga, G., & Rice-Evans, C. A. (1997). The identification of flavonoids as caffeine on anthropometric measures: A systematic review and meta- glycosides in human plasma. FEBS Letters, 401, 78–82. analysis. American Journal of Clinical Nutrition, 91, 73–81. https://doi.org/10.3945/ajcn.2009.28157. Paixao,˜ J., Dinis, T. C. P., & Almeida, L. M. (2012). Malvidin-3-glucoside protects endothelial cells up-regulating endothelial NO synthase and Pimpao,˜ R. C., Dew, T., Figuera, M. E., McDougall, G. J., Stewart, D., inhibiting peroxynitrite-induced NF-kB activation. Chemico-Biological Ferreira, R. B., . . . Williamson, G. (2014). Urinary metabolite profiling Interactions, 199, 192–200. https://doi.org/10.1016/j.cbi.2012.08.013. identifies colonic metabolites and conjugates of phenolics in healthy volunteers. Molecular Nutrition Food Research, 58, 1414–1425. Pallauf, K., Rimbach, G., Rupp, P. M., Chin, D., & Wolf, I. M. (2016). https://doi.org/10.1002/mnfr.201300822. Resveratrol and lifespan in model organisms. Current Medicinal Chemistry, 23, 4639–4680. https://doi.org/10.2174/0929867323666161024151233. Prior, R. L. (2012). Anthocyanins: Understanding their absorption and metabolism.InJ.P.E.Spencer&A.Crozier(Eds.),Flavonoids and related Panthong, A., Tassaneeyakul, W., Kanjanapothi, D., Tantiwachwuttikul, P., & compounds. Bioavailability and function (pp. 79–92). Boca Raton: Reutrakul, V. (1989). Anti-inflammatory activity of 5,7-dimethoxyflavone. CRC Press. Planta Medica, 55, 133–136. https://doi.org/10.1055/s-2006-961905. Qian, Y., Li, P., Zhang, J., Shi, Y., Chen, K., Yang, J., . . . Ye, X. (2016). Parkar, S. G., Stevenson, D. E., & Skinner, M. A. (2008). The potential Association between peroxisome proliferator-activated receptor-alpha, delta, influence of fruit polyphenols on colonic microflora and human gut health. and gamma polymorphisms and risk of coronary heart disease: A case- International Journal of Food and Microbiology, 124, 295–298. control study and meta-analysis. Medicine (Baltimore), 95, e4299. https://doi.org/10.1016/j.ijfoodmicro.2008.03.017. https://doi.org/10.1097/md.0000000000004299. Pase, M. P., Scholey, A. B., Pipingas, A., Kras, M., Nolidin, K., Gibbs, A., Quintieri, A. M., Baldino, N., Filice, E., Seta, L., Vitetti, A., Tota, B., ...... Stough, C. (2013). Cocoa polyphenols enhance positive mood states but Angelone, T. (2013). Malvidin, a red wine polyphenol, modulates not cognitive performance: A randomized, placebo-controlled trial. Journal mammalian myocardial and coronary performance and protects the heart of Psychopharmacology, 27, 451–458. https://doi.org/10.1177/ against ischemia/reperfusion injury. Journal of Nutritional. Biochemistry, 24, 0269881112473791. 1221–1231. https://doi.org/10.1016/j.jnutbio.2012.09.006. Patel, S., Mathan, J. J., Vaghefi, E., & Braakhuis, A. J. (2015). The effect of Racker, E. (1986). Effect of quercetin on ATP-driven pumps and glycolysis. flavonoids on visual function in patients with glaucoma or ocular Progress in Clinical and Biological Research, 213, 257–271. hypertension: A systematic review and meta-analysis. Graefe’s Archives for Clinical and Experimental Ophthalmology, 253, 1841–1850. https://doi.org/ Rajendran, P., Rengarajan, T., Thangavel, J., Nishigaki, Y., Sakthisekaran, D., 10.1007/s00417-015-3168-y. Sethi, G., & Nishigaki, I. (2013). The vascular endothelium and human diseases. International Journal of Biological Sciences, 9, 1057–1069. Pearson, W. N. (1957). Flavonoids in human nutrition and medicine. Journal https://doi.org/10.7150/ijbs.7502. of the American Medical Association, 164, 1675–1678

r 1108 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

Rao, S. S., Lu, C., & Schulze-Delrieu, K. (1996). Duodenum as immediate Roowi, S., Mullen, W., Edwards, C. A., & Crozier, A. (2009). Yoghurt brake to gastric outflow: A videofluoroscopic and manometric assessment. impacts on the excretion of phenolic acids derived from colonic breakdown Gastroenterology, 110, 740–747. of orange juice flavanones in humans. Molecular Nutrition Food Research, 53, Rechner, A. R., Kuhnle, G., Hu, H., Roedig-Penman, A., van den Braak, S68–S75. https://doi.org/10.1002/mnfr.2000800287. M. H., Moore, K. P., & Rice-Evans, C. A. (2002). The metabolism of Roowi, S., Stalmach, A., Mullen, W., Lean, M. E. J., Edwards, C. A., & dietary polyphenols and the relevance to circulating levels of conjugated Crozier, A. (2010). Green tea flavan-3-ols: Colonic degradation and urinary metabolites. Free Radical Research, 36, 1229–1241. https://doi.org/10.1080/ excretion of catablites by humans. Journal of Agricultural and Food Chemistry, 246-1071576021000016472. 58, 1296–1304. https://doi.org/10.1021/jf9032975. Rein, D., Lotito, S., Holt, R. R., Keen, C. L., Schmitz, H. H., & Fraga, C. Rosenberg Zand, R. S., Jenkins, D. J., & Diamandis, E. P. (2002). Flavonoids G. (2000). Epicatechin in human plasma: In vivo determination and effect of and steroid hormone-dependent cancers. Journal of Chromatography B, 777, chocolate consumption on plasma oxidation status. Journal of Nutrition, 130, 219–232. https://doi.org/10.1016/S11570-0232(02)00213-1. 2109S–2114S. Rothwell, J. A., Urpi-Sarda, M., Boto-Ordonez, M., Llorach, R., Renault, S., & de Lorgeril, M. (1992). Wine, alcohol and the French Paradox Farran-Codina, A., Barupal, D. K., . . . Scalbert, A. (2016). Systematic for coronary heart disease. Lancet, 339, 1523–1536. analysis of the polyphenol metabolome using the Phenol-Explorer database. Rendeiro, C., Rhodes, J. S., & Spencer, J. P. (2015). The mechanisms of Molecular Nutrition and Food Research, 60, 203–211. https://doi.org/ action of flavonoids in the brain: Direct versus indirect effects. Neurochemistry 10.1002/mnfr.201500435. International, 89, 126–139. https://doi.org/10.1016/j.neuint.2015.08.002. Rotondo, S., Di Castelnuovo, A., & de Gaetano, G. (2001). The relationship Rice-Evans, C. A., & Miller, N. J. (1996). Antioxidant activities of flavonoids between wine consumption and cardiovascular risk: From epidemiological as bioactive components of food. Biochemical Society Transactions, 24, evidence to biological plausibility. Italian Heart Journal, 2,1–8. 790–795. Roura, E., Andres-Lacueva,´ C., Jauregui,´ O., Badia, E., Estruch, R., Rice-Evans, C. A., Miller, N. J., & Paganga, G. (1996). Structure-antioxidant Izquierdo-Pulido, M., & Lamuela-Raventos,´ R. M. (2005). Rapid liquid activity relationships of flavonoids and phenolic acids. Free Radical Biology chromatography tandem mass spectrometry assay to quantify plasma and Medicine, 20, 933–956. https://doi.org/0891584995022279. (−)-epicatechin metabolites after ingestion of a standard portion of cocoa Richelle, M., Tavazzi, I., Enslen, M., & Offord, E. A. (1999). Plasma kinetics beverage in humans. Journal of Agricultural and Food Chemistry, 53, in man of epicatechin from black chocolate. European Journal of Clinical 6190–6194. https://doi.org/10.1021/jf050377u. Nutrition, 53, 22–26. Russell, W. R., Labat, A., Scobbie, L., & Duncan, S. H. (2007). Availability Ried, K., Sullivan, T. R., Fakler, P., Frank, O. R., & Stocks, N. P. (2012). of blueberry phenolics for microbial metabolism in the colon and the Effect of cocoa on blood pressure. Cochrane Database of Systematic Reviews, 8, potential inflammatory implications. Molecular Nutrition and Food Research, Cd008893. https://doi.org/10.1002/14651858.CD008893.pub2. 51, 726–731. https://doi.org/10.1002/mnfr.200700022. Rimm, E. B., Giovannucci, E. L., Willett, W. C., Colditz, G. A., Ascherio, Ryter, S. W., Otterbein, L. E., Morse, D., & Choi, A. M. (2002). Heme A., Rosner, B., & Stampfer, M. J. (1991). Prospective study of alcohol oxygenase/carbon monoxide signaling pathways: Regulation and functional consumption and risk of coronary disease in men. Lancet, 338(8765), significance. Molecular and Cellular Biochemistry, 234–235, 249–263. 464–468. https://doi.org/0140-6736(91)90542-W. Saha, S., Hollands, W., Needs, P. W., Ostertag, L. M., de Roos, B., Duthie, Riso, P., Klimis-Zacas, D., Bo’, C., Martini, D., Campolo, J., Vendrame, S., G. G., & Kroon, P. A. (2012). Human O-sulfated metabolites of . . . Porrini, M. (2013). Effect of a wild blueberry (Vaccinium angustifolium) (−)-epicatechin and methyl-(−)-epicatechin are poor substrates for drink intervention on markers of oxidative stress, inflammation and commercial aryl-sulfatases: Implications for studies concerned with endothelial function in humans with cardiovascular risk factors. European quantifying epicatechin bioavailability. Pharmacology Research, 65, 592–602. Journal of Nutrition, 52, 949–961. https://doi.org/10.1016/j.phrs.2012.02.005. https://doi.org/10.1007/s00394-012-0402-9. Sakagami, H., Oi, T., & Satoh, K. (1999). Prevention of oral diseases by Robinson, M. J., & Cobb, M. H. (1997). Mitogen-activated protein kinase polyphenols. In Vivo, 13, 155–171. pathways. Current Opinion in Cell Biology, 9, 180–186. https://doi.org/ Sanchez, M., Galisteo, M., Vera, R., Villar, I. C., Zarzuelo, A., Tamargo, J., S0955-0674(97)80061-0. . . . Duarte, J. (2006). Quercetin downregulates NADPH oxidase, increases Robinson, J. W., L’Herminier, M., & Claudet, H. G. (1979). The effect of eNOS activity and prevents endothelial dysfunction in spontaneously naringenin on the intestinal and renal transport of organic solutes. Naunyn hypertensive rats. JournalofHypertension, 24, 75–84. Retrieved from Schmiedeberg’s Archives of Pharmacology, 307, 79–89. https://doi.org/00004872-200601000-00014 Rodriguez-Mateos, A. M., Rendeiro, C., Bergillos-Meca, T., Tabatabaee, S., Sanchez, M., Lodi, F., Vera, R., Villar, I. C., Cogolludo, A., Jimenez, R., . . . George, T., Heiss, C., & Spencer, J. P. E. (2013). Intake and time Duarte, J. (2007). Quercetin and isorhamnetin prevent endothelial dependence of blueberry flavonoid-induced improvements in vascular dysfunction, superoxide production, and overexpression of p47phox function: A randomized, controlled, double-blind, crossover intervention induced by angiotensin ii in rat aorta. Journal of Nutrition, 137, 910–915. study with mechanistic insights into biological activity. American Journal of Sandhu, A. K., Huang, Y., Xiao, D., Park, E., Edirisinghe, I., & Clinical Nutrition, 98, 1179–1191. https://doi.org/10.3945/ajcn. Burton-Freeman, B. (2016). Pharmacokinetic characterization and 113.066639. bioavailability of strawberry anthocyanins relative to meal intake. Journal of Rodriguez-Mateos, A., Heiss, C., Borges, G., & Crozier, A. (2014a). Berry Agricultural and Food Chemistry, 64, 4891–4899. https://doi.org/10.1021/ (poly)phenols and cardiovascular health. Journal of Agricultural and Food acs.jafc.6b00805. Chemistry, 62, 3842–3851. https://doi.org/10.1021/jf403757g. Sansone, R., Rodriguez-Mateos, A., Heuel, J., Falk, D., Wagstaff, R., Rodriguez-Mateos, A., Pino-Garcia, R. D., George, T. W., Vidal-Diez, A., Kuhnle, G. G., . . . Heiss, C. (2015). Cocoa flavanol intake improves Heiss, C., & Spencer, J. P. (2014b). Impact of processing on the endothelail function and Framingham Risk Score in healthy men and bioavailability and vascular effects of blueberry (poly)phenols. Molecular women: A randomised, controlled double-masked trial: The Flaviola Health Nutrition and Food Research, 58, 1952–1961. 19 https://doi.org/10.1002/ Study. British Journal of Nutrtion, 114, 1246–1255. https://doi.org/ mnfr.201400231. 10.1017/S0007114515002822. Rodriguez-Mateos, A., Vauzour, D., Kreuger, C. G., Shanmuganayagam, D., Sansone, R., Ottaviani, J. I., Rodriguez-Mateos, A., Heinen, Y., Noske, D., Reed, J. D., Calani, L., . . . Crozier, A. (2014c). Flavonoids and related Spencer, J. P. E., . . . Heiss, C. (2017). Methylxanthines enhance the effects compounds, bioavailability, bioactivity and impact on human health: An of cocoa flavanols on cardiovascular function: Randomized, double-masked update. Archives in Toxicology, 88, 1803–1853. https://doi.org/10.1007/ controlled studies. American Journal of Clinical Nutrition, 105, 352–360. s00204-014-1330-7. https://doi.org/10.3945/ajcn.116.140046. Roger, C. R. (1988). The nutritional incidence of flavonoids: Some Sanchez-Pat´ an,´ F., Chioua, M., Garrido, I., Cueva, C., Samadi, A., physiological and metabolic considerations. Experientia, 44, 725–733. Marco-Contelles, J., . . . Monaga, M. (2011). Synthesis, analytical features, Rogers, J. C., & Williams, D. L., Jr. (1989). Kaempferol inhibits myosin light and biological relevance of 5-(3 ,4 -dihydroyxphenyl)-γ -valerolactone, a chain kinase. Biochemical and Biophysical Research Communications, 164, microbial metabolite derived from the catabolism of dietary flavan-3-ols. 419–425. Journal of Agricultural and Food Chemistry, 59, 7083–7091. https://doi.org/ Romero, M., Jimenez, R., Sanchez, M., Lopez-Sepulveda, R., Zarzuelo, M. 10.1021/jf2020182. J., O’Valle, F., . . . Duarte, J. (2009). Quercetin inhibits vascular superoxide Scalbert, A., Brennan, L., Manach, C., Andres-Lacueva, C., Dragsted, L. O., production induced by endothelin-1: Role of NADPH oxidase, uncoupled Draper, J., . . . Wishart, D. S. (2014). The food metabolome: A window eNOS and PKC. Atherosclerosis, 202, 58–67. https://doi.org/10.1016/ over dietary exposure. American Journal of Clinical Nutrition, 99, 1286–1308. j.atherosclerosis.2008.03.007. https://doi.org/10.3945/ajcn.113.076133.

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1109 Dietary ﬂavonoids: a historical review . . .

Scalbert, A., Morand, C., Manach, C., & Remesy, C. (2002). Absorption oxide synthesis in human endothelial cells. Maturitas, 70, 169–175. and metabolism of polyphenols in the gut and impact on health. Biomedicine https://doi.org/10.1016/j.maturitas.2011.07.004. Pharmacotherapy, 56, 276–282. Singh, R. P., & Agarwal, R. (2006). Natural flavonoids targeting deregulated Scalbert, A., & Williamson, G. (2000). Dietary intake and bioavailability of cell cycle progression in cancer cells. Current Drug Targets, 7, 345–354. polyphenols. Journal of Nutrition, 130(8S Suppl), 2073S–2085S. https://doi.org/10.2174/138945006776055004. Scambia, G., Ranelletti, F. O., Panici, P. B., De Vincenzo, R., Bonanno, G., Skibola, C. F., & Smith, M. T. (2000). Potential health impacts of excessive Ferrandina, G., . . . Mancusco, S. (1994). Quercetin potentiates the effect flavonoid intake. Free Radical Biology and Medicine, 29, 375–383. of adriamycin in a multidrug-resistant MCF-7 human breast-cancer cell Smidowicz, A., & Regula, J. (2015). Effect of nutritional status and dietary line: P-glycoprotein as a possible target. Cancer Chemotherapy Pharmacology, patterns on human serum C-reactive protein and interleukin-6 34, 459–464. concentrations. Advances in Nutrition, 6, 738–747. https://doi.org/ Schewe, T., Steffen, Y., & Sies, H. (2008). How do dietary flavanols improve 10.3945/an.115.009415. vascular function? A position paper. Archives of Biochemistry and Biophysics, Socci, V., Tempesta, D., Desideri, G., De Gennaro, L., & Ferrara, M. (2017). 476, 102–106. https://doi.org/10.1016/j.abb.2008.03.004. Enhancing human cognition with cocoa flavonoids. Frontiers in Nutrition, 4, Scholey, A. B., French, S. J., Morris, P. J., Kennedy, D. O., Milne, A. L., & 19. https://doi.org/10.3389/fnut.2017.00019. Haskell, C. F. (2010). Consumption of cocoa flavanols results in acute Sokolov, A. N., Pavlova, M. A., Klosterhalfen, S., & Enck, P. (2013). improvements in mood and cognitive performance during sustained mental Chocolate and the brain: Neurobiological impact of cocoa flavanols on effort. Journal of Psychopharmacology, 24, 1505–1514. cognition and behavior. Neuroscience and Biobehavioral Reviews, 37, https://doi.org/10.1177/0269881109106923. 2445–2453. https://doi.org/10.1016/j.neubiorev.2013.06.013. Scholz, E. P., Zitron, E., Katus, H. A., & Karle, C. A. (2010). Cardiovascular Soleas, G. J., Diamandis, E. P., & Goldberg, D. M. (1997). Wine as a ion channels as a molecular target of flavonoids. Cardiovascular Therapeutics, biological fluid: History, production, and role in disease prevention. Journal 28, e46–52. https://doi.org/10.1111/j.1755-5922.2010.00212.x. of Clinical Laboratory Analysis, 11, 287–313. Schroeter,H.,Heiss,C.,Balzer,J.,Kleinbongard,P.,Keen,C.L., Sorond,F.A.,Hurwitz,S.,Salat,D.H.,Greve,D.N.,&Fisher,N.D. − Hollenberg, N. K., . . . Kelm, M. (2006). ( )-Epicatechin mediates (2013). Neurovascular coupling, cerebral white matter integrity, and beneficial effects of flavonol-rich cocoa on vascular function in humans. response to cocoa in older people. Neurology, 81, 904–909. Proceedings of the National Academy of Science USA, 103, 1024–1029. https://doi.org/10.1212/WNL.0b013e3182a351aa. https://doi.org/10.1073/pnas.0510168103. Sorrenti, V., Mazza, F., Campisi, A., Di Giacomo, C., Acquaviva, R., Vanella, Self, H. L., Brown, R. R., & Price, J. M. (1960). Quantitative studies on the L., & Galvano, F. (2007). Heme oxygenase induction by metabolites of tryptophan in urine of swine. Journal of Nutrition, 70, cyanidin-3-O-β-glucoside in cultured human endothelial cells. Molecular 21–25. Nutrition and Food Reearch, 51, 580–586. https://doi.org/10.1002/ Selma, M. V., Esp´ın, J. C., & Tomas-Barb´ eran,´ F. A. (2009). Interaction mnfr.200600204. between phenolics and gut microbiota: Role in human health. Journal of Spagnuolo, C., Russo, M., Bilotto, S., Tedesco, I., Laratta, B., & Russo, G. Agricultural and Food Chemistry, 57, 6485–6501. https://doi.org/10.1021/ L. (2012). Dietary polyphenols in cancer prevention: The example of the jf902107d. flavonoid quercetin in leukemia. Annals of the New York Academy of Sciences, Serban, M. C., Sahebkar, A., Zanchetti, A., Mikhailidis, D. P., Howard, G., 1259, 95–103. https://doi.org/10.1111/j.1749-6632.2012.06599.x. Antal, D., . . . Banach, M. (2016). Effects of quercetin on blood pressure: A Speciale, A., Canali, R., Chirafisi, J., Saija, A., Virgili, F., & Cimino, F. systematic review and meta-analysis of randomized controlled trials. Journal (2010). Cyanidin-3-O-glucoside protection against TNF-alpha-induced of the American Heart Association, 5, https://doi.org/10.1161/jaha.115. endothelial dysfunction: Involvement of nuclear factor-kappaB signaling. 002713. Journal of Agricultural and Food Chemistry, 58, 12048–12054. Sesink, A. L. A., O’Leary, K. A., & Hollman, P. C. H. (2001). Quercetin https://doi.org/10.1021/jf1029515. glucuronides but not glucosides are present in human plasma after Spencer, J. P. E. (2010). The impact of fruit flavonoids on memory and consumption of quercetin-3-glucoside or quercetin-4 -glucoside. Journal of cognition. British Journal of Nutrition, 104(Suppl. S3), S40–S47. Nutrition, 131, 1938–1941. https://doi.org/10.1017/S0007114510003934. Sharma, P. K., He, M., Jurayj, J., Gou, D. M., Lombardy, R., Romanczyk, L. Spencer, J. P. E., Vafeiadou, K., Williams, R. J., & Vauzour, D. (2012). J. Jr., & Schroeter, H. (2010). Enantioselective syntheses of sulfur analogues Neuroinflammation: Modulation by flavonoids and mechanisms of action. of flavan-3-ols. Molecules, 15, 5595–5619. https://doi.org/10:3390/ Molecular Aspects of Medicine, 33, 83–97. https://doi.org/10.1016/ molecules15085595. j.mam.2011.10.016. Shaw, I. C., Hackett, A. M., & Griffiths, L. A. (1982). Metabolism and Stagg, G. V., & Millin, D. J. (1975). The nutritional and therapeutic value of + excretion of the liver-protective agent ( )-catechin in experimental tea - a review. Journal of the Science of Food and Agriculture, 26, 1439–1459. hepatitis. Xenobiotica, 12, 405–416. Stalmach, A., Mullen, W., Barron, D., Uchida, K., Yokota, T., Cavin, C., . . . Shi, Y., & Williamson, G. (2016). Quercetin lowers uric acid in Crozier, A. (2009). Metabolite profiling of hydroxycinnamate derivatives in pre-hyperuricaemic males: A randomized, double-blinded, plasma and urine after the ingestion of coffee by humans: Identification of placebo-controlled, cross-over trial. British Journal of Nutrition, 115, biomarkers of coffee consumption. Drug Metabolism and Disposition, 37, 800–806. https://doi.org/10.1017/S0007114515005310. 1749–1758. https://doi.org/10.1124/dmd.109.028019. Shils, M. E., & Goodhart, R. S. (1956). The flavonoids in biology and medicine. Stalmach, A., Mullen, W., Steiling, H., Williamson, G., Lean, M. E. J., & New York: The National Vitamin Foundation, Inc. Crozier, A. (2010). Absorption, metabolism and excretion of flavan-3-ols in Shin, J. Y., Sohn, J., & Park, K. H. (2013). Chlorogenic acid decreases retinal humans with an ileostomy. Molecular Nutrition and Food Research, 54, vascular hyperpermeability in diabetic rat model. Journal of Korean Medical 323–334. https://doi.org/10.1002/mnfr.201100566. Science, 28, 608–613. https://doi.org/10.3346/jkms.2013.28.4.608. Stalmach, A., Edwards, C. A., Wightman, J. D., & Crozier, A. (2012). Shrime, M. G., Bauer, S. R., McDonald, A. C., Chowdhury, N. H., Coltart, Gastrointestinal stability and bioavailability of (poly)phenolic compounds C. E., & Ding, E. L. (2011). Flavonoid-rich cocoa consumption affects following ingestion of Concord grape juice by humans. Molecular Nutrition multiple cardiovascular risk factors in a meta-analysis of short-term studies. Food Research, 56, 497–509. https://doi.org/10.1002/mnfr.201100566. Journal of Nutrition, 141, 1982–1988. https://doi.org/10.3945/jn.111. Stalmach, A., Edwards, C. A., Wightman, J., Crozier, A. (2013). Colonic 145482. catabolism of dietary (poly)phenolic compounds from Concord grapes. Food Siess, M. H., Guillermic, M., Le Bon, A. M., & Suschetet, M. (1989). and Function, 4, 52–62. https://doi.org/10.1039/c2fo30151b. Induction of monooxygenase and transferase activities in rat by dietary Steffen, Y., Gruber, C., Schewe, T., & Sies, H. (2008). Mono-O-methylated administration of flavonoids. Xenobiotica, 19, 1379–1386. flavanols and other flavonoids as inhibitors of endothelial NADPH oxidase. https://doi.org/10.3109/00498258909043189. Archives of Biochemistry and Biophysics, 469, 209–219. https://doi.org/ Silveira, J. Q., Cesar, T. B., Manthey, J. A., Baldwin, E. A., Bai, J., & 10.1016/jabb.2007.10.012. Raithmorere, S. (2014). Pharmacokinetics of flavanone glycosides after Steffen, Y., Schewe, T., & Sies, H. (2007). (−)-Epicatechin elevates nitric ingestion of single doses of fresh-squeezed orange juice versus commercially oxide in endothelial cells via inhibition of NADPH oxidase. Biochemical and processed orange juices in health humans. Journal of Agricultural and Food Biophysical Research Communications, 359, 828–833. https://doi.org/ Chemistry, 62, 12576–12584. https://doi.org/10.1021/jf5038163. 10.1016/j.bbrc.2007.05.200. Simoncini, T., Lenzi, E., Zochling, A., Gopal, S., Goglia, L., Russo, E., . . . Stepkowski, T. M., & Kruszewski, M. K. (2011). Molecular cross-talk Genazzani, A. R. (2011). Estrogen-like effects of wine extracts on nitric between the NRF2/KEAP1 signaling pathway, autophagy, and apoptosis.

r 1110 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.17,2018 C 2018 Institute of Food Technologists® Dietary ﬂavonoids: a historical review . . .

Free Radical Biology and Medicine, 50, 1186–1195. https://doi.org/10.1016/ of Science, USA, 108(Suppl 1), 4531–4538. freeradbiomed.2011.01.033. https://doi.org/10.1073/pnas.1000098107. Stewart, E. J. (2012). Growing unculturable bacteria. Journal of Bacteriology, van Duynhoven, J. P. M., van Velzen, E. J. J., Westerhuis, J. A., Foltz, M., 194, 4151–4160. https://doi.org/10.1128/jb.00345-12. Jacobs, D. M., & Smilde, A. K. (2012). Nutrikinetics: Concept, Stoupi, S., Williamson, G., Drynan, J. W., Barron, D., & Clifford, M. N. technologies, applications, perspectives. Trends in Food Science and Technology, (2010). Procyanidin B2 catabolism by human fecal: Partial characterization 26, 4–13. https://doi.org/10.1016/j.tifs.2012.01.004. of ‘dimeric” intermediates. Archives of Biochemistry and Biophysics, 501, van der Hooft, J. J. J., de Vos, R. C. H., Bino, R. J., Mihaleva, V., Ridder, L., 73–78. https://doi.org/10.1016/j.abb.2010.02.009. de Roo, N., . . . Vervoort, J. (2012). Structural elucidation and Sudano, I., Flammer, A. J., Roas, S., Enseleit, F., Ruschitzka, F., Corti, R., & quantification of phenolic conjugates present in human urine after tea Noll, G. (2012). Cocoa, blood pressure, and vascular function. Current intake. Analytical Chemistry, 84, 7263–7271. Hypertension Reports, 14, 279–284. https://doi.org/10.1007/s11906- https://doi.org/10.1021/ac3017339. 012-0281-8. Vallejo, F., Larrosa, M., Escudero, E., Zafrilla, M. P., Cerda,´ B., Boza, J., . . . Suganya, N., Bhakkiyalakshmi, E., Sarada, D. V., & Ramkumar, K. M. To m as-Barber´ an,´ F. A. (2010). Concentration and solubility of flavanones in (2016). Reversibility of endothelial dysfunction in diabetes: Role of orange juice beverages affect their bioavailability in humans. Journal of polyphenols. British Journal of Nutrition, 116, 223–246. Agricultural and Food Chemistry, 58, 6516–6524. https://doi.org/10.1021/ https://doi.org/10.1017/s0007114516001884. jf100752j. Takanaga, H., Ohnishi, A., Matsuo, H., & Sawada, Y. (1998). Inhibition of Varma, S. D. (1976). Inhibition of lens aldose reductase by flavonoids–their vinblastine efflux mediated by P-glycoprotein by grapefruit juice possible role in the prevention of diabetic cataracts. Biochemical Pharmacology, components in caco-2 cells. Biological and Pharmaceutical Bulletin, 21, 25, 2505–2513. 1062–1066. Vauzour, D. (2014). Effect of flavonoids on learning, memory and Talalay, P. (1989). Mechanisms of induction of enzymes that protect against neurocognitive performance: Relevance and potential implications for chemical carcinogenesis. Advances in Enzyme Regulation, 28, 237–250. Alzheimer’s disease pathophysiology. JournaloftheScienceofFoodand Agriculture, 94, 1042–1056. https://doi.org/10.1002/jsfa.6473. Tangney, C. C., & Rasmussen, H. E. (2013). Polyphenols, inflammation, and cardiovascular disease. Current Atherosclerosis Reports, 15, 324. Vendrame, S., Guglielmetti, S., Riso, P., Arioli, S., Klimis-Zacas, D., & https://doi.org/10.1007/s11883-013-0324-x. Porrini, M. (2011). Six-week consumption of a wild blueberry powder drink increases bifidobacteria in the human gut. Journal of Agricultural and Terao, J. (2009). Dietary flavonoids as antioxidants. Forum in Nutrition, 61, Food Chemistry, 59, 12815–12820. https://doi.org/10.1021/jf2028686. 87–94. https://doi.org/10.1159/000212741. Vepsalainen, S., Koivisto, H., Pekkarinen, E., Makinen, P., Dobson, G., Toh, J. Y., Tan, V. M., Lim, P. C., Lim, S. T., & Chong, M. F. (2013). McDougall, G. J., . . . Hiltunen, M. (2013). Anthocyanin-enriched bilberry Flavonoids from fruit and vegetables: A focus on cardiovascular risk factors. and blackcurrant extracts modulate amyloid precursor protein processing Current Atherosclerosis Reports, 15, 368. https://doi.org/10.1007/s11883- and alleviate behavioral abnormalities in the APP/PS1 mouse model of 013-0368-y. Alzheimer’s disease. Journal of Nutritional Biochemistry, 24, 360–370. To m as-Barber´ an,´ F. A., Cienfuegos-Jovellanos, E., Mar´ın, A., Muguerza, B., https://doi.org/10.1016/j.jnutbio.2012.07.006. Gil-Izquierdo, A., Cerda, B., . . . Espin, J. C. (2007). A new process to Vezza, T., Rodriguez-Nogales, A., Algieri, F., Utrilla, M. P., Rodriguez- develop a cocoa powder with higher flavonoid monomer content and Cabezas, M. E., & Galvez, J. (2016). Flavonoids in inflammatory bowel enhanced bioavailability in healthy humans. Journal of Agricultural and Food disease: A review. Nutrients, 8, 211. https://doi.org/10.3390/nu8040211. Chemistry, 55, 3926–3935. https://doi.org/10.1021/jf070121. Vladutiu, G. D., & Middleton, E., Jr. (1986). Effects of flavonoids on enzyme To m as-Navarro,´ M., Vallejo, F., Sentandreu, E., Navarro, J. L., & Tomas-´ secretion and endocytosis in normal and mucolipidosis II fibroblasts. Life Barberan,´ F. A. (2014). Volunteers stratification is more relevant than Sciences, 39, 717–726. technological treatment of orange juice flavanone bioavailability. Journal of Agricultural and Food Chemistry, 62, 24–27. Vuong, Q. V. (2014). Epidemiological evidence linking tea consumption to https://doi.org/10.1021/jf4048989. human health: A review. Critical Reviews in Food Science and Nutrition, 54, 523–536. https://doi.org/10.1080/10408398.2011.594184. Tomasian, D., Keaney, J. F., & Vita, J. A. (2000). Antioxidants and the bioactivity of endothelium-derived nitric oxide. Cardiovascular Research, 47, Wallace, T. C. (2011). Anthocyanins in cardiovascular disease. Advances in 426–435. Nutrition, 2,1–7.https://doi.org/10.3945/an.110.000042. Tonelo, D., Providencia, R., & Goncalves, L. (2013). Holiday heart Wallace, T. C., Slavin, M., & Frankenfeld, C. L. (2016). Systematic review of syndrome revisited after 34 years. Arquivos Brasileiros de Cardiologia, 101, anthocyanins and markers of cardiovascular disease. Nutrients, 8, 183–189. https://doi.org/10.5935/abc.20130153. https://doi.org/10.3390/nu8010032. Trevisanato, S. I., & Kim, Y. I. (2000). Tea and health. Nutrition Reviews, 58, Walle, U. K., French, K. L., Walgren, R. A., & Walle, T. T. (1999). Transport 1–10. of genistein-7-glucoside by human intestinal Caco-2 cells: Potential role for MRP2. Research Communications in Molecular Pathology and Pharmacology, 103, Trichopoulou, A., Vasilopoulou, E., & Lagiou, A. (1999). Mediterranean diet 45–56. and coronary heart disease: Are antioxidants critical? Nutrition Reviews, 57, 253–255. Wang, Z. Y., Cheng, S. J., Zhou, Z. C., Athar, M., Khan, W. A., Bickers, D. R., & Mukhtar, H. (1989). Antimutagenic activity of green tea Tsuji, P. A., Stephenson, K. K., Wade, K. L., Liu, H., & Fahey, J. W. (2013). polyphenols. Mutatation Research, 223, 273–285. Structure-activity analysis of flavonoids: Direct and indirect antioxidant, and antiinflammatory potencies and toxicities. Nutrition and Cancer, 65, Wang, C., Schramm, D. D., Holt, R. R., Ensunsa, J. L., Fraga, C. G., 1014–1025. https://doi.org/10.1080/01635581.2013.809127. Schmitz, H. H., & Keen, C. L. (2000). A dose-response effect from chocolate consumption on plasma epicatechin and oxidative damage. Journal Tzounis, X., Vulevic, J., Kuhnle, G. G., George, T., Leonczak, J., Gibson, G., of Nutrition, 130(Supple. 8), S2109–S2114. . . . Spencer, J. P. E. (2008). Flavanol monomer-induced changes to the human faecal microflora. British Journal of Nutrition, 99, 782–792. Wang, X., Wolkoff, A. W., & Morris, M. E. (2005). Flavonoids as a novel https://doi.org/10.1017/s0007114507853384. class of human organic anion-transporting polypeptide OATP1B1 (OATP-C) modulators. Drug Metabolism and Disposition, 33, 1666–1672. Urpi-Sarda, M., Rothwell, J., Morand, C., & Manach, C. (2012). https://doi.org/10.1124/dmd.105.005926. Bioavailability of flavanones. In J. P. E. Spencer & A. Crozier (Eds.), Flavonoids and related compounds. Bioavailability and function (pp. 1–44). Boca Wang, D., Wei, X., Yan, X., Jin, T., & Ling, W. (2010). Protocatechuic acid, Raton: CRC Press. a metabolite of anthocyanins, inhibits monocyte adhesion and reduces atherosclerosis in apolipoprotein E-deficient mice. Journal of Agricultural and Ursini, F., Tubaro, F., Rong, J., & Sevanian, A. (1999). Optimization of Food Chemistry, 58, 12722–12728. https://doi.org/10.1021/jf103427j. nutrition: Polyphenols and vascular protection. Nutrition Reviews, 57, 241–249. https://doi.org/10.1111/j.1753-4887.1999.tb06951.x. Wang, J., Ferruzi, M. G., Ho, L., Blount, J., Janie, E. M., Gong, B., . . . Pasinetti, G. M. (2012). Brain-targeted proanthocyanidin metabolites for Vafeiadou, K., Vauzour, D., & Spencer, J. P. (2007). Neuroinflammation and Alzheimer’s disease treatment. Journal of Neuroscience, 32, 5144–5150. its modulation by flavonoids. Endocrine Metabolism and Immune Disorders - https://doi.org/10.1523/jneurosci.6437-11.2012. Drug Targets, 7, 211–224. https://doi.org/10.2174/187153007781662521. Wang, X., Ouyang, Y. Y., Liu, J., & Zhao, G. (2014). Flavonoid intake and van Duynhoven, J., Vaughan, E. E., Jacobs, D. M., Kemperman, R. A., van risk of CVD: A systematic review and meta-analysis of prospective cohort Velzen, E. J., Gross, G., . . . Van de Wiele, T. (2011). Metabolic fate of studies. British Journal of Nutrition, 111, 1–11. polyphenols in the human superorganism. Proceedings of the National Academy https://doi.org/10.1017/s000711451300278x.

r C 2018 Institute of Food Technologists® Vol.17,2018 ComprehensiveReviewsinFoodScienceandFoodSafety 1111 Dietary ﬂavonoids: a historical review . . .

Wang, Y., Huang, Q., Liu, J., Wang, Y., Zheng, G., Lin, L., . . . Huang, Z. Wood, A. W., Smith, D. S., Chang, R. L., Huang, M. T., & Conney, A. H. (2017). Vascular endothelial growth factor A polymorphisms are associated (1986). Effects of flavonoids on the metabolism of xenobiotics. Progress in with increased risk of coronary heart disease: A meta-analysis. Oncotarget, 8, Clinical and Biological Resesrch, 213, 195–210. 30539–30551. https://doi.org/10.18632/oncotarget.15546. Wright, E. M., Loo, D. D., & Hirayama, B. A. (2011). Biology of human Wardyn, J. D., Ponsford, A. H., & Sanderson, C. M. (2015). Dissecting sodium glucose transporters. Physiological Reviews, 91, 733–794. molecualr cross-talk between Nrf2 and NF-κB resposne pathways. https://doi.org/10.1152/physrev.00044.2009. Biochemical Society Transactions, 43, 621–626, https://doi.org/10,1042/ Wu, X., Cao, G., & Prior, R. L. (2002). Absorption and metabolism of BST20150014. anthocyanins in elderly women after consumption of elderberry or Warner, E. F., Zhang, Q., Raheem, K. S., O’Hagan, D., O’Connell, M. A., blueberry. Journal of Nutrition, 132, 865–871. & Kay, C. D. (2016). Common phenolic metabolites of flavonoids, but not Xu, J. W., Ikeda, K., & Yamori, Y. (2004a). Cyanidin-3-glucoside regulates their unmetabolized precursors, reduce the secretion of vascular cellular phosphorylation of endothelial nitric oxide synthase. FEBS Letter, 574, adhesion molecules by human endothelial cells. Journal of Nutrition, 146, 176–180. https://doi.org/10.1016/j.febslet.2004.08.027. 465–473. https://doi.org/10.3945/jn.115.217943. Xu, J. W., Ikeda, K., & Yamori, Y. (2004b). Upregulation of endothelial Warner, E. F., Smith, M. J., Zhang, Q., Raheem, K. S., O’Hagan, D., nitric oxide synthase by cyanidin-3-glucoside, a typical anthocyanin O’Connell, M. A., & Kay, C. D. (2017). Signatures of anthocyanin pigment. Hypertension, 44, 217–222. https://doi.org/10.1161/01.HYP. metabolites identified in humans inhibit biomarkers of vascular 0000135868.38343.c6. inflammation in human endothelial cells. Molecular Nutrition and Food Research, https://doi.org/10.1002/mnfr.201700053. Xu,J.W.,Ikeda,K.,Kobayakawa,A.,Ikami,T.,Kayano,Y.,Mitani,T.,& Yamori, Y. (2005). Downregulation of Rac1 activation by caffeic acid in Welch, A. A., & Hardcastle, A. C. (2014). The effects of flavonoids on bone. aortic smooth muscle cells. Life Sciences, 76, 2861–2872. Current Osteoporosis Reports, 12, 205–210. https://doi.org/10.1007/ https://doi.org/10.1016/j.lfs.2004.11.015. s11914-014-0212-5. Yang, C. S., Lee, M. J., Chen, L., & Yang, G. Y. (1997). Polyphenols as Welch, I. M., Cunningham, K. M., & Read, N. W. (1988). Regulation of inhibitors of carcinogenesis. Environment Health Perspectives, 105(Suppl. 4), gastric emptying by ileal nutrients in humans. Gastroenterology, 94, 401–404. 971–976. Welton, A. F., Hurley, J., & Will, P. (1988). Flavonoids and arachidonic acid Yang, C. S., Chung, J. Y., Yang, G. Y., Li, C., Meng, X., & Lee, M. J. (2000). metabolism. Progress in Cliical and Bioogical Research, 280, 301–312. Mechanisms of inhibition of carcinogenesis by tea. Biofactors, 13, 73–79. Wenzel, E., & Somoza, V. (2005). Metabolism and bioavailability of https://doi.org/10.1002/biof.55201301114. trans-resveratrol. Molecular Nutrition and Food Research, 49, 472–481. Yang, J. H., Hsia, T. C., Kuo, H. M., Chao, P. D., Chou, C. C., Wei, Y. H., https://doi.org/10.1002/mnfr.200500010. & Chung, J. G. (2006). Inhibition of lung cancer cell growth by quercetin Whitley, A. C., Sweet, D. H., & Walle, T. (2005). The dietary polyphenol glucuronides via G2/M arrest and induction of apoptosis. Drug Metabolism ellagic acid is a potent inhibitor of hOAT1. Drug Metabolism and Disposition, and Disposition, 34, 296–304. https://doi.org/10.1124/dmd.105.005280. 33, 1097–1100. https://doi.org/10.1124/dmd.105.004275. Yang, H., Xiao, L., & Wang, N. (2017). Peroxisome proliferator-activated Wightman, J. D., & Heuberger, R. A. (2015). Effect of grape and other receptor alpha ligands and modulators from dietary compounds: Types, berries on cardiovascular health. Journal of the Science of Food and Agriculture, screening methods and functions. Journal of Diabetes, 9, 341–352. 95, 1584–1597. https://doi.org/10.1002/jsfa.6890. https://doi.org/10.1111/1753-0407.12506. Williamson, G. (2013). Possible effects of dietary polyphenols on sugar Yasumatsu, K., Nakayama, T., & Chichester, C. (1965). Flavonoids of absorption. Molecular Nutrition and Food Research, 57, 48–57. sorghum. Journal of Food Science, 30, 663–667. https://doi.org/10.1002/mnfr.201200511. Youdim, K. A., McDonald, J., Kalt, W., & Joseph, J. A. (2002). Potential role Williamson, G., & Clifford, M. N. (2010). Colonic metabolites of berry of dietary flavonoids in reducing microvascular endothelium vulnerability to polyphenols: The missing link to biological activity? British Journal of oxidative and inflammatory insults. Journal of Nutritional Biochemistry, 13, Nutrition, 104(Suppl 3), S48–S66. https://doi.org/10.1017/ 282–288. https://doi.org/S0955286301002212. S0007114510003946. Zamora-Ros, R., Jimenez, C., Cleries, R., Agudo, A., Sanchez, M. J., Williamson, G., & Clifford, M. N. (2017). Role of the small intestine, colon, Sanchez-Cantalejo, E., . . . Gonzalez, C. A. (2013). Dietary flavonoid and and microbiota in determining the metabolic fate of polyphenols. Biochemical lignan intake and mortality in a Spanish cohort. Epidemiology, 24, 726–733. Pharmacology, 139, 24–39. https://doi.org/10.1016/j.bcp.2017.03.012. https://doi.org/10.1097/EDE.0b013e31829d5902. Williamson, G., & Manach, C. (2005). Bioavailability and bioefficacy of Zhang, S., Yang, X., & Morris, M. E. (2004). Flavonoids are inhibitors of polyphenols in humans. II. Review of 93 intervention studies. American breast cancer resistance protein (ABCG2)-mediated transport. Molecular Journal of Clinical Nutrition, 81(Suppl. 1), 243S–255S. Pharmacology 200, 65, 1208–1216. https://doi.org/10.1124/mol.65.5.1208. Williamson, G., Barron, D., Shimoi, K., & Terao, J. (2005). In vitro Zhang, M., Jagdmann, G. E., Van Zandt, M., Beckett, P., & Schroeter, H. biological properties of flavonoid conjugates found in vivo. Free Radical (2013a). Enantioselective synthesis of orthogonally protected (2R,3R)- Research, 39, 457–469. https://doi.org/10.1080/10715760500053610. (−)-epicatechin derivatives, key intermediates in the de novo chemical − Williamson, G., Aeberli, I., Miguet, L., Zhang, Z., Sanchez, M. B., Crespy, synthesis of ( )-epicatechin glucuronides and sulfates. Tetrahedron V., . . . Grigorov, M. (2007). Interaction of positional isomers of quercetin Asymmetry, 24, 362–373. https://doi.org/10.1016/j.tetasy.2013.02.012. glucuronides with the transporter ABCC2 (cMOAT, MRP2). Drug Zhang, M., Jagdmann, G. E., Van Zandt, M., Sheeler, R., Beckett, P., & Metabolism and Disposition, 35, 1262–1268. https://doi.org/10.1124/ Schroeter, H. (2013b). Chemical synthesis and characterization of dmd.106.014241. epicatechin glucuronides and sulfates: Bioanalytical standards for epicatechin Wiseman, S. A., Balentine, D. A., & Frei, B. (1997). Antioxidants in tea. metabolite indentification. Journal of Natural Products, 76, 157–169. Critical Reviews in Food Science and Nutrition, 37, 705–718. https://doi.org/ https://doi.org/10.1021/np300568m. 10.1080/10408399709527798. Zhong, S., Sandu, A., Edirisinghe, I., & Burton-Freeman, B. (2017). Wittig, J., Herderich, M., Graefe, E. U., & Veit, M. (2001). Indentification of Characterization of wild blueberry polyphenols bioavailability and kinetic quercetin glucuronides in human plasma by high-performance liquid profile in plasma over 24-h period in human subjects. Molecular Nutrition chromatography-tandem mass spectrometry. Journal of Chromatography B, Food Research, https://doi.org/10.1002/mnfr.201700405. 753, 237–243. Zhou, B., Xiao, J. F., & Ressom, H. W. (2012). LC-MS-based metabolomics. Wong, C. C., Barron, D., Orfila, C., Dionisi, F., Krajcsi, P., & Williamson, G. Molecular Systems, 8, 470–481. https://doi.org/10.1039/c1mb05350g. (2011a). Interaction of hydroxycinnamic acids and their conjugates with Zhou, Y., Zheng, J., Li, Y., Xu, D. P., Li, S., Chen, Y. M., & Li, H. B. organic anion transporters and ATP-binding cassette transporters. Molecular (2016). Natural polyphenols for prevention and treatment of cancer. Nutrition Food Research, 55, 979–988. https://doi.org/1010.1002/mnfr. Nutrients, 8, 1–35. https://doi.org/10.3390/nu8080515. 201000652 Ziberna, L., Lunder, M., Tramer, F., Drevensek, G., & Passamonti, S. (2013). Wong, C. C., Botting, N. P., Orfila, C., Al-Maharik, N., & Williamson, G. The endothelial plasma membrane transporter bilitranslocase mediates rat (2011b). Flavonoid conjugates interact with organic anion transporters aortic vasodilation induced by anthocyanins. Nutrition, Metabolism, and (OATs) and attenuate cytotoxicity of adefovir mediated by organic anion Cardiovascular Disease, 23, 68–74. transporter 1 (OAT1/SLC22A6). Biochemical Pharmacology, 81, 942–949. https://doi.org/10.1016/j.numecd.2011.02.005. https://doi.org/10.1016/bcp.2011.01.004. Zilva, S. S. (1937). Vitamin P. Biochemical Journal, 31, 915–919.

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