Adisa et al Tropical Journal of Pharmaceutical Research, September 2008; 7 (3): 1089-1099 © Pharmacotherapy Group, Faculty of Pharmacy, University of Benin, Benin City, 300001 Nigeria. All rights reserved . Available online at http://www.tjpr.org Review Article Flavonoids as Nutraceuticals: A Review AR Tapas *1 , DM Sakarkar 1, and RB Kakde 2 1Department of Pharmaceutical Chemistry, Sudhakarrao Naik Institute of Pharmacy, Pusad- 445204, Dist.-Yavatmal (Maharashtra INDIA), 2University Department of Pharmaceutical Sciences, R.T.M. Nagpur University, Nagpur- 440033, Maharashtra, INDIA. Abstract Phenolic compounds form one of the main classes of secondary metabolites. They display a large range of structures and are responsible for the major organoleptic characteristics of plant-derived foods and beverages, particularly color and taste properties. They also contribute to the nutritional qualities of fruits and vegetables. Among these compounds, flavonoids constitute one of the most ubiquitous groups of plant phenolics. Owing to their importance in food organoleptic properties and human health, a better understanding of their structures and biological activities indicates their potentials as therapeutic agents and also for predicting and controlling food quality. Due to the variety of pharmacological activities in the mammalian body, flavonoids are more correctly referred as “nutraceuticals”. Keywords: Bioflavonoids, Structure-Classification, Nutraceuticals, Antimicrobial activities, Anti-oxidant activity, Metabolic effects *Corresponding author: Email: [email protected]; Tel:+91 07233 247308; +91 09325377391 1089 Trop J Pharm Res, September 2008; 7 (3) Tapas et al INTRODUCTION (2) and the isoflavones derivatives (6) : the Phenolic compounds constitute one of the pterocarpans and the rotenoids 6. The different main classes of secondary metabolites. They ways to close this ring associated with the display a large range of structures and they different oxidation degrees of ring A provide are responsible for the major organoleptic the various classes of flavonoids. characteristics of plant-derived foods and The six-membered ring condensed with the beverages, particularly color and taste benzene ring is either a γ-pyrone (flavones (1) properties and they also contribute to the flavonols (3)) or its dihydroderivative (flavanones nutritional qualities of fruits and vegetables. (4) and flavan-3-ols (5)). The position of the benzenoid substituent divides the flavonoids into The most important natural pigments are two classes: flavonoids (1) (2-position) and carotenoids which are tetrapyrrole derivatives isoflavonoids (6) (3-position). Most flavonoids occur of naturally occurring phenolic compounds naturally associated with sugar in conjugated form ubiquitously distributed in plant kingdom. and, within any one class, may be characterized as Among these compounds, flavonoids monoglycosidic, diglycosidic, etc. The glycosidic constitute one of the most ubiquitous groups linkage is normally located at position 3 or 7 and the carbohydrate unit can be L-rhamnose, D- of all plant phenolics. So far, over 8,000 8 varieties of flavonoids have been identified 1. glucose, glucorhamnose, galactose or arabinose . Until ~50 years ago, information on the working mechanisms of flavonoids was scare. FLAVONOIDS AS NUTRACEUTICAL “Nutraceutical” is a term coined in 1979 by But it has been widely known for centuries 9 that compounds of plant origin possess a Stephen DeFelice . It is defined “as a food or broad spectrum of biological activity 2. In 1930, parts of food that provide medical or health Szent-Gyorgyi isolated a new substance from benefits, including the prevention and oranges and classified it as vitamin P but treatment of disease.” Nutraceuticals may later, it became clear that this substance was range from isolated nutrients, dietary actually a flavonoid 3. Flavonoids drew greater supplements, and diets to genetically attention from researchers with the discovery engineered “designer” food, herbal products, of the French Paradox, i.e., the decrease and processed products such as cereals, incidence of cadio-vascular disease observed soups, and beverages. A nutraceutical is any in the Mediterranean population which was nontoxic food extract supplement that has scientifically proven health benefits for both associated with red wine consumption, and a 10 greater amount of saturated fat the average the treatment and prevention of disease . diet than in other countries 3. The increasing interest in nutraceuticals reflects the fact that consumers hear about STRUCTURE AND CLASSIFICATION OF epidemiological studies indicating that a FLAVONOIDS specific diet or component of the diet is Flavonoids occur as aglycones, glycosides associated with a lower risk for a certain and methylated derivatives 4. In plants, disease. flavonoids aglycones (i.e., flavonoids without The major active nutraceutical ingredients in attached sugar) occur in a variety of structural plants are flavonoids. As is typical for phenolic forms. All contain fifteen carbon atoms in their compounds, they can act as potent basic nucleus: two six-membered rings linked antioxidants and metal chelators. They also with a three carbon unit which may or may not have long been recognized to possess anti- be a part of a third ring 5. For convenience, the inflammatory, antiallergic, hepatoprotective, rings are labeled A, B, and C (see Fig 1). The antithrombotic, antiviral, and anticarcinogenic individual carbon atoms are based on a activities, as discussed in the subsections that numbering system which uses ordinary follow: numerals for the A and C and “primed” Antioxidant activity numerals for B-ring (1) . Primed modified The best-described property of almost every numbering system is not used for chalcones group of flavonoids is their capacity to acts as 1090 Trop J Pharm Res September 2008; 7 (3) Tapas et al 3' O 2' 4' OH O 8 1 B O 2 5' 7 A C 6' OH 6 3 4 O O 5 O 3-Hydroxy-2-phenyl 2-Phenyl-chroman-4-one O 1-(2-Hydroxy-phenyl)- -chromen-4-one (Flavanone) 2-Phenyl-chromen-4-one 3-phenyl-propenone (Flavonol) 4 (Flavone) (Chalcone) 3 1 2 O O O+ O OH OH O O 3-Hydroxy-2-phenyl- OH 3-Hydroxy-2-phenyl- 2-Phenyl-chroman-3-ol chromenylium 3-Phenyl-chromen-4-one (Anthocyanidine) chroman-4-one (Flavan-3-ols) (Isoflavone) (Flavanonol) Flavylium Salt 5 6 8 7 Fig.1: Chemical structures of some representative flavonoids antioxidants. The flavones and catechins catechin > 5,7-dihydroxy-3’,4’,5’-trimethoxy- seem to be the most powerful flavonoids for flavone > robinin > kaempferol > flavone 17 . protecting the body against reactive oxygen Antimicrobial activity species (ROS). Body cells and tissues are Flavonoids and esters of phenolic acids have continuously threatened by the damage also been investigated for their antibacterial, caused by free radicals and ROS which are antifungal and antiviral activities. produced during normal oxygen metabolism or are induced by exogeneous damage 11,12 . Antibacterial activity Free radicals and ROS have been implicated Antibacterial activity has been displayed by a in a large number of human diseases 13,14 . number of flavonoids. Quercetin has been Quercetin, kaempferol, morin, myricetin and reported to completely inhibit the growth of rutin, by acting as antioxidants, exhibited Staphylococcus aureus . Most of the beneficial effects such as anti-inflammatory, flavonones having no sugar moiety showed antiallergic, antiviral, as well as anticancer antimicrobial activities whereas none of the activity. They have also been suggested to flavonols and flavonolignans tested showed play a protective role in liver diseases, inhibitory activity on microorganisms 23 . cataracts, and cardiovascular diseases. Antifungal activity Quercetin and silybin, acting as free radical scavengers, were shown to exert a protective A number of flavonoids isolated from the effect in liver reperfusion ischemic tissue peelings of tangerine orange, when tested for 15,16 fungistatic activity towards Deuterophoma damage . The scavenging activity of tracheiphila were found to be active; nobiletin flavonoids has been reported to be in the order: Myrcetin > quercetin > rhamnetin > and langeritin exhibited strong and weak morin > diosmetin > naringenin > apigenin > activities, respectively, while hesperidin could stimulate fungal growth slightly. Chlorflavonin 1091 Trop J Pharm Res September 2008; 7 (3) Tapas et al 3' 2' 4' 8 1 B O O 5' O+ 7 2 6' A C 6 3 OH 4 OH 5 (Flavan-3-ols) O Flavylium Salt Fig. 2: General structures for various classes of flavonoids Table 1: Substitution patterns of series of flavonoids Group 3 5 6 7 8 3’ 4’ 5’ C2=C 3 Flavones Apigenin H OH H OH H H OH H + Diosmin H OH H Oru H OH OH H + Luteolin H OH H OH H OH OH H + Flavonol Quercetin OH OH H OH H OH OH H + Kaempferol OH OH H OH H H OH H + Galangin OH OH H OH H H H H + Fisetin OH H H OH H OH OH H + Myricetin OH OH H OH H OH OH OH + Vitexicarpin OCH 3 OH OCH OCH 3 H OH OCH 3 H + Flavanone Naringenin H OH H OH H H OH H - Eriodictyol H OH OH OH H OH OH H - Pinocembrin H OH H OH H H H H - Liquiritigenin H H H OH H H OH H - Flavanonol Taxifolin H OH H OH H OH OH H - Isoflavone Genistein - OH H OH H H OH H + Tectorigenin - OH OCH 3 OH H H OH H + Daidzein - H H OH H H OH H + Formononetin - H H OH H H OCH 3 H + Flavan-3-ols (+) Catechin βOH OH H OH H OH OH H - (-) Epicatechin αOH OH H OH H OH OH H - (-) Epigallocatechin αOH OH H OH H OH OH OH - Flavylium Salts Cyanidin OH OH H OH H OH OH H - Pelargonidine OH OH H OH H H OH H - was the first chlorine-containing flavonoid-type Antiviral activity antifungal antibiotic produced by strains of 24 Naturally occurring flavonoids with antiviral Aspergillus candidus . activity have been recognized since the 1940s 1092 Trop J Pharm Res September 2008; 7 (3) Tapas et al but only recently have attempts been made to Some recent studies have indicated that make synthetic modifications of natural flavonoids possess antiulcerogenic activity.