Diabetic Cardiomyopathy: the Case for a Role of Fructose in Disease Etiology

Diabetes Volume 65, December 2016 3521

Lea M.D. Delbridge,1 Vicky L. Benson,2 Rebecca H. Ritchie,3 and Kimberley M. Mellor1,2,4

Diabetic Cardiomyopathy: The Case for a Role of Fructose in Disease Etiology

Diabetes 2016;65:3521–3528 | DOI: 10.2337/db16-0682

A link between excess dietary sugar and cardiac disease as a specific myocardial pathology, the occurrence of which is clearly evident and has been largely attributed to is independent of coronary and hypertensive disease. Di- systemic metabolic dysregulation. Now a new paradigm abetic cardiomyopathy is generally characterized by early is emerging, and a compelling case can be made that signs of diastolic dysfunction, which precede progression to fructose-associated heart injury may be attributed to the systolic failure (6,7). direct actions of fructose on cardiomyocytes. Plasma While the relationship between excess fructose exposure and cardiac fructose levels are elevated in patients with and cardiac disease development has been identified, the DIABETES IN PERSPECTIVES diabetes, and evidence suggests that some unique underlying mechanisms are as yet only partially under- fi properties of fructose (vs. glucose) have speci c car- stood. Aspects of diabetic cardiomyopathy that may be diomyocyte consequences. Investigations to date have attributed specifically to high fructose intake or to selective demonstrated that cardiomyocytes have the capacity to myocardial fructose metabolic dysregulation have not been transport and utilize fructose and express all of the determined. Whether cardiac vulnerability associated with necessary proteins for fructose metabolism. When dietary fructose intake is elevated and myocardial glucose fructose exposure produces an injury response beyond uptake compromised by insulin resistance, increased effects that may be attributed to general overnutrition or fi cardiomyocyte fructose flux represents a hazard in- to overall excess consumption of re ned sugar (either volving unregulated glycolysis and oxidative stress. The glucose or fructose) in different diabetic settings is also high reactivity of fructose supports the contention that not yet known (8,9). fructose accelerates subcellular hexose sugar-related In this Perspective, these questions relating to fructose, protein modifications, such as O-GlcNAcylation and ad- diabetes, and the heart are examined, and the case for a role vanced glycation end product formation. Exciting recent of fructose in diabetic cardiomyopathy disease etiology is discoveries link heart failure to induction of the specific explored. Evidence to support the proposition that fructose high-affinity fructose-metabolizing enzyme, fructokinase, is a distinctive cardiopathogenic agent in diabetes and in an experimental setting. In this Perspective, we review states of metabolic disturbance is considered. Findings from key recent findings to synthesize a novel view of fructose a diverse range of investigative approaches are reviewed to as a cardiopathogenic agent in diabetes and to identify synthesize a novel view of fructose (of exogenous and en- important knowledge gaps for urgent research focus. dogenous origin) as a perpetrator of cardiac damage. New insights into fructose-induced myocardial functional and signaling dysregulation are discussed, and knowledge gaps Links between excess fructose consumption, diabetes in- for priority research focus are identified. cidence, and cardiovascular disease risk have been clearly demonstrated (1–4). The systemic effects of high fructose DIETARY FRUCTOSE AND CARDIOMYOPATHY intake have been well described experimentally and include Dietary Fructose Increases Cardiovascular Risk hyperglycemia, dyslipidemia, atherosclerosis, and in some The dramatic rise in the prevalence of diabetes has oc- cases hypertension (5). Diabetic cardiomyopathy is recognized curred in parallel with an escalation in dietary sugar

1Department of Physiology, University of Melbourne, Victoria, Australia Received 31 May 2016 and accepted 9 September 2016. 2 Department of Physiology, University of Auckland, Auckland, New Zealand © 2016 by the American Diabetes Association. Readers may use this article as 3 Heart Failure Pharmacology, Baker IDI Heart and Diabetes Institute, Victoria, long as the work is properly cited, the use is educational and not for profit, and the Australia work is not altered. More information is available at http://www.diabetesjournals 4 Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand .org/content/license. Corresponding author: Lea M.D. Delbridge, [email protected]. 3522 Fructose-Induced Cardiac Pathology Diabetes Volume 65, December 2016 consumption. In “westernized” cultures, the use of added results in metabolic dysregulation and cell death vulnera- sweeteners containing fructose(sucroseandhigh-fructose bility. Rodents fed a high-fructose diet for several months corn syrup) has increased by approximately 25% over the display significant decreases in the levels of phosphory- past three decades (10). Meta-analyses of cohort studies lated Akt (Ser473) and the downstream signaling inter- have determined that high intake of fructose-sweetened mediate S6 (Ser235/236) with decreased PI3K activity beverages is associated with a 26% greater risk of cardio- and phosphorylation of Akt (19,20). Interestingly, insulin metabolic pathology (2). Experimental studies of hepatic growth factor 1 (IGF1) and IGF1 receptor expression are fructose metabolism have shown that genetically modified both decreased in this setting, suggesting involvement rodents unable to metabolize fructose (fructokinase knock- from the IGF1 signaling pathway in addition to insulin- out) are protected from high-carbohydrate–induced meta- receptor–mediated effects (20). Fructose feeding also di- bolic syndrome, supporting the contention that fructose is minishes cardiac glucose uptake (21). Thus despite elevated the toxic component of the sugar complex (11,12). Although extracellular glucose levels, intracellular glucose availability increased cardiovascular disease risk may be partially attrib- is reduced, which is associated with upregulation of cardiac uted to fructose-induced dyslipidemia, atherosclerosis, hy- lipid derivatives and transporters (22), indicative of a sub- pertension, obesity, or insulin resistance/diabetes/metabolic strate shift from glucose to fatty acids for energy supply. syndrome (13,14), it is increasingly apparent that fructose- Energetic disturbances may manifest as triggers for oxi- specific cardiac factors are important. Recent studies have dative stress in response to excess dietary fructose (23). demonstrated that dietary fructose is not necessarily asso- Mitochondrial uncoupling is evident in hearts of fructose- ciated with changes in blood pressure (15), and the relation- fed rodents (24) and is associated with elevated myocar- ship between high sugar intake and increased risk for both dial production of reactive oxygen species (25). Impaired type 2 diabetes and cardiovascular disease is independent of glucose uptake and utilization has also been linked to an BMI (2,16), which indicates that calorie intake and adipose inability to respond to an ischemic challenge. In contrast deposition are not the underlying etiology. to controls, fructose-fed animals do not increase cardiomyo- Emerging evidence suggests that cardiac complications cyte GLUT4 translocation and glycolytic flux in response to in patients with diabetes (and their attenuation) are not ischemia (26), a response deficit that may underlie chronic alwayslinkedtothedegreeofbloodglucosecontrol.Meta- ischemic vulnerability in diabetic settings. Interestingly, two analyses of large randomized controlled clinical trials report studies have reported smaller infarct size in isolated hearts that drugs used to lower blood glucose levels in patients with from fructose-fed rats (27,28), suggesting that metabolic diabetes may exacerbate heart failure symptoms and in- adaptation involving modified routes of cardiomyocyte crease the risk of heart failure (17,18). While some glucose- hexose sugar uptake may actually have a role in acute lowering agents (metformin, emphafliglozin) have been cardioprotection. shown to be cardioprotective in patients with diabetes, others do not improve cardiac dysfunction and can lead Dietary Fructose–Induced Cardiac Cell Loss to increased heart failure risk (e.g., peroxisome proliferator– and Dysfunction activated receptor agonists, dipeptidyl peptidase 4 inhibitors, Downregulation of the cardiomyocyte PI3K/Akt “cell sur- thiazolidinediones). Thus negative cardiac impacts in di- vival’’ pathway can promote cell death signaling as inhibi- abetes involve mechanisms not necessarily responsive to tion of programmed cell death pathways via the PI3K/Akt normalization of circulating glucose levels. As cardiac tis- axis is relieved. Fructose feeding in rodents is associated sue is both insulin sensitive and glycolysis dependent, with low-level constitutive loss of cardiomyocytes coupled increased cardiac vulnerability to fructose in the context with increased collagen deposition, producing a progressive of metabolic dysregulation is plausible (5) and supported fibrotic replacement of viable myocardium (19). In feeding by an accumulating experimental evidence base. As empha- interventions where the metabolic disturbance is moderate, sized in important recent commentaries (4,12), although of apoptotic signaling pathways are not found to be activated caloric equivalence, fructose and glucose are very different but autophagy markers are significantly upregulated (19). sugars. The consequences of these differences in relation to Autophagy, a subcellular phagolysosomal degradation process, diet-induced dysregulation of cardiomyocyte signaling, me- is essential for physiological turnover of macromolecules and tabolism, and energetics are considered below. organelles. Sustained, high-level autophagic activity is considered deleterious and is associated with induction of a Myocardial Metabolic Dysregulation With High Dietary nonapoptotic form of programmed cell death (29–31). Fructose Intake More work is required to establish the nature of the links Myocardial signaling adaptations in response to high between dietary fructose, cardiomyocyte loss, and induc- dietary fructose intake are reported. In animal models, tissue tion of autophagy triggers. In rodent models where the insulin resistance is evident, characterized by downregulation extent of myocardial metabolic disturbance that develops of the phosphoinositide 3-kinase (PI3K)/Akt insulin sig- in response to high-fructose feeding is more severe, acti- naling pathway (19). The PI3K/Akt pathway regulates GLUT4 vation of apoptotic signaling is evident (20). These findings translocation, glucose uptake, and cardiac cell growth and suggest that loss of cardiomyocyte viability with fructose survival, and thus suppression of this major signaling nexus insult may be mediated initially through autophagic pathways, diabetes.diabetesjournals.org Delbridge and Associates 3523 subsequently transitioning to apoptotic demise as cardio- that fructose has direct cardiomyocyte “assault” access pathology progresses. (36). Although not yet well characterized in cardiac tis- The myocardial functional consequences of high fructose sues, increased fructose metabolic flux has the potential intake have not been extensively studied. Some insights to cause damage as a consequence of increased conversion have been gained from in vivo (hemodynamic) analyses and of fructose to F1P. In noncardiac tissues, this reaction from in vitro cardiomyocyte contractility and Ca2+ handling step results in the ultimate production of uric acid and studies. In vivo left ventricular dysfunction is evident in is linked with cell nucleotide depletion (4,38). Further rodents administered fructose drinking solution (10%) for investigation is required to fully characterize the extent only 2 weeks, as characterized by reduced left ventricular and regulation of fructose fuel usage in the heart in both end-systolic elastance (a measure of intrinsic left ventricular physiological and pathophysiological circumstances. contractility independent of preload, afterload, and heart Endogenous fructose production is also potentially a rate) (32). In cardiomyocytes isolated from fructose-fed major factor in determining local exposure to this hexose mice, a marked Ca2+ handling disturbance is observed, even sugar. In hepatic and renal tissues, there is clear evidence with maintenance of twitch contractile performance (33). of significant endogenous fructose production via aug- Contractile myofilament sensitivity to Ca2+ is increased by mented polyol pathway throughput (conversion of glucose high fructose intake (33), which may have important im- to fructose via sorbitol) in disease states (11,39). Condi- plications for impaired relaxation and diastolic dysfunction tions of enhanced polyol activity in myocardial tissues are in vivo. There is also recent evidence that high fructose less well described, but an important observation is that intake increases cardiomyocyte arrhythmogenic suscepti- myocardial fructose content is measured to be 60-fold bility. Cardiomyocytes obtained from animals exposed to higher in diabetic rats (40). This observation supports fructose drinking solution exhibit Ca2+ handling defects, the proposition that stimulated intracellular production with increased instability of internal Ca2+ stores associ- of fructose via the polyol pathway in the diabetic heart ated with spontaneous arrhythmogenic events (34). may also be significant and pathological. A recent pivotal Collectively these clinical and experimental studies dem- report has demonstrated that cardiac fructose uptake, onstrate the negative impacts of high fructose intake on transporter expression, and content are elevated in three myocardial structural and functional integrity— effects that mouse models of heart failure (1-kidney-1-clip [1K1C], may not necessarily be contingent on systemic or cardiac transverse aortic constriction [TAC], and chronic isopro- insulin resistance. Evidence suggests that the unique prop- terenol perfusion) and in cardiac biopsies from humans erties of fructose, which differentiate this hexose sugar with aortic stenosis and hypertrophic cardiomyopathy from glucose, have selective cardiomyocyte metabolic con- (37).Crucially,thefinding that cardiac-specificknockdown sequences that undermine cellular integrity. These specific of Sf3b1, a positive regulator of fructokinase (C isoform, also aspects of fructose action are considered below. known as ketohexokinase-C), attenuates 1K1C- and TAC- induced elevated cardiac fructose levels and cardiac dysfunc- SPECIFIC MYOCARDIAL FRUCTOSE ACTIONS tion and hypertrophy (37) demonstrates a central role for Cardiomyocyte Fructose Exposure—A Central Role fructose metabolism in cardiac pathology. This study also in Cardiac Pathology? determined that TAC-induced cardiac dysfunction was pre- Although systemic fructose levels are maintained within vented in global fructokinase knockout mice (37), a model the micromolar range by hepatic clearance of absorbed previously reported to exhibit elevated plasma fructose levels fructose, plasma fructose concentration is elevated in (11). Thus cardioprotection was achieved despite cardiomyo- patients with diabetes (35). Thus it is feasible that elevated cyte exposure to elevated plasma fructose. These findings plasma fructose levels exert cardiomyocyte influence. Work suggest that direct negative effects of fructose exposure on with isolated cardiomyocytes has demonstrated that these cardiomyocytes may be dependent on the pathological set- cells have the capacity to transport and utilize exogenously ting and involvement of hepatic fructose dysregulation (e.g., supplied fructose. A key study has shown that the high- extent of concomitant insulin resistance/diabetes, increased affinity fructose-specific transporter, GLUT5, is expressed lactic acid, increased uric acid). Clearly more work is needed in adult rat cardiomyocytes (36). Importantly GLUT5- to elucidate the hepatic dependent and independent aspects mediated glucose uptake is negligible, and thus the operation of myocardial fructose vulnerability. of this transporter is not influenced by fructose-glucose com- Increased intracellular fructose availability has the petition. In isolated cardiomyocytes, the contractile deficit potential to significantly modify cardiomyocyte metabolic induced by inhibition of glucose oxidation is abrogated by processes. In contrast to the tightly regulated process of fructose supplementation, providing direct evidence that glucose metabolism, fructose can bypass the glycolytic cardiomyocyte fructose uptake and utilization is operational rate-limiting enzyme, phosphofructokinase, and proceed (36). Production of fructose 1-phosphate (F1P) from exoge- through glycolysis to pyruvate and lactate end products nous fructose has been demonstrated in cultured neonatal in a relatively unregulated manner (41). Accumulation of cardiomyocytes using 13C-radiolabeled fructose (37). These lactate in particular has been shown to have adverse ef- findings not only establish that fructose has a role in acute fects in cardiomyocytes (42). Fructose can also enter the modulation of cardiomyocyte fuel usage but also confirm hexosamine biosynthesis pathway (HBP) to generate uridine 3524 Fructose-Induced Cardiac Pathology Diabetes Volume 65, December 2016 diphosphate (UDP)-GlcNAc, the precursor for O-GlcNAcylation (see below). The importance of the HBP in myocardial metabolic control and disease vulnerability is increasingly recognized (43,44). Regulatory factors that deter- mine the balance between glycolytic and HBP fructose flux have not yet been identified. Qualitative and quan- titative shifts in cardiomyocyte fructose shunting likely play an important role in determining the impacts of altered intracellular fructose on cardiomyocytes. New metabolic studies in this area will be especially informative in relation to understanding adverse actions of cardiomyocyte fructose metabolism. In particular the application of metabolic tracing methodologies to track fructose uptake and/or production and disposal in pathophysiological conditions will yield valuable insights (45).

Fructose and Cardiomyocyte O-GlcNAcylation in the Heart O-GlcNAcylation is a major posttranslational modification involved in normal physiological signaling regulation and has also been implicated in a number of pathological processes (43,46). O-GlcNAcylation is a dynamic/reversible covalent attachment of an O-GlcNAc moiety onto serine or threonine residues of target proteins, catalyzed by O-GlcNAc transferase, and its removal is catalyzed by O-GlcNAcase. Attach- ment of the O-GlcNAc substrate can influence transcription, translation, nuclear transport, and cell signaling, and there is evidence of interaction and/or competition for the Figure 1—Pathways of glucose- and fructose-mediated O-GlcNAcylation target amino acid residues between phosphorylation and and glycolysis. Fructose phosphorylation by hexokinase to F6P directly O O provides substrate for the HBP. Glucose phosphorylation by glucoki- -GlcNAcylation (47,48). -GlcNAcylation has been iden- nase or hexokinase to glucose 6-phosphate (G6P) also produces F6P. tified as an important mediator of diabetic heart pathol- Fructose can also be phosphorylated by fructokinase to F1P and can ogy. Promotion of O-GlcNAc removal by overexpression then be further metabolized to generate F6P via dihydroxyacetone of O-GlcNAcase restores contractile function and Ca2+ han- phosphate (DHAP) or glyceraldehyde (GA), both of which can be converted to glyceraldehyde 3-phosphate (G3P), fructose 1,6-bisphos- dling in cardiomyocytes of diabetic rodents (47). More recently, phate (F16BP), and F6P. G3P is also a substrate for glycolysis to it has been demonstrated that specific O-GlcNAcylation of produce end products lactate and acetyl-CoA. F6P enters the gly- Ca2+-dependent calmodulin kinase II, a key regulator of colytic pathway via conversion to F16BP, a step catalyzed by the myocyte Ca2+ cycling and contractility, mediates cardiac dys- rate-limiting enzyme, phosphofructokinase (PFK). The HBP produces UDP-GlcNAc, and O-GlcNAc transferase (OGT) catalyzes the attach- function and arrhythmias in diabetic hearts (49). Thus ment of O-GlcNAc to a serine or threonine amino acid residue in a O-GlcNAcylation may prove to be an effective thera- protein. LDH, lactate dehydrogenase; PDH, pyruvate dehydrogenase. peutic target in diabetic cardiomyopathy. While glucose has been established as the main con- O fi tributor toward -GlcNAcylation, recent ndings suggest O that fructose may also play a significant role. Fructose can cardiomyocyte glucose- and fructose-induced -GlcNAcylation be converted to fructose 6-phosphate (F6P), the substrate activity in vitro has yet to be reported. In human hepa- tocarcinoma HepG2 lineage cells, incubation with either for the HBP, providing for consequent production of O UDP-O-GlcNAc. This conversion is either via direct phos- glucose or fructose produces a similar increase in UDP- - fi GlcNAc levels in a 24-h period (51). Although involving non- phorylation of fructose by hexokinase to F6P (low af n- fi ity) (50,51) or via phosphorylation of fructose to F1P by cardiac cell types, these ndings are consistent with the fructokinase, followed by generation of F6P involving contention that fructose can act as a substrate for the HBP and subsequent O-GlcNAcylation. These data suggest that intermediate steps via dihydroxyacetone phosphate or O glyceraldehyde, glyceraldehyde-3-phosphate, and fructose fructose can induce -GlcNAcylation to a similar extent as glucose, but further work with cardiac cell types and map- 1,6-biphosphate (51), as detailed in Fig. 1. Literature O reporting the direct effects of fructose on the HBP and ping fructose-induced -GlcNAc to downstream cardiac con- O-GlcNAcylation is limited, and measurement of fructose sequences using in vivo experimental models is required. metabolic flux into the HBP is warranted. Left ventricular Fructose-Induced Glycation of Cardiac Proteins tissues from fructose-fed rodents exhibit significant elevation In contrast to the dynamic, regulated nature of O-GlcNAcylation in the level of O-GlcNAcylation (52). Direct comparison of reactions, advanced glycation end products (AGEs) are adducts diabetes.diabetesjournals.org Delbridge and Associates 3525 produced from the irreversible nonenzymatic glycation Heyns products (a fructose homolog to the glucose- and oxidation of proteins and lipids. Clinical and experi- derived Amadori product) (58). Fructose naturally exists mental studies have demonstrated an association between in its open-chain conformation more often than glucose AGE formation and dysfunction in the diabetic heart (63), which promotes faster glycation kinetics (58,62,64). (53,54). In general, literature has focused on extracellular Hence, the conversion of Heyns products into Fru-AGEs AGEs and in particular the cross-linking of collagen resulting occurs more rapidly than the conversion of the glucose in myocardial stiffness and diastolic dysfunction of extracel- equivalent, which has significant implications for greater lular matrix origin. There is some evidence that intracellular Fru-AGE production (65). Glu-AGEs are thought to be AGEs may also elicit significant impact on cardiomyocyte developed over periods ranging from weeks to months, function (55,56). whereas Fru-AGE formation is believed to be much more AGEs are formed from the attachment of a single hexose rapid (Fig. 2) (62,64) and subsequently may have more molecule by its aldehyde group to the NH2-terminal of a severe protein damage outcomes. New investigative initia- basic amino acid residue (usually lysine or arginine) to tives are required to understand the pathological impor- form a Schiff base (57). Schiff bases are then rearranged tance of Fru-AGEs and Glu-AGEs in the myocardium and into Amadori products, which can develop into reactive thecardiomyocyte.Indiabeticcardiomyocytes, Glu-AGEs are intermediates such as 3-deoxyglucosone and glyoxal (58). detected even on short-lived proteins involved in electrome- A series of oxidation-based Maillard reactions involving chanical transduction and Ca2+ handling (55,56), with chemical cleavage, cross-linking, and conformational change reported half-life times of 3–8 days (66,67). Given the transform the reactive intermediates into irreversible AGEs established timelines of AGE formation, this suggests that (57),asdetailedinFig.2.Notonlydothereducingproper- AGEs may impair protein turnover—a positive feedback ties of the bound AGE alter protein structure and function, scenario that would facilitate even more extensive AGE for- but AGEs can also bind to cell membranes via receptors for mation. In a cellular environment where fructose-driven AGEs (RAGEs) to activate signaling cascades involving oxi- AGE formation is particularly promoted, the accumulation dative stress, pathological growth, and induction of cell death of Fru-AGE adducts conferring functional and structural de- processes (53,59,60). The combination of hyperglycemia and formation of affected proteins could be much accelerated. reactive oxygen species in the diabetic heart provides a con- Using novel Fru-AGE antibodies, it has been demon- ducive environment for extracellular AGE production. strated that patients with type 1 diabetes exhibit fourfold AGE formation within the extracellular matrix of the higher serum Fru-AGE levels than patients without non- diabetic heart has been mostly attributed to hyperglycemia diabetes (65). No studies to date have directly explored the (53,61). But with evidence of intracellular AGEs in the presence of intracellular Fru-AGEs in cardiomyocytes, but context of impaired glucose uptake in diabetic cardiomyo- some literature from in vitro studies working with purified cytes, a recognition of the importance of alternative sub- proteins and using noncardiomyocyte cell culture experiments strates for AGE production, including fructose, is emerging. is available. In experiments involving incubation of purified In vitro studies with purified proteins have shown that proteins with fructose, it has been shown that Fru-AGE for- fructose-related AGEs (Fru-AGEs) are more reactive than mation is increased in parallel with significant modification of their Glu-AGE equivalents (62,63). Fructose can undergo the protein function. In these experiments, Fru-AGE forma- nonenzymatic condensation with protein amino groups to tion is found to be markedly more rapid and/or more exten- form Schiff bases in a similar manner to glucose (58,62,63), sive than Glu-AGE formation and renders the protein more which subsequently undergo Heyns rearrangement to form resistant to biological enzymatic breakdown (62,64,65,68). In a noncardiac cell culture system, when gene transfer methods are used to promote intracellular fructose synthesis by stim- ulation of the polyol pathway, a coincident increase in the level of intracellular Fru-AGEs is observed (65). Together these various experimental approaches demonstrate that intracellular formation of Fru-AGEs may be an important pathophysiological event with specific cellular structural and functional adverse outcomes. Exploration of the role of cardiomyocyte Fru-AGE formation as a substrate of heart damage, particularly in the context of high cardiac fructose in diabetes, is required. The development of selective and sensitive molecular tools for identifying fructose-specific adduct types will allow new research, mapping the evolution of Figure 2—Fructose- and glucose-derived AGE formation. Both fruc- fructose-dependent AGE pathology in the myocardium. tose and glucose covalently attach to lysine or arginine residues in peptides to form a Schiff base. These attachments can rearrange to OVERVIEW AND NEW DIRECTIONS form Amadori products and Heyns products for glucose and fructose, respectively. Fru-AGEs are produced from AGE precursors faster Consideration of the literature from epidemiological, clinical, (days to weeks) than glucose-derived adducts (weeks to months). and experimental perspectives provides an abundance of 3526 Fructose-Induced Cardiac Pathology Diabetes Volume 65, December 2016 evidence attesting to fructose participation in the etiology As urgent investigation priorities, fructose-driven AGE of diabetic cardiomyopathy—including involvement in formation and O-GlcNAcylation processes, as well as the cardiac metabolic, structural, and electromechanical involvement of these events in inflicting cardiac damage, pathologies. The findings indicate that when dietary are highlighted. New studies that track diabetic disease provocation is a factor in diabetes induction, fructose induction and parameters of cardiac function mapped (more than glucose) constitutes a particular “toxic” sugar against shifts in systemic and myocardial fructose han- challenge. Moreover, in the insulin-resistant/deficient dling are required. Defining the pathophysiological attri- diabetic cardiac milieu, abnormalities in fructose metabo- butes of the fructose-damaged heart can potentially lism have the potential to contribute directly to myocardial provide impetus in establishing a case for dietary fructose disease evolution. Bringing together key clinical and intake limitation as a cardioprotective measure. Charac- experimental observations, the evidence suggests that terizing the role of cardiomyocyte fructose dysregulation dysregulated tissue fructose metabolism, and not specifi- in the development of diabetic cardiomyopathy will pro- cally systemic glycemic exposure, is associated with the vide a substrate for identifying targeted interventions to ultimate progression of diabetic cardiomyopathy to car- achieve damage remediation. diac failure state. Fructose is increasingly recognized as a critical cellular energy intermediate and signaling agent in many cell types. Acknowledgments. We acknowledge Brendan Ma from the University of The available evidence suggests that cardiomyocyte fruc- Melbourne and Andrew Lim from the University of Auckland for their assistance in tose vulnerability could arise from exposure to elevated the early stages of literature compilation for manuscript development. We extracellular fructose (both direct and indirect conse- acknowledge funding support from the Diabetes Australia Research Trust. Duality of Interest. No potential conflicts of interest relevant to this article quences of dietary conditions) and to augmented in- were reported. tracellular fructose production (with polyol synthetic pathway involvement). In particular fructose-driven extra- References cellular and intracellular posttranslational modifications, 1. Dhingra R, Sullivan L, Jacques PF, et al. Soft drink consumption and risk of which exert both dynamic and permanent influence on developing cardiometabolic risk factors and the metabolic syndrome in middle- myocardial structure and function (Fig. 3), have been iden- aged adults in the community. Circulation 2007;116:480–488 tified as potential pathological provocateurs. 2. Malik VS, Popkin BM, Bray GA, Després JP, Willett WC, Hu FB. Sugar- sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis. Diabetes Care 2010;33:2477–2483 3. DiNicolantonio JJ, O’Keefe JH, Lucan SC. Added fructose: a principal driver of type 2 diabetes mellitus and its consequences. Mayo Clin Proc 2015;90:372–381 4. Johnson RJ, Nakagawa T, Sanchez-Lozada LG, et al. Sugar, uric acid, and the etiology of diabetes and obesity. Diabetes 2013;62:3307–3315 5. Mellor KM, Ritchie RH, Davidoff AJ, Delbridge LM. Elevated dietary sugar and the heart: experimental models and myocardial remodeling. Can J Physiol Pharmacol 2010;88:525–540 6. Boudina S, Abel ED. Diabetic cardiomyopathy revisited. Circulation 2007; 115:3213–3223 7. Jia G, DeMarco VG, Sowers JR. Insulin resistance and hyperinsulinaemia in diabetic cardiomyopathy. Nat Rev Endocrinol 2016;12:144–153 8. Jia G, Aroor AR, Martinez-Lemus LA, Sowers JR. Overnutrition, mTOR signaling, and cardiovascular diseases. Am J Physiol Regul Integr Comp Physiol 2014;307:R1198–R1206 9. Bugger H, Abel ED. Molecular mechanisms of diabetic cardiomyopathy. Diabetologia 2014;57:660–671 10. Marriott BP, Cole N, Lee E. National estimates of dietary fructose intake increased from 1977 to 2004 in the United States. J Nutr 2009;139:1228S–1235S 11. Lanaspa MA, Ishimoto T, Li N, et al. Endogenous fructose production and metabolism in the liver contributes to the development of metabolic syndrome. Nat Commun 2013;4:2434 12. Lyssiotis CA, Cantley LC. Metabolic syndrome: F stands for fructose and fat. Nature 2013;502:181–182 13. Rippe JM, Angelopoulos TJ. Fructose-containing sugars and cardiovascular disease. Adv Nutr 2015;6:430–439 14. Stanhope KL, Medici V, Bremer AA, et al. A dose-response study of con- suming high-fructose corn syrup-sweetened beverages on lipid/lipoprotein risk fac- Figure 3—Potential pathways of direct fructose-induced cardiomyo- tors for cardiovascular disease in young adults. Am J Clin Nutr 2015;101:1144–1154 cyte actions. Fructose can enter cardiomyocytes via the GLUT5 fructose-specifictransporterandbeproducedfromglucoseviathepolyol 15. Angelopoulos TJ, Lowndes J, Sinnett S, Rippe JM. Fructose containing pathway to participate in AGE protein damage, O-GlcNAcylation of sugars do not raise blood pressure or uric acid at normal levels of human signaling proteins, and glycolytic disturbance. consumption. J Clin Hypertens (Greenwich) 2015;17:87–94 diabetes.diabetesjournals.org Delbridge and Associates 3527

16. Malik VS, Popkin BM, Bray GA, Després JP, Hu FB. Sugar-sweetened 37. Mirtschink P, Krishnan J, Grimm F, et al. HIF-driven SF3B1 induces KHK-C beverages, obesity, type 2 diabetes mellitus, and cardiovascular disease risk. to enforce fructolysis and heart disease. Nature 2015;522:444–449 Circulation 2010;121:1356–1364 38. Jia G, Aroor AR, Whaley-Connell AT, Sowers JR. Fructose and uric acid: is 17. Udell JA, Cavender MA, Bhatt DL, Chatterjee S, Farkouh ME, Scirica BM. there a role in endothelial function? Curr Hypertens Rep 2014;16:434 Glucose-lowering drugs or strategies and cardiovascular outcomes in patients 39. Lanaspa MA, Ishimoto T, Cicerchi C, et al. Endogenous fructose production with or at risk for type 2 diabetes: a meta-analysis of randomised controlled and fructokinase activation mediate renal injury in diabetic nephropathy. J Am trials. Lancet Diabetes Endocrinol 2015;3:356–366 Soc Nephrol 2014;25:2526–2538 18. Castagno D, Baird-Gunning J, Jhund PS, et al. Intensive glycemic control 40. Kashiwagi A, Obata T, Suzaki M, et al. Increase in cardiac muscle fructose has no impact on the risk of heart failure in type 2 diabetic patients: evidence content in streptozotocin-induced diabetic rats. Metabolism 1992;41:1041–1046 from a 37,229 patient meta-analysis. Am Heart J 2011;162:938–948.e2 41. Mayes PA. Intermediary metabolism of fructose. Am J Clin Nutr 1993;58 19. Mellor KM, Bell JR, Young MJ, Ritchie RH, Delbridge LM. Myocardial (Suppl.):754S–765S autophagy activation and suppressed survival signaling is associated with insulin 42. Kalogeris T, Baines CP, Krenz M, Korthuis RJ. Cell biology of ischemia/ resistance in fructose-fed mice. J Mol Cell Cardiol 2011;50:1035–1043 reperfusion injury. Int Rev Cell Mol Biol 2012;298:229–317 20. Cheng SM, Cheng YJ, Wu LY, et al. Activated apoptotic and anti-survival 43. McLarty JL, Marsh SA, Chatham JC. Post-translational protein modification effects on rat hearts with fructose induced metabolic syndrome. Cell Biochem by O-linked N-acetyl-glucosamine: its role in mediating the adverse effects of Funct 2014;32:133–141 diabetes on the heart. Life Sci 2013;92:621–627 21. Perret P, Slimani L, Briat A, et al. Assessment of insulin resistance in 44. Lauzier B, Vaillant F, Merlen C, et al. Metabolic effects of glutamine on the fructose-fed rats with 125I-6-deoxy-6-iodo-D-glucose, a new tracer of glucose heart: anaplerosis versus the hexosamine biosynthetic pathway. J Mol Cell transport. Eur J Nucl Med Mol Imaging 2007;34:734–744 Cardiol 2013;55:92–100 22. Huang JP, Cheng ML, Wang CH, Shiao MS, Chen JK, Hung LM. High- 45. Ruiz M, Gélinas R, Vaillant F, Lauzier B, Des Rosiers C. Metabolic tracing fructose and high-fat feeding correspondingly lead to the development of lysoPC- using stable isotope-labeled substrates and mass spectrometry in the perfused associated apoptotic cardiomyopathy and adrenergic signaling-related cardiac mouse heart. Methods Enzymol 2015;561:107–147 hypertrophy. Int J Cardiol 2016;215:65–76 46. Marsh SA, Collins HE, Chatham JC. Protein O-GlcNAcylation and cardio- 23. Mellor KM, Ritchie RH, Delbridge LM. Reactive oxygen species and insulin- vascular (patho)physiology. J Biol Chem 2014;289:34449–34456 resistant cardiomyopathy. Clin Exp Pharmacol Physiol 2010;37:222–228 47. Hu Y, Belke D, Suarez J, et al. Adenovirus-mediated overexpression of O-GlcNAcase 24. Lou PH, Lucchinetti E, Zhang L, et al. Loss of IntralipidÒ- but not sevo- improves contractile function in the diabetic heart. Circ Res 2005;96:1006–1013 flurane-mediated cardioprotection in early type-2 diabetic hearts of fructose-fed 48. Belke DD. Swim-exercised mice show a decreased level of protein rats: importance of ROS signaling. PLoS One 2014;9:e104971 O-GlcNAcylation and expression of O-GlcNAc transferase in heart. J Appl Physiol 25. Mellor K, Ritchie RH, Meredith G, Woodman OL, Morris MJ, Delbridge LM. (1985) 2011;111:157–162 High-fructose diet elevates myocardial superoxide generation in mice in the 49. Erickson JR, Pereira L, Wang L, et al. Diabetic hyperglycaemia activates absence of cardiac hypertrophy. Nutrition 2010;26:842–848 CaMKII and arrhythmias by O-linked glycosylation. Nature 2013;502:372–376 26. Morel S, Berthonneche C, Tanguy S, et al. Early pre-diabetic state alters 50. Medrano A, García-Gil N, Ramió L, et al. Hexose-specificity of hexokinase adaptation of myocardial glucose metabolism during ischemia in rats. Mol Cell and ADP-dependence of pyruvate kinase play important roles in the control of Biochem 2005;272:9–17 monosaccharide utilization in freshly diluted boar spermatozoa. Mol Reprod Dev 27. Jordan JE, Simandle SA, Tulbert CD, Busija DW, Miller AW. Fructose-fed 2006;73:1179–1194 rats are protected against ischemia/reperfusion injury. J Pharmacol Exp Ther 51. Hirahatake KM, Meissen JK, Fiehn O, Adams SH. Comparative effects of 2003;307:1007–1011 fructose and glucose on lipogenic gene expression and intermediary metabolism 28. Joyeux-Faure M, Rossini E, Ribuot C, Faure P. Fructose-fed rat hearts are in HepG2 liver cells. PLoS One 2011;6:e26583 protected against ischemia-reperfusion injury. Exp Biol Med (Maywood) 2006; 52. Hecker PA, Mapanga RF, Kimar CP, et al. Effects of glucose-6-phosphate 231:456–462 dehydrogenase deficiency on the metabolic and cardiac responses to obesogenic 29. Mellor KM, Reichelt ME, Delbridge LM. Autophagy anomalies in the diabetic or high-fructose diets. Am J Physiol Endocrinol Metab 2012;303:E959–E972 myocardium. Autophagy 2011;7:1263–1267 53. Candido R, Forbes JM, Thomas MC, et al. A breaker of advanced glycation 30. Mellor KM, Bell JR, Ritchie RH, Delbridge LM. Myocardial insulin resistance, end products attenuates diabetes-induced myocardial structural changes. Circ metabolic stress and autophagy in diabetes. Clin Exp Pharmacol Physiol 2013;40: Res 2003;92:785–792 56–61 54. van Heerebeek L, Hamdani N, Handoko ML, et al. Diastolic stiffness of the 31. Mellor KM, Reichelt ME, Delbridge LM. Autophagic predisposition in the failing diabetic heart: importance of fibrosis, advanced glycation end products, insulin resistant diabetic heart. Life Sci 2013;92:616–620 and myocyte resting tension. Circulation 2008;117:43–51 32. Chang KC, Liang JT, Tseng CD, et al. Aminoguanidine prevents fructose- 55. Bidasee KR, Nallani K, Yu Y, et al. Chronic diabetes increases advanced induced deterioration in left ventricular-arterial coupling in Wistar rats. Br J glycation end products on cardiac ryanodine receptors/calcium-release channels. Pharmacol 2007;151:341–346 Diabetes 2003;52:1825–1836 33. Mellor KM, Wendt IR, Ritchie RH, Delbridge LM. Fructose diet treatment in mice 56. Bidasee KR, Zhang Y, Shao CH, et al. Diabetes increases formation of induces fundamental disturbance of cardiomyocyte Ca2+ handling and myofilament advanced glycation end products on Sarco(endo)plasmic reticulum Ca2+-ATPase. responsiveness. Am J Physiol Heart Circ Physiol 2012;302:H964–H972 Diabetes 2004;53:463–473 34. Sommese L, Valverde CA, Blanco P, et al. Ryanodine receptor phosphory- 57. Cho SJ, Roman G, Yeboah F, Konishi Y. The road to advanced glycation end lation by CaMKII promotes spontaneous Ca(2+) release events in a rodent model products: a mechanistic perspective. Curr Med Chem 2007;14:1653–1671 of early stage diabetes: The arrhythmogenic substrate. Int J Cardiol 2016;202: 58. Schalkwijk CG, Stehouwer CD, van Hinsbergh VW. Fructose-mediated non- 394–406 enzymatic glycation: sweet coupling or bad modification. Diabetes Metab Res Rev 35. Kawasaki T, Akanuma H, Yamanouchi T. Increased fructose concentrations 2004;20:369–382 in blood and urine in patients with diabetes. Diabetes Care 2002;25:353–357 59. Hou X, Hu Z, Xu H, et al. Advanced glycation endproducts trigger autophagy in 36. Mellor KM, Bell JR, Wendt IR, Davidoff AJ, Ritchie RH, Delbridge LM. cadiomyocyte via RAGE/PI3K/AKT/mTOR pathway. Cardiovasc Diabetol 2014;13:78 Fructose modulates cardiomyocyte excitation-contraction coupling and Ca²⁺ 60. Yan D, Luo X, Li Y, et al. Effects of advanced glycation end products on handling in vitro. PLoS One 2011;6:e25204 calcium handling in cardiomyocytes. Cardiology 2014;129:75–83 3528 Fructose-Induced Cardiac Pathology Diabetes Volume 65, December 2016

61. Liu J, Masurekar MR, Vatner DE, et al. Glycation end-product cross-link 65. Takeuchi M, Iwaki M, Takino J, et al. Immunological detection of fructose- breaker reduces collagen and improves cardiac function in aging diabetic heart. derived advanced glycation end-products. Lab Invest 2010;90:1117–1127 Am J Physiol Heart Circ Physiol 2003;285:H2587–H2591 66. Ferrington DA, Krainev AG, Bigelow DJ. Altered turnover of calcium regu- 62. Suárez G, Rajaram R, Oronsky AL, Gawinowicz MA. Nonenzymatic glycation latory proteins of the sarcoplasmic reticulum in aged skeletal muscle. J Biol of bovine serum albumin by fructose (fructation). Comparison with the Maillard Chem 1998;273:5885–5891 reaction initiated by glucose. J Biol Chem 1989;264:3674–3679 67. Shimura M, Minamisawa S, Takeshima H, et al. Sarcalumenin alleviates 63. Bunn HF, Higgins PJ. Reaction of monosaccharides with proteins: possible stress-induced cardiac dysfunction by improving Ca2+ handling of the sarco- evolutionary signiﬁcance. Science 1981;213:222–224 plasmic reticulum. Cardiovasc Res 2008;77:362–370 64. McPherson JD, Shilton BH, Walton DJ. Role of fructose in glycation and 68. Sakai M, Oimomi M, Kasuga M. Experimental studies on the role of fructose cross-linking of proteins. Biochemistry 1988;27:1901–1907 in the development of diabetic complications. Kobe J Med Sci 2002;48:125–136