Effect of melatonin on myocardial susceptibility to ischaemia and reperfusion damage in a rat model of high-fat diet-induced obesity

[摘要] ENGLISH ABSTRACT: Obesity has reached epidemic proportions worldwide and is currently a serious health problem.It is associated with metabolic abnormalities, oxidative stress, hypertension, insulin resistanceand an increased disposition for the development of cardiovascular disease.Elucidation of the pathophysiological mechanisms underlying obesity and its relationship withmetabolic and cardiovascular diseases is essential for prevention and management of thesedisorders. Melatonin, the pineal gland hormone, is a powerful antioxidant and has been shownto protect the myocardium against ischaemia/reperfusion (I/R) injury. Long- as well as shorttermmelatonin treatment also reversed several of the harmful effects of obesity in an animalmodel of hyperphagia-induced obesity (DIO). However, its effects on myocardial I/R injuryand intracellular signalling in obesity induced by a high fat diet (HFD) are still unknown.Aims of study: (i) To evaluate the ability of a high fat diet (HFD) to induce obesity in rats. Apart fromevaluating its effects on the biometric parameters and resistance to ischaemia/reperfusioninjury (as indicated by infarct size in regional ischaemia and functional recovery afterglobal ischaemia), special attention will be given on the interplay between adiponectin,AMPK, leptin, and FFA in this model.(ii) To evaluate the effect of daily oral administration of melatonin to rats on the HFD as wellas their littermate controls, on the parameters listed above as well as on the developmentof obesity. In this study melatonin will be administered from the onset of the feeding ofthe high fat diet.Methods:Male Wistar rats were divided into 4 groups: (i) control rats (receiving normal rat chow) (C);(ii) control rats receiving melatonin (CM); (iii) obese rats (receiving HFD) (HFD); (iv) obeserats receiving melatonin (HM). Animals were kept on the diet for 16 weeks and melatonintreatment (10mg/kg/day, added to the drinking water) started at the onset of the feeding.Following feeding and treatment, the animals were grouped into fasted/ non-fasted of whichbiometric parameters were recorded and blood collected at the time of sacrifice for metabolicand biochemical assays. Hearts were perfused in the working mode for evaluation ofmyocardial function and infarct size determination after exposure to 35min regionalischaemia/60min reperfusion. For study of intracellular signaling, hearts were perfused in theworking mode, subjected to 20min global ischaemia/10min reperfusion and freeze-clamped for Western blotting. Plasma leptin, adiponectin, free fatty acid, triglycerides, total cholesterol,phospholipids, conjugated dienes and thiobarbituric reactive substances (TBARS) levels weredetermined. Several kinases were investigated including, the RISK (reperfusion injury salvagekinase) (PKB/Akt and ERK p44/42) and SAFE (survivor activating factor enhancement)(STAT-3) pathways, AMPK and JNK under baseline conditions or following 10 minreperfusion. In addition, expression of UCP-3 and PGC1-α was determined.Results:Significant increases in body weight, visceral fat, blood glucose, insulin, HOMA index andleptin and a reduction in adiponectin levels were observed in the fasted high fat diet (HFD)group when compared with controls (C). Significant increases in free fatty acid and triglyceridelevels were also noted the HFD group while other serum lipid parameters, including TBARS,remained unchanged. No differences in functional recovery during reperfusion or infarct sizeafter exposure to 35 min regional ischaemia, as well as functional recovery during reperfusionafter 20 min global ischaemia were observed between the control and HFD groups. Baselineand 10 min reperfusion data were similar for the RISK and SAFE pathway kinases for thecontrol vs HFD groups. The HFD also had no effect on the expression and phosphorylation ofmyocardial AMPK and JNK, as well as on the expression of UCP-3 and PGC1-α, whencompared to the controls. Treatment with melatonin significantly reduced body weight, visceralfat, blood glucose, HOMA index and serum leptin levels in HFD treated groups, while havingno effect on the lipid profile. Although melatonin significantly reduced infarct size in bothcontrol [% of area at risk: 20.59 ± 2.29 (CM) vs 38.08 ± 2.77 (C)] and high-fat diet groups [%of area at risk: 11.43 ± 2.94 (HM) vs 38.06 ± 3.59 (H)], it was without effect on myocardialfunctional recovery during reperfusion. Melatonin had no effect on the intracellular signalingpathways studied.Conclusions:The HFD proved to be a useful model of diet-induced obesity with a more pronounced impacton biometric and metabolic changes compared to the DIO model. Long-term melatonintreatment successfully prevented the development of metabolic abnormalities associated withthe high fat diet and obesity as well as significantly reduced myocardial infarct size. Themechanisms involved in melatonin-induced cardioprotection in obesity have not been fullyelucidated in this study and require further investigation. However, the anti-obesogenic andcardioprotective properties of melatonin were very significant indeed and support thesuggestion of this hormone as a potential tool in the treatment of obesity and associatedcardiovascular complications.

[发布机构] Stellenbosch University