Browsing by Author "Kaskar, Rafee'ah"
Now showing 1 - 1 of 1
Results Per Page
- ItemEffect of melatonin on myocardial susceptibility to ischaemia and reperfusion damage in a rat model of high-fat diet-induced obesity(Stellenbosch : Stellenbosch University, 2015-12) Kaskar, Rafee'ah; Lochner, Amanda; Huisamen, Barbara; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Medical Physiology.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 resistance and an increased disposition for the development of cardiovascular disease. Elucidation of the pathophysiological mechanisms underlying obesity and its relationship with metabolic and cardiovascular diseases is essential for prevention and management of these disorders. Melatonin, the pineal gland hormone, is a powerful antioxidant and has been shown to protect the myocardium against ischaemia/reperfusion (I/R) injury. Long- as well as shortterm melatonin treatment also reversed several of the harmful effects of obesity in an animal model of hyperphagia-induced obesity (DIO). However, its effects on myocardial I/R injury and 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 from evaluating its effects on the biometric parameters and resistance to ischaemia/reperfusion injury (as indicated by infarct size in regional ischaemia and functional recovery after global 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 well as their littermate controls, on the parameters listed above as well as on the development of obesity. In this study melatonin will be administered from the onset of the feeding of the 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) obese rats receiving melatonin (HM). Animals were kept on the diet for 16 weeks and melatonin treatment (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 which biometric parameters were recorded and blood collected at the time of sacrifice for metabolic and biochemical assays. Hearts were perfused in the working mode for evaluation of myocardial function and infarct size determination after exposure to 35min regional ischaemia/60min reperfusion. For study of intracellular signaling, hearts were perfused in the working 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 were determined. Several kinases were investigated including, the RISK (reperfusion injury salvage kinase) (PKB/Akt and ERK p44/42) and SAFE (survivor activating factor enhancement) (STAT-3) pathways, AMPK and JNK under baseline conditions or following 10 min reperfusion. In addition, expression of UCP-3 and PGC1-α was determined. Results: Significant increases in body weight, visceral fat, blood glucose, insulin, HOMA index and leptin 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 triglyceride levels were also noted the HFD group while other serum lipid parameters, including TBARS, remained unchanged. No differences in functional recovery during reperfusion or infarct size after exposure to 35 min regional ischaemia, as well as functional recovery during reperfusion after 20 min global ischaemia were observed between the control and HFD groups. Baseline and 10 min reperfusion data were similar for the RISK and SAFE pathway kinases for the control vs HFD groups. The HFD also had no effect on the expression and phosphorylation of myocardial AMPK and JNK, as well as on the expression of UCP-3 and PGC1-α, when compared to the controls. Treatment with melatonin significantly reduced body weight, visceral fat, blood glucose, HOMA index and serum leptin levels in HFD treated groups, while having no effect on the lipid profile. Although melatonin significantly reduced infarct size in both control [% 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 myocardial functional recovery during reperfusion. Melatonin had no effect on the intracellular signaling pathways studied. Conclusions: The HFD proved to be a useful model of diet-induced obesity with a more pronounced impact on biometric and metabolic changes compared to the DIO model. Long-term melatonin treatment successfully prevented the development of metabolic abnormalities associated with the high fat diet and obesity as well as significantly reduced myocardial infarct size. The mechanisms involved in melatonin-induced cardioprotection in obesity have not been fully elucidated in this study and require further investigation. However, the anti-obesogenic and cardioprotective properties of melatonin were very significant indeed and support the suggestion of this hormone as a potential tool in the treatment of obesity and associated cardiovascular complications.