glucagon-like peptide-1 (GLP-1) and oxidative stress in rats. Rats were fed casein (C) or sardine protein (S) with or without high-fructose (HF) for 2 months. Plasma glucose, insulin, GLP-1, lipid and protein oxidation and antioxidant enzymes

The current study investigated whether sardine protein mitigates the adverse effects of fructose on plasma glucagon-like peptide-1 (GLP-1) and oxidative stress in rats. Rats were fed casein (C) or sardine protein (S) with or without high-fructose (HF) for 2 months. Plasma glucose, insulin, GLP-1, lipid and protein oxidation and antioxidant enzymes were assayed. HF rats developed obesity, hyperglycemia, hyperinsulinemia, insulin resistance and oxidative stress despite reduced energy and food intakes. High plasma creatinine and uric acid levels, in addition to albuminuria were observed in the HF groups. The S-HF diet reduced plasma glucose, insulin, creatinine, uric acid and homeostasis model assessment-insulin resistance index levels, however increased GLP-1 levels compared with the C-HF diet. Hydroperoxides were reduced in the liver, kidney, heart and muscle of S-HF fed rats compared with C-HF fed rats. A reduction in liver, kidney and heart carbonyls was observed in S-HF fed rats compared with C-HF fed rats. Reduced levels of nitric oxide (NO) were detected in the liver, kidney and heart of the S-HF fed rats compared with C-HF fed rats. The S diet compared with the C diet reduced levels of liver hydroperoxides, heart carbonyls and kidney NO. The S-HF diet compared with the C-HF diet increased the levels of liver and kidney superoxide dismutase, liver and muscle catalase, liver, heart and muscle glutathione peroxidase and liver ascorbic acid. The S diet prevented and reversed insulin resistance and oxidative stress, and may have benefits in patients with metabolic syndrome. Introduction Metabolic syndrome (MS) is considered to be a clustering of metabolic alterations conferring a high risk of developing type-2 diabetes (T2D) and cardiovascular disease (CVD) (1,2). The prevalence of MS has markedly increased worldwide due to modern lifestyles and an increased consumption of high-sugar diets, in particular fructose (3). Previous data suggests that fructose consumption in humans results in increased visceral adiposity, lipid dysregulation and reduced insulin sensitivity, all of which have been associated with increased risk for CVD and T2D (4). Fructose has become an important causative factor in the development of MS (4,5). The fructose-fed rat is therefore used as an animal model for insulin resistance, and is considered to mirror MS observed in humans (6). Animal studies have demonstrated that rats fed a high-fructose (HF) diet exhibit hepatic oxidative damage and an altered lipid metabolism due to hepatic stress as a result of the burden on the fructose metabolism (7). Previous studies have focused upon types of seafood that may be beneficial in preventing MS and possibly reducing the risk of various diseases (8,9). The reduced incidence of CVD among populations consuming fish‐rich diets has been attributed to a greater proportion of omega-3 polyunsaturated fatty acids in fish oil (10‐12). There is evidence that the type of protein in the diet may serve an important role in the secretion of insulin by the pancreas (13) and in the regulation of hepatic lipogenesis mediated by sterol regulatory element binding protein-1 (14). In previous animal studies regarding the health effects of fish protein, fish proteins have been demonstrated to prevent insulin resistance in high-fat fed obese rats (15,16), and diminish the development of high blood pressure and hypercholesterolemia (17,18). Furthermore, in insulin-resistant males and females the consumption of a cod protein diet for 4 weeks improved insulin sensitivity compared with a diet of lean beef, pork, veal, eggs, milk and milk products (19). The objective of the current study was to investigate the specific effect of the type of dietary protein on insulin resistance, plasma glucagon-like peptide-1 (GLP-1), in addition to oxidative stress in the tissues of HF-fed rats. Sardine protein diet increases plasma glucagon-like peptide-1 levels and prevents tissue oxidative stress in rats fed a high-fructose diet ZOHRA MADANI1, ABDULLAH SENER2, WILLY J. MALAISSE3 and AIT YAHIA DALILA1 1Department of Biology, Faculty of Natural and Life Sciences, University of Oran, Oran 31000, Algeria; 2Laboratory of Physiology and Pharmacology, Faculty of Medicine, Free University of Brussels; 3Department of Biochemistry, Free University of Brussels, Brussels B-1070, Belgium Received March 10, 2015; Accepted July 22, 2015 DOI: 10.3892/mmr.2015.4324 Correspondence to: Professor Ait Yahia Dalila, Department of Biology, Faculty of Natural and Life Sciences, University of Oran, BP 1524 El M'Naouer, Es Sénia, Oran 31000, Algeria E-mail: [email protected]