Effects of dietary niacin on liver health in genetically improved farmed tilapia (Oreochromis niloticus)

Abstract

Pharmacological doses of niacin can improve lipid metabolism in humans and some homothermal model organisms, but flushing and hepatotoxicity are the main side-effects. Our previous study indicated that genetically improved farmed tilapia (GIFT, Oreochromis niloticus) fed the diet with 1000 mg/kg niacin decreased the lipid content in serum and liver, suggesting that high niacin intake also affects lipometabolism in fish. Thus, to investigate the liver health status of GIFT fed high level of niacin, a 2 × 2 factorial experiment with two niacin (100 or 1000 mg/kg diet) and two energy (16 or 18 MJ/kg diet) levels was carried out for 8 weeks. The 276 fish (mean body weight, 24.45 ± 0.07 g) were divided into four treatments, and each treatment had three replicates. Each replicate was stocked with 23 fish and fed to apparent satiety thrice daily. Neither dietary niacin nor energy level affected weight gain, specific growth rate, feed conversion ratio, condition factor, viscerosomatic index, mesenteric fat index, or liver histology and apoptosis rate of hepatocytes. The high niacin intake reduced the hepatosomatic index, alleviated glycogen and lipid accumulation in the liver, and decreased the hepatic mRNA expression level of claudin-7a, and the activities of glutathione peroxidase (GPx) and catalase (CAT), raised the hepatic glycogen distribution, and mRNA expression levels of zonula occludens-1 and tumour necrosis factor-alpha (TNF-α). In fish fed high rather than normal energy diets, high niacin intake enhanced superoxide dismutase activity, lowered GPx, CAT activities and inhibition of hydroxyl radicals capacity, and upregulated interleukin-1-beta and TNF-α mRNA expression levels in the liver. These results suggested that feeding a diet containing 1000 mg/kg niacin had no adverse effects on liver health, and the effects of high niacin intake on the hepatic antioxidative capacity and inflammatory factors mRNA expression in GIFT depended on dietary energy. Keywords: Aquaculture, Growth, Histology, Oxidative stress, Inflammatory