Calcium pyruvate supplementation ameliorates fat accumulation and hepatic health by enhancing lipid utilization and inhibiting gluconeogenesis in Nile tilapia fed high-fat diets

Calcium pyruvate (CP) supplementation has been reported to attenuate high-fat diets (HFDs)-induced fat accumulation and improve mammals’ health. However, its impact on fish remains uncertain due to limited research. This study aimed to investigate effects of CP on fat deposition in Nile tilapia (Oreochromis niloticus) fed a control diet, HFD or four HFDs containing different amounts of CP (0.4 %, 0.8 %, 1.2 % and 1.6 %) for eight weeks. The results showed that dietary CP significantly decreased weight gain rate, specific growth rate, hepatosomatic index and mesenteric fat index. As dietary CP increased, triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) levels in serum and liver were significantly decreased, while high-density lipoprotein cholesterol were increased. Genes of lipid catabolism including hormone-sensitive lipase (hsl), carnitine palmitoyltransferase 1a (cpt1a), acyl-CoA oxidase (aco), peroxisome proliferator-activated receptor alpha (pparα), AMP-activated protein kinase (ampk) and adiponectin receptor 1 (adiporl) were up-regulated in fish fed CP diets. Conversely, CP down-regulated the expression of lipogenic genes (acetyl-Coenzyme A carboxylase alpha, accα; diacylglycerol acyltransferase 2, dgat2; sterol regulatory element binding protein 1, srebp1). Reduced serum glucose and liver glycogen contents revealed that glucose metabolism was changed, along with lower mRNA values of gluconeogenesis and glycogenesis (fructose-1, 6-bisphosphatase, fbpase; glucose-6-phosphatase catalytic subunit, g6pase; glycogen synthase kinase 3 beta, gsk3b). Moreover, fish fed CP showed considerable improvement in anti-oxidant and immune capacities. Increased enzymatic activities (superoxide dismutase, SOD; catalase, CAT; alkaline phosphatase, AKP; acid phosphatase, ACP) and transcript levels (CAT and SOD), and decreased expression of pro-inflammatory factor (il-6 and tnf-α) were observed in the CP treatments. Notably, excessive amounts of CP (1.6 %) posed potential risks of causing hepatic oxidative damage, as evidenced by higher values of serum TC, LDL-C, GPT and GOT. Consequently, 0.4 %-1.2 % CP supplementation in HFDs alleviates fat accumulation and increases anti-oxidant and immune abilities by enhancing lipid utilization and inhibiting gluconeogenesis. These findings provide valuable references for the application of CP in HFDs of cultured omnivorous fish.