Calcium pyruvate attenuates fat deposition by augmenting fatty acid oxidation and inhibiting glucose oxidation in juvenile large yellow croaker (Larimichthys crocea) consuming a high-fat diet

Calcium pyruvate (CP), known as an energetic aid, has been shown to enhance lipid utilization and prevent obesity in mammals. However, very few studies were conducted to evaluate the potential implications of CP for aquatic animals. This study examined the role of CP on fat deposition in large yellow croaker by feeding fish with high-fat diets containing four levels of dietary CP (0, 0.375%, 0.75% and 1.5%). After a 70-d feeding trial, fish fed higher doses of CP significantly decreased weight gain (WG) and hepatosomatic index (HSI). Lipid percentages and triglyceride (TG) contents of whole fish, liver and muscle were negatively correlated with dietary CP. Plasma TG, total cholesterol (TC), LDL-cholesterol (LDL-c) and non-esterified fatty acids (NEFAs) levels significantly decreased with increasing dietary CP, whereas plasma HDL-cholesterol (HDL-c) and beta-hydroxybutyrate (beta-HB) levels came to a climax in fish fed the 1.5% CP diet. The fish fed CP diets also exhibited smaller hepatic lipid droplet size. The expression of lipogenic genes (fatty acid synthase, fas; acetyl-CoA carboxylase, acc; diacylglycerol acyltransferase 2, dgat2) were significantly down-regulated in the liver and muscle of the CP-treated fish. Conversely, the expression of lipolytic genes (adipose triglyceride lipase, atgl; hormone-sensitive lipase, hsl; carnitine palmitoyltransferase 1, cpt1) were markedly elevated. This was accompanied by enhanced tricarboxylic acid (TCA) cycle capacity (citrate content; succinate dehydrogenase, SDH; malate dehydrogenase, MDH). Further Western blot analysis revealed that CP may dose-dependently induce phosphorylations of AMP-activated protein kinase (AMPK) and ACC in the liver and muscle, together with protein expression of CPT1 and fatty acid translocase 36 (CD36). Surprisingly, treatment with CP impaired glucose utilization, as evidenced by raised plasma glucose and weakened glucose metabolism-related enzymatic activities (hexokinase, HK; phosphofructokinase, PFK; pyruvate kinase, PK; pyruvate dehydrogenase, PDH) and gene expression (glucokinase, gk; hk; phosphofructokinase-liver type, pfkl; pyruvate kinase-muscle type, pkma) in the liver and muscle. Notably, increased plasma liver enzyme activities (alanine aminotransferase, ALT; aspartate aminotransferase, AST) and hepatic inflammation-related gene expression (interleukin-1 beta, il-1 beta and cyclooxygenase 2, cox-2) and reduced hepatic antioxidant capacity (total antioxidative capacity, T-AOC; catalase, CAT) were found in high-dose CP treatment. These findings indicated that dietary CP could attenuate fat deposition by stimulating beta-oxidation through the AMPK-ACC-CPT1 cascade and inhibiting lipogenesis and glucose oxidation. Considering both lipid-lowering effect and growth performance, dietary supplementation with 0.375% similar to 0.75% CP is suitable for alleviating fat deposition of juvenile large yellow croaker.