Influence of Dietary Inositol Supplementation on Growth, Liver Histology, Lipid Metabolism, and Related Genes Expression on Juvenile Hybrid Grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) Fed High-Lipid Diets

Abstract

An 8-week feeding trial was conducted to investigate the effects of dietary inositol on growth performance, lipid metabolism, and expression of lipid related genes of hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) (initial body weight $6.76\pm 0.34$  g). Six isonitrogenous and isolipidic (16.35%) diets were formulated to contain graded levels of inositol (0.17 g/kg (J1), 0.62 g/kg (J2), 1.03 g/kg (J3), 1.78 g/kg (J4), 3.43 g/kg (J5), and 6.59 g/kg (J6)). The results indicated that (a) weight gain rate appeared gradually increasing trend and significant increase in four inositol treatments (J3, J4, J5, and J6) ( $P<0.05$ ). Protein efficiency ratio was slightly improved in the J4 group ( $P<0.05$ ), but there was no significant difference exhibiting in survival rate between the inositol-treated groups and the control group ( $P>0.05$ ). (b) In serum, dietary inositol significantly reduced the contents of triglyceride (TG), total cholesterol (TC), low-density lipoprotein, and clearly increased the content of high-density lipoprotein ( $P<0.05$ ). In the liver, dietary inositol significantly decreased contents of TG, TC, and very low-density lipoprotein ( $P<0.05$ ). The activities of lipoprotein lipase, hepatic lipase, and adipose triglyceride lipase were slightly improved in the inositol-treated groups ( $P<0.05$ ). (c) With increasing of inositol supplement, decreasing of lipid droplet could be observed in hepatocyte. (d) In the liver, dietary inositol significantly downregulated the mRNA levels of fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), 6-phosphogluconate dehydrogenase (6PGD), and sterol regulatory element-binding protein-1 (SREBP1) ( $P<0.05$ ), while it remarkably upregulated the mRNA levels of lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), and carnitine palmitoyl transferase1 (CPT1) ( $P<0.05$ ). In summary, dietary inositol improved growth and reduced lipid composition in the liver of hybrid grouper through decreasing of fatty acid synthesis and increasing of lipid catabolism. Under the experimental conditions, broken-line regression analysis showed that 1.23~1.67 g/kg dietary inositol was recommended in juvenile grouper high-lipid diets.