Effects of Bacillus subtilis on hepatic lipid metabolism and oxidative stress response in grass carp (Ctenopharyngodon idellus) fed a high-fat diet

Bacillus subtilis is widely used in aquaculture as a probiotic. However, few studies have been conducted to examine the effect of B. subtilis on liver lipid metabolism. A total of 135 healthy grass carp (50.24 +/- 1.38 g) were randomly divided into three groups: control (Con), high-fat diet (HF), and high-fat diet + B. subtilis (HF + B. subtilis), and fed for 8 weeks. The results showed that compared with the HF group, the weight gain rate (WGR) significantly increased (P < 0.05) and the hepatic lipid content, serum low-density lipoprotein cholesterol (LDL-C), and aspartate aminotransferase (AST) decreased in the group supplemented with B. subtilis (P < 0.05). Moreover, the hepatic mRNA expression of fatty acid synthase (FAS) was significantly down-regulated and the carnitine palmitoyl transferases (CPT1 alpha 1a) were up-regulated in the HF + B. subtilis group compared to the HF group (P < 0.05), respectively. Additionally, in the HF + B. subtilis group, glutathione (GSH) significantly increased (P < 0.05), while hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents significantly decreased compared to the HF group (P < 0.05). B. subtilis may reduce the hepatic lipid content by inhibiting its synthesis and promoting beta-oxidation of fatty acids. B. subtilis may also alleviate dyslipidaemia and prevent oxidative damage in the liver caused by the high-fat diet of grass carp. Hence, dietary supplementation with B. subtilis shows promise as a therapeutic or preventive tool against fatty liver disease.