The suppressive mechanism of dietary macroalgae Saccharina japonica against hepatic lipid accumulation in black seabream A. schlegelii

Hepatic lipid accumulation (HLA) is a major risk factor for the development of liver diseases in cultured fish species, which can lead to severe health problems and decrease harvest yields, thus result in economic losses. Macroalgae Saccharina japonica (SJ) has been reported to reduce HLA in mammals, but effects and underlying mechanism of dietary SJ on HLA in fish remain elusive. This study aimed to investigate the effect of dietary SJ on HLA of black seabream (A. schlegelii), an important marine economic fish. Juvenile black seabream (2.78 +/- 0.16 g) was fed diets with three levels of SJ (0, 2.5 and 10%) for 90 days, and then blood and liver tissues were extracted for biochemical, histological and multiple-omic analyses. This study demonstrated that dietary supplementation of 2.5% and 10% SJ improved HLA-related parameters, including reducing serum lipid content and the activity of aminotransferase. Meanwhile, histological analysis showed that dietary SJ reduced lipid vacuoles in hepatocytes. The transcriptomic analysis of differentially expressed genes (DEG) showed that all the DEG in primary bile acid biosynthesis and biosynthesis of unsaturated fatty acids were down-regulated in SJ2.5% group and SJ10% group, respectively. Besides, all the DEG in regulation of autophagy were up-regulated in SJ2.5% and SJ10% groups compared with SJ10% group. Moreover, the metabolomic analysis of the differentially expressed metabolites (DEM) found that lipid metabolism was the main type of pathway in SJ supplementation groups. Furthermore, the analysis of both of DEG and DEM co-enriched in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway related to lipid metabolism found that the significant enriched pathways were primary bile acid biosynthesis, glycerophospholipid metabolism, biosynthesis of unsaturated fatty acids and fatty acid biosynthesis metabolism in SJ2.5% and SJ10% groups compared with SJ10% group. However, there were no pathways co-enriched between SJ10% and SJ2.5% group. In short, 2.5% and 10% SJ supplementation diets may reduce serum lipid content and HLA of black seabream through promoting autophagy and inhibiting the synthesis of fatty acids and bile acids.

Automated summary

This study found that dietary supplementation of Saccharina japonica (SJ) can reduce serum lipid content and hepatic lipid accumulation (HLA) in black seabream by promoting autophagy and inhibiting the synthesis of fatty acids and bile acids.