RESUMO
A high-carbohydrate diet lowers the rearing cost and decreases the ammonia emission into the environment, whereas it can induce liver injury, which can reduce harvest yields and generate economic losses in reared fish species. Macroalgae Saccharina japonica (SJ) has been reported to improve anti-diabetic, but the protective mechanism of dietary SJ against liver injury in fish fed a high-carbohydrate diet has not been studied. Therefore, a 56-day nutritional trial was designed for swamp eel Monopterus albus, which was fed with the normal diet [20% carbohydrate, normal carbohydrate (NC)], a high carbohydrate diet (32% carbohydrate, HC), and a HC diet supplemented with 2.5% SJ (HC-S). The HC diet promoted growth and lowered feed coefficient (FC), whereas it increased hepatosomatic index (HSI) when compared with the NC diet in this study. However, SJ supplementation increased iodine contents in muscle, reduced HSI, and improved liver injury, such as the decrease of glucose (GLU), total bile acid (TBA), and alanine aminotransferase (ALT) in serum, and glycogen and TBA in the liver. Consistently, histological analysis showed that SJ reduced the area of lipid droplet, glycogen, and collagen fiber in the liver (p < 0.05). Thoroughly, the underlying protective mechanisms of SJ supplementation against HC-induced liver injury were studied by liver transcriptome sequencing coupled with pathway analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the differentially expressed genes (DEGs), such as the acetyl-coenzyme A synthetase (acss1), alcohol dehydrogenase (adh), interferon-induced protein with tetratricopeptide repeats 1 (ifit1), aldo-keto reductase family 1 member D1 (akr1d1), cholesterol 7-alpha-monooxygenase (cyp7a1), and UDP-glucuronosyltransferase (ugt), indicated that the pathway of glycolysis/gluconeogenesis was the main metabolic pathway altered in the HC group compared with the NC group. Meanwhile, hepatitis C, primary BA biosynthesis, and drug metabolism-cytochrome P450 were the three main metabolic pathways altered by SJ supplementation when compared with the HC group. Moreover, the BA-targeted metabolomic analysis of the serum BA found that SJ supplementation decreased the contents of taurohyocholic acid (THCA), taurochenodeoxycholic acid (TCDCA), taurolithocholic acid (TLCA), nordeoxycholic acid (NorDCA), and increased the contents of ursocholic acid (UCA), allocholic acid (ACA), and chenodeoxycholic acid (CDCA). In particular, the higher contents of UCA, ACA, and CDCA regulated by SJ were associated with lower liver injury. Overall, these results indicate that the 2.5% supplementation of SJ can be recommended as a functional feed additive for the alleviation of liver injury in swamp eel-fed high-carbohydrate diets.
RESUMO
The use of an artificial diet often leads to the increase of risk factors for the development of liver diseases, such as hepatic lipid accumulation (HLA) in commercially cultured fish species. Our previous study showed that dietary Saccharina japonica could effectively alleviate HLA in black seabream (Acanthopagrus schlegelii), which may be linked predominantly to S. japonica fucoidan. Thus, a 56d nutritional trial was designed to investigate the effects of dietary fucoidan (CTRL, 0 g kg-1; ASJ1, 0.75 g kg-1; ASJ2, 3.00 g kg-1) on growth performance, fillets nutritional values, and HLA of black seabream. Results showed that dietary fucoidan significantly improved the growth and the contents of n-3 polyunsaturated fatty acids (n-3PUFA) in fillets of black seabream. Moreover, dietary fucoidan improved HLA-related parameters, including reducing serum and liver lipid contents and the activity of aminotransferase. Meanwhile, histological analysis showed that dietary fucoidan reduced the area of hepatic lipid droplets in black seabream (P < 0.05). In addition, the transcriptomic analysis of differentially expressed gene (DEG) showed that all DEG in fatty acid metabolism, primary bile acid biosynthesis, and fatty acid biosynthesis were down-regulated, and all DEG in the regulation of autophagy were up-regulated in the ASJ1 group compared with CTRL group. Moreover, the metabolomic analysis of differentially expressed metabolite (DEM) found that lipid metabolism was the main type of KEGG pathway altered by fucoidan supplementation. Furthermore, the combined transcriptomic and metabolomic analysis found that dietary fucoidan mainly modified the lipid metabolic pathway of primary bile acid biosynthesis, glycerophospholipid metabolism, and arachidonic acid metabolism in the liver. In general, dietary fucoidan effectively alleviated HLA of black seabream, and the underlying mechanism may be ascribed to promoting the autophagy and inhibiting the synthesis of lipids and bile acids.