Hepatic triacylglycerol secretion, lipid transport and tissue lipid uptake in blunt snout bream (Megalobrama amblycephala) fed high-fat diet

High-fat diets may have favorable effects on growth partly based on protein-sparing, but high-fat diets often lead to excessive fat deposition in the liver of some fish. The goal of the study was therefore to investigate effects of fat-rich diet on mechanisms involved in fat deposition in the liver. Three hundred blunt snout bream (Megalobrama amblycephala) juveniles (initial weight 18.00 ± 0.05 g) were fed with two diets (5% or 15% fat) for 8 weeks. Histological and biochemical parameters were determined. The hepatic triacylglycerol (TG) secretion rate was measured by intraperitoneal injection with poloxamer 407 (a lipoprotein lipase inhibitor). Lipid transport was studied by determining components of lipoproteins. We also examined lipid uptake by assaying lipoprotein lipase (LPL) activities and mRNA expressions in tissues. Our results showed that ultrastructural lesions of organelles in hepatocytes occurred after intake of a high-fat diet. The hepatic TG secretion rate and plasma very low density lipoprotein (VLDL) amount of fish fed high-fat diet were significantly lower compared to those of fish fed control diet. Concomitantly, variations of components of lipoproteins were also apparent. In the liver, muscle and mesenteric fat tissue, the percentage of polyunsaturated fatty acid (PUFA) was significantly increased, while both saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) percentages decreased in high-fat group. Both activities and mRNA expressions of LPL were also increased in these tissues. On the whole, a low level of lipid transport out of the liver, alterations of lipid transport and elevated lipid uptake contributed to fatty liver of blunt snout bream fed high-fat diet.