Long-term intake of a high-carbohydrate diet induced steatosis, hepatitis, and fibrosis in the liver of juvenile Chinese soft-shelled turtle (Pelodiscus sinensis)

Abstract

A high intake of carbohydrate has been associated with liver health problems in aquaculture animals. The objective of this study was to evaluate whether prolonged consumption of a high-carbohydrate diet (HCD) would induce the metabolic disorders and histopathological abnormalities in the liver that characterize nonalcoholic steatohepatitis (NASH) in P. sinensis juveniles. Two isonitrogenous and isolipidic diets containing 14 % (normal carbohydrate diet, CON) and 28 % corn starch (HCD) were formulated to feed juvenile P. sinensis (5.15 ± 0.05 g) for 60 d. The experimental turtles were sampled on the 20th d, 40th d, and 60th d. The results indicated that significant hepatic lipid accumulation (triglyceride content and Oil red O-stained area percentage) was observed in the HCD group on the 40th d and 60th d compared to the CON group (P < 0.05), which were probably associated with significantly higher mRNA levels of genes involved in fatty acids uptake and lipid synthesis in liver (P < 0.05), while it was not related with lipolysis in liver. The more interesting is that the hepatic TG content in the HCD group were not further increased from 40th d to 60th d, which was partly attributed to the enhanced triglyceride (TG) excretion from liver into plasma on the 60th d as reflected by significantly increased levels of plasma low-density lipoprotein (LDL), plasma TG content, and apolipoprotein B (apob) transcript on this day (P < 0.05). Moreover, a 40-d and 60-d intake of HCD induced hepatic inflammation as indicated by significantly higher mRNA levels of pro-inflammatory cytokines and M1 macrophage number (fluorescence intensity). Furthermore, HCD caused significantly higher protein expressions of hepatic fibrosis markers (α-smooth muscle actin and vimentin), accompanied with higher fibrosis index (Masson-stained collagen) and higher mRNA levels of fibrosis-related genes (P < 0.05). Taken together, these results demonstrated that long-term intake of HCD in juvenile P. sinensis induced hepatic steatosis and inflammation, which are key contributors to the development of fibrosis.