Title : Acute stress due to dietary pectin induces cholestasis and chronic stress induces hepatic steatosis and fibrosis in yellow catfish, Pelteobagrus fulvidraco
Green liver syndrome and hepatic steatosis, named “hepatobiliary syndrome” (HBS) in China, was found to appear in fish fed diet with high level of plant ingredients. Plant ingredients are rich in non-starch polysaccharides (NSPs), and this study was conducted to explore the induction of NSPs on HBS with yellow catfish, Pelteobagrus fulvidraco, as a model fish. Pectin, an important soluble NSP in plant feedstuffs, was included in diets at 0 (FM), 10 g kg-1 (PEC1), 50 g kg-1 (PEC5), 150 g kg-1 (PEC15) and 300 g kg-1 (PEC30), respectively. Fish with an initial mean weight of 9.65 ± 0.08 g were fed the above diets for 56 days. Interval sampling was conducted at 2, 7, 14, 28, and 56 days in fish fed the PEC30 and FM diets. The results showed that in fish fed PEC30 diet, green liver syndrome occurred after 2 days and peaked after 7 days, when the total bile acids (TBA) in the serum and liver were 80 and 3 times higher, respectively, than in fish fed FM diet. The green liver syndrome was not observed after 28 and 56 days, and the color of the bile became light after 28 days and colorless after 56 days. The expression of LXRa, CYP7A1, and NTCP was upregulated and CYP8B1 was downregulated in the liver after 7 days, and all these genes were expressed weakly and much lower than in fish fed FM diet after 56 days (P < 0.05). Obvious diffuse adipose degeneration and fibrosis of hepatocytes were observed after 56 days. The fish fed diets with different levels of pectin for 56 days were compared, and the total bilirubin, direct bilirubin, triglyceride, total cholesterol, total protein, albumin and seroglobulin were decreased with increasing dietary pectin. However, indirect bilirubin and TBA were the highest in fish fed the PEC15 and PEC5 diets, respectively. In addition, green liver syndrome and cholestasis were also observed in fish fed PEC5 and PEC15 diets for 56 days. These results suggested that the nutritional stress of pectin was dose- and time-dependent. Acute stress induced hypersynthesis of bile acids and then cholestasis, and chronic stress induced hepatic steatosis and fibrosis in yellow catfish. Soluble NSPs are likely the cause of fish HBS.