The effects of cholesterol supplementation in full-plant protein diets derived from different lipid sources on liver and intestinal health, bile acid metabolism in largemouth bass (Micropterus salmoides)

Cholesterol plays an important role in the physiological metabolism of farmed animals. However, the cholesterol content in plant protein feeds does not meet the requirements of farmed animals. This study aimed to investigate the effects of dietary cholesterol supplementation on liver and intestinal health, cholesterol and bile acid metabolism in largemouth bass ( Micropterus salmoides ) fed full-plant protein diets using fish oil (FO) or soybean oil (SO) as lipid sources. Five diets were formulated: a FM-based control diet (FFM), two full-plant protein diets with FO and SO as lipid sources (PFO, PSO), and two additional full-plant protein diets supplemented with 5 g kg −1 exogenous cholesterol using FO or SO as lipid sources (PFC, PSC). A 50-day feeding trial was conducted. The results showed that fish fed full-plant protein diets exhibited liver inflammation. Cholesterol supplementation alleviated liver damage induced by full-plant protein diets via down-regulating pro-inflammatory -related genes ( tnfα , il1β , nrf2 , keap1 ) and oxidative stress-related genes ( bach1 , prx2 , sod , cat ). Intestinal health was compromised in fish fed full-plant protein diets, as evidenced by shortened intestinal mucosal length and width. Cholesterol supplementation improved intestinal health by up-regulating tight junction protein genes ( claudin5 , claudin11 , occludin ) and anti-inflammatory gene tgfβ , while down-regulating pro-inflammatory genes ( tnfα , il1β , nrf2 , keap1 ). Additionally, cholesterol supplementation significantly increased the contents of taurocholic acid, tauroursodeoxycholic acid, glycocholic acid in the gallbladder of fish fed FO-based diets. Further analysis revealed that cholesterol down-regulated the expression of cholesterol metabolism genes ( srebp1, srebp2, hmgcr1, sqleα, npc1l1, ldlr ), and up-regulated the expression of bile acid synthesis genes ( cyp8β1 , hmgcr ), bile acid transport genes ( mrp2 , mdr3 , bsep ), and bile acid reabsorption-related genes ( ostα , ostβ , abst ). In conclusion, cholesterol supplementation in full-plant protein diets promotes liver and intestinal health and helps maintain metabolic homeostasis, thereby providing a scientific basis for enhancing plant protein utilization in aquafeeds. • Cholesterol ameliorates hepatic injury induced by full-plant protein diet. • Cholesterol mitigates adverse intestinal effects induced by full-plant protein diet. • Soybean oil as a fat source triggers vacuolization of hepatocytes. • Cholesterol helps maintain normal cholesterol and bile acid metabolism.