Effects of single or conjoint administration of poly-β-hydroxybutyrate and Bacillus subtilis on growth, antioxidant capacity and apoptosis of common carp (Cyprinus carpio)

Abstract

This study aims to assess single or conjoint administration of poly-β-hydroxybutyrate (PHB) and Bacillus subtilis on growth, the function and morphology of hepatopancreas and intestines, antioxidant capacity, inflammation and apoptosis in common carp (Cyprinus carpio). In this study, four diets were formulated according to a 2 × 2 factorial design, including control diet (without PHB and B. subtilis), B. subtilis diet (with 1 × 10⁸ CFU/g B. subtilis), PHB diet (4 %PHB) and PHB+B. subtilis diet (with 4 %PHB and 1 × 10⁸ CFU/g B. subtilis). Common carp (3.50 ± 0.03 g) were allocated into 4 groups (3 replicates per group, 30 fish per replicate) and fed for 8 weeks. Results demonstrated that single or conjoint administration of 4 %PHB and 1 × 10⁸ CFU/g B. subtilis promoted the growth performance and feed utilization, with interaction (P<0.05). 4 %PHB and 1 × 10⁸ CFU/g B. subtilis increased the levels of protease in intestines, lipase and amylase in hepatopancreas and intestines, AST and ALT in hepatopancreas, intestinal permeability (DAO, D-LA, 5-HT and ET-1), intestinal tight junction protein-related mRNA, intestinal growth indexes (fold height and muscular layer thickness), antioxidant capacity (CAT, T-AOC, T-SOD and GSH-PX in hepatopancreas and intestines, Nrf2, SOD, CAT and GSH-PX mRNA in hepatopancreas and intestines, HO-1 mRNA in hepatopancreas), anti-inflammatory and anti-apoptosis (TGF-β, IL-10 and Bcl-2 mRNA in hepatopancreas and intestines) (P<0.05), decreased the levels AST and ALT in serum, intestinal growth indexes (lamina propria width), oxidative stress indicator (MDA) and Keap1 mRNA in hepatopancreas and intestines, pro-inflammatory and pro-apoptosis (NF-κB, TNF-α, IL-1β, IL-6, Bax, Caspase-3, Caspase-8 and Caspase-9 mRNA in hepatopancreas and intestines) (P<0.05), improved the morphology of hepatopancreas and intestines. Whereas the levels of protease in hepatopancreas were only increased by 1 × 10⁸ CFU/g B. subtilis (P<0.05), the levels of HO-1 mRNA in intestines were only up-regulated by 4 %PHB (P<0.05). Furthermore, the interaction between 4 %PHB and 1 × 10⁸ CFU/g B. subtilis was discovered for the levels of AST, ALT and 5-HT in serum, intestinal Occludin mRNA, MDA in hepatopancreas and intestines, Keap1, HO-1 and IL-1β mRNA in hepatopancreas, GSH-PX mRNA in hepatopancreas and intestines, Bcl-2 and Caspase-3 mRNA in intestines (P<0.05). In conclusion, this study indicated that conjoint administration of 4 %PHB and 1 × 10⁸ CFU/g B. subtilis had synergistic promotion on the growth performance, digestive function, antioxidant capacity, hepatopancreatic and intestinal functions of common carp.