Bacillus subtilis and xylo-oligosaccharide ameliorates NaHCO3-induced intestinal barrier dysfunction and autophagy by regulating intestinal microflora and PI3K/Akt pathway of crucian carp (Carassius auratus)

This study was to demonstrate that the alleviate effect of synbiotics (Bacillus subtilis and xylo-oligosaccharide) on NaHCO3-induced intestinal barrier dysfunction and autophagy of crucian carp (Carassius auratus). In a 2x2 factorial design, crucian carp were divided into 4 groups, fed with diets contained two levels of synbiotics (0 and 1x 10(8) CFU/g) and treated with two levels of NaHCO3 (0 and 50 mmol/L) for 56 days. The results showed that NaHCO3 and synbiotics significantly affected intestinal fold height, permeability, the mRNA expression of tight junction, antioxidant capacity, immunity function (except LZM), inflammation response, the mRNA and protein expression of autophagy (except Beclin1 protein) and PI3K/Akt pathway (P<0.05). Intestinal muscular layer thickness, the levels of LZM and the protein expression of Beclin1 only affected by NaHCO3 (P<0.05). In addition, the interaction between NaHCO3 and synbiotics was observed for intestinal fold height, the mRNA expression of Claudin 4, Nrf2, Keap1, HO-1, SOD, GPX4a, GPX4b, TNF-alpha, IL-6, PI3K, ATG5 and ATG7, the levels of ROS and ACP, the protein expression of p-PI3K/PI3K, p-Akt/Akt, ATG5, ATG7, Beclin1 and LC3II/LC3I (P<0.05). Additionally, this study highlights that the synbiotics facilitated the colonisation Bacillus and Cetobacterium, while concurrently inhibited the growth of Aeromonas in intestines. These findings suggested that dietary synbiotics (Bacillus subtilis and xylo-oligosaccharide) can effectively alleviated NaHCO3-induced intestinal dysfunction oxidative stress and autophagy by regulating intestinal microflora and PI3K/Akt pathway.