Prolonged Hyperbaric Exposure Alters Gut Mucus, Microbiota Composition And Intestinal Antimicrobial Defense In Mice

Abstract

PURPOSE: Divers with prolonged hyperbaric exposure may suffer from digestive dysfunctions, which relate to impairment of intestinal mucosal immune system and gut microbiota homeostasis. We studied the effects of a 4-day hyperbaric exposure on gut microbiota and intestinal antimicrobial peptides (AMPs) in mice. METHODS: 20 male C57 Mice, 8-week old, were randomly divided into hyperbaric exposure group (HE, n=10) and control group (CON, n=10). The Hyperbaric environment was established by compressed N2/O2 mixed gas, and sustained the ambient pressure at 500kPa for 4 days in the pressure chamber. Intestines were excised and stained with Hematoxylin and Eosin (H&E) and alcian blue-periodic acid-schiff staining (AB-PAS). Feces and intestines were collected and extract gDNA and RNA respectively. We used qPCR to assay bacterial population (Bacteroides, Clostridia, Lactobacilli, Enterobacteria, and Akkermansia muciniphila) of the feces, and the AMPs (Defa5, Defb1, Retnlb, Reg3b and Reg3g) of small intestine and colon. RESULTS: During the hyperbaric exposure, the mice did not exhibit any behavioral abnormality, including nitrogen narcosis. According to the AB-PAS staining, the mucus was reduced in colons post hyperbaric exposure. And there was no significant morphological difference between intestines and colons from the mice of HE group and CON by H&E staining. By comparing with the 16S rRNA genes, results revealed a significant increase in the relative abundances of A. muciniphila (9.28±5.67) and Clostridia (3.45±0.63) in HE. The relative abundance of Lactobacilli was lower (0.40±0.24) in HE. Moreover, a distinct increase of Enterobacteria (23.34±8.88) was observed in HE compared with CON. Gene expressions for Defa5 and Defb1 in HE were decreased in small intestine, while Defb1 and Reg3g in HE were significantly decreased, and Defa5 and Reg3b increased in colon. CONCLUSIONS: In sum, the data showed that a four-day hyperbaric exposure induced changes in the mucus of colon, the mRNA level of AMPs, and the gut microbiota composition in mice.