AUTHOR=Cai Yulan , Luo Yanhong , Dai Ninan , Yang Yan , He Ying , Chen Huajun , Zhao Manlu , Fu Xiaoyun , Chen Tao , Xing Zhouxiong 

TITLE=Functional metagenomic and metabolomics analysis of gut dysbiosis induced by hyperoxia

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1197970

DOI=10.3389/fmicb.2023.1197970

ISSN=1664-302X

ABSTRACT=<sec id="sec1"><title>Background</title><p>Inhaled oxygen is the first-line therapeutic approach for maintaining tissue oxygenation in critically ill patients, but usually exposes patients to damaging hyperoxia. Hyperoxia adversely increases the oxygen tension in the gut lumen which harbors the trillions of microorganisms playing an important role in host metabolism and immunity. Nevertheless, the effects of hyperoxia on gut microbiome and metabolome remain unclear, and metagenomic and metabolomics analysis were performed in this mouse study.</p></sec><sec id="sec2"><title>Methods</title><p>C57BL/6 mice were randomly divided into a control (CON) group exposed to room air with fractional inspired oxygen (FiO<sub>2</sub>) of 21% and a hyperoxia (OXY) group exposed to FiO<sub>2</sub> of 80% for 7 days, respectively. Fecal pellets were collected on day 7 and subjected to metagenomic sequencing. Another experiment with the same design was performed to explore the impact of hyperoxia on gut and serum metabolome. Fecal pellets and blood were collected and high-performance liquid chromatography with mass spectrometric analysis was carried out.</p></sec><sec id="sec3"><title>Results</title><p>At the phylum level, hyperoxia increased the ratio of <italic>Firmicutes/Bacteroidetes</italic> (<italic>p</italic> = 0.049). At the species level, hyperoxia reduced the abundance of <italic>Muribaculaceae bacterium Isolate-037</italic> (<italic>p</italic> = 0.007), <italic>Isolate-114</italic> (<italic>p</italic> = 0.010), and <italic>Isolate-043</italic> (<italic>p</italic> = 0.011) <italic>etc</italic>. Linear discriminant analysis effect size (LEfSe) revealed that <italic>Muribaculaceae</italic> and <italic>Muribaculaceae bacterium Isolate-037</italic>, both belonging to <italic>Bacteroidetes</italic>, were the marker microbes of the CON group, while <italic>Firmicutes</italic> was the marker microbes of the OXY group. Metagenomic analysis using Kyoto Encyclopedia of Genes and Genomes (KEGG) and Carbohydrate-Active enZYmes (CAZy) revealed that hyperoxia provoked disturbances in carbohydrate and lipid metabolism. Fecal metabolomics analysis showed hyperoxia reduced 11-dehydro Thromboxane B2-d4 biosynthesis (<italic>p</italic> = 1.10 × 10<sup>−11</sup>). Hyperoxia blunted fecal linoleic acid metabolism (<italic>p</italic> = 0.008) and alpha-linolenic acid metabolism (<italic>p</italic> = 0.014). We showed that 1-docosanoyl-glycer-3-phosphate (<italic>p</italic> = 1.58 × 10<sup>−10</sup>) was the most significant differential serum metabolite inhibited by hyperoxia. In addition, hyperoxia suppressed serum hypoxia-inducible factor-1 (HIF-1, <italic>p</italic> = 0.007) and glucagon signaling pathways (<italic>p</italic> = 0.007).</p></sec><sec id="sec4"><title>Conclusion</title><p>Hyperoxia leads to gut dysbiosis by eliminating beneficial and oxygen strictly intolerant <italic>Muribaculaceae</italic> with genomic dysfunction of carbohydrate and lipid metabolism. In addition, hyperoxia suppresses unsaturated fatty acid metabolism in the gut and inhibits the HIF-1 and glucagon signaling pathways in the serum.</p></sec>