Hypoxia: The "Invisible Pusher" of Gut Microbiota

Abstract

Oxygen is important to the human body. Cell survival and operations depend on oxygen. When the body becomes hypoxic, it affects the organs, tissues and cells and can cause irreversible damage. Hypoxia can occur under various conditions, including external environmental hypoxia and internal hypoxia. The gut microbiota plays different roles under hypoxic conditions, and its products and metabolites interact with susceptible tissues. This review was conducted to elucidate the complex relationship between hypoxia and the gut microbiota under different conditions. We describe the changes of intestinal microbiota under different hypoxic conditions: external environment and internal environment. For external environment, altitude was the mayor cause induced hypoxia. With the increase of altitude, hypoxia will become more serious, and meanwhile gut microbiota also changed obviously. Body internal environment also became hypoxia because of some diseases (such as cancer, neonatal necrotizing enterocolitis, even COVID-19). In addition to the disease itself, this hypoxia can also lead to changes of gut microbiota. The relationship between hypoxia and the gut microbiota are discussed under these conditions.

Keywords: COVID-19; gut microbiota; high altitude; hypoxia; tumor microenvironment.

FIGURE 1

Changes of intestinal microbiota in animals and humans under environmental hypoxia. Environmental hypoxia can be divided into acute hypobaric hypoxia and chronic hypobaric hypoxia. Acute hypobaric hypoxia usually refers to the environment from plain to plateau. In this case, the intestinal microorganisms in animals and human will change greatly. In animals, Bacteroides increased significantly, while Corynebacterium, Prevotella and Coprococcus decreased significantly. The acute changes in human were mainly reflected in the significant increase of Bacteroides, Proteobacteria, Escherichia coli and Clostridium perfringens, and the significant decrease of some probiotics, including Bifidobacterium, Lactobacillus, Atopodium, Coriobacterium, and Eggerthella lenta. Chronic hypobaric hypoxia mainly refers to animals and people living in plateau environment for a long time. There is a high abundance of Rumencoccus and Christensenellaceae in animals living in plateau environment for a long time. However, there are some differences between human living in plateau environment and the plain, mainly in the higher abundance of Acidaminocus, Actinomyces, Blautia, Butyrimionas, Clostridium, Desulfovibrio, Helicobacter, Leuconostoc, Peptostrecoccaceae incertae sedis, Prevotellae uncultured, Prevotella, Rc9 gut group and Rhodococcus. Based on the above two kinds of hypoxia conditions, it shows that hypoxia can indeed affect the intestinal microorganisms in vivo.