Figure 3.

Intestinal microbiota affects oxidative stress. The induction of oxidative stress can be attributed to the iron-dependent Fenton reaction, as well as enzymes belonging to the NOX family and mitochondria. Microbes can remove substrates of the Fenton reaction, assimilate Fe²⁺, and decompose H₂O₂ using enzymes synthesized by the bacteria themselves. Microbes can also enhance mitochondrial functions, including oxidative phosphorylation and β-oxidation, under physiological stress or mitochondrial dysfunction by activating the PGC1α signaling pathway. Microbes can increase NOX1 levels and activate the NRF2 pathway, while suppressing histone deacetylase activity to prevent ROS formation. Additionally, SOD in microbes can reduce ROS levels in the host. The level of ROS can also affect the microbes themselves. NOX, nicotinamide adenine dinucleotide phosphate oxidase; H₂O_2, Hydrogen peroxide; PGC1α, peroxisome proliferator-activated receptor-gamma coactivator-1alpha; NRF2, Nuclear factor erythroid 2-related factor 2; ROS, reactive oxygen stress; SOD, superoxide dismutases.