Here, we found that butyrate controlled ROS production by down-regulating the expression of the main catalytic domain Nox2 but also of the other NADPH complex components Cyba, Ncf1, and Ncf4. Similarly, butyrate has been linked to reduction in murine arthritis development through decreasing NADPH oxidase subunit p22phox (Cyba) expression and thus, oxidative stress in endothelial cells.32 Here, FMO5 is linked to arthritic joint disease.