To discover the potential source of ROS, we verified the expressions of NOX2 proteins (a type of NAD[P]H oxidase subunits that are mainly expressed in cardiomyocytes) in vivo and in vitro, and we found that the expressions of NOX2 proteins were significantly elevated in the hearts of CKD rats, which could be partially reversed by BB536 (Figure 4, G and I). Here, FMO5 is linked to chronic kidney disease.