NADPH oxidases are widely expressed in various cells: NOX2 in macrophage and neutrophils; NOX2, NOX4, with some NOX1 and NOX5 in endothelial cells (DeVallance et al., 2019); NOX4 and NOX1 in vascular smooth muscle cells (VSMCs) (Akoumianakis and Antoniades, 2019); NOX4 in adipocytes (DeVallance et al., 2019); and NOX2, NOX4, and NOX5 in renal epithelial cells (Yang et al., 2020; Yang et al., 2021), all playing critical roles in the pathogenesis of MetS. Here, FMO5 is linked to metabolic syndrome.