Several oxidative enzyme systems such as NADPH oxidase, xanthine oxidase, cyclooxygenases, lipoxygenases, myeloperoxidases, cytochrome P450 monooxygenase, uncoupled NOS, and peroxidases lead to the inactivation of NO, which represents a critical mechanism leading to endothelial dysfunction through an elevated level of superoxide anion (O2•−) [19]. This evidence concerns the gene FMO5 and endothelial dysfunction.