NADPH is an electron donor complex that reduces molecular oxygen to superoxide (O2•−) or H2O2, depending on the isoform [85]; the predominant isoform in the pulmonary vascular system is Nox4, which has been shown to be overexpressed during pulmonary artery remodeling and in subsequent hypoxia-induced pulmonary artery hypertension (normobaric hypoxia; 10% O2; [86]). This evidence concerns the gene NOX4 and pulmonary arterial hypertension.