Since NOX4 is the most expressed NADPH oxidase in endothelial cells (Drummond and Sobey, 2014), the only isoform that is constitutively expressed and that requires only the p22phox component to be active (Martyn et al., 2006; Nisimoto et al., 2010; Tang et al., 2019), and also in agreement with the results obtained for the analysis of NOX4 expression, our results may indicate a possible reduction in the expression and activity of this enzyme, leading to a diminished NO bioavailability, reinforcing the signals of a condition of endothelial dysfunction (Langbein et al., 2016). Here, FMO5 is linked to endothelial dysfunction.