NADPH oxidase 4-derived hydrogen peroxide counterbalances testosterone-induced endothelial dysfunction and migration

Background: High levels of testosterone (Testo) are associated with cardiovascular risk by increasing reactive oxygen species (ROS) formation. NADPH oxidases (NOX) are the major source of ROS in the vasculature in cardiovascular diseases. NOX4 is a unique isotype, which produces hydrogen peroxide (H₂O₂), and its participation in cardiovascular biology is controversial. So far, it is unclear whether NOX4 protects from Testo-induced endothelial injury. Thus, we hypothesized that supraphysiological levels of Testo induce endothelial NOX4 expression to attenuate endothelial injury. Methods: Human Mesenteric Vascular Endothelial Cells (HMEC) and Human Umbilical Vein Endothelial Cells (HUVEC) were treated with Testo (10⁻⁷ M) with or without a NOX4 inhibitor [GLX351322 (10^-4 M)] or NOX4 siRNA. In vivo, 10-week-old C57Bl/6J male mice were treated with Testo (10 mg/kg) for 30 days to study endothelial function. Results: Testo increased mRNA and protein levels of NOX4 in HMEC and HUVEC. Testo increased superoxide anion (O₂⁻) and H₂O₂ production, which were abolished by NOX1 and NOX4 inhibition, respectively. Testo also attenuated bradykinin-induced NO production, which was further impaired by NOX4 inhibition. In vivo, Testo decreased H₂O₂ production in aortic segments and triggered endothelial dysfunction [decreased relaxation to acetylcholine (ACh)], which was further impaired by GLX351322 and by a superoxide dismutase and catalase mimetic (EUK134). Finally, Testo led to a dysregulated endothelial cells migration, which was exacerbated by GLX351322. Conclusion: These data indicate that supraphysiological levels of Testo increase the endothelial expression and activity of NOX4 to counterbalance the deleterious effects caused by Testo in endothelial function.