Sex-based differential regulation of oxidative stress in the vasculature by nitric oxide

BACKGROUND: Nitric oxide ((•)NO) is more effective at inhibiting neointimal hyperplasia following arterial injury in male versus female rodents, though the etiology is unclear. Given that superoxide (O2(•-)) regulates cellular proliferation, and (•)NO regulates superoxide dismutase-1 (SOD-1) in the vasculature, we hypothesized that (•)NO differentially regulates SOD-1 based on sex. MATERIALS AND METHODS: Male and female vascular smooth muscle cells (VSMC) were harvested from the aortae of Sprague-Dawley rats. O2(•-) levels were quantified by electron paramagnetic resonance (EPR) and HPLC. sod-1 gene expression was assayed by qPCR. SOD-1, SOD-2, and catalase protein levels were detected by Western blot. SOD-1 activity was measured via colorimetric assay. The rat carotid artery injury model was performed on Sprague-Dawley rats ±(•)NO treatment and SOD-1 protein levels were examined by Western blot. RESULTS: In vitro, male VSMC have higher O2(•-) levels and lower SOD - 1 activity at baseline compared to female VSMC (P < 0.05). (•)NO decreased O2(•-) levels and increased SOD - 1 activity in male (P<0.05) but not female VSMC. (•)NO also increased sod- 1 gene expression and SOD - 1 protein levels in male (P<0.05) but not female VSMC. In vivo, SOD-1 levels were 3.7-fold higher in female versus male carotid arteries at baseline. After injury, SOD-1 levels decreased in both sexes, but (•)NO increased SOD-1 levels 3-fold above controls in males, but returned to baseline in females. CONCLUSIONS: Our results provide evidence that regulation of the redox environment at baseline and following exposure to (•)NO is sex-dependent in the vasculature. These data suggest that sex-based differential redox regulation may be one mechanism by which (•)NO is more effective at inhibiting neointimal hyperplasia in male versus female rodents.