Hypercholesterolemia-Induced Erectile Dysfunction: Endothelial Nitric Oxide Synthase (eNOS) Uncoupling in the Mouse Penis by NAD(P)H Oxidase

Introduction: Hypercholesterolemia induces erectile dysfunction (ED) mostly by increasing oxidative stress and impairing endothelial function in the penis, but the mechanisms regulating reactive oxygen species (ROS) production in the penis are not understood. Aims: We evaluated whether hypercholesterolemia activates nicotinamide adenine dinucleotide phosphate (NAD[P]H) oxidase in the penis, providing an initial source of ROS to induce endothelial nitric oxide synthase (eNOS) uncoupling and endothelial dysfunction resulting in ED. Methods: Low-density-lipoprotein receptor (LDLR)-null mice were fed Western diet for 4 weeks to induce early-stage hyperlipidemia. Wild type (WT) mice fed regular chow served as controls. Mice received NAD(P)H oxidase inhibitor apocynin (10 mM in drinking water) or vehicle. Erectile function was assessed in response to cavernous nerve electrical stimulation. Markers of endothelial function (phospho [P]-vasodilator-stimulated-protein [VASP]-Ser-239), oxidative stress (4-hydroxy-2-nonenal [HNE]), sources of ROS (eNOS uncoupling and NAD[P]H oxidase subunits p67^phox, p47^phox, and gp91^phox), P-eNOS-Ser-1177, and eNOS were measured by Western blot in penes. Main Outcome Measures: The main outcome measures are the molecular mechanisms of ROS generation and endothelial dysfunction in hypercholesterolemia-induced ED. Results: Erectile response was significantly (P < 0.05) reduced in hypercholesterolemic LDLR-null mice compared with WT mice. Relative to WT mice, hypercholesterolemia increased (P < 0.05) protein expressions of NAD(P)H oxidase subunits p67^phox, p47^phox and gp91^phox, eNOS uncoupling, and 4-HNE-modified proteins, and reduced (P < 0.05) P-VASP-Ser-239 expression in the penis. Apocynin treatment of LDLR-null mice preserved (P < 0.05) maximal intracavernosal pressure, and reversed (P < 0.05) the abnormalities in protein expressions of gp67^phox and gp47^phox, 4-HNE, P-VASP-Ser-239, and eNOS uncoupling in the penis. Apocynin treatment of WT mice did not affect any of these parameters. Protein expressions of P-eNOS-Ser-1177 and total eNOS were unaffected by hypercholesterolemia. Conclusion: Activated NAD(P)H oxidase in the penis is an initial source of oxidative stress resulting in eNOS uncoupling, thus providing a mechanism of eNOS uncoupling and endothelial dysfunction in hypercholesterolemia-induced ED.