Travis D. Strong

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.

Sildenafil Inhibits Superoxide Formation and Prevents Endothelial Dysfunction in a Mouse Model of Secondhand Smoke Induced Erectile Dysfunction

PURPOSE We determined the effect of passive secondhand cigarette smoke on 1) erectile function in vivo, 2) molecular mechanisms involved in penile vascular function, and 3) erectile function and penile molecular signaling in the presence of phosphodiesterase type 5 inhibitor therapy. MATERIALS AND METHODS Four groups of mice were used, including group 1--controls, group 2--mice exposed to 3 weeks of secondhand smoke (5 hours per day for 5 days per week), group 3--control plus sildenafil (100 mg/kg per day) and group 4--smoke exposed plus sildenafil (100 mg/kg per day). Cavernous nerve electrical stimulation and intracavernous injection of acetylcholine were done to assess erectile function. Constitutive and inducible nitric oxide synthase activity, reactive oxygen species generation, nitrotyrosine formation and superoxide anion levels were assessed. RESULTS Decreased erectile responses to cavernous nerve electrical stimulation and impaired endothelium dependent erectile responses to ACh in mice exposed to secondhand smoke were observed. Superoxide anion was increased in endothelial and corporeal smooth muscle cells of smoking mouse penises. In mice exposed to secondhand smoke constitutive nitric oxide synthase activity was decreased, and inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation increased. Sildenafil therapy restored constitutive nitric oxide synthase activity in the penis of smoking mice, decreased inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation, and improved erectile responses to cavernous nerve electrical stimulation and acetylcholine. CONCLUSIONS Short-term exposure to secondhand smoke impairs erectile function through excessive penile reactive oxygen species signaling and inducible nitric oxide synthase activity. Decreased penile constitutive nitric oxide synthase activity may be attributable to the decreased endothelial nitric oxide synthase activity resulting from increased oxidative stress. Sildenafil therapy restored nitric oxide synthase activity and decreased reactive oxygen species signaling, resulting in improved erectile function.

Activated RhoA/Rho Kinase Impairs Erectile Function After Cavernous Nerve Injury in Rats

PURPOSE RhoA and rho kinase serve as key regulators of penile vascular homeostasis. The role of RhoA/rho kinase signaling in the penis after cavernous nerve injury has not been fully investigated. We characterized the molecular expression profiles of RhoA/rho kinase signaling that occur in the penis after cavernous nerve injury. We hypothesized that erectile dysfunction after bilateral cavernous nerve injury is accompanied by up-regulation of RhoA/rho kinase activity in the rat penis. MATERIAL AND METHODS We used 2 groups, including sham operation and bilateral cavernous nerve injury. At 14 days after nerve injury each group underwent cavernous nerve stimulation to determine erectile function at baseline and after intracavernous injection of the rho kinase inhibitor Y-27632 (Tocris Bioscience, Ellisville, Missouri). Penes were assessed at baseline for protein expression of neuronal nitric oxide synthase, RhoA, and rho kinase 1 and 2 by Western blot, immunoreactivity of neuronal nitric oxide synthase, rho kinase 1 and 2, RhoA-guanosine triphosphatase and rho kinase activity. RESULTS Erectile function was decreased in nerve injured rats. Neuronal nitric oxide synthase protein was significantly decreased while RhoA and rho kinase 2 protein levels were significantly increased in rat penes with nerve injury. Rho kinase 1 protein expression was equivalent. Rho kinase immunoreactivity was qualitatively increased in the corporeal smooth muscle of nerve injured rats. RhoA-guanosine triphosphatase and rho kinase activity was significantly increased in injured rat penes compared to that in sham operated penes. Intracavernous injection of Y-27632 caused a significantly greater increase in intracavernous pressure in nerve injured rats compared to that in sham operated rats, suggesting increased rho kinase activity. CONCLUSIONS Data suggest that RhoA/rho kinase up-regulation in response to cavernous nerve injury contributes to penile vasculature dysfunction after cavernous nerve injury. Thus, the RhoA/rho kinase pathway may be a suitable target for treating post-radical prostatectomy erectile dysfunction.

Serum Biomarker Measurements of Endothelial Function and Oxidative Stress After Daily Dosing of Sildenafil in Type 2 Diabetic Men With Erectile Dysfunction

PURPOSE We investigated changes in serum biomarkers of vascular function after short-term, continuous sildenafil dosing in men with type 2 diabetes with erectile dysfunction. MATERIALS AND METHODS Men with erectile dysfunction associated with type 2 diabetes mellitus were randomized to receive continuous, daily sildenafil (50 mg for 1 week run-in and 100 mg for 3 weeks) (148), or placebo (144) for 4 weeks (phase I) and then sildenafil (25, 50 or 100 mg) on demand for 12 weeks (phase II). Blood draws at baseline and after phases I and II were analyzed for cyclic guanosine monophosphate (endothelial function marker), 8-isoprostane (oxidative stress marker), and interleukin-6 and interleukin-8 (inflammatory cytokines). Primary and secondary erectile function outcome variables were affirmative responses on Sexual Encounter Profile question 3 (ability to maintain erection sufficient for sexual intercourse) and Erection Hardness Score, respectively. RESULTS Serum cyclic guanosine monophosphate levels were increased in the sildenafil group relative to the placebo group at 4 (p <0.01) and 16 (p <0.05) weeks, correlating with affirmative responses to Sexual Encounter Profile question 3 at the 4-week interval only (p <0.05). Serum 8-isoprostane levels were decreased to a nonsignificant degree in the sildenafil group at 4 weeks with no further change at 16 weeks, whereas interleukin-6 and interleukin-8 levels were unchanged at either interval, and these levels were unassociated with erectile function outcomes. CONCLUSIONS These data suggest that short-term, continuous sildenafil treatment causes systemic endothelial function to be enhanced and remain so for a duration after its discontinuation. However, they do not indicate any influence of this treatment on systemic oxidative stress or inflammation, or an effect on long-term erectile function improvement.

Endothelial Nitric Oxide Synthase Regulation in Female Genital Tract Structures

INTRODUCTION Female sexual arousal disorder (FSAD) is a major component of female sexual dysfunctions, affecting 25-70% of women. The mechanisms of FSAD are poorly understood. Estrogen contributes to the control of genital blood flow during the sexual response. Vascular effects of estrogen are mostly attributed to its regulation of endothelial nitric oxide (NO) production. However, the role of endothelial NO synthase (eNOS) and the mechanisms that regulate eNOS in female genital tract structures are largely unknown. AIM To review available evidence of the mechanisms of eNOS regulation in female genital tract structures. METHODS This article reviews the literature that relates to the role of NO and eNOS in female sexual arousal and its modulation by estrogen. MAIN OUTCOME MEASURES Association between female sexual arousal, NO, and eNOS. RESULTS The NO/cyclic guanosine monophosphate pathway is believed to have a primary role in the regulation of clitoral and vaginal blood flow, and smooth muscle relaxation during sexual arousal. Estrogen is critical for maintaining vaginal and clitoral blood flow and vaginal transudate production. Estrogen regulates eNOS by genomic mechanisms, involving augmented mRNA transcription and protein synthesis, and by non-genomic mechanisms, which occur without alterations in gene expression. However, limited studies have evaluated the physiological role of endothelial NO and the molecular mechanisms of eNOS regulation in the female genital tract. CONCLUSIONS The effects of estrogen on increasing genital blood flow and smooth muscle relaxation have been attributed mostly to regulation of eNOS. However, the exact mechanisms of eNOS regulation in female genital tract structures and the molecular basis for the eNOS defect with aging and vascular diseases warrant further investigation.

Attenuated RhoA/Rho-kinase signaling in penis of transgenic sickle cell mice.

OBJECTIVES The Ras homolog gene family, member A (RhoA) and its main downstream effector, Rho-kinase (ROCK) are important in maintaining the penis in the flaccid state. The pathophysiology of sickle cell disease-associated priapism is not well defined. We hypothesized that the RhoA/ROCK vasoconstrictive pathways might be involved in the development of priapism. Therefore, the objective of the present study was to evaluate the molecular changes in RhoA and ROCK in an established transgenic sickle cell mouse model of priapism. METHODS Two groups of mice were used: wild type (WT; C57BL/6) mice and transgenic sickle cell mice. We evaluated RhoA guanosine triphosphatase and total ROCK activities, as well as ROCK1 and ROCK2 protein expression, in WT and sickle mice penises. We also evaluated the in vivo erectile responses to cavernous nerve stimulation and the frequency and duration of spontaneous erections before and after cavernous nerve stimulation. RESULTS Sickle mice demonstrated significantly (P <.05) enhanced erectile responses to cavernous nerve stimulation and frequency of spontaneous erections both before and after cavernous nerve stimulation compared with the WT mice. The sickle mice penises had a significant decline in RhoA guanosine triphosphatase (P <.01) and total ROCK activities (P <.05) compared with the WT mice. A significant (P <.05) reduction in ROCK2 protein expression in sickle mice penises compared with WT mice protein expression. No change in ROCK1 protein expression was observed in either cohort of mice penises. CONCLUSIONS These data suggest that sickle cell disease associated-priapism might be contributed by a lack of RhoA/ROCK-mediated vasoconstriction and highlight a novel molecular mechanism in the pathophysiology of priapism.

Phosphodiesterase-5A (PDE5A) is localized to the endothelial caveolae and modulates NOS3 activity

AIMS It has been well demonstrated that phosphodiesterase-5A (PDE5A) is expressed in smooth muscle cells and plays an important role in regulation of vascular tone. The role of endothelial PDE5A, however, has not been yet characterized. The present study was undertaken to determine the presence, localization, and potential physiologic significance of PDE5A within vascular endothelial cells. METHODS AND RESULTS We demonstrate primary location of human, mouse, and bovine endothelial PDE5A at or near caveolae. We found that the spatial localization of PDE5A at the level of caveolin-rich lipid rafts allows for a feedback loop between endothelial PDE5A and nitric oxide synthase (NOS3). Treatment of human endothelium with PDE5A inhibitors resulted in a significant increase in NOS3 activity, whereas overexpression of PDE5A using an adenoviral vector, both in vivo and in cell culture, resulted in decreased NOS3 activity and endothelium-dependent vasodilation. The molecular mechanism responsible for these interactions is primarily regulated by cGMP-dependent second messenger. PDE5A overexpression also resulted in a significant decrease in protein kinase 1 (PKG1) activity. Overexpression of PKG1 rapidly activated NOS3, whereas silencing of the PKG1 gene with siRNA inhibited both NOS3 phosphorylation (S1179) and activity, indicating a novel role for PKG1 in direct regulation of NOS3. CONCLUSION Our data collectively suggest another target for PDE5A inhibition in endothelial dysfunction and provide another physiologic significance for PDE5A in the modulation of endothelial-dependent flow-mediated vasodilation. Using both in vitro and in vivo models, as well as human data, we show that inhibition of endothelial PDE5A improves endothelial function.

Whole genome microarray of the major pelvic ganglion after cavernous nerve injury: New insights into molecular profile changes after nerve injury

Whats known on the subject? and What does the study add?

Stem and endothelial progenitor cells in erection biology.

Erectile dysfunction (ED) is defined as the consistent inability to obtain or maintain an erection for satisfactory sexual relations. The past 20 years of basic science research on erection physiology has been devoted to investigating the pathogenesis of ED and has led to the conclusion that ED is predominately a disease of vascular origin with dramatic changes occurring in the endothelium. Research has also led to an understanding of the biochemical factors and intracellular mechanisms responsible for corporal smooth muscle contraction and relaxation and the influence of endothelium-derived relaxing factors. The development of methods to deliver both stem and endothelial cells to the penis has kindled a keen interest in treating ED with gene- and cell-based therapies. In this paper, erection physiology and stem cell biology is reviewed, and the potential application of novel cell-based therapies for the treatment of ED is discussed.

Post‐translational Regulation of Endothelial Nitric Oxide Synthase (eNOS) by Estrogens in the Rat Vagina

INTRODUCTION Estrogens control vaginal blood flow during female sexual arousal mostly through nitric oxide (NO). Although vascular effects of estrogens are attributed to an increase in endothelial NO production, the mechanisms of endothelial NO synthase (eNOS) regulation by estrogens in the vagina are largely unknown. AIMS Our hypothesis was that estrogens regulate eNOS post-translationally in the vagina, providing a mechanism to affect NO bioavailability without changes in eNOS protein expression. METHODS We measured eNOS phosphorylation and eNOS interaction with caveolin-1 and heat shock protein 90 (HSP90) in the distal and proximal vagina of female rats at diestrus, 7 days after ovariectomy and 2 days after replacement of ovariectomized rats with estradiol-17beta (15 microg). MAIN OUTCOME MEASURES Molecular mechanisms of eNOS regulation by estrogen in the rat vagina. RESULTS We localized phospho-eNOS (Ser-1177) immunohistochemically to the endothelium lining blood vessels and vaginal sinusoids. Estrogen withdrawal decreased phosphorylation of eNOS on its positive regulatory site (Ser-1177) and increased eNOS binding to its negative regulator caveolin-1 (without affecting eNOS/HSP90 interaction), and they were both normalized by estradiol replacement. Protein expressions of phosphorylated Akt (protein kinase B) and extracellular signal-regulated protein kinase 1/2 (ERK1/2) were not affected by estrogen status, suggesting that the effect of estrogens on eNOS (Ser-1177) phosphorylation was not mediated by activated AKT or ERK1/2. eNOS phosphorylation on its negative regulatory site (Ser-114) was increased in the vagina by estrogen withdrawal and normalized by estradiol replacement, implying that the maintenance of low phosphorylation of eNOS on this site by estradiol may limit eNOS interaction with caveolin-1 and preserve the enzymes activity. Total eNOS, inducible NOS, caveolin-1, and HSP90 protein expressions were not affected by ovariectomy or estradiol replacement in the distal or proximal vagina. CONCLUSIONS These results define novel estrogen signaling mechanisms in the vagina which involve eNOS phosphorylation and eNOS-caveolin-1 interaction.