Endothelial nitric oxide synthase protein expression, localization, and activity in the penis of the alloxan-induced diabetic rat

Treatment Outcomes of Diabetic Patients With Erectile Dysfunction Prescribed High-Dose Tadalafil

Objective: To assess the treatment outcome of diabetic patients with erectile dysfunction who are prescribed an alternate daily high dose of tadalafil over a 120-day treatment period. Methods: This was a single-site, retrospective, observational study of 63 diabetic men with erectile dysfunction prescribed an alternate daily dose of 30mg of tadalafil between January 1, 2021, and December 31, 2021. Treatment outcomes accessed medication compliance, adverse drug reactions, and patient treatment satisfaction at 60- and 120-days treatment. Results: Mean age of patients was 58.3 years and included patients who suffered from comorbidities ranging from hypertension (54.0%), dyslipidemia (52.3%), and depression (9.5%). At 60 days in the study, 69.8% were satisfied and continued the treatment. However, at the end of the 120-treatment period, a low number of men (17.5%) were satisfied with the treatment and therefore did not remain on the treatment protocol. These patients reported a lack of medication dose efficacy (86.5%), non-compliance with treatment as prescribed (65.4%), and adverse drug reactions (30.8%) as reasons for discontinuing treatment. None of the identified patient demographics were significantly associated with 120-day continuous treatment. Similarly, the odds ratio derived from the logistic regression did not demonstrate an association between the selected variables and the outcome of 120-day continuous treatment retention. Conclusion: This retrospective case series study found that 82.5% of diabetic patients were not satisfied with treatment with alternate dosing of 30mg tadalafil to treat their ED at the end of the 120-day treatment period suggesting an alternative treatment plan.

Erectile Dysfunction Severity: The Role of Glycometabolic Compensation and Antihyperglycemic Drugs

Background: The aim of this study was to evaluate the prevalence of DM among patients with ED and the impact of glycometabolic compensation and antihyperglycemic treatment on ED severity. Methods: In total, 1332 patients with ED were enrolled. The diagnosis was performed through the International-Index-of-Erectile-Function questionnaire. ED severity was considered according to presence/absence of spontaneous erections, maintenance/achievement deficiency and response to PDE5-i. DM patients were clustered according to antihyperglycemic treatment: “metformin”/“insulin”/“old antihyperglycemic drugs”/“new antihyperglycemic drugs”. Results: The prevalence of DM patients was 15.8% (Group A, patients with ED and DM). Among these, the prevalence of spontaneous erections (21.0%) was lower than in the remaining patients (Group B, patients with ED without DM) (32.0%, p < 0.001). The prevalence of poor response to PDE5-i was lower in Group B (10.0%) than in Group A (35.0%, p < 0.001). Patients with good response to PDE5-i therapy showed lower HbA1c values than patients with poor/no response (6.6 ± 1.1% vs. 7.7 ± 1.9%, p = 0.02). The prevalence of absent response to PDE5-i was higher in patients treated with old antidiabetic drugs than in the population treated with new drugs (p = 0.03). Conclusion: The severity of ED and lower response to PDE5-i were higher in DM patients. A better glycometabolic profile, as well as new antihyperglycemic drugs, seem to have a positive effect on ED.

Effect of leech-centipede medicine on improving erectile function in diabetes-induced erectile dysfunction rats via PDE5 signalling pathway-related molecules

CONTEXT

The leech and centipede granules have good curative effects on many diabetic vascular diseases, including diabetes-induced erectile dysfunction (DIED).

OBJECTIVE

To explore the effect of leech and centipede on erectile function in rats with diabetes-induced erectile dysfunction and its possible mechanism.

MATERIALS AND METHODS

Thirty male Sprague-Dawley DIED rats were randomly divided into the model group (Group M), low-dose group (Group DD), high-dose group (Group DG) and tadalafil group (Group T) (n = 6); diabetic rats were induced by streptozotocin. Apomorphine was used to induce diabetic erectile dysfunction. The 'leech-centipede' granules (0.15 and 0.6 g/kg) were intragastrically administered in the DD and DG groups for 8 weeks. Blood glucose, serum insulin, testosterone, cGMP levels and protein expression changes were measured in each group.

RESULTS

After 8 weeks, the erectile function of rats in the DG group significantly improved (1.26 ± 0.73). Penis tissue cGMP levels were higher in the DG group (1.48 ± 0.11) than in the M group (0.58 ± 0.15). Protein and mRNA expression levels of NOS were significantly higher (0.77 ± 0.05; 0.61 ± 0.02) but those of PDE5 (0.43 ± 0.05; 0.61 ± 0.03) were lower in the DG group than in the M group (0.37 ± 0.06; 0.51 ± 0.01; 0.78 ± 0.06; 0.81 ± 0.04).

CONCLUSION

The leech-centipede can improve erectile dysfunction in DIED rats by regulating the expression of cGMP, NOS, and PDE5-related molecules in the PDE5 pathway. This study provides a potential mechanism for the treatment of DIED with leech-centipede.

Constitutive LH receptor activity impairs NO-mediated penile smooth muscle relaxation

Timely activation of the luteinizing hormone receptor (LHCGR) is critical for fertility. Activating mutations in LHCGR cause familial male-limited precocious puberty (FMPP) due to premature synthesis of testosterone. A mouse model of FMPP (KiLHRD582G), expressing a constitutively activating mutation in LHCGR, was previously developed in our laboratory. KiLHRD582G mice became progressively infertile due to sexual dysfunction and exhibited smooth muscle loss and chondrocyte accumulation in the penis. In this study, we tested the hypothesis that KiLHRD582G mice had erectile dysfunction due to impaired smooth muscle function. Apomorphine-induced erection studies determined that KiLHRD582G mice had erectile dysfunction. Penile smooth muscle and endothelial function were assessed using penile cavernosal strips. Penile endothelial cell content was not changed in KiLHRD582G mice. The maximal relaxation response to acetylcholine and the nitric oxide donor, sodium nitroprusside, was significantly reduced in KiLHRD582G mice indicating an impairment in the nitric oxide (NO)-mediated signaling. Cyclic GMP (cGMP) levels were significantly reduced in KiLHRD582G mice in response to acetylcholine, sodium nitroprusside and the soluble guanylate cyclase stimulator, BAY 41-2272. Expression of NOS1, NOS3 and PKRG1 were unchanged. The Rho-kinase signaling pathway for smooth muscle contraction was not altered. Together, these data indicate that KiLHRD582G mice have erectile dysfunction due to impaired NO-mediated activation of soluble guanylate cyclase resulting in decreased levels of cGMP and penile smooth muscle relaxation. These studies in the KiLHRD582G mice demonstrate that activating mutations in the mouse LHCGR cause erectile dysfunction due to impairment of the NO-mediated signaling pathway in the penile smooth muscle.

Elevated pigment epithelium-derived factor induces diabetic erectile dysfunction via interruption of the Akt/Hsp90β/eNOS complex

AIMS/HYPOTHESIS

Diabetes mellitus erectile dysfunction (DMED) is a common complication of diabetes. The level of pigment epithelium-derived factor (PEDF) is significantly upregulated in the serum of individuals with obesity and diabetes. However, whether elevated PEDF levels contribute to DMED remains unknown. This study aimed to investigate the pathogenic role of PEDF and its related mechanism in DMED.

METHODS

We enrolled 65 men, of whom 20 were nondiabetic control participants, 21 participants with diabetes but without erectile dysfunction, and 24 with DMED. The International Index of Erectile Function (IIEF-5) questionnaire was administered to evaluate erectile function. Plasma PEDF in diabetic participants and streptozotocin (STZ)-induced diabetic animals was detected by ELISA. Erectile function was evaluated by measuring the intracavernous pressure (ICP) and the ICP/mean arterial pressure (MAP) ratio in STZ-induced diabetic rats treated with PEDF-neutralising antibody (PEDF-Ab), db/db mice treated with PEDF-Ab, and Pedf knockout mice with STZ-induced diabetes. The overexpression of PEDF was implemented by intraperitoneal injection of recombinant PEDF and intracavernous injection of PEDF-expressing adenovirus. A mechanistic study was performed by immunofluorescence staining, bimolecular fluorescence complementation (BiFC), immunoprecipitation and western blotting.

RESULTS

We found that the plasma level of PEDF was significantly higher in participants with DMED compared with diabetic counterparts without erectile dysfunction and nondiabetic controls. Interestingly, PEDF levels were negatively correlated with plasma nitrite/nitrate levels and erectile function in DMED patients and STZ-induced diabetic rats. Furthermore, overexpression of PEDF significantly suppressed ICP and endothelial nitric oxide synthase (eNOS) phosphorylation in control rats. In contrast, the PEDF-Ab and Pedf knockout ameliorated ICP and eNOS phosphorylation in diabetic rats and mice. Mechanistically, PEDF promoted the membrane translocation of Hsp90β and directly bound to the amino acid residues 341-724 of Hsp90β on the endothelial cell surface, subsequently blocking intracellular Hsp90β/Akt/eNOS complex formation and downregulating eNOS phosphorylation.

CONCLUSIONS/INTERPRETATION

These results indicate that elevated PEDF levels contribute to impaired erectile function by suppressing Hsp90β-mediated eNOS phosphorylation and that PEDF may represent a novel therapeutic target for diabetic erectile dysfunction. Graphical abstract.

Malaysian propolis and metformin mitigate subfertility in streptozotocin-induced diabetic male rats by targeting steroidogenesis, testicular lactate transport, spermatogenesis and mating behaviour

BACKGROUND

Diabetes mellitus is one of the risk factors for male subfertility/infertility. Malaysian propolis is reported to decrease hyperglycaemia in diabetic state.

OBJECTIVES

The present study investigated the protective effect of Malaysian propolis on diabetes-induced subfertility/infertility. Additionally, its combined beneficial effects with metformin were investigated.

MATERIALS AND METHODS

Forty adult male Sprague Dawley rats were randomly assigned into five groups, namely normal control, diabetic control, diabetic + Malaysian propolis (300 mg/k.g. b.w.), diabetic + metformin (300 mg/kg b.w.) and diabetic + Malaysian propolis + metformin. Diabetes was induced using a single intraperitoneal injection of streptozotocin (60 mg/kg b.w.) and treatment lasted for 4 weeks. During the 4th week, mating behavioural experiments were performed using sexually receptive female rats. Thereafter, fertility parameters were assessed in the female rats.

RESULTS

Malaysian propolis increased serum and intratesticular free testosterone levels, up-regulated the mRNA levels of AR and luteinizing hormone receptor, up-regulated the mRNA and protein levels of StAR, CYP11A1, CYP17A1, 3β-HSD and 17β-HSD in the testes of diabetic rats. Furthermore, Malaysian propolis up-regulated testicular MCT2, MCT4 and lactate dehydrogenase type C mRNA levels, in addition to improving sperm parameters (count, motility, viability and normal morphology) and decreasing sperm nDNA fragmentation in diabetic rats. Malaysian propolis improved mating behaviour by increasing penile guanosine monophosphate levels. Malaysian propolis also improved fertility outcome as seen with decreases in pre- and post-implantation losses, increases in gravid uterine weight, litter size per dam and foetal weight. Malaysian propolis's effects were comparable to metformin. However, their combination yielded better results relative to the monotherapeutic interventions.

CONCLUSION

Malaysian propolis improves fertility potential in diabetic state by targeting steroidogenesis, testicular lactate metabolism, spermatogenesis and mating behaviour, with better effects when co-administered with metformin. Therefore, Malaysian propolis shows a promising complementary effect with metformin in mitigating Diabetes mellitus-induced subfertility/infertility.

Translational Perspective on the Role of Testosterone in Sexual Function and Dysfunction

INTRODUCTION

The biological importance of testosterone is generally accepted by the medical community; however, controversy focuses on its relevance to sexual function and the sexual response, and our understanding of the extent of its role in this area is evolving.

AIM

To provide scientific evidence examining the role of testosterone at the cellular and molecular levels as it pertains to normal erectile physiology and the development of erectile dysfunction and to assist in guiding successful therapeutic interventions for androgen-dependent sexual dysfunction.

METHODS

In this White Paper, the Basic Science Committee of the Sexual Medicine Society of North America assessed the current basic science literature examining the role of testosterone in sexual function and dysfunction.

RESULTS

Testosterone plays an important role in sexual function through multiple processes: physiologic (stimulates activity of nitric oxide synthase), developmental (establishes and maintains the structural and functional integrity of the penis), neural (development, maintenance, function, and plasticity of the cavernous nerve and pelvic ganglia), therapeutically for dysfunctional regulation (beneficial effect on aging, diabetes, and prostatectomy), and phosphodiesterase type 5 inhibition (testosterone supplement to counteract phosphodiesterase type 5 inhibitor resistance).

CONCLUSION

Despite controversies concerning testosterone with regard to sexual function, basic science studies provide incontrovertible evidence for a significant role of testosterone in sexual function and suggest that properly administered testosterone therapy is potentially advantageous for treating male sexual dysfunction.

Improvement of erectile dysfunction by the active pepide from Urechis unicinctus by high temperature/pressure and ultra - wave assisted lysis in Streptozotocin Induced Diabetic Rats

Introduction:

We investigate the effect of active peptide from Urechis unicinctus (UU) by high temperature/pressure and ultra-wave assisted lysis on erectile dysfunction in streptozotocin-induced diabetic rats.

Materials and Methods:

Forty 12-week-old Sprague-Dawley rats were used in this study. Diabetes was induced by a one-time intraperitoneal injection of streptozotocin (50mg/kg). One week later, the diabetic rats were randomly divided into four groups: normal control, untreated diabetes control, and groups treated with 100 or 500mg/kg/d UU peptide. Rats were fed with UU peptide by intragastric administration for 8 weeks. After 8 weeks, penile hemodynamic function was evaluated in all groups by measuring the intracavernosal pressure after electrostimulating the cavernous nerve. Nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) activities were measured and endothelial nitric oxide synthase (eNOS) and neuronal NOS (nNOS) protein expression was determined by Western blot.

Results:

Maximum intracavernosal pressure in diabetic control rats decreased significantly compared to normal control rats, and was increased significantly compared to untreated diabetic rats after UU peptide supplementation. Treatment with the higher dose of UU peptide significantly increased the NO and cGMP levels compared with the diabetic control group. Decreased activity and expression eNOS and nNOS were found in the diabetic rats compared with the normal control group. Decreased eNOS and nNOS in diabetic rats were improved by UU peptide administration.

Conclusions:

Active peptide from UU ameliorates erectile function in a streptozotocin induced diabetic rat model of erectile dysfunction.

Animal models of erectile dysfunction

Animal models have contributed to a great extent to understanding and advancement in the field of sexual medicine. Many current medical and surgical therapies in sexual medicine have been tried based on these animal models. Extensive literature search revealed that the compiled information is limited. In this review, we describe various experimental models of erectile dysfunction (ED) encompassing their procedures, variables of assessment, advantages and disadvantages. The search strategy consisted of review of PubMed based articles. We included original research work and certain review articles available in PubMed database. The search terms used were “ED and experimental models,” “ED and nervous stimulation,” “ED and cavernous nerve stimulation,” “ED and central stimulation,” “ED and diabetes mellitus,” “ED and ageing,” “ED and hypercholesteremia,” “ED and Peyronie's disease,” “radiation induced ED,” “telemetric recording,” “ED and mating test” and “ED and non-contact erection test.”

Understanding and targeting the Rho kinase pathway in erectile dysfunction

Erectile dysfunction (ED) is a common disorder that affects a quarter of US men, and has many causes, including endothelial impairment, low testosterone levels, prior surgical manipulation, and/or psychogenic components. Penile erection is a complex process requiring neurally mediated relaxation of arteriolar smooth muscle and engorgement of cavernosal tissues, mediated by nitric oxide (NO). Current medical therapies for ED largely seek to maximize endogenous NO signalling. Certain aetiologies, including diabetes, are difficult to treat with current modalities, emphasizing the need for new molecular targets. Research has demonstrated the importance of RhoA-Rho-associated protein kinase (ROCK) signalling in maintaining a flaccid penile state, and inhibition of RhoA-ROCK signalling potentiates smooth-muscle relaxation in an NO-independent manner. The mechanisms and effects of RhoA-ROCK signalling and inhibition suggest that the RhoA-ROCK pathway could prove to be a new therapeutic target for the treatment of ED.

Hydroxyl fasudil, an inhibitor of Rho signaling, improves erectile function in diabetic rats: a role for neuronal ROCK

INTRODUCTION

The pathogenesis of diabetic erectile dysfunction (ED) includes neuropathy, but the molecular basis for neurogenic ED is incompletely understood. The RhoA/ROCK pathway has been implicated in diabetic neuropathy and in ED, but its role in diabetic neurogenic ED is not known.

AIMS

The aim of this study was to determine whether hydroxyl fasudil, a ROCK inhibitor, affects diabetic neuropathy-related ED.

METHODS

Type 1 diabetes mellitus was induced in male rats by streptozotocin (75 mg/kg, intraperitoneally). After 8 weeks, diabetic rats were administered hydroxyl fasudil, a selective ROCK inhibitor (10 mg/kg/day, intraperitoneally) or vehicle, for 4 weeks. Age-matched control, nondiabetic, rats were treated intraperitoneally for 4 weeks with saline. At week 12, after a 2 day washout, neuro-stimulated erectile function was evaluated. Major pelvic ganglia (MPG) were collected for Western blot analysis of RhoA, ROCK-1, ROCK-2, phospho (P)-AKT (Ser(473) ), and P-phosphatase and tensin homolog (P-PTEN) (Ser(380) /Thr(382/383) ).

MAIN OUTCOME MEASURES

Effect of ROCK inhibitor hydroxyl fasudil on erectile function and ROCK/P-AKT/P-PTEN pathway in the MPG of diabetic rats.

RESULTS

Erectile response was significantly (P < 0.05) reduced in diabetic rats compared with nondiabetic rats and was preserved (P < 0.05) in diabetic rats treated with hydroxyl fasudil. In diabetic rats, RhoA and ROCK-2 protein expressions in MPG were increased (P < 0.05) and remained increased in hydroxyl fasudil-treated rats. P-AKT (Ser(473) ) expression was decreased (P < 0.05), whereas P-PTEN (Ser(380) /Thr(382/383) ) expression was increased (P < 0.05) in MPG of diabetic rats compared with nondiabetic rats, and both were reversed (P < 0.05) in diabetic rats treated with hydroxyl fasudil.

CONCLUSION

Improved erectile function and restored P-AKT and P-PTEN in the MPG with hydroxyl fasudil treatment suggest the role of Rho signaling via PTEN/AKT pathway in neurogenic diabetic ED.

Panax notoginseng saponins improve erectile function through attenuation of oxidative stress, restoration of Akt activity and protection of endothelial and smooth muscle cells in diabetic rats with erectile dysfunction

Panax notoginseng saponins (PNS), which have an antioxidant property, are a widely used traditional Chinese medicine. In this study we investigated whether PNS can improve erectile function in rats with erectile dysfunction and the underlying mechanism by using a rat diabetic erectile dysfunction model. The rats were randomly divided into four groups: three PNS-treated groups (50, 100 and 150 mg/kg) and one saline-treated control group. Four weeks post treatment, electrostimulation was applied to the cavernous nerve and intracavernous pressure was measured to assess erectile function. Malondialdehyde, superoxide dismutase and glutathione were detected in the penises of all rats. Ultrastructural changes in the penises were examined by electron microscopy. Expression of Akt was detected by immunohistochemistry. The results showed that intracavernous pressure was increased in PNS-treated groups (100 and 150 mg/kg) compared to the control group. The levels of superoxide dismutase, glutathione and Akt were increased (p < 0.05) while that of malondialdehyde was decreased in the PNS groups. Ruptured endothelium, impaired smooth muscle cells and thrombus in the penises were detected by electron microscopy in the control group, but not in the PNS groups (10 and 150 mg/kg). The results suggest that PNS improves erectile function in diabetic rats. This improvement was associated with increased Akt expression, suppressed oxidative stress and restored functions of endothelial cells and smooth muscle cells in the penis.

Nitric Oxide Synthase is Necessary for Normal Urogenital Development

Introduction

Neuronal nitric oxide synthase (NOS-I) is significantly decreased with Cavernous Nerve (CN) injury in Erectile Dysfunction (ED) models. Increased apoptosis and collagen deposition accompany decreased NOS/CN injury, however these changes are typically attributed to the altered signaling of other factors, and a contribution of NOS in maintenance of urogenital structures has not previously been examined. Morphological changes in the corpora cavernosa occur at the same time as decreased NOS, suggesting a potential connection between decreased/inhibited NOS and morphological changes associated with ED. In this study we propose that NOS impacts urogenital morphology during development and will examine this hypothesis by NOS inhibition with L-NAME.

Methods

Primary outcomes were H&E, western and TUNEL to determine if penis, prostate and bladder morphology were altered with L-NAME treatment of Postnatal day 4 (P4) Sprague Dawley rats for 8 days. Tissue weight and immunohistochemical analysis for NOS were performed. Secondary evaluation of NOS-I regulation by Sonic Hedgehog (SHH) was examined by SHH inhibition in the pelvic ganglia (PG) and NOS-I protein was quantified by western in the PG/CN and penis. Nos abundance was quantified by RT-PCR during urogenital development and after CN injury.

Results

Apoptosis increased and penis, prostate and bladder morphology were altered with L-NAME. NOS inhibition decreased bladder weight 25%. SHH inhibition decreased NOS-I 35% in the PG/CN and 47% in the penis. Nos-III expression spiked within the first two weeks after birth in the penis but remained abundant in the adult. In the prostate, Nos-III was abundant immediately after birth and declined steadily with age. Nos-I expression in the PG/CN decreased sharply with CN injury and returned to baseline by 7 days.

Conclusions

NOS is required for normal urogenital development. Since NOS is decreased with ED, it may contribute to the abnormal morphology observed in ED patients and animal models.

Diabetes severity, metabolic syndrome, and the risk of erectile dysfunction

INTRODUCTION

Erectile dysfunction (ED) is more common in men with type 2 diabetes mellitus (T2DM), obesity, and/or the metabolic syndrome (MetS).

AIM

The aim of this study is to investigate the associations among proxy measures of diabetic severity and the presence of MetS with ED in a nationally representative U.S. data sample.

METHODS

We performed a cross-sectional analysis of adult participants in the 2001-2004 National Health and Nutrition Examination Survey.

MAIN OUTCOME MEASURES

ED was ascertained by self-report. T2DM severity was defined by calculated measures of glycemic control and insulin resistance (IR). IR was estimated using fasting plasma insulin (FPI) levels and the homeostasis model assessment of IR (HOMA-IR) definition. We classified glycemic control using hemoglobin-A1c (HbA1c) and fasting plasma glucose (FPG) levels. MetS was defined by the American Heart Association and National Heart, Lung, and Blood Institute criteria. Logistic regression models, adjusted for sociodemographics, risk factors, and comorbidities, were fitted for each measure of T2DM severity, MetS, and the presence of ED.

RESULTS

Proxy measures of glycemic control and IR were associated with ED. Participants with FPG between 100-126 mg/dL (5.6-7 mmol/L) and ≥ 126 mg/dL (>7 mmol/L) had higher odds of ED, odds ratio (OR) 1.22 (confidence interval or CI, 0.83-1.80), and OR 2.68 (CI, 1.48-4.86), respectively. Participants with HbA1c 5.7-6.4% (38.8-46.4 mmol/mol) and ≥ 6.5% (47.5 mmol/mol) had higher odds of ED (OR 1.73 [CI, 1.08-2.76] and 3.70 [CI, 2.19-6.27], respectively). When FPI and HOMA-IR were evaluated by tertiles, there was a graded relation among participants in the top tertile. In multivariable models, a strong association remained between HbA1c and ED (OR 3.19 [CI,1.13-9.01]). MetS was associated with >2.5-fold increased odds of self reported ED (OR 2.55 [CI, 1.85-3.52]).

CONCLUSIONS

Poor glycemic control, impaired insulin sensitivity, and the MetS are associated with a heightened risk of ED.

Akita spontaneously type 1 diabetic mice exhibit elevated vascular arginase and impaired vascular endothelial and nitrergic function

BACKGROUND

Elevated arginase (Arg) activity is reported to be involved in diabetes-induced vascular endothelial dysfunction. It can reduce L-arginine availability to nitric oxide (NO) synthase (NOS) and NO production. Akita mice, a genetic non-obese type 1 diabetes model, recapitulate human diabetes. We determined the role of Arg in a time-course of diabetes-associated endothelial dysfunction in aorta and corpora cavernosa (CC) from Akita mice.

METHODS AND RESULTS

Endothelium-dependent relaxation, Arg and NOS activity, and protein expression levels of Arg and constitutive NOS were assessed in aortas and CC from Akita and non-diabetic wild type (WT) mice at 4, 12 and 24 wks of age. Systolic blood pressure (SBP) was assessed by tail cuff. In aorta and CC, Akita mice exhibited a progressive impairment of vascular endothelial and nitrergic function increased Arg activity and expression (Arg1 in aorta and both Arg1 and Arg2 in CC) compared with that of age-matched WT mice. Treatment of aorta and CC from Akita mice with an Arg inhibitor (BEC or ABH) reduced diabetes-induced elevation of Arg activity and restored endothelial and nitrergic function. Reduced levels of phospho-eNOS at Ser(1177) (in aorta and CC) and nNOS expression (in CC) were observed in Akita mice at 12 and 24 wks. Akita mice also had decreased NOS activity in aorta and CC at 12 and 24 wks that was restored by BEC treatment. Further, Akita mice exhibited moderately increased SBP at 24 wks and increased sensitivity to PE-induced contractions in aorta and sympathetic nerve stimulation in CC at 12 and 24 wks.

CONCLUSIONS

Over 24 wks of diabetes in Akita mice, both aortic and cavernosal tissues exhibited increased Arg activity/expression, contributing to impaired endothelial and nitrergic function and reduced NO production. Our findings demonstrate involvement of Arg activity in diabetes-induced impairment of vascular function in Akita mouse.

Nitric oxide-releasing polymeric microspheres improve diabetes-related erectile dysfunction

INTRODUCTION

We have used a long-acting nitric oxide (NO)-releasing polymer to develop injectable biodegradable microspheres capable of localized NO release over prolonged periods of time.

AIM

The aim of this study was to evaluate the therapeutic potential of these microspheres for diabetes-related erectile dysfunction (ED) in the rat model.

METHODS

NO-releasing microspheres were incubated in physiologic buffer, and in vitro NO release was measured using a Griess assay. To ensure no migration, microspheres were fluorescently tagged and injected into the corpus cavernosum of adult rats, and fluorescent imaging was performed weekly for 4 weeks, at which point rats were sacrificed. To assess physiologic efficacy, diabetes was induced in 40 rats using streptozotocin (STZ), whereas 10 rats were kept as age-matched controls. Diabetic rats were divided into four groups: no treatment, sildenafil, NO-releasing microspheres, and combination therapy. For each rat, the cavernosal nerve (CN) was stimulated at various voltages, and intracavernosal pressure (ICP) and mean arterial pressure (MAP) were measured via corpus cavernosum and carotid artery catheterization, respectively. Long-term efficacy was determined by injecting diabetic rats with microspheres and measuring erectile response at predetermined intervals for up to 5 weeks.

MAIN OUTCOME MEASURES

Erectile response was determined via calculation of mean peak ICP/MAP and area under curve (AUC) for each experimental group.

RESULTS

Under physiologic conditions in vitro, microspheres continued NO release for up to 4 weeks. Fluorescent imaging revealed no detectable signal in tissues besides cavernosal tissue at 4 weeks postinjection. Upon CN stimulation, peak ICP/MAP ratio and AUC of diabetic rats improved significantly (P < 0.05) in microsphere and combination therapy groups compared with no treatment and sildenafil groups. In long-term efficacy studies, microspheres augmented the effect of sildenafil for 3 weeks following injection (P < 0.05).

CONCLUSIONS

NO-releasing microspheres significantly improved erectile response in diabetic rats for 3 weeks and hence offer a promising approach to ED therapy, either as monotherapy or combination therapy.

Panax notoginseng saponins improve the erectile dysfunction in diabetic rats by protecting the endothelial function of the penile corpus cavernosum

Diabetes mellitus (DM)-associated ED is predominantly due to neurovascular dysfunction mediated by nitric oxide (NO) suppression. Panax notoginseng saponins (PNS) are widely used for treating cardiovascular disease in China. The aim of this study was to evaluate the effects of PNS on penile erection and corpus cavernosum tissues in rats with diabetes-associated ED. Four weeks after PNS treatment, erectile function was assessed by intracavernous pressure (ICP) and mean arterial pressure (MAP) measurements. The level of NO, cyclic guanosine monophosphate (cGMP) and advanced glycation end products (AGEs) in cavernous tissue were assessed. Immunohistochemical staining and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) were performed for detecting endothelial NO synthase (eNOS) and apoptosis, respectively. The results show that ICP/MAP ratio was significantly increased in high-dose (150 mg kg(-1) per day) PNS-treated group compared with the diabetic ED untreated group (DM group). Compared with the untreated group, the expression of eNOS and the levels of NO and cGMP were increased in the PNS-treated groups. Moreover, apoptosis was markedly decreased in the group that received 150 mg kg(-1) per day of PNS. These results suggest that PNS may be used for improving the ED in diabetic rats via the NO/cGMP pathway and restores the function of endothelium in corpus cavernosum.

Arginase II deletion increases corpora cavernosa relaxation in diabetic mice

INTRODUCTION

Diabetes-induced erectile dysfunction involves elevated arginase (Arg) activity and expression. Because nitric oxide (NO) synthase and Arg share and compete for their substrate L-arginine, NO production is likely linked to regulation of Arg. Arg is highly expressed and implicated in erectile dysfunction.

AIM

It was hypothesized that Arg-II isoform deletion enhances relaxation function of corpora cavernosal (CC) smooth muscle in a streptozotocin (STZ) diabetic model.

METHODS

Eight weeks after STZ-induced diabetes, vascular functional studies, Arg activity assay, and protein expression levels of Arg and constitutive NOS (using Western blots) were assessed in CC tissues from nondiabetic wild type (WT), diabetic (D) WT (WT + D), Arg-II knockout (KO), and Arg-II KO+D mice (N = 8-10 per group).

MAIN OUTCOME MEASURES

Inhibition or lack of arginase results in facilitation of CC relaxation in diabetic CC.

RESULTS

Strips of CC from Arg-II KO mice exhibited an enhanced maximum endothelium-dependent relaxation (from 70 + 3% to 84 + 4%) and increased nitrergic relaxation (by 55%, 71%, 42%, 42%, and 24% for 1, 2, 4, 8 and 16 Hz, respectively) compared with WT mice. WT + D mice showed a significant reduction of endothelium-dependent maximum relaxation (44 + 8%), but this impairment of relaxation was significantly prevented in Arg-II KO+D mice (69 + 4%). Sympathetic-mediated and alpha-adrenergic agent-induced contractile responses also were increased in CC strips from D compared with non-D controls. Contractile responses were significantly lower in Arg-II KO control and D versus the WT groups. WT + D mice increased Arg activity (1.5-fold) and Arg-II protein expression and decreased total and phospho-eNOS at Ser-1177, and nNOS levels. These alterations were not seen in Arg-II KO mice. Additionally, the Arg inhibitor BEC (50 µM) enhanced nitrergic and endothelium-dependent relaxation in CC of WT + D mice.

CONCLUSION

These studies show for the first time that Arg-II deletion improves CC relaxation in type 1 diabetes.

Association Analysis of Endothelial Nitric Oxide Synthase G894T Gene Polymorphism and Erectile Dysfunction Complaints in a Population-Based Survey

Introduction

Erectile dysfunction (ED) is a common disorder leading to a serious, negative impact on the quality of the patient’s life. The gene encoding endothelial nitric oxide synthase (eNOS) is an interesting candidate gene for understanding the physiopathology of ED, as it is involved in the catalytic production of nitric oxide (NO), the neurotransmitter that plays a critical role in penile tumescence and erection.

Aim

To evaluate a potential association between the G894T polymorphism in the eNOS gene and ED complaints in a population-based sample in São Paulo, Brazil.

Main Outcome Measures

The prevalence of ED complaints was estimated according to the answer to the question “How would you describe your ability to get and keep an erection that is adequate for satisfactory intercourse?” ED was considered to be present if the response was “sometimes” or “never.”

Methods

A total of 449 men were enrolled in the study and answered an eight-item questionnaire to ascertain sexual performance/ED and satisfaction. The eNOS G894T polymorphism was genotyped using a standard polymerase chain reaction method.

Results

Univariate analysis demonstrated that ED was associated with diabetes, hypertension, sleep apnea severity, increasing age and body mass index, as well as testosterone levels (P &lt;0.05). Forward multiple regression models indicated that age was the only independent factor associated with ED in this population (odds ratio=1.09; 95% CI 1.06–1.11; P &lt;0.0001). Genotypic and allelic analyses provided no evidence for an association between this polymorphism and the risk for ED complaints in this sample. Population stratification did not affect the association test results.

Conclusions

This is the first study to examine the effect of polymorphisms in the eNOS gene and the risk for ED utilizing a case-control approach in the Brazilian population. Our results do not support a major role for eNOS gene polymorphisms in ED in this population.

Type 1 and Type 2 diabetic-erectile dysfunction: same diagnosis (ICD-9), different disease?

INTRODUCTION

Although hyperglycemia is a common defining feature of both type 1 and type 2 diabetes, many unique characteristics distinguish these diseases, including insulin and lipid levels, obesity status, and inflammatory agent profiles. In the laboratory, the presence of erectile dysfunction (ED) has been established in animal models of both type 1 and type 2 diabetes.

AIM

The purpose of this study was to determine whether unique mechanisms underlie ED in type 1 vs. type 2 diabetic animal models.

MAIN OUTCOME MEASURES

Many mechanisms can underlie ED, including impaired dilatory signaling, heightened contractile sensitivity, and veno-occlusive disorder.

METHODS

Using PubMed, the literature was mined to evaluate what is known about which mechanism underlie ED in type 1 vs. type 2 diabetic animal models.

RESULTS

Impaired cavernosal vasodilation has been established in type 1 diabetic rodents. This dysfunction appears to be mediated by a severe defect in non-adrenergic-non-cholinergic nerve signaling, as well as impairment in penile endothelial function. In contrast, type 2 diabetic animals appear to have minimal impairment in parasympathetic-mediated dilatory function, but do have evidence of endothelial dysfunction. Type 2 diabetic models also exhibit a significant and striking increase in cavernosal contractile sensitivity, and a significant veno-occlusive disorder, neither of which is consistently reported in type 1 diabetic animals.

CONCLUSIONS

With the distinct mechanisms underlying the ED phenotype in animal models of type 1 and type 2 diabetes, tailoring therapeutic treatments for diabetic-ED to the specific mechanisms underlying this disease complication may be warranted. Further examination of mechanisms underlying ED in diabetic human patients may thus lead to significant changes in the way urologists diagnose, code, and treat diabetic-ED.

Increased expression of the nitric oxide synthase gene and protein in corpus cavernosum by repeated dosing of udenafil in a rat model of chemical diabetogenesis

Erectile dysfunction (ED) is a major complication of diabetes mellitus (DM). This study investigates the relationship between ED and the downregulation of constitutive nitric oxide synthase (cNOS) in the corpus cavernosum (CC) of diabetic rats. It also examines the effects of udenafil, a phosphodiesterase type 5 (PDE5) inhibitor, on ED and cNOS expression levels. After 16 weeks of daily oral treatment with udenafil in diabetic rats, the intracavernous pressure/mean arterial pressure (ICP/MAP) ratio was recorded to measure erectile function, and cNOS expression was measured using reverse transcriptase (RT)-PCR and immunoblots. Although the ICP/MAP ratio and the expression levels of endothelial NOS (eNOS) and neuronal NOS (nNOS) in the CC were markedly decreased in diabetic rats, long-term udenafil treatment improved the erectile function and increased cNOS expression compared with diabetic controls. These findings suggest that ED in DM is closely related to decreased cNOS expression in the CC and that udenafil has the ability to compensate for this pathological change by modulating cNOS expression. Udenafil also has an inhibitory role in cGMP (cyclic guanosine monophosphate) degradation.

Recent trends in the treatment of testosterone deficiency syndrome

Testosterone deficiency syndrome (TDS) is defined as a clinical and biochemical syndrome associated with advancing age and is characterized by typical symptoms and deficiency in serum testosterone levels. TDS is a result of the interaction of hypothalamo-pituitary and testicular factors. Now, treatment of TDS with testosterone is still controversial due to a lack of large, controlled clinical trials on efficacy. The risks of treatment with testosterone appear to be minimal, although long-term studies on the safety of testosterone therapy are lacking. The aim of the therapy is to establish a physiological concentration of serum testosterone in order to correct the androgen deficiency, relieve its symptoms and prevent long-term sequelae. All of the available products, despite their varying pharmacodynamic and pharmacokinetic profiles, are able to reach this goal. Newer testosterone patches seem not to cause severe skin irritation. Testosterone gels minimize the skin irritation while providing flexibility in dosing and a low discontinuation rate. Oral testosterone undecanoate (TU) is free of liver toxicity. Recent formulation of oral TU markedly increased shelf-live, a major drawback in the older preparation. Producing swings in testosterone levels rising rapidly to the supraphysiological range is not the case with the new injectable long-acting preparation of TU. To be able to rapidly react and stop treatment in cases where side-effects and contraindications are detected, the short-acting transdermal and oral delivery modes have certain advantages. However, there is no evidence that the use of an injectable long-acting TU in men with TDS has limitations in clinical application for this reason. The use of dehydroepiandrosterone is still controversial because of a lack of well designed long-term trials, although some recent studies suggest positive effects on various body systems. Only a few studies have been carried out to investigate the effect of hCG (human chorionic gonadotropin) in TDS with some positive results on various body systems.

Efficacy of tadalafil once daily in men with diabetes mellitus and erectile dysfunction

AIMS

Erectile dysfunction (ED) is a common comorbidity in men with diabetes mellitus. Tadalafil 10 or 20 mg taken on demand is efficacious and safe for men with diabetes and ED. Recently, continuous treatment with tadalafil has been proposed, addressing ED management as any other chronic condition. This study examined whether once-daily tadalafil 2.5 and 5 mg is efficacious for men with diabetes and ED.

METHODS

This randomized, double-blind, placebo-controlled, multicentre, 12-week study enrolled 298 men with diabetes and ED to once-daily treatment with placebo, tadalafil 2.5 mg or tadalafil 5 mg. Primary efficacy measures were International Index of Erectile Function Erectile Function (IIEF EF) Domain score, and patient success rates for vaginal penetration and completion of intercourse. Patient satisfaction, endothelial function biomarkers, and safety were also assessed.

RESULTS

Patients receiving either dose of tadalafil had clinically and statistically significant improvements in IIEF EF and statistically significant improvements in mean success rates for vaginal penetration, completion of intercourse, and overall treatment satisfaction (P < or = 0.005 tadalafil vs. placebo, all measures). Endothelial dysfunction biomarkers were unchanged. The most common adverse events were headache, back pain and dyspepsia.

CONCLUSIONS

In this first study of men with diabetes and ED, once-daily tadalafil 2.5 and 5 mg was efficacious and well tolerated, suggesting this may be an alternative to on-demand treatment for some men, eliminating the need to plan sex within a limited timeframe.

Erectile dysfunction: does insulin resistance play a part?

OBJECTIVE

To review MEDLINE literature for correlations between insulin resistance and erectile dysfunction (ED).

DESIGN

MEDLINE literature review (1966 to present).

SETTING

Academic medical center.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

None.

RESULT(S)

Erectile dysfunction affects more than half of men over the age of 40. Fortunately, most men with ED can be successfully treated with phosphodiesterase 5A (PDE-5) inhibitors, which up-regulate the vasodilatory effects of nitric oxide (NO). Insulin resistance affects 25% of U.S. adults and increases to a 60% occurrence in individuals who are overweight. Endothelial dysfunction, which is associated with insulin resistance states, can cause disturbances in the subcellular signaling pathways required for NO production. Because endothelial production of NO and insulin sensitivity are positively related in healthy humans, the relationships among insulin resistance, NO, and ED are the target of this review of MEDLINE literature.

CONCLUSION(S)

Insulin resistance states are characterized by defective vascular NO production and impaired insulin-induced vasodilation, both of which are likely to cause ED. Diagnosing and treating insulin resistance should be part of the initial management plan for ED. Future studies concerning the cause and effect relationship of insulin resistance and ED should be implemented.

Cardiovascular disease, metabolic syndrome and erectile dysfunction

PURPOSE OF REVIEW

Erectile dysfunction and cardiovascular disease share the same risk factors such as hypertension, diabetes, dyslipidemia, obesity, and smoking, all of which are implicated in causing endothelial dysfunction. In this review, an overview is given on the role of endothelium in the pathophysiology of erectile dysfunction, cardiovascular disease, and the metabolic syndrome as well as the links between them.

RECENT FINDINGS

Current literature offers strong evidence that endothelial dysfunction and erectile dysfunction are linked. Erectile dysfunction appears to be one of the earliest signs of systemic vascular disease and might be considered as an early marker for subclinical cardiovascular disease. Obesity is one of the many risk factors for cardiovascular disease and is also associated with hypertension, dyslipidemia, glucose intolerance, and insulin resistance, which together define the metabolic syndrome. Experimental, clinical, and epidemiologic studies support the association between metabolic syndrome and cardiovascular disease.

SUMMARY

The above-mentioned risk factors are a potential threat to the penile endothelium and the smooth muscle tissue leading to functional and structural changes. These important pathophysiologic factors are the foundation for the strong link between erectile dysfunction and cardiovascular disease. Recent literature supports the link between metabolic syndrome and erectile dysfunction and highlights metabolic syndrome as a potential risk factor for the development of erectile dysfunction.

Endothelial dysfunction in diabetic erectile dysfunction

Erectile dysfunction (ED) is highly prevalent in diabetes mellitus. Pathophysiological mechanisms underlying diabetes-associated ED are in large part due to endothelial dysfunction, which functionally refers to the inability of the endothelium to produce vasorelaxing messengers and to maintain vasodilation and vascular homeostasis. The precise mechanisms leading to endothelial dysfunction in the diabetic vasculature, including the penis, are not yet fully understood. Hyperglycemia affects endothelial nitric oxide synthase activity and nitric oxide production/bioavailability, nitric oxide-independent relaxing factors, oxidative stress, production and/or action of hormones, growth factors and/or cytokines, and generation and activity of opposing vasoconstrictors. Considering recent advances in the field of vascular biology and diabetes, the emphasis in this review is placed on the mechanisms of hyperglycemia-induced endothelial dysfunction in the pathophysiology of diabetes-associated ED.

Fluid shear stress-induced nitric oxide production in human cavernosal endothelial cells: inhibition by hyperglycaemia

OBJECTIVE

To investigate whether fluid shear stress (FSS) induces endothelial nitric oxide synthase (eNOS) activity and NO production in isolated human corpus cavernosal endothelial cells (HCCECs), and whether this response is altered during hyperglycaemia in vitro, as haemodynamic signalling during penile erection induces eNOS-mediated NO production in vivo.

MATERIALS AND METHODS

ECs were cultured from HCC and characterized by the uptake of acetylated low-density lipoprotein and the expression of von Willebrand factor, VE-cadherin, CD31 and eNOS. HCCECs were exposed to FSS (1.2 Pa (12 dynes/cm2), 5 min) using a cone-and-plate viscometer in the presence or absence of high glucose (30 mm, 48 h). The phosphorylation of ser1177 on eNOS and total eNOS protein expression after FSS was examined by Western blot. NO in the conditioned media was assessed by measuring nitrate and nitrite levels.

RESULTS

Compared to static conditions, FSS induced a significant increase in the phosphorylation of eNOS on ser1177 in HCCECs, and the release of NO to the conditioned media. Treatment of HCCECs with high glucose levels did not alter the ratio FSS-induced phosphorylated eNOS/total eNOS, but did result in the down-regulation of total eNOS and significantly attenuated FSS-induced NO release.

CONCLUSION

These in vitro data suggest that FSS contributes to eNOS activation and NO release in HCCECs, and supports in vivo reports suggesting a role for haemodynamic signalling in the erectile response. Treatment with high glucose levels prevented FSS-induced NO release, suggesting a mechanism that may contribute to decreased erectile function associated with diabetes.

Superoxide anion production in the rat penis impairs erectile function in diabetes: influence of in vivo extracellular superoxide dismutase gene therapy

INTRODUCTION

Superoxide anion may contribute to erectile dysfunction (ED) in diabetes mellitus by reducing cavernosal nitric oxide (NO) bioavailability. The purpose of this study was to determine if gene transfer of extracellular superoxide dismutase (EC-SOD) can reduce superoxide anion formation and determine if this reactive oxygen species may contribute to diabetes-related ED in an experimental model of diabetes.

METHODS

Three groups of animals were utilized: (1) control; (2) streptozotocin (STZ)-diabetic rats [60 mg/kg intraperitoneally (ip)] intracavernosally injected with AdCMVbetagal (negative control); and (3) STZ-rats intracavernosally injected with AdCMVEC-SOD. Two months after ip injection of STZ, groups 2 and 3 were transfected with the adenoviruses and 2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Confocal microscopy for superoxide anion and von Willebrand Factor (vWF) was performed in the STZ-diabetic rat. Superoxide anion production, total SOD activity, and cyclic guanosine monophosphate (cGMP) levels were measured in each experimental group of rats.

RESULTS

Confocal microscopy demonstrated superoxide in smooth muscle and endothelial cells of the STZ-rat cavernosum and colocalized with vWF in the endothelium. Higher superoxide anion levels and decreased cGMP levels were found in the penis of STZ-rats at a time when erectile function was reduced. Two days after administration of AdCMVEC-SOD, superoxide anion levels were significantly lower in the penis of STZ-rats. Total SOD activity and cavernosal cGMP was increased in the penis of EC-SOD-transfected rats. STZ-rats transfected with AdCMVEC-SOD had a peak intracavernosal pressure (ICP) and total ICP to CNS that was similar to control rats.

CONCLUSIONS

These data demonstrate that in vivo adenoviral gene transfer of EC-SOD can reduce corporal superoxide anion levels and raise cavernosal cGMP levels by increasing NO bioavailability thus restoring erectile function in the STZ-diabetic rat.

Linking erectile dysfunction and coronary artery disease

Coronary artery disease (CAD) and erectile dysfunction (ED) are both highly prevalent conditions that frequently coexist. Additionally, they share mutual vascular risk factors, suggesting that they are both manifestations of systemic vascular disease. The role of endothelial dysfunction in CAD is well established. Normal erectile function is primarily a vascular event that relies heavily on endothelially derived, nitric oxide-induced vasodilation. Accordingly, endothelial dysfunction appears to be a common pathological etiology and mechanism of disease progression between CAD and ED. The risk factors of diabetes mellitus, hypertension, hyperlipidemia, obesity and tobacco abuse contribute to endothelial dysfunction. This article reviews the role of vascular endothelium in health, the abnormalities resulting from vascular risk factors, and clinical trials evaluating the role of endothelial dysfunction in ED.

Inactivation of phosphorylated endothelial nitric oxide synthase (Ser-1177) by O-GlcNAc in diabetes-associated erectile dysfunction

Impaired endothelial nitric oxide synthase (eNOS) function is associated with erectile dysfunction in diabetes mellitus, but the exact molecular basis for the eNOS defect in the diabetic penis remains unclear. We investigated whether hyperglycemia increases O-GlcNAc modification of eNOS in the penis, preventing phosphorylation at the primary positive regulatory site on the enzyme and hampering mechanisms of the erectile response. Type I diabetes mellitus was induced in male rats by alloxan (140 mg/kg, i.p.). After 5 wk, the diabetic rat penis exhibited increased O-GlcNAc modification of eNOS and decreased eNOS phosphorylation at Ser-1177 at baseline compared with the control rat penis; eNOS phosphorylation at Thr-495, Ser-615, and Ser-633 was not affected. In addition, eNOS phosphorylation at Ser-1177 was impaired in the diabetic rat penis in response to penile blood flow (shear stress) elicited by electrical stimulation of the cavernous nerve (ES) and to recombinant human VEGF165. Phosphorylation of Akt, a mediator of shear stress-induced eNOS phosphorylation at Ser-1177, was decreased in the diabetic penis at baseline, but it was restored by ES. Erectile response to shear stress elicited by ES and to VEGF was decreased in diabetic compared with control rats. This work demonstrates that eNOS inactivation occurs in the diabetic penis by a glycosylation mechanism specifically at Ser-1177, by which the enzyme is rendered incapable of activation by fluid shear stress stimuli and VEGF signaling. In vivo penile erection paradigm supports the physiologic relevance of O-GlcNAc modification in vascular disorders associated with diabetes.

A comparative study of sildenafil, NCX-911 and BAY41-2272 on the anococcygeus muscle of diabetic rats

We compared the effects of a nitric oxide (NO)-releasing sildenafil (NCX-911), NO-independent soluble guanylate cyclase activator (BAY41-2272) and sildenafil on the anococcygeus muscle from streptozotocin-induced 16-weeks diabetic rats. NCX-911, BAY41-2272 and sildenafil reduced the phenylephrine-induced tone in the control group (EC50=1088.8+/-165.0, 151.6+/-9.3 and 827.1+/-167.3 nM, respectively). The potencies of NCX-911 and BAY41-2272 were not altered, but that of sildenafil was significantly reduced in the diabetic group. EC50 values for NCX-911, BAY41-2272 and sildenafil in the diabetic group were 1765.9+/-303.5, 209.7+/-27.3 and 2842.2+/-640.3 nM, respectively (P<0.05 for sildenafil). Nitrergic relaxation responses were significantly decreased in the diabetic group. The remaining nitrergic relaxation responses were potentiated by BAY41-2272 but not by sildenafil or NCX-911. These results confirm that endogenous NO derived from nitrergic nerves is significantly decreased in diabetes, and suggest that NO-releasing PDE5 inhibitors and NO-independent soluble guanylate cyclase activators could be more useful than PDE5 inhibitors in the treatment of ED in long-term diabetes.

Nitric oxide-cyclic GMP pathway with some emphasis on cavernosal contractility

Nitric oxide (NO) is formed from the conversion of L-arginine by nitric oxide synthase (NOS), which exists in three isoforms: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). nNOS is expressed in penile neurons innervating the corpus cavernosum, and eNOS protein expression has been identified primarily in both cavernosal smooth muscle and endothelium. NO is released from nerve endings and endothelial cells and stimulates the activity of soluble guanylate cyclase (sGC), leading to an increase in cyclic guanosine-3',5'-monophosphate (cGMP) and, finally, to calcium depletion from the cytosolic space and cavernous smooth muscle relaxation. The effects of cGMP are mediated by cGMP dependent protein kinases, cGMP-gated ion channels, and cGMP-regulated phosphodiesterases (PDE). Thus, cGMP effect depends on the expression of a cell-specific cGMP-receptor protein in a given cell type. Numerous systemic vasculature diseases that cause erectile dysfunction (ED) are highly associated with endothelial dysfunction, which has been shown to contribute to decreased erectile function in men and a number of animal models of penile erection. Based on the increasing knowledge of intracellular signal propagation in cavernous smooth muscle tone regulation, selective PDE inhibitors have recently been introduced in the treatment of ED. Phosphodiesterase 5 (PDE5) inactivates cGMP, which terminates NO-cGMP-mediated smooth muscle relaxation. Inhibition of PDE5 is expected to enhance penile erection by preventing cGMP degradation. Development of pharmacologic agents with this effect has closely paralleled the emerging science.

Effect of combination endothelial nitric oxide synthase gene therapy and sildenafil on erectile function in diabetic rats

Erectile dysfunction associated with diabetes mellitus is caused in part by disordered endothelial smooth muscle relaxation, neuropathy, and a decrease in cavernosal nitric oxide synthase (NOS) activity. The purpose of this study was to determine whether a combination of sildenafil and adenoviral gene transfer of endothelial NOS (eNOS) could enhance the erectile response in diabetic rats. Five groups of animals were utilized: (1) age-matched control rats, (2) streptozotocin (STZ)-induced diabetic rats (60 mg/kg i.p.), (3) STZ-rats + sildenafil (2 mg/kg i.v.), (4) STZ-rats transfected with AdCMVbetagal or AdCMVeNOS, and (5) STZ-rats transfected with AdCMVeNOS +sildenafil (2 mg/kg i.v.). At 2 months after i.p. injection of STZ, groups 4 and 5 were transfected with the adenoviruses and 1-2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Cyclic 3',5'-guanosine monophosphate (cGMP) levels were assessed in the cavernosal tissue. STZ-diabetic rats had a significant decrease in erectile function as determined by the peak intracavernosal pressure (ICP) and total ICP (area under the erectile curve; AUC) after CNS when compared to control rats. STZ-diabetic rats+AdCMVeNOS had a peak ICP and AUC, which were similar to control animals. STZ-diabetic rats administered sildenafil demonstrated a significant increase in peak ICP at the 5 and 7.5 V settings, while the AUC was significantly increased at all voltage (V) settings. The increase in both ICP and AUC of STZ-diabetic rats transfected with AdCMVeNOS at all V settings was greater than STZ-diabetic rats transfected with AdCMVbetagal. STZ-diabetic rats transfected with AdCMVeNOS and administered sildenafil had a significant increase in total ICP that was greater than eNOS gene therapy alone. Cavernosal cGMP levels were significantly decreased in STZ-diabetic rats, but were increased after transfection with AdCMVeNOS to values greater than control animals. In conclusion, overexpression of eNOS and cGMP in combination with sildenafil significantly increased both the peak ICP and total ICP to CNS in the STZ-diabetic rat, which was similar to the response observed in control rats. Moreover, the total erectile response was greater in STZ-diabetic rats receiving eNOS gene therapy plus sildenafil than STZ-rats receiving sildenafil or eNOS gene therapy alone.

RhoA/Rho-kinase suppresses endothelial nitric oxide synthase in the penis: a mechanism for diabetes-associated erectile dysfunction

Significant impairment in endothelial-derived nitric oxide is present in the diabetic corpus cavernosum. RhoA/Rho-kinase may suppress endothelial nitric oxide synthase (eNOS). Here, we tested the hypothesis that RhoA/Rho-kinase contributes to diabetes-related erectile dysfunction and down-regulation of eNOS in the streptozotocin (STZ)-diabetic rat penis. Colocalization of Rho-kinase and eNOS protein was present in the endothelium of the corpus cavernosum. RhoA/Rho-kinase protein abundance and MYPT-1 phosphorylation at Thr-696 were elevated in the STZ-diabetic rat penis. In addition, eNOS protein expression, cavernosal constitutive NOS activity, and cGMP levels were reduced in the STZ-diabetic penis. To assess the functional role of RhoA/Rho-kinase in the penis, we evaluated the effects of an adeno-associated virus encoding the dominant-negative RhoA mutant (AAVTCMV19NRhoA) on RhoA/Rho-kinase and eNOS and erectile function in vivo in the STZ-diabetic rat. STZ-diabetic rats transfected with AAVCMVT19NRhoA had a reduction in RhoA/Rho-kinase and MYPT-1 phosphorylation at a time when cavernosal eNOS protein, constitutive NOS activity, and cGMP levels were restored to levels found in the control rats. There was a significant decrease in erectile response to cavernosal nerve stimulation in the STZ-diabetic rat. AAVT19NRhoA gene transfer improved erectile responses in the STZ-diabetic rat to values similar to control. These data demonstrate a previously undescribed mechanism for the down-regulation of penile eNOS in diabetes mediated by activation of the RhoA/Rho-kinase pathway. Importantly, these data imply that inhibition of RhoA/Rho-kinase improves eNOS protein content and activity thus restoring erectile function in diabetes.

Effect of testosterone supplementation on sexual function in hypogonadal men with erectile dysfunction

OBJECTIVES

To evaluate the impact of normalization of testosterone levels in men with documented hypogonadism and erectile dysfunction on erectile function and sexual satisfaction. Although the data support the role of testosterone in the preservation of libido and nocturnal erectile function, the evidence supporting the use of testosterone supplementation in hypogonadal men with erectile dysfunction is weak.

METHODS

This analysis used two validated questionnaires, the International Index of Erectile Function and the Erectile Dysfunction Inventory of Treatment Satisfaction, in a serial fashion at baseline (before treatment) and 1, 3, and 6 months after the achievement of a therapeutic testosterone level.

RESULTS

A total of 32 men met all inclusion criteria; 69% of men achieved therapeutic testosterone levels using transdermal testosterone gel, 19% required a transdermal patch, and 12% required intramuscular delivery. Statistical significance was reached for the difference between the baseline and 1-month International Index of Erectile Function erectile function domain score and all post-treatment International Index of Erectile Function libido scores. A steady decrease occurred in the Erectile Dysfunction Inventory of Treatment Satisfaction scores from the 1 to 6-month values that reached statistical significance.

CONCLUSIONS

In men with documented hypogonadism and erectile dysfunction, normalization of serum testosterone levels was associated with only short-term improvement in erectile function and sexual satisfaction. The use of testosterone supplementation in this population for the treatment of erectile dysfunction is questionable.

Effect of PDE5 inhibition combined with free oxygen radical scavenger therapy on erectile function in a diabetic animal model

Phosphodiesterase (PDE) inhibitors represent an important advance in the treatment of erectile dysfunction (ED). In spite of widespread use and generally good efficacy, as a class they remain ineffective in 15-57% of men. Specific cohorts of patients with severe vascular or neurogenic basis to their ED, such as diabetic men or those who have undergone radical pelvic surgery, demonstrate lower response rates with PDE inhibition treatment. We believe that circulating levels of nitric oxide (NO) may be enhanced through delivery of adequate concentrations of free oxygen radical scavenger molecules such as vitamin E. Higher levels of NO, theoretically, should produce increased penile blood flow with the potential for a synergistic effect when combined with a PDE5 inhibitor. With this hypothesis in mind, 20 adult male Sprague-Dawley streptozotocin-induced (60 mg/kg i.p.) diabetic rats were divided into four therapeutic groups (n=5). Group I--control animals received peanut oil, group II--vitamin E 20 IU/day, group III--sildenafil 5 mg/kg/day and group IV--vitamin E 20 IU/day plus sildenafil 5 mg/kg/day, by oral gavage daily for 3 weeks. Erectile function was assessed as a rise in intracavernous pressure following cavernous nerve electrostimulation. Penile tissue was harvested to determine the changes in tissue morphology including neuronal nitric oxide synthase, smooth muscle alpha-actin and endothelial cell integrity. PDE5 protein content and activity were measured. Significant increases in intracavernous pressure were measured in the animals receiving combined vitamin E plus sildenafil treatment. Immunohistochemical staining showed increases of neuronal nitric oxide synthase, endothelial cell and smooth muscle cell staining. Western blot analysis did not show significant differences of PDE5 protein between the groups. However, higher PDE5 activity was measured in the sildenafil group and lower activity of PDE5 was recorded in the cohort receiving vitamin E with sildenafil. Vitamin E enhanced the therapeutic effect of the PDE5 inhibitor in a meaningful way in this animal model of diabetes. This study indicates a potential means of salvaging erectile function among patients who are refractory to sildenafil.

Gene transfer of endothelial nitric oxide synthase partially restores nitric oxide synthesis and erectile function in streptozotocin diabetic rats

PURPOSE

We determined whether adenoviral gene transfer of endothelial nitric oxide synthase (eNOS) to the penis of streptozotocin induced diabetic rats could improve the impaired erectile response.

MATERIALS AND METHODS

Two experimental groups of animals were transfected with adenoviruses, including streptozotocin (Sigma Chemical Company, St. Louis, Missouri) diabetic rats with AdCMVbetagal and streptozotocin diabetic rats with AdCMVeNOS. At 1 to 2 days after transfection these study animals underwent cavernous nerve stimulation to assess erectile function and their responses were compared with those of age matched control rats. In control and transfected streptozotocin diabetic rats eNOS and neuronal NOS (nNOS) were examined by Western blot analysis. Constitutive and inducible NOS activities were evaluated in the presence and absence of calcium by L-arginine to L-citrulline conversion and nitrate plus nitrite levels were measured. In control and streptozotocin diabetic penes beta-galactosidase activity and localization were determined.

RESULTS

After transfection with AdCMVbetagal beta-galactosidase was localized to the endothelium and smooth muscle cells of the streptozotocin diabetic rat penis. Streptozotocin diabetic rats had a significant decrease in erectile function, as determined by peak and total intracavernous pressure (area under the curve) after cavernous nerve stimulation compared with control rats. Streptozotocin diabetic rats transfected with AdCMVeNOS had peak intracavernous pressure and area under the curve similar to those in control animals. This change in erectile function was a result of eNOS over expression with an increase in eNOS protein expression and constitutive NOS activity as well as an increase in nitric oxide biosynthesis, as reflected by an increase in cavernous nitrate plus nitrite formation. There was no change in nNOS protein expression or calcium independent conversion of NOS (inducible NOS activity).

CONCLUSIONS

Adenoviral gene transfer of eNOS significantly increased peak and total intracavernous pressure to cavernous nerve stimulation in streptozotocin diabetic rats to a value similar to the response observed in control rats. Our results suggest that eNOS contributes significantly to the physiology of penile erection. These data demonstrate that in vivo adenoviral gene transfer of eNOS can physiologically improve erectile function in the streptozotocin diabetic rat.

Nitric oxide in the human hair follicle: constitutive and dihydrotestosterone-induced nitric oxide synthase expression and NO production in dermal papilla cells

The free radical nitric oxide, generated by different types of epidermal and dermal cells, has been identified as an important mediator in various physiological and pathophysiological processes of the skin, such as regulation of blood flow, melanogenesis, wound healing, and hyperproliferative skin diseases. However, little is known about the role of NO in the human hair follicle and in hair cycling processes. Here we demonstrate for the first time that dermal papilla cells derived from human hair follicles spontaneously produce NO by measuring nitrate and nitrite levels in culture supernatants. This biomolecule is apparently formed by the endothelial isoform of nitric oxide synthase, which was detected at the mRNA and protein levels. Remarkably, basal NO level was enhanced threefold by stimulating dermal papilla cells with 5alpha-dihydrotestosterone (DHT) but not with testosterone. Addition of N-[3-(aminomethyl)benzyl]acetamidine (1400W), a highly selective inhibitor of inducible nitric oxide synthase, restrained the elevation in NO level induced by DHT. Analyses of DHT-stimulated cells at the mRNA and protein levels confirmed the expression of inducible nitric oxide synthase. These findings suggest NO as a signaling molecule in human dermal papilla cells and implicate basal and androgen-mediated NO production to be involved in the regulation of hair follicle activity.

Akt-dependent phosphorylation of endothelial nitric-oxide synthase mediates penile erection

In the penis, nitric oxide (NO) can be formed by both neuronal NO synthase and endothelial NOS (eNOS). eNOS is activated by viscous drag/shear stress in blood vessels to produce NO continuously, a process mediated by the phosphatidylinositol 3-kinase (PI3kinase)/Akt pathway. Here we show that PI3-kinase/Akt physiologically mediates erection. Both electrical stimulation of the cavernous nerve and direct intracavernosal injection of the vasorelaxant drug papaverine cause rapid increases in phosphorylated (activated) Akt and eNOS. Phosphorylation is diminished by wortmannin and LY294002, inhibitors of PI3-kinase, the upstream activator of Akt. The two drugs also reduce erection. Penile erection elicited by papaverine is reduced profoundly in mice with targeted deletion of eNOS. Our findings support a model in which rapid, brief activation of neuronal NOS initiates the erectile process, whereas PI3-kinase/Akt-dependent phosphorylation and activation of eNOS leads to sustained NO production and maximal erection.