Posttranslational modification of constitutive nitric oxide synthase in the penis

Nitric oxide synthase and its function in animal reproduction: an update

Nitric oxide (NO), a free radical labile gas, is involved in the regulation of various biological functions and physiological processes during animal reproduction. Recently, increasing evidence suggests that the biological role and chemical fate of NO is dependent on dynamic regulation of its biosynthetic enzyme, three distinct nitric oxide synthase (NOS) according to their structure, location and function. The impact of NOS isoforms on reproductive functions need to be timely elucidated. Here, we focus on and the basic background and latest studies on the development, structure, importance inhibitor, location pattern, complex functions. Moreover, we summarize the exactly mechanisms which involved some cell signal pathways in the regulation of NOS with cellular and molecular level in the animal reproduction. Therefore, this growing research area provides the new insight into the important role of NOS male and female reproduction system. It also provides the treatment evidence on targeting NOS of reproductive regulation and diseases.

Histologic and physiologic analysis of the relationship between the dorsal nerve of the penis and the corpus cavernosum on a rat model. A complementary pathway on the innervation of penile erection?

AIM

The dorsal nerve of the penis (DNP) is the terminal branch of the pudendal nerve which is responsible for the somatic innervation of the penis. This study aims to outline any direct role of the DNP in the hemodynamics of erection histologically and physiologically.

MATERIALS AND METHODS

Fifteen Wistar albino rats were sorted into the electrical activity (n = 6), intracavernous pressure (n = 4), and control (n = 5) groups. The dorsal nerve was electrostimulated and the simultaneous changes in intracavernous pressure and smooth muscle activity were recorded. Penile tissues were collected, fixed, and sectioned, the slides were stained with either hematoxylin-eosin for morphological evaluation or using the indirect immunoperoxidase technique to analyze the distributions of eNOS, iNOS, and nNOS.

RESULTS

During electrostimulation, there was a simultaneous statistically significant decrease in the electrical activity inside the corpora in electromyography and an increase in intracavernous pressure. eNOS and iNOS immunoreactivities were higher in the study group than in the control group. nNOS immunoreactivity was moderate in both study and control groups.

CONCLUSION

Some fibers in the dorsal nerve of penis continue into the corpora cavernosa through the tunica albuginea and have an active, direct role in the hemodynamic process of erection, which may be complementary to the main route of innervation.

Alterations in the phosphodiesterase type 5 pathway and oxidative stress correlate with erectile function in spontaneously hypertensive rats

To explore how alterations in the phosphodiesterase type 5 (PDE5) signalling pathway and oxidative stress correlate with changes in the expression of relaxation and contraction molecules and erectile dysfunction (ED) in the corpus cavernosum smooth muscle (CCSM) of spontaneously hypertensive rats (SHR). In this study, SHR and Wistar‐Kyoto (WKY) rats were used. Erectile function was determined by apomorphine test and electrical stimulation (ES) of cavernous nerve. Masson's trichrome staining and confocal microscopy were performed. Nitric oxide synthase (NOS), PDE5, phosphorylated‐PDE5 and α1‐adrenergic receptor (α1AR) were determined by RT‐PCR and Western blotting while oxidative stress in CC was determined by colorimetric analysis. SHR exhibited obvious ED. CC of SHR showed less SM but more collagen fibres. The expression of NOS isoforms in SHR was significantly decreased while all α1AR isoforms were increased. In addition, PDE5 and phosphorylated‐PDE5 were down‐regulated and its activity attenuated in the hypertensive rats. Meanwhile, the SHR group suffered oxidative stress, which may be modulated by endoplasmic reticulum stress and NADPH oxidase up‐regulation. Dysregulation of NOS and α1AR, histological changes and oxidative stress in CC may be associated with the pathophysiology of hypertension‐induced ED. In addition, PDE5 down‐regulation may lead to the decreased efficacy of PDE5 inhibitors in some hypertensive ED patients and treatment of oxidative stress could be used as a new therapeutic target for this type of ED.

The role of resistin on metabolic syndrome-induced erectile dysfunction and the possible therapeutic effect of Boldine

BACKGROUND

Resistin is known as a potential mediator of obesity-associated insulin resistance. The high resistin level disrupts nitric oxide (NO)-mediated relaxation which is also important in erectile function. An antioxidant alkaloid, Boldine, is known as anti-diabetic and protects endothelial functions.

OBJECTIVES

We aimed to investigate resistin expression in penile tissue in the presence of insulin resistance (IR) and the effect of Boldine treatment on erectile functions in the metabolic syndrome (MetS) rat model.

MATERIALS AND METHODS

Wistar rats were randomly divided into three groups: Control, MetS, and boldine treated MetS group. MetS parameters were assessed by serum triglycerides (TG), uric acid (UA), glucose, insulin levels, HOMA index, and waist circumference (WC)/tibia length (TL) ratio. To evaluate erectile functions, intracavernous pressure (ICP)/mean arterial pressure (MAP) ratio was performed during cavernous nerve stimulation. Protein expressions of resistin, endothelial nitric oxide synthase (eNOS), p(S1177) eNOS, and insulin receptor-β were evaluated by Western blotting.

RESULTS

TG, glucose, insulin levels, weight, WC/TL ratio, HOMA index and resistin expression in penile tissue were significantly increased and ICP/MAP values, and p (S1177) eNOS expression in penile tissue were decreased in MetS group. Boldine treatment enhanced ICP/MAP values, insulin receptor-β and p(S1177) eNOS expressions compared with the MetS group.

DISCUSSION AND CONCLUSION

MetS caused a deterioration in erectile function accompanied by an increase in resistin expression and a reduction in eNOS enzyme activation in the rat penile tissues. Boldine treatment resulted in an improvement in erectile function, independent of resistin expression.

Clinical and Genetic Predictors of Priapism in Sickle Cell Disease: Results from the Recipient Epidemiology and Donor Evaluation Study III Brazil Cohort Study

INTRODUCTION

Priapism is the persistent and painful erection of the penis and is a common sickle cell disease (SCD) complication.

AIM

The goal of this study was to characterize clinical and genetic factors associated with priapism within a large multi-center SCD cohort in Brazil.

METHODS

Cases with priapism were compared to SCD type-matched controls within defined age strata to identify clinical outcomes associated with priapism. Whole blood single nucleotide polymorphism genotyping was performed using a customized array, and a genome-wide association study (GWAS) was conducted to identify single nucleotide polymorphisms associated with priapism.

MAIN OUTCOME MEASURE

Of the 1,314 male patients in the cohort, 188 experienced priapism (14.3%).

RESULTS

Priapism was more common among older patients (P = .006) and more severe SCD genotypes such as homozygous SS (P < .0001). In the genotype- and age-matched analyses, associations with priapism were found for pulmonary hypertension (P = .05) and avascular necrosis (P = .01). The GWAS suggested replication of a previously reported candidate gene association of priapism for the gene transforming growth factor beta receptor 3 (TGFBR3) (P = 2 × 10-4).

CLINICAL IMPLICATIONS

Older patients with more severe genotypes are at higher risk of priapism, and there is a lack of consensus on standard treatment strategies for priapism in SCD.

STRENGTHS & LIMITATIONS

This study characterizes SCD patients with any history of priapism from a large multi-center cohort. Replication of the GWAS in an independent cohort is required to validate the results.

CONCLUSION

These findings extend the understanding of risk factors associated with priapism in SCD and identify genetic markers to be investigated in future studies to further elucidate priapism pathophysiology. Ozahata M, Page GP, Guo Y, et al. Clinical and Genetic Predictors of Priapism in Sickle Cell Disease: Results from the Recipient Epidemiology and Donor Evaluation Study III Brazil Cohort Study. J Sex Med 2019;16:1988-1999.

Calpain inhibition improves erectile function in diabetic mice via upregulating endothelial nitric oxide synthase expression and reducing apoptosis

Calpain activation contributes to hyperglycemia-induced endothelial dysfunction and apoptosis. This study was designed to investigate the role of calpain inhibition in improving diabetic erectile dysfunction (ED) in mice. Thirty-eight-week-old male C57BL/6J mice were divided into three groups: (1) nondiabetic control group, (2) diabetic mice + vehicle group, and (3) diabetic mice + MDL28170 (an inhibitor of calpain) group. Type 1 diabetes was induced by intraperitoneal injection of streptozotocin at 60 mg kg⁻¹ body weight for 5 consecutive days. Thirteen weeks later, diabetic mice were treated with MDL28170 or vehicle for 4 weeks. The erectile function was assessed by electrical stimulation of the cavernous nerve. Penile tissues were collected for measurement of calpain activity and the endothelial nitric oxide synthase (eNOS)-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway. Terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling (TUNEL) staining was used to evaluate apoptosis. Caspase-3 expression and activity were also measured to determine apoptosis. Our results showed that erectile function was enhanced by MDL28170 treatment in diabetic mice compared with the vehicle diabetic group. No differences in calpain-1 and calpain-2 expressions were observed among the three groups. However, calpain activity was increased in the diabetic group and reduced by MDL28170. The eNOS-NO-cGMP pathway was upregulated by MDL28170 treatment in diabetic mice. Additionally, MDL28170 could attenuate apoptosis and increase the endothelium and smooth muscle levels in corpus cavernosum. Inhibition of calpain could improve erectile function, probably by upregulating the eNOS-NO-cGMP pathway and reducing apoptosis.

Epalrestat, an Aldose Reductase Inhibitor, Restores Erectile Function in Streptozocin-induced Diabetic Rats

Epalrestat, an aldose reductase inhibitor (ARI), was adopted to improve the function of peripheral nerves in diabetic patients. The aim of this study was to investigate whether epalrestat could restore the erectile function of diabetic erectile dysfunction using a rat model. From June 2016, 24 rats were given streptozocin (STZ) to induce the diabetic rat model, and epalrestat was administered to ten diabetic erectile dysfunction (DED) rats. Intracavernous pressure (ICP) and mean systemic arterial pressure (MAP), levels of aldose reductase (AR), nerve growth factor (NGF), neuronal nitric oxide synthase (nNOS), α-smooth muscle antigen (α-SMA), and von Willebrand factor (vWF) in the corpus cavernosum were analyzed. We discovered that epalrestat acted on cavernous tissue and partly restored erectile function. NGF and nNOS levels in the corpora were increased after treatment with epalrestat. We also found that the content of α-SMA-positive smooth muscle cells and vWF-positive endothelial cells in the corpora cavernosum were declined. Accordingly, epalrestat might improve erectile function by increasing the upregulation of NGF and nNOS to restore the function of the dorsal nerve of the penis.

Icariside II Promotes the Differentiation of Adipose Tissue-Derived Stem Cells to Schwann Cells to Preserve Erectile Function after Cavernous Nerve Injury

Icariside II (ICA II) is used in erectile dysfunction treatment. Adipose tissue-derived stem cells (ADSCs) are efficient at improving erectile function. This study aimed to explore the action mechanism of ADSCs in improving erectile function. ADSCs were isolated from the adipose tissues of rats. Cell proliferation was determined using the Cell Counting Kit-8 (CCK-8) assay. The expressions of mRNA and protein were determined separately through qRT-PCR and western blot. The endogenous expressions of related genes were regulated using recombinant plasmids and cell transfection. A Dual-Luciferase Reporter Assay was performed to determine the interaction between miR-34a and STAT3. Rat models with bilateral cavernous nerve injuries (BCNIs) were used to assess erectile function through the detection of mean arterial pressure (MAP) and intracavernosal pressure (ICP). ICA II promoted ADSCs' proliferation and differentiation to Schwann cells (SCs) through the inhibition of miR-34a. Suppressed miR-34a promoted the differentiation of ADSCs to SCs by upregulating STAT3. ICA II promoted the differentiation of ADSCs to SCs through the miR-34a/STAT3 pathway. The combination of ICA II and ADSCs preserved the erectile function of the BCNI model rats. ADSCs treated with ICA II markedly preserved the erectile function of the BCNI model rats, which was reversed through miR-34a overexpression. ICA II promotes the differentiation of ADSCs to SCs through the miR-34a/STAT3 pathway, contributing to erectile function preservation after the occurrence of a cavernous nerve injury.

The expression, localization and function of α7 nicotinic acetylcholine receptor in rat corpus cavernosum

OBJECTIVES

Alpha7 nicotinic acetylcholine receptor (α7-nAChR), an emerging pharmacological target for a variety of medical conditions, is expressed in the most mammalian tissues with different effects. So, this study was designed to investigate the expression, localization and effect of α7-nAChR in rat corpus cavernosum (CC).

METHODS & KEY FINDINGS

Reverse transcription polymerase chain reaction (RT-PCR) revealed that α7-nAChR was expressed in rat CC and double immunofluorescence studies demonstrated the presence of α7-nAChR in corporal neurons. The rat CC segments were mounted in organ bath chambers and contracted with phenylephrine (0.1 μm -300 μm) to investigate the relaxation effect of electrical field stimulation (EFS,10 Hz) assessed in the presence of guanethidine (adrenergic blocker, 5 μm) and atropine (muscarinic cholinergic blocker, 1 μm) to obtain non-adrenergic non-cholinergic (NANC) response. Cumulative administration of nicotine significantly potentiated the EFS-induced NANC relaxation (-log EC50 = 7.5 ± 0.057). Whereas, the potentiated NANC relaxation of nicotine was significantly inhibited with different concentrations of methyllycaconitine citrate (α7-nAChR antagonist, P < 0.05) in preincubated strips. L-NAME (non-specific nitric oxide synthase inhibitor, 1 μm) completely blocked the neurogenic relaxation induced by EFS plus nicotine.

CONCLUSION

To conclude α7-nAChR is expressed in rat CC and modulates the neurogenic relaxation response to nicotine.

Aging and sexual health: getting to the problem

Erectile dysfunction (ED) is one of the most common disorders in male and is often associated with other age-related comorbidities. The aging process affects the structural organization and function of penile erectile components such as smooth muscle cell and vascular architecture. These modifications affect penile hemodynamics by impairing cavernosal smooth muscle cell relaxation, reducing penile elasticity, compliance and promoting fibrosis. This review aims to identify the mechanisms of ED in the penile aging process in experimental and clinical data. It also highlights areas that are in need of more research. The search strategies yielded total records screened from PubMed. Clarification of the molecular mechanisms that accompanies corpus cavernosum aging and aging-associated ED will aid new perspectives in the development of novel mechanism-based therapeutic approaches. Age is not a limiting factor for ED medical management, and it is never too late to treat. Hypogonadism should be managed regardless of age, and synergistic effects have been found during testosterone (T) replacement therapy when used along with oral phosphodiesterase-5 (PDE-5) inhibitors. Therefore, the clinical management of ED related to aging can be done by therapeutic interventions that include PDE-5 inhibitors, and other pharmacological treatments.

Neuronal Voltage Gated Potassium Channels May Modulate Nitric Oxide Synthesis in Corpus Cavernosum

Potassium channels (K⁺Ch) in corpus cavernosum play an important role in the regulation of erection. Nitric oxide (NO) acts through opening of K⁺Ch leading to hyperpolarization and relaxation.

Aim : This study aims to update knowledge about the role of voltage-gated K⁺Ch (K_V) channels in erectile machinery and investigate their role in the control of NO action &/or synthesis in the corpus cavernosum.

Methods : Tension studies using isolated rabbit corpus cavernosum (CC) strips and rat anococcygeus muscle were conducted. Results are expressed as mean ± SEM.

Results : Electric field stimulation (EFS, 2–16 Hz) evoked frequency-dependent relaxations of the PE (phenylephrine)-precontracted CC strips. At 2 Hz, EFS-induced relaxation amounted to 73.17 ± 2.55% in presence 4-AP (10⁻³ M) compared to 41.98 ± 1.45% as control. None of the other selective K⁺Ch blockers tested inhibited EFS-induced relaxation. 4-AP (10⁻³M) significantly attenuated ACh-induced relaxation of rabbit CC where dose-response curve was clearly shifted upward, and attenuated SNP- induced relaxation, for example, to 49.28 ± 4.52% compared to 65.53 ± 3.01% as control at 10⁻⁶ M SNP. The potentiatory effect of 4-AP on EFS was abolished or reversed in presence of N^G-nitro-L-arginine (L-NNA, non-selective nitric oxide synthase inhibitor, 10⁻⁵M, and 2 × 10⁻⁴M). Same results were observed in rat anococcygeus muscle which is a part of the erectile machinery in rats.

Conclusion : This study provides evidence for the presence of prejunctional voltage-gated K⁺Ch in CC, the blockade of which may increase the neuronal synthesis of NO.

Adipose tissue-derived stem cell therapy for erectile dysfunction in rats: a systematic review and meta-analysis

OBJECTIVE

We aimed to systematically assess the effect of adipose tissue-derived stem cell (ADSC) therapy and its influential factors on the treatment of erectile dysfunction (ED) in rats.

METHODS

Two authors independently searched for published studies through PubMed and EMBASE from study inception until August 31, 2016. A meta-analysis was used to combine the effect estimate from the published studies. A subgroup analysis was performed to identify the effect of some influential factors. The pooled standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated by a fixed-effects or random-effects model analysis.

RESULTS

Twenty studies with a total of 248 rats were included in this meta-analysis. The pooled analysis showed that ADSC therapy significantly increased the ratio of intracavernous pressure and mean arterial pressure (ICP/MAP; SMD 3.46, 95% CI 2.85-4.06; P < 0.001) compared to control therapy. The levels of neuronal nitric oxide synthase (nNOS; SMD 6.37, 95% CI 4.35-8.39; P < 0.001), the cavernous smooth muscle content (CSMC; SMD 3.65, 95% CI 2.65-4.65; P < 0.001), the ratio of cavernous smooth muscle and collagen (CSM/collagen; SMD 4.16, 95% CI 2.59-5.72; P < 0.001), and the cyclic guanosine monophosphate (cGMP; SMD 7.12, 95% CI 2.76-11.48; P = 0.001) were higher following ADSC therapy than following control therapy. Subgroup analysis showed that ADSCs modified by growth or neurotrophic factors significantly recovered erectile function (P < 0.001) compared with ADSC therapy.

CONCLUSION

The adequate data indicated that ADSC therapy recovered erectile function and regenerated cavernous structures in ED rats, and ADSCs modified by some growth and neurotrophic factors accelerated the recovery of erectile function and cavernous structures in ED rats.

Molecular and functional characterization of Kv 7 channels in penile arteries and corpus cavernosum of healthy and metabolic syndrome rats

BACKGROUND AND PURPOSE

KCNQ-encoded voltage-dependent potassium channels (Kv 7) are involved in the regulation of vascular tone. In this study we evaluated the influence of Kv 7 channel activation on smooth muscle relaxation in rat penile arteries and corpus cavernosum from normal and spontaneously hypertensive, heart failure-prone (SHHF) rats - a rat model of human metabolic syndrome.

EXPERIMENTAL APPROACH

Quantitative PCR and immunohistochemistry were used to determine the expression of KCNQ isoforms in penile tissue. Isometric tension was measured in intracavernous arterial rings and corpus cavernosum strips isolated from normal and SHHF rats.

KEY RESULTS

Transcripts for KCNQ3, KCNQ4 and KCNQ5 were detected in penile arteries and corpus cavernosum. KCNQ1 was only found in corpus cavernosum. Immunofluorescence signals to Kv 7.4 and Kv 7.5 were found in penile arteries, penile veins and corpus cavernosum. The Kv 7.2-7.5 activators, ML213 and BMS204352, relaxed pre-contracted penile arteries and corpus cavernosum independently of nitric oxide synthase or endothelium-derived hyperpolarization. Relaxations to sildenafil, a PDE5 inhibitor, and sodium nitroprusside (SNP), an nitric oxide donor, were reduced by blocking Kv 7 channels with linopirdine in penile arteries and corpus cavernosum. In SHHF rat penile arteries and corpus cavernosum, relaxations to ML213 and BMS204352 were attenuated, and the blocking effect of linopirdine on sildenafil-induced and SNP-induced relaxations reduced. KCNQ3, KCNQ4 and KCNQ5 were down-regulated, and KCNQ1 was up-regulated in corpus cavernosum from SHHF rats. KCNQ1-5 transcripts remained unchanged in penile arteries from SHHF rats.

CONCLUSIONS AND IMPLICATIONS

These data suggest that Kv 7 channels play a role in erectile function and contribute to the pathophysiology of erectile dysfunction, an early indicator of cardiovascular disease.

Effect of acute lithium administration on penile erection: involvement of nitric oxide system

BACKGROUND

Lithium has been the treatment of choice for bipolar disorder (BD) for many years. Although erectile dysfunction is a known adverse effect of this drug, the mechanism of action by which lithium affects erectile function is still unknown.

OBJECTIVE

The aim was to investigate the possible involvement of nitric oxide (NO) in modulatory effect of lithium on penile erection (PE). We further evaluated the possible role of Sildenafil in treatment of lithium-induced erectile dysfunction.

MATERIALS AND METHODS

Erectile function was determined using rat model of apomorphine-induced erections. For evaluating the effect of lithium on penile erection, rats received intraperitoneal injection of graded doses of lithium chloride 30 mins before subcutaneous injection of apomorphine. To determine the possible role of NO pathway, sub-effective dose of N (G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, was administered 15 min before administration of sub-effective dose of lithium chloride. In other separate experimental groups, sub- effective dose of the nitric oxide precursor, L-arginine, or Sildenafil was injected into the animals 15 min before administration of a potent dose of lithium. 30 min after administration of lithium chloride, animals were assessed in apomorphine test. Serum lithium levels were measured 30 min after administration of effective dose of lithium.

RESULTS

Lithium at 50 and 100 mg/kg significantly decreased number of PE (p<0.001), whereas at lower doses (5, 10 and 30 mg/kg) had no effect on apomorphine induced PE. The serum Li+ level of rats receiving 50 mg/kg lithium was 1±0.15 mmol/L which is in therapeutic range of lithium. The inhibitory effect of Lithium was blocked by administration of sub-effective dose of nitric oxide precursor L-arginine (100 mg/kg) (p<0.001) and sildenafil (3.5 mg/kg) (p<0.001) whereas pretreatment with a low and sub-effective dose of L-NAME (10mg/kg) potentiated sub-effective dose of lithium, (p<0.001).

CONCLUSION

These results suggest acute treatments with lithium cause erectile dysfunction in an in-vivo rat model. Furthermore it seems that the NO pathway might play role in erectile dysfunction associated with lithium treatment. Findings also suggest that Sildenafil may be effective in treatment of lithium-associated erectile dysfunction.

Nitrergic Mechanisms for Management of Recurrent Priapism

INTRODUCTION

Priapism is a condition involving prolonged penile erection unrelated to sexual interest or desire. The ischemic type, including its recurrent variant, is often associated with both physical and psychological complications. As such, management is of critical importance. Ideal therapies for recurrent priapism should address its underlying pathophysiology.

AIM

To review the available literature on priapism management approaches particularly related to nitrergic mechanisms.

METHODS

A literature review of the pathophysiology and management of priapism was performed using PubMed.

MAIN OUTCOME MEASURE

Publications pertaining to mechanisms of the molecular pathophysiology of priapism.

RESULTS

Nitrergic mechanisms are characterized as major players in the molecular pathophysiology of priapism. PDE5 inhibitors represent an available therapeutic option with demonstrated ability in attenuating these underlying nitrergic derangements. Several additional signaling pathways have been found to play a role in the molecular pathophysiology of priapism and have also been associated with these nitrergic mechanisms.

CONCLUSION

An increasing understanding of the molecular pathophysiology of priapism has led to the discovery of new potential targets. Several mechanism-based therapeutic approaches may become available in the future.

Effects of Icariside II on corpus cavernosum and major pelvic ganglion neuropathy in streptozotocin-induced diabetic rats

Diabetic erectile dysfunction is associated with penile dorsal nerve bundle neuropathy in the corpus cavernosum and the mechanism is not well understood. We investigated the neuropathy changes in the corpus cavernosum of rats with streptozotocin-induced diabetes and the effects of Icariside II (ICA II) on improving neuropathy. Thirty-six 8-week-old Sprague-Dawley rats were randomly distributed into normal control group, diabetic group and ICA-II treated group. Diabetes was induced by a one-time intraperitoneal injection of streptozotocin (60 mg/kg). Three days later, the diabetic rats were randomly divided into 2 groups including a saline treated placebo group and an ICA II-treated group (5 mg/kg/day, by intragastric administration daily). Twelve weeks later, erectile function was measured by cavernous nerve electrostimulation with real time intracorporal pressure assessment. The penis was harvested for the histological examination (immunofluorescence and immunohistochemical staining) and transmission electron microscopy detecting. Diabetic animals exhibited a decreased density of dorsal nerve bundle in penis. The neurofilament of the dorsal nerve bundle was fragmented in the diabetic rats. There was a decreased expression of nNOS and NGF in the diabetic group. The ICA II group had higher density of dorsal nerve bundle, higher expression of NGF and nNOS in the penis. The pathological change of major pelvic nerve ganglion (including the microstructure by transmission electron microscope and the neurite outgrowth length of major pelvic nerve ganglion tissue cultured in vitro) was greatly attenuated in the ICA II-treated group (p < 0.01). ICA II treatment attenuates the diabetes-related impairment of corpus cavernosum and major pelvic ganglion neuropathy in rats with Streptozotocin-Induced Diabetes.

Nitric oxide synthase: non-canonical expression patterns

Science can move ahead by questioning established or canonical views and, so it may be with the enzymes, nitric oxide synthases (NOS). Nitric oxide (NO) is generated by NOS isoforms that are often described by their tissue-specific expression patterns. NOS1 (nNOS) is abundant in neural tissue, NOS2 is upregulated in activated macrophages and known as inducible NOS (iNOS), and NOS3 (eNOS) is abundant in endothelium where it regulates vascular tone. These isoforms are described as constitutive or inducible, but in this perspective we question the broad application of these labels. Are there instances where "constitutive" NOS (NOS1 and NOS3) are inducibly expressed; conversely, are there instances where NOS2 is constitutively expressed? NOS1 and NOS3 inducibility may be linked to post-translational regulation, making their actual patterns activity much more difficult to detect. Constitutive NOS2 expression has been observed in several tissues, especially the human pulmonary epithelium where it may regulate airway tone. These data suggest that expression of the three NOS enzymes may include non-established patterns. Such information should be useful in designing strategies to modulate these important enzymes in different disease states.

Gas what: NO is not the only answer to sexual function

The ability to get and keep an erection is important to men for several reasons and the inability is known as erectile dysfunction (ED). ED has started to be accepted as an early indicator of systemic endothelial dysfunction and subsequently of cardiovascular diseases. The role of NO in endothelial relaxation and erectile function is well accepted. The discovery of NO as a small signalling gasotransmitter led to the investigation of the role of other endogenously derived gases, carbon monoxide (CO) and hydrogen sulphide (H2 S) in physiological and pathophysiological conditions. The role of NO and CO in sexual function and dysfunction has been investigated more extensively and, recently, the involvement of H2 S in erectile function has also been confirmed. In this review, we focus on the role of these three sister gasotransmitters in the physiology, pharmacology and pathophysiology of sexual function in man, specifically erectile function. We have also reviewed the role of soluble guanylyl cyclase/cGMP pathway as a common target of these gasotransmitters. Several studies have proposed alternative therapies targeting different mechanisms in addition to PDE-5 inhibition for ED treatment, since some patients do not respond to these drugs. This review highlights complementary and possible coordinated roles for these mediators and treatments targeting these gasotransmitters in erectile function/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.

Molecular analysis of erection regulatory factors in sickle cell disease associated priapism in the human penis

PURPOSE

Priapism is a vasculopathy that occurs in approximately 40% of patients with sickle cell disease. Mouse models suggest that dysregulated nitric oxide synthase and RhoA/ROCK signaling as well as increased oxidative stress may contribute to the mechanisms of sickle cell disease associated priapism. We examined changes in the protein expression of nitric oxide synthase and ROCK signaling pathways, and a source of oxidative stress, NADPH oxidase, in penile erectile tissue from patients with a priapism history etiologically related and unrelated to sickle cell disease.

MATERIALS AND METHODS

Human penile erectile tissue was obtained from 5 patients with sickle cell disease associated priapism and from 6 with priapism of other etiologies during nonemergent penile prosthesis surgery for erectile dysfunction or priapism management and urethroplasty. Tissue was also obtained from 5 control patients without a priapism history during penectomy for penile cancer. Samples were collected, immediately placed in cold buffer and then frozen in liquid nitrogen. The expression of phosphodiesterase 5, endothelial nitric oxide synthase, neuronal nitric oxide synthase, inducible nitric oxide synthase, RhoA, ROCK1, ROCK2, p47(phox), p67(phox), gp91(phox) and β-actin were determined by Western blot analysis. Nitric oxide was measured using the Griess reaction.

RESULTS

In the sickle cell disease group phosphodiesterase 5 (p <0.05), endothelial nitric oxide synthase (p <0.01) and RhoA (p <0.01) expression was significantly decreased, while gp91(phox) expression (p <0.05) was significantly increased compared to control values. In the nonsickle cell disease group endothelial nitric oxide synthase, ROCK1 and p47(phox) expression (each p <0.05) was significantly decreased compared to control values. Total nitric oxide levels were not significantly different between the study groups.

CONCLUSIONS

Mechanisms of sickle cell disease associated priapism in the human penis may involve dysfunctional nitric oxide synthase and ROCK signaling, and increased oxidative stress associated with NADPH oxidase mediated signaling.

Androgen depletion in humans leads to cavernous tissue reorganization and upregulation of Sirt1-eNOS axis

Aging and physiological androgen decay leads to structural changes in corpus cavernosum (CC) that associate with erectile function impairment. There is evidence that such changes relate to nitric oxide (NO) bioavailability, an endothelial compound produced by the action of endothelial NO synthase (eNOS), and is regulated by sirtuin-1 (Sirt1), a NAD(+)-dependent protein deacetylase. Taking into account the reduced NO synthesis observed in aging and erectile dysfunction, we aimed to characterize human CC of androgen-deprived, young, and aged individuals postulating that androgen deprivation induces modifications similar to those observed in aging. Human penile fragments were collected from young individuals submitted to male-to-female sex reassignment procedure, who undergone an androgen deprivation chemical regimen, from young organ donors and from aged patients submitted to penile deviation surgery. They were processed for histomorphometric analysis of smooth muscle (SM) and connective tissues (CT), and dual-immunofluorescence of alpha-actin/vWf or Sirt1, and endothelin-1/eNOS. Estrogen receptors were analyzed by immunohistochemistry and semiquantification of Sirt1, eNOS, and phospho-Akt was assayed by Western blotting. Androgen withdrawal, similarly to aging, leads to a noteworthy reduction of SM-to-CT ratio in CC. However, in contrast to young and aged, a significant increase in penile Sirt1 expression accompanied by an increase in total eNOS expression was observed in androgen-depleted individuals. No changes were evidenced in phospho-Akt system and estrogen receptors were undetectable. These findings indicate that Sirt1 regulates the expression of eNOS in human CC employing mechanisms influenced by androgen depletion.

Preserved fertility despite erectile dysfunction in mice lacking the nitric oxide receptor

Nitric oxide (NO) and cGMP have been shown to be important mediators of penile erection. Erectile dysfunction may result from reduced or non-functional signal transduction within this cascade. There is, however, some inconsistency in the available data as mice lacking NO synthases (endothelial and neuronal nitric oxide synthase, or both) appear to be fertile whereas mice deficient in cGMP-dependent protein kinase I (PKGI) suffer from erectile dysfunction. To clarify this discrepancy we performed studies on mice lacking the NO receptor NO-sensitive guanylyl cyclase (NO-GC). In addition, we generated cell-specific NO-GC knockout (KO) lines to investigate the function of NO in individual cell types. NO-GC was specifically deleted in smooth muscle or endothelial cells (SM-guanylyl cyclase knockout (SM-GCKO) and EC-GCKO, respectively) and these KO lines were compared with total knockouts (GCKO) and wild-type animals. We investigated expression of NO-GC, NO-induced relaxation of corpus cavernosum smooth muscle and their ability to generate offspring. NO-GC-positive immunostaining was detected in smooth muscle and endothelial cells of murine corpus cavernosum but not in interstitial cells of Cajal. NO released from NO donors as well as from nitrergic neurons failed to relax precontracted corpus cavernosum from GCKO mice in organ bath experiments. Similar results were obtained in corpus cavernosum from SM-GCKO mice whereas deletion of NO-GC in endothelial cells did not affect relaxation. The lack of NO-induced relaxation in GCKO animals was not compensated for by guanosine 3,5-cyclic monophosphate (cGMP) signalling. To our surprise, GCKO males were fertile although their ability to produce offspring was decreased. Our data show that deletion of NO-GC specifically in smooth muscle cells abolishes NO-induced corpus cavernosum relaxation but does not lead to infertility.

Sickling cells, cyclic nucleotides, and protein kinases: the pathophysiology of urogenital disorders in sickle cell anemia

Sickle cell anemia is one of the best studied inherited diseases, and despite being caused by a single point mutation in the HBB gene, multiple pleiotropic effects of the abnormal hemoglobin S production range from vaso-occlusive crisis, stroke, and pulmonary hypertension to osteonecrosis and leg ulcers. Urogenital function is not spared, and although priapism is most frequently remembered, other related clinical manifestations have been described, such as nocturia, enuresis, increased frequence of lower urinary tract infections, urinary incontinence, hypogonadism, and testicular infarction. Studies on sickle cell vaso-occlusion and priapism using both in vitro and in vivo models have shed light on the pathogenesis of some of these events. The authors review what is known about the deleterious effects of sickling on the genitourinary tract and how the role of cyclic nucleotides signaling and protein kinases may help understand the pathophysiology underlying these manifestations and develop novel therapies in the setting of urogenital disorders in sickle cell disease.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Edaravone ameliorates diabetes-induced dysfunction of NO-induced relaxation in corpus cavernosum smooth muscle in the rat

INTRODUCTION

Diabetes mellitus (DM) represents a major risk factor for erectile dysfunction (ED). Although the etiology of diabetes-induced ED is multifactorial and still unknown, reactive oxygen species are thought to be one of the key factors.

AIM

The aim of this article is to investigate whether administration of edaravone, a free radical scavenger, could prevent type 1 diabetes-induced dysfunction of nitric oxide (NO)-induced relaxation in corpus cavernosum smooth muscle in the rat.

METHODS

Six-week-old male Wistar rats were randomly divided into three groups. One group was treated with citrate-phosphate buffer plus normal saline (group Cont), whereas in the other two groups, diabetes was induced by streptozotocin (50 mg/kg intraperitoneally [i.p.]). Subsequently, the diabetic rats were treated for 4 weeks either with edaravone (10 mg/kg/day, i.p.; group DM + E) or with normal saline (group DM).

MAIN OUTCOME MEASURES

Serum glucose and malondialdehyde levels as well as penile cyclic guanosine monophosphate (cGMP) concentrations were determined, and penile function was estimated by organ bath studies with norepinephrine-mediated contractions and acetylcholine-mediated relaxations. The participation mRNA levels of muscarinic M(3) receptors, neuronal nitrous oxide synthase (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS), and participation protein levels of nNOS, eNOS, phosphorylated nNOS, and phosphorylated eNOS were investigated by quantitative real-time polymerase chain reaction (PCR) and immunoblot analysis, respectively.

RESULTS

Treatment with edaravone prevented partially but significantly the decreased body and penile weight induced by diabetes. Treatment with edaravone significantly improved the increased diabetes-induced malondialdehyde levels, the decreased penile cGMP concentrations, the increased diabetes-induced norepinephrine-mediated contractions, and the decreased acetylcholine-mediated relaxation. Although there were no significant differences in expression levels of mRNAs in nNOS, diabetes-induced upregulation of muscarinic M(3) receptor and iNOS mRNAs as well as diabetes-induced downregulations of eNOS, phosphorylated nNOS, and phosphorylated eNOS were significantly prevented by edaravone.

CONCLUSIONS

Edaravone decreases the oxidative insult in the penile corpus cavernosum by ameliorating the NO-NOS system and thus preventing partially the developing ED in DM in the rat.

Post-translational inactivation of endothelial nitric oxide synthase in the transgenic sickle cell mouse penis

INTRODUCTION

Sickle cell disease (SCD)-associated priapism is characterized by endothelial nitric oxide synthase (eNOS) dysfunction in the penis. However, the mechanism of decreased eNOS function/activation in the penis in association with SCD is not known.

AIMS

Our hypothesis in the present study was that eNOS is functionally inactivated in the SCD penis in association with impairments in eNOS post-translational phosphorylation and the enzyme's interactions with its regulatory proteins.

METHODS

Sickle cell transgenic (sickle) mice were used as an animal model of SCD. Wild-type (WT) mice served as controls. Penes were excised at baseline for molecular studies. eNOS phosphorylation on Ser-1177 (positive regulatory site) and Thr-495 (negative regulatory site), total eNOS, and phosphorylated AKT (upstream mediator of eNOS phosphorylation on Ser-1177) expressions, and eNOS interactions with heat-shock protein 90 (HSP90) and caveolin-1 were measured by Western blot. Constitutive NOS catalytic activity was measured by conversion of L-[14C]arginine-to-L-[14C]citrulline in the presence of calcium.

MAIN OUTCOME MEASURES

Molecular mechanisms of eNOS dysfunction in the sickle mouse penis.

RESULTS

eNOS phosphorylated on Ser-1177, an active portion of eNOS, was decreased in the sickle mouse penis compared with WT penis. eNOS interaction with its positive protein regulator HSP90, but not with its negative protein regulator caveolin-1, and phosphorylated AKT expression, as well as constitutive NOS activity, were also decreased in the sickle mouse penis compared with WT penis. eNOS phosphorylated on Thr-495, total eNOS, HSP90, and caveolin-1 protein expressions in the penis were not affected by SCD.

CONCLUSIONS

These findings provide a molecular basis for chronically reduced eNOS function in the penis by SCD, which involves decreased eNOS phosphorylation on Ser-1177 and decreased eNOS-HSP90 interaction.

Impact of the estrus cycle and reduction in estrogen levels with aromatase inhibition, on renal function and nitric oxide activity in female rats

Estradiol increases mRNA and/or protein expression of the nitric oxide synthase (NOS) isoforms in a variety of tissues including kidney. In this study we determined the relationship between cyclical variations in estradiol levels and renal function and total NO production in the virgin female rat. In addition, we used an aromatase inhibitor (Anastrozole), to inhibit synthesis of estradiol from testosterone. Estradiol levels were higher in proestrus vs. diestrus, and were markedly suppressed by 7 days treatment with aromatase inhibitor. There was no difference in total NO production (from urinary and plasma nitrate+nitrite=NO(X)) between proestrus and diestrus but aromatase inhibition resulted in increases in total NO production. The renal cortical NOS activity and protein abundance also increased in aromatase-inhibited female rats. There were no differences in blood pressure (BP) in any group but the renal vascular resistance (RVR) was low in proestrus, increased in diestrus and did not change further after aromatase inhibition. In summary, the cyclical changes in renal function correlate with estradiol but not NO levels. Pharmacologic castration with aromatase inhibition leads to a marked increase in total and renal NOS. This contrasts to earlier work where surgical castration causes decreased NOS.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.