Protein inhibitor of nitric oxide synthase (NOS) and the N-methyl-D-aspartate receptor are expressed in the rat and mouse penile nerves and colocalize with penile neuronal NOS

Biosynthesis and Degradation of Free D-Amino Acids and Their Physiological Roles in the Periphery and Endocrine Glands

It was long believed that D-amino acids were either unnatural isomers or laboratory artifacts, and that the important functions of amino acids were exerted only by L-amino acids. However, recent investigations have revealed a variety of D-amino acids in mammals that play important roles in physiological functions, including free D-serine and D-aspartate that are crucial in the central nervous system. The functions of several D-amino acids in the periphery and endocrine glands are also receiving increasing attention. Here, we present an overview of recent advances in elucidating the physiological roles of D-amino acids, especially in the periphery and endocrine glands.

The Acute Effects and Mechanism of Ketamine on Nicotine-Induced Neurogenic Relaxation of the Corpus Cavernosum in Mice

The present study aimed to investigate the acute effects and the mechanism of ketamine on nicotine-induced relaxation of the corpus cavernosum (CC) in mice. This study measured the intra-cavernosal pressure (ICP) of male C57BL/6 mice and the CC muscle activities using an organ bath wire myograph. Various drugs were used to investigate the mechanism of ketamine on nicotine-induced relaxation. Direct ketamine injection into the major pelvic ganglion (MPG) inhibited MPG-induced increases in ICP. D-serine/L-glutamate-induced relaxation of the CC was inhibited by MK-801 (N-methyl-D-aspartate (NMDA) receptor inhibitor), and nicotine-induced relaxation was enhanced by D-serine/L-glutamate. NMDA had no effect on CC relaxation. Nicotine-induced relaxation of the CC was suppressed by mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist), lidocaine, guanethidine (an adrenergic neuronal blocker), N^w-nitro-L-arginine (a non-selective nitric oxide synthase inhibitor), MK-801, and ketamine. This relaxation was almost completely inhibited in CC strips pretreated with 6-hydroxydopamine (a neurotoxic synthetic organic compound). Ketamine inhibited cavernosal nerve neurotransmission via direct action on the ganglion and impaired nicotine-induced CC relaxation. The relaxation of the CC was dependent on the interaction of the sympathetic and parasympathetic nerves, which may be mediated by the NMDA receptor.

NMDA Receptor Hypofunction in the Aging-Associated Malfunction of Peripheral Tissue

Glutamatergic transmission through NMDA receptors (NMDARs) is important for the function of peripheral tissues. In the bone, NMDARs and its co-agonist, D-serine participate in all the phases of the remodeling. In the vasculature, NMDARs exerts a tonic vasodilation decreasing blood perfusion in the corpus cavernosum and the filtration rate in the renal glomerulus. NMDARs are relevant for the skin turnover regulating the proliferation and differentiation of keratinocytes and the formation of the cornified envelope (CE). The interference with NMDAR function in the skin leads to a slow turnover and repair. As occurs with the brain and cognitive functions, the manifestations of a hypofunction of NMDARs resembles those observed during aging. This raises the question if the deterioration of the glomerular vasculature, the bone remodeling and the skin turnover associated with age could be related with a hypofunction of NMDARs. Furthermore, the interference of D-serine and the effects of its supplementation on these tissues, suggest that a decrease of D-serine could account for this hypofunction pointing out D-serine as a potential therapeutic target to reduce or even prevent the detriment of the peripheral tissue associated with aging.

cAMP-dependent post-translational modification of neuronal nitric oxide synthase neuroprotects penile erection in rats

OBJECTIVES

To evaluate neuronal nitric oxide (NO) synthase (nNOS) phosphorylation, nNOS uncoupling, and oxidative stress in the penis and major pelvic ganglia (MPG), before and after the administration of the cAMP-dependent protein kinase A (PKA) agonist colforsin in a rat model of bilateral cavernous nerve injury (BCNI),which mimics nerve injury after prostatectomy.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were divided into BCNI and sham-operated groups. Each group included two subgroups: vehicle and colforsin (0.1 mg/kg/day i.p.). After 3 days, erectile function (intracavernosal pressure) was measured and penis and MPG were collected for molecular analyses of phospho (P)-nNOS (Ser-1412 and Ser-847), total nNOS, nNOS uncoupling, binding of protein inhibitor of nNOS (PIN) to nNOS, gp91^phox subunit of NADPH oxidase, active caspase 3, PKA catalytic subunit α (PKA-Cα; by Western blot) and oxidative stress (hydrogen peroxide [H₂ O₂ ] and superoxide by Western blot and microdialysis method).

RESULTS

Erectile function was decreased 3 days after BCNI and normalized by colforsin. nNOS phosphorylation on both positive (Ser-1412) and negative (Ser-847) regulatory sites, and nNOS uncoupling, were increased after BCNI in the penis and MPG, and normalized by colforsin. H₂ O₂ and total reactive oxygen species production were increased in the penis after BCNI and normalized by colforsin. Protein expression of gp91^phox was increased in the MPG after BCNI and was normalized by colforsin treatment. Binding of PIN to nNOS was increased in the penis after BCNI and was normalized by colforsin treatment. Protein expression of active Caspase 3 was increased in the MPG after BCNI and was normalized by colforsin treatment. Protein expression of PKA-Cα was decreased in the penis after BCNI and normalized by colforsin.

CONCLUSION

Collectively, BCNI impairs nNOS function in the penis and MPG by mechanisms involving its phosphorylation and uncoupling in association with increased oxidative stress, resulting in erectile dysfunction. PKA activation by colforsin reverses these molecular changes and preserves penile erection in the face of BCNI.

Post-translational regulation of neuronal nitric oxide synthase: implications for sympathoexcitatory states

INTRODUCTION

Nitric oxide (NO) synthesized via neuronal nitric oxide synthase (nNOS) plays a significant role in regulation/modulation of autonomic control of circulation. Various pathological states are associated with diminished nNOS expression and blunted autonomic effects of NO in the central nervous system (CNS) including heart failure, hypertension, diabetes mellitus, chronic renal failure etc. Therefore, elucidation of the molecular mechanism/s involved in dysregulation of nNOS is essential to understand the pathogenesis of increased sympathoexcitation in these diseased states. Areas covered: nNOS is a highly regulated enzyme, being regulated at transcriptional and posttranslational levels via protein-protein interactions and modifications viz. phosphorylation, ubiquitination, and sumoylation. The enzyme activity of nNOS also depends on the optimal concentration of substrate, cofactors and association with regulatory proteins. This review focuses on the posttranslational regulation of nNOS in the context of normal and diseased states within the CNS. Expert opinion: Gaining insight into the mechanism/s involved in the regulation of nNOS would provide novel strategies for manipulating nNOS directed therapeutic modalities in the future, including catalytically active dimer stabilization and protein-protein interactions with intracellular protein effectors. Ultimately, this is expected to provide tools to improve autonomic dysregulation in various diseases such as heart failure, hypertension, and diabetes.

The effect of PnTx2-6 protein from Phoneutria nigriventer spider toxin on improvement of erectile dysfunction in a rat model of cavernous nerve injury

OBJECTIVE

To explore the therapeutic potential of PnTx2-6 injected 3 times a week for 4 weeks into the intracavernosal tissue in a rat model of bilateral cavernous nerve crush injury (BCNI).

METHODS

Eight-week-old male Sprague-Dawley rats were randomly divided into the following 6 groups (n = 5 per group): age-matched control (normal group), BCNI (injury group), post-BCNI phosphate-buffered saline injection (PBS group), post-BCNI Sf9 cell-lysate injection (N/C group), post-BCNI injection of cell lysate from S9 cells infected with wild-type recombinant baculovirus (W/T group), and post-BCNI injection of cell lysate from S9 cells infected with recombinant baculovirus containing PnTx2-6 (PnTx2-6 group). Injections were delivered 3 times a week for 4 weeks. After 4 weeks, intracavernosal pressure-to-mean arterial pressure ratio, smooth muscle and collagen content via the Masson trichrome staining, levels of neural nitric oxide synthase, phosphoendothelial nitric oxide synthase, and cyclic guanosine monophosphate were all measured.

RESULTS

The PnTx2-6 group showed significantly higher intracavernosal pressure-to-mean arterial pressure ratio (P <.05), smooth muscle-to-collagen ratio (P <.01), expression levels of neural nitric oxide synthase, phosphoendothelial nitric oxide synthase (P <.05), and cyclic guanosine monophosphate (P <.05) than all other experimental groups.

CONCLUSION

We conclude that PnTx2-6 improved erectile function and prevented muscle atrophy in a rat model of BCNI via increased synthesis of nitric oxide and cyclic guanosine monophosphate.

Intracellular calcium concentration of corpus cavernosum smooth muscle cells is decreased by the overexpression of PnNOS gene in adipose tissue-derived stem cells

The study investigated the effects of adipose tissue-derived stem cells (ADSCs) modified with penile neuronal nitric oxide synthase (PnNOS) gene on intracellular calcium concentration in rat corpus cavernosum smooth muscle cells (CCSMCs). ADSCs and CCSMCs of Sprague-Dawley (SD) rats were isolated and cultured in vitro respectively. The rat PnNOS gene was transferred into the ADSCs mediated by a recombinant adenovirus vector. The expression of the PnNOS gene was detected. At the same time, the concentration of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) was assayed. After coculturing with the CCSMCs of SD rats, which were isolated and expanded ex vivo, the cGMP and NO levels of ADSCs and CCSMCs were measured. Intracellular calcium concentration ([Ca(2+) ]i ) in rat CCSMCs was measured with Fluo-3/AM by flow cytometer after cocultured with ADSCs overexpressing PnNOS gene. The mRNA and protein expression of PnNOS gene mediated by recombinant adenovirus vector significantly overexpressed and lasted at least 2 weeks. Meanwhile, the concentration of NO and cGMP in ADSCs was greatly increased. The concentration of cGMP was significantly increased, and [Ca(2+) ]i was obviously decreased in CCSMCs compared with the control groups (P < 0.05) after cocultured with ADSCs for 3 days. These findings demonstrated that ADSCs overexpressing PnNOS gene might decrease [Ca(2+) ]i in CCSMCs by up-regulating NO-cGMP signalling pathway.

Myosin Va plays a role in nitrergic smooth muscle relaxation in gastric fundus and corpora cavernosa of penis

The intracellular motor protein myosin Va is involved in nitrergic neurotransmission possibly by trafficking of neuronal nitric oxide synthase (nNOS) within the nerve terminals. In this study, we examined the role of myosin Va in the stomach and penis, proto-typical smooth muscle organs in which nitric oxide (NO) mediated relaxation is critical for function. We used confocal microscopy and co-immunoprecipitation of tissue from the gastric fundus (GF) and penile corpus cavernosum (CCP) to localize myosin Va with nNOS and demonstrate their molecular interaction. We utilized in vitro mechanical studies to test whether smooth muscle relaxations during nitrergic neuromuscular neurotransmission is altered in DBA (dilute, brown, non-agouti) mice which lack functional myosin Va. Myosin Va was localized in nNOS-positive nerve terminals and was co-immunoprecipitated with nNOS in both GF and CCP. In comparison to C57BL/6J wild type (WT) mice, electrical field stimulation (EFS) of precontracted smooth muscles of GF and CCP from DBA animals showed significant impairment of nitrergic relaxation. An NO donor, Sodium nitroprusside (SNP), caused comparable levels of relaxation in smooth muscles of WT and DBA mice. These normal postjunctional responses to SNP in DBA tissues suggest that impairment of smooth muscle relaxation resulted from inhibition of NO synthesis in prejunctional nerve terminals. Our results suggest that normal physiological processes of relaxation of gastric and cavernosal smooth muscles that facilitate food accommodation and penile erection, respectively, may be disrupted under conditions of myosin Va deficiency, resulting in complications like gastroparesis and erectile dysfunction.

Combined therapeutic effect of udenafil and adipose-derived stem cell (ADSC)/brain-derived neurotrophic factor (BDNF)-membrane system in a rat model of cavernous nerve injury

OBJECTIVE

To prevent cavernous nerve injury and corpus cavernosum apoptosis-induced erectile dysfunction (ED) after prostatectomy surgery, we investigated whether oral administration of udenafil combination with covering adipose-derived stem cells (ADSCs) and brain-derived neurotrophic factor (BDNF) immobilized poly-lactic-co-glycolic (PLGA) membrane on the injured cavernous nerve could further improve erectile dysfunction.

METHODS

Adult Sprague-Dawley rats were divided into 5 groups: normal group (sham-operated group), bilateral cavernous nerve injury (BCNI) group (BCNI group), udenafil group (oral administration of udenafil 20 mg/kg daily), AB group (BCNI group with ADSCs covered with BDNF membrane on cavernous nerve), AB/udenafil group (AB group with udenafil group). After 4 weeks, erectile function was examined before tissue harvest. Penile tissues were evaluated in terms of the expression of smooth muscle actin (SMA), neuronal nitric oxide synthase (nNOS), and vascular endothelial growth factor (VEGF). The cyclic guanosine monophosphate (cGMP) level of the corpus cavernosum was quantified by cGMP assay.

RESULTS

AB/udenafil treatment markedly improved erectile function and prevented the architecture damage of the corpus cavernosum, compared with other treated groups. Udenafil had no statistical significance on increasing nNOS expression, but enhanced VEGF expression. On the contrary, the AB group had no statistical significance on enhancing VEGF expression, but increased nNOS expression. AB/udenafil treatment significantly increased nNOS expression, VEGF expression, and elevated cGMP level, compared with the udenafil group and AB group.

CONCLUSION

The orally administered udenafil combination with ADSC/BDNF-membrane system protected cavernous nerve and improved angiogenesis in the corpus cavernosum, which further maintained erectile function in a rat model of postprostatectomy erectile dysfunction.

Emerging tools for erectile dysfunction: a role for regenerative medicine

Erectile dysfunction (ED) is the most common sexual disorder reported by men to their health-care providers and the most investigated male sexual dysfunction. Currently, the treatment of ED focuses on 'symptomatic relief' of ED and, therefore, tends to provide temporary relief rather than providing a cure or reversing the cause. The identification of a large population of "difficult-to-treat" patients has triggered researchers to identify novel treatment approaches, which focus on cure and restoration of the underlying cause of ED. Regenerative medicine has developed extensively in the past few decades and preclinical trials have emphasized the benefit of growth factor therapy, gene transfer, stem cells and tissue engineering for the restoration of erectile function. Development of clinical trials involving immunomodulation in postprostatectomy ED patients and the use of maxi-K channels for gene therapy are illustrative of the advances in the field. However, the search for novel treatment targets and a wealth of preclinical studies represent a dynamic and continuing field of enquiry.

Therapeutic effect of adipose-derived stem cells and BDNF-immobilized PLGA membrane in a rat model of cavernous nerve injury

INTRODUCTION

Cavernous nerve injury is the main reason for post-prostatectomy erectile dysfunction (ED). Stem cell and neuroprotection therapy are promising therapeutic strategy for ED.

AIM

To evaluate the therapeutic efficacy of adipose-derived stem cells (ADSCs) and brain-derived neurotrophic factor (BDNF) immobilized Poly-Lactic-Co-Glycolic (PLGA) membrane on the cavernous nerve in a rat model of post-prostatectomy ED. Methods.  Rats were randomly divided into five groups: normal group, bilateral cavernous nerve crush injury (BCNI) group, ADSC (BCNI group with ADSCs on cavernous nerve) group, BDNF-membrane (BCNI group with BDNF/PLGA membrane on cavernous nerve) group, and ADSC/BDNF-membrane (BCNI group with ADSCs covered with BDNF/PLGA membrane on cavernous nerve) group. BDNF was controlled-released for a period of 4 weeks in a BDNF/PLGA porous membrane system.

MAIN OUTCOME MEASURES

Four weeks after the operation, erectile function was assessed by detecting the ratio of intra-cavernous pressure (ICP)/mean arterial pressure (MAP). Smooth muscle and collagen content were determined by Masson's trichrome staining. Neuronal nitric oxide synthase (nNOS) expression in the dorsal penile nerve was detected by immunostaining. Phospho-endothelial nitric oxide synthase (eNOS) protein expression and cyclic guanosine monophosphate (cGMP) level of the corpus cavernosum were quantified by Western blotting and cGMP assay, respectively.

RESULTS

In the ADSC/BDNF-membrane group, erectile function was significantly elevated, compared with the BCNI and other treated groups. ADSC/BDNF-membrane treatment significantly increased smooth muscle/collagen ratio, nNOS content, phospho-eNOS protein expression, and cGMP level, compared with the BCNI and other treated groups.

CONCLUSIONS

ADSCs with BDNF-membrane on the cavernous nerve can improve erectile function in a rat model of post-prostatectomy ED, which may be used as a novel therapy for post-prostatectomy ED.

Gene therapy as future treatment of erectile dysfunction

IMPORTANCE OF THE FIELD

Erectile dysfunction (ED) is a major men's health problem. Although the high success rate of treating ED by phosphodiesterase 5 (PDE5) inhibitors has been reported, there are a significant number of ED patients who do not respond to currently available treatment modalities.

AREAS COVERED IN THIS REVIEW

To elucidate the current status of gene therapy applications for ED, gene therapy approaches for ED treatment are reviewed.

WHAT THE READER WILL GAIN

Gene therapy strategies that can enhance nitric oxide (NO) production or NO-mediated signaling pathways, growth factor-mediated nerve regeneration or K(+) channel activity in the smooth muscle could be promising approaches for the treatment of ED. Although the majority of gene therapy studies are still in the preclinical phase, the first clinical trial using non-viral gene transfer of Ca(2+)-activated, large-conductance K(+) channels into the corpus cavernosum of ED patients showed positive results.

TAKE HOME MESSAGE

Gene therapy represents an exciting future treatment option for ED, especially for people with severe ED unresponsive to current first-line therapies such as PDE5 inhibitors although the long-term safety of both viral and non-viral gene therapies should be established.

Emerging gene and stem cell therapies for the treatment of erectile dysfunction

Erectile dysfunction is a prevalent condition that leads to significant morbidity and distress, not just for affected men but also for their partners. Very few currently available treatments ameliorate the underlying causes of the disorder and 'cure' the disease state. Much recent effort has been focused on the development of gene and cell-based approaches to rectify the molecular and tissue defects responsible for ED. Gene therapy has been investigated in animal models as a means to restore normal function to the penis; at this time, however, only one human trial has been published in the peer-reviewed literature. Recent gene therapy studies have focused on the modulation of enzymes associated with the NOS/cGMP pathway, and supplementation of trophic factors, peptides and potassium channels. Stem cell therapy has been a topic of interest in more recent years but there are currently very few published reports in animal models and none in human men. Although stem cell therapy offers the potential for restoration of functional tissues, legitimate concerns remain regarding the long-term fate of stem cells. The long-term safety of both gene and stem cell therapy must be thoroughly investigated before large-scale human studies can be considered.

Posttranslational modification of constitutive nitric oxide synthase in the penis

Erectile dysfunction (ED) is a common men's health problem characterized by the consistent inability to sustain an erection sufficient for sexual intercourse. Basic science research on erectile physiology has been devoted to investigating the pathogenesis of ED and has led to the conclusion that ED is predominately a disease of vascular origin, neurogenic dysfunction, or both. The constitutive forms of nitric oxide synthase (NOS, endothelial [eNOS] and neuronal [nNOS]) are important enzymes involved in the production of nitric oxide (NO) and thus regulate penile vascular homeostasis. Given the effect of endothelial- and neuronal-derived NO in penile vascular biology, a great deal of research over the past decade has focused on the role of NO synthesis from the endothelium and nitrergic nerve terminal in normal erectile physiology, as well as in disease states. Loss of the functional integrity of the endothelium and subsequent endothelial dysfunction plays an integral role in the occurrence of ED. Therefore, molecular mechanisms involved in dysregulation of these NOS isoforms in the development of ED are essential to discovering the pathogenesis of ED in various disease states. This communication reviews the role of eNOS and nNOS in erectile physiology and discusses the alterations in eNOS and nNOS via posttranslation modification in various vascular diseases of the penis.

Fibrosis and loss of smooth muscle in the corpora cavernosa precede corporal veno-occlusive dysfunction (CVOD) induced by experimental cavernosal nerve damage in the rat

INTRODUCTION

Corporal veno-occlusive dysfunction (CVOD), which usually is associated with a loss of smooth muscle cells (SMC) and an increase in fibrosis within the corpora cavernosa, can be induced by an injury to the cavernosal nerves. The corporal tissue expresses inducible nitric oxide synthase (iNOS), presumably as an antifibrotic and SMC-protective response.

AIMS

We studied the temporal relationship in the corpora between the expression of iNOS, other histological and biochemical changes, and the development of CVOD, after bilateral cavernosal nerve resection (BCNR) in the rat.

METHODS

Rats underwent either BCNR or sham operation. Cavernosometry was performed 1, 3, 7, 15, 30, and 45 days (N = 8/groups) after surgery. Penile tissue sections were subjected to Masson trichrome staining for SMC and collagen, and immunodetection for alpha smooth muscle actin, iNOS, neuronal NOS (nNOS), endothelial NOS (eNOS), proliferating cell nuclear antigen (PCNA), and terminal transferase dUTP nick end labeling (TUNEL). Quantitative western blot analysis was done in homogenates.

MAIN OUTCOME MEASURES

Time course on the development of fibrosis and CVOD.

RESULTS

Following BCNR, CVOD was detectable 30 days later, and it became more pronounced by 45 days. In contrast, the SMC/collagen ratio in the BCNR corpora was reduced at 7 days and bottomed at 30 and 45 days, due in part to the reduction of SMC, presumably caused by an increase in apoptosis peaking at 3 days. PCNA also peaked at 3 days, but then decayed. nNOS was reduced early (3-7 days) and disappeared at 30 days, whereas eNOS was not affected. iNOS was induced at day 3, and steadily increased peaking at 30 days.

CONCLUSIONS

CVOD develops in the BCNR rat as a result of the early loss of corporal SMC by the neuropraxia-induced apoptosis, which the initial cell replication response cannot counteract, followed by fibrosis. The time course of iNOS induction supports the antifibrotic role of iNOS.

Antisense and Short Hairpin RNA (shRNA) Constructs Targeting PIN (Protein Inhibitor of NOS) Ameliorate Aging-Related Erectile Dysfunction in the Rat

INTRODUCTION

Over-expression of penile neuronal nitric oxide synthase (PnNOS) from a plasmid ameliorates aging-related erectile dysfunction (ED), whereas over-expression of the protein inhibitor of NOS (PIN), that binds to nNOS, increases ED.

AIM

To improve this form of gene therapy for ED by comparing the electrical field response of short hairpin RNA (shRNA) for PIN with that of antisense PIN RNA.

MAIN OUTCOME MEASURE

Both shRNA and antisense RNA gene therapy vectors increased intracavernosal pressure in aged rats.

METHODS

PIN small interfering RNA (siRNA), and plasmid constructs for cytomegalovirus promoter plasmid vector (pCMV-PIN), pCMV-PIN antisense RNA, pSilencer2.1-U6-PIN-shRNA; and pSilencer2.1-U6-randomer-shRNA were prepared and validated by transfection into HEK293 cells, determining the effects on PIN expression by Western blot. Plasmid constructs were then injected, followed by electroporation, into the penile corpora cavernosa of aged (20-month-old) Fisher 344 rats and, 1 month later, the erectile response was measured by intracavernosal pressure increase following electrical field stimulation (EFS) of the cavernosal nerve. PIN was estimated in penile tissue by Western blot and real-time reverse transcriptase-polymerase chain reaction. Cyclic guanosine monophosphate (cGMP) measurements were conducted by competitive enzyme immunoassay (EIA). Immunohistofluorescence detected PIN in corporal tissue sections.

RESULTS

In cell culture, PIN siRNA and plasmid-expressed pU6-PIN-shRNA effectively reduced PIN expression from pCMV-PIN. pSilencer2.1-U6-PIN-shRNA corrected the impaired erectile response to EFS in aged rats and raised it above the value for young rats, more efficiently than pCMV-PIN antisense RNA. PIN mRNA expression in the penis was decreased by >70% by the shRNA but remained unaffected by the antisense RNA, whereas PIN protein expression was reduced in both cases, particularly in the dorsal nerve. PIN antisense increased cGMP concentration in treated tissue by twofold.

CONCLUSION

pSilencer2.1-U6-PIN-shRNA gene therapy was more effective than the antisense PIN mRNA in ameliorating ED in the aged rat, thereby suggesting that PIN is indeed a physiological inhibitor of nNOS and nitrergic neurotransmission in the penis.

Physiology of erectile function

INTRODUCTION

There are numerous investigations concerning the balance and interactions between relaxant and contractile factors regulating penile smooth muscle (arterial and trabecular) tone, the determinant of penile flaccidity or erection. Enhanced knowledge of erectile physiology may improve management of men with erectile dysfunction. Aim. To provide state-of-the-art knowledge on the physiology of erectile function.

METHODS

An international consultation in collaboration with the major urology and sexual medicine associations assembled over 200 multidisciplinary experts from 60 countries into 17 committees. Committee members established specific objectives and scopes for various male and female sexual medicine topics. The recommendations concerning state-of-the-art knowledge in the respective sexual medicine topic represent the opinion of experts from five continents developed in a process over a two-year period. Concerning the physiology of erectile function and pathophysiology of erectile dysfunction committee, there were seven experts from five countries.

MAIN OUTCOME MEASURE

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Key roles in the mechanism determining the tone of penile smooth muscle are played by the rise of the intracellular concentration of free calcium and the sensitivity of the contractile machinery to calcium, endothelial health, endothelium-derived nitric oxide, endothelium-derived hyperpolarizing factor (EDHF), neuronal nitric oxide, cyclic guanosine monophosphate-dependent protein kinase and phosphodiesterase type 5.

CONCLUSIONS

A number of new mechanisms have been identified for the local regulation of penile smooth muscle contractility and therefore penile erection. Molecules participating in these pathways can be considered targets for the development of new treatments to treat erectile dysfunction.

Molecular pathophysiology and gene therapy of aging-related erectile dysfunction

Erectile dysfunction (ED) is a major public health problem that seriously affects the quality of life of patients and their partners. ED is mainly associated with vascular disease, diabetes, smoking, and radical prostatectomy, and its prevalence increases significantly with aging. Vasculogenic ED, specifically corporal veno-occlusive dysfunction (CVOD), is caused by the impairment of the relaxation of the smooth muscle in the penile corpora cavernosa and occurs in 2/3 of cases, whereas the less common neurogenic ED is due to a defective nitrergic neurotransmission triggered by the sexual stimulus, either at the central hypothalamic and spinal levels or at the penile nerves. Based on animal and cell studies, neurogenic ED is assumed to be caused mainly by: (a) an insufficient synthesis of nitric oxide (NO) due to a decrease in the levels of the penile neuronal nitric oxide synthase (PnNOS) or the impairment of its regulation by protein effectors (NMDA receptor, protein inhibitor of nNOS: PIN), occurring in the neuronal bodies or nerve terminals, or (b) a loss of the cells themselves by apoptosis caused by the induction of inducible NOS (iNOS) and the production of peroxynitrite. In contrast vasculogenic ED, although may involve endothelial damage and down-regulation of endothelial NOS (eNOS), appears to be mainly caused by the relative loss of smooth muscle cells and replacement by collagen fibers (fibrosis) that impairs tissue compliance. In this case, iNOS induction may not be deleterious, but a defense mechanism preventing excessive collagen deposition. Gene therapy to the penile corpora cavernosa of cDNAs expressing PnNOS or eNOS, or counteracting PIN, has been effective in ameliorating ED in the aging rat model that exhibits both neurogenic ED and CVOD. cDNA constructs for other genes involved in the control of penile erection have also been successfully tested. Gene transfer into the penis may soon translate to the clinic as a therapy aimed to cure the underlying conditions in ED, including fibrosis, as opposed to the facilitation of erection on demand offered by the current oral therapies.

Association of single nucleotide polymorphisms in klotho with priapism in sickle cell anaemia

The complications of sickle cell disease are probably determined by genes whose products modify the pathophysiology initiated by the sickle haemoglobin mutation. Priapism, one vaso-occlusive manifestation of sickle cell disease, affects more than 30% of males with the disease. We examined the possible association of single nucleotide polymorphisms (SNPs) in 44 candidate genes of different functional classes for an association with the occurrence of priapism. One hundred and forty-eight patients with sickle cell anaemia and incident or a confirmed history of priapism were studied, along with 529 controls that had not developed priapism. Polymorphisms in the KLOTHO gene (KL; 13q12) showed an association with priapism by genotypic [reference SNP cluster identifier number (rs)2249358; odds ratio (OR) = 2.6 (1.4-5.5); rs211239; OR = 1.7 (1.2-2.6)] and haplotype analyses [rs211234 and rs211239; OR = 2.3 (1.5-3.4)]. These findings may have broader implications in sickle cell disease, as KL encodes a membrane protein that regulates many vascular functions, including vascular endothelial growth factor expression and endothelial nitric oxide release.

Inhibition of nitric oxide release in vivo by ethanol

OBJECTIVE

Previous studies indicate that the nitric oxide (NO(.)) pathway is involved in the acute or chronic effects of ethanol on the central nervous system. However, direct evidence for the effect of ethanol on NO(.) production in vivo is lacking, and it is not clear whether it is inhibition or stimulation of the NO(.) pathway that contributes to the behavioral effects of ethanol. Herein the release of NO(.) in the rat striatum in vivo in response to NMDA receptor activation--the dominant mechanism controlling NO(.) formation-has been investigated after systemic or local injections of ethanol.

METHODS

NMDA-induced release of authentic NO(.) was measured directly in the striatum of urethane-anesthetized (1.2 g/kg intraperitoneally) male Sprague-Dawley rats by using a direct-current amperometric method coupled to an electrically modified carbon microelectrode. An injector cannula was implanted in the proximity of the electrode (250 microm apart) for focal drugs application.

RESULTS

Local application of NMDA (1 microl, 100 microM) produced a sharp and transient NO(.) signal. Systemic ethanol, 1 or 2.5 g/kg intraperitoneally, caused a long-lasting, dose-dependent inhibition of NMDA-induced NO(.) release to 12.2 +/- 5.9 and 6.4 +/- 3.7% of control, respectively, 60 min after ethanol administration. Dizocilpine (0.5 mg/kg intraperitoneally) mimicked the ethanol effect, inhibiting NO release to 1.6 +/- 0.66% of control. Local application of ethanol (1 microl, 2.5% v/v) in the striatum reduced the NMDA-induced response to 28.6 +/- 3.8% of control. Focal application of the competitive NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoic acid (100 microM) or the nonselective NO synthase inhibitor L-N(G)-nitro-arginine methyl esther (100 microM) also caused inhibition of NMDA-induced NO(.) release to 2.4 +/- 0.7 and 4.3 +/- 0.9% of control, respectively.

CONCLUSIONS

Ethanol, at pharmacologically significant doses, strongly inhibits striatal NO(.) production and release apparently through inhibition of NMDA receptor function. Inhibition of NMDA receptor-mediated activation of the NO(.) pathway could be a primary neurobiological mechanism contributing to the effects of ethanol.

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.

Gene Transfer of Inducible Nitric Oxide Synthase Complementary DNA Regresses the Fibrotic Plaque in an Animal Model of Peyronie’s Disease1

The goal of the present study was to investigate the antifibrotic role of inducible nitric oxide synthase (iNOS) in Peyronie's disease (PD) by determining whether a plasmid expressing iNOS (piNOS) injected into a PD-like plaque can induce regression of the plaque. A PD-like plaque was induced with fibrin in the penile tunica albuginea of mice and then injected with a luciferase-expressing plasmid (pLuc), either alone or with piNOS, following luciferase expression in vivo by bioluminescence imaging. Rats were treated with either piNOS, an empty control plasmid (pC), or saline. Other groups were treated with pC or piNOS, in the absence of fibrin. Tissue sections were stained for collagen, transforming growth factor (TGF) beta1, and plasminogen-activator inhibitor (PAI-1) as profibrotic factors; copper-zinc superoxide dismutase (CuZn SOD) as scavenger of reactive oxygen species (ROS); and nitrotyrosine to detect nitric oxide reaction with ROS. Quantitative image analysis was applied. Both iNOS and xanthine oxido-reductase (XOR; oxidative stress) were estimated by Western blot analysis. Luciferase reporter expression was restricted to the penis, peaked at 3 days after injection, but continued for at least 3 wk. In rats receiving piNOS, iNOS expression also peaked at 3 days, but expression decreased at the end of treatment, when a considerable reduction of plaque size occurred. Protein nitrotyrosine, XOR, and CuZn SOD increased, and TGFbeta1 and PAI-1 decreased. The piNOS gene transfer regressed the PD plaque and expression of profibrotic factors, supporting the view that endogenous iNOS induction in PD is defense mechanism by the tissue against fibrosis.

Penile neuronal nitric oxide synthase and its regulatory proteins are present in hypothalamic and spinal cord regions involved in the control of penile erection

Control of penile erection requires the coordination of the hypothalamus and the L6-S1 region of the spinal cord. Erection requires the activation of neuronal nitric oxide synthase (nNOS), which is tightly regulated. Because variants of nNOS (penile nNOS: PnNOS) and the N-methyl-D-aspartate receptor (truncated NMDAR subunit 1: NMDAR1-T) as well as protein inhibitor of NOS (PIN) have all been located in the pelvic ganglia and penile nerves, this work aims to determine whether these proteins are also present in the hypothalamus. It was found that PnNOS, the brain-type nNOS, and PIN, were expressed in the hypothalamus. In contrast, NMDAR1-T was expressed only in the penis, whereas the brain-type NMDAR1 was present in the brain and sacral spinal cord and not in the penis. PnNOS was found in the media preoptic area, posterior magnocellular, and the parvocellular regions of the paraventricular nucleus, supraoptic nucleus, septohypothalamic nucleus, medial septum, cortex, and in some of the nNOS staining neurons throughout the brain. It was absent in the organum vasculosum of the lamina terminalis. PIN staining was present in neurons of the medial preoptic area, paraventricular nucleus, medial septum, and cortex, but not in the supraoptic nucleus, septohypothalamic nucleus, or organum vasculosum of the lamina terminalis. Colocalization between PnNOS and PIN was found in the medial preoptic area, medial septum, and cortex, and less in the paraventricular nucleus. PnNOS and oxytocin were colocalized in the paraventricular nucleus and supraoptic nucleus. In hypothalamic extracts, recombinant PIN-GST protein bound to PnNOS in the extracts and partially inhibited NOS activity. These results indicate that both nNOS variants, and their respective regulatory proteins are present and colocalize in the hypothalamic and spinal cord regions involved in penile erection.