Chronic Administration of an Oral Rho Kinase Inhibitor Prevents the Development of Vasculogenic Erectile Dysfunction in a Rat Model

A Review of Current and Emerging Therapeutic Options for Erectile Dysfunction

Contemporary treatment algorithms for erectile dysfunction (ED) involve the use of medical therapies such as phosphodiesterase type 5 (PDE5) inhibitors and intracavernosal injection therapy of vasoactive agents, as well as vacuum erection devices and penile prosthesis implants in medically refractory cases. However, the current therapeutic options only address the symptoms of ED and not the underlying pathogenesis that results in ED. Newer and novel ED therapies aspire to reverse ED conditions by preventing cavernosal fibrosis, promoting endothelial revascularization and modulating various neuro-hormonal pathways. Regenerative therapeutic strategies such as low-intensity shock wave, gene and cellular-based therapies, and penile transplants are designed to improve penile hemodynamics and revitalize the cavernosal smooth muscle to mitigate and/or reverse underlying ED. This state-of-art article evaluates current and emerging therapeutic options for ED.

A New Strategy for Deleting Animal drugs from Traditional Chinese Medicines based on Modified Yimusake Formula

Traditional Chinese medicine (TCM), such as Uyghur Medicine (UM) has been used in clinical treatment for many years. TCM is featured as multiple targets and complex mechanisms of action, which is normally a combination of medicinal herbs and sometimes even contains certain rare animal medicinal ingredients. A question arises as to whether these animal materials can be removed replaced from TCM applications due to their valuable rare resources or animal ethics. Here, we select a classical UM Yimusake formula, which contains 3 animal drugs and other 8 herbs, and has got wealthy experience and remarkable achievements in treating erectile dysfunction (ED) in China. The active components, drug targets and therapeutic mechanisms have been comprehensively analyzed by systems-pharmacology methods. Additionally, to validate the inhibitory effects of all candidate compounds on their related targets, in vitro experiments, computational analysis and molecular dynamics simulations were performed. The results show that the modified, original and three animal materials display very similar mechanisms for an effective treatment of ED, indicating that it is quite possible to remove these three animal drugs from the original formula while still keep its efficiency. This work provides a new attempt for deleting animal materials from TCM, which should be important for optimization of traditional medicines.

Association of nNOS and Rho-kinase with age-associated erectile dysfunction in Sprague-Dawley rats

The present study aimed to investigate the changes of Rho-associated kinase (Rho-kinase) and neuronal nitric oxide synthase (nNOS) expression in age-associated erectile dysfunction (ED) in Sprague-Dawley (SD) rats. A total of 100 intact male SD rats were divided into 20 groups according to their age (5-24 months; rats that were the same age in months were in the same group). Erectile response measurements were performed and the functional index intracavernosal pressure/mean arterial pressure (ICP/MAP) was tested, followed by detection of Rho-kinase and nNOS protein by western blot analysis. Finally, correlation analyses of the association between ICP/MAP and Rho-kinase, nNOS, or nNOS/Rho-kinase, as well as between age and nNOS or Rho-kinase, were performed. The functional index ICP/MAP decreased with age in SD rats. Moreover, the expression of nNOS protein decreased, while Rho-kinase expression increased, indicating that the nNOS/Rho-kinase ratio decreased with age. The Pearson's correlation coefficients for the association between ICP/MAP and Rho-kinase, nNOS and nNOS/Rho-kinase ratio were -0.917, 0.853 and 0.937, respectively (P<0.01). Furthermore, nNOS was found to be significantly negatively correlated with age (r=-0.855; P<0.01), whereas Rho-kinase was positively correlated with age (r=0.943; P<0.01). Age-associated ED was therefore correlated with decreased nNOS and increased Rho-kinase, indicating that the nNOS/Rho-kinase ratio may be used as a candidate indicator of age-associated ED.

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.

The selective Rho-kinase inhibitor azaindole-1 has long-lasting erectile activity in the rat

OBJECTIVE

To investigate the effects of the selective Rho-associated protein kinase (ROCK) inhibitor azaindole-1 on erectile function under physiologic and pathophysiologic conditions in the rat.

METHODS

The effect of intracavernosal (i.c.) injections of azaindole-1 on change in intracavernous pressure (ICP), ICP/mean arterial pressure (MAP), area under the curve (AUC), and response duration were investigated in the anesthetized rat under control conditions and when nonadrenergic noncholinergic neurotransmission and cholinergic function or soluble guanylyl cyclase (sGC) were inhibited or after cavernosal nerve crush injury.

RESULTS

The i.c. injections of azaindole-1 produced dose-related increases in ICP/MAP and AUC that were long-lasting at the highest doses studied compared with the prototypical ROCK inhibitor fasudil. Erectile responses were not altered by 7-nitroindazole and atropine in doses that reduced the response to cavernosal nerve stimulation by 86%, indicating that they were independent of NO release by cavernosal nerves or activation of muscarinic receptors in the corpora cavernosa. Erectile responses to azaindole-1 were not altered by the sGC inhibitor ODQ in a dose that attenuated responses to the NO donor sodium nitroprusside, indicating that they were independent of an action on sGC. The erectile response to i.c. injections of azaindole-1 or Y-27632, which was reported to be NO/cyclic guanosine monophosphate-dependent, was not attenuated after cavernosal nerve crush injury.

CONCLUSION

The present studies indicate that azaindole-1 has long-lasting erectile activity that is independent of NO release, muscarinic receptor, or sGC activation or the integrity of the cavernosal nerves.

The promise of inhibition of smooth muscle tone as a treatment for erectile dysfunction: where are we now?

Ten years ago, the inhibition of Rho kinase by intracavernosal injection of Y-27632 was found to induce an erectile response. This effect did not require activation of nitric oxide-mediated signaling, introducing a novel target pathway for the treatment of erectile dysfunction (ED), with potential added benefit in cases where nitric oxide bioavailability is attenuated (and thus phosphodiesterase type 5 (PDE5) inhibitors are less efficacious). Rho-kinase antagonists are currently being developed and tested for a wide range of potential uses. The inhibition of this calcium-sensitizing pathway results in blood vessel relaxation. It is also possible that blockade of additional smooth muscle contractile signaling mechanisms may have the same effect. In this review, we conducted an extensive search of pertinent literature using PUBMED. We have outlined the various pathways involved in the maintenance of penile smooth muscle tone and discussed the current potential benefit for the pharmacological inhibition of these targets for the treatment of ED.

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.

Hypercholesterolemia-induced erectile dysfunction: endothelial nitric oxide synthase (eNOS) uncoupling in the mouse penis by NAD(P)H oxidase

INTRODUCTION

Hypercholesterolemia induces erectile dysfunction (ED) mostly by increasing oxidative stress and impairing endothelial function in the penis, but the mechanisms regulating reactive oxygen species (ROS) production in the penis are not understood.

AIMS

We evaluated whether hypercholesterolemia activates nicotinamide adenine dinucleotide phosphate (NAD[P]H) oxidase in the penis, providing an initial source of ROS to induce endothelial nitric oxide synthase (eNOS) uncoupling and endothelial dysfunction resulting in ED.

METHODS

Low-density-lipoprotein receptor (LDLR)-null mice were fed Western diet for 4 weeks to induce early-stage hyperlipidemia. Wild type (WT) mice fed regular chow served as controls. Mice received NAD(P)H oxidase inhibitor apocynin (10 mM in drinking water) or vehicle. Erectile function was assessed in response to cavernous nerve electrical stimulation. Markers of endothelial function (phospho [P]-vasodilator-stimulated-protein [VASP]-Ser-239), oxidative stress (4-hydroxy-2-nonenal [HNE]), sources of ROS (eNOS uncoupling and NAD[P]H oxidase subunits p67(phox) , p47(phox) , and gp91(phox) ), P-eNOS-Ser-1177, and eNOS were measured by Western blot in penes.

MAIN OUTCOME MEASURES

The main outcome measures are the molecular mechanisms of ROS generation and endothelial dysfunction in hypercholesterolemia-induced ED.

RESULTS

Erectile response was significantly (P<0.05) reduced in hypercholesterolemic LDLR-null mice compared with WT mice. Relative to WT mice, hypercholesterolemia increased (P<0.05) protein expressions of NAD(P)H oxidase subunits p67(phox) , p47(phox) and gp91(phox) , eNOS uncoupling, and 4-HNE-modified proteins, and reduced (P<0.05) P-VASP-Ser-239 expression in the penis. Apocynin treatment of LDLR-null mice preserved (P<0.05) maximal intracavernosal pressure, and reversed (P<0.05) the abnormalities in protein expressions of gp67(phox) and gp47(phox) , 4-HNE, P-VASP-Ser-239, and eNOS uncoupling in the penis. Apocynin treatment of WT mice did not affect any of these parameters. Protein expressions of P-eNOS-Ser-1177 and total eNOS were unaffected by hypercholesterolemia.

CONCLUSION

Activated NAD(P)H oxidase in the penis is an initial source of oxidative stress resulting in eNOS uncoupling, thus providing a mechanism of eNOS uncoupling and endothelial dysfunction in hypercholesterolemia-induced ED.

Emerging role for TNF-α in erectile dysfunction

INTRODUCTION

A role for cytokines in the pathophysiology of erectile dysfunction (ED) has emerged. Cytokines induce genes that synthesize other peptides in the cytokine family and several mediators, such as prostanoids, leukotrienes, nitric oxide, bradykinin, reactive oxygen species, and platelet-activating factor, all of which can affect vascular function. Consistent with the fact that the cavernosal tissue is a complex extension of the vasculature, risk factors that affect the vasculature have been shown to affect cavernosal function as well. Accordingly, the penile tissue has been recognized as an early sentinel for atherosclerosis that underlies coronary artery disease and cardiovascular diseases (CVD).

AIM

To review the literature pertaining to the role of tumor necrosis factor-alpha (TNF-α) in ED.

METHODS

PubMed search for pertinent publications on the role of cytokines, particularly TNF-α, in CVD and ED.

MAIN OUTCOME MEASURES

Clinical and experimental evidence demonstrates that TNF-α may play a role in ED.

RESULTS

TNF-α has been shown to play an important role in CVD, mainly due to its direct effects on the vasculature. In addition, high levels of TNF-α were demonstrated in patients with ED. In this review, we present a short description of the physiology of erection and the cytokine network. We focus on vascular actions of TNF-α that support a role for this cytokine as a potential candidate in the pathophysiology of ED, particularly in the context of CVD. A brief overview of its discovery, mechanisms of synthesis, receptors, and its main actions on the systemic and penile vasculature is also presented.

CONCLUSIONS

Considering that ED results from a systemic arterial defect not only confined to the penile vasculature, implication of TNF-α in the pathophysiology of ED offers a humoral linking between CVD and ED.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

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

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

Redox control of GTPases: from molecular mechanisms to functional significance in health and disease

Small GTPases, including the proto-oncoprotein Ras and Rho GTPases, are involved in various cellular signaling events. Some of these small GTPases are redox sensitive, including Ras, Rho, Ran, Dexras1, and Rhes GTPases. Thus, the redox-mediated regulation of these GTPases often determines the course of their cellular signaling cascades. This article takes into consideration the application of Marcus theory to potential redox-based molecular mechanisms in the regulation of these redox-sensitive GTPases and the relevance of such mechanisms to a specific redox-sensitive motif. The discussion also takes into account various diseases, including cancers, heart, and neuronal disorders, that are often linked with the dysregulation of the redox signaling cascades associated with these redox-sensitive GTPases.

Vardenafil and resveratrol synergistically enhance the nitric oxide/cyclic guanosine monophosphate pathway in corpus cavernosal smooth muscle cells and its therapeutic potential for erectile dysfunction in the streptozotocin-induced diabetic rat: preliminary findings

INTRODUCTION

Phosphodiesterase type 5 (PDE5) inhibitors are very effective agents for erectile dysfunction; however, specific patient populations are hard to treat. The efficacy of PDE5 inhibitors is limited because a minimum amount of nitric oxide (NO) is necessary. Resveratrol, a plant polyphenol, is reported to activate endothelial NO synthase (eNOS) through activation of sirtuin 1. We previously reported that human corpus cavernosal smooth muscle cells (CCSMCs) express eNOS and synthesize cyclic guanosine monophosphate (cGMP) via the NO/cGMP pathway.

AIM

To investigate the ability of resveratrol and/or vardenafil to increase cGMP in an in vitro model using CCSMCs and to improve erectile function in an in vivo rat model of streptozotocin (STZ)-induced diabetes.

METHODS

CCSMCs were treated with resveratrol and/or vardenafil. Twenty male Sprague-Dawley rats were randomly divided into five groups (N = 4 in each group): age-matched controls, diabetic controls, and diabetic rats treated with resveratrol, vardenafil, or both in combination for the last 4 weeks of an 8-week period of diabetes induction.

MAIN OUTCOME MEASURES

Intracellular cGMP measurement, intracovernous pressure (ICP)/mean arterial pressure (MAP) ratio, and smooth muscle/collagen ratio.

RESULTS

Intracellular cGMP level was elevated by resveratrol treatment in CCSMCs. The combination treatment of resveratrol and vardenafil had a synergistic effect. Diabetic rats showed impairment of erectile function. Treatment with either resveratrol or vardenafil improved ICP/MAP ratio, and combination therapy with resveratrol and vardenafil had a synergistic effect in improvement of ICP/MAP.

CONCLUSIONS

Treatment with either resveratrol or vardenafil elevated cGMP level in CCSMCs and improved erectile function in STZ-induced diabetic rats. Furthermore, a synergistic effect was observed in vitro and in vivo. Resveratrol or combination therapy of resveratrol and vardenafil can improve erectile function in which NO release is impaired, although further study is needed to confirm the results.

The future is today: emerging drugs for the treatment of erectile dysfunction

IMPORTANCE OF THE FIELD

Erectile dysfunction (ED) is the most common male sexual dysfunction presented for treatment affecting between 10 and 20% of men. PDE type 5 inhibitors (PDE5I) now account for the largest segment of the ED market. While these drugs are highly efficacious for many men, a relatively large subset of ED patients who do not respond to PDE5I is increasingly recognized.

AREAS COVERED IN THIS REVIEW

In this review, we discuss clinical and preclinical evidence supporting various emerging compounds that regulate penile erection both centrally (clavulanic acid, dopamine and melanocortin receptor agonists) and peripherally (novel PDE5I, soluble and particulate guanylil cyclase activators, rho-kinase inhibitors and maxi-K channel openers).

WHAT THE READER WILL GAIN

The reader will gain a broad understanding of erectile (patho-)physiology and gain insights in the mechanisms of action, efficacy and adverse events of various compounds under development for the treatment of ED.

TAKE HOME MESSAGE

We expect emerging drugs to allow treatment protocols tailored to the specific needs of each individual patient, taking into consideration the efficacy of erectile performance enhancement and the potential for adverse events. This tailored approach may include combination of various emerging drugs to enhance efficacy in difficult-to-treat patients.

Change of erectile function and responsiveness to phosphodiesterase type 5 inhibitors at different stages of streptozotocin-induced diabetes in rats

INTRODUCTION

It has been suggested that risk of erectile dysfunction (ED) increases with duration of diabetes and phosphodiesterase type 5 inhibitors (PDE5I) are not as effective in treatment of diabetes-associated ED. However, few studies have investigated time-dependent change in erectile function during the course of diabetes.

AIM

To investigate time-dependent change in erectile function and responsiveness to PDE5I in streptozotocin-induced diabetic rats and to understand the pathophysiology of diabetic ED.

MAIN OUTCOME MEASURES

At 6, 8, 10, 12, and 14 weeks after diabetic induction, erectile function was assessed by cavernous nerve stimulation before and after administration of DA-8159, a novel PDE5I. Penile tissue was assessed for apoptosis with immunohistochemistry. Protein expression of Rho-kinase 2 (ROCK2), myosin phosphatase targeting subunit 1 (MYPT1), and endothelial nitric oxide synthase (eNOS) was evaluated by Western blot.

METHODS

Streptozotocin was injected into 50 8-week-old male Sprague-Dawley rats, which were then classified into five diabetic groups according to the observation period.

RESULTS

Diabetic rats maintained normal erectile responses until 6 weeks of diabetes. Following 8 weeks, the rats showed lower erectile responses at higher frequencies of nerve stimulation, which were normalized to control by administration of DA-8159. In contrast, erectile responses were significantly decreased in 10-week diabetic rats, and administration of DA-8159 resulted in partial recovery of normal responses. At more than 12 weeks, rats demonstrated severe deterioration of erectile function, which did not fully respond to PDE5I. Corporal apoptosis was significantly increased after 10 weeks. Upregulation of ROCK2 was found at 6 weeks, and was followed by an increase of MYPT1 phosphorylation. Phosphorylation of eNOS showed marked suppression at 6 weeks and remained lower during the experimental period.

CONCLUSIONS

Impairment of erectile function was followed by decreased responsiveness to PDE5I during the course of diabetes. The RhoA/ROCK pathway played an important role in diabetes-associated ED.

Activated RhoA/Rho kinase impairs erectile function after cavernous nerve injury in rats

PURPOSE

RhoA and rho kinase serve as key regulators of penile vascular homeostasis. The role of RhoA/rho kinase signaling in the penis after cavernous nerve injury has not been fully investigated. We characterized the molecular expression profiles of RhoA/rho kinase signaling that occur in the penis after cavernous nerve injury. We hypothesized that erectile dysfunction after bilateral cavernous nerve injury is accompanied by up-regulation of RhoA/rho kinase activity in the rat penis.

MATERIAL AND METHODS

We used 2 groups, including sham operation and bilateral cavernous nerve injury. At 14 days after nerve injury each group underwent cavernous nerve stimulation to determine erectile function at baseline and after intracavernous injection of the rho kinase inhibitor Y-27632 (Tocris Bioscience, Ellisville, Missouri). Penes were assessed at baseline for protein expression of neuronal nitric oxide synthase, RhoA, and rho kinase 1 and 2 by Western blot, immunoreactivity of neuronal nitric oxide synthase, rho kinase 1 and 2, RhoA-guanosine triphosphatase and rho kinase activity.

RESULTS

Erectile function was decreased in nerve injured rats. Neuronal nitric oxide synthase protein was significantly decreased while RhoA and rho kinase 2 protein levels were significantly increased in rat penes with nerve injury. Rho kinase 1 protein expression was equivalent. Rho kinase immunoreactivity was qualitatively increased in the corporeal smooth muscle of nerve injured rats. RhoA-guanosine triphosphatase and rho kinase activity was significantly increased in injured rat penes compared to that in sham operated penes. Intracavernous injection of Y-27632 caused a significantly greater increase in intracavernous pressure in nerve injured rats compared to that in sham operated rats, suggesting increased rho kinase activity.

CONCLUSIONS

Data suggest that RhoA/rho kinase up-regulation in response to cavernous nerve injury contributes to penile vasculature dysfunction after cavernous nerve injury. Thus, the RhoA/rho kinase pathway may be a suitable target for treating post-radical prostatectomy erectile dysfunction.

p38 Mitogen-activated protein kinase (MAPK) increases arginase activity and contributes to endothelial dysfunction in corpora cavernosa from angiotensin-II-treated mice

INTRODUCTION

Angiotensin II (AngII) activates p38 mitogen-activated protein kinase (MAPK) and elevates arginase activity in endothelial cells. Upregulation of arginase activity has been implicated in endothelial dysfunction by reducing nitric oxide (NO) bioavailability. However, signaling pathways activated by AngII in the penis are largely unknown.

AIM

We hypothesized that activation of p38 MAPK increases arginase activity and thus impairs penile vascular function in AngII-treated mice.

METHODS

Male C57BL/6 mice were implanted with osmotic minipumps containing saline or AngII (42 µg/kg/h) for 14 days and cotreated with p38 MAPK inhibitor, SB 203580 (5 µg/kg/day), beginning 2 days before minipump implantation. Systolic blood pressure (SBP) was measured. Corpus cavernosum (CC) tissue was used for vascular functional studies and protein expression levels of p38 MAPK, arginase and constitutive NO synthase (NOS), and arginase activity.

MAIN OUTCOME MEASURES

Arginase expression and activity; expression of phospho-p38 MAPK, endothelial NOS (eNOS) and neuronal NOS proteins; endothelium-dependent and nitrergic nerve-mediated relaxations were determined in CC from control and AngII-infused mice.

RESULTS

AngII increased SBP (22%) and increased CC arginase activity and expression (∼twofold), and phosphorylated P38 MAPK levels (30%) over control. Treatment with SB 203580 prevented these effects. Endothelium-dependent NO-mediated relaxation to acetylcholine was significantly reduced by AngII and this effect was prevented by SB 203580 (P < 0.01). AngII (2 weeks) did not alter nitrergic function. However, SB 203580 significantly increased nitrergic relaxation in both control and AngII tissue at lower frequencies. Maximum contractile responses for phenylephrine and electrical field stimulation were increased by AngII (56% and 171%, respectively) and attenuated by SB 203580 treatment. AngII treatment also decreased eNOS phosphorylation at Ser-1177 compared to control. Treatment with SB 203580 prevented all these changes.

CONCLUSION

p38 MAPK inhibition corrects penile arginase activity and protects against erectile dysfunction caused by AngII.

Expression of cyclic AMP-dependent protein kinase isoforms in human cavernous arteries: functional significance and relation to phosphodiesterase type 4

INTRODUCTION

The cyclic adenosine monophosphate-dependent protein kinase (cAK) is considered a key protein in the control of smooth muscle tone in the cardiovascular system. There is evidence that erectile dysfunction might be linked to systemic vascular disorders and arterial insufficiency, subsequently resulting in structural changes in the penile tissue. The expression and significance of cAK in human cavernous arteries (HCA) have not been evaluated.

AIMS

To evaluate the expression of cAK isoforms in HCA and examine the role of cAK in the cyclic adenosine monophosphate (cAMP)- and cyclic guanosine monophosphate (cGMP)-mediated control of penile vascular smooth muscle.

METHODS

The expression and distribution of phosphodiesterase type 4 (PDE4) and cAK isoforms in sections of HCA were investigated by means of immunohistochemistry and Western blot analysis. The effects of the cAK inhibitor Rp-8-CPT-cAMPS on the relaxation of isolated preparations of HCA (diameter > 100 µm) induced by rolipram, sildenafil, tadalafil, and vardenafil were studied using the organ bath technique.

MAIN OUTCOME MEASURES

Investigate the expression of cAK in relation to α-actin and PDE4 in HCA and evaluate the effects of an inhibition of cAK on the relaxation induced by inhibitors of PDE4 and PDE5 of isolated penile arteries.

RESULTS

Immunosignals specific for cAKIα, IIα, and IIβ were observed within the wall of HCA. Double stainings revealed colocalization of cAK with α-actin and PDE4. The expression of cAK isoforms was confirmed by Western blot analysis. The reversion of tension induced by inhibitors of PDE4 and PDE5 of isolated penile vascular tissue were attenuated significantly by Rp-8-CPT-cAMPS.

CONCLUSIONS

Our results demonstrate the expression of cAK isoforms in the smooth musculature of HCA and its colocalization with PDE4. A significant role for cAK in the regulation mediated by cAMP and cGMP of vascular smooth muscle tone in HCA can also be assumed.

A Review of the Pathophysiology and Novel Treatments for Erectile Dysfunction

Erectile dysfunction (ED) affects up to 50% of men between the ages of 40 and 70. Treatment with PDE-5 inhibitors is effective in the majority of men with ED. However, PDE-5 inhibitors are not effective when levels of nitric oxide (NO), the principle mediator of erection, are low. The pharmacologic actions of three new potential treatments for ED are discussed in this paper: (1) sGC stimulators/activators, (2) Rho-kinase inhibitors, and (3) sodium nitrite.

Impaired nerve-mediated relaxation of penile tissue from caveolin-1 deficient mice

Caveolin-1-deficient mice are characterised by a high vascular NO production. Because NO-dependent smooth muscle relaxation is considered to play an important role in penile erection, it was hypothesized that the erectile function would be affected by genetic ablation of caveolae. This study assessed penile erectile mechanisms in caveolin-1 knockout (KO) mice ex vivo. Immunofluorescence confirmed caveolin-1 expression primarily in the endothelium surrounding the sinusoids of the corpus cavernosum, but also in smooth muscle cells of the sinusoidal bundles. In KO mice, caveolin-1 was absent, and the expression of the caveola-associated protein PTRF-Cavin was reduced. Nitric oxide synthase (endothelial and neuronal) and caveolin-3 levels were not affected, and staining of the neuronal marker PGP 9.5 did not disclose any apparent change in the density or pattern of innervation. Moreover, no apparent morphological differences were noted. Functionally, the force response following stimulation of alpha(1)-adrenergic receptors, and the sensitivity to the Rho-kinase inhibitor Y27632, were unaltered, whereas relaxation of alpha(1)-precontracted corpus cavernosum in response to electrical field stimulation and the muscarinic agonist carbachol were impaired. The nitric oxide donor sodium nitroprusside produced less relaxation in KO as compared to wild type corpus cavernosum. We conclude that nerve-mediated dilatation of the corpus cavernosum is impaired in the absence of caveolin-1, and that this is due in part to reduced sensitivity of the target tissue to NO. All in all our data support an important role of caveolin-1 in penile erection.

Sexual dysfunction: the 'prima ballerina' of hypertension-related quality-of-life complications

Sexual dysfunction is currently considered a serious quality-of-life-related health problem, exerting a major impact on patients' and their sexual partners' life. Available data indicate that essential hypertension is a risk factor for sexual dysfunction, as male and female sexual dysfunction is more prevalent in hypertensive patients than normotensive individuals. Several mechanisms have been implicated in the pathogenesis of sexual dysfunction in hypertensive patients, and major determinants include severity and duration of hypertension, age, and antihypertensive therapy. Female sexual dysfunction, although more frequent than its male counterpart, remains largely under-recognized. Older antihypertensive drugs (diuretics, beta-blockers, centrally acting) exert negative results, whereas newer drugs have either neutral (calcium antagonists, angiotensin-converting enzyme inhibitors) or beneficial effects (angiotensin receptor blockers). Erectile dysfunction is related to ischemic heart disease and might be an 'early therapeutic window' of asymptomatic coronary artery disease. It seems of utmost importance for every physician treating hypertensive patients to become familiar with sexual dysfunction (through better education and specific seminars) for the proper management of these patients.

Common approach to managing lower urinary tract symptoms and erectile dysfunction

The present paper serves as a review of the associations between lower urinary tract symptoms (LUTS) and erectile dysfunction (ED), with a focus on common and combined pathways for treatment. LUTS and ED are common conditions seen in general urologic practice. Research has started to establish epidemiologic and pathophysiologic links between the two conditions and a strong association confirmed across multiple studies. Men seeking care for one condition should always be interviewed for complaints of the other condition. Proposed common pathways include alpha-1 adrenergic receptor imbalance, Rho-kinase overactivity, endothelial cell dysfunction and atherosclerosis-induced ischemia. Medical therapy has replaced surgery as the first-line treatment for LUTS in most patients, with the incorporation of alpha-adrenergic receptor antagonists (alpha-ARAs) and 5-alpha-reductase inhibitors (5-ARIs) into everyday practice. Treatment with alpha-ARAs contributes to some improvement in ED, whereas use of 5-ARIs results in worsened sexual function in some patients. Phosphodiesterase-5 (PDE-5) inhibitors have revolutionized the treatment of ED with a simple oral regimen, and new insights demonstrate a benefit of combined use of PDE-5 inhibitors and alpha-ARAs. The mechanisms of action of these medications support these observed benefits, and they are being studied in the basic science and clinical settings. In addition, novel mechanisms for therapy have been proposed based on clinical and research observations. The minimally invasive and surgical treatments for LUTS are known to have adverse effects on ejaculatory function, while their effects on erectile function are still debated. Much remains to be investigated, but it is clear that the associations between LUTS and ED lay the foundation for future therapies and possible preventative strategies.

Efficient gene expression system using the RTP801 promoter in the corpus cavernosum of high-cholesterol diet-induced erectile dysfunction rats for gene therapy

INTRODUCTION

The application of gene therapy for a nonlife-threatening disease, such as erectile dysfunction (ED), requires a higher safety level and more efficacious systems for gene transfer.

AIM

To establish a novel technique for gene expression in a rat model of hypercholesterolemic ED that uses the RTP801 promoter, a hypoxia-inducible promoter.

METHODS

Two-month-old male Sprague-Dawley rats were fed a diet containing 4% cholesterol and 1% cholic acid, and age-matched control animals were fed a normal diet, for 3 months.

MAIN OUTCOME MEASURES

Cavernous expression of hypoxia-inducible factor (HIF)-1alpha was evaluated by Western blot. After intracavernous injection of pSV-Luc or pRTP801-Luc, gene expression was evaluated by luciferase assay, and the gene expression area was evaluated by immunohistochemistry.

RESULTS

HIF-1alpha was up-regulated in the corpus cavernosum of hypercholesterolemic rats. Although pSV-Luc did not induce gene expression in either the control or the cholesterol group, pRTP801-Luc significantly induced gene expression in the cholesterol group and resulted in higher luciferase activity than did pSV-Luc up to 14 days after injection. Immunohistochemistry showed that the gene expression area was also greater in the pRTP801-Luc group than in the pSV-Luc group, but the difference was not as great as that in luciferase activity. This suggests that pRTP801-Luc exerts its effect mainly by inducing promoter activity under hypoxia, not by increasing the number of transfected cells.

CONCLUSION

The RTP801 promoter-driven gene expression system increased gene expression in the corpus cavernosum tissue of rats with cholesterol-induced ED. This may be a useful system for the development of gene therapy in vasculogenic ED.

Expression and distribution of cyclic GMP-dependent protein kinase-1 isoforms in human penile erectile tissue

INTRODUCTION

Besides the bioavailability of nitric oxide (NO), downstream guanine monophosphate (cGMP) effector proteins are also considered to play a significant role in penile vascular disease. In animal studies, a downregulation of the cGMP-dependent protein kinase-1 (cGKI) alpha isoform has been linked to erectile dysfunction and diabetes mellitus. So far, the expression of cGKI alpha and beta isoforms has not been evaluated in human penile erectile tissue.

AIM

To evaluate the expression of cGKI alpha and beta isoforms in relation to smooth muscle alpha-actin, cGMP, and endothelial NO synthase (eNOS) in human cavernous arteries (HCAs) and human corpus cavernosum (HCC).

METHODS

Cryostat sections of HCA and HCC were incubated with primary antibodies directed against alpha-actin, cGMP, eNOS, cGKI, cGKI alpha, and cGKI beta. Visualization of double-labeled immunofluorescent stainings was achieved by laser microscopy. Western blot analysis was performed in order to confirm the expression of cGKI isoforms.

MAIN OUTCOME MEASURES

Expression of cGKI alpha and beta isoforms in relation to smooth muscle alpha-actin, cGMP, and eNOS in human penile erectile tissue.

RESULTS

Immunoreactivities specific for cGKI, cGKI alpha, and cGKI beta were observed within the smooth musculature and the endothelium of cavernous arteries and sinusoids. Double stainings revealed the colocalization of alpha-actin, cGMP, eNOS, and cGKI isoforms. The expression of cGKI isoforms was confirmed by Western blot analysis.

CONCLUSIONS

Our results demonstrate, for the first time, the expression of both cGKI alpha and beta isoforms in the smooth musculature of HCA and HCC. Corresponding to recent findings from animal studies, the presence of cGKI alpha and beta provides further evidence for a significant role of these enzymes in the control of smooth muscle function in human penile erectile tissue.

Hydrogen Sulphide: A Novel Endogenous Gasotransmitter Facilitates Erectile Function

INTRODUCTION

In a pilot study, we found that the novel gasotransmitter, hydrogen sulfide (H2S), had a vasodilatory and proerectile action on the cavernosum. In the present work, we explored the ability of the cavernosum to synthesize H2S and its mechanism on the cavernosal pathways.

AIM

To evaluate the physiopharmacological responses and mechanism in the erectile function of H2S in rabbit cavernosum.

METHODS

Rabbit corpus cavernosum (CC) smooth muscle tissue (N = 5) was homogenized and incubated with L-cysteine (10 mM) and pyridoxal 5'-phosphate (2 mM) to detect H2S formation. In isometric tension studies on rabbits (N = 12), the effect of sodium hydrogen sulfide (NaHS; stable H2S donor, 100 microM-3.2 mM) was evaluated on the relaxant and contractile pathways in the cavernous smooth muscle using standard pharmacological tools.

MAIN OUTCOME MEASURES

In vitro evidences for cavernosal H2S formation and proerectile pharmacological effects.

RESULTS

H2S was readily synthesized in the rabbit CC (2.1 +/- 0.4 nmol/mg protein). In organ bath studies, NaHS consistently relaxed the rabbit CC in a concentration-dependent manner. MDL 12,330A and 1-H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one inhibited the NaHS relaxation by 22.5% and 14.7%, respectively. All three enzyme inhibitors (aminooxyacetic acid [AOAA], beta-cyanoalanine [beta-CA], and DL-propargylglycine [PAG][1 mM]) markedly increased the noradrenergic contractile neurotransmission of CC strips to field stimulation with minimal reversal by cysteine (1 mM) indicating the possible inherent inhibition of the relaxant H2S formation. AOAA, beta-CA, or PAG had no significant effect on nitrergic relaxation of noradrenaline-precontracted CC strips.

CONCLUSION

These pioneering studies provide evidence for the endogenous formation of H2S and its proerectile relaxant effect on the cavernosum, with the possibility of involvement of the cyclic adenosine monophosphate pathway.

The future of the oral pharmacotherapy of male erectile dysfunction: things to come

The convincing clinical data on the use of the orally active phosphodiesterase inhibitors sildenafil, vardenafil and tadalafil for the treatment of male erectile dysfunction have boosted research activities on the physiology of the male erectile mechanism. This included both peripheral intracellular signal transduction in the corpus cavernosum as well as central brain and spinal cord pathways controlling penile erection. This work provided the basis for the development and introduction of several new therapeutic modalities into the management of erectile dysfunction, some of which are already offered to the patients. As the concept of 'taking a pill' as a cure for an illness or the relief of symptoms of a disease has become widely accepted by the consumers, the pharmacologic treatment of erectile dysfunction has primarily focussed on selective, orally available drugs acting by influencing intracellular or central regulatory mechanisms, combining a high response rate and the advantage of an on-demand intake. These agents are regarded as more efficacious, and have a faster onset of drug action in the target tissue and an improved effect to side-effect ratio. The purpose of this review is to describe the major novel and evolving pharmacologic advances in the field of oral pharmacotherapy for the treatment of male erectile dysfunction.

Neurophysiological basis of penile erection

Penile erection involves a complex interaction between the central nervous system and local factors. It is a neurovascular event modulated by psychological and hormonal factors. The discovery of nitric oxide (NO) as an intercellular messenger or neurotransmitter paved the way for identifying important mechanisms underlying physiological and pathophysiological events in the penis, in addition to providing the knowledge for the development of new therapeutics based on a novel concept of molecule and cell interaction. Despite the fact that sinusoidal endothelial cells also produce and release NO in response to chemical and possibly physical stimuli, roles of neurogenic NO in penile erection appear to be more attractive and convincing, since the pharmacological neuromodulation represents an essential step to attaining penile erection. Erectile dysfunction (ED) is caused by a variety of pathogenic factors, particularly impaired formation and action of NO. Hence, a thorough knowledge of the physiology of erection is essential for future pharmacological innovations in the field of male ED, particularly targeting NO or intracellular cyclic GMP, which represent the most promising therapeutic approach to treat patients with ED.

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.