Topical application of a Rho-kinase inhibitor in rats causes penile erection

Immunomodulatory Yersinia outer proteins (Yops)-useful tools for bacteria and humans alike

Human-pathogenic Yersinia produce plasmid-encoded Yersinia outer proteins (Yops), which are necessary to down-regulate anti-bacterial responses that constrict bacterial survival in the host. These Yops are effectively translocated directly from the bacterial into the target cell cytosol by the type III secretion system (T3SS). Cell-penetrating peptides (CPPs) in contrast are characterized by their ability to autonomously cross cell membranes and to transport cargo - independent of additional translocation systems. The recent discovery of bacterial cell-penetrating effector proteins (CPEs) - with the prototype being the T3SS effector protein YopM - established a new class of autonomously translocating immunomodulatory proteins. CPEs represent a vast source of potential self-delivering, anti-inflammatory therapeutics. In this review, we give an update on the characteristic features of the plasmid-encoded Yops and, based on recent findings, propose the further development of these proteins for potential therapeutic applications as natural or artificial cell-penetrating forms of Yops might be of value as bacteria-derived biologics.

Effect of a novel BKCa opener on BKCa currents and contractility of the rabbit corpus cavernosum

Large-conductance Ca2+-activated K+ (BKCa) channels are thought to play a key role in the regulation of corpus cavernosum smooth muscle (CCSM) excitability. Few BKCa channel openers have been accepted for clinical development. The effect of the novel BKCa channel opener GoSlo-SR5-130 on electrical activity in isolated rabbit CCSM cells and mechanical activity in strips of rabbit CCSM was examined. Single-channel currents were observed in inside-out patches. These channels were sensitive to Ca2+, blocked by penitrem A, and had a conductance of 291 ± 20 pS ( n = 7). In the presence of GoSlo-SR5-130, the number of open BKCa channels increased. Using voltage-ramp protocols, GoSlo-SR5-130 caused currents to activate at more negative potentials in a concentration-dependent manner, shifting the half-maximal activation voltage potential to the left on the voltage axis. Therefore, BKCa channels were open within the physiological range of membrane potentials in the presence of GoSlo-SR5-130. GoSlo-SR5-130 also resulted in an increase in the activity of spontaneous transient outward currents in myocytes isolated from CCSM, and this effect was reversed by iberiotoxin. In current-clamp mode, GoSlo-SR5-130 hyperpolarized the cell membrane. Isometric tension recording of strips of rabbit corpus cavernosum showed that GoSlo-SR5-130 inhibited spontaneous contractions in a concentration-dependent manner. This effect was reversed in the presence of iberiotoxin, suggesting that GoSlo-SR5-130 exerts its effect through BKCa channels. These findings suggest that GoSlo-SR5-130 is an effective tool for the study of BKCa channels and that these channels can modulate CCSM activity and are possible targets for the treatment of erectile dysfunction.

Modulation of soluble guanylate cyclase for the treatment of erectile dysfunction

Nitric oxide (NO) is the principal mediator of penile erection, and PDE-5 inhibitors are the first-line agents used to treat erectile dysfunction (ED). When NO formation or bioavailability is decreased by oxidative stress and PDE-5 inhibitors are no longer effective, a new class of agents called soluble guanylate cyclase (sGC) stimulators like BAY 41-8543 will induce erection. sGC stimulators bind to the normally reduced, NO-sensitive form of sGC to increase cGMP formation and promote erection. The sGC stimulators produce normal erectile responses when NO formation is inhibited and the nerves innervating the corpora cavernosa are damaged. However, with severe oxidative stress, the heme iron on sGC can be oxidized, rendering the enzyme unresponsive to NO or sGC stimulators. In this pathophysiological situation, another newly developed class of agents called sGC activators can increase the catalytic activity of the oxidized enzyme, increase cGMP formation, and promote erection. The use of newer agents that stimulate or activate sGC to promote erection and treat ED is discussed in this brief review article.

Screening for Rho-kinase 2 inhibitory potential of Indian medicinal plants used in management of erectile dysfunction

THE AIM OF THE STUDY

Activation of Rho-kinase 2 (ROCK-II) results in contraction of corpus cavernosum smooth muscle and ROCK-II inhibitors relax corpus cavernosum in vitro and in vivo hence, plant extracts capable of inhibiting ROCK-II enzyme may be useful in management of erectile dysfunction (ED). The aim of the study was to screen selected Indian medicinal plants, having similar ethnopharmacological use for ROCK-II inhibition.

MATERIALS AND METHODS

Some Indian medicinal plants reported as aphrodisiacs in Ayurveda and modern scientific literature were collected, authenticated and extracted. Direct methanol and successive aqueous extracts of these plants were screened for ROCK-II inhibitory activity using HTRF(®)KinEASE™ STK S2 Kit (Cisbio Bioassays). Relaxant effect of potent extract was recorded on isolated rat corpus cavernosum.

RESULTS

Methanolic and successive aqueous extracts of 30 plants were screened for ROCK-II inhibition and 15 herbal extracts showed inhibition ranging between 50 and 88% at 50 μg/mL. While IC(50) of Y-27632, a standard ROCK-II inhibitor, was found to be 163.8 ± 1.2 nM. The Methanolic extract of Terminalia chebula (METC) with IC(50) value of 6.09 ± 0.17 μg/mL was found to be most potent and relaxed isolated rat corpus cavernosum significantly (p<0.01). Chebulagic and chebulinic acid of METC were found to inhibit ROCK-II and might be responsible for the inhibitory potential of the extract. The traditional use of plants like Butea frondosa, Syzygium aromaticum, Butea superba, Chlorophytum borivilianum and Mucuna pruriens, as aphrodisiacs and for male sexual disorder (MSD) might be in part due to the ROCK II inhibitory potential of these plants.

CONCLUSION

Some of the Indian medicinal plants have ROCK-II inhibitory potential and those deserve further investigation.

Effects of integrin-linked kinase on human corpus cavernosum smooth muscle cell cytoskeletal organisation

We investigated the effects of integrin-linked kinase (ILK) on the in vitro attachment, spreading, migration and microfilament dynamics of human corpus cavernosum smooth muscle cells. ILK small interfering RNA (siRNA) was used to transfect human corpus cavernosum smooth muscle cells; and cell attachment, spreading and migration were assessed. Additionally, microfilament dynamics were evaluated using Alexa Fluor 488 and phalloidin staining. We found that ILK gene knock-down significantly inhibited human corpus cavernosum smooth muscle cell attachment, spreading and migration. Moreover, blocking the expression of ILK disturbed actin cytoskeleton reorganisation and morphology in human corpus cavernosum smooth muscle cells. These results show that the targeting of ILK with siRNA significantly inhibited cell attachment, spreading, migration and microfilament dynamics in human corpus cavernosum smooth muscle cells. These findings indicate that ILK might be a potential therapeutic molecular target for the treatment of erectile dysfunction.

Future prospects in the treatment of erectile dysfunction: focus on avanafil

The treatment of erectile dysfunction (ED) has been revolutionized in the last 15 years with the introduction of type 5 phosphodiesterase (PDE5) inhibitors. Their efficacy, safety, and ease of administration have made them first-line treatment for ED. This article reviews the current therapies available for ED, and the new PDE5 inhibitors that are being investigated. Furthermore, it examines all the current ED treatment options that are in different phases of development (including oral and topical pharmacotherapy, gene therapy, and tissue engineering). A special emphasis is on avanafil, a new PDE5 inhibitor that has been studied extensively in Phase I and II clinical trials and has undergone several Phase III trials. Avanafil is a promising medication for ED due to its favorable pharmacokinetics, safety, and efficacy.

Guanylin peptide family: history, interactions with ANP, and new pharmacological perspectives

The guanylin family of peptides has 3 subclasses of peptides containing either 3 intramolecular disulfide bonds found in bacterial heat-stable enterotoxins (ST), or 2 disulfides observed in guanylin and uroguanylin, or a single disulfide exemplified by lymphoguanylin. These peptides bind to and activate cell-surface receptors that have intrinsic guanylate cyclase (GC) activity. These hormones are synthesized in the intestine and released both luminally and into the circulation, and are also produced within the kidney. Stimulation of renal target cells by guanylin peptides in vivo or ex vivo elicits a long-lived diuresis, natriuresis, and kaliuresis by both cGMP-dependent and independent mechanisms. Uroguanylin may act as a hormone in a novel endocrine axis linking the digestive system and kidney as well as a paracrine system intrarenally to increase sodium excretion in the postprandial period. This highly integrated and redundant mechanism allows the organism to maintain sodium balance by eliminating excess sodium in the urine. In addition, small concentrations of the atrial natriuretic peptide (ANP) can synergize with low concentrations of both guanylin or uroguanylin, which do not induce natriuresis per se, to promote significant natriuresis. Interestingly, the activation of the particulate guanylate cyclase receptors by natriuretic peptides can promote relaxation of animal and human penile erectile tissue and increase intracavernosal pressure to induce penile erection. These peptides can be prototypes for new drugs to treat erectile dysfunction, especially in patients with endothelial and nitrergic dysfunction, such as in diabetes.

Hydrogen sulfide and erectile function: a novel therapeutic target

Hydrogen sulfide (H(2)S) is a gaseous transmitter involved in the control of vascular homeostasis. H(2)S is formed endogenously from L-cysteine or L-methionine by two enzymes, cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE), and normally circulates in blood. Studies from the past few years have demonstrated the involvement of H(2)S in erectile mechanisms in animal and human tissues. Exogenous H(2)S relaxes human and animal tissues in vitro and increases intracavernous pressure in experimental animal models. Electrical field stimulation studies on animal and human tissues have demonstrated that endogenous H(2)S is involved in the physiological control of penile tone. In humans, both CBS and CSE are widely expressed on trabecular muscle, implying that the smooth muscle component is the major source of H(2)S. Thus, the L-cysteine-H(2)S pathway may represent a promising target for development of new therapeutics for erectile dysfunction.

The relaxation induced by uroguanylin and the expression of natriuretic peptide receptors in human corpora cavernosa

INTRODUCTION

Receptors for natriuretic peptides have been demonstrated as potential targets for the treatment of male erectile dysfunction.

AIM

This study investigates the relaxant effects of the atrial natriuretic peptide (ANP) and uroguanylin (UGN), and expression of natriuretic peptide receptors on strips of human corpora cavernosa (HCC).

MAIN OUTCOME MEASURES

Quantitative analysis of natriuretic receptor expression and relaxation of precontracted strips were used to assess the membrane-bound guanylate cyclase-cyclic guanosine monophosphate (cGMP) pathway in HCC strips.

METHODS

HCC was obtained from a cadaver donor at the time of collection of organs for transplantation (14-47 years) and strips were mounted in organ baths for isometric studies.

RESULTS

ANP and UGN both induced concentration-dependent relaxation on HCC strips with a maximal response attained at 300 nM, corresponding to 45.4±4.0% and 49±4.8%, respectively. The relaxation is not affected by 30 µM 1H-[1,2,4]oxaolodiazolo[4,3-a]quinoxalin-1-one (ODQ) (a soluble guanylate cyclase inhibitor), but it is significantly blocked by 10 µM isatin, a nonspecific particulate guanylate cyclase (pGC) inhibitor. UGN was unable to potentiate electrical field stimulation (EFS) or acetylcholine-induced relaxations. The potential role of pGC activation and cGMP generation in this effect is reinforced by the potentiation of this effect by phosphodiesterase-5 inhibitor vardenafil (55.0±7.5-UGN vs. 98.6±1.4%-UGN+vardenafil; P<0.05). The relaxant effect was also partially (37.6%) blocked by the combination iberitoxin-apamin but was insensitive to glybenclamide. The expression of guanylate cyclase receptors (GC-A, GC-B, GC-C) and the expression of the natriuretic peptide "clearance" receptor (NPR-C) were confirmed by real-time polymerase chain reaction. The exposure of HCC strips to ANP (1 µM) and UGN (10 µM) significantly increased cGMP, but not cyclic adenosine monophosphate (cAMP) levels.

CONCLUSIONS

UGN relaxes HCC strips by a guanylate cyclase and K(ca)-channel-dependent mechanism. These findings obtained in HCC reveal that the natriuretic peptide receptors are potential targets for the development of new drugs for the treatment of erectile dysfunction.

RhoA, a possible target for treatment of airway hyperresponsiveness in bronchial asthma

Airway hyperresponsiveness to nonspecific stimuli is one of the characteristic features of allergic bronchial asthma. An elevated contractility of bronchial smooth muscle has been considered as one of the causes of the airway hyperresponsiveness. The contraction of smooth muscles including airway smooth muscles is mediated by both Ca²+-dependent and Ca²+-independent pathways. The latter Ca²+-independent pathway, termed Ca²+ sensitization, is mainly regulated by a monomeric GTP-binding protein, RhoA, and its downstream target Rho-kinase. In animal models of allergic bronchial asthma, an augmented agonist-induced, RhoA-mediated contraction of bronchial smooth muscle has been suggested. The RhoA/Rho-kinase signaling is now proposed as a novel target for the treatment of airway hyperresponsiveness in asthma. Herein, we will discuss the mechanism of development of bronchial smooth muscle hyperresponsiveness, one of the causes of the airway hyperresponsiveness, based on the recent studies using animal models of allergic bronchial asthma and/or cultured airway smooth muscle cells. The possibility of RhoA as a therapeutic target in asthma, especially airway hyperresponsiveness, will also be described.

Comparison of miniaturized time-resolved fluorescence resonance energy transfer and enzyme-coupled luciferase high-throughput screening assays to discover inhibitors of Rho-kinase II (ROCK-II)

Kinases are important drug discovery targets for a wide variety of therapeutic indications; consequently, the measurement of kinase activity remains a common high-throughput screening (HTS) application. Recently, enzyme-coupled luciferase-kinase (LK) format assays have been introduced. This format measures luminescence resulting from metabolism of adenosine triphosphate (ATP) via a luciferin/luciferase-coupled reaction. In the research presented here, 1536-well format time-resolved fluorescence resonance energy transfer (TR-FRET) and LK assays were created to identify novel Rho-associated kinase II (ROCK-II) inhibitors. HTS campaigns for both assays were conducted in this miniaturized format. It was found that both assays were able to consistently reproduce the expected pharmacology of inhibitors known to be specific to ROCK-II (fasudil IC50: 283 +/- 27 nM and 336 +/- 54 nM for TR-FRET and LK assays, respectively; Y-27632 IC50: 133 +/- 7.8 nM and 150 +/- 22 nM for TR-FRET and LK assays, respectively). In addition, both assays proved robust for HTS efforts, demonstrating excellent plate Z' values during the HTS campaign (0.84 +/- 0.03; 0.72 +/- 0.05 for LK and TR-FRET campaigns, respectively). Both formats identified scaffolds of known and novel ROCK-II inhibitors with similar sensitivity. A comparison of the performance of these 2 assay formats in an HTS campaign was enabled by the existence of a subset of 25,000 compounds found in both our institutional and the Molecular Library Screening Center Network screening files. Analysis of the HTS campaign results based on this subset of common compounds showed that both formats had comparable total hit rates, hit distributions, amount of hit clusters, and format-specific artifact. It can be concluded that both assay formats are suitable for the discovery of ROCK-II inhibitors, and the choice of assay format depends on reagents and/or screening technology available.

Inhibition of rho-kinase impairs fibroblast stress fiber formation, confluence, and contractility in vitro

Rho kinase is an enzyme that has been implicated in pathological wound healing. In our study, we aimed to characterize the dosages of Y-27632 (a competitive inhibitor of rho kinase) at which fibroblast stress fiber formation is inhibited, to determine the effect of Y-27632 on fibroblast confluence, and to determine the effect of varying concentrations of Y-27632 on fibroblast-mediated gel contraction. First, 3T3 fibroblasts were exposed to various concentrations of Y-27632, and stress fiber dissolution was assessed with immunofluorescence. Next, 10 microM Y-27632 was applied to 3T3 fibroblast monolayer cultures immediately after plating and at 8 hours after plating to determine the effect on fibroblast confluence. Finally, a three-dimensional model was used to assess the effect of Y-27632 on gel contraction. Increasing doses of Y-27632 resulted in a dose-dependent increase in stress fiber dissolution as well as a dose-dependent inhibition of gel contraction. Median number of days to confluence were 3, 5, and 6 after no, immediate, and delayed incubation with Y-27632, respectively (P < .05). Our results further characterize the dosages at which Y-27632 may be most effective in the modulation of wound contraction in burn patients. In addition, our confluence study suggests that patients need not necessarily be pretreated with Y-27632.

RhoA/Rho kinase-mediated Ca2+ sensitization in the contraction of human prostate

AIMS

The contractile mechanisms of prostatic smooth muscle have been extensively investigated at the receptor level. However, the intracellular mechanisms have not yet been fully elucidated, especially in human tissue. In the present study, we examined the functional role of RhoA/Rho kinase (ROCK), one of the major intracellular molecules involved in smooth muscle contraction, in the contraction of the human prostate.

METHODS

Ring preparations made of cultured human prostatic stromal cells (CHPSCs) or fresh human prostatic tissue was used for an isometric tension study. Gene transfer using baculovirus vector and alpha-toxin permeabilized preparations were also used.

RESULTS

RhoA, ROCK I and ROCK II proteins were all expressed in CHPSCs and fresh human prostatic tissue. In CHPSCs ring preparations, the contraction induced by endothelin (ET)-1 was enhanced by over-expression of RhoA and inhibited by ROCK inhibitor. In alpha-toxin permeabilized preparations, ET-1 or GTP-gammaS induced an additional contraction at a constant [Ca2+]i, that was inhibited by ROCK inhibitor. In fresh human prostatic tissue, norepinephrine (NE)-induced contraction was inhibited by ROCK inhibitor at a constant [Ca2+]i in alpha-toxin permeabilized preparations.

CONCLUSIONS

These results suggested that RhoA/ROCK-mediated Ca2+ sensitization is likely involved in the contraction of the human prostate. The antagonisms of this pathway may thus be useful as an alternative target in the treatment of benign prostatic hyperplasia (BPH).

RhoA/Rho-kinase in erectile tissue: mechanisms of disease and therapeutic insights

Penile erection is a complicated event involving the regulation of corpus cavernosal smooth muscle tone. Recently, the small monomeric G-protein RhoA and its downstream effector Rho-kinase have been proposed to be important players for mediating vasoconstriction in the penis. RhoA/Rho-kinase increases MLC (myosin light chain) phosphorylation through inhibition of MLCP (MLC phosphatase) thereby increasing Ca2+ sensitivity. This review will outline the RhoA/Rho-kinase signalling pathway, including the upstream regulators, guanine nucleotide exchange factors, GDP dissociation inhibitors and GTPase-activating proteins. We also summarize the current knowledge about the physiological roles of RhoA/Rho-kinase in both male and female erectile tissues and its aberrations contributing to erectile dysfunction in several disease states. Understanding the RhoA/Rho-kinase signalling pathway in the regulation of erection is important for the development of therapeutic interventions for erectile dysfunction.

Phosphodiesterase type 5 inhibitors for erectile dysfunction

The cyclic nucleotide signalling pathway mediates the smooth-muscle relaxing effects of nitric oxide necessary for normal erectile function. Down-regulation of this pathway is central to the pathophysiology of many forms of erectile dysfunction (ED), which is often associated with other chronic diseases (e.g. hypertension, type 2 diabetes mellitus) and treatments (e.g. certain drugs, radical prostatectomy). Conversely, selective inhibition of the enzyme that catalyses the degradation of cGMP (phosphodiesterase type 5, PDE-5) promotes erectile responses to sexual stimulation. The successful launch and commercialization of the selective PDE5 inhibitor (PDE5I) sildenafil transformed the treatment of ED, not only by providing an effective, well tolerated oral ED therapy, but also by fostering greater candour about the problem among men. Sildenafil is highly effective in promoting erectile responses across a wide spectrum of severity and causes of ED, including patients with ED that is often refractory to treatment. The recent advent of vardenafil, which has the highest in vitro potency of all available PDE5Is, and tadalafil, which has a prolonged half-life that may enable couples to have sexual activity with less planning, represent further advances. Other PDE5Is offering further potential improvements are under active investigation.

The role of RhoA-mediated Ca2+ sensitization of bronchial smooth muscle contraction in airway hyperresponsiveness

Smooth muscle contraction is mediated by Ca2+-dependent and Ca2+-independent pathways. The latter Ca2+-independent pathway, termed Ca2+ sensitization, is mainly regulated by a monomeric GTP binding protein RhoA and its downstream target Rho-kinase. Recent studies suggest a possible involvement of augmented RhoA/Rho-kinase signaling in the elevated smooth muscle contraction in several human diseases. An increased bronchial smooth muscle contractility, which might be a major cause of the airway hyperresponsiveness that is a characteristic feature of asthmatics, has also been reported in bronchial asthma. Here, we will discuss the role of RhoA/Rho-kinase-mediated Ca2+ sensitization of bronchial smooth muscle contraction in the pathogenesis of airway hyperresponsiveness. Agonist-induced Ca2+ sensitization is also inherent in bronchial smooth muscle. Since the Ca2+ sensitization is sensitive to a RhoA inactivator, C3 exoenzyme, and a Rho-kinase inhibitor, Y-27632, the RhoA/Rho-kinase pathway is involved in the signaling. It is of interest that the RhoA/Rho-kinase-mediated Ca2+ sensitization of bronchial smooth muscle contraction is markedly augmented in experimental asthma. Moreover, Y-27632 relaxes the bronchospasm induced by contractile agonists and antigens in vivo. Y-27632 also has an ability to inhibit airway hyperresponsiveness induced by antigen challenge. Thus, the RhoA/Rho-kinase pathway might be a potential target for the development of new treatments for asthma, especially in airway hyperresponsiveness.

Ejaculatory disorders and lower urinary tract symptoms

A growing body of literature supports the observed association between lower urinary tract symptoms and sexual dysfunction. The causal relationship between these two conditions has not been determined. Ejaculatory function is an important aspect of sexual functioning and recent studies have shown a high prevalence of this ejaculatory dysfunction in men with lower urinary tract symptoms. Furthermore, the degree of bother associated with ejaculatory dysfunction is quite high, making it an important problem for patients. Thus, health care providers should have a heightened sense of awareness for the presence of ejaculatory dysfunction and appropriate patient counseling should be undertaken before initiation of specific treatments for lower urinary tract symptoms.