Obstruction alters muscarinic receptor-coupled RhoA/Rho-kinase pathway in the urinary bladder of the rat

Pathophysiology of Overactive Bladder and Pharmacologic Treatments Including β3-Adrenoceptor Agonists -Basic Research Perspectives

Overactive bladder (OAB) is a symptom-based syndrome defined by urinary urgency, frequency, and nocturia with or without urge incontinence. The causative pathology is diverse; including bladder outlet obstruction (BOO), bladder ischemia, aging, metabolic syndrome, psychological stress, affective disorder, urinary microbiome, localized and systemic inflammatory responses, etc. Several hypotheses have been suggested as mechanisms of OAB generation; among them, neurogenic, myogenic, and urothelial mechanisms are well-known hypotheses. Also, a series of local signals called autonomous myogenic contraction, micromotion, or afferent noises, which can occur during bladder filling, may be induced by the leak of acetylcholine (ACh) or urothelial release of adenosine triphosphate (ATP). They can be transmitted to the central nervous system through afferent fibers to trigger coordinated urgency-related detrusor contractions. Antimuscarinics, commonly known to induce smooth muscle relaxation by competitive blockage of muscarinic receptors in the parasympathetic postganglionic nerve, have a minimal effect on detrusor contraction within therapeutic doses. In fact, they have a predominant role in preventing signals in the afferent nerve transmission process. β3-adrenergic receptor (AR) agonists inhibit afferent signals by predominant inhibition of mechanosensitive Aδ-fibers in the normal bladder. However, in pathologic conditions such as spinal cord injury, it seems to inhibit capsaicin-sensitive C-fibers. Particularly, mirabegron, a β3-agonist, prevents ACh release in the BOO-induced detrusor overactivity model by parasympathetic prejunctional mechanisms. A recent study also revealed that vibegron may have 2 mechanisms of action: inhibition of ACh from cholinergic efferent nerves in the detrusor and afferent inhibition via urothelial β3-AR.

Are there different patterns of detrusor overactivity which are clinically relevant? ICI-RS 2018

INTRODUCTION

Different patterns of detrusor overactivity (DO) have been described and included in several standardization terminology documents. However, it is unclear if these different patterns have any clinical significance.

METHODS

This is a report of the proceedings of Proposal 3: "Are there different patterns of detrusor overactivity which are clinically relevant?" from the annual International Consultation on Incontinence-Research Society (ICIRS) meeting, which took place from 14 to 16 June 2018, in Bristol, UK.

RESULTS

We have collected and discussed, as a committee, the evidence about different urodynamic (UD) patterns of detrusor overactivity and their potential clinical significance. We reviewed the important previous basic research and clinical studies and compiled summaries. The discussion focused on clinical relevance of different UD patterns of DO and what further research is required.

CONCLUSIONS

There are several UD definitions of patterns of detrusor overactivity, however the clinical relevance of these definitions remains unclear. Future research should concentrate on defining the pattern of DO in relation to clinical diagnosis, gender, age, and treatment outcomes.

Dysregulated NO/PDE5 signaling in the sickle cell mouse lower urinary tract: Reversal by oral nitrate therapy

AIMS

Nitric oxide (NO) has a critical, but not well understood, influence in the physiology of the lower urinary tract. We evaluated the effect of NO/phosphodiesterase (PDE)5 signaling in voiding dysfunction in the sickle cell disease (SCD) mouse, characterized by low NO bioavailability.

MAIN METHODS

Adult SCD (Sickle) and wild-type (WT) male mice were treated daily with sodium nitrate (10 mM) or vehicle. After 18 days, blood was obtained for nitrite measurement, urethra was collected for organ bath study, and bladder and urethra were collected for Western blot analysis of PDE5 phosphorylation (Ser-92) (activated form). Non-anesthetized mice underwent evaluation of urine volume by void spot assay. eNOS phosphorylation (Ser-1177) and nNOS phosphorylation (Ser-1412) (positive regulatory sites) were evaluated in the bladder and urethra of untreated mice.

KEY FINDINGS

Sickle mice exhibited decreased eNOS, nNOS, and PDE5 phosphorylation in the bladder and urethra, decreased plasma nitrite levels, increased relaxation of phenylephrine-contracted urethral tissue to an NO donor sodium nitroprusside, and increased total urine volume, compared with WT mice. Nitrate treatment normalized plasma nitrite levels, relaxation of urethra to sodium nitroprusside, PDE5 phosphorylation in the urethra and bladder, and urine volume in Sickle mice.

SIGNIFICANCE

Derangement in PDE5 activity associated with basally low NO bioavailability in the bladder and urethra contributes to the molecular basis for voiding abnormalities in Sickle mice. Inorganic nitrate supplementation normalized voiding in Sickle mice through mechanisms likely involving upregulation of PDE5 activity. These findings suggest that interventions targeting dysregulatory NO/PDE5 signaling may ameliorate overactive bladder in SCD.

Pharmacological modulation of the spatiotemporal disposition of micromotions in the intact resting urinary bladder of the rabbit; their pattern is under both myogenic and autonomic control

OBJECTIVES

To explore and characterize the disposition and dynamics of micromotions in the wall of the intact resting teradotoxinized urinary bladder of the rabbit before and after the administration of adrenergic and cholinergic pharmaceutical agents.

METHODS

Spatiotemporal maps and related intravesical pressure were used to analyse propagating patches of contractions (PPCs) and their component individual myogenic contractions [propagating individual contractions (PICs)] in the wall of the tetradotoxinized urinary bladder.

RESULTS

The bladder wall exhibited two contractile states that were of similar frequencies to those of the two types of electrophysiological discharge described in previous studies; the first, in which cyclic PPCs predominated, the second in which small irregular PICs predominated. The addition of carbachol increased the size, frequency, speed and distance of propagation of PPCs, whereas the addition of isoprenaline temporarily halted the incorporation of PICs into PPCs, and reduced patch size and total area undergoing contraction. The RhoA kinase (ROCK) inhibitor Y-27632 reduced both largest patch index and mean patch size. Both carbenoxolone and ROCK inhibition decreased the duration of PPCs. Carbenoxolone also prolonged duration and accelerated PPC propagation velocity. The authors postulate that these differences arise from differing effects of these agents on myocytes and interstitial cells within the stress environment of the bladder, influencing the development, coordination and propagation of PPCs.

CONCLUSIONS

The timings and structure of spontaneous micromotions in the wall of the isolated bladder change when it is treated with sympathetic/parasympathetic agonists and with myogenically active agents. Correspondingly, disorders of bladder wall contraction may result from disorders of either neurogenic or myogenic signalling and may be amenable to treatment with combinations of agents that influence both.

Protective Effect of a Rho-kinase Inhibitor on Bladder Dysfunction in a Rat Model of Chronic Bladder Ischemia

OBJECTIVE

To investigate the effect of fasudil, a Rho-kinase inhibitor, on chronic ischemia-related bladder dysfunction.

MATERIALS AND METHODS

Male Sprague-Dawley rats (16 weeks old) were divided into control, chronic bladder ischemia (CBI), and CBI with fasudil treatment (CBI-Fa) groups. The CBI and CBI-Fa groups underwent balloon endothelial injury of bilateral iliac arteries and received a 2% cholesterol diet for 8 weeks after the procedure to induce CBI. The CBI-Fa group was given oral fasudil (30 mg/kg/day) using zonde for 8 weeks after the procedure. The control group received a regular diet for 8 weeks. After cystometry in a conscious state, rats from each group were euthanized, and the bladders and common iliac arteries were harvested for pharmacologic and histologic examination.

RESULTS

Mean wall thickness of the common iliac arteries was significantly greater in the CBI group than in controls. Contractile responses of muscle strips were significantly lower in CBI group rats than in controls. In the CBI group, micturition interval was significantly shorter, and bladder capacity was significantly lower compared with those in controls. In the CBI-Fa group, arterial wall thickening was significantly suppressed compared with the CBI group. Significant improvements in muscle strip contractility and cystometric parameters were seen in the CBI-Fa group compared with the CBI group.

CONCLUSION

Our results suggest that chronic treatment with fasudil could prevent neointimal formation in arteries and bladder dysfunction in this rat model. Fasudil may be therapeutically useful in protecting bladder function in chronically ischemic bladders.

Benefits and limitations of animal models in partial bladder outlet obstruction for translational research

The functions of the lower urinary tract have been investigated for more than a century. Lower urinary tract symptoms, such as incomplete bladder emptying, weak urine stream, daytime urinary frequency, urgency, urge incontinence and nocturia after partial bladder outlet obstruction, is a frequent cause of benign prostatic hyperplasia in aging men. However, the pathophysiological mechanisms have not been fully elucidated. The use of animal models is absolutely imperative for understanding the pathophysiological processes involved in bladder dysfunction. Surgical induction has been used to study lower urinary tract functions of numerous animal species, such as pig, dog, rabbit, guinea pig, rat and mouse, of both sexes. Several morphological and functional modifications under partial bladder outlet obstruction have not only been observed in the bladder, but also in the central nervous system. Understanding the changes of the lower urinary tract functions induced by partial bladder outlet obstruction would also contribute to appropriate drug development for treating these pathophysiological conditions. In the present review, we discuss techniques for creating partial bladder outlet obstruction, the characteristics of several species, as well as issues of each model, and their translational value.

Comprehensive approach for post-prostatectomy incontinence in the era of robot-assisted radical prostatectomy

Robot-assisted radical prostatectomy (RARP) has enabled steady and stable surgical procedures due to both meticulous maneuvers and magnified, clear, 3-dimensional vision. Therefore, better surgical outcomes have been expected with RARP than with other surgical modalities. However, even in the RARP era, post-prostatectomy incontinence has a relatively high incidence as a bothersome complication. To overcome post-prostatectomy incontinence, it goes without saying that meticulous surgical procedures and creative surgical procedures, i.e., "Preservation", "Reconstruction", and "Reinforcement" of the anatomical structures of the pelvis, are most important. In addition, medication and appropriate pad usage might sometimes be helpful for patients with post-prostatectomy incontinence. However, patients who have 1) BMI > 26 kg/m², 2) prostate volume > 70 mL, 3) eGFR < 60 mL/min, or a 4) Charlson comorbidity index > 2 have a tendency to develop post-prostatectomy incontinence despite undergoing the same surgical procedures. It is important for patients who have a high risk for post-prostatectomy incontinence to be given information about delayed recovery of post-prostatectomy incontinence. Thus, not only the surgical procedures, but also a comprehensive approach, as mentioned above, are important for post-prostatectomy incontinence.

Preventative effects of a HIF inhibitor, 17-DMAG, on partial bladder outlet obstruction-induced bladder dysfunction

Posterior urethral valves are the most common cause of partial bladder outlet obstruction (PBOO) in the pediatric population. Pathological changes in the bladder developed during PBOO are responsible for long-lasting voiding dysfunction in this population despite early surgical interventions. Increasing evidence showed PBOO induces an upregulation of hypoxia-inducible factors (HIFs) and their transcriptional target genes, and they play a role in pathophysiological changes in the obstructed bladders. We hypothesized that blocking HIF pathways can prevent PBOO-induced bladder dysfunction. PBOO was surgically created by ligation of the bladder neck in male C57BL/6J mice for 2 wk. PBOO mice received intraperitoneal injection of either saline or 17-DMAG (alvespimycin, 3 mg/kg) every 48 h starting from day 1 postsurgery. Sham-operated animals received injection of saline on the same schedule as PBOO mice and served as controls. The bladders were harvested after 2 wk, and basal activity and evoked contractility of the detrusor smooth muscle (DSM) were evaluated in vitro. Bladder function was assessed in vivo by void spot assay and cystometry in conscious, unrestrained mice. Results indicated the 17-DMAG treatment preserved DSM contractility and partially prevented the development of detrusor over activity in obstructed bladders. In addition, PBOO caused a significant increase in the frequency of micturition, which was significantly reduced by 17-DMAG treatment. The 17-DMAG treatment improved urodynamic parameters, including increases in the bladder pressure at micturition and nonvoid contractions observed in PBOO mice. These results demonstrate that treatment with 17-DMAG, a HIF inhibitor, significantly alleviated PBOO-induced bladder pathology in vivo.

The Effect of the Vesical Adaptation Response to Diuresis on Lower Urinary Tract Symptoms after Robot-Assisted Laparoscopic Radical Prostatectomy: A Pilot Proof of Concept Study

BACKGROUND

When urine output increases, voided volume at each voiding also increases in normal subjects. This is generally understood as a vesical adaptation response to diuresis (VARD). Because lower urinary tract symptoms (LUTS) are supposed to be improved by the change in bladder function after robot-assisted laparoscopic radical prostatectomy (RARP), the aim of the present study was to investigate whether VARD is involved in the improvement of LUTS after RARP.

METHODS

100 consecutive patients who underwent RARP and had the International Prostate Symptom Score (IPSS), quality of life (QOL) index, a frequency-volume chart (FVC), uroflowmetry, and post-voided residual urine (PVR) available were evaluated before and after RARP. This cohort was divided into patients with and without preoperative LUTS according to the preoperative IPSS total score. VARD was defined as the presence of a significant correlation between the urine output rate and voided volume at each voiding (R2>0.2).

RESULTS

In patients with preoperative LUTS, the IPSS total, storage, and voiding symptom scores were significantly improved after RARP (all P<0.001). The QOL index was also significantly improved after RARP (P<0.05). Although VARD was not seen before RARP (R2 = 0.05), it was seen after RARP (3 months R2 = 0.22, 12 months R2 = 0.23). PVR was significantly reduced after RARP (P = 0.004).

CONCLUSIONS

Improvement of LUTS was seen with acquisition of VARD after RARP. As a result, urinary QOL was also improved in patients with preoperative LUTS. RARP might be an effective procedure for amelioration of LUTS by the acquisition of VARD.

Uni-axial stretch induces actin stress fiber reorganization and activates c-Jun NH2 terminal kinase via RhoA and Rho kinase in human bladder smooth muscle cells

Background

Excessive mechanical overload may be involved in bladder wall remodelling. Since the activity of Rho kinase is known to be upregulated in the obstructed bladder, we investigate the roles of the RhoA/Rho kinase pathway in mechanical overloaded bladder smooth muscle cells.

Methods

Human bladder smooth muscle cells were stimulated on silicon culture plates by 15 % elongated uni-axial cyclic stretch at 1 Hz. The activity of c-Jun NH₂-terminal kinase was measured by western blotting and actin stress fibers were observed by stained with phallotoxin conjugated with Alexa-Fluor 594.

Results

The activity of c-Jun NH₂-terminal kinase 1 peaked at 30 min (4.7-fold increase vs. before stretch) and this activity was partially abrogated by the RhoA inhibitor, C3 exoenzoyme or by the Rho kinase inhibitor, Y-27632. Stretch induced the strong formation of actin stress fibers and these fibers re-orientated in a direction that was perpendicular to the stretch direction. The average angle of the fibers from the perpendicular to the direction of stretch was significantly different between before, and 4 h after, stretch. Actin stress fibers reorganization was also suppressed by the C3 exoenzyme or Y-27632.

Conclusions

Bladder smooth muscle cells appear to have elaborate mechanisms for sensing mechanical stress and for adapting to mechanical stress overload by cytoskeletal remodeling and by activating cell growth signals such as c-Jun NH₂-terminal kinase via RhoA/Rho kinase pathways.

Spontaneous Contractile Activity of the Detrusor Muscle and Its Role in the Pathogenesis of Overactive Bladder Syndrome

There is accumulated evidence that spontaneous contractions (SCs) in the bladder wall are associated with afferent nerve firing in the bladder. The role of the urothelium in bladder sensation might be restricted to pathological conditions, such as interstitial cystitis or chemical cystitis in which the release of urothelium-derived mediators such as adenosine triphosphate is increased. Recent publications imply that SCs in bladders with detrusor overactivity due to spinal cord injury or bladder outlet obstruction are modulated by intracellular signal transduction mechanisms such as the RhoA/Rho-kinase pathway, denervation-supersensitivity to acetylcholine, changes in ion channel activity, enhanced gap-junctional intercellular communication, alterations in interstitial cells of Cajal, the actions of local mediators in the detrusor and the influence of the urothelium. Spontaneous contractions and possible consequent afferent nerve firing might participate in the generation of overactive bladder syndrome.

The influence of Rho-kinase inhibition on acetic acid-induced detrusor overactivity

AIMS

Accumulating evidence has shown that Rho-kinase (ROCK) is involved in the regulation of bladder contraction. Our objective was to examine whether the ROCK inhibitor, GSK 269962, could prevent acetic acid (AA)-induced detrusor overactivity and to assess its influence on urine production (UP) and mean arterial pressure (MAP).

METHODS

The bladder was catheterized from the external urethral orifice. 0.25 % (AA) solution was infused into the bladder for 5 min. In the same session a catheter was inserted into the apex of the bladder dome. In order to measure the blood pressure, the carotid artery was cannulated. Three days after the intravesical instillation of AA, the ROCK-GSK 269962 inhibitor was administered in a single dose of 10 mg/kg and a cystometry was carried out, along with a 24 hr measurement of UP and MAP.

RESULTS

GSK 269962 reversed the changes induced by AA causing a drop in basal pressure, threshold pressure, micturition voiding pressure, bladder contraction duration, relaxation time, detrusor overactivity index, amplitude, and frequency of nonvoiding contractions while an increase in voided volume, post-void residual, volume threshold, voiding efficiency, intercontraction interval, bladder compliance, and volume threshold to elicit nonvoiding contractions. ROCK inhibition did not show any significant changes in UP and MAP.

DISCUSSION

The results obtained indicate that ROCK inhibition may ameliorate AA-induced bladder overactivity.

CONCLUSION

ROCK inhibitors appear to represent a potentially attractive pharmacological option for the treatment of lower urinary tract disorders associated with changes in detrusor contractility. Neurourol. Urodynam. 36:263-270, 2017. © 2015 Wiley Periodicals, Inc.

Mast Cell Accumulation and Degranulation in Rat Bladder with Partial Outlet Obstruction

INTRODUCTION

Benign prostatic hyperplasia causes partial bladder outlet obstruction (pBOO), and many patients with pBOO are affected by not only voiding symptoms but also storage symptoms. We previously suggested that enhancement of 5-hydroxytryptamine (5-HT)-induced bladder contraction in the pBOO bladder may be one cause of storage symptoms. However, little is known about the presence of 5-HT in rat bladders. In this study, we hypothesized that mast cells are a source of 5-HT and investigated the distribution of mast cells and 5-HT in the bladders of rats with pBOO.

METHODS

The bladders of female Sprague-Dawley rats were subjected to pBOO and sham operations for 1 week, were isolated, and were fixed for light or electron microscopy. Mast cells and 5-HT in the bladders were detected by toluidine blue staining and immunohistochemical staining, respectively. The mast cells were counted under a light microscope. Degranulated mast cells were observed under an electron microscope and counted under a light microscope.

RESULTS

Mast cells were present in the mucosa/submucosa region in sham rat bladders. Their number was increased in the detrusor muscle/subserosa/serosa region, especially the subserosal layer, in pBOO rat bladders. The localization of mast cells almost matched that of 5-HT-positive cells in consecutive sections. Degranulated mast cells were present in sham and pBOO rat bladders, but the proportion of degranulated mast cells was significantly increased in every region in pBOO rat bladders compared with that in sham rat bladders.

CONCLUSION

These results suggest that mast cells contain 5-HT and are more abundant locally in the subserosal layer of pBOO rat bladders. 5-HT released from mast cells could stimulate 5-HT2 receptors on the detrusor muscle, and this may underlie storage symptoms.

FUNDING

Asahi Kasei Pharma Corp.

Research Findings on Overactive Bladder

Several physiopathologic conditions lead to the manifestation of overactive bladder (OAB). These conditions include ageing, diabetes mellitus, bladder outlet obstruction, spinal cord injury, stroke and brain injury, Parkinson's disease, multiple sclerosis, interstitial cystitis, stress and depression. This review has discussed research findings in human and animal studies conducted on the above conditions. Several structural and functional changes under these conditions have not only been observed in the lower urinary tract, but also in the brain and spinal cord. Significant changes were observed in the following areas: neurotransmitters, prostaglandins, nerve growth factor, Rho-kinase, interstitial cells of Cajal, and ion and transient receptor potential channels. Interestingly, alterations in these areas showed great variation in each of the conditions of the OAB, suggesting that the pathophysiology of the OAB might be different in each condition of the disease. It is anticipated that this review will be helpful for further research on new and specific drug development against OAB.

Proteomic profile of an acute partial bladder outlet obstruction

INTRODUCTION

Partial bladder outlet obstruction (pBOO) is a ubiquitous problem in urology. From posterior urethral valves to prostatic hypertrophy, pBOO results in significant morbidity and mortality. However, the pathophysiology is not completely understood. Proteomics uses mass spectrometry to accurately quantify change in tissue protein concentration. Therefore, we have applied proteomic analysis to a rodent model to assess for protein changes after a surgically induced pBOO. We hypothesize that proteomic analysis after an acute obstruction will determine the most prevalent initial protein response and, potentially, novel molecular pathways.

METHODS

Sprague Dawley rats underwent a surgically induced pBOO (n = 3 per group) for 3, 7, or 14 days. Bladders were assessed for weight and urodynamic parameters. Proteomics used liquid-chromatography based mass spectrometry. Polymerase chain reaction (PCR) was performed on tissue samples to confirm increased mRNA transcription.

RESULTS

Bladder weight and capacity increased over the experimental period, but no changes were seen in bladder pressure. Statistically significant increases in protein quantities were seen in 3 proteins related to endoplasmic reticulum stress: GRP-78 (3.66-fold), RhoA (1.90-fold), and RhoA-GDP (1.95-fold), and 2 cytoskeleton molecules: actin (1.7-fold) and tubulin a/b (3.01-fold). Decorin and lumican, members of the small leucine rich proteoglycan (SLRP) family, were also elevated (0.35- and 0.34-fold, respectively). Real-time PCR data confirmed protein elevation.

CONCLUSION

Our experiment confirms that molecular changes occur very soon after the initiation of pBOO, and implicates several molecular pathways. We believe these insights may provide insight into novel prevention and treatment strategies targeted at the pathophysiology of pBOO.

Tadalafil effect on metabolic syndrome-associated bladder alterations: an experimental study in a rabbit model

INTRODUCTION

Metabolic syndrome (MetS) and lower urinary tract symptoms (LUTS) are often associated. Bladder detrusor hyper-contractility-a major LUTS determinant-is characterized by increased Ras homolog gene family, member A/Rho-associated protein kinase (RhoA/ROCK) signaling, which is often upregulated in MetS.

AIM

This study investigated the effects of tadalafil dosing on RhoA/ROCK signaling in bladder, in a rabbit model of high-fat diet (HFD)-induced MetS.

METHODS

Adult male rabbits feeding a HFD for 12 weeks. A subset of HFD animals was treated with tadalafil (2 mg/kg/day, 1 week: the last of the 12 weeks) and compared with HFD and control (feeding a regular diet) rabbits.

MAIN OUTCOME MEASURES

In vitro contractility studies to evaluate the relaxant effect of the selective ROCK inhibitor, Y-27632, in carbachol precontracted bladder strips. Evaluation of RhoA activation by its membrane translocation. Immunohistochemistry for ROCK expression has been performed to evaluate ROCK expression in bladder from the different experimental groups. mRNA expression of inflammation, pro-fibrotic markers by quantitative RT-PCR has been performed to evaluate the effect of tadalafil on MetS-induced inflammation and fibrosis within the bladder. The in vitro effect of tadalafil on RhoA/ROCK signaling in bladder smooth muscle cells was evaluated by using chemotaxis assay.

RESULTS

Bladder strips from HFD rabbits showed hyper-responsiveness to Y-27632, indicating RhoA/ROCK overactivity in HFD bladder compared with matched controls. Accordingly, the fraction of activated (translocated to the membrane) RhoA as well as ROCK expression are increased in HFD bladder. Tadalafil dosing normalized HFD-induced bladder hypersensitivity to Y-27632, by reducing RhoA membrane translocation and ROCK overexpression. Tadalafil dosing reduced mRNA expression of inflammatory, pro-fibrotic, and hypoxia markers. A direct inhibitory effect of tadalafil on RhoA/ROCK signaling in bladder smooth muscle cell was demonstrated by using chemotaxis assay. Pre-treatment with tadalafil inhibited both basal and PDGF-induced migration of bladder smooth muscle cells.

CONCLUSIONS

Tadalafil dosing reduced RhoA/ROCK signaling and smooth muscle overactivity in an animal model of MetS-associated bladder alterations. Our findings suggest a novel mechanism of action of tadalafil in alleviating LUTS in MetS patients.

Effects of Rho-kinase inhibition on myosin light chain phosphorylation and obstruction-induced detrusor overactivity

OBJECTIVES

To study the relationship between myosin light chain phosphorylation of the detrusor muscle and spontaneous smooth muscle contractions in a rabbit model of partial outlet obstruction.

METHODS

New Zealand white rabbit urinary bladders were partially obstructed for 2 weeks. Rabbits were euthanized, detrusor muscle strips were hung on a force transducer and spontaneous activity was measured at varying concentrations (0-0.03 μM/L) of the Rho-kinase inhibitors GSK 576371 or 0.01 μM/L Y27632. Basal myosin light chain phosphorylation was measured by 2-D gel electrophoresis in control and GSK 576371-treated strips.

RESULTS

Both drugs suppressed the force of spontaneous contractions, whereas GSK 576371 had a more profound effect on the frequency of the contractions. The IC₅₀ values for the inhibition of frequency and force of spontaneous contractions were 0.17 μM/L and 0.023 μM/L for GSK 576371, respectively. The compound significantly decreased the basal myosin light chain phosphorylation from 28.0 ± 3.9% to 13.5 ± 1.9% (P < 0.05). At 0.01 μM/L, GSK 576371 inhibited spontaneous bladder overactivity by 50%, but inhibited carbachol-elicited contractions force by just 25%.

CONCLUSIONS

These data suggest that Rho-kinase regulation of myosin light chain phosphorylation contributes to the spontaneous detrusor activity induced by obstruction. This finding could have therapeutic implications by providing another therapeutic option for myogenic, overactive bladder.

Future direction in pharmacotherapy for non-neurogenic male lower urinary tract symptoms

BACKGROUND

The pathophysiology of male lower urinary tract symptoms (LUTS) is highly complex and multifactorial. The shift in perception that LUTS are not sex or organ specific has not been followed by significant innovations regarding the available drug classes.

OBJECTIVE

To review pathophysiologic mechanisms and clinical and experimental data related to the development of new pharmacologic treatments for male LUTS.

EVIDENCE ACQUISITION

The PubMed database was used to identify articles describing experimental and clinical studies of pathophysiologic mechanisms contributing to male LUTS and, supported by them, new pharmacotherapies with clinical or experimental evidence in the field.

EVIDENCE SYNTHESIS

Several pathologic processes (eg, androgen signaling, inflammation, and metabolic factors) and targets (eg, the urothelium, prostate, interstitial cells, detrusor, neurotransmitters, neuromodulators, and receptors) have been implicated in male LUTS. Some newly introduced drugs, such as phosphodiesterase type 5 inhibitors and β3-adrenergic agonists, have just started broad use in clinical practice. Drugs with potential benefit, such as vitamin D3 receptor analogs, gonadotropin-releasing hormone antagonists, cannabinoids, and drugs injected into the prostate, have been evaluated in experimental studies and have progressed to clinical trials. However, safety and efficacy data for these drugs are still scarce. Some compounds with interesting profiles have only been tested in experimental settings (eg, transient receptor potential channel blockers, Rho-kinase inhibitors, purinergic receptor blockers, and endothelin-converting enzyme inhibitors).

CONCLUSIONS

New pathophysiologic mechanisms of male LUTS are described that lead to the continuous development of new pharmacotherapies. To date, few drugs have been added to the current armamentarium, and several are in various phases of clinical or experimental investigation.

5-Hydroxytryptamine-induced bladder hyperactivity via the 5-HT2A receptor in partial bladder outlet obstruction in rats

We investigated the effects of partial bladder outlet obstruction (BOO) on the function and gene expression of 5-hydroxytryptamine (5-HT) receptor subtypes in rat bladder. Isometric contractions of the isolated bladders from sham-operated control and BOO rats were examined. The contractile responses to 5-HT were significantly increased in BOO rat bladder strips, while the responses to KCl, carbachol, or phenylephrine were not different from the control. The 5-HT-induced hypercontraction in BOO rat bladder strips was inhibited by ketanserin, a 5-HT(2A) receptor antagonist. The contractile responses to 5-HT in bladder strips were not affected by urothelium removal from the intact bladder. The gene expression of 5-HT receptor subtypes in the bladders was analyzed by RT-PCR. The mRNA expression of the 5-HT(2A), 5-HT(2B), 5-HT(2C), 5-HT(4), and 5-HT(7) receptors was detected in both the control and BOO rat bladders. Quantitative RT-PCR analysis showed there was a significant increase of 5-HT(2A) receptor mRNA in the BOO rat bladder compared with the control bladder. On the other hand, the gene expression of the 5-HT(4) receptor was not changed in the BOO rat bladder. These results suggest that the increased contractile responses to 5-HT in BOO rat bladder may be partly caused by 5-HT(2A) receptor upregulation in the detrusor smooth muscles.

Large-conductance calcium-activated potassium channel activity, as determined by whole-cell patch clamp recording, is decreased in urinary bladder smooth muscle cells from male rats with partial urethral obstruction

OBJECTIVES

To examine the effect of partial urethral obstruction (PUO) on bladder smooth muscle outward potassium current and the contribution of the large-conductance calcium-activated potassium (Maxi-K, BKCa) channel to this activity in smooth muscle cells isolated from bladders of sham-operated and PUO male rats using whole-cell patch clamp recording techniques. To determine the effect of PUO on the expression of the Maxi-K channel α and β1 subunits and in vitro detrusor contractility.

MATERIALS AND METHODS

Twenty adult male Sprague-Dawley rats were divided equally into two groups and subjected to surgical ligation of the urethra (PUO) or sham surgery (SHAM). After 2 weeks, the detrusors from PUO and SHAM rats were used for molecular analyses (mRNA and protein quantification of Maxi-K subunits) or organ bath contractility studies, or myocytes were isolated for conventional whole-cell patch clamp analyses.

RESULTS

PUO increased bladder mass 2.5-fold and detrusor strips exhibited a more tonic-type contraction and increased contractility compared with controls (SHAM). Iberiotoxin (300 nM) sensitive Maxi-K channel current comprised about 40% of the outward whole-cell current in SHAM bladders but only about 8% in PUO bladders. Expression of the α subunit of the Maxi-K channel was significantly decreased ~40% while the expression of the β1 subunit was increased ~2-fold at the mRNA level. The increase in β1 expression was confirmed by Western blotting.

CONCLUSIONS

Our findings show that obstruction of the rat bladder is associated with decreased Maxi-K channel activity of bladder smooth muscle cells, determined via direct current measurement. Increased expression of the β1 subunit points to a compensatory reaction to decreased Maxi-K channel activity. Maxi-K channel openers or gene therapy may therefore provide therapeutic benefit for the overactive bladder.

Blebbistain, a myosin II inhibitor, as a novel strategy to regulate detrusor contractility in a rat model of partial bladder outlet obstruction

Partial bladder outlet obstruction (PBOO), a common urologic pathology mostly caused by benign prostatic hyperplasia, can coexist in 40–45% of patients with overactive bladder (OAB) and is associated with detrusor overactivity (DO). PBOO that induces DO results in alteration in bladder myosin II type and isoform composition. Blebbistatin (BLEB) is a myosin II inhibitor we recently demonstrated potently relaxed normal detrusor smooth muscle (SM) and reports suggest varied BLEB efficacy for different SM myosin (SMM) isoforms and/or SMM vs nonmuscle myosin (NMM). We hypothesize BLEB inhibition of myosin II as a novel contraction protein targeted strategy to regulate DO. Using a surgically-induced male rat PBOO model, organ bath contractility, competitive and Real-Time-RT-PCR were performed. It was found that obstructed-bladder weight significantly increased 2.74-fold while in vitro contractility of detrusor to various stimuli was impaired ∼50% along with decreased shortening velocity. Obstruction also altered detrusor spontaneous activities with significantly increased amplitude but depressed frequency. PBOO switched bladder from a phasic-type to a more tonic-type SM. Expression of 5’ myosin heavy chain (MHC) alternatively spliced isoform SM-A (associated with tonic-type SM) increased 3-fold while 3’ MHC SM1 and essential light chain isoform MLC_17b also exhibited increased relative expression. Total SMMHC expression was decreased by 25% while the expression of NMM IIB (SMemb) was greatly increased by 4.5-fold. BLEB was found to completely relax detrusor strips from both sham-operated and PBOO rats pre-contracted with KCl, carbachol or electrical field stimulation although sensitivity was slightly decreased (20%) only at lower doses for PBOO. Thus we provide the first thorough characterization of the response of rat bladder myosin to PBOO and demonstrate complete BLEB-induced PBOO bladder SM relaxation. Furthermore, the present study provides valuable evidence that BLEB may be a novel type of potential therapeutic agent for regulation of myogenic and nerve-evoked DO in OAB.

Rho-kinase, a common final path of various contractile bladder and ureter stimuli

Normal urinary bladder function is based on the proper contraction and relaxation of smooth muscle (SM), which constitutes the majority of the bladder wall. The contraction and relaxation of all SM involves a phosphorylation-dephosphorylation pathway involving the enzymes smooth muscle myosin light chain kinase (SMMLCK) and smooth muscle myosin light chain phosphatase (SMMLCP), respectively. Although originally thought to function just as a passive opposition to SMMLCK-driven SM contraction, it is now clear that SMMLCP activity is under an extremely complex molecular regulation via which SMMLCP inhibition can induce "calcium sensitization." This review provides a thorough summary of the literature regarding the molecular regulation of the SMMLCP with a focus on one of its major inhibitory pathways that is RhoA/Rho-kinase (ROK) including its activation pathways, effector molecules, and its roles in various pathological conditions associated with bladder dysfunction. Newly emerging roles of ROK outside of SM contractility are also discussed. It is concluded that the RhoA/ROK pathway is critical for the maintenance of basal SM tone of the urinary bladder and serves as a common final pathway of various contractile stimuli in rabbits, rats, mice, and pigs as well as humans. In addition, this pathway is upregulated in response to a number of pathological conditions associated with bladder SM dysfunction. Similarly, RhoA/Rho-kinase signaling is essential for normal ureteral function and development and is upregulated in response to ureteral outlet obstruction. In addition to its critical role in bladder SM function, a role of ROK in the urothelium is also beginning to emerge as well as roles for ROK in bladder infection and invasion and metastasis of bladder cancer.

Endothelin-1-induced activation of rat renal pelvic contractions depends on cyclooxygenase-1 and Rho kinase

Upper urinary tract peristalsis is generated in the proximal renal pelvis that connects to the renal parenchyma at the pelvis-kidney junction. It may be exposed to the high renal endothelin-1 (ET-1) concentrations. Dietary NaCl restriction increases renal pelvic ET(A) receptor expression. We investigated the contribution of ET(A) and ET(B) receptors to ET-1-stimulated rat renal pelvic contractions and whether the sensitivity of renal pelvic contractile activity to ET-1 stimulation increases with dietary NaCl restriction. We tested whether ET-1-induced contractile activity depends on cyclooxygenase (COX)-1 or -2 and to what extent spontaneous as well as agonist-induced peristalsis depends on Rho kinases (ROCK). Contractions of isolated renal pelvises were investigated by myography. ET-1 concentration-dependently increased pelvic contractile activity up to 400% of basal activity. ET(A) but not ET(B) receptor blockade inhibited ET-1-induced pelvic contractions. Basal and ET-1-stimulated contractions were similar in renal pelvises from rats on a high-NaCl diet or on a NaCl-deficient diet. COX-1 inhibition reduced spontaneous and almost completely blocked the ET-1-induced pelvic contractions. ROCK inhibition reduced spontaneous and ET-1 stimulated pelvic contractile activity by 90%. RT-PCR revealed that both ROCK isoenzymes are present in the renal pelvic wall. Western blot analyses did not show increased phosphorylation of ROCK substrates myosin phosphatase target subunit 1, ezrin, radixin, and moesin in ET-1-treated isolated renal pelvises. ET-1 is a powerful ET(A) receptor-dependent activator of renal pelvic contractions. COX-1 and ROCK activity are required for the ET-1 effects on pelvic contractions, which are not significantly affected by dietary NaCl intake.

Effect of the rho-kinase inhibitor hydroxyfasudil on bladder overactivity: an experimental rat model

OBJECTIVES

To investigate the effects of the rho-kinase inhibitor hydroxyfasudil on bladder overactivity in cyclophosphamide (CYP)-induced cystitis.

METHODS

Female Sprague-Dawley rats received a single intraperitoneal injection of CYP (200 mg/kg). Four days later, bladder function was evaluated by: (i) monitoring micturition behavior in metabolic cages between hydroxyfasudil- and vehicle-treated animals; (ii) measuring changes in continuous cystometrograms in response to intravenous hydroxyfasudil under anesthesia; and (iii) conducting a functional study examining the effect of hydroxyfasudil on the concentration-response curves to carbachol in bladder tissue strips.

RESULTS

Intraperitoneal injection of hydroxyfasudil (10 mg/kg) significantly increased both the average and maximal voided volumes. Hydroxyfasudil significantly decreased the maximal detrusor pressure, whereas the intercontraction interval was not significantly affected. After administration of 0.1, 0.3, 1, and 3 microM hydroxyfasudil, the maximal contraction of the concentration-response curves to carbachol was significantly reduced to 74.5 +/- 4.2%, 55.2 +/- 5.6%, 29.4 +/- 5.6%, and 21.6 +/- 8.2% of the control values, respectively.

CONCLUSIONS

The present findings indicate that hydroxyfasudil might be a new treatment option for CYP-induced detrusor overactivity.