Mechanisms and urodynamic effects of a potent and selective EP4 receptor antagonist, MF191, on cyclophosphamide and prostaglandin E2-induced bladder overactivity in rats

PGE2 receptors in detrusor muscle: Drugging the undruggable for urgency

Overactive bladder (OAB) syndrome is a prevalent condition of the lower urinary tract that causes symptoms, such as urinary frequency, urinary urgency, urge incontinence, and nocturia, and disproportionately affects women and the elderly. Current medications for OAB merely provide symptomatic relief with considerable limitations, as they are no more than moderately effective, not to mention that they may cause substantial adverse effects. Identifying novel molecular targets to facilitate the development of new medical therapies with higher efficacy and safety for OAB is in an urgent unmet need. Although the molecular mechanisms underlying the pathophysiology of OAB largely remain elusive and are likely multifactorial, mounting evidence from preclinical studies over the past decade reveals that the pro-inflammatory pathways engaging cyclooxygenases and their prostanoid products, particularly the prostaglandin E2 (PGE₂), may play essential roles in the progression of OAB. The goals of this review are to summarize recent progresses in our knowledge on the pathogenic roles of PGE₂ in the OAB and to provide new mechanistic insights into the signaling pathways transduced by its four G-protein-coupled receptors (GPCRs), i.e., EP1-EP4, in the overactive detrusor smooth muscle. We also discuss the feasibility of targeting these GPCRs as an emerging strategy to treat OAB with better therapeutic specificity than the current medications.

EP4 receptor as a novel promising therapeutic target in colon cancer

The most prevalent malignancy that can occur in the gastrointestinal tract is colon cancer. The current treatment options for colon cancer patients include chemotherapy, surgery, radiotherapy, immunotherapy, and targeted therapy. Although the chance of curing the disease in the early stages is high, there is no cure for almost all patients with advanced and metastatic disease. It has been found that over-activation of cyclooxygenase 2 (COX-2), followed by the production of prostaglandin E2 (PGE2) in patients with colon cancer are significantly increased. The tumorigenic function of COX-2 is mainly due to its role in the production of PGE2. PGE2, as a main generated prostanoid, has an essential role in growth and survival of colon cancer cell's. PGE2 exerts various effects in colon cancer cells including enhanced expansion, angiogenesis, survival, invasion, and migration. The signaling of PGE2 via the EP4 receptor has been shown to induce colon tumorigenesis. Moreover, the expression levels of the EP4 receptor significantly affect tumor growth and development. Overexpression of EP4 by various mechanisms increases survival and tumor vasculature in colon cancer cells. It seems that the pathway starting with COX2, continuing with PGE2, and ending with EP4 can promote the spread and growth of colon cancer. Therefore, targeting the COX-2/PGE2/EP4 axis can be considered as a worthy therapeutic approach to treat colon cancer. In this review, we have examined the role and different mechanisms that the EP4 receptor is involved in the development of colon cancer.

Prostaglandin E2 and F2alpha Modulate Urinary Bladder Urothelium, Lamina Propria and Detrusor Contractility via the FP Receptor

Current pharmacological treatment options for many bladder contractile dysfunctions are not suitable for all patients, thereby bringing interest to the investigation of therapies that target a combination of receptors. This study aimed to compare responses of PGE₂ on the urinary bladder urothelium with lamina propria (U&LP, also called the bladder mucosa) or detrusor smooth muscle and attempt to identify the receptor subtypes mediating PGE₂ contractile responses in these tissues. In the presence of selective EP1 – 4 receptor antagonists, varying concentrations of PGE₂ were applied to isolated strips of porcine U&LP and detrusor that were mounted in organ baths filled with Krebs-bicarbonate solution and gassed with carbogen. The addition of PGE₂ (1 and 10 μM) and PGF_2α (10 μM) to U&LP preparations caused significant increases in the baseline tension and in the spontaneous phasic contractile frequency. In detrusor preparations, significant increases in the baseline tension were observed in response to PGE₂ (1 and 10 μM) and PGF_α (10 μM), and spontaneous phasic contractions were initiated in 83% of preparations. None of the selective PGE₂ receptor antagonists inhibited the increases in baseline tension in both U&LP and detrusor. However, the antagonism of PGF_2α receptor showed significantly inhibited contractile responses in both layers of the bladder. This study presents prostaglandin receptor systems as a potential regulator of urinary bladder contractility. The main contractile effects of PGE₂ in both U&LP and detrusor are mediated via the FP receptor with no observed contribution from any of the four EP receptors.

Stimulation of the pelvic nerve increases bladder capacity in the PGE2 cat model of overactive bladder

Selective electrical stimulation of the pudendal nerve exhibits promise as a potential therapy for treating overactive bladder (OAB) across species (rats, cats, and humans). More recently, pelvic nerve (PelN) stimulation was demonstrated to improve cystometric bladder capacity in a PGE₂ rat model of OAB. However, PelN stimulation in humans or in an animal model that is more closely related to humans has not been explored. Therefore, our objective was to quantify the effects of PGE₂ and PelN stimulation in the cat. Acute cystometry experiments were conducted in 14 α-chloralose-anesthetized adult, neurologically intact female cats. Intravesical PGE₂ decreased bladder capacity, residual volume, threshold contraction pressure, and mean contraction pressure. PelN stimulation reversed the PGE₂-induced decrease in bladder capacity and increased evoked external urethral sphincter electromyographic activity without influencing voiding efficiency. The increases in bladder capacity generated by PelN stimulation were similar in the rat and cat, but the stimulation parameters to achieve this effect differed (threshold amplitude at 10 Hz in the rat vs. twice threshold amplitude at 1 Hz in the cat). These results highlight the potential of PGE₂ as a model of OAB and provide further evidence that PelN stimulation is a promising approach for the treatment of OAB symptoms.

C-Phycocyanin Alleviates Bladder Inflammation and Dysfunction in Cyclophosphamide-Induced Cystitis in a Mouse Model by Inhibiting COX-2 and EP4

Objective

To explore the effect of C-phycocyanin (C-PC) on voiding behavior and histological changes in cyclophosphamide- (CYP-) induced cystitis in mice.

Methods

Sixty female mice were included. The mice in the C-PC group received C-PC (25 mg/kg, twice, i.p.) and then CYP (200 mg/kg, i.p.) two hours later, while the mice in the CYP group only received the equivalent CYP. Saline was injected in the mice in the control group. A voided stain on paper (VSOP) test was conducted to analyze the micturition. The bladders were harvested for histological evaluation and measurements of inflammatory factors.

Results

C-PC reduced the micturition frequency in the mice with CYP-induced cystitis. The bladder/body weight ratio and edema were remarkably higher in the CYP group compared to the C-PC group. C-PC suppressed the expressions of COX-2, PGE₂, and EP4 (prostaglandin E receptor 4) according to the ELISA assay. Immunohistochemical staining also indicated that C-PC reduced the expressions of COX-2 in urothelium and EP4 in smooth muscles.

Conclusions

C-PC relieved symptoms associated with CYP-induced cystitis in mice by inhibiting bladder inflammation through COX-2 and EP4 expression.

Further characterization of a novel EP2 and EP3 receptor dual agonist, ONO-8055, on lower urinary tract function in normal and lumbar canal stenosis rats

AIMS

To further explore the effects of a novel EP2 and EP3 dual agonist, ONO-8055, on detrusor contractility, we investigated the responses of bladder strips from sham and lumbar canal stenosis (LCS) rats to this agonist, its effects on lower urinary tract function in normal rats, and mRNA expression of EP2 and EP3 receptors in the sham and LCS rats.

METHODS

The responses of bladder strips from sham and LCS rats to ONO-8055 were measured. The effects of ONO-8055 on LUT function of normal rats were investigated with awake cystometry and intraurethral perfusion pressure (Pura) measurements. The relative mRNA of bladder and urethral tissue of the sham and LCS rats was quantified using specific probes for EP1, EP2, EP3, and EP4 genes.

RESULTS

Compared with the vehicle, the muscle tensions of both the sham and LCS rats were significantly increased after adding this agonist. On awake cystometry of normal rats, bladder capacity and Pura were decreased in the ONO-8055 groups, but a statistically significant difference in mean changes was demonstrated only between the vehicle group and the group receiving the highest dose. Compared with the sham rats, mRNA expressions of the four EP receptors in the lower urinary tract of the LCS rats did not show a statistically significant difference.

CONCLUSIONS

This agonist did not augment bladder contractility or urethral relaxation in normal rats.

The role of prostaglandin and E series prostaglandin receptor type 4 receptors in the development of bladder overactivity in a rat model of chemically induced prostatic inflammation

OBJECTIVES

To evaluate, using a rat model of non-bacterial prostatic inflammation, the prostaglandin production and expression profiles of E-series prostaglandin (EP) receptor subtypes, which are reportedly implicated in the development of overactive bladder, in the bladder mucosa, and to investigate the effect of EP receptor type 4 (EP4) blockade on bladder overactivity after prostatic inflammation.

METHODS

Male Sprague-Dawley rats were used. Prostatic inflammation was induced by formalin injection (5%; 50 μL per lobe) into the bilateral ventral lobes of the prostate. At 10 days after induction of prostatic inflammation or vehicle injection, bladder tissues from the deeply anaesthetized rats were harvested and separated into mucosal and detrusor layers. Then, prostaglandin E2 (PGE2) concentrations and protein levels of PGE2 receptors (EP1-4) in the bladder mucosa and detrusor were measured by ELISA and Western blotting, respectively. In separate groups of control and formalin-treated rats, awake cystometry was performed to evaluate the changes in bladder activity after prostatic inflammation. In addition, the effect of intravesical administration of a selective EP4 antagonist (ONO-AE3-208; 30 μm) on bladder activity was evaluated in control rats and rats with prostatic inflammation.

RESULTS

PGE2 concentration and protein levels of EP4, but not other EP receptor subtypes, in the bladder mucosa and detrusor layers were significantly increased in formalin-injected rats vs vehicle-injected control rats. In cystometry, rats with prostatic inflammation exhibited a significant decrease in intercontraction intervals (ICIs) compared with control rats. Intravesical application of ONO-AE3-208 (30 μm), but not vehicle application, significantly increased ICIs in rats with prostatic inflammation, whereas ONO-AE3-208 at this concentration did not significantly affect any cystometric values in control rats.

CONCLUSIONS

Because intravesical administration of an EP4 antagonist effectively improved bladder overactivity after prostatic inflammation, EP4 activation, along with increased PGE2 production in the bladder mucosa, seems to be an important contributing factor to bladder overactivity induced by prostatic inflammation. Thus, blockade of EP4 in the bladder could be a therapeutic approach to male lower urinary tract symptoms attributable to benign prostatic hyperplasia with prostatic inflammation.

Inhibitory Effects of Urothelium-related Factors

The urothelium of the bladder has long been recognized as a protective barrier between detrusor and urine. In recent years, it has become more evident that the urothelium plays a role as an active source of mediators. The urothelium can release neurotransmitters and modulators such as acetylcholine, ATP, nitric oxide, prostaglandins and neuropeptides. They exert both excitatory and inhibitory effects in modulating urinary tract motility. In addition, several studies have reported the existence of an urothelium-derived unknown inhibitory factor in the urinary bladder. By the use of a new serial cascade superfusion bioassay on guinea pig ureter, recent studies confirm that the guinea pig bladder urothelium releases a substance with inhibitory bioactivity, which was resistant to treatment with nitric oxide synthase inhibitor and cyclooxygenase inhibitor and to adenosine A1/A2 receptor blockade. Lately, a marked and quickly inactivated novel release of PGD₂ from the bladder urothelium was discovered, together with localization of prostaglandin D synthase therein. PGD₂ was found to have an inhibitory influence on nerve-induced contractions in guinea pig urinary bladder and on spontaneous contractions in the out-flow region. An altered release of excitatory and inhibitory factors is likely to play an important part in bladder motility disturbances, of which the prostanoids are a notable group. Due to the fact that the bladder is relaxed 99% of the time, not only excitatory mechanisms in the bladder are necessary to study, but also inhibitory mechanisms need considerable attention, which will contribute to the discovery of new targets to treat bladder motility disorders.

A Hydrogel-Based Epirubicin Delivery System for Intravesical Chemotherapy

This study aimed to examine the efficacy of epirubicin-loaded gelatin hydrogel (EPI-H) in the treatment of superficial urothelium carcinoma. Hydrogel was prepared by Schiff base-crosslinking of gelatin with glutaraldehyde. EPI-H exhibited high entrapment efficiency (59.87% ± 0.51%). EPI-H also increased epirubicin accumulation in AY-27 cells when compared with the effect of aqueous solutions of epirubicin (EPI-AQ); respective epirubicin-positive cell counts were 69.0% ± 7.6% and 38.3% ± 5.8%. EPI-H also exhibited greater cytotoxicity against AY-27 cells than that of EPI-AQ; IC50 values were 13.1 ± 1.1 and 7.5 ± 0.3 μg/mL, respectively. Cystometrograms showed that EPI-H reduced peak micturition, threshold pressures, and micturition duration, and that it increased bladder compliance more so than EPI-AQ. EPI-H enhanced epirubicin penetration into basal cells of urothelium in vivo, whereas EPI-AQ did so only to the umbrella cells. EPI-H inhibited tumor growth upon intravesical instillation to tumor-bearing bladder of F344 rats, inducing higher levels of caspase-3 expression than that observed with EPI-AQ treatment; the number of caspase-3 positive cells in treated urothelium carcinoma was 13.9% ± 4.0% (EPI-AQ) and 34.1% ± 1.0%, (EPI-H). EPI-H has value as an improved means to administer epirubicin in intravesical instillation treatments for bladder cancer.

Activation of soluble guanylyl cyclase by BAY 58-2667 improves bladder function in cyclophosphamide-induced cystitis in mice

Activators of soluble guanylyl cyclase (sGC) interact directly with its prosthetic heme group, enhancing the enzyme responsiveness in pathological conditions. This study aimed to evaluate the effects of the sGC activator BAY 58-2667 on voiding dysfunction, protein expressions of α1 and β1 sGC subunits and cGMP levels in the bladder tissues after cyclophosphamide (CYP) exposure. Female C57BL/6 mice (20-25 g) were injected with CYP (300 mg/kg ip) to induce cystitis. Mice were pretreated or not with BAY 58-2667 (1 mg/kg, gavage), given 1 h before CYP injection. The micturition patterns and in vitro bladder contractions were evaluated at 24 h. In freely moving mice, the CYP injection produced reduced the micturition volume and increased the number of urine spots. Cystometric recordings in CYP-injected mice revealed significant increases in basal pressure, voiding frequency, and nonvoiding contractions (NVCs), along with decreases in bladder capacity, intercontraction interval, and compliance. BAY 58-2667 significantly prevented the micturition alterations observed in both freely moving mice and cystometry and normalized the reduced in vitro carbachol-induced contractions in the CYP group. Reduced protein expressions of α1 and β1 sGC subunits and of cGMP levels were observed in the CYP group, all of which were prevented by BAY 58-2667. CYP exposure significantly increased reactive-oxygen species (ROS) generation in both detrusor and urothelium, and this was normalized by BAY 58-2667. The increased myeloperoxidase and cyclooxygenase-2 activities in the bladders of the CYP group remained unchanged by BAY 58-2667. Activators of sGC may constitute a novel and promising therapeutic approach for management of interstitial cystitis.

Cascade bioassay evidence for the existence of urothelium-derived inhibitory factor in Guinea pig urinary bladder

Our aim was to investigate whether guinea pig urothelium-derived bioactivities compatible with the existence of urothelium-derived inhibitory factor could be demonstrated by in vitro serial bioassay and whether purinergic P1 receptor agonists, nitric oxide, nitrite or prostaglandins might explain observed activities. In a cascade superfusion system, urothelium-denuded guinea pig ureters were used as bioassay tissues, recording their spontaneous rhythmic contractions in presence of scopolamine. Urothelium-intact or -denuded guinea pig urinary bladders were used as donor tissues, stimulated by intermittent application of carbachol before or during the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), the adenosine/P1 nucleoside receptor antagonist 8-(p-sulfophenyl)theophylline (8-PST) or the cyclo-oxygenase inhibitor diclofenac infused to bath donor and bioassay tissues. The spontaneous contractions of bioassay ureters were unaltered by application of carbachol 1-5 µM in the presence of scopolamine 5-30 µM. When carbachol was applied over the urothelium-denuded bladder, the assay ureter contraction rate was unaltered. Introducing carbachol over the everted urothelium-intact bladder significantly inhibited the contraction frequency of the assay ureter, suggesting the transfer of an inhibitory activity from the bladder to the assay ureter. The transmissible inhibitory activity was not markedly antagonized by L-NAME, 8-PST or diclofenac, while L-NAME nearly abolished nitrite release from the urothelium-intact bladder preparations. We suggest that urothelium-derived inhibitory factor is a transmissible entity over a significant distance as demonstrated in this novel cascade superfusion assay and seems less likely to be nitric oxide, nitrite, an adenosine receptor agonist or subject to inhibition by administration of a cyclo-oxygenase inhibitor.

Effects of sensory neuron-specific receptor agonist on bladder function in a rat model of cystitis induced by cyclophosphamide

PURPOSE

To investigate the effects of activation of sensory neuron-specific receptors (SNSRs) on cyclophosphamide (CYP) bladder overactivity in rats.

METHODS

Female Sprague-Dawley rats (235-258 g) were used. Rats were injected with either CYP (200 mg/kg, intraperitoneally) or saline (control). Continuous cystometrograms (0.04 ml/min) were recorded 48 h after CYP or saline injection under urethane anesthesia. After stable micturition cycles were established, a selective rat SNSR1 agonist, bovine adrenal medulla 8-22 (BAM8-22), was administered intravenously or intrathecally.

RESULTS

Cyclophosphamide treatment-induced higher baseline pressure and shorter intercontraction intervals compared with the control group. Intravenous administration of BAM8-22 at 10, 30 and 100 μg/kg significantly increased intercontraction intervals in the CYP-treated group. Intrathecal administration of BAM8-22 at 0.03, 0.1 and 0.3 μg also significantly increased intercontraction intervals in the CYP-treated group. Intravenous or intrathecal administration of BAM8-22 did not change baseline pressure or maximum voiding pressure in the CYP-treated group.

CONCLUSIONS

These findings indicate that activation of SNSRs can suppress CYP-induced bladder overactivity, probably due to suppression of bladder afferent activity.

E-type prostanoid receptor 4 (EP4) in disease and therapy

The large variety of biological functions governed by prostaglandin (PG) E2 is mediated by signaling through four distinct E-type prostanoid (EP) receptors. The availability of mouse strains with genetic ablation of each EP receptor subtype and the development of selective EP agonists and antagonists have tremendously advanced our understanding of PGE2 as a physiologically and clinically relevant mediator. Moreover, studies using disease models revealed numerous conditions in which distinct EP receptors might be exploited therapeutically. In this context, the EP4 receptor is currently emerging as most versatile and promising among PGE2 receptors. Anti-inflammatory, anti-thrombotic and vasoprotective effects have been proposed for the EP4 receptor, along with its recently described unfavorable tumor-promoting and pro-angiogenic roles. A possible explanation for the diverse biological functions of EP4 might be the multiple signaling pathways switched on upon EP4 activation. The present review attempts to summarize the EP4 receptor-triggered signaling modules and the possible therapeutic applications of EP4-selective agonists and antagonists.