Succinate decreases bladder function in a rat model associated with metabolic syndrome

Emerging therapies for overactive bladder: preclinical, phase I and phase II studies

INTRODUCTION

Overactive bladder syndrome is a common chronic condition with a significant impact on quality of life and economic burden. Persistence with pharmacologic therapy has been limited by efficacy and side effects. A greater understanding of the pathophysiology of overactive bladder has led to the initial evaluation of several drugs affecting ion channels, the autonomic nervous system, and enzymes which may provide useful alternatives for the management of overactive bladder.

AREAS COVERED

A comprehensive review was performed using PubMed and Cochrane databases as well as reviewing clinical trials in the United States. The current standard of care for overactive bladder will be discussed, but this paper focuses on investigational drugs currently in preclinical studies and phase I and II clinical trials.

EXPERT OPINION

Current therapies for overactive bladder have limitations in efficacy and side effects. A greater understanding of the pathophysiology of overactive bladder has identified the role(s) of other pathways in the overactive bladder syndrome. Targeting alternative pathways including ion channels and enzymes may provide alternative therapies of overactive bladder and a more tailored approach to the management of overactive bladder.

Vinpocetine Ameliorates Metabolic-Syndrome-Associated Bladder Overactivity in Fructose-Fed Rats by Restoring Succinate-Modulated cAMP Levels and Exerting Anti-Inflammatory Effects in the Bladder Detrusor Muscle

Succinate and its receptor, the G protein-coupled receptor 91 (GPR91), have pathological implications in metabolic syndrome (MetS) and its associated bladder dysfunction, particularly in decreasing bladder cAMP levels and promoting proinflammation. Using fructose-fed rats (FFRs), a rat model of MetS, we investigate the effects of vinpocetine (a phosphodiesterase-1 inhibitor) and celecoxib (a selective cyclooxygenase-2 inhibitor) on MetS-associated bladder overactivity. Phenotypes of the overactive bladder, including increased micturition frequency and a shortened intercontractile interval in cystometry, were observed in FFRs, together with elevated succinate levels in the liver and serum and the downregulation of GPR91 in the liver and urinary bladder. Treatments with vinpocetine and celecoxib improved tissue fibrosis and ameliorated the overexpression of the inflammatory cytokines, such as IL-1β, in the liver and bladder. In bladder organ bath studies, vinpocetine, but not celecoxib, treatment restored the contraction and relaxation responses of the detrusor muscle strip in response to KCl, carbachol, and forskolin stimulation. At a molecular level, vinpocetine and celecoxib treatments modulated the downstream messengers of GPR91 (i.e., ERK1/2 and JNK), suppressed NF-κB and IL-1β expressions in the bladder, and prevented the fibrogenesis observed in FFRs. The exogenous application of succinate to a bladder organ bath significantly reduced the forskolin-induced cAMP production by the detrusor muscle, which was notably restored in the presence of vinpocetine. Together, these results suggest that vinpocetine may alleviate the MetS-associated bladder overactivity by restoring the succinate-modulated detrusor cAMP production and exerting the anti-inflammatory effects in the bladder detrusor muscle.

Metabolic Syndrome and Overactive Bladder Syndrome May Share Common Pathophysiologies

Metabolic syndrome (MetS) is defined by a group of cardiovascular risk factors, including impaired glucose tolerance, central obesity, hypertension, and dyslipidemia. Overactive bladder (OAB) syndrome consists of symptoms such as urinary urgency, frequency, and nocturia with or without urge incontinence. The high prevalences of metabolic syndrome (MetS) and overactive bladder (OAB) worldwide affect quality of life and cause profound negative impacts on the social economy. Accumulated evidence suggests that MetS might contribute to the underlying mechanisms for developing OAB, and MetS-associated OAB could be a subtype of OAB. However, how could these two syndromes interact with each other? Based on results of animal studies and observations in epidemiological studies, we summarized the common pathophysiologies existing between MetS and OAB, including autonomic and peripheral neuropathies, chronic ischemia, proinflammatory status, dysregulation of nutrient-sensing pathways (e.g., insulin resistance at the bladder mucosa and excessive succinate intake), and the probable role of dysbiosis. Since the MetS-associated OAB is a subtype of OAB with distinctive pathophysiologies, the regular and non-specific medications, such as antimuscarinics, beta-3 agonist, and botulinum toxin injection, might lead to unsatisfying results. Understanding the pathophysiologies of MetS-associated OAB might benefit future studies exploring novel biomarkers for diagnosis and therapeutic targets on both MetS and OAB.

Osr1 Is Required for Mesenchymal Derivatives That Produce Collagen in the Bladder

The extracellular matrix of the bladder consists mostly of type I and III collagen, which are required during loading. During bladder injury, there is an accumulation of collagen that impairs bladder function. Little is known about the genes that regulate production of collagens in the bladder. We demonstrate that the transcription factor Odd-skipped related 1 (Osr1) is expressed in the bladder mesenchyme and epithelium at the onset of development. As development proceeds, Osr1 is mainly expressed in mesenchymal progenitors and their derivatives. We hypothesized that Osr1 regulates mesenchymal cell differentiation and production of collagens in the bladder. To test this hypothesis, we examined newborn and adult mice heterozygous for Osr1, Osr1^+/−. The bladders of newborn Osr1^+/− mice had a decrease in collagen I by western blot analysis and a global decrease in collagens using Sirius red staining. There was also a decrease in the cellularity of the lamina propria, where most collagen is synthesized. This was not due to decreased proliferation or increased apoptosis in this cell population. Surprisingly, the bladders of adult Osr1^+/− mice had an increase in collagen that was associated with abnormal bladder function; they also had a decrease in bladder capacity and voided more frequently. The results suggest that Osr1 is important for the differentiation of mesenchymal cells that give rise to collagen-producing cells.

Adaptation to partial urethral obstruction in healthy aging LOU rats and the role of nerve growth factor signaling pathway in the bladder

AIM

Aging is associated with poor ability to adapt to stress and abnormal nerve growth factor (NGF) profile. Lower urinary tract symptoms frequently disturb the quality of life of the aging population with no optimal treatment for both genders. The aim of the study was to compare the bladder response to bladder outflow obstruction in young and old LOU rats, a model of healthy aging that does not develop insulin resistance, and its relation to proNGF/NGF imbalance.

METHODS

6- and 36-month-old female LOU rats were subjected to partial bladder urethral obstruction (PUO) for 2 weeks. Morphometric parameters (body and bladder weight) and glycemia were evaluated. Cystometry was carried out to measure functional parameters followed by ex vivo assessment of muscle strip contractile characteristics. Tissue proteins were examined by immunoblotting and morphology was examined by microscopy.

RESULTS

Body weight and glycaemia were not affected by surgery. PUO increases significantly bladder weight with increased thickness and fibrosis of the bladder wall as revealed by histological examination in both age groups. Cystometry showed that old PUO rats had a significant reduction in the intercontraction interval and the bladder capacity, a pattern opposite to young rats with PUO. Contractile properties of bladder strip were not affected by age or PUO. On the molecular level, the old rats had lower abundance of the mature NGF relative to proNGF, with signs of p75^NTR activation suggested by the higher expression of TNF-α and JNK phosphorylation in the bladder tissue.

CONCLUSION

Bladder adaptation to PUO occurs only in young LOU rats to maintain efficient bladder contractility. Old LOU rats display proNGF/NGF imbalance and the associated p75^NTR activation. This can further induce tissue damage and degeneration through activation of JNK pathway and release of TNF-α which in turn interferes with the necessary bladder adaptation.

Receptor GPR91 contributes to voiding function and detrusor relaxation mediated by succinate

AIM

Succinate activates the receptor GPR91 identified in the bladder. The present study aims to unravel the mechanisms of bladder relaxation by succinate and how the receptor is involved in structural and functional changes of the bladder.

METHODS

Physiological recordings of bladder function were carried out by cystometry and organ bath from C57BL/6 mice, homozygous GPR91^-/- mice, and Sprague-Dawley (SD) rats. GPR91 expression was confirmed by polymerase chain reaction and tissue morphology was examined by light (Masson trichrome) and fluorescence microscopy. Nitric oxide (NO) and ATP secretion were measured.

RESULTS

Bladders of GPR91 KO mice had a greater mass to body weight ratio with a thicker bladder wall compared to C57BL/6 mice. They also displayed increased basal and maximal bladder pressures, and decreased intercontraction intervals, bladder capacity, micturition volume, and compliance. During cystometry, bladders of SD rats and C57BL/6 mice instilled with succinate (10 mM) showed signs of relaxation while bladders of GPR91 KO mice were unresponsive. Similarly, in organ bath, succinate relaxed bladder strips preincubated with carbachol, except GPR91 KO ones. Relaxation was stronger in the presence of urothelium and independent of NO synthesis. Bladder strips from all mice groups showed similar responses to KCl, carbachol, and electrical stimulation. In vitro, succinate increased NO secretion in urothelial cell culture of both C57BL6 and GPR91 KO mice while ATP secretion was potently decreased by succinate in C57BL6 culture only.

CONCLUSION

Succinate through GPR91 is essential to bladder structure and contraction. GPR91 relaxes the detrusor partially by decreasing urothelial ATP secretion.

Construction and application of urinary system model with functional bladder module

In order to study the construction and application of urinary system model with functional bladder module, bladder model was designed, and appropriate materials was selected to make it, and its performance was studied. The results showed that in the analysis of pressure performance of bladder model, more detrusor instability was found in the model than in the urodynamic test, and there was significant statistical difference (P < 0.01). In the analysis of bladder safety capacity, it was found that the bladder safety capacity in the model was much larger than that measured by urodynamics, and there was significant statistical difference (P < 0.01). In the analysis of detrusor workmanship and contraction rate, it was found that the normal model group was significantly smaller than the obstruction group, and there was significant statistical difference (P < 0.01). Comparing the detrusor contraction rate of the two groups, it was found that the normal group and the obstruction group had significant difference at t3, and there was no statistical difference between the other two groups. Therefore, through this study, it is found that the understanding of urinary system can be enhanced by building bladder model, and the basic operating skills of medical staff can be improved more easily by using bladder model, which achieves the expected results of the experiment. Although some shortcomings have been found in the course of the study, it still provides experimental reference for the clinical study of bladder in the future.

Urinary metabolomics predict the severity of overactive bladder syndrome in an aging female population

INTRODUCTION AND HYPOTHESIS

To identify urinary metabolites that can facilitate the diagnosis and the characterization of the underlying pathophysiology of the association between the overactive bladder syndrome (OAB) and metabolic syndrome.

METHODS

We used gas chromatography-mass spectrometry to compare the urinary metabolome of 20 females of 50-80 years of age with OAB to that of 20 controls of the same age group. We performed urinary metabolomic analysis and obtained serum markers of metabolic syndrome for each subject. Participants completed a clinical evaluation and validated self-reported questionnaires of lower urinary tract symptoms as well as a one-day voiding diary.

RESULTS

In the OAB subjects, we identified increased urinary levels of markers of mitochondrial dysfunction (itaconate, malate and fumarate), oxidative stress (L-pyroglutamate and α-hydroxyglutarate) and ketosis (α-hydroxybutyrate and α-hydroxyisobutyrate). The increased levels of these markers correlated significantly with the OAB symptoms score on questionnaires. We found, using a multiple linear regression model, that age, blood glucose and urine metabolites (malate, fumarate and α-hydroxyisobutyrate) were significant predictive factors of OAB severity. Fumarate had high sensitivity as a biomarker of OAB due to metabolic syndrome, based on a statistically significant receiver-operating characteristic (ROC) curve, indicating its potential as a diagnostic tool.

CONCLUSIONS

Altogether, these findings establish that urinary metabolites of mitochondrial dysfunction, ketosis and oxidative stress can be potential biomarkers of OAB severity and diagnosis.

Sorafenib-loaded PAMAM dendrimer attenuates liver fibrosis and its complications in bile-duct-ligated rats

We assessed the effect of sorafenib-loaded polyamidoamine (PAMAM) dendrimer on liver fibrosis induced by bile duct ligation (BDL). Male Wistar rats were divided into 9 groups: intact, sham, DMSO + BDL, BDL, sorafenib (30 mg/kg), sorafenib (60 mg/kg), PAMAM + BDL, sorafenib (30 mg/kg) + PAMAM + BDL, sorafenib (60 mg/kg) + PAMAM + BDL. BDL was induced and then rats were treated daily with sorafenib and (or) PAMAM for 4 weeks. Improvement of liver was detected via assessment of ascites formation, collagen deposition, liver blood flow, vascular endothelial growth factor level, and blood cells count. Sorafenib-loaded PAMAM dendrimer in both 30 and 60 mg/kg doses reduced ascites formation, reduced collagen deposition, and improved drug-induced hematological side effects of sorafenib alone in comparison with sorafenib-alone treatment. Sorafenib-loaded PAMAM dendrimer increased liver blood flow compared with sorafenib-received groups. Sorafenib-loaded PAMAM dendrimer reduced BDL-induced liver injury compared with sorafenib-received groups. Moreover, sorafenib-loaded PAMAM dendrimer decreased vascular endothelial growth factor level in serum and liver tissue in comparison with sorafenib-received groups. Sorafenib-loaded PAMAM dendrimer profoundly improved the therapeutic effects of sorafenib in BDL rats.

Beta-3 Adrenoceptor Signaling Pathways in Urothelial and Smooth Muscle Cells in the Presence of Succinate

Succinate, an intermediate metabolite of the Krebs cycle, can alter the metabolomics response to certain drugs and controls an array of molecular responses in the urothelium through activation of its receptor, G-protein coupled receptor 91 (GPR91). Mirabegron, a β3-adrenergic receptor (β3-AR) agonist used to treat overactive bladder syndrome (OAB), increases intracellular cAMP in the detrusor smooth muscle cells (SMC), leading to relaxation. We have previously shown that succinate inhibits forskolin-stimulated cAMP production in urothelium. To determine whether succinate interferes with mirabegron-mediated bladder relaxation, we examined their individual and synergistic effect in urothelial-cell and SMC signaling. We first confirmed β3-AR involvement in the mirabegron response by quantifying receptor abundance by immunoblotting in cultured urothelial cells and SMC and cellular localization by immunohistochemistry in rat bladder tissue. Mirabegron increased cAMP levels in SMC but not in urothelial cells, an increase that was inhibited by succinate, suggesting that it impairs cAMP-mediated bladder relaxation by mirabegron. Succinate and mirabegron increased inducible nitric oxide synthesis and nitric oxide secretion only in urothelial cells, suggesting that its release can indirectly induces SMC relaxation. Succinate exposure decreased the expression of β3-AR protein in whole bladder in vivo and in SMC in vitro, indicating that this metabolite may lead to impaired pharmacodynamics of the bladder. Together, our results demonstrate that increased levels of succinate in settings of metabolic stress (e.g., the metabolic syndrome) may lead to impaired mirabegron and β3-AR interaction, inhibition of cAMP production, and ultimately requiring mirabegron dose adjustment for its treatment of OAB related to these conditions.