Early sequential changes in bladder function after partial bladder outlet obstruction in awake sprague-dawley rats: focus on the decompensated bladder

Is bladder outlet obstruction rat model to induce overactive bladder (OAB) has similarity to human OAB? Research on the events in smooth muscle, collagen, interstitial cell and telocyte distribution

BACKGROUND

Cellular and cytoskeletal events of overactive bladder (OAB) have not been sufficiently explored in human bladder due to different limitations. Bladder outlet obstruction (BOO) had been induced in different animal models with different methods to induce (OAB). Similarity of the animal models of BOO to the human OAB is postulated but has not been confirmed. The interstitial cells of Cajal (ICCs), and telocytes (TCs) are an important players in smooth muscles conductivity, they had not been well investigated in the previous BOO models. Objectives are to investigate the morphological pattern of cellular, cytoskeleton and telocytes distribution in BOO rat model and to match the events in two time periods and compare it to the findings in real-world human OAB.

METHODS

Female Sprague-Dawley rats (Rattus norvegicus) were randomly divided into: sham (n = 10), BOO 6 W (n = 10), BOO 8 W (n = 10). Operative procedure to Induce BOO was done under anesthesia with intraperitoneal Ketamine administration. The Effect of induction of BOO was evaluated after 6 and 8 weeks. The rats were anesthetized, and the urinary bladder was removed, while the rat was unconscious under anaesthesia it was transferred to the inhalation anaesthesia cage for euthanasia, rats were sacrificed under light anesthesia using isoflurane. Care of animals, surgical procedure, and euthanasia adhered to Guide for the Care and Use of Laboratory Animals, and AVMA Guidelines for the Euthanasia of Animals. The retrieved bladder was processed for examination with histopathology, immunohistochemistry (IHC), and transmission electron microscopy (EM).

RESULTS

Histological examination of the bladder shows thinner urothelium, condensation of collagen between muscle bundles. IHC with c-kit shows the excess distribution of ICCs between smooth muscle bundles. EM shows frequent distribution of TCs that were situated between collagen fibers. Finings in BOO 6 W group and BOO 8 W group were comparable.

CONCLUSION

The animal model study demonstrated increased collagen/ smooth muscle ratio, high intensity of ICCs and presence of TCs. Findings show that a minimally invasive procedure to induce BOO in rats had resulted in an OAB that has morphological changes that were stable in 6 & 8 weeks. We demonstrated the distribution of TCs and ICCs in the rat animal model and defined them. The population of TCs in the BOO rat model is described for the first time, suggests that the TCs and ICCs may contribute to the pathophysiology of OAB. Similarity of animal model to human events OAB was demonstrated. These findings warrant further study to define the role of TCs in OAB.

CLINICAL TRIAL REGISTRY

The study does not require a clinical trial registration; it is an experimental animal study in basic science and does not include human subjects.

Excitatory purinergic and cholinergic expression changed in a partial bladder outlet obstruction-induced overactive bladder rat model

Overactive bladder (OAB) is a common, long-term symptom complex with a high prevalence in women worldwide. OAB has caused a social burden, and effective treatments are urgently needed. However, the pathogenesis of OAB has yet to be elucidated. Model rats underwent bladder outlet obstruction surgery. In the 2nd, 3rd, and 4th weeks after surgery, metabolic cages were used to detect the 12 h urine volume of rats in the sham and model groups. The urodynamic parameters bladder leak point pressure (BPLL), maximum voiding pressure (MVP), residual volume (RV), maximum bladder capacity (MBC), bladder compliance (BC), voided efficiency (VE), and non-voiding contractions (NVCs) were also detected. Moreover, the contractile responses of isolated detrusor muscles to electrical and carbachol stimulation were examined at the abovementioned time points. At the 4th week after surgery, the bladders of both groups were obtained for hematoxylin-eosin (H&E) and Masson's trichrome staining. Real-time qPCR and Western blot were performed to quantify the expression of choline acetyltransferase (ChAT) and solute carrier family 17 member 9 (SLC17A9). At week 4, compared with the sham group, the 12 h urine volume of PBOO group increased significantly. The BLPP, MVP, VE, MBC, and NVCs increased significantly, and the VE was significantly reduced in 4-week PBOO group. The contractile responses of isolated detrusor muscles to electrical and carbachol stimulation significantly increased in 4-week PBOO group. In the 4-week PBOO group, the bladder wall and the ratio of bladder muscle to collagen within the bladder smooth muscle layer wall were significantly higher than those in the sham group. ChAT and SLC17A9 mRNA and protein expression in the OAB model rats significantly increased. At 4 weeks after PBOO, the OAB model was successfully established. The gene and protein expression levels of ChAT and SLC17A9 increased in the bladder of the OAB model, suggesting that OAB may be related to increased excitatory purinergic and cholinergic expression.

Ejaculatory Duct Obstruction Affects Seminal Vesicle Contractile Efficacy and Smooth Muscle Ultrastructure in a Rat Model

The purpose of this study was to investigate the effects of ejaculatory duct obstruction (EDO) on contractile efficacy, smooth muscle ultrastructure, and α1A and M3 receptors of rat seminal vesicles (SVs). A total of 48 male rats, aged 14-15 weeks, were randomly divided into three groups, namely, the control, complete EDO, and partial EDO. SV tissues were collected at 4 and 8 weeks postoperatively for further experiments. Results revealed a marked reduction in SV contractile efficacy over time following obstruction in the complete EDO group. The contractile force and frequency decreased and increased in the partial EDO group at week 4, respectively, whereas contractile efficacy significantly reduced at week 8. Moreover, obstruction resulted in significant downregulation in expression of α1A and M3 proteins and mRNAs in rats from the complete EDO group over time. Rats in the partial EDO group initially exhibited an increase followed by a decrease. Analysis of the ultrastructure of SV smooth muscles confirmed the above changes. In conclusion, complete EDO can lead to a progressive decrease in contractile efficiency of SVs. On the other hand, partial EDO can first compensate for the contraction of SVs and gradually decompensate afterwards.

Urethral meatus stricture BOO stimulates bladder smooth muscle cell proliferation and pyroptosis via IL‑1β and the SGK1‑NFAT2 signaling pathway

Bladder outlet obstruction (BOO), which is primarily caused by benign prostatic hyperplasia, is a common chronic disease. However, previous studies have most commonly investigated BOO using the acute obstruction model. In the present study, a chronic obstruction model was established to investigate the different pathological alterations in the bladder between acute and chronic obstruction. Compared with chronic obstruction, acute obstruction led to increased expression of proliferating cell nuclear antigen and interleukin-1β, which are markers of proliferation and inflammation, respectively. Furthermore, increased fibrosis in the bladder at week 2 was observed. Low pressure promoted mice bladder smooth muscle cell (MBSMC) proliferation, and pressure overload inhibited cell proliferation and increased the proportion of dead MBSMCs. Further investigation using serum/glucocorticoid regulated kinase 1 (SGK1) small interfering RNAs indicated that low pressure may promote MBSMC proliferation by upregulating SGK1 and nuclear factor of activated T-cell expression levels. Therefore, the present study suggested that acute obstruction led to faster decompensation of bladder function and chronic bladder obstruction displayed an enhanced ability to progress to BOO.

β-Adrenoceptor signaling regulates proliferation and contraction of human bladder smooth muscle cells under pathological hydrostatic pressure

BACKGROUND

Partial bladder outlet obstruction (PBOO) promotes bladder detrusor hyperplasia, increases bladder pressure, and decreases bladder compliance. To extensively explore its underlying mechanism, our study aimed to investigate the effect of pathological hydrostatic pressure on human bladder smooth muscle cell (hBSMC) proliferation and contraction through β-adrenoceptor (ADRB) signaling in vitro.

METHODS

hBSMCs were subjected to pathological hydrostatic pressure (100 cm H₂ O) to investigate the effect of ADRBs on the proliferation and contraction of hBSMCs treated with its agonists and/or antagonists.

RESULTS

Firstly, exposure to 100 cm H₂ O hydrostatic pressure significantly upregulated the expression of α-smooth muscle actin (α-SMA) in hBSMCs at 6 hours, and promoted cell proliferation at 24 hours. When subjected to hydrostatic pressure alone, hBSMCs treated with ADRB2 and ADRB3 agonists for 6 hours inhibited α-SMA expression compared with untreated cells. By contrast, hBSMCs treated with ADRB2 agonists for 24 hours suppressed cell proliferation compared with untreated cells. The two classical pathways of ADRB, protein kinase A (PKA), and exchange factor directly activated by cAMP (EPAC) inhibited the contraction of hBSMCs under hydrostatic pressure via regulating mothers against decapentaplegic homolog 2 (SMAD2) activity. The proliferation of hBSMCs was mainly regulated by the EPAC pathway through extracellular signal-regulated kinase 1/2 (ERK1/2) activity.

CONCLUSION

The contraction of hBSMCs under hydrostatic pressure was regulated by ADRB2 and ADRB3 via the PKA/EPAC-SMAD2 pathway, and the proliferation of hBSMCs was regulated by ADRB2 via the EPAC-ERK1/2 pathway. Compared with ADRB3, ADRB2 played a predominant role under pathological hydrostatic pressure. These findings markedly uncovered the underlying mechanism of ADRBs in PBOO and provided new insights into the efficient treatment of patients with PBOO.

AMPK Alters Detrusor Contractility During Emptying in Normal Bladder and Hypertrophied Bladder with Partial Bladder Outlet Obstruction via CaMKKβ

AMP-activated protein kinase (AMPK) has been implicated in contractility changes in bladders with partial bladder outlet obstruction (PBOO), but the role of AMPK in the contractile response of normal bladder remains unclear. We investigated the phosphorylation of AMPKα and expression of the involved upstream AMPK kinases (AMPKKs) in a model of bladders with PBOO and sought to determine whether the pharmacological inhibition of these two factors affected detrusor contractility in normal bladders, using female Sprague–Dawley rats. Cystometry and Western blot analysis were performed in rats that were subjected to PBOO induction or a sham operation. Cystometry was performed in normal rats that received selective inhibitors of AMPKα and Ca²⁺/calmodulin-dependent protein kinase kinase (CaMKKβ) (compound C and STO-609, respectively) at doses determined in the experiments. In the PBOO bladders, bladder weight and micturition pressure (MP) were higher and AMPKα phosphorylation (T172) and CaMKKβ expression was significantly reduced. Compound C and STO-609 increased MP. The increased contractile response in bladders with PBOO-induced hypertrophy was related to decreased CaMKKβ/AMPK signaling activity, and the pharmacological inhibition of this pathway in normal bladders increased detrusor contractility, implying a role of CaMKKβ/AMPK signaling in the bladder in the regulation of detrusor contractility.

The preventive effect of a free radical scavenger on oxidative stress after the relief of partial bladder outlet obstruction in a rat model

Aims

To investigate the effect of a free radical scavenger (tempol) after relief of partial bladder outlet obstruction (pBOO) on bladder function in a rat model.

Methods

pBOO was induced in 50 eight-week-old female Sprague-Dawley rats and relieved 3 weeks later. The rats were divided randomly into 5 groups: sham-operated, tempol-treated for 1 week (Treat-1w) or 3 weeks (Treat-3w), and no treatment for 1 week (nonTreat-1w) or 3 weeks (nonTreat-3w). Awaken cystometrograms were obtained 1 or 3 weeks after relief according to the grouping. The bladders were isolated and weighed. H&E, Masson’s trichrome and TUNEL staining were used to analyze histological changes. The oxidative stress assessed using malondialdehyde. The expression of beta-3 adrenoreceptor was examined by Western blotting.

Results

The tempol-treated groups exhibited a significant decrease in the number of non-voiding contractions per voiding cycle (nonTreat-1w vs. Treat-1w, 1.18±0.82 vs. 0.36±0.40, P = 0.010; nonTreat-3w vs. Treat-3w, 1.51±0.69 vs. 0.23±0.25, P = 0.002). The thickness and collagen fiber deposition of the detrusor muscle layer was significantly decreased in the treated groups. Apoptosis detected was mainly observed in the urothelial cell layer, although the rate of apoptosis was significantly decreased in the treated groups (48.9±3.36% vs. 32.7±11.10%, P = 0.024; 25.8±4.67% vs. 15.7±9.83%, P = 0.314). The tempol-treated groups showed significant decreases in the MDA concentrations at both 1 and 3 weeks after relief. The expression of the beta-3 adrenoreceptor was increased in the tempol-treated rats.

Conclusions

Ischemic reperfusion injury after relief of pBOO caused histological and functional changes in the bladder. Free radical scavenger treatment prevented this oxidative stress.

Voided volumes predict degree of partial bladder outlet obstruction in a murine model

The partial bladder outlet obstruction animal model (pBOO) is commonly used as a model for obstructive uropathy. Unfortunately, pBOO demonstrates variable degrees of obstruction requiring bladder weight (BW) or urodynamic studies to determine true obstruction. Our objective is to identify extent of obstruction by correlating early post-operative Void Stains on Paper (VSOP) assays with ultimate BW in mice. pBOO was performed on 32 mice 1- and 4-week VSOPs were quantified for mean voided volume (mVV). At 4 weeks, bladders were harvested and weighed. Correlation was evaluated through bivariate kernel density estimation and a Pearson correlation coefficient (SAS). Single variable histogram of the data established groups based on BWs and mVV. mVV's and bladder weights within group pairings were averaged and plotted to render a non-linear regression model. A significant correlation was found between 1-week mVVs and 4-week BWs upon bivariate analysis with a correlation coefficient of -0.758 (p = 0.0294). A non-linear regression of plotted data defined a statistically significant fit equation correlating 1-week mVV to 4-week BW. We demonstrate a novel method for forecasting degree of obstruction in pBOO based on 1-week post-operative VSOP mVV.

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.

Nerve-sparing Mid-urethral Obstruction (NeMO) in Female Small Rodents

Partial bladder outlet obstruction (pBOO) has a high prevalence, causes significant patient burden, and immense health care costs. The most common animal model to investigate bladder remodeling in pBOO are female rodents undergoing partial obstruction at the proximal urethra. Variability in the degree of obstruction and animal mortality are major concerns with proximal obstruction. Furthermore, dissecting around the proximal urethra and bladder neck jeopardizes bladder innervation. We developed a nerve-sparing mid-urethral obstruction (NeMO) model for pBOO avoiding the disadvantages of the traditional model. We approached the urethra just inferior to the pubic symphysis, which obviated the need for laparotomy as well as for dissection in this area; also, the striated urethral sphincter remained untouched. We performed NeMO in female Sprague-Dawley rats (12 obstructions, 6 sham animals) as well as in female C57/bl6 mice (20 obstructions, 18 sham animals). After two weeks, we evaluated bladder function, bladder mass, and body mass. We had no mortalities among obstructed- or sham-operated female rats; as described for the traditional proximal pBOO-method, we tied the suture around the proximal urethra and a temporarily placed 0.9 mm metal rod. NeMO induced an 85% increase in bladder mass after two weeks, average residual urine volume was 0.4 mL in partially obstructed rats while only 0.03 mL in sham animals. In mice, we tested 3 sizes of cannulas that we placed along the urethra when tying the suture. We found that using a 27-gauge cannula resulted in over 50% animal mortality; placing the 25-gauge cannula did not yield the desired response in increasing bladder mass; utilizing a 26-gauge cannula yielded favorable results with minimal animal mortality (1/8) yet a significant 2-fold increase in bladder mass.

The NLRP3 Inflammasome Mediates Inflammation Produced by Bladder Outlet Obstruction

PURPOSE

While bladder outlet obstruction is well established to elicit an inflammatory reaction in the bladder that leads to overactive bladder and fibrosis, little is known about the mechanism by which this is initiated. NLRs (NOD-like receptors) and the structures that they form (inflammasomes) have been identified as sensors of cellular damage, including pressure induced damage, and triggers of inflammation. Recently we identified these structures in the urothelium. In this study we assessed the role of the NLRP3 (NACHT, LRR and PYD domains-containing protein 3) inflammasome in bladder dysfunction resulting from bladder outlet obstruction.

MATERIALS AND METHODS

Bladder outlet obstruction was created in female rats by inserting a 1 mm outer diameter transurethral catheter, tying a silk ligature around the urethra and removing the catheter. Untreated and sham operated rats served as controls. Rats with bladder outlet obstruction were given vehicle (10% ethanol) or 10 mg/kg glyburide (a NLRP3 inhibitor) orally daily for 12 days. Inflammasome activity, bladder hypertrophy, inflammation and bladder function (urodynamics) were assessed.

RESULTS

Bladder outlet obstruction increased urothelial inflammasome activity, bladder hypertrophy and inflammation, and decreased voided volume. Glyburide blocked inflammasome activation, reduced hypertrophy and prevented inflammation. The decrease in voided volume was also attenuated by glyburide mechanistically as an increase in detrusor contraction duration and voiding period.

CONCLUSION

Results suggest the importance of the NLRP3 inflammasome in the induction of inflammation and bladder dysfunction secondary to bladder outlet obstruction. Arresting these processes with NLRP3 inhibitors may prove useful to treat the symptoms that they produce.

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.

Cystometric parameters and the activity of signaling proteins in association with the compensation or decompensation of bladder function in an animal experimental model of partial bladder outlet obstruction

We conducted this study to determine whether the degree of detrusor contractility is associated with the compensation or decompensation of bladder function depending on the residual volume (RV) during the first two weeks after the onset of partial bladder outlet obstruction (BOO). Moreover, we also examined whether the degree of the phosphorylation and expression of signaling proteins [AMP-activated kinase (AMPK), extracellular signal‑regulated protein kinases 1 and 2 (ERK1/2) and protein kinase C (PKC)] is associated with the prevalence of compensation or decompensation of bladder function. Twenty-seven female Sprague-Dawley (SD) rats were randomly assigned to either the sham-operated group (n=7) or the group with partial bladder outlet obstruction (BOO) (n=20). We then measured cystometric parameters from three reproducible micturition cycles and averaged the results for a comparison between the two groups. Based on a cut-off value of a mean RV% of 25%, we subdivided our experimental animals into two subgroups: the subgroup with bladder compensation (mean RV%, <25%) and the subgroup with bladder decompensation (mean RV%, >25%). Our results indicated that the degree of detrusor overactivity (DO) was associated with the compensation or decompensation of bladder function depending on the RV during the first two weeks after the onset of BOO in an animal experimental model of partial BOO. Moreover, we also demonstrate that AMPK and ERK1/2 are involved in the compensation or decompensation of bladder function. Furthermore, our results suggest that PKC is not involved in two-phase bladder contraction. Alterations in the activities of signaling proteins, such as AMPK and ERK1/2 may prove to be helpful in the treatment of patients with voiding difficulty.