Concomitant alteration in number and affinity of P2X and muscarinic receptors are associated with bladder dysfunction in early stage of diabetic rats

Methylglyoxal and Advanced Glycation End Products (AGEs): Targets for the Prevention and Treatment of Diabetes-Associated Bladder Dysfunction?

Methylglyoxal (MGO) is a highly reactive α-dicarbonyl compound formed endogenously from 3-carbon glycolytic intermediates. Methylglyoxal accumulated in plasma and urine of hyperglycemic and diabetic individuals acts as a potent peptide glycation molecule, giving rise to advanced glycation end products (AGEs) like arginine-derived hydroimidazolone (MG-H1) and carboxyethyl-lysine (CEL). Methylglyoxal-derived AGEs exert their effects mostly via activation of RAGE, a cell surface receptor that initiates multiple intracellular signaling pathways, favoring a pro-oxidant environment through NADPH oxidase activation and generation of high levels of reactive oxygen species (ROS). Diabetic bladder dysfunction is a bothersome urological complication in patients with poorly controlled diabetes mellitus and may comprise overactive bladder, urge incontinence, poor emptying, dribbling, incomplete emptying of the bladder, and urinary retention. Preclinical models of type 1 and type 2 diabetes have further confirmed the relationship between diabetes and voiding dysfunction. Interestingly, healthy mice supplemented with MGO for prolonged periods exhibit in vivo and in vitro bladder dysfunction, which is accompanied by increased AGE formation and RAGE expression, as well as by ROS overproduction in bladder tissues. Drugs reported to scavenge MGO and to inactivate AGEs like metformin, polyphenols, and alagebrium (ALT-711) have shown favorable outcomes on bladder dysfunction in diabetic obese leptin-deficient and MGO-exposed mice. Therefore, MGO, AGEs, and RAGE levels may be critically involved in the pathogenesis of bladder dysfunction in diabetic individuals. However, there are no clinical trials designed to test drugs that selectively inhibit the MGO-AGEs-RAGE signaling, aiming to reduce the manifestations of diabetes-associated bladder dysfunction. This review summarizes the current literature on the role of MGO-AGEs-RAGE-ROS axis in diabetes-associated bladder dysfunction. Drugs that directly inactivate MGO and ameliorate bladder dysfunction are also reviewed here.

Diabetic bladder dysfunction progresses from an overactive to an underactive phenotype in a type-1 diabetic mouse model (Akita female mouse) and is dependent on NLRP3

AIMS

Diabetic bladder dysfunction (DBD) is a prevalent diabetic complication thought to progress from overactive (OAB) to underactive (UAB) bladder. Previously we found OAB at 15 weeks in the Akita mouse, a genetic model of Type 1 diabetes. The first aim of this study assesses bladder function at 30 weeks to assess progression. In addition, inflammation triggered by the NLRP3 inflammasome is implicated in DBD. In a second aim we assessed a role for NLRP3 by crossing Akita mice with NLRP3-/- mice.

MAIN METHODS

Akita mice were bred with NLRP3-/- mice. The effect of diabetes was assessed by comparing nondiabetic to diabetic mice (all NLRP3+/+). The effect of diabetes in the absence of the NLRP3 inflammasome was assessed by comparing nondiabetic/NLRP3-/- to diabetic/NLRP3-/- mice. Mice were assessed at 30 weeks for blood glucose (glucometer), inflammation (Evans blue), bladder morphology (histology) and bladder function (urodynamics).

KEY FINDINGS

At 30 weeks blood glucose of nondiabetics and diabetics was not affected by the presence of absence of NLRP3. Diabetic/NLRP3+/+ mice showed bladder inflammation and detrusor hypertrophy which was blocked in the diabetic/NLRP3-/- mice, clearly showing a role for NLRP3. When bladder function was examined, diabetic/NLRP3+/+ showed an increase in voiding volume and a decrease in frequency, two signs of underactive bladder. However, in the NLRP3-/- mice, diabetes was unable to effectuate these changes, demonstrating that NLRP3-induced inflammation is responsible for UAB symptoms in these mice.

SIGNIFICANCE

Akita diabetic mice progress from OAB to UAB. NLRP3 is a possible target to treat DBD.

The Effect of Low-Intensity Extracorporeal Shockwave Treatment on the Urinary Bladder in an Experimental Diabetic Rat Model

Purpose

Preclinical data increasingly support an impact of low-intensity extracorporeal shockwave therapy (Li-ESWT) on the bladder. We investigated the molecular effects of Li-ESWT on the bladder of a streptozotocin-induced diabetic rat model.

Methods

Fifteen 8-week-old male Wistar rats were randomized into 3 groups: a control group (n=5), a group of diabetic rats without treatment (diabetes mellitus [DM], n=5) and a group of diabetic rats treated with Li-ESWT (DM-ESWT, n=5). A single intraperitoneal dose of streptozotocin (60 mg/kg) was used to induce diabetes. Twenty days after diabetes induction, each rat in the DM-ESWT group received 300 shockwaves with an energy flux density of 0.09 mJ/mm². Sessions were repeated 3 times/week for 2 weeks, followed by a 2-week washout period. Total RNA from bladder tissue was extracted, cDNA was synthesized, and quantitative real-time polymerase chain reaction was performed to analyze the expression pattern of transient receptor potential vanilloid 1 (Trpv1), interleukin-1β (Il1b), and the muscarinic receptors M1, M2, and M3 (Chrm1, Chrm2, and Chrm3).

Results

The expression of Trpv1, Il1b, and Chrm2 genes was significantly different between the 3 groups (P=0.002, P<0.0001, and P=0.011, respectively; 1-way analysis of variance). In the DM group, the expression of all genes was higher than in the control group, but statistical significance was observed only for Trpv1 and Il1b (P=0.002 and P<0.0001, respectively). Li-ESWT significantly reduced the expression of Il1b and Chrm2 (P=0.001 and P=0.011, respectively), whereas a nonsignificant tendency for reduced expression was noted for Trpv1 (P=0.069).

Conclusions

The induction of diabetes was associated with increased expression of genes related to mechanosensation, inflammation/ischemia, and contraction in the rat bladder. Li-ESWT reduced the expression of IL1b, Chrm2, and to a lesser extent Trpv1 toward the control levels, suggesting the therapeutic potential of this treatment modality for diabetic cystopathy.

EP2 and EP3 receptors as therapeutic targets for underactive bladder/detrusor underactivity due to diabetic cystopathy in a type 1 diabetic rat model

OBJECTIVES

Diabetic cystopathy (DC) is recognized as one of the major etiologies of underactive bladder (UAB)/detrusor underactivity (DU). Although DC was first reported about three decades ago, there is a distinct lack of effective pharmacological management methods for UAB/DU due to DC with a robust certainty of evidence. In this study, we investigated whether EP2 and EP3 receptors are promising targets of pharmacological management of UAB/DU due to DC.

METHODS

We used streptozotocin (STZ)-induced diabetic Sprague-Dawley rats with postvoid residual urine (PVR) greater than 0.1 mL. Sixteen weeks after induction of diabetes, we performed awake single cystometry after oral administration of the vehicle, an α-blocker (tamsulosin [TAM], 0.1 and 0.3 mg/kg), a cholinesterase inhibitor (distigmine [DIS], 0.3 and 1.0 mg/kg), or an EP2/3 dual agonist (ONO-8055, 0.01 and 0.03 mg/kg). We compared cystometric parameters after administration of the vehicle and drugs using a paired t test. P < .05 was considered to be statistically significant.

RESULTS

Compared with the vehicle, TAM significantly decreased maximum intravesical pressure during voiding (Pmax), while DIS significantly increased it. However, neither drug significantly affected PVR or the residual urine rate (RUR). On the other hand, ONO-8055 significantly decreased PVR and tended to decrease RUR, although it did not significantly affect Pmax.

CONCLUSION

The present study was unable to demonstrate that stimulation of EP2 and EP3 receptors caused major improvements in UAB/DU due to DC. However, this equivocal result could arise from inherent limitations of the STZ-induced diabetic rat as a UAB/DU model.

Pathophysiological changes of the lower urinary tract behind voiding dysfunction in streptozotocin-induced long-term diabetic rats

We evaluated pathophysiological characteristics of the lower urinary tract dysfunction in a streptozotocin (STZ)-induced diabetic rat model. STZ (60 mg/kg) was injected intraperitoneally into male Wistar rats. In vitro bladder muscle strip experiments, in vivo cystometry, and simultaneous recordings of bladder pressure + urethral perfusion pressure (BP + UPP) with or without intravenous administration of L-arginine (300 mg/kg) or tadalafil (0.03 mg/kg) were performed at several time points. In vitro muscle strip experiments demonstrated that diabetic rats had significantly higher contractile responses to carbachol at 4-16 weeks, and a tendency for higher contractile responses to electrical field stimulation at 4-12 weeks, but this was reversed at 16 weeks. Diabetic rats had significant increases in voided volume, residual volume, bladder capacity, maximal voiding pressure, and amplitude and frequency of non-voiding contractions at 16 weeks. Tadalafil decreased the residual volume in diabetic rats. Diabetic rats had significantly higher UPP nadir and mean UPP during high-frequency oscillation at 16 weeks, which were reversed by tadalafil or L-arginine administration. The present results suggest that urethral relaxation failure, probably related to impairment of the NO/cGMP signalling pathway, rather than bladder contractile dysfunction may be a prominent cause for voiding dysfunction in STZ-induced chronic diabetic rats.

Tadalafil, a phosphodiesterase type 5 inhibitor, restores urethra and detrusor function in the initial phase of diabetes in rats

OBJECTIVE

This study investigated the effects of tadalafil on the urethra and detrusor in the initial phase of diabetes in rats.

METHODS

Thirty-six female Sprague-Dawley rats were assigned to a non-diabetes (ND), diabetes (D), or tadalafil-treated diabetes (DT) group (n = 12 per group), with the DT group receiving oral tadalafil (2 mg/kg/d) for 7 days before the experiments. Seven weeks after diabetes induction (by a single intraperitoneal injection of streptozotocin), urethral and intravesical pressure were simultaneously recorded in vivo, whereas responses of detrusor strips to potassium chloride (30 mM), electrical field stimulation (EFS) and carbachol were measured in vitro.

RESULTS

The intravesical pressure at which the urethra started to relax was significantly lower in the DT than D group (mean [± s.d.] 18.9 ± 2.9 vs 29.1 ± 6.6 cm H₂ O; P < .05). In addition, the reduction in urethral pressure was significantly larger in the DT than D group (-10.9 ± 4.0 vs -4.0 ± 2.9 cm H₂ O; P < .05). Detrusor stimulation revealed that the mean contractile responses to EFS and carbachol were significantly lower in the ND and DT groups than in the D group (120.7 ± 26.5% and 130.8 ± 15.8% vs 200.1 ± 47.9% of the 30 mM KCl-induced contraction, respectively, in response to 50 Hz EFS [P < .05]; 211.1 ± 35.4% and 208.4 ± 25.3% vs 425.7 ± 125.0% of the 30 mM KCl-induced contraction, respectively, in response to 10^-3 M carbachol [P < .05]).

CONCLUSIONS

Tadalafil restored urethral relaxation function and detrusor responses to EFS and carbachol during the initial phase of diabetes.

Administration of human umbilical cord blood mononuclear cells restores bladder dysfunction in streptozotocin-induced diabetic rats

OBJECTIVE

This study evaluated the effect of human umbilical cord blood mononuclear cells (HUCB-MNCs) on bladder dysfunction in streptozotocin (STZ; 35 mg/kg, i.v.)-induced diabetic rats.

METHODS

Adult male Sprague-Dawley rats (n = 30) were equally divided into three groups: control group, STZ-diabetic group, and HUCB-MNC-treated group (1 × 10⁶ cells). HUCB-MNCs were isolated by density gradient centrifugation from eight healthy donors and injected into the corpus cavenosum in STZ-diabetic rats 4 weeks after the induction of diabetes. Studies were performed 4 weeks after HUCB-MNC or vehicle injection. In vitro organ bath studies were performed on bladder strips, whereas protein expression of hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF), and α-smooth muscle actin (SMA) in the bladder and the ratio of smooth muscle cells (SMCs) to collagen were determined using western blotting and Masson trichrome staining.

RESULTS

Neurogenic contractions of detrusor smooth muscle strips were 55% smaller in the diabetic group than control group (P < 0.05); these contractions were normalized by HUCB-MNC treatment. In addition, HUCB-MNC treatment restored the impaired maximal carbachol-induced contractile response in detrusor strips in the diabetic group (29%; P < 0.05). HUCB-MNC treatment improved the KCl-induced contractile response in the diabetic bladder (68%; P < 0.05), but had no effect on ATP-induced contractile responses. Increased expression of HIF-1α and VEGF protein and decreased expression of α-SMA protein and the SMC/collagen ratio in diabetic rats were reversed by HUCB-MNC.

CONCLUSION

Administration of HUCB-MNCs facilitates bladder function recovery, which is likely related to downregulation of HIF-1α expression and attenuation of fibrosis in STZ-diabetic rats.

Suo Quan Wan Protects Mouse From Early Diabetic Bladder Dysfunction by Mediating Motor Protein Myosin Va and Transporter Protein SLC17A9

Objective: To investigate the effects of Suo Quan Wan (SQW), a traditional Chinese herbal formula, on the overactive bladder (OAB) of type 2 diabetes mellitus (T2DM) mouse models, particularly on its function of mediating the gene and protein expression levels of myosin Va and SLC17A9.

Materials and Methods: After 4 weeks high-fat diet (HFD) feeding, C57BL/6J mice were injected with streptozotocin (100 mg/kg) for four times. After 3 weeks, the diabetic mice were treated with SQW for another 3 weeks. Voided stain on paper assay, fasting blood glucose (FBG) test, and oral glucose tolerance test (OGTT) were conducted. Urodynamic test, tension test [α,β-methylene ATP, electrical-field stimulation (EFS), KCl, and carbachol] and histomorphometry were also performed. Western blot analysis and qPCR assays were used to quantify the expression levels of myosin Va and SLC17A9.

Results: The diabetic mice exhibited decreased weight but increased water intake, urine production, FBG, and OGTT. No significant changes were observed after 3 weeks SQW treatment. Urodynamic test indicated that the non-voiding contraction (NVC) frequency, maximum bladder capacity (MBC), residual volume (RV), and bladder compliance (BC) were remarkably increased in the diabetic mice, whereas the voided efficiency (VE) was decreased as a feature of overactivity. Compared with the model mice, SQW treatment significantly improved urodynamic urination with decreased NVC, MBC, RV, and BC, and increased VE. Histomorphometry results showed that the bladder wall of the diabetic mice thickened, and SQW effectively attenuated the pathological alterations. The contract responses of bladder strips to all stimulators were higher in the DSM strips of diabetic mice, whereas SQW treatment markedly decreased the contraction response for all stimuli. Moreover, the protein and gene expression levels of myosin Va and SLC17A9 were up-regulated in the bladders of diabetic mice, but SQW treatment restored such alterations.

Conclusion: T2DM mice exhibited the early phase of diabetic bladder dysfunction (DBD) characterized by OAB and bladder dysfunction. SQW can improve the bladder storage and micturition of DBD mice by mediating the protein and gene expression levels of myosin Va and SLC17A9 in the bladder, instead of improving the blood glucose level.

The phosphodiesterase type 4 inhibitor roflumilast suppresses inflammation to improve diabetic bladder dysfunction rats

PURPOSE

To demonstrate that phosphodiesterase type 4 (PDE4) inhibitors could potentially treat diabetic bladder dysfunction (DBD) through modulation of the systemic inflammatory response.

METHODS

In this 6-week study, 60 female Sprague-Dawley rats were divided into three groups: (i) vehicle-treated control rats; (ii) vehicle-treated streptozocin (STZ)-injected rats; and (iii) roflumilast-treated STZ-injected rats. Oral roflumilast (5 mg/kg/day) was administered during the last 4 weeks of STZ injection to induce diabetes in the test group. At 6 weeks, a urodynamic study was performed in each group. The expression of nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and IL-1β in detrusor smooth muscle (DSM) was analyzed using quantitative reverse transcription-polymerase chain reaction and Western blotting.

RESULTS

A significant decrease in bodyweight and significant increases in bladder weight and blood glucose level were observed in the diabetic rats and were not ameliorated by roflumilast treatment. Cystometry showed the increased bladder capacity, voiding volume, residual urine volume, and voiding interval in the diabetic rats and the prevention of these changes by roflumilast. These changes were accompanied by significantly enhanced expression of NF-κB, TNF-α, IL-6, and IL-1β in DSM tissue from diabetic rats. Furthermore, roflumilast attenuated the expression of inflammatory factors in DSM tissue.

CONCLUSIONS

Oral treatment with roflumilast in diabetic rats improves bladder function and inhibits the expression of inflammatory factors in DSM tissue, indicating that PDE4 is a potential therapeutic target for DBD.