Functional and morphological alterations of the urinary bladder in type 2 diabetic FVB(db/db) mice

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.

Evidence that methylglyoxal and receptor for advanced glycation end products are implicated in bladder dysfunction of obese diabetic ob/ob mice

Glycolytic overload in diabetes causes large accumulation of the highly reactive dicarbonyl compound methylglyoxal (MGO) and overproduction of advanced glycation end products (AGEs), which interact with their receptors (RAGE), leading to diabetes-associated macrovascular complications. The bladder is an organ that stays most in contact with dicarbonyl species, but little is known about the importance of the MGO-AGEs-RAGE pathway to diabetes-associated bladder dysfunction. Here, we aimed to investigate the role of the MGO-AGEs-RAGE pathway in bladder dysfunction of diabetic male and female ob/ob mice compared with wild-type (WT) lean mice. Diabetic ob/ob mice were treated with the AGE breaker alagebrium (ALT-711, 1 mg/kg) for 8 wk in drinking water. Compared with WT animals, male and female ob/ob mice showed marked hyperglycemia and insulin resistance, whereas fluid intake remained unaltered. Levels of total AGEs, MGO-derived hydroimidazolone 1, and RAGE in bladder tissues, as well as fluorescent AGEs in serum, were significantly elevated in ob/ob mice of either sex. Collagen content was also markedly elevated in the bladders of ob/ob mice. Void spot assays in filter paper in conscious mice revealed significant increases in total void volume and volume per void in ob/ob mice with no alterations of spot number. Treatment with ALT-711 significantly reduced the levels of MGO, AGEs, RAGE, and collagen content in ob/ob mice. In addition, ALT-711 treatment normalized the volume per void and increased the number of spots in ob/ob mice. Activation of AGEs-RAGE pathways by MGO in the bladder wall may contribute to the pathogenesis of diabetes-associated bladder dysfunction.NEW & NOTEWORTHY The involvement of methylglyoxal (MGO) and advanced glycation end products (AGEs) in bladder dysfunction of diabetic ob/ob mice treated with the AGE breaker ALT-711 was investigated here. Diabetic mice exhibited high levels of MGO, AGEs, receptor for AGEs (RAGE), and collagen in serum and/or bladder tissues along with increased volume per void, all of which were reduced by ALT-711. Activation of the MGO-AGEs-RAGE pathway in the bladder wall contributes to the pathogenesis of diabetes-associated bladder dysfunction.

Effects of different diets used to induce obesity/metabolic syndrome on bladder function in rats

Preclinical and human studies on the relationship between obesity/metabolic syndrome (MetS) and lower urinary tract dysfunction (LUTD) are inconsistent. We compared the temporal effects of feeding four different diets used to induce obesity/MetS, including 60% fructose, 2% cholesterol +10% lard, 30% fructose + 20% lard, or 32.5% lard diet, up to 42 wk, on metabolic parameters and bladder function in male Sprague-Dawley rats. Rats fed a 30% fructose + 20% lard or 32.5% lard diet consumed less food (grams), but only the 32.5% lard diet group took in more calories. Feeding rats a 60% fructose or 30% fructose + 20% lard diet led to glucose intolerance and increased blood pressure. Higher body weight and increased cholesterol levels were observed in the rats maintained on a 2% cholesterol +10% lard diet, whereas exposure to a 32.5% lard diet affected most of the above parameters. Voiding behavior measurement showed that voiding frequency and the total voided volume were lower in the experimental diet groups except for the 30% fructose + 20% lard group. The mean voided volume was lower in the 30% fructose + 20% lard and 32.5% lard groups compared with the control group. Cystometric analysis revealed a decreased bladder capacity, mean voided volume, intermicturition interval, and compliance in the 32.5% lard diet group. In conclusion, experimental diets including 60% fructose, 30% fructose + 20% lard, or 2% cholesterol + 10% lard diet differently affected physiological and metabolic parameters and bladder function to a limited extent, while exposure to a 32.5% lard diet had a greater impact.

Functional and Immunofluorescence Evaluations of Vascular and Neural Integrities in Urinary Bladder of Streptozotocin-Induced Diabetic Mice

Purpose

To assess functional and structural changes in vascular and neural structures associated with diabetic bladder dysfunction (DBD) in the bladders of streptozotocin (STZ)-induced diabetic mice.

Methods

Eight-week-old C57BL/6 mice were injected with STZ at 50 mg/kg daily for 5 consecutive days. Catheters were inserted 12 weeks later, and 5 days after catheter placement bladder functions were assessed by conscious cystometry. Neurovascular and extracellular matrix marker changes in harvested urinary bladders were investigated by immunofluorescent staining. Body weights and fasting and postprandial blood glucose levels were measured 12 weeks after STZ injection.

Results

STZ-induced diabetic mice had significantly lower body weights and significantly higher blood glucose levels. Assessment of bladder function in STZ-induced diabetic mice revealed a nearly 3-fold increase in bladder capacity and intercontractile interval compared to controls. However, basal pressure, maximal bladder pressure, and threshold pressure were not significantly different. Morphological and structural analysis showed that STZ-induced diabetic mice had significantly reduced microvascular density in lamina propria (33% of the nondiabetic control values), and severely decreased nerve contents in the detrusor region (42% of the nondiabetic control values).

Conclusions

STZ-induced diabetic mice exhibit functional and structural derangements in urinary bladder. The present study provides a foundation and describes a useful means of evaluating the efficacies of therapeutic targets and exploring the detailed mechanism of DBD.

Enhanced RAGE Expression and Excess Reactive-Oxygen Species Production Mediates Rho Kinase-Dependent Detrusor Overactivity After Methylglyoxal Exposure

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound implicated in diabetes-associated diseases. In vascular tissues, MGO induces the formation of advanced glycation end products (AGEs) that bounds its receptor RAGE, initiating the downstream tissue injury. Outside the cardiovascular system, MGO intake produces mouse voiding dysfunction and bladder overactivity. We have sought that MGO-induced bladder overactivity is due to activation of AGE-RAGE-reactive-oxygen species (ROS) signaling cascade, leading to Rho kinase activation. Therefore, female mice received 0.5% MGO orally for 12 weeks, after which in vitro bladder contractions were evaluated in the presence or not of superoxide dismutase (PEG-SOD) or the Rho kinase inhibitor Y27632. Treatment with MGO significantly elevated the serum levels of MGO and fluorescent AGEs, as well as the RAGE immunostaining in the urothelium, detrusor, and vascular endothelium. RAGE mRNA expression in the bladder was also higher in the MGO group. Methylglyoxal significantly increased the ROS production in both urothelium and detrusor smooth muscle, with the increases in detrusor markedly higher than urothelium. The bladder activity of superoxide dismutase (SOD) was significantly reduced in the MGO group. Gene expressions of L-type Ca²⁺ channels, RhoA, ROCK-1, and ROCK-2 in bladder tissues were significantly elevated in the MGO group. Increased bladder contractions to electrical-field stimulation, carbachol α,β-methylene ATP, and extracellular Ca²⁺ were observed after MGO exposure, which was significantly reduced by prior incubation with either PEG-SOD or Y27632. Overall, our data indicate serum MGO accumulation elevates the AGEs levels and activates the RAGE-ROS signaling leading to Rho kinase-induced muscle sensitization, ultimately leading to detrusor overactivity.

Metformin abrogates the voiding dysfunction induced by prolonged methylglyoxal intake

Methylglyoxal (MGO) is a reactive carbonyl species found at high levels in blood of diabetic patients. The anti-hyperglycemic drug metformin can scavenger MGO and reduce the formation of advanced glycation end products (AGEs). Here, we aimed to investigate if MGO-induced bladder dysfunction can be reversed by metformin. Male C57/BL6 mice received 0.5% MGO in drinking water for 12 weeks, and metformin (300 mg/kg, daily gavage) was given in the last two weeks. The bladder functions were evaluated by performing voiding behavior assays, cystometry and in vitro bladder contractions. MGO intake markedly elevated the levels of MGO and fluorescent AGEs in serum and reduced the mRNA expression and activity of glyoxalase (Glo1) in bladder tissues. Glucose levels were unaffected among groups. MGO intake also increased the urothelium thickness and collagen content of the bladder. Void spot assays in conscious mice revealed an increased void volume in MGO group. The cystometric assays in anesthetized mice revealed increases of basal pressure, non-voiding contractions frequency, bladder capacity, inter-micturition pressure and residual volume, which were accompanied by reduced voiding efficiency in MGO group. In vitro bladder contractions to carbachol, α,β-methylene ATP and electrical-field stimulation were significantly greater in MGO group. Metformin normalized the changes of MGO and AGEs levels, Glo1 expression and activity, urothelium thickness and collagen content. The MGO-induced voiding dysfunction were all restored by metformin treatment. Our findings strongly suggest that the amelioration of MGO-induced voiding dysfunction by metformin relies on its ability to scavenger MGO, preventing its accumulation in blood.

Morphological Peculiarities of Parasitic (Trichosomoides crassicauda) Infection in Rat Urinary Bladder

Trichosomoides crassicauda (T. crassicauda) is a parasite commonly localized in the urinary bladder (UB) of laboratory and wild rats. The presence of these helminths can influence the prediction of pathological changes in the UB. Therefore, the purpose of this research was to make a comprehensive study of the features of the morphological changes in the UB wall of white laboratory rats as a result of T. crassicauda infestation. The study was performed on male rats using histological (Hematoxyline-Eosin and Alcian Blue staining) and immunohistochemical (Ki-67, Hsp70, Hsp90α, CD3 and CD20) methods. T. crassicauda was detected in both urine and UB samples. Morphological changes were observed as disruption in urothelial cell stratification and insignificant proliferative and immune responses in the UB. Increased heat shock protein levels were observed which may suggest a natural body’s resistance to this parasite.

Are there relevant animal models to set research priorities in LUTD? ICI-RS 2019

AIM

To discuss animal models of lower urinary tract disorders (LUTD) and their translational impact.

METHODS

Report of discussions based on presented literature-search based reviews relevant for the purpose.

RESULTS

Animal models can be used to investigate fundamental biological mechanisms, but also as tools to elucidate aspects of the pathogenesis of disease and to provide early evidence of any safety risk. Several different models may be required to obtain information that can have a translational impact. The term "translational research" covers not only the process of directly transferring knowledge from basic sciences to human trials to produce new drugs, devices, and treatment options for patients (T1 type translation) but also the implementation of early clinical research findings (phases I-III) into practice to improve care for patients (T2 type). Direct transfer of animal data to T2 is rarely possible, and the process often does not continue after the first trials in humans (phase I). It should be emphasized that many preclinical observations do not have (and do not need to have) immediate translational impact.

CONCLUSIONS

No single animal model can mimic the complexity of the human disease. Still, animal models can be useful for gaining information on LUT function in humans, for elucidating pathophysiological mechanisms, and for the definition of targets for future drugs to treat LUT disorders.

The influence of hyperglycemia on the remodeling of urethral connective tissue in pregnant rats

OBJECTIVE

To analyze the distribution and quantification of the key structural extracellular matrix components of the urethral tissue in a rat model of hyperglycemia and pregnancy.

STUDY DESIGN

A total of 120 female Wistar rats were distributed into the following four experimental groups: virgin, pregnant, hyperglycemic and hyperglycemic + pregnant groups. The urethra was harvested for histochemical, morphometric, immunohistochemical, Western blot and glycosaminoglycan analyses. All protocols were approved by the Institutional Animal Care and Use Committee of Botucatu Medical School (process number 828-2010).

RESULTS

The hyperglycemic + pregnant group showed significantly increased stiffness in urethral tissue. The total striated muscle was decreased, with increased deposition of collagen fibers around the muscle fibers and a change in the organization of the collagen fibrils. An increase in the relative collagen type I/III ratio and a decrease in total glycosaminoglycans were also observed.

CONCLUSIONS

This study provides the first line of experimental evidence supporting a metabolic relationship between hyperglycemia and urethral remodeling of connective tissue in pregnant rats. The different organization of the collagen fibrils and the profile of glycosaminoglycans found in urethral samples suggest that the pathology of the urethral fibromuscular system could be related to hyperglycemia-induced pelvic floor dysfunction in women, which has direct clinical implications with the possibility to develop new multidisciplinary treatments for improving the health care of these women.

Serotonin Receptor 5-HT3A Affects Development of Bladder Innervation and Urinary Bladder Function

The autonomic and sensory nervous systems are required for proper function of all visceral organs, including the lower urinary tract (LUT). Despite the wide prevalence of bladder dysfunction, effective treatment options remain limited. Pelvic innervation regenerative strategies are promising, but surprisingly little is known about the molecular factors driving the development of bladder innervation. Given prior evidence that serotonin receptor 5-HT3A is expressed early in LUT development and is an important mediator of adult bladder function, we sought to determine if 5-HT3A is required for the development of autonomic innervation of the bladder. We found that 5-HT3A is expressed early in fetal mouse pelvic ganglia and is maintained through adulthood. Htr3a knockout male mice, but not females, exhibit increased urinary voiding frequency compared to wild type littermates. Analysis of LUT function via anesthetized cystometry revealed decreased voiding efficiency in male Htr3a mutants. Htr3a^−/− mutant animals exhibit a transient disturbance of autonomic neuronal subtype markers (tyrosine hydroxylase and choline acetyl transferase) within the fetal pelvic ganglia, although the imbalance of neuronal subtype markers assayed is no longer apparent in adulthood. Loss of 5-HT3A activity results in a higher density of autonomic and sensory neuronal fibers supplying bladder smooth muscle in both fetal and adult mice. Collectively, our findings highlight 5-HT3A as a critical component in the autonomic control of micturition and identify a novel role for this serotonin receptor in peripheral nervous system development.

A genetic female mouse model with congenital genitourinary anomalies and adult stages of urinary incontinence

AIMS

To characterize the urinary incontinence observed in adult Gli2^+/- ; Gli3^Δ699/+ female mice and identify the defects underlying the condition.

METHODS

Gli2^+/- and Gli3^Δ699/+ mice were crossed to generate: wild-type, mutant Gli2 (Gli2^+/- ), mutant Gli3 (Gli3^Δ699/+ ), and double mutant (Gli2^+/- ; Gli3^Δ699/+ ) female mice, verified via Polymerase Chain Reactions. Bladder functional studies including cystometrogram (CMG), leak point pressure (LPP), and voiding testing were performed on adult female mice. Female bladders and urethras were also analyzed via ink injection and histological assays.

RESULTS

CMG tracing showed no signal corresponding to the filling of the Gli2^+/- ; Gli3^Δ699/+ bladders. LPP were significantly reduced in Gli2^+/- ; Gli3^Δ699/+ mice compared to wild-type mice. CMG studies revealed a decrease in peak micturition pressure values in Gli2^+/- ; Gli3^Δ699/+ mice compared with all other groups. No significant differences between mutant and wild-type mice were detected in urinary output. Histological analyses revealed Gli2^+/- ; Gli3^Δ699/+ mice exhibited a widened urethra and a decrease in smooth muscle layer thickness in the bladder outlet and urethra, with increased mucosal folding.

CONCLUSIONS

Gli2^+/- ; Gli3^Δ699/+ adult female mice display persistent urinary incontinence due to the malformation of the bladder outlet and urethra. This presents a consistent and reliable genetic mouse model for female urinary incontinence and alludes to the key role of genetic factors involved in the condition.

Path of translational discovery of urological complications of obesity and diabetes

Diabetes mellitus (DM) is a prevalent chronic disease. Type 1 DM (T1DM) is a metabolic disorder that is characterized by hyperglycemia in the context of absolute lack of insulin, whereas type 2 DM (T2DM) is due to insulin resistance-related relative insulin deficiency. In comparison with T1DM, T2DM is more complex. The natural history of T2DM in most patients typically involves a course of obesity to impaired glucose tolerance, to insulin resistance, to hyperinsulinemia, to hyperglycemia, and finally to insulin deficiency. Obesity is a risk factor of T2DM. Diabetes causes some serious microvascular and macrovascular complications, such as retinopathy, nephropathy, neuropathy, angiopathy and stroke. Urological complications of obesity and diabetes (UCOD) affect quality of life, but are not well investigated. The urological complications in T1DM and T2DM are different. In addition, obesity itself affects the lower urinary tract. The aim of this perspective is to review the available data, combined with the experience of our research teams, who have spent a good part of last decade on studies of association between DM and lower urinary tract symptoms (LUTS) with the aim of bringing more focus to the future scientific exploration of UCOD. We focus on the most commonly seen urological complications, urinary incontinence, bladder dysfunction, and LUTS, in obesity and diabetes. Knowledge of these associations will lead to a better understanding of the pathophysiology underlying UCOD and hopefully assist urologists in the clinical management of obese or diabetic patients with LUTS.