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

Strict glucose control and elimination of NLRP3-induced inflammation prevents diabetic bladder dysfunction in the female Akita mouse model

PURPOSE

Diabetic bladder dysfunction (DBD) is the most common diabetic complication. Logically, regulation of blood glucose should reverse dysfunction, but the Epidemiology of Diabetes Interventions and Complications study found strict control ineffective. However, it is possible that strict control may prevent DBD if initiated before symptoms appear. We examine the effect of early glucose control on development of DBD in the female diabetic Akita mouse (Type 1) and test the potential of inhibiting/deleting NLRP3 as adjunct therapy to glucose control.

MATERIALS AND METHODS

Female Akita mice were bred NLRP3+/+ or NLRP3-/-. At 6 weeks of age, diabetics received either no glucose control or insulin pellets (s.c., Linshin) designed to poorly or strictly control blood glucose. At Week 15, blood glucose (glucometer), the extravasation potential of bladder (an indirect measurement of inflammation) and bladder function (urodynamics) were assessed.

RESULTS

Blood glucose of diabetics was reduced in poorly controlled and strongly reduced in strictly controlled groups. Levels were not affected by deletion of NLRP3. Evans blue dye extravasation correlated with glucose control and was eliminated in the NLRP3-/- groups. Urodynamics found markers of overactivity in diabetics which was improved in the poorly controlled group and eliminated in the strictly controlled group. In the NLRP3-/- mice, no bladder dysfunction developed, regardless of glucose control.

CONCLUSIONS

Early-initiated strict glycemic control and NLRP3 elimination can effectively prevent DBD, suggesting hyperglycemia acts through NLRP3-induced inflammation to trigger DBD.

Specialized pro-resolution mediators in the bladder: effects of resolvin E1 on diabetic bladder dysfunction in the type 1 diabetic male Akita mouse model

BACKGROUND

One of the most common, but least studied, diabetic complication is diabetic bladder dysfunction. Current therapies include glucose control and symptom-based interventions. However, efficacy of these therapies is mixed and often have undesirable side effects. Diabetes is now known to be a chronic inflammatory disease. Specialized pro-resolving mediators are a class of compounds that promote the resolution of inflammation and have been shown to be effective in treating chronic inflammatory conditions. In this study we examine the ability of resolvin E1 to improve signs of diabetic bladder dysfunction.

METHODS

Male Akita mice (Type 1 diabetic) develop hyperglycemia at 4 weeks and signs of bladder underactivity by 15 weeks. Starting at 15 weeks, mice were given one or two weeks of daily resolvin E1 and compared to age-matched wild type and untreated Akita mice.

RESULTS

Resolvin E1 did not affect diabetic blood glucose after one week, although there was a slight decrease after two weeks. Diabetes decreased body weight and increased bladder weights and this was not affected by resolvin E1. Evan's blue dye extravasation (an indirect index of inflammation) was dramatically suppressed after one week of resolvin E1 treatment, but, surprisingly, had returned to diabetic levels after two weeks of treatment. Using cystometry, untreated Akita mice showed signs of underactivity (increased void volumes and intercontraction intervals). One week of resolvin E1treatment restored these cystometric findings back to control levels. After two weeks of treatment, cystometric changes were changed from controls but still significantly different from untreated levels, indicating a durable treatment effect even in the presence of increased inflammation at 2 weeks.

CONCLUSIONS

Resolvin E1 has a beneficial effect on diabetic bladder dysfunction in the type 1 diabetic male Akita mouse model.

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.

Male Akita mice develop signs of bladder underactivity independent of NLRP3 as a result of a decrease in neurotransmitter release from efferent neurons

Diabetic bladder dysfunction (DBD) is a prevalent diabetic complication that is recalcitrant to glucose control. Using the Akita mouse model (type 1) bred to be NLR family pyrin domain containing 3 (NLRP3)+/+ or NLRP3-/-, we have previously found that females (mild hyperglycemia) progress from an overactive to underactive bladder phenotype and that this progression was dependent on NLRP3-induced inflammation. Here, we examined DBD in the male Akita mouse (severe hyperglycemia) and found by urodynamics only a compensated underactive-like phenotype (increased void volume and decreased frequency but unchanged efficiency). Surprisingly, this phenotype was still present in the NLRP3-/- strain and so was not dependent on NLRP3 inflammasome-induced inflammation. To examine the cause of the compensated underactive-like phenotype, we assessed overall nerve bundle density and afferent nerve bundles (Aδ-fibers). Both were decreased in density during diabetes, but denervation was absent in the diabetic NLRP3-/- strain so it was deemed unlikely to cause the underactive-like symptoms. Changes in bladder smooth muscle contractility to cell depolarization and receptor activation were also not responsible as KCl (depolarizing agent), carbachol (muscarinic agonist), and α,β-methylene-ATP (purinergic agonist) elicited equivalent contractions in denuded bladder strips in all groups. However, electrical field stimulation revealed a diabetes-induced decrease in contractility that was not blocked in the NLRP3-/- strain, suggesting that the bladder compensated underactive-like phenotype in the male Akita mouse is likely through a decrease in efferent neurotransmitter release.NEW & NOTEWORTHY In this study, we show that diabetic bladder dysfunction (the most common diabetic complication) manifests through different mechanisms that may be related to severity of hyperglycemia and/or sex. Male Akita mice, which have severe hyperglycemia, develop bladder underactivity as a result of a decrease in efferent neurotransmitter release that is independent of inflammation. This contrasts with females, who have milder hyperglycemia, where diabetic bladder dysfunction progresses from overactivity to underactivity in an inflammation-dependent manner.

The potential involvement of MRP5 pump in urethral dysfunction in streptozotocin-induced diabetic rats

PURPOSE

To examine the effects of i.v. administration of MK-571, a MRP4/5 pump inhibitor, on urethral function in the urethane-anesthetized rat, and the changes of urethral multidrug resistance protein 5 (MRP5) pump in streptozotocin (STZ)-induced diabetes mellitus (DM) rats.

METHODS

Isovolumetric cystometry and urethral perfusion pressure (UPP) measurements were carried out in normal control (NC) group and 8week DM groups under urethane anesthesia. When stable rhythmic bladder contractions were showed, UPP parameters were recorded after successive administration of various dose of MK-571. Additionally, urethral cyclic guanosine monophosphate (cGMP) protein level was evaluated by ELISA, and changes of MRP5 pump and neurogenic nitric oxide synthase (nNOs) in the urethra were examined with immunohistochemical staining and Western blot analysis.

RESULTS

In NC group, UPP_nadir was significantly decreased but UPP change increased after administration of MK-571, while no significant differences in UPP parameters were observed in 8-week DM group. Furthermore, urethral MRP5 protein level was up-regulated, whereas urethral cGMP and nNOS protein levels were down-regulated in 8-week DM group.

CONCLUSIONS

MK-571 could not restore NO-mediated urethral relaxation dysfunction in DM rats, which may be attributed to the up-regulation of urethral MRP5 pump, and thus decrease of intracellular cGMP concentration in the urethra. These novel results would be useful for a better understanding of DM-related lower urinary tract dysfunction LUT (LUTD). Also, they could be helpful to study the importance of MRP pumps in the control of urethral relaxation mechanisms under physiological and pathological states.

Current research and future directions in non-malignant urologic research - proceedings of the annual CAIRIBU meeting

The Annual Collaborating for the Advancement of Interdisciplinary Research (CAIRIBU) Meeting in 2022 highlighted basic, translational, and clinical non-malignant urology research within five main areas affecting the urinary tract: urinary dysfunction due to prostate disease, microbes and infection, bladder function and physiology, neurology and neuromuscular influences and calculi and obstruction. In this paper, we summarize main findings and future directions outlined by CAIRIBU-affiliated scientists who presented as part of the scientific sessions.

Diabetes causes NLRP3-dependent barrier dysfunction in mice with detrusor overactivity but not underactivity

Approximately half of the patients with diabetes develop diabetic bladder dysfunction (DBD). The initiation and progression of DBD is largely attributed to inflammation due to dysregulated glucose and the production of toxic metabolites that activate the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome. NLRP3 activation leads to the production and release of proinflammatory cytokines and causes urothelial pyroptosis, a form of programmed cell necrosis, which we hypothesize compromises urothelial barrier integrity. Here, we investigated how NLRP3-dependent inflammation impacts barrier function during the progression of diabetes using a type 1 diabetic female Akita mouse model that progresses from an early overactive to a late underactive detrusor phenotype at 15 and 30 wk, respectively. To determine the specific role of NLRP3, Akita mice were crossbred with mice lacking the NLRP3 gene. To determine barrier function, permeability to small molecules was assessed, ex vivo using Evans blue dye and in vivo using sulfo-NHS-biotin. Both ex vivo and in vivo permeabilities were increased in diabetic mice at 15 wk. Expression of uroplakin and tight junction components was also significantly downregulated at 15 wk. Interestingly, diabetic mice lacking the NLRP3 gene showed no evidence of barrier damage or downregulation of barrier genes and proteins. At the 30-wk time point, ex vivo and in vivo barrier damage as well as barrier component downregulation was no longer evident in diabetic mice, suggesting urothelial repair or remodeling occurs between the overactive and underactive stages of DBD. Collectively, these findings demonstrate the role of NLRP3-mediated inflammation in urothelial barrier damage associated with detrusor overactivity but not underactivity.NEW & NOTEWORTHY This is the first study to demonstrate that NLRP3-mediated inflammation is responsible for urothelial barrier damage in type 1 diabetic female Akita mice with an overactive bladder. Eliminating the NLRP3 gene in these diabetic mice prevented barrier damage as a result of diabetes. By the time female Akita mice develop an underactive phenotype, the urothelial barrier has been restored, suggesting that inflammation is a critical causative factor early in the development of diabetic bladder dysfunction.

Inflammation triggered by the NLRP3 inflammasome is a critical driver of diabetic bladder dysfunction

Diabetes is a rapidly expanding epidemic projected to affect as many as 1 in 3 Americans by 2050. This disease is characterized by devastating complications brought about high glucose and metabolic derangement. The most common of these complications is diabetic bladder dysfunction (DBD) and estimates suggest that 50-80% of patients experience this disorder. Unfortunately, the Epidemiology of Diabetes Interventions and Complications Study suggests that strict glucose control does not decrease ones risk for incontinence, although it does decrease the risk of other complications such as retinopathy, nephropathy and neuropathy. Thus, there is a significant unmet need to better understand DBD in order to develop targeted therapies to alleviate patient suffering. Recently, the research community has come to understand that diabetes produces a systemic state of low-level inflammation known as meta-inflammation and attention has focused on a role for the sterile inflammation-inducing structure known as the NLRP3 inflammasome. In this review, we will examine the evidence that NLRP3 plays a central role in inducing DBD and driving its progression towards an underactive phenotype.