Detrusor Underactivity: The Current Concept of the Pathophysiology

Insight into SLC9A3 deficiency-mediated micturition dysfunction caused by electrolyte imbalance

BACKGROUND

Solute carrier family nine isoform 3 (SLC9A3) is an Na⁺/H⁺ exchanger that regulates Ca₂⁺ homeostasis. SLC9A3 is largely involved in the transepithelial absorption of Na⁺/H⁺ and frequently functions in pair with a Cl^-/HCO3^- exchanger.

OBJECTIVE

To investigate the impact and pathophysiological mechanisms of long-term SLC9A3 deficiency on lower urinary tract symptoms (LUTS) in a mouse model MATERIALS AND METHODS: Slc9a3 knockout and wild-type mice (average >6 months) were used. The effects of SLC9A3 depletion on bladder and urethral functions and effectiveness of voiding were assessed using a cystometrogram (CMG). Histology, blood electrolytes, and gene expression were also analyzed.

RESULTS

The SLC9A3-deficient mice had smaller gross bladders than the wild-type mice. The CMG analysis revealed normal peak micturition pressure, higher threshold pressure, short intercontraction interval, less voided volume, and poor compliance in the SLC9A3-deficient mice, similar to clinical LUTS. Histological analysis revealed loose detrusor muscle and loss of transformability of the urothelium in the SLC9A3-deficient mice. Masson's trichrome analysis revealed severe collagen deposition in the detrusor muscle. Immunofluorescence staining also demonstrated a significant decrease in cytokeratins 5 and 20. Gene and protein expression analyses confirmed that SLC9A3 does not act directly on bladder tissue. Homeostasis was correlated with bladder dysfunction in the SLC9A3-deficient mice.

DISCUSSION

Fibrosis and collagen deposition in the bladder of the SLC9A3-deficient mice is due to bladder inflammation because of decreased blood flow and deregulated systemic homeostasis. Long-term SLC9A3 depletion causes progressive bladder dysfunction, similar to human LUTS.

CONCLUSION

Electrolyte imbalance causes SLC9A3 deficiency-mediated progressive micturition dysfunction.

Two types of detrusor underactivity in men with nonneurogenic lower urinary tract symptoms

AIMS

To clarify the clinical features of men with nonneurogenic detrusor underactivity (DU) by focusing on storage dysfunction (SD).

METHODS

We retrospectively reviewed the clinical and urodynamic data of men with nonneurogenic DU. Patients were divided into two groups according to the presence or absence of SD, such as detrusor overactivity (DO) and reduced bladder compliance (BC). Patient characteristics, lower urinary tract symptoms (LUTS), and urodynamic parameters were compared. DU was defined as bladder contractility index (BCI) ≤ 100 and bladder outlet obstruction index (BOOI) ≤ 40.

RESULTS

Of 212 men with DU, 123 (58.0%) had concomitant SD (SD + DU group), and 89 (42.0%) had only DU (DU-only group). Age, prostate volume, and severity of storage symptoms were significantly higher in the SD + DU group. Particularly, >80% of men in the SD + DU group met the diagnostic criteria for overactive bladder in Japan, which was significantly higher than the 26% of men in the DU-only group. The frequency of urinary urgency incontinence (UUI) was also significantly higher in the SD + DU group (65% vs. 12% in DU-only group). In contrast, voiding symptoms, including straining, were more severe in the DU-only group. Regarding the urodynamic parameters, compared to the DU-only group, bladder capacity was significantly smaller and BOOI and BCI were significantly higher in the SD + DU group. However, there was no significant difference in the maximum flow rate and bladder voiding efficiency.

CONCLUSIONS

Approximately 60% of men with DU had SD, such as DO and/or reduced BC, whereas the remaining 40% had increased bladder capacity without an increase in detrusor pressure during the storage phase. There were significant differences in the storage and voiding symptoms between the groups. It is important to divide patients with DU based on SD to accurately clarify the clinical picture of DU.

Clinical Correlation of Bladder Electron Microscopic Characteristics in Patients with Detrusor Underactivity of Various Etiologies

This study aimed to investigate the ultrastructural characteristics of the bladder of patients with detrusor underactivity (DU) of various etiologies. Twenty-five patients with DU and control subjects underwent urodynamic testing and transmission electron microscopic examination of bladder specimens. The epithelium, lamina propria, and muscle layers were analyzed separately. The DU bladders exhibited total epithelial denudation (52%). In the bladders with remaining epithelium, apical cell uroplakins (44.4%) and tight junction complexes (77.8%) were also noted. The lamina propria was characterized by loose extracellular connective tissue (48%) and a lack of nerve terminals (76%). Smooth muscle shrinkage and a loss of their regular spindle shape (91.6%) were also noted in the detrusor layer. Patients with DU with intact epithelial cell layers had significantly larger void volumes and maximal flow rates than those with mild or severe epithelial denudation. Patients with remaining nerve terminals in lamina propria had a stronger first sensation of filling and smaller residual urine volume than those without nerve terminals. The proportion of ultrastructural defects of the bladder was not significantly different among patients with DU of various etiologies and treatment outcomes. DU bladders were characterized by ultrastructural defects in the entire bladder, and the defects were correlated to clinical parameters.

Efficacy of TAC-302 for patients with detrusor underactivity and overactive bladder: a randomized, double-blind, placebo-controlled phase 2 study

PURPOSE

This multicenter, randomized, double-blind, placebo-controlled phase 2 study evaluated the efficacy and safety of TAC-302, a novel drug that restores neurite outgrowth, in patients with detrusor underactivity (DU) and overactive bladder (OAB).

METHODS

After 2-4 weeks of observation, patients were randomized 2:1 to receive oral TAC-302 200 mg or placebo twice daily for 12 weeks. The primary endpoint was detrusor contraction strength, estimated by bladder contractility index (BCI) for males and projected isovolumetric pressure 1 (PIP1) for females. Secondary endpoints included changes in bladder voiding efficiency (BVE) and safety.

RESULTS

Seventy-six patients were included (TAC-302, n = 52; placebo, n = 24). The mean (standard deviation [SD]) BCI for males was 64.6 (16.6) at baseline and 75.2 (21.1) at week 12 (p < 0.001) with TAC-302 (n = 27), and 61.3 (16.6) and 60.5 (16.7) (p = 0.82) with placebo (n = 11). The respective mean (SD) PIP1 for females was 18.8 (6.6) and 29.4 (9.4) (p < 0.001) with TAC-302 (n = 15), and 20.6 (7.5) and 25.5 (9.6) (p = 0.14) with placebo (n = 7). TAC-302 significantly increased BCI in males and BVE in both sexes. TAC-302 efficacy on OAB was not clearly shown. The incidences of adverse events (AEs), serious AEs, and AEs leading to dose interruption were similar between groups; no adverse drug reactions occurred.

CONCLUSION

Considering the significant effects on BCI in males and BVE in both sexes, TAC-302 may benefit patients with DU.

REGISTRATION

ClinicalTrials.gov Identifier NCT03175029 registered 6/5/2017.

Potential predictors of detrusor underactivity in a urology outpatient clinic: a 5-year single center experience study

BACKGROUND Detrusor underactivity (DU) is diagnosed using urodynamics, which caused by a combination of strength and duration of the bladder muscle and resulted in prolonged bladder emptying. Invasive urodynamics, which are limited in many clinical settings, should be performed efficiently in high-risk patients to reduce the risk of emerging complications during and after the procedure. Therefore, this study was aimed to identify the potential predictors of DU for limited clinical settings. METHODS This retrospective study was retrieved from the medical records of patients who underwent urodynamics in the Department of Urology, Cipto Mangunkusumo Hospital from 2015 to 2020. Age, sex, bladder capacity, bladder compliance, bladder outlet obstruction, history of stroke, diabetes mellitus (DM) status, and neurological abnormalities were analyzed using chi-square and Mann–Whitney to examine the potential predictors of DU. The odds ratio (OR) of each factor was also calculated. Logistic regression was furtherly used for the analysis. RESULTS A total of 649 patients were included in this study. Male (OR = 1.74, 95% CI = 1.28–2.38) and DM patients (OR = 2.06, 95% CI = 1.36–3.11) had a higher risk of DU, while bladder outlet obstruction (OR = 0.54, 95% CI = 0.39–0.76) was the protective factor of DU. Furthermore, multivariate analysis showed that the potential predictors of DU were male (OR = 1.903, 95% CI = 1.37–2.64), DM (OR= 1.899, 95% CI = 1.22–2.95), and bladder outlet obstruction (OR = 0.32, 95% CI = 0.32–0.65). CONCLUSIONS Age, sex, bladder outlet obstruction, and history of DM could become the predictors of DU.

Irreversible Bladder Remodeling Induced by Fibrosis

Underactive bladder and impaired bladder compliance are irreversible problems associated with bladder fibrosis. Remodeling of the extracellular matrix is regarded as an important mechanism associated with bladder fibrosis. However, various risk factors and conditions contribute to the functional impairment of the bladder associated with fibrosis, and there is limited knowledge about bladder fibrosis-associated problems in the field of neurourology. Further studies are thus necessary to elucidate the underlying mechanism of bladder fibrosis and to identify effective treatment.

Therapeutic effect of adipose-derived regenerative cells on bladder function in rats with underactive bladder

We examined the effect of adipose-derived regenerative cells (ADRC) on bladder functions in a rat model of detrusor underactivity (DU) induced by bladder over-distention. Adult female Sprague Dawley rats were divided into 3 groups: sham group (control); over-distention group; and over-distention with ADRC treatment group. Bladder was over-distended with saline (2.7mL) on day 1, 8, 15 and 22 of the study. ADRCs, which were harvested from male F344 rats, expanded via culture, were injected into the bladder wall at day 15. Cystometry and in vitro organ bath functional studies were performed on day 28. Moreover, histological assessment of the bladder was performed. In cystometry, significant prolongation of the inter-contraction interval (ICI) and decrease of voiding efficiency (VE) were observed in the over-distention group, compared to that in the control group. Significant improvement in ICI and VE was seen in the ADRC treatment group in comparison with the over-distention group. The over-distention group showed significantly weaker bladder contractile responses to carbachol and electrical field stimulation than the control group, while bladder contractile responses were significantly stronger in the ADRC treatment group than that in the over-distention group. The over-distention group showed substantial fibrosis of the bladder compared to the control group, whereas bladder fibrosis was alleviated in the ADRC treatment group. In conclusion, the injection of ADRC into bladder wall improved bladder dysfunction and histological changes induced by bladder over-distention. ADRCs-based regenerative therapy could be novel treatment for DU.

Safety, Tolerability, Pharmacokinetics, and Food Effects on TAC-302 in Healthy Participants: Randomized, Double-Blind, Placebo-Controlled, Single-Dose and Multiple-Dose Studies

TAC-302 stimulates neurite outgrowth activity and is expected to restore urinary function in patients with lower urinary tract dysfunction. We conducted 2 phase 1, randomized, placebo-controlled studies to confirm the safety and pharmacokinetics (PK) of TAC-302 in healthy adult Japanese male volunteers. In the first-in-human single-dose study (n = 60), TAC-302 was administered at doses from 100 to 1200 mg after an overnight fast. The effects of a meal on the PK of TAC-302 400 mg were also examined. A multiple-dose study (n = 36) evaluated the effects of meal fat content on the PK of single doses of TAC-302 (100, 200, or 400 mg) and multiple doses of TAC-302 administered for 5 days (100, 200, and 400 mg twice daily). TAC-302 showed linear PK up to doses of 1200 mg in the fasting state, and across the dose range of 100-400 mg in the fed state. No accumulation of TAC-302 was observed. Food, particularly with high fat content, increased TAC-302 plasma concentrations. No differences were observed in the adverse event incidence between the TAC-302 and placebo groups in either study. TAC-302 showed a wide safety margin.

Current and Future Directions of Stem Cell Therapy for Bladder Dysfunction

Stem cells are capable of self-renewal and differentiation into a range of cell types and promote the release of chemokines and progenitor cells necessary for tissue regeneration. Mesenchymal stem cells are multipotent progenitor cells with enhanced proliferation and differentiation capabilities and less tumorigenicity than conventional adult stem cells; these cells are also easier to acquire. Bladder dysfunction is often chronic in nature with limited treatment modalities due to its undetermined pathophysiology. Most treatments focus on symptom alleviation rather than pathognomonic changes repair. The potential of stem cell therapy for bladder dysfunction has been reported in preclinical models for stress urinary incontinence, overactive bladder, detrusor underactivity, and interstitial cystitis/bladder pain syndrome. Despite these findings, however, stem cell therapy is not yet available for clinical use. Only one pilot study on detrusor underactivity and a handful of clinical trials on stress urinary incontinence have reported the effects of stem cell treatment. This limitation may be due to stem cell function loss following ex vivo expansion, poor in vivo engraftment or survival after transplantation, or a lack of understanding of the precise mechanisms of action underlying therapeutic outcomes and in vivo behavior of stem cells administered to target organs. Efficacy comparisons with existing treatment modalities are also needed for the successful clinical application of stem cell therapies. This review describes the current status of stem cell research on treating bladder dysfunction and suggests future directions to facilitate clinical applications of this promising treatment modality, particularly for bladder dysfunction.

Understanding underactive bladder: a review of the contemporary literature

Underactive bladder (UAB) is characterized by prolonged voiding, hesitancy, and slow and/or intermittent stream with or without a sensation of incomplete bladder emptying. The overlap of UAB lower urinary tract symptoms with those of overactive bladder or bladder outlet obstruction, as well as its multifactorial etiology, make UAB study, as well as its diagnosis and management, a very arduous and challenging task. Therefore, despite its incidence and significant impact in the quality of life of both men and women, UAB remains a poorly understood urologic condition with insufficient and ineffective treatment options available. In this review, we will focus on the etiology theories that have been proposed and the animal models available to test those theories.

Long-term diabetes causes molecular alterations related to fibrosis and apoptosis in rat urinary bladder

Diabetes induces time-dependent alterations in urinary bladders. Long-term diabetes causes an underactive bladder. However, the fundamental mechanisms are still elusive. This study aimed to examine the histological changes and the potential molecular pathways affected by long-term diabetes in the rat bladder. Diabetes was induced in 8-week-old male Lewis rats by streptozotocin, while age-matched control rats received citrate buffer only. Forty-four weeks after diabetes induction, bladders were harvested for histological and molecular analyses. The expressions of proteins related to fibrosis, apoptosis and oxidative stress as well as the cellular signaling pathway in the bladder were examined by immunoblotting. Histological examinations illustrated diabetes caused detrusor hypertrophy and fibrotic changes in the bladder. Immunoblotting analysis demonstrated higher collagen I but lower elastin expression in the bladder in diabetic rats. These were accompanied by an increase in the expression of transforming growth factor-beta1, along with the downregulation of matrix metalloptoteinase-1, and upregulation of tissue inhibitor of metalloproteinase-1. Diabetic rats showed an increase in nitrotyrosine, but decrease in nuclear factor erythroid-related factor 2 (Nrf2) levels in the bladder. Enhanced apoptotic signaling was observed, characterized by increased expression of Bcl-2-associated X protein (Bax), decreased expression of Bcl-2, in the diabetic bladder. The nerve growth factor level was decreased in the diabetic bladder. A significant suppression in the protein expressions of phosphorylated extracellular signal-regulated kinases 1/2 was found in diabetic bladders. This study demonstrated that long-term diabetes caused molecular changes that could promote fibrosis and apoptosis in the bladder. Oxidative stress may be involved in this context.

Correlation of tools for objective evaluation of infravesical obstruction of men with lower urinary tract symptoms

Purpose

To identify how the most frequently used parameters in daily clinical practice diagnosing bladder outlet obstruction (BOO) due to benign prostate hyperplasia (BPH) correlate to each other.

Materials and methods

The study included 452 patients with lower urinary tract symptoms (LUTS) of the UNICAMP urology outpatient clinic of LUTS. Inclusion criteria: patients with BOO due to BPH who agreed to participate in the study. Exclusion criteria: patients with urinary tract infection, neurological diseases that compromised the lower urinary tract, prior prostatic surgery, radiotherapy or urethral stenosis. Patient assessment: history, international prostate symptoms score (IPSS), nocturnal quality of life score (NQoL) questionnaires, physical and digital rectal examination (DRE), PSA, transabdominal ultrasound with intravesical prostate protrusion (IPP), post-mictional residue and free uroflowmetry.

Results

There was no strong Spearman correlation among the studied variables. The only moderate correlations occurred between IPSS and NQoL (p <0001; c=0.56) and between IPP and prostate volume (p <0001; c=0.57). Weak correlations between IPP and post-mictional residue (p <0001; c=0.31) and free uroflowmetry (p <0001; c=-0.26); and between IPSS and free uroflowmetry (p <0001, c=-0.21) were observed.

Conclusion

In this study, we found moderate, weak, very weak and absent correlation among the various parameters used in the diagnosis and management of BOO due to BPH. As the value of these tools is variable, the creation of a logical and objective algorithm was not possible and the treatment is based on the interpretation of clinical symptoms.

Toward Self-Control Systems for Neurogenic Underactive Bladder: A Triboelectric Nanogenerator Sensor Integrated with a Bistable Micro-Actuator

Aging, neurologic diseases, and diabetes are a few risk factors that may lead to underactive bladder (UAB) syndrome. Despite all of the serious consequences of UAB, current solutions, the most common being ureteric catheterization, are all accompanied by serious shortcomings. The necessity of multiple catheterizations per day for a physically able patient not only reduces the quality of life with constant discomfort and pain but also can end up causing serious complications. Here, we present a bistable actuator to empty the bladder by incorporating shape memory alloy components integrated on flexible polyvinyl chloride sheets. The introduction of two compression and restoration phases for the actuator allows for repeated actuation for a more complete voiding of the bladder. The proposed actuator exhibits one of the highest reported voiding percentages of up to 78% of the bladder volume in an anesthetized rat after only 20 s of actuation. This amount of voiding is comparable to the common catheterization method, and its one time implantation onto the bladder rectifies the drawbacks of multiple catheterizations per day. Furthermore, the scaling of the device for animal models larger than rats can be easily achieved by adjusting the number of nitinol springs. For neurogenic UAB patients with degraded nerve function as well as degenerated detrusor muscle, we integrate a flexible triboelectric nanogenerator sensor with the actuator to detect the fullness of the bladder. The sensitivity of this sensor to the filling status of the bladder shows its capability for defining a self-control system in the future that would allow autonomous micturition.

Crystallizing the Definition of Underactive Bladder Syndrome, a Common but Under-recognized Clinical Entity

Detrusor underactivity (DU) is an important contributor to lower urinary tract symptoms (LUTS). While DU has been defined in the literature in urodynamic terms, current definitions lack specific parameters. In addition, the clinical syndrome associated with and manifesting itself as DU, underactive bladder (UAB), has not been well defined in the literature. In the absence of a precise definition of UAB, it is difficult to appreciate the true nature and burden of this condition. We review the evidence regarding the epidemiology, pathogenesis, diagnosis, and treatment of DU and UAB and discuss the challenges in gathering data in the absence of precise definitions. DU may be idiopathic or caused by ageing, medications, or a number of causes of neurogenic, myogenic, or iatrogenic origin. Treatments are largely palliative due to a lack of curative options, and include watchful waiting, catheterization, medications, and surgical interventions. In light of the evidence available in the literature, we propose that a new symptom-based definition of UAB syndrome should be developed as a first step in furthering more standardized research. Further discussion on this proposed definition to reach expert consensus will enable researchers to gather more robust data, allowing greater insights into DU and UAB diagnosis and treatment.