Lower urinary tract dysfunction (LUTD) is caused by hyperglycemia-induced vascular endothelial damage in diabetes mellitus (DM). Moreover, chronic bladder ischemia induces bladder overactivity in the early stage and underactivity in the advanced stage in vascular endothelial dysfunction (1). Therefore, early treatment of bladder overactivity is important for patient health. Various pharmacotherapeutics, including anticholinergic agents, are used for the first-line treatment of detrusor overactivity in patients with DM at a risk of upper urinary tract damage. However, anticholinergic medications are not always effective, often causing adverse events, such as dry mouth and constipation. Vibegron, a new β3-adrenoceptor agonist, was approved for overactive bladder treatment in Japan in 2018. Notably, β3-adrenoceptor agonists, such as mirabegron, cause fewer clinical adverse events than anticholinergic medications (2). Moreover, vibegron suppresses bladder fibrosis in mice with spinal cord injury (3). These reports suggest vibegron as a potential therapeutic for LUTD in DM. However, specific effects of vibegron on DM-induced bladder dysfunction remain unknown. Therefore, in this study, we investigated the inflammatory and ischemic changes in the bladder of DM rats with or without vibegron treatment. To the best of our knowledge, this is the first study to determine the effects of vibegron on bladder activity due to DM.

Female Sprague–Dawley rats (age: 11–12 weeks old; weight: 250–300 g) were used in this study. The rats were maintained under a 12/12 h light/dark cycle with free access to water and laboratory food (CLEA Rodent Diet CE-2; CLEA Japan, Tokyo, Japan). All rats were divided into three groups: non-diabetic (N), diabetic (D), and vibegron-treated diabetic (DV) groups (n = 12 rats/group). Diabetes was induced via a single intraperitoneal injection of streptozotocin (65 mg/kg), and the control rats were injected with an equivalent volume of saline. Experiments were performed 8 weeks after diabetes induction (Fig. 1). From each group, one set of six rats was used for in vivo pressure recordings and another set was used for in vitro tests. Moreover, 24-h voiding assays were performed to evaluate the urodynamic parameters of all groups via awake cystometry//cystometrogram (CMG). Subsequently, 8-hydroxydeoxyguanosine (8-OHdG) levels in urine and mRNA expression levels of ischemia-related and inflammatory markers in bladder tissues were evaluated. Several parameters, including opening pressure (pressure at which the urethra opens and urine flows), intercontraction intervals (ICIs), number of non-voiding contractions (NVCs) per voiding, post-void residual (PVR) urine volume, bladder capacity, bladder compliance, and voiding efficiency (VE), were measured in CMG. NVC is defined as > 8 cm H2O increase in intravesical pressure above the baseline. Gene expression levels of ischemia-related and inflammatory markers, such as the hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β1, and tumor necrosis factor (TNF)-α, were quantified using real-time polymerase chain reaction (PCR). All values are expressed as the mean ± standard deviation. The Mann–Whitney U test was used to evaluate the statistical differences between groups. Statistical significance was set at p < 0.05.

Body weight was significantly lower in group D than in groups N and DV (237.0 ± 13.5 vs. 261.5 ± 10.5 and 262.3 ± 12.9 g [p = 0.0022 and p = 0.0043], respectively). Blood glucose levels were significantly higher in groups D and DV than in group N (487.5 ± 30.6 and 479.2 ± 51.0 vs. 140.5 ± 21.8 mg/dL [p = 0.0022 and p = 0.0022], respectively) (Fig. 2A). The 24-h voiding assays revealed significantly higher total voided volume (165.3 ± 47.6 and 141.6 ± 34.8 vs. 14.1 ± 2.1 mL [p = 0.0022 and p = 0.0022], respectively), tidal voided volume (3.4 ± 0.4 and 3.1 ± 0.5 vs. 0.9 ± 0.3 mL [p = 0.0022 and p = 0.0022], respectively), water intake (187.5 ± 51.8 and 166.7 ± 34.2 vs. 27.5 ± 5.2 mL [p = 0.0022 and p = 0.0022], respectively), and urine frequency (32.7 ± 6.3 and 35.7 ± 7.7 vs. 10.2 ± 2.9 [p = 0.0022 and p = 0.0022], respectively) in groups D and DV than in group N. Notably, no significant differences were observed between groups D and DV. Moreover, 8-OHdG levels in urine were significantly higher in group D than in groups N and DV (93.6 ± 18.2 vs. 25.2 ± 10.5 and 63.8 ± 17.2 ng/mg Cr [p = 0.0043 and p = 0.0303], respectively) (Fig. 2B). CMG revealed significantly higher opening pressure (44.1 ± 11.8 vs. 21.9 ± 3.1 and 28.5 ± 6.7 cm H2O [p = 0.0022 and p = 0.0022], respectively) and NVCs (0.2 ± 0.1 vs. 0.0 ± 0.0 and 0.0 ± 0.0 NVCs/min [p = 0.0087 and p = 0.0022], respectively) in group D than in groups N and DV (Fig. 3AB). Furthermore, ICIs (27.9 ± 8.1 and 23.0 ± 9.4 vs. 12.1 ± 2.4 min [p = 0.0022 and p = 0.0022], respectively), voided volume (1.8 ± 0.6 and 2.0 ± 0.7 vs. 0.5 ±　0.1 mL [p = 0.0022 and p = 0.0022], respectively), and PVR volume (0.2 ± 0.1 and 0.2 ± 0.1 vs. 0.0 ± 0.0 mL [p = 0.0022 and p = 0.0022], respectively) were significantly higher in groups D and DV than in group N. VE was significantly lower in groups D and DV than in group N (90.9 ± 3.2 and 90.9 ± 2.5 vs. 99.5 ± 1.1 % [p = 0.0022 and p = 0.0022], respectively). In molecular studies, mRNA expression levels of HIF-1α (1.3 ± 0.1- vs. 1.0 ± 0.2- and 0.9 ± 0.1-fold [p = 0.0022 and p = 0.0022], respectively), VEGF (1.9 ± 0.7- vs. 1.0 ± 0.3- and 0.9 ± 0.2-fold [p = 0.0043 and p = 0.0022], respectively), TGF-β1 (2.0 ± 2.0- vs. 1.0 ± 0.2- and 1.0 ± 0.1-fold [p = 0.0043 and p = 0.0022], respectively), and TNF-α (5.6 ± 9.2- vs. 1.0 ± 0.3- and 1.0 ± 0.4-fold [p = 0.0022 and p = 0.0022], respectively) in the bladder were significantly higher in group D than in groups N and DV (Fig. 2C).

Compared to normal rats, diabetic rats exhibited higher urinary oxidative stress indicated by increased 8-OHdG levels in the urine. Furthermore, NVCs, micturition pressure, and residual urine volume increased but VE decreased in diabetic rats, indicating the exacerbation of urinary storage and micturition symptoms. Reverse transcript (RT)-PCR revealed increased bladder ischemia and inflammatory marker levels in diabetic rats. Our results suggest that vibegron alleviates urinary oxidative stress by reducing the bladder ischemic inflammatory marker levels, which improves the bladder micturition pressure and reduces NVCs, thereby improving LUTD.

Vibegron, a new β3-adrenoceptor agonist approved for overactive bladder treatment, reduces the NVCs, opening pressure, and mRNA expression levels of HIF-1α, VEGF, TGF-β1, and TNF-α in early-stage DM (at 8 weeks), acting as a potnetial candidate for DM-induced detrusor overactivity treatment and bladder remodeling.

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