Overflow urinary incontinence (OUI) due to intrapelvic nerve impairment is a frequent complication of pelvic surgery. Since refractory cases require the use of pads or self-catheterization, which significantly reduces the patient’s quality of life, the establishment of an effective treatment for postoperative OUI is desired. Recently, the efficacy of stem cell therapy for various lower urinary tract dysfunctions has been reported. However, challenges exist in stem cell therapy, such as complicated storage and high cost. To solve this problem, we focused on stem cell contents and reported that bone marrow-derived stem cell lysate (BSCL), not the cells themselves, improved bladder function and bladder fibrosis in a neurogenic OUI rat model (ICS 2020). However, the effects of BSCL on detrusor muscle contraction remain unknown. Therefore, in the present study, we aimed to clarify the validity of BSCL in a neurogenic OUI rat model by focusing on detrusor muscle contraction.

Bone marrow-derived stem cells were isolated from the bone marrow of rats, cultured, and suspended in phosphate buffered saline (PBS) at a concentration of 1.0×10⁶ cells/mL. BSCL was obtained by freeze-fracturing and filtering the suspension. Neurogenic OUI model was developed based on our previously established bilateral accessory nerve injury (BAI) model [1]. Seven- or eight-week-old male Wistar/ST rats were divided into sham, BAI, or BAI+BSCL groups. BAI surgery was performed by identifying and crushing the bilateral accessory nerves, which extend from the major pelvic ganglion, using reverse-action tweezers for 1 min. Sham surgery was performed by identifying the accessory nerves bilaterally. The BAI+BSCL group received BSCL (100 µL/body) intravenously through tail vein, immediately after surgery, while the sham and BAI groups received equal volumes of PBS. After six days, the bladders were removed and used for the isometric tension study and real-time PCR analysis. In the isometric tension study, contractile responses of the detrusor muscle to 80 mM KCl, carbachol (a muscarinic receptor agonist; 10⁻¹⁰-10⁻⁴ M), and electrical field stimulation (EFS; 1-64 Hz) were measured. For carbachol evaluation, the maximum response (Emax) and concentration inducing half of the Emax (EC50) were analyzed from the dose-response curves. To evaluate EFS, EFS-induced contractile responses were measured with no inhibitor or with atropine (a muscarinic inhibitor). The differences between the contractile responses before and after the addition of atropine were considered as muscarinic components.

There were no differences in 80 mM KCl-induced contractile responses among the three groups. Fig. 1A shows the dose-response curves for carbachol. Emax was significantly enhanced in the BAI group compared to the sham group, while it was significantly attenuated in the BAI+BSCL group compared to the BAI group (Fig. 1B). However, there were no differences in EC50 among the three groups (Fig. 1C). The EFS-induced contractile responses with no inhibitor were attenuated in the BAI and BAI+BSCL groups compared to those in the sham group (Fig. 2A). Cholinergic component-induced contractile responses were attenuated in the BAI group compared to those in the sham group (Fig. 2B). In the BAI+BSCL group, a trend toward improved cholinergic component-induced contractile responses was observed, although this was not significant. The mRNA expression levels of Chrm2 and Chrm3, which encode the muscarinic receptors M2 and M3, respectively, were higher in the BAI group than in the sham group, whereas they were lower in the BAI+BSCL group than in the BAI group.

BAI attenuates cholinergic component-induced contractile responses and enhances carbachol-induced contractile responses. These results suggest that acetylcholine released from parasympathetic nerve endings decreases after BAI. It is possible that the mRNA expression levels of muscarinic receptors increase to compensate for the low nervous input. Interestingly, BSCL improved carbachol-induced contractile responses and the mRNA expression levels of muscarinic receptors after BAI, which might be related to the increased acetylcholine release.

In the neurogenic OUI model, acetylcholine release from the parasympathetic nerve ending decreases, resulting in attenuated detrusor muscle contraction. BSCL may improve detrusor muscle contraction by increasing acetylcholine release. Therefore, BSCL are expected to be an effective treatment option for OUI after pelvic surgery.

Maeda K, Hotta Y, Shibayama M et al. Impairment of accessory nerves around major pelvic ganglion leading to overflow urinary incontinence in rats. Neurourol Urodyn. 2021; 40(2): 624-631.

Continence 7S1 (2023) 100860
DOI: 10.1016/j.cont.2023.100860