Ultrasound-assisted intravesical botulinum toxin A delivery attenuates acetic acid-induced bladder hyperactivity in rats

Qinggang Liu; Yi Gao; Huiling Cong; Limin Liao

doi:10.3389/fphar.2023.1214145

Ultrasound-assisted intravesical botulinum toxin A delivery attenuates acetic acid-induced bladder hyperactivity in rats

Front Pharmacol. 2023 Jul 24:14:1214145. doi: 10.3389/fphar.2023.1214145. eCollection 2023.

Authors

Qinggang Liu^{1

2

3

4

5}, Yi Gao^{2

5

6}, Huiling Cong^{2

5

6}, Limin Liao^{2

1

3

4

5

6}

Affiliations

¹ Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.
² Department of Urology, China Rehabilitation Research Center, Beijing, China.
³ School of Health and Life Sciences, University of Health and Rehabilitation Sciences, Qingdao, Shandong, China.
⁴ China Rehabilitation Science Institute, Beijing, China.
⁵ Beijing Key Laboratory of Neural Injury and Rehabilitation, Beijing, China.
⁶ School of Rehabilitation, Capital Medical University, Beijing, China.

Abstract

Background: Intradetrusor injection of botulinum toxin A (BTX-A) is an effective treatment for overactive bladder (OAB). However, the occurrence of adverse events associated with BTX-A injection therapy hinders its acceptance among patients and its clinical promotion. Intravesical instillation of BTX-A offers a promising alternative to injection therapy for treating OAB. Nevertheless, due to the presence of the bladder permeability barrier (BPB) and the high molecular weight of BTX-A, direct instillation is unable to penetrate the bladder urothelium. Purpose: This study aims to investigate the safety and feasibility of ultrasound-assisted intravesical delivery of BTX-A and its potential benefits in a rat model of bladder hyperactivity induced by acetic acid instillation. Methods: Hengli BTX-A and microbubbles (MB) were mixed and prepared as a novel complex. The size distribution and zeta potentials of the complex were measured. On day 1, rats' bladders were instilled with 1 mL of saline, BTX-A (20 U in 1 mL), MB, or MB-BTX-A (20 U in 1 mL) complex with or without ultrasound (US) exposure (1 MHz, 1.5 W/cm², 50% duty cycle, sonication for 10 s with a 10-s pause for a total of 10 min). The instillations were maintained for 30 min. After 7 days, cystometry was performed by filling the bladder with saline and 0.3% acetic acid (AA). Bladders were collected, weighed, and processed for immunoblotting, enzyme-linked immunosorbent assay (ELISA), histologic, and immunofluorescence analyses. Expression and distribution of SNAP-25 and SNAP-23 were assessed using Western blot and immunofluorescence. Calcitonin gene-related peptide (CGRP) in the bladder was detected using ELISA. Results: Intercontraction intervals (ICI) decreased by 72.99%, 76.16%, and 73.96% in rats pretreated with saline, BTX-A, and US + MB, respectively. However, rats treated with US + MB + BTX-A showed a significantly reduced response to AA instillation (57.31% decrease in ICI) without affecting amplitude, baseline pressure, or threshold pressure. Rats treated with US + MB + BTX-A exhibited increased cleavage of SNAP-25 and CGRP expression compared to the control group. Conclusion: Ultrasound-assisted intravesical delivery of BTX-A, with the assistance of MB cavitation, led to cleavage of SNAP-25, inhibition of calcitonin gene-related peptide release from afferent nerve terminals, and amelioration of acetic acid-induced bladder hyperactivity. These results support ultrasound-assisted intravesical delivery as an efficient non-injection method for administering BTX-A.

Keywords: bladder hyperactivity; botulinum toxin A; intravesical delivery; microbubbles; ultrasound.

Grants and funding

This study was funded by the National Natural Science Foundation of China (Grant number 82170792), the Research Projects of China Rehabilitation Research Center (Grant number 2021ZX-Q7; 2022HZ-08), and the fundamental research funds for central public welfare research institutes (Grant number 2023CZ-1).