Effect of botulinum toxin A on urothelial-release of ATP and expression of SNARE targets within the urothelium

Abstract

Aims Botulinum neurotoxin serotype A (BoNT/A) has emerged as an effective treatment of urinary bladder overactivity. Intravesical lipotoxin (BoNT/A delivery using liposomes), which may target the urothelium, is effective in blocking acetic acid induced hyperactivity in animals. The objective of this study was to assess the possible site of toxin action within the urothelium. Methods We examined expression of the toxin receptor (SV2) and its cleavage targets (SNAP-25 and SNAP-23) within urothelium as well as effects of the toxin on mechanically evoked release of ATP from cultured rat urothelial cells. ATP release was measured using the luciferin-luciferase assay; we examined expression of SNAP-23 and -25 in urothelial cells and mucosa of rat and human bladders. Results BoNT/A (1.5U; 1–3 hr) blocked hypotonic evoked release of urothelial ATP, without affecting morphology. The expression of protein targets for BoNT/A binding (SV2) was detected in human and rat bladder mucosa and catalytic action (SNAP-23, -25) in urothelial cells and mucosa (differed in intensity) fromrat and human bladder. Incubation of cultured (rat) urothelial cells with BoNT/A decreased expression levels of both SNAP-23 (44%) and SNAP-25 (80%). Conclusions Our findings reveal that the bladder urothelium expresses the intracellular targets and the binding protein for cellular uptake of BoNT/A; and that the toxin is able to suppress the levels of these targets as well as hypotonic-evoked ATP release. These data raise the possibility that intravesical treatment with BoNT/A suppresses bladder reflex and sensory mechanisms by affecting a number of urothelial functions including release of transmitters.

Mucosal modulation of contractility in bladder strips from normal and overactive rat models and the effect of botulinum toxin A on overactive bladder strips

“…In spinal cord injured (SCI) rats, BoNT‐A significantly reduced ATP release into the bladder lumen, presumably from the urothelium and in patients with neurogenic and idiopathic detrusor overactivity, BoNT‐A decreased expression of sensory receptors P2X 3 and TRPV1 . SNAP‐25 expression has been identified in human and mouse urothelium and BoNT‐A was found to inhibit ATP release from urothelial cells . In contrast, in another study, SNAP‐25 was not detected in human urothelial or muscle cells but in nerve fibres that permeated the urothelium and muscle layers …”

Loss of VAMP5 in mice results in duplication of the ureter and insufficient expansion of the lung

“…Hydroureter may reflect the retention of urine caused by lowering of the activity of urinary systems. VAMP2, SNAP23, and SNAP25 were detected in the urothelial cells, and were suggested to be targets of botulinum toxin (Hanna-Mitchell et al, 2015). The basal epithelial cells sense the extent of urine volume in the bladder by receiving neurotransmitters from neurons, and releasing ATP and NO to regulate contraction of the bladder and ureter (Cruz, 2014).…”

Current and potential urological applications of botulinum toxin A

“…17,18 Despite this apparent accumulation of BoNTA in parasympa thetic nerves, in 2014, the presence of binding protein SV2 as well as the target protein SNAP25 was demon strated within the bladder mucosa using immunohisto chemical staining and western blotting methods. 19,20 This finding indicates that the effects of BoNTA in the urinary bladder are more complex than previously thought, and intravesical delivery of BoNTA into the urothelium by might be both possible and clinically relevant.…”