In the Human Urothelium and Suburothelium, Intradetrusor Botulinum Neurotoxin Type A Does Not Induce Apoptosis: Preliminary Results

Medium- to long-term outcomes of botulinum toxin A for idiopathic overactive bladder

Botulinum toxin A (BoNT-A) has become an important therapeutic tool in the management of refractory overactive bladder (OAB). Over the last decade, there have been growing numbers of patients receiving repeat injections and these outcomes have begun to be reported in large, high-quality cohorts. This article reviews the current evidence for the medium- to long-term use of BoNT-A in adults with idiopathic detrusor overactivity (IDO) receiving repeat injections. We find that medium-term outcomes are encouraging but long-term outcomes are not as extensively reported. There is high-quality evidence that efficacy following the first injection persists across multiple treatment cycles. There are no additional safety concerns from repeat injections up to six treatment cycles. However, there is a need for further data to confirm the efficacy and safety of BoNT-A beyond the follow-up period in the current literature.

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

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 (1.5 U; 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) from rat 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.

Effects of botulinum toxin type a in the bladder wall of children with neurogenic bladder dysfunction: a comparison of histological features before and after injections

PURPOSE

Botulinum toxin type A has gained popularity in urology. Most reported studies have been in adults at urology centers and most have addressed long-term safety. Since botulinum toxin type A treatment for neurogenic bladder dysfunction requires repeat injections, verifying that such treatment does not induce fibrosis in children seems essential.

MATERIALS AND METHODS

The study was approved by the institutional review board and patients were enrolled after we obtained written consent. Patients with neurogenic bladder dysfunction not responding to conventional treatment (anticholinergics and clean intermittent catheterization) were treated with 10 IU/kg botulinum toxin type A up to a maximum of 300 IU. Endoscopic cold cup biopsies were obtained from the posterolateral bladder wall 1.5 to 2 cm above the ureteral orifice. Bladder wall findings were categorized into 3 groups, including inflammatory infiltration, edema and fibrosis. Each criterion was then graded as mild or severe and analyzed by Fisher's exact test (p <0.05).

RESULTS

A total of 46 bladder wall biopsies were obtained from 40 patients 2 to 18 years old. Biopsies were evaluated in groups 1 and 2, including group 1-20 from patients with no botulinum toxin type A injection and group 2-20 after botulinum toxin type A injection. Group 2 was subdivided into group 3-10 biopsies after 1 injection and group 4-10 after multiple injections. Six patients underwent biopsy twice, that is before the first and second treatments. Histological changes were present in all biopsies. When comparing groups 1 and 2, there was no statistically significant difference in inflammation and edema. However, there was a significant difference in fibrosis between groups 1 and 4 (p <0.05) with apparently decreased fibrosis after multiple injections.

CONCLUSIONS

In our experience repeat botulinum toxin type A injections into the detrusor in children do not lead to increased fibrosis in the bladder wall. This study confirms the long-term safety of botulinum toxin type A in the pediatric population.