Spread of onabotulinumtoxinA after bladder injection. Experimental study using the distribution of cleaved SNAP-25 as the marker of the toxin action

Abstract

Background: OnabotulinumtoxinA (Onabot/A) has been used to treat detrusor overactivity disorders. The treatment is based on several injections of toxin throughout the bladder wall. However, injection protocols are not well established among clinicians, varying in dose and dilution.

Objective: Study the distribution and neurochemistry of cleaved synaptosome-associated protein of 25 kDa (cSNAP-25) after Onabot/A administration in the guinea pig bladder. In addition, we analyzed which factor, dose or volume, contributes more to the diffusion of the toxin.

Design, setting, and participants: Guinea pig bladders were treated with Onabot/A via intramural injection or an instillation.

Measurements: Bladder cryostat sections were processed for single or dual immunohistochemistry staining with antibodies against cSNAP-25, vesicular acetylcholine transporter, tyrosine hydroxylase, and calcitonin gene-related peptide. Different administration methods and doses were analyzed. Statistical analysis was performed using the chi-square test for colocalization studies after multiple injections and the t test for the evaluation of affected fibers after a single injection.

Results and limitations: cSNAP-25 immunoreactive fibers were abundant throughout the bladder tissue in the mucosa and muscular layer. Double labeling showed that parasympathetic fibers are more affected than sympathetic or sensory. A single Onabot/A injection is more effective if diluted in a higher volume. Onabot/A instillation in the bladder does not cleave SNAP-25 protein.

Conclusions: A single Onabot/A injection spreads the neurotoxin activity to the opposite side of the guinea pig bladder. This action is more evident when high saline volumes are used to dissolve Onabot/A. The toxin cleaves the SNAP-25 protein mainly in cholinergic but also in adrenergic and sensory fibers. In contrast with intramural injection, instillation of Onabot/A does not cleave SNAP-25 in nerve fibers.