Expression of cleaved SNAP-25 after bladder wall injection of onabotulinumtoxinA or abobotulinumtoxinA: A comparative study in the mice.

Aims To study the expression of cleaved synaptosomal associated protein of 25 kDa (cSNAP-25) in the bladder wall injected with onabotulinumtoxinA (onabotA) or abobotulinumtoxinA (abobotA) and compare the relative potency of these two brands. Methods One injection of 0.5 U of onabotA or abobotA diluted in 2 µl of saline was carried out in the bladder dome of adult female mice, whose bladders were exposed by laparotomy. Three days later bladders were collected, divided in five segments (dome, upper, middle and lower body, and trigone) and each one was sectioned and immunoreacted against cSNAP-25, the end product of botulinum toxin type A (BoNT/A) activity. From each of the five segments one section was taken at random and the number of cSNAP-25 immunoreactive (IR) fibers was determined. Results Each injection resulted in the cleavage of SNAP-25 in all bladder sections, including those of the more distant segment from the injection point. The average number of cSNAP-25 positive fibers was higher in the onabotA, 341 ± 301, than in the abobotA-treated mice, 208 ± 152 (P = 0.003). The number of cSNAP-25 IR fibers varied three to five-fold between animals of each experimental group. Conclusions These findings confirm that, when injected in the bladder wall, in the same unit amount and same volume, onabotA is 1.6 times more potent to cleave SNAP-25 than abobotA. The conversion ratio suggested by these experiments is 1:1.6 between onabotA and abobotA. Each injection, although preformed in the same way, may induce substantially different amounts of cSNAP-25. Neurourol. Urodynam. © 2015 Wiley Periodicals, Inc.