Early experimental results of using a novel delivery carrier, hyaluronan-phosphatidylethanolamine (HA-PE), which may allow simple bladder instillation of botulinum toxin A as effectively as direct detrusor muscle injection

Abstract

Introduction: Botulinum toxin A (BTX-A) is a neurotoxin that inhibits acetylcholine release by cleaving cytosolic synaptosome-associated protein 25 (SNAP-25) and results in bladder relaxation. A BTX-A intravesical injection has been established as an effective option for treating detrusor overactivity.

Study design: Sixty female Sprague Dawley rats were equally divided into control and experimental groups. Control Groups 1 to 3 received: BTX-A 10 units + saline instillation; hyaluronan-phosphatidylethanolamine (HA-PE) 0.5 g + saline instillation; and BTX-A 5 Uintra-detrusor injections, respectively. Treatment Groups 4 to 6 received: Alexa^®594-labeled BTX-A 10 U + HA-PE 0.5 g + saline instillation; BTX-A 5 U + HA-PE 0.2-0.5 g instilled for 60 min; and BTX-A 10 U + HA-PE 0.2-0.5 g instilled for 30 min, respectively. All procedures were performed under isoflurane general anesthesia. The primary outcome of this study was the degree of SNAP-25 staining in control and experimental groups compared to Group 3 (detrusor muscle injection). Urodynamic studies were performed at baseline and at day 14 after 1% acetic acid (AA) instillation, to evaluate the maximum pressure during filling (MP) and inter-contraction intervals (ICI). Group 4 rats were examined for Alexa^®594 fluorescence to demonstrate physical translocation of BTX-A-HA-PE complex. Standard histology was performed to assess the effect of HA-PE on bladder mucosa and detrusor muscle.

Results: Group 3 showed the least SNAP-25 staining (7.3 ± 5.0%) compared with all groups except Group 5A (12.4 ± 12.27%, P = 1.0). Group 6A, which had high HA-PE dose but a shorter instillation time, showed fairly extensive SNAP-25 staining (22.9 ± 10%). Confocal microscopy of Group 4 confirmed the presence of Alexa^®594 fluorescence across the urothelium. Urodynamic parameters were not significantly different at baseline (P = 1.0). After acetic acid instillation, Group 5A showed minimal change in ICI, which was comparable to ICI in Group 3 rats.

Discussion: SNAP-25 staining in Group 5A was comparable to Group 3, suggesting that adequate HA-PE and instillation time allows the efficacy of this carrier mechanism to be comparable to standard intra-detrusor injections. All other groups showed significantly higher SNAP-25 staining compared to Group 3. A dose response effect was demonstrated; higher dose of HA-PE (Group 5A vs Group 5B) and longer instillation time (Group 5 vs Group 6) led to lower SNAP-25 staining.

Conclusion: This novel method of BTX-A delivery to the bladder using a carrier (HA-PE) is promising and requires further investigation. Using a larger animal model, identifying an optimal dose of HA-PE and instillation time, and reproducing the current results are further required to validate this carrier.

Keywords: Bladder instillations; Botulinum toxin A; Detrusor overactivity; Modulated carrier; Neurogenic bladder; SNAP-25.