Objective: The seven serotypes A-G of botulinum neurotoxins (BoNT) are extremely potent poisons but also highly effective medicines to treat hyperactive cholinergic neurons in different diseases and symptoms such as dystonias, spasticity, pain and hyperhidrosis. However, during long-term treatment patients may become non-responsive to the approved BoNT/A and B due to antibody formation. The remaining serotypes C-G might display treatment alternatives. BoNT/D is least related with A and B thereby circumventing neutralisation in A/B non-responder. Interestingly, no human intoxication has been reported with BoNT/D. Here, we produced BoNT/D and compared its potency in mice hemidiaphragm preparations and human extensor digitorum brevis muscle (EDB) with BoNT/A and incobotulinumtoxinA.
Methods: BoNT/D was expressed recombinantly in E. coli and isolated by various chromatographic steps. The potency of BoNT/D and native BoNT/A was determined at the mouse phrenic nerve hemidiaphragm preparation. Different dosages of BoNT/D and incobotulinumtoxinA were injected into EDB muscle of human volunteersand its compound muscle action potential was measured at 11 time points.
Results: BoNT/A and D are similarly effective in mice tissue. Contrarily, in human muscle BoNT/D displayed ˜8-fold lower potency and shortened duration of action (60 vs. 140 days).
Conclusions: BoNT/D acts in human neurons but higher dosing and shortened duration of action limits its usage as treatment alternative.
