Different time courses of recovery after poisoning with botulinum neurotoxin serotypes A and E in humans

Botulinum toxin serotypes A and E (BoNT/A and /E) cleave the carboxy-terminus of synaptosomal associated protein-25 (SNAP-25) removing nine and 26 residues, respectively. To investigate the effect of these lesions of the same target molecule, 11 volunteers were injected with 3 IU of BoNT/A in the extensor digitorum brevis (EDB) muscle of one foot and with 3 IU of BoNT/E in the contralateral one. In addition, seven volunteers were similarly injected with mixtures of BoNT/A + BoNT/E. Compound muscular action potential (CMAP) was measured at different time intervals and the percentage variation of CMAP (%CMAP) was calculated. Unexpectedly, a much faster recovery of %CMAP after BoNT/E injections was observed. Double poisoned EBD muscles recovered similarly to BoNT/E. So, a larger deletion of the SNAP-25 molecule caused by BoNT/E leads to a faster functional recovery.