Dissociation of the 900kDa neurotoxin complex from C. botulinum under physiological conditions

This study assesses the stability of the 900kDa botulinum neurotoxin complex and its dissociation under physiological conditions. The medicinal botulinum neurotoxin product Xeomin super(()R) consists of the 150kDa neurotoxin molecule free of complexing proteins. In contrast, first-generation neurotoxin products contain the 900kDa neurotoxin complex consisting of the 150kDa neurotoxin molecule and several non-toxic proteins known as complexing proteins. It has been claimed that these complex proteins serve to prolong neurotoxin persistence and inhibit neurotoxin diffusion into adjacent tissues. The 900kDa neurotoxin complex was exposed to various pH values and then separated to differentiate between the resulting neurotoxin entities. Separation conditions were qualified by Western blot and the toxin activity. The 150kDa neurotoxin molecule is released from the 900kDa complex in less than a minute when exposed to physiological pH values. This time frame is extremely short in comparison to the onset of the therapeutic effect, which is measured in days. Therefore, the complexing proteins cannot stabilize the neurotoxin or inhibit its diffusion as claimed. Accordingly, the necessity of these complexing proteins in medicinal formulations must be questioned. Finally, these data aid in understanding the clinical equipotency of Xeomin super(()R), the 150kDa neurotoxin molecule free of complexing proteins, and botulinum neurotoxin preparations containing complexing proteins.