Botulinum Neurotoxins: History, Mechanism, and Applications. A Narrative Review

Botulinum neurotoxins (BoNTs), produced by Clostridium botulinum, exert their potent neuroparalytic effects by specifically targeting presynaptic cholinergic nerve terminals. BoNTs consist of a heavy chain that mediates high-affinity neuronal binding and endocytosis, and a light chain that, once translocated into the cytosol, acts as a zinc-dependent metalloprotease. The light chain cleaves SNARE proteins essential for synaptic vesicle fusion, thereby inhibiting acetylcholine release and leading to flaccid paralysis. This intoxication spans foodborne, wound, and infant botulism, all characterized by commonly observed heat-resistant endospores that enable bacterial survival under adverse conditions. BoNT intoxication induces flaccid paralysis, and both natural and synthetic neurotoxins disrupt neuronal communication by targeting synaptic components. However, BoNTs differ in their origin, mechanism of action, structure, and interactions. Clinical harnessing of non-poisoning low doses of BoNT/A and BoNT/B serotypes is used for alleviating symptoms of diverse diseases. Molecular engineering and clinical formulation enabled BoNTs optimization into pharmacologically safe and targeted therapeutic agents that replicate the selective neuronal silencing observed in their natural forms.