Botulism

Botulinum neurotoxins are known to have seven serotypes (BoNT/A-G). Here we report a new BoNT serotype, tentatively named BoNT/X, which has the lowest sequence identity with other BoNTs and is not recognized by antisera against known BoNTs. Similar to BoNT/B/D/F/G, BoNT/X cleaves vesicle-associated membrane proteins (VAMP) 1, 2 and 3, but at a novel site (Arg66-Ala67 in VAMP2). Remarkably, BoNT/X is the only toxin that also cleaves non-canonical substrates VAMP4, VAMP5 and Ykt6. To validate its activity, a small amount of full-length BoNT/X was assembled by linking two non-toxic fragments using a transpeptidase (sortase). Assembled BoNT/X cleaves VAMP2 and VAMP4 in cultured neurons and causes flaccid paralysis in mice. Thus, BoNT/X is a novel BoNT with a unique substrate profile. Its discovery posts a challenge to develop effective countermeasures, provides a novel tool for studying intracellular membrane trafficking, and presents a new potential therapeutic toxin for modulating secretions in cells.

The delivery of genetic information has emerged as a valid therapeutic approach. Various reports have demonstrated that mRNA, besides its remarkable potential as vaccine, can also promote expression without inducing an adverse immune response against the encoded protein. In the current study, we set out to explore whether our technology based on chemically unmodified mRNA is suitable for passive immunization. To this end, various antibodies using different designs were expressed and characterized in vitro and in vivo in the fields of viral infections, toxin exposure, and cancer immunotherapies. Single injections of mRNA-lipid nanoparticle (LNP) were sufficient to establish rapid, strong, and long-lasting serum antibody titers in vivo, thereby enabling both prophylactic and therapeutic protection against lethal rabies infection or botulinum intoxication. Moreover, therapeutic mRNA-mediated antibody expression allowed mice to survive an otherwise lethal tumor challenge. In conclusion, the present study demonstrates the utility of formulated mRNA as a potent novel technology for passive immunization.

Clostridium botulinum, a polyphyletic Gram-positive taxon of bacteria, is classified purely by their ability to produce botulinum neurotoxin (BoNT). BoNT is the primary virulence factor and the causative agent of botulism. A potentially fatal disease, botulism is classically characterized by a symmetrical descending flaccid paralysis, which is left untreated can lead to respiratory failure and death. Botulism cases are classified into three main forms dependent on the nature of intoxication; foodborne, wound and infant. The BoNT, regarded as the most potent biological substance known, is a zinc metalloprotease that specifically cleaves SNARE proteins at neuromuscular junctions, preventing exocytosis of neurotransmitters, leading to muscle paralysis. The BoNT is now used to treat numerous medical conditions caused by overactive or spastic muscles and is extensively used in the cosmetic industry due to its high specificity and the exceedingly small doses needed to exert long-lasting pharmacological effects. Additionally, the ability to form endospores is critical to the pathogenicity of the bacteria. Disease transmission is often facilitated via the metabolically dormant spores that are highly resistant to environment stresses, allowing persistence in the environment in unfavourable conditions. Infant and wound botulism infections are initiated upon germination of the spores into neurotoxin producing vegetative cells, whereas foodborne botulism is attributed to ingestion of preformed BoNT. C. botulinum is a saprophytic bacterium, thought to have evolved its potent neurotoxin to establish a source of nutrients by killing its host.

Botulinum toxin (BT) is infamous for its extreme toxicity. If it enters the bloodstream, it can cause botulism presenting with a typical pattern of motor and autonomic dysfunction. An international expert panel organised by IAB-Interdisciplinary Working Group for Movement Disorders explored iatrogenic botulism after BT's medical use (IB), reached conclusions and formulated recommendations. When injected into its target tissue, BT binds to gangliosides on cholinergic nerve terminals before it is internalised permanently. Small amounts of BT, however, are circulating within the bloodstream. When BT type B is applied, IB-B occurs frequently, typically affecting the autonomic nervous system. When BT type A is applied, IB-A only occurs in special circumstances, even when high doses are used. We identified 236 patients with IB-A in the literature. All IB-A was mild or moderate and fully reversible. In 212 patients, it occurred with unapproved BT use. In 116 of them, unapproved BT preparations were used, in 81, unapproved indications were treated and in 15, underlying neuromuscular impairment including myasthenia gravis, Lambert-Eaton myasthenic syndrome, amyotrophic lateral sclerosis and spinal muscle atrophy were contraindications for BT use. In 24 patients, IB-A occurred in approved BT use. Their evaluation was frequently incomplete, so that causes for IB-A often remain unclear. They may include presence of differential diagnosis, subclinical neuromuscular impairment and interference with additional diseases. When IB is suspected, proper evaluation is necessary to verify it and to identify its causes. Off-label use is common in BT therapy. However, it should be performed with caution, especially in children and when high doses are applied. High BT doses should not be applied to low volumes of target tissues, in order not to exceed the BT binding capacity.