Thioredoxin and Its Reductase Are Present on Synaptic Vesicles, and Their Inhibition Prevents the Paralysis Induced by Botulinum Neurotoxins

• Published in: Cell reports (Cambridge) Vol. 8; no. 6; pp. 1870 - 1878
• Main Authors: Pirazzini, Marco, Azarnia Tehran, Domenico, Zanetti, Giulia, Megighian, Aram, Scorzeto, Michele, Fillo, Silvia, Shone, Clifford C., Binz, Thomas, Rossetto, Ornella, Lista, Florigio, Montecucco, Cesare
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25-09-2014; Elsevier
• Subjects: Animals; Botulinum Toxins - toxicity; Cerebral Cortex - drug effects; Cerebral Cortex - metabolism; Curcumin - pharmacology; Curcumin - therapeutic use; Cytoplasm - metabolism; Disulfides - pharmacology; Disulfides - therapeutic use; Enzyme Activation - drug effects; Enzyme Inhibitors - pharmacology; Enzyme Inhibitors - therapeutic use; Imidazoles - pharmacology; Imidazoles - therapeutic use; Male; Mice; Neurons - drug effects; Neurons - metabolism; Paralysis - etiology; Paralysis - prevention & control; Serotyping; Synaptic Vesicles - drug effects; Synaptic Vesicles - enzymology; Synaptosomal-Associated Protein 25 - metabolism; Thioredoxin-Disulfide Reductase - antagonists & inhibitors; Thioredoxin-Disulfide Reductase - metabolism; Thioredoxins - antagonists & inhibitors; Thioredoxins - metabolism
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2014.08.017

Botulinum neurotoxins consist of a metalloprotease linked via a conserved interchain disulfide bond to a heavy chain responsible for neurospecific binding and translocation of the enzymatic domain in the nerve terminal cytosol. The metalloprotease activity is enabled upon disulfide reduction and causes neuroparalysis by cleaving the SNARE proteins. Here, we show that the thioredoxin reductase-thioredoxin protein disulfide-reducing system is present on synaptic vesicles and that it is functional and responsible for the reduction of the interchain disulfide of botulinum neurotoxin serotypes A, C, and E. Specific inhibitors of thioredoxin reductase or thioredoxin prevent intoxication of cultured neurons in a dose-dependent manner and are also very effective inhibitors of the paralysis of the neuromuscular junction. We found that this group of inhibitors of botulinum neurotoxins is very effective in vivo. Most of them are nontoxic and are good candidates as preventive and therapeutic drugs for human botulism.
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•Synaptic vesicles possess an active thioredoxin reductase-thioredoxin system•The two proteins are on the cytosolic side of the synaptic vesicle membrane•This system reduces the interchain disulfide bond of botulinum neurotoxins•Specific inhibitors prevent the neuroparalysis induced by botulinum neurotoxins
About 40 botulinum neurotoxins have been recently discovered, highlighting the need for chemical inhibitors that target these potent toxins. Pirazzini et al. now find that synaptic vesicles possess the thioredoxin reductase-thioredoxin system and show that it is responsible for the selective cleavage of a key toxin disulfide bond, a step required for the entry of all such neurotoxins into neurons. The authors thus uncover a class of inhibitors capable of acting in vivo.