Botulinum neurotoxins intoxication

Mechanism of Action of Botulinum Neurotoxin and Overview of Medical Countermeasures for Intoxication... 

The botulinum neurotoxins (BoNTs) comprise a family of seven distinct neurotoxic proteins (A-G) produced by immunologically discrete strains of the anaerobic bacterium Clostridium botulinum and in rare cases by Clostridium baratii and Clostridium butyricum (Habermann and Dreyer, 1986 Harvey et ah, 2002 Simpson, 2004). These toxins act on peripheral cholinergic synapses to inhibit spontaneous and impulse-dependent release of acetylcholine (ACh) (Brooks, 1956 Kao et al., 1976). Intoxication by BoNT results in muscle weakness, which can be fatal when the diaphragm and intercostal muscles become sufficiently compromised to impair ventilation (Dickson and Shevky, 1923). The BoNTs are the most potent substances in nature, and exposure to as httle as 1-3 ng/kg may be sufficient to cause human lethahty (GUI, 1982 Middlebrook and Franz, 1997 Amon et al., 2001). 

Dickerson, T.J. and Janda, K.D. 2006. The use of small molecules to investigate molecular mechanisms and therapeutic targets for treatment of botulinum neurotoxin A intoxication. ACS Chem. Biol. 1 359-369. 

Botulism, a neuroparalytic life-threatening disease, is caused by the botulinum neurotoxin serotype A (BoNTA). Although antibodies are effective in preventing the extracellular toxin to continue the intoxication process, they have no effect on prior intoxicated neurons. Targeting the BoNTA endopeptidase (BoNTAe) could be a valid alternative, since its inhibition may potentially neutralize the intracellular BoNTA. 

Botulinum neurotoxin (BoNT) is the most potent poison known to mankind. Currently no antidote is available to rescue poisoned synapses. An effective medical countermeasure strategy would require developing a drug that could rescue poisoned neuromuscular synapses and include its efficient delivery specifically to poisonedpresynaptic nerve terminals. Here we report a drug delivery strategy that could directly deliver toxin inhibitors into the intoxicated nerve terminal cytosol. 

An effective Botulinum neurotoxin-based drug delivery vehicle can be used to directly deliver toxin inhibitors into the intoxicated nerve terminal cytosol. The concept may possibly be utilized for drug delivery for other neuronal and neuromuscular disorders. Besides a BoNT therapeutic approach, this report also provides new fundamental knowledge of endocytosis and exocytosis as well as of BoNT trafficking in neurons. 

Figure 2. Schematic diagram of botulinum neurotoxin showing its light and heavy chains. The two different domains of the heavy chain shaded with different patterns indicate the N-terminal and C-terminal halves (about 50 kDa each). These two domains are believed to play different functional roles during the intoxication process. The light chain has been shown to contain the toxic site.

Matsuda, M., Sugimoto, N., Ozutsumi, K. and Hirai, T., 1982, Acute botulinum-like intoxication of tetanus neurotoxin in mice. Biochem. Biophys. Res. Commun. 104 799-805. 

Although inhalational botulinum intoxication was investigated in other animal species, these studies have not provided specific data on toxin absorption. The behavior of BoNTs in the respiratory tract was only recently investigated. Park and Simpson (2003) studied the properties of pure BoNT/A neurotoxin both in vivo and in vitro using mice and pulmonary cell culture models, respectively. Mean survival times were compared in mice receiving various doses of pure BoNT/A either IN or IP. Pure BoNT/A was found to be a potent intranasal poison, although the toxicity (as determined by mean survival time) associated with IP administration was somewhat higher. Mean survival times in mice were less than 100 (IP) or 600 min (IN) after administration of 0.1 pg pure toxin 75 (IP) or 400 min (IN) for 1 pg toxin and 120 min (IN) for 10 pg toxin (Park and... 

A. Characteristics. Botulism is caused by intoxication with any of the seven distinct neurotoxins produced by the bacillus Clostridium botulinum. The toxins are proteins that bind to the presynaptic membrane of neurons at peripheral cholinergic synapses to prevent release of acetylcholine and block neurotransmi ssion. 

Botulinum Toxins. Other neurotoxins, such as the botulinum toxins, must enter nerve terminals before they can block the release of neurotransmitters, which normally cause muscle contraction. These large-protein neurotoxins generally kill by relatively slow onset respiratory failure (within hours to days). The intoxicated individual may not show... 

General supportive measures are likely to be effective in therapy of intoxication. Artificial ventilation could be lifesaving in the case of neurotoxins such as the botulinum toxins and saxitoxin. Oxygen therapy, with or without artificial ventilation, may be beneficial for intoxication with toxins such as ricin that directly damage the alveolar-capillary membrane of the lung. Vasoactive drugs and volume expanders could be used to treat the shocklike state that accompanies some intoxications (eg, with staphylococcal enterotoxin B). These measures could be used in conjunction with more specific therapies. 

Since botulinum is a neurotoxin, large-scale production should meet biosafety level 3 containment and strict handling to avoid the possible human intoxication. Fermentation is carried out in complex medium containing casein hydrolysate, yeast extract, and glucose for 4 days. Then, botulinum toxin is precipitated with 3 N sulfuric acid followed by purification with DEAE-Sephadex column. Botulinum toxin was crystallized then and purified by additional steps using various affinity and size exclusion chromatography. Purity and quality were checked by animal testing. Production and purification steps vary with Clostridium strain used and botulinum type to be produced. ... 

The toxin BoTx, produced by the anaerobe Clostridium botulinum, has the reputation of being the most toxic substance by weight known to humans, being at least 5000 times more toxic than sarin. Botulism is a disease of both humans and animals. Seven dilferent functionally related neurotoxins are produced by various strains (A-G). Botulism is essentially an intoxication, brought on by ingestion of the toxin produced by clostridial infection of food, usually incorrectly canned meats. Primary botulism, a direct infection, is rare and only affects infants in the human species. Botulinum intoxication can, however, be treated, and this modifies the toxicity considerably. It is estimated that less than 10 % of natural cases receiving ventilatory and antitoxin support are fatal. 

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