BoNTs cause neuroparalysis by blocking neurotransmitter release from presynaptic neurons at the neuromuscular junctions. Among the seven serotypes of BoNTs, designated A to G, the BoNT/A serotype is the most toxic with its potency at a picomolar (pM) concentration. BoNT/A is a dichain peptide consisting of about a 100-kDa heavy Z-VAD-FMK chemical structure chain (HC) and a 50-kDa light chain (LC). Each of these two peptide components serves its specific function in the mechanism of BoNT/A action. The sequential steps in the mechanism consist of (a) toxin internalization into neurons via specific receptor binding by the HC followed by vesicular endocytosis of the holotoxin;

(b) separation of the LC from the HC inside a lower pH environment of the endosomes via the cleavage of the disulfide linkage between the HC and LC; (c) formation by the HCs

of endosomal membrane pores, which Selleckchem Screening Library serve as conduits for the release of the LCs into the cytosol; and finally, (d) an endopeptidase function of the LC in the neuronal cytosol causing the degradation of the 25-kDa vesicle fusion protein called synaptosomal-associated membrane protein (SNAP-25) and, thus, inhibiting the Ca2+-dependent stimulus-induced release of neurotransmitter molecules e.g., acetylcholine from presynaptic neurons. Attempts to develop BoNT/A countermeasures have mostly focused on inhibiting one or more of these steps. However, our previous reports ( Ray et al., 1993, Ray et al., 1999 and Ishida et al., 2004) have indicated that besides the BoNT/A LC-induced SNAP-25 hydrolysis

mechanism described above, there could be an alternate mechanism of inhibition of neuroexocytosis by BoNT/A. We had proposed that this alternate mechanism involves BoNT/A effects on the roles of PLA2, arachidonic acid (AA), lysophosphatidic acid (LPA) and RhoB in stimulated neuroexocytosis. We had also demonstrated that in nerve growth factor-differentiated PC-12 cells, Mas plus high (80 mM) K+ caused ACh release in an apparently SNAP-25 independent manner ( Ray et al., 1997). These observations, taken together, would suggest the PLA2-dependent mechanisms of neuroexocytosis as an alternate therapeutic ADAMTS5 target for botulinum intoxication. In this report, we provide a proof of this concept by showing that a potent PLA2 activator, Mas-7 can rescue BoNT/A-poisoned cultured spinal cord neurons by restoring their stimulus-induced neurotransmitter release function. BoNTs are extremely potent food poisons, with a mouse LD50 of 0.1 ng/kg for BoNT/A (Greenfield et al., 2002 and Arnon et al., 2001). Contamination of restaurant, catered or commercial foodstuffs or beverages could cause illness in a large number of consumers (Greenfield et al., 2002). Aerosol exposure of BoNTs does not occur naturally, but could be attempted by bioterrorists to achieve a widespread effect.