Acute exposure to insecticides such as organophosphates and carbamates induces functional changes at the neuromuscular junction of skeletal muscles that ultimately causes muscle necrosis. There is recent evidence that oxygen radical formation may be a factor in the toxicity of these insecticides. One of the well-recognized targets of free radical induced injury is peroxidation of lipids. Recently it was found that prostaglandin F2 (PGF2)-like compounds (termed F2-isoprostanes) are produced in vivo by a non-cyclooxygenase mechanism involving free radical-catalyzed peroxidation of arachidonic acid. We can detect F2-isoprostanes, following TLC purification, by gas chromatography/negative-ion chemical ionization. Quantification of these compounds provides a useful approach to determine whether oxygen free radicals initiate the insecticide-induced muscle necrosis by: (1) establishing the time course relationship between insecticide treatment, F2-isoprostanes production, and muscle injury, using light and electron microscope techniques, (2) determining whether the insecticide-induced muscle hyperactivity is causally related to F2- isoprostanes increase and injury by preventing fasciculations, (3) determining whether antioxidants and free radical scavengers such as the endogenous glutathione, inhibitors of xanthine oxidase such as allopurinol and inhibitors of lipid peroxidation such as the lazaroids prevent increases in F2-isoprostanes and muscle injury, (4) establishing whether F2-isoprostanes participates as a pathophysiological mediator of oxidant injury by treating control muscle with F2-isoprostanes, (5) determining metabolic conditions in muscle conducive to the production of oxygen free radicals through changes in ATP and creatine phosphate, changes in mitochondrial Ca+ + homeostasis and changes in the activity of cytochrome- c-oxidase and xanthine oxidase. Our preliminary data support the hypothesis that oxygen free radicals play a causative role in insecticide- induced muscle necrosis is a tenable one, and our proposed studies should determine whether, indeed, agents such organophosphates and carbamates induce muscle necrosis via lipid peroxidation and generation of F2- isoprostanes. As such, these studies will provide fundamental new insights into the molecular events underlying insecticide-induced injury as well as offer a therapeutic strategy for protection, namely treatment with antioxidants.

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Toxicology Subcommittee 2 (TOX)
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Vanderbilt University Medical Center
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