Sensory nerve endings in the skin, airways, eyes and mucous membranes are activated by a wide range of hazardous chemicals. These include pulmonary chemical agents as well as vesicants and noxious industrial chemicals. Activation of sensory nerve endings in the nasal passages and airways induces pain, irritation and apnea. Extended chemical exposure promotes injury by causing the release of inflammatory neuropeptides that contribute to edema formation in the lung and skin, ocular damage, mucus hypersecretion, pulmonary obstruction, and blister formation. In animal models these effects can be strongly reduced by prior neural desensitization or denervation. Thus, pharmacological blockade of neural activation, as well as block of neuropeptide receptors in target tissues, could represent effective measures to prevent and alleviate the deleterious effects of pulmonary agents and vesicants. The molecular targets for pulmonary agents and vesicants on sensory neurons are largely unknown. Recently, a new class of sensory chemoreceptors, the TRP ion channels, was discovered. The founding member, TRPV1, is the receptor for capsaicin, the pungent and inflammatory ingredient in chili peppers that is used as an incapacitating agent. TRPA1, a novel TRP ion channel, is activated by mustard oil (allyl isothiocyanate), a potent irritant and neuroinflammatory agent. We found that TRPA1 is exclusively expressed in sensory fibers that are also sensitive to capsaicin. Mustard oil and other plant-derived activators of TRPA1 show intriguing structural similarities with sulfur mustard. In addition, we found that TRPA1 is strongly activated by hazardous industrial chemicals. These include a,p-unsaturated aldehydes such as acrolein, a pulmonary agent used in the First World War. Our functional and behavioral analysis of mice deficient in TRPA1 showed that TRPA1 is essential for sensory neural responses to mustard oil, acrolein and other chemical hazards. Thus TRPA1, and potentially other TRP channels, may represent effective targets to prevent and treat the toxic effects of pulmonary agents and vesicants.
Our specific aims are to investigate the role of TRP channels in the response to pulmonary agents and vesicants in vitro and in vivo and to analyze the efficacy of TRP channel blockers and neuropeptide antagonists in the reduction of warfare agent toxicity. ? ? ?
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