Synergistic Protective Effects of Selected Arginine Analogues against Sulphur Mustard Toxicity in Neuron Culture

Abstract

Previous studies in this laboratory have shown that the arginine analoguesl-thiocitrulline (l-TC) andl-nitroarginine methyl ester (l-NAME) have potent protective activity against sulphur mustard (HD) toxicity that was not related to their nitric oxide synthase inhibiting activities. Furthermore, their characteristics of action suggested that they act at different sites to exert their protection.l-TC acted rapidly (minutes of preincubation) and was equipotent in protecting either immature or mature cultures of chick embryo neurons against the toxicity of HD whilel-NAME was only effective in mature cultures. Maximal protection occurred at mM drug concentrations and increased the LC50 of HD by ∼200% (l-NAME) to ∼800% (l-TC).l-NAME did not alter the efficacy ofl-TC in immature cultures but increased the LC50 up to 1500% in mature cultures. Removal ofl-NAME eliminated this synergism, leaving only the persistent protection ofl-TC.l-Nitroarginine andd-NAME also increased the protective efficacy ofl-TC in a concentration-related manner in mature cultures. The timing of drug administration before or after HD culture exposure was critical. Drug coadministration resulted in synergistic protection only whenl-TC was added to the cultures prior to HD treatment. Thus, synergistic protective effects were also achieved whenl-NAME was added up to 8 h after HD exposure, if they were pretreated withl-TC. Based on these findings, it is proposed that HD initiates its toxicity extremely rapidly through a cell surface-mediated event that can be blocked byl-TC. A signal is transduced into the cell that results in an additional event or lesion that manifests itself several hours downstream. This event/lesion progresses to cell death unless blocked reversibly byl-NAME.