Synergistic protective effects of selected arginine analogues against sulphur mustard toxicity in neuron culture

Previous studies in this laboratory have shown that the arginine analogues L-thiocitrulline (L-TC) and L-nitroarginine methyl ester (L-NAME) have pote nt protective activity against sulphur mustard (HD) toxicity that was not r elated to their nitric oxide synthase inhibiting activities. Furthermore, t heir characteristics of action suggested that they act at different sites t o exert their protection. L-TC acted rapidly (minutes of preincubation) and was equipotent in protecting either immature or mature cultures of chick e mbryo neurons against the toxicity of HD while L-NAME was only effective in mature cultures. Maximal protection occurred at mM drug concentrations and increased the LC50 of HD by similar to 200% (L-NAME) to similar to 800% (L -TC), L-NAME did not alter the efficacy of L-TC in immature cultures but in creased the LC50 up to 1500% in mature cultures, Removal of L-NAME eliminat ed this synergism, leaving only the persistent protection of L-TC, L-Nitroa rginine and D-NAME also increased the protective efficacy of L-TC in a conc entration-related manner in mature cultures. The timing of drug administrat ion before or after HD culture exposure was critical. Drug coadministration resulted in synergistic protection only when L-TC was added to the culture s prior to HD treatment, Thus, synergistic protective effects were also ach ieved when L-NAME was added up to 8 h after HD exposure, if they were pretr eated with L-TC. Based on these findings, it is proposed that HD initiates its toxicity extremely rapidly through a cell surface-mediated event that c an be blocked by L-TC, A signal is transduced into the cell that results in an additional event or lesion that manifests itself several hours downstre am. This event/lesion progresses to cell death unless blocked reversibly by L-NAME, (C) 1999 Academic Press.