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 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 while L-NAME was only effective in mature cultures. Maximal protection occurred at mM drug concentrations and increased the LC50 of HD by approximately 200% (L-NAME) to approximately 800% (L-TC). L-NAME did not alter the efficacy of L-TC in immature cultures but increased the LC50 up to 1500% in mature cultures. Removal of L-NAME eliminated this synergism, leaving only the persistent protection of L-TC. L-Nitroarginine and d-NAME also increased the protective efficacy of L-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 when L-TC was added to the cultures prior to HD treatment. Thus, synergistic protective effects were also achieved when L-NAME was added up to 8 h after HD exposure, if they were pretreated with L-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 by L-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 by L-NAME.
Medical Countermeasures Section, Defence Research Establishment Suffield, Medicine Hat, Alberta, T1A 8K6, Canada.
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Sawyer
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002273:Carcinogens / Q000633:toxicity*; D002478:Cells, Cultured; D002642:Chick Embryo; D002956:Citrulline / Q000031:analogs & derivatives* / Q000494:pharmacology; D004357:Drug Synergism; D009151:Mustard Gas / Q000633:toxicity*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D018696:Neuroprotective Agents / Q000494:pharmacology*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology
D002273:Carcinogens; D018696:Neuroprotective Agents; C086715:thiocitrulline; D002956:Citrulline; D001120:Arginine; D013890:Thiourea; D009151:Mustard Gas; D019331:NG-Nitroarginine Methyl Ester