Comparison of several oximes on reactivation of soman-inhibited blood,brain and tissue cholinesterase activity in rats

The ability of three oximes, HI-6, MMB-4 and ICD-467, to reactivate cholinesterase (ChE) inhibited by the organophosphorus compound soman was compared in blood (plasma and erythrocytes), brain regions (including spinal cord) and peripheral tissues of rats. Animals were intoxicated with soman (100 g/kg, SC; equivalent to 0.9 × LD₅₀ dose) and treated 1 min later with one of these oximes (100 or 200 mol/kg, IM). Toxic sign scores and total tissue ChE activities were determined 30 min later. Soman markedly inhibited ChE activity in blood (93–96%), brain regions (ranging from 78% to 95%), and all peripheral tissues (ranging from 48.9% to 99.8%) except liver (11.9%). In blood, treatment with HI-6 or ICD-467 resulted in significant reactivation of soman-inhibited ChE. In contrast, MMB-4 was completely ineffective. HI-6 and ICD-467 were equally effective at the high dose. At the low dose ICD-467 treatment resulted in significantly higher plasma ChE than HI-6 treatment, whereas HI-6 treatment resulted in higher erythrocyte ChE than ICD-467 treatment. However, none of these three oximes reactivated or protected soman-inhibited ChE in the brain. In all peripheral tissues (except liver) studied, MMB-4 was not effective. HI-6 reactivated soman-inhibited ChE in all tissues except lung, heart, and skeletal muscle. ICD-467 was highly effective in reactivating ChE in all tissues and afforded a complete recovery of ChE to control levels in intercostal muscle and salivary gland. Oxime treatments did not modify the toxic scores produced by soman. However, treatment with the high dose (200 mol/kg) of ICD-467 depressed respiration and two of the six rats died in 10 min. These observations indicate that MMB-4 is completely ineffective in protecting and/or reactivating soman-inhibited ChE, HI-6 is an effective ChE reactivator as reported earlier in rats and other species, and the imidazolium oxime ICD-467 is a powerful reactivator of somaninhibited ChE; however, its toxic interactions with soman may not be related to tissue ChE levels.The experiments reported here were conducted according to the Guide for the Care and Use of Laboratory Animals (1985), as prepared by the Committee on Care and Use of Laboratory Animals, National Research Council, NIH Publication No. 85-23. The opinions or assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense