New method for retrospective detection of exposure to organophosphorus anticholinesterases: application to alleged sarin victims of Japanese terrorists.

With regard to detection of exposure to anticholinesterase, the presently used methods have the disadvantage that they cannot detect either low-level exposures with certainty or the structure of the agent and the extent of poisoning. In principle, organophosphate-inhibited butyrylcholinesterase in human plasma is the most persistent and abundant source for biomonitoring of exposure to organophosphate anticholinesterases. Fluoride ions reactivate the inhibited enzyme readily at pH 4, converting the organophosphate moiety into the corresponding phosphofluoridate. Subsequent quantitation of the latter product provides a reliable, highly sensitive and retrospective method for detection of exposure to, or handling of, organophosphates such as nerve agents and organophosphorus pesticides. We applied the new procedure to serum samples from victims of the Tokyo subway attack by the AUM Shinriyko sect and from an earlier incident at Matsumoto. In serum of 10 of 11 victims from the Tokyo incident and of 2 of the 7 samples from the Matsumoto incident, reactivation with fluoride ions yielded sarin concentrations in the range of 0.2-4.1 ng/ml serum. Evidently, these victims had been exposed to an organophosphate with the structure PriO(CH3)P(O)X, presumably with X = F (sarin). Several applications of the new procedure to establish nerve agent and/or organophosphate (OP) pesticide exposure can be envisaged, e.g., (i) in biomonitoring of exposure for health surveillance of those handling organophosphates, (ii) in cases of alleged exposure to nerve agents and/or OP pesticides in armed conflict situations or terrorist attacks, (iii) in medical treatment of intoxication, and (iv) in forensic cases against suspected terrorists that may have handled anticholinesterases.