This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Mason, H.J. Articles by Wilson, H.K. Search for Related Content PubMed PubMed Citation Articles by Mason, H.J. Articles by Wilson, H.K. Social Bookmarking                         What's this?

Aging and Spontaneous Reactivation of Human Plasma Cholinesterase Activity After Inhibition by Organophosphorus Pesticides

Occupational Medicine and Hygiene Laboratory, Health & Safety Executive, Broad Lane, Sheffield S3 7HQ, UK

E. Waine

Occupational Medicine and Hygiene Laboratory, Health & Safety Executive, Broad Lane, Sheffield S3 7HQ, UK

A. Stevenson

Occupational Medicine and Hygiene Laboratory, Health & Safety Executive, Broad Lane, Sheffield S3 7HQ, UK

H.K. Wilson

Occupational Medicine and Hygiene Laboratory, Health & Safety Executive, Broad Lane, Sheffield S3 7HQ, UK

The in vitro rates of aging and spontaneous reactivation of human plasma cholinesterase (ChE) after inhibition by several organophosphorus pesticides (OPs) have been studied. After inhibition by OP the enzyme can undergo two simultaneous reactions; spontaneous reactivation to the active enzyme and 'aging' to an irreversibly inhibited form of the enzyme. The rates of these two reactions depend on the nature of the phosphoryl group of the OP bound to the active site of ChE. Most OPs registered for use in the UK have dimethoxy or diethoxy groups attached to the phosphorus atom. Reaction rate constants for aging and spontaneous reactivation are reported. Dimethoxy OPs cause half-lives of aging in human plasma ChE of approximately 6 hours and 23 hours at 37°C and 22°C respectively; for diethoxy OPs the values are 12 hours and 39 hours. Reappearance of enzyme activity, after removal of OP, reduced any inhibition by a maximum of 25% for dimethoxy OPs; this reappearance of enzyme activity occurs with a 'half-life' of 5 hours and 15 hours at 37°C and 22°C. These effects, both in vivo and ex vivo, may have relevance in developing a monitoring strategy for dimethoxy OPs using plasma ChE measurements. Inhibition by diethoxy OPs spontaneously reactivates very slowly, even at 37°C, and would not practically influence the measured inhibition. No spontaneous reactivation was detected in human plasma ChE inhibited by the methoxy-ethylamino substituted OP (propetamphos) or the methoxy-methylamino substituted OP (crufomate) during 45 hours incubation at 37°C.

Human & Experimental Toxicology, Vol. 12, No. 6, 497-503 (1993)
DOI: 10.1177/096032719301200606


CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?