Comparison of inhibitory actions of organophosphate pesticides on cholinesterase and lecithin-cholesterol acyltransferase in human plasma.

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Abstract
The inhibitory actions of organophosphate pesticides on cholinesterase and lecithincholesterol acyltransferase in human plasma and acetone powder of human plasma were compared in vitro. Acetone powder of human plasma as well as native human plasma was able to use as an enzyme source of the esterification of cholesterol in sonicated dispersion of lecithin and cholesterol mixture. The acyltransferase in acetone powder of human plasma was inhibited approximately 55, 60 and 97% by the addition of 1×10-3M sumithion, dimethyldichlorovinylphosphate (DDVP) and diisopropylfluorophosphate (DFP), respectively. On the other hand, even though human plasma preincubated with 1×10-3M sumithion, DDVP or DFP for 60 min at 37° and then extracted with cold acetone, the decreased acyltransferase activity was not recovered. In addition, the decreased acyltransferase activities in human plasma with 1×10-3M DDVP and acetone powder prepared from human plasma preincubated with 1×10-3M DDVP were not recovered by the addition of 1×10-5M or 1×10-3M 2-pyridine aldoxime methiodide (PAM). Human plasma cholinesterase was also inhibited at concentrations of DDVP ranging from 1×10-7M to 1×10-5M in vitro. In particular, the cholinesterase was completely inhibited by the addition of 1×10-5M DDVP. However, cholinesterase activity in acetone powder prepared from human plasma preincubated with 1×10-3M DDVP exhibited approximately 8-15% of that in acetone powder prepared from human plasma preincubated without DDVP. The decreased cholinesterase activities in human plasma with 1×10-7-10-5M DDVP and in acetone powder prepared from human plasma preincubated with 1×10-3M DDVP were recovered by the addition of 1×10-3M PAM. These results suggest that the inhibitory action of organophosphate pesticides on the acyltransferase in human plasma may be different from that on plasma cholinesterase.
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