Concentration-dependent interactions of the organophosphates chlorpyrifos oxon and methyl paraoxon with human recombinant acetylcholinesterase.

For many decades it has been thought that oxygen analogs (oxons) of organophosphorus insecticides phosphorylate the catalytic site of acetylcholinesterase by a mechanism that follows simple Michaelis-Menten kinetics. More recently, the interactions of at least some oxons have been shown to be far more complex and likely involve binding of oxons to a second site on acetylcholinesterase that modulates the inhibitory capacity of other oxon molecules at the catalytic site. The current study has investigated the interactions of chlorpyrifos oxon and methyl paraoxon with human recombinant acetylcholinesterase.

Concentration-dependent kinetics of acetylcholinesterase inhibition by the organophosphate paraoxon.

For decades the interaction of the anticholinesterase organophosphorus compounds with acetylcholinesterase has been characterized as a straightforward phosphylation of the active site serine (Ser-203) which can be described kinetically by the inhibitory rate constant k(i). However, more recently certain kinetic complexities in the inhibition of acetylcholinesterase by organophosphates such as paraoxon (O,O-diethyl O-(p-nitrophenyl) phosphate) and chlorpyrifos oxon (O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphate) have raised questions regarding the adequacy of the kinetic scheme on which k(i) is based. The present article documents conditions in which the inhibitory capacity of paraoxon towards human recombinant acetylcholinesterase appears to change as a function of oxon concentration (as evidenced by a changing k(i)), with the inhibitory capacity of individual oxon molecules increasing at lower oxon concentrations.

Mefloquine inhibits cholinesterases at the mouse neuromuscular junction.

Mefloquine is effective against drug-resistant Plasmodium falciparum. This property, along with its unique pharmacokinetic profile, makes mefloquine a widely prescribed antimalarial drug. However, mefloquine has neurologic effects which offset its therapeutic advantages.

Incorporation of the genetic control of alcohol dehydrogenase into a physiologically based pharmacokinetic model for ethanol in humans.

The assessment of the variability of human responses to foreign chemicals is an important step in characterizing the public health risks posed by nontherapeutic hazardous chemicals and the risk of encountering adverse reactions with drugs. Of the many sources of interindividual variability in chemical response identified to date, hereditary factors are some of the least understood. Physiologically based pharmacokinetic modeling linked with Monte Carlo sampling has been shown to be a useful tool for the quantification of interindividual variability in chemical disposition and/or response when applied to biological processes that displayed single genetic polymorphisms.