Characterization of the in vitro kinetic interaction of chlorpyrifos-oxon with rat salivary cholinesterase: a potential biomonitoring matrix.
Kousba AA; Poet TS; Timchalk C
Toxicology 2007 Jun; 188(2-3):219-232
The primary mechanism of action for organophosphorus (OP) insecticides such as chlorpyrifos (CPF) involves the inhibition of acetylcholinesterase (AChE) by their active oxon metabolites resulting in a wide range of neurotoxic effects. These oxons also inhibit other cholinesterases (ChE) such as butyrylcholinesterase (BuChE), which represents a detoxification mechanism and a potential biomarker for OP insecticide exposure/response. Salivary biomonitoring has recently been explored as a practical method for examination of chemical exposure, however, there are few studies exploring the use of saliva for OP insecticides. To evaluate the use of salivary ChE as a biological monitor for OP insecticide exposure, a modified Ellman assay in conjunction with a pharmacodynamic model was used to characterize salivary ChE in adult male Sprague-Dawley rats. Comparison of rat saliva, brain, and plasma ChE activity in the presence of selective inhibitors of AChE and BuChE (BW284C51 and iso-OMPA, respectively) with different ChE substrates indicated that rat salivary ChE activity is primarily associated with BuChE (>95%). Further characterization of rat salivary BuChE kinetics yielded an average total BuChE active site concentration of 1.20+/-0.13 fmol ml-1 saliva, an average reactivation rate constant (Kr) of 0.070+/-0.008 h-1, and an inhibitory rate constant (Ki) of 9 nM-1 h-1. The pharmacodynamic model successfully described the in vitro BuChE activity profile as well as the kinetic parameters. These results support the potential utility of saliva as a biomonitoring matrix for evaluating occupational and environmental exposure to CPF and other OP insecticides.
Insecticides; Laboratory-animals; Animal-studies; Metabolism; Models; Pharmacodynamics; Biodynamics; Biochemical-analysis; Environmental-contamination; Environmental-factors; Environmental-exposure; Pesticides; Biomarkers; Metabolic-rate; Metabolism; Blood-tests; Blood-samples; Organo-phosphorus-pesticides; Salivary-gland-disorders; Salivary-glands; Cerebrovascular-system-disorders; Cerebrovascular-system; Brain-electrical-activity; Brain-function; Chemical-hypersensitivity
Charles Timchalk, Pacific Northwest National Laboratory, 902 Battelle Blvd, PO Box 999, Richland, WA 99352
Research Tools and Approaches: Exposure Assessment Methods
Battelle Memorial Institute, Richland, Washington