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Metabolism and cholinesterase inhibition in lungs of rats following in vitro chlorpyrifos exposure.

Timchalk-C; Fox-RM; Meyer-KM; Lee-S; Smith-JN; Busby-AL; Poet-TS
Toxicologist 2009 Mar; 108(1):286
Chlorpyfios (CPF) is an organophosphorous insecticide that is routinely applied to crops as an aerosol spray, hence there is potential for workers and bystanders to be exposed via inhalation. Though inhalation represents a primary occupational route of exposure, little is known about lung metabolism or cholinesterase (ChE) response following a CPF exposure. Hence, this study evaluated the in vitro metabolism and ChE response following exposure to CPF or its active metabolite CPFoxon in rat lung tissue. Rat microsomes were prepared from naive S-D rat lungs and liver. The comparative metabolism of CPF to the major metabolite trichloropyridinol (TCPy) was evaluated over a range of CPF concentrations (50 . 500 mu M), and the amount of TCPy generated was analyzed by GC/MS. The maximum velocity (Vmax) of lung metabolism was approximately 44% of the liver (0.72 vs. 1.62 mu g/min/mg protein) and the predicted Km for the lung and liver microsomes were 5.9 and 21 mu M. For in vitro ChE determination, whole lung from naive S-D rats were homogenized and optimally diluted for the Ellman assay. Substrates for the assay included acetylthiocholine (ATC) and butyrylthiocholine (BTC). The lung homogenates were then incubated with a broad range of CPF-oxon concentration (1 . 1E4 nM). Overall, the BTC substrate was approximately 43% of the ATC response, suggesting that butyrylcholinesterase (BuChE) represents approximately 40% of the lung ChE activity. The estimated IC50 for CPF-oxon ChE inhibition in lung for ATC and BTC were 76.5 and 52.7 nM, respectively. These in vitro studies confirm that the rat lung has the capacity to metabolize CPF, and CPF-oxon can readily inhibit lung ChE activity. Future in vivo studies will be conducted to quantify the lung pharmacokinetic and pharmacodynamic dose-response. Finally, these data will then be utilized to further refine the CPF PBPK/PD model to accommodate inhalation exposure.
Aerosols; Agricultural-chemicals; Agricultural-industry; Agricultural-workers; Agriculture; Biological-effects; Biological-factors; Breathing; Chemical-hypersensitivity; Chemical-reactions; Dose-response; Environmental-exposure; Exposure-assessment; Exposure-levels; Exposure-methods; Inhalation-studies; Insecticides; Laboratory-animals; Laboratory-testing; Lung-function; Lung-irritants; Metabolism; Microscopic-analysis; Occupational-exposure; Occupational-hazards; Occupational-health; Occupational-respiratory-disease; Organo-phosphorus-compounds; Organo-phosphorus-pesticides; Pesticides-and-agricultural-chemicals; Pulmonary-system; Pulmonary-system-disorders; Respiratory-hypersensitivity; Respiratory-irritants; Respiratory-system-disorders; Respiratory-hypersensitivity; Respiratory-system-disorders; Statistical-analysis
Publication Date
Document Type
Funding Type
Fiscal Year
Identifying No.
Grant-Number-R01-OH-008173; Grant-Number-R01-OH-003629
Issue of Publication
Priority Area
Agriculture, Forestry and Fishing; Research Tools and Approaches: Exposure Assessment Methods
Source Name
The Toxicologist. Society of Toxicology 48th Annual Meeting and ToxExpo, March 15-19, 2009, Baltimore, Maryland
Performing Organization
Battelle Pacific Northwest Laboratories
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division