Characterization of the In Vitro Kinetic Interaction of Chlorpyrifos-Oxon with Rat Salivary Cholinesterase: A Potential Biomonitoring Matrix

Journal Article · Wed Feb 12 00:00:00 EST 2003 · Toxicology, 188(2-3):219-232

DOI:https://doi.org/10.1016/S0300-483X(03)00090-8· OSTI ID:15004605

Kousba, Ahmed A ^[1]; Poet, Torka S ^[1]; Timchalk, Charles ^[2]

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1. BATTELLE (PACIFIC NW LAB)
2. Pacific Northwest National Laboratory

Chlorpyrifos (CPF) is a commonly used organophosphate insecticide (OP). The primary mechanism of action for CPF involves the inhibition of acetylcholinesterase (AChE) by the active metabolite, CPF-oxon, with subsequent accumulation of acetylcholine (ACh) resulting in a wide range of neutotoxicity. CPF-oxon, can likewise inhibit other non-target cholinesterases (ChE) such as butyrylcholinesterase (BuChE), which represents a detoxification mechanism and a potential biomarker of exposure/response. Biological monitoring for OPs has focused on measuring parent chemical or metabolite in blood and urine or blood ChE inhibition. Salivary biomonitoring has recently been explored as a practical method for examination of chemical exposure; however, there are a limited number of studies exploring its use for OPs. To evaluate the use of salivary ChE as a biological monitor for OP exposure, the current study characterized salivary ChE activity in Sprague-Dawley rats through its comparison with brain and plasma ChE using BW284C51 and iso-OMPA as selective inhibitors of AChE and BuChE, respectively. The study also estimated the kinetic constants describing BuChE interaction with CPF-oxon. A modified Ellman assay in conjunction with pharmacodynamic (PD) modeling was used to characterize the in vitro titration of diluted rat salivary ChE enzyme with CPF-oxon. The results indicated that, more than 95% of rat salivary ChE activity was associated with BuChE activity, total BuChE active site concentration was 0.0012 0.00013 nmol/ml saliva, reactivation rate constant (Kr) was 0.068 0.008 h-1 and inhibitory (Ki) rate constant of 8.825 and 9.80 nM-1h-1 determined experimentally and using model optimization respectively. These study results would be helpful for further evaluating the potential utility of salivary ChE as a practical tool for biological monitor of OP exposures.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 15004605
• Report Number(s): PNWD-SA-5873; TRN: US201015%%757
• Journal Information: Toxicology, 188(2-3):219-232, Vol. 188, Issue 2-3; ISSN 0300-483X
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
ACETYLCHOLINE
BLOOD
BRAIN
CHOLINESTERASE
DETOXIFICATION
ENZYMES
IN VITRO
INSECTICIDES
KINETICS
METABOLITES
MONITORING
MONITORS
OPTIMIZATION
PLASMA
SALIVA
SIMULATION
TITRATION
URINE
saliva
cholinesterase
organophosphate insecticide
chlorpyrifos
chloropyrifos oxon
biomonitoring