Metabolism of chlorpyrifos and chlorpyrifos oxon by human hepatocytes*

Abstract

The metabolism of chlorpyrifos (CPS) and chlorpyrifos oxon (CPO) by human hepatocytes and human liver S9 fractions was investigated using LC-MS/MS. Cytochrome P450 (CYP)-dependent and phase II-related products were determined following incubation with CPS and CPO. CYP-related products, 3,5,6-trichloro-2-pyridinol (TCP), diethyl thiophosphate, and dealkylated CPS, were found following CPS treatment and dealkylated CPO following CPO treatment. Diethyl phosphate was not identified because of its high polarity and lack of retention with the chromatographic conditions employed. Phase II-related conjugates, including O- and S-glucuronides as well as 11 GSH-derived metabolites, were identified in CPS-treated human hepatocytes, although the O-sulfate of TCP conjugate was found only when human liver S9 fractions were used as the enzyme source. O-Glucuronide of TCP was also identified in CPO-treated hepatocytes. CPS and CPO were identified using HPLC-UV after CPS metabolism by the human liver S9 fraction. However, CPO was not found following treatment of human hepatocytes with either CPS or CPO. These results suggest that human liver plays an important role in detoxification, rather than activation, of CPS.

Review of the Toxicology of Chlorpyrifos With an Emphasis on Human Exposure and Neurodevelopment

“…During the first 72 h following exposure, approximately 30% of the urinary TCPy was present as free TCPy, whereas after 96 h, less than 10% was free, suggesting that either the rate of glucuronide conjugation of TCPy is slow, and/or that glucuronidation capacity was saturated at relatively high substrate concentration. Choi et al (2006) also identified the O-glucuronides of both TCPy and DCPy following incubation of human hepatocytes with chlorpyrifos. Interestingly, they also identified an S-glucuronide conjugate of chlorpyrifos, which they proposed was the result of secondary displacement of 2-aminopropanoic acid from the chlorpyrifos-cysteine conjugate that was derived from the chlorpyrifos-glutathione conjugate.…”

“…These would shift the balance toward detoxication even further. Studies in rats (Sultatos et al, 1984) and humans (Choi et al, 2006) have indeed indicated that chlorpyrifos oxon does not escape the liver, confirming that the active metabolite, once formed, is readily detoxified. Extrahepatic sites of activation and detoxication (with the exception of plasma PON1 and carboxylesterases) have not been studied to a great extent, and should be further investigated.…”

“…Several other in vitro studies with human liver have further evaluated the role of glutathione conjugation in the overall disposition of chlorpyrifos. In a detailed study of chlorpyrifos biotransformation in human hepatocytes and pooled S9 liver fractions, Choi et al (2006) identified 15 chlorpyrifosderived and 6 chlorpyrifos-oxon-derived metabolites by liquid chromatography (LC)-mass spectroscopy (MS)/MS analysis. The pyridinyl-2-glutathione conjugate of chlorpyrifos and chlorpyrifos-oxon were identified when pooled samples of human liver S9 were incubated with chlorpyrifos or chlorpyrifos-oxon.…”

“…The pyridinyl-2-glutathione conjugate of chlorpyrifos and chlorpyrifos-oxon were identified when pooled samples of human liver S9 were incubated with chlorpyrifos or chlorpyrifos-oxon. Incubations of human hepatocytes with chlorpyrifos yielded multiple different metabolites derived from glutathione S-transferase (GST) conjugation, including γ -glutamyl-cysteine, cysteinyl-glycine, and cysteine conjugates of chlorpyrifos, and the glutathione and cysteine conjugates of TCPy (Choi et al, 2006).…”

A novel immunochromatographic electrochemical biosensor for highly sensitive and selective detection of trichloropyridinol, a biomarker of exposure to chlorpyrifos

“…Organophosphorus insecticides, like chlorpyrifos (CPF) and chlorpyrifos-methyl (CPFm), were a large class of toxic chemical compounds that have been widely used in the agriculture production and home application (Jiang et al, 2008;Singh and Walker, 2006;Choi et al, 2006). In recent years there has been increasing attention given to the accidents linked to organophosphorus insecticides (Caldas et al, 2008).…”