title: Human metabolic interactions of environmental chemicals.
abstract: Investigations utilizing recombinant human xenobiotic-metabolizing enzymes as well as human hepatocytes have revealed a number of interactions not only between different environmental chemicals (ECs) but also between ECs and endogenous metabolites. Organophosphorus insecticides (OPs) are potent inhibitors of the human metabolism of carbaryl, carbofuran, DEET and fipronil, as well as the jet fuel components, nonane and naphthalene. OPs are potent irreversible inhibitors of testosterone metabolism by cytochrome P450 (CYP) 3A4 and of estradiol metabolism by CYP3A4 and CYP1A2. All of these CYP inhibitions are believed to be due to the release of reactive sulfur during CYP-catalyzed oxidative desulfuration. It has also been shown that the esterase(s) responsible for the initial step in permethrin metabolism in human liver is inhibited by both chlorpyrifos oxon and carbaryl. A number of pesticides, including chlorpyrifos, fipronil and permethrin, and the repellent, DEET, have been shown to be inducers of CYP isoforms in human hepatocytes, with fipronil being the most potent. Several agrochemicals, including fipronil and the pyrethroids, permethrin and deltamethrin, show toxicity toward human hepatocytes with fipronil being the most potent in this regard. Endosulfan-alpha, which has shown promise as a model substrate for phenotyping CYP3A4 and CYP2B6 in human liver microsomes, is also an inducer of CYP2B6, acting through the PXR receptor.
authors.affiliation: Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh NC 27695-7633, USA. ernest_hodgson@ncsu.edu
authors.forename: Ernest
authors.initials: E
authors.lastname: Hodgson
authors.forename: Randy L
authors.initials: RL
authors.lastname: Rose
mesh_terms: D002800:Cholinesterase Inhibitors / Q000378:metabolism*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004785:Environmental Pollutants / Q000737:chemistry / Q000378:metabolism*; D004790:Enzyme Induction; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000201:enzymology; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D010575:Pesticides / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D013739:Testosterone / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D002800:Cholinesterase Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004785:Environmental Pollutants; D007527:Isoenzymes; D010575:Pesticides; D011994:Recombinant Proteins; D013739:Testosterone; D004958:Estradiol; D003577:Cytochrome P-450 Enzyme System