title: Environmentally persistent free radical-containing particulate matter competitively inhibits metabolism by cytochrome P450 1A2.
abstract: Combustion processes generate different types of particulate matter (PM) that can have deleterious effects on the pulmonary and cardiovascular systems. Environmentally persistent free radicals (EPFRs) represent a type of particulate matter that is generated after combustion of environmental wastes in the presence of redox-active metals and aromatic hydrocarbons. Cytochromes P450 (P450/CYP) are membrane-bound enzymes that are essential for the phase I metabolism of most lipophilic xenobiotics. The EPFR formed by chemisorption of 2-monochlorophenol to silica containing 5% copper oxide (MCP230) has been shown to generally inhibit the activities of different forms of P450s without affecting those of cytochrome P450 reductase and heme oxygenase-1. The mechanism of inhibition of rat liver microsomal CYP2D2 and purified rabbit CYP2B4 by MCP230 has been shown previously to be noncompetitive with respect to substrate. In this study, MCP230 was shown to competitively inhibit metabolism of 7-benzyl-4-trifluoromethylcoumarin and 7-ethoxyresorufin by the purified, reconstituted rabbit CYP1A2. MCP230 is at least 5- and 50-fold more potent as an inhibitor of CYP1A2 than silica containing 5% copper oxide and silica, respectively. Thus, even though PM generally inhibit multiple forms of P450, PM interacts differently with the forms of P450 resulting in different mechanisms of inhibition. P450s function as oligomeric complexes within the membrane. We also determined the mechanism by which PM inhibited metabolism by the mixed CYP1A2-CYP2B4 complex and found that the mechanism was purely competitive suggesting that the CYP2B4 is dramatically inhibited when bound to CYP1A2.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics and The Stanley S. Scott Cancer Center, Louisiana State University Health Sciences Center, 533 Bolivar St., New Orleans, LA 70112, USA. Electronic address: rreed@lsuhsc.edu.
authors.forename: James R
authors.initials: JR
authors.lastname: Reed
authors.affiliation: The Department of Environmental Sciences and LSU Superfund Research Center, Louisiana State University A&M College, Baton Rouge, LA 70803, USA. Electronic address: adelac2@tigers.lsu.edu.
authors.forename: Albert Leo N
authors.initials: AL
authors.lastname: dela Cruz
authors.affiliation: The Department of Environmental Sciences and LSU Superfund Research Center, Louisiana State University A&M College, Baton Rouge, LA 70803, USA. Electronic address: slomni1@lsu.edu.
authors.forename: Slawo M
authors.initials: SM
authors.lastname: Lomnicki
authors.affiliation: Department of Pharmacology and Experimental Therapeutics and The Stanley S. Scott Cancer Center, Louisiana State University Health Sciences Center, 533 Bolivar St., New Orleans, LA 70112, USA. Electronic address: wbacke@lsuhsc.edu.
authors.forename: Wayne L
authors.initials: WL
authors.lastname: Backes
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D020134:Catalytic Domain; D003374:Coumarins / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D065609:Cytochrome P-450 CYP1A2 Inhibitors / Q000378:metabolism / Q000633:toxicity*; D000072467:Cytochrome P450 Family 2; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000378:metabolism / Q000633:toxicity*; D005609:Free Radicals / Q000378:metabolism / Q000633:toxicity*; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D010078:Oxazines / Q000378:metabolism; D052638:Particulate Matter / Q000378:metabolism / Q000633:toxicity*; D011485:Protein Binding; D011817:Rabbits; D013379:Substrate Specificity
chemical_list: C419147:7-benzyloxy-4-trifluoromethylcoumarin; D003374:Coumarins; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004785:Environmental Pollutants; D005609:Free Radicals; D010078:Oxazines; D052638:Particulate Matter; C007649:ethoxyresorufin; D001189:Aryl Hydrocarbon Hydroxylases; D019388:Cytochrome P-450 CYP1A2; D000072467:Cytochrome P450 Family 2; C465241:cytochrome P-450 CYP2B4 (rabbit)
keywords: Cytochrome P450 1A2; Environmentally persistent free radicals; Inhibition; Particulate matter