title: Inhibition of cytochrome P450 2B4 by environmentally persistent free radical-containing particulate matter.
abstract: Combustion processes generate particulate matter (PM) that can affect human health. The presence of redox-active metals and aromatic hydrocarbons in the post-combustion regions results in the formation of air-stable, environmentally persistent free radicals (EPFRs) on entrained particles. Exposure to EPFRs has been shown to negatively influence pulmonary and cardiovascular functions. Cytochromes P450 (P450/CYP) are endoplasmic reticulum resident proteins that are responsible for the metabolism of foreign compounds. Previously, it was shown that model EPFRs, generated by exposure of silica containing 5% copper oxide (CuO-Si) to either dicholorobenzene (DCB230) or 2-monochlorophenol (MCP230) at ≥ 230 °C, inhibited six forms of P450 in rat liver microsomes (Toxicol. Appl. Pharmacol. (2014) 277:200-209). In this study, the inhibition of P450 by MCP230 was examined in more detail by measuring its effect on the rate of metabolism of 7-ethoxy-4-trifluoromethylcoumarin (7EFC) and 7-benzyloxyresorufin (7BRF) by the purified, reconstituted CYP2B4 system. MCP230 inhibited the CYP2B4-mediated metabolism of 7EFC at least 10-fold more potently than non-EPFR controls (CuO-Si, silica, and silica generated from heating silica and MCP at 50 °C, so that EPFRs were not formed (MCP50)). The inhibition by EPFRs was specific for the P450 and did not affect the ability of the redox partner, P450 reductase (CPR) from reducing cytochrome c. All of the PM inhibited CYP2B4-mediated metabolism noncompetitively with respect to substrate. When CYP2B4-mediated metabolism of 7EFC was measured as a function of the CPR concentration, the mechanism of inhibition was competitive. EPFRs likely inhibit CYP2B4-mediated substrate metabolism by physically disrupting the CPR·P450 complex.
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: 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: 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 / Q000037:antagonists & inhibitors*; D001555:Benzene Derivatives / Q000494:pharmacology; D002733:Chlorophenols / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D000072467:Cytochrome P450 Family 2; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D051381:Rats
chemical_list: D001555:Benzene Derivatives; D002733:Chlorophenols; D004791:Enzyme Inhibitors; D003300:Copper; D001189:Aryl Hydrocarbon Hydroxylases; D000072467:Cytochrome P450 Family 2; C465241:cytochrome P-450 CYP2B4 (rabbit); C030683:2-chlorophenol; C030973:cupric oxide
keywords: Cytochrome P450 2B4; Inhibition; Particulate matter, Environmentally persistent free radicals
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