Title: Environmentally persistent free radicals inhibit cytochrome P450 activity in rat liver microsomes.
Authors: Reed, James R; Cawley, George F; Ardoin, Taylor G; Dellinger, Barry; Lomnicki, Slawomir M; Hasan, Farhana; Kiruri, Lucy W; Backes, Wayne L
Published In Toxicol Appl Pharmacol, (2014 Jun 1)
Abstract: Combustion processes generate particulate matter that affects human health. When incineration fuels include components that are highly enriched in aromatic hydrocarbons (especially halogenated varieties) and redox-active metals, ultrafine particulate matter containing air-stable, environmentally persistent free radicals (EPFRs) is generated. The exposure to fine EPFRs (less than 2.5 μm in diameter) has been shown to negatively influence pulmonary and cardiovascular functions in living organisms. The goal of this study was to determine if these EPFRs have a direct effect on cytochrome P450 function. This was accomplished by direct addition of the EPFRs to rat liver microsomal preparations and measurement of several P450 activities using form-selective substrates. The EPFRs used in this study were formed by heating vapors from an organic compound (either monochlorophenol (MCP230) or 1,2-dichlorobenzene (DCB230)) and 5% copper oxide supported on silica (approximately 0.2 μm in diameter) to 230°C under vacuum. Both types of EPFRs (but not silica, physisorbed silica, or silica impregnated with copper oxide) dramatically inhibited the activities of CYP1A, CYP2B, CYP2E1, CYP2D2 and CYP3A when incubated at concentrations less than 0.1 mg/ml with microsomes and NADPH. Interestingly, at the same concentrations, the EPFRs did not inhibit HO-1 activity or the reduction of cytochrome c by NADPH-cytochrome P450 reductase. CYP2D2-selective metabolism by rat liver microsomes was examined in more detail. The inhibition of CYP2D2-selective metabolism by both DCB230- and MCP230-EPFRs appeared to be largely noncompetitive and was attenuated in the presence of catalase suggesting that reactive oxygen species may be involved in the mechanism of inhibition.
PubMed ID: 24713513
MeSH Terms: Animals; Aryl Hydrocarbon Hydroxylases/antagonists & inhibitors; Aryl Hydrocarbon Hydroxylases/metabolism; Catalase/metabolism; Chlorobenzenes/metabolism; Chlorobenzenes/toxicity*; Chlorophenols/metabolism; Chlorophenols/toxicity*; Cytochrome P-450 Enzyme Inhibitors*; Cytochrome P-450 Enzyme System/metabolism; Dose-Response Relationship, Drug; Enzyme Inhibitors/metabolism; Enzyme Inhibitors/toxicity*; Free Radicals/metabolism; Free Radicals/toxicity*; Isoenzymes; Kinetics; Male; Microsomes, Liver/drug effects*; Microsomes, Liver/enzymology; Particle Size; Particulate Matter/metabolism; Particulate Matter/toxicity*; Rats; Rats, Sprague-Dawley; Substrate Specificity