A reexamination of the cytochrome P-450-catalyzed free radical production from a dihydropyridine. Evidence of trace transition metal catalysis.
Radical production from 3,5-bis(ethoxycarbonyl)-4-ethyl-2,6-dimethyl-1,4- dihydropyridine (DDEP) in rat liver microsomes has been attributed to one-electron oxidation via cytochrome P-450 followed by extrusion of an ethyl radical. In the presence of the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN), this radical was detected as the 4-POBN/ethyl radical adduct by electron paramagnetic resonance spectroscopy. The addition of catalase resulted in over a 50% decrease in radical production. The concentration of the 4-POBN/ethyl radical adduct increased about 9-fold in the presence of EDTA and approximately 2-fold in the presence of either diethylenetriaminepentaacetic acid (DTPA) or deferoxamine mesylate. When DDEP was incubated with deferoxamine mesylate-washed microsomes and NADPH in Chelex-treated incubation buffer, much less 4-POBN/ethyl radical formation occurred. Addition of either DTPA, EDTA, or the ferric complexes of these chelators greatly stimulated production of the 4-POBN/ethyl radical adduct in this system. These results suggest that the ethyl radicals produced from DDEP in a microsomal system arise via trace transition metal-catalyzed reactions.
Kennedy
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Laboratory of Molecular Biophysics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Mason
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D000818:Animals; D002458:Cell Fractionation; D002614:Chelating Agents / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism* / Q000648:ultrastructure; D009589:Nitrogen Oxides; D011725:Pyridines; D011739:Pyrimethamine / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013113:Spin Labels
D002614:Chelating Agents; D005609:Free Radicals; D009589:Nitrogen Oxides; D011725:Pyridines; D013113:Spin Labels; C043438:alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone; C013909:etoprine; D003577:Cytochrome P-450 Enzyme System; D011739:Pyrimethamine