title: Inhibition of microsomal lipid peroxidation and cytochrome P-450-catalyzed reactions by beta-lapachone and related naphthoquinones.
abstract: The lipophilic o-naphthoquinones beta-lapachone, 3,4-dihydro-2-methyl-2-ethyl-2H-naphtho[1,2b]pyran-5,6-dione (CG 8-935), 3,4-dihydro-2-methyl-2-phenyl-2H-naphtho[1,2b]pyran-5,6-dione (CG 9-442), and 3,4-dihydro-2,2-dimethyl-9-chloro-2H-naphtho[1,2b]pyran-5,6-dione (CG 10-248) (a) inhibited NADPH-dependent, iron-catalyzed microsomal lipid peroxidation; (b) prevented NADPH-dependent cytochrome P-450 destruction; (c) inhibited microsomal aniline 4-hydroxylase, aminopyrine N-demethylase and 7-ethoxycoumarin deethylase; (d) did not inhibit the ascorbate- and tert-butyl hydroperoxide-dependent lipid peroxidation and the cumenyl hydroperoxide-linked aniline 4-hydroxylase reaction; and (e) stimulated NADPH oxidation, superoxide anion radical generation and Fe(III)ADP reduction by NADPH-supplemented microsomes. In the presence of ascorbate, the same o-naphthoquinones stimulated oxygen uptake and semiquinone formation, as detected by ESR measurements. The p-naphthoquinones alpha-lapachone and menadione were relatively less effective than the o-naphthoquinones. These observations support the hypothesis that, in the micromolar concentration range, o-naphthoquinones inhibit microsomal lipid peroxidation and cytochrome P-450-catalyzed reactions, by diverting reducing equivalents from NADPH to dioxygen.
authors.affiliation: Centro de Investigaciones Bioenergéticas, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
authors.forename: M
authors.initials: M
authors.lastname: Dubin
authors.forename: S H
authors.initials: SH
authors.lastname: Fernandez Villamil
authors.forename: A O
authors.initials: AO
authors.lastname: Stoppani
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D015227:Lipid Peroxidation / Q000187:drug effects*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009285:Naphthoquinones / Q000494:pharmacology*; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013481:Superoxides / Q000378:metabolism
chemical_list: D009285:Naphthoquinones; C029936:adenosine diphosphate-ferric chelate; D013481:Superoxides; D009249:NADP; D000244:Adenosine Diphosphate; C014638:beta-lapachone; D003577:Cytochrome P-450 Enzyme System; D001205:Ascorbic Acid