title: Bioflavonoid effects on the mitochondrial respiratory electron transport chain and cytochrome c redox state.
abstract: The polyphenolic structure common to flavonoids enables them to donate electrons and exert antioxidant activity. Since the mitochondrial electron transport chain consists of a series of redox intermediates, the effect of flavonoids in a complex mixture of polyphenols, as well as related pure flavonoids, was evaluated on the rat liver mitochondrial electron transport chain. A French maritime pine bark extract (PBE), a complex mixture of polyphenols and related pure flavonoids, was able to reduce cytochrome c reversibly, possibly by donation of electrons to the iron of the heme group; the donated electrons can be utilized by cytochrome c oxidase. Among single flavonoids tested, (-)-epicatechin gallate had the greatest ability to reduce cytochrome c. In addition, PBE competitively inhibited electron chain activity in both whole mitochondria and submitochondrial particles. A 3.5-fold increase in the apparent Km value for succinate was calculated from reciprocal plots. Among the flavonoids tested, taxifolin and (-)-epicatechin gallate showed minor inhibitory effects, while (+/-)-catechin and (+)-epicatechin were ineffective. Activities of NADH-ubiquinone, succinate-ubiquinone, and ubiquinol-cytochrome c reductases were inhibited by low concentrations of PBE to a similar extent. However, inhibition of cytochrome c oxidase activity required 4-fold higher PBE concentrations. These results suggest that flavonoids reduce cytochrome c and that PBE inhibits electron transport chain activity mainly through NADH-ubiquinone, succinate-ubiquinone, and ubiquinol-cytochrome c reductases.
authors.affiliation: Department of Molecular and Cell Biology, University of California at Berkeley 94720-3200, USA.
authors.forename: H
authors.initials: H
authors.lastname: Moini
authors.forename: A
authors.initials: A
authors.lastname: Arroyo
authors.forename: J
authors.initials: J
authors.lastname: Vaya
authors.forename: L
authors.initials: L
authors.lastname: Packer
mesh_terms: D000818:Animals; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects*; D005419:Flavonoids / Q000494:pharmacology*; D008297:Male; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D010936:Plant Extracts / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D003574:Cytochrome c Group; D005419:Flavonoids; D010936:Plant Extracts; D009243:NAD