title: Simultaneous detection of the antioxidant and pro-oxidant activity of dietary polyphenolics in a peroxidase system.
abstract: The ability to reduce the peroxidase (myeloglobin/H2O2)-generated ABTS*+ [2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) radical cation] has been used to rank the antioxidant activity of various agents including dietary flavonoids and chalcones. Surprisingly, we found that in the presence of catalytic concentrations of the phenol B-ring containing flavonoids, apigenin, naringenin and the chalcone phloretin, the formation of the ABTS*+ was initially increased. The enhanced formation of the ABTS*+ was attributed to the peroxidase/H2O2 mediated generation of polyphenolic phenoxyl radicals that were able to co-oxidize ABTS. The relative ABTS*+ generating ability of these dietary polyphenolics correlated with their ability to co-oxidize NADH to the NAD* radical with the resultant generation of superoxide. This pro-oxidant activity was not observed for either luteolin or eriodyctiol, which are B-ring catecholic analogues of apigenin and naringenin, respectively, suggesting that these antioxidants are incapable of the transition metal-independent generation of reactive oxygen species. This pro-oxidant activity of the polyphenolics therefore needs to be taken into account when quantifying antioxidant activity.
authors.affiliation: Department of Pharmaceutical Science, University of Toronto, 19 Russell Street, Toronto, Ont., Canada, M5S 2S2.
authors.forename: Tom S
authors.initials: TS
authors.lastname: Chan
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Galati
authors.forename: Ananth S
authors.initials: AS
authors.lastname: Pannala
authors.forename: Catherine
authors.initials: C
authors.lastname: Rice-Evans
authors.forename: Peter J
authors.initials: PJ
authors.lastname: O'Brien
mesh_terms: D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology*; D047310:Apigenin; D052160:Benzothiazoles; D002412:Cations; D004305:Dose-Response Relationship, Drug; D044950:Flavanones / Q000378:metabolism; D005419:Flavonoids / Q000378:metabolism*; D005609:Free Radicals; D007202:Indicators and Reagents / Q000494:pharmacology; D008956:Models, Chemical; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D016877:Oxidants / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010101:Oxygen Consumption; D010544:Peroxidases / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism*; D010693:Phloretin / Q000378:metabolism; D059808:Polyphenols; D017382:Reactive Oxygen Species / Q000378:metabolism; D013053:Spectrophotometry; D013451:Sulfonic Acids / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000975:Antioxidants; D052160:Benzothiazoles; D002412:Cations; D044950:Flavanones; D005419:Flavonoids; D005609:Free Radicals; D007202:Indicators and Reagents; D016877:Oxidants; D010636:Phenols; D059808:Polyphenols; D017382:Reactive Oxygen Species; D013451:Sulfonic Acids; D009243:NAD; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D047310:Apigenin; D010544:Peroxidases; C005273:naringenin; D010693:Phloretin; D010100:Oxygen