Isoorientin-6"-O-glucoside, a water-soluble antioxidant isolated from Gentiana arisanensis

The antioxidant activities of isoorientin-6 "-O-glucoside were studied using various models. Isoorientin-6 "-O-glucoside was more potent than Trolox, probucol and butylated hydroxytoluene (BHT) in reducing the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). It also scavenged superoxide anion, peroxyl and hydroxyl radicals that were generated by xanthine/xanthine oxidase, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and Fe3+-ascorbate-EDTA-H2O2 system, respectively. The IC50 value, stoichiometry factor and second-order rate constant were 9.0 +/- 0.8 mu M, 1.8 +/- 0.1 and 2.6 x 10(10) M-1 s(-1) for superoxide generation, peroxyl and hydroxyl radicals. However, isoorientin-6 "-O-glucoside did not inhibit xanthine oxidase activity or scavenge hydrogen peroxide (H2O2), carbon radical or 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN)-derived peroxyl radical in hexane. Isoorientin-6 "-O-glucoside inhibited Cu2+-induced oxidation of human low-density lipoprotein (LDL) as measured by fluorescence intensity, thiobarbituric acid-reactive substance formation and electrophoretic mobility. Since isoorientin-6 "-O-glucoside did not possess pro-oxidant activity, it may be an effective water-soluble antioxidant that can prevent LDL against oxidation. (C) 1998 Elsevier Science B.V.