Protective mechanism of quercetin and rutin on 2,2'-azobis(2-amidinopropane)dihydrochloride or Cu2+-induced oxidative stress in HepG2 cells.

Protective effects of quercetin and rutin against oxidative stress were evaluated using in vitro and intracellular antioxidant assay. Quercetin showed higher peroxyl and hydroxyl radical-scavenging activity in a dose-dependent manner than did rutin in oxygen-radical absorbance capacity (ORAC). At 10 and 100 μM, quercetin had higher metal-chelating activity than rutin carrying rutinose at position C-3 and was also more efficient than rutin in reducing intracellular oxidative stress caused by peroxyl radicals and Cu(2+). The protective activities of 10 and 100 μM quercetin against Cu(2+)-induced intracellular oxidation were 13.8% and 44.8%, respectively. Rutin showed no protective activity against Cu(2+)-induced oxidative stress. Quercetin showed significantly lower intracellular Cu(2+)-chelating activity than did 1,10-phenanthroline but offered greater protection from Cu(2+)-induced oxidative stress. Thus, quercetin may diffuse through the cell membrane more efficiently than rutin because quercetin does not carry rutinose, is hydrophilic, and reduces Cu(2+)-induced oxidative stress by scavenging radicals instead of chelating with metal ions.