Table 2

Reactive oxygen species that can be scavenged or whose formation can be inhibited by flavonoids

O⨪2(Superoxide anion)One-electron reduction product of O2. Produced by phagocytes, formed in autoxidation reactions (flavoproteins, redox cycling), and generated by oxidases (heme proteins).
HO⨪2 (Perhydroxy radical)Protonated form of O⨪2
H2O2 (Hydrogen peroxide)Two-electron reduction product of O2 formed from O⨪2(HO⨪2) by dismutation or directly from O⨪2. Reactivity of O⨪2 and H2O2 is amplified in the presence of heme proteins.
OH (Hydroxyl radical)Three-electron reduction product of O2 generated by Fenton reaction, transition metal (iron, copper)-catalyzed Haber-Weiss reaction; also formed by decomposition of peroxynitrite produced by the reaction of O⨪2 with NO· (nitric oxide radical).
RO (Alkoxyl radical)Example: Lipid radical (LO).
ROO (Peroxyl radical)Example: Lipid peroxy radical (LOO) produced from organic hydroperoxide (e.g. lipid hydroperoxide, LOOH), ROOH by hydrogen abstraction.
1O2 Singlet oxygen.