Oxidative stress flavonoid protection against

The above findings are supported in the other studies of the inhibitory effects of flavonoids on iron-stimulated lipid peroxidation. Quercetin was found to be an inhibitor of iron-stimulated hepatic microsomal lipid peroxidation (/50 = 200 pmol I ) [134]. Flavonoids eriodictyol, luteolin, quercetin, and taxifolin inhibited ascorbate and ferrous ion-stimulated MDA formation and oxidative stress (measured by fluorescence of 2,7,-dichlorodihydro-fluorescein) in cultured retinal cells [135]. It should be mentioned that in recent work Heijnen et al. [136] revised the structure activity relationship for the protective effects of flavonoids against lipid peroxidation. 

The flavonoids protect cells against oxidative stress. 

Figure 8 Major pathways by which flavonoids inhibit macrophage-mediated oxidation of LDL. Flavonoids (FI) affect LDL directly by their interaction with the lipoprotein and inhibition (FI ) of LDL oxidation. Flavonoids can also protect LDL indirectly, by their accumulation in arterial cells and protection of arterial macrophages against oxidative stress. This latter effect is associated with inhibition (FI -) of the formation of oxidized macrophages and reduction in the capacity of macrophages to oxidize LDL. In addition, flavonoids preserve/increase (FI +) paraoxonase activity, thereby increasing hydrolysis of lipid peroxides either in the LDL or in oxidized macrophages, resulting in further protection of LDL from oxidation. LDL, low-density lipoprotein.

The flavonol quercetin has been the subject of much interest in terms of its beneficial properties against oxidative stress [62] and has been shown to exert a potent protective actions against hydrogen peroxide-induced apoptosis of rat thymocytes [63] and cell death in rat hepatocytes (BL-9) [60], as well as reducing oxidative stress and cell damage in fiver tumor cells induced by AAPH (2,2-azobis(2-aminopropane) dihydrochloride) [64]. Quercetin and another flavonol, kaempferol, as well as catechin and the flavone taxifolin, have been observed to suppress the cytotoxicity of 02 and H2O2 to Chinese hamster V79 cells, as assessed by the ability of the flavonoids to prevent the decrease in the number of cell colonies induced by the oxidants [65]. Furthermore, quercetin has been shown to protect cutaneous tissue-associated cells (human skin fibroblasts, keratinocytes, and endothelial cells) from oxidative injury induced by buthionine sulfoximine (BSO), an inhibitor of GSH synthesis [66]. 

Flavonoid pretreatment of cells may act to prevent the peroxidation of cellular membrane lipids. For example, the preincubation of cultured retinal cells with eriodictyol, luteolin, quercetin, and taxifolin evoked protection against Fe " ascorbate-induced lipid peroxidation and increases in intracellular oxidative stress... 

Gao Z, Fluang K, Xu H. Protective effects of flavonoids in the roots of Scutellaria baicalensis Georgi against hydrogen peroxide-induced oxidative stress in HS-SY5Y cells. Pharmacol Res 2001 43 173-178. 

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