| Abstract
| - Five procyanidin fractions with different structural complexities were obtained after fractionation of agrape seed extract. The procyanidin fraction's abilities to inhibit lipid peroxidation induced by 2,2‘-azobis-2-methyl-propanimidamide dihydrochloride in a liposomal membrane system were examined.The antioxidant capacities of all fractions were evaluated through monitoring oxygen consumptionand by measuring the formation of conjugated dienes. All tested fractions provided protection ofmembranes against peroxyl radicals by increasing the induction time of oxidation. This effect increasedup to fraction II but decreased with the increase of the structural complexity of further procyanidinfractions, possibly due to steric hindrance effects exhibited by the more complex fractions. In addition,the antiradical properties and the reducing power of these fractions were determined by using 2,2-diphenyl-1-picrylhydrazyl and ferric reducing/antioxidant power methods, respectively. Moreover,3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide reduction and DNA synthesis weremeasured in Michigan Cancer Foundation 7 (MCF-7), a human breast cancer cell line, treated withcatechin or procyanidin fractions in order to evaluate the effect of these compounds on cell viabilityand proliferation. The results obtained showed that at 30 μg/mL, fractions I and II decreased cellviability and proliferation, which was not observed with 60 μg/mL of the same fractions. Catechinwas also able to decrease cell viability and proliferation at 30 and 60 μg/mL. It is interesting to noticethat the procyanidin fractions that exhibited higher antioxidant activity were the same to affect cellviability and proliferation. Keywords: Antioxidant; antiproliferative agents; breast cancer; grape seed extract; MCF-7 cells;procyanidins
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