| The antioxidant activity of five polyphenols, such as tea polyphenol (multi-hydroxyl groups) , gallic acid (three hydroxyl groups) , quercetin (five hydroxyl groups) , kaempferol (four hydroxyl groups) , apigenin (three hydroxyl groups) andα-Tocopherol (mono- hydroxyl group, as a control), were evaluated by different chemical methods, includingα-deoxyribose assay, pyrogallol autoxidant assay, DPPH assay, ABTS assay and reducing power assay. SAS software was applied to analyze the correlation between the results obtained in these methods. Meanwhile,the potential hepatoprotective effects of five polyphenols against damages induced by hydrogen peroxide or carbon tetrachloride were evaluated in human hepatocytes. Correlation analysis of the indexes between oxidative injury systems (MDA formation and GSH content) for hepatocytes and antioxidation evaluated by chemical methods in vitro(·OH,·O2-,·DPPH,·ABTS+ scavenging activity of polyphenols) were also analyzed, for finding out whether there is a relationship between antioxidant activity evaluated by chemical methods in vitro and antioxidant activity evaluated in cells. The results showed as follows:1 Five polyphenols showed·OH,·O2-,·DPPH,·ABTS + scavenging-activity and reducing power, which revealed that they had good antioxidant activity. The total antioxidant activity of gallic acid, quercetin and tea polyphenol were higher than those of kaempferol,α-Tocopherol and apigenin. Polyphenols were with higher scavenging-activity for·ABTS+ and·DPPH than others. Antioxidant activity of polyphenols had nothing to do with the numbers of hydroxyl group contained in polyphenols .2 The results obtained in reducing power assay had extremely significant positive correlation with the results obtained in DPPH assay or ABTS assay(P<0.01). Meanwhile, the results obtained in ABTS assay had significant positive correlation with the results obtained in DPPH assay orα-deoxyribose assay; the results obtained in pyrogallol autoxidant assay also had significant positive correlation with the results obtained inα-deoxyribose assay(P<0.05).3 Polyphenlos had a clearly protective effect on human hepatocytes damages induced by H2O2 or CCl4. They could obviously improve cell viability and the content of GSH in cells, and also reduce both dehydrogenase (LDH) leakage and formation of MDA in cells. Hepatoprotective effects of polyphenols ranked in the following order: gallic acid >quercetin > tea polyphenol > apigenin >α-Tocopherol > kaempferol. Hepatoprotective effects of polyphenols also had nothing to do with the numbers of hydroxyl group contained in polyphenols .4 The results obtained in protective effects of polyphenols on human hepatocytes damages induced by H2O2 or CCl4 had a good correlation with the results obtained in different chemical evaluation methods for antioxidation of polyphenols. Therefore, the protective effect on human hepatocytes may be associated with the high radical-scavenging activity of polyphenlos.
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