Antioxidant activities of phytochemicals from five flavonoid groups in a heme-amyloid β-enhanced oxidation reaction

Age-associated neurodegenerative disorders such as Alzheimers represent a major and growing international health problem, and there is much research interest in prevention strategies. There is some evidence, based both on epidemiological and biochemical studies, that dietary factors such as flavonoids may contribute to moderating such neurodegeneration. The major aim of our current study was to compare antioxidant activities of aglycone flavonoids, one from each of five subclasses-catechin (flavanols), delphinidin (anthocyanidins), quercetin (flavonols), luteolin (flavones), eriodictyol (flavanones)-in biochemical assays of potential relevance to neurodegenerative disorders. The methods involved a biochemical assay based on an N-N-N'-N'-tetra-methyl-p-phenylenediamine oxidation reaction promoted by heme and amyloid-beta(1–42), two components implicated in oxidative stress related to Alzheimers. Each flavonoid was tested at 10 microM concentrations, n=4 for each assay. The results indicate that quercetin, the flavonol, exhibited the greatest decrease in oxidation rates, 25.3±7.2% below that of control, p<0.05. All flavonoids exhibited statistically significant (p<0.05) decreases in oxidation rates with the exception of eridyctiol. The average oxidation decrease of all five flavonoids was 19.5±3.0%. The main conclusion is that quercetin, delphinidin, luteolin, and catechin representatives of four different structural flavonoid subclasses, have significant antioxidant activity against a reaction that may be of neuropathological relevance. In terms of future directions, we have begun to compare these data with other results, involving the same flavonoids and flavonoid subclasses, from epidemiological studies and from biochemical studies based on other oxidation reactions. It will also be of interest to test phytochemical combinations for possible synergistic or antagonistic activities, and phytochemical metabolites.