ANTHOCYANIN INTERACTIONS WITH DNA: INTERCALATION, TOPOISOMERASE I INHIBITION AND OXIDATIVE REACTIONS

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Abstract
Anthocyanins and their aglycone anthocyanidins are pigmented flavonoids found in significant amounts in many commonly consumed foods. They exhibit a complex chemistry in aqueous solution, which makes it difficult to study their chemistry under physiologic conditions. Here we used a gel electrophoresis assay employing supercoiled DNA plasmid to examine the ability of these compounds (1) to intercalate DNA; (2) to inhibit human topoisomerase I through both inhibition of plasmid relaxation activity (catalytic inhibition) and stabilization of the cleavable DNA–topoisomerase complex (poisoning); and (3) to inhibit or enhance oxidative single‐strand DNA nicking. We found no evidence of DNA intercalation by anthocyan(id)ins in the physiologic pH range for any of the compounds used in this study – cyanidin chloride, cyanidin 3‐O‐glucoside, cyanidin 3,5‐O‐diglucoside, malvidin 3‐O‐glucoside and luteolinidin chloride. The anthocyanins inhibited topoisomerase relaxation activity only at high concentrations (>50 µM), and we could find no evidence of topoisomerase I cleavable complex stabilization by these compounds. However, we observed that all of the anthocyan(id)ins used in this study were capable of inducing significant oxidative DNA strand cleavage (nicking) in the presence of 1 mM dithiothreitol, while the free radical scavenger, dimethyl sulfoxide (DMSO), at concentrations typically used in similar studies, completely inhibited DNA nicking. Finally, we proposed a mechanism to explain the anthocyan(id)in‐induced oxidative DNA cleavage observed under our experimental conditions. PRACTICAL APPLICATIONS This study provided improved understanding of the mechanisms by which anthocyan(id)ins interact with DNA. By characterizing the chemistry and solution properties of these important dietary components, we obtained improved information on how the anthocyan(id)ins might function in living systems.

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