Antioxidant versus prooxidant properties of the flavonoid, galangin: ROS scavenging activity, flavonoid-DNA interaction, copper-catalyzed Fenton reaction and DNA damage study

Abstract

Flavonoids are natural antioxidants, found in vegetables, fruits, flowers, coffee, tea, wine, and other foodstuffs. They are well known for their health benefits, and various clinical trials have determined that a sufficient intake of flavonoids is related to lower mortality from cardiovascular diseases, metabolic diseases, and cancer. In addition, flavonoids are of great current interest in regard to sporting activities, in that the intake of these compounds by sportsmen may both shorten their recovery periods and improve their overall health status. In this work, we present results demonstrating the antioxidant, and also prooxidant, properties of the flavonoid, galangin, which is currently under intense investigation as a health supplement. The prooxidant environment has been simulated using Cu-catalyzed-Fenton and Cu-Ascorbate systems. UV–Vis spectroscopy revealed that galangin is coordinated to Cu(II) through oxygen donor atoms from both the benzoyl (4-CO/5-OH groups) and the cinnamoyl (3-OH/4-CO) moieties of the molecule; however, the interaction occurs preferentially via the cinnamoyl unit. The radical scavenging activity of galangin and Cu(II)-galangin complexes were studied using the ABTS assay, which confirmed an inhibitory/scavenging activity of the systems studied, but chelation resulted in only a modest increase in activity. Electronic absorption titrations showed that both free galangin and the Cu(II)-galangin complex interact with DNA through hydrogen-bonding and van der Waals interactions. The values evaluated for the binding constants (K) indicate an intermediate binding strength between the given flavonoid systems and DNA. The results from gel electrophoresis have shown that, in the ROS-producing prooxidant systems, galangin provided a concentration-dependent protective effect against DNA damage via both Cu(II)-chelation and ROS-scavenging mechanisms. The ROS scavengers, l-histidine, DMSO, and SOD, confirmed the formation of singlet oxygen (1O2), hydroxyl radicals (•OH), and superoxide radical anions (O2•−).