Protective Effect of Water Yam (Dioscorea alata L.) Extract on the Copper-driven Fenton Reaction and X-ray Induced DNA Damage in vitro

The rhizome extract of Dioscorea has been shown to possess radical scavenging activity. In this study, the protective effect of water yam (Dioscorea alata L.) rhizome extract on calf thymus DNA and plasmid DNA strand breakage by the copper-driven Fenton reaction and X-irradiation was examined. The protective activity in vitro of four lyophilized extracts obtained from yam rhizomes: (1) aqueous extract (YAE); (2) 30% ethanolic extract (YEE); (3) aqueous extract boiled for 30 min (BYAE); and (4) 30% ethanolic extract boiled for 30 min (BYEE) were evaluated by ethidium bromide binding assay and DNA nicking assay. The YAE, YEE, and BYEE effectively inhibited the copper-driven Fenton reaction-induced damage of calf thymus DNA, while inhibition was less pronounced in the case of X-ray induced strand breakage of plasmid DNA. While BYAE potently inhibited X-ray induced strand breaks in plasmid pGL3 DNA, it failed to inhibit, and even greatly enhanced copper-H2O2 induced damage of calf thymus DNA. The present results demonstrate strong copper chelating and weak hydroxyl radical scavenging activities in yam rhizome extracts, and these activities may vary depending on the procedures used in preparing the extract.