Antioxidant Activity of Far-Infrared Radiated Rice Hull Extracts on Reactive Oxygen Species Scavenging and Oxidative DNA Damage in Human Lymphocytes

The antioxidant activities of methanolic extracts of far-infrared irradiated rice hull (FRH) and non-irradiated intact rice hull (IRH) were determined. The antioxidant effects against reactive oxygen species (ROS) were evaluated by measuring scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, superoxide, hydrogen peroxide (H₂O₂), and nitric oxide radical and capacity for chelating metals. Except for H₂O₂ scavenging activity, FRH showed higher scavenging activity than IRH; for example, the 50% inhibitory concentration (mg/mL) values for DPPH radical scavenging of FRH and IRH were 0.067 and 0.085, respectively, as compared with 0.362 and 0.012 for butylated hydroxytoluene andα-tocopherol, respectively. The effect of rice hull extract on DNA damage induced by H₂O₂ in human lymphocytes was also evaluated by comet assay. The protective effect of rice hull extract increased as its concentration increased from 12.5 to 50µg/mL, as indicated by DNA strand breakage decreasing from 38% to 22% with FRH and from 49% to 28% with IRH as compared with H₂O₂-treated positive controls. When human lymphocytes were post-incubated with rice hull extract for 30 minutes after exposure to H₂O₂, the protective ability of the rice hulls remained unchanged. These results suggest that methanol extracts of rice hulls possess significant ROS scavenging and metal chelating activities and protective effect against oxidative DNA damage.