Rice hull is known to contain an antioxidant defense system to protect rice seed from oxidative stress. The aim of this study was to evaluate the effect of methanol extract of rice hull on oxidative DNA damage induced by H₂O₂ in human lymphocytes. Cells incubated in medium with 1 % DMSO (negative control) or with various concentration of rice hull extracts (12.5, 25, 50, 100μg/ml) for 30 min at 37^oC were further treated with H₂O₂ (200μM) as an oxidative stimulus for 5 min on ice. Oxidative damage was evaluated by Comet assay (single-cell gel electrophoresis) and quantified as % tail DNA. Cell viability measured by trypan blue exclusion test was above 95% for all treatments. An increased oxidative DNA damage by H₂O₂ expressed by % tail DNA was significantly inhibited by pre-incubating with rice hull extracts in a dose dependent manner. When human lymphocytes were post-incubated with rice hull extract for 30 min after exposure to H₂O₂ or incubated with rice hull and H₂O₂ simultaneously, the protective ability of the rice hull was not changed. These results indicate that rice hull supplementation to human lymphocytes followed by H₂O₂ treatment inhibited damage to cellular DNA, supporting a protective effect of rice hull against oxidative damage.

Keywords: Rice hull extract, DNA damage, Comet assay, Hydrogen peroxide, Lymphocytes