Abstract: OBJECTIVE: Oxidative DNA-damaging effects of mono-2-ethylexyl phthalate (MEHP) on MCF-7 cells were investigated. METHODS：MCF-7 cells were treated with MEHP at various concentrations (6.25，12.5，25，50 and 100 μmol/L) or dimethyl sulphoxide alone (DMSO，solvent control，final concentration <1‰). Cell proliferation was measured by the MTT assay at 12 and 24 h after the treatment. At the time points (1.5，3，6，12 and 24 h)，the content of malondialdehyde (MDA) and activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were measured using the corresponding kits. The level of (8-hydroxy-2'-deoxyguanosine，8-OHdG) in MEHP-treated cells was estimated using high-pressure liquid chromatography with electrochemical detection HPLC-ECD method. RESULTS：At 12 h after treatment， cell proliferation rates significantly increased in MEHP-treated groups (6.25 and 12.5μmol/L，P<0.05 for both). However，cell proliferation rates significantly decreased at 24 h after treatment，in the higher MEHP-treated groups (25-100μmol/L，P<0.05 for all). There were no significant changes in the levels of MDA，GSH-Px and 8-OHdG (P>0.05 for all).After MCF-7 cells were treated with MEHP for short periods (1.5，3 and 6 h)，the levels of MDA and 8-OHdG in all treatment groups were increased (P<0.05)，but SOD and GSH-Px activities were reduced (P<0.05 for all). CONCLUSION：Short periods(≤6 h) of treatment with MEHP at a certain concentration induced oxidative stress in MCF-7 cells，and accelerated DNA oxidative damage. The underlying mechanisms of MEHP mediated oxidative DNA damage MCF-7 cells need to be investigated.

Key words: MEHP, oxidative stress, DNA oxidative damage, 8-OHdG