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This study investigated the conjoined cellular oxidative damage of human embryo kidney 293T (HEK293T) cells induced by cadmium chloride (CdCl2) and nanometer titanium dioxide (nano-TiO2).RT-PCR technique was used to detect the expressions of Heme oxygenase-1(HO-1) and 8-oxoguanine DNA glycosylase (OGG1).The activities of superoxide dismutase (SOD) and catalase enzyme (CAT) and concentrations of reactive oxygen species (ROS) and maldondialdehyde (MDA)were measured by different approaches.The results showed that CdCl2 and nano-TiO2 at a low concentration of 0.75 total toxic unit (TU) exerted an additive effects on HO-1 gene expression,CAT activities and MDA concentrations.When the total TU was increased to 1 or 1.25 TU,the interaction was synergetic.Moreover,the mixture with high proportion of CdCl2 produced an additive effect on the OGG1gene expression,and the interaction was changed to be synergetic when the concentration of CdCl2 was lower than or equal to that of nano-TiO2.Synergetic effects of CdCl2 and nano-TiO2 on cellular oxidative damage of HEK293T cells were found as indicated by the changes in the SOD activities and ROS concentrations.It was concluded that CdCl2 and nano-TiO2 exerts synergistic effects on the cellular oxidative damage of HEK293T cells,and the sensitivity of these indicators of oxidative damage varies with the proportion of CdCl2 and nano-TiO2 in the mixture.