Abstract: Objective To study the effection on proliferation and apoptosis of SMMC-7721 cells induced by cadmium and its mechanism.Methods SMMC-7721 cells were incubated with 0,40,80,160μmol/L CdCl₂ for 0-48 hours.Cell viability was measured by methyl thiazolyl tetrazolium assay(MTT).The occurrence of apoptosis was determined by flow cytometry.Absorption spectrometry was adopted to measure the relative activity of Caspase-3.The expression of Caspase-3 gene in SMMC-7721 cells after treatment with cadmium was determined by the methods of reverse transcription polymerase chain reaction(RT-PCR)and western-blot analysis.Results Cell viability decreased in dose-dependent manner with the dose increase of cadmium.The inhibition ratio of cell proliferation incubated with 40,80,160μmol/L CdCl₂ was 33.94%,48.04%,and 68.54%,respectively.Compared with 0μmol/L cadmium,the inhibition ratio increased obviously(P<0.01).The apoptosis rate of SMMC-7721 cell incubated with 40,80,160μmol/L CdCl₂ was 25.77±4.66%,34.97±9.25%,and 55.14±5.67%,respectively.Compared with 0μmol/L cadmium,the apoptosis rate increased obviously in the incubated cells with 40,80,160μmol/L cadmium(P<0.01 for all).With the dose increase of cadmium,we found that the enzyme activity of Caspase-3 increased obviously.RT-PCR analysis revealed that the incubated cell with 40μmol/L cadmium for 12,24 and 48 hours,the expression of Caspase-3 mRNA was 4.1,3.7, and 3.9 times higher compared with that of the controls.Western blot analysis revealed that in the incubated cells with 40 μmol/L cadmium for 12,24,and 48 hours,the expressin of Caspase-3 was 5.8,6.0,and 7.2 times higher compared to that of the controls,respectively.Conclusion CdCl₂ can obviously restrain the proliferation and induce apoptosis of SMMC-7721 cell.The results suggest that Caspase-3 could play an important role in cadmium-induced cell apoptosis.