Abstract :Objective 　To investigate the similarities and differences of homocysteine and cysteine on pathogenesis of As in cultured human vascular smooth muscle cells (HVSMCs) . Methods 　Cultured HVSMCs were treated by different concentrations of Hcy and Cys for 24 h. (1) The SOD activity and MDA contents were measured by hromatometry. (2)The rates of apoptosis of HVSMCs were detected by flow cytometry. The expression of caspases23 mRNA in HVSMCs was detected by reverse2trascription polymerase chain reaction (RT2PCR) . (3) The proliferative activities of HVSMCs were examined by MTT assay. (4) HVSMCs were incubated with 1000μmolPL Hcy and Cys for 24 , 48 and 72h respectively ,then the DNA methylation status were assayed by nested methylation2specific polymerase chain reaction , and the expressions of ERαmRNA of HVSMCs were detected by RT2PCR. Results 　(1) Hcy significantly increased the MDA contents and SOD activities in a dose2dependent manner , but the increase of MDA contents and SOD activities were much weaker induced by Cys ( P < 0. 01) . (2) The results of flow cytometry , expression of caspases23 mRNA , and MTT test showed that the effects of Hcy and Cys on rate of apoptosis and proliferation of HVSMCs were not much different. (3) Hcy obviously induced de novo methylation in the promoter region of the ERα gene in HVSMCs , and the expressions of ERα mRNA were correspondingly down2regulated. The Cys had no effect on methylation modification of ERα gene , and very mild effect on ERαmRNA expression. Conclusion 　The oxidative stress and the methylative modification induced by Hcy may have the top position in its pathogenic mechanismof pro2atherosclerosis. The pro2apoptotic and proliferation2promoting effects of Hcy were similar with Cys , which suggested that these two effects might just play mild roles in its pro2 atheroscleroatic traits.

Key words :homocysteine , cysteine , atherosclerosis , pathogenic effect , human vascular smooth mscle cell