[The pathogenic mechanism of homocysteine -induced endothelial nitric oxide synthase dysfunction and the antagonistic effects by folic acid].

To investigate the pathogenic mechanism of homocysteine-induced endothelial nitric oxide synthase dysfunction and the antagonistic effects by folic acid (FA). Human umbilical vein endothelial cells (HUVEC)were cultured to the third generation. Then HUVEC were cultured with Hcy at different concentrations (0,10,30,100 and 300 micromol/L),with or without FA(100 micromol/L)for 72 hours. The mRNA and protein levels of endothelial nitric oxide synthase (eNOS) were analyzed by RT-PCR and immunohistochemistry respectively. Asymmetric dimethylarginine (ADMA)was measured by reversed-phase high performance liquid chromatography. The dimethylarginine dimethylaminohydrolase(DDAH), activity of eNOS and the production of NO were analyzed simulta- neously. After HUVEC were exposed to Hcy at different concentrations for 72 hours, the level of eNOS mRNA and the content of eNOS protein, the eNOS activity, and the production of nitric oxide (NO) were all significantly and dose-dependently reduced compared with the control group (P< 0.05). The activity of DDAH has a parallel decrease and the ADMA concentration showed a cor- responding increase. The addition of folic acid (100 micromol/L)resulted in partial antagonistic effects against the injury of Hcy on NOS system of endothelial cells, the eNOS protein level and eNOS activity, and NO production increased,and so does the DDAH activity,and the ADMA concentration reduced. But the FA didn't influence the eNOS mRNA expression. The pathogenic mechanism of homocysteine-induced eNOS dysfunction may involve two levels,the level of eNOS protein and eNOS activity,and the level of the expression of eNOS gene. The injury on the level of eNOS protein and eNOS activity may go through the DDAH-ADMA pathway. Folic acid can exert partial protective roles against the Hcy in the level of eNOS protein and eNOS activity,but without impact on the expression of eNOS gene.