Dimethylarginine dimethylaminohydrolase-2 overexpression improves impaired nitric oxide synthesis of endothelial cells induced by glycated protein

Nitric oxide (NO) synthesis is modulated by dimethylarginine dimethylaminohydrolase (DDAH) via metabolizing asymmetric dimethylarginine (ADMA), an endogenous NO synthase (NOS) inhibitor. This study investigated whether glycosylated bovine serum albumin (GBSA) could impair NO synthesis by inhibition of DDAH expression and activity, and whether DDAH2 overexpression could reverse the impaired NO synthesis induced by GBSA in endothelial cells. Overexpression of DDAH2 gene was established by liposome-mediated gene transfection in ECV304 endothelial cell line. Cells were incubated with 1.70 mmol/L GBSA for 48 h. And the expressions of DDAH1 and DDAH2, gene activities of DDAH and NOS in cells, as well as concentrations of ADMA and NO in media were assayed. The activity of DDAH and expression of DDAH2 gene but not DDAH1 gene were inhibited in endothelial cells after exposure to GBSA, whereas the concentrations of ADMA were increased concomitantly with the decrease of NOS activity in cells and NO production in media. Overexpression of DDAH2 gene could prevent the inhibition of DDAH activity induced by GBSA (0.55 ± 0.02 vs 0.42 ± 0.02 U/g pro; n = 3; P < 0.05), decrease ADMA concentration (0.59 ± 0.04 vs 1.13 ± 0.11 μmol/L; n = 3; P < 0.01), and increase NOS activity and NO production (53.77 ± 3.40 vs 34.59 ± 2.57 μmol/L; P < 0.05) compared with untransfected cells treated with GBSA. These results suggest that decreased DDAH activity and subsequent elevated endogenous ADMA are implicated in the inhibition of NO synthesis induced by GBSA, and overexpression of DDAH2 gene can prevent these changes in DDAH/ADMA/NOS/NO pathway of endothelial cells exposed to GBSA.