Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, accumulates in plasma during chronic kidney disease (CKD). High plasma levels of ADMA can increase transforming growth factor-beta (TGF-beta) expression, related to renal fibrosis, but the precise molecular mechanism is not explicit. The present study was designed to determine the mechanism through which long-term low-dose ADMA induces TGF-beta expression in endothelial cells and to investigate the molecular mechanism of its action. Human umbilical vein endothelial cells (HUVECs) were exposed to low-dose ADMA (5 and 10 mu mol/l) for 7 passages and TGF-beta expression was determined. Human renal glomerular endothelial cells (HRGECs) were exposed to high-dose ADMA (100 mu mol/l) which were used to clarify the molecular mechanism. The results showed that long-term low-dose ADMA (5 and 10 mu mol/l) increases TGF-beta production in both mRNA and protein levels in HUVECs in a time-dependent manner. We confirmed that exogenous ADMA (100 mu mol/l) significantly enhanced stress fiber formation in HRGECs and upregulated TGF-beta expression. Such effects of ADMA in HRGECs were inhibited by pre-treatment with actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In addition, we demonstrated that ADMA (100 mu mol/l) significantly activated nuclear factor-kappa B (NF-kappa B) in HRGECs, which was markedly attenuated by actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In brief, the present study demonstrated that long-term low-dose ADMA induces TGF-beta expression in endothelial cells at both the gene