Insulin and adiponectin inhibit the TNFα-induced ADMA accumulation in human endothelial cells: The role of DDAH

ObjectiveInsulin and adiponectin exert important effects on the vasculature. We wanted to explore whether the eNOS inhibitor asymmetric dimethylarginine (ADMA) contribute to their effects.MethodsHuman umbilical vein endothelial cells (HUVECs) and human coronary artery endothelial cells (HCAECs) were incubated with growth medium in the presence or absence of tumor necrosis factor-alpha (TNFα), d-glucose, insulin or adiponectin. Further, cells exposed to TNFα for 24 h were co-stimulated with insulin or adiponectin for additional 24 h. Concentrations of ADMA in conditioned media and activity of dimethylarginine dimethylaminohydrolase (DDAH) in cell lysates were determined.ResultsThe dose-dependent TNFα-induced ADMA accumulation was significantly inhibited when co-stimulated with insulin or adiponectin in both cell lines (p < 0.01 for all), accompanied by significant increases in DDAH activity in all conditions. Insulin alone resulted in a significant, but inversely dose-dependent accumulation of ADMA as compared to control cells in both cell lines, accompanied by increased DDAH activity. Adiponectin alone tended, dose-dependently to decrease ADMA, but without an increase of DDAH activity.ConclusionThe results indicate that ADMA accumulation in human cultured endothelial cells is influenced by both insulin and adiponectin, and both mediators counteract the TNFα-induced accumulation of ADMA through the DDAH pathway.