Interaction of the cardiovascular risk marker asymmetric dimethylarginine (ADMA) with the human cationic amino acid transporter 1 (CAT1).

Elevated plasma concentrations of endogenously formed asymmetric (ADMA) and symmetric dimethyl-l-arginine (SDMA) are associated with adverse clinical outcomes. Our aim was to investigate the cellular uptake properties of ADMA by the human cationic amino acid transporter 1 (CAT1; SLC7A1). Human embryonic kidney cells (HEK293) stably overexpressing CAT1 (HEK-CAT1) and vector-transfected control cells (HEK-VC) were established to determine cellular uptake of labeled [(3)H]ADMA and [(3)H]l-arginine. Uptake of ADMA and l-arginine were significantly (p<0.001) higher in HEK-CAT1 than in HEK-VC at all investigated concentrations. Apparent V(max) values of cellular ADMA and l-arginine uptake by CAT1 were 26.9 ± 0.8 and 11.0 ± 0.2 nmol mg protein(-1) min(-1), respectively. K(m) values were 183 ± 21 μmoll(-1) (ADMA) and 519 ± 36 μmoll(-1) (l-arginine). Uptake of ADMA was inhibited by l-arginine and SDMA with IC(50) values (95% CI) of 227 (69-742) μmoll(-1) and 273 (191-390) μmoll(-1), respectively. ADMA and SDMA inhibited CAT1-mediated uptake of l-arginine with IC(50) values of 758 (460-1251) μmoll(-1) and 789 (481-1295) μmoll(-1), respectively. Efflux of ADMA was significantly increased in HEK-CAT1 cells as compared to HEK-VC (p<0.05). CAT1 mediates the cellular uptake of ADMA. In its physiological concentration range ADMA is unlikely to impair CAT1-mediated transport of l-arginine. Conversely, high (but still physiological) concentrations of l-arginine can inhibit CAT1-mediated cellular uptake of ADMA.