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 [H-3]ADMA and [H-3]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 mu mol l(-1) (ADMA) and 519 +/- 36 mu mol l(-1) (L-arginine). Uptake of ADMA was inhibited by L-arginine and SDMA with IC50 values (95% CI) of 227 (69-742) mu mol l(-1) and 273 (191-390) mu mol l(-1), respectively. ADMA and SDMA inhibited CAT1-mediated uptake of L-arginine with IC50 values of 758 (460-1251) mu mol l(-1) and 789 (481-1295) mu mol l(-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. (C) 2012 Elsevier Ltd. All rights reserved.