Abstract 5269: Asymmetric Dimethylarginine Triggers Vasculo-Renal Interaction in CKD Mice
Background: Patients with chronic kidney disease (CKD) also suffer increased morbidity and mortality from cardiovascular diseases (CVD). Endothelial dysfunction is a major factor underlying the pathogenesis of CVD. Asymmetric dimethylarginine (ADMA), an endogenous endothelial nitric oxide synthase (eNOS) inhibitor, is elevated in CKD. We hypothesized that ADMA has a role in endothelial dysfunction in CKD.
Methods and Results: We created a CKD model by performing 5/6 nephrectomy (Nx) in mice. Blood and 24-hour urine were collected for measurements of renal function and ADMA, and NOx levels at 4 weeks after Nx. Nx induced renal failure (serum blood urea nitrogen, controls: 26.9±1.6 mg/dL, Nx mice: 61.0±3.8 mg/dL, p <0.001; serum creatinine, controls: 0.19±0.01 mg/dl, Nx mice: 0.31±0.03 mg/dL, p <0.01) without changing blood pressure. The serum ADMA level was higher (p <0.01) in Nx mice (1.20±0.05 nmol/mL) than in controls (1.00±0.05 nmol/mL). Urinary NOx was lower in Nx mice (controls: 2153±189 nmol/L, Nx mice: 706±335 nmol/L, p <0.05). Isometric tension study using aortic rings showed that endothelium-mediated relaxation induced by acetylcholine was impaired in Nx mice. Furthermore, pretreatment with exogenously administered ADMA at a serum concentration comparable to that in Nx mice reduced acetylcholine-induced relaxation in the aorta of controls. Western blotting showed the phosphorylated eNOS level of the aorta was lower in Nx mice than in controls, whereas eNOS levels were similar. The expression level of dimethylarginine dimethylaminohydrolase-1 (DDAH-1), a degradation enzyme of ADMA, was reduced in the kidney, but not in the aorta of Nx mice. In an ex vivo experiment using cultured human umbilical vein endothelial cells, ADMA treatment with a concentration corresponding to the serum level in Nx mice reduced the eNOS phosphorylation level.
Conclusions: Elevated levels of circulating ADMA, probably resulting from decreased DDAH-1 expression in the kidney, appear to impair endothelial function by inhibiting eNOS activity in CKD. ADMA may thus have a triggering role in the vasculo-renal interaction in CKD.