Elevated Plasma Asymmetric Dimethylarginine as a Marker of Cardiovascular Morbidity in Early Diabetic Nephropathy in Type 1 Diabetes LISE TARNOW, MD, DMSC 1 PETER HOVIND, MD 1 TOM TEERLINK, PHD 2 COEN D.A. STEHOUWER, MD, PHD 2 HANS-HENRIK PARVING, MD, DMSC 1,3 OBJECTIVE — Increased plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, has been associated with endothelial dysfunction, insulin resistance, and atherosclerosis in nondiabetic populations. In end-stage renal failure, circulating ADMA is elevated and a strong predictor of cardiovascular outcome. This study investigated the relation between ADMA and diabetic micro- and macrovascular complications in a large cohort of type 1 diabetic patients with and without early diabetic nephropathy. RESEARCH DESIGN AND METHODS — ADMA concentrations in plasma were de- termined by a high-performance liquid chromatography method in 408 type 1 diabetic patients with overt diabetic nephropathy (252 men; mean age 42.7 years [SD 11.0], mean duration of diabetes 28 years [SD 9], median serum creatinine level 102 mol/l [range 52– 684]). A group of 192 patients with longstanding type 1 diabetes and persistent normoalbuminuria served as control subjects (118 men; mean age 42.6 years [SD 10.2], mean duration of diabetes 27 years [SD 9]). RESULTS — In patients with diabetic nephropathy, mean  SD plasma ADMA concentration was elevated 0.46  0.08 vs. 0.40  0.08 mol/l in normoalbuminuric patients (P  0.001). An increase in plasma ADMA of 0.1 mol/l increased the odds ratio of nephropathy to 2.77 (95% CI 1.89 – 4.05) (P  0.001). Circulating ADMA increased in nephropathy patients with declining kidney function, as indicated by elevated values in the lower quartiles of glomerular filtration rate (76 ml  min –1  1.73 m –2 )(P  0.001 ANOVA). Mean ADMA levels were similar in patients with or without diabetic retinopathy (P  0.2). However, in 44 patients with nephropathy and history of myocardial infarction and/or stroke, ADMA was significantly elevated at 0.48  0.08 mol/l compared with 0.46  0.08 mol/l in patients without major cardiovascular events (P = 0.05). CONCLUSIONS — Elevated circulating ADMA may contribute to the excess cardiovascular morbidity and mortality in early diabetic nephropathy. Diabetes Care 27:765–769, 2004 N itric oxide is synthesized by the vas- cular endothelium from the amino acid L-arginine by constitutive and inducible nitric oxide synthases and plays an important role as vasodilator and in the maintenance of vascular homeostasis (1). The endogenous L-arginine metabolite, asymmetric dimethylarginine (ADMA), inhibits cellular L-arginine uptake and ni- tric oxide synthase activity competitively. In contrast, its stereoisomer symmetrical dimethylarginine (SDMA) is produced in equivalent amounts but has no inhibitory effect on nitric oxide synthase (2). Accumulation of ADMA has first been shown in chronic renal failure (3) and has subsequently been confirmed by other studies of advanced nondiabetic kidney disease (4,5). The idea was simple: as the kidneys fail, ADMA excretion diminishes and its concentration in plasma increases to levels sufficient to block nitric oxide generation and thereby cause cardiovas- cular, neurological, and other unwanted effects (3). Later reports of ADMA as a potential mediator of cardiovascular mor- bidity and mortality in patients with chronic renal impairment have supported this concept (6,7). However, the recent finding of a marked increase in ADMA in nondiabetic kidney disease, when glo- merular filtration rate is still within the normal range (8), suggests that other mechanisms may be involved. Although a proportion of ADMA is excreted in the urine, its major catabolism is via the enzyme dimethylarginine di- methylaminohydrolase (4), shown to be colocalized with nitric oxide synthases in various renal cell types (9). In vitro, hy- perglycemia impairs dimethylarginine dimethylaminohydrolase activity in vas- cular smooth muscle cells and the endo- thelium, leading to elevated ADMA levels (10). In addition, a significant relation- ship has been reported between increased plasma concentrations of ADMA, type 2 diabetes, and insulin resistance, a condi- tion closely associated with a constella- tion of risk factors for cardiovascular disease (11,12). Because cardiovascular disease clus- ters in type 1 diabetic patients with dia- betic nephropathy and, furthermore, because insulin resistance has been sug- gested to play a role in the pathogenesis of this microvascular complication, we aimed to study the role of ADMA in type 1 diabetes. Therefore, the objective of the present study was to investigate the rela- tion between ADMA and diabetic micro- and macrovascular complications in a large cohort of type 1 diabetic patients ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● From the 1 Steno Diabetes Center, Gentofte, Denmark; the 2 VU University Medical Center, Amsterdam, the Netherlands; and the 3 Faculty of Health Science University of Aarhus, Aarhus, Denmark. Address correspondence and reprint requests to Lise Tarnow, MD, DMSc, Steno Diabetes Center, Niels Steensens Vej 2, DK-2820 Gentofte, Denmark. E-mail: ltar@steno.dk. Received for publication 20 August 2003 and accepted in revised form 20 November 2003. Abbreviations: ADMA, asymmetric dimethylarginine; SDMA, symmetrical dimethylarginine. © 2004 by the American Diabetes Association. Pathophysiology/Complications O R I G I N A L A R T I C L E DIABETES CARE, VOLUME 27, NUMBER 3, MARCH 2004 765