HPLC-tandem mass spectrometric method for rapid quantification of dimethylarginines in human plasma.

Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are derived from posttranslational methylation of arginine residues in proteins and after proteolytic release. Whereas protein methylation appears to be important in RNA binding and protein sorting, ADMA evolved as a competitive inhibitor of nitric oxide synthase at the arginine-binding site (1)(2). At a constant arginine supply, increased ADMA concentrations decrease NO formation and impair vascular homeostasis by multiple mechanisms (3). Consequently, arginine supplementation improves small-vessel function (4). Inactivation of ADMA occurs via dimethylarginine dimethylaminohydrolase, and it has been hypothesized that this enzyme might be inhibited by homocysteine. The role of SDMA is less clear; it probably is an inhibitor of arginine transport across the cell membrane (5). From the clinical perspective, ADMA has been established as a possible risk factor for the development of endothelial dysfunction and cardiovascular disease (6). Its plasma concentrations also predict the probability of restenosis after stent implantation. The possible contribution of high-resistance placental circulation, endothelial dysfunction, and increased ADMA concentrations to the development of preeclampsia has been investigated (7). Recently, a significant decrease in circulating ADMA was reported during hormone replacement therapy in postmenopausal women (8). Plasma concentrations of ADMA are also influenced by insulin sensitizers such as rosiglitazone, indicating a possible link of NOS activity to the metabolic syndrome (9). Thus, there is considerable demand for specific, sensitive, and rapid methods for ADMA determination in biological fluids. Previously, several methods for ADMA and SDMA determination have been described, including gas chromatography–tandem mass spectrometry (MS/MS) (10), liquid chromatography …