A Simple and Fast Liquid Chromatography-tandem Mass Spectrometry Method for Measurement of Underivatized L-arginine, Symmetric Dimethylarginine, and Asymmetric Dimethylarginine and Establishment of the Reference Ranges

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and an established biomarker for endothelial function, while symmetric dimethylarginine (SDMA), an emerging biomarker for renal function, has been shown to outperform creatinine-based equations for estimated glomerular filtration rate. In order to study these analytes for clinical research, a fast and simple method for measuring arginine (ARG), SDMA, and ADMA in plasma by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed. Plasma (50 μL) was mixed with 50 μL of internal standard of (13)C-arginine and d(7)-ADMA followed by protein precipitation with methanol containing 1% ammonium acetate (300 μL). After centrifugation, the supernatant (100 μL) was mixed with 300 μL of acetonitrile with 1% formic acid, and the mixture was injected onto a silica column monitored by a mass spectrometer. The analytical cycle time was 5.0 min. The method was linear from 5.7 to 489.7 μM for ARG, 0.06 to 5.15 μM for SDMA, and from 0.34 to 5.65 μM for ADMA, with an accuracy of 99.0-120.0%. Total coefficients of variation for all analytes ranged from 2.7% to 7.7% for three concentration levels. The effects of hemolysis, lipemia, uremia, icterus, specimen tube types, storage at different temperature, and freeze/thaw were thoroughly investigated. Reference ranges were established using 51 well-defined reference subjects (12 men and 39 women, age 19-64 years): 53.1-129.7 μM for ARG, 0.32-0.65 μM for SDMA, and 0.36-0.67 μM for ADMA. In conclusion, the validated LC-MS/MS method described here offers a fast and reliable ARG, SDMA, and ADMA quantitation in plasma with minimum sample preparation.