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Background: Nitric oxide is synthesized from the amino acid Arg by the enzyme endothelial nitric oxide synthase, which is competitively inhibited by the arginine metabolite asymmetric dimethylarginine (ADMA). In this way, increased concentrations of ADMA lead to reduced nitric oxide production associated with a range of cardiac diseases. Research in this field requires the measurement of Arg and of ADMA and its closely related substance, symmetric dimethylarginine (SDMA).  Methods: We quantified Arg, ADMA, and SDMA in human plasma, human urine, and cell culture supernatant by HPLC–electrospray tandem mass spectrometry. Sample preparation required only protein precipitation. Separation was by liquid chromatography on a 150 × 3 mm silica column with an isocratic mobile phase consisting of water–acetonitrile–trifluoroacetic acid–propionic acid (10:90:0.025:1 by volume). The chromatographic run time was 7 min.  Results: The chromatograms were interference-free in all matrices. In the low-concentration quality-control samples, the interassay CVs in plasma were 4.7% for Arg, 7.7% for ADMA, and 4.9% for SDMA. Similar values were obtained in urine and cell culture supernatants. The calibration functions were linear and covered the ranges of healthy and pathologic samples.  Conclusion: The new method requires neither derivatization nor complete chromatographic separation between ADMA and SDMA for quantification of the 3 metabolites, has calibration functions that are independent of the sample matrix, and provides measured concentrations that agree with those reported in the literature.

clinical chemistry

Fast and Efficient Determination of Arginine, Symmetric Dimethylarginine, and Asymmetric Dimethylarginine in Biological Fluids by Hydrophilic-Interaction Liquid Chromatography–Electrospray Tandem Mass Spectrometry