Chromatographic-mass spectrometric methods for the quantification of l-arginine and its methylated metabolites in biological fluids

l-Arginine (Arg) and its methylated metabolites play a major role in the synthesis of the cell signaling molecule nitric oxide (NO). Arg serves as a substrate for the enzyme NO synthase (NOS), which produces NO, whereas monomethylarginine (l-NMMA) and asymmetric dimethylarginine (ADMA) act as competitive inhibitors of NOS. Symmetric dimethylarginine (SDMA) has virtually no inhibitory effect on NOS activity, but shares the pathway for cell entry and transport with Arg and ADMA. Accurate and reliable quantification of these substances in various biological fluids is essential for scientific research in this field. In this review, chromatographic-mass spectrometric methods for Arg and its methylated metabolites ADMA and SDMA are discussed. Mass spectrometric detection provides an intrinsic higher selectivity than detection by means of UV absorbance or fluorescence. Taking advantage of the high selectivity, approaches involving mass spectrometric detection require less laborious sample preparation and produce reliable results. A consensus emerges that the concentration values in plasma of young healthy volunteers are about 65 μM for Arg, 0.4 μM for ADMA and 0.5 μM for SDMA.