Determination of arginine and asymmetric dimethylarginine (ADMAL) in human plasma by liquid chromatography/mass spectrometry with the isotope dilution technique

Arginine (ARG) is a substrate for endogenous nitric oxide (NO) production whereas its metabolite, asymmetric dimethylarginine (ADMA), acts as an inhibitor. Sufficient NO production is essential for cardiovascular key functions, thus elevated concentration levels of ADMA are related to a range of cardiovascular diseases. Owing to the lack of reliable methods for the measurement of ARG and ADMA in human plasma, concentration values determined with these methods can differ considerably. We present here a simple and very robust liquid chromatographic/mass spectrometric method for the determination of ARG and ADMA utilizing isotope-labeled internal standards. Sample preparation requires only protein precipitation; the analytes were derivatized with o-phthalaldehyde-mercaptoethanoI and separated on a reversed-phase C-18 column with gradient elution. The analytes were detected with an electrospray ionization ion trap instrument working in the full-scan single mass spectrometry mode. Concentration values obtained with this method for healthy controls were ARG = 63.9 +/- 23.9 mum and ADMA = 0.355 +/- 0.066 mum, with a normal range for ADMA from 0.225 to 0.485 mum. The corresponding values for end-stage chronic renal failure patients are ARG = 48.1 +/- 18.5 mum, p < 0.01 and ADMA = 0.673 +/- 0.134 m, p < 0.001. Copyright (C) 2004 John Wiley Sons, Ltd.