Determination of asymmetric dimethyl arginine in human serum by liquid chromatography-tandem mass spectrometry: clinical application in hypertensive subjects

Background: Asymmetric dimethylarginine (ADMA), an endogenous competitive inhibitor of nitric oxide synthase plays an important role in endothelial dysfunction processes. Recent studies have linked high ADMA levels with several pathological conditions. The interest as a marker of endothelial dysfunction has increased in the last few years. In this paper, a method for serum ADMA quantification by liquid chromatography tandem mass spectrometry has been described. To test the utility in a pathological condition ADMA levels in hypertensive subjects have been measured. Methods: HPLC separation was performed by hydrophilic interaction chromatography using acetonitrile/water containing 0.1\% formic acid and 20 mmol/L ammonium formate. Selected reaction monitoring was performed following the transitions m/z 203.1 -> 46.4 for ADMA and 210.1 -> 46.3 for the internal standard {[H-2(7)]ADMA. Results: The method was linear up to 10 mu mol/L, limit of detection and limit of quantification were 0.005 mu mol/L and 0.01 mu mol/L, respectively. Recovery was higher than 96\%. Intra- and inter-assay imprecision were lower than 6\%. The accuracy, expressed as bias \%, was <2.5. ADMA in ``healthy'' subjects ranged from 0.343 to 0.608 mu mol/L and resulted significantly lower than that measured in hypertensive subjects (p < 0.001). Conclusions: The method developed is selective and sensitive, thus suitable not only for research purposes, but also for routinely work.}