Simultaneous determination of tyrosine, phenylalanine and deoxyguanosine oxidation products by liquid chromatography-tandem mass spectrometry as non-invasive biomarkers for oxidative damage

We developed an isotope dilution HPLC-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/MS) method for the simultaneous determination of p-tyrosine, phenylalanine, o,o'-dityrosine, m-tyrosine, o-tyrosine, 3-chlorotyrosine and 3-nitrotyrosine and 8-hydroxy-2'-deoxyguanosine (8-OHdG) that requires no extensive sample pre-treatment. p-[H-2(4)]Tyrosine and o,o'-[H-2(6)]dityrosine were used as internal standards. Calibration curves of the method were linear (r(2) = 0.990-0.999) over a concentration range of 0.03-10 muM for o-tyrosine; 0.04-10 muM for 3-nitrotyrosine and 3-chlorotyrosine; 0.05-10 muM for o,o'-dityrosine; and for m-tyrosine; 1.0-100 muM for p-tyrosine and for phenylalanine; and 0.01-10 muM for 8-OHdG. The detection limits were from 0.025 to 0.05 muM for the tyrosine derivatives; 0.01 muM for 8-OHdG; and 0.5 muM for p-tyrosine and for phenylalanine, respectively. Within-day coefficients of variation (CV) for spiked human urine samples ranged from 2.7 to 7.0%, except for 8-OHdG (13.7%). Between-day variations ranged from 7.9 to 13.0%, except for o-tyrosine (CV = 18.2%), and for 8-OHdG (CV = 24.7%). The background levels of p-tyrosine, phenylalanine, o,o'-dityrosine, and o-tyrosine in morning urine of eight healthy volunteers were 3890 +/- 590, 3420 +/- 730, 5.8 +/- 0.3, and 9.2 +/- 1.5 mumol/mol creatinine, respectively. Using the present HPLC-APCI-MS/MS method, the urinary background levels of m-tyrosine, 3-chlorotyrosine, 3-nitrotyrosine and 8-OHdG were below the limit of detection. (C) 2003 Elsevier B.V. All rights reserved.