Determination of the L-DOPA/L-tyrosine ratio in human plasma by high-performance liquid chromatography - Usefulness as a marker in metastatic malignant melanoma

A first procedure was devised for determining 3,4-dihydroxyphenylalanine (L-DOPA) in human plasma by isocratic RP-HPLC coupled with electrochemical detection. A second procedure was devised for determining 3-hydroxyphenylalanine (L-tyrosine) in human plasma by isocratic RP-HPLC coupled with fluorescence detection. These methods were used to ascertain the L-DOPA/L-tyrosine ratio in plasma of patients with melanoma. Reference values were established by analysis of the L-DOPA/L-tyrosine ratio in the plasma of 35 normal healthy subjects. For 29 patients diagnosed as having melanoma without metastasis, the L-DOPA/L-tyrosine (11.96x10(-5)+/-2.69x10(-5)) level was not significantly different from that of 35 normal controls (11.20x10(-5)+/-2.92x10(-5)). However, this level was significantly increased (p<0.05) in the plasma of 17 patients with developing metastasis (21.02x10(-5)+/-4.68x10(-5)). (C) 1997 Elsevier Science B.V.