No abstract

A sensitive and specific high performance liquid chromatography (HPLC) method was developed to quantify 4-amino-3-hydroxyphenylalanine (4-AHP) and 3-amino-4-hydroxyphenylalanine (3-AHP) in urine. In degradation studies of melanin pigment, 4-AHP and 3-AHP are derived from benzothiazine units of pheomelanin and pheomelanin-related metabolites such as trichochromes. 5-S-Cysteinyldopa-derived benzothiazine products give 4-AHP while 2-S-cysteinyldopa-derived benzothiazine products give 3-AHP. 3-AHP is also derived from nitrotyrosine formed by nitration of tyrosine with reactive nitrogen species. For this reason, the influence of this biological process on the amount of 3-AHP found in biological material have been investigated. The method is based on hydriodic acid hydrolysis of the melanin polymer and reversed-phase HPLC with electrochemical detection of the degradation products 4-AHP and 3-AHP. The mobile phase consists of 25 mM ammonium acetate and sodium octanesulfonate as an ion-pairing reagent. The 4-AHP and 3-AHP peaks were well separated and the detector response was linear within the range 0-2 ng injected for both compounds. With the developed chromatographic system, 4-AHP and 3-AHP showed good separation in the biological samples. There was a strong correlation between 4-AHP and 3-AHP in the urine of 50 malignant melanoma patients and two healthy subjects (R0.977). The two compounds were also strongly correlated with 5-S-cysteinyldopa in urine, the correlation coefficients being 0.862 and 0.907, respectively. The method described is sensitive enough for analysis of pheomelanin in urine and in several other biological samples. The results indicate that 3-AHP in urine is not influenced by excreted 3-nitrotyrosine and the data indicate that pheomelanins are excreted in the urine of melanoma patients.

In a series of 92 patients with malignant melanoma, clinical stage III or IV, both 5-S-cysteinyldopa (5SCD) and 6-hydroxy-5-methoxyindole-2-carboxylic acid (6H5MI2C) were measured in urine during chemotherapy. A total of 434 urine specimens were analysed. The sensitivity of 5SCD for the detection of stage III-IV melanoma was 83%, while the corresponding sensitivity of 6H5MI2C was 52%. Fifty per cent of patients with one metastatic site had increased 5SCD excretion, while all patients with four or more metastatic sites had increased excretion. A significant correlation was found between 5SCD decrease and clinical regression (P<0.001) and between 5SCD increase and clinical progression (P<0.001). Corresponding correlations were not found for 6H5MI2C. Increments in 5SCD excretion (median 269 micromol/mol creatinine) were seen for 83% of the occasions when clinical progression was recorded, and decrements in 5SCD excretion (median 145 micromol/mol creatinine) were seen for 85% of the occasions when clinical regression was seen. During clinical 'stable disease' increases in 5SCD excretion were seen in 59% and decreases in 41%. The median value of 5SCD changes for stable disease was 7.0 micromol/mol creatinine, indicating a chemical marker stability in many cases. We recommend the use of 5SCD in urine as a valuable, reliable and simple biochemical marker to use in the clinical follow-up of melanoma patients with advanced disease.