Analysis of eumelanin-related indolic compounds in urine by high-performance liquid chromatography with fluorimetric detection

Imaging, chemical and spectroscopic studies of the methylation-induced decomposition of melanosomes

The morphological and chemical changes associated with the exposure of melanosomes to methyl iodide are assessed by a variety of analytical, imaging and spectroscopic methods. Scanning electron microscopy, light scattering and N(2) adsorption measurements all indicate significant changes in the morphology of the pigment following methylation. Solid-state nuclear magnetic resonance (SS-NMR) spectroscopy and chemical degradation analysis reveals the methylation results in the introduction of ester groups into the pigment structures. Amino acid analysis further reveals that Arg, Cys, His, Ser and Tyr undergo methylation; the SS-NMR data provide additional evidence for the methylation of the sulfur of Cys. Methylation results in increased solubility of the melanosome; the absorption properties of the dissolved material are characterized by an absorption maximum at 225 nm, with a long tail throughout the UV-A and UV-B, indicating that the solubilized material is a combination of protein and pigment. The methylation-induced decomposition of the melanosomes provides new insights into both the observed increase in O-methyl derivatives of the indolic precursor to eumelanin in the urine of melanoma patients and how increased levels of biologic methylating agents in the brain induce symptoms that resemble Parkinson's disease.

The stability of 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid in human urine

5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid are important intermediate metabolites in the formation of cutaneous melanin pigment. Since they both are serious candidates as markers of melanoma progression, their stability in urine has been investigated during storage at various conditions. The results show that storage at -20 degrees C is necessary. Both compounds are nonstable at room temperature, particularly if the urine was not acidified to pH 4-5. Reference levels were obtained from analysis of urine from 31 men and 40 women. The mean (SD) excretion of 5-S-cysteinyldopa was 32 (12.5) mumol/mol creatinine (women). Corresponding figures for 6H5MI2C were 23 (10.3) and 24 (8.1) mumol/mol creatinine for men and women respectively.

Cysteine and indole derivatives as markers for malignant melanoma

Malignant melanoma is a skin tumour, which carries a very unfavourable prognosis. The early detection of a melanoma and even more its metastasis is of decisive importance for the survival prognosis of the patients. So there is always a desire for simple, economical and meaningful serological markers. From the cysteine- and indole-related derivatives, 5-S-cysteinyldopa (5-SCD) and 6-hydroxy-5-methoxy-indole-2-carboxylic acid (6H5MI2C) are the most important substances for this purpose. For 5-SCD, the sample pretreatment was carried out either by a manual extraction onto alumina, by an automated method onto boronic acid affinity gels or by an automated solid-phase extraction. For 6H5MI2C, liquid-liquid extractions or direct injection techniques were applied. The chromatographic analyses in the early years were mostly performed with GC-MS. Today HPLC is the nearly exclusively used separation technique. For HPLC, standard RP18 separating columns and usual compositions of eluents were applied. As detectors both the ECD and the FD showed a sufficient sensitivity and selectivity. 5-SCD and 6H5MI2C are very sensitive to light and oxidation. These properties must be taken into account in the complete analysis procedure, including the sample collection, otherwise false low values will result especially for plasma samples. For a critical discussion of the analytical methods and still more for the interpretation of the obtained results, the detailed analytical procedures must be considered. 5-SCD in plasma is one of the best markers of malignant melanoma. It shows an excellent specificity and also an adequate sensitivity in the metastatic melanoma stages. For the detection of primary melanomas and for urine instead of plasma samples, the sensitivity of 5-SCD is generally lower. Altogether, the sensitivity of this parameter is not yet sufficient. 6H5MI2C and other indole derivatives have been investigated far less than 5-SCD. 6H5MI2C correlates less clearly with the different stages of the melanoma and is therefore a less suitable marker. To improve the sensitivity of the findings, in future the investigations should be performed as multi-marker analysis with the simultaneous measurements of more than one marker substance in a given patient sample. Not only one measurement should be carried out per patient, it would be more meaningful to observe the patients with laboratory diagnostics in the follow-up.

The value of cysteinyldopa in the follow-up of disseminated malignant melanoma

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.

Catechol-O-methyltransferase as a target for melanoma destruction?

Catechols may interfere in melanogenesis by causing increased levels of toxic quinones. Several catechols and known inhibitors of the enzyme catechol-O-methyltransferase (COMT) were therefore tested for their toxicity towards a pigmented melanoma cell line, UCLA-SO-(M14). The inhibition of thymidine incorporation as a result of exposure to the compounds was measured. All agents were compared to 4-hydroxyanisole (4HA), a depigmenting agent extensively studied as an antimelanoma drug. The compounds were also tested on the epithelial cell line, CNCM-I-(221) in the presence and absence of tyrosinase. All the compounds were more effective than 4HA towards the M14-cells at either 10(-4) M or 10(-5) M. The toxicity of 4HA towards the 221-cells was shown to be completely dependent on the presence of tyrosinase. Effects of the test agents on the 221-cells were also observed in the absence of tyrosinase. Although some of them were shown to be good substrates for tyrosinase only small changes in toxicity were observed as a result of the presence of the enzyme in comparison with 4HA. No direct correlation of the toxicity of the agents and COMT inhibition was observed. The possible mode of action of the compounds through inhibition of COMT and interference in melanogenesis is discussed together with other possibilities and factors involved.

Metabolism of 3-indolylacetic acid during percutaneous absorption in human skin

This study assessed the in vitro percutaneous absorption and metabolism of 3-indolylacetic acid after topical dosing to human skin from four sources. The metabolism of the compound during percutaneous absorption was assessed. The absorbed and metabolized chemicals were analyzed by radioactive scintillation counting and thin-layer chromatography: 1.2% +/- 0.04%, 1.4% +/- 0.07%, 3.0% +/- 1.0%, and 0.1% +/- 0.02% of the applied doses permeated through human skin samples from sources A to D, respectively, whereas 3.4% +/- 0.5% to 20.0% +/- 0.2% of the applied doses were retained by the skin. Of the absorbed dose, 2.1% +/- 1.0% to 12.1% +/- 3.5% was present as metabolites in the receptor fluid, and 2.2% +/- 0.5% to 5.2% +/- 0.1% was present as metabolites retained in the skin. Microsomal fractions were prepared from the skin samples, and the actions of these preparations on 3-indolylacetic acid were estimated. 5'-Hydroxyl-3-indolylacetic acid, 5',6'-dihydroxy-3-indolylacetic acid, and 5,6-dihydroxyindole were formed both during percutaneous absorption and by skin microsomal preparations. In addition, the skin samples biotransformed the acid to metabolic indican (3-indoxylsulfuric acid) and to the glucuronide conjugate of indole. The possible functional significance of the metabolism is discussed.

Preparation of monoclonal mouse antibodies against two specific eu-melanin related compounds

Two eu-melanin precursors, 6-hydroxy-5-methoxyindole-2-carboxylic acid (HMI2C) and 5,6-dihydroxyindole-2-carboxylic acid (DHI2C) were synthesized and coupled to bovine serum albumin, hemocyanin and polylysine by the combined action of carbodiimide and succinimide. These indole-carrier conjugates served as antigens for the production of specific antibodies against DHI2C and HMI2C in BALB/c mice. The specificity of these antibodies was tested using a combination of affinity chromatography and ELISA procedures. Polyclonal mouse antibodies reacted with the indole-carrier conjugates, but not with the unbound indole compounds. Monoclonal antibodies from two hybridoma cell lines were obtained from a HMI2C-immunized mouse after a fusion with four subclonings. They reacted with free HMI2C and to a lesser extent with unbound DHI2C. One monoclonal showed 50% inhibition in the ELISA test at concentrations of 0.6 mumol.l-1 and 5 mumol.l-1 for HMI2C and DHI2C, respectively. These antibodies did not show any cross-reactivity with nine structurally related compounds and should be valuable reagents for the detection and quantification of HMI2C and other eu-melanin related compounds.

Chromatographic methods for the analysis of basic neurotransmitters and their acidic metabolites

Chromatographic techniques for the determination of trace amounts of neurotransmitters were reviewed. The two techniques found to be most useful were GC-MS and the reversed-phase mode of HPLC with an electrochemical or fluorescent detector. For structure determination or unequivocal peak identification, GC-MS is the method of choice. In addition the limits of detection of GC-MS were better than those obtained by HPLC. However for routine analyses, HPLC is now being used in studies of mental illness and other diseases. Good resolution, reproducibility and sensitivity can be obtained without the derivatisation steps required for GC-MS, and catecholamines, serotonin, and their acidic metabolites can be concomitantly determined in one analysis.

Temperature-sensitive tyrosinase associated with peripheral pigmentation in oculocutaneous albinism

Several types of autosomal recessive oculocutaneous albinism (OCA) are associated with abnormal tyrosinase function and a generalized reduction in or absence of cutaneous and eye melanin. Each is thought to result from a different mutant allele at the tyrosinase locus, with the mutation producing an enzyme with little or no activity in all involved tissues. In this paper, we report a new type of OCA that results from a tyrosinase allele producing a temperature-sensitive enzyme. The proband had white hair in the warmer areas (scalp and axilla) and progressively darker hair in the cooler areas (extremities) of her body. Melanocyte and melanosome architecture were normal. Quantitative hairbulb tyrosinase (dopa oxidase) assay demonstrated a loss of activity above 35-37 degrees C. Plasma pheomelanin and urine eumelanin intermediates were reduced and correlated with hair melanin content. This is the first temperature-sensitive tyrosinase mutation to be reported in humans and is analogous to the Siamese mutation in the cat and the Himalayan mutation in the mouse.

Determination of catechol O-methyltransferase activity in relation to melanin metabolism using high-performance liquid chromatography with fluorimetric detection

A new sensitive method for the determination of catechol O-methyltransferase activity has been developed. The method is based on the O-methylation of the indolic intermediates of melanin metabolism. The substrate, 5,6-dihydroxyindole-2-carboxylic acid, is converted by the enzyme to two O-methylated products, which can be separated by high-performance liquid chromatography and measured with fluorimetric detection. The physiological presence of both substrate and products could be detected in crude melanoma cell extracts. The limit of sensitivity for detection of the O-methylated products is less than 0.5 pmol per injection. The method was compared with an earlier described HPLC method which makes use of uv detection of O-methylated products of 3,4-dihydroxybenzoic acid. The described method will be used to study the importance of catechol O-methyltransferase as a protective enzyme in (malignant) melanocytes.

Role of the clinical laboratory in the diagnosis and management of malignant melanoma

The biosynthesis of melanin from tyrosine is reviewed as the basis for assessment of laboratory tests that might potentially aid in the diagnosis and management of patients with malignant melanoma. These tests include qualitative and quantitative assays for the intermediates in metabolism of melanin and catecholamines, enzyme assays, metal ion analyses, and, most recently, immunoassays. Although currently no role exists for the clinical laboratory in the early diagnosis of malignant melanoma, serial quantitative analyses of total or individual melanogens or of catecholamine metabolites in urine or plasma specimens may be of value in the management of patients with this disorder. Immunologically based methods for the diagnosis and management of malignant melanoma hold some promise for the future.

Chromatography of urinary indole derivatives

Latest strategies are discussed for the routine chromatographic analysis of clinically important indole derivatives in urine. Analysis of 5-hydroxyindoleacetic acid and, perhaps more importantly, serotonin and 5-hydroxytryptophan remains attractive in the screening for carcinoid tumours and their differentiation. Analyses of two precursors of the skin pigment eumelanin seem to be promising in the monitoring of treatment of malignant melanoma and screening for pigmentation disorders and gallstone formation. Studies on the clinical relevance of the determination of tetrahydro-beta-carbolines and melatonin-related indoles await routine application of chromatographic methods designed to take into consideration the relative instability of these compounds. Application of GC-MS, although confined to larger and/or governmental laboratories remains attractive as a way of improving the specificity of analyses and in establishing reference methods. As for HPLC, the recent development of chromatographic and detection methods for the concurrent determination of different clinically important and metabolically related compounds from the same sample, preferably by direct injection techniques, seems to be fruitful and should be continued.

Preparation of eumelanin-related metabolites 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, and their O-methyl derivatives

5,6-Dihydroxyindole (5,6DHI) and 5,6-dihydroxyindole-2-carboxylic acid (5,6DHI2C) are ultimate precursors of the black melanin, eumelanin. These indolic metabolites and their O-methyl derivatives are excreted in urine of melanoma patients at high levels and of healthy persons at low levels. We describe here a simplified procedure for preparing milligram to subgram quantities of 5,6DHI and 5,6DHI2C and their O-methyl derivatives. Dopachrome generated in situ by ferricyanide oxidation of dopa at pH 6.5 underwent spontaneous decarboxylation to give 5,6DHI in 40% isolation yield, while treatment of dopachrome with alkali at pH 13 afforded 5,6DHI2C in 38% isolation yield. Two isomeric O-methyl derivatives of 5,6DHI were prepared by treatment with diazomethane, while those of 5,6DHI2C were prepared by treatment with diazomethane followed by alkaline hydrolysis of the methyl esters. 5,6DHI and 6-hydroxy-5-methoxyindole were also obtained by heating the corresponding carboxylic acids in decalin. 5-Hydroxy-6-methoxyindole and 6-hydroxy-5-methoxyindole-2-carboxylic acid could also be prepared by debenzylation of the commercially available O-benzyl derivatives.