Identification of three indolic compounds in a pigmented-melanoma cell-culture supernatant by gas chromatography-mass spectrometry

A frame-shift mutation in COMTD1 is associated with impaired pheomelanin pigmentation in chicken

The biochemical pathway regulating the synthesis of yellow/red pheomelanin is less well characterized than the synthesis of black/brown eumelanin. Inhibitor of gold (IG phenotype) is a plumage colour variant in chicken that provides an opportunity to further explore this pathway since the recessive allele (IG) at this locus is associated with a defect in the production of pheomelanin. IG/IG homozygotes display a marked dilution of red pheomelanin pigmentation, whilst black pigmentation (eumelanin) is only slightly affected. Here we show that a 2-base pair insertion (frame-shift mutation) in the 5th exon of the Catechol-O-methyltransferase containing domain 1 gene (COMTD1), expected to cause a complete or partial loss-of-function of the COMTD1 enzyme, shows complete concordance with the IG phenotype within and across breeds. We show that the COMTD1 protein is localized to mitochondria in pigment cells. Knockout of Comtd1 in a mouse melanocytic cell line results in a reduction in pheomelanin metabolites and significant alterations in metabolites of glutamate/glutathione, riboflavin, and the tricarboxylic acid cycle. Furthermore, COMTD1 overexpression enhanced cellular proliferation following chemical-induced transfection, a potential inducer of oxidative stress. These observations suggest that COMTD1 plays a protective role for melanocytes against oxidative stress and that this supports their ability to produce pheomelanin.

Analysis of oxidative stress status, catalase and catechol-O-methyltransferase polymorphisms in Egyptian vitiligo patients

Vitiligo is the most common depigmentation disorder of the skin. Oxidative stress is implicated as one of the probable events involved in vitiligo pathogenesis possibly contributing to melanocyte destruction. Evidence indicates that certain genes including those involved in oxidative stress and melanin synthesis are crucial for development of vitiligo. This study evaluates the oxidative stress status, the role of catalase (CAT) and catechol-O-Methyltransferase (COMT) gene polymorphisms in the etiology of generalized vitiligo in Egyptians. Total antioxidant capacity (TAC) and malondialdehyde (MDA) levels as well as CAT exon 9 T/C and COMT 158 G/A polymorphisms were determined in 89 patients and 90 age and sex-matched controls. Our results showed significantly lower TAC along with higher MDA levels in vitiligo patients compared with controls. Meanwhile, genotype and allele distributions of CAT and COMT polymorphisms in cases were not significantly different from those of controls. Moreover, we found no association between both polymorphisms and vitiligo susceptibility. In conclusion, the enhanced oxidative stress with the lack of association between CAT and COMT polymorphisms and susceptibility to vitiligo in our patients suggest that mutations in other genes related to the oxidative pathway might contribute to the etiology of generalized vitiligo in Egyptian population.

ASSESSMENT OF MC1R AND α-MSH GENE SEQUENCES IN IRANIAN VITILIGO PATIENTS

Background:

Vitiligo is an acquired pigmentary disorder of the skin that is caused by unknown factors and is characterized by white and depigmented patches that enlarge and become more numerous with time. Genetic factors, oxidative stress, autoimmunity, and neurochemical agents, such as catecholamines might also contribute to vitiligo. Cutaneous pigmentation is determined by the amounts of eumelanin and pheomelanin synthesized by the epidermal melanocytes and interference of melanocortin-1 receptor (MC1R), a G-protein coupled receptor, its normal agonist, alpha-melanocyte stimulating hormone (α-MSH), and key enzymes, such as tyrosinase, to protect against sun-induced DNA damage. The MC1R, a 7 pass trans-membrane G-protein coupled receptor, is a key control point in melanogenesis. Loss-of-function mutations at the MC1R are associated with a switch from eumelanin to pheomelanin production, resulting in a red or yellow coat color.

Aim:

In this research, we aim to examine the genetic variety of MC1R and α-MSH gene in 20 Iranian vitiligo patients and 20 healthy controls.

Materials and Methods:

Analysis of the MC1R coding gene was performed with direct sequencing.

Results:

We found the following 9 MC1R coding region variants: Arg163Gl (G488A), Arg227Leu (G680A), Val 97Phe (G289T), Asp184Asn (G550A), Arg227Lys (G680A), Arg142His (G425A), Val60Leu (G178T), Val247Met (C739A), and Val174Ile (G520A). We also found 2 frameshift changes: one of them was the Insertion of C (frameshift in Pro136, stop at Trp148) and the other, Insertion of G (frameshift in Pro256, stop at Trp 333). Of all the changes, the most common was Val60Leu at 5% in patients vs 20% in controls, Val247Met at 15% in patients vs 0% in controls and Val174Ile at 15% in controls and 0% in patients. The other variants showed a frequency <5% in both patients and controls. Also in this study, we have examined the frequency of single nucleotide polymorphisms within the α-MSH genes with direct sequencing in 20 patients and 20 healthy subjects but found no changes along this gene.

Conclusion:

We could not find any relationship between MC1R and α-MSH genes and their effect on the disease in Iranian vitiligo patients.

A functional single-nucleotide polymorphism in the catechol-O-methyltransferase gene alter vitiligo risk in a Chinese population

Vitiligo is an acquired hypomelanotic skin disorder resulting from the loss of functional melanocytes. The COMT-158 polymorphism can reduce COMT enzyme activity and may thus lead to the overproduction of toxic radicals in the melanocyte microenvironment. To determine whether this polymorphism in the COMT gene is associated with an increased risk of vitiligo in Chinese populations, we used a polymerase chain reaction sequence-specific primer (PCR-SSP) technique to determine the frequency of the polymorphism COMT-158 G > A in 749 vitiligo patients and 763 healthy controls. We found that compared to the COMT-158 GG genotype, the COMT-158 GA genotype (adjusted odds ratio [OR], 1.39; 95% confidence interval [CI], 1.13-1.72) and the combined GA + AA genotype (adjusted OR, 1.41; 95% CI, 1.15-1.74) were associated with an increased risk of generalized vitiligo. The association was more pronounced in patients with early-onset vitiligo (adjusted OR, 1.95; 95% CI, 1.45-2.60), those with a family history of vitiligo (adjusted OR, 3.84; 95% CI, 2.47-5.96), and female patients (adjusted OR, 1.74; 95% CI, 1.29-2.36). When we further clinically stratified the vitiligo patients according to their disease types, we found that the combined GA + AA genotype was associated with vitiligo vulgaris (adjusted OR, 1.31; 95% CI, 1.02-1.68), focal vitiligo (adjusted OR, 1.62; 95% CI, 1.17-2.25), and universal vitiligo (adjusted OR, 1.50; 95% CI, 0.98-2.30), but not with acrofacial vitiligo (adjusted OR, 1.53; 95% CI, 0.86-2.73) or segmental vitiligo (adjusted OR, 1.35; 95% CI, 0.72-2.51). In conclusion, this COMT gene polymorphism may have contributed to the etiology of vitiligo in our Chinese population. Larger population-based studies are required to verify our findings.

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.

Oxidative damage caused by free radicals produced during catecholamine autoxidation: protective effects of O-methylation and melatonin

Catecholamine autoxidation produces reactive oxygen species that have been implicated in the loss of dopaminergic neurons in the nigrostriatal region of the brain that occurs during normal aging and in Parkinson's disease. In the present study, the potential protective effects of catecholamine O-methylation and of melatonin against catecholamine autoxidation-induced protein damage were assessed in vitro using the oxygen radical absorbance capacity (ORAC) assay. The rate of oxidation of the fluorescent protein porphyridium cruentum beta-phycoerythrin (beta-PE) caused by the oxidizing agent CuSO4 was shown to be accelerated by addition of the catecholamines dopamine and L-dopa. Replacement of dopamine and L-dopa in the assay with their O-methylated metabolites 3-O-methyldopamine and 3-O-methyldopa significantly decreased the rate of beta-PE oxidation. When melatonin was added to the ORAC assay in combination with dopamine or L-dopa, the rate of beta-PE oxidation was decreased as well. These findings were consistent with the following interpretations: (1) O-methylated catecholamines are less susceptible to autoxidation than their nonmethylated precursors, and (2) melatonin, which has recently been shown to be a powerful antioxidant, is capable of scavenging free radicals produced during catecholamine autoxidation. These findings suggest that O-methylation and melatonin may be important components of the brain's antioxidant defenses against catecholamine autoxidation and may protect against consequent dopaminergic neurodegeneration.

Some aspects of melanin formation of melanocytes cultured on collagen-coated microcarrier beads

Melanocytes cultured on collagen-coated Cytodex 3 microcarrier Sephadex beads caused remarkable pigmentation of the beads during the period of culture when optimal density was reached. Electron microscopy of melanocytes on the microcarriers revealed that the cells and their dendrites invaginate into the microcarrier surface layer. Removal of the cells by trypsinization showed that some pigment granules were left on the carrier surface and within the cavities present on the microcarrier surface. In order to investigate whether the pigmentation of the microcarriers could be a result of indole intermediates of melanogenesis present in the culture medium, extracts were studied by gas chromatography/mass spectrometry for the presence of these compounds. Two compounds (5,6-dihydroxyindole-2-carboxylic acid and 6-hydroxy-5-methoxyindole-2-carboxylic acid) so far have been identified in the medium extracts. Results indicate that microcarrier culture of melanocytes can serve as an interesting model for electron microscopy studies of melanocytes with regard to pigmentation and cell attachment.

O-methylation of L-dopa in melanin metabolism and the presence of catechol-O-methyltransferase in melanocytes

O-Methylation of L-dopa was investigated as a possible regulatory mechanism in melanin metabolism. The methylation product of L-dopa, 3-O-methoxytyrosine was detected in extracts of cultured human melanocytes. The enzyme catechol-O-methyltransferase is responsible for this O-methylation and that of the dihydroxyindolic intermediates of melanogenesis. The enzyme is present in melanocytes in its soluble and membrane-bound isoforms. Immuno-electron microscopy suggests the presence of the membrane-bound enzyme in the endoplasmic reticulum. This localization may indicate a role of catechol-O-methyltransferase in protecting the melanocyte against reactive dihydroxyphenolic intermediates of melanogenesis leaking from the melanogenic compartments. On the other hand, the O-methylation of L-dopa may serve as a regulatory point in melanogenesis during early stage of tyrosinase processing in the endoplasmic reticulum.

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.

Catechol-O-methyltransferase in vitiligo

Catechol-O-methyltransferase (COMT) is involved in the metabolism of neurotransmitters such as epinephrine, norepinephrine and dopamine. For melanocytes, the enzyme is of particular importance in preventing the formation of toxic o-quinones during melanin synthesis. It has been suggested that COMT plays a regulatory role in melanin synthesis. Indeed, when the melanin precursor molecule DHI(2C) is methylated by COMT it is no longer available for incorporation into melanin. Auto-destruction by intermediates of melanin metabolism has been implicated in the aetiology of vitiligo. Therefore enzyme activities in vitiligo patients and in healthy controls were compared. Systemic COMT activities were measured using red blood cells (RBC) as starting material. However, as local alterations in COMT activity may be specifically involved in vitiligo, the enzyme activity was also measured in epidermal homogenates. Finally, to ascribe epidermal COMT activity to the responsible cell type(s), enzyme activity was measured in cultured vitiligo non-lesional melanocytes and melanocytes from healthy controls as well as in cultured keratinocytes from lesional skin and in purified keratinocytes from control skin. It was found that epidermal homogenates from vitiligo patients expressed higher levels of COMT activity than homogenates from healthy controls. Such differences were not found at the systemic level (i.e. in RBC) nor could they be explained by measurements on separately cultured epidermal cell types, indicating that the COMT activity was induced at the tissue level by extracellular factors.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Melanogenesis: a realistic target for antimelanoma therapy?

Melanin is a widely-distributed pigment in the biosphere. In the human adult, the enzymatically-catalysed process of melanin generation is the exclusive prerogative of melanocytes. Melanogenesis generates a number of reactive intermediates including orthoquinones and has been recognised as a potential hazard to melanocytes. Amplification of this cytotoxic hazard to selectively damage malignant melanogenic cells has been investigated as a rational therapeutic strategy for melanoma. A number of surrogate substrates for tyrosinase have been studied, including a range of phenols and catechols. Initial attempts to use these agents for the treatment of disseminated melanoma have foundered on problems due to unfavourable pharmacokinetics, primary toxicity or pharmacological actions of the analogue substrates, and the toxicity of hepatic metabolites. Successful exploitation of the undoubted potential of the metabolic targeting strategy presented by the subversion of melanogenesis depends on the development of prodrugs with minimal primary toxicity and improved pharmacokinetics. The range of possible novel approaches is being extended by the emergent understanding of the complexities of melanogenesis which are outlined.

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.

Identification of ester glucuronide and sulfate conjugates of 5-hydroxy-6-methoxyindole-2-carboxylic acid and 6-hydroxy-5-methoxyindole-2-carboxylic acid in melanoma urine

HPLC analysis of urine sample from a patient with wide-spread melanoma revealed the presence of unknown indolic compounds at extraordinarily high levels, detectable with electrochemical and/or fluorescent detectors. By enzymic and chemical hydrolyses, they were identified as ester glucuronide and sulfate conjugates of 5-hydroxy-6-methoxyindole-2-carboxylic acid and 6-hydroxy-5-methoxyindole-2-carboxylic acid. Urine samples from B16 melanoma-bearing mice contained the sulfate conjugates but not the ester glucuronide conjugates.

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.

Sunlight, melanogenesis and radicals in the skin

Melanocytes are cells of neural crest origin residing at the dermal-epidermal juncture. They produce specialized organelles called melanosomes within which the biochemical processes of melanization occurs. UV radiation is capable of inducing melanogenesis and, during the biosynthesis of melanins, several of the putative precursors "leak out" of the melanosome and can be detected in the skin, serum and urine of individuals undergoing active melanogenesis. Most notable are the cysteinyldopas (formed by nucleophilic addition of cysteine to dopaquinone) and several dihydroxyindoles (formed by intramolecular cyclization of dopaquinone). These catechols often are methylated in the melanocyte to afford a mixture of the monomethoxy derivatives and, in some cases, the dimethoxy species. Recent investigations in our laboratories have demonstrated that the cysteinyldopas, dihydroxyindoles, and their various methylated derivatives are photochemically unstable. Irradiation with biologically relevant ultraviolet radiation (i.e. wavelengths greater than 300 nm) results in the rapid destruction of the precursors/metabolites and the production of a variety of free radical species. The photochemistry and potential photobiological significance of melanogenic intermediates is discussed.

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.

Photogeneration of free radicals from eumelanogenic intermediates and metabolites

We have recently demonstrated that cysteinyldopas, pheomelanogenic precursors and excreted eumelanogenic metabolites, are photolabile and initiate DNA damage in vitro. In this study we have extended our photochemical investigations to eumelanogenic indole intermediates and metabolites. Continuous-wave photolysis of 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), or its 5-methoxylated metabolite (HMICA) with biologically relevant ultraviolet radiation (i.e., wavelengths greater than 300 nm) resulted in rapid destruction of starting material. Using ESR spin-trapping techniques we observed the initial production of free radical species; prolonged photolysis resulted in the formation of polymeric photoproducts. Radicals were trapped by the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and characterized by their ESR spectra as hydrated electrons and hydrogen atoms. Experiments further demonstrated that while DHI photoionizes, the two indole-2-carboxylic acid derivatives do not ionize appreciably upon irradiation, rather homolysis of X-H bonds appears to be a significant photochemical pathway. The potential photobiological significance of melanogenic indole intermediates is discussed.

A new possible pathogenesis of some gallstones

A new possible pathogenesis of gallstones is described. The theory is based on the presence of indolic melanin precursors in biological fluids. It is proposed that the increased concentration of these compounds in bile could lead to the formation of melanin polymer as a network nucleus for a future concrement. An activation of the pigmentary system (e.g. insolation, gravidity) and the presence of hydrolytic enzymes (beta-glucuronidase and/or arylsulphatase) in biliary tract might belong to the risk factors of gallstone formation. The detection of 5-hydroxy-6-methoxyindolyl-2-carboxylic acid in bile and 5,6-dihydroxyindole in the extract of an alkali fused gallstone provided the first support of this theory.

Identification of Thormählen-positive compound “B” in urine of patients with malignant melanoma

The identification of the entire structure of the Thormählen-positive compound B from melanotic urine is described. The compound was separated from other Thormählen-positive compounds using DEAE-cellulose column chromatography. On the basis of differential enzymic hydrolysis followed by gas chromatography-mass spectrometry analysis and comparison with synthetically prepared compounds it is possible to conclude that the Thormählen-positive compound B is a mixture of O-sulphate 5-hydroxy-6-methoxyindole and 6-hydroxy-5-methoxyindole with predominance of the latter.