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PubMedDate not supplied

Malignant melanoma presenting as nasal obstruction.

Mucosal melanomas arising in the nasal cavity are rare tumors comprising less than 1 percent of all melanomas. Often, the common clinical symptom is nasal obstruction. Grossly, they may or may not be pigmented and frequently attain large sizes. Histologic diagnosis of these tumors may be difficult, requiring immunohistochemical or electron microscopic confirmation. Aggressive surgical management is the treatment of choice in clinical stage I disease. Subsequent surveillance for recurrence is mandatory. Markers such as 5-S-cysteinyldopa may prove useful in staging, prognosticating, and postoperative surveillance for early recurrence, but their exact role has yet to be delineated. Ultimate prognosis is poor.

Aged↗
PubMed1987

Hypopigmentation in the Prader-Willi syndrome.

Cutaneous and ocular pigmentation were evaluated in 29 individuals with the Prader-Willi syndrome (PWS). Criteria for hypopigmentation included the presence of type I or II skin, the lightest skin type in the family by history, and iris translucency on globe transillumination. On the basis of these criteria, 48% of the PWS individuals were hypopigmented. The presence of hypopigmentation correlated with a small interstitial deletion on the proximal long arm of chromosome 15; however, this deletion was also found in individuals who did not meet the full criteria for hypopigmentation. Hairbulb tyrosinase activity and glutathione content, as well as urine cysteinyldopa excretion, were low in PWS individuals with and without hypopigmentation and did not separate these two groups. We conclude that hypopigmentation is found in a significant proportion of individuals with PWS and that the hypopigmentation may be associated with a deletion of the long arm of chromosome 15. The mechanism for the hypopigmentation is unknown.

Chromosome Deletion↗
PubMed1983

Methaemoglobin-catalysed formation of dopa and 6-OH-dopa from tyrosine.

An extract of bovine retina and choroid with tyrosine hydroxylating and dopa-oxidizing capacity also showed marked formation of 6-OH-dopa on incubation with tyrosine and ascorbic acid. The extract contained appreciable amounts of methaemoglobin as determined spectrophotometrically, and boiled extracts also showed catalytic activity. The effect of methaemoglobin on the oxidation of tyrosine and dopa was therefore investigated. Methaemoglobin catalysed the formation of dopa and 6-OH-dopa in the presence of tyrosine and ascorbic acid. Hydrogen peroxide plays an important role in this reaction: the rates of formation of both dopa and 6-OH-dopa were increased by addition of hydrogen peroxide but diminished by addition of catalase. Methaemoglobin also catalysed the formation of cysteinyldopa from dopa and cysteine.

Animals↗
PubMed1983

Tyrosinase activity in the medium of human melanoma cell cultures.

The medium of cultured melanoma cells was studied for tyrosine hydroxylation and dopa-oxidizing activity. The supernatant obtained after centrifugation at 100 000 g for 2 hours was treated with ammonium sulphate, and the precipitate obtained between 35 and 50% saturation was used. Dopa was determined as the product of tyrosine hydroxylation and 5-S-cysteinyldopa as the product of dopa oxidase activity. Determinations were performed with HPLC and electrochemical detection. Our preparation of culture medium of cells showed the following. 1) No hydroxylation of tyrosine in the absence of co-factor. 2) Hydroxylation of L-tyrosine in the presence of dopamine. No hydroxylation with boiled medium. Minimal effect of catalase on hydroxylation. 3) Hydroxylation of tyrosine in the presence of ascorbic acid. Hydroxylation was catalyzed also with boiled medium. Catalase strikingly diminished hydroxylation. 4) Oxidation of L-dopa to dopaquinone determined as its main reaction product with cysteine, 5-S-cysteinyl-dopa. There was negligible oxidation with boiled medium. 5) With dopamine as co-factor the catalysis of tyrosine hydroxylation was stereospecific for L-tyrosine. Dopa oxidase activity was also stereospecific for L-dopa.

Ascorbic Acid↗
PubMed1983

Dopa oxidation and tyrosine oxygenation by human melanoma tyrosinase.

A tyrosinase purified from cultured human melanoma cells was studied for dopa oxidation and tyrosine oxygenation. Km for oxidation of L-dopa was 0.5 mM, and for D-dopa 3 mM. L-tyrosine was oxygenated only in the presence of a cosubstrate. L-Dopa was superior to D-dopa, dopamine, L- and D-alpha-methyldopa, dopac, and 5,6-dihydroxyindole-2-carboxylic acid as cosubstrate. Ascorbic acid, 5-S-cysteinyldopa, and 5-OH-dopa did not function as cosubstrates. The rate of tyrosine hydroxylation was much lower than that of dopa oxidation. Tyrosine inhibits dopa oxidation, and dopa in high concentrations inhibits tyrosine hydroxylation. The cosubstrate function of dopa, the substrate functions of dopa and tyrosine, and the mutual inhibition of tyrosinase by these compounds are explained in three equations.

Catechol Oxidase↗
PubMed1984

Characterization of melanogenesis and morphogenesis of melanosomes by physicochemical properties of melanin and melanosomes in malignant melanoma.

This study elucidates the nature of melanogenesis in B16 and Harding-Passey (HP) mouse melanomas producing melanin and melanosomes of different color and fine structure, i.e., brown-black eumelanosome-like B16 granules and reddish brown pheomelanosome-like HP granules, and compares them with "typical" 3,4-dihydroxyphenylalanine (DOPA) and sepia eumelanins and sepia eumelanosomes. The melanin content of B16 melanosomes was more than three times higher than that of HP melanosomes. The content of free and protein-bound DOPA and 5-S-cysteinyldopa varied greatly in B16, HP, and sepia melanosomes and was unrelated to melanin content. Chemical analysis of the eumelanin: pheomelanin ratio in melanosomes and elemental analysis of isolated melanin showed that B16 and HP melanins are primarily eumelanic, with a higher ratio of pheomelanic component in HP melanin. The spectra of electron spin resonance and IR and X-ray small-angle scattering of B16 and HP melanins were basically similar to those of sepia and DOPA melanins. B16, HP, and DOPA melanins were dissolved in aqueous NH3, while sepia melanin was dissolved to a far lesser extent. It was concluded that both B16 and HP melanomas are primarily involved in eumelanogenesis, although the fine structure of their melanosomes is entirely different, and that the marked color difference in the two melanosomes is related to a difference in the absolute content of eumelanin, the presence of a small amount of pheomelanin, and the mode of chemical bindings of melanin to structural proteins. In contrast to normal skin and hair, melanosome morphogenesis may not directly correspond to melanogenesis type in malignant melanoma.

Animals↗
PubMed2000

Glutathione transferase M2-2 catalyzes conjugation of dopamine and dopa o-quinones.

Human glutathione transferase M2-2 prevents the formation of neurotoxic aminochrome and dopachrome by catalyzing the conjugation of dopamine and dopa o-quinone with glutathione. NMR analysis of dopamine and dopa o-quinone-glutathione conjugates revealed that the addition of glutathione was at C-5 to form 5-S-glutathionyl-dopamine and 5-S-glutathionyl-dopa, respectively. Both conjugates were found to be resistant to oxidation by biological oxidizing agents such as O(2), H(2)O(2), and O(*-)(2), and the glutathione transferase-catalyzed reaction can therefore serve a neuroprotective antioxidant function.

Benzoquinones↗
PubMed1985

Detection of 5-S-cysteinyldopamine in human brain.

5-S-Cysteinyldopamine was synthesized and used as reference compound in HPLC analyses of extracts from various regions of human brain. The compound could be detected in brain regions rich in dopamine (caudate nucleus, putamen, globus pallidus and substantia nigra) but not in other regions (cerebellum, occipital cortex). The occurrence of 5-S-cysteinyldopamine in dopaminergic brain regions supports the hypothesis that dopamine in part undergoes autoxidation, leading to formation of highly reactive quinones. The newly discovered metabolite may prove useful in future studies of dopamine autoxidation and the possibly resultant cytotoxicity in aging and degenerative brain disorders.

Aged↗
PubMed1989

A marked rise in 5-S-cysteinyl-dopamine levels in guinea-pig striatum following reserpine treatment.

Reserpine administration (5 mg/kg, i.p.) to guinea pigs resulted in marked and long lasting dopamine (DA) depletion and a rapid, short lasting, increase of 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum. A marked and sustained increase of the level of 5-S-cysteinyl-dopamine, which is an adduct presumably formed following autoxidation of DA, started 3-4 h following the DA and DOPAC changes. Only small changes in the levels of the 5-S-cysteinyl adducts of DOPAC and 3,4-dihydroxyphenylalanine (DOPA) were found.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1985

Tyrosinase-catalyzed conjugation of dopa with glutathione.

A convenient method is described for the preparation of 5-S- and 2-S-glutathionyldopa, based on tyrosinase oxidation of dopa in the presence of glutathione. The yields of 5-S, 2-S, and 6-S isomers produced were about 76, 12, and 5%, respectively.

Cysteinyldopa↗
PubMed1987

Synthesis of 5-S-L-cysteinyl-glycine-L-dopa, a natural substrate for serum and melanocyte dipeptidase.

A method for synthesis of the phaeomelanin pigment intermediate compound 5-S-L-cysteinyl-glycine-L-dopa is presented. This thioether has been suggested as a precursor to 5-S-L-cysteinyl-L-dopa, the key intermediate compound in phaeomelanin pigment formation. 5-S-Glutathione-L-dopa is first synthesized by the tyrosinase-catalyzed reaction between L-dopa and glutathione. The 5-S-glutathione-L-dopa is then converted to 5-S-L-cysteinyl-glycine-L-dopa using the enzyme gamma-glutamyl transpeptidase. The compound thus obtained was suitable as a substrate for melanoma cell and serum dipeptidase which converts the compound into 5-S-L-cysteinyl-L-dopa and glycine. The optimum pH for the dipeptidase from melanoma cells was 7.5 and the Km was 1.2 mM.

Chromatography, High Pressure Liquid↗
PubMed1985

Stimulation of pheomelanogenesis in cultured B16 melanoma cells by 4-tertiary butylcatechol.

Intermediates of pheomelanin in tissue cultured B16 melanoma cells were analyzed by high performance liquid chromatography, and reduced glutathione (GSH), L-dopa, 2-[(L)-S-cysteinyl]-L-dopa (2-SCD) and 5-[(L)-S-cysteinyl]-L-dopa (5-SCD) were quantified. The effects of 4-tertiary butylcatechol (TBC), an antioxidant which causes skin depigmentation, on the levels of the intermediate were then examined. A concentration of 10(-4) M TBC increased the intracellular levels of GSH, 2-SCD and 5-SCD, whereas the L-dopa level was unchanged. The time-course of the increased intermediates corresponded to the elevation of glutathione-metabolizing enzyme activities previously reported by Kawashima et al. [J. invest. Derm. 82, 53 (1984)] in the same cell line exposed to 10(-4) M TBC. The findings establish chemical evidence that TBC stimulates pheomelanogenesis in melanocytes.

Animals↗
PubMed1994

Inhibition of human glutathione S-transferases by dopamine, alpha-methyldopa and their 5-S-glutathionyl conjugates.

The reversible and irreversible inhibition of human glutathione S-transferases (GST) by dopamine, alpha-methyldopa and their 5-S-glutathionyl conjugates (termed 5-GSDA and 5-GSMDOPA, respectively) was studied using purified isoenzymes. The reversible inhibition, using CDNB as substrate and expressed as I50, ranged from 0.18-0.24 (GST M1a-1a), 0.19-0.24 (GST M1b-1b) to 0.5-0.54 mM (GST A1-1) for 5-GSDA and 5-GSMDOPA, respectively. About 20% inhibition was observed for GST A2-2 and P1-1, using 0.5 mM of both 5-GSDA and 5-GSMDOPA. No significant reversible inhibition was observed with dopamine and alpha-methyldopa. Tyrosinase was used to generate ortho-quinones from dopamine and alpha-methyldopa which may bind covalently to GST and thereupon irreversibly inhibit GST. In this respect, GST P1-1 was by far the most sensitive enzyme. The inhibition (expressed as a % of control) after incubating 0.5 microM GST in the presence of 100 units/ml tyrosinase with 5 microM of the catecholamines for 10 min at 25 degrees, was 99% and 67% for dopamine and alpha-methyldopa, respectively. Moderate irreversible inhibition of GST A1-1 by both dopamine and alpha-methyldopa (33% and 25%, respectively), and of GST M1b-1b by dopamine (45%) was also observed. GST P1-1 is also the only isoenzyme susceptible to irreversible inhibition by 5-GSDA (33% inhibition), while no significant inhibition was observed with 5-GSMDOPA. A minor part of the inhibition by dopamine (23%), and the complete inhibition by 5-GSDA was restored by reduction with dithiotreitol. This suggests that GST P1-1 is inhibited by disulfide formation in the case of 5-GSDA, while this oxidative pathway also substantially contributes to the inactivation by dopamine. This was supported by the HPLC-profile of the GST P1-1 subunit which was strongly affected by dopamine, while for 5-GSDA after reduction with dithiotreitol the original elution profile of the subunit returned.

Cysteinyldopa↗
PubMed1986

Occurrence and distribution of 5-S-cysteinyl derivatives of dopamine, dopa and dopac in the brains of eight mammalian species.

The 5-S-cysteinyl derivatives of dopamine, dopa (3,4-dihydroxyphenylalanine) and dopac (3,4-dihydroxyphenylacetic acid) were synthesized and used as reference compounds in high performance liquid chromatography analyses of extracts from various brain regions of eight mammalian species. All three metabolites were detected in the brains of all the species studied. The regional distribution of the metabolites was similar to that of dopamine; the metabolite concentrations ranged from less than 0.1 percent to more than 1 percent of the dopamine level, the highest ratios generally being found in substantia nigra. It is suggested that the 5-S-cysteinyl catechol metabolites have been formed after autoxidation of catechols to quinones and subsequent coupling to glutathione. The adduct thus formed is finally split by peptidases to yield the 5-S-cysteinyl derivatives.

Animals↗