Ganglioside profiles of experimental melanomas and of their melanosomal fractions.

We compared ganglioside profiles of animal tumours (B16 and Cloudman S91 murine melanomas, Bomirski Syrian hamster melanoma), which are widely used as models of human melanoma, and of their melanosomal fractions. A ganglioside fraction was extracted and purified and the amount of each component ganglioside was assessed by thin-layer chromatography. GM3 was the dominant ganglioside species in the murine melanomas studied. Unlike human melanomas, the GD3 expression in mouse melanomas was low. GD3 and GM3 were major gangliosides in Bomirski hamster melanoma. Alkali-labile O-acetyl-GD3, a melanoma-specific ganglioside, was detected only in Bomirski melanoma. GD2, which in human melanoma is seen as a distinct signal of tumour progression, was not found in the animal melanomas studied. Melanosomes isolated from B16 and Bomirski melanomas contained GM3 and GD3 as their major ganglioside components. These data extend the group of common antigenic determinants shared by melanosomes and cell surface of pigment cells.

Evaluation of serum sialic acid fractions as markers for malignant melanoma.

Increased total serum sialic acid levels have proved to be a useful non-specific marker of various neoplastic diseases including melanoma. In some malignancies, specific fractions of sialic acid were reported to be more reliable for monitoring disease progression. In this study various fractions of sialic acid were measured in the sera of Bomirski melanoma-bearing Syrian hamsters using the modified thiobarbituric acid method of Skoza and Mohos. Significantly higher serum levels of total sialic acid, 601.0 +/- 49.1 micrograms/ml, were demonstrated in animals with melanoma in comparison with control hamsters, 463.1 +/- 33.0 micrograms/ml (P < 0.01). Free sialic acid concentration was found to be negligible compared with that found in the sera of melanoma patients. Lipid bound sialic acid measurements carried out according to Bhatavdekar et al. were shown to be influenced by interfering substances. Hence, only the estimation of total sialic acid in sera can be recommended for monitoring melanoma progression. Bomirski melanoma proved to be a good model of human melanoma.

Morphometric parameters of isolated melanosomes.

Basic morphometric parameters of melanosomes isolated from mouse hair, hamster eye and hamster hair are given and tabelized with those published formerly to enlarge the widest published collection of melanosomes isolated from different types of pigmented tissues up to 17 types. The splitting of melanosomes isolated from mixed tissue of hamster eyes into two subpopulations confirmed the presence of double origin of melanosomes in the eye. The close correspondence of subpopulations of hamster eye melanosomes with hamster hair and hamster melanoma (type Bomirski) respectively supports the hypothesis of high structural stability of melanosomes even under pathological conditions.

Melanosome--a sophisticated organelle.

Melanosome is a clear out organelle of its own. The experience of the authors in the melanosome investigation has been reviewed and put to context with the literature data. Melanin moiety, a prominent feature of melanosome, was found to vary between 20-60 weight %. Melanosome concentration in pigment tissues was demonstrated to be remarkably high which explains their capacity to perform various functions both cytoprotective and cytotoxic-ascribed to the presence of melanin. Putative relation of melanosomes to other cell organelles was critically analysed. Systems of melanosome maturation were explained. The ultrastructure of melanosomes determined by the quality of their protein matrix was described and basic morphometric data summarized. The importance of the compartmentalization of melanogenesis was underlined and the fragility of melanosomal limiting membrane shown. The melanosome degradation repeatedly observed by electron microscopy has not been confirmed by biochemical means.

An estimate of melanosome concentration in pigment tissues.

Concentration of melanosomes in various tissues has been unknown because of the impracticability of their direct quantification. Using an indirect approach comprising the estimation of melanin both in freeze-dried tissue samples and in isolated melanosomes, we obtained data on the amount of melanosomes in various pigment tissues. The concentrations of melanosomes found in the tissues were relatively high, not only reflecting the dark color of pigment tissues but also explaining their capacity to perform various functions ascribed to the presence of melanin.

Protein determination in materials containing melanin.

Strategy of protein determination in melanin containing samples was analyzed, and the prerequisites under which the Lowry procedure could be used were established. (a) Complete solubilization of proteins from melanosomes was not reached until the treatment with 3% sodium dodecylsulfate at 100 degrees C was prolonged to 5 h. (b) It is necessary to correct the data obtained with Folin reaction to eliminate melanin interference. (c) The correction is based upon the determination of the extent of solubilized melanin and subtraction of the corresponding Folin-Ciocalteu reaction values. (d) The extent of correction due to the melanin interference was found to be about 40% of the absorbance value. It was concluded that correction of the data obtained with Lowry assay is possible, but the procedure is complicated and time-consuming. However, a more simple modification has not been developed.

RNA and DNA in melanosomes of hamster melanoma.

The melanosomes were isolated from Syrian hamster melanoma Ma by three different methods. Levels of about 0.2% RNA and less than 0.05% of DNA were detected in the melanosome preparations. The higher the purification of the melanosome samples, the lower the DNA content observed. Consequently, traces of DNA in melanosomes could originate from contamination. The irreversible interaction of DNA with melanosomes in vitro was not demonstrated.

Lipid composition in melanosomes of tumor- and chorioidea cells.

The lipid composition of melanosomes from hamster and bovine eye pigmented tissues (chorioidea) and of melanosomes from Harding-Passey mouse melanomas, hamster melanomas Ma and human liver melanoma metastases was investigated. The lipid composition of melanosomes was analogous to that of other subcellular melanocytic fractions as it had been reported in literature. The main difference between tumor and chorioidea melanosomes consisted in the absence of phospholipids in the latter case, other differences were quantitative. The role of melanosomes in melanomas should not be different from that in normal pigmented tissues.

Comparison of lipids between tumor and normal hamster melanosomes.

A study of lipid components of melanosomes isolated from eye pigment tissues and pigmented melanoma type Bomirski line Ma of Syrian hamster by thin-layer chromatography is described. Tumor melanosomes contained 8-10% of total lipids, approximately one half of which were phospholipids. Eye melanosomes contained only 3-4% of total lipids, among which no phospholipids could be detected. Cholesterol, cholesteryl esters, free fatty acids and triacylglycerols were found in the fraction of neutral lipids. Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin constituted 70-80% of the phospholipid fraction.