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Melanins are polymorphous and multifunctional biopolymers with a relatively high concentration of freeradicals. EPR spectroscopy was used to study o-semiquinone free radicals in model eumelanins synthesizedfrom 3,4-dihydroxyphenylalanine (DOPA) and tyrosine in the presence of tyrosinase, and melanins isolatedfrom A-375 and G-361 human melanoma malignum cells exposed to two compounds: 5,7-dimethoxycoumarin(DMC) and valproic acid (VPA). Changes were determined in the concentrations of free radicals in theindividual melanins from tumour cells treated with DMC and VPA. A strong decrease in the concentrationsof free radicals characterizes melanins isolated from tumour cells treated together with DMC and VPA.Slow spin-lattice relaxation processes were noted in the melanins tested with homogeneous broadened EPRspectra. The EPR technique may be useful not only for the elucidation of free radicals in melanins fromA-375 and G-361 cells treated with VPA and DMC but it could also be applied to establish the relationshipbetween melanin type and the malignancy of melanoma malignum

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Our results show that betulin and 28-O-propynoylbetulin were effective in inhibition of cell growth and induction of apoptosis in a human melanoma cell line. The addition of the propynoyl group at the C-28 hydroxyl group of betulin led to a greater proapoptotic and antiproliferative effect in comparison to unmodified betulin. These observations suggest that the obtained derivative is a potent anti-melanoma agent.

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Neuromelanin (NM) is a complex polymer pigment found in catecholaminergic neurons of the human brain. The structure, formation pathway, and physiological function of NM have not yet been clarified, but interest in this polymer has been sparked by the suggestion that NM is involved in cell death in Parkinson's disease. In the current study, pyrolysis-gas chromatography/mass spectrometry analysis was applied for structural investigation of NM isolated from the human substantia nigra, using synthetic eumelanin and pheomelanin-type pigments as reference materials. None of the heterocyclic, sulfur-containing compounds being characteristic thermal degradation products of cysteinyldopamine-derived units of synthetic pheomelanin standard was detected in the pyrolysates of natural NM. The results suggest that nigral pigment isolated from normal brain tissue does not contain benzothiazine-type monomer units. Pyrolytic experiments in the presence of a derivatizing agent allowed identification of high levels of saturated and monounsaturated straight-chain C14-C18 fatty acids and led to the conclusion that a part of a lipid component is chemically bound to the NM macromolecule. The nigral pigment was also shown to be tightly associated with an isoprenoid-type compound.

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