Dopamine-melanin protects against tyrosine nitration, tryptophan oxidation and Ca(2+)-ATPase inactivation induced by peroxynitrite.

The effects of dopamine-melanin (DA-melanin), a synthetic model of neuromelanin, on peroxynitrite-mediated 3-nitrotyrosine formation, oxidation of tryptophan in bovine serum albumin and inactivation of erythrocyte membrane Ca(2+)-ATPase activity were investigated in the absence and in the presence of bicarbonate. DA-melanin inhibited nitration of free tyrosine, loss of tryptophan residues and Ca(2+)-ATPase inactivation by peroxynitrite in a dose dependent manner. In the presence of bicarbonate, this inhibitory effect was lower for nitration and insignificant for oxidative protein modifications. These results suggest that neuromelanin can protect against nitrating and oxidizing action of peroxynitrite but is a worse protector against the peroxynitrite-CO(2) adduct. As peroxynitrite may be a mediator of neurotoxic processes, the obtained results suggest that neuromelanin may be important as a physiological protector against peroxynitrite.

Peroxynitrite mediated linoleic acid oxidation and tyrosine nitration in the presence of synthetic neuromelanins.

Peroxynitrite-mediated linoleic acid oxidation and tyrosine nitration were analysed in the presence of synthetic model neuromelanins: dopamine (DA) -melanin, cysteinyldopamine (CysDA) -melanin and various DA/CysDA copolymers. The presence of melanin significantly decreased the amount of 3-nitrotyrosine formed. This inhibitory effect depended on the type and concentration of melanin polymer. It was found that incorporation of CysDA-derived units into melanin attenuated its protective effect on tyrosine nitration induced by peroxynitrite. In the presence of bicarbonate, the melanins also inhibited 3-nitrotyrosine formation in a concentration dependent manner, although the extent of inhibition was lower than in the absence of bicarbonate. The tested melanins inhibited peroxynitrite-induced formation of linoleic acid hydroperoxides, both in the absence and in the presence of bicarbonate. In the presence of bicarbonate, among the oxidation products appeared 4-hydroxynonenal (HNE). CysDA-melanin inhibited the formation of HNE, while DA-melanin did not affect the aldehyde level. The results of the presented study suggest that neuromelanin can act as a natural scavenger of peroxynitrite.

GC-MS analysis of fatty acids in phospholipids from Chlorella vulgaris cultivated synchronously in the presence of propranolol.

Changes in the content and composition of fatty acids in phospholipids were determined to estimate the effect of propranolol on the growth of unicellular green algae Chlorella vulgaris cultivated synchronously. The general biological activity of the cells and the division coefficient (DC) as well as the cell synchronisation were disturbed by propranolol in a concentration dependent manner. Also, the effect of propranolol on the fatty acids content of Chlorella vulgaris phospholipids was proportional to its concentration.

Model neuromelanins as antioxidative agents during lipid peroxidation.

The oxidative pathway of dopamine metabolism in the human brain leads to formation and accumulation of neuromelanin in the cytoplasm of most nigrostriatal dopaminergic neurons. The physiological significance of neuromelanin and its contribution to the neurodegenerative processes underlying Parkinson's disease are still controversial. The effect of model neuromelanins on Fe(II)/ascorbate-induced lipid peroxidation in micelles of linoleic acid and in lecithin liposomes was determined. Synthetic neuromelanins were obtained from dopamine (DA), 5-S-cysteinyldopamine (CysDA) or from equimolar mixture of these precursors. Thiobarbituric acid test and reverse-phase HPLC, used for measurements of primary and secondary oxidation products, showed that all melanins tested significantly suppressed peroxidation of both, linoleic acid and liposomal lecithin. The inhibitory effect of CysDA-melanin was lower than of DA/CysDA-melanin and DA-melanin. All the melanins were able to reduce linoleic acid hydroperoxides to their stable hydroxy derivatives. The results obtained suggest that neuromelanin can act as natural antioxidant. The fatty acid hydroperoxide-reducing ability demonstrated for the model neuromelanins appears to be involved in the mechanism of antioxidative activity of neuromelanin.

Reduction of 13-hydroperoxy-9,11-octadecadienoic acid by dopamine-melanin.

The effect of dopamine-melanin (DA-melanin), synthetic model of neuromelanin, on the stability of 13-hydroperoxyoctadecadienoic acid (13-HPODE) has been investigated using a reverse-phase high-performance liquid chromatography (HPLC) with UV detection. It was found that DA-melanin effectively accelerated the decomposition of 13-HPODE, both in the absence and in the presence of ferrous ions. The disappearance of 13-HPODE was accompanied by the formation of 13-hydroxyoctadecadienoic acid (13-HODE). The results obtained indicate that DA-melanin is able to reduce linoleic acid hydroperoxide to its stable hydroxyl derivative. The fatty acid hydroperoxide-reducing ability of DA-melanin appears to play an important role in the antioxidative activity of neuromelanin in the process of lipid peroxidation.

Effect of cadmium on photosynthetic pigments in synchronously growing Chlorella cells.

Cadmium ions introduced at concentration of 30 ppm to the cultivation medium of synchronously growing Chlorella vulgaris decreased concentration of chlorophylls a and b, carotenes alpha and beta and lutein at various stages of the cell cycle, while at concentration of 1 ppm synthesis of the photosynthetic pigments was stimulated. The pigment content in the cadmium treated cells was related to the morphometrically determined changes in the size and shape of the cells.