Dopamine-melanin is actively phagocytized by PC12 cells and cerebellar granular cells: possible implications for the etiology of Parkinson's disease.

Neuromelanin in the substantia nigra may be associated with the pathogenesis of nigral cell death in Parkinson's disease. We used synthetic dopamine-melanin (DA-M) as a model compound for neuromelanin and examined its toxic effects on mice cerebellar granule cells and a rat pheochromocytoma cell line (PC12). The DA-M and dopamine-treated cells showed an accumulation of black deposits when examined by light microscopy. Electron microscopy revealed different stages of DA-M phagocytosis, starting with DA-M binding, engulfment of the particles and the formation of phagosomes located in the cytoplasm. Using absorption assays, we found that NaN3 and low temperature inhibit the internalization of DA-M, pointing to an energy-dependent phagocytosis mechanism. These results suggest that neuromelanin can be phagocytised by neuronal cells which may thus be subjected to its toxic effects. These findings may contribute to our understanding of the formation and disposition of neuromelanin and its possible role in the etiology of Parkinson's disease.

Collapse of K+ and ionic balance during photodynamic inactivation of leukemic cells, erythrocytes and Staphylococcus aureus.

1. The immediate and fast ionic fluxes in Friend erythroleukemic cells (FELC), erythrocytes and Staphylococcus aureus during short intervals of porphyrin mediated photosensitization were determined uniquely by X-ray microanalysis (XRMA) combined with electron microscopy. 2. Photodynamic inactivation of FELC was mediated by either endogenous protoporphyrin induced by 5-amino levulinic acid (5-ALA), or Photofrin-II. We describe the predominant phenomena of > 85% K-loss within 2-10 min of photoactivation. However the accompanied Na inflow and the collapse of the cellular balance of elemental-composition were inconsistent and acted as a function of cell damage. 3. Erythrocytes treated with hematoporphyrin (HP) lost most of their intracellular K yet instantly gained Na. Nevertheless the K/Na molar ratio of the control erythrocytes was nearly 12/1 while after photosensitization and K loss it changed to 1/1. 4. The S. aureus bacteria photosensitized with HP showed entire K-loss as well as marked Na efflux which increased with irradiation time; this was accompanied by the decline of other cell elements. 5. The prevailing K loss in FELC, erythrocytes and bacteria during the first minutes of photosensitization is deduced to be an immediate primary consequence of the photodynamic effect, while other ionic changes are joined in order with the development of cellular damage.

The effect of EDTA and serum on endogenous porphyrin accumulation and photodynamic sensitization of human K562 leukemic cells.

The interrelationship between the effect of serum on the induction of porphyrin synthesis, intracellular porphyrin accumulation and photodynamic sensitization of human K562 cells is described. Endogenous porphyrins, synthesized from supplemented 5-amino levulinic acid (5-ALA), were shown to accumulate in the cells, while an addition of serum triggered porphyrin translocation from the cell to the serum. In order to enhance porphyrin accumulation in the cells themselves, they were further stimulated by EDTA, which in combination with 5-ALA reduces Fe++ cellular content. The higher porphyrin cellular content under EDTA and 5-ALA induction was exploited to photoinactivate the human leukemic cells by more then 3 orders of magnitude.

Bactericidal effects of photoactivated porphyrins--an alternative approach to antimicrobial drugs.

Photoactivated porphyrins display a potent cytotoxic activity towards a variety of Gram positive bacteria, mycoplasma and yeasts, but not Gram negative cells. The prerequisite for photosensitization of a microbial cell is the binding of porphyrin to the cytoplasmic membrane in a pH-dependent manner. On illumination, the membrane bound, and possibly, cytoplasmic porphyrin molecules generate singlet oxygen and radicals which sensitize biomolecules and lead to cell death. The immediate inhibition of cell growth on photodynamic treatment is accompanied by alterations in cell wall and membrane synthesis, leading to the formation of large mesosomes adjacent to the unaccomplished septa. Hemin bound to microbial cells exerts cytotoxic activity by peroxidative and oxidative reactions independent of light. Future research in the field may enhance the possibility of using porphyrin photosensitization for treatment of microbial infections. Such clinical use will be unrelated to the antibiotic resistance of the pathogen. Resistance of Gram negative bacteria to porphyrin photosensitization is the main impediment to its use as a broad spectrum antibacterial method.

Stimulation of Friend erythroleukemic cell cytodifferentiation by 5-amino levulinic acid; porphyrins, cell size, segregation of sialoglycoproteins, and nuclear translocation.

The late events of erythroid differentiation in Friend erythroleukemic cells (FELC), stimulated by 5-amino levulinic acid (5-ALA), were studied. Cultivation of the cells in 5-ALA-enriched media triggered a chain reaction, beginning with an immediate and rapid accumulation of endogenous porphyrins, in particular protoporphyrin and hemin. Incorporation of 14C-ALA was rapid and independent of dimethylsulfoxide (DMSO) induction. In parallel, on the second day of growth, a marked decrease in cell volume was elucidated by flow cytometry. The total protein content was reduced, while Fe uptake and hemoglobin synthesis were increased. The combination of DMSO and 5-ALA produced the most effective induction of the FELC, and the differentiation criteria were the most advanced. The cells exposed to the combined stimulation became loaded with heme and hemoglobin and their generation time was prolonged up to 35 h. Transmission electron microscopy of these treated cells showed a morphological alteration to pearlike cells, associated with a typical nuclear translocation phenomenon and a regional segregation of sialoglycoproteins. An uneven distribution of organelles was revealed; one part of the cell contained numerous ribosomes and the nucleus, while the other part was hemoglobinized, contained mitochondria, and the outer membrane was heavily labeled with ferritin hydrazide, a marker for sialoglycoproteins. The enhanced stimulation of Friend cells by 5-ALA promoted an advanced step of erythroid maturation that has much in common with the late events of normal nuclear extrusion process.