Ação anticancerígena da melatonina sobre a proliferação de células do carcinoma colônico humano (caco-2) e células obtidas de um modelo murino do tumor ascítico de Ehrlich

Abstract

Among the tumor models can highlight the Ehrlich ascites tumor (TAE) cells and CaCO2. These experimental models are a useful resource for the study of tumorigenesis by allowing quantification and analysis of growth and regression of the tumor mass. Among the substances oncostáticas melatonin has shown effectiveness in limiting tumor cell proliferation. Thus the study investigated the action of melatonin on cell proliferation of human colon carcinoma (Caco-2) cells obtained from a murine model of Ehrlich ascites tumor. We evaluated tumor growth, time and percentage of survival, metastasis and ultrastructure of cells in mice undergoing TAE pinealectomy or not, underwent dose of 150 and 300 μg/30g animal weight of melatonin for 12 consecutive days. For cells CaCo-2 investigated the effect of different concentrations (50, 25, 12.5, 6.25, 3.125, 1.56 and 0.78 mg / mL) of melatonin in order to check the cytotoxicity and ultrastructural . According to the results it was found that the abdominal circumference of melatonin-treated mice was significantly reduced, more significant at a dose of 300 μg. Significant reduction, regardless of the dose, the volume of ascites fluid and cell viability TAE, and increasing the lifespan of the animals. Ultrastructurally TAE cells after treatment with melatonin showed morphological changes, with the cell surface displaying numerous projections, and some with fork. In the cytoplasm was evidenced process of degeneration of mitochondria and abundant vacuoles. The nucleus appeared quite fragmented and without evidence of heterochromatic nucleolus Histopathology of organs showed metastasis in the lungs and kidneys, only the control group animals. Lung tumor cells were found in the alveoli and bronchioles. Kidney revealed the presence of tumor cells both in cortical region but also in the spinal region. No metastasis was observed in liver, small intestine and large intestine in any of the animals of the experimental groups. Cytotoxicity was inversely proportional to the concentrations of melatonin, the concentration 0.78 μg/mL to that caused greater toxicity in Caco-2 cells, followed by concentration 1.56 μg/mL, and the concentration of 50μg/mL was that showed the lowest cytotoxicity not differing from the other concentrations and control. The ultrastructural aspect of cells treated with melatonin did not show formation of monolayers. In the group in which cells showed less cytotoxicity CaCo-2 (50 μg /mL melatonin) was visualized changes in cell morphology, presence of microvilli, large nucleus with peripheral heterochromatin areas, with numerous cytoplasmic vacuoles, mitochondrial degeneration, abundant ribosomes and reduction of reserves glycogen. However, treatments that showed cytotoxicity medium and high (1.56 and 0.78 μg/ml of melatonin, respectively), CaCo-2 cells also showed altered morphology, but with characteristics degeneration of cells in the presence of numerous vacuoles and absence of microvillus. It was also observed absence of glycogen, a significant reduction of ribosomes, mitochondrial degeneration, vacuoles, sometimes containing electron-lucent substance, and nuclear fragmentation. Thus, we can conclude that daily doses of 150 and 300 μg/30g of body weight of melatonin for 12 consecutive days have a very effective oncostática activity on cells TAE and that doses of 1.56 and 0.78 μg/mL Melatonin promotes cytotoxicity in cells CaCo-2