RESUMO
INTRODUCTION: One of the different molecules involved in the development of astrocytomas is nitric oxide (NO), a gaseous radical that, depending on the cell type and the experimental paradigm selected in the pathology, can play either a cytotoxic or a cytoprotective role. DEVELOPMENT: During the development of an astrocytoma NO acts as a tumouricidal agent, although it can also alter vascular reactivity and lead to neovascularisation, thereby contributing to the invasive capacity (aggressiveness) of the tumour. One of the mechanisms of tumoural progression consists in the protein inactivation resulting from the NO nitration of tyrosine from proteins coded for by tumour-suppressing genes, such as p53. Furthermore, in malignant astrocytes, nitrosoglutathione, a natural NO-donor, has been seen to play a role in the chemoresistance displayed against nitrosourea derivatives. The NO excreted by irradiated astrocytoma cells also appears to be involved in the resistance to the radiotherapy shown by non-irradiated cells. CONCLUSIONS: The molecular mechanisms behind the complex and paradoxical activity of NO in glioblastoma multiforme have still not been fully explained and its implications in vivo are even further from being completely understood.
