LDL and HDL affect nitric oxide metabolism in human astrocytoma cells

Astrocytes provide structural, trophic and metabolic support to neurons and modulate synaptic activity. Under physiological conditions, neuronal-derived nitric oxide (NO) plays an important role in the modulation of a variety of central nervous system (CNS) functions. NO, although short lived, can travel sufficient distances to be able to act as an intercellular messenger in the brain. Its targets include adjacent neurons and astrocytes. The aim of the present study was performed in order to investigate the effects produced by incubation of lipoproteins, at different times, with human astrocytoma cells and thus measuring NO and its metabolite production. NO and peroxynitrite production, iNOS and nNOS expression by Western immunoblot were evaluated. The LDL and HDL-treated cells showed an increased production of NO, more evident after 12 h, compared to basal levels; concerning peroxynitrite production, LDL and HDL-treated cells showed a higher fluorescence, more evident at 3 h. nNOS and iNOS protein levels were significantly higher in the cells incubated with control LDL and HDL. The present work supports the hypothesis that lipoproteins can induce the formation of reactive astrocytes, inducing iNOS as reported by other authors, giving experimental support to a role played by LDL and HDL inducing a reactive response.