Excitotoxic neuronal injury in acute homocysteine neurotoxicity: Role of calcium and mitochondrial alterations

In this study we tested if calcium imbalance and mitochondrial dysfunction, which have been implicated in the conventional mechanisms of excitotoxicity induced by glutamate (Glu), are also involved in homocysteine (Hcy) neurotoxicity. Primary cultures of rat cerebellar granule cells were incubated for 30 min in the presence of 25 mM d,l-Hcy or 1 mM Glu. At these concentrations both amino acids induced comparable neurodegeneration and chromatin condensation, evaluated after 24 h using the propidium iodide and Hoechst 33258 staining. These effects were partially prevented by cyclosporin A (CsA), but not FK506. Hcy-induced release of [3H]inositol phosphates and increase in intracellular calcium level (evaluated with fluo-3 fluorescent probe) were weakly expressed. Hcy- and Glu-induced mitochondrial swelling was visualized under electron microscope, and the release of Cytochrome c was evaluated using immunocytochemical method and confocal microscopy. Comparing to Glu, the effects of Hcy were slightly less expressed and less sensitive to CsA, while FK506 did not modify mitochondrial alterations. These data indicate that mitochondrial alterations play a similar role in acute Hcy and Glu neurotoxicity, although the mechanisms triggering Glu- and Hcy-evoked mitochondrial dysfunction seem to differ, Hcy toxicity being less dependent on calcium.