Assessment of mitochondrial electron transport chain function in a primary astrocyte cell model of hyperhomocystinaemia

Elevated plasma homocysteine (Hcy) has been detected in patients with various neurodegenerative conditions. Studies on neurones and cerebral tissue have revealed that hyperhomocystinaemia may inhibit mitochondrial electron transport chain (ETC) enzyme activity resulting in neuronal morbidity. As astrocytes convey a protective and supportive role towards neurones, we postulated that Hcy-induced astrocytic ETC inhibition may contribute to neurological dysfunction. In order to investigate this hypothesis, we established a cellular model of hyperhomocystinaemia using primary rat astrocytes. Which were incubated were incubated with 200 mu M, 500 mu M Hcy and the Hcy metabolite, thiolactone (10 mu M). Following 96 h of incubation with 200 mu M and 500 mu M Hcy, an approximate two-fold (1.11 nmol/mg) and threefold (1.45 nmol/mg) increase in mitochondrial levels of Hcy, respectively, were detected compared to control levels (0.54 nmol/mg). However, on exposure to Hcy (200 or 500 mu M) and Hcy-thiolactone (10 mu M), the activities of astrocytic ETC complex I, II-III and IV were found to be comparable to control levels. In addition, the extracellular lactate: pyruvate ratio and the intracellular glutathione status of primary rat astrocytes were not significantly different between Hcy (200 or 500 mu M) treated and controls. In conclusion, the results of this study suggest that Hcy induced impairment of astrocytic ETC function may not contribute to the pathophysiology of hyperhomocystinaemia.