Impaired glutamate clearance as a consequence of energy failure caused by MPP+ in astrocytic cultures

Astrocytes are the site of bioactivation of the parkinsonism-inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into its toxic 1-methy l-4-phenylpyridinium (MPP+) metabolite. The mechanism by which MPP+ is capa ble of decreasing astrocytic glutamate uptake was evaluated in this study u sing primary cultures of astrocytes. Addition of glutamate to these culture s was followed by its efficient clearance from the extracellular space. How ever, when astrocytes were preincubated with MPP+, glutamate clearance was significantly impaired. This effect was concentration-dependent, became mor e pronounced by prolonging the incubation in the presence of MPP+ and occur red at a time when cell membrane integrity was still preserved. No evidence was found that reactive oxygen species contributed to MPP+-induced decreas e in glutamate clearance. Indeed, neither the spin trapping agent alpha-phe nyl-tert-butyl nitrone, the lazaroid antioxidant U-74389G, nor the disulfid e-reducing agent dithiothreitol was capable of restoring glutamate net upta ke. The effect of MPP+ on glutamate clearance: (i) was accompanied by a dec rease in cellular ATP; (ii) could be enhanced by withdrawing glucose from t he incubation medium or by inhibiting glycolysis with 2-deoxyglucose, and ( iii) could be reproduced using the mitochondrial complex I inhibitor roteno ne. Taken together, these results indicate that, by acting as a mitochondri al poison, MPP+ impairs energy metabolism of astrocytes and significantly r educes their ability to maintain low levels of extracellular glutamate. (C) 1999 Academic Press.