Metabolic effects of 1-methyl-4-phenylpyridinium (MPP+) in primary neuron cultures

Disruption of mitochondrial function has been proposed as an action of 1-me thyl-4-phenylpyridinium (MPP+) that is responsible for its toxicity. In ord er to characterize effects of MPP+ on energy metabolism in primary culture neurons, we monitored levels of several metabolites in cultured rat cerebel lar granule cells exposed to MPP+ The toxin produced a rapid concentration- dependent reduction in intracellular phosphocreatine (PCr), amounting to a 50-80% decrease within 30-60 min at 50 muM, that was maintained through the 1 week exposure interval examined. In contrast, ATP levels remained compar able to those of untreated neurons for approximately 4 days, at that time a 50% reduction in ATP was observed in association with a decrease in cell v iability. Acute decreases in PCr were accompanied by increases in creatine such that the total creatine levels were maintained. Lactate levels in the culture medium were significantly increased (from 4.5 to 6.0 mM) within 6 h r after addition of MPP+, with a concentration dependence similar to that o bserved for the reduction in PCr. Increased lactate production in the prese nce of MPP+ coincided with a more rapid depletion of glucose in the culture medium. MPP+ induced a rapid and sustained decrease in intracellular pH ca lculated from the creatine kinase equilibrium, and this acidification is co nsidered primarily responsible for the observed decrease in PCr. These stud ies provide direct evidence that toxic concentrations of MPP+ have acute ef fects on energy metabolism in primary culture neurons, consistent with an i ncreased dependence on glycolysis to meet metabolic demand, but indicate th at toxicity is not associated with overt, immediate failure to maintain cel lular ATP. (C) 2000 Wiley-Liss, Inc.