Parkinson-like disease by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity on energy-linked non-synaptic and intra-synaptic mitochondrial enzyme systems from Macaca fascicularis brain

Abstract. The maximum rates (Vmax) of some mitochondrial enzymatic activities related to energy transduction such as citrate synthase, succinate dehydrogenase, malate dehydrogenase for Krebs’ cycle; NADH-cytochrome c reductase (both total and rotenone sensitive), succinate CoQ reductase, succinate cytochrome c reductase, cytochrome oxidase, for the electron transfer chain (ETC); glutamate dehydrogenase, glutamate-pyruvate-transaminase, glutamate-oxaloacetate-transaminase for glutamate and aminoacids metabolism were evaluated in non-synaptic and intra-synaptic mitochondria from cerebral cortex of Macaca fascicularis (Cynomolgus monkey). These three types of mitochondria were isolated from dopaminergic terminals of monkey’s cerebral cortex after a Parkinson’s Disease like syndrome induced by e.v. injections of MPTP neurotoxin. In control (vehicle-treated) animals, the biochemical machinery is differently expressed in non-synaptic mitochondria with respect to "light" and "heavy" intra-synaptic ones and also between intra-synaptic themselves. The activities of citrate synthase, succinate dehydrogenase, malate dehydrogenase, NADH-cytochrome c reductase, succinate cytochrome c reductase, glutamate dehydrogenase and glutamate-pyruvate- and glutamate-oxaloacetate- transaminases are lower, while cytochrome oxidase is higher in intra-synaptic “light” and “heavy” mitochondria than those in non-synaptic ones, being succinate cytochrome c reductase activity the same in all mitochondria types. Some enzyme activities are lower in “heavy” than in “light” intra-synaptic mitochondria, confirming that in various types of brain mitochondria also from primates, a different metabolic machinery exists, due to their different location in vivo, in soma or synapses. In the MPTP-treated animals (Parkinson’s like syndrome), the systemic treatment with the neurotoxin (i.v., 0.3 mg/kg/day for 5 days) increased the activity of succinate dehydrogenase and succinate CoQ reductase only in “light” intra-synaptic mitochondria (decreasing the glutamate dehydrogenase activity) and the neurotoxin decreased also cytochrome oxidase activities in all mitochondria types and that of of non-synaptic mitochondria. Thus, MPTP stimulated the succinate metabolism, increasing the activity of Complex II, but decreasing the activity of Complex IV, the most sensitive Complex to neurotoxin, not affecting the activities of Complex I, Complex I-III, Complex II-III; also glutamate metabolism is affected by MPTP, decreasing the activity of glutamate dehydrogenase (“light” intra-synaptic mitochondria) and particularly that of glutamate-pyruvate-transaminase on non-synaptic mitochondria. The data on functional proteomics of these different types of mitochondria suggest that the treatment with MPTP, as a model of Parkinson’s Disease, affected the activities linked mainly to succinate metabolism of “light” intra-synaptic mitochondria, instead of Complex I, as previously hypothesized, indicating that the link between the Krebs’ cycle and ETC seems to be of primary pathogenetic significance, indicating a specific subcellular trigger site of action. These results presented in this chapter also suggest a specific molecular trigger mode of action on energy metabolism of cerebral dopaminergic terminals, being the neurotoxin effective also on enzyme activities of non-synaptic mitochondria for transamination of pyruvate, while Complex IV activity was already decreased by MPTP, thus impairing the ATP synthesis in any case