Differential Inhibition by Hyperammonemia of the Electron Transport Chain Enzymes in Synaptosomes and Non-Synaptic Mitochondria in Ornithine Transcarbamylase-Deficient spf-Mice: Restoration by Acetyl-L-Carnitine |
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Authors: | Qureshi Karim Rao K. V. Rama Qureshi Ijaz. A. |
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Affiliation: | (1) Department of Pediatrics, University of Montreal, Hôpital Sainte-Justine, Montreal, Quebec, Canada |
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Abstract: | Sparse-fur (spf) mouse is the ideal animal model to study the neuropathology of congenital ornithine transcarbamylase (OTC) deficiency. Our current hypothesis implies that an ammonia-induced depletion of energy metabolism in the spf mouse, could be due to a reduction in the activities of the enzymes of the electron transport chain and a treatment with acetyl-L-carnitine could normalize this abnormality. We also hypothesized that there might be a differential degree of inhibition in synaptosomal and non-synaptic mitochondria, for the enzymes of the electron transport chain, caused by congenital hyperammonemia. We have therefore measured the activities of NADH-cytochrome C oxidoreductase, succinate cytochrome C oxidoreductase and cytochrome C oxidase in synaptosomes and non-synaptic mitochondria, isolated from spf mice and CD-1 controls with and without acetyl-L-carnitine treatment. Our results indicate a significant reduction (19–34%) in the activities of these complexes in synaptosomes in untreated spf mice, whereas in non-synaptic mitochondria, there was a tendency for the activities to decrease. Acetyl-L-carnitine treatment enhanced these activities (15–64%) for all the three enzyme complexes and its effect was more prominent on succinate cytochrome C oxidoreductase activity (64%). These studies point out that: (a) ammonia-induced disturbances in the energy metabolism could be more pronounced in neuronal mitochondria, and (b) the effect of acetyl-L-carnitine on the restoration of cerebral ATP in hyperammonemia could be through an enhancement of the activities of various electron transport chain enzymes. |
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Keywords: | Ornithine transcarbamylase deficiency brain synaptosomes non-synaptic mitochondria electron transport chain acetyl-L-carnitine |
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