title: 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.
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.
authors.affiliation: Department of Pediatrics, University of Montreal, Hôpital Sainte-Justine, Quebec, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Qureshi
authors.forename: K V
authors.initials: KV
authors.lastname: Rao
authors.forename: I A
authors.initials: IA
authors.lastname: Qureshi
mesh_terms: D000108:Acetylcarnitine / Q000494:pharmacology*; D000641:Ammonia / Q000097:blood*; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D004579:Electron Transport / Q000187:drug effects; D003576:Electron Transport Complex IV / Q000378:metabolism; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology; D009245:NADH Dehydrogenase / Q000378:metabolism; D009954:Ornithine Carbamoyltransferase / Q000235:genetics; D020163:Ornithine Carbamoyltransferase Deficiency Disease; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000201:enzymology
chemical_list: D000108:Acetylcarnitine; D000641:Ammonia; D013384:Succinate Cytochrome c Oxidoreductase; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D009954:Ornithine Carbamoyltransferase