Disruption of brain redox homeostasis in glutaryl-CoA dehydrogenase deficient mice treated with high dietary lysine supplementation.

Deficiency of glutaryl-CoA dehydrogenase (GCDH) activity or glutaric aciduria type I (GA I) is an inherited neurometabolic disorder biochemically characterized by predominant accumulation of glutaric acid and 3-hydroxyglutaric acid in the brain and other tissues. Affected patients usually present acute striatum necrosis during encephalopathic crises triggered by metabolic stress situations, as well as chronic leukodystrophy and delayed myelination. Considering that the mechanisms underlying the brain injury in this disease are not yet fully established, in the present study we investigated important parameters of oxidative stress in the brain (cerebral cortex, striatum and hippocampus), liver and heart of 30-day-old GCDH deficient knockout (Gcdh(-/-)) and wild type (WT) mice submitted to a normal lysine (Lys) (0.9% Lys), or high Lys diets (2.8% or 4.7% Lys) for 60 h. It was observed that the dietary supplementation of 2.8% and 4.7% Lys elicited noticeable oxidative stress, as verified by an increase of malondialdehyde concentrations (lipid oxidative damage) and 2-7-dihydrodichlorofluorescein (DCFH) oxidation (free radical production), as well as a decrease of reduced glutathione levels and alteration of various antioxidant enzyme activities (antioxidant defenses) in the cerebral cortex and the striatum, but not in the hippocampus, the liver and the heart of Gcdh(-/-) mice, as compared to WT mice receiving the same diets. Furthermore, alterations of oxidative stress parameters in the cerebral cortex and striatum were more accentuated in symptomatic, as compared to asymptomatic Gcdh(-/-) mice exposed to 4.7% Lys overload. Histopathological studies performed in the cerebral cortex and striatum of these animals exposed to high dietary Lys revealed increased expression of oxidative stress markers despite the absence of significant structural damage. The results indicate that a disruption of redox homeostasis in the cerebral cortex and striatum of young Gcdh(-/-) mice exposed to increased Lys diet may possibly represent an important pathomechanism of brain injury in GA I patients under metabolic stress.

Alpha-ketoisocaproic acid and leucine provoke mitochondrial bioenergetic dysfunction in rat brain.

Patients affected by maple syrup urine disease (MSUD) present severe neurological symptoms and brain abnormalities, whose pathophysiology is poorly known. In the present study we investigated the in vitro effects of leucine (Leu), alpha-ketoisocaproic acid (KIC) and alpha-hydroxyisovaleric acid (HIV), respectively, the branched-chain amino, keto and hydroxy acids that most accumulate in MSUD, on brain bioenergetic homeostasis, evaluating respiratory parameters obtained by oxygen consumption, membrane potential (Psim), NAD(P)H content, swelling and citric acid cycle enzyme activities in mitochondrial preparations from rat forebrain using glutamate plus malate, succinate or alpha-ketoglutarate as respiratory substrates. KIC increased state 4 and decreased the respiratory control ratio with all substrates, in contrast with Leu and HIV. Furthermore, KIC and Leu, but not HIV, decreased state 3 using alpha-ketoglutarate. A KIC-induced selective inhibition of alpha-ketoglutarate dehydrogenase activity was also verified, with no alteration of the other citric acid cycle activities. The ADP/O ratio and the mitochondrial NAD(P)H levels were also reduced by KIC using glutamate/malate and alpha-ketoglutarate. In addition, KIC caused a reduction in the Psim when alpha-ketoglutarate was the substrate. Finally, KIC was not able to induce mitochondrial swelling. The present data indicate that KIC acts as an uncoupler of oxidative phosphorylation and as a metabolic inhibitor possibly through its inhibitory effect on alpha-ketoglutarate dehydrogenase activity, while Leu acts as a metabolic inhibitor. It is suggested that impairment of mitochondrial homeostasis caused by the major metabolites accumulating in MSUD may be involved in the neuropathology of this disease.