Experimental evidence that bioenergetics disruption is not mainly involved in the brain injury of glutaryl-CoA dehydrogenase deficient mice submitted to lysine overload.

Bioenergetics dysfunction has been postulated as an important pathomechanism of brain damage in glutaric aciduria type I, but this is still under debate. We investigated activities of citric acid cycle (CAC) enzymes, lactate release, respiration and membrane potential (ΔΨm) in mitochondrial preparations from cerebral cortex and striatum of 30-day-old glutaryl-CoA dehydrogenase deficient (Gcdh-/-) and wild type mice fed a baseline or a high lysine (Lys, 4.7%) chow for 60 or 96h. Brain histological analyses were performed in these animals, as well as in 90-day-old animals fed a baseline or a high Lys chow during 30 days starting at 60-day-old. A moderate reduction of citrate synthase and isocitrate dehydrogenase activities was observed only in the striatum from 30-day-old Gcdh-/- animals submitted to a high Lys chow. In contrast, the other CAC enzyme activities, lactate release, the respiratory parameters state 3, state 4, the respiratory control ratio and CCCP-stimulated (uncoupled) state, as well as ΔΨm were not altered in the striatum. Similarly, none of the evaluated parameters were changed in the cerebral cortex from these animals under baseline or Lys overload. On the other hand, histological analyses revealed the presence of intense vacuolation in the cerebral cortex of 60 and 90-day-old Gcdh-/- mice fed a baseline chow and in the striatum of 90-day-old Gcdh-/- mice submitted to Lys overload for 30 days. Taken together, the present data demonstrate mild impairment of bioenergetics homeostasis and marked histological alterations in striatum from Gcdh-/- mice under a high Lys chow, suggesting that disruption of energy metabolism is not mainly involved in the brain injury of these animals.

Acute lysine overload provokes protein oxidative damage and reduction of antioxidant defenses in the brain of infant glutaryl-CoA dehydrogenase deficient mice: a role for oxidative stress in GA I neuropathology.

We evaluated the antioxidant defense system and protein oxidative damage in the brain and liver of 15-day-old GCDH deficient knockout (Gcdh(-/-)) mice following an acute intraperitoneal administration of Lys (8 µmol/g). We determined reduced glutathione (GSH) concentrations, sulfhydryl content, carbonyl formation and the activities of the antioxidant enzymes glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) in the brain and liver of these animals. 2',7'-dihydrodichlorofluorescein (DCFH) oxidation was also measured as an index of free radical formation. The only parameters altered in Gcdh(-/-) compared to wild type (Gcdh(+/+)) mice were a reduction of liver GSH concentrations and of brain sulfhydryl content. Acute Lys injection provoked a decrease of GSH concentration in the brain and sulfhydryl content in the liver, and an increase in carbonyl formation in the brain and liver of Gcdh(-/-) mice. Lys administration also induced a decrease of all antioxidant enzyme activities in the brain, as well as an increase of the activities of SOD and CAT in the liver of Gcdh(-/-) mice. Finally, Lys elicited a marked increase of DCFH oxidation in the brain and liver. It is concluded that Lys overload compromises the brain antioxidant defenses and induces protein oxidation probably secondary to reactive species generation in infant Gcdh(+/+) mice.

Increased glutamate receptor and transporter expression in the cerebral cortex and striatum of gcdh-/- mice: possible implications for the neuropathology of glutaric acidemia type I.

We determined mRNA expression of the ionotropic glutamate receptors NMDA (NR1, NR2A and NR2B subunits), AMPA (GluR2 subunit) and kainate (GluR6 subunit), as well as of the glutamate transporters GLAST and GLT1 in cerebral cortex and striatum of wild type (WT) and glutaryl-CoA dehydrogenase deficient (Gchh-/-) mice aged 7, 30 and 60 days. The protein expression levels of some of these membrane proteins were also measured. Overexpression of NR2A and NR2B in striatum and of GluR2 and GluR6 in cerebral cortex was observed in 7-day-old Gcdh-/-. There was also an increase of mRNA expression of all NMDA subunits in cerebral cortex and of NR2A and NR2B in striatum of 30-day-old Gcdh-/- mice. At 60 days of life, all ionotropic receptors were overexpressed in cerebral cortex and striatum of Gcdh-/- mice. Higher expression of GLAST and GLT1 transporters was also verified in cerebral cortex and striatum of Gcdh-/- mice aged 30 and 60 days, whereas at 7 days of life GLAST was overexpressed only in striatum from this mutant mice. Furthermore, high lysine intake induced mRNA overexpression of NR2A, NR2B and GLAST transcripts in striatum, as well as of GluR2 and GluR6 in both striatum and cerebral cortex of Gcdh-/- mice. Finally, we found that the protein expression of NR2A, NR2B, GLT1 and GLAST were significantly greater in cerebral cortex of Gcdh-/- mice, whereas NR2B and GLT1 was similarly enhanced in striatum, implying that these transcripts were translated into their products. These results provide evidence that glutamate receptor and transporter expression is higher in Gcdh-/- mice and that these alterations may be involved in the pathophysiology of GA I and possibly explain, at least in part, the vulnerability of striatum and cerebral cortex to injury in patients affected by GA I.