Striatum is more vulnerable to oxidative damage induced by the metabolites accumulating in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency as compared to liver.

The present work investigated the in vitro effects of 3-hydroxy-3-methylglutarate, 3-methylglutarate, 3-methylglutaconate and 3-hydroxyisovalerate, which accumulate in 3-hydroxy-3-methylglutaric aciduria, on important parameters of oxidative stress in striatum and liver of young rats, tissues that are injured in this disorder. Our results show that all metabolites induced lipid peroxidation (thiobarbituric acid-reactive substances increase) and decreased glutathione levels in striatum, whereas 3-hydroxy-3-methylglutarate, besides inducing the strongest effect, also altered thiobarbituric acid-reactive substances and glutathione levels in the liver. Furthermore, 3-hydroxy-3-methylglutarate, 3-methylglutarate and 3-methylglutaconate oxidized sulfhydryl groups in the striatum, but not in the liver. Our data indicate that 3-hydroxy-3-methylglutarate behaves as a stronger pro-oxidant agent compared to the other metabolites accumulating in 3-hydroxy-3-methylglutaric aciduria and that the striatum present higher vulnerability to oxidative damage relatively to the liver.

D-serine induces lipid and protein oxidative damage and decreases glutathione levels in brain cortex of rats.

The present work investigated the in vitro effects of D-serine (D-Ser) on important parameters of oxidative stress in cerebral cortex of young rats. Our results show that D-Ser significantly induced lipid peroxidation, as determined by increase of thiobarbituric acid-reactive substances and chemiluminescence levels, as well as protein oxidative damage since carbonyl formation and sulfhydryl oxidation were enhanced by this amino acid. Furthermore, the addition of free radical scavengers significantly prevented D-Ser-induced lipid oxidative damage, suggesting that free radicals were involved in this effect. D-Ser also significantly diminished glutathione levels in cortical supernatants, decreasing therefore the major brain antioxidant defense. Finally, D-Ser oxidized a glutathione commercial solution in a medium devoid of brain supernatants, indicating that it behaved as a direct acting oxidant. In contrast, L-serine, L-alanine and L-threonine at concentrations as high as 5 mM did not significantly change chemiluminescence values, carbonyl content and GSH concentrations, implying a selective effect for D-serine. However, cortical supernatants exposed to 5 mM L-serine for different periods resulted in a gradual enhancement of TBA-RS levels as pre-incubation time increased. The present data indicate that D-Ser induces oxidative stress in cerebral cortex of young rats. Therefore, it is presumed that this mechanism may be involved at least in part in the neurological damage found in patients affected by disorders in which D-Ser metabolism is compromised, leading to altered concentrations of this D-amino acid.

Glycine provokes lipid oxidative damage and reduces the antioxidant defenses in brain cortex of young rats.

Patients affected by nonketotic hyperglycinemia (NKH) usually present severe neurological symptoms and suffer from acute episodes of intractable seizures with leukoencephalopathy. Although excitotoxicity seems to be involved in the brain damage of NKH, the mechanisms underlying the neuropathology of this disease are not fully established. The objective of the present study was to investigate the in vitro effects of glycine (GLY), that accumulate at high concentrations in the brain of patients affected by this disorder, on important parameters of oxidative stress, such as lipid peroxidation (thiobarbituric acid-reactive substances (TBA-RS) and chemiluminescence) and the most important non-enzymatic antioxidant defense reduced glutathione (GSH) in cerebral cortex from 30-day-old rats. GLY significantly increased TBA-RS and chemiluminescence values, indicating that this metabolite provokes lipid oxidative damage. Furthermore, the addition of high doses of the antioxidants melatonin, trolox (soluble vitamin E) and GSH fully prevented GLY-induced increase of lipid peroxidation, indicating that free radicals were involved in this effect. GLY also decreased GSH brain concentrations, which was totally blocked by melatonin treatment. Finally, GLY significantly reduced sulfhydryl group content from a commercial GSH solution, but did not oxidize reduced cytochrome C. Our data indicate that oxidative stress elicited in vitro by GLY may possibly contribute at least in part to the pathophysiology of the neurological dysfunction in NKH.

Influence of ketone bodies on oxidative stress parameters in brain of developing rats in vitro.

Pro-oxidant and antioxidant properties have been found for acetoacetate (AcAc) and beta-hydroxybutyrate (BHB) in peripheral tissues. In the present study we investigated the role of AcAc and BHB at concentrations found in diabetic patients during ketoacidotic crises and in individuals affected by succinyl CoA: 3-oxoacid CoA transferase and acetoacetyl-CoA thiolase deficiencies, disorders clinically characterized by neurological symptoms, on a large number of oxidative stress parameters in fresh cerebral cortex of developing rats. Lipid peroxidation (chemiluminescence and thiobarbituric acid-reactive substances levels), protein oxidative damage (carbonyl formation and sulfhydryl oxidation), 2',7'-dichlorofluorescin diacetate oxidation and the non-enzymatic (total antioxidant reactivity and glutathione levels) and enzymatic (glutathione peroxidase, superoxide dismutase and catalase activities) antioxidant defenses were not changed by doses of BHB and AcAc as high as 25 mM in cortical supernatants under basal conditions. Furthermore, BHB did not affect the increased thiobarbituric acid-reactive substances levels provoked by 3-hydroxy-3-methylglutaric and 3-methylglutaconic acids and by a hydroxyl-induced generation system. Finally, BHB and AcAc were not able to oxidize sulfhydryl groups from a commercial GSH solution. Therefore, under basal conditions or under situations with high production of free radicals, AcAc and BHB were not able to reduce or increase the oxidative stress parameters in the brain. Taken together, our present results do not support the hypothesis that BHB and AcAc act as potent direct or indirect pro-oxidants or antioxidants in the CNS.