Tetrahydrobiopterin: Beyond Its Traditional Role as a Cofactor.

Tetrahydrobiopterin (BH4) is an endogenous cofactor for some enzymatic conversions of essential biomolecules, including nitric oxide, and monoamine neurotransmitters, and for the metabolism of phenylalanine and lipid esters. Over the last decade, BH4 metabolism has emerged as a promising metabolic target for negatively modulating toxic pathways that may result in cell death. Strong preclinical evidence has shown that BH4 metabolism has multiple biological roles beyond its traditional cofactor activity. We have shown that BH4 supports essential pathways, e.g., to generate energy, to enhance the antioxidant resistance of cells against stressful conditions, and to protect from sustained inflammation, among others. Therefore, BH4 should not be understood solely as an enzyme cofactor, but should instead be depicted as a cytoprotective pathway that is finely regulated by the interaction of three different metabolic pathways, thus assuring specific intracellular concentrations. Here, we bring state-of-the-art information about the dependency of mitochondrial activity upon the availability of BH4, as well as the cytoprotective pathways that are enhanced after BH4 exposure. We also bring evidence about the potential use of BH4 as a new pharmacological option for diseases in which mitochondrial disfunction has been implicated, including chronic metabolic disorders, neurodegenerative diseases, and primary mitochondriopathies.

d-Serine administration provokes lipid oxidation and decreases the antioxidant defenses in rat striatum.

The present work investigated the effects of intrastriatal administration of d-serine on relevant parameters of oxidative stress in striatum of young rats. d-Serine significantly induced lipid peroxidation, reflected by the significant increase of thiobarbituric acid-reactive substances, and significantly diminished the striatum antioxidant defenses, as verified by a decrease of the levels of reduced glutathione and total antioxidant status. Finally, d-serine inhibited superoxide dismutase activity, without altering the activities of glutathione peroxidase and catalase. In contrast, this d-amino acid did not alter sulfhydryl oxidation, a measure of protein oxidative damage. The present data indicate that d-serine in vivo administration induces lipid oxidative damage and decreases the antioxidant defenses in the striatum of young rats. Therefore, it is presumed that this oxidative stress may be a pathomechanism involved at least in part in the neurological damage found in patients affected by disorders in which d-serine metabolism is compromised, leading to altered concentrations of this d-amino acid.

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.

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.

Lysine induces lipid and protein damage and decreases reduced glutathione concentrations in brain of young rats.

The present work investigated the in vitro effects of lysine on important parameters of oxidative stress in cerebral cortex of young rats. Our results show that lysine 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 lysine-induced lipid oxidative damage, suggesting that free radicals were involved in this effect. Lysine also significantly diminished glutathione levels in cortical supernatants, decreasing, therefore, the major brain antioxidant defense. Finally, lysine markedly oxidized a glutathione commercial solution in a medium devoid of brain supernatants, indicating that it behaved as a direct acting oxidant. The present data indicate that lysine induces oxidative stress in cerebral cortex of young rats. Therefore, it is presumed that this pathomechanism may be involved at least in part in the neurological damage found in patients affected by disorders with hyperlysinemia.