Pipecolic acid induces oxidative stress in vitro in cerebral cortex of young rats and the protective role of lipoic acid.

Pipecolic acid (PA) levels are increased in severe metabolic disorders of the central nervous system such as Zellweger syndrome, infantile Refsum disease, neonatal adrenoleukodystrophy and hyperlysinemia. The affected individuals present progressive neurological dysfunction, hypotonia and growth retardation. The mechanisms of brain damage of these disorders remain poorly understood. Since PA catabolism can produce H2O2 by oxidases, oxidative stress may be a possible mechanism involved in the pathophysiology of these diseases. Lipoic acid (LA) is considered an efficient antioxidant and has been shown to prevent oxidative stress in experimental models of many disorders of the neurologic system. Considering that to our knowledge no study investigated the role of PA on oxidative stress, in the present work we investigated the in vitro effects of PA on some oxidative stress parameters and evaluated the LA efficacy against possible pro-oxidant effects of PA in cerebral cortex of 14-day-old rats. The activities of catalase (CAT), glutathione peroxidase (GPx), glucose 6-phosphate dehydrogenase (G6PD), and glutathione S-transferase (GST) along with reduced glutathione (GSH) content were significantly decreased, while superoxide dismutase (SOD) activity and thiobarbituric acid-reactive substances (TBA-RS) were significantly enhanced by PA. LA was able to prevent these effects by improving the activity of antioxidant enzymes, increasing GSH content and reducing TBA-RS. In contrast, glutathione reductase and 6-phosphogluconate dehydrogenase activities and sulfhydryl content were not affected. Taken together, it may be presumed that PA in vitro elicits oxidative stress and LA is able to prevent these effects.

Glutathione metabolism enzymes in brain and liver of hyperphenylalaninemic rats and the effect of lipoic acid treatment.

Phenylketonuria (PKU) is a disorder caused by a deficiency in phenylalanine hydroxylase activity, which converts phenylalanine (Phe) to tyrosine, leading to hyperphenylalaninemia (HPA) with accumulation of Phe in tissues of patients. The neuropathophysiology mechanism of disease remains unknown. However, recently the involvement of oxidative stress with decreased glutathione levels in PKU has been reported. Intracellular glutathione (GSH) levels may be maintained by the antioxidant action of lipoic acid (LA). The aim of this study was to evaluate the activity of the enzymes involved in the metabolism and function of GSH, such as glutathione peroxidase (GSH-Px), glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase (GR), glutamate-cysteine ligase (GCL), glutathione-S-transferase (GST) and GSH content in brain and liver of young rats subjected to a chemically induced model of HPA and the effect of LA for a week. In brain, the administration of Phe reduced the activity of the GSH-Px, GR and G6PD and LA prevented these effects totally or partially. GCL activity was increased by HPA and was not affect by LA antioxidant treatment. GST activity did not differ between groups. GSH content was increased by LA and decreased by HPA treatment in brain samples. Considering the liver, all parameters analyzed were increased in studied HPA animals and LA was able to hinder some effects except for the GCL, GST enzymes and GSH content. These results suggested that HPA model alter the metabolism of GSH in rat brain and liver, which may have an important role in the maintenance of GSH function in PKU although liver is not a directly affected organ in this disease. So, an antioxidant therapy with LA may be useful in the treatment of oxidative stress in HPA.

Role of catalase and superoxide dismutase activities on oxidative stress in the brain of a phenylketonuria animal model and the effect of lipoic acid.

Phenylketonuria (PKU) is an inherited metabolic disorder caused by deficiency of phenylalanine hydroxylase which leads to accumulation of phenylalanine and its metabolites in tissues of patients with severe neurological involvement. Recently, many studies in animal models or patients have reported the role of oxidative stress in PKU. In the present work we studied the effect of lipoic acid against oxidative stress in rat brain provoked by an animal model of hyperphenylalaninemia (HPA), induced by repetitive injections of phenylalanine and α-methylphenylalanine (a phenylalanine hydroxylase inhibitor) for 7 days, on some oxidative stress parameters. Lipoic acid prevented alterations on catalase (CAT) and superoxide dismutase (SOD), and the oxidative damage of lipids, proteins, and DNA observed in HPA rats. In addition, lipoic acid diminished reactive species generation compared to HPA group which was positively correlated to SOD/CAT ratio. We also observed that in vitro Phe inhibited CAT activity while phenyllactic and phenylacetic acids stimulated superoxide dismutase activity. These results demonstrate the efficacy of lipoic acid to prevent oxidative stress induced by HPA model in rats. The possible benefits of lipoic acid administration to PKU patients should be considered.

Experimental hyperprolinemia induces mild oxidative stress, metabolic changes, and tissue adaptation in rat liver.

The present study investigated the effects of chronic hyperprolinemia on oxidative and metabolic status in liver and serum of rats. Wistar rats received daily subcutaneous injections of proline from their 6th to 28th day of life. Twelve hours after the last injection the rats were sacrificed and liver and serum were collected. Results showed that hyperprolinemia induced a significant reduction in total antioxidant potential and thiobarbituric acid-reactive substances. The activities of the antioxidant enzymes catalase and superoxide dismutase were significantly increased after chronic proline administration, while glutathione (GSH) peroxidase activity, dichlorofluorescin oxidation, GSH, sulfhydryl, and carbonyl content remained unaltered. Histological analyses of the liver revealed that proline treatment induced changes of the hepatic microarchitecture and increased the number of inflammatory cells and the glycogen content. Biochemical determination also demonstrated an increase in glycogen concentration, as well as a higher synthesis of glycogen in liver of hyperprolinemic rats. Regarding to hepatic metabolism, it was observed an increase on glucose oxidation and a decrease on lipid synthesis from glucose. However, hepatic lipid content and serum glucose levels were not changed. Proline administration did not alter the aminotransferases activities and serum markers of hepatic injury. Our findings suggest that hyperprolinemia alters the liver homeostasis possibly by induction of a mild degree of oxidative stress and metabolic changes. The hepatic alterations caused by proline probably do not implicate in substantial hepatic tissue damage, but rather demonstrate a process of adaptation of this tissue to oxidative stress. However, the biological significance of these findings requires additional investigation.

Regular exercise prevents oxidative stress in the brain of hyperphenylalaninemic rats.

Phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase, leading to accumulation of phenylalanine and its metabolites. Clinical features of PKU patients include mental retardation, microcephaly, and seizures. Oxidative stress has been found in these patients, and is possibly related to neurophysiopatology of PKU. Regular exercise can leads to adaptation of antioxidant system, improving its capacity to detoxification reactive species. The aim of this study was to verify the effects of regular exercise on oxidative stress parameters in the brain of hyperphenylalaninemic rats. Animals were divided into sedentary (Sed) and exercise (Exe) groups, and subdivided into saline (SAL) and hyperphenylalaninemia (HPA). HPA groups were induced HPA through administration of alpha-methylphenylalanine and phenylalanine for 17 days, while SAL groups (n = 16-20) received saline. Exe groups conducted 2-week aerobic exercise for 20 min/day. At 18th day, animals were killed and the brain was homogenized to determine thiobarbituric acid reactives substances (TBA-RS) content, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activities. Soleus muscles were collected to determine glycogen content as a marker of oxidative adaptation. Exe groups showed enhanced glycogen content. HPA condition caused an increase in TBA-RS and SOD, and reduces CAT and GPx. Exercise was able to prevent all changes seen in the HPA group, reaching control values, except for SOD activity. No changes were found in the ExeSAL group compared to SedSAL. Hyperphenylalaninemic rats were more responsive to the benefits provided by regular exercise. Physical training may be an interesting strategy to restore the antioxidant system in HPA.

In vivo neuroprotective effect of L-carnitine against oxidative stress in maple syrup urine disease.

Maple syrup urine disease (MSUD) is an autosomal recessive inborn error of metabolism caused by deficiency of the activity of the mitochondrial enzyme complex branched-chain α-keto acid dehydrogenase (BCKAD) leading to accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine and valine and their corresponding branched-chain α-keto acids. Affected patients present severe brain dysfunction manifested such as ataxia, seizures, coma, psychomotor delay and mental retardation. The mechanisms of brain damage in this disease remain poorly understood. Recent studies have shown that oxidative stress may be involved in neuropathology of MSUD. L-Carnitine (L-Car) is considered a potential antioxidant through its action against peroxidation as a scavenger of reactive oxygen species and by its stabilizing effect of damage to cell membranes. In this study we evaluate the possible neuroprotective in vivo effects of L-Car against pro-oxidative effects of BCAA in cerebral cortex of rats. L-Car prevented lipoperoxidation, measured by thiobarbituric acid-reactive substances, protein damage, measured by sulfhydryl and protein carbonyl content and alteration on catalase and glutathione peroxidase activity in rat cortex from a chemically-induced model of MSUD. Our data clearly show that L-Car may be an efficient antioxidant, protecting against the oxidative stress promoted by BCAA. If the present results are confirmed in MSUD patients, this could represent an additional therapeutic approach to the patients affected by this disease.

Neuroprotective role of lipoic acid against acute toxicity of N-acetylaspartic acid.

N-Acetylaspartic acid (NAA) accumulates in Canavan disease, a severe inherited neurometabolic disorder clinically characterized by mental retardation, hypotonia, macrocephaly, and seizures. The mechanisms of brain damage in this disease remain poorly understood. Recent studies developed by our research group showed that NAA induces oxidative stress in vitro and in vivo in cerebral cortex of rats. Lipoic acid is considered as an efficient antioxidant which can easily cross the blood-brain barrier. Considering the absence of specific treatment to Canavan disease, this study evaluates the possible prevention of the oxidative stress promoted by NAA in vivo by the antioxidant lipoic acid to preliminarily evaluate lipoic acid efficacy against pro-oxidative effects of NAA. Fourteen-day-old Wistar rats received an acute administration of 0.6 mmol NAA/g body weight with or without lipoic acid (40 mg/kg body weight). Catalase (CAT), glutathione peroxidase (GPx), and glucose 6-phosphate dehydrogenase activities, hydrogen peroxide content, thiobarbituric acid-reactive substances (TBA-RS), spontaneous chemiluminescence, protein carbonyl content, total antioxidant potential, and DNA-protein cross-links were assayed in the cerebral cortex of rats. CAT, GPx activities, and total antioxidant potential were significantly reduced, while hydrogen peroxide content, TBA-RS, spontaneous chemiluminescence, and protein carbonyl content were significantly enhanced by acute administration of NAA. Those effects were all prevented by lipoic acid pretreatment. Our results clearly show that lipoic acid may protect against the oxidative stress promoted by NAA. This could represent a new therapeutic approach to the patients affected by Canavan disease.