L-tyrosine induces DNA damage in brain and blood of rats.

Mutations in the tyrosine aminotransferase gene have been identified to cause tyrosinemia type II which is inherited in an autosomal recessive manner. Studies have demonstrated that an excessive production of ROS can lead to reactions with macromolecules, such as DNA, lipids, and proteins. Considering that the L-tyrosine may promote oxidative stress, the main objective of this study was to investigate the in vivo effects of L-tyrosine on DNA damage determined by the alkaline comet assay, in brain and blood of rats. In our acute protocol, Wistar rats (30 days old) were killed 1 h after a single intraperitoneal L-tyrosine injection (500 mg/kg) or saline. For chronic administration, the animals received two subcutaneous injections of L-tyrosine (500 mg/kg, 12-h intervals) or saline administered for 24 days starting at postnatal day (PD) 7 (last injection at PD 31), 12 h after the last injection, the animals were killed by decapitation. We observed that acute administration of L-tyrosine increased DNA damage frequency and damage index in cerebral cortex and blood when compared to control group. Moreover, we observed that chronic administration of L-tyrosine increased DNA damage frequency and damage index in hippocampus, striatum, cerebral cortex and blood when compared to control group. In conclusion, the present work demonstrated that DNA damage can be encountered in brain from animal models of hypertyrosinemia, DNA alterations may represent a further means to explain neurological dysfunction in this inherited metabolic disorder and to reinforce the role of oxidative stress in the pathophysiology of tyrosinemia type II.

Late brain alterations in sepsis-survivor rats.

Central nervous system (CNS) dysfunction secondary to sepsis is characterized by long-term cognitive impairment. It was observed that oxidative damage, energetic metabolism impairment, and cytokine level alteration seen in early times in an animal model of sepsis may persist for up to 10 days and might be associated with cognitive damage. In order to understand these mechanisms, at least in part, we evaluated the effects of sepsis on cytokine levels in the cerebrospinal fluid (CSF), oxidative parameters, and energetic metabolism in the brain of rats at both 30 and 60 days after sepsis induction by cecal ligation and perforation (CLP). To this aim, male Wistar rats underwent CLP with "basic support" or were sham-operated. Both 30 and 60 days after surgery, the CSF was collected and the animals were killed by decapitation. Then, the prefrontal cortex, hippocampus, striatum, and cortex were collected. Thirty days after surgery, an increase of IL-6 level in the CSF; an increase in the thiobarbituric acid-reactive species (TBARS) in prefrontal cortex and a decrease in hippocampus, striatum, and cortex; a decrease of carbonyl protein formation only in prefrontal cortex and an increase in striatum; and an increase in the complex IV activity only in hippocampus were observed. Sixty days after sepsis, an increase of TNF-α level in the CSF; a decrease of TBARS only in hippocampus; an increase of carbonyl protein formation in striatum; and a decrease of complex I activity in prefrontal cortex, hippocampus, and striatum were observed. These findings may contribute to understanding the role of late cognitive impairment. Further studies may address how these findings interact during sepsis development and contribute to CNS dysfunction.

Effect of acute administration of L-tyrosine on oxidative stress parameters in brain of young rats.

Tyrosinemia type II, also known as Richner-Hanhart syndrome, is an autosomal recessive inborn error of metabolism caused by a deficiency of hepatic cytosolic tyrosine aminotransferase, and is associated with neurologic and development difficulties in numerous patients. Considering that the mechanisms underlying the neurological dysfunction in hypertyrosinemic patients are poorly known and that studies demonstrated that high concentrations of tyrosine provoke oxidative stress in vitro and in vivo in the cerebral cortex of rats, in the present study we investigate the oxidative stress parameters (enzymatic antioxidant defenses, thiobarbituric acid-reactive substances and protein carbonyl content) in cerebellum, hippocampus and striatum of 30-old-day rats after acute administration of L-tyrosine. Our results demonstrated that the acute administration of L-tyrosine increased the thiobarbituric acid reactive species levels in hippocampus and the carbonyl levels in cerebellum, hippocampus and striatum. In addition, acute administration of L-tyrosine significantly decreased superoxide dismutase activity in cerebellum, hippocampus and striatum, while catalase was increased in striatum. In conclusion, the oxidative stress may contribute, along with other mechanisms, to the neurological dysfunction characteristic of hypertyrosinemia and the administration of antioxidants may be considered as a potential adjuvant therapy for tyrosinemia, especially type II.

Histone deacetylase inhibitors reverse manic-like behaviors and protect the rat brain from energetic metabolic alterations induced by ouabain.

Studies have revealed alterations in mitochondrial complexes in the brains of bipolar patients. However, few studies have examined changes in the enzymes of the tricarboxylic acid cycle. Several preclinical studies have suggested that histone deacetylase inhibitors may have antimanic effects. The present study aims to investigate the effects of lithium, valproate and sodium butyrate, a histone deacetylase inhibitor, on the activity of tricarboxylic acid cycle enzymes in the brains of rats subjected to an animal model of mania induced by ouabain. Wistar rats received a single intracerebroventricular injection of ouabain or cerebrospinal fluid. Starting on the day following the intracerebroventricular injection, the rats were treated for 7days with intraperitoneal injections of saline, lithium, valproate or sodium butyrate. Risk-taking behavior, locomotor and exploratory activities were measured using the open-field test. Citrate synthase, succinate dehydrogenase, and malate dehydrogenase were examined in the frontal cortex and hippocampus. All treatments reversed ouabain-related risk-taking behavior and hyperactivity in the open-field test. Ouabain inhibited tricarboxylic acid cycle enzymes in the brain, and valproate and sodium butyrate but not lithium reversed this ouabain-induced dysfunction. Thus, protecting the tricarboxylic acid cycle may contribute to the therapeutic effects of histone deacetylase inhibitors.

Effect of L-tyrosine in vitro and in vivo on energy metabolism parameters in brain and liver of young rats.

Tyrosinemia is a rare disease caused by a single mutation to the gene that code for the enzyme responsible for tyrosine catabolism. Because the mechanisms underlying the neurological dysfunction in hypertyrosinemic patients are poorly understood, we evaluated the in vitro and in vivo effect of L-tyrosine on the activities of the enzymes citrate synthase, malate dehydrogenase, succinate dehydrogenase and complexes of the mitochondrial respiratory chain in the brains and livers of young rats. Thirty-day-old Wistar rats were killed by decapitation, and the brains and livers were harvested. L-Tyrosine (0.1, 1.0, 2.0 or 4.0 mM) was added to the reaction medium. For in vivo studies, Wistar rats were killed 1 h after a single intraperitoneal injection of either tyrosine (500 mg/kg) or saline. The activities of energy metabolism enzymes were evaluated. In this research, we demonstrated in vitro that L-tyrosine inhibited citrate synthase activity in the posterior cortex and that succinate dehydrogenase was increased in the posterior cortex, hippocampus, striatum and liver. The complex I activity was only inhibited in the hippocampus, whereas complex II activity was inhibited in the hippocampus, cortex and liver. Complex IV activity decreased in the posterior cortex. The acute administration of L-tyrosine inhibited enzyme malate dehydrogenase, citrate synthase and complexes II, II-III and IV in the posterior cortex and liver. The enzyme succinate dehydrogenase and complex I activity were inhibited in the posterior cortex and increased in the striatum. These results suggest impairment in energy metabolism that is likely mediated by oxidative stress.

Brain energy metabolism is increased by chronic administration of bupropion.

OBJECTIVES: Based on the hypothesis that energy impairment may be involved in the pathophysiology of depression, we evaluated the activities of citrate synthase, malate dehydrogenase, succinate dehydrogenase (SDH), mitochondrial respiratory chain complexes I, II, II-III, IV and creatine kinase (CK) in the brain of rats submitted to chronic administration of bupropion. METHODS: Animals received daily administration of bupropion dissolved in saline (10 mg/kg, intraperitoneal) at 1.0 ml/kg body weight. The rats received injections once a day for 14 days; control rats received an equivalent volume of saline. Twelve hours after the last administration, the rats were killed by decapitation and brain was rapidly removed and kept on an ice plate. The activities of the enzymes were measured in different brain areas. RESULTS: We observed that the activities of citrate synthase and malate dehydrogenase, mithocondrial respiratory chain complexes I, II-III and IV and CK were not altered after chronic administration of bupropion. However, SDH activity was increased in the prefrontal cortex and cerebellum. In the hippocampus, cerebellum and striatum the activity of complex II was increased after chronic administration of bupropion. CONCLUSIONS: Our results demonstrated that bupropion increased some enzymes of brain energy metabolism. These findings are in accordance with other studies which showed that some antidepressants may improve energy metabolism. The present results reinforce the hypothesis that antidepressants modulate brain energy metabolism.

L-tyrosine administration increases acetylcholinesterase activity in rats.

Tyrosinemia is a rare genetic disease caused by mutations on genes that codify enzymes responsible for tyrosine metabolism. Considering that tyrosinemics patients usually present symptoms associated with central nervous system alterations that ranges from slight decreases in intelligence to severe mental retardation, we decided to investigate whether acute and chronic administration of L-tyrosine in rats would affect acetylcholinesterase mRNA expression and enzymatic activity during their development. In our acute protocol, Wistar rats (10 and 30 days old) were killed one hour after a single intraperitoneal L-tyrosine injection (500 mg/kg) or saline. Chronic administration consisted of L-tyrosine (500 mg/kg) or saline injections 12 h apart for 24 days in Wistar rats (7 days old) and rats were killed 12 h after last injection. Acetylcholinesterase activity was measured by Ellman's method and acetylcholinesterase expression was carried out by a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) assay. We observed that acute (10 and 30 days old rats) and chronic L-tyrosine administration increased acetylcholinesterase activity in serum and all tested brain areas (hippocampus, striatum and cerebral cortex) when compared to control group. Moreover, there was a significant decrease in mRNA levels of acetylcholinesterase in hippocampus was observed after acute protocol (10 and 30 days old rats) and in striatum after chronic protocol. In case these alterations also occur in the brain of the patients, our results may explain, at least in part, the neurological sequelae associated with high plasma concentrations of tyrosine seen in patients affected by tyrosinemia type II.

Mitochondrial respiratory chain activity in an animal model of mania induced by ouabain.

OBJECTIVES: Bipolar disorder (BD) is a mental illness associated with higher rates of suicide. The present study aims to investigate the brain mitochondrial respiratory chain activity in an animal model of mania induced by ouabain. METHODS: Adult male Wistar rats received a single intracerebroventricular administration of ouabain (10-3 and 10-2 M) or vehicle. Locomotor activity was measured using the open field test. Mitochondrial respiratory chain activity was measured in the brain of rats 1 h and 7 days after ouabain administration. RESULTS: Our results showed that spontaneous locomotion was increased 1 h and 7 days after ouabain administration. Complexes I, III and IV activities were increased in the prefrontal cortex, hippocampus and striatum immediately after the administration of ouabain, at the concentration of 10-3 and 10-2 M. Moreover, complex II activity was increased only in the prefrontal cortex at the concentration of 10-2 M. On the other hand, no significant alterations were observed in complex I activity 7 days after ouabain administration. However, an increase in complexes II, III and IV activities was observed only in the prefrontal cortex at the concentration of 10-2 M. CONCLUSION: Our findings suggest an increase in the activities of mitochondrial respiratory chain in this model of mania. A possible explanation is that these findings occur as a rebound effect trying to compensate for a decrease of ATP deprivation in BD. The present findings suggest that this model may present good face validity and a limitation in construct validity.

Effect of chronic administration of ketamine on the mitochondrial respiratory chain activity caused by chronic mild stress.

UNLABELLED: Rezin GT, Gonçalves CL, Daufenbach JF, Carvalho-Silva M, Borges LS, Vieira JS, Hermani FV, Comim CM, Quevedo J, Streck EL. Effect of chronic administration of ketamine on the mitochondrial respiratory chain activity caused by chronic mild stress. OBJECTIVE: Recently, we reported that mitochondrial respiratory chain complexes I, III and IV were inhibited in the cerebral cortex and cerebellum of rats submitted to chronic mild stress (CMS) and that acute ketamine administration reversed this effect. Therefore, we investigated whether the inhibition of these enzymes may be reversed by chronic administration of ketamine. METHODS: Adult male Wistar rats were submitted to CMS and chronically treated with ketamine. After 40 days of CMS, consumption of sweet food, adrenal gland weight, body weight and enzymatic activity of the complexes were measured. RESULTS: We verified that CMS decreased the intake of sweet food, increased the adrenal gland weight and the control group gained weight after 40 days but the stressed group did not; ketamine administration reversed these effects. We also verified that chronic administration of ketamine reversed the inhibition of complexes I, III and IV in cerebral cortex. However, in cerebellum, only complex IV inhibition was reversed. The chronic ketamine administration partially reverses the inhibition caused by CMS. CONCLUSION: We hypothesise that CMS inhibits complexes I, III and IV activities and that chronic administration of ketamine administration partially reverses such an effect. Therefore, it seems reasonable to propose that ketamine administration might be a useful therapy for patients affected by major depression.