Nitric oxide synthase inhibition by L-NAME prevents the decrease of Na+,K+-ATPase activity in midbrain of rats subjected to arginine administration

In vitro galactose impairs energy metabolism in the brain of young rats: protective role of antioxidants

We, herein, investigated the in vitro effects of galactose on the activity of pyruvate kinase, succinate dehydrogenase (SDH), complex II and IV (cytochrome c oxidase) of the respiratory chain and Na+K+-ATPase in the cerebral cortex, cerebellum and hippocampus of 30-day-old rats. We also determined the influence of the antioxidants, trolox, ascorbic acid and glutathione, on the effects elicited by galactose. Galactose was added to the assay at concentrations of 0.1, 3.0, 5.0 and 10.0 mM. Control experiments were performed without galactose. Galactose, at 3.0, 5.0 and 10.0 mM, decreased pyruvate kinase activity in the cerebral cortex and at 10.0 mM in the hippocampus. Galactose, at 10.0 mM, reduced SDH and complex II activities in the cerebellum and hippocampus, and reduced cytochrome c oxidase activity in the hippocampus. Additionally, decreased Na+K+-ATPase activity in the cerebral cortex and hippocampus; conversely, galactose, at 3.0 and 5.0 mM, increased this enzyme's activity in the cerebellum. Data show that galactose disrupts energy metabolism and trolox, ascorbic acid and glutathione addition prevented the majority of alterations in the parameters analyzed, suggesting the use of antioxidants as an adjuvant therapy in Classic galactosemia.

Argininic acid alters markers of cellular oxidative damage in vitro: Protective role of antioxidants

We, herein, investigated the in vitro effects of argininic acid on thiobarbituric acid-reactive substances (TBA-RS), total sulfhydryl content and on the activities of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in the blood, kidney and liver of 60-day-old rats. We also verified the influence of the antioxidants (each at 1.0mM) trolox and ascorbic acid, as well as of N^G-nitro-l-arginine methyl ester (L-NAME) at 1.0mM, a nitric oxide synthase inhibitor, on the effects elicited by argininic acid on the parameters tested. The liver, renal cortex and renal medulla were homogenized in 10vol (1:10w/v) of 20mM sodium phosphate buffer, pH 7.4, containing 140mM KCl; and erythrocytes and plasma were prepared from whole blood samples obtained from rats. For in vitro experiments, the samples were pre-incubated for 1h at 37°C in the presence of argininic acid at final concentrations of 0.1, 1.0 and 5.0μM. Control experiments were performed without the addition of argininic acid. Results showed that argininic acid (5.0μM) enhanced CAT and SOD activities and decreased GSH-Px activity in the erythrocytes, increased CAT and decreased GSH-Px activities in the renal cortex and decreased CAT and SOD activities in the renal medulla of 60-day-old rats, as compared to the control group. Antioxidants and/or L-NAME prevented most of the alterations caused by argininic acid on the oxidative stress parameters evaluated. Data suggest that argininic acid alters antioxidant defenses in the blood and kidney of rats; however, in the presence of antioxidants and L-NAME, most of these alterations in oxidative stress were prevented. These findings suggest that oxidative stress may be make an important contribution to the damage caused by argininic acid in hyperargininemic patients and that treatment with antioxidants may be beneficial in this pathology.

Spermidine decreases Na⁺,K⁺-ATPase activity through NMDA receptor and protein kinase G activation in the hippocampus of rats

Spermidine is an endogenous polyamine with a polycationic structure present in the central nervous system of mammals. Spermidine regulates biological processes, such as Ca(2+) influx by glutamatergic N-methyl-d-aspartate receptor (NMDA receptor), which has been associated with nitric oxide synthase (NOS) and cGMP/PKG pathway activation and a decrease of Na(+),K(+)-ATPase activity in rats' cerebral cortex synaptosomes. Na(+),K(+)-ATPase establishes Na(+) and K(+) gradients across membranes of excitable cells and by this means maintains membrane potential and controls intracellular pH and volume. However, it has not been defined whether spermidine modulates Na(+),K(+)-ATPase activity in the hippocampus. In this study we investigated whether spermidine alters Na(+),K(+)-ATPase activity in slices of hippocampus from rats, and possible underlying mechanisms. Hippocampal slices and homogenates were incubated with spermidine (0.05-10 μM) for 30 min. Spermidine (0.5 and 1 μM) decreased Na(+),K(+)-ATPase activity in slices, but not in homogenates. MK-801 (100 and 10 μM), a non-competitive antagonist of NMDA receptor, arcaine (0.5μM), an antagonist of the polyamine binding site at the NMDA receptor, and L-NAME (100μM), a NOS inhibitor, prevented the inhibitory effect of spermidine (0.5 μM). ODQ (10 μM), a guanylate cyclase inhibitor, and KT5823 (2 μM), a protein kinase G inhibitor, also prevented the inhibitory effect of spermidine on Na(+),K(+)-ATPase activity. Spermidine (0.5 and 1.0 μM) increased NO(2) plus NO(3) (NOx) levels in slices, and MK-801 (100 μM) and arcaine (0.5 μM) prevented the effect of spermidine (0.5 μM) on the NOx content. These results suggest that spermidine-induced decrease of Na(+),K(+)-ATPase activity involves NMDA receptor/NOS/cGMP/PKG pathway.

A more accurate profile of Achyrocline satureioides hypocholesterolemic activity

The aim of this study was to investigate the effect of the aqueous extract (AE) of Achyrocline satureioides on serum lipid profile, liver oxidative profile and Na(+),K(+)-ATPase activity of rats submitted to a hyperlipidic diet. The animals were divided into four groups: control (C), AE 10% (A(10)), hyperlipidic (H) and hyperlipidic/AE 10% (HA(10)). In serum, we measured the levels of total cholesterol (TC), high-density lipoprotein, very-low-density lipoprotein, low-density lipoprotein (LDL) and triglyceride (TG). In liver homogenates, we measured the thiobarbituric acid reactive substances, the carbonyl proteins, the non-protein thiols (NPSHs) and the activity of superoxide dismutase, catalase (CAT) and Na(+),K(+)-ATPase. We observed a significant increase in the TC and LDL levels in the H group. A. satureioides prevented these effects, decreased the TG levels in the HA(10) group and increased the NPSH levels in the A(10) and HA(10) groups. The H group showed an increase in the carbonyl protein level and a decrease in CAT and Na(+),K(+)-ATPase activities. With the use of this model, results show that increased levels of lipids are related to a redox imbalance in the liver, which is also related to the inhibition of Na(+),K(+)-ATPase activity, and that chronic administration of the AE of A. satureioides is capable of changing this profile.

3-Methylcrotonylglycine disrupts mitochondrial energy homeostasis and inhibits synaptic Na(+),K (+)-ATPase activity in brain of young rats

Deficiency of 3-methylcrotonyl-CoA carboxylase activity is an inherited metabolic disease biochemically characterized by accumulation and high urinary excretion of 3-methylcrotonylglycine (3MCG), and also of 3-hydroisovalerate in lesser amounts. Affected patients usually have neurologic dysfunction, brain abnormalities and cardiomyopathy, whose pathogenesis is still unknown. The present study investigated the in vitro effects of 3MCG on important parameters of energy metabolism, including CO(2) production from labeled acetate, enzyme activities of the citric acid cycle, as well as of the respiratory chain complexes I-IV (oxidative phosphorylation), creatine kinase (intracellular ATP transfer), and synaptic Na(+),K(+)-ATPase (neurotransmission) in brain cortex of young rats. 3MCG significantly reduced CO(2) production, implying that this compound compromises citric acid cycle activity. Furthermore, 3MCG diminished the activities of complex II-III of the respiratory chain, mitochondrial creatine kinase and synaptic membrane Na(+),K(+)-ATPase. Furthermore, antioxidants were able to attenuate or fully prevent the inhibitory effect of 3MCG on creatine kinase and synaptic membrane Na(+),K(+)-ATPase activities. We also observed that lipid peroxidation was elicited by 3MCG, suggesting the involvement of free radicals on 3MCG-induced effects. Considering the importance of the citric acid cycle and the electron flow through the respiratory chain for brain energy production, creatine kinase for intracellular energy transfer, and Na(+),K(+)-ATPase for the maintenance of the cell membrane potential, the present data indicate that 3MCG potentially impairs mitochondrial brain energy homeostasis and neurotransmission. It is presumed that these pathomechanisms may be involved in the neurological damage found in patients affected by 3-methylcrotonyl-CoA carboxylase deficiency.

Role of antioxidants on Na(+),K (+)-ATPase activity and gene expression in cerebral cortex of hyperprolinemic rats

Considering that Na(+),K(+)-ATPase is an embedded-membrane enzyme and that experimental chronic hyperprolinemia decreases the activity of this enzyme in brain synaptic plasma membranes, the present study investigated the effect of chronic proline administration on thiobarbituric acid-reactive substances, as well as the influence of antioxidant vitamins E plus C on the effects mediated by proline on Na(+),K(+)-ATPase activity in cerebral cortex of rats. The expression of Na(+),K(+)-ATPase catalytic subunits was also evaluated. Results showed that proline increased thiobarbituric acid-reactive substances, suggesting an increase of lipid peroxidation. Furthermore, concomitant administration of vitamins E plus C significantly prevented the increase of lipid peroxidation, as well as the inhibition of Na(+),K(+)-ATPase activity caused by proline. We did not observe any change in levels of Na(+),K(+)-ATPase mRNA transcripts after chronic exposure to proline and vitamins E plus C. These findings provide insights into the mechanisms through which proline exerts its effects on brain function and suggest that treatment with antioxidants may be beneficial to treat neurological dysfunctions present in hyperprolinemic patients.

Protective effect of antioxidants on blood oxidative stress caused by arginine

In this study, we investigated in vivo and in vitro effect of arginine on parameters of oxidative stress namely thiobarbituric acid-reactive substances (TBA-RS) and total radical-trapping antioxidant parameter (TRAP) in plasma and on the antioxidant enzymes activities catalase (CAT), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) in erythrocytes of rats. Results showed that acute administration reduced TRAP and CAT activity and increased TBA-RS. Furthermore, in vitro studies did not alter oxidative parameters studied. The influence of N(ω)-nitro-L-arginine methyl ester (L-NAME) and antioxidants (α-tocopherol plus ascorbic acid) on the effects elicited by arginine was also studied. In addition, simultaneous injection of L-NAME or treatment with antioxidants prevented the alteration on TRAP, TBA-RS, and CAT activity caused by arginine. Data indicate that oxidative stress induction is probably mediated by the generation of NO and/or ONOO(-) and other free radicals, because L-NAME and these antioxidants prevented these effects caused by arginine.

Neurochemical evidence that lysine inhibits synaptic Na+,K+-ATPase activity and provokes oxidative damage in striatum of young rats in vivo

Lysine (Lys) accumulation in tissues and biological fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and other inherited metabolic disorders. In the present study we investigated the effects of acute administration of Lys on relevant parameters of energy metabolism and oxidative stress in striatum of young rats. We verified that Lys in vivo intrastriatal injection did not change the citric acid cycle function and creatine kinase activity, but, in contrast, significantly inhibited synaptic Na(+),K(+)-ATPase activity in striatum prepared 2 and 12 h after injection. Moreover, Lys induced lipid peroxidation and diminished the concentrations of glutathione 2 h after injection. These effects were prevented by the antioxidant scavengers melatonin and the combination of α-tocopherol and ascorbic acid. Lys also inhibited glutathione peroxidase activity 12 h after injection. Therefore it is assumed that inhibition of synaptic Na(+),K(+)-ATPase and oxidative damage caused by brain Lys accumulation may possibly contribute to the neurological manifestations of FH and other neurometabolic conditions with high concentrations of this amino acid.

Profiling of oxidative stress in patients with inborn errors of metabolism

Free radical formation resulting in oxidative stress is a hallmark of mitochondrial dysfunction. Indeed, oxidative stress has been demonstrated to be an underlying pathophysiologic process in various inborn errors of metabolism. Metabolic profiling of oxidative stress may provide a non-specific measure of disease activity that may further enable physicians to monitor disease. In the present study, we investigated two markers of oxidative damage in urinary samples from IEM subjects and controls: F-2 isoprostanes, a measure of lipid peroxidation and di-tyrosine, a measure of protein oxidation. We also determined urinary antioxidant activity in these samples. Subsets of IEM patients showed significantly higher levels of the damage markers isoprostanes and di-tyrosine. Of note, patients with cobalamin disorders (i.e., CblB and CblC) consistently had the highest levels of oxidative damage markers. Lower urine antioxidant capacity was seen in all subject categories, particularly cobalamin disorders and propionic acidemia. Longitudinal studies in subjects with MSUD showed good concordance between markers of oxidative damage and acute decompensation. Overall, quantifying oxidative stress offers a unique perspective to IEM. These measures may provide a means of addressing mitochondrial function in IEM and aid in the development of therapeutic targets and clinical monitoring in this diverse set of disorders.

Protective effect of antioxidants on cerebrum oxidative damage caused by arginine on pyruvate kinase activity

We have demonstrated that acute arginine administration decreases antioxidant defenses and compromises enzymes of respiratory chain in rat brain. In this study we evaluated in vivo and in vitro effect of arginine on pyruvate kinase activity, as well as its effect on an important parameter of oxidative stress namely thiobarbituric acid-reactive substances (TBA-RS) in cerebrum of rats. We also tested the influence of antioxidants, namely alpha -tocopherol plus ascorbic acid on the effects elicited by arginine in order to investigate the possible participation of free radicals on the effects of arginine on these parameters. Results showed that arginine acute administration inhibited pyruvate kinase activity in cerebrum of rats, as well as increased TBA-RS. By the other hand, arginine added to the incubation medium, in vitro studies, did not alter these parameters in rat cerebrum. In addition, pretreatment with antioxidants prevented the reduction of pyruvate kinase activity and the increase of TBA-RS caused by arginine. The data indicate that acute administration of arginine induces lipid peroxidation in rat cerebrum and that the inhibition of pyruvate kinase activity caused by this amino acid was probably mediated by free radicals since antioxidants prevented such effect. It is presumed that these results might be associated, at least in part, with the neuronal dysfunction of patients affected by hyperargininemia. Finally, we suggest that the administration of antioxidants should be considered as an adjuvant therapy to specific diets in hyperargininemia.

The study of Na+, K(+)-ATPase activity of rat brain during Crush syndrome

Crush syndrome (CS) results from severe traumatic damage to the organism that is characterized by stress, acute homeostatic failure of the tissues, and myoglobinuria with severe intoxication. This leads to an acute impairment of kidneys and heart. The peripheral and central nervous systems are also the subject of significant changes in CS. Na(+), K(+)-ATPase is a critical enzyme in neuron that is essential for the regulation of neuronal membrane potential, cell volume as well as transmembrane fluxes of Ca(++) and Excitatory Amino Acids. In the present study, Na(+), K(+)-ATPase activity of rat brain regions [Olfactory lobes (OL), Cerebral cortex (CC), Cerebellum (CL), and Medulla oblongata (MO)] during CS was investigated. Experimental model of CS in albino rats was induced by 2-h of compression followed by 2, 24, and 48-h of decompression of femoral muscle tissue. In this study, we have observed elevation in Na(+), K(+)-ATPase activity above normal/control levels in all parts of brain (OL: 34.4%; CC: 1.0%; CL: 3.3% and MO: 45%) during 2-h compression in comparison to controls.

Inhibition of CO(2) production from glucose by arginine in brain slices of rats

In the present study we evaluated the in vivo effect of arginine on CO(2) production from glucose in a medium with physiological and high extracellular K(+) concentrations. We also tested the influence of the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), on the effects elicited by arginine in order to investigate the possible participation of NO and/or its derivatives on the effects of arginine on CO(2) production from glucose. Sixty-day-old rats were treated with a single intraperitoneal injection of saline (control; group I), arginine (0.8 g/kg; group II), L-NAME (2.0 mg/kg; group III) or arginine (0.8 g/kg) plus L-NAME (2.0 mg/kg; group IV) and were killed 1 h later. Results showed that arginine administration inhibited CO(2) production from glucose at physiological extracellular K(+) concentration and L-NAME prevented such effect. In contrast, arginine administration had no effect on CO(2) production from glucose at high extracellular K(+) concentration. Based on these data, we also investigated the in vitro effect of arginine on CO(2) production from glucose in a medium with physiological extracellular K(+) concentration in hippocampus slices. Results showed that arginine (0.1-1.5 mM) when added to the incubation medium did not alter CO(2) production from glucose in hippocampus slices of untreated rats. In addition, we also demonstrated that arginine inhibits Na(+), K(+)-ATPase activity. The data indicate that the reduction of CO(2) production by arginine was probably mediated by NO and/or its derivatives, which could act inhibiting the activity of Na(+), K(+)-ATPase. The results suggest that arginine impairs energy metabolism in hippocampus slices of rats.

NTPDase and 5'-nucleotidase activities of synaptosomes from hippocampus of rats subjected to hyperargininemia

ATP is an important excitatory neurotransmitter and adenosine acts as a neuromodulatory structure inhibiting neurotransmitters release in the central nervous system. Since the ecto-nucleotidase cascade that hydrolyzes ATP to adenosine is involved in the control of brain functions and previous studies realized in our laboratory have recently reported that acute administration of Arg decreases the NTPDase and 5'-nucleotidase activities of rat blood serum, in the present study we investigated the effect of arginine administration on NTPDase and 5'-nucleotidase activities by synaptosomes from hippocampus of rats. First, sixty-days-old rats were treated with a single or a triple intraperitoneal injection of arginine (0.8 g/Kg) or an equivalent volume of 0.9% saline solution (control) and were killed 1 h later. Second, rats received an intracerebroventricular injection of 1.5 mM arginine solution or saline (5 microL) and were killed 1 h later. We also tested the in vitro effect of arginine (0.1-1.5 mM) on nucleotide hydrolysis in synaptosomes from rat hippocampus. Results showed that intraperitoneal arginine administration did not alter nucleotide hydrolysis. On the other hand, arginine administered intracerebroventricularly reduced ATP (32%), ADP (30%) and AMP (21%) hydrolysis, respectively. In addition, arginine added to the incubation medium, provoked a decrease on ATP (19%), ADP (17%) and AMP (23%) hydrolysis, respectively. Furthermore, kinetic studies showed that the inhibitory effect of arginine was uncompetitive in relation to ATP, ADP and AMP. In conclusion, according to our results it seems reasonable to postulate that arginine alters the cascade involved in the extracellular degradation of ATP to adenosine.

Arginine administration reduces creatine kinase activity in rat cerebellum

In the present study were evaluated the in vivo effects of arginine administration on creatine kinase (CK) activity in cerebellum of rats. We also tested the influence of antioxidants, namely alpha-tocopherol and ascorbic acid and the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), on the effects elicited by Arg in order to investigate the possible participation of nitric oxide (NO) and/or its derivatives peroxynitrite (ONOO(-)) and other/or free radicals on the effects of arginine on CK activity. Sixty-day-old rats were treated with a single i.p. injection of saline (control, group I), arginine (0.8 g/kg) (group II), L-NAME (2.0 mg/kg or 20.0 mg/kg) (group III) or Arg (0.8 g/kg) plus L-NAME (2.0 mg/kg or 20.0 mg/kg) (group IV) and were killed 1 h later. In another set of experiments, the animals were pretreated for 1 week with daily i.p. administration of saline (control) or alpha-tocopherol (40 mg/kg) and ascorbic acid (100 mg/kg). Twelve hours after the last injection of the antioxidants, the rats received one i.p. injection of arginine (0.8 g/kg) or saline and were killed 1 h later. Results showed that total and cytosolic CK activities were significantly inhibited by arginine administration in cerebellum of rats, in contrast to mitochondrial CK activity which was not affected by this amino acid. Furthermore, simultaneous injection of L-NAME (20.0 mg/kg) and treatment with alpha-tocopherol and ascorbic acid prevented these effects. The data indicate that the reduction of CK activity in cerebellum of rats caused by arginine was probably mediated by NO and/or its derivatives ONOO(-)and other free radicals. Considering the importance of CK for the maintenance of energy homeostasis in the brain, if this enzyme inhibition also occurs in hyperargininemic patients, it is possible that CK inhibition may be one of the mechanisms by which arginine is neurotoxic in hyperargininemia.

PKU is a reversible neurodegenerative process within the nigrostriatum that begins as early as 4 weeks of age in Pah(enu2) mice

Phenylketonuria (PKU) is a common genetic disorder in humans that arises from deficient activity of phenylalanine hydroxylase (PAH), which catalyzes the conversion of phenylalanine to tyrosine. There is a resultant hyperphenylalanemia with subsequent impairment in cognitive abilities, executive functions and motor coordination. The neuropathogenesis of the disease has not been completely elucidated, however, oxidative stress is considered to be a key feature of the disease process. Hyperphenylalanemia also adversely affects monoaminergic metabolism in the brain. For this reason we chose to evaluate the nigrostriatum of Pah(enu2) mice, to determine if alterations of monoamine metabolism resulted in morphologic nigrostriatal pathology. Furthermore, we believe that recent developments in adeno-associated virus (AAV)-based vectors have greatly increased the potential for long-term gene therapy and may be a viable alternative to dietary treatment for this metabolic disorder. In this study we identified neurodegenerative changes with regenerative responses in the nigrostriatum of Pah(enu2) mice that are consistent with oxidative injury and occurred as early as 4 weeks of age. These neuropathologic changes were reversed following portal vein delivery of a recombinant adeno-associated virus-mouse phenylalanine hydroxylase-woodchuck hepatitis virus post-transcriptional response element (rAAV-mPAH-WPRE) vector to Pah(enu2) mice and corresponded to rapid reduction of serum Phe levels.

NO donors inhibit Na,K-ATPase activity by a protein kinase G-dependent mechanism in the nonpigmented ciliary epithelium of the porcine eye

1. We developed a novel method to isolate nonpigmented epithelial (NPE) cells from porcine eyes in order to examine Na,K-ATPase responses to nitric oxide (NO) donors specifically in the epithelium. 2. Cells were treated with NO donors and other test compounds for 20 min prior to Na,K-ATPase activity measurement. 3. NO donors, sodium nitroprusside (SNP, 1 microM-1 mM), sodium azide (100 nM-1 microM) and S-nitroso-N-acetylpenicillamine (1 microM-1 mM) caused significant concentration-dependent inhibition of Na,K-ATPase activity. Detection of nitrite in the medium of L-arginine and SNP-treated NPE confirmed NO generation. 4. Concentration-dependent inhibition of Na,K-ATPase was also obtained by L-arginine (1-3 mM), a physiological precursor of NO and 8p-CPT-cGMP (1-100 microM), a cell permeable analog of cGMP. The L-arginine effect was abolished when the NO synthesizing enzyme, NO-synthase, was inhibited by L-NAME (100 microM). 5. The inhibitory effect of SNP or sodium azide on Na,K-ATPase activity was suppressed by soluble guanylate cyclase (sGC) inhibitors, ODQ (10 microM) or methylene blue (10 microM). 6. The inhibitory effect of 8p-CPT-cGMP on Na,K-ATPase was abolished by protein kinase G (PKG) inhibitors, H-8 (1 microM) and H-9 (20 microM), but not by the protein kinase A (PKA) inhibitor H-89 (100 nM). H-8 and H-9 partially suppressed the inhibitory effect of SNP on Na,K-ATPase. 7. Taken together the results indicate that Na,K-ATPase inhibition response to NO donors involves activation of sGC, generation of cGMP and activation of PKG. These findings suggest that Na,K-ATPase inhibition in NPE may contribute to the ability of NO donors to reduce aqueous humor secretion.

Alpha-tocopherol and ascorbic acid administration prevents the impairment of brain energy metabolism of hyperargininemic rats

1. We have previously demonstrated that arginine administration induces oxidative stress and compromises energy metabolism in rat hippocampus. In the present study we initially investigated the influence of pretreatment with alpha-tocopherol and ascorbic acid on the effects produced by arginine on hippocampus energy metabolism. We also tested the effect of acute administration of arginine on various parameters of energy metabolism, namely glucose uptake, lactate release and on the activities of succinate dehydrogenase, complex II and cytochrome c oxidase in rat cerebellum, as well as the influence of pretreatment with alpha-tocopherol and ascorbic acid on the effects elicited by arginine on this structure. 2. Sixty-day-old female Wistar rats were treated with a single i.p. injection of saline (control) or arginine (0.8 g/kg) and were killed 1 h later. In another set of experiments, the animals were pretreated for 1 week with daily i.p. administration of saline (control) or alpha-tocopherol (40 mg/kg) and ascorbic acid (100 mg/kg). Twelve hours after the last injection of the antioxidants the rats received one i.p. injection of arginine (0.8 g/kg) or saline and were killed 1 h later. 3. Results showed that arginine administration significantly increased lactate release and diminished glucose uptake and the activities of succinate dehydrogenase and complex II in rat cerebellum. In contrast, complex IV (cytochrome c oxidase) activity was not changed by this amino acid. Furthermore, pretreatment with alpha-tocopherol and ascorbic acid prevented the impairment of energy metabolism caused by hyperargininemia in cerebellum and hippocampus of rats.

Dietary soy prevents brain Na+, K(+)-ATPase reduction in streptozotocin diabetic rats

The aim of this study was to investigate Na+, K(+)-ATPase activity in cerebral cortex, hippocampus and hypothalamus of diabetic rats. The action of dietary soy protein on the effect produced by diabetes on this activity was also tested. Forty-nine-day-old Wistar were divided into two groups: diabetes streptozotocin (50 mg/kg body weight) and control (citrate solution). Rats were sacrificed 56 days later. In other set of experiments, rats received a dietary with casein (control) from day 21 to the 49 of postnatal-age and were subjected to diabetes or received citrate (control). One week later, rats received a special dietary with soy protein with isoflavones or casein (control) from day 56 to the 105 of postnatal-age. Results showed that diabetic rats presented a reduction ( approximately 40%) of Na+, K(+)-ATPase activity in all structures studied. Pretreatment with soy protein prevented the inhibitory effects of diabetes on the enzyme activity. Assuming the possibility that these effects might also occur in the human condition, our findings may be relevant to explain, at least in part, the neurologic dysfunction associated with diabetes and might support a novel therapeutic strategy (soy protein) to slow the progression of neurodegeneration in this disorder.

L-NAME administration prevents the inhibition of nucleotide hydrolysis by rat blood serum subjected to hyperargininemia

The main objective of the present study was to evaluate the in vivo and in vitro effect of Arg on serum nucleotide hydrolysis. The action of Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, on the effects produced by Arg was also examined. Sixty-day-old rats were treated with a single or a triple (with an interval of 1 h between each injection) intraperitoneal injection of saline (group I), Arg (0.8 g/kg) (group II), L-NAME (2.0 mg/kg or 20 mg/kg) (group III) or Arg (0.8 g/kg) plus L-NAME (2.0 mg/kg or 20 mg/kg) (group IV) and were killed 1 h later. The present results show that a triple Arg administration decreased ATP, ADP and AMP hydrolysis. Simultaneous injection of L-NAME (20 mg/kg) prevented such effects. Arg in vitro did not alter nucleotide hydrolysis. It is suggested that in vivo Arg administration reduces nucleotide hydrolysis in rat serum, probably through nitric oxide or/and peroxynitrite formation.

Effect of hypoxanthine on Na+,K+-ATPase activity and some parameters of oxidative stress in rat striatum

The main objective of this study was to investigate the effects of preincubation of rat striatum homogenate in the presence of hypoxanthine, a metabolite accumulated in Lesch-Nyhan disease, on Na+,K+-ATPase activity and on some parameters of oxidative stress namely thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant parameter (TRAP) and membrane protein thiol content. Results showed that hypoxanthine significantly increased TBA-RS and reduced Na+,K+-ATPase activity, TRAP and membrane protein thiol content. In addition, we also evaluated the effect of glutathione, trolox, allopurinol and Nvarpi-nitro-L-arginine methyl ester (L-NAME) on the inhibitory effect of hypoxanthine on Na+,K+-ATPase activity in the same rat cerebral structure. All tested compounds per se did not alter Na+,K+-ATPase activity, but only glutathione and trolox prevented the effect of hypoxanthine on the enzyme activity. The effect of glutathione and trolox on hypoxanthine-induced increase of TBA-RS levels was also investigated. These antioxidants alone or combined with hypoxanthine reduced TBA-RS levels. Our present findings show that hypoxanthine induces oxidative stress in rat striatum and that the inhibition of Na+,K+-ATPase activity caused by this oxypurine was probably mediated by reactive oxygen species. It is presumed that these results might be associated with the neuronal dysfunction of patients affected by Lesch-Nyhan disease.

In vivo and in vitro effects of homocysteine on Na+,K+‐ATPase activity in parietal, prefrontal and cingulate cortex of young rats

In the present study we determined the effect of chronic administration of homocysteine on Na+,K+-ATPase activity in synaptic membranes from parietal, prefrontal and cingulate cortex of young rats. We also studied the in vitro effect of homocysteine on this enzyme activity and on some oxidative stress parameters, namely thiobarbituric acid-reactive substances (TBA-RS) and total radical-trapping antioxidant potential (TRAP) in the same cerebral structures. For the in vivo studies, we induced elevated levels of homocysteine in blood (500 microM), comparable to those of human homocystinuria, and in brain (60 nmol/g wet tissue) of young rats by injecting subcutaneously homocysteine (0.3-0.6 micromol/g of body weight) twice a day at 8 h intervals from the 6th to the 28th postpartum day. Controls received saline in the same volumes. Rats were killed 12 h after the last injection. Chronic administration of homocysteine significantly decreased (50%) Na+,K+-ATPase activity in parietal, increased (36%) in prefrontal and did not alter in cingulate cortex of young rats. In vitro homocysteine decreased Na+,K+-ATPase activity and TRAP and increased TBA-RS in all cerebral structures studied. It is proposed that the alteration of Na+,K+-ATPase and induction of oxidative stress by homocysteine in cerebral cortex may be one of the mechanisms related to the neuronal dysfunction observed in human homocystinuria.

Evaluation of the mechanism underlying the inhibitory effect of guanidinoacetate on brain Na + , K + ‐ATPase activity

Guanidinoacetate methyltransferase deficiency (GAMT-deficiency) is an inherited neurometabolic disorder clinically characterized by epilepsy and mental retardation and biochemically by accumulation of guanidinoacetate (GAA) and depletion of creatine. Although the neurological symptoms are predominant, the pathogenesis of the brain dysfunction in this disorder is not yet established. In the present study we investigated the in vitro effect of GAA on Na+, K+-ATPase and Mg2+-ATPase activities in synaptic plasma membrane from hippocampus of young rats. Results showed that GAA significantly inhibited Na+, K+-ATPase activity without affecting Mg2+-ATPase activity. We also evaluated the effect of glutathione (GSH), trolox, Nomega-nitro-L-arginine methyl ester (L-NAME) and taurine (Tau) on the inhibition elicited by GAA on Na+, K+-ATPase activity. GSH, trolox, L-NAME and Tau per se did not alter Na+, K+-ATPase activity. However, L-NAME and taurine prevented the inhibitory effect of GAA on this enzyme activity. Our findings suggest that the inhibition of Na+, K+-ATPase activity caused by GAA is possibly mediated by nitric oxide (NO) formation and/or synaptic membrane alteration. The present data may contribute to the understanding of the neurological dysfunction characteristic of GAMT-deficient patients.

Inhibition of Na+, K+-ATPase activity in rat striatum by the metabolites accumulated in Lesch-Nyhan disease

In the present study, we investigated the in vitro effect of hypoxanthine, xanthine and uric acid, metabolites accumulating in tissue of patients with Lesch-Nyhan disease, on Na(+), K(+)-ATPase activity in striatum of neonate rats. Results showed that all compounds significantly inhibited Na(+), K(+)-ATPase activity. We also studied the kinetics of the inhibition of Na(+), K(+)-ATPase activity caused by hypoxanthine. The apparent K(m) and V(max) of Na(+), K(+)-ATPase activity for ATP as the substrate and hypoxanthine as the inhibitor were 0.97 mM and 0.69 nmol inorganic phosphate (Pi) released per min per mg of protein, respectively. K(i)-value was 1.9 microM, and the inhibition was of the non-competitive type. We also observed that the inhibitory effects of hypoxanthine, xanthine and uric acid probably occur through the same mechanism, suggesting a common binding site for these oxypurines on Na(+), K(+)-ATPase. Therefore, it is conceivable that inhibition of brain Na(+), K(+)-ATPase activity may be involved at least in part in the neuronal dysfunction characteristic of patients with Lesch-Nyhan disease.

The role of oxidative damage in the neuropathology of organic acidurias: insights from animal studies

Organic acidurias represent a group of inherited disorders resulting from deficient activity of specific enzymes of the catabolism of amino acids, carbohydrates or lipids, leading to tissue accumulation of one or more carboxylic (organic) acids. Patients affected by organic acidurias predominantly present neurological symptoms and structural brain abnormalities, of which the aetiopathogenesis is poorly understood. However, in recent years increasing evidence has emerged suggesting that oxidative stress is possibly involved in the pathology of some organic acidurias and other inborn errors of metabolism. This review addresses some of the recent developments obtained mainly from animal studies indicating oxidative damage as an important determinant of the neuropathophysiology of some organic acidurias. Recent data showing that various organic acids are capable of inducing free radical generation and decreasing brain antioxidant defences is presented. The discussion focuses on the relatively low antioxidant defences of the brain and the vulnerability of this tissue to reactive species. This offers new perspectives for potential therapeutic strategies for these disorders, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on removing toxic compounds and using special diets and pharmacological agents, such as cofactors and L-carnitine.

Evidence that oxidative stress is involved in the inhibitory effect of proline on Na(+),K(+)-ATPase activity in synaptic plasma membrane of rat hippocampus

In the present study, we investigated the effect of Vitamins E and C on the inhibition of Na(+),K(+)-ATPase activity provoked by proline (Pro) administration in rat hippocampus. Five-day-old rats were pretreated for 1 week with daily i.p. administration of saline (control) or Vitamin E (40 mg/kg) and Vitamin C (100 mg/kg). Twelve hours after the last injection, animals received one single injection of Pro (12.8 micromol/g of body weight) or saline and were killed 1h later. Results showed that Na(+),K(+)-ATPase activity was decreased in the Pro-treated rats and that the pretreatment with Vitamins E and C prevented this effect. In another set of experiments, we investigated the in vitro effect of 1.0 mM Pro on Na(+),K(+)-ATPase activity from synaptic membranes of hippocampus of rats. Pro significantly inhibited (30%) Na(+),K(+)-ATPase activity. We also evaluated the effect of preincubating glutathione, trolox and N(pi)-nitro-L-arginine methyl ester (L-NAME) alone or combined with Pro on Na(+),K(+)-ATPase activity. Tested drugs did not alter Na(+),K(+)-ATPase activity, but glutathione prevented the inhibitory effect of Pro on this enzyme activity. These results suggest that the in vivo and in vitro inhibitory effect of Pro on Na(+),K(+)-ATPase activity is probably mediated by free radicals that may be involved in the neurological dysfunction found in hyperprolinemic patients.

Reduction of energy metabolism in rat hippocampus by arginine administration

Hyperargininemia is an inherited metabolic disease biochemically characterized by tissue accumulation of arginine. Mental retardation and other neurological features are common symptoms in hyperargininemic patients. Considering that the underlying mechanisms of brain damage in this disease are poorly established, in this work we investigated the effect of arginine administration to adult Wistar rats on some parameters of energy metabolism (CO(2) production, glucose uptake, lactate release and the activities of succinate dehydrogenase, complexes II and IV of the respiratory chain) in rat hippocampus. The action of L-NAME, an inhibitor of oxide nitric oxide synthase, on the effects produced by arginine was also tested. Sixty-day-old rats were treated with a single intraperitoneal injection of saline (group I, control), arginine (0.8 g/kg) (group II) or arginine (0.8 g/kg) plus L-NAME (2 mg/kg) (group III) and were killed 1 h later. Results showed that arginine administration significantly increased lactate release and diminished CO(2) production, glucose uptake, succinate dehydrogenase and complex II activities. In contrast, complex IV (cytochrome c oxidase) activity was not changed by this amino acid. Furthermore, simultaneous injection of L-NAME prevented some of these effects, except CO(2) production and lactate release. The present data indicate that in vivo arginine administration impairs some parameters of energy metabolism in hippocampus of rats probably through NO formation.

Brain Na+,K(+)-ATPase inhibition induced by arginine administration is prevented by vitamins E and C

Hyperargininemia is a metabolic disorder caused by deficiency of arginase activity resulting in tissue accumulation of arginine and neurological dysfunction. We have previously demonstrated that arginine induces oxidative stress and decreases Na+,K(+)-ATPase in rat midbrain. In the present study we investigated the action of vitamins E and C on the inhibition of Na+,K(+)-ATPase provoked by arginine in the midbrain of 60-day-old rats. Animals were pretreated for 1 week with daily IP administration of saline (control) or vitamins E (40 mg/kg) and C (100 mg/kg). Twelve h after the last injection, animals received one injection of arginine (0.8 micromol/g of body weight) or saline. Chemiluminescence was significantly increased, whereas total antioxidant capacity and Na+,K(+)-ATPase activity were significantly decreased. Furthermore, treatment with vitamins E and C prevented these effects. If these effects also occur in the human condition, it is possible that antioxidant administration might slow the progression of neurodegeneration in this disorder.

Arginine administration inhibits hippocampal Na+,K+-ATPase activity and impairs retention of an inhibitory avoidance task in rats

In the present study we investigated the effect of acute administration of L-arginine (Arg) on hippocampal Na(+),K(+)-ATPase activity and on retrieval of step-down inhibitory avoidance in adult rats. The action of L-NAME on the effects produced by Arg was also tested. Sixty-day-old rats were treated with a single intraperitoneal injection of saline (group I, control), arginine (0.8 g/kg) (group II), L-NAME (2 mg/kg) (group III) or arginine (0.8 g/kg) plus L-NAME (2 mg/kg) (group IV). Na(+),K(+)-ATPase activity was significantly reduced in arginine-treated rats; this effect was prevented by L-NAME. Retrieval of the avoidance task was also significantly impaired by arginine, whereas the simultaneous injection of L-NAME prevented this effect. Present data strongly indicate that in vivo Arg administration reduces both Na(+),K(+)-ATPase activity and memory modulation in rats probably through NO formation.

Arginine administration reduces catalase activity in midbrain of rats

Hyperargininemia is an inherited neurometabolic disorder biochemically characterized by tissue accumulation of arginine and clinically by severe neurological symptoms whose pathophysiology is poorly understood. In the present study we investigated the effect of arginine administration on the antioxidant enzyme activities catalase, glutathione peroxidase and superoxide dismutase in rat midbrain. We also tested the effect of L-NAME on the effects produced by Arg. The results showed that arginine decreased catalase activity, without altering the other two activities. L-NAME had no effect on catalase activity, but prevented the reduction of this enzyme provoked by arginine, suggesting that NO formation is involved in the reduction of catalase activity caused by the amino acid. If these findings also occur in the human condition, it may be presumed that oxidative stress contributes to the brain dysfunction observed in hyperargininemia.