Contributory mechanisms in the causation of neurodegenerative disorders

Neuropathology in Drosophila mutants with increased seizure susceptibility

Genetic factors are known to contribute to seizure susceptibility, although the long-term effects of these predisposing factors on neuronal viability remain unclear. To examine the consequences of genetic factors conferring increased seizure susceptibility, we surveyed a class of Drosophila mutants that exhibit seizures and paralysis following mechanical stimulation. These bang-sensitive seizure mutants exhibit shortened life spans and age-dependent neurodegeneration. Because the increased seizure susceptibility in these mutants likely results from altered metabolism and since the Na(+)/K(+) ATPase consumes the majority of ATP in neurons, we examined the effect of ATPalpha mutations in combination with bang-sensitive mutations. We found that double mutants exhibit strikingly reduced life spans and age-dependent uncoordination and inactivity. These results emphasize the importance of proper cellular metabolism in maintaining both the activity and viability of neurons.

Oxidative stress modulates membrane bound ATPases in brain regions of PCB (Aroclor 1254) exposed rats: Protective role of α-tocopherol

Polychlorinated biphenyls (PCBs) are a class of widely dispersed and environmentally persistent organic compounds. PCBs exhibit a wide range of toxicological effects including neurotoxicity. Vitamin E (alpha-tocopherol) is an important lipid soluble antioxidant placed in a special region of membranes. Large amounts of energy are required to maintain the signaling activities of the cells in the central nervous system (CNS). Membrane proteins that control ion gradients across organellar and plasma membranes appear to be particularly susceptible to oxidation-induced changes. The aim of this study was to determine the protective role of vitamin E on Aroclor 1254 induced modulation in membrane bound ATPases in brain regions of rats. One group of rats received corn oil as vehicle for 30days as control. The other group of rats were administered Aroclor 1254 at a dose of 2mgkg(-1) bwday(-1) intraperitoneally for 30days. One group of rats received vitamin E (50mgkg(-1) bwday(-1)) orally simultaneously with Aroclor 1254 for 30days. After 30days, the animals were euthanized and the brain was dissected to hypothalamus and hippocampus to determine the following parameters. Hydrogen peroxide (H2O2), Lipid peroxidation (LPO) and the activities of Na+K+-ATPase, Ca2+-ATPase and Mg2+-ATPase were determined. Reduced glutathione (GSH) level was also determined. Activities of all the enzymes were decreased while an increase in H2O2 and LPO were observed in selected brain regions of PCB treated animals. Simultaneous vitamin E treatment in PCB exposed animals restored all the parameters significantly. These results suggest that oxidative stress is involved in the inhibitory effect of PCB (Aroclor 1254) on membrane bound ATPases in selected brain regions. alpha-tocopherol acts against PCB induced neurotoxicity by decreasing oxidative stress.

Effect of hypermethioninemia on some parameters of oxidative stress and on Na(+),K (+)-ATPase activity in hippocampus of rats

In the present study we investigated the effect of chronic administration of methionine, a metabolite accumulated in many inherited pathological conditions such as methionine adenosyltransferase deficiency and homocystinuria, on some parameters of oxidative stress, namely thiobarbituric acid reactive substances (TBARS), catalase activity and total thiol content, as well as on Na(+),K(+)-ATPase activity in rat hippocampus. For chronic treatment, rats received subcutaneous injections of methionine (1.34-2.68 mumol/g of body weight), twice a day, from the 6th to the 28th day of age and controls received saline. Animals were killed 12 h after the last injection. Results showed that chronic hypermethioninemia significantly increased TBARS, decreased Na(+),K(+)-ATPase activity but did not alter catalase and total thiol content. Since chronic hypermethioninemia altered TBARS and Na(+),K(+)-ATPase activity at 12 h after methionine administration, we also investigated the effect of acute administration of this amino acid on the same parameters studied after chronic methionine administration. For acute treatment,29-day-old rats received one single injection of methionine (2.68 mumol/g of body weight) or saline and were killed 1, 3 or 12 h later. Results showed that rats subjected to acute hypermethioninemia presented a reduction of Na(+),K(+)-ATPase activity and an increase in TBARS when the animals were killed at 3 and 12 h, but not at 1 h, after methionine administration. These data indicate that hypermethioninemia increases lipid peroxidation which may, at least partially, explain the effect of methionine on the reduction in Na(+),K(+)-ATPase activity. If confirmed in human beings, our findings could suggest that the induction of oxidative stress and the inhibition of Na(+),K(+)-ATPase activity caused by methionine might contribute to the neurophysiopathology observed in patients with severe hypermethioninemia.

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.

Ebselen and diorganylchalcogenides decrease in vitro glutamate uptake by RAT brain slices: Prevention by DTT and GSH

The purpose of this study was to investigate the possible involvement of the glutamatergic system in the neurotoxicity of diorganylchalcogenides or organochalcogenides from slices of cerebral cortex in different ages of development: 12- and 60-day-old rats. Glutamate uptake was evaluated in cortical slices of 12 and 60 days old rats. Cortex slices were incubated with three different organochalcogenides with or without reduced glutathione or dithiothreitol. At 100 microM, ebselen, diphenyl diselenide (PhSe)2 and diphenyl ditelluride (PhTe)2 in vitro inhibited the [3H]glutamate uptake in both age. Both 60-day-old rats and for 12-day-old rats, GSH and DTT prevented the (PhTe)2-induced inhibition of glutamate uptake but did not protect the inhibition caused by ebselen and (PhSe)2. These findings suggest that the neurotoxicity of organochalcogenides could be related to their effects on brain glutamate uptake, conceivably involving a redox modulation of reactive amino acids from the glutamate transporter proteins.

Isovaleric acid reduces Na+, K+-ATPase activity in synaptic membranes from cerebral cortex of young rats

1. Patients affected by isovaleric acidemia (IVAcidemia) suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. The objective of the present study was to investigate the in vitro effects of the metabolites that predominantly accumulate in IVAcidemia, namely isovaleric acid (IVA), 3-hydroxyisovaleric acid (3-OHIVA) and isovalerylglycine (IVG), on important parameters of energy metabolism, such as (14)CO(2) production from acetate and the activities of the respiratory chain complexes I-IV, creatine kinase and Na(+), K(+)-ATPase in synaptic plasma membranes from cerebral cortex homogenates of 30-day-old rats. 2. We observed that 3-OHIVA acid and IVG did not affect all the parameters analyzed. Similarly, (14)CO(2) production from acetate (Krebs cycle activity), the activities of creatine kinase, and of the respiratory chain complexes was not modified by IVA. In contrast, IVA exposition to cortical homogenates provoked a marked inhibition of Na(+), K(+)-ATPase activity. However, this activity was not changed when IVA was directly exposed to purified synaptic plasma membranes, suggesting an indirect effect of this organic acid on the enzyme. Furthermore, pretreatment of cortical homogenates with alpha-tocopherol and creatine totally prevented IVA-induced inhibition on Na(+), K(+)-ATPase activity from synaptic plasma membranes, whereas glutathione (GSH) and the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) did not alter this inhibition. 3. These data indicate that peroxide radicals were probably involved in this inhibitory effect. Since Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning and necessary to maintain neuronal excitability, it is presumed that the inhibitory effect of IVA on this activity may be involved in the pathophysiology of the neurological dysfunction of isovaleric acidemic patients.

Intrastriatal hypoxanthine reduces Na(+),K (+)-ATPase activity and induces oxidative stress in the rats

The main objective of this study was to investigate the effects of a single intrastriatal injection of hypoxanthine, a metabolite accumulated in Lesch Nyhan disease and possibly involved in its neuropathology, on Na(+),K(+)-ATPase activity, as well as on some parameters of oxidative stress, namely chemiluminescence (an index of lipid peroxidation), total radical-trapping antioxidant parameter--TRAP (an index of total antioxidant capacity of the tissue) and total thiol protein membrane content, in striatum, cerebral cortex and hippocampus of rats. Results show that hypoxanthine significantly decreased Na(+),K(+)-ATPase activity and TRAP while increased chemiluminescence in all ipsislateral structures tested. However, no effect on total thiol protein membrane content was detected. We suggest that hypoxanthine induces oxidative stress in all cerebral structures studied (striatum, hippocampus and cerebral cortex) and that the reduction of Na(+),K(+)-ATPase activity was probably mediated by reactive oxygen species.

Synaptic plasma membrane Na(+), K (+)-ATPase activity is significantly reduced by the alpha-keto acids accumulating in maple syrup urine disease in rat cerebral cortex

The objective of the present study was to investigate the in vitro effects of the branched-chain alpha-keto acids accumulating in maple syrup urine disease, namely L-2-ketoisocaproic acid, L-2-keto-3-methylvaleric acid and L-2-ketoisovaleric acid on Na(+), K(+)-ATPase activity in synaptic plasma membranes from cerebral cortex of 35-day-old rats. All keto acids significantly inhibited Na(+), K(+)-ATPase activity at concentrations similar (1 mM) or even lower (0.5 mM) than those found in blood and cerebrospinal fluid of maple syrup urine disease patients. We also tested the effects of alanine on this enzyme activity. Alanine per se did not alter Na(+), K(+)-ATPase activity, but totally prevented the branched-chain alpha-keto acids-induced Na(+), K(+)-ATPase inhibition, indicating that alanine and the keto acids may possibly bind to the same site on the enzyme. We also observed that the branched-chain amino acids leucine, isoleucine and valine also inhibited Na(+) K(+)-ATPase activity to a similar degree as that of the branched-chain alpha-keto acids and that alanine was able to fully prevent these effects. Considering that Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings may be involved in the pathophysiology of the neurological dysfunction of maple syrup urine disease.

Intrastriatal hypoxanthine administration affects Na+,K+‐ATPase, acetylcholinesterase and catalase activities in striatum, hippocampus and cerebral cortex of rats

The aim of this study was to investigate the effects of a single intrastriatal injection of hypoxanthine, the major metabolite accumulating in Lesch-Nyhan disease, on Na(+),K(+)-ATPase, acetylcholinesterase and catalase activities in striatum, cerebral cortex and hippocampus of rats at different post-infusion periods. Adult Wistar rats were divided in two groups: (1) vehicle-injected group (control) and (2) hypoxanthine-injected group. For Na(+),K(+)-ATPase activity determination, the animals were sacrificed 3h, 24h and 7 days after drug infusion. For the evaluation of acetylcholinesterase and catalase activities, the animals were sacrificed 30min, 3h, 24h and 7 days after hypoxanthine infusion. Results show regional and time dependent effects of hypoxanthine on Na(+),K(+)-ATPase, acetylcholinesterase and catalase activities. The in vitro effect of hypoxanthine on the same enzymes in striatum was also investigated. Results showed that hypoxanthine inhibited Na(+),K(+)-ATPase, but not the activities of acetylcholinesterase and catalase in rat striatum. We suggest that these modification on cerebral biochemical parameters (Na(+),K(+)-ATPase, acetylcholinesterase and catalase activities) induced by intrastriatal administration of hypoxanthine in all cerebral structures studied, striatum, hippocampus and cerebral cortex, could be involved in the pathophysiology of Lesch-Nyhan disease.

Effects of electroconvulsive seizures on Na+,K+-ATPase activity in the rat hippocampus

Although several advances have occurred concerning the use of electroconvulsive therapy, little progress has been made in understanding the mechanisms underlying its therapeutic or side effects. Na(+),K(+)-ATPase is an important enzyme of central nervous system, responsible for ionic gradient maintenance and consumption of approximately 40-50% of brain ATP. This work was performed in order to determine Na(+),K(+)-ATPase activity after acute and chronic electroconvulsive shock. Results showed an inhibition of Na(+),K(+)-ATPase activity in the hippocampus 48 h, 7, 30, 60 and 90 days after a single electroconvulsive shock. Chronic treatment diminished the enzyme activity in the hippocampus 7 and 30 days after electroconvulsive (ECS) sessions. Our findings demonstrated that Na(+),K(+)-ATPase activity is altered by ECS.

Inhibition of NTPDase, 5'-nucleotidase, Na+/K+-ATPase and acetylcholinesterase activities by subchronic treatment with Casearia sylvestris

The aqueous extract of Casearia sylvestris was tested in cortical membrane preparations. C. sylvestris was obtained commercially from two different sources, designated as Sample A and Sample B. The enzymes studied in this work were NTPDase-like, 5'-Nucleotidase, Na(+)/K(+)-ATPase and acetylcholinesterase (AChE). Adult rats received aqueous extracts from C. sylvestris in a dose of 20mg/kg body wt. daily for a 75-day-period, by oral administration (gavage). Our study showed that this treatment caused an inhibition of NTPDase-like activity with both, ATP (19.41% with Sample A and 25.03% with Sample B) and ADP (41.57% with Sample A and 31.20% with Sample B) as substrates. This treatment also caused an inhibition of 5'-nucleotidase activity (28.34% with Sample A and 31.46% with Sample B) and Na(+)/K(+)-ATPase (25.08% with Sample A and 24.81% with Sample B). The rate of acetylcholine degradation was reduced, as shown by the inhibition of AChE (31.65% and 26.74%, Samples A and B, respectively). These results suggest that extracts of C. sylvestris can cause neurochemical alterations in the purinergic and cholinergic systems of the central nervous system.

Metabolic disruption in Drosophila bang-sensitive seizure mutants

We examined a number of Drosophila mutants with increased susceptibility to seizures following mechanical or electrical stimulation to better understand the underlying factors that predispose neurons to aberrant activity. Several mutations in this class have been molecularly identified and suggest metabolic disruption as a possible source for increased seizure susceptibility. We mapped the bang-sensitive seizure mutation knockdown (kdn) to cytological position 5F3 and identified citrate synthase as the affected gene. These results further support a role for mitochondrial metabolism in controlling neuronal activity and seizure susceptibility. Biochemical analysis in bang-sensitive mutants revealed reductions in ATP levels consistent with disruption of mitochondrial energy production in these mutants. Electrophysiological analysis of mutants affecting mitochondrial proteins revealed an increased likelihood for a specific pattern of seizure activity. Our data implicate cellular metabolism in regulating seizure susceptibility and suggest that differential sensitivity of neuronal subtypes to metabolic changes underlies distinct types of seizure activity.

EGCG protects HT-22 cells against glutamate-induced oxidative stress

(-)-Epigallocatechin-3-gallate (EGCG) is a major polyphenol in green tea. Many health promoting effects of EGCG have been reported based on its antioxidative and gene modulation properties, but no study has demonstrated a protective effect of EGCG against glutamate-induced neuronal damage. Excessive glutamate stimulation on neuronal cells leads to accumulation of reactive oxygen species (ROS) which ultimately contribute to cell death in stroke, trauma and other neurodegenerative disorders. In this study, mouse hippocampal cell line, HT-22, was used to determine the effect of EGCG on glutamate neurotoxicity. It was found that EGCG protected HT-22 cells against glutamate neurotoxicity when administered 10 h after glutamate incubation. The protective action of EGCG is mainly due to its antioxidative effect.

Intrastriatal administration of guanidinoacetate inhibits Na+, K+-ATPase and creatine kinase activities in rat striatum

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 this disease is predominantly characterized by severe neurological findings, the underlying mechanisms of brain injury are not yet established. In the present study, we investigated the effect of intrastriatal administration of GAA on Na+, K+-ATPase activity, total (tCK), cytosolic (Cy-CK), and mitochondrial (Mi-CK) creatine kinase (CK) activities in rat striatum. We verified that Na+, K+-ATPase, tCK, and Mi-CK activities were significantly inhibited by GAA, in contrast to Cy-CK which was not affected by this guanidino compound. Since these enzyme activities can be affected by reactive species, we also investigated the effect of intrastriatal administration of GAA on thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation in rats. We found that this metabolite significantly increased this oxidative stress parameter. Considering the importance of Na+, K+-ATPase and CK activities for brain metabolism homeostasis, our results suggest that the inhibition of these enzymes by increased intracerebral levels of GAA may contribute to the neuropathology observed in patients with GAMT-deficiency.

Na+, K+ ATPase activity is markedly reduced by cis-4-decenoic acid in synaptic plasma membranes from cerebral cortex of rats

We have previously demonstrated that octanoic (OA) and decanoic acids (DA) inhibit Na+, K+ ATPase activity in synaptic plasma membranes from rat brain. The objective of the present study was to investigate the in vitro effects of the other metabolites that accumulate in tissues of medium-chain acyl-CoA dehydrogenase (MCAD)-deficient patients, namely cis-4-decenoic acid (cDA), octanoylcarnitine (OC), hexanoylcarnitine (HC), hexanoylglycine (HG), phenylpropionylglycine (PPG) and suberoylglycine (SG), on Na+, K+ ATPase activity in synaptic plasma membrane from cerebral cortex of 30-day-old rats. cDA, the pathognomonic compound found in this disorder, provoked the strongest inhibition on this enzyme activity at concentrations as low as 0.25 mM, whereas OC inhibited this activity at 1.0 mM and higher concentrations in a dose-dependent manner. In contrast, HC, HG, PPG and SG did not affect Na+, K+ ATPase activity. Furthermore, pre-treatment of cortical homogenates with the antioxidant enzymes catalase plus superoxide dismutase totally prevented cDA-induced Na+, K+ ATPase inhibition. We also provided evidence that cDA, as well as OA and DA, caused lipid peroxidation, which may explain, at least in part, the inhibitory properties of these compounds towards Na+, K+ ATPase. Considering that Na+, K+ ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings, especially those regarding to the marked inhibitory effect of cDA, may be involved in the pathophysiology of the neurological dysfunction of MCAD-deficient patients.

Neuropathology in Drosophila membrane excitability mutants

Mutations affecting ion channels and neuronal membrane excitability have been identified in Drosophila as well as in other organisms and characterized for their acute effects on behavior and neuronal function. However, the long-term effect of these perturbations on the maintenance of neuronal viability has not been studied in detail. Here we perform an initial survey of mutations affecting Na+ channels and K+ channels in Drosophila to investigate their effects on life span and neuronal viability as a function of age. We find that mutations that decrease membrane excitability as well as those that increase excitability can trigger neurodegeneration to varying degrees. Results of double-mutant interactions with dominant Na+/K+ ATPase mutations, which themselves cause severe neurodegeneration, suggest that excitotoxicity owing to hyperexcitability is insufficient to explain the resultant phenotype. Although the exact mechanisms remain unclear, our results suggest that there is an important link between maintenance of proper neuronal signaling and maintenance of long-term neuronal viability. Disruption of these signaling mechanisms in any of a variety of ways increases the incidence of neurodegeneration.

Effect of diphenyl diselenide, diphenyl ditelluride and ebselen on cerebral Na+, K+-ATPase activity in rats

In the present study, we investigated the in vitro effect of diphenyl ditelluride, diphenyl diselenide and ebselen on Na(+), K(+)-ATPase activity of rat brain. The results demonstrated that all compounds significantly inhibited (in the muM range) Na(+), K(+)-ATPase activity. Diphenyl ditelluride, at low concentrations, provoked an increase in Na(+), K(+)-ATPase activity. Dithiothreitol (DTT), at 3mM, protected the inhibition caused by diphenyl ditelluride, diphenyl diselenide and ebselen in Na(+), K(+)-ATPase activity. Post-incubation of diphenyl diselenide-treated homogenate with DTT completely recovered enzyme activity. DTT was able to recover the enzyme inhibition induced by 20muM of diphenyl ditelluride, but was partially able to recover inhibition induced by high concentrations of organotellurium compound. Conversely, DTT did not recover ebselen-induced Na(+), K(+)-ATPase inhibition. The mechanism of inhibition by diphenyl diselenide, diphenyl ditelluride and ebselen in Na(+), K(+)-ATPase activity revealed: decreased maximal velocity and K(m). Cerebral Na(+), K(+)-ATPase is a potential molecular target for the toxic effect of organochalcogens and the inhibition may occur through a change in the crucial thiol groups of this enzyme.

Excitatory amino acid neurotransmission

In recent years great progress has been made in understanding the function of ionotropic and metabotropic glutamate receptors; their pharmacology and potential therapeutic applications. It should be stressed that there are already N-methyl-D-aspartate (NMDA) antagonists in clinical use, such as memantine, which proves the feasibility of their therapeutic potential. It seems unlikely that competitive NMDA receptor antagonists and high-affinity channel blockers will find therapeutic use due to limiting side-effects, whereas agents acting at the glycineB site, NMDA receptor subtype-selective agents and moderate-affinity channel blockers are far more promising. This is supported by the fact that there are several glycineB antagonists, NMDA moderate-affinity channel blockers and NR2B-selective agents under development. Positive and negative modulators of AMPA receptors such as the AMPAkines and 2,3-benzodiazepines also show more promise than e.g. competitive antagonists. Great progress has also been made in the field of metabotropic glutamate receptors since the discovery of novel, allosteric modulatory sites for these receptors. Selective agents acting at these transmembrane sites have been developed that are more drug-like and have a much better access to the central nervous system than their competitive counterparts. The chapter will critically review preclinical and scarce clinical experience in the development of new ionotropic and metabotropic glutamate receptor modulators according to the following scheme: rational, preclinical findings in animal models and finally clinical experience, where available.

Methionine alters Na+,K+‐ATPase activity, lipid peroxidation and nonenzymatic antioxidant defenses in rat hippocampus

In the present study we investigated the effect of methionine exposure of hippocampus homogenates on Na+,K+-ATPase activity from synaptic plasma membrane of rats. Results showed that methionine significantly decreased this enzyme activity. We also evaluated the effect of incubating glutathione (GSH) and trolox (alpha-tocopherol) alone or combined with methionine on Na+,K+-ATPase activity. The tested antioxidants per se did not alter the enzymatic activity, but prevented the inhibitory action of methionine on Na+,K+-ATPase activity, indicating that Met inhibitory effect was probably mediated by free radical formation. Besides, we tested the in vitro effect of methionine on some parameters of oxidative stress, namely chemiluminescence, thiobarbituric acid reactive substances (TBARS), total radical-trapping antioxidant potential (TRAP), as well as on the antioxidant enzyme activities catalase, glutathione peroxidase and superoxide dismutase in rat hippocampus. We observed that methionine significantly increased chemiluminescence and TBARS, decreased TRAP, but did not change the activity of the antioxidant enzymes. These findings suggest that reduction of Na+,K+-ATPase activity and induction of oxidative stress may be involved in the brain damage observed in human hypermethioninemia.

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.

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.

Suckling rat brain regional distribution of Na+,K+-atpase activity in the in vitro galactosaemia: the effect of L-cysteine and glutathione

Inhibition of Na+,K+-ATPase activity causes edema and cell death in central nervous system. We determined the in vitro effects of galactose-l-phosphate (Gal-1-P), galactitol (Galtol) and galactose (Gal) (mix A = classical galactosaemia) or Galtol and Gal (mix B = galactokinase deficiency galactosaemia), on Na+,K+-ATPase activity in suckling rat brain frontal cortex, hippocampus or hypothalamus homogenates. Gal-1-P or Galtol alone at different concentrations, significantly inhibited Na+,K+-ATPase whereas Gal activated the enzyme in all investigated brain regions. Both mix A and mix B inactivated the enzyme by 20-30% (p < 0.001) in all studied areas. L-Cysteine (Cys) and glutathione (GSH) supplementation in mix B not only reversed the enzyme inhibition but also resulted in an activation of 50-60%, (p < 0.001) in all brain areas. Their presence in mix A also activated the inhibited Na+,K+-ATPase in hippocampus and hypothalamus to a lower degree, whereas Cys reversed the frontal cortex enzyme activity to control value only. These findings indicate that oxidation of the enzyme critical groups may be involved in galactosaemia, producing inhibitory effect. This phenomenon is reversed by antioxidants Cys and GSH, implying that free radicals may be implicated in the observed enzyme inactivation.

Adenosine A1 receptors and the anticonvulsant potential of drugs effective in the model of 3-nitropropionic acid-induced seizures in mice

The role of adenosine A1 receptors in the activity of drugs and substances protecting against seizures evoked by mitochondrial toxin, 3-nitropropionic acid (3-NPA) was studied in mice. Non-selective A1/A2 adenosine receptor antagonist, aminophylline and selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) diminished the anticonvulsive effects of diazepam, phenobarbital, valproate and gabapentin. In contrast, A1/A2 adenosine receptor antagonist, 8-(p-sulfophenyl)theophylline (8pSPT) not penetrating via blood-brain barrier was ineffective. Aminophylline and DPCPX but not 8pSPT also reversed the protective action of A1/A2 adenosine receptor agonist, 2-chloroadenosine (2-CADO) and selective A1 adenosine receptor agonist, R-N6-phenylisopropyloadenosine (R-PIA), against 3-NPA-evoked convulsions. Obtained results suggest that the central adenosine A1 receptor stimulation may play a role in the anticonvulsive potential of diazepam, phenobarbital, valproate and gabapentin in a novel model of 3-NPA-evoked seizures. Moreover, concomitant application of aminophylline with these drugs may reduce their clinical antiepileptic efficacy, especially among patients suffering from seizures related to the disturbances of mitochondrial respiratory chain.

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.

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.

The NMDA receptor antagonist memantine as a symptomatological and neuroprotective treatment for Alzheimer's disease: preclinical evidence

There is increasing evidence for the involvement of glutamate-mediated neurotoxicity in the pathogenesis of Alzheimer's disease (AD). We suggest that glutamate receptors of the N-methyl-D-aspartate (NMDA) type are overactivated in a tonic rather than a phasic manner in this disorder. This continuous mild activation may lead to neuronal damage and impairment of synaptic plasticity (learning). It is likely that under such conditions Mg(2+) ions, which block NMDA receptors under normal resting conditions, can no longer do so. We found that overactivation of NMDA receptors using a direct agonist or a decrease in Mg(2+) concentration produced deficits in synaptic plasticity (in vivo: passive avoidance test and/or in vitro: LTP in the CA1 region). In both cases, memantine-an uncompetitive NMDA receptor antagonists with features of an 'improved' Mg(2+) (voltage-dependency, kinetics, affinity)-attenuated this deficit. Synaptic plasticity was restored by therapeutically-relevant concentrations of memantine (1 microM). Moreover, doses leading to similar brain/serum levels provided neuroprotection in animal models relevant for neurodegeneration in AD such as neurotoxicity produced by inflammation in the NBM or beta-amyloid injection to the hippocampus. As such, if overactivation of NMDA receptors is present in AD, memantine would be expected to improve both symptoms (cognition) and to slow down disease progression because it takes over the physiological function of magnesium.

Evidence that antioxidants prevent the inhibition of Na+,K(+)-ATPase activity induced by octanoic acid in rat cerebral cortex in vitro

The objective of the present study was to investigate the in vitro effects of octanoic acid, which accumulates in medium-chain acyl-CoA dehydrogenase (MCAD) deficiency and in Reye syndrome, on key enzyme activities of energy metabolism in the cerebral cortex of young rats. The activities of the respiratory chain complexes I-IV, creatine kinase, and Na+,K(+)-ATPase were evaluated. Octanoic acid did not alter the electron transport chain and creatine kinase activities, but, in contrast, significantly inhibited Na+,K(+)-ATPase activity both in synaptic plasma membranes and in homogenates prepared from cerebral cortex. Furthermore, decanoic acid, which is also increased in MCAD deficiency, and oleic acid strongly reduced Na+,K(+)-ATPase activity, whereas palmitic acid had no effect. We also examined the effects of incubating glutathione and trolox (alpha-tocopherol) alone or with octanoic acid on Na+,K(+)-ATPase activity. Tested compounds did not affect Na+,K(+)-ATPase activity by itself, but prevented the inhibitory effect of octanoic acid. These results suggest that inhibition of Na+,K(+)-ATPase activity by octanoic acid is possibly mediated by oxidation of essential groups of the enzyme. Considering that Na+,K(+)-ATPase is critical for normal brain function, it is feasible that the significant inhibition of this enzyme activity by octanoate and also by decanoate may be related to the neurological dysfunction found in patients affected by MCAD deficiency and Reye syndrome.

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.

In vitro effect of homocysteine on some parameters of oxidative stress in rat hippocampus

Homocystinuria is an inherited metabolic disease characterized biochemically by increased blood and brain levels of homocysteine caused by severe deficiency of cystathionine beta-synthase activity. Affected patients present mental retardation, seizures, and atherosclerosis. Oxidative stress plays an important role in the pathogenesis of many neurodegenerative and vascular diseases, such Alzheimer's disease, stroke, and atherosclerosis. However, the mechanisms underlying the neurological damage characteristic of homocystinuria are still poorly understood. To evaluate the involvement of oxidative stress on the neurological dysfunction present in homocystinuria, we measured thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation, and total radical-trapping antioxidant potential (TRAP) and antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) in rat hippocampus in the absence (controls) or in the presence of homocysteine (10-500 microM) in vitro. We demonstrated that homocysteine significantly increases TBARS and decreases TRAP, both in a dose-dependent manner, but did not change antioxidant enzymes. Our results suggest that oxidative stress is involved in the neurological dysfunction of homocystinuria. However, further studies are necessary to confirm and extend our findings to the human condition and also to determine whether antioxidant therapy may be of benefit to these patients.

Inhibition of Na+, K+-ATPase activity in rat striatum by guanidinoacetate

The aim of this work was to investigate the effect of guanidinoacetate (GAA), the principal metabolite accumulating in guanidinoacetate methyltransferase (GAMT)-deficiency, on Na(+), K(+)-ATPase, Mg(2+)-ATPase and acetylcholinesterase (AChE) activities in striatum of young rats. We also studied the kinetics of the inhibition of Na(+), K(+)-ATPase activity caused by guanidinoacetate. Guanidinoacetate did not alter acetylcholinesterase and Mg(2+)-ATPase activities, but significantly inhibited Na(+), K(+)-ATPase activity. The apparent K(m) and V(max) of Na(+), K(+)-ATPase for ATP as substrate were 0.20mM and 0.82nmol inorganic phosphate (Pi) released per min per mg of protein, respectively. K(i) value was 7.18mM, and the inhibition was of the uncompetitive type. The results also showed a competition between guanidinoacetate and argininic acid (AA), suggesting a common binding site for the guanidino compounds (GC) on the enzyme. It is proposed that Na(+), K(+)-ATPase inhibition by guanidinoacetate may be one of the mechanisms involved in the neuronal dysfunction observed in GAMT-deficiency and in other diseases which accumulate guanidinoacetate.

Proline induces oxidative stress in cerebral cortex of rats

In the present study we investigated the in vivo and in vitro effects of proline on some parameters of oxidative stress, such as chemiluminescence, total radical-trapping antioxidant potential (TRAP) and the activity of the antioxidant enzymes catalase, glutathione peroxidase and superoxide dismutase in rat cerebral cortex. Ten-day-old rats received one subcutaneous injection of proline (12.8 micromol/g body weight), while control rats received saline in the same volumes. The animals were killed 1h after injection, the cerebral cortex was isolated and the assays immediately carried out. For the in vitro studies, homogenates from cerebral cortex of 10-day-old untreated rats were incubated for 1h at 37 degrees C with various concentrations of proline (3.0 microM-1.0mM). Results showed that proline-treated rats presented a decrease of TRAP (30%) and an increase of chemiluminescence (78%). In contrast, the activities of catalase, glutathione peroxidase and superoxide dismutase were not modified by proline acute treatment. Furthermore, the presence of proline in the medium increased chemiluminescence, decreased TRAP and the activity of superoxide dismutase at proline concentrations similar to those observed in tissues of hyperprolinemic patients (0.5-1.0mM). However, catalase and glutathione peroxidase activities were not affected by the presence of proline in the medium. The results indicate that proline induces oxidative stress in the brain, which may be related, at least in part, to the neurological dysfunction observed in hyperprolinemia.

Neural dysfunction and neurodegeneration in Drosophila Na+/K+ ATPase alpha subunit mutants

The Na+/K+ ATPase asymmetrically distributes sodium and potassium ions across the plasma membrane to generate and maintain the membrane potential in many cell types. Although these pumps have been hypothesized to be involved in various human neurological disorders, including seizures and neurodegeneration, direct genetic evidence has been lacking. Here, we describe novel mutations in the Drosophila gene encoding the alpha (catalytic) subunit of the Na+/K+ ATPase that lead to behavioral abnormalities, reduced life span, and severe neuronal hyperexcitability. These phenotypes parallel the occurrence of extensive, age-dependent neurodegeneration. We have also discovered that the ATPalpha transcripts undergo alternative splicing that substantially increases the diversity of potential proteins. Our data show that maintenance of neuronal viability is dependent on normal sodium pump activity and establish Drosophila as a useful model for investigating the role of the pump in human neurodegenerative and seizure disorders.

Alterations of kynurenic acid content in the retina in response to retinal ganglion cell damage

The present study is the first to examine the modulation of retinal kynurenic acid (KYNA) content in response to N-methyl-D-aspartate (NMDA)-induced cell death in adult rat retinal ganglion cells (RGC). Adult Brown Norway rats were intravitreally injected with NMDA or PBS. Surviving RGC were retrogradely labeled with fluorogold and counted in wholemounts of retinas 2, 7 and 14 days after injection. Retinal KYNA content was measured by HPLC at the same time points. RGC numbers decreased significantly 2, 7 and 14 days after NMDA injection if compared to control retinas. KYNA concentration increased significantly two days after NMDA-injection. However, 7 and 14 days after injection retinal KYNA content was found markedly decreased in NMDA-treated eyes as compared to controls. It is conceivable that KYNA deficiency is causally related to the pathology of excitotoxic retinal diseases.

Estrogen receptor-mediated neuroprotection from oxidative stress requires activation of the mitogen-activated protein kinase pathway

It is well documented that estrogen mediates responses by both genomic and nongenomic mechanisms, both of which are important for cell survival. Because direct evidence showing that the estrogen receptors (ERs) alpha and/or beta can activate rapid signaling that may mediate neuroprotection is lacking, the hippocampal-derived cell line, HT22, was stably transfected with ERalpha (HTERalpha), ERbeta (HTERbeta), or a mutated form of ERalpha (HTERalphaHE27), which lacks the ability to mediate ER element-mediated transcription. Treatment of HT22, HTERalpha, HTERbeta, and HTERalphaHE27 cells with glutamate (5 mM) resulted in a significant decrease in cell viability. Pretreatment for 15 min with 10 nM 17beta-estradiol resulted in a 50% increase in the number of living cells in HTERalpha and HTERbeta cells but not in HT22 cells. The ER antagonist ICI 182,780 and the MEK inhibitor PD98059 prevented 17beta-estradiol-mediated protection. In HTERalphaHE27 cells, 17beta-estradiol rapidly phosphorylated ERK2 (within 15 min), in the absence of estrogen response element-mediated transcription. Treatment of HTERalphaHE27 cells with 10 nM 17beta-estradiol partially reversed the cell death produced by glutamate treatment. This study demonstrates that activation of either ERalpha or ERbeta can result in neuroprotection and that activation of the MAPK pathway is an important part of the neuroprotective mechanism.

Inhibition of Na(+),K(+)-ATPase activity in hippocampus of rats subjected to acute administration of homocysteine is prevented by vitamins E and C treatment

In the present study we evaluated the effect of acute homocysteine (Hcy) administration on Na(+),K(+)-ATPase activity, as well as on some parameters of oxidative stress such as total radical-trapping antioxidant potential (TRAP) and on activities of antioxidant enzymes catalase (CAT), superoxide dismutase and glutathione peroxidase in rat hippocampus. Results showed that Hcy significantly decreased TRAP, Na(+),K(+)-ATPase and CAT activities, without affecting the activities of superoxide dismutase and glutathione peroxidase. We also verified the effect of chronic pretreatment with vitamins E and C on the reduction of TRAP, Na(+),K(+)-ATPase and CAT activities caused by Hcy. Vitamins E and C per se did not alter these parameters, but prevented the reduction of TRAP, Na(+),K(+)-ATPase and CAT activities caused by Hcy. Our results indicate that oxidative stress is probably involved in the pathogenesis of homocystinuria and that reduction of Na(+),K(+)-ATPase activity may be related to the neuronal dysfunction found in homocystinuric patients.

Reduction of Na(+),K(+)-ATPase activity in hippocampus of rats subjected to chemically induced hyperhomocysteinemia

Hyperhomocysteinemia occurs in homocystinuria, an inherited metabolic disease clinically characterized by thromboembolic episodes and a variable degree of neurological dysfunction whose pathophysiology is poorly known. In this study, we induced elevated levels of homocysteine (Hcy) 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-hr intervals from the 6th to the 28th postpartum day. Controls received saline in the same volumes. Na(+),K(+)-ATPase and Mg(2+)-ATPase activities were determined in the hippocampus of treated Hcy- and saline-treated rats. Chronic administration of Hcy significantly decreased (40%) Na(+),K(+)-ATPase activity but did not alter Mg(2+)-ATPase activity. Considering that Na(+),K(+)-ATPase plays a crucial role in the central nervous system, our results suggest that the brain dysfunction found in homocystinuria may be related to the reduction of brain Na(+),K(+)-ATPase activity.

Microglia enhance beta-amyloid peptide-induced toxicity in cortical and mesencephalic neurons by producing reactive oxygen species

The purpose of this study was to assess and compare the toxicity of beta-amyloid (Abeta) on primary cortical and mesencephalic neurons cultured with and without microglia in order to determine the mechanism underlying microglia-mediated Abeta-induced neurotoxicity. Incubation of cortical or mesencephalic neuron-enriched and mixed neuron-glia cultures with Abeta(1-42) over the concentration range 0.1-6.0 microm caused concentration-dependent neurotoxicity. High concentrations of Abeta (6.0 microm for cortex and 1.5-2.0 microm for mesencephalon) directly injured neurons in neuron-enriched cultures. In contrast, lower concentrations of Abeta (1.0-3.0 microm for cortex and 0.25-1.0 microm for mesencephalon) caused significant neurotoxicity in mixed neuron-glia cultures, but not in neuron- enriched cultures. Several lines of evidence indicated that microglia mediated the potentiated neurotoxicity of Abeta, including the observations that low concentrations of Abeta activated microglia morphologically in neuron-glia cultures and that addition of microglia to cortical neuron-glia cultures enhanced Abeta-induced neurotoxicity. To search for the mechanism underlying the microglia-mediated effects, several proinflammatory factors were examined in neuron-glia cultures. Low doses of Abeta significantly increased the production of superoxide anions, but not of tumor necrosis factor-alpha, interleukin-1beta or nitric oxide. Catalase and superoxide dismutase significantly protected neurons from Abeta toxicity in the presence of microglia. Inhibition of NADPH oxidase activity by diphenyleneiodonium also prevented Abeta-induced neurotoxicity in neuron-glia mixed cultures. The role of NADPH oxidase-generated superoxide in mediating Abeta-induced neurotoxicity was further substantiated by a study which showed that Abeta caused less of a decrease in dopamine uptake in mesencephalic neuron-glia cultures from NADPH oxidase-deficient mutant mice than in that from wild-type controls. This study demonstrates that one of the mechanisms by which microglia can enhance the neurotoxicity of Abeta is via the production of reactive oxygen species.

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.

Pretreatment with vitamins E and C prevent the impairment of memory caused by homocysteine administration in rats

Homocystinuria is a metabolic disorder caused by deficiency of cystathione beta-synthase activity leading to tissue accumulation of homocysteine (Hcy); affected patients present neurological dysfunction. Considering that Hcy induces free radical formation and that memory is impaired by oxidative stress, in the present study we investigated the effect of an acute administration of Hcy on retrieval of step-down inhibitory avoidance in adult rats. The action of vitamins E and C on the effects produced by Hcy was also tested. Adult Wistar rats were pretreated for 1 week with daily i.p. administration of saline (control group) and vitamins E and C (vitamin E 40 mg/kg and vitamin C 100 mg/kg). Hcy (11 mmol/kg) or an equivalent volume of 0.9% saline were administered 1 h before training, 1 h before testing, or immediately after training sessions. Memory was significantly impaired in Hcy-treated group, whereas the rats chronically treated with vitamins E and C had this effect prevented. Present data strongly indicate that Hcy administration impairs memory, an effect probably mediated by oxidative stress since treatment with vitamins E and C prevented amnesia. Assuming the possibility that this might occur in the human condition, reported results may be relevant to explain, at least in part, neurologic dysfunction associated with homocystinuria.

Inhibition of Na+, K+-ATPase activity by the metabolites accumulating in homocystinuria

Homocystinuria is an inborn error of sulfur amino acid metabolism characterized predominantly by vascular and nervous system dysfunction. In this study we determined the in vitro effects of homocysteine and methionine, metabolites which accumulate in homocystinuria, on Na+, K+-ATPase, and Mg2+-ATPase activities in synaptic membranes from the hippocampus of rats. The results showed that both metabolites significantly inhibit Na+, K+-ATPase but not Mg2+-ATPase activity at concentrations usually observed in plasma of homocystinuric patients. Furthermore, incubation of hippocampal homogenates with homocysteine also elicited an inhibition of the enzyme activity which was however prevented by the simultaneous addition of cysteine to the medium. In addition, cysteine or methionine per se did not modify the two enzymatic activities. These findings indicate that oxidation of critical groups in the enzyme may possibly be involved in homocysteine inhibitory effect. Moreover, kinetic studies performed to investigate the interaction between homocysteine and methionine on Na+, K+-ATPase inhibition suggested a common site for the two amino acids in the enzyme. Considering the critical role exerted by Na+, K+-ATPase in brain, it is proposed that the inhibition provoked by homocysteine and methionine on the enzyme activity may be possibly related to the brain dysfunction characteristic of homocystinuria.

In vivo effects of high phenylalanine blood levels on Na+,K+-ATPase, Mg2+-ATPase activities and biogenic amine concentrations in phenylketonuria

OBJECTIVE

To evaluate the activities of Na+,K+-ATPase and Mg2+-ATPase in erythrocyte membranes from phenylketonuric (PKU) patients and to correlate the enzyme activities with their blood phenylalanine (Phe) levels, biogenic amines as well as with their precursors tyrosine (Tyr) and tryptophan (Try).

DESIGN AND METHODS

Twenty three PKU patients were divided into group A (n = 12) on a restricted diet (Phe 1.57 +/- 0.52 mg/dL or 0.10 +/- 0.03 mM) and group B (n = 11) on a "loose" diet (Phe 24.45 +/- 1.50 mg/dL or 1.72 +/- 0.09 mM). The enzyme activities were measured spectrophotometrically, the amino acids with an automatic amino analyser and the biogenic amines with HPLC methods.

RESULTS

In group B, plasma amino acids (Tyr, Try), their biogenic amines [adrenaline (A), noradrenaline (NA), dopamine (DA) and serotonin (5HT)], (Na+,K+)-ATPase and Mg2+-ATPase activities were found remarkably decreased (p < 0.001).

CONCLUSIONS

High Phe and/or low NA, DA, 5HT plasma levels may indirectly inhibit the erythrocyte membrane Na+,K+-ATPase and Mg2+-ATPase in PKU patients. The observed enzyme inhibitions could be a very informative peripheral marker as regards the neurotoxic Phe brain effects.

Chronic treatment with glutaric acid induces partial tolerance to excitotoxicity in neuronal cultures from chick embryo telencephalons

Glutaryl-CoA dehydrogenase deficiency (GDD) is characterized biochemically by an accumulation of glutaric (GA) and 3-hydroxyglutaric (3-OH-GA) acids and clinically by the development of acute striatal degeneration. 3-OH-GA was recently shown to induce neuronal damage via N-methyl-D-aspartate (NMDA) receptors. The pathogenetic role of GA, however, remains unclear. We demonstrate that GA exerts a dual action in cultured chick embryo neurons. Short-term incubation with millimolar concentrations of GA induces a weak neuronal damage, adding to 3-OH-GA neurotoxicity. In contrast, chronic treatment with subtoxic, micromolar concentrations of GA results in partial tolerance to 3-OH-GA- and NMDA-induced cell damage. A downregulation of NMDA receptors, in particular of the NR2B subunit, is critically involved in this GA-induced effect, resulting in a reduced Ca(2+) increase and generation of reactive oxygen species after acute exposure to NMDA or 3-OH-GA. Furthermore, GA decreases Na(+)/K(+)-ATPase activity, which is prevented by glutathione, suggesting a modulation of NMDA receptor function via resting membrane potential and Na(+)-dependent glutamate transport. In contrast, GA does not inhibit mitochondrial respiratory chain and beta-oxidation of fatty acids, virtually excluding an activation of NMDA receptors secondary to ATP depletion. These results strongly suggest that GA modulates the NMDA receptor-mediated neurotoxicity of 3-OH-GA, providing an explanatory basis for the non-linear relationship between organic acid concentrations and disease progression in GDD patients. Furthermore, GA-induced downregulation of NMDA receptors might be involved in the delayed cerebral maturation of GDD patients, resulting in frontotemporal atrophy and a reduced opercularization, which are common neuroradiological findings in GDD patients.

The expression of the glutamate re-uptake transporter excitatory amino acid transporter 1 (EAAT1) in the normal human CNS and in motor neurone disease: an immunohistochemical study

A monoclonal antibody to excitatory amino acid transporter 1 (EAAT1) has been generated which robustly stains paraffin-embedded, formaldehyde-fixed as well as snap-frozen human post-mortem brain tissue. We have used this antibody to map the distribution of EAAT1 throughout normal human CNS tissue. In addition this antibody has been used to perform a semi-quantitative immunohistochemical analysis of the expression of EAAT1 in motor cortex and cervical cord tissue taken from motor neurone disease cases (n=17) and neurologically normal controls (n=12). By comparing the relative optical density measurements of identical regions of motor cortex and cervical spinal cord an increase in the expression levels of EAAT1 was observed in motor neurone disease tissue compared to the control tissue and in both motor cortex and cervical spinal cord (9-17% and 13-33% increases respectively). EAAT1 was observed to be the most abundant transporter in more "caudal" brain regions such as the diencephalon and brainstem and its expression in other regions was frequently more uniform than that of EAAT2. In the motor cortex, EAAT1 immunoreactivity was present in all grey matter laminae, with some staining of individual astrocytes in the white matter. In spinal cord, EAAT1 immunoreactivity was strongest in the substantia gelatinosa. In the ventral horn, motor neurones were surrounded with a dense rim of perisomatic EAAT1 immunoreactivity, and the neuropil showed diffuse staining. Additional studies using double-labelling immunocytochemistry demonstrated that astrocytic co-localisation of EAAT1 and EAAT2 may occasionally be seen, but was not widespread in the human CNS and that in general astrocytes were positive for either EAAT1 or EAAT2. These results demonstrate that the EAAT1 has a widespread abundance throughout all regions of the human CNS examined and that there exist discrete populations of astrocytes that are positive solely for either EAAT1 or EAAT2. Furthermore, there is evidence to suggest that altered EAAT1 expression in motor neurone disease follows a different pattern to the reported changes of EAAT2 expression in this condition, indicating that the role of glutamate transporters in the pathogenesis of motor neurone disease appears more complex than previously appreciated.

Inhibition of rat brain Na+, K+-ATPase activity induced by homocysteine is probably mediated by oxidative stress

The objective of the present study was to investigate the effects of preincubation of hippocampus homogenates in the presence of homocysteine or methionine on Na+, K+-ATPase and Mg2+-ATPase activities in synaptic membranes of rats. Homocysteine significantly inhibited Na+, K+-ATPase activity, whereas methionine had no effect. Mg2+-ATPase activity was not altered by the metabolites. We also evaluated the effect of incubating glutathione, cysteine, dithiothreitol, trolox, superoxide dismutase and GM1 ganglioside alone or incubation with homocysteine on Na+, K+-ATPase activity. Tested compounds did not alter Na+, K+-ATPase and Mg2+-ATPase activities, but except for trolox, prevented the inhibitory effect of homocysteine on Na+, K+-ATPase activity. These results suggest that inhibition of this enzyme activity by homocysteine is possibly mediated by free radicals and may contribute to the neurological dysfunction found in homocystinuric patients.