Free radical-induced endothelial membrane dysfunction at the site of blood-brain barrier: relationship between lipid peroxidation, Na,K-ATPase activity, and 51Cr release

Expression of Neuronal Na+/K+-ATPase α Subunit Isoforms in the Mouse Brain Following Genetically Programmed or Behaviourally-induced Oxidative Stress

The Na⁺/K⁺-ATPase is a transmembrane ion pump that has a critical homeostatic role within every mammalian cell; however, it is vulnerable to the effects of increased oxidative stress. Understanding how expression of this transporter is influenced by oxidative stress may yield insight into its role in the pathophysiology of neurological and neuropsychiatric diseases. In this study we investigated whether increased oxidative stress could influence Na⁺/K⁺-ATPase expression in various brain regions of mice. We utilized two different models of oxidative stress: a behavioural chronic unpredictable stress protocol and the Aldh2^-/- mouse model of oxidative stress-based and age-related cognitive impairment. We identified distinct regional baseline mRNA and protein expression patterns of the Na⁺/K⁺-ATPase α1 and α3 isoforms within the neocortex, hippocampus, and brainstem of wildtype mice. Consistent with previous studies, there was a higher proportion of α3 expression relative to α1 in the brainstem versus neocortex, but a higher proportion of α1 expression relative to α3 in the neocortex versus the brainstem. The hippocampus had similar expression levels of both α1 and α3. Despite increased staining for oxidative stress in higher brain, no differences in α1 or α3 expression were noted in Aldh2^-/- mice versus wildtype, or in mice exposed to a 28-day chronic unpredictable stress protocol. In both models of oxidative stress, gene and protein expression of Na⁺/K⁺-ATPase α1 and α3 isoforms within the higher and lower brain was remarkably stable. Thus, Na⁺/K⁺-ATPase function previously reported as altered by oxidative stress is not through induced changes in the expression of pump isoforms.

Possible involvement of membrane lipids peroxidation and oxidation of catalytically essential thiols of the cerebral transmembrane sodium pump as component mechanisms of iron-mediated oxidative stress-linked dysfunction of the pump's activity

The precise molecular events defining the complex role of oxidative stress in the inactivation of the cerebral sodium pump in radical-induced neurodegenerative diseases is yet to be fully clarified and thus still open. Herein we investigated the modulation of the activity of the cerebral transmembrane electrogenic enzyme in Fe²⁺-mediated in vitro oxidative stress model. The results show that Fe²⁺ inhibited the transmembrane enzyme in a concentration dependent manner and this effect was accompanied by a biphasic generation of aldehydic product of lipid peroxidation. While dithiothreitol prevented both Fe²⁺ inhibitory effect on the pump and lipid peroxidation, vitamin E prevented only lipid peroxidation but not inhibition of the pump. Besides, malondialdehyde (MDA) inhibited the pump by a mechanism not related to oxidation of its critical thiols. Apparently, the low activity of the pump in degenerative diseases mediated by Fe²⁺ may involve complex multi-component mechanisms which may partly involve an initial oxidation of the critical thiols of the enzyme directly mediated by Fe²⁺ and during severe progression of such diseases; aldehydic products of lipid peroxidation such as MDA may further exacerbate this inhibitory effect by a mechanism that is likely not related to the oxidation of the catalytically essential thiols of the ouabain-sensitive cerebral electrogenic pump.

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Fe²⁺ evoked lipid peroxidation (LPO) and inhibition of sodium pump (SP) in rat brain.

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However, dithiothreitol prevented both Fe²⁺-mediated LPO and inhibition of SP.

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Conversely, vitamin E prevented only Fe²⁺-mediated LPO but not inhibition of SP.

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Thus Fe²⁺ mediated inactivation of SP likely by oxidizing the essential thiol on SP.

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However, malondialdehyde inhibited SP by a mechanism not related to thiol oxidation.

Coenzyme Q10 benefits symptoms in Gulf War veterans: results of a randomized double-blind study

We sought to assess whether coenzyme Q10 (CoQ10) benefits the chronic multisymptom problems that affect one-quarter to one-third of 1990-1 Gulf War veterans, using a randomized, double-blind, placebo-controlled study. Participants were 46 veterans meeting Kansas and Centers for Disease Control criteria for Gulf War illness. Intervention was PharmaNord (Denmark) CoQ10 100 mg per day (Q100), 300 mg per day (Q300), or an identical-appearing placebo for 3.5 ± 0.5 months. General self-rated health (GSRH), the primary outcome, differed across randomization arms at baseline, and sex significantly predicted GSRH change, compelling adjustment for baseline GSRH and prompting sex-stratified analysis. GSRH showed no significant benefit in the combined-sex sample. Among males (85% of participants), Q100 significantly benefited GSRH versus placebo and versus Q300, providing emphasis on Q100. Physical function (summary performance score, SPS) improved on Q100 versus placebo. A rise in CoQ10 approached significance as a predictor of improvement in GSRH and significantly predicted SPS improvement. Among 20 symptoms each present in half or more of the enrolled veterans, direction-of-difference on Q100 versus placebo was favorable for all except sleep problems; sign test 19:1, p=0.00004) with several symptoms individually significant. Significance for these symptoms despite the small sample underscores large effect sizes, and an apparent relation of key outcomes to CoQ10 change increases prospects for causality. In conclusion, Q100 conferred benefit to physical function and symptoms in veterans with Gulf War illness. Examination in a larger sample is warranted, and findings from this study can inform the conduct of a larger trial.

Amphetamine toxicities: classical and emerging mechanisms

The drugs of abuse, methamphetamine and MDMA, produce long-term decreases in markers of biogenic amine neurotransmission. These decreases have been traditionally linked to nerve terminals and are evident in a variety of species, including rodents, nonhuman primates, and humans. Recent studies indicate that the damage produced by these drugs may be more widespread than originally believed. Changes indicative of damage to cell bodies of biogenic and nonbiogenic amine-containing neurons in several brain areas and endothelial cells that make up the blood-brain barrier have been reported. The processes that mediate this damage involve not only oxidative stress but also include excitotoxic mechanisms, neuroinflammation, the ubiquitin proteasome system, as well as mitochondrial and neurotrophic factor dysfunction. These mechanisms also underlie the toxicity associated with chronic stress and human immunodeficiency virus (HIV) infection, both of which have been shown to augment the toxicity to methamphetamine. Overall, multiple mechanisms are involved and interact to promote neurotoxicity to methamphetamine and MDMA. Moreover, the high coincidence of substituted amphetamine abuse by humans with HIV and/or chronic stress exposure suggests a potential enhanced vulnerability of these individuals to the neurotoxic actions of the amphetamines.

Antioxidant enzyme activity and lipid peroxidation in liver of female rats co-exposed to lead and cadmium: Effects of vitamin E and Mn2+

The oxidative status of liver of female rats exposed to lead acetate and cadmium acetate either alone or in combination at a dose of 0.05 mg/kg body wt intraperitoneally for 15 days was studied. After the administration of lead alone, the activity of superoxide dismutase (SOD) decreased in liver, whereas no changes were observed in catalase (CAT) activity, and glutathione (GSH) and thiobarbituric acid (TBARS) levels. Cadmium exposure and combined exposure to lead and cadmium led to decrease in GSH content and increased TBARS levels. Moreover, animals exposed to either cadmium alone or in combination with lead showed a decrease in SOD activity and an increase in CAT activity. The in vitro experiments showed that vitamin E failed to restore the antioxidant enzyme activities in metal treated postmitochondrial supernatant fraction of liver. But Mn2+ ions protected the mitochondria from lipid peroxidation and could completely restore Mn-superoxide dismutase (Mn-SOD) activity following metal intoxication. The results of this study indicate that despite the ability of lead and cadmium to induce oxidative stress the effect in liver is not intensified by combined exposure to both lead and cadmium. The observed changes in various oxidative stress parameters in the liver of rats co-exposed to lead and cadmium may result from an independent effect of lead and cadmium and also from their interaction such as changes in metal accumulation and content of essential elements like Cu, Zn and Fe. These results suggest that when lead and cadmium are present together in similar concentrations, cadmium mediates major effects due to its more reactive nature.

Mechanisms of C-reactive protein-induced blood-brain barrier disruption

BACKGROUND AND PURPOSE

Increased mortality after stroke is associated with brain edema formation and high plasma levels of the acute phase reactant C-reactive protein (CRP). The aim of this study was to examine whether CRP directly affects blood-brain barrier stability and to analyze the underlying signaling pathways.

METHODS

We used a cell coculture model of the blood-brain barrier and the guinea pig isolated whole brain preparation.

RESULTS

We could show that CRP at clinically relevant concentrations (10 to 20 microg/mL) causes a disruption of the blood-brain barrier in both approaches. The results of our study further demonstrate CRP-induced activation of surface Fcgamma receptors CD16/32 followed by p38-mitogen-activated protein kinase-dependent reactive oxygen species formation by the NAD(P)H-oxidase. The resulting oxidative stress increased myosin light chain kinase activity leading to an activation of the contractile machinery. Blocking myosin light chain phosphorylation prevented the CRP-induced blood-brain barrier breakdown and the disruption of tight junctions.

CONCLUSIONS

Our data identify a previously unrecognized mechanism linking CRP and brain edema formation and present a signaling pathway that offers new sites of therapeutic intervention.

Immunohistochemical localization of 2-Cys peroxiredoxins in human ciliary body

2-Cys peroxiredoxins (PRDX) are novel antioxidant enzymes that eliminate the hydrogen peroxide in cells to protect the cellular components from reactive oxygen species. To evaluate whether 2-Cys PRDX family plays a role in human ciliary body, the expression of PRDX I, II and III on normal human ciliary body was investigated. Three normal human ciliary body tissues obtained from three donor eyeballs were examined by an immunohistochemistry using light microscopy and fluorescent microscopy with antibodies directed against the PRDX I, II and III. In the normal human ciliary body, PRDX I, II and III were immunolocalized to the non-pigmented epithelial cells and ciliary muscle fibers. It suggests that 2-Cys PRDXs may have physiological functions to protect cells in human ciliary body.

Influence of human haptoglobin polymorphism on oxidative stress induced by free hemoglobin on red blood cells

BACKGROUND

An in vitro study was conducted to determine whether haptoglobin phenotypes differed in their protective effect against oxidative stress induced by extracellular hemoglobin on red blood cells.

METHODS

Conjugated dienes and thiobarbituric acid-reactive substances (TBARS) were determined in human red blood cell membranes in the presence of hemoglobin and various concentrations of each type of purified haptoglobin. In addition, the release of K+ and lactate dehydrogenase from red blood cells was measured.

RESULTS

A protective effect of haptoglobin was observed in terms of results obtained for the four parameters examined, with significant differences (p<0.001) between the three haptoglobin types; type 1-1 was the most active and type 2-2 the least active. A proportion of oxidative damage was not sensitive to haptoglobin, but to desferrioxamine (an iron chelator), indicating the participation of two actors, hemoglobin and free iron, in the oxidative stress of membrane lipids.

CONCLUSIONS

The antioxidant role of haptoglobin and the phenotype dependence were confirmed for preventing possible oxidative damage induced by free hemoglobin and iron release during its catabolism.

Causes and consequences of methamphetamine and MDMA toxicity

Methamphetamine (METH) and its derivative 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) are 2 substituted amphetamines with very high abuse liability in the United States. These amphetamine-like stimulants have been associated with loss of multiple markers for dopaminergic and serotonergic terminals in the brain. Among other causes, oxidative stress, excitotoxicity and mitochondrial dysfunction appear to play a major role in the neurotoxicity produced by the substituted amphetamines. The present review will focus on these events and how they interact and converge to produce the monoaminergic depletions that are typically observed after METH or MDMA administration. In addition, more recently identified consequences of METH or MDMA-induced oxidative stress, excitotoxicity, and mitochondrial dysfunction are described in relation to the classical markers of METH-induced damage to dopamine terminals.

Inhibition of mitochondrial creatine kinase activity by D-2-hydroxyglutaric acid in cerebellum of young rats

D-2-Hydroxyglutaric aciduria (DHGA) is a neurometabolic disorder biochemically characterized by tissue accumulation and excretion of high amounts of D-2-hydroxyglutaric acid (DGA). Although the affected patients have predominantly severe neurological findings, the underlying mechanisms of brain injury are virtually unknown. In previous studies we have demonstrated that DGA, at concentrations as low as 0.25 mM, significantly decreased creatine kinase activity and other parameters of energy metabolism in cerebral cortex of young rats. In the present study, we investigated the effect of DGA (0.25-5 mM) on total creatine kinase (tCK) activity, as well as on CK activity in cytosolic (Cy-CK) and mitochondrial (Mi-CK) preparations from cerebellum of 30-day-old Wistar rats in order to test whether the inhibitory effect of DGA on CK was tissue specific. We verified that tCK (22% inhibition) and Mi-CK (40% inhibition) activities were moderately inhibited by DGA at concentrations of 2.5 mM and higher, in contrast to Cy-CK, which was not affected by the acid. Kinetic studies revealed that the inhibitory effect of DGA was noncompetitive in relation to phosphocreatine. We also observed that this inhibition was fully prevented by preincubation of the homogenates with reduced glutathione, suggesting that the inhibition of CK activity by DGA is possibly mediated by modification of essential thiol groups of the enzyme. Our present results therefore demonstrate a relatively weak inhibitory effect of DGA on cerebellum Mi-CK activity, as compared to that provoked in cerebral cortex, and may possibly be related to the neuropathology of DHGA, characterized by cerebral cortex abnormalities.

Modulation of intercellular communication mediated at the cell surface and on extracellular, plasma membrane-derived vesicles by ionizing radiation

The plasma membrane is a dynamic organelle whose function includes receptor-mediated signal transduction into the cell. Conversely, the plasma membrane is the origin of inter-cellular signaling. In addition to expressing and releasing growth factors in a soluble form(through exocytosis) and via proteolysis of cell surface components, membrane ligands may signal nearby cells through juxtacrine stimulation or by the exfoliation or shedding of plasma membrane-derived vesicles. Ionizing radiation (IR) has a profound effect on plasma membrane structure and function. IR-induced ultrastructural alterations are mediated via lipid interaction with water radiolysis products (e.g., hydroxyl radicals, hydrogen radicals, and hydrated electrons). Ionizing radicals act directly on lipid molecules to promote lipid hydro-peroxides and lipid hydroperoxide breakdown products (e.g., alpha, beta unsaturated aldehydes) that contribute to altered plasma membrane lipid composition. A change in lipid composition increases membrane lipid microviscosity and results in membrane fenestrations that enhance permeability to small molecules and ions. Reactive ionizing species also stimulate sphingomyelinase activity, leading to sphingomyelin hydrolysis and ceramide generation that further contributes to altered membrane lipid composition and cellular apoptosis. In addition, exposure to IR results in impaired rate of and cumulative shedding of plasma membrane-associated growth factors. Mechanisms of exfoliation are reviewed for normal cells and the impact of radiation on modulating signal transduction mediated by exfoliation is summarized.

Lipid peroxidation and antioxidant vitamins prior to, during, and after correction of diabetic ketoacidosis

Oxidative stress plays an important role in the chronic complications of insulin-dependent diabetes mellitus (IDDM). Hyperketonemia, as well as hyperglycemia, is involved in the generation of oxygen-free radicals. We have studied the degree of oxidative stress in six patients before, during, and after correction of diabetic ketoacidosis (DKA) by determining the plasma ratios of C20 and C18 fatty acids to C16 fatty acids in the cholesteryl esters of the lipoproteins as well as in the plasma concentrations of the antioxidant vitamins A, C, and E. Lipid peroxidation was slightly increased prior to treatment. However, the C20/C16 ratio at 120 h was significantly decreased in comparison to the ratio at pretreatment (P<.025), at 6-8 h (P<.005), and at 24 h (P<.025). The C18/16 ratio at 120 h was also decreased in comparison to the ratio at 6-8 h (P<.025), indicating an increase in lipid peroxidation after correction of DKA. Vitamin A was below normal at pretreatment and was increased at 120 h (P<.05). Vitamin C was normal at pretreatment and decreased to low normal at 24 h (P<.005). Vitamin E was normal at pretreatment and decreased to below normal at 24 and 120 h, although the changes were not statistically significant. These data demonstrate that there is an increase in lipid peroxidation after the correction of DKA and therefore support the position that administering antioxidant vitamins during the treatment of DKA could be beneficial in minimizing oxidative stress and possibly both the acute and chronic complications of IDDM.

Cocaine activates redox-regulated transcription factors and induces TNF-alpha expression in human brain endothelial cells

Cocaine abuse is frequently associated with cerebrovascular pathology. Although the cellular and molecular mechanisms of these alterations are not fully understood, they may involve oxidative injury or dysfunction of brain microvascular endothelial cells. To test this hypothesis, total glutathione levels, activation of nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1), as well as induction of the TNF-alpha gene expression were determined in human brain microvascular endothelial cells (HBMEC) exposed to cocaine. Exposure of HBMEC to cocaine resulted in a dose-dependent depletion of total glutathione levels. In addition, cocaine markedly activated redox-regulated transcription factors, NF-kappaB and AP-1. Activation of these transcription factors was accompanied by induction of AP-1- or NF-kappaB-dependent transcription, as measured by dual luciferase assay in HBMEC transfected with the AP-1- or NF-kappaB-responsive reporter constructs. Furthermore, HBMEC treatment with cocaine induced a dose-dependent expression of the tumor necrosis factor-alpha (TNF-alpha) gene. These results indicate that exposure to cocaine can trigger inflammatory pathways via activation of redox-sensitive transcription factors and induction of expression of the inflammatory genes in HBMEC. These events may contribute to the cerebrovascular insults observed in cocaine-abused patients.

Methamphetamine induces AP-1 and NF-kappaB binding and transactivation in human brain endothelial cells

Cellular and molecular mechanisms of methamphetamine (METH)-induced neurotoxicity may involve alterations of cellular redox status and induction of inflammatory genes in endothelial cells. To study these hypotheses, molecular signaling pathways of METH-induced inflammatory responses via activation of redox-sensitive transcription factors were investigated in human brain microvascular endothelial cells (HBMEC). A dose-dependent depletion of total glutathione levels was detected in HBMEC exposed to METH. In addition, electrophoretic mobility shift assay (EMSA) showed significant increases in DNA binding activities of redox-responsive transcription factors, AP-1 and NF-kappaB, in HBMEC treated with METH. METH-mediated AP-1 or NF-kappaB activation was accompanied by induction of transactivation of AP-1 or NF-kappaB, as measured by dual luciferase assay using specific reporter plasmids. Because NF-kappaB and AP-1 are known to regulate expression of inflammatory genes, expression of the gene encoding for tumor necrosis factor-alpha (TNF-alpha) was also studied in METH-treated HBMEC. A dose-dependent overexpression of the TNF-alpha gene was observed in HBMEC treated with METH. The importance of AP-1 and NF-kappaB in METH-induced TNF-alpha gene was confirmed in functional promoter studies using constructs of the TNF-alpha promoter with mutated AP-1 or NF-kappaB sites. These results indicate that METH-induced disturbances in cellular redox status and activation of AP-1 and NF-kappaB can play critical roles in the signaling pathways leading to upregulation of inflammatory genes in human brain endothelial cells.

Influence of antioxidants on the blood-brain barrier permeability during epileptic seizures

Pentylenetetrazol-induced seizures in rats lead to the breakdown of the blood-brain barrier. We compared the disruption of the blood-brain barrier during epileptic seizure in untreated rats and in rats treated with vitamin E or selenium. The rats were supplemented with nontoxic doses of sodium selenite (4 pp) in drinking water for 3 months, or vitamin E (70 mg/kg) was given intraperitoneally for 30 min before the pentylenetetrazole injection. Evans-blue was used as a blood-brain barrier tracer and was given intravenously at a dose of 4 ml/kg of a 2% solution. The rats were divided into four experimental groups. Group I: control (n = 24); Group II: pentylenetetrazole-induced seizure (n = 12); Group III: vitamin E injected + seizure (n = 12); Group IV: Selenium supplemented + seizure (n = 12). The rats subjected to epileptic seizures showed Evans-blue albumin extravasations especially in the thalamic nuclei, brainstem, occipital, and frontal cortex. Mean values for Evans-blue dye were found to be 0.28 +/- 0.04 mg % brain tissue in control rats and 1.6 +/- 0.2 mg % brain tissue after epileptic seizures (P < 0.01). The magnitude of distribution of the blood-brain barrier during epileptic seizures was significantly less in rats treated with vitamin E or selenium. The mean value for Evans-blue dye was found to be 1.2 +/- 0.1 mg % brain tissue in selenium supplemented rats and 1.2 +/- 0.1 mg % brain tissue in vitamin E injected rats after epileptic seizures. This difference between treated and untreated animals was found to be significant (P < 0.05). The findings of the present study suggest that free radicals contribute to disruption of the blood-brain barrier during pentylenetetrazol-induced seizures.

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.

*NO and oxyradical metabolism in new cell lines of rat brain capillary endothelial cells forming the blood-brain barrier

To investigate the relevance of *NO and oxyradicals in the blood-brain barrier (BBB), differentiated and well-proliferating brain capillary endothelial cells (BCEC) are required. Therefore, rat BCEC (rBCEC) were transfected with immortalizing genes. The resulting lines exhibited endothelial characteristics (factor VIII, angiotensin-converting enzyme, high prostacyclin/thromboxane release rates) and BBB markers (gamma-glutamyl transpeptidase, alkaline phosphatase). The control line rBCEC2 (mock transfected) revealed fibroblastoid morphology, less factor VIII, reduced gamma-glutamyl transpeptidase, weak radical defence, low prostanoid metabolism, and limited proliferation. Lines transfected with immortalizing genes (especially rBCEC4, polyoma virus large T antigen) conserved primary properties: epitheloid morphology, subcultivation with high proliferation rate under pure culture conditions, and powerful defence against reactive oxygen species (Mn-, Cu/Zn-superoxide dismutase, catalase, glutathione peroxidase, glutathione) effectively controlling radical metabolism. Only 100 microM H2O2 overcame this defence and stimulated the formation of eicosanoids similarly as in primary cells. Some BBB markers were expressed to a lower degree; however, cocultivation with astrocytes intensified these markers (e.g., alkaline phosphatase) and paraendothelial tightness, indicating induction of BBB properties. Inducible NO synthase was induced by a cytokine plus lipopolysaccharide mixture in all lines and primary cells, resulting in *NO release. Comparing the cell lines obtained, rBCEC4 are stable immortalized and reveal the best conservation of properties from primary cells, including enzymes producing or decomposing reactive species. These cells can be subcultivated in large amounts and, hence, they are suitable to study the role of radical metabolism in the BBB and in the cerebral microvasculature.

Glutathione homeostasis and leukotriene-induced permeability in human blood-brain barrier endothelial cells subjected to in vitro ischemia

Ischemic alterations in the glutathione (GSH) redox system of the blood-brain barrier (BBB) may facilitate oxidative injury and formation of vasogenic brain edema. In this study, both the intra- and extracellular GSH contents of human cerebromicrovascular endothelial cells (HCEC) were reduced by 35% after exposing the cells to 4 h in vitro ischemia and 24 h-recovery. The intracellular/extracellular GSH ratio was not affected, indicating a constant rate of GSH efflux. The activities of the peroxide detoxifying enzymes, glutathione peroxidase and glutathione S-transferase, increased by 35%-50%, whereas the GSH regenerating enzyme, glutathione reductase, remained unchanged in ischemic HCEC. gamma-glutamyl transpeptidase (GGTP), a GSH catabolizing enzyme enriched in brain capillaries, was reduced by 30-50% in ischemic HCEC. The effect of in vitro ischemia on HCEC permeability was assessed by measuring sodium fluorescein clearance across a compartmentalized in vitro BBB model. Sodium fluorescein clearance across HCEC monolayers exposed to leukotriene C4 in the presence of the GGTP inhibitor, acivicin (1 microM), or after in vitro ischemia was increased by 60% and 30%, respectively, suggesting that oxidative stress and loss of GGTP may 'unmask' BBB permeabilizing actions of leukotrienes. These results indicate that oxidative stress and loss of GGTP activity in HCEC contribute to ischemic BBB disruption and vasogenic brain edema.

Sex-dependent changes in blood-brain barrier permeability and brain NA(+),K(+) ATPase activity in rats following acute water intoxication

To understand the increased susceptibility of the development of serious complications to hypoosmotic hyponatremia in young females, we examined the resistance of blood brain barrier (BBB) permeability to water along with the synaptosomal Na(+),K(+)ATPase activity in both sexes of rats during acute water intoxication. Four groups of rats were used: Group I and II were normal female and male rats injected with only Evans-blue. Group III and IV were water intoxicated female and male rats respectively. BBB permeability in female rats was found to be increased following acute water intoxication. In contrast, synaptosomal Na(+),K(+)ATPase activities in both water intoxicated male and female rats were found significantly lower than those in control rats. But inhibition in enzyme activity in synaptosomes from water intoxicated female rats was more pronounced than those of corresponding male rats. Our results concluded that female sex steroids may be responsible for the highly significant decrease in synaptosomal Na(+),K(+)ATPase activity and increased BBB permeability in female rats following water intoxication.

Influence of antioxidants on blood-brain barrier permeability during adrenaline-induced hypertension

We have examined the effect of antioxidants (vitamin E, and selenium) on the blood-brain barrier permeability during adreneline-induced acute hypertension in the female rats. The rats supplemented with nontoxic doses of sodium selenite in drinking water for three months or vitamin E was given intraperitoneally before adrenaline-induced acute hypertension. Evans-blue was used as a blood-brain barrier tracer. Mean values for Evans-blue dye were found to be 0.28 +/- 0.04 microg/g tissue in control animals and 1.0 +/- 0.2 microg tissue after adrenaline-induced acute hypertension (p < .01). Rats pretreated with selenium or vitamin E also showed macroscopic leakage of Evans-blue albumin after adrenaline injection i.e., there was no significant difference in protein extravasation between untreated and treated animals (p > .5). The mean value for Evans-blue dye was found to be 1.0 +/- 0.2 microg/g tissue in acute hypertension group, 0.9 +/- 0.2 microg/g tissue in selenium pretreated animals and 1.0 +/- 0.2 micrg/g tissue vitamin E injected animals after acute hypertension. The results show that antioxidants did not influence the blood-brain barrier breakdown during adrenaline-induced acute hypertension.

Increase in vulnerability of middle-aged rat brain to lead by cerebral energy depletion

The neurotoxic effects of low-level lead (Pb) during senescence are increasing interests of importance. We investigated the effects of low-level Pb on the brain in a normal condition and a pathophysiological condition of energy shortage that is commonly found in age-related neurological diseases. Middle-aged rats (15 months old) were exposed to 200 mg/l Pb acetate in drinking water for 2 months and thereafter received bilateral intracerebroventricular injections of streptozotocin (STZ). After 1 month's additional exposure to the same level of Pb solution as before the rats were sacrificed. Blood and brain Pb levels were measured by graphite furnace atomic absorption spectrophotometry. Energy-rich phosphate levels in the brain were determined by high-performance liquid chromatography equipped with a UV detector. Astroglial activation and glucose-regulated protein (GRP)94 expression were examined immunohistochemically. Exposure to Pb increased the blood Pb level to 10.8 microg/dl and the brain Pb level to 0.052 microg/g. But a significant additional increase in the brain Pb level, to 0.101 microg/g, became obvious in rats treated with Pb + STZ. Both Pb and STZ induced perturbation in brain energy metabolism, but no further alteration in energy metabolite levels was found in rats treated with Pb + STZ. Astroglial activation and GRP94-positive astrocytes and neurons were found only in the brains of Pb + STZ-treated rats. These results suggest that exposure to low-level Pb can perturb brain energy metabolism and the brain becomes more vulnerable to Pb when it is under energy stress.

Astrocyte cultures from transgenic mice to study the role of metallothionein in cytotoxicity of tert-butyl hydroperoxide

The cell viability, lipid peroxidation (LPO) and hydrogen peroxide (H(2)O(2)) generation were measured in cultured primary astrocytes, from metallothionein (MT)-I isoform overexpressing transgenic (MT-I*), MT-I/MT-II null and control mice after exposure to tert-butylhydroperoxide (tBH). Astrocytes from MT-I* mice have high basal levels of both MT-I mRNA and MT protein, whereas there is only MT-III isoform in astrocytes from MT-I/MT-II null mice. The results showed that (1) cultured astrocytes from MT-I* mice were most resistant to the cytotoxicity of tBH and those from MT-I/MT-II null mice were most sensitive to the cytotoxicity of tBH; (2) LPO after exposure to tBH were increased in all cells, but the levels were the highest in astrocytes from MT-I/MT-II null mice, while those in MT-I* mice were the lowest; (3) the levels of H(2)O(2) in cultured astrocytes from MT-I* mice were the lowest, while those in astrocytes from MT-I/MT-II null mice were the highest. These results support the hypothesis that MT can scavenge free radicals and protect astrocytes from oxidative stress.

Inflammatory mediators of cerebral endothelium: a role in ischemic brain inflammation

Brain inflammation has been implicated in the development of brain edema and secondary brain damage in ischemia and trauma. Adhesion molecules, cytokines and leukocyte chemoattractants released/presented at the site of blood-brain barrier (BBB) play an important role in mobilizing peripheral inflammatory cells into the brain. Cerebral endothelial cells (CEC) are actively engaged in processes of microvascular stasis and leukocyte infiltration by producing a plethora of pro-inflammatory mediators. When challenged by external stimuli including cytokines and hypoxia, CEC have been shown to release/express various products of arachidonic acid cascade with both vasoactive and pro-inflammatory properties, including prostaglandins, leukotrienes, and platelet-activating factor (PAF). These metabolites induce platelet and neutrophil activation and adhesion, changes in local cerebral blood flow and blood rheology, and increases in BBB permeability. Ischemic CEC have also been shown to express and release bioactive inflammatory cytokines and chemokines, including IL-1beta, IL-8 and MCP-1. Many of these mediators and ischemia in vitro and in vivo have been shown to up-regulate the expression of both selectin and Ig-families of adhesion molecules in CEC and to facilitate leukocyte adhesion and transmigration into the brain. Collectively, these studies demonstrate a pivotal role of CEC in initiating and regulating inflammatory responses in cerebral ischemia.

Membrane ion transport systems during oxidative stress in rodent brain: protective effect of stobadine and other antioxidants

The effect of oxidative stress in vitro induced by radical generating systems (RGS) (Fe2+-EDTA and Fe2+-EDTA plus H2O2) on synaptosomal and microsomal ion transport systems as well as on the membrane fluidity was investigated. Oxidative insult reduced Na+, K+-ATPase activity by 50.7% and Na+-dependent Ca2+ uptake measured in choline media by 46.7%. Membrane fluidity was also significantly reduced as observed with the fluorescent probe. Stobadine (ST) prevented the decrease in membrane fluidity and Na+-dependent Ca2+ uptake, however Na+, K+-ATPase activity was only partially protected, indicating a more complex mechanism of inhibition. Incubation of microsomes with RGS led to the loss of ability of membranes to sequester Ca2+, as well as to the decrease of Ca2+-ATPase activity and to the increase of Ca2+ permeability to 125.1%. The relative potency of the two RGS to decrease membrane fluidity correlated well with the system's potencies to induce lipid peroxidation. The extent of protection against depression of Ca2+ uptake values and Ca2+-ATPase activity by membrane soluble antioxidants (U-74500A, U-83836E, t-butylated hydroxytoluene-BHT and ST) was dependent on the experimental conditions and on the dose and nature of antioxidant used. ST seems to be at least as affective as BHT and 21-aminosteroids, and more potent than tocopherol acetate. Water soluble glutathione had no significant effect on the RGS induced inhibition of Ca2+-ATPase activity. Combination of ST with glutathione enhanced ST antioxidant efficacy, so drug combination might be beneficial therapeutically.

Developmental pattern of reactive oxygen species generation and antioxidative defense machinery in rat cerebral microvessels

The developmental profile of certain enzymatic antioxidants as well as the generation of reactive oxygen species was studied in the rat cerebral microvessels during first three weeks of life and the levels were compared to those present in adults. The data showed a higher generation of superoxide anion (+67%) and H2O2 (+200%) at postnatal day (PND) 21. Superoxide anion production was significantly lower (-24%) at PND 14 and almost comparable to adult values at PND 7. The activity of superoxide dismutase increased with development and attained an adult level at PND 21. Catalase was higher in neonates with a maximum activity at PND 7 and 14 (+68, 69%). The measurement of microvessel glutathione and glutathione-related antioxidant enzymes showed that glutathione level was higher at PND 7, which declined to an adult level at PND 14. Se-dependent GPx showed a marked increase between PND 14 and 21, however, it declined in adults. The activity of Se-independent glutathione peroxidase was very low in cerebral microvessels. Glutathione reductase activity in 7-day-old, that was comparable to adult level, declined at PND 14 and 21. The level of glutathione S-transferase was higher (+43%) at PND 21. The activity of microvessel marker enzyme gamma-glutatmyl transpeptidase increased with age, whereas, alkaline phosphatase showed a slight increase up to PND 14 and thereafter it declined. Lipid peroxidation was found to be significantly lower (-18%) at PND 21 as compared to adults. It may be concluded that developing cerebral microvessels contain high levels of several antioxidant enzymes that are more or equal to those present in adult brain microvessels.

Increased doxorubicin uptake and toxicity in multicellular tumour spheroids treated with DC electrical fields

Electrochemotherapy (ECT) is a new approach to the treatment of tumours. In the present study, multicellular prostate tumour spheroids were treated with non-lethal direct current (DC) electrical fields, and uptake and toxicity of doxorubicin were investigated. An electrical field with a field strength of 500 Vm(-1) applied for a duration of 90 s resulted in neither reversible nor irreversible membrane breakdown as revealed by fluid phase uptake studies of the membrane impermeant tracer Lucifer yellow. However, treated spheroids showed an increased uptake of doxorubicin and, consequently, an increased toxicity following electrical field exposure. The electrical field raised intracellular reactive oxygen species (ROS) as revealed using 2',7'-dichlorofluorescein diacetate (H2DCFDA) as an indicator. ROS induced membrane lipid peroxidation since the lipid peroxidation end products malondialdehyde (MDA) and 4-hydroxy-2-(E)-nonenal (4-HNE) were detected after electrical field treatment. Moreover, lipid peroxidation decreased the lipid diffusion coefficient D from 4.2 x 10(-10) cm2 s(-1) to 2.7 x 10(-10) cm2 s(-1) in the control and treated sample, respectively, as revealed by fluorescence recovery after photobleaching (FRAP) experiments. The field effects could be mimicked by incubating spheroids with 100 nM hydrogen peroxide and were inhibited by the radical scavengers dehydroascorbate (DHA) and alpha-tocopherol (vitamin E), indicating that the increased uptake of doxorubicin after electrical field treatment is owing to lipid peroxidation and decreased membrane lipid mobility. Treatment of tumours with low intensity electrical fields may be useful to improve the cytotoxic capacity of anthracyclines.

Stimulation of active sodium-potassium transport by hydrogen peroxide in cultured rabbit nonpigmented ciliary epithelium

PURPOSE

Studies were conducted to examine the effect of hydrogen peroxide on active sodium-potassium transport in a cell line derived from nonpigmented ciliary epithelium of the rabbit eye.

METHODS

Studies were carried out using a rabbit nonpigmented ciliary epithelium cell line. 86Rb uptake by intact cells was measured in the presence or absence of ouabain. The ouabain-sensitive potassium (86Rb) uptake rate was used as an index of the rate of active sodium-potassium transport. Cell sodium content was measured by atomic absorption spectrophotometry. Na,K-ATPase activity was determined by measuring ATP hydrolysis in the presence or absence of ouabain, using membrane material isolated by centrifugation of cell homogenates.

RESULTS

Ouabain-sensitive potassium (86Rb) uptake rate measured in cells that had been preincubated with 200microM hydrogen peroxide for either 30 min or 60 min was increased to 196% and 181% of the control uptake rate, respectively. Lesser concentrations of hydrogen peroxide caused lesser degrees of stimulation. 200microM hydrogen peroxide caused an increase of cell sodium content. Such a change of cell sodium content is likely to be responsible, at least in part, for the observed stimulation of active sodium-potassium transport. However, the response may also be partly dependent on activation of a protein kinase since the serine/threonine protein kinase inhibitors staurosporine (1microM) and H-89 (20microM) were both found to prevent the stimulatory effect of 200microM hydrogen peroxide on ouabain-sensitive potassium (86Rb) uptake. Interestingly, neither H-89 nor staurosporine prevented the elevation of sodium content in cells that received 200microM hydrogen peroxide.

CONCLUSIONS

Taken together, these findings suggest a low concentration of hydrogen peroxide causes increased sodium entry into the cell and also activates a protein kinase-dependent mechanism for sodium pump stimulation. The protein kinase-dependent mechanism does not appear to be triggered by an increased rate of sodium entry since staurosporine did not prevent the stimulation of ouabain-sensitive potassium (86Rb) uptake elicited by an increase in sodium permeability caused by amphotericin B.

Decreased endothelial cell glutathione and increased sensitivity to oxidative stress in an in vitro blood-brain barrier model system

Using a cell culture model of the blood-brain barrier (BBB) we have evaluated the role of endothelial cell glutathione in protecting barrier integrity against nitric oxide (NO)-induced oxidative stress. The co-culture of human umbilical vein endothelial cells (ECV304) with rat (C6) glioma cells, or incubation with glioma cell or primary astrocytic conditioned medium, resulted in a decline in endothelial cell glutathione. Exposure to a single addition of NO gas induced a rapid breakdown in model barrier integrity in endothelial/glioma co-cultures. Addition of NO gas or tumour necrosis factor-alpha (TNF-alpha) also resulted in a loss of membrane integrity, as measured by an enhanced release of lactate dehydrogenase, only from endothelial cells treated with glioma conditioned medium. Furthermore, assessment of viability in endothelial cells grown alone or treated with glioma conditioned medium, by propidium iodide labelled flow cytometry. demonstrated no difference in the number of positively stained cells after NO exposure. These results indicate that when enhanced endothelial monolayer barrier formation occurs via astrocytic-endothelial interactions, cellular glutathione levels are decreased. This renders the barrier cells, under these conditions, more susceptible to oxidative stress but does no necessarily lead to greater cell death.

Evidence that functional glutamate receptors are not expressed on rat or human cerebromicrovascular endothelial cells

Excitatory amino acids can modify the tone of cerebral vessels and permeability of the blood-brain barrier (BBB) by acting directly on endothelial cells of cerebral vessels or indirectly by activating receptors expressed on other brain cells. In this study we examined whether rat or human cerebromicrovascular endothelial cells (CEC) express ionotropic and metabotropic glutamate receptors. Glutamate and the glutamate receptor agonists N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA), and kainate failed to increase [Ca2+]i in either rat or human microvascular and capillary CEC but elicited robust responses in primary rat cortical neurons, as measured by fura-2 fluorescence. The absence of NMDA and AMPA receptors in rat and human CEC was further confirmed by the lack of immunocytochemical staining of cells by antibodies specific for the AMPA receptor subunits GluR1, GluR2/3, and GluR4 and the NMDA receptor subunits NR1, NR2A, and NR2B. We failed to detect mRNA expression of the AMPA receptor subunits GluR1 to GluR4 or the NMDA receptor subunits NR1(1XX); NR1(0XX), and NR2A to NR2C in both freshly isolated rat and human microvessels and cultured CEC using reverse transcriptase polymerase chain reaction (RT-PCR). Cultured rat CEC expressed mRNA for KA1 or KA2 and GluR5 subunits. Primary rat cortical neurons were found to express GluR1 to GluR3 and NR1, NR2A, and NR2B by both immunocytochemistry and RT-PCR and KA1, KA2, GluR5, GluR6, and GluR7 by RT-PCR. Moreover, the metabotropic glutamate receptor agonist 1-amino-cyclopentyl-1S, 3R-dicorboxylate (1S,3R-trans-ACPD), while eliciting both inositol trisphosphate and [Ca2+]i increases and inhibiting forskolin-stimulated cyclic AMP in cortical neurons, was unable to induce either of these responses in rat or human CEC. These results strongly suggest that both rat and human CEC do not express functional glutamate receptors. Therefore, excitatory amino acid-induced changes in the cerebral microvascular tone and BBB permeability must be affected indirectly, most likely by mediators released from the adjacent glutamate-responsive cells.

Glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures exposed to ischemia

In this study we demonstrate the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to a sublethal ischemic insult in vitro. To measure sodium pump activity and glutamate uptake, 3H-glutamate and 86Rb were simultaneously added to the cultures in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive 86Rb uptake. Cell death was assessed by exclusion of the vital dye, calcein-AM from cells. Concomitant transient increases (2-3 fold above control levels) in both Na,K-ATPase and glutamate transporter activities were observed in astrocytes after 2-4 hours of ischemia. By contrast, 24 hours of ischemia caused a profound loss of both activities which paralleled significant cell death. The addition of 5 mM glucose to the cells after 4 hours of ischemia prevented the loss of sodium pump activity and glutamate uptake, and rescued astrocytes from the lethal effects of 24 hours of ischemia.

Iron-induced inhibition of Na+, K(+)-ATPase and Na+/Ca2+ exchanger in synaptosomes: protection by the pyridoindole stobadine

The effect of oxidative stress, induced by Fe(2+)-EDTA system, on Na+,K(+)-ATPase, Na+/CA2+ exchanger and membrane fluidity of synaptosomes was investigated. Synaptosomes isolated from gerbil whole forebrain were incubated in the presence of 200 microM FeSO4-EDTA per mg of protein at 37 degrees C for 30 min. The oxidative insult reduced Na+,K(+)-ATPase activity by 50.7 +/- 5.0% and Na+/Ca2+ exchanger activity measured in potassium and choline media by 47.1 +/- 7.2% and 46.7 +/- 8.6%, respectively. Membrane fluidity was also significantly reduced as observed with the 1,6-diphenyl-1,3,5-hexatriene probe. Stobadine, a pyridoindole derivative, prevented the decrease in membrane fluidity and in Na+/Ca2+ exchanger activity. The Na+,K(+)-ATPase activity was only partially protected by this lipid antioxidant, indicating a more complex mechanism of inhibition of this protein. The results of the present study suggest that the Na+/Ca2+ exchanger and the Na+,K(+)-ATPase are involved in oxidation stress-mediated disturbances of intracellular ion homeostasis and may contribute to cell injury.

Stimulation of glutamate uptake and Na,K-ATPase activity in rat astrocytes exposed to ischemia-like insults

The postsynaptic actions of glutamate are rapidly terminated by high affinity glutamate uptake into glial cells. In this study we demonstrate the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to sublethal ischemia-like insults. Primary cultures of neonatal rat cortical astrocytes were subjected to hypoxia, or to serum- and glucose-free medium, or to both conditions (ischemia). Cell death was assessed by propidium iodide staining of cell nuclei. To measure sodium pump activity and glutamate uptake, 3H-glutamate and 86Rb were both simultaneously added to the cell culture in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive 86Rb uptake. Concomitant transient increases (2-3 times above control levels) of both Na,K-ATPase and glutamate transporter activities were observed in astrocytes after 4-24 h of hypoxia, 4 h of glucose deprivation, and 2-4 h of ischemia. A 24 h ischemia caused a profound loss of both activities in parallel with significant cell death. The addition of 5 mM glucose to the cells after 4 h ischemia prevented the loss of both sodium pump activity and glutamate uptake and rescued astrocytes from death observed at the end of 24 h ischemia. Reoxygenation after the 4 h ischemic event caused the selective inhibition of Na,K-ATPase activity. The observed increases in Na,K-ATPase activity and glutamate uptake in cultured astrocytes subjected to sublethal ischemia-like insults may model an important functional response of astrocytes in vivo by which they attempt to maintain ion and glutamate homeostasis under restricted energy and oxygen supply.