Na/K-ATPase and oxidative stress

Impact of manganese accumulation on Na,K-ATPase expression and function in the cerebellum and striatum of C57Bl/6 mice

Overexposure to Mn causes a neurological disorder-manganism-with motor symptoms that overlap closely with disorders associated with haploinsufficiency in the gene encoding for α3 isoform of Na+,K+-ATPase (NKA). The present study was designed to test the hypothesis that behavioral changes in the mouse model of manganism may be associated with changes in the expression and activity of α3 NKA in the cerebellum (CB) and striatum (STR)-the key brain structures responsible for motor control in adult mice. C57Bl/6 mice were exposed to MnCl2 at 0.5 g/L (in drinking water) for up to eight weeks. After four weeks of Mn consumption, Mn levels were increased in the CB only. Behavioral tests demonstrated decreased performance of Mn-treated mice in the shuttle box test (third through sixth weeks), and the inclined grid walking test (first through sixth weeks), suggesting the development of learning impairment, decreased locomotion, and motor discoordination. The activity of NKA significantly decreased, and the expression of α1-α3 isoforms of NKA increased in the second week in the CB only. Thus, signs of learning and motor disturbances developing in this model of manganism are unlikely to be directly linked to disturbances in the expression or activity of NKA in the CB or STR. Whether these early changes may contribute to the pathogenesis of later behavioral deficits remains to be determined.

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.

Effects of natural polyphenol-rich pomegranate juice supplementation on plasma ion and lipid profiles following resistance exercise: a placebo-controlled trial

Background

Pomegranate juice (POMj) contains abundant soluble polyphenolic antioxidant compounds and is recommended for its cardioprotective/atheroprotective properties. However, very few studies have investigated the efficacy of POMj supplementation to alter physiological responses during intensive physical exercise. This placebo-controlled study aimed to examine whether supplementation with natural polyphenol-rich-POMj could influence the ionic or lipid responses to an intensive resistance training session in elite athletes.

Methods

Nine elite weightlifters (21 ± 1 years) performed two Olympic-weightlifting sessions after ingesting placebo and POMj supplements. Venous blood samples were collected at rest and 3 min after each session for assessment of plasma sodium ([Na⁺]), potassium ([K⁺]), chloride ([Cl^-]), calcium ([Ca²⁺]), triglyceride ([TG]) and high-density lipoprotein ([HDL-C]), low-density lipoprotein ([HDL-C]) and total ([TC]) cholesterol concentrations.

Results

Plasma [K⁺] and [TG] were lowered post-exercise compared to resting values in the PLA condition (p = 0.03 for K⁺ and p = 0.02 for TG) with no pre-to-post exercise differences in the other plasma ion and lipid markers (p > 0.05). Compared to rest, plasma [Na⁺] and [Cl^-] were increased (p = 0.04, %change = 4.10% for Na⁺ and p = 0.02, %change = 4.44% for Cl^-), but there were no differences in the other plasma ion or lipid markers post-exercise after POMj supplementation (p > 0.05). Post-exercise plasma [Na⁺], [Cl^-], and [HDL-C] were greater following POMj supplementation compared to PLA (p = 0.01 for Cl- and HDL-C, p = 0.02 for Na+, and p = 0.04 for TC), with no between-supplement post-exercise differences in the other ion and lipid markers (p > 0.05).

Conclusion

In conclusion, supplementation with POMj has the potential to attenuate the acute imbalance of plasma [K⁺] and to improve blood lipid responses (i.e., HDL-C) following resistance exercises in elite weightlifters. However, further large research in both athletic and non-athletic populations is needed to corroborate these preliminary observations and to elucidate the potential underlying mechanisms and translational potential of our novel observations.

Trial registration

Name of the registry:ClinicalTrials.gov PRSThe registration number:NCT02697903.Date of Registry: 03/03/2016 'Retrospectively registered'.The registration title: Pomegranate Improve Biological Recovery Kinetics in Elite Weightlifter.

Graphical abstract

Sigma-1 Receptor Antagonists Haloperidol and Chlorpromazine Modulate the Effect of Glutoxim on Na+ Transport in Frog Skin

Using voltage-clamp technique, the involvement of sigma-1 receptors in the regulation of Na+ transport in frog skin by the immunomodulatory drug glutoxim was investigated. We have shown for the first time that preincubation of the frog skin with the sigma-1 receptor antagonists haloperidol and chlorpromazine attenuates the stimulatory effect of glutoxim on the Na+ transport. The results suggest the possible involvement of the sigma-1 receptors in the regulation of Na+ transport in frog skin epithelium by glutoxim.

Molecular stressors underlying exercise training-induced improvements in K+ regulation during exercise and Na+ ,K+ -ATPase adaptation in human skeletal muscle

Despite substantial progress made towards a better understanding of the importance of skeletal muscle K⁺ regulation for human physical function and its association with several disease states (eg type-II diabetes and hypertension), the molecular basis underpinning adaptations in K⁺ regulation to various stimuli, including exercise training, remains inadequately explored in humans. In this review, the molecular mechanisms essential for enhancing skeletal muscle K⁺ regulation and its key determinants, including Na⁺ ,K⁺ -ATPase function and expression, by exercise training are examined. Special attention is paid to the following molecular stressors and signaling proteins: oxygenation, redox balance, hypoxia, reactive oxygen species, antioxidant function, Na⁺ ,K⁺ , and Ca²⁺ concentrations, anaerobic ATP turnover, AMPK, lactate, and mRNA expression. On this basis, an update on the effects of different types of exercise training on K⁺ regulation in humans is provided, focusing on recent discoveries about the muscle fibre-type-dependent regulation of Na⁺ ,K⁺ -ATPase-isoform expression. Furthermore, with special emphasis on blood-flow-restricted exercise as an exemplary model to modulate the key molecular mechanisms identified, it is discussed how training interventions may be designed to maximize improvements in K⁺ regulation in humans. The novel insights gained from this review may help us to better understand how exercise training and other strategies, such as pharmacological interventions, may be best designed to enhance K⁺ regulation and thus the physical function in humans.

Lipoxygenases modulate the effect of glutoxim on Na+ transport in the frog skin epithelium

Using voltage-clamp technique, the involvement of lipoxygenases in the effect of immunomodulatory drug glutoxim on Na⁺ transport in frog skin was investigated. It was shown for the first time that preincubation of the skin with lipoxygenase inhibitors caffeic acid, baicalein, and nordihydroguaiaretic acid significantly decreases the stimulatory effect of glutoxim on Na⁺ transport. The data suggest the involvement of lipoxygenase oxidation pathway of arachidonic acid metabolism in the glutoxim effect on Na⁺ transport in frog skin epithelium.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

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.

Carnosine prevents necrotic and apoptotic death of rat thymocytes via ouabain-sensitive Na/K-ATPase

It is known that ouabain, a selective inhibitor of Na/K-ATPase, not only can cause the activation of signal cascades, which regulate the cell viability, but also can cause the accumulation of free radicals, which can evoke the oxidative stress. We have shown that the nanomolar concentrations of ouabain result in the temporary increase in the level of intracellular free radicals, but the millimolar concentration of ouabain induces a stable intracellular accumulation of free radicals in rat thymocytes. The increasing level of free radicals resulting from both low and high concentrations of ouabain can be attenuated by the antioxidant, carnosine. Moreover, the long-term incubation with ouabain leads to the cell death by necrosis and apoptosis. Ouabain-mediated apoptosis and necrosis were also abolished by carnosine.

Altered energy status of primary cerebellar granule neuronal cultures from rats exposed to lead in the pre- and neonatal period

This paper examines the effect of pre- and neonatal exposure of rats to lead (0.1% lead acetate in drinking water, resulting in rat offspring whole blood lead concentration (Pb-B) 4μg/dL) on the energy status of neuronal mitochondria by measuring changes in ATP, ADP, AMP, adenosine, TAN concentration, adenylate energy charge value (AEC) and mitochondrial membrane potential in primary cerebellar granule neurons (CGC) in dissociated cultures. Fluorescence studies were performed to imaging and evaluate mitochondria mass, mitochondrial membrane potential, intracellular and mitochondrial reactive oxygen species (ROS) production. The Na(+)/K(+) ATPase activity in intact CGC was measured spectrophotometrically. Our data shows that pre- and neonatal exposure of rats to Pb, even below the threshold of whole blood Pb value considered safe for people, affects the energy status of cultured primary cerebellar granule neurons through a decrease in ATP and TAN concentrations and AEC value, inhibition of Na(+)/K(+) ATPase, and increase in intracellular and mitochondrial ROS concentration. These observations suggest that even these low levels of Pb are likely to induce important alterations in neuronal function that could play a role in neurodegeneration.

Quantitative proteomic analysis of mitochondria in aging PS-1 transgenic mice

Accumulating evidence suggests mitochondrial alterations are intimately associated with the pathogenesis of Alzheimer's disease (AD). In order to determine if mutations of presenilin-1 (PS-1) affect levels of mitochondrial proteins at different ages we enriched mitochondrial fractions from 3-, 6-, 12-month-old knock-in mice expressing the M146V PS-1 mutation and identified, and quantified proteins using cleavable isotope-coded affinity tag labeling and two-dimensional liquid chromatography/tandem mass spectrometry (2D-LC/MS/MS). Using this approach, 165 non-redundant proteins were identified with 80 of them present in all three age groups. Specifically, at young ages (3 and 6 months), Na(+)/K(+) ATPase and several signal transduction proteins exhibited elevated levels, but dropped dramatically at 12 months. In contrast, components of the oxidative phosporylation pathway (OXPHOS), the mitochondrial permeability transition pore (MPTP), and energy metabolism proteins remained unchanged at 3 months but significantly increased with age. We propose that alterations in calcium homeostasis induced by the PS-1 mutation have a major impact in young animals by inhibiting the function of relevant proteins and inducing compensatory changes. However, in older mice combination of the PS-1 mutation and accumulated oxidative damage results in a functional suppression of OXPHOS and MPTP proteins requiring a compensatory increase in expression levels. In contrast, signal transduction proteins showed decreased levels due to a break down in the compensatory mechanisms. The dysfunction of Na(+)/K(+) ATPase and signal transduction proteins may induce impaired cognition and memory before neurodegeneration occurs.

N-acetylcysteine attenuates the decline in muscle Na+,K+-pump activity and delays fatigue during prolonged exercise in humans

Reactive oxygen species (ROS) have been linked with both depressed Na(+),K(+)-pump activity and skeletal muscle fatigue. This study investigated N-acetylcysteine (NAC) effects on muscle Na(+),K(+)-pump activity and potassium (K(+)) regulation during prolonged, submaximal endurance exercise. Eight well-trained subjects participated in a double-blind, randomised, crossover design, receiving either NAC or saline (CON) intravenous infusion at 125 mg kg(-1) h(-1) for 15 min, then 25 mg kg(-1) h(-1) for 20 min prior to and throughout exercise. Subjects cycled for 45 min at 71% , then continued at 92% until fatigue. Vastus lateralis muscle biopsies were taken before exercise, at 45 min and fatigue and analysed for maximal in vitro Na(+),K(+)-pump activity (K(+)-stimulated 3-O-methyfluorescein phosphatase; 3-O-MFPase). Arterialized venous blood was sampled throughout exercise and analysed for plasma K(+) and other electrolytes. Time to fatigue at 92% was reproducible in preliminary trials (c.v. 5.6 +/- 0.6%) and was prolonged with NAC by 23.8 +/- 8.3% (NAC 6.3 +/- 0.5 versus CON 5.2 +/- 0.6 min, P < 0.05). Maximal 3-O-MFPase activity decreased from rest by 21.6 +/- 2.8% at 45 min and by 23.9 +/- 2.3% at fatigue (P < 0.05). NAC attenuated the percentage decline in maximal 3-O-MFPase activity (%Deltaactivity) at 45 min (P < 0.05) but not at fatigue. When expressed relative to work done, the %Deltaactivity-to-work ratio was attenuated by NAC at 45 min and fatigue (P < 0.005). The rise in plasma [K(+)] during exercise and the Delta[K(+)]-to-work ratio at fatigue were attenuated by NAC (P < 0.05). These results confirm that the antioxidant NAC attenuates muscle fatigue, in part via improved K(+) regulation, and point to a role for ROS in muscle fatigue.

Na-K-ATPase in rat cerebellar granule cells is redox sensitive

Redox-induced regulation of the Na-K-ATPase was studied in dispersed rat cerebellar granule cells. Intracellular thiol redox state was modulated using glutathione (GSH)-conjugating agents and membrane-permeable ethyl ester of GSH (et-GSH) and Na-K-ATPase transport and hydrolytic activity monitored as a function of intracellular reduced thiol concentration. Depletion of cytosolic and mitochondrial GSH pools caused an increase in free radical production in mitochondria and rapid ATP deprivation with a subsequent decrease in transport but not hydrolytic activity of the Na-K-ATPase. Selective conjugation of cytosolic GSH did not affect free radical production and Na-K-ATPase function. Unexpectedly, overloading of cerebellar granule cells with GSH triggered global free radical burst originating most probably from GSH autooxidation. The latter was not followed by ATP depletion but resulted in suppression of active K(+) influx and a modest increase in mortality. Suppression of transport activity of the Na-K-ATPase was observed in granule cells exposed to both permeable et-GSH and impermeable GSH, with inhibitory effects of external and cytosolic GSH being additive. The obtained data indicate that redox state is a potent regulator of the Na-K-ATPase function. Shifts from an "optimal redox potential range" to higher or lower levels cause suppression of the Na-K pump activity.

Hypoxic responses of Na+/K+ ATPase in trout hepatocytes

Reduction in oxygenation induces inhibition of Na+/K+ ATPase in a number of cells and tissues, including hepatocytes. When not reversed, decrease in Na+/K+ pump activity leads to a gradual Na+ accumulation, cell swelling and death. However, when accompanied by suppression of dissipative cation pathways, it has also been shown to be a beneficial adaptive strategy used by some hypoxia-tolerant species to reduce ATP consumption during prolonged periods of anoxia. This study aims to investigate acute hypoxic responses of the Na+/K+ ATPase in primary cultures of trout hepatocytes. Gradual decrease in oxygenation was followed by an instantaneous transient dose-dependent downregulation of the Na+/K+ ATPase transport activity, but was without an effect on hydrolytic function of the enzyme. Hypoxia-induced inhibition of active K+ influx was reversed spontaneously when hypoxic incubation time exceeded 20 min. The stimulating effect of prolonged hypoxic exposure on the Na+/K+ pump is most probably secondary to hypoxia-induced activation of the Na+/H+ exchanger with the following Na+ accumulation leading to Na+/K+ ATPase activation. Hypoxia-induced inhibition of the Na+/K+ pump was not caused by ATP depletion or global oxidative stress. However, local controlled production of reactive oxygen species seems to play an important role in hypoxia-induced regulation of the Na+/K+ ATPase. Treatment of cells with mercaptopropionyl glycine (MPG), a scavenger of OH*-, abolished hypoxia-induced inhibition of the Na+/K+ ATPase. Earlier on we have shown that activation of Na+/H+ exchanger under hypoxic conditions can be opposed by MPG treatment as well. Taken together our results suggest that regulation of both oxygen-sensitive transporters may be accomplished by local changes in free radical production.

Osmoadaptation-related genes in inner medulla of mouse kidney using microarray

To distinguish biological molecular processes of osmotic stress occurring in inner medulla, we utilized microarrays to monitor expression profiles. RNAs from three segments (cortex, outer medulla, and inner medulla) of mouse kidney were isolated and applied to microarrays. We found 35 genes expressed highly in inner medulla. Next, microarrays for the RNAs from mouse medullary collecting duct cell line (mIMCD) cells and osmotically adapted mIMCD cells (HT cells) were performed (designed as resistant to 1270mOsm/H(2)O). Of 35 genes highly expressed in inner medulla, 6 genes such as; B-cell translocation gene protein (BTG), myc-basic motif homologue, gelsolin, cell surface glycoprotein, laminin beta2, and tubulo-interstitial nephritis antigen, were also expressed highly in HT cells. Using real-time PCR, we confirmed the expression of six genes. Additionally acute osmotic stress induced the BTG. By comparing the inner medulla to a mIMCD3, we identified genes which respond to acute and chronic hyperosmotic stress.

Pivotal role of reduced glutathione in oxygen-induced regulation of the Na(+)/K(+) pump in mouse erythrocyte membranes

This study addresses the mechanisms of oxygen-induced regulation of ion transport pathways in mouse erythrocyte, specifically focusing on the role of cellular redox state and ATP levels. Mouse erythrocytes possess Na(+)/K(+) pump, K(+)-Cl(-) and Na(+)-K(+)-2Cl(-) cotransporters that have been shown to be potential targets of oxygen. The activity of neither cotransporter changed in response to hypoxia-reoxygenation. In contrast, the Na(+)/K(+) pump responded to hypoxic treatment with reversible inhibition. Hypoxia-induced inhibition was abolished in Na(+)-loaded cells, revealing no effect of O(2) on the maximal operation rate of the pump. Notably, the inhibitory effect of hypoxia was not followed by changes in cellular ATP levels. Hypoxic exposure did, however, lead to a rapid increase in cellular glutathione (GSH) levels. Decreasing GSH to normoxic levels under hypoxic conditions abolished hypoxia-induced inhibition of the pump. Furthermore, GSH added to the incubation medium was able to mimic hypoxia-induced inhibition. Taken together these data suggest a pivotal role of intracellular GSH in oxygen-induced modulation of the Na(+)/K(+) pump activity.

Lazaroid attenuates edema by stabilizing ATPase in the traumatized rat brain

OBJECTIVE

The aim of the present study was to determine the potential therapeutic value of the lazaroid U-83836E on blood brain barrier (BBB) breakdown and edema with respect to the changes in the synaptosomal Na+/K+ and Mg(2+)/Ca(2+)-adenosinetriphosphatase (ATPase) activities, tissue malondialdehyde levels and the neuronal viability in the rat brain subjected to cerebral trauma.

METHODS

Traumatic brain injury (TBI) was introduced by applying a 75 gm. cm force to the right parietal cortex using the weight-drop method. The first set of animals was used for determining time course changes of the synaptosomal Na+/K+ and Mg(2+)/Ca(2+)-ATPase and the malondialdehyde levels and were sacrificed 2, 6 and 24h after lesion production. A group of the animals was treated with U-83836E proir to TBI and sacrificed 24h after cerebral injury. A second set of animals was used for evaluating the alterations in BBB disruption and tissue water content and were sacrificed 2, 6 and 24h after lesion production. Two groups of animals were treated with U-83836E and sacrificed after 2 and 24h following TBI. U-83836E was given intraperitoneally thirty minutes before trauma at a dose of 10 mg/kg. Neuronal necrosis was also evaluated in the groups of U-83836E and physiological saline-treated animals.

RESULTS

Extravasation of Evans blue into the traumatized hemisphere was maximum at 2h (p<0.001) and returned close to the control levels at 24h after TBI (p>0.05). Edema had developed progressively over time and reached the maximum degree of 2.1% (p<0.001) at 24h. U-83836E showed no effect on the BBB breakdown and the tissue water content at 2h and still had no effect on the BBB breakdown after 24h following the trauma (p>0.05), although it reduced edema after 24h (p<0.01). The losses of Na+/K+ and Mg(2+)/Ca(2+)-ATPase activities were found as 39.5% (p<0.001) and 29.4% (p<0.01) of the control value, respectively, and remained at the decreased levels throughout the experiment. Malondialdehyde level continued to increase over time reaching up to 209% (p<0.001) of the control value 24h after TBI. Both ATPase activities were improved to near control values (p>.05) by the effect of U-83836E. U-83836E inhibited the increase of lipid peroxidation (p<0.001) and also salvaged neuronal necrosis (p<0.05).

CONCLUSION

U-83836E given prophylactically after cerebral trauma appears to reduce edema, possibly by inhibiting increases in lipid peroxidation and by stabilizing ATPase. Further studies are recommended to verify the similar effects of the brain penetrating lazaroids when they are given after trauma.

Effect of microcystin on ion regulation and antioxidant system in gills of the estuarine crab Chasmagnathus granulatus (Decapoda, Grapsidae)

The objective of this work was to evaluate mechanisms of microcystin toxicity on crustacean species. Adult male crabs of Chasmagnathus granulatus (13.97+/-0.35 g) acclimated to low salinity (2 per thousand ) were injected with saline (control) or Microcystis aeruginosa aqueous extract (39.2 microg/l) at 24 h intervals for 48 h. After the exposure period, the anterior and posterior gills were dissected, measuring Na(+),K(+)-ATPase and glutathione-S-transferase (GST) activity. Total oxyradical scavenging capacity (TOSC) and lipid peroxides (LPO) content were also determined. Na(+),K(+)-ATPase activity in anterior gills was significantly lower in crabs injected with toxin than in control crabs, while no significant difference in the enzyme activity was detected in posterior gills. Both sodium and chloride concentration in the hemolymph were not affected by toxin exposure. Significant changes in GST activity were detected in posterior gills, with higher values being observed in the toxin-injected crabs. Crabs exposed to microcystin also showed a significant increase in the TOSC value against peroxyl radicals, for both anterior and posterior gills. Lipid peroxides level did not change in both gill types after exposure to the toxin. The increased levels of TOSC suggest the occurrence of a crab response against oxidative stress induced by toxin injection, which prevents lipid peroxidation.

Induction of mRNAs and proteins for Na/K ATPase alpha1 and beta1 subunits following hypoxia/reoxygenation in astrocytes

Characteristics of the cellular response to oxygen deprivation and subsequent reoxygenation (hypoxia/reoxygenation) include redirection of energy metabolism, increased glucose utilization and expression of oxygen-regulated proteins. Inhibition of protein synthesis during early reoxygenation period prevented effective astrocyte adaptation to hypoxia/reoxygenation, resulting in eventual cell death. To elucidate the role of astrocytes in the central nervous system in response to hypoxia/reoxygenation, we analyzed the cDNA library derived from the cultured rat astrocytes subjected to 24 h of hypoxia followed by reoxygenation by differential display, and isolated a cDNA corresponding to Na/K ATPase alpha1 subunit. The expression of Na/K ATPase alpha1 subunit mRNA as well as beta1subunit mRNA was transiently increased after reoxygenation, whereas hypoxia itself did not induce any gene expression change. Na/K ATPase alpha1 subunit protein was transiently increased, whereas the protein expression for Na/K ATPase beta1 subunit showed sustained induction after reoxygenation. Overexpression of beta1 subunit in HEK 293 cells subjected to hypoxia/reoxygenation promoted survival of the cells. These findings suggest that Na/K ATPases may contribute to maintain the cellular environment of astrocytes subjected to hypoxia/reoxygenation.

Carotenoid oxidative degradation products inhibit Na+-K+-ATPase

This study investigates the biological significance of carotenoid oxidation products using inhibition of Na+-K+-ATPase activity as an index. Beta-carotene was completely oxidized by hypochlorous acid and the oxidation products were analyzed by capillary gas-liquid chromatography and high performance liquid chromatography. The Na+-K+-ATPase activity was assayed in the presence of these oxidized carotenoids and was rapidly and potently inhibited. This was demonstrated for a mixture of beta-carotene oxidative breakdown products, beta-Apo-10'-carotenal and retinal. Most of the beta-carotene oxidation products were identified as aldehydic. The concentration of the oxidized carotenoid mixture that inhibited Na+-K+-ATPase activity by 50% (IC50) was equivalent to 10 microM non-degraded beta-carotene, whereas the IC50 for 4-hydroxy-2-nonenal, a major lipid peroxidation product, was 120 microM. Carotenoid oxidation products are more potent inhibitors of Na+-K+-ATPase than 4-hydroxy-2-nonenal. Enzyme activity was only partially restored with hydroxylamine and/or beta-mercaptoethanol. Thus, in vitro binding of carotenoid oxidation products results in strong enzyme inhibition. These data indicate the potential toxicity of oxidative carotenoid metabolites and their activity on key enzyme regulators and signal modulators.