Pharmacological protection of reoxygenation damage to in vitro brain slice tissue

Combination of mild hypothermia with neuroprotectants has greater neuroprotective effects during oxygen-glucose deprivation and reoxygenation-mediated neuronal injury

Co-treatment of neuroprotective reagents may improve the therapeutic efficacy of hypothermia in protecting neurons during ischemic stroke. This study aimed to find promising drugs that enhance the neuroprotective effect of mild hypothermia (MH). 26 candidate drugs were selected based on different targets. Primary cultured cortical neurons were exposed to oxygen-glucose deprivation and reoxygenation (OGD/R) to induce neuronal damage, followed by either single treatment (a drug or MH) or a combination of a drug and MH. Results showed that, compared with single treatment, combination of MH with brain derived neurotrophic factor, glibenclamide, dizocilpine, human urinary kallidinogenase or neuroglobin displayed higher proportion of neuronal cell viability. The latter three drugs also caused less apoptosis rate in combined treatment. Furthermore, co-treatment of those three drugs and MH decreased the level of reactive oxygen species (ROS) and intracellular calcium accumulation, as well as stabilized mitochondrial membrane potential (MMP), indicating the combined neuroprotective effects are probably via inhibiting mitochondrial apoptosis pathway. Taken together, the study suggests that combined treatment with hypothermia and certain neuroprotective reagents provide a better protection against OGD/R-induced neuronal injury.

WITHDRAWN: Superoxide generation in different brain regions of rats during normoxia and hypoxia-reoxygenation

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.neures.2012.10.010. The duplicate article has therefore been withdrawn.

Superoxide generation in different brain regions of rats during normoxia and hypoxia-reoxygenation

The superoxide-dependent chemiluminescent intensity in different brain regions was examined in ex vivo tissue slices of rat brain during normoxia and hypoxia-reoxygenation with lucigenin. The chemiluminescent intensity increased during reoxygenation after hypoxic treatment. There was a higher level of chemiluminescent intensity in the hippocampus during normoxia, and a lower level in the white matter during normoxia and hypoxia-reoxygenation. A weak correlation was found between the chemiluminescent intensity and the glucose uptake rate during normoxia. Then we examined whether hypoxic strength correlates to superoxide generation. The chemiluminescent intensity increased in a hypoxic strength-dependent manner. The generation mechanism of superoxide was examined using carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, genipin, an inhibitor for uncoupling protein-2, alloprinol, a xanthine oxidase inhibitor, or apocynin, an NADPH oxidase inhibitor. The chemiluminescent signal was significantly inhibited by CCCP under normoxic condition and enhanced by genipin during normoxia and hypoxia-reoxygenation, but not by allopurinol or apocynin. These results suggest that superoxide generation is high in the hippocampus during normoxia and low in the white matter during normoxia and hypoxia-reoxygenation, superoxide generation in the hypoxia-reoxygenation brain correlates with the strength of hypoxia influenced by oxygen delivery, and mitochondrion is the major sites of intracellular superoxide generation.

Reduction of brain taurine: Effects on neurotoxic and metabolic actions of kainate

The effects of chronic administration of 2-guanidinoethane sulfonic acid on the levels of intra- and extracellular amino acids in the rat hippocampus were studied. The tissue content of taurine was selectively reduced by almost one third after 9 days of peroral administration of 1% 2-guanidinoethane sulfonate. Extracellular levels of amino acids were monitored with the brain microdialysis method. The taurine concentration in the extracellular fluid was depressed in relation to the decrease in intracellular taurine. Unexpectedly, extracellular (but not intracellular) glutamate was doubled in 2-guanidinoethane sulfonate treated animals. The kainic acid evoked release of taurine was suppressed in the 2-guanidinoethane sulfonate group, whereas the kainate stimulated efflux of glutamate was elevated after 2-guanidinoethane sulfonate administration. The acute metabolic effects of kainate were studied by measuring the efflux of the adenosine triphosphate breakdown products hypoxanthine, xanthine, inosine and adenosine. No differences were found between control and 2-guanidinoethane sulfonate treated rats with respect to basal or kainic acid evoked release of purine catabolites. Also, the neuronal loss caused by kainate injection into the hippocampus was not modified by 2-guanidinoethane sulfonate treatment, suggesting that endogenous taurine does not affect these responses. We conclude that chronic administration of 2-guanidinoethane sulfonate does not sensitize central neurons to the metabolic and toxic actions of kainate.

Superoxide dismutase deficiency enhances superoxide levels in brain tissues during oxygenation and hypoxia-reoxygenation

To determine whether the mitochondria or cytoplasm produces superoxide during ischemia-reperfusion of the brain, we analyzed lucigenine-enhanced chemiluminescence emission in slices of brain tissue prepared from manganese-superoxide dismutase (Mn-SOD)-deficient (Sod2-deficient) and copper and zinc-superoxide dismutase (Cu,Zn-SOD)-deficient (Sod1-deficient) mice during oxygenation and hypoxia-reoxygenation. The steady-state level of chemiluminescence under oxygenated conditions was significantly enhanced by a lack of either Sod. We hypothesize that the enhanced chemiluminescence produced by Sod2 and Sod1 deficiency reflects in situ superoxide generation in the mitochondria and cytoplasm, respectively. Based on this hypothesis, the major site of intracellular superoxide generation was assumed to be the cytoplasm. However, mitochondria occupy less cellular space than the cytoplasm. In terms of volume, the superoxide concentration is assumed to be higher in mitochondria than in the cytoplasm. Mn-SOD activity was 18% of the Cu,Zn-SOD activity observed in the wild-type mouse brain. However, when mitochondrial SOD activity was expressed as per volume, it was assumed to be equal to that observed in the cytoplasm. This imbalance between superoxide and SOD activity is expected to cause mitochondrial oxidative damage. The chemiluminescence intensity increased significantly during reoxygenation and was enhanced by Sod2 deficiency but was not significantly affected by Sod1 deficiency. The superoxide concentration in the reoxygenated brain would be higher in the mitochondria than in the cytoplasm. The present study indicated that the major site of intracellular superoxide generation in the brain during oxygenation is the cytoplasm, whereas it is the mitochondria during reoxygenation.

Hyperbaric hyperoxia and normobaric reoxygenation increase excitability and activate oxygen-induced potentiation in CA1 hippocampal neurons

Breathing hyperbaric oxygen (HBO) is common practice in hyperbaric and diving medicine. The benefits of breathing HBO, however, are limited by the risk of central nervous system O2 toxicity, which presents as seizures. We tested the hypothesis that excitability increases in CA1 neurons of the rat hippocampal slice (400 microm) over a continuum of hyperoxia that spans normobaric and hyperbaric pressures. Amplitude changes of the orthodromic population spike were used to assess neuronal O2 sensitivity before, during, and following exposure to 0, 0.6, 0.95 (control), 2.84, and 4.54 atmospheres absolute (ATA) O2. Polarographic O2 electrodes were used to measure tissue slice PO2 (PtO2). In 0.95 ATA O2, core PtO2 at 200 microm deep was 115±16 Torr (mean±SE). Increasing O2 to 2.84 and 4.54 ATA increased core PtO2 to 1,222±77 and 2,037±157 Torr, respectively. HBO increased the orthodromic population spike amplitude and usually induced hyperexcitability (i.e., secondary population spikes) and, in addition, a long-lasting potentiation of the orthodromic population spike that we have termed "oxygen-induced potentiation" (OxIP). Exposure to 0.60 ATA O2 and hypoxia (0.00 ATA) decreased core PtO2 to 84±6 and 20±4 Torr, respectively, and abolished the orthodromic response. Reoxygenation from 0.0 or 0.6 ATA O2, however, usually produced a response similar to that of HBO: hyperexcitability and activation of OxIP. We conclude that CA1 neurons exhibit increased excitability and neural plasticity over a broad range of PtO2, which can be activated by a single, hyperoxic stimulus. We postulate that transient acute hyperoxia stimulus, whether caused by breathing HBO or reoxygenation following hypoxia (e.g., disordered breathing), is a powerful stimulant for orthodromic activity and neural plasticity in the CA1 hippocampus.

Age-related increase of superoxide generation in the brains of mammals and birds

Oxidative stress, an imbalance between endogenous levels of oxygen radicals and antioxidative defense, increases with aging. However, it is not clear which of these two factors is the more critical. To clarify the production of oxygen radicals increases with age, we examined oxygen radical-dependent chemiluminescent signals in ex vivo brain slices using a novel photonic imaging method. The chemiluminescent intensity was significantly decreased by the membrane permeable superoxide dismutase (SOD)/catalase mimic, but not by Cu,Zn-SOD. Inhibitors for complex I, III, and IV of the mitochondrial electron transport chain transiently enhanced the chemiluminescent signal. The superoxide-dependent chemiluminescent intensity in senescence accelerated mouse (SAM) brain tissues increases with age. Moreover, the slope of the age-dependent increase was steeper in SAMP10, a strain characterized by a short lifespan and atrophy in the frontal cerebral cortex, than the senescence-resistant strain SAMR1, which has a longer lifespan. An increase in chemiluminescence with age was also observed in C57/BL6 mice, Wistar rats, and pigeons, although levels of chemiluminescence were lower in the pigeons than murines. The rate of age-related increases of superoxide-dependent chemiluminescence was inversely related to the maximum lifespan of the animals. The activity of superoxide dismutase was unchanged during the aging process in the brain. This suggested that superoxide production itself may increase with age. We speculated that reactive oxygen may be a signal to determine the aging process.

Hyperbaric oxygen treatment attenuated the decrease in regional glucose metabolism of rats subjected to focal cerebral ischemia: A high resolution positron emission tomography study

Cerebral hypoxia may be the main component of cell damage caused by ischemia. Previous studies demonstrated a neuroprotective effect of early hyperbaric oxygen (HBO) treatment in various animal models of focal cerebral ischemia. Neuropathologic study showed that exposure of HBO may prevent cell death in ischemic cortex. In the present study, we aimed to assess cellular function of ischemic rat brain after HBO treatment by means of a high-resolution positron emission tomography scanner (microPET) used specifically for small animal imaging. The male Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO), with the regional cerebral blood flow monitored in vivo by laser Doppler flowmetry. One hour after ischemia, HBO therapy (3 atm absolute, 1 h) was initiated. Local cerebral glucose utilization in the ischemic area was measured before, 1 h and 3 h after ischemia, with 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG) as a tracer. Neurological deficits and infarct volumes were assessed at 24 h after ischemia. Our study showed that early HBO therapy significantly reduced infarct volume of brain 24 h after ischemia. Moreover, glucose utilization in the ischemic area underwent a severe decrease during 1-3 h after MCAO, while the early HBO treatment significantly attenuated the decrease in cerebral metabolic rate of glucose in the ischemic core of the cortex compared with controls. We report for the first time the application of microPET to quantify the rates of glucose metabolism in the ischemic core of rats exposed to HBO. Our results suggest that the early exposure of HBO can partially reverse the downward trend for glucose utilization in the ischemic core, which might contribute to the reported beneficial effects of early HBO therapy on permanent cerebral ischemia.

Excitatory amino acid release and electrocortical brain activity after hypoxemia in near-term lambs

BACKGROUND

Energy failure due to insufficient cerebral O(2)-supply leads to excess accumulation of calcium ions in presynaptic neurons, followed by excess release of excitatory amino acids (EAAs), which are potent neurotoxins, into the synaptic cleft.

AIM

The aim of the present study was to determine whether extracellular EAAs release after prolonged hypoxemia affects electrocortical brain activity (ECBA), as a measure of brain cell function, in near-term born lambs.

METHODS

Ten near-term lambs (term: 147 days) were delivered at 131 days of gestation. After a stabilization period, prolonged hypoxemia (FiO(2): 0.10; duration 2.5h) was induced. Mean values of physiologic variables, including ECBA, were calculated over the last 3 min of normoxemia as well as of hypoxemia. Cerebral arterial and venous blood gases were determined at the end of the normoxemic and hypoxemic periods. Cerebrospinal fluid (CSF) was obtained at the end of the hypoxemic period. CSF from six normoxemic sibs was used for comparison. HPLC was used to measure EAAs in the CSF.

RESULTS

During hypoxemia, aspartate and glutamate concentration increased significantly (4.8 and 6.0 times, respectively), while asparagine and glutamine did not. ECBA decreased to 30% of the normoxemic value. Glutamate was significantly higher in lambs with a flat cerebral function monitor (CFM) tracing than in lambs with a burst-suppression pattern.

CONCLUSIONS

After prolonged hypoxemia aspartate and glutamate accumulated excessively in the CSF of near-term born lambs. Especially glutamate concentrations in CSF were related to the decline in brain cell function.

Cryopreservation of rat hippocampal slices by vitrification

Although much interest has attended the cryopreservation of immature neurons for subsequent therapeutic intracerebral transplantation, there are no reports on the cryopreservation of organized adult cerebral tissue slices of potential interest for pharmaceutical drug development. We report here the first experiments on cryopreservation of mature rat transverse hippocampal slices. Freezing at 1.2 degrees C/min to -20 degrees C or below using 10 or 30% v/v glycerol or 20% v/v dimethyl sulfoxide yielded extremely poor results. Hippocampal slices were also rapidly inactivated by simple exposure to a temperature of 0 degree C in artificial cerebrospinal fluid (aCSF). This effect was mitigated somewhat by 0.8 mM vitamin C, the use of a more "intracellular" version of aCSF having reduced sodium and calcium levels and higher potassium levels, and the presence of a 25% w/v mixture of dimethyl sulfoxide, formamide, and ethylene glycol ("V(EG) solutes"; Cryobiology 48, pp. 22-35, 2004). It was not mitigated by glycerol, aspirin, indomethacin, or mannitol addition to aCSF. When RPS-2 (Cryobiology 21, pp. 260-273, 1984) was used as a carrier solution for up to 50% w/v V(EG) solutes, 0 degree C was more protective than 10 degrees C. Raising V(EG) concentration to 53% w/v allowed slice vitrification without injury from vitrification and rewarming per se, but was much more damaging than exposure to 50% w/v V(EG). This problem was overcome by using the analogous 61% w/v VM3 vitrification solution (Cryobiology 48, pp. 157-178, 2004) containing polyvinylpyrrolidone and two extracellular "ice blockers." With VM3, it was possible to attain a tissue K(+)/Na(+) ratio after vitrification ranging from 91 to 108% of that obtained with untreated control slices. Microscopic examination showed severe damage in frozen-thawed slices, but generally good to excellent ultrastructural and histological preservation after vitrification. Our results provide the first demonstration that both the viability and the structure of mature organized, complex neural networks can be well preserved by vitrification. These results may assist neuropsychiatric drug evaluation and development and the transplantation of integrated brain regions to correct brain disease or injury.

Development of real-time bioradiographic system for functional and metabolic imaging in living brain tissue

We have developed a novel imaging system "real-time bioradiography", which is able to estimate the dynamic changes of physiological function and metabolism in living tissues using positron emitter-labeled tracers and chemiluminescence probes. The apparatus is comprised of a photon-counting camera, image-controller, culturing chamber, reflexible solid scintillator and temperature-controlled imaging chamber. The image distribution of radioactivity and chemiluminescence was acquirable with the reflexible solid scintillator and without, respectively. The reflexible solid scintillator is effective to exclude the affect of intra-objective different light reflectivity on radiation detection and to improve the efficiency of radiation detection. To test and to demonstrate the efficacy of this system, we examined the glucose metabolism and superoxide formation during hypoxia-reoxygenation in living brain tissues using 2-[18F]fluoro-2-deoxy-D-glucose (FDG) and Lucigenin, respectively. FDG uptake and chemiluminescence images were obtained at time frames of every 15 min. Glucose metabolism was enhanced during the hypoxic treatment, but the superoxide formation was enhanced during reoxygenation. The enhanced glucose metabolism during hypoxia might cause the increase in superoxide formation during reoxygenation. Thus, this new method would open up possibilities to approach simultaneous biological monitoring of a variety of biochemical events with various combinations of positron emitter-labeled tracers and chemiluminescence probes in living tissues.

Purine and pyrimidine metabolism and electrocortical brain activity during hypotension in near-term lambs

BACKGROUND

Insufficient cerebral O2 supply leads to cellular energy failure and loss of brain cell function. The relationship between the severity of cellular energy failure due to hemorrhagic hypotension and the loss of electrocortical brain activity (ECBA), as a measure of brain cell function, is not yet fully elucidated in near-term born lambs.

OBJECTIVES

To study the relationship between cerebral purine and pyrimidine metabolism, as a measure of brain cell energy failure, and brain cell function after hemorrhagic hypotension in near-term born lambs.

METHODS

Eight near-term lambs (term 147 days) were delivered at 131 days of gestation. After a stabilization period, mean arterial blood pressure was reduced till 30% of baseline by withdrawal of blood. Cerebrospinal fluid (CSF) was obtained at the end of the hypotensive period (2.5 h). CSF from 8 siblings was used for comparison. HPLC was used to determine purine and pyrimidine metabolites in CSF, as a measure of cellular energy failure. ECBA was calculated as the root mean square value of a band-filtered (2-16 Hz) one-channel EEG.

RESULTS

Values of guanosine, inosine, hypoxanthine, xanthine and uridine were significantly higher, while ECBA was significantly lower after hemorrhagic hypotension than control values. The concentrations of inosine, hypoxanthine, xanthine and uridine were significantly negatively linearly related to ECBA.

CONCLUSIONS

Brain cell function is negatively related to concentrations of inosine, hypoxanthine, xanthine and uridine in the CSF after hemorrhagic hypotension in near-term born lambs.

Demonstration of hyperaccumulation of [18F]2-fluoro-2-deoxy-D-glucose under oxygen deprivation in living brain slices using bioradiography

To clarify the mechanism of hyperaccumulation of glucose in acute brain ischemia by PET, changes of glucose metabolism and mitochondrial electron transfer function were examined in living brain slices in vitro during control, hypoxic, and anoxic conditions by positron autoradiography using [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [(15)O]oxygen. [(15)O]Oxygen fixation reflecting mitochondrial electron transfer function was reduced and [(18)F]FDG uptake reflecting glucose metabolism was increased in proportion to the strength of oxygen deprivation during anoxia and hypoxia. Mitochondrial electron transfer function decreased with no regional differences, whereas the glucose metabolism was the most enhanced in the hippocampus and thalamus. The enhanced glucose metabolism was associated with an increased glutamate efflux after hypoxia and anoxia. Glucose metabolism was also increased by the addition of glutamate and was attenuated by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 in the hippocampus and thalamus. The hyperaccumulation of glucose in acute brain ischemia was demonstrated in living brain slices using bioradiography with reduced mitochondrial electron transfer. The activation of NMDA receptors by glutamate during acute brain ischemia might be responsible for hyperutilization of glucose in the hippocampus and thalamus.

Purine and pyrimidine metabolism and electrocortical brain activity during hypoxemia in near-term lambs

Insufficient cerebral O(2) supply leads to brain cell damage and loss of brain cell function. The relationship between the severity of hypoxemic brain cell damage and the loss of electrocortical brain activity (ECBA), as measure of brain cell function, is not yet fully elucidated in near-term newborns. We hypothesized that there is a strong relationship between cerebral purine and pyrimidine metabolism, as measures of brain cell damage, and brain cell function during hypoxemia. Nine near-term lambs (term, 147 d) were delivered at 131 (range, 120-141) d of gestation. After a stabilization period, prolonged hypoxemia (fraction of inspired oxygen, 0.10; duration, 2.5 h) was induced. Mean values of carotid artery blood flow, as a measure of cerebral blood flow, and ECBA were calculated over the last 3 min of hypoxemia. At the end of the hypoxemic period, cerebral arterial and venous blood gases were determined and CSF was obtained. CSF from 11 normoxemic siblings was used for baseline values. HPLC was used to determine purine and pyrimidine metabolites in CSF, as measures of brain cell damage. Concentrations of purine and pyrimidine metabolites were significantly higher in hypoxemic lambs than in their siblings, whereas ECBA was lower in hypoxemic lambs. Significant negative linear relationships were found between purine and pyrimidine metabolite concentrations and, respectively, cerebral O(2) supply, cerebral O(2) consumption, and ECBA. We conclude that brain cell function is related to concentrations of purine and pyrimidine metabolites in the CSF. Reduction of ECBA indeed reflects the measure of brain damage due to hypoxemia in near-term newborn lambs.

Deferoxamine, allopurinol and oxypurinol are not neuroprotective after oxygen/glucose deprivation in an organotypic hippocampal model, lacking functional endothelial cells

Reactive oxygen species-induced reperfusion injury of the brain is an important cause of neonatal morbidity and mortality following perinatal hypoxia-ischemia. Deferoxamine, allopurinol and oxypurinol have previously been shown to be neuroprotective in vivo during or directly after hypoxia-ischemia. To further characterize and more precisely elucidate whether the neuroprotective properties of these agents are mediated via neuronal and glial cells, or whether endothelial cells contribute to this effect, we tested their ability to protect CA1 neurons in organotypic hippocampal slices. Hippocampal slices obtained from 8-day-old rats were cultured for 7 days and exposed to oxygen/glucose deprivation for 50 min, or used as control slices. Cell damage was assessed at 48 h after oxygen/glucose deprivation using propidium iodide staining. At different time points following oxygen/glucose deprivation we administered dizocilpine, 6-cyano-7-nitroquinoxaline-2,3-dione, and alpha-phenyl-N-tert-butyl nitrone for validation purposes. Deferoxamine, allopurinol or oxypurinol were used as test substances. As expected, 89% and 98% protection was demonstrated with dizocilpine present during or during/after oxygen/glucose deprivation resp. alpha-Phenyl-N-tert-butyl nitrone administered during/after oxygen/glucose deprivation provided 44% protection. However, iron chelation with deferoxamine and inhibition of xanthine oxidase by allopurinol or oxypurinol did not confer neuroprotection. The neuroprotective effect of deferoxamine, allopurinol or oxypurinol, as seen in vivo, may be obtained via inhibition of the production of damaging factors by blood born substances or endothelial cells.

Does xanthine oxidase contribute to the hydroxyl radical generation in ischemia and reperfusion of the cochlea?

We investigated the effect of a hydroxyl radical scavenger, 1,3-dimethyl-2-thiourea (dimethylthiourea), and two xanthine oxidase inhibitors, oxypurinol and allopurinol, on the threshold shift of the compound action potential (CAP) after transient ischemia of the cochlea. Transient ischemia of 30 min duration was induced in albino guinea pigs via a skull base approach. The animals were treated with perilymphatic perfusion of dimethylthiourea, oxypurinol or allopurinol from 10 min before the onset of ischemia to 4 h after the termination of ischemia. Dimethylthiourea ameliorated the CAP threshold shifts at 4 h after the onset of reperfusion in a dose-dependent manner. However, oxypurinol and allopurinol did not affect the post-ischemic cochlear dysfunction. These results imply that the hydroxyl radical plays an important role in generation of cochlear dysfunction induced by ischemia-reperfusion and that xanthine oxidase may not be the primary source of this radical.

Effect of in vitro ischemic or hypoxic treatment on mitochondrial electron transfer activity in rat brain slices assessed by gas-tissue autoradiography using

We have investigated the effect of in vitro ischemic or hypoxic treatment on mitochondrial electron transport function in brain slices using gas-tissue autoradiography technique with [15O]O2. Brain slices were preincubated in Krebs-Ringer phosphate medium bubbled with 100% O2 for 30 min at 37 degrees C. (1) Control culture was incubated in the same medium bubbled with 100% O2 for 5-40 min at 37 degrees C, then for another 30 min under the same conditions. (2) In vitro ischemia was induced by placing the culture in the medium deprived of glucose and bubbled with 100% N2 for 5-40 min, then returning it to control conditions and culturing for another 30 min. (3) In vitro hypoxia was induced by placing the culture in the medium with glucose and bubbled with 100% N2 for 5-40 min, then returning it to the control conditions for 30 min. After the three different treatments, the [15O]O2 fixation by brain slices reflect to mitochondrial electron transport function was determined using gas-tissue autoradiography technique with [15O]O2. The fixation of [15O]O2 by striatum, cerebral cortex and hippocampus was reduced dependent upon the period of in vitro ischemic treatment. In contrast, the [15O]O2 fixation by those brain regions was only slightly reduced by hypoxia treatment. The reduction in [15O]O2 fixation induced by ischemic treatment was prevented by an antioxidant: glutathione, glutathione monoethyl ester or acetylsalicylic acid. The preventive effect of antioxidants on the mitochondrial damage induced by ischemia was more remarkable in the striatum than in the cerebral cortex and hippocampus. In the comparison of [15O]O2 fixation between ischemia-treated young and senescent brain slices, reduction of 15O fixation by every brain region examined was more prominent in senescence than in the young. These results suggest that gas-tissue autoradiography using [15O]O2 is useful to assess mitochondrial electron transport dysfunction induced by ischemia treatment in brain slices and that the oxidative stress participates in the mechanism of ischemia-induced dysfunction in mitochondria.

Neuronal cell death and reactive oxygen species

1. We have investigated the role of reactive oxygen species (ROS) in cell death induced by ischemia or application of the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA) or kainate (KA), in acutely isolated rat cerebellar granule cell neurons, studied by flow cytometry. Various fluorescent dyes were used to monitor intracellular calcium concentration, ROS concentration, membrane potential, and viability in acutely dissociated neurons subjected to ischemia and reoxygenation alone, NMDA or kainate alone, and ischemia and reoxygenation plus NMDA or kainate. 2. With ischemia followed by reoxygenation, ROS concentrations rose slightly and there was only a modest increase in cell death after 60 min. 3. When NMDA or kainate alone was applied to the cells there was a large increase in ROS and in intracellular calcium concentration but only a small loss of cellular viability. However, when NMDA or kainate was applied during the reoxygenation period there was a large loss of viability, accompanied by membrane depolarization, but the elevations of ROS and intracellular calcium concentration were not greater than seen with the excitatory amino acids alone. 4. These observations indicate that other factors beyond ROS and intracellular calcium concentration contribute to cell death in cerebellar granule cell neurons.

Is indomethacin harmful in spinal cord injury treatment? An experimental study

This study was designed to analyze the effect of early indomethacin on the lipid peroxidation after spinal cord injury in rats. The use of anti-inflammatory drugs to affect delayed and secondary injury after trauma to the spinal cord has now become a matter of standard clinical practice. However, spinal cord injury remains an enormous clinical problem and research that may lead to improved treatment is to be encouraged and commended. Three experimental groups consisting of 40 rats each were formed. Using microsurgical technique, total laminectomy between T5 and T10 was performed. Spinal cord injury was achieved with an epidural aneurysm clip, and pharmacological treatment immediate after the injury was performed by injecting indomethacin intraperitoneally (i.p.) at a dose of 3 mg/kg to indomethacin-treated group. The three main groups were divided into subgroups of 8 rats each. It was planned to stop the biochemical reactions at a different time in each of these subgroups, by the application of liquid nitrogen to the spinal cord and paravertebral structures at the end of the 1st, 15th, 30th, 60th, and 90th minutes. All the spinal cords were removed and protected from further reactions by immersing in the liquid nitrogen tank. The lipid peroxidation levels were assessed by determining thiobarbituric acid reactive substances formation. The results of the study showed that the administration of 3 mg/kg indomethacin immediately after spinal cord injury induces lipid peroxidation to a significant degree (p<0.05 one-way ANOVA and Tukey HSD tests) when compared to the saline-treated group. This result suggests that early posttraumatic indomethacin treatment may be harmful in spinal cord injury.

Restoring adenine nucleotides in a brain slice model of cerebral reperfusion

Tissue adenine nucleotides are depleted during cerebral ischemia, impeding recovery after reperfusion. Although prior studies have attempted to prevent the initial loss of adenylates, the present study tests the hypothesis that stimulating synthesis of adenine nucleotides, through either adenosine kinase or adenine phosphoribosyltransferase, would result in significant cerebroprotection. To study the effects on neurons and glia directly while avoiding the influence of the cerebral vasculature, hippocampal brain slices were used for the model of transient ischemia with reperfusion. The standard brain slice insult of brief exposure to anoxia with aglycemia was modified based on studies which showed that a 30-minute exposure to air with 1 mmol/L glucose produced a stable, moderate reduction in ATP during the insult and that, 2 hours after return to normal conditions, there was moderate depletion of tissue adenine nucleotides and histologic injury. Treatments with 1 mmol/L adenosine, AMP, or adenine were equivalent in partially restoring adenine nucleotides. Despite this, only adenosine afforded histologic protection, suggesting a protective role for adenosine receptors. There also was evidence for metabolic cycling among adenine nucleotides, nucleosides, and purines. Adenosine may exert direct cerebroprotective effects on neural tissue as well as indirect effects through the cerebral vasculature.

Effect of allopurinol on NMDA receptor modification following recurrent asphyxia in newborn piglets

The present study tests the hypothesis that repeated episodes of asphyxia will lead to alterations in the characteristics of the N-methyl-d-aspartate (NMDA) receptor in the brain cell membrane of newborn piglets and that pre-treatment with allopurinol, a xanthine oxidase inhibitor, will prevent these modifications. Eighteen newborn piglets were studied. Six untreated and six allopurinol treated animals were subjected to eight asphyxial episodes and compared to six normoxic, normocapneic controls. Brain cell membrane Na+,K+-ATPase activity was determined to assess membrane function. Na+,K+-ATPase activity was decreased from control following asphyxia in both the untreated and treated animals (47.7+/-3.2 vs. 43.0+/-2.2 and 41.0+/-5.3 micromol Pi/mg protein/h, p<0.05, respectively). 3H-MK-801 binding studies were performed to measure NMDA receptor binding characteristics. The receptor density (Bmax) in the untreated asphyxia group was decreased compared to control animals (0.80+/-0.11 vs. 1.13+/-0.33, p<0.05); furthermore, the dissociation constant (Kd) was also decreased (3.8+/-0.7 vs. 9.2+/-2.2, p<0.05), indicating an increase in receptor affinity. In contrast, Bmax in the allopurinol treated asphyxia group was similar to control (1. 06+/-0.37); and Kd was higher (lower affinity) than in the untreated group (6.5+/-1.4, p<0.05). The data indicate that recurrent asphyxial episodes lead to alterations in NMDA receptor characteristics; and that despite cell membrane dysfunction as seen by a decrease in Na+,K+-ATPase activity, allopurinol prevents modification of NMDA receptor-ion channel binding characteristics induced by repeated episodes of asphyxia.

Measurements of (Na+,K+)ATPase after in vitro hypoxia and reoxygenation are affected by methods of membrane preparation

(Na+,K+ )ATPase activity was evaluated in membranes from rat hippocampal slices after in vitro hypoxia and reoxygenation. Membranes were prepared with two different methods, one using an isotonic medium and another using a hypotonic one. The changes that were found after hypoxia went into opposite directions in the two cases. Membranes prepared in a hypotonic medium are probably more suitable for these measurements. Using these membranes, hypoxia results in a slight decrease of (Na+,K+)ATPase activity and in a further decrease after reoxygenation. We also found that expressing (Na+,K+)ATPase activity as a percent of total ATPase activity is appropriate for membranes prepared under hypotonic conditions and can unveil (by reducing variability between experiments) significant changes that may be masked in small samples like ours.

Increasing vulnerability of astrocytes to oxidative injury with age despite constant antioxidant defenses

This paper investigates the vulnerability of astrocytes to oxidative injury as a function of age in culture in mice. Primary murine cortical astrocyte cultures of different ages were exposed to H2O2, combined oxygen-glucose deprivation or glucose deprivation. Astrocytes became more vulnerable to damage from each injury paradigm with age, showing transitions between 15 and 22 days. Both the antioxidant glutathione and superoxide dismutase activity increased after 30 days in culture, while catalase activity did not change up to 34 days. When the decrease in glutathione with injury was measured, young cells showed no change with H2O2 and decreases of < 20% after oxygen-glucose deprivation or glucose deprivation, while older cultures lost > 50% of their glutathione with the same insults. Since iron can be a catalyst for hydroxyl radical formation, we stained cultures and found both iron staining and ferritin immunoreactivity increased with age. Increased iron correlated with protection by deferoxamine against H2O2 injury. The three injury paradigms each had a unique pattern of protection by antioxidants. Dimethylthiourea, a hydrophilic antioxidant, protected from all three insults. Trolox, a lipophilic antioxidant, protected older astrocytes from oxygen-glucose deprivation and glucose deprivation. Deferoxamine provided near complete protection from H2O2, partial protection from oxygen-glucose deprivation and no protection from glucose deprivation. As evidence of increasing oxidative stress, lipid peroxidation resulting from oxygen-glucose deprivation increased with age, assessed with cis-parinaric acid. The increasing sensitivity of ageing astrocytes to oxidative injury occurs while antioxidant defenses are maintained. Increased sensitivity to H2O2 or oxygen-glucose deprivation correlates with iron accumulation.

Purine metabolism and inhibition of xanthine oxidase in severely hypoxic neonates going onto extracorporeal membrane oxygenation

The effect of allopurinol to inhibit purine metabolism via the xanthine oxidase pathway in neonates with severe, progressive hypoxemia during rescue and reperfusion with extracorporeal membrane oxygenation (ECMO) was examined. Twenty-five term infants meeting ECMO criteria were randomized in a double-blinded, placebo-controlled trial. Fourteen did not receive allopurinol, whereas 11 were treated with 10 mg/kg after meeting criteria and before cannulation, in addition to a 20-mg/kg priming dose to the ECMO circuit. Infant plasma samples before cannulation, and at 15, 30, 60, and 90 min, and 3, 6, 9, and 12 h on bypass were analyzed (HPLC) for allopurinol, oxypurinol, hypoxanthine, xanthine, and uric acid concentrations. Urine samples were similarly evaluated for purine excretion. Hypoxanthine concentrations in isolated blood-primed ECMO circuits were separately measured. Hypoxanthine, xanthine, and uric acid levels were similar in both groups before ECMO. Hypoxanthine was higher in allopurinol-treated infants during the time of bypass studied (p = 0.022). Xanthine was also elevated (p < 0.001), and uric acid was decreased (p = 0.005) in infants receiving allopurinol. Similarly, urinary elimination of xanthine increased (p < 0.001), and of uric acid decreased (p = 0.04) in treated infants. No allopurinol toxicity was observed. Hypoxanthine concentrations were significantly higher in isolated ECMO circuits and increased over time during bypass (p < 0.001). This study demonstrates that allopurinol given before cannulation for and during ECMO significantly inhibits purine degradation and uric acid production, and may reduce the production of oxygen free radicals during reoxygenation and reperfusion of hypoxic neonates recovered on bypass.

In vitro and in vivo activity of a novel series of radical trapping agents in model systems of CNS oxidative damage

Many laboratory and clinical studies suggest that oxygen radical formation and resultant cell damage contribute to CNS injury following stroke and neurotrauma. Accordingly, antioxidants represent a viable therapeutic approach for management of CNS oxidative damage. Recently, several investigators have reported that the spin trap PBN protects against stroked-induced damage and reduces aging-associated neurological deficits. We have prepared and tested a cyclic analog of PBN, MDL 101,002, in a number of in vitro and in vivo assays designed to assess its neuroprotective properties. MDL 101,002 was found to be an effective .OH trap, to inhibit lipid peroxidation, and to decrease infarct size in a gerbil model of stroke. These results further indicate that oxidative damage arising from stroke contributes to infarct formation, and that spin traps are effective in ameliorating ischemia and reperfusion-induced CNS injury.

Triggering and execution of neuronal death in brain ischaemia: two phases of glutamate release by different mechanisms

A reduced blood or oxygen supply to the brain leads to neuronal death caused by excessive activation of glutamate receptors. Recent evidence suggests that two distinct phases of glutamate release produce this death. During ischaemia or hypoxia, glutamate is released by reversed operation of glutamate uptake carriers. It activates N-methyl-D-aspartate (NMDA) receptors, increases the intracellular concentration of Ca2+, and triggers a long-lasting potentiation of NMDA-receptor-gated currents. After ischaemia, glutamate released by Ca(2+)-dependent exocytosis activates an excessive influx of Ca2+ largely through potentiated NMDA-receptor-channels, which leads to neuronal death. The therapeutic implications of such a scheme are discussed.

Effect of allopurinol on uric acid levels and brain cell membrane Na+,K(+)-ATPase activity during hypoxia in newborn piglets

Oxygen-free radicals generated by xanthine oxidase during hypoxia-ischemia may result in cellular injury through harmful effects on membrane phospholipids. The present study investigated the effect of administration of allopurinol, an inhibitor of xanthine oxidase, on free-radical generation and brain cell membrane injury during hypoxia by inhibiting the breakdown of hypoxanthine to uric acid. Brain cell membrane Na+,K(+)-ATPase activity and lipid peroxidation products (conjugated dienes and fluorescent compounds) were determined as indices of brain membrane function and structure. Cerebral oxygenation was continuously monitored during hypoxia by 31P-NMR spectroscopy. Plasma and brain tissue levels of uric acid were measured to evaluate xanthine oxidase activity and purine degradation. Na+,K(+)-ATPase activity decreased significantly in both hypoxic groups; however, the allopurinol-treated hypoxic group showed a smaller decrease than the untreated hypoxic group (47.3 +/- 4.9 vs. 42.0 +/- 2.7 mumol Pi/mg protein/h, P < 0.05), respectively. Conjugated dienes increased significantly in the untreated hypoxic compared to control animals (0.070 +/- 0.045 vs. 0.004 +/- 0.006 mumol/g brain, P < 0.05), with the allopurinol-treated animals having intermediate values (0.053 +/- 0.039 mumol/g brain). Fluorescent compounds were lower in the allopurinol-treated hypoxic group compared to the untreated hypoxic group (0.79 +/- 0.19 vs. 1.06 +/- 0.60 micrograms/quinine sulfate/g brain, P < 0.05). Measurements of serum and brain tissue uric acid were significantly lower during hypoxia in the allopurinol-treated compared to the untreated group (30.3 +/- 15.6 vs. 45.7 +/- 10.6 microM (P < 0.05) and 1.69 +/- 0.97 vs. 4.27 +/- 2.37 nmol/g (P < 0.05), respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes by hypoxia and TRH analogue on synaptic ATPase activities

Some synaptosomal energy-requiring ATPases were evaluated in the cerebral cortex from 3- and 24-month-old normoxic rats and rats submitted to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. Furthermore, 4-week treatment with saline or TRH analogue posatireline was performed. The activities of Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to chronic intermittent mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: a) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The TRH analogue posatireline increased the high-affinity Ca(2+)-ATPase in both 3- and 24-month-old hypoxic rats, concomitant with an increase in Mg(2+)-ATPase activity in 24-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: a) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the enzymatic form located in the synaptic plasma membranes, concomitant with an increase in the form located in the synaptic vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptosomal non-mitochondrial ATPase activities: age-related alterations by chronic normobaric intermittent hypoxia

In synaptosomes and synaptosomal subfractions (namely, synaptosomal plasma membranes and synaptic vesicles) the age-related alteration in the plasticity of synaptic energy-requiring ATPases (Na+, K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase and Ca2+, Mg(2+)-ATPase) were assayed in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats; and (ii) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats and (ii) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the activity of the enzymatic form located in the synaptic plasma membranes (involved in ATP hydrolysis to adenosine production), concomitant with an increase in the activity of the form located in the synaptic vesicles (involved in the turnover of transmitters, e.g., glutamate).

Modifications by hypoxia and drug treatment of cerebral ATPase plasticity

The plasticity of synaptosomal non-mitochondrial ATPases was evaluated in cerebral cortex from 3-month-old normoxic rats and rats subjected to either mild or severe intermittent normobaric hypoxia [12 hr daily exposure to N2:O2 (90:10 or 91.5:8.5) for four weeks]. The activities of Na+, K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. The evaluations were performed after a 4-week treatment with saline (controls) or alpha-adrenergic agents (delta-yohimbine, clonidine), a vasodilator compound (papaverine), and an oxygen-partial pressure increasing agent (almitrine). These treatments differently changed the adaptation to chronic intermittent hypoxia characterized by a decrease in the activity of Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase, and high-affinity Ca(2+)-ATPase, concomitant with a modification in the activity of Mg(2+)-ATPase supported in a different way by the enzymatic forms located into the synaptosomal plasma membranes and synaptic vesicles.

Effects of two dual-function compounds, U92798 and U92032, on transient focal ischemia in rats

Two newly-developed compounds (U92798 and U92032), which inhibit lipid peroxidation and block calcium entry, were studied for their effects on neocortical damage after transient focal ischemia. Ischemia was induced in Sprague-Dawley rats by simultaneous occlusion of the left middle cerebral artery and both common carotid arteries for a period of 3 hours. Compounds (1 mg/kg) were administered intravenously 30 minutes before occlusion and again 2.5 hours after the cessation of blood flow. After a 72-hour period of reperfusion, the animals were killed and examined for cerebral infarction and edema. Treatment with U92798 or U92032 significantly reduced the volume of cortical infarction. Edema was also reduced in these groups; however, this effect did not achieve statistical significance. These results suggest that dual function compounds, which both inhibit lipid peroxidation and block calcium entry, are promising therapeutic agents for the amelioration of ischemic cerebral damage.

Age-related alterations by chronic intermittent hypoxia on cerebral synaptosomal ATPase activities

The age-related alterations in the plasticity of synaptic energy-requiring ATPases [Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase, and Ca2+,Mg(2+)-ATPase] were assayed in synaptosomes and synaptosomal subfractions [namely, synaptosomal plasma membranes and synaptic vesicles] in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (four weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and (ii) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and (ii) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the activity of the enzymatic form located in the synaptic plasma membranes [involved in ATP hydrolysis to adenosine production], concomitant with an increase in the activity of the form located in the synaptic vesicles [involved in the turnover of transmitters, e.g., glutamate].

Effect of intermittent mild hypoxia and drug treatment on synaptosomal nonmitochondrial ATPase activities

Synaptosomal nonmitochondrial ATPases linked to the energy-utilizing systems were evaluated in cerebral cortex from normoxic rats and rats submitted to mild intermittent normobaric hypoxia [12 hr daily exposure to N2:O2 (90:10) mixture for 4 weeks]. The activities of Na+,K(+)-ATPase; high- and low-affinity Ca(2+)-ATPase; basal Mg(2+)-ATPase; and Ca2+, Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely, synaptosomal plasma membranes and synaptic vesicles. The evaluations were performed either in normoxic rats or in hypoxic rats submitted to 4-week treatment with saline (controls) or a vasodilator agent (papaverine), an energy-metabolism interfering agent (theniloxazine), a calcium blocker (nicardipine), and a lipid-metabolism interfering agent (phosphatidylcholine) in order to define the plasticity and the selective changes in individual ATPases. In synaptosomes from rat cerebral cortex, the enzyme adaptation to the daily mild intermittent hypoxia for 4 weeks was characterized by an increase in the activity of Mg(2+)-ATPase, concomitant with a decrease in the activities of Na+,K(+)-ATPase, high-affinity Ca(2+)-ATPase, and Ca2+, Mg(2+)-ATPase. In hypoxic rats the enzyme adaptation to the 4-week treatment with phosphatidylcholine was characterized by an increase in Ca2+, Mg(2+)-ATPase activity and a decrease in Mg(2+)-ATPase activity. The action involves the enzymatic form located in the synaptic plasma membranes. In hypoxic rats the adaptation to the 4 week treatment with nicardipine was characterized by an increase in high-affinity Ca(2+)-ATPase activity, while the 4-week-treatment with theniloxazine induced an increase in Na+,K(+)-ATPase activity. The actions of both nicardipine and theniloxazine were related to the enzymatic forms located in the synaptic plasma membranes. The effects on the biophase induced by the sequential cycles of hypoxia/normoxia and the treatment with the various agents tested should also be related to the changes induced in the activity of some synaptosomal ATPases.

Molecular cloning of a cDNA coding for mouse liver xanthine dehydrogenase. Regulation of its transcript by interferons in vivo

The cDNA coding for xanthine dehydrogenase (XD) is isolated from mouse liver mRNA by cross-hybridization with a DNA fragment of the Drosophila melanogaster homologue. Two lambda bacteriophage overlapping clones represent the copy of a 4538-nucleotide-residue-long transcript with an open reading frame of 4005 nucleotide residues, coding for a putative polypeptide of 1335 amino acid residues. Comparison of the deduced amino acid sequence of the mouse XD with those of the Drosophila and the rat homologues shows a high conservation of this protein (55% identity between mouse and Drosophila, and 94% identity between mouse and rat). RNA blotting analysis demonstrates that interferon-alpha (IFN-alpha) and its inducers, i.e. poly(I).poly(C), bacterial lipopolysaccharide (LPS) and tilorone (2,7-bis-[2-(diethylamino)ethoxy]fluoren-9-one), increase the expression of XD mRNA in liver. Poly(I).poly(C) also induces XD mRNA in several other tissues in vivo. Protein synthesis de novo is not required for the elevation of XD mRNA after IFN-alpha treatment, since cycloheximide does not block the induction. The elevation of XD mRNA concentration is relatively fast and precedes the induction of both XD and xanthine oxidase (XO) enzymic activities.

Glucose and oxygen deprivation induces a Ca(2+)-mediated decrease in (Na(+)+K+)-ATPase activity in rat brain slices

Exposure of rat brain cortical slices to a medium lacking in glucose, oxygen or both glucose and oxygen, resulted in a decrease of the tissue ATP content and a reduction of (Na(+)+K+)-ATPase activity in membranes prepared from the slices. These treatments also inhibited partial reactions of (Na(+)+K+)-ATPase such as Na(+)-dependent phosphorylation and K(+)-stimulated phosphatase, as well as specific binding of [3H]ouabain in membranes prepared from the slices. Glucose deprivation and hypoxia decreased (Na(+)+K+)-ATPase activity in the absence of extracellular Ca2+, but the effects were blocked by 1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid tetra-acetomethyl ester (BAPTA-AM), a chelator of intracellular Ca2+. Metabolic inhibitors mimicked the effects of glucose deprivation and hypoxia. The effect of glucose-free hypoxia was dependent on extracellular Ca2+. It was blocked by Mg2+ at high concentration, bepridil or amiloride, but not by voltage-sensitive Ca2+ channel antagonists and glutamate receptor antagonists. None of the drugs tested here, except for dithiothreitol, affected the inhibitory effect of glucose-free hypoxia on the enzyme activity. In contrast to brain (Na(+)+K+)-ATPase, the kidney enzyme was insensitive to glucose and oxygen deprivation and metabolic inhibitors which depleted the tissue ATP.

Na+ influx-induced decrease of (Na+ + K+)-ATPase activity in rat brain slices: role of Ca2+

Treatment of rat brain slices with veratrine and monensin decreased (Na+ + K+)-ATPase activity in the membranes in a dose-dependent manner. The effect of monensin, like that of veratrine, was accompanied by a decrease of maximal binding sites for ouabain. The inhibitory effect of monensin on the enzyme activity was dependent on external Ca2+ at low concentrations, but not at a high concentration. The decreased enzyme activity induced by monensin was restored by subsequent incubation of the slices in a Ca(2+)-free medium containing 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM), a chelator of intracellular Ca2+. The effect of monensin at a low concentration on enzyme activity was antagonized by amiloride (1 mM), bepridil (5 microM), quinacrine (30 microM) or verapamil (30 microM), but not by nifedipine (1 microM) or omega-conotoxin (1 microM). Furthermore, the inhibitory effect of monensin at a high concentration under Ca(2+)-free conditions was blocked by BAPTA-AM (30 microM) and by bepridil (100 microM) or diazepam (500 microM), inhibitors of mitochondrial Na(+)-Ca2+ exchange. Inhibitors of calmodulin, protein kinase C, phospholipase A2 and calpain did not affect the monensin-induced decrease of enzyme activity. Dithiothreitol (10 mM) blocked the effect of monensin on enzyme activity but did not affect the ionophore-induced influx of Ca2+ in the slices.

The protective effects of allopurinol and superoxide dismutase-polyethylene glycol on ischemic and reperfusion-induced cochlear damage

The purpose of this study was to assess the protective effects of allopurinol, a blocker of free oxygen radical (FOR) formation, and superoxide dismutase-polyethylene glycol (SOD-PEG), a scavenger of FORs, on ischemic and reperfusion-induced cochlear damage. Fifteen Wistar Kyoto rats (WKY) were randomly assigned to three groups: (1) a control group (5 animals) that was exposed to 15 minutes of cochlear ischemia by clamping the anterior inferior cerebellar artery (AICA), followed by 15 minutes of reperfusion as documented by laser Doppler flowmetry; (2) a drug-treated group (5 animals) that received allopurinol before ischemia/reperfusion; and (3) a drug-treated group (5 animals) that received SOD-PEG before ischemia/reperfusion. In the control group, the tone burst-evoked compound action potential (CAP) recorded from the round window (RW) of the cochlea was abolished, and the cochlear microphonic (CM) was reduced after ischemia. In contrast, both allopurinol and SOD-PEG-treated animals showed post-reperfusion sensitivity in CAP and CM measures. We interpret these results to indicate that damage to the cochlear from ischemia and subsequent reperfusion can be attenuated by pretreatment with allopurinol or SOD-PEG. This provides indirect evidence that FORs may be partially responsible for cochlear damage resulting from ischemic conditions.

Inhibition of sodium-potassium-ATPase: a potentially ubiquitous mechanism contributing to central nervous system neuropathology

Direct and indirect evidence suggests that Na+/K(+)-ATPase activity is reduced or insufficient to maintain ionic balances during and immediately after episodes of ischemia, hypoglycemia, epilepsy, and after administration of excitotoxins (glutamate agonists). Recent results show that inhibition of this enzyme results in neuronal death, and thus a hypothesis is proposed that a reduction and/or inhibition of this enzyme contributes to producing the central neuropathy found in the above disorders, and identifies potential mechanisms involved. While the extent of inhibition of Na+/K(+)-ATPase during ischemia, hypoglycemia and epilepsy may be insufficient to cause neuronal death by itself, unless the inhibition is severe and prolonged, there are a number of interactions which can lead to a potentiation of the neurotoxic actions of glutamate, a prime candidate for causing part of the damage following trauma. Presynaptically, inhibition of the Na+/K(+)-ATPase destroys the sodium gradient which drives the uptake of acidic amino acids and a number of other neurotransmitters. This results in both a block of reuptake and a stimulation of the release not only of glutamate but also of other neurotransmitters which modulate the neurotoxicity of glutamate. An exocytotic release of glutamate can also occur as inhibition of the enzyme causes depolarization of the membrane, but exocytosis is only possible when ATP levels are sufficiently high. Postsynaptically, the depolarization could alleviate the magnesium block of NMDA receptors, a major mechanism for glutamate-induced neurotoxicity, while massive depolarization results in seizure activity. With less severe inhibition, the retention of sodium results in osmotic swelling and possible cellular lysis. A build-up of intracellular calcium also occurs via voltage-gated calcium channels following depolarization and as a consequence of a failure of the sodium-calcium exchange system, maintained by the sodium gradient.

Failure of allopurinol to protect against cerebral injury when given after the start of hypoxia

One cause of ischemic brain injury is free radical formation during recirculation. Allopurinol inhibits xanthine oxidase, an important source of free oxygen radicals. It is known that allopurinol pre-treatment has a protective action during cerebral ischemia. In the present study we exposed slices from the rat hippocampus to 9 minutes of hypoxia to test whether it is sufficient that allopurinol is present in the tissue at the time of reoxygenation. Forty-six slices loaded with allopurinol (10(-5) M) prior to reoxygenation (during hypoxia) were compared to 34 control slices. The response of the pyramidal cell population to orthodromic stimulation was reduced in both groups and there was not a significant difference between the two groups.

Cephaloconiosis: a free radical perspective on the proposed particulate-induced etiopathogenesis of Alzheimer's dementia and related disorders

By analogy to the etiology of the pneumoconioses, exogenous dust-induced diseases of the lung, and endogenous crystal-induced arthropathies such as gout, it is proposed that Alzheimer's dementia and allied disorders are causally related to the accumulation of fibriform inorganic deposits within the brain. Hence the neonosological term 'Cephaloconiosis'. It is proposed that: 1) either by the extrinsic migration or intrinsic formation and deposition of insoluble and persistent inorganic reactive nidi, the particle-induced generation of tissue-damaging free-radical oxygen metabolites by stimulated brain glial macrophage-type and allied phagocytic cells, provides a rationale for the etiopathogenesis of neurodegenerative processes; 2) the modulation of the injurious oxidative metabolic reaction by micronutrient and pharmacological antioxidant agents is a rational and potentially feasible strategy for future therapeutic clinical investigations.

Calpain inhibitors improve the recovery of synaptic transmission from hypoxia in hippocampal slices

Two inhibitors of calcium activated proteases (calpains) were tested for their effects on hypoxia-induced synaptic dysfunction in hippocampal slices. Hypoxic episodes lasting for either one or two minutes beyond the point at which action potentials (fiber volleys) disappeared were used. Leupeptin and calpain inhibitor I had no reliable effects on the rate at which synaptic transmission declined during hypoxia or the time required for loss of action potentials, but both drugs did substantially improve the degree of recovery. Moreover, the percentage of slices meeting an arbitrary criterion for viability after hypoxic treatment was greatly increased by the drug treatment. These results point to the conclusion that proteolysis triggered by calcium influx during hypoxia contributes to pathophysiology.

The regional difference of neuronal susceptibility in the dentate gyrus to hypoxia

The effects of hypoxia on neuronal activity in dentate gyrus granule cells were studied in submerged guinea pig hippocampal slices. In all regions of the dentate gyrus granule, the amplitude of the population spike recorded from the dentate granule cell layers, in response to electrical stimulation of the perforant path, decreased during hypoxia and recovered during reoxygenation. However, the ventral dentate gyrus granule cells (upper blade) were more susceptible to hypoxia than the dorsal ones (lower blade), indicating regional differences of neuronal susceptibility to hypoxia in the dentate gyrus.

Anoxia reveals a vulnerable period in the development of long-term potentiation

Transient anoxia occurring 1-2 min after high-frequency stimulation selectively prevented the stable expression of long-term potentiation (LTP). Anoxia occurring after this brief vulnerable period did not reverse LTP. Experiments on the duration of anoxia necessary to block LTP expression indicated that simply reducing synaptic transmission was insufficient but that membrane depolarization was not required. The effects of anoxia on LTP were blocked by antagonists of A1 adenosine receptors. It is concluded that LTP develops in about one minute and that the chemistries operating in this period are easily disrupted by an event triggered by adenosine receptors.

Proteolytic conversion of xanthine dehydrogenase to xanthine oxidase: evidence against a role for calcium-activated protease (calpain)

The present study tested the hypothesis that calpain is responsible for the limited proteolytic conversion of xanthine dehydrogenase (XD) to xanthine oxidase (XO). We compared the effects of various proteases on the activity and molecular weight of a purified preparation of xanthine dehydrogenase from rat liver. In agreement with previous reports, trypsin treatment produced a complete conversion of XD to XO accompanied by a limited proteolysis of XDH from an Mr of 140 kD to an Mr of 90 kD. Treatment with calpain I or calpain II did not produce a conversion from XD to XO nor did it result in partial proteolysis of the enzyme. Similarly, trypsin treatment partially degraded a reversibly oxidized form of xanthine dehydrogenase while calpain I or calpain II were ineffective. The possibility that an endogenous inhibitor prevented the proteolysis of XDH by calpain I or II was excluded by verifying that brain spectrin, a known calpain substrate, was degraded under the same incubation conditions. The results indicate that calpain is not likely to be responsible for the in vivo conversion of XD to XO under pathological conditions.

Actions of brain-protecting substances against both oxygen and glucose deprivation in the guinea pig hippocampal neurons studied in vitro

A study was made of the protective effects of several drugs (mannitol, phenytoin, vitamin E and dexamethasone) on the electrical activities of guinea pig hippocampal neurons in vitro when they were treated with a bathing medium deprived of both oxygen and glucose. Using guinea pig hippocampal slices, antidromic field potentials in the granular cell layer of the dentate gyrus were recorded stimulating mossy fibers. A model of ischemia in vivo in the slices was achieved by removing both oxygen and glucose from the perfusing medium. In standard medium, after 10 min of both oxygen and glucose deprivation, the field potentials exhibited minimum recovery with an amplitude of 6% of the control after 60 min. The protective effect of the drugs was evaluated by recovery of the field potential amplitude of the 60 min post-deprivation response and histological examination of the brain slice tissue. Drugs were added during 30 min of pre-deprivation and during deprivation. In this experiment we demonstrated that (1) phenytoin and vitamin E clearly showed protective action against neuronal damage caused by both oxygen and glucose deprivation in guinea pig hippocampal slices, (2) combined application of these drugs was more effective, and (3) mannitol showed no protective action in vitro. It was also demonstrated that (4) the dentate antidromic field response can be a useful index of cell death.