Acidosis-induced ischemic brain damage: are free radicals involved?

Precision Cardiac Arrest Resuscitation Based on Etiology

Cardiac arrest results from a broad range of etiologies that can be broadly grouped as sudden and asphyxial. Animal studies point to differences in injury pathways invoked in the heart and brain that drive injury and outcome after these different forms of cardiac arrest. Present guidelines largely ignore etiology in their management recommendations. Existing clinical data reveal significant heterogeneity in the utility of presently employed resuscitation and postresuscitation strategies based on etiology. The development of future neuroprotective and cardioprotective therapies should also take etiology into consideration to optimize the chances for successful translation.

Opioid-Associated Out-of-Hospital Cardiac Arrest: Distinctive Clinical Features and Implications for Health Care and Public Responses: A Scientific Statement From the American Heart Association

Opioid overdose is the leading cause of death for Americans 25 to 64 years of age, and opioid use disorder affects >2 million Americans. The epidemiology of opioid-associated out-of-hospital cardiac arrest in the United States is changing rapidly, with exponential increases in death resulting from synthetic opioids and linear increases in heroin deaths more than offsetting modest reductions in deaths from prescription opioids. The pathophysiology of polysubstance toxidromes involving opioids, asphyxial death, and prolonged hypoxemia leading to global ischemia (cardiac arrest) differs from that of sudden cardiac arrest. People who use opioids may also develop bacteremia, central nervous system vasculitis and leukoencephalopathy, torsades de pointes, pulmonary vasculopathy, and pulmonary edema. Emergency management of opioid poisoning requires recognition by the lay public or emergency dispatchers, prompt emergency response, and effective ventilation coupled to compressions in the setting of opioid-associated out-of-hospital cardiac arrest. Effective ventilation is challenging to teach, whereas naloxone, an opioid antagonist, can be administered by emergency medical personnel, trained laypeople, and the general public with dispatcher instruction to prevent cardiac arrest. Opioid education and naloxone distributions programs have been developed to teach people who are likely to encounter a person with opioid poisoning how to administer naloxone, deliver high-quality compressions, and perform rescue breathing. Current American Heart Association recommendations call for laypeople and others who cannot reliably establish the presence of a pulse to initiate cardiopulmonary resuscitation in any individual who is unconscious and not breathing normally; if opioid overdose is suspected, naloxone should also be administered. Secondary prevention, including counseling, opioid overdose education with take-home naloxone, and medication for opioid use disorder, is important to prevent recurrent opioid overdose.

Neuroprotective effect of ethanol and Modafinil on focal cerebral ischemia in rats

Ethanol is known as an effective agent against cerebral lesions after ischemia. Modafinil is a stimulant of the central nervous system (CNS) with antioxidant properties. We assessed the neuroprotective effect of modafinil in combination with ethanol after focal cerebral ischemia. Male wistar rats weighing 280-300 g were divided into nine groups (n = 12 each group): The groups consisted of the MCAO (middle cerebral artery occlusion) group (i.e. ischemia without treatment); the vehicle group(Dimethylsulfoxide); the modafinil group including three subgroups which pretreated with Modafinil (10, 30, 100 mg/kg), respectively, for seven days prior to the induction of MCAO; the ethanol group which received 1.5g/kg ethanol at the time of reperfusion; and modafinil+ethanol group which was divided into three subgroups that received three doses of modanifil (10, 30,100 mg/kg), respectively, for seven days prior to MCAO as well as ethanol at the time of reperfusion. Transient cerebral ischemia was induced by 60-min intraluminal occlusion of the right middle cerebral artery. Edema, infarct volume, glial scar formation (gliosis) and apoptosis were analyzed. The ethanol alone treatment (with a less significant effect), modafinil (in a dose-dependent way), and the combination of modafinil and ethanol significantly decreased the brain infarct volume, edema, apoptosis, and gliosis (P ≤ 0.05). Additionally, modafinil+ethanol mediated the restoration of aerobic metabolism and hyper-glycolysis suppress, thereby resulting in an increase in pyruvate dehydrogenase and a decrease in lactate dehydrogenase activity, respectively, which ultimately reduced oxidative reperfusion injury. These results demonstrate that pretreatment with modafinil (100 mg/kg) and modafinil+ethanol(1.5 g/kg) may prevent ischemic brain injuries.

Role of acidosis, NMDA receptors, and acid-sensitive ion channel 1a (ASIC1a) in neuronal death induced by ischemia

This review collects data on the influence of intracellular and extracellular acidosis on neuronal viability and the effect of acidosis on neuronal damage progressing under brain ischemia/hypoxia. Particular attention is devoted to the involvement of ionotropic glutamic receptors and acid-sensitive ion channel 1a in these processes.

Late expression of Na+/H+ exchanger 1 (NHE1) and neuroprotective effects of NHE inhibitor in the gerbil hippocampal CA1 region induced by transient ischemia

Although acidosis may be involved in neuronal death, the participation of Na(+)/H(+) exchanger (NHE) in delayed neuronal death in the hippocampal CA1 region induced by transient forebrain ischemia has not been well established. In the present study, we investigated the chronological alterations of NHE1 in the hippocampal CA1 region using a gerbil model after ischemia/reperfusion. In the sham-operated group, NHE1 immunoreactivity was weakly detected in the CA1 region. Two and 3 days after ischemia/reperfusion, NHE1 immunoreactivity was observed in glial components, not in neurons, in the CA1 region. Four days after ischemia/reperfusion, NHE1 immunoreactivity was markedly increased in CA1 pyramidal neurons as well as glial cells. These glial cells were identified as astrocytes based on double immunofluorescence staining. Western blot analysis also showed that NHE protein level in the CA1 region began to increase 2 days after ischemia/reperfusion. The treatment of 10 mg/kg 5-(N-ethyl-N-isopropyl) amiloride, a NHE inhibitor, significantly reduced the ischemia-induced hyperactivity 1 day after ischemia/reperfusion. In addition, NHE inhibitor potently protected CA1 pyramidal neurons from ischemic damage, and NHE inhibitor attenuated the activation of astrocytes and microglia in the ischemic CA1 region. In addition, NHE inhibitor treatment blocked Na(+)/Ca(2+) exchanger 1 immunoreactivity in the CA1 region after transient forebrain ischemia. These results suggest that NHE1 may play a role in the delayed death, and the treatment with NHE inhibitor protects neurons from ischemic damage.

Glucose management during and after intensive delivery room resuscitation

Hypoxic-ischemic encephalopathy remains a major cause of morbidity and mortality in preterm and full-term infants. Experimental data from animal studies suggest that interventions that improve survival of injured neurons and prevent delayed neuronal loss may decrease hypoxic ischemic brain injury. Considerable attention has focused on optimizing management of newborns in the period immediately after resuscitation from perinatal asphyxia to minimize delayed neuronal death. The evidence regarding the role of glucose in modifying post-asphyxia brain injury and resuscitation was reviewed to better define optimal glucose management after perinatal asphyxia and resuscitation.

Acidosis has opposite effects on neuronal survival during hypoxia and reoxygenation

To study the effect of extracellular acidosis on apoptosis and necrosis during ischemia and reoxygenation, we exposed human post-mitotic NT2-N neurones to oxygen and glucose deprivation (OGD) followed by reoxygenation. In some experiments, pH of the cell medium was lowered to 5.9 during either OGD or reoxygenation or both. Staurosporine, used as a positive control for apoptosis, caused Poly(ADP-ribose)-polymerase (PARP) cleavage and nuclear fragmentation, but no PARP cleavage and little fragmentation were seen after OGD. Low molecular weight DNA fragments were found after staurosporine treatment, but not after OGD. No protective effect of caspase inhibitors was seen after 3 h of OGD and 21 h of reoxygenation, but after 45 h of reoxygenation caspase inhibition induced a modest improvement in 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) cleavage. While acidosis during OGD accompanied by neutral medium during reoxygenation protected the neurones (MTT: 228 +/- 117% of neutral medium, p < 0.001), acidosis during reoxygenation only was detrimental (MTT: 38 +/- 25%, p < 0.01). We conclude that apoptotic mechanisms play a minor role after OGD in NT2-N neurones. The effect of acidosis on neuronal survival depends on the timing of acidosis, as acidosis was protective during OGD and detrimental during reoxygenation.

Post-ischemic transcriptional and translational responses of EC-SOD in mouse brain and serum

Extracellular superoxide dismutase (EC-SOD) is neuroprotective, but its role in cerebral ischemia remains to be determined. We herein describe the topographical localization and quantitative changes in EC-SOD and its mRNA expression following cerebral ischemia in mice. Mice were subjected to transient forebrain ischemia and varied intervals of reperfusion. The measurements of EC-SOD using ELISA showed increased brain EC-SOD after 24 h of reperfusion and an increase in EC-SOD brain/serum ratio after 3 h. The immunohistochemical examination in normal mice showed strong EC-SOD immunoreactivity in the choroid plexus, pia mater, and ventral tuberal area of the hypothalamus. EC-SOD immunoreactivity in cortical and striatal capillary wall was conspicuous after 3 h. EC-SOD immunoreactivity was also noted in cortical neurons after 24 h. Northern blot analysis showed an increased EC-SOD mRNA expression in the brain after 24 h. An in situ hybridization study in normal mice demonstrated the mRNA expression of EC-SOD in choroid plexus and neurons through the brain especially in the cortex or ventral tuberal area of the hypothalamus, but demonstrated no mRNA expression of EC-SOD in the capillary wall. These findings suggest that EC-SOD accumulates on endothelial cells in response to this injury by an unknown mechanism, while cortical neurons produce EC-SOD themselves after cerebral ischemia with reperfusion.

Production of hydroxyl free radical by brain tissues in hyperglycemic rats subjected to transient forebrain ischemia

Preischemic hyperglycemia is known to aggravate brain damage resulting from transient ischemia. In the present study, we explored whether this aggravation is preceded by an enhanced formation of reactive oxygen species (ROS) during the early reperfusion period. To that end, normo- and hyperglycemic rats were subjected to 15 min of forebrain ischemia and allowed recovery periods of 5, 15, and 60 min. Sodium salicylate was injected intraperitoneally in a dose of 100 mg/kg, and tissues were sampled during recirculation to allow analyses of salicylic acid (SA) and its hydroxylation products, 2,3- and 2,5-dihydroxybenzoate (DHBA). Tissue sampled from thalamus and caudoputamen in normoglycemic animals failed to show an increase in 2,3- or 2,5-DHBA after 5 and 15 min of recirculation. However, such an increase was observed in the neocortex after 60 min of recirculation, with a suggested increase in the hippocampus as well. Hyperglycemia had three effects. First, it increased 2,5-DHBA in the thalamus and caudoputamen to values exceeding normoglycemic ones after 15 min of recirculation. Second, it increased basal values of 2,5- and total DHBA in the neocortex. Third, it increased the 60-min values for 2,5- and total DHBA in the hippocampus. These results hint that, at least in part, hyperglycemia may aggravate damage by enhancing basal- and ischemia-triggered production of ROS.

Acidosis potentiates oxidative neuronal death by multiple mechanisms

Both acidosis and oxidative stress contribute to ischemic brain injury. The present study examines interactions between acidosis and oxidative stress in murine cortical cultures. Acidosis (pH 6.2) was found to potentiate markedly neuronal death induced by H2O2 exposure. To determine if this effect was mediated by decreased antioxidant capacity at low pH, the activities of several antioxidant enzymes were measured. Acidosis was found to reduce the activities of glutathione peroxidase and glutathione S-transferase by 50-60% (p < 0.001) and the activity of glutathione reductase by 20% (p < 0.01) in lysates of the cortical cultures. Like acidosis, direct inhibition of glutathione peroxidase with mercaptosuccinate also potentiated H2O2 toxicity. Because acidosis may accelerate hydroxyl radical production by the Fenton reaction, the effect of iron chelators was also examined. Both desferrioxamine and N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, two structurally different iron chelators, significantly reduced H2O2-induced neuronal death under both pH 7.2 and pH 6.2 conditions. These results suggest that the increased cell death produced by severe acidosis during cerebral ischemia may result in part from exacerbation of oxidative injury. This exacerbation may result from both impaired antioxidant enzyme functions and increased intracellular free iron levels.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Overexpression of thioredoxin in transgenic mice attenuates focal ischemic brain damage

Thioredoxin (TRX) plays important biological roles both in intra- and extracellular compartments, including in regulation of various intracellular molecules via thiol redox control. We produced TRX overexpressing mice and confirmed that there were no anatomical and physiological differences between wild-type (WT) mice and TRX transgenic (Tg) mice. In the present study we subjected mice to focal brain ischemia to shed light on the role of TRX in brain ischemic injury. At 24 hr after middle cerebral artery occlusion, infarct areas and volume were significantly smaller in Tg mice than in WT mice. Moreover neurological deficit was ameliorated in Tg mice compared with WT mice. Protein carbonyl content, a marker of cellular protein oxidation, in Tg mice showed less increase than did that of WT mice after the ischemic insult. Furthermore, c-fos expression in Tg mice was stronger than in WT mice 1 hr after ischemia. Our results suggest that transgene expression of TRX decreased ischemic neuronal injury and that TRX and the redox state modified by TRX play a crucial role in brain damage during stroke.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Comparison of brain tissue oxygen tension to microdialysis-based measures of cerebral ischemia in fatally head-injured humans

This study investigated the relationship between brain tissue oxygen tension (PbtO2) and cerebral microdialysate concentrations of several compounds in five patients with refractory intracranial hypertension after severe head injury. The following substances were assayed: lactate and glucose; the excitatory amino acids glutamate and aspartate; and the cations potassium, calcium, and magnesium. Glucose concentrations did not correlate with PbtO2, but lactate increased as PbtO2 decreased. The lactate/glucose ratio exhibited a close relationship to PbtO2, increasing sharply only when oxygen tension reached zero. Although glucose and oxygen eventually reached very low levels and zero, respectively, in these fatally head-injured patients, the terminal decrease in PbtO2 slightly preceded that of glucose in four of the five patients. This time lag is the cause of the poor correlation between glucose and PbtO2. Glutamate and aspartate concentrations both demonstrated a close relationship to PbtO2, with sharp increases not occurring until PbtO2 was zero. Concentrations of these amino acids exhibited a similar pattern in response to decreasing glucose concentrations. Potassium concentrations began increasing at a PbtO2 of 35 mm Hg, which is not generally considered indicative of hypoxia. Sharper increases began occurring once PbtO2 dropped below 15 mm Hg, with a slight rise in the minimum potassium concentrations recorded at these low PbtO2 values. Calcium and magnesium concentrations did not vary in response to PbtO2. In summary, the most robust biochemical indicators of cerebral anoxia were elevations in the lactate/glucose ratio and in the concentrations of lactate and of the excitatory amino acids glutamate and aspartate. Furthermore, the fact that glucose concentrations continue to decrease for a short period after oxygen levels reach zero suggests that cells continue to utilize glucose anaerobically for such functions as maintenance of cellular integrity, with collapse of the cell membrane as evidenced by increases of extracellular glutamate and aspartate not occurring until both oxygen and glucose concentrations reach zero.

Redox control of neuronal damage during brain ischemia after middle cerebral artery occlusion in the rat: immunohistochemical and hybridization studies of thioredoxin

Thioredoxin (TRX) is a small, multifunctional protein with a redox-active site and multiple biological functions that include reducing activity for reactive oxygen intermediates. We assayed TRX and TRX mRNA by immunohistochemical methods and hybridization experiments in the rat brain after middle cerebral artery (MCA) occlusion. During ischemia, the immunoreactivity for TRX decreased; it disappeared after MCA occlusion in the ischemic regions. It rapidly decreased and nearly disappeared at 4 and 16 hours after MCA occlusion in the lateral striatum and frontoparietal cortex, respectively. On the other hand, in the perifocal ischemic region, the penumbra, TRX immunoreactivity began to increase 4 hours after MCA occlusion and continued to increase until 24 hours after occlusion. In hybridization experiments, TRX mRNA decreased and nearly disappeared 4 hours after MCA occlusion in the lateral striatum. In the frontoparietal cortex, it decreased until 24 hours after MCA occlusion. In the perifocal ischemic region, TRX mRNA began to increase 4 hours after MCA occlusion and continued to increase until 24 hours. Northern blot analysis showed that total TRX mRNA in the operated hemispheres was induced from 8 hours and increased until 24 hours after the surgical procedures. We previously reported that recombinant TRX promotes the in vitro survival of primary cultured neurons. We now suggest that TRX in the penumbra has neuroprotective functions and that decreased levels of TRX in the ischemic core modify neuronal damage during focal brain ischemia.

Synergy between chronic corticosterone treatment and cerebral ischemia in producing damage in noncalbindinergic neurons

Administration of endogenous corticosterone to intact animals induces calbindin-D28k protein in the hippocampal CA1-CA2 subfields. The fact that this effect on calbindin-D28k was shown to be specific for the hippocampus argues for a receptor-mediated effect on gene expression. In addition, chronic pretreatment with corticosterone aggravates ischemia-induced neuronal damage in the CA3-CA4 subfields. This effect is similar to that of preischemic hyperglycemia, which also induces postischemic seizures and aggravates brain damage, since corticosterone raises blood glucose level and enhances tissue lactic acidosis during ischemia. The energetically compromising qualities of corticosterone indicates that it is a key factor in hippocampal vulnerability. We assume that the increase of calbindin-D28k expression in the CA1-CA2 subfields in corticosterone-treated animals is an adaptive response to the exogenous stress. The lack of adaptive response in CA3-CA4 neurons endangers them by impairing the ability of these neurons to counteract the deleterious effects of calcium. This finding, supports: (1) the hypothesis that corticosterone treatment, when paired with an ischemic insult, causes a prolonged elevation of neuronal [Ca2+]i, in an energy dependent manner, probably through the reduction of calcium efflux and (2) that neurons which do contain calbindin-D28k are particularly predisposed to ischemic insults. The CA1-CA2 neurons express high amounts of calbindin-D28k under stress conditions because their activity may involve a high rate of calcium buffering.

In vitro ischemia promotes glutamate-mediated free radical generation and intracellular calcium accumulation in hippocampal pyramidal neurons

Ischemia-induced cell damage studies have revealed a complex mechanism that is thought to involve glutamate excitotoxicity, intracellular calcium increase, and free radical production. We provide direct evidence that free radical generation occurs in rat CA1 pyramidal neurons of organotypic slices subjected to a hypoxic-hypoglycemic insult. The production of free radicals is temporally correlated with intracellular calcium elevation, as measured by injection of fluo-3 in individual pyramidal cells, using patch electrodes. Free radical production (measured as changes in the fluorescence emission of dihydrorhodamine 123) peaked during reoxygenation and paralleled rising intracellular calcium. Electrophysiological whole-cell recordings revealed membrane potential depolarization and decreased input resistance during the ischemic insult. Glutamate receptor blockade resulted in decreased free radical production and markedly diminished intracellular calcium accumulation, and prevented neuronal depolarization and input resistance decrease during the ischemic episode. These results provide evidence for a direct involvement of glutamate in oxidative damage resulting from ischemic episodes.

Hyperglycemia increases brain injury caused by secondary ischemia after cortical impact injury in rats

OBJECTIVE

To examine the effects of glucose infusion on the histologic brain damage caused by controlled cortical impact injury alone and by cortical impact injury complicated by secondary ischemia.

DESIGN

Prospective, randomized study.

SETTING

University laboratory.

SUBJECTS

Male Long-Evans rats.

INTERVENTIONS

Three experimental conditions were studied: a) 2.5-mm deformation impact (velocity 4 m/sec) injury followed by 40 mins of bilateral carotid occlusion; b) sham impact injury followed by 40 mins of bilateral carotid occlusion; and c) 2.5-mm deformation impact (velocity 4 m/sec) injury followed by sham carotid occlusion. For each experimental condition, animals were randomized to receive either glucose solution or saline solution before the induced injury and the sham impact injury. Contusion volume and neuron density in the CA1 and CA3 regions of the hippocampus were measured 2 wks after the injury.

MEASUREMENTS AND MAIN RESULTS

Parenteral administration of 2.2 g/kg glucose solution increased the blood glucose concentration from 6.7 +/- 3.3 to 17.9 +/- 10.6 mmol/L before the impact injury, and to 12.3 +/- 5.6 mmol/L before carotid occlusion. Hyperglycemia had the greatest effect on the consequences of the impact injury complicated by secondary ischemia, increasing contusion volume from 1 to 30.6 mm3 in the animals that received saline or glucose solution, respectively (p = .005), and reducing the density of normal appearing neurons in the CA1 area of the hippocampus from 201 to 144 cells/mm2 in the animals that received saline solution and glucose solution, respectively (p = .038). The impact injury alone and bilateral carotid occlusion alone caused minimal neuronal loss in the hippocampus and minimal contusion or infarction at the impact site. Individually, these mild injuries were not adversely affected by infusion of glucose solution.

CONCLUSION

Hyperglycemia increases brain damage when traumatic brain injury is complicated by secondary ischemia.

Central nervous system resuscitation

Traumatic injury to the central nervous system induces delayed neuronal death, which may be mediated by acute and chronic neurochemical changes. Experimental identification of these injury mechanisms and elucidation of the neurochemical cascade following trauma may provide enhanced opportunities for treatment with novel neuroprotective strategies.

Extracellular acidosis delays cell death against glucose-oxygen deprivation in neuroblastoma x glioma hybrid cells

OBJECTIVE

To determine whether extracellular acidosis delays cell death against glucose-oxygen deprivation and, if so, whether this result is due to inhibition of calcium (Ca2+) influx or preservation of cellular energy state.

DESIGN

Randomized, controlled, prospective study.

SETTING

University research laboratory.

SUBJECTS

Differentiated neuroblastoma x glioma NG108-15 cells.

INTERVENTIONS

Experiment 1: cells were incubated for 8 hrs in N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid-buffered medium under glucose-oxygen deprivation at pH 7.4, 6.8, 6.5, 6.2, 5.6, or 5.0. Experiment 2: cells were incubated for 8 hrs under glucose-oxygen deprivation after excluding extracellular calcium from culture medium at pH 7.4 or 6.2. Experiment 3: cells were incubated for 2, 4, 6, or 8 hrs in N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid-buffered medium under glucose-oxygen deprivation at pH 7.4 or 6.2 and assayed for high-energy phosphates.

MEASUREMENTS AND MAIN RESULTS

Cell viability was measured with flow cytometry after the cells were stained with fluorescein diacetate and propidium iodide. Cellular adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate were analyzed with high-performance liquid chromatography. Cell viability was significantly greater at pH 6.2 than at pH 7.4 in experiment 1. By excluding extracellular calcium, a significant difference in viability between pH 7.4 and 6.2 persisted in experiment 2. Energy charge and the concentration of adenosine triphosphate were significantly greater at pH 6.2 than at pH 7.4 in the intervals preceding manifestation of a differential effect of acidosis on cell viability in experiment 3.

CONCLUSIONS

Extracellular acidosis at pH 6.2 delayed cell death against glucose-oxygen deprivation. This protective effect by extracellular acidosis may be due to preservation of the cellular energy state in NG108-15 cells, although this study does not exclude the possibility that in other cell types, inhibition of calcium influx may have an effect.

Cerebral resuscitation after global brain ischemia: linking research to practice

Despite significant advances in resuscitation medicine, neurologic recovery continues to be the major limiting factor in achieving successful resuscitation outcomes. Clinicians must recognize that successful resuscitation outcomes are not limited to the restoration of normal cardiac rhythm and hemodynamics, but rather the restoration of human mentation. It is well recognized that a cascade of injurious events begins within minutes of ischemia and that ischemic and postischemic events cause significant neuronal damage. An increased understanding of the pathophysiology of global brain ischemia provides evidence of a therapeutic window of opportunity during which interventions hold the potential to improve neurologic outcome. The research basis for understanding global brain ischemia, its clinical prognosis, and potential intervention strategies are examined.

Neuronal injury in experimental status epilepticus in the rat: role of acidosis

Systemic and cerebral acidosis accompanies generalized tonic-clonic seizures and status epilepticus. Acidosis during status may be modified by neuromuscular paralysis, intubation and ventilation, or administration of a base, but the effect of acidosis on neuronal injury from status is uncertain. We studied the effect of acidosis, induced by hypercarbic ventilation, on heat-shock protein (HSP72) induction in rat brain as a measure of neuronal injury in experimental status epilepticus. Acidosis was found to attenuate neuronal injury, independent of its anticonvulsant effect.

pH-associated Brain Injury in Cerebral Ischemia and Circulatory Arrest

Neuronal injury remains a major limitation in therapies directed toward cardiopulmonary resuscitation and cerebral ischemia. We summarize clinical and experimental information regarding pH-modulated mechanisms of cerebral ischemic injury and the status of antiacidosis therapies relative to the brain. A large body of evidence in animals and humans indicates that cerebral pH can modulate, and perhaps mediate, ischemic brain pathology and influence functional outcome. The importance of low pH and brain bicarbonate levels during reperfusion as a secondary injury remains an open question of therapeutic importance. Under specific conditions, acidosis may be neuroprotective, but this is an area of current controversy. Effective antiacidosis therapy must address the possibility of synergism and competition among multiple injury mechanisms.

Amelioration of impaired cerebral metabolism after severe acidotic ischemia by tirilazad posttreatment in dogs

BACKGROUND AND PURPOSE

Acidosis may contribute to ischemic injury by mobilizing iron because the iron chelator deferoxamine improves early metabolic recovery from hyperglycermic ischemia. Mobilized iron may then promote oxygen radical-induced lipid peroxidative injury during reperfusion. We tested the hypothesis that administration of the antioxidant tirilazad at the start of reperfusion improves early metabolic recovery after severe acidotic ischemia and ameliorates depletion of the endogenous antioxidant glutathione.

METHODS

In anesthetized dogs, arterial glucose concentration was increased to 500 to 600 mg/dL and global incomplete cerebral ischemia was produced for 30 minutes by ventricular fluid infusion to reduce perfusion pressure to 10 to 12 mm Hg. Metabolic recovery and intracellular pH were measured by phosphorus MR spectroscopy. In the first experiment, four groups of eight dogs each received either vehicle or 0.25, 1, or 2.5 mg/kg of tirilizad mesylate at reperfusion. Cerebral blood flow was measured with microspheres. In the second experiment, two groups of eight dogs each each received either vehicle or 2.5 mg/kg of tirilazad at reperfusion, and cortical glutathione was measured at 3 hours of reperfusion.

RESULTS

Cerebral blood flow decreased to approximately 6 mL/min per 100 g and intracellular pH decreased to approximately 5.6 during ischemia in all groups. In the vehicle group, ATP recovery was transient and pH remained less than 6.0. Cerebral blood flow, O2 consumption, and ATP eventually declined to near-zero levels by 3 hours. Recovery was improved by tirilazad posttreatment in a dose-dependent fashion. At the highest dose, cerebral blood flow and O2 consumption were sustained near preischemic levels, and five of eight dogs had recovery of ATP greater than 50% and of pH greater than 6.7. Recovery of ATP and phosphocreatine became significantly greater than that in the vehicle group by 17 minutes of reperfusion despite similar levels of early hyperemia, indicating that the drug was acting before the onset of hypoperfusion. Cortical glutathione concentration in the vehicle group was 27% less than that in the tirilazad group and 34% less than that in nonischemic controls.

CONCLUSIONS

Decreased depletion of the endogenous antioxidant glutathione is consistent with tirilazad acting as an antioxidant in vivo. Improvement in high-energy phosphate recovery 17 minutes after starting tirilazad infusion during reperfusion is consistent with an early onset of a functionally significant oxygen radical injury. Thus, severe acidosis appears to contribute to early ischemic injury through an oxygen radical mechanism sufficient to impede metabolic recovery.

Deferoxamine reduces early metabolic failure associated with severe cerebral ischemic acidosis in dogs

BACKGROUND AND PURPOSE

Postischemic metabolic injury may be mediated by acidosis and tissue bicarbonate depletion, with consequent-iron mobilization and oxygen radical formation during reperfusion. We have previously shown that reducing intracellular pH to below 5.7 and bicarbonate ion to below 1 to 2 mmol/L during hyperglycemic ischemia produces a profound secondary deterioration of brain ATP and cerebral blood flow during reperfusion. This study tested the hypothesis that pretreatment with free deferoxamine ameliorates metabolic decay and delayed hypoperfusion after global hyperglycemic ischemia. In addition, deferoxamine conjugated to a high-molecular-weight starch was administered to determine the importance of an intravascular site of action. Iron-loaded deferoxamine was used to determine whether the iron chelation properties of deferoxamine are important to postischemic viability as distinguished from the agent's significant radical scavenging potential.

METHODS

Cerebral ATP, phosphocreatine, and pH were measured by 31P magnetic resonance spectroscopy in anesthetized dogs. Tissue bicarbonate concentration was calculated from the Henderson-Hasselbalch equation. Incomplete cerebral ischemia was produced by intracranial pressure elevation for 30 minutes with plasma glucose at 540 +/- 15 mg/dL. Free deferoxamine, saline vehicle, hydroxyethyl starch-conjugated deferoxamine, hydroxyethyl starch vehicle, and deferoxamine loaded with equimolar ferric chloride were administered intravenously in five groups of dogs. The dose of deferoxamine was 50 mg/kg before ischemia, 50 mg/kg at the onset of reperfusion, and 50 mg/kg over the 180-minute reperfusion period.

RESULTS

Ischemic hemispheric blood flow (mean, 6 to 8 mL/min per 100 g), intracellular pH (5.7 to 6.0), and bicarbonate levels (1 to 2 mmol/L) were similar in all groups. During reperfusion, cerebral pH and bicarbonate recovered only in the free-deferoxamine group. Both ATP and phosphocreatine initially increased in all groups, but recovery was sustained only in the free-deferoxamine group. Secondary losses of energy phosphates and cerebral oxygen consumption were observed in all other groups, accompanied by progressive reduction of perfusion.

CONCLUSIONS

These data support the hypothesis that iron catalyzed oxygen radical production plays an important role in acidosis-mediated mechanisms of ischemic brain injury. The results with free and iron-loaded deferoxamine suggest that iron scavenging is an important, but not necessarily the principal, component of this mechanism. The poor recovery seen with conjugated deferoxamine indicates that the beneficial action of deferoxamine is not localized within the intravascular compartment.

Transient acidosis induces delayed neurotoxicity in cultured hippocampal slices

It remains unknown if tissue acidosis contributes to neuronal loss during cerebral ischemia. We report that brief intracellular acidification (pH 6.62) results in delayed neuronal loss in cultured hippocampal slices. Cell loss was located primarily in stratum pyramidale and the hilus suggesting that neurons were preferentially damaged. Removal of molecular oxygen greatly attenuated cell loss suggesting that generation of reactive oxygen species may underlie acidosis-induced toxicity. These data suggest that acidosis and incomplete anoxia contributes to the delayed neuronal loss in the ischemic penumbra.

Tirilazad pretreatment improves early cerebral metabolic and blood flow recovery from hyperglycemic ischemia

Acidosis may augment cerebral ischemic injury by promoting lipid peroxidation. We tested the hypothesis that when acidosis is augmented by hyperglycemia, pretreatment with the 21-aminosteroid tirilazad mesylate (U74006F), a potent inhibitor of lipid peroxidation in vitro, improves early cerebral metabolic recovery. In a randomized, blinded study, anesthetized dogs received either tirilazad mesylate (1 mg/kg plus 0.2 mg/kg/h; n = 8) or vehicle (n = 8). Hyperglycemia (400-500 mg/dl) was produced prior to 30 min of global incomplete cerebral ischemia. Intracellular pH and high energy phosphates were measured by phosphorus magnetic resonance spectroscopy. During ischemia, microsphere-determined CBF decreased to 8 +/- 4 ml min-1 100 g-1 and intracellular pH decreased to 5.6 +/- 0.2 in both groups. During the first 20 min of reperfusion, ATP partially recovered in the vehicle group to 57 +/- 21% of baseline, but then declined progressively in association with elevated intracranial pressure. By 30 min, ATP recovery was greater in the tirilazad group (77 +/- 35 vs. 36 +/- 19%), although postischemic hyperemia was similar. By 45 min, the tirilazad group had a higher intracellular pH (6.5 +/- 0.5 vs. 5.9 +/- 0.6) and a lower intracranial pressure (18 +/- 6 vs. 52 +/- 24 mm Hg). By 180 min, blood flow and ATP were undetectable in seven of eight vehicle-treated dogs, whereas ATP was > 67% and pH was > 6.7 in six of eight tirilazad-treated dogs. Thus, tirilazad acts during early reperfusion to prevent secondary metabolic decay associated with severe acidotic ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Postischemic inhibition of cerebral cortex pyruvate dehydrogenase

Postischemic, mitochondrial respiratory impairment can contribute to prolonged intracellular lactic acidosis, secondary tissue deenergization, and neuronal cell death. Specifically, reperfusion-dependent inhibition of pyruvate dehydrogenase (PDH) may determine the degree to which glucose is metabolized aerobically vs. anaerobically. In this study, the maximal activities of pyruvate and lactate dehydrogenase (LDH) from homogenates of canine frontal cortex were measured following 10 min of cardiac arrest and systemic reperfusion from 30 min to 24 h. Although no change in PDH activity occurred following ischemia alone, a 72% reduction in activity was observed following only 30 min of reperfusion and a 65% inhibition persisted following 24 h of reperfusion. In contrast, no significant alteration in LDH activity was observed in any experimental group relative to nonarrested control animals. A trend toward reversal of PDH inhibition was observed in tissue from animals treated following ischemia with acetyl-L-carnitine, a drug previously reported to inhibit brain protein oxidation, and lower postischemic cortical lactate levels and improve neurological outcome. In vitro experiments indicate that PDH is more sensitive than LDH to enzyme inactivation by oxygen dependent free radical-mediated protein oxidation. This form of inhibition is potentiated by either elevated Ca2+ concentrations or substrate/cofactor depletion. These results suggest that site-specific protein oxidation may be involved in reperfusion-dependent inhibition of brain PDH activity.

Dichloroacetate attenuates neuronal damage in a gerbil model of brain ischemia

Dichloroacetate facilitated a reduction in brain lactate following ischemia in the gerbil. This treatment also improved high-energy metabolite and pyruvate dehydrogenase enzyme recovery. The purpose of this study was to determine the effect of dichloroacetate on ischemia-induced neuronal damage in the hippocampus of the gerbil. In adult male gerbils, carotid arteries were clamped bilaterally for 5 min. After ischemia, each gerbil was graded neurologically and received an ip injection of dichloroacetate (75 or 225 mg/kg) or an equal volume (5 mL/kg) of sodium acetate (66 mg/kg). On the following morning, gerbils received a second injection, and 3 d later were anesthetized and perfused intracardially. Brains were processed, and stained sections were analyzed for neuronal damage. Gerbils treated with 225 mg/kg dichloroacetate exhibited significantly less damage than the untreated group (p = 0.05, Dunn's test). Gerbils with a normal neurologic score evidenced no neuronal damage. Abnormal neurologic scores immediately after ischemia did not correlate with degree of neuronal damage observed 4 d later. These results indicate that neuronal damage is less in gerbils treated after ischemia with an appropriate dose of dichloroacetate. The lack of any histological evidence for an adverse effect of dichloroacetate in the controls supports the safety of this drug in this protocol. Normal neurologic scores immediately after ischemia can be used to identify gerbils mimicking ischemia in this model.

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

Effects of dimethylthiourea on ischemic brain damage in hyperglycemic rats

Hyperglycemia is known to worsen the outcome of transient global or forebrain ischemia. The aggravating effect is believed to be mediated by the additional formation of lactate- and of H+. Recent evidence suggests that reactive oxygen species contribute to the damage after brain ischemia. Since acidosis accelerates free radical damage in vitro, we decided to explore if ischemic damage in hyperglycemic subjects is ameliorated by dimethylthiourea (DMTU), an established free radical scavenger. In one series of hyperglycemic rats, we studied whether preischemic administration of DMTU alters the clinical outcome, notably the incidence and frequency of seizures. In two different series, the effect of DMTU on tissue damage was assessed by light microscopy after 15 h of recovery. Longer periods could not be studied since seizures developed. In the first of these series the animals were anesthetized with isoflurane, and in the second with halothane. The latter anesthesia largely suppressed the "early" postischemic seizures, i.e. those occurring after 1-4 h. Dimethylthiourea treatment altered the clinical outcome after ischemia. Thus, the "late" postischemic seizures appeared milder and occurred significantly later than in untreated animals. The fatal outcome was also delayed since treated animals died after 35.5 +/- 8.2 h (mean +/- SD) of recirculation, as compared to 19.8 +/- 3.6 h of recirculation in control animals. However, all DMTU-treated (and control) animals died. In the first morphological series (isoflurane anesthesia) the histopathological analysis was complicated by the occurrence of prefixation seizures; such seizures were recognized in 4/16 animals. When these 4 animals were excluded from the analysis (2 treated and 2 control animals), DMTU pretreatment did not ameliorate the damage, except in the substantia nigra pars reticulata (P < 0.05). In the second series, comprising animals anesthetized with halothane, only one animal out of 16 had "early" seizures, and none showed "late" seizures before death. Among these animals DMTU treatment significantly ameliorated damage to caudoputamen and cingulate cortex (P < 0.01). We conclude that treatment with the free radical scavenger DMTU partly ameliorates ischemic brain damage associated with excessive acidosis, and marginally delays the development of post-ischemic seizures. However, the effects were moderate and could, at least in part, have been caused by nonspecific effects of DMTU. Furthermore, all DMTU-treated animals died. The results thus give little support to the notion that the aggravating effects of acidosis is due to enhancement of free radical production.

Ion homeostasis in rat brain in vivo: intra- and extracellular [Ca2+] and [H+] in the hippocampus during recovery from short-term, transient ischemia

Changes in intra- and extracellular [Ca2+] and [H+], together with alterations in tissue PO2 and local blood flow, were measured in areas CA1 and CA3 of the hippocampus during recovery (up to 8 h) after an 8-min period of low-flow ischemia. Restoration of blood supply was followed by an immediate rise in flow and tissue PO2 above normal, with large fluctuations in both persisting for up to 4 h. In area CA1, [Ca2+]i decreased rapidly from an ischemic mean value of 30 microM to a control mean level of 73.1 nM in 20-30 min, whereas normalization of [Ca2+]e took approximately 1 h. Recovery of [Ca2+]i was accelerated by preischemic administration of a calcium antagonist, nifedipine, and a free radical scavenger, N-tert-butyl-alpha-phenylnitrone (PBN), but not by MK-801, a blocker of N-methyl-D-aspartate receptors. There was a secondary rise in [Ca2+]i in many cells beginning approximately 2 h after reperfusion. This was attenuated somewhat by PBN but not clearly influenced by either nifedipine or MK-801. Changes of [Ca2+]i in area CA3 were much smaller and slightly slower than in area CA1 and were not affected by the drugs mentioned above. In both areas CA1 and CA3, pHe and pHi fell during ischemia to an average value of 6.2, from which there was a rapid initial recovery in the first 5-10 min when blood flow was restored. Thereafter tissue pH rose slowly and did not reach control levels for approximately 1 h, and in some microareas not at all. It is concluded that (a) effective mechanisms for restoring normal [Ca2+]i remain intact after 8 min of low-flow ischemia; (b) in neurons of area CA1, some insidious change in the homeostasis of calcium triggers a secondary rise in its free cytosolic concentration, which may be causally related to activation of irreversible cell damage; and (c) the changes in [Ca2+]i and [Ca2+]e during and following 8 min of ischemia can be adequately accounted for by movements of a fixed pool of Ca between intra- and extracellular compartments, and possible mechanisms are discussed.

Ubiquinone protects cultured neurons against spontaneous and excitotoxin-induced degeneration

Ubiquinone is an endogenous quinone with pharmacological actions mainly related to its antioxidant properties. Here we report that ubiquinone protects cultured cerebellar granule cells against glutamate-induced neurotoxicity. In control cultures at 9 days of maturation in vitro (DIV), a 30-min exposure to 100 microM glutamate induced neuronal degeneration, as reflected by the great percentage (greater than 90%) of cells labeled with propidium iodide 24 h after the exposure. Glutamate-induced neuronal death was dramatically reduced in cultures treated daily with ubiquinone since the second DIV. In these cultures, glutamate failed to induce a "delayed" increase in the influx of 45Ca2+, an established parameter of excitotoxicity. Similarly, repeated addition of ubiquinone attenuated in a concentration-dependent manner the age-dependent degeneration of granule cells that is due to the toxic action of the endogenous glutamate progressively released into the medium. These results suggest that ubiquinone may be a useful drug in the therapy of acute and chronic neurodegenerative diseases related to hyperactivity of excitatory amino acid neurotransmission.