Xanthine oxidase-derived hydrogen peroxide contributes to ischemia reperfusion-induced edema in gerbil brains

Marked elevation in cortical urate and xanthine oxidoreductase activity in experimental bacterial meningitis

Experimental bacterial meningitis due to Streptococcus pneumoniae in infant rats was associated with a time-dependent increase in CSF and cortical urate that was approximately 30-fold elevated at 22 h after infection compared to baseline. This increase was mirrored by a 20-fold rise in cortical xanthine oxidoreductase activity. The relative proportion of the oxidant-producing xanthine oxidase to total activity did not increase, however. Blood plasma levels of urate also increased during infection, but part of this was as a consequence of dehydration, as reflected by elevated ascorbate concentrations in the plasma. Administration of the radical scavenger alpha-phenyl-tert-butyl nitrone, previously shown to be neuroprotective in the present model, did not significantly affect either xanthine dehydrogenase or xanthine oxidase activity, and increased even further cortical accumulation of urate. Treatment with the xanthine oxidoreductase inhibitor allopurinol inhibited CSF urate levels earlier than those in blood plasma, supporting the notion that urate was produced within the brain. However, this treatment did not prevent the loss of ascorbate and reduced glutathione in the cortex and CSF. Together with data from the literature, the results strongly suggest that xanthine oxidase is not a major cause of oxidative stress in bacterial meningitis and that urate formation due to induction of xanthine oxidoreductase in the brain may in fact represent a protective response.

Oxidant stress and endothelial cell dysfunction

Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-kappaB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion. Particular emphasis is placed on the regulation of cell-cell and cell-surface adhesion molecules, the actin cytoskeleton, key protein kinases, and signal transduction events.

Antioxidant LY231617 enhances electrophysiologic recovery after global cerebral ischemia in dogs

OBJECTIVE

The potent antioxidant LY231617 (2,6-bis(1,1-dimethylethyl)-4-[[(1-ethyl)amino]methyl]phenol hydrochloride) is cytoprotective in models of focal and global cerebral ischemia. We tested the hypothesis that administration of LY231617, before the insult, would improve recovery of cerebral electrical activity and metabolic function after transient global cerebral ischemia by improving cerebral blood flow (CBF) during the reperfusion period.

DESIGN

Randomized, controlled, prospective study.

SETTING

Research laboratory at a university teaching hospital.

SUBJECTS

Twenty-four male beagle dogs.

INTERVENTIONS

All experiments were performed under pentobarbital anesthesia and controlled conditions of normoxia, normocarbia, and normothermia. Twelve control dogs received 20 mL/kg saline (vehicle) bolus into the right atrium and 0.01 mL/kg/min i.v., beginning 20 mins before 13 mins of global cerebral ischemia (by aortic occlusion). The dogs in the drug-treated group received LY231617 as a 10-mg/kg bolus 20 mins before ischemia and 5 mg/kg/hr throughout reperfusion (n = 12). CBF was measured using radiolabeled microspheres.

MEASUREMENTS AND MAIN RESULTS

Total CBF, cerebral oxygen consumption, and somatosensory evoked potentials (SEP) were measured during 240 mins of reperfusion. CBF was similar in both vehicle- and LY231617-treated animals at baseline and throughout the experimental period. In all animals, SEP became isoelectric between 60 and 100 secs after cross-clamping of the ascending aorta. SEP amplitude recovery was significantly higher in drug-treated animals compared with controls (73%+/-15% vs. 39%+/-14% [mean+/-SEM] from baseline at 120 mins [p<.05] and 86%+/-12% vs. 49%+/-14% from baseline at 240 mins [p< .05]).

CONCLUSIONS

LY231617 improves recovery of cerebral electrical function after complete transient global ischemia via mechanisms unrelated to cerebral circulatory effects.

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.

Effect of allopurinol on hypoxia-induced modification of the NMDA receptor in newborn piglets

The present study tests the hypothesis that pretreatment with allopurinol, a xanthine oxidase inhibitor, will prevent modification of the NMDA receptor during cerebral hypoxia in newborn piglets. Eighteen newborn piglets were studied. Six normoxic control animals were compared to six untreated hypoxic and six allopurinol (20 mg/kg i.v.) pretreated hypoxic piglets. Cerebral hypoxia was induced by lowering the FiO2 to 0.05-0.07 for 1 hour and tissue hypoxia was confirmed biochemically by the measurement of ATP and phosphocreatine. Brain cell membrane Na+,K+-ATPase activity was determined to assess membrane function. Na+,K+-ATPase activity was decreased from control in both the untreated and treated hypoxic animals (46.0+/-1.0 vs 37.9+/-2.5 and 37.3+/-1.4 micromol Pi/mg protein/hr, respectively, p < 0.05). [3H]MK-801 binding was determined as an index of NMDA receptor modification. The receptor density (Bmax) in the untreated hypoxic group was decreased compared to normoxic control (1.09+/-0.17 vs 0.68+/-0.22 pmol/mg protein, p < 0.01). The dissociation constant (Kd) was also decreased in the untreated group (10.0+/-2.0 vs 4.9+/-1.4 nM, p < 0.01), indicating an increase in receptor affinity. However, in the allopurinol treated hypoxic group, the Bmax (1.27+/-0.09 pmol/mg protein) was similar to normoxic control and the Kd (8.1+/-1.2 nM, p < 0.05) was significantly higher than in the untreated hypoxic group. The data show that the administration of allopurinol prior to hypoxia prevents hypoxia-induced modification of the NMDA receptor-ion channel binding characteristics, despite neuronal membrane dysfunction. By preventing NMDA receptor-ion channel modification, allopurinol may produce a neuromodulatory effect during hypoxia and attenuate NMDA receptor mediated excitotoxicity.

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.

Blockade of tetrahydrobiopterin synthesis protects neurons after transient forebrain ischemia in rat: a novel role for the cofactor

The generation of nitric oxide (NO) aggravates neuronal injury. (6R)-5,6,7,8-Tetrahydro-L-biopterin (BH4) is an essential cofactor in the synthesis of NO by nitric oxide synthase (NOS). We attempted to attenuate neuron degeneration by blocking the synthesis of the cofactor BH4 using N-acetyl-3-O-methyldopamine (NAMDA). In vitro data demonstrate that NAMDA inhibited GTP cyclohydrolase I, the rate-limiting enzyme for BH4 biosynthesis, and reduced nitrite accumulation, an oxidative metabolite of NO, without directly inhibiting NOS activity. Animals exposed to transient forebrain ischemia and treated with NAMDA demonstrated marked reductions in ischemia-induced BH4 levels, NADPH-diaphorase activity, and caspase-3 gene expression in the CA1 hippocampus. Moreover, delayed neuronal injury in the CA1 hippocampal region was significantly attenuated by NAMDA. For the first time, these data demonstrate that a cofactor, BH4, plays a significant role in the generation of ischemic neuronal death, and that blockade of BH4 biosynthesis may provide novel strategies for neuroprotection.

Ontogenetic aspects of traumatic brain edema--facts and suggestions

Diffuse brain swelling (DBS) after severe traumatic brain injury (TBI) occurs more commonly in children than adults. Most of the recent clinical studies suggest that young children are more negatively affected by DBS. Until now studies in young animals in which the pathophysiology of DBS was evaluated remained seldom. However, pathogenetic mechanisms of edema formation after TBI in the immature brain appeared to be different in comparison to adult brains. There are evidences that vasogenic as well as cytotoxic edema components may be responsible for the development of DBS. Besides mechanical disturbance, the blood-brain barrier seems to be strongly endangered by oxidative stress after TBI because regional antioxidative capacity is obviously diminished. In addition, cytotoxic components of DBS may be caused by at least two different mechanisms. First, it was shown that a sustained posttraumatic cerebral hypoperfusion occurs in the immature brain. Moreover, a transient increase of NMDA receptor expression at this period of life may be responsible for an increased threat of intracellular sodium ion accumulation in brain cells. Obviously, brain swelling can be detrimental because it can elevate intracranial pressure, impair CBF, and may represent ongoing secondary brain injury.

Blockade of tetrahydrobiopterin synthesis protects neurons after transient forebrain ischemia in rat: a novel role for the cofactor

The generation of nitric oxide (NO) aggravates neuronal injury. (6R)-5,6,7,8-Tetrahydro-L-biopterin (BH4) is an essential cofactor in the synthesis of NO by nitric oxide synthase (NOS). We attempted to attenuate neuron degeneration by blocking the synthesis of the cofactor BH4 using N-acetyl-3-O-methyldopamine (NAMDA). In vitro data demonstrate that NAMDA inhibited GTP cyclohydrolase I, the rate-limiting enzyme for BH4 biosynthesis, and reduced nitrite accumulation, an oxidative metabolite of NO, without directly inhibiting NOS activity. Animals exposed to transient forebrain ischemia and treated with NAMDA demonstrated marked reductions in ischemia-induced BH4 levels, NADPH-diaphorase activity, and caspase-3 gene expression in the CA1 hippocampus. Moreover, delayed neuronal injury in the CA1 hippocampal region was significantly attenuated by NAMDA. For the first time, these data demonstrate that a cofactor, BH4, plays a significant role in the generation of ischemic neuronal death, and that blockade of BH4 biosynthesis may provide novel strategies for neuroprotection.

Effect of hemorrhagic hypotension on hydroxyl radicals in cat brain

This study investigated the relationships between blood pressure, cortical oxygen pressure and hydroxyl radicals in the brain of adult cats during hemorrhagic hypotension and retransfusion. Oxygen pressure in the blood of the cortex was measured optically by the oxygen dependent quenching of phosphorescence and hydroxyl radicals by in vivo microdialysis. Following a 2 h stabilization period after implantation of the microdialysis probe in the striatum, the mean arterial blood pressure (MAP) was decreased in a stepwise manner from 132 +/- 2 Torr (control) to 90 +/- 1 Torr, 70 +/- 3 Torr and 50 +/- 3 Torr, holding the pressure at each level for 15 min. The whole blood was then retransfused and measurements were continued for 90 min. Cortical oxygen pressure progressively decreased with decrease in MAP, decreasing from 50 +/- 2 Torr (control) to 42 +/- 1 Torr, 31 +/- 2 Torr and 22 +/- 2 Torr, respectively. The level of hydroxyl radical increased by 20-25% following first 15 min of bleeding and stay on this level during the remaining period of hypotension. Maximal increase (by 78%) in level of hydroxyl radicals was observed after 15 min of retransfusion. The present study demonstrated that during hypotension and retransfusion there was an increase in the level of hydroxyl radicals in striatum. These can be important mediators of postischemic injury to the striatum.

Free oxygen radicals--predictors of neonatal outcome following perinatal asphyxia

The study was undertaken to evaluate the role of free oxygen radicals in asphyxiated neonates. Thirty term neonates appropriate for gestational age and with severe birth asphyxia (Apgar score of 3 or less at 1 minute of life) formed the study subjects. The levels of superoxide dismutase (SOD), glutathione peroxidase (GPx), creatine phosphokinase (CPK) and lipid peroxidase (LPO) in the CSF of these neonates were estimated between 12 and 48 hrs of life. Enzyme estimation was performed by standard methods and the results were analysed statistically using Multivariate Logistic Regression analysis and non parametric tests namely Kruskal Wallis test and Wilcoxon's rank sum test. Out of the thirty babies, 14 were observed to be neurologically normal, 9 had significant morbidity and 7 died. The SOD levels ranged from 12.4 to 140 units/ml, GPx from 128 to 1933 nmol/min/dl, CPK from 2 to 2098 IU/dl and LPO from 5.4 to 30.8 umol/hr/dl. The SOD and GPx levels had an inverse relationship whereas rise in LPO and CPK levels were directly proportional to the extent of neurological damage and ultimate clinical outcome. CPK levels higher than 140 IU/ml were lethal and associated with 100% mortality whereas all normal neonates had CPK below 37 IU/ml. The levels of antioxidant enzymes can reliably and significantly predict mortality and morbidity whereas level of an enzyme cannot confidently confer normalcy. Hence antioxidant enzyme levels with a cut off value can be a useful marker and serve as a prognostic indicator in times to come.

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.

Effect of allopurinol on postasphyxial free radical formation, cerebral hemodynamics, and electrical brain activity

OBJECTIVE

Free radical-induced postasphyxial reperfusion injury has been recognized as an important cause of brain tissue damage. We investigated the effect of high-dose allopurinol (ALLO; 40 mg/kg), a xanthine-oxidase inhibitor and free radical scavenger, on free radical status in severely asphyxiated newborns and on postasphyxial cerebral perfusion and electrical brain activity.

METHODS

Free radical status was assessed by serial plasma determination of nonprotein-bound iron (microM), antioxidative capacity, and malondialdehyde (MDA; microM). Cerebral perfusion was investigated by monitoring changes in cerebral blood volume (delta CBV; mL/100 g brain tissue) with near infrared spectroscopy; electrocortical brain activity (ECBA) was assessed in microvolts by cerebral function monitor. Eleven infants received 40 mg/kg ALLO intravenously, and 11 infants served as controls (CONT). Plasma nonprotein-bound iron, antioxidative capacity, and MDA were measured before 4 hours, between 16 and 20 hours, and at the second and third days of age. Changes in CBV and ECBA were monitored between 4 and 8, 16 and 20, 58 and 62, and 104 and 110 hours of age.

RESULTS

Six CONT and two ALLO infants died after neurologic deterioration. No toxic side effects of ALLO were detected. Nonprotein-bound iron (mean +/- SEM) in the CONT group showed an initial rise (18.7 +/- 4.6 microM to 21.3 +/- 3.4 microM) but dropped to 7.4 +/- 3.5 microM at day 3; in the ALLO group it dropped from 15.5 +/- 4.6 microM to 0 microM at day 3. Uric acid was significantly lower in ALLO-treated infants from 16 hours of life on. MDA remained stable in the ALLO group, but increased in the CONT group at 8 to 16 hours versus < 4 hours (mean +/- SEM; 0.83 +/- 0.31 microM vs 0.50 +/- 0.14 microM). During 4 to 8 hours, delta CBV-CONT showed a larger drop than delta CBV-ALLO from baseline. During the subsequent registrations CBV remained stable in both groups. ECBA-CONT decreased, but ECBA-ALLO remained stable during 4 to 8 hours of age. Neonates who died had the largest drops in CBV and ECBA.

CONCLUSION

This study suggests a beneficial effect of ALLO treatment on free radical formation, CBV, and electrical brain activity, without toxic side effects.

Mechanisms of calcium and sodium fluxes in anoxic myelinated central nervous system axons

Electron probe X-ray microanalysis was used to measure water content and concentrations of elements (i.e. Na, K, Cl and Ca) in selected morphological compartments of rat optic nerve myelinated axons. Transaxolemmal movements of Na+ and Ca2+ were modified experimentally and corresponding effects on axon element and water compositions were determined under control conditions and following in vitro anoxic challenge. Also characterized were effects of modified ion transport on axon responses to postanoxia reoxygenation. Blockade of Na+ entry by tetrodotoxin (1 microM) or zero Na+/Li(+)-substituted perfusion reduced anoxic increases in axonal Na and Ca concentrations. Incubation with zero-Ca2+/EGTA perfusate prevented axoplasmic and mitochondrial Ca accumulation during anoxia but did not affect Na increases or K losses in these compartments. Inhibition of Na(+)-Ca2+ exchange with bepridil (30 microM) selectively prevented increases in intra-axonal Ca, whereas neither nifedipine (5 microM) nor nimodipine (5 microM) influenced the effects of anoxia on axonal Na, K or Ca. X-ray microanalysis also showed that prevention of Na and Ca influx during anoxia obtunded severe elemental deregulation normally associated with reoxygenation. Results of the present study suggest that during anoxia, Na+ enters axons mainly through voltage-gated Na+ channels and that subsequent increases in axoplasmic Na+ are functionally coupled to extra-axonal Ca2+ import. Na+i-dependent, Ca2+o entry is consistent with reverse operation of the axolemmal Na(+)-Ca2+ exchanger and we suggest this route represents a primary mechanism of Ca2+ influx. Our findings also implicate a minor route of Ca2+ entry directly through Na+ channels.

Anoxic and ischemic injury of myelinated axons in CNS white matter: from mechanistic concepts to therapeutics

White matter of the brain and spinal cord is susceptible to anoxia and ischemia. Irreversible injury to this tissue can have serious consequences for the overall function of the CNS through disruption of signal transmission. Myelinated axons of the CNS are critically dependent on a continuous supply of energy largely generated through oxidative phosphorylation. Anoxia and ischemia cause rapid energy depletion, failure of the Na(+)-K(+)-ATPase, and accumulation of axoplasmic Na+ through noninactivating Na+ channels, with concentrations approaching 100 mmol/L after 60 minutes of anoxia. Coupled with severe K+ depletion that results in large membrane depolarization, high [Na+]i stimulates reverse Na(+)-Ca2+ exchange and axonal Ca2+ overload. A component of Ca2+ entry occurs directly through Na+ channels. The excessive accumulation of Ca2+ in turn activates various Ca(2+)-dependent enzymes, such as calpain, phospholipases, and protein kinase C, resulting in irreversible injury. The latter enzyme may be involved in "autoprotection," triggered by release of endogenous gamma-aminobutyric acid and adenosine, by modulation of certain elements responsible for deregulation of ion homeostasis. Glycolytic block, in contrast to anoxia alone, appears to preferentially mobilize internal Ca2+ stores; as control of internal Ca2+ pools is lost, excessive release from this compartment may itself contribute to axonal damage. Reoxygenation paradoxically accelerates injury in many axons, possibly as a result of severe mitochondrial Ca2+ overload leading to a secondary failure of respiration. Although glia are relatively resistant to anoxia, oligodendrocytes and the myelin sheath may be damaged by glutamate released by reverse Na(+)-glutamate transport. Use-dependent Na+ channel blockers, particularly charged compounds such as QX-314, are highly neuroprotective in vitro, but only agents that exist partially in a neutral form, such as mexiletine and tocainide, are effective after systemic administration, because charged species cannot penetrate the blood-brain barrier easily. These concepts may also apply to other white matter disorders, such as spinal cord injury or diffuse axonal injury in brain trauma. Moreover, whereas many events are unique to white matter injury, a number of steps are common to both gray and white matter anoxia and ischemia. Optimal protection of the CNS as a whole will therefore require combination therapy aimed at unique steps in gray and white matter regions, or intervention at common points in the injury cascades.

Ischemic stroke injury is reduced in mice lacking a functional NADPH oxidase

BACKGROUND AND PURPOSE

Free radicals account for a significant proportion of the brain damage that occurs during ischemic stroke. Using mutant mice (X-CGD) with a dysfunctional phagocytic NADPH oxidase, we investigated the role of this superoxide-generating enzyme as a mediator of the reperfusion injury in a mouse model of middle cerebral artery occlusion.

METHODS

Transient (2 hour) middle cerebral artery occlusion was performed in X-CGD or wild-type litter mates (8- to 10-week-old). After 22 hours of reperfusion, brains were harvested and infarct volume delineated using 2,3,5-triphenyl-tetrazolium chloride. To elucidate the origin of the damaging NADPH oxidase, transient ischemia was also performed in X-CGD or wild-type mice transplanted with wild-type C57 B1/6J or X-CGD bone marrow, respectively.

RESULTS

The infarct volume induced by transient ischemia was significantly less in X-CGD mice (29.1 +/- 5.6 mm3; n = 13) than wild-type littermates (54.0 +/- 10.6 mm3; n = 10; P < .05). The elimination of a functional NADPH oxidase from either the circulation or the central nervous system, by performing the appropriate bone marrow transplant experiments, did not reduce the infarct size induced by transient ischemia. This suggests that in order to confer protection against transient ischemia and reperfusion, a putative neuronal and circulating NADPH oxidase need to be inactivated.

CONCLUSIONS

Brain injury was reduced in mice lacking a functional NADPH oxidase in both the central nervous system and peripheral leukocytes, suggesting a pivotal role for the NADPH oxidase in the pathogenesis of ischemia-reperfusion injury in the brain.

Hydrogen peroxide opposes the hypoxic depression of evoked synaptic transmission in rat hippocampal slices

Hydrogen peroxide (H2O2, 3.3 mM) partially reversed the hypoxic depression of the evoked population spike recorded from CA1 region of rat hippocampal slices. It is known that elevated endogenous adenosine contributes to the hypoxic inhibition of the population spike. Exogenous adenosine (100 microM) inhibited the population spike that had been partially resuscitated by H2O2 during maintained hypoxia. It is concluded that the ability of H2O2 to oppose hypoxic depression does not occur at the level of the adenosine receptor since added adenosine was still effective in inhibiting the evoked potential in the presence of H2O2.

Xanthine dehydrogenase/xanthine oxidase and oxidative stress

Xanthine dehydrogenase (XDH) and xanthine oxidase (XOD) are single-gene products that exist in separate but interconvertible forms. XOD utilizes hypoxanthine or xanthine as a substrate and O2 as a cofactor to produce superoxide (·O2 (-)) and uric acid. XDH acts on these same substrates but utilizes NAD as a cofactor to produce NADH instead of ·O2 (-) and uric acid. XOD has been proposed as a source of oxygen radicals in polymorphonuclear, endothelial, epithelial, and connective tissue cells. However, several questions remain about the physiological significance and functions of XOD on aging and oxidative stress. XOD is reported to play an important role in cellular oxidative status, detoxification of aldehydes, oxidative injury in ischemia-reperfusion, and neutrophil mediation. For example, XOD may serve as a messenger or mediator in the activation of neutrophil, T cell, cytokines, or transcription in defense mechanisms rather than as a free radical generator of tissue damage. Emerging evidence on the synergistic interactions of ·O2 (-), a toxic product of XOD and nitric oxide, may be another illustration of XOD involvement in tissue injury and cytotoxicity in an emergent condition such as ischemia or inflammation.

Redox changes in perfusates following intracerebral penetration of microdialysis probes

Microdialysis probe insertion into rat cerebral cortex significantly affects the levels of redox-active substances in brain extracellular fluid. Ascorbic acid levels are high immediately after probe insertion, decline rapidly, and then rise as the rat recovers from anesthesia 5-8 hours after surgery. Uric acid is at a low level for 5 hours and then rapidly increases in parallel with ascorbic acid. High ascorbic acid levels immediately after probe insertion are likely due to a shift from intracellular to extracellular fluids, whereas the delayed increase in uric acid may be due to increased enzymatic formation. After removal from the brain, hydrogen peroxide (H2O2) in microdialysis samples produces catalase-sensitive oxidative chemiluminescence. Microdialysis samples also produce high level catalase-resistant chemiluminescence associated with ascorbic acid levels after penetration injury. Although ascorbic acid is likely an antioxidant at concentrations estimated to be in brain extracellular fluid, it may have prooxidant effects when complexed with transition metals released into the neuronal microenvironment during traumatic brain injury.

Melatonin administration protects CA1 hippocampal neurons after transient forebrain ischemia in rats

Melatonin administered at the beginning of cerebral reperfusion protected CA1 neurons against 10, 20 and 30 min of transient forebrain ischemia. Intraperitoneal injections of saline or melatonin (10 mg/kg) were given after 0, 2 and 6 h, or 1, 2 and 6 h of cerebral reperfusion, or 30 min prior to ischemia. One week later, quantitative histological analysis demonstrated that CA1 neuronal density was significantly increased in the melatonin groups that were treated at 0, 2, 6 h compared to the saline-treated controls. Ischemic protection of CA1 was lost in the animals in which the melatonin treatment was delayed by 1 h, or given 30 min prior to the ischemia.

The role of neutrophils in the production of hypoxic-ischemic brain injury in the neonatal rat

Neutrophils contribute to ischemic brain injury in adult animals. The role of neutrophils in perinatal hypoxic-ischemic (HI) brain injury is unknown. Allopurinol reduces neutrophil accumulation after tissue ischemia and is protective against HI brain injury. This study was designed to investigate how neutrophils contribute to perinatal hypoxic ischemic brain injury and how neutropenia compared with allopurinol in its neuroprotective effects. A HI insult was produced in the right cerebral hemisphere of 7-d-old rats by right common carotid artery ligation and systemic hypoxia. Half the rats were rendered neutropenic with an anti-neutrophil serum (ANS). At 15 min of recovery from hypoxia, half the neutropenic and nonneutropenic rats received allopurinol (135 mg/kg, s.c.). The protective effect of the four treatment combinations was determined on brain swelling at 42 h of recovery. Neutropenia reduced brain swelling by about 70%, p < 0.01. Allopurinol alone produced similar protection so that the relatively small number of animals studied did not permit assessment of an additive effect. Neutrophil accumulation in cerebral hemispheres was measured by myeloperoxidase (MPO) activity assay and by neutrophil counts in 6-microm sections stained by MPO and ANS immunostaining. MPO activity peaked between 4 and 8 h of recovery in both hemispheres. Hemispheric neutrophil counts peaked at the end of the HI insult and again at 18 h of recovery. Neutrophils were stained within blood vessels and did not infiltrate the injured brain before infarction had occurred. We conclude that neutrophils contribute to HI brain injury in the neonate and that neutrophil depletion before the insult is neuroprotective.

Acceleration of hypertensive cerebral injury by the inhibition of xanthine-xanthine oxidase system in stroke-prone spontaneously hypertensive rats

It is well-known that, in ischemic cerebral injury, a free radical and its byproducts are generated by xanthine-xanthine oxidase system and eliminated by scavengers such as superoxide dismutase (SOD), catalase, uric acid and ascorbic acid. To investigate the possible involvement of the xanthine-xanthine oxidase system in hypertensive cerebral injury, we examined chronological changes in uric acid level in the cerebral cortex and the effects of the inhibition of xanthine oxidase or catalase using stroke-prone spontaneously hypertensive rats (SHRSP). In young SHRSP, uric acid content was lower than age-matched Wistar-Kyoto rats (WKY), but in mature SHRSP strongly exposed to oxidative stress uric acid content had risen dramatically. Administration of allopurinol, an inhibitor of xanthine oxidase, caused a marked decrease in uric acid content. In these SHRSP, cerebral injury was much more intense compared to the control group. On the other hand, administration of aminotriazole, an inhibitor of catalase, did not affect the brain pathology of SHRSP, in spite of a mild reduction in tissue uric acid content. These results suggest that the xanthine-xanthine oxidase system is not the major source of free radical generation in hypertensive cerebral injury. Moreover, the results also suggest that tissue uric acid may have a key role for the incidence of hypertensive cerebral injury in SHRSP.

Neuroprotective nitric oxide synthase inhibitor reduces intracellular calcium accumulation following transient global ischemia in the gerbil

By observing the ultrastructural intracellular Ca2+ distribution with Ca(2+)-oxalate-pyroantimonate method, we examined whether the protective mechanism of the nitric oxide (NO) synthase inhibitor, N omega-nitro-L-arginine (LNNA), involves change of the intracellular Ca2+ movement in delayed neuronal death (DND) in gerbil hippocampal CA1 neurons following 5-min forebrain ischemia. In the group intraventricularly administered 5.0 mg/ml LNNA, 15 min after reperfusion the intracellular Ca2+ deposits and the mitochondrial Ca2+ uptake index increased to levels similar to those in the control group administered only artificial cerebro-spinal fluid, but by 180 min after reperfusion they had returned to the preischemic level. By 15 min after reperfusion Ca2+ deposits in the endoplasmic reticulum (ER) had almost disappeared in both groups, but at 180 min of reperfusion, the ER in only the LNNA group showed Ca2+ deposits. It is suggested that the neuronal toxicity of NO involves the dysfunction of the intracellular Ca2+ transport system including the mitochondria and ER.

Necrosis of the substantia nigra, pars reticulate, in flurothyl-induced status epilepticus is ameliorated by the spin trap alpha phenyl-N-tert-butyl nitrone

The objective of the present study was to explore whether a diffusible free radical scavenger can ameliorate the pan-neurotic lesions of the substantia nigra, pars reticulate (SNPR), which are incurred in rats subjected to status epilepticus of more than 30 min duration. Vehicle-injected animals had flurothyl seizures induced for 45 min. The seizures were then terminated and the animals were recovered for 7 d to allow histopathological evaluation of the SNPR lesions. Drug-treated animals, which were otherwise treated identically, were given either 100-800 mg/ kg of dimethylthiourea (DMTU), a diffusible hydroxyl ion scavenger, or the diffusible spin trap alpha-phenyl N-tert-butyl nitrone (PBN) in a dose of 100 mg/kg i.p.. All animals given DMTU died 2 to 8 h after status epilepticus, but PBN was tolerated well by the animals. The amount of flurothyl required to sustain the electrographic seizures was identical in the vehicle- and drug-injected groups, demonstrating that PBN did not suppress seizure activity. Vehicle-injected animals had large bilateral infarcts localized to the SNPR. Of the six animals treated with PBN, one had a small, unilateral lesions, and in all other animals the SNPR had a normal histological appearance. The results strongly suggest that the pan-necrotic lesions of the SNPR incurred during ongoing seizure activity represent a free radical-mediated lesion.

Nitric oxide synthase inhibitor reduces delayed neuronal death in gerbil hippocampal CA1 neurons after transient global ischemia without reduction of brain temperature or extracellular glutamate concentration

We planned a study to determine whether or not the mechanism of nitric oxide (NO) neurotoxicity involves the elevation of extracellular glutamate or changes of brain temperature in the pathogenesis of delayed neuronal death of gerbil hippocampal CA1 neurons following 5-min transient forebrain ischemia. Intraventricular injection of 5 microliters of 5.0 mg/ml N omega-nitro-L-arginine (LNNA) significantly preserved neuronal density in the central part of the CA1 region examined 7 days after 5-min ischemia [188.5 +/- 8.5/mm: 90.0% of the 209.5 +/- 11.1/mm density in the sham-operated controls vs. 16.7 +/- 6.4/mm in those injected with artificial cerebrospinal fluid (CSF) only]. There was no difference between these two groups in hippocampal temperature before, during or after 5-min ischemia. The glutamate concentration ([Glu]) during 5-min ischemia measured by a microdialysis technique was similar in the two groups (peak [Glu.] = 2.76 +/- 0.62 pmol/microliters dialysate in the artificial CSF group and = 2.93 +/- 0.64 pmol/microliters dialysate in the LNNA group). It was found that the neuronal toxicity of NO does not involve hyperthermia or the increase of extracellular glutamate concentration in the hippocampal CA1 region during 5-min ischemia.

The generation of byproducts of lipid peroxidation following carotid endarterectomy

The aim of this study was to determine whether free radical-induced lipid peroxidation occurs following transient carotid clamping. Jugular vein plasma levels of malondialdehyde (MDA) and diene conjugates (DC) were estimated in 24 patients undergoing carotid endarterectomy, at the beginning of the operation (To), just prior to clamping the carotid artery before the shunt was removed for closure of the arteriotomy (Ts), and at 30 (T30), 60 (T60), 120 (T120), 180 (T180) and 300 (T300) seconds after the clamps were released. Carotid clamp times were recorded. Significant elevations in the concentrations of both MDA and DC were observed at T60 after clamp release (MDA = 559 +/- 64 pmol/ml, DC = 428 +/- 32 units/ml), in comparison to concentrations at To (MDA = 408 +/- 34 pmol/ml, p < 0.01; DC = 374 +/- 28 units/ml, p < 0.05), returning to baseline at T300. There was a significant correlation between the percentage rise in MDA concentration and the duration of clamp-induced ischaemia (r = 0.45, p = 0.03). The significance of this burst of MDA and DC is unclear especially as the one patient who sustained a postoperative neurological deficit displayed no rise in the concentration of either. If this rise is related to free radical generation following ischaemia-reperfusion injury it may play an important role in influencing the clinical outcome in the patients.

Neuroprotective effects of hypothermia and U-78517F in cerebral ischemia are due to reducing oxygen-based free radicals: an electron paramagnetic resonance study with gerbils

Free radicals are implicated as causative agents in various forms of tissue destruction. Considerable circumstantial evidence suggests that oxygen-based free radicals generated as blood flow returns to formerly ischemic brain areas are mainly responsible for the neurodegeneration that follows periods of cerebral ischemia. In general, oxygen-based free radicals are highly reactive and exist for only a brief period of time. This makes the direct measurement of many of these free radicals rather difficult. Much of the current knowledge of free radicals in cerebral ischemia is based on observations of chemical changes brought about by the free radicals rather than on direct observations of the free radicals themselves. Low temperature electron paramagnetic resonance spectroscopy is one method that allows the direct study of free radicals. Compared to samples from sham-operated controls, samples of hippocampus taken from gerbils exposed to 15 min of forebrain ischemia followed by 15 min of reperfusion, frozen in liquid nitrogen less than 20 sec after sacrifice, and scanned by low temperature (100 K) electron paramagnetic resonance, show a significant increase in oxygen-based free radicals and a decrease in carbon-based ubiquinone-like free radicals. The ischemia-induced increase in oxygen-based free radicals is prevented by the intraperitoneal injection of the antioxidant drug U-78517F at the start of reperfusion and by hypothermia. However, neither intervention alters the ischemia-induced reduction in the ubiquinone-like free radicals. This suggests that the neuroprotective actions of hypothermia and U-78517F include a direct reduction in the oxygen-based free radical burden of the post-ischemic tissue.

Cerebroprotective effects of aminoguanidine in a rodent model of stroke

BACKGROUND AND PURPOSE

During a cerebral infarction, a complex cascade of cytotoxic events ultimately determines the volume of brain cell loss. The studies presented here demonstrate that aminoguanidine, an experimental therapeutic currently in clinical trials to prevent diabetic complications, is cerebroprotective in focal cerebral infarction.

METHODS

Adult Lewis rats (n = 6 to 12 per group) were anesthetized with ketamine and subjected to focal cerebral infarction by tandem permanent occlusion of the right middle cerebral artery and ipsilateral common carotid artery (CCA), followed by temporary occlusion of the contralateral CCA. Infarct volume (cortical) was assessed 24 hours after the onset of ischemia by planimetric analysis of coronal brain slices stained with tetrazolium.

RESULTS

Aminoguanidine (320 mg/kg IP) administered 15 minutes after the onset of ischemia resulted in a significant reduction of infarct volume (7.6 +/- 2.6% of hemisphere in controls versus 1.3 +/- 0.2% of hemisphere in aminoguanidine-treated rats; P < .05). Administration of aminoguanidine conferred significant cerebroprotection even when administered 1 or 2 hours after the onset of ischemia (88% and 85% reduction from control, respectively; P < .05). Cerebroprotection by aminoguanidine was independent of systemic physiological variables known to influence stroke size (eg, temperature, mean arterial blood pressure, blood glucose, and arterial pH, PCO2, and PO2).

CONCLUSIONS

These results indicate that the stroke-reducing properties of aminoguanidine are dose and time dependent, with substantial cerebroprotection persisting even with drug delivery up to 2 hours after the onset of ischemia. It is now plausible to pursue development of aminoguanidine as an experimental therapeutic in stroke, and possible mechanisms of these cerebroprotective effects are under consideration.

Neuroprotective effects of alpha-lipoic acid and its enantiomers demonstrated in rodent models of focal cerebral ischemia

The purpose of this study was to investigate whether alpha-lipoic acid (LA), the oxidized form of the radical scavenger dihydrolipoic acid (DLA), protected brain tissue against ischemic damage and whether there were differences in the neuroprotective potencies between its enantiomers. We used the models of focal cerebral ischemia in mice and rats. The infarct area on the mouse brain surface and the infarct volume of the rat brain were determined by means of an image analyzing system. The LA was capable of reducing the infarct area only when it was administered subcutaneously, but not when it was administered intraperitoneally or into the cisterna magna. Both the R- and the S-enantiomer of LA protected brain tissue against ischemic damage, but their protective activities seemed to be related to the time period of pretreatment. In mice, both enantiomers revealed a similar neuroprotective potency when they were administered subcutaneously 1 or 2 hr before occlusion of the middle cerebral artery (MCA), whereas a longer time period of pretreatment (4 or 6 hr) failed to exert neuroprotection. In rats, subcutaneous pretreatment with R- or S-LA for 2 hr before ischemia significantly diminished the infarct volume. We assume that LA has to be reduced to DLA which finally causes neuroprotection.

Intraventricular administration of nitric oxide synthase inhibitors prevents delayed neuronal death in gerbil hippocampal CA1 neurons

We performed experiments to investigate the participation of nitric oxide (NO) in the delayed neuronal death (DND) of gerbil hippocampal CA1 neurons, following 5-min forebrain ischemia with pretreatment of stereotaxic intraventricular administration of several types of NO synthase inhibitors and biologically inactive control drugs. The number of surviving neurons in the control drug groups administered NG-monomethyl-D-arginine or NG-nitro-D-arginine methyl ester was comparable to that in the group administered artificial cerebro-spinal fluid, while the groups administered NOS inhibitors, such as NG-monomethyl-L-arginine or NG-nitro-L-arginine methyl ester, showed significant preservation of the neuronal densities compared with the control drug groups, to over 60% of the sham operation group value. Furthermore, intraventricular administration of N omega-nitro-L-arginine at various concentrations disclosed a dose-dependent protection against the DND. These results suggest that the generation of NO may act to promote the establishment of DND.

Structural alterations in synaptosomal membrane-associated proteins and lipids by transient middle cerebral artery occlusion in the cat

We have previously reported that ischemia reperfusion injury results from free radical generation following transient global ischemia, and that this radical induced damage is evident in the synaptosomal membrane of the gerbil. [Hall et al, (1995) Neuroscience 64: 81-89]. In the present study we have extended these observations to transient focal ischemia in the cat. We prepared synaptosomal membranes from frontal, parietal-temporal, and occipital regions of the cat cerebral cortex with reperfusion times of 1 and 3 hours following 1 hour right middle cerebral artery occlusion. The membranes were selectively labeled with protein and lipid specific paramagnetic spin labels and analyzed using electron paramagnetic resonance spectrometry. There were significant motional changes of both the protein and lipid specific spin labels in the parietal-temporal and occipital regions with 1 hour reperfusion; but, both parameters returned to control values by 3 hours reperfusion. No significant changes were observed in the normally perfused frontal pole at either reperfusion time. These results support the argument that free radicals play a critical role in cell damage at early reperfusion times following ischemia.

Neurotoxicity of advanced glycation endproducts during focal stroke and neuroprotective effects of aminoguanidine

Cerebral infarction (stroke) is a potentially disastrous complication of diabetes mellitus, principally because the extent of cortical loss is greater in diabetic patients than in nondiabetic patients. The etiology of this enhanced neurotoxicity is poorly understood. We hypothesized that advanced glycation endproducts (AGEs), which have previously been implicated in the development of other diabetic complications, might contribute to neurotoxicity and brain damage during ischemic stroke. Using a rat model of focal cerebral ischemia, we show that systemically administered AGE-modified bovine serum albumin (AGE-BSA) significantly increased cerebral infarct size. The neurotoxic effects of AGE-BSA administration were dose- and time-related and associated with a paradoxical increase in cerebral blood flow. Aminoguanidine, an inhibitor of AGE cross-linking, attenuated infarct volume in AGE-treated animals. We conclude that AGEs may contribute to the increased severity of stroke associated with diabetes and other conditions characterized by AGE accumulation.

In vivo detection of superoxide anion production by the brain using a cytochrome c electrode

A cytochrome c-coated platinized carbon electrode was utilized to detect superoxide generated by the brain during hypoxia/hypercarbia, focal ischemia, and reperfusion and following fluid percussion brain injury with and without hemorrhagic hypotension and reperfusion in the rat. All three of these forms of brain injury were associated with an increase in the superoxide signal. The cytochrome c electrode proved to be sensitive and responsive enough for minute-by-minute measurement of superoxide generation by brain tissue.

Measurement of striatal H2O2 by microdialysis following global forebrain ischemia and reperfusion in the rat: correlation with the cytotoxic potential of H2O2 in vitro

Toxic reactive oxygen species have been implicated as important mediators of tissue injury after reperfusion of ischemic organs. When rats are subject to 30 min global forebrain ischemia, 24 h following this insult, there is substantial loss of medium-sized neurones as revealed by histological sectioning of the striatal region of the forebrain. The goal of this study was to utilize microdialysis to directly measure one of the more stable intermediates of reduced molecular oxygen, H2O2 in the rat striatum following 4-vessel occlusion and reperfusion, and to correlate these levels with H2O2 toxicity to neurones grown in culture. A significant rise in striatal H2O2 levels was observed for about 1 h during reperfusion, amounting to an increase of approximately 100 microM at the peak. In control experiments where the dialysis probe was embedded in cortical regions surrounding the striatum (where there is no neuronal loss due to the ischemic episode), there was no measurable increase in tissue H2O2 levels. H2O2 has been previously shown to be neurotoxic to PC12 cells as well as rat primary hippocampal neurones at comparable concentrations striatal neurones experience during reperfusion. We demonstrate that H2O2 is also neurotoxic to the human cortical neuronal cell line, HCN-1A. These experiments establish an important link between oxidant generation and neuronal loss in this tissue following global forebrain ischemia.

Attenuation of Ca(2+)-induced increase in oxidative metabolism by cooling and calmodulin antagonist in mammalian brain neurons: a flow-cytometric study

Effects of cooling and calmodulin antagonist on ionomycin-induced increase in oxidative metabolism (or formation of reactive oxygen species) of rat cerebellar neurons was examined using a flow cytometer and 2',7'-dichlorofluorescin diacetate, a fluorescent dye for intracellular hydrogen peroxide. Cooling neurons to temperatures below 16 degrees C greatly attenuated ionomycin-induced augmentation of oxidative metabolism without affecting the Ca2+ influx produced by ionomycin. Rewarming neurons to 36 degrees C in presence of ionomycin increased the oxidative metabolism, indicating a temperature-sensitive metabolic process. Substitution of Ca2+ with Ba2+ or Sr2+ completely abolished an ionomycin-induced increase in the oxidative metabolism. Pretreatment with W-7, a calmodulin antagonist, at concentrations of 10 microM or higher (up to 100 microM) produced a dose-dependent attenuation of ionomycin-induced increase in oxidative metabolism. Results suggest that calmodulin is involved in the ionomycin-induced increase in oxidative metabolism of dissociated cerebellar neurons.

Effects of antioxidants on the blood-brain barrier and postischemic hyperemia

The role of free oxygen radicals in blood-brain barrier (BBB) disruption and postischemic hyperemia was evaluated in the rabbit model of focal cerebral ischemia-reperfusion. Six groups of rabbits underwent clipping of the anterior cerebral, middle cerebral, and intracranial internal carotid arteries. Cerebral blood flow (CBF) was measured by using radiolabeled microspheres, before, during, and 15 minutes after 1-hour occlusion of these arteries. After 50 minutes of ischemia, Group 1 animals (control) received a placebo. Animals in Groups 2-4 received one of three drugs: catalase at 10 mg/kg, methimazole at 5 mg/kg, or indomethacin at 10 mg/kg. A fifth group received a tungsten-supplemented diet for 14 days before ischemia was induced, and a sixth group was sham operated. Microvascular integrity within the brain was determined by the presence or absence of Evan's Blue (EB)-albumin dye leakage across the BBB and was measured by microspectrofluorometry. In the control group during ischemia, CBF dropped to 14%, 7%, and 11% of preischemic levels in rostral, middle, and caudal sections of the brain, respectively, as characterized by extensive EB-albumin dye leakage through the BBB into the ischemic hemisphere. During early reperfusion, postischemic hyperemia was associated with an increase in CBF of 128%, 123%, and 129% of control in the rostral, middle, and caudal sections of the brain, respectively. In all treated groups and in the group receiving a tungsten-supplemented diet, BBB integrity was protected during reperfusion without inhibition of postischemic hyperemia. This study suggests that early disruption of the BBB to large molecules is mediated by free oxygen radicals, which inhibit rather than cause postischemic hyperemia.

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)

Reduction of free radical generation minimises lower limb swelling following femoropopliteal bypass surgery

Oxygen-derived free radicals have been implicated as contributors to the development of lower limb oedema observed after femoropopliteal bypass grafting. This study investigates the occurrence of free radical-induced lipid peroxidation after this operation and the possible effects of allopurinol (xanthine oxidase inhibitor) in reducing free radical injury in order to minimise lower leg oedema. Twenty-nine patients undergoing femoropopliteal bypass surgery were randomised in a double blind fashion into two groups; those in one were given allopurinol 200 mg orally (n = 15) at 24 h and 2 h preoperatively and again at 24 h postoperatively, while those in the second group received a placebo (n = 14). Daily lower limb volume was calculated to assess swelling. Blood samples were taken from the femoral vein for measurements of malondialdehyde (MDA), an end product of lipid peroxidation, before the application of the femoral artery clamp, just prior to and immediately after clamp release, and at 20 minute intervals thereafter for 1 hour. The increase in lower limb volume in the placebo group was almost twice (8.9 +/- 1.6%) that of the allopurinol group (4.6 +/- 1%; p = 0.02). Six out of the 14 patients receiving placebo suffered swelling of 10% or more of original lower limb volume in comparison to only one out of 15 in those given allopurinol (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

An immunohistochemical study of copper/zinc superoxide dismutase and manganese superoxide dismutase following focal cerebral ischemia in the rat

We investigated immunohistochemically the localization and changes of copper/zinc superoxide dismutase (CuZn-SOD) and manganese superoxide dismutase (Mn-SOD) in the rat brain following 1 h of middle cerebral artery (MCA) occlusion. In normal brain, immunoreactivity to both SODs was observed in medium-sized neurons in the striatum and in many neurons in the neocortex. Mn-SOD was predominantly stained in cortical interneurons. The immunostaining of both SODs rapidly decreased or disappeared in neurons in the lateral segment of the striatum (ischemic center) 4 h after MCA occlusion, when the neurons were degenerating. Most neurons in the neocortex (ischemic penumbra) decreased their CuZn-SOD immunoreactivity but not Mn-SOD immunoreactivity 4 h after ischemia, when only a few neurons showed histopathological changes. CuZn-SOD immunoreactivity in almost all cortical neurons disappeared 1 day after ischemia, but Mn-SOD immunoreactivity was still preserved in interneurons, when cortical neurons showed typical pathological changes. Some cortical neurons in the boundary zone between normal and infarcted areas showed intense immunostaining to both SODs and glial SOD immunoreactivity appeared after 3 and 7 days. These results suggest that early loss of the scavenging system of free radicals may lead to neuronal damage after ischemic insult, and that induced SODs in the boundary zone between the normal and infarcted areas may act as a defense mechanism against damage.

Potentiation of oxidant-induced toxicity in hamster lung slices by dimethylthiourea

Dimethylthiourea (DMTU) is an effective scavenger of reactive oxygen metabolites. This property has been successfully exploited, experimentally, in the protection of cells and tissues against oxidative damage. In this study, however, we have observed that levels of nonprotein sulfhydryls (NPSH) in hamster lung slices were markedly decreased by incubation with 10 or 40 mM DMTU. These changes were associated with morphological signs of injury, increased levels of oxidised glutathione (GSSG), and an increased activity of the pentose phosphate pathway (PPP), suggesting that the loss of NPSH was due to their oxidation. Incubation with 40 mM, but not 10 mM DMTU, also resulted in a decreased ability to oxidise [6-14C]glucose or to synthesise proteins, suggesting that at the high concentration, DMTU may cause functional impairment of the tissue. Furthermore, the ability of the slices to accumulate putrescine decreased after incubation with the oxidative toxins paraquat (PQ), tert-butyl hydroperoxide (t-BOOH) or hydrogen peroxide (H2O2) and was further decreased by co-incubation with DMTU. Putrescine uptake, a function specific to the alveolar type I and II epithelial cells, was not affected by incubation with DMTU alone. DMTU did not exacerbate the effect of the nonoxidative toxin iodoacetamide (IAA) on putrescine uptake but it did affect markers of general cell damage or dysfunction. We suggest, therefore, that the toxicity of oxidants toward lung tissue is potentiated in alveolar epithelial cells by DMTU.

Deferoxamine posttreatment reduces ischemic brain injury in neonatal rats

BACKGROUND AND PURPOSE

Iron catalyzes the formation of damaging reactive species during cerebral reperfusion. Brain iron concentration is highest at birth, so the brain of the asphyxiated newborn may be at increased risk of iron-dependent injury. We investigated whether the ferric iron chelator deferoxamine could reduce hypoxic-ischemic brain injury in neonatal rats. Because deferoxamine has concentration-dependent activities other than iron chelation, we measured brain deferoxamine levels and calculated deferoxamine pharmacokinetic parameters.

METHODS

We produced hypoxic-ischemic injury to the right cerebral hemisphere of 7-day-old rats by right common carotid artery ligation followed by 2.25 hours of hypoxia in 8% oxygen. At 5 minutes of recovery from hypoxia the rats received 100 mg/kg deferoxamine mesylate or saline subcutaneously. Rats (saline, n = 33; deferoxamine, n = 38) were killed at 42 hours of recovery to assess early acute edema by measurement of hemispheric water content. Other rats (saline, n = 31; deferoxamine, n = 32) were killed at 30 days of age for morphometric determination of right hemisphere atrophy. In still other rats, we measured deferoxamine levels in blood and brain after hypoxia-ischemia.

RESULTS

Deferoxamine significantly reduced right hemisphere injury as measured by early water content (P < .01) and later atrophy (P = .019). Deferoxamine brain levels peaked between 100 and 200 mumol/L at 40 to 60 minutes after injection and exceeded serum levels by +/- 70%.

CONCLUSIONS

Deferoxamine administered after induction of cerebral hypoxia-ischemia reduces injury in 7-day-old rats. Deferoxamine concentrates in the brain at levels between 100 and 200 mumol/L. At the concentrations achieved, deferoxamine might protect the brain through mechanisms unrelated to its ability to chelate iron.

Superoxide dismutase ameliorates neuronal death from hypoxia in culture

BACKGROUND AND PURPOSE

Studies showing efficacy with free radical scavengers have been conflicting, and when protection was demonstrated it was attributed to action at the level of the vascular endothelium. The purpose of this study was to test the hypotheses that neuronal free radical formation plays a role in the ischemic cascade and occurs intracellularly and that free radical scavengers, if taken up intracellularly, will protect against hypoxic damage.

METHODS

A tissue culture model of hypoxia followed by restoration of oxygen was employed, using both superior cervical ganglia and hippocampal neurons. Cells were exposed to an anoxic atmosphere of 95% N2 and 5% CO2 and examined 2 to 24 hours later after restoration of oxygen. Determination of survival was measured by trypan blue exclusion. Nitroblue tetrazolium stain was used to assess free radical formation.

RESULTS

Pretreatment with free superoxide dismutase did not decrease cell death after hypoxia as measured by trypan blue exclusion. However, when superoxide dismutase was taken up intracellularly under depolarizing conditions (55 mmol/L KCl in the medium), cell death was decreased significantly compared with hypoxic controls (28.7 +/- 4.34 versus 40.3 +/- 4.33; P < .03). During hypoxia neurons reduced nitroblue tetrazolium to form the blue precipitate formazan, and the color change was blocked in neurons pretreated with superoxide dismutase in depolarizing medium. Similar findings occurred in both superior cervical ganglia and hippocampal neurons.

CONCLUSIONS

These findings provide evidence to support the role of neuronal free radical formation in cell death secondary to hypoxia. In addition, free radical scavengers, if taken up intracellularly, may partially ameliorate their deleterious effect.

Peroxidative status and glutathione content of the brain in normal weight and intra-uterine growth-retarded newborn piglets

The peroxidative and glutathione status as well as the production of reactive oxygen species were studied in the brain of normal weight (NW) and intra-uterine growth-retarded (IUGR) newborn piglets. In NW as well as IUGR newborn piglets reduced (GSH) and oxidized (GSSG) glutathione, lipid peroxides, iron stimulated lipid peroxidation, H2O2 production and lucigenin and luminol amplified chemiluminescence are very similar in the different brain regions, with one exception. In the cerebellum, higher GSH concentration, higher superoxide anion generation, lower levels of lipid peroxides and a tendency toward a lower capacity of H2O2 production were seen. But the intra-uterine growth retardation to body weights of half the average body weights of the respective litter did not influence the peroxidative status and the GSH/GSSG equilibrium in the brain of newborn piglets.

Myricetin and quercetin, the flavonoid constituents of Ginkgo biloba extract, greatly reduce oxidative metabolism in both resting and Ca(2+)-loaded brain neurons

The antioxidant action of myricetin and quercetin, the flavonoid constituents of the extract of Ginkgo biloba (EGb), on oxidative metabolism of brain neurons dissociated from the rats was examined using 2',7'-dichlorofluorescin (DCFH) which is retained within the neuron and then is oxidized by cellular hydrogen peroxide to be highly fluorescent. Incubation with myricetin or quercetin reduced the oxidation of DCFH in resting brain neurons, more profoundly than EGb. Myricetin decreased the oxidative metabolism at concentrations of 3 nM or more. It was 10 nM or more for the case of quercetin. Incubation with each flavonoid constituent also reduced the Ca(2+)-induced increase in the oxidative metabolism without affecting the cellular content of DCFH or the intracellular concentrations of Ca2+. Such an antioxidant action of myricetin or quercetin may be responsible for a part of the beneficial effects of EGb on brain neurons subject to ischemia.

Characterization of 2',7'-dichlorofluorescin fluorescence in dissociated mammalian brain neurons: estimation on intracellular content of hydrogen peroxide

The fluorescence of 2',7'-dichlorofluorescin (DCF) was measured in acutely dissociated rat cerebellar neurons as a mean of estimating the formation of reactive oxygen species (ROS). N,N-Diethyldithiocarbamate, an inhibitor for superoxide dismutase, reduced the intensity of DCF fluorescence in a dose-dependent fashion at concentrations of 30 nM to up to 10 microM. N-Ethylmaleimide, an inhibitor for glutathione peroxidase, augmented the DCF fluorescence in a dose-dependent manner at concentration of 10 microM to 1 mM while 3-amino-1,2,4-triazole, an inhibitor for catalase, did not change the fluorescence intensity even at concentrations as high as 1 mM. Hydrogen peroxide, applied externally at concentrations between 3 microM and 3 mM, augmented the fluorescence in a dose-dependent fashion. These results suggest the possibility that the DCF fluorescence may be useful in estimating the intracellular content of hydrogen peroxide of mammalian brain neurons.