Polyethylene glycol superoxide dismutase and catalase attenuate increased blood-brain barrier permeability after ischemia in piglets

Sex-based differences of antioxidant enzyme nanoparticle effects following traumatic brain injury

Following traumatic brain injury (TBI), reactive oxygen species (ROS) are released in excess, causing oxidative stress, carbonyl stress, and cell death, which induce the additional release of ROS. The limited accumulation and retention of small molecule antioxidants commonly used in clinical trials likely limit the target engagement and therapeutic effect in reducing secondary injury. Small molecule drugs also need to be administered every several hours to maintain bioavailability in the brain. Therefore, there is a need for a burst and sustained release system with high accumulation and retention in the injured brain. Here, we utilized Pro-NP™ with a size of 200 nm, which was designed to have a burst and sustained release of encapsulated antioxidants, Cu/Zn superoxide dismutase (SOD1) and catalase (CAT), to scavenge ROS for >24 h post-injection. Here, we utilized a controlled cortical impact (CCI) mouse model of TBI and found the accumulation of Pro-NP™ in the brain lesion was highest when injected immediately after injury, with a reduction in the accumulation with delayed administration of 1 h or more post-injury. Pro-NP™ treatment with 9000 U/kg SOD1 and 9800 U/kg CAT gave the highest reduction in ROS in both male and female mice. We found that Pro-NP™ treatment was effective in reducing carbonyl stress and necrosis at 1 d post-injury in the contralateral hemisphere in male mice, which showed a similar trend to untreated female mice. Although we found that male and female mice similarly benefit from Pro-NP™ treatment in reducing ROS levels 4 h post-injury, Pro-NP™ treatment did not significantly affect markers of post-traumatic oxidative stress in female CCI mice as compared to male CCI mice. These findings of protection by Pro-NP™ in male mice did not extend to 7 d post-injury, which suggests subsequent treatments with Pro-NP™ may be needed to afford protection into the chronic phase of injury. Overall, these different treatment effects of Pro-NP™ between male and female mice suggest important sex-based differences in response to antioxidant nanoparticle delivery and that there may exist a maximal benefit from local antioxidant activity in injured brain.

Low Serum Superoxide Dismutase Is Associated With a High Risk of Cognitive Impairment After Mild Acute Ischemic Stroke

Background

Post-stroke cognitive impairment (PSCI) is a common complication after stroke, but effective therapy is limited. Identifying potential risk factors for effective intervention is warranted. We investigated whether serum superoxide dismutase (SOD) levels were related to cognitive impairment after mild acute ischemic stroke (AIS) by using a prospective cohort design.

Methods

A total of 187 patients diagnosed with mild AIS (National Institutes of Health Stroke Scale ≤ 8) were recruited. Serum SOD, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and interleukin-6 (IL-6) levels were measured, and cognitive assessments (Mini-Mental State Examination, MMSE; Montreal Cognitive Assessment, MoCA) were performed in the early phase (within 2 weeks). These indexes and assessments were repeated at 3 months after onset. MoCA < 22 was defined as early cognitive impairment (CI-E) within 2 weeks and late cognitive impairment (CI-L) at 3 months after stroke.

Results

In a survey, 105 of 187 (56.1%) patients were identified as CI-E after mild AIS. Lower serum SOD associated with higher inflammatory biomarkers (ESR, CRP, and IL-6) and worse cognitive scores was observed in CI-E patients. In a survey, 39 of 103 (37.9%) stroke patients who completed the 3-month follow-up were identified as CI-L. Serum SOD was consistently lower in CI-L patients at baseline and 3 months and positively associated with cognitive scores. In adjusted analyses, low serum SOD at baseline was independently associated with high risks of CI-E and CI-L, with odds ratios (ORs) of 0.64 and 0.33 per standard deviation increase in serum SOD, respectively. Multiple-adjusted spline regression models showed linear associations between serum SOD and CI-E (P = 0.044 for linearity) and CI-L (P = 0.006 for linearity). Moreover, 35.2% (19/54) of CI-E patients cognitively recovered during the 3-month follow-up. In multivariable analysis, SOD was identified as a protective factor for cognitive recovery after stroke (OR 1.04, 95% CI: 1.01-1.08, P = 0.024).

Conclusion

We demonstrate that low serum SOD is associated with a high risk of cognitive impairment after mild AIS, indicating SOD may be a potential modifiable factor for PSCI.

Rho and Reactive Oxygen Species at Crossroads of Endothelial Permeability and Inflammation

Significance: Increased endothelial permeability and inflammation are two major hallmarks of the life-threatening conditions such as acute respiratory distress syndrome and sepsis. There is a growing consensus in the field that the Rho family of small guanosine triphosphates are critical regulators of endothelial function at both physiological and pathological states. A basal level of reactive oxygen species (ROS) is essential for maintaining metabolic homeostasis, vascular tone, and angiogenesis; however, excessive ROS generation impairs endothelial function and promotes lung inflammation. In this review, we will focus on the role of Rho in control of endothelial function and also briefly discuss a nexus between ROS generation and Rho activation during endothelial dysfunction. Recent Advances: Extensive studies in the past decades have established that a wide range of barrier-disruptive and proinflammatory agonists activate the Rho pathway that, ultimately, leads to endothelial dysfunction via disruption of endothelial barrier and further escalation of inflammation. An increasing body of evidence suggests that a bidirectional interplay exists between the Rho pathway and ROS generation during endothelial dysfunction. Rac, a member of the Rho family, is directly involved in ROS production and ROS, in turn, activate RhoA, Rac, and Cdc42. Critical Issues: A precise mechanism of interaction between ROS generation and Rho activation and its impact on endothelial function needs to be elucidated. Future Directions: By employing advanced molecular techniques, the sequential cascades in the Rho-ROS crosstalk signaling axis need to be explored. The therapeutic potential of the Rho pathway inhibitors in endothelial-dysfunction associated cardiopulmonary disorders needs to be evaluated.

The choroid plexus as a sex hormone target: Functional implications

The choroid plexuses (CPs) are highly vascularized branched structures that protrude into the ventricles of the brain, and form a unique interface between the blood and the cerebrospinal fluid (CSF). In recent years, novel functions have been attributed to this tissue such as in immune and chemical surveillance of the central nervous system, brain development, adult neurogenesis and circadian rhythm regulation. Sex hormones (SH) are widely recognized as modulators in several neurodegenerative diseases, and there is evidence that estrogens and androgens regulate several fundamental biological functions in the CPs. Therefore, SH are likely to affect the composition of the CSF impacting on brain homeostasis. This review will look at implications of the CPs' sex-related specificities.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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NADPH oxidase mediates TNF-α-evoked in vitro brain barrier dysfunction: roles of apoptosis and time

The pro-inflammatory cytokine TNF-α severely perturbs the integrity of the blood-brain barrier (BBB). This study explored the specific roles of NADPH oxidase and associated downstream effectors by using human brain microvascular endothelial cells (HBMECs) and human astrocytes (HAs), the key components of BBB, alone or in co-cultures to mimic human BBB. Exposure to TNF-α (6h) impaired BBB integrity as evidenced by marked decreases in transendothelial electrical resistance and concurrent increases in paracellular flux which appeared to subside with time (24h). Increased barrier dysfunction concurred with increases in endothelial NADPH oxidase activity, O2(-) production, actin stress fibre formation, MMP-2/9 activities and concomitant decreases in antioxidant (CuZn-SOD and catalase) and tight junction (claudin-5 and occludin) protein expressions. Conversely, TNF-α did not affect astrocytic MMP activities and antioxidant enzyme expressions. Unlike BBB damage, rates of HBMEC and HA apoptosis increased by time. Suppression of NADPH oxidase by apocynin or diphenyleneiodonium prevented TNF-α-evoked morphological changes and apoptosis, attenuated endothelial MMP activity and helped retain usual tight junction protein expression and barrier function. In conclusion, HBMECs constitute the main source of oxidative stress and basement-membrane degrading endopeptidases in inflammatory conditions associated with excessive release of TNF-α where targeting NADPH oxidase may prove extremely beneficial in maintaining proper barrier activity through prevention of cytoskeletal and tight junction reorganisations.

Nanoparticles for targeted delivery of antioxidant enzymes to the brain after cerebral ischemia and reperfusion injury

Stroke is one of the major causes of death and disability in the United States. After cerebral ischemia and reperfusion injury, the generation of reactive oxygen species (ROS) and reactive nitrogen species may contribute to the disease process through alterations in the structure of DNA, RNA, proteins, and lipids. We generated various nanoparticles (liposomes, polybutylcyanoacrylate (PBCA), or poly(lactide-co-glycolide) (PLGA)) that contained active superoxide dismutase (SOD) enzyme (4,000 to 20,000 U/kg) in the mouse model of cerebral ischemia and reperfusion injury to determine the impact of these molecules. In addition, the nanoparticles were untagged or tagged with nonselective antibodies or antibodies directed against the N-methyl-D-aspartate (NMDA) receptor 1. The nanoparticles containing SOD protected primary neurons in vitro from oxygen-glucose deprivation (OGD) and limited the extent of apoptosis. The nanoparticles showed protection against ischemia and reperfusion injury when applied after injury with a 50% to 60% reduction in infarct volume, reduced inflammatory markers, and improved behavior in vivo. The targeted nanoparticles not only showed enhanced protection but also showed localization to the CA regions of the hippocampus. Nanoparticles alone were not effective in reducing infarct volume. These studies show that targeted nanoparticles containing protective factors may be viable candidates for the treatment of stroke.

Therapeutic potential of targeting hydrogen peroxide metabolism in the treatment of brain ischaemia

For many years after its discovery, hydrogen peroxide (H₂O₂) was viewed as a toxic molecule to human tissues; however, in light of recent findings, it is being recognized as an ubiquitous endogenous molecule of life as its biological role has been better elucidated. Indeed, increasing evidence suggests that H₂O₂ may act as a second messenger with a pro-survival role in several physiological processes. In addition, our group has recently demonstrated neuroprotective effects of H₂O₂ on in vitro and in vivo ischaemic models through a catalase (CAT) enzyme-mediated mechanism. Therefore, the present review summarizes experimental data supporting a neuroprotective potential of H₂O₂ in ischaemic stroke that has been principally achieved by means of pharmacological and genetic strategies that modify either the activity or the expression of the superoxide dismutase (SOD), glutathione peroxidase (GPx) and CAT enzymes, which are key regulators of H₂O₂ metabolism. It also critically discusses a translational impact concerning the role played by H₂O₂ in ischaemic stroke. Based on these data, we hope that further research will be done in order to better understand the mechanisms underlying H₂O₂ functions and to promote successful H₂O₂ signalling based therapy in ischaemic stroke.

Ischemia-reperfusion impairs blood-brain barrier function and alters tight junction protein expression in the ovine fetus

The blood-brain barrier is a restrictive interface between the brain parenchyma and the intravascular compartment. Tight junctions contribute to the integrity of the blood-brain barrier. Hypoxic-ischemic damage to the blood-brain barrier could be an important component of fetal brain injury. We hypothesized that increases in blood-brain barrier permeability after ischemia depend upon the duration of reperfusion and that decreases in tight junction proteins are associated with the ischemia-related impairment in blood-brain barrier function in the fetus. Blood-brain barrier function was quantified with the blood-to-brain transfer constant (K(i)) and tight junction proteins by Western immunoblot in fetal sheep at 127 days of gestation without ischemia, and 4, 24, or 48 h after ischemia. The largest increase in K(i) (P<0.05) was 4 h after ischemia. Occludin and claudin-5 expressions decreased at 4 h, but returned toward control levels 24 and 48 h after ischemia. Zonula occludens-1 and -2 decreased after ischemia. Inverse correlations between K(i) and tight junction proteins suggest that the decreases in tight junction proteins contribute to impaired blood-brain barrier function after ischemia. We conclude that impaired blood-brain barrier function is an important component of hypoxic-ischemic brain injury in the fetus, and that increases in quantitatively measured barrier permeability (K(i)) change as a function of the duration of reperfusion after ischemia. The largest increase in permeability occurs 4 h after ischemia and blood-brain barrier function improves early after injury because the blood-brain barrier is less permeable 24 and 48 than 4 h after ischemia. Changes in the tight junction molecular composition are associated with increases in blood-brain barrier permeability after ischemia.

Vascular and neuronal ischemic damage in cryonics patients

Cryonics technology seeks to cryopreserve the anatomical basis of the mind so that future medicine can restore legally dead cryonics patients to life, youth, and health. Most cryonics patients experience varying degrees of ischemia and reperfusion injury. Neurons can survive ischemia and reperfusion injury more than is generally believed, but blood vessels are more vulnerable, and such injury can impair perfusion of vitrifying cryoprotectant solution intended to eliminate ice formation in the brain. Forms of vascular and neuronal damage are reviewed, along with means of mitigating that damage. Recommendations are also made for preventing such damage.

Quercetin in hypoxia-induced oxidative stress: novel target for neuroprotection

Oxidative stress in the central nervous system is one of the key players for neurodegeneration. Thus, antioxidants could play important roles in treating several neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and aging-related brain disorders. This review is focused on the new developments in oxidative stress-induced neurodegeneration. Further, based on our own investigations, new roles of quercetin, an antioxidant compound in hypoxia and ischemia induced neuroprotection in relation to suppression of oxidative stress, improvement in behavioral function, reduction in infarct volume, brain swelling, and cellular injury in both in vivo and in vitro models are discussed. Our new findings clearly suggest that antioxidant compounds have potential role in therapeutic strategies to treat neurodegenerative diseases in clinical settings.

Transient forebrain ischemia impact on lymphocyte DNA damage, glutamic acid level, and SOD activity in blood

AIMS

Brain ischemia-reperfusion injury remains incompletely understood but appears to involve a complex series of interrelated biochemical pathways caused mainly by a burst of reactive oxygen species (ROS). In the present work we studied the impact of postischemic condition in the early phase of reperfusion on plasma and blood cells.

METHODS

Transient forebrain ischemia was induced in Wistar rats by four-vessel occlusion model. Blood samples collected during postischemic reperfusion 20, 40, 60, 90, and 120 min after ischemia were used for assessing breaks of lymphocyte DNA, fluorimetric measurement of whole blood glutamate concentration, and spectrophotometrical determination of SOD activity in plasma and blood cells.

RESULTS

Our results showed the most interesting changes of all observed parameters mainly at 40 and 120 min of reperfusion, when we observed peak DNA damage of lymphocytes and highest glutamate level and total and Cu/Zn SOD activity. At those time points, Mn SOD activity was low in plasma, as well as in blood cells. On the contrary, at 60 and 90 min, all studied parameters were approximately at the level of control.

CONCLUSION

Ischemia/reperfusion injury has influence on blood cells and has at least two waves of impact on DNA damage of peripheral lymphocytes, affects activity of major antioxidant enzymes SODs, as well as blood glutamic acid level. Elevation of Mn SOD activity probably plays an important role in the processes of elimination of postischemic damage in blood cells.

Antioxidants attenuate hyperglycaemia-mediated brain endothelial cell dysfunction and blood-brain barrier hyperpermeability

AIMS

Hyperglycaemia (HG), in stroke patients, is associated with worse neurological outcome by compromising endothelial cell function and the blood-brain barrier (BBB) integrity. We have studied the contribution of HG-mediated generation of oxidative stress to these pathologies and examined whether antioxidants as well as normalization of glucose levels following hyperglycaemic insult reverse these phenomena.

METHODS

Human brain microvascular endothelial cell (HBMEC) and human astrocyte co-cultures were used to simulate the human BBB. The integrity of the BBB was measured by transendothelial electrical resistance using STX electrodes and an EVOM resistance meter, while enzyme activities were measured by specific spectrophotometric assays.

RESULTS

After 5 days of hyperglycaemic insult, there was a significant increase in BBB permeability that was reversed by glucose normalization. Co-treatment of cells with HG and a number of antioxidants including vitamin C, free radical scavengers and antioxidant enzymes including catalase and superoxide dismutase mimetics attenuated the detrimental effects of HG. Inhibition of p38 mitogen-activated protein kinase (p38MAPK) and protein kinase C but not phosphoinositide 3 kinase (PI3 kinase) also reversed HG-induced BBB hyperpermeability. In HBMEC, HG enhanced pro-oxidant (NAD(P)H oxidase) enzyme activity and expression that were normalized by reverting to normoglycaemia.

CONCLUSIONS

HG impairs brain microvascular endothelial function through involvements of oxidative stress and several signal transduction pathways.

Regulation of endothelial barrier function by reactive oxygen and nitrogen species

Excessive generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), by activated neutrophils and endothelial cells, has been implicated in the pathophysiology of endothelial barrier dysfunction. Disruption of the integrity of this barrier markedly increases permeability to fluids, solutes and inflammatory cells and is the hallmark of many disorders such as acute lung injury (ALI) and sepsis. There has been considerable progress in our understanding of the sequence of molecular and structural events that mediate the response of endothelial cells to oxidants and nitrosants. In addition, substantial experimental evidence demonstrates improvement of endothelial barrier dysfunction with antioxidant strategies. However, no significant benefits have been observed, so far, in clinical trials of antioxidants for the treatment of endothelial barrier dysfunction. This article will review the available evidence implicating ROS and RNS in endothelial barrier dysfunction, explore potential underlying mechanisms, and identify areas of further research.

Lifelong consumption of sodium selenite: gender differences on blood-brain barrier permeability in convulsive, hypoglycemic rats

The aim of this study was to compare the effects of hypoglycemia and induced convulsions on the blood-brain barrier permeability in rats with or without lifelong administration of sodium selenite. There is a significant decrease of the blood-brain barrier permeability in three brain regions of convulsive, hypoglycemic male rats treated with sodium selenite when compared to sex-matched untreated rats (p<0.05), but the decrease was not significant in female rats (p>0.05). The blood-brain barrier permeability of the left and right hemispheres of untreated, moderately hypoglycemic convulsive rats of both genders was better than their untreated counterparts (p<0.05). Our results suggest that moderate hypoglycemia and lifelong treatment with sodium selenite have a protective effect against blood-brain barrier permeability during convulsions and that the effects of sodium selenite are gender-dependent.

Anti-oxidant strategies

Oxidative stress plays an important role in causing organ injury in the compromised fetus and neonate. Recent experimental research and clinical studies have clarified important pathways in the production of reactive oxygen and nitrogen species. Free radicals are involved in causing cerebral damage after perinatal hypoxia-ischemia affecting membrane lipids, proteins, and DNA. Anti-oxidant strategies can be used as add-on neuroprotective therapy after perinatal oxidative stress. Selective inhibitors of neuronal and inducible nitric oxide synthase, allopurinol, melatonin, and erythropoietin are among the first compounds that are ready for clinical trials.

Ischemia-reperfusion injury of retinal endothelium by cyclooxygenase- and xanthine oxidase-derived superoxide

The formation of reactive oxygen species (ROS) may be important in the pathogenesis of microvascular dysfunction and injury in ischemic retinopathies. The authors hypothesized that retinal endothelial cells can generate injurious levels of superoxide radical in response to ischemia/reperfusion, that endothelial xanthine oxidase and cyclooxygenase are important enzymatic sources of superoxide radical under these conditions, and that superoxide scavengers and inhibitors of these enzymes can protect endothelium from ischemic injury. The authors used confluent cultures of mouse retinal endothelial cells (MREC) subjected to exogenously generated superoxide or simulated ischemia-reperfusion to test these hypotheses. Cell injury was assessed biochemically by lactate dehydrogenase release into the culture medium. MREC were injured in a duration-dependent fashion by exposure to the superoxide-generating mix of hypoxanthine and xanthine oxidase. Increasing periods of oxygen and glucose deprivation (OGD) for 5-9 hr followed by replenishment of substrates for 2 hr led to progressive increases in endothelial cell injury; a significant proportion of the injury occurred during the period of substrate replenishment. Significant MREC protection was achieved by the superoxide scavengers SOD (1000 U ml(-1)) and a carboxylic acid derivative of carboxyfullerene (10 microM), the xanthine oxidase inhibitors oxypurinol (100 microM) and diphenyleneiodonium (DPI) (100 n M), and the cyclooxygenase inhibitors indomethacin (300 microM) and ibuprofen (300 microM). It is concluded that MREC are vulnerable to auto-oxidative injury by superoxide radical generated following a period of OGD. Both xanthine oxidase- and cyclooxygenase-dependent pathways are important enzymatic sources of superoxide formation in this setting. These enzymes and the ROS produced from their activity may be viable therapeutic targets to reduce microvascular dysfunction and injury in ischemic retinopathies.

Catalase and alpha-tocopherol attenuate blood-brain barrier breakdown in pentylenetetrazole-induced epileptic seizures in acute hyperglycaemic rats

Experimental data indicate that acute hyperglycaemia can aggravate the consequences of epileptic seizures on the permeability of the blood-brain barrier (BBB). The purpose of this study was to examine the effects of chronic administration of alpha -tocopherol (vitamin E) and acute catalase administration on the disrupted BBB during experimentally pentylenetetrazole-induced status epilepticus in acute hyperglycaemic rats. The integrity of the BBB was tested using the Evans Blue (EB) dye extravasation. The concentration of EB dye was measured in four regions of the brain. Epileptic seizures induced a significant increase in EB dye extravasation in the brain regions compared with that of the groups of rats treated with saline, glucose, catalase and alpha -tocopherol (P< 0.01). The content of EB dye in the brain regions of animals in the acute hyperglycaemia plus epileptic group was higher than that of the saline, glucose, catalase, alpha -tocopherol and epileptic groups (P< 0.01). The increased EB dye transfer from blood to the brain in status epilepticus and acute hyperglycaemia plus status epilepticus was attenuated by the treatment with catalase and alpha -tocopherol. These data suggest that a partial reduction in the production of reactive oxygen species by catalase and alpha -tocopherol contributes to decreases in the content of EB dye across the BBB during pentylenetetrazole-induced status epilepticus in acute hyperglycaemic rats.

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

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

Acute mountain sickness; prophylactic benefits of antioxidant vitamin supplementation at high altitude

Acute mountain sickness; prophylactic benefits of Free-radical-mediated damage to the blood-brain barrier may be implicated in the pathophysiology of acute mountain sickness (AMS). To indirectly examine this, we conducted a randomized double-blind placebo-controlled trial to assess the potentially prophylactic benefits of enteral antioxidant vitamin supplementation during ascent to high altitude. Eighteen subjects aged 35 +/- 10 years old were randomly assigned double-blind to either an antioxidant (n = 9) or placebo group (n = 9). The antioxidant group ingested 4 capsules/day(-1) (2 after breakfast/2 after evening meal) that each contained 250 mg of L-ascorbic acid, 100 IU of dl-a-tocopherol acetate and 150 mg of alpha-lipoic acid. The placebo group ingested 4 capsules of identical external appearance, taste, and smell. Supplementation was enforced for 3 weeks at sea level and during a 10-day ascent to Mt. Everest base camp (approximately 5,180 m). Antioxidant supplementation resulted in a comparatively lower Lake Louise AMS score at high altitude relative to the placebo group (2.8 +/- 0.8 points versus 4.0 +/- 0.4 points, P = 0.036), higher resting arterial oxygen saturation (89 +/- 5% versus 85 +/- 5%, P = 0.042), and total caloric intake (13.2 +/- 0.6 MJ/day(-1) versus 10.1 +/- 0.7 MJ/day(-1), P = 0.001); the latter is attributable to a lower satiety rating following a standardized meal. These findings indicate that the exogenous provision of water and lipid-soluble antioxidant vitamins at the prescribed doses is an apparently safe and potentially effective intervention that can attenuate AMS and improve the physiological profile of mountaineers at high altitude.

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.

Temporal profiles of the levels of endogenous antioxidants after four-vessel occlusion in rats

Although it is known that development of lipid peroxidation after ischemia occurs predominantly in vulnerable regions, temporal profiles of antioxidants after ischemia have not been regionally elucidated. After reperfusion periods of 0, 3, 24, and 72 hours following 20 minutes of four-vessel occlusion (n = 6 in each group), the concentration of total glutathione (GSH) and the activities of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px) were assayed in the hippocampus, parietal cortex, striatum, thalamus, and brain stem. The levels of all antioxidants were unchanged in all regions without reperfusion; however, the concentration of total GSH significantly decreased in the hippocampus at 3 hours after the onset of reperfusion, and showed a maximum decrease in the hippocampus (68% of the sham-control level), parietal cortex (78% of the sham-control level), and striatum (76% of the sham-control level) after 24 hours of reperfusion. After 72 hours of reperfusion, these regions and the thalamus showed restoration and an increase in the total GSH concentration, respectively. The activities of SOD, GSH-Px, and catalase were stable during the reperfusion period, but the hippocampus showed significant increases in these enzyme activities and the parietal cortex and striatum showed significant increases in SOD activities at 72 hours after the onset of reperfusion. These results indicate that endogenous antioxidants take 72 hours for restoration in vulnerable regions after 20 minutes of four-vessel occlusion in rats.

Malondialdehyde, glutathione peroxidase and superoxide dismutase in peripheral blood erythrocytes of patients with acute cerebral ischemia

The levels of malondialdehyde (MDA), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD-1) were measured in the red blood cells (RBC) of 34 patients with acute ischemic hemispheric stroke on the first and seventh day after their stroke onset, and compared with 30 control individuals matched for sex, age and stroke risk factors. Within the first 24 h after stroke, SOD and GSH-Px activities were significantly decreased and MDA levels were significantly elevated in the patients compared with control subjects. Decrease in SOD and GSH-Px activities and increase in MDA levels showed significant correlation with infarct size, initial stroke severity assessed by NIH stroke scale and poor short-term prognosis. Observed changes in the RBC oxygen scavenging process returned to values not different from those of control subjects within seven days after stroke. Our results indicated that antioxidant enzyme concentrations decreased below normal levels in the acute period following ischemic stroke. Until the recovery of antioxidant defence mechanisms, which occurred up to seven days after stroke onset according to our results, the use of neuroprotective therapy against oxyradical injury seems reliable.

Superoxide radical scavenging and attenuation of hypoxia-reoxygenation injury by neurotransmitter ferric complexes in isolated rat hepatocytes

Reactive oxygen species have been implicated in the pathogenesis of hypoxia-reoxygenation injury. Previously, we demonstrated that 2:1 catecholic iron complexes were more effective than uncomplexed catechols at (a) scavenging superoxide radicals generated enzymatically, and (b) protecting hepatocytes against hypoxia-reoxygenation injury [25]. Based on these findings, we sought to demonstrate similar effects using catecholamine neurotransmitters. Various catecholamine-iron complexes were shown to be more effective than uncomplexed catecholamines at scavenging superoxide radicals and could be used to protect cells from hypoxia-reoxygenation injury. alpha-Methyl-3, 4-dihydroxyphenylalanine (alpha-methylDOPA) complexed with ferric ion (2:1) showed the greatest superoxide scavenging potency amongst the catecholamine-iron complexes. The uncomplexed catecholamines were much less effective at scavenging superoxide radicals than the iron-catecholamine complexes. Dopamine was the most effective superoxide scavenger among the uncomplexed catecholamines. The superoxide scavenging effectiveness of the latter seemed to correlate with their reduction potentials, but not directly to their pK(a) values. Furthermore, dopamine:iron(III) complex protected isolated hepatocytes against hypoxia-reoxygenation injury at concentrations four-fold lower than that required for protection by dopamine alone.

Induction of cyclooxygenase-2 by overexpression of the human catalase gene in cerebral microvascular endothelial cells

Prostaglandin (PG) formation by the inducible (type 2) cyclooxygenase (COX-2) and reactive oxygen species (ROS) have been proposed to play important roles in cerebrovascular pathological processes. To explore the relationship between ROS and COX-2 expression, adenovirus (Ad) vectors containing cDNA for human antioxidant enzymes including catalase (AdCAT:), copper/zinc superoxide dismutase (AdCu/ZnSOD), and manganese superoxide dismutase (AdMnSOD) were transferred into murine cerebral microvascular endothelial cells. AdCAT: (100 multiplicity of infection) infection increased the content and enzymatic activity of cellular Cat threefold and decreased the intracellular peroxide level. The expression of COX-2 mRNA and protein in cell lysates was up-regulated, and the amount of PGE(2) formed from exogenous arachidonic acid increased following AdCAT: infection in a dose-dependent manner, paralleling the expression of COX-2 protein. The AdCAT:-induced increase in PGE(2) formation was inhibited by NS-398, a selective inhibitor of COX-2 enzymatic activity. AdCAT: infection did not change the expression of the constitutive (type 1) COX protein. Although AdCu/ZnSOD and AdMnSOD infection increased the expression of superoxide dismutase proteins, COX-2 expression was not induced. An in vitro nuclear transcription assay indicated that overexpression of the Cat gene increases the transcription of the COX-2 gene. Furthermore, the stability of COX-2 mRNA induced by lipopolysaccharide was increased after AdCAT: gene transfer. These results indicate that AdCAT: gene transfer induces the transcriptional activation of the COX-2 gene and increases COX-2 mRNA stability. Therefore, peroxide may have regulatory effect on COX-2 function in the cerebral microcirculation.

NOC/oFQ contributes to hypoxic-ischemic impairment of N-methyl-D-aspartate-induced cerebral vasodilation

Previous studies in piglets show that either hypoxia, ischemia-reperfusion (I+R) or combined hypoxia-ischemia-reperfusion (H+I+R) attenuated N-methyl-D-aspartate (NMDA)-induced pial artery dilation. This study was designed to determine the contribution of the newly described opioid nociceptin orphanin FQ (NOC/oFQ) to hypoxic-ischemic impairment of NMDA induced cerebral vasodilation in piglets equipped with a closed cranial window. Global cerebral ischemia was produced via elevated intracranial pressure. Hypoxia decreased P(O(2)) to 35+/-3 mmHg with unchanged P(CO(2)). I+R elevated CSF NOC/oFQ from 67+/-4 to 266+/-29 pg/ml ( approximately 10(-10) M) while H+I+R elevated CSF NOC/oFQ to 483+/-67 pg/ml within 1 h of reperfusion. Such elevated NOC/oFQ levels returned to control within 4 h in I+R animals and within 12 h in H+I+R animals. Topical NOC/oFQ (10(-10) M) had no effect on pial artery diameter by itself but attenuated NMDA (10(-8), 10(-6) M) induced pial dilation (control, 9+/-1 and 16+/-1; coadministered NOC/oFQ, 5+/-1 and 10+/-1%). NMDA induced pial artery dilation was attenuated by I+R or H+I+R; but such dilation was partially restored by pretreatment with the putative NOC/oFQ antagonist [F/G] NOC/oFQ (1-13) NH(2) (10(-6) M) (control, 9+/-1 and 16+/-1; I+R, 3+/-1 and 5+/-1; I+R+NOC/oFQ antagonist, 6+/-1 and 11+/-1%) Similar results were obtained for glutamate. These data suggest that NOC/oFQ release contributes to impaired NMDA and glutamate-induced cerebrovasodilation following I+R or H+I+R.

Desmethyl tirilazad improves neurologic function after hypoxic ischemic brain injury in piglets

OBJECTIVE

Desmethyl tirilazad is a lipid-soluble free radical quencher. Deferoxamine reduces free radicals by chelating iron and reducing hydroxyl formation. Free radical inhibitors have shown promise in several hypoxic ischemic brain injury models, and we wished to see if this work could be extended to our newborn piglet model.

DESIGN

Randomized controlled trial.

SUBJECTS

Piglets (0 to 3 days old).

INTERVENTION

Carotid snares and arterial and venous catheters were placed under 1.5% isoflurane anesthesia. In Experiment 1, piglets were randomly assigned to receive either 3 mg/kg desmethyl tirilazad or vehicle at -15 and 90 mins. In Experiment 2, piglets were randomly assigned to receive either 20 mg/kg desmethyl tirilazad at -15 mins followed by 8 mg/kg/hr for 90 mins or 100 mg/kg deferoxamine at -15 mins or vehicle. At time 0, both carotid arteries were clamped and blood was withdrawn to reduce the blood pressure to two-thirds normal. At 15 mins, inspired oxygen was reduced to 6%. At 30 mins, the carotid snares were released, the withdrawn blood was reinfused, and the oxygen was switched to 100%. On the third day after the hypoxic ischemic injury, the animals were killed by perfusing their brains with 10% formalin. We tested the timing of lipid peroxidation and inhibition of lipid peroxidation by these agents by freezing the brains of a subset of pigs in liquid nitrogen.

MEASUREMENTS

Neurologic examination and brain pathology were scored by blinded observers. Thiobarbituric acid-reactive substance and oxidized and reduced glutathione were measured on frozen brains.

MAIN RESULTS

Desmethyl tirilazad (20 mg/kg) and 100 mg/kg deferoxamine inhibit lipid peroxidation. Desmethyl tirilazad (20 mg/kg) improves neurologic exam, but 3 mg/kg Desmethyl tirilazad or 100 mg/kg deferoxamine does not. Neither desmethyl tirilazad nor deferoxamine improves pathologic results.

CONCLUSIONS

High-dose desmethyl tirilazad improves neurologic function after hypoxic ischemic brain injury in the newborn piglet.

Ischemia-reperfusion rapidly increases COX-2 expression in piglet cerebral arteries

In the newborn, cyclooxygenase (COX)-derived products play an important role in the cerebrovascular dysfunction after ischemia-reperfusion (I/R). We examined effects of I/R on expression of COX-1 and COX-2 isoforms in large cerebral arteries of anesthetized piglets. The circle of Willis, the basilar, and the middle cerebral arteries were collected from piglets at 0.5-12 h after global ischemia (2.5-10 min, n = 50), hypoxia (n = 3), or hypercapnia (n = 2) and from time-control (n = 19) or untreated animals (n = 7). Tissues were analyzed for COX-1 and COX-2 mRNA and protein using RNase protection assay and immunoblot analysis, respectively. Ischemia increased COX-2 mRNA by 30 min, and maximal levels were reached at 2 h. Hypoxia or hypercapnia had minimal effects on COX-2 mRNA. COX-2 protein levels were also consistently elevated by 8 h after I/R. Increases in COX-2 mRNA or protein were not influenced by pretreatment with either indomethacin (5 mg/kg iv, n = 5) or nitro-L-arginine methyl ester (15 mg/kg iv, n = 7). COX-1 mRNA levels were low in time controls, and ischemic stress had no significant effect on COX-1 expression. Thus ischemic stress leads to relatively rapid, selective induction of COX-2 in cerebral arteries.

Neuroprotective effects of combination therapy with tirilazad and magnesium in rats subjected to reversible focal cerebral ischemia

OBJECTIVE

Cell death after cerebral ischemia is mediated by release of excitatory amino acids, calcium influx into cells, and generation of free radicals. We examined the hypothesis that concurrent administration of tirilazad, a well-known antioxidant, and magnesium, an antagonist of calcium and excitatory amino acids, would result in a synergistic neuroprotective effect.

METHODS

Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion and assigned to one of four treatment arms (n = 10 in each): 1) vehicle, 2) tirilazad, 3) MgCl2, or 4) tirilazad and MgCl2. Cortical blood flow was recorded using laser Doppler flowmetry. Functional deficits were quantified by performing daily neurological examinations. Infarct volume was assessed after 7 days.

RESULTS

There was no difference in cortical blood flow among groups. Animals that received tirilazad or MgCl2 monotherapy had significantly better neurological function compared with control animals only on postoperative Days 3 and 4, whereas animals treated with both drugs had significantly better neurological function than did control animals from postoperative Days 2 through 7. Magnesium reduced total infarct volume by 25% (nonsignificant), tirilazad by 48% (P<0.05), and combination therapy by 59% (P<0.05) compared with control data.

CONCLUSION

Combined therapy with antagonists of excitatory amino acids and free radicals provides better neuroprotection from the effects of transient focal ischemia than does therapy with either antagonist alone. In contrast to many experimental agents, tirilazad and magnesium offer the advantage of being licensed for clinical use. This drug combination could be of great benefit when administered before temporary artery occlusion in patients undergoing cerebrovascular surgery.

Mechanisms of hyperoxia-induced reductions in retinal blood flow in newborn pig

Although reductions in retinal blood flow (RBF) in response to acute hyperoxia are well described, the mechanistic basis of this response has yet to be clarified. The present study was undertaken in order to determine the possible involvement of two arachidonic acid-derived vasoconstrictors, the cyclooxygenase metabolite thromboxane and the cytochrome P450 metabolite 20-HETE, as well as the involvement of the peptide endothelin and superoxide free radical. Fluorescein videoangiography was performed on the intact eyes of isoflurane-anesthetized newborn piglets. RBF responses to 20 min of hyperoxia were calculated from the angiograms off-line, using changes in mean arteriovenous transit times and arteriolar and venular diameters. The effect of hyperoxia (PaO2=351+/-9 mmHg; n=39) on RBF was examined in each animal under control conditions and again after intravitreal perivascular administration of drugs that block the synthesis or receptors of known vasoconstrictors. Estimated RBF decreased by a maximum of 42+/-3% in the 7 animal groups in response to 20 min of hyperoxia. The magnitude and time course of the change in RBF resulting from two successive hyperoxic challenges did not differ, and were unaffected by intravitreal administration of vehicle. The response to hyperoxia was attenuated 46+/-6 (n=6; P=0.001) after intravitreal CGS 22652 (2 nmol), a combined thromboxane synthesis inhibitor and receptor antagonist. DDMS (12.5 nmol), a competitive inhibitor of the P450 enzyme omega-hydroxylase that forms 20-HETE, blocked hyperoxic constriction by 23+/-7% (n=6; P=0.01). Intravitreal pretreatment with TBC 1241z (2 nmol), a receptor antagonist of the peptide endothelin, blocked the hyperoxic response by 26+/-5% (n=6; P=0.01). A combination of CGS 22652 (2 nmol), DDMS (12.5 nmol), and TBC 1241z (2 nmol), blocked the hyperoxic flow response by 51+/-3% (n=5; P=0.003). Administration of a combination of superoxide dismutase (10 U intravitreally, 10000 U kg-1 of the polyethylene glycol-conjugate intravenously) and catalase (10 U intravitreally, 10000 U kg-1 intravenously) was without effect on hyperoxia-induced reductions in RBF (n=5). The present results indicate that the arachidonic acid metabolites thromboxane and 20-HETE, and the peptide endothelin, participate in mediating the acute reduction in RBF in response to hyperoxia.

Xanthine oxidase-derived superoxide causes reoxygenation injury of ischemic cerebral endothelial cells

Oxygen free radicals, generated by cerebral ischemia, have been widely implicated in the damage of vascular endothelium. Endothelial cells have been proposed as a significant source of oxygen free radicals. In the present study, we developed an anoxia-reoxygenation (AX/RO) model using pure cultures of cerebral endothelial cells (CECs) isolated from piglet cortex to measure CEC oxygen free radical production and determine its role in AX/RO-induced CEC injury. CEC injury, as measured by lactate dehydrogenase efflux into the culture medium, increased progressively with the duration of anoxic exposure, becoming significant after 10 h. Reoxygenation significantly increased CEC anoxic injury in a time-dependent manner. A 55% increase in oxygen free radical production, determined by fluorescence detection of dihydroethidium oxidation, was measured at the end of 4-h reoxygenation in CECs subjected to AX/RO conditions that killed 40% of the cells. Blockade of oxygen free radical production with superoxide dismutase (SOD; 250 and 1000 U/ml) or oxypurinol (50 and 200 microM), a potent xanthine oxidase inhibitor, reduced this injury by 32-36% and 30-39%, respectively. Results from our in vitro model indicate that CECs produce significant amounts of oxygen free radicals following ischemia, primarily from the xanthine oxidase pathway. These radicals ultimately have a cytotoxic effect on the very cells that produced them. Thus, reductions in oxygen free radical-mediated vascular injury may contribute to improvements in neurophysiologic outcome following treatment with oxygen free radical inhibitors and scavengers.

Postischemic infusion of Cu/Zn superoxide dismutase or SOD:Tet451 reduces cerebral infarction following focal ischemia/reperfusion in rats

Oxygen-free radicals play a major role in neuronal cell injury following cerebral ischemia/reperfusion. The free-radical scavenging enzyme, Cu/Zn superoxide dismutase (SOD-1), ameliorates various types of brain injury resulting from temporary CNS ischemia. We have compared the cerebroprotective properties of human SOD-1 (hSOD-1) with a novel recombinant SOD-1 hybrid protein, SOD:Tet451, composed of hSOD-1 linked to the neuronal binding fragment of tetanus toxin (TTxC). Following 2 h of temporary middle cerebral artery occlusion, rats infused with equivalent activities of either hSOD-1 or SOD:Tet451 for the initial 3 h of reperfusion showed reductions in cerebral infarct volume of 43 and 57%, respectively, compared to saline-treated controls (P < 0.01). Serum hSOD-1 concentrations in rats receiving SOD:Tet451 were seven-fold higher than those in rats receiving the native enzyme. Animals treated with SOD:Tet451 also demonstrated an extended persistence of hSOD-1 in the bloodstream during drug washout as compared to animals given free enzyme. Immunohistochemical examination of brain sections from an SOD:Tet451-treated ischemic rat showed positive immunoreactivity in the ipsilateral cerebral cortex using either anti-TTxC or anti-human SOD-1 antibodies. Our results document that both hSOD-1 and SOD:Tet451 significantly reduce brain infarct volume in a model of transient focal ischemia/reperfusion in rats. Additionally, our findings suggest that the cerebroprotective effects of SOD-1 may be enhanced by neuronal targeting as seen with the hybrid protein SOD:Tet451.

Influence of the xanthine derivative denbufylline and the anti-inflammatory agent nabumetone on microsomal free radical production and lipid peroxidation in rat liver

The influence of denbufylline, nabumetone and its main metabolite BRL 10,720 on iron stimulated lipid peroxidation (LPO), cytochrome P 450 dependent H2O2 and chemiluminescence (CL) production was investigated in rat liver microsomes in vitro (10(-5)-10(-3) M) and in vivo after treatment of rats (5-300 mg/kg b.m. orally on three consecutive days). In rat liver slices the release of thiobarbituric acid reactants (TBAR) was measured after 1 hour of incubation with the drugs. Denbufylline, nabumetone and BRL 10,720 exerted a significant inhibition of iron stimulated LPO in vitro. Nabumetone showed the strongest antioxidative activity, which was also seen in liver slices. These antioxidative effects were not found after in vivo treatment of rats. Denbufylline (10(-3) M) additionally inhibited H2O2 formation and the luminol and lucigenin amplified CL in vitro. Unexpectedly, nabumetone increased H2O2 formation both in vitro and in vivo, but in vitro only lucigenin amplified CL. BRL 10,720 increased microsomal H2O2 production in vivo. Moreover, BRL 10,720 enhanced CL in vitro and in vivo significantly, which is interpreted as an increase of the production of superoxide anion radicals and other reactive oxygen species such as H2O2, but lipid peroxidation in liver microsomes was not enhanced. These results suggest that denbufylline, nabumetone and BRL 10,720 in contrast to the in vitro effects did not exert antioxidative activities after treatment of rats. On the contrary, BRL 10,720 was found to support the formation of reactive oxygen species in liver microsomes.

Endogenous superoxide dismutase activity in reperfusion injuries

To elucidate the relationship between reperfusion injuries and free radicals, we monitored the endogenous superoxide dismutase (SOD) activity by intracerebral microdialysis. Six cats underwent a transient occlusion of the middle cerebral artery for 60 minutes after microdialysis probes were implanted bilaterally into the white matter under the ectosylvian gyrus. Dialysates were collected at 30 minute intervals over the course of 5 hours after reperfusion. The SOD activity of the dialysates was measured with electron spin resonance spectrometry. Regional cerebral blood flow was measured simultaneously and the water content of the white matter was assayed at the end of the experiment. After reperfusion, SOD activity increased significantly in the first 30 minutes compared with the preoperative value, and decreased over 4-4.5 hours and 4.5-5 hours in the occluded side. The water content in the occluded side was significantly higher than that in the contralateral side. The highest SOD activity during reperfusion and the water content in the occluded side seemed to correlate, although not significantly. A leakage of intracellular SOD or a reactive increase of SOD activity in response to the reperfusion injury are possible mechanisms of increase in extracellular SOD.

Pharmacologic management of neonatal cerebral ischemia and hemorrhage: old and new directions

New developments in pharmacologic management of cerebral ischemia and hemorrhage are reviewed. A number of agents with diverse modes of action have now been shown to be neuroprotective in adult and neonatal animal models when administered either before or after a hypoxic-ischemic insult. As experience improves with these agents in hypoxic-ischemic injury and periventricular-intraventricular hemorrhage in human neonates, there is reason to be optimistic that effective neuroprotective strategies will soon be clinically available.