Brain eicosanoid levels in spontaneously hypertensive rats after ischemia with reperfusion: leukotriene C4 as a possible cause of cerebral edema

Biomechanical properties of the hypoxic and dying brain quantified by magnetic resonance elastography

Respiratory arrest is a major life-threatening condition leading to cessation of vital functions and hypoxic-anoxic injury of the brain. The progressive structural tissue changes characterizing the dying brain biophysically are unknown. Here we use noninvasive magnetic resonance elastography to show that biomechanical tissue properties are highly sensitive to alterations in the brain in the critical period before death. Our findings demonstrate that brain stiffness increases after respiratory arrest even when cardiac function is still preserved. Within 5 min of cardiac arrest, cerebral stiffness further increases by up to 30%. This early mechanical signature of the dying brain can be explained by water accumulation and redistribution from extracellular spaces into cells. These processes, together, increase interstitial and intracellular pressure as revealed by magnetic resonance spectroscopy and diffusion-weighted imaging. Our data suggest that the fast response of cerebral stiffness to respiratory arrest enables the monitoring of life-threatening brain pathology using noninvasive in vivo imaging. STATEMENT OF SIGNIFICANCE: Hypoxia-anoxia is a life-threatening condition eventually leading to brain death. Therefore, monitoring vital brain functions in patients at risk is urgently required during emergency care or treatment of acute brain damage due to insufficient oxygen supply. In mouse model of hypoxia-anoxia, we have shown for the first time that biophysical tissue parameters such as brain stiffness changed markedly during the process of death.

The leukotriene receptor antagonist montelukast and its possible role in the cardiovascular field

BACKGROUND

Cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are pro-inflammatory mediators of the 5-lipooxygenase (5-LO) pathway, that play an important role in bronchoconstriction, but can also enhance endothelial cell permeability and myocardial contractility, and are involved in many other inflammatory conditions. In the late 1990s, leukotriene receptor antagonists (LTRAs) were introduced in therapy for asthma and later on, approved for the relief of the symptoms of allergic rhinitis, chronic obstructive pulmonary disease, and urticaria. In addition, it has been shown that LTRAs may have a potential role in preventing atherosclerosis progression.

PURPOSE

The aims of this short review are to delineate the potential cardiovascular protective role of a LTRA, montelukast, beyond its traditional use, and to foster the design of appropriate clinical trials to test this hypothesis.

RESULTS AND CONCLUSIONS

What it is known about leukotriene receptor antagonists? •Leukotriene receptor antagonist, such as montelukast and zafirlukast, is used in asthma, COPD, and allergic rhinitis. • Montelukast is the most prescribed CysLT₁ antagonist used in asthmatic patients. • Different in vivo animal studies have shown that leukotriene receptor antagonists can prevent the atherosclerosis progression, and have a protective role after cerebral ischemia. What we still need to know? • Today, there is a need for conducting clinical trials to assess the role of montelukast in reducing cardiovascular risk and to further understand the mechanism of action behind this effect.

Cysteinyl Leukotrienes and Their Receptors: Emerging Therapeutic Targets in Central Nervous System Disorders

Cysteinyl leukotrienes are a group of the inflammatory lipid molecules well known as mediators of inflammatory signaling in the allergic diseases. Although they are traditionally known for their role in allergic asthma, allergic rhinitis, and others, recent advances in the field of biomedical research highlighted the role of these inflammatory mediators in a broader range of diseases such as in the inflammation associated with the central nervous system (CNS) disorders, vascular inflammation (atherosclerotic), and in cancer. Among the CNS diseases, they, along with their synthesis precursor enzyme 5-lipoxygenase and their receptors, have been shown to be associated with brain injury, Multiple sclerosis, Alzheimer's disease, Parkinson's disease, brain ischemia, epilepsy, and others. However, a lot more remains elusive as the research in these areas is emerging and only a little has been discovered. Herein, through this review, we first provided a general up-to-date information on the synthesis pathway and the receptors for the molecules. Next, we summarized the current findings on their role in the brain disorders, with an insight given to the future perspectives.

Brain Volume Determination in Subarachnoid Hemorrhage Using Rats

Brain edema is routinely measured using the wet-dry method. Volume, however, is the sum total of all cerebral tissues, including water. Therefore, volumetric change following injury may not be adequately quantified using percentage of edema. We thus tested the hypothesis that dried brains can be reconstituted with water and then re-measured to determine the actual volume. Subarachnoid hemorrhage (SAH) was induced by endovascular perforation in adult male Sprague-Dawley rats (n = 30). Animals were euthanized at 24 and 72 h after evaluation of neurobehavior for determination of brain water content. Dried brains were thereafter reconstituted with equal parts of water (lost from brain edema) and centrifuged to remove air bubbles. The total volume was quantified using hydrostatic (underwater) physics principles that 1 ml water (mass) = 1 cm(3) (volume). The amount of additional water needed to reach a preset level marked on 2-ml test tubes was added to that lost from brain edema, and from the brain itself, to determine the final volume. SAH significantly increased both brain water and volume while worsening neurological function in affected rats. Volumetric measurements demonstrated significant brain swelling after SAH, in addition to the brain edema approach. This modification of the "wet-dry" method permits brain volume determination using valuable post hoc dried brain tissue.

Blocking leukotriene synthesis attenuates the pathophysiology of traumatic brain injury and associated cognitive deficits

Neuroinflammation is a component of secondary injury following traumatic brain injury (TBI) that can persist beyond the acute phase. Leukotrienes are potent, pro-inflammatory lipid mediators generated from membrane phospholipids. In the absence of injury, leukotrienes are undetectable in the brain, but after trauma they are rapidly synthesized by a transcellular event involving infiltrating neutrophils and endogenous brain cells. Here, we investigate the efficacy of MK-886, an inhibitor of 5-lipoxygenase activating protein (FLAP), in blocking leukotriene synthesis, secondary brain damage, synaptic dysfunction, and cognitive impairments after TBI. Male Sprague Dawley rats (9-11weeks) received either MK-886 or vehicle after they were subjected to unilateral moderate fluid percussion injury (FPI) to assess the potential clinical use of FLAP inhibitors for TBI. MK-886 was also administered before FPI to determine the preventative potential of FLAP inhibitors. MK-886 given before or after injury significantly blocked the production of leukotrienes, measured by reverse-phase liquid chromatography coupled to tandem mass spectrometry (RP LC-MS/MS), and brain edema, measured by T2-weighted magnetic resonance imaging (MRI). MK-886 significantly attenuated blood-brain barrier disruption in the CA1 hippocampal region and deficits in long-term potentiation (LTP) at CA1 hippocampal synapses. The prevention of FPI-induced synaptic dysfunction by MK-886 was accompanied by fewer deficits in post-injury spatial learning and memory performance in the radial arm water maze (RAWM). These results indicate that leukotrienes contribute significantly to secondary brain injury and subsequent cognitive deficits. FLAP inhibitors represent a novel anti-inflammatory approach for treating human TBI that is feasible for both intervention and prevention of brain injury and neurologic deficits.

Brain water content. A misunderstood measurement?

Brain edema is a major contributor to poor outcome following ischemic and hemorrhagic stroke. In animal models, edema has historically been quantified as a change in % brain water content (water content/wet weight). As described in this communication, this number can be misleading, as 'small' changes in % brain water content actually reflect much bigger changes in brain swelling. Using either water content, expressed as g/g dry weight, or a measure of brain swelling, better reflect the impact of edema after stroke and brain injury.

Inflammation after stroke: mechanisms and therapeutic approaches

Reperfusion of ischemic brain can reduce injury and improve outcome, but secondary injury due to inflammatory mechanisms limits the efficacy and time window of such treatments for stroke. This review summarizes the cellular and molecular basis of inflammation in ischemic injury as well as possible therapeutic strategies.

Ameliorative potential of montelukast on ischemia-reperfusion injury induced vasculitic neuropathic pain in rat

AIMS

Ischemia-reperfusion (I/R) event in vascular and nervous system has been documented to rising ischemic and vasculitic neuropathic pain, clinically resembles the complex regional pain syndrome (CRPS). The present study evaluated the effect of montelukast, a cysteinyl leukotriene receptor (Cys-LTC(4) and Cys-LTD(4)) antagonist on ischemia -reperfusion (I/R) induced vasculitic neuropathic pain in rats.

MAIN METHODS

Behavioral parameters were assessed at different time intervals (i.e. 0, 1, 7, 14 and 21st day) and biochemical analysis in sciatic nerve tissue samples were also performed along with histopathological studies.

KEY FINDINGS

Behavioral pain assessment has shown increase in paw and tail withdrawal threshold in montelukast treated groups against thermal and mechanical stimuli as compared to I/R control group. We observed a decrease in the total calcium, thiobarbituric acid reactive substance (TBARS) and myeloperoxidase (MPO) activity levels, whereas there is rise in reduced glutathione level in montelukast treated groups as compared to I/R control group. However, significant behavioral and biochemical results were observed only in medium and high dose of treated groups which were comparable to normal control group. Moreover, histopathological study has revealed the reduction of I/R induced neuronal edema and axonal degeneration due to montelukast.

SIGNIFICANCE

Montelukast has ameliorated I/R induced vasculitic neuropathic pain, these effects may be due to inhibition of lipid peroxidation, reduction of oxidative stress, release of inflammatory mediators and neuroprotective actions. Hence, it could be used as a novel therapeutic agent for the management of vasculitic inflammation related neuropathic pain.

Synthesis of lipoxin A4 by 5-lipoxygenase mediates PPARgamma-dependent, neuroprotective effects of rosiglitazone in experimental stroke

Peroxisome proliferator-activated receptors gamma (PPARgamma) are nuclear receptors with essential roles as transcriptional regulators of glucose and lipid homeostasis. PPARgamma are also potent anti-inflammatory receptors, a property that contributes to the neuroprotective effects of PPARgamma agonists in experimental stroke. The mechanism of these beneficial actions, however, is not fully elucidated. Therefore, we have explored further the actions of the PPARgamma agonist rosiglitazone in experimental stroke induced by permanent middle cerebral artery occlusion (MCAO) in rodents. Rosiglitazone induced brain 5-lipoxygenase (5-LO) expression in ischemic rat brain, concomitantly with neuroprotection. Rosiglitazone also increased cerebral lipoxin A(4) (LXA(4)) levels and inhibited MCAO-induced production of leukotriene B4 (LTB(4)). Furthermore, pharmacological inhibition and/or genetic deletion of 5-LO inhibited rosiglitazone-induced neuroprotection and downregulation of inflammatory gene expression, LXA(4) synthesis and PPARgamma transcriptional activity in rodents. Finally, LXA(4) caused neuroprotection, which was partly inhibited by the PPARgamma antagonist T0070907, and increased PPARgamma transcriptional activity in isolated nuclei, showing for the first time that LXA(4) has PPARgamma agonistic actions. Altogether, our data illustrate that some effects of rosiglitazone are attributable to de novo synthesis of 5-LO, able to induce a switch from the synthesis of proinflammatory LTB(4) to the synthesis of the proresolving LXA(4). Our study suggests novel lines of study such as the interest of lipoxin-like anti-inflammatory drugs or the use of these molecules as prognostic and/or diagnostic markers for pathologies in which inflammation is involved, such as stroke.

Leukotriene modifiers in the treatment of cardiovascular diseases

Cysteinyl-leukotrienes (Cys-LTs) and LTB4 are potent proinflammatory mediators derived from arachidonic acid through the 5-lipoxygenase (5-LO) pathway, which exerts important pharmacological effects through their interaction with specific receptors: Cys-LT receptors (CysLT1 and CysLT2) and LTB4 receptors (BLT1 and BLT2). Published evidence justifies a broader role for LT receptor antagonists (LTRAs), in particular, montelukast, in the treatment of bronchial asthma, allergic rhinitis, and recently, in cardiocerebrovascular disease. The actions of Cys-LTs on the cardiovascular (CV) system are well-documented and include a broad array of activities with promising therapeutic targets in animal models exploring the use of selective 5-LO (or 5-LO-activating protein) inhibitors or dual LO-cycloxygenase-blocking agents in experimentally induced acute myocardial infarction. The picture that emerges from studies with LTRAs is more controversial at the moment, and some findings suggest a role for Cys-LTs in the extension of ischemic damage and in cardiac dysfunction during reperfusion; others do not. The aim of this short review is to summarize the state of present research about LT modifier treatment in CV disease.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Cerebral ischemia in 5-lipoxygenase knockout mice

Cerebral ischemia induces 5-lipoxygenase translocation and leukotriene production in the brain. We tried to clarify the pathological significance of 5-lipoxygenase on cerebral ischemia using 5-lipoxygenase knockout mice. No significant difference was observed in the infarct size following permanent and transient ischemia for 60 min between both types of mice. The present study did not support the idea that leukotriene production is involved in infarct expansion in focal cerebral ischemia.

Post-stroke inflammatory response: effects of stroke evolution and outcome

Recovery after stroke is often hindered by further neurologic deterioration, which can affect up to 45% of patients. It has been suggested that one of the major causes of this neurologic deterioration may be post-ischemic cerebral inflammation. This review presents the basis of pathophysiologic mechanisms of post-stroke inflammation and discusses possible targets and routes for therapeutic intervention.

Temporal profiles of cerebrospinal fluid leukotrienes, brain edema and inflammatory response following experimental brain injury

The post-traumatic changes of leukotrienes LTC4, LTD4, LTE4, and LTB4 in cerebrospinal fluid of rats from 10 min to 7 days were investigated after controlled cortical impact in relation to brain edema and cellular inflammatory response. LTC4 increased five-fold at 4 h, normalized at 24 h, and showed another four-fold increase at 7 days. The same pattern was observed for LTD4 and LTE4. LTB4 however, behaved differently: concentrations were lower and levels peaked two-fold at 24 h. Edema in the injured hemisphere increased continuously up to 24 h without change contralaterally. Leukocyte infiltration, macrophage presence and microglia activation were most prominent at 24 h, 7 days and 24 h respectively. Leukotriene changes in CSF seem to reflect those in the affected tissue, with a time delay and in lower concentrations, and were not linearly correlated to brain edema. The initially high leukotriene levels are rather likely to contribute to the cytotoxic edema than to enhance a vasogenic edema component. The profile of LTB4 was parallel to the time course of leukocyte infiltration, indicating initiation of infiltration as well as prolonged production by leukocytes themselves. The second leukotriene peak at 7 days is likely to follow a different pathway and might be related to a production in macrophages or activated glia.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Production of leukotrienes in a model of focal cerebral ischaemia in the rat

1. The aim of this work was to evaluate the role of leukotrienes in brain damage in vivo in a model of focal cerebral ischaemia in the rat, obtained by permanent occlusion of middle cerebral artery. 2. A significant (P < 0.01) elevation of LTC(4), LTD(4) and LTE(4) (cysteinyl-leukotrienes) levels occurred 4 h after ischaemia induction in the ipsilateral cortices of ischaemic compared to sham-operated animals (3998 +/- 475 and 897 +/- 170 fmol g(-1) tissue, respectively, P < 0.01). 3. The NMDA receptor antagonist MK-801 and the adenosine A(2A) receptor antagonist SCH 58261 were administered in vivo at doses known to reduce infarct size and compared with the leukotriene biosynthesis inhibitor MK-886. 4. MK-886 (0.3 and 2 mg kg(-1) i.v.) and MK-801 (3 mg kg(-1) i.p.) decreased cysteinyl-leukotriene levels (-78%, P < 0.05; -100%, P < 0.01; -92%, P < 0.01, respectively) 4 h after permanent occlusion of the middle cerebral artery, whereas SCH 58261 (0.01 mg kg(-1) i.v.) had no significant effects. 5. MK-886 (2 mg kg(-1) i.v.) was also able to significantly reduce the cortical infarct size by 30% (P < 0.05). 6. We conclude that cysteinyl-leukotriene formation is associated with NMDA receptor activation, and that it represents a neurotoxic event, the inhibition of which is able to reduce brain infarct area in a focal ischaemic event.

Neurogenesis and neuroprotection in the adult brain. A putative role for 5-lipoxygenase?

5-Lipoxygenase (5-LOX) and cyclooxygenase-2 (COX-2) are two enzymes that are critical for the synthesis of eicosanoids, the inflammatory metabolites of arachidonic acid. Both 5-LOX and COX-2 are expressed in the brain, including in CNS neurons. The physiologic role of these proteins in neuronal functioning is not clear. In non-neuronal tissues these two enzymes often assume similar roles: in addition to their function in inflammation, 5-LOX and COX-2 appear to be associated with cell proliferation, that is, with tumor growth. High 5-LOX expression has been noticed in the proliferating brain or pancreatic tumor cells; reduction in tumor cell proliferation and/or destruction of tumor cells was achieved with 5-LOX inhibitors. Proliferation of immature neurons/neuroblasts is an important component of mitotic neurogenesis. We investigated the role of 5-LOX in proliferation using cultures of human neuronal precursor cells, NT2. We found that these cells express 5-LOX mRNA and we used 3H-thymidine incorporation as a measure of cell proliferation; this was reduced by treating the cultures with 5-LOX inhibitor AA-861. We propose that the 5-LOX pathway plays a crucial role in mitotic neurogenesis. Additional studies should explore whether 5-LOX may participate in neurogenesis related pathologies and whether it should be considered a target for procedures aimed at altering neurogenesis for therapeutic purposes.

Induction of tolerance against ischemia/reperfusion injury in the rat brain by preconditioning with the endotoxin analog diphosphoryl lipid A

OBJECT

Inflammatory responses and oxygen free radicals have increasingly been implicated in the development of ischemic brain injury. In some cases, an attenuation of inflammation or free-radical injury can provide tissue protection. Diphosphoryl lipid A (DPL) is a detoxified derivative of a lipopolysaccharide (endotoxin) of Salmonella minnesota strain R595, which is capable of stimulating the immune system without eliciting direct toxic effects. In this study the authors examined the influence of preconditioning with DPL on ischemia/reperfusion injury in rats.

METHODS

Sprague-Dawley rats were injected intravenously with either DPL or vehicle. Twenty-four hours later, some animals were tested for superoxide dismutase (SOD) activity. Others were subjected to a 3-hour period of focal cerebral ischemia and, after a reperfusion period of 24 hours, were killed. Infarction volume, SOD activity, and myeloperoxidase (MPO) activity were assayed in the postischemic animals. Pretreatment with DPL produced significant reductions in cerebral infarction and MPO activity in the ischemic penumbra. A significant enhancement of basal SOD activity was observed 24 hours after DPL treatment (that is, before ischemia), and a further enhancement of SOD activity was seen in the ischemic penumbra 24 hours after reperfusion.

CONCLUSIONS

These data provide the first evidence of a neuroprotective effect of preconditioning with DPL in an in vivo model of cerebral ischemia. Although the precise mechanisms through which DPL exerts its neuroprotective influence remain to be established, an inhibition of the complex inflammatory response to ischemia and an enhancement of endogenous antioxidant activity are leading candidates.

Arachidonic acid and leukotriene C4: role in transient cerebral ischemia of gerbils

Accumulation of arachidonic acid (AA) is greatest in brain regions most sensitive to transient ischemia. Free AA released after ischemia is either: 1) reincorporated into the membrane phospholipids, or 2) oxidized during reperfusion by lipoxygenases and cyclooxygenases, producing leukotrienes (LT), prostaglandins, thromboxanes and oxygen radicals. AA, its metabolite LTC4 and lipid peroxides (generated during AA metabolism) have been implicated in the blood-brain barrier (BBB) dysfunction, edema and neuronal death after ischemia/reperfusion. This report describes the time course of AA release, LTC4 accumulation and association with the physiological outcome during transient cerebral ischemia of gerbils. Significant amount of AA was detected immediately after 10 min ischemia (0 min reperfusion) which returned to sham levels within 30 min reperfusion. A later release of AA occurred after 1 d. LTC4 levels were elevated at 0-6 h and 1 d after ischemia. Increased lipid peroxidation due to AA metabolism was observed between 2-6 h. BBB dysfunction occurred at 6 h. Significant edema developed at 1 and 2 d after ischemia and reached maximum at 3 d. Ischemia resulted in approximately 80% neuronal death in the CA1 hippocampal region. Pretreatment with a 5-lipoxygenase inhibitor, AA861 resulted in significant attenuation of LTC4 levels (Baskaya et al. 1996. J. Neurosurg. 85: 112-116) and CA1 neuronal death. Accumulation of AA and LTC4, together with highly reactive oxygen radicals and lipid peroxides, may alter membrane permeability, resulting in BBB dysfunction, edema and ultimately to neuronal death.

Reperfusion injury after focal cerebral ischemia: the role of inflammation and the therapeutic horizon

Recent evidence indicates that thrombolysis may be an effective therapy for the treatment of acute ischemic stroke. However, the reperfusion of ischemic brain comes with a price. In clinical trials, patients treated with thrombolytic therapy have shown a 6% rate of intracerebral hemorrhage, which was balanced against a 30% improvement in functional outcome over controls. Destruction of the microvasculature and extension of the infarct area occur after cerebral reperfusion. We have reviewed the existing data indicating that an inflammatory response occurring after the reestablishment of circulation has a causative role in this reperfusion injury. The recruitment of neutrophils to the area of ischemia, the first step to inflammation, involves the coordinated appearance of multiple proteins. Intercellular adhesion molecule-1 and integrins are adhesion molecules that are up-regulated in endothelial cells and leukocytes. Tumor necrosis factor-alpha, interleukin-1, and platelet-activating factor also participate in leukocyte accumulation and subsequent activation. Therapies that interfere with the functions of these factors have shown promise in reducing reperfusion injury and infarct extension in the experimental setting. They may prove to be useful adjuncts to thrombolytic therapy in the treatment of acute ischemic stroke.

Delayed adjuvant therapy with the 21-aminosteroid U74006F and the anion channel blocker L644-711 does not improve outcome following thrombolytic therapy in a rabbit model of thromboembolic stroke

BACKGROUND

Both the 21-aminosteroid U74006F, a potent inhibitor of lipid peroxidation, and L644-711, an anion channel blocker that inhibits both neutrophil and astrocyte function, have been previously shown to reduce brain injury in pretreatment paradigms of cerebral ischemia. It was therefore of interest to examine the effect of these agents in combination, when given on a delayed basis as adjuvants to thrombolytic therapy in a rabbit model of thromboembolic stroke.

METHODS

Animals were mechanically ventilated and arterial blood gases controlled. Core and brain temperature, intracranial pressure, and mean arterial pressure were continuously monitored. Regional cerebral blood flow and hematocrit were measured hourly. Blood samples were taken to measure neutrophil (aggregation and chemiluminescence) and platelet (aggregation) activity. Following delivery of an autologous clot via the carotid artery, all experiments were continued for an 8-hour period. U74006F (3 mg/kg I.V.) and L644,711 (12 mg/kg I.V.) or their vehicle control (n = 8, each group) were given 3.5 hours following autologous clot embolization. Both groups received tissue-type plasminogen activator (t-PA) (6.3 mg/kg I.V.), beginning 4 hours following thromboembolic stroke and continuing over a 2-hour infusion period. Infarct size was determined following staining and image analysis.

RESULTS

In the L644,711/U74006F group, neutrophil chemiluminescence was reduced following drug therapy; however, there were no significant differences between groups regarding infarct size (50.3 +/- 8.7 vs. 49.9 +/- 10.6, treatment vs. t-PA control, mean +/- SEM), or in regional cerebral blood flow or intracranial pressure over time.

CONCLUSIONS

It is concluded that prolonged (3.5 hours) delay of the initiation of therapy with the anion channel blocker L644,711 and the 21-aminosteroid U74006F fails to further reduce brain injury when given in combination with tissue plasminogen activator in a rabbit model of thromboembolic stroke.

Regional generation of leukotriene C4 after experimental brain injury in anesthetized rats

Regional concentrations of leukotriene C4 and extravasation of Evans blue were measured after lateral fluid-percussion brain injury in rats. Tissue levels of LTC4 were elevated in the injured cortex at 10 min, 30 min, and 1 h after injury; these levels returned to normal by 2 h after injury. Increases in the levels of LTC4 were also observed in the ipsilateral hippocampus after brain injury, and these elevations persisted for 2 h after injury. No significant increase in levels of LTC4 was observed in the contralateral cortex at any time after injury. A substantial extravasation of Evans blue was observed only in the ipsilateral cortex and hippocampus at 3 h and 6 h after brain injury. Although a temporal association between LTC4 and blood-brain barrier (BBB) breakdown is suggested by these data, no cause-and-effect relationship has been addressed in this study. However, it is possible that, as is true for cerebral ischemia, LTC4 may play a role as a mediator in the BBB breakdown associated with fluid-percussion brain injury in rats.

Intraischemic hypothermia attenuates neutrophil infiltration in the rat neocortex after focal ischemia-reperfusion injury

OBJECTIVE

The mechanisms by which hypothermia influences postischemic outcome remain a matter of discussion. One mechanism thought to play an important role in neuronal damage after ischemia/reperfusion is the accumulation of polymorphonuclear leukocytes in compromised brain tissue. To better understand the potential impact of hypothermia on this injurious mechanism, the present study examined the effect of intraischemic hypothermia on polymorphonuclear leukocyte accumulation after transient focal ischemia.

METHODS

The effect of intraischemic hypothermia (30 degrees C) on the accumulation of polymorphonuclear leukocytes was quantified by measuring myeloperoxidase (MPO) activity in the neocortex of Sprague-Dawley rats. Reversible focal ischemia was created by subjecting rats to temporary occlusion of the left middle cerebral artery and both carotid arteries for 3 hours; animals were killed 24 hours after reperfusion.

RESULTS

Normothermic animals exhibited significantly greater MPO activity in the infarction core (P < 0.05) and the pericore areas (P < 0.05), compared with corresponding areas in sham-operated animals. Hypothermic animals exhibited significantly greater MPO activity in the core (P < 0.05) but not in the pericore region, compared with sham-operated animals. MPO activity in the pericore region of the hypothermic group was significantly less than that observed in the corresponding region of the normothermic group (P < 0.01). In addition, the total volume of cerebral infarction was reduced by 59% in the hypothermic group.

CONCLUSION

These findings demonstrate that intraischemic hypothermia attenuates the inflammatory response to transient focal ischemia in the pericore region, i.e., the region spared from infarction under hypothermic conditions. The findings raise the possibility that a reduction in the inflammatory response after ischemia/reperfusion contributes to the neuroprotective effects of hypothermia.

Protective effect of the 5-lipoxygenase inhibitor AA-861 on cerebral edema after transient ischemia

This study examined the effect of AA-861, a specific 5-lipoxygenase inhibitor, on brain levels of leukotriene C4 (LTC4) and correlated any changes with changes in edema formation and cerebral blood flow (CBF) after transient ischemia in gerbils. Brain levels of LTC4 were observed to be increased at 1, 2, and 6 hours of reperfusion following 20 minutes of occlusion. At 2 hours of reperfusion, a pretreatment dose of 1000 mg/kg of AA-861 was required to inhibit more than 90% of the reperfusion-induced increases in brain LTC4. At this dose, inhibition of LTC4 production was observed at 2 and 6 hours of reperfusion. The specific gravity of both the cortex and subcortex was decreased at 6 hours of reperfusion after 20 minutes of occlusion. At 2 hours of reperfusion, no significant difference was observed in the specific gravity of the cortex and subcortex regions of gerbils pretreated with AA-861 or with vehicle, but at 6 hours of reperfusion significant positive differences were observed. Cerebral blood flow decreased to approximately 10% of preocclusion values during occlusion and returned to near-preocclusion values after 10 minutes of reperfusion. No significant differences were observed in regional CBF in the AA-861- and vehicle-pretreated gerbils during reperfusion. These findings indicate that LTC4 production after transient cerebral ischemia may be an important contributor to the development of cerebral edema and that CBF does not mediate the LTC4-involved development of edema.

Thrombin stimulates activation of the cerebral 5-lipoxygenase pathway during blood-brain cell contact

The purpose of this study was to identity the trigger mechanism activating the 5-lipoxygenase pathway during blood-brain cell contact and to estimate the contribution of blood and brain cells to the cysteinyl-leukotriene (LT) biosynthesis observed under these conditions. Incubation of dissociated rat brain cells in Krebs-Henseleit solution for up to 60 min did not stimulate any detectable cysteinyl-LT biosynthesis. Incubation of recalcified rat whole blood in vitro for up to 60 min led to release of only small amounts of cysteinyl-LT into the serum samples. However, coincubation of dissociated rat brain cells with physiologically recalcified autologous whole blood triggered a time-dependent release of large amounts of immunoreactive cysteinyl-LT into the serum samples. By reverse-phase HPLC, immunoreactive cysteinyl-LT was identified as a mixture of LTC4, LTD4, and LTE4. The extent of the 5-lipoxygenase stimulation depended on the amount of autologous blood coincubated with the dissociated brain cells. Activation of the 5-lipoxygenase pathway also occurred with coincubation of dissociated rat brain cells with recalcified autologous plasma. Stimulation of cysteinyl-LT biosynthesis during blood-brain cell contact remained unaffected by aprotinin, but concentration-dependent inhibition by the structurally and functionally unrelated thrombin inhibitors D-Phe-Pro-Arg-CH2Cl and recombinant hirudin was seen. Finally, when dissociated rat brain cells were incubated in Krebs-Henseleit solution in the presence of human alpha-thrombin, a concentration-dependent release of cysteinyl-LT into the buffer samples was observed. These data demonstrate that, in rats, during blood-brain cell contact, stimulation of the 5-lipoxygenase pathway in brain cells proceeds via alpha-thrombin as effector molecule.

Effect of KBT-3022, a new cyclooxygenase inhibitor, on experimental brain edema in vitro and in vivo

The effect of KBT-3022 (ethyl 2-[4,5-bis(4-methoxyphenyl)thiazol-2-yl]pyrrol-1-ylacetate), a new cyclooxygenase inhibitor, on experimental brain edema was studied. In vitro, KBT-3022 (100 microM) and its metabolite desethyl KBT-3022 (10 and 100 microM), but neither acetylsalicylic acid nor indomethacin, inhibited arachidonic acid-induced swelling of guinea pig cortical slices. KBT-3022 (3-100 microM) and desethyl KBT-3022 (3-30 microM), but neither acetylsalicylic acid nor indomethacin, inhibited lipid peroxidation in guinea pig brain homogenate. In vivo, oral administration of KBT-3022 (1, 3 and 10 mg/kg) and indomethacin (10 and 30 mg/kg), but not acetylsalicylic acid, prevented brain edema induced by bilateral carotid occlusion and recirculation in gerbils. Indomethacin then prevented postischemic hyperthermia, but not KBT-3022. KBT-3022 (10 mg/kg) and indomethacin (30 mg/kg) inhibited lactate accumulation in gerbil brain after ischemia and recirculation. These results suggest that KBT-3022 prevents development of both cytotoxic edema in vitro and vasogenic edema in vivo.

Optimization of epoxyeicosatrienoic acid syntheses to test their effects on cerebral blood flow in vivo

Epoxyeicosatrienoic acids (EETs), normally present in brain and blood, appear to be released from atherosclerotic vessels in large amounts. Once intravascular, EETs can constrict renal arteries in vivo and dilate cerebral and coronary arteries in vitro. Whether EETs in blood will alter cerebral blood flow (CBF) in vivo is unknown. In the present study, the chemical synthesis of four EET regioisomers was optimized, and their identity and structural integrity established by chromatographic and mass spectral methods. The chemically labile EETs were converted to a sodium salt, complexed with albumin, and infused into anesthetized rats via the common carotid. The objective was to test whether sustained, high levels of intravascular EETs alter CBF. The CBF (cortical H2 clearance) was measured before and 30 min after the continuous infusion of 14,15- (n = 5), 11,12- (n = 5), 8,9- (n = 7) and 5,6-EET (unesterified or as the methyl ester, n = 5 for each). Neither the CBF nor the systemic blood pressure was affected by EETs. Because the infusions elevated the plasma concentrations of EETs about 700-fold above normal levels (1.0 nM), it is unlikely that EETs released from atherosclerotic vessels will alter CBF.

Effects of the lipid peroxidation inhibitor tirilazad mesylate (U-74006F) on gerbil brain eicosanoid levels following ischemia and reperfusion

The present study measured the production of eicosanoids in the gerbil brain during early reperfusion after either a 3-h unilateral carotid occlusion (UCO, model of focal ischemia) or a 10-min bilateral carotid occlusion (BCO, model of global ischemia). Arachidonic acid (AA) metabolites were examined to determine if pretreatment with the 21-aminosteroid lipid peroxidation inhibitor U-74006F (tirilazad mesylate) could influence postreperfusion synthesis of brain eicosanoids. In the 3-h UCO focal ischemia model, there was an early (5-min) postreperfusion elevation in brain levels of PGF2 alpha, TXB2 and LTC4 (P < 0.05 vs. sham for all three eicosanoids). LTB4 also rose but not significantly. On the other hand, PGE2 and 6-keto-PGF1 alpha tended to decrease during ischemia and at 5-min postreperfusion (P < 0.05 vs. sham for PGE2). Pretreatment with known neuroprotective doses of U-74006F in this model (10 mg/kg i.p. 10 min before and again immediately upon reperfusion) did not affect the increase in PGF2 alpha or TXB2 but significantly blunted the elevations in LTC4 and LTB4. The postreperfusion decrease in PGE2 was also attenuated. In the 10-min BCO global ischemia model, there was also an increase in each of the measured eicosanoids, except LTB4, at 5 min after reperfusion. Pretreatment with U-74006F (10 mg/kg i.p. 10 min before ischemia) selectively decreased the rise in LTC4 but did not significantly affect the other eicosanoids. In contrast, the antioxidant actually caused a significant enhancement of the postreperfusion increase in PGE2 vs. vehicle-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 21-aminosteroid lipid peroxidation inhibitor, U74006F, in the rat middle cerebral artery occlusion model

The aim of this study was to evaluate the effect of 21-aminosteroid lipid peroxidation inhibitor, U74006F, on ischaemic brain tissue damage using the rat middle cerebral artery occlusion model. Under anaesthesia, the left middle cerebral artery was exposed without cutting the dura mater via a subtemporal craniotomy, under an operating microscope. Photo-illumination (wave length; 540 nm) was applied to the middle cerebral artery and then rose bengal (20 mg/kg) was administered intravenously. The middle cerebral artery was completely occluded by thrombus about 6 min after the administration of rose bengal. U74006F (1.0 mg/kg) was then injected intravenously just after the cessation of illumination. Twenty four hours after the operation, the extent of ischaemic damage was measured by magnetic resonance imaging technique. After measuring the extent of ischaemic damage, the brain was immediately removed from animals treated with or without U74006F for determination of lipid peroxidation, and the generation of free arachidonic acid in the brain. U74006F significantly (P < 0.01) reduced the size of ischaemic damage. Twenty-four hours after the operation, lipid peroxidation and the concentration of free arachidonic acid in the left hemisphere (infarction side) were significantly (P < 0.05) higher than in the right hemisphere. U74006F significantly (P < 0.05) decreased the content of lipid peroxidation products and free arachidonic acid. There was a significant (P < 0.05) correlation between the extent of ischaemic damage and the concentration of lipid peroxidation products in the left hemisphere 24 h after the operation. In conclusion, U74006F might reduce the extent of ischaemic damage by inhibiting lipid peroxidation in the brain, thus minimizing oxidative damage to neural tissues.

LTC4/LTB4 alterations in rat forebrain ischemia and reperfusion and effects of AA-861, CV-3988

LTC4, which enhances vascular permeability and promotes tissue edema, and LTB4, which is a potent chemotactic and activating factor for leukocytes, were measured in rat brain after ischemia and several time periods of reperfusion. Forebrain ischemia was induced by 4-vessel occlusion. LTC4/LTB4 in the brain were measured by RIA. We also studied the effects of a 5-lipoxygenase inhibitor, AA-861 and a PAF antagonist, CV-3988 on LTC4/LTB4 concentrations. LTC4 in brain tissue increased during 30 min forebrain ischemia (p < 0.001). After reperfusion, LTC4 increased further, but at 15 min reperfusion LTC4 returned to the control level. Tissue levels of LTB4 in the brain increased during 30 min ischemia and remained high until 5 min after reperfusion (p < 0.01) returning at 15 min reperfusion to the control level. AA-861 inhibited elevation of LTC4/LTB4 in the reperfusion phase, but was not effective during ischemia. CV-3988 had a similar effect. LTC4 and LTB4 may be involved in the pathogenesis of ischemia brain edema and leukocyte infiltration. Further, PAF and LTs have many similarities of their pathophysiological properties, and may interact therefore in pathologic process.

Effect of ibuprofen on regional eicosanoid production and neuronal injury after forebrain ischemia in rats

Post-ischemic metabolism of arachidonic acid by cyclooxygenase results in the elaboration of numerous eicosanoids and in the generation of free radicals. Accordingly, the effect of cyclooxygenase inhibition by ibuprofen on post-ischemic eicosanoid production and delayed neuronal death was evaluated in Wistar-Kyoto rats subjected to incomplete forebrain ischemia. In control (C) and ibuprofen-treated groups (n = 5 each), pre- and post-ischemic eicosanoid production in the caudate nucleus (CN) and dorsal hippocampus (HPC) were evaluated by microdialysis. The ibuprofen-treated animals were given ibuprofen, 15 mg/kg i.v., prior to insertion of microdialysis probes. Forebrain ischemia was induced by bilateral carotid artery occlusion (BCAO) for 10 min with simultaneous hypotension to 35 Torr. The concentrations of thromboxane B2 (TxB2), 6-keto-PGF1 alpha and PGF2 alpha in the microdialysate were measured by radioimmunoassay. In two additional concurrent groups of rats (n = 10 each), neuronal injury in the HPC, CN and cortex (parietal, temporal and entorhinal regions) was evaluated histologically three days after 10 min of forebrain ischemia with and without pre-ischemic ibuprofen administration. In the control microdialysis group, levels of TxB2, 6-keto-PGF1 alpha and PGF2 alpha increased in both CN and HPC after probe insertion. These probe related increases were substantially reduced in the ibuprofen group. After ischemia and reperfusion in the control group, the levels of TxB2 and PGF2 alpha increased in both CN and HPC. Levels of 6-keto-PGF1 alpha increased in the CN but not in the HPC. The administration of ibuprofen substantially reduced post-ischemic TxB2 and PGF2 alpha levels in both CN and HPC and decreased 6-keto-PGF1 alpha levels in the CN. The results of these initial microdialysis studies left the possibility that, in the ibuprofen group, the reduction in eicosanoid levels after probe penetration might have influenced the subsequent post-ischemic eicosanoid production. Therefore, in an additional group of animals (n = 5), ibuprofen was administered after probe insertion. Only PGF2 alpha levels were measured in this group. Increased levels of PGF2 alpha comparable to the original control group were detected after probe penetration. Nonetheless, after ibuprofen administration, the pre- and post-ischemic levels of PGF2 alpha were again significantly reduced. In the histologic evaluation groups, overall neuronal injury was significantly less in the ibuprofen treated animals. This protective effect of ibuprofen was most clearly evident in the CA3 sector of the HPC.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential expression of arachidonate 5-lipoxygenase transcripts in human brain tumors: evidence for the expression of a multitranscript family

In addition to the important role of leukotrienes as mediators in allergy and inflammation, these compounds are also linked to pathophysiological events in the brain including cerebral ischemia, brain edema, and increased permeability of the blood-brain barrier in brain tumors. Although brain tumors have been shown to secrete leukotrienes, no studies to date have provided evidence for the tumor expression of genes encoding enzymes involved in leukotriene production. Therefore, the present study determined the abundance of the mRNA for arachidonate 5-lipoxygenase (5-LO; arachidonate:oxygen 5-oxidoreductase, EC 1.13.11.34), which is the rate-limiting enzyme in leukotriene synthesis, in a series of human brain tumors. Macrophage/monocyte infiltration of the tumor was estimated by measuring the abundance of the transcript for the 91-kDa glycoprotein phagocyte-specific oxidase (gp91-phox), which is the phagocyte-specific cytochrome b heavy chain. The present study shows that (i) the 5-LO transcript is expressed in normal bovine brain and in human brain tumors; (ii) the 5-LO gene in human brain tumors and in the dimethyl sulfoxide-induced promyelocytic human leukemic HL-60 cells is expressed as a multitranscript family (2.7, 3.1, 4.8, 6.4, 8.6 kilobases); and (iii) the abundance of 5-LO transcripts, the expression of the larger transcripts, and the 5-LO/gp91-phox ratio correlate with the tumor malignancy. Overall, the present study supports the hypothesis that the 5-LO gene product may play a role in human tumor-induced brain edemas and provides evidence for tumor-associated expression of high molecular weight 5-LO transcripts in human brain tumors.

The effect of the 21-aminosteroid U74006F in a rabbit model of thromboembolic stroke

U74006F, a novel 21-aminosteroid, is an inhibitor of iron-dependent lipid peroxidation that is devoid of glucocorticoid and mineralocorticoid side effects. The efficacy of U74006F in reducing cerebral infarct size was investigated in a rabbit model of thromboembolic stroke. Each animal received either U74006F (3.0 mg/kg immediately before and 2 hr after embolization, n = 8) or vehicle control (n = 10). Hematocrit, mean arterial pressure, PCO2, PO2, and pH were measured and controlled both before and after the administration of an autologous clot into one internal carotid artery. Regional cerebral blood flow (in ml/100 g/min, mean +/- SEM) measured by hydrogen clearance was similar in both groups, being reduced from 68.2 +/- 9.6 to 5.2 +/- 1.9 in the control group immediately after clot embolization and from 73.3 +/- 14.9 to 7.0 +/- 1.7 in the U74006F group. Four hours after embolization the brain was harvested and cerebral infarct size was determined using the triphenyl-tetrazolium chloride technique (% hemisphere, mean +/- SEM). In the U74006F-treated group, the infarct size was significantly reduced (P < 0.05) to 14.8 +/- 6.4 from a control value of 36.0 +/- 6.4. Additionally, cerebral blood flow values after embolization were consistently higher in the U74006F group, although the differences were not statistically significant. This data suggests that the 21-aminosteroid U74006F may have a protective effect in cerebral ischemia.

The effect of 5-lipoxygenase inhibition on blood-brain barrier permeability in experimental brain tumors

To determine if leukotrienes are important mediators of vascular permeability in brain tumors, the effect of 5-lipoxygenase inhibitors on blood-tumor barrier permeability in rats harboring HK Walker 256 brain tumors was examined using quantitative autoradiography with alpha-14C-aminoisobutyric acid. The 5-lipoxygenase enzyme converts arachidonic acid to leukotrienes. Three 5-lipoxygenase inhibitors were utilized: BW755C, nordihydroguaiaretic acid, and AA-861. All three 5-lipoxygenase inhibitors significantly decreased vascular permeability both within the tumors and in brain adjacent to tumor. This suggests that capillary permeability in and adjacent to tumors is influenced by endogenous leukotrienes and that leukotrienes play an important role in brain tumor edema.

Selective blood-tumor barrier disruption by leukotrienes

The authors have previously reported that intracarotid infusion of 5 micrograms leukotriene C4 (LTC4) selectively increases blood-tumor barrier permeability in rat RG-2 tumors. In this study, rats harboring RG-2 tumors were given 15-minute intracarotid infusions of LTC4 at concentrations ranging from 0.5 microgram to 50.0 micrograms (seven rats in each dose group). Blood-tumor and blood-brain barrier permeability were determined by quantitative autoradiography using 14C aminoisobutyric acid. The transfer constant for permeability (Ki) within the tumors was increased twofold by LTC4 doses of 2.5, 5.0, and 50.0 micrograms compared to vehicle alone (90.00 +/- 21.14, 92.68 +/- 15.04, and 80.17 +/- 16.15 vs. 39.37 +/- 6.45 microliters/gm/min, respectively; mean +/- standard deviation; p less than 0.01). No significant change in Ki within the tumors was observed at the 0.5-microgram LTC4 dose. Blood-brain barrier permeability was selectively increased within the tumors. At no dose in this study did leukotrienes increase permeability within normal brain. To determine the duration of increased opening of the blood-tumor barrier by LTC4 administration, Ki was measured at 15, 30, and 60 minutes after termination of a 15-minute LTC4 infusion (seven rats at each time point). The mean Ki value was still high at 15 minutes (92.68 +/- 15.04 microliters/gm/min), but declined at 30 minutes (56.58 +/- 12.50 microliters/gm/min) and 60 minutes (55.40 +/- 8.10 microliters/gm/min) after the end of LTC4 infusion. Sulfidopeptide leukotrienes LTC4, LTD4, LTE4 and LTF4 were infused to compare their potency in opening the blood-tumor barrier. The mean leukotriene E4 was the most potent, increasing the permeability value 3 1/2-fold compared with vehicle alone (139.86 +/- 23.95 vs. 39.37 +/- 6.45 microliters/gm/min).

Pathophysiology and treatment of focal cerebral ischemia. Part II: Mechanisms of damage and treatment

The mechanisms that give rise to ischemic brain damage have not been definitively determined, but considerable evidence exists that three major factors are involved: increases in the intercellular cytosolic calcium concentration (Ca++i), acidosis, and production of free radicals. A nonphysiological rise in Ca++i due to a disturbed pump/leak relationship for calcium is believed to cause cell damage by overactivation of lipases and proteases and possibly also of endonucleases, and by alterations of protein phosphorylation, which secondarily affects protein synthesis and genome expression. The severity of this disturbance depends on the density of ischemia. In complete or near-complete ischemia of the cardiac arrest type, pump activity has ceased and the calcium leak is enhanced by the massive release of excitatory amino acids. As a result, multiple calcium channels are opened. This is probably the scenario in the focus of an ischemic lesion due to middle cerebral artery occlusion. Such ischemic tissues can be salvaged only by recirculation, and any brain damage incurred is delayed, suggesting that the calcium transient gives rise to sustained changes in membrane function and metabolism. If the ischemia is less dense, as in the penumbral zone of a focal ischemic lesion, pump failure may be moderate and the leak may be only slightly or intermittently enhanced. These differences in the pump/leak relationship for calcium explain why calcium and glutamate antagonists may lack effect on the cardiac arrest type of ischemia, while decreasing infarct size in focal ischemia. The adverse effects of acidosis may be exerted by several mechanisms. When the ischemia is sustained, acidosis may promote edema formation by inducing Na+ and Cl- accumulation via coupled Na+/H+ and Cl-/HCO3- exchange; however, it may also prevent recovery of mitochondrial metabolism and resumption of H+ extrusion. If the ischemia is transient, pronounced intraischemic acidosis triggers delayed damage characterized by gross edema and seizures. Possibly, this is a result of free-radical formation. If the ischemia is moderate, as in the penumbral zone of a focal ischemic lesion, the effect of acidosis is controversial. In fact, enhanced glucolysis may then be beneficial. Although free radicals have long been assumed to be mediators of ischemic cell death, it is only recently that more substantial evidence of their participation has been produced. It now seems likely that one major target of free radicals is the microvasculature, and that free radicals and other mediators of inflammatory reactions (such as platelet-activating factor) aggravate the ischemic lesion by causing microvascular dysfunction and blood-brain barrier disruption.(ABSTRACT TRUNCATED AT 400 WORDS)

Protective effects of benidipine on arachidonic acid-induced acute cerebral ischemia in rats

Acute cerebral ischemia was produced in rats by injection of arachidonic acid (AA) into the internal carotid artery. Evans blue (EB) was intravenously injected and its extravasation into the brain was determined as an indicator of disturbances in the blood-brain barrier and endothelial cells. Control animals showed severe cerebral edema and marked blue staining of the brain. Benidipine (30 micrograms/kg, i.p.) suppressed the increase in cerebral water content and the extravasation of EB. Similarly nicardipine (100 micrograms/kg, i.p.) suppressed the elevation of water content and the extravasation of EB. Furthermore, both benidipine (30 micrograms/kg, i.p.) and nicardipine (100 micrograms/kg, i.p.) improved the neuronal injuries following AA-injection. An antiplatelet agent, ticlopidine (100 mg/kg, i.p.), and a thromboxane A2 synthetase inhibitor, OKY-1581 (3 mg/kg, i.p.), also suppressed the elevation of cerebral water content. A lipoxygenase inhibitor, AA-561 (200 mg/kg, p.o.), and a cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.p.), did not prevent the increase in cerebral water content. Neither benidipine (3-30 micrograms/kg, i.v.) nor nicardipine (100 micrograms/kg, i.v.) inhibited the AgNO3-induced thrombus formation of the abdominal aorta, whereas ticlopidine (100 mg/kg, p.o.) and OKY-1581 (3 mg/kg, i.v.) prevented the thrombus formation. From the present results, it is suggested that benidipine, as well as nicardipine, may protect against AA-induced acute cerebral infarction via a mechanism independent of antithrombotic action.

5-lipoxygenase inhibitors and their anti-inflammatory activities

A wide variety of agents have been reported as 5-LO inhibitors. The majority of the series appear to be lipophilic reducing agents, including phenols, partially saturated aromatics, and compounds containing heteroatom-heteroatom bonds. Many of these are not selective 5-LO inhibitors, but often affect CO and other LOs as well. In vivo systemic activity for many of these has been, in general, disappointing, probably because of poor bioavailability caused by lipophilicity and metabolic instability (oxidation, and conjugation of phenolic compounds). However, topically a number of agents have shown promise for skin inflammation, with Syntex's lonapalene the most advanced of these. Most results published to date appear more disappointing in the allergy/asthma field. More excitingly, a few structural types are selective 5-LO inhibitors which have shown systemic activity in vivo and in the clinic. Abbott's zileuton (136) appears to be one of the leading compounds in this category, along with other hydroxamates such as BW-A4C (129) from Burroughs-Wellcome. Recent selective non-reducing agents such as Wyeth-Ayerst's Wy-50,295 (143) and the similar ICI compounds such as ICI 216800 (145) also hold promise. The enantiospecific effects of (106) and (145) are especially interesting for the design of new inhibitors. If compounds like these validate the hypothesis that inhibition of 5-LO will have a significant anti-inflammatory effect, a redoubling of effort throughout the industry to find second- and third-generation selective agents may be expected. Part of the difficulty in interpreting and comparing the 5-LO literature is the plethora of test methods and activity criteria. As pointed out in the introduction, inhibition of product release from cells, often stimulated with A23187, has commonly been used to demonstrate 5-LO inhibition. However, this type of assay cannot be assumed to be diagnostic for 5-LO inhibition. Only if specificity for 5-LO product generation and (ideally) activity in cell-free enzymes is also shown should mechanistic interpretations be made. Recently, a new class of compounds was found at Merck which inhibited LT biosynthesis without inhibiting 5-LO, but apparently by a novel, specific mechanism. L-655,240 (169) and L-663,536 (MK-886) (170) were both active in human ISN, with IC50 values in the low micromolar range. Both also orally inhibited GPB (< 1 mg/kg). MK-886 was effective in Ascaris-induced asthma in squirrel monkeys, in rat carrageenan pleurisy, in rat Arthus pleurisy, and (topically) in guinea-pig ear oedema induced by A23187.(ABSTRACT TRUNCATED AT 400 WORDS)

NMDA receptor-mediated arachidonic acid release in neurons: role in signal transduction and pathological aspects

The N-methyl-D-aspartate (NMDA)-sensitive subtype of glutamate receptor, which gates Ca(2+)-permeable ion channels, is known for its role in learning and memory formation, in the induction of long-term potentiation, and also in seizure activity and neurotoxicity. In primary cultures of cerebellar neurons, agonists of NMDA receptors induce a dose-dependent release of [3H]arachidonic acid ([3H]AA), which is potentiated by activation of the glycine-positive modulatory site and inhibited by NMDA receptor antagonists. NMDA receptor-induced [3H]AA release is inhibited by quinacrine and partially depends on the presence of extracellular calcium. The [3H]AA release is not sensitive, however, to pretreatment with pertussis or cholera toxin, which suggests a Ca(2+)-dependent activation of phospholipase A2 not employing G proteins. Pretreatment of cultures with the natural and semisynthetic sphingolipids GT1b and PKS 3, respectively, inhibits NMDA receptor-mediated [3H]AA release. We also demonstrated glutamate-evoked [3H]AA release from rat hippocampal slices, which is NMDA receptor mediated, calcium dependent and sensitive to quinacrine. Arachidonic acid and its metabolites have been shown to play a role as second messengers and to modulate neuronal activity. Moreover, they are thought to act as transsynaptic modulators in the mechanism of NMDA receptor-induced long-term potentiation in the hippocampus. Their role in ischemic brain pathology has also been postulated. Our experiments on cultured cerebellar granule cells, incubated in a Mg(2+)-free medium deprived of glucose and oxygen, demonstrated a time-dependent stimulation of [3H]AA release. This release was inhibited by antagonists of NMDA receptors and by quinacrine. Stimulation of NMDA-sensitive glutamate receptors and the subsequent calcium-mediated activation of phospholipase A2 may play a role in the in vivo release of arachidonic acid during brain ischemia. This hypothesis is supported by the observation that the enhanced level of thromboxane B2 in the gerbil brain after 5 min of global ischemia is reduced by the systemic application of either the NMDA antagonist MK-801 or the ganglioside GM1.

Ischemic brain damage: focus on lipids and lipid mediators

The last two decades of research have produced detailed information not only on how ischemia causes degradation of phospholipids and accumulation of potentially cytotoxic breakdown products of such lipids, but also on reactions elicited by the subsequent conversion of these products into a series of lipids, mediating an array of cellular and intercellular reactions. It now seems clear that PAF, as well as several of the cyclooxygenase and lipoxygenase products of arachidonic acid, can induce changes, particularly in the microvasculature, which jeopardize cell survival in reperfused tissue. It is equally clear that, at least following long periods of ischemia, free radicals generated in reactions that are interacting with those producing eicosanoids and PAF play a similar role. A somewhat more speculative mechanism links sustained activation and membrane translocation of PKC to delayed neuronal death following transient ischemia. All of these interactions underscore the importance of lipolytic events for cell damage in ischemia and other conditions with a compromised cellular energy metabolism.

The influence of one hyperbaric oxygen-induced seizure on brain eicosanoid content

The levels of prostaglandin F1 (6-keto-PGF1 alpha), thromboxane B2 (11-dehydro-TxB2), and peptidoleukotriene C4 (LTC4) were measured (acetylcholinesterase immunoassay) in the frontal cortex (FC) and the striatum (SA) of the rat brain to study the possible role of eicosanoids in seizures induced by hyperbaric oxygen (HBO). The rats were exposed to (1) hyperbaric oxygen (HBO, 6 ATA O2) up to the first seizure (2) compressed air (6 ATA air, i.e., approximately equal to 1.25 ATA O2) or (3) atmospheric pressure (1 ATA air, i.e., 0.21 ATA O2); there was no seizure in groups 2 and 3. Transition from 6 ATA to atmospheric pressure was obtained in 15 min; the rats were then decapitated and their heads frozen in liquid nitrogen before extraction and analysis of prostanoids. Whatever the conditions, cortical levels of 6-keto-PGF1 alpha and 11-dehydro-Tx B2 are higher than striatal levels; considering the same area, 11-dehydro-Tx B2 and LTC4 concentrations were not significantly different whatever the condition, but there is a trend for lower 6-keto-PGF1 alpha levels in FC after HBO seizure. Biochemical mechanisms are discussed. Eicosanoids do not seem to play a major role in HBO seizures, although some modifications of their metabolism may take place.

Leukotrienes in brain: natural occurrence and induced changes

Peptidoleukotrienes (SP-LTs) (both total product and individual LTC4 and LTE4 and LTB4 were measured by radioimmunoassay in cerebrospinal fluid (CSF) collected from the third ventricle of conscious cats. Total SP-LT was expressed as LTE4 after treating samples with crude gamma-glutamyltranspeptidase. Prostaglandin (PG) E2 and thromboxane (TX) B2, the stable metabolite of TXA2, were also assayed in part of the experiments. Under basal conditions, SP-LT and LTC4 were consistently measurable (respectively, 327 +/- 14 and 244 +/- 41 pg/ml), while native LTE4 was below the threshold of the assay (60-280 pg/ml) in most cases. LTB4 was barely detectable (30 +/- 2 pg/ml) or not detectable at all. PGE2 was normally less abundant than TXB2 (31 +/- 4 vs 281 +/- 47 pg/ml). Intracerebroventricular (i.c.v.) administration of arachidonic acid (40 microgram) caused a 4-fold increase in SP-LT levels which was relatively small and transient compared to PGE2 (76-fold) and TXB2 (23-fold), while there was no change in either native LTE4 or LTB4. A similar response was obtained with platelet-activating factor (PAF, 1 microgram i.c.v.), though SP-LT elevation (4-fold) was more persistent. A further rise in SP-LT (9-fold) was noted when PAF administration was preceded by indomethacin (500 microgram i.c.v.), whereas PAF effect was reversed by pretreatment with either the PAF antagonist, BN52021 (1 microgram i.c.v.), or the 5-lipoxygenase inhibitors, U-60,257 (75 micrograms i.c.v.) and L-651,392 (10 mg/kg p.o.). PAF was also effective in causing a 3-fold rise in LTC4. Unlike PAF, pyrogens (endotoxin i.c.v. or i.v.; interleukin-1 i.v.) at doses above threshold for fever had no effect on LT levels in CSF, both in the absence and presence of indomethacin pretreatment. We conclude that SP-LTs are a normal constituent of CSF, LTC4, being the major species. The response to PAF accords with a pathogenetic role of the compounds in inflammatory processes and the reactive changes to injury. No evidence was obtained for the involvement of SP-LTs in the central mechanism of fever.

On the relation between cerebral cysteinyl-leukotriene formation and epileptic seizures

In gerbils pentylenetetrazole- or handling-induced seizures were accompanied by cerebral formation of small amounts of cysteinyl-leukotrienes (LT) but large amounts of prostaglandin (PG) F2 alpha. By contrast, in rats injected with pentylenetetrazole or bicuculline very large amounts of PGF2 alpha but no cysteinyl-LT could be detected in the brain tissues. The data indicate that at least in rats the extensive neuronal activity during tonic-clonic convulsions is not necessarily sufficient for the activation of the 5-lipoxygenase pathway. Apparently important species differences do exist.

Low-energy laser irradiation--a new measure for suppression of arachidonic acid metabolism in the optic nerve

Helium-neon low-energy laser (LEL) irradiation, known for its therapeutic effects in arthritis, wound healing, and muscular strain, was applied to eyes of rats that had sustained an optic nerve crush injury. Crush injury to the optic nerve resulted in a long-lasting in vitro elevation of prostaglandin E2 (PGE2) production (1.8-3.9-fold above control values during the 12 day study period). LEL irradiation per se had no effect in vitro on PGE2 production by the optic nerve; however, LEL irradiation of eyes with crushed optic nerve inhibited the enhanced production of PGE2 and leukotriene B4 in vitro by 55% and 75% during the late and immediate phase after trauma, respectively. Our findings of the suppressive effect of LEL irradiation on arachidonic acid metabolism are reminiscent of the actions of steroidal and nonsteroidal anti-inflammatory drugs, and might indicate, for the first time, the possible biochemical mechanisms associated with the clinical anti-inflammatory effects of LEL irradiation.