Cerebrovascular and cerebrometabolic effects of intracarotid infused platelet-activating factor in rats

Amoxicillin-clavulanic acid-induced type II Kounis syndrome during general anaesthesia complicated with hypoxic-ischaemic encephalopathy

Anaphylaxis is a severe acute multisystem syndrome involving massive mediator release from mast cells and basophils. Although the entire arterial system can be affected, when coronary arteries are the main targets, Kounis syndrome needs to be considered. Cerebral artery involvement has also been suggested in rarer MC-mediator release episodes; so-called 'Kounis-like' syndrome. Cerebral ischaemic lesions can then result from low blood pressure or direct proinflammatory and/or vasoconstrictive mediator action in the cerebral arterial system. Diagnosis can be difficult in anaesthetised patients, as low blood pressure can have multiple causes. Treatment is also challenging, as administering adrenaline can worsen ischaemia. We report the first case of amoxicillin-clavulanic acid-induced type II Kounis syndrome under general anaesthesia, complicated with severe, irreversible and subsequently fatal encephalopathy of ischaemic origin. This case can contribute to awareness of less common Kounis syndrome manifestations, including severe cerebral involvement, or other anaphylactic reactions with atypical presentations.

Novel neuroprotection using antioxidant nanoparticles in a mouse model of head trauma

INTRODUCTION

Free radicals and reactive oxygen species are related to deteriorating pathological conditions after head trauma because of their secondary effects. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) scavenges free radicals; however, this molecule is also toxic. Here, we have evaluated the neuroprotective effect of antioxidant nanoparticles, which consisted of a novel core-shell type nanoparticle containing 4-amino-TEMPO, that is, redox-active nitroxide radical-containing nanoparticles (RNPs).

METHODS

Institute of Cancer Research mice were subjected to a head-impact procedure, randomly divided into four groups and intravenously (3 mg/kg) administered phosphate-buffered saline, TEMPO, micelle (a self-assembling block copolymer micelle without a TEMPO moiety), or RNP through the tail vein immediately thereafter and intraperitoneally at days 1, 3, and 5 after traumatic brain injury (TBI). The RNP distribution was detected by rhodamine labeling. Cognitive behavior was assessed using the neurological severity score and a rotarod test at days 1, 3, and 7 following TBI, and contusion volume was measured at day 7 after TBI. Free radical-scavenging capacity was analyzed by electron paramagnetic resonance on day 1 after TBI, and immunostaining was used to observe mobilization of microglia (Iba-1) and rescued neuronal cells (NeuN).

RESULTS

Redox-active nitroxide radical-containing nanoparticle was detected in the microvessels around the injured area in the brain. Cognitive behavior assessment was significantly better, and contusion volume was significantly smaller in the RNP group compared with the other groups. Superoxide anion scavenging capacity was significantly higher in the RNP group, and neuronal loss was significantly suppressed around the injured area at day 7 after TBI. Furthermore, in the RNP group, neurodegenerative microglia production was suppressed at days 3 and 7 after TBI, whereas neuroprotective microglia production was higher at day 7 after TBI.

CONCLUSION

The RNP administration after TBI improved cognitive behavior and reduced contusion volume by improving reactive oxygen species scavenging capacity. Therefore, RNP may have a neuroprotective effect after TBI.

LEVEL OF EVIDENCE

Therapeutic test.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

Neuroprotection during cardiac surgery: a randomised trial of a platelet activating factor antagonist

OBJECTIVE

To assess platelet activating factor (PAF) antagonists, potent neuroprotective agents in experimental cerebral dysfunction, in clinical practice.

DESIGN

Double blind, minimised, placebo controlled trial of low and high dose PAF antagonist (lexipafant).

SETTING

Cardiac surgery unit.

PATIENTS

150 patients undergoing coronary artery bypass graft (CABG) surgery using cardiopulmonary bypass.

INTERVENTIONS

Randomisation to placebo, low dose (10 mg) or high dose (100 mg) lexipafant.

MAIN OUTCOME MEASURES

Incidence of impairment on four established cognitive tests, undertaken before, five days, and three months after CABG, examined by three methods for defining impairment.

RESULTS

The three groups were similar with respect to preoperative and intraoperative factors. Observed levels of cognitive impairment were less than had been predicted from previous studies. There was no difference in the groups in cognitive change scores at five days or three months. Group mean analysis showed significant time factors for all four tests but not for interactions or for the lexipafant group. A composite cognitive index, based on the aggregate of four normally distributed tests, showed a significant effect for timing of the test but not for the lexipafant group or interaction. Age, but not duration of bypass, was the most important determinant of postoperative cognitive impairment.

CONCLUSIONS

The neuroprotective PAF antagonist lexipafant did not differentially reduce the level of cognitive impairment after CABG as determined by power estimates derived from published studies. The strongest predictors of cognitive impairment were age and timing of the test after operation.

Production of platelet-activating factor by neuronal cells in the rat brain with cold injury

The production and localization of platelet-activating factor (PAF) in the brain following focal brain injury were examined. Immunofluorescent staining was used to detect PAF in the rat brain with cold-induced local brain injury. After cold injury, immediate-early PAF staining was observed within the cold lesion followed later by immunoreactivity in the ipsilateral white matter. PAF immunoreactivity was also clearly seen both in cortical neurons adjacent to the cold lesion and in the ipsilateral hippocampus which showed delayed neuronal degeneration. The data suggest that PAF synthesis occurs in the neuronal cells in the perilesional area and hippocampus as well as within the cold lesion site during the early stages of cold-induced brain injury. PAF expression may contribute to the onset and progression of further brain damage, such as delayed axotomy and delayed neuronal loss.

Role of platelet-activating factor in cardiovascular pathophysiology

Platelet-activating factor (PAF) is a phospholipid mediator that belongs to a family of biologically active, structurally related alkyl phosphoglycerides. PAF acts via a specific receptor that is coupled with a G protein, which activates a phosphatidylinositol-specific phospholipase C. In this review we focus on the aspects that are more relevant for the cell biology of the cardiovascular system. The in vitro studies provided evidence for a role of PAF both as intercellular and intracellular messenger involved in cell-to-cell communication. In the cardiovascular system, PAF may have a role in embryogenesis because it stimulates endothelial cell migration and angiogenesis and may affect cardiac function because it exhibits mechanical and electrophysiological actions on cardiomyocytes. Moreover, PAF may contribute to modulation of blood pressure mainly by affecting the renal vascular circulation. In pathological conditions, PAF has been involved in the hypotension and cardiac dysfunctions occurring in various cardiovascular stress situations such as cardiac anaphylaxis and hemorrhagic, traumatic, and septic shock syndromes. In addition, experimental studies indicate that PAF has a critical role in the development of myocardial ischemia-reperfusion injury. Indeed, PAF cooperates in the recruitment of leukocytes in inflamed tissue by promoting adhesion to the endothelium and extravascular transmigration of leukocytes. The finding that human heart can produce PAF, expresses PAF receptor, and is sensitive to the negative inotropic action of PAF suggests that this mediator may have a role also in human cardiovascular pathophysiology.

Platelet-activating factor receptor antagonism improves cerebral recovery after circulatory arrest

BACKGROUND

The aim of this study was to determine the effects of antagonism of platelet-activating factor receptors on cerebral recovery after deep hypothermic circulatory arrest (DHCA).

METHODS

Fourteen 1-week-old piglets were randomly assigned to either placebo (n = 7), or 10 mg/kg intravenous ginkgolide B (BN52021), a naturally occurring platelet-activating factor receptor antagonist. All piglets had cardiopulmonary bypass, cooling to 18 degrees C, 60 minutes of circulatory arrest followed by 60 minutes of reperfusion and rewarming. Global and regional cerebral blood flow, cerebral oxygen metabolism and renal blood flow were determined at baseline before DHCA and after 60 minutes of reperfusion.

RESULTS

Blood flow was significantly reduced in all regions of the brain (p < 0.001) and the kidneys (p = 0.02) after DHCA in control animals. Cerebral oxygen metabolism was also significantly reduced after DHCA to 59.2% +/- 3.2% of the pre-DHCA value (p = 0.0003). In the ginkgolide B group, recovery of global cerebral blood flow to 60.4% +/- 2.8% of pre-DHCA level and of global cerebral oxygen metabolism to 77.1% +/- 5.8% of pre-DHCA value were significantly higher than the recovery in the control group (p < 0.02). Regional recovery of cerebral blood flow and oxygen metabolism in the gingkolide B group was greatest in the cerebellum and brainstem. Renal blood flow did not decrease significantly after DHCA in the gingkolide B group (p = 0.23).

CONCLUSIONS

These results suggest that production of platelet-activating factor is increased in the brain after DHCA. Platelet-activating factor receptor antagonism with ginkgolide B before the circulatory arrest period can significantly improve recovery of cerebral blood flow and oxygen metabolism and renal blood flow after DHCA.

Influence of platelet-activating factor on cerebral microcirculation in rats: part 1. Systemic application

BACKGROUND AND PURPOSE

Platelet-activating factor (PAF) has been demonstrated to have a mediator function in shock, with some of its deleterious effects being attributed to its influence on microcirculation. Systemic PAF concentrations as found in shock could also compromise the cerebral microcirculation. Our purpose in the present study was to examine the influence of systemically applied PAF on microvascular perfusion and leukocyte-endothelium interactions in cerebral microvessels.

METHODS

A closed cranial window technique was used for intravital fluorescence microscopy of the brain surface. PAF was infused in concentrations of 10(-12), 10(-9), and 10(-6) mol/L into the carotid artery (5 mL/h for 20 min) of Sprague-Dawley rats (n=30). The selective PAF receptor antagonist WEB 2170BS (2 mg/kg body weight) was used to inhibit specific PAF effects.

RESULTS

The number of leukocytes (cells/100 microm. min) rolling along or adhering at the venular endothelium increased following infusion of PAF 10(-6) mol/L from 7.7+/-2.5 to 24.4+/-8.9 (P<0.05) and from 1.9+/-0.5 to 6.9+/-2.2 (P<0.05), respectively, within 2 hours. Mean arterial pressure decreased from 92+/-22 mm Hg to 49+/-17 mm Hg (P<0.05). The lower concentrations of PAF were less effective to decrease mean arterial pressure but also induced leukocyte-endothelium interactions. The intravenous administration of WEB 2170BS 15 min before the infusion of PAF 10(-6) mol/L prevented both systemic hypotension and activation of leukocyte-endothelium interactions.

CONCLUSIONS

Increased systemic blood levels of PAF as found during shock can not only cause systemic arterial hypotension but also induce leukocyte-endothelium interactions in cerebral venules. The activation of leukocytes was found to be independent of PAF-induced arterial hypotension. The specificity of these results is confirmed by the findings that WEB 2170BS could inhibit the PAF-induced systemic hypotension as well as the activation of leukocytes.

Plasma platelet-activating factor levels in newborn infants with and without perinatal asphyxia: is it an additional marker of perinatal asphyxia?

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is still a very important cause of neonatal mortality and morbidity. Recently platelet-activating factor (PAF) has been accused of being responsible for the neuronal damage in hypoxic-ischemic brain.

METHODS

Therefore, we conducted a study in newborns with perinatal asphyxia to try to show the relationship between the clinical severity and plasma PAF levels.

RESULTS

Mean plasma levels of 19 asphyxiated infants (997.8 +/- 363.5 pg/mL) were significantly higher than that of 20 healthy infants (410.2 +/- 148.6 pg/mL, P < 0.0001). Patients with clinically severe HIE had significantly higher levels of PAF (1494.2 +/- 386.6 pg/mL) when compared with patients with mild HIE (815 +/- 114.5 pg/mL) and with moderate HIE (828.3 +/- 61.1 pg/mL). There was a significant correlation between plasma PAF concentration and arterial pH and base deficit, but no correlation with platelet and leukocyte counts.

CONCLUSIONS

Plasma PAF levels correlating with the severity of HIE is interpreted to mean that high PAF levels may be an indicator of clinical severity and probably the poorer prognosis of patients with HIE.

Hemodynamic depression and microthrombosis in the peripheral areas of cortical contusion in the rat: role of platelet activating factor

Cerebrovascular damages leading to subsequent reductions in regional cerebral blood flow (rCBF) may play an important role in secondary cell damages following traumatic brain injury (TBI). Recent studies have demonstrated that rCBF markedly decrease in experimental model of TBI (e.g. fluid percussion injury, acute subdural hematoma, contusion). However, precise mechanisms underlying post-traumatic CBF reduction remain unclear. In the present study, the rCBF changes and microthrombosis formation were investigated in a cortical contusional model in rats, and the effects of etizolam (platelet activating factor antagonist) on microthrombosis were tested. The rCBF in the peripheral areas increased transiently, and decreased to ischemic level 3 hours post- injury. The histological examinations revealed microthrombosis formation in the contused area, extending from the center to the peripheral areas within 6 hours post-injury. The rCBF decrease and the contusion necrosis volume were significantly attenuated by etizolam administration. These results indicate that platelet activating factor is involved in microthrombosis formation and hemodynamic depression, and resultant ischemic damages within areas surrounding the contusion.

Production of platelet-activating factor during focal cerebral ischemia and reperfusion in the rat

Platelet-activating factor (PAF) is a phospholipid mediator implicated in a diverse range of pathological processes. Beneficial effects of PAF antagonists have been shown in various models of central nervous system ischemia. In this study, we evaluated the production of PAF during focal cerebral ischemia and reperfusion in the rat. Ischemia was induced by occlusion of the middle cerebral artery with a thread. Quantification of PAF was performed with the radioimmunoassay technique. PAF was detected in the brain under normal conditions. Tissue PAF level in the ischemic cerebral hemisphere significantly decreased by prolonged ischemia (P<.05). Conversely, the decreased tissue PAF level during ischemia was significantly increased again by reperfusion (P<.05), but was still low compared with the control. This study indicates that the production of PAF in the brain tissue decreased by prolonged ischemia, and suggests the role of PAF in the reperfusion phase rather than during ischemia in the pathophysiology of ischemic brain injury.

Involvement of platelet-activating factor (PAF) in glutamate neurotoxicity in rat neuronal cultures

To clarify the role of platelet-activating factor (PAF) in glutamate neurotoxicity, in vitro experiments using primary neuronal cultures were performed. The anti-PAF immunoglobulin-G (aPAF-IgG) and the three PAF receptor antagonists (BN52021, CV6209, and E5880) were tested for their neuroprotective activity in primary neuronal cultures isolated from embryonic rat cerebral cortex. The cultured neurons were exposed to glutamate (1 mM) for 60 min. Twenty-four hours after this exposure, aPAF-IgG demonstrated evidence of protective effects against neuronal damage in a dose-dependent manner. Protective effects also were observed in cultures treated with the three PAF antagonists (P < 0.05 at 1 microg/ml aPAF-IgG, P < 0.01 at 100 microM BN52021, P < 0.05 at 10 nM CV6209 and P < 0.01 at 10 nM E5880). The Fura-2 assay was used to estimate whether low dosages of exogenous PAF affect cultured neurons. The cultured neurons were loaded with Fura-2/AM. After preincubation for 120 min, the Fura-2-loaded neurons were exposed to various concentrations of PAF for 60 min. By measuring the fluorescent intensity of the medium as representing the amount of Fura-2 released from damaged neurons, we detected an increased release of Fura-2, even at low doses of PAF (P < 0.01 at 10 nM PAF). We further studied PAF production by neurons in response to glutamate. The level of PAF measured in the medium exposed to glutamate was significantly higher than the level in the medium unexposed to glutamate (P < 0.05). Our results suggest an important role of PAF in glutamate neurotoxicity.

Platelet-activating factor in the CNS

Platelet-activating factor (PAF) is a phospholipid synthesized in a variety of cells throughout the body. Platelet-activating factor has been identified in the CNS and has a number of diverse physiological and pathological functions. It has been shown to be a modulator of many CNS processes, ranging from long-term potentiation (LTP) to neuronal differentiation. Excessive levels of PAF appear to play an important role in neuronal cell injury, such as that resulting from ischaemia, inflammation, human immunodeficiency syndrome (HIV) and meningitis. The beneficial effects of PAF receptor antagonists are many and give rise to possible therapeutic strategies for neurotrauma.

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.

Platelet-activating factor production by human fetal microglia. Effect of lipopolysaccharides and tumor necrosis factor-alpha

Since platelet-activating factor (PAF) exerts neurotoxic effects on brain cells, we explored the possibility of PAF production by human fetal microglial cells in vitro. PAF content in pure cultures was assayed and characterized in basic conditions, and after stimulation with growth factors and cytokines. Results showed that microglia cells synthesized PAF when challenged with tumor necrosis factor-alpha and lipopolysaccharides, whereas other molecules, such as gamma-interferon or basic fibroblast growth factor, were ineffective. The induced PAF production was concentration- and time-dependent. These results are in line with the hypothesis that microglia can start a cascade of events leading to tissue damage, thus playing a central role in the pathogenesis of several central nervous system diseases.

MgATP inhibits the synthesis of 1-alkyl-2-acetyl-sn-glycero-3-phosphate by microsomal acetyltransferase of immature rabbit cerebral cortex

The activity of 1-alkyl-sn-glycero-3-phosphate (AGP) acetyltransferase was studied using microsomal fractions isolated from cerebral cortices of 15-day-old rabbits. Fraction P3A was isolated using buffered 0.32 M sucrose containing mercaptoethanol, EDTA and NaF. This fraction had specific AGP acetyltransferase activities which were 4.9-times those of microsomal fraction P3B isolated in 0.32 M sucrose alone. This P3B activity was increased 2.4-times after a preincubation in the presence of ATP, MgCl2 and a high-speed supernatant fraction from cerebral cortex. Further, the activities of both P3A and P3B were almost completely eliminated by preincubation in the presence of alkaline phosphatase. Thus an activation of the AGP acetyltransferase by phosphorylation was indicated. While there was little inhibition of the P3A AGP acetyltransferase in the presence of added ATP, the magnesium salt form of ATP (1 mM) was severely inhibitory, bringing about 86% inhibition for P3A and 91% for P3B. The inhibitory effects of MgADP and MgAMP were smaller, and MgATP was a much more effective inhibitor than MgCTP, MgGTP and MgUTP which brought about 20-38% inhibitions of P3A activity at 1 mM concentrations. The effect of MgATP may be of particular relevance to the synthesis of platelet activating factor (PAF) following a period of ischemia in brain. Falling MgATP levels during energy failure could relieve the inhibition of AGP acetyltransferase seen in healthy cells and allow the formation of 1-alkyl-2-acetyl-sn-glycero-3-phosphate, which is the first committed intermediate in the de novo pathway of PAF synthesis.

Effect of platelet-activating factor antagonist on brain injury in rats

The ability of a platelet-activating factor (PAF) antagonist to reduce infarct size has been reported in a animal model of focal brain ischemia. The authors studied the effect of PAF antagonist (TCV-309) on cold brain injury in rats. Twenty-four hours after injury, water content was determined by both drying-weighing and specific gravimetric techniques, and ischemic brain damage was assessed with 2,3,5-triphenyltetrazolium chloride in multiple coronal sections. Pretreatment with TCV-309 (lmg/kg) significantly reduced the water content (p < 0.01) and volume of ischemic damage (p < 0.001) produced by the cold brain injury. These results indicate that PAF antagonist can ameliorate secondary brain tissue damage following brain injury.

Platelet-activating factor and its methoxy-analogue ET-18-OCH3 stimulate immediate early gene expression in rat astroglial cultures

In the present paper we analyzed c-fos and zif/268 expression in rat primary astroglial cell cultures after treatment with Platelet-activating Factor (PAF) and its 2-O-methyl-analogue, 1-O-octadecyl-2-O-methoxy-glycero-3-phosphocholine (ET-18-OCH3). Both compounds, at a dose (2 microM) that did not produce toxic effects on astroglial cells, induced a rapid and transient increase of c-fos and zif/268 mRNA level. Pretreatment of astroglial cells with the PAF antagonist BN50730 (5 microM) 10 min prior to the addition of alkyl-phospholipids almost completely prevented the activation of the immediate early genes. On the contrary triazolam, another PAF inhibitor, did not block PAF induced gene expression when added to the medium at 5 microM concentration. ET-18-OCH3 effect on gene expression is blocked by the same antagonist (BN50730) which is effective in inhibiting PAF effect on astrocytes, suggesting that both substances act through the same binding site. Results obtained support the view that astroglial cells are a cellular target for this lipid mediator, and, like macrophages, respond to its methoxy-analogue.

Platelet-activating factor antagonists reduce excitotoxic damage in cultured neurons from embryonic chick telencephalon and protect the rat hippocampus and neocortex from ischemic injury in vivo

The neuroprotective effects of the platelet-activating factor (PAF) antagonists BN 52020 and BN 52021 were determined in a temperature-controlled model of transient forebrain ischemia in the rat (occlusion of both common carotid arteries combined with lowering of the mean arterial blood pressure to 40 mm Hg for 10 min). After 7 days of recirculation, the ischemic neuronal damage was evaluated histologically within the hippocampus and neocortex. Combined pre- and post-treatment with the PAF antagonists (2 x 25 mg/kg, s.c.) significantly reduced the resulting neuronal damage of the CA1 and CA3 hippocampal subfields and of the occipital and parietal cerebral cortex. The two PAF antagonists were also tested for their neuroprotective activity in primary neuronal cultures isolated from embryonic chick telencephalon. Since an excessive activation of excitatory amino acid receptors is discussed to be of importance for the ischemic brain damage, the cultured neurons were exposed to the excitatory amino acid L-glutamate (1 mM) for a period of 60 min. Twenty hours after the excitotoxic insult, BN 52020- and BN 52021-treated cultures (1-100 microM) showed both a better preserved morphology, as well as a dose-dependent increase in cell viability and protein content compared to the control cultures. Our results demonstrate that the PAF antagonists BN 52020 and BN 52021 have the capacity to protect brain tissue against ischemic neuronal damage independent of hypothermic effects and are also capable of reducing excitotoxic damage of telencephalic neurons from chick embryos cultured in the absence of glial or endothelial cells. We thus propose that PAF plays an important role in the pathophysiology of ischemic/excitotoxic neuronal injury via a direct action on neurons.

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.

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

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

Excitable membranes, lipid messengers, and immediate-early genes. Alteration of signal transduction in neuromodulation and neurotrauma

The physical nature of neuronal cells, particularly in the functional and morphological segregation of synapse, soma, and dendrites, imparts special importance on the integrity of their cell membranes for the localization of function, generation of intrinsic second messengers, and plasticity required for adaptation and repair. The component phospholipids of neural membranes are important sources of bioactive mediators that participate in such diverse phenomena as memory formation and cellular damage following trauma. A common role for PAF in these processes is established through the suppressive effects of its antagonists. Furthermore, being both an extracellular and intracellular agonist of phospholipase activation, in addition to being a product of phospholipase activity, PAF assumes a centralized role in the cellular metabolism following neural stimulation. The linkage of PAF to neural immediate-early gene expression, both in vitro and in vivo, suggests that its effects are initiating to long-term formative and reparative processes. Such a common link between destructive and plastic responses provides an important view of cellular and tissue maintenance in the nervous system.

Protein kinase C activator phorbol 12, 13-dibutyrate inhibits platelet activating factor-stimulated Ca2+ mobilization and phosphoinositide turnover in neurohybrid NG108-15 cells

The protein kinase C (PKC) activator, phorbol 12, 13-dibutyrate (PDBu) dose-dependently inhibited platelet-activating factor (PAF)-induced [Ca2+]i elevation and inositol monophosphate (IP1) accumulation in neurohybrid NG108-15 cells with IC50 values of 162 nM and 35 nM, respectively. Pretreatment of NG108-15 cells with PKC inhibitor H-7 partially prevented the inhibitory effect of PDBu on PAF-induced [Ca2+]i elevation as well as PI metabolism in NG108-15 cells. Pretreatment of the cells with pertussis toxin (PTX) resulted in a dose-dependent inhibition of PAF-induced IP1 and IP3 accumulation but only slightly affected PAF-induced [Ca2+]i elevation in NG108-15 cells. The results reveal that PAF receptor-mediated Ca2+ mobilization and PI metabolism in NG108-15 cells are regulated by PKC while a PTX-sensitive G protein is coupled to PAF receptor for inducing activation of phospholipase C.

Uncoupled cerebral blood flow and metabolism after severe global ischemia in rats

In a rat model of complete global brain ischemia (neck tourniquet) lasting either 3 min or 20 min, we monitored global CBF (sagittal sinus H2 clearance) and CMRO2 for 6 h to test the hypothesis that delayed postischemic hyperemia and uncoupling of CBF and CMRO2 occur depending on the severity of the insult. Early postischemic hyperemia occurred in both the 3-min and 20-min groups (p less than 0.05 vs. baseline values) and resolved by 15 min. Hypoperfusion occurred in the 3-min group between 15 and 60 min postischemia (approximately 23% reduction), and in the 20-min group from 15 to 120 min postischemia (approximately 50% reduction) (p less than 0.05), and then resolved. CMRO2 was not significantly different from baseline at any time after ischemia in the 3-min group. After 20 min of ischemia, however, CMRO2 was decreased (approximately 60%) throughout the postischemic period (p less than 0.05). At 5 min after ischemia, CBF/CMRO2 was increased in both groups but returned to baseline from 60 to 120 min postischemia. In the 3-min group, CBF/CMRO2 remained at baseline throughout the rest of the experiment. However, in the 20-min group, CBF/CMRO2 once again increased (approximately 100%), reaching a significant level at 180 min and remaining so for the rest of the 6-h period (p less than 0.05). These data demonstrate biphasic uncoupling of CBF and CMRO2 after severe (20 min) global ischemia in rats. This relatively early reemergence of CBF/CMRO2 uncoupling after 180 min of reperfusion is similar to that observed after prolonged cardiac arrest and resuscitation in humans.

Infarct reduction by the platelet activating factor antagonist apafant in rats

BACKGROUND AND PURPOSE

Recent findings suggest a key role for platelet activating factor in neuroinjury. For this reason we evaluated the effects of the platelet activating factor antagonist apafant (4-(2-chlorophenyl)-9-methyl-2[3(4-morpholinyl)-3-propanol-1- yl[6H-thieno[3.2-f[[1.2.4]triazolo]4,3-1]]1.4]diazepine on farct volume and local cerebral blood flow following irreversible occlusion of the left middle cerebral artery in rats to assess the direct and vascular components of apafant's action.

METHODS

We measured infarct volume 48 hours after middle cerebral artery occlusion. The effect of multiple doses of apafant (30 mg/kg p.o.) was tested in both pretreatment (n = 8) and posttreatment (n = 8) groups. In the pretreatment group apafant was given 30 minutes before and 2, 6, and 18 hours after occlusion. Rats of the posttreatment group received apafant 1, 6, and 18 hours after middle cerebral artery occlusion. We also examined the effect of a single dose of apafant given 30 minutes prior to occlusion (n = 9) on local cerebral blood flow determined 2 hours after middle cerebral artery occlusion.

RESULTS

Both regimens of apafant effectively decreased infarct volume. The reduction in cortical infarct volume was 59% (p less than 0.01; H test, U test) when the rats were treated before and after vessel occlusion whereas the decrease was 47% (p less than 0.05; H test, U test) when treatment began 1 hour after occlusion. Apafant did not change local cerebral blood flow after occlusion compared with controls.

CONCLUSIONS

We suggest that the cytoprotection afforded by apafant occurs mainly via a direct effect on brain tissue and has no major vascular component.

Platelet-activating factor in stroke and brain injury

Platelet-activating factor, an endogenous phospholipid of proinflammatory, hemostatic, and vasoactive properties, is synthesized by neurons and in injured brain. Platelet-activating factor is released together with eicosanoids such as thromboxane A2, prostacyclin, and leukotrienes. Its effects in neurons are mediated through a specific receptor coupled to phospholipase C and phosphoinositol metabolism. The cerebrovascular effects of platelet-activating factor include disruption of the blood-brain barrier, edema formation, and vasospasm. It has also been described to possess direct toxicity to neuronal cells in culture. Discovery and development of several highly potent and selective antagonists to platelet-activating factor receptors facilitated experimental studies underscoring the role of this factor as an endogenous mediator in cerebral disorders, particularly cerebral ischemia and trauma. Significant biochemical, microvascular, functional, and behavioral recovery has been demonstrated using these antagonists in an array of experimental models of focal and global ischemia in the central nervous system (CNS). Clearly, studies of platelet-activating factor in experimental models of CNS ischemia and reperfusion injury open a new perspective on phospholipid metabolism in stroke and offer an exceptionally promising therapeutic prospect. Data supporting this factor as a mediator of specific pathological sequelae in stroke and neuroinjury are surveyed in this review. We discuss the mechanisms and significance of platelet-activating factor-mediated effects and propose directions for future studies.

Priming by platelet-activating factor of endotoxin-induced lung injury and cardiovascular shock

Platelet-activating factor (PAF) is a glycerophospholipid known for its unusual potent vasoactive and proinflammatory activities. The present study examined whether PAF might serve as a priming factor in endotoxin-induced tumor necrosis factor-alpha (TNF alpha) synthesis, cardiovascular shock, and lung injury in anesthetized rats. Intravenous infusion of PAF (1 pmol/kg/min for 60 minutes, n = 5) alone or endotoxin (0.1 micrograms/kg i.v. bolus, n = 5) failed to alter blood pressure, serum TNF alpha and thromboxane B2, platelet and leukocyte count, and hematocrit, nor was lung histology, myeloperoxidase activity, and water content changed. In contrast, the combined administration of PAF and endotoxin markedly elevated serum TNF alpha (1,359 +/- 362 pg/ml, n = 5, p less than 0.01) and thromboxane B2 (43 +/- 5 pg/100 microliters, n = 8, p less than 0.01) along with hypotension, hemoconcentration, leukopenia, and thrombocytopenia. Most notably, the combined regimen caused neutrophil aggregation, adhesion, and accumulation into the lung parenchyma along with platelet-fibrin deposits in postcapillary venules, pulmonary edema, and increased lung myeloperoxidase activity. The role of PAF in this process was confirmed by 1) the prevention of the priming effect by pretreatment with the PAF antagonist BN 50739 (n = 5), and 2) the failure of lyso-PAF, the cardinal nonactive PAF-metabolite, to prime for endotoxin-induced production of TNF alpha (n = 4). These data suggest that PAF could serve as a key mediator in priming for endotoxin-induced tissue injury, especially the typical pulmonary pathophysiology of adult respiratory distress syndrome, a severe pathological outcome of septic shock, burns, and multiple organ injury.

Characterization of platelet-activating factor-induced elevation of cytosolic free-calcium level in neurohybrid NCB-20 cells

The effect of platelet-activating factor on the intracellular cytosolic level of free calcium ([Ca2+]i) was studied in neurohybrid NCB-20 cells. In fura-2-loaded NCB-20 cells, platelet-activating factor induced an immediate and concentration-dependent increase in [Ca2+]i with a maximum increase of 334 +/- 27 nM above a basal value of 147 +/- 6 nM (n = 40). Platelet-activating factor-induced [Ca2+]i mobilization was inhibited by the platelet-activating factor antagonists BN 50739, WEB 2086, SRI 63-441 and BN 52021 in a dose-dependent manner with IC50 values of 12, 38, 897 and 45000 nM, respectively. The calcium-channel blockers nifedipine (10 microM) and diltiazem (10 microM) had no effect on the platelet-activating factor-induced increase in [Ca2+]i; however, extracellular Ca(2+)-depletion caused a 63.6 +/- 4.7% reduction of platelet-activating factor-induced increase in [Ca2+]i (n = 5, P less than 0.001). The remaining 36% contributed from intracellular sources was completely inhibited by 10 microM of 8-(N,N-diethylamine)octyl 3,4,5-trimethoxytenzoate hydrochloride (TMB-8). NCB-20 cells exhibited homologous desensitization to sequential addition of platelet-activating factor, but no heterologous desensitization between platelet-activating factor and bradykinin or ATP was observed. These data suggest that activation of the neuronal platelet-activating factor receptor results in an increase in [Ca2+]i primarily via a receptor-operated rather than a voltage-dependent calcium-channel and to a lesser extent from intracellular Ca2+ release. Our findings may contribute to an understanding of the mechanism of platelet-activating factor actions on neuronal cells.

Platelet-activating factor antagonists do not attenuate delayed posttraumatic cerebral edema in rats

Platelet-activating factor (PAF) receptor antagonists reportedly improve early postischemic neurological recovery and cerebral blood flow in selected experimental models. Their effects on posttraumatic cerebral edema have, however, not been examined. In a rat model of right hemispheric percussive cerebral trauma, we examined the effects of two PAF receptor antagonists on posttraumatic edema formation. Two groups of rats received either BN 52021 (n = 14) or WEB 2086 (n = 11), 10 mg/kg i.v. at 15 min posttrauma. Two other groups treated with the BN 52021 (n = 17) and WEB 2086 (n = 10) vehicles served as controls. Hemispheric percent brain water was determined at 24 h. Edema occurred in all groups. Neither PAF receptor antagonist significantly reduced right hemispheric percent brain water (81.08 +/- 0.25 and 81.04 +/- 0.15 in Bn 52021 and WEB 2086-treated rats, respectively, versus 81.31 +/- 0.23 and 81.14 +/- 0.17% brain water in BN 52021 vehicle and WEB 2086 vehicle-treated rats). Mortality was not statistically different between groups. These data do not support a major role for PAF in the development of posttraumatic cerebral edema.

Evidence for platelet-activating factor as a novel mediator in experimental stroke in rabbits

Platelet-activating factor is a potent mediator of inflammation, which has untoward effects on cerebrovascular and neural elements. While several investigators have reported attenuation of ischemic damage after treatment with antagonists of platelet-activating factor, no study has proved endogenous production of platelet-activating factor in ischemia of the central nervous system. We hypothesized that endogenous production of platelet-activating factor participates in the early pathologic manifestations of deteriorating stroke. In 12 rabbits, we found tissue levels of platelet-activating factor measured by the release of serotonin from washed platelets to be elevated by approximately 20-fold in spinal cord injured by 25 minutes of ischemia and 2 hours of reperfusion (2.80 +/- 0.98 ng/g) compared with that in normal spinal cord (0.15 +/- 0.06 ng/g, p less than 0.01). Given during ischemia to seven rabbits, 10 mg/kg i.p. of a highly selective and potent antagonist of platelet-activating factor (BN 50739) accentuated the early postischemic hyperemia and prevented the delayed hypoperfusion measured by on-line laser-Doppler flowmetry (-35 +/- 7% of baseline [n = 7] without versus 33 +/- 14% with treatment, p less than 0.01) and the edema formation measured as the increase in tissue water content (4.4 +/- 0.7% without [n = 6] versus 2.1 +/- 0.6% with [n = 7]treatment, p less than 0.05) after 2 hours of reperfusion. This neurochemical and pharmacologic evidence emphasizes a new perspective of ischemia-induced phospholipid degradation and suggests an important role for platelet-activating factor in the early manifestations of stroke.

Platelet-activating factor and progressive brain damage following focal brain injury

The effects of a platelet-activating factor (PAF) antagonist on brain edema, cortical microcirculation, blood-brain barrier (BBB) disruption, and neuronal death following focal brain injury are reported. A neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used to induce highly reproducible focal cortical lesions in anesthetized rats. Secondary brain damage in this model was characterized by progressive cortical hypoperfusion, edema, and BBB disruption in the vicinity of the hemispheroid lesion occurring acutely after injury. The histopathological evolution was followed for up to 4 days. Neuronal damage in the cortex and the hippocampus (CA-1) was assessed quantitatively, revealing secondary and progressive loss of neuronal tissue within the first 24 hours following injury. Pretreatment with the PAF antagonist BN 50739 ameliorated the severe hypoperfusion in 12 rats (increasing local cerebral blood flow from a mean +/- standard error of the mean of 40.5% +/- 8.3% to 80.2% +/- 7.8%, p less than 0.01) and reduced edema by 70% in 10 rats (p less than 0.05) acutely after injury. The PAF antagonist also reduced the progression of neuronal damage in the cortex and the CA-1 hippocampal neurons (decrease of neuronal death from 88.0% +/- 3.9% to 49.8% +/- 4.2% at 24 hours in the cortex and from 40.2 +/- 5.0% to 13.2% +/- 2.1% in the hippocampus in 30 rats; p less than 0.05). This study provides evidence to support progressive brain damage following focal brain injury, associated with secondary loss of neuronal cells. In this latter process, PAF antagonists may provide significant therapeutic protection in arresting secondary brain damage following cerebral ischemia and neurological trauma.

Actions of platelet-activating factor on isolated feline and human cerebral arteries

The effects of platelet-activating factor (PAF) were studied on isolated feline basilar arteries (BAs) and human pial arteries (PAs). PAF contracted the BAs by 67% of the contraction induced by 124 mM K+ and the PAs by 80%. The contraction in BAs was unaffected by both indomethacin and the thromboxane receptor antagonist AH23848. PAF relaxed prostaglandin F2 alpha-contracted arteries. In BAs 10(-6) M PAF reduced the contraction by 17% and in PAs by 47%. The relaxant effects in both arteries were unaffected by indomethacin. In conclusion, PAF can act both as a constrictor and as a dilator of isolated feline and human cerebral arteries. The effects are seemingly unrelated to vascular prostanoid production.

Endogenous platelet activating factor does not modulate blood flow and metabolism in normal rat brain

Both platelet activating factor and eicosanoids participate in the cerebrovascular response to ischemia. Eicosanoids also modulate cerebrovascular tone under normal physiologic circumstances, but a similar role for platelet activating factor has not been investigated. Therefore, using 16 rats, we studied the effects of the platelet activating factor receptor blockers BN 52021 (10 mg/kg, n = 4 or 30 mg/kg, n = 2) and WEB 2086 (5 mg/kg, n = 6) on global cerebral blood flow and the cerebral metabolic rate for oxygen and compared them with the effect of indomethacin (10 mg/kg, n = 4). Neither antagonist altered cerebral blood flow (112 +/- 16 and 107 +/- 14 ml/100 g/min at baseline versus 108 +/- 16 and 105 +/- 18 ml/100 g/min after BN 52021 and WEB 2086, respectively). In contrast, indomethacin significantly (p less than 0.05) decreased cerebral blood flow from 106 +/- 8 to 69 +/- 4 ml/100 g/min. No treatment altered the cerebral metabolic rate for oxygen compared with baseline. These data suggest that in normal rat brain, concentrations of platelet activating factor, unlike those of eicosanoids, are subthreshold and do not modulate cerebral blood flow or the cerebral metabolic rate for oxygen.

Early polymorphonuclear leukocyte accumulation correlates with the development of posttraumatic cerebral edema in rats

To evaluate the role of polymorphonuclear leukocytes (PMNs) in the development of posttraumatic cerebral edema, we quantitatively assessed the time course and magnitude of PMN accumulation and its relationship to cerebral edema formation after cerebral trauma in 78 rats. 111In-labeled PMN accumulation was measured in 26 rats in the first 8 h after right hemispheric percussive cerebral trauma or a sham control condition. 51Cr-labeled erythrocyte accumulation was measured simultaneously in 22 rats to assess the contribution of expansion of blood volume to early posttraumatic PMN accumulation. Edema formation [right-left (R-L) hemispheric difference in percent brain water], R-L hemispheric labeled-PMN accumulation, and blood volume index-adjusted PMN accumulation were measured between 0-2 h and 4-8 h posttrauma. PMN accumulation was elevated markedly in the first 2 h posttrauma compared with values in sham controls (13.45 +/- 2.53 vs -0.03 +/- 0.31, p less than 0.01) but not when adjusted for blood volume index (BVI), suggesting that PMN accumulation in the first 2 h posttrauma was due to expansion of blood volume. Between 4 and 8 h posttrauma, however, both total (2.56 +/- 0.82 vs -0.29 +/- 0.52) and BVI-adjusted (8.78 +/- 3.97 vs -0.48 +/- 0.79) PMN accumulation were elevated (p less than 0.05) compared with sham. Brain edema and total PMN accumulation were significantly correlated at both 2 h and 8 h posttrauma (r2 = 0.77, p less than 0.001, and r2 = 0.69, p less than 0.002, respectively), but a significant correlation between edema and BVI-adjusted PMN accumulation was observed only at 8 h posttrauma (r2 = 0.96, p less than 0.001). These data show that PMN accumulation after traumatic brain injury occurs with an initial phase explained by an increase in blood volume in the first 2 h posttrauma followed by a subsequent acute inflammatory phase. The significant correlation between PMN accumulation and the development of cerebral edema is the first quantitative relationship demonstrated between PMN accumulation and a relevant pathophysiological variable. A causal role for PMNs in the genesis of posttraumatic cerebral edema has yet to be proved.

Platelet-activating factor stimulates a fos/jun/AP-1 transcriptional signaling system in human neuroblastoma cells

Platelet-activating factor (PAF) elicits a rapid and transient activation of the proto-oncogenes c-fos and c-jun in SH-SY5Y neuroblastoma cells, but only to a minor extent in Molt-4 T-lymphocytes. This effect is inhibited by pretreatment of cells with the PAF antagonist BN 52021, suggesting the involvement of a specific receptor. Moreover, PAF treatment can activate gene expression through an AP-1 element, and we propose that genomic trans-activation may occur in target genes containing a functional AP-1 transcription sequence. These results may further understanding of the molecular mechanisms by which PAF contributes to long-term phenotypic changes in the nervous system.