Platelet-activating factor antagonist BN 50730 attenuates hypoxic-ischemic brain injury in neonatal rats

Plasma Lipolysis and Changes in Plasma and Cerebrospinal Fluid Signaling Lipids Reveal Abnormal Lipid Metabolism in Chronic Migraine

Background

Lipids are a primary storage form of energy and the source of inflammatory and pain signaling molecules, yet knowledge of their importance in chronic migraine (CM) pathology is incomplete. We aim to determine if plasma and cerebrospinal fluid (CSF) lipid metabolism are associated with CM pathology.

Methods

We obtained plasma and CSF from healthy controls (CT, n = 10) or CM subjects (n = 15) diagnosed using the International Headache Society criteria. We measured unesterified fatty acid (UFA) and esterified fatty acids (EFAs) using gas chromatography-mass spectrometry. Glycerophospholipids (GP) and sphingolipid (SP) levels were determined using LC-MS/MS, and phospholipase A₂ (PLA₂) activity was determined using fluorescent substrates.

Results

Unesterified fatty acid levels were significantly higher in CM plasma but not in CSF. Unesterified levels of five saturated fatty acids (SAFAs), eight monounsaturated fatty acids (MUFAs), five ω-3 polyunsaturated fatty acids (PUFAs), and five ω-6 PUFAs are higher in CM plasma. Esterified levels of three SAFAs, eight MUFAs, five ω-3 PUFAs, and three ω-6 PUFAs, are higher in CM plasma. The ratios C20:4n-6/homo-γ-C20:3n-6 representative of delta-5-desaturases (D5D) and the elongase ratio are lower in esterified and unesterified CM plasma, respectively. In the CSF, the esterified D5D index is lower in CM. While PLA₂ activity was similar, the plasma UFA to EFA ratio is higher in CM. Of all plasma GP/SPs detected, only ceramide levels are lower (p = 0.0003) in CM (0.26 ± 0.07%) compared to CT (0.48 ± 0.06%). The GP/SP proportion of platelet-activating factor (PAF) is significantly lower in CM CSF.

Conclusions

Plasma and CSF lipid changes are consistent with abnormal lipid metabolism in CM. Since plasma UFAs correspond to diet or adipose tissue levels, higher plasma fatty acids and UFA/EFA ratios suggest enhanced adipose lipolysis in CM. Differences in plasma and CSF desaturases and elongases suggest altered lipid metabolism in CM. A lower plasma ceramide level suggests reduced de novo synthesis or reduced sphingomyelin hydrolysis. Changes in CSF PAF suggest differences in brain lipid signaling pathways in CM. Together, this pilot study shows lipid metabolic abnormality in CM corresponding to altered energy homeostasis. We propose that controlling plasma lipolysis, desaturases, elongases, and lipid signaling pathways may relieve CM symptoms.

Differential Effects of Pentoxifylline on Learning and Memory Impairment Induced by Hypoxic-ischemic Brain Injury in Rats

Objective

Hypoxic-ischemic (HI) brain injury in the human perinatal period often leads to significant long-term neurobehavioral dysfunction in the cognitive and sensory-motor domains. Using a neonatal HI injury model (unilateral carotid ligation followed by hypoxia) in postnatal day seven rats, the present study investigated the long-term effects of HI and potential behavioral protective effect of pentoxifylline.

Methods

Seven-day-old rats underwent right carotid ligation, followed by hypoxia (F_iO₂ = 0.08). Rats received pentoxifylline immediately after and again 2 hours after hypoxia (two doses, 60‒100 mg/kg/dose), or serum physiologic. Another set of seven-day-old rats was included to sham group exposed to surgical stress but not ligated. These rats were tested for spatial learning and memory on the simple place task in the Morris water maze from postnatal days 77 to 85.

Results

HI rats displayed significant tissue loss in the right hippocampus, as well as severe spatial memory deficits. Low-dose treatment with pentoxifylline resulted in significant protection against both HI-induced hippocampus tissue losses and spatial memory impairments. Beneficial effects are, however, negated if pentoxifylline is administered at high dose.

Conclusion

These findings indicate that unilateral HI brain injury in a neonatal rodent model is associated with cognitive deficits, and that low dose pentoxifylline treatment is protective against spatial memory impairment.

Platelet activating factors in depression and coronary artery disease: a potential biomarker related to inflammatory mechanisms and neurodegeneration

The persistence of a depressive episode in coronary artery disease (CAD) patients not only heightens the risk of acute ischemic events, but it is also associated with accelerated cognitive decline. Antidepressant interventions for depression in CAD have only modest effects and novel approaches are limited by a poor understanding of etiological mechanisms. This review proposes that the platelet activating factor (PAF) family of lipids might be associated with the persistence of a depressive episode and related neurodegenerative pathology in CAD due to their association with leading etiological mechanisms for depression in CAD such as inflammation, oxidative and nitrosative stress, vascular endothelial dysfunction, and platelet reactivity. The evidence implicating PAFs in CAD, vascular pathology, and neurodegenerative processes is also presented. We also propose future directions for the investigation of PAFs as mediators of persistent depression. In summary, PAFs are implicated in leading mechanisms associated with depression in CAD. PAFs may therefore be associated with the persistence of depression in CAD and related to neurodegenerative and cognitive sequelae.

Apoptotic mechanisms in the immature brain: involvement of mitochondria

Brain injury after hypoxic-ischemic encephalopathy often develops with delayed appearance, opening a therapeutic window. Clinical studies in newborns show that post-hypoxic-ischemic hypothermia improves outcome. This has generated renewed interest in the molecular mechanisms of hypoxic-ischemic brain injury. In this brief review, we propose that mitochondrial permeabilization is crucial for injury to advance beyond the point of no return. We suggest that excitatory amino acids, nitric oxide, inflammation, trophic factor withdrawal, and an increased pro- versus antiapoptotic Bcl-2 protein ratio will trigger Bax-dependent mitochondrial outer membrane permeabilization. Mitochondrial outer membrane permeabilization, in turn, elicits mitochondrial release of cytochrome C, apoptosis-inducing factor, second mitochondria-derived activator of caspase/Diablo, and HtrA2/Omi. Cytochrome C efflux activates caspase-9/-3, leading to DNA fragmentation. Apoptosis-inducing factor interacts with cyclophilin A and induces chromatinolysis. Blockage of mitochondrial outer membrane permeabilization holds promise as a strategy for perinatal brain protection.

Developmental motor deficits induced by combined fetal exposure to lipopolysaccharide and early neonatal hypoxia/ischemia: a novel animal model for cerebral palsy in very premature infants

A critical issue in animal models of perinatal brain injury is to adapt the pertinent pathophysiological scenarios to their corresponding developmental window in order to induce neuropathological and behavioral characteristics reminiscent to perinatal cerebral palsy (CP). A major problem in most of these animal models designed up to now is that they do not present motor deficits characteristic of CP. Using a unique rat paradigm of prenatal inflammation combined to an early postnatal hypoxia-ischemia pertinent to the context of very early premature human newborns, we were interested in finding out if such experimental conditions might reproduce both histological damages and behavioral deficits previously described in the human context. We showed that exposure to lipopolysaccharide (LPS) or hypoxia-ischemia (H/I) induced behavioral alterations in animals subjected to forced motor activity. When both LPS and H/I aggressions were combined, the motor deficits reached their highest intensity and affected both spontaneous and forced motor activities. LPS+H/I-exposed animals also showed extensive bilateral cortical and subcortical lesions of the motor networks affecting the frontal cortices and underlying white matters fascicles, lenticular nuclei and the substantia nigra. These neuropathological lesions and their associated motor behavioral deficits are reminiscent of those observed in very preterm human neonates affected by subsequent CP and validate the value of the present animal model to test new therapeutic strategies which might open horizons for perinatal neuroprotection.

Down-regulation of platelet-activating factor receptor gene expression during focal reversible cerebral ischemia in rats

Platelet-activating factor (PAF) is an endogenous potent phospholipid mediator in stroke and related to the post-ischemic brain damage. The aim of this study was to investigate the regulation and mechanisms of PAF receptor gene expression in the perifocal regions of cerebral infarction after middle cerebral artery occlusion/reperfusion. Sixty mature Wistar rats were randomly divided into 12 groups: sham-operated control group, simple ischemia 90 min group, 6, 12, 18 h, 1 day (1 d), 2, 3, 4, 5, 6, 7 d reperfusion groups. After the right middle cerebral artery occluded, the rats were suffered from ischemia for 90 min, and then reperfusion was allowed for different time courses. Reverse transcription-polymerase chain reaction (RT-PCR) and radioimmunoassay were applied to evaluate the PAF receptor messenger RNA (mRNA) expression and PAF levels in the perifocal regions of cerebral infarction respectively. RT-PCR analysis revealed that PAF receptor mRNA was 0.95 +/- 0.15 in control group. However, following ischemia-reperfusion, the levels of PAF receptor mRNA progressively decreased until 2 d of reperfusion (0.54 +/- 0.10), then returned to control group's levels gradually. Compared with the control group's (582 +/- 72 pg/g wet weight), the PAF concentrations of simple ischemic and 6, 12, 18 h, 1, 2 d reperfusion group were significantly higher than that of any other groups. These results indicate that PAF receptor gene expression may be subject to down-regulation in the perifocal regions of cerebral infarction after cerebral ischemia-reperfusion and relative to the increase of endogenous PAF concentrations.

Platelet-activating factor antagonist (ABT-491) decreases neuronal apoptosis in neonatal rat model of hypoxic ischemic brain injury

Hypoxic ischemic brain injury (HIBI) is a common cause of neonatal mortality and morbidity. To date, no study has investigated the role of platelet-activating factor (PAF) antagonists on neuronal apoptosis in neonatal rat model of HIBI. In the present study, we evaluated the effect of a highly potent and selective PAF antagonist (ABT-491) on neuronal apoptosis in neonatal rat model of HIBI. Seven-day-old Wistar rat pups were subjected to right common carotid artery ligation and hypoxia (92% nitrogen and 8% oxygen) for 2 h. They were treated with ABT-491 or saline either immediately before or after hypoxia. In sham group animals, neither ligation, nor hypoxia was performed. Neuronal apoptosis was evaluated by the terminal-transferase mediated dUTP biotin nick-end-labeling (TUNEL) and caspase-3 staining methods. Administration of ABT-491 either before or after hypoxia resulted in significant reduction of the numbers of apoptotic cells in both hemispheres, when compared to saline treatment group. The numbers of apoptotic cells in right hemispheres in all groups were significantly higher than that in the left hemispheres. These results suggested that ABT-491, a highly potent and selective PAF antagonist, administration either before or after hypoxia reduces apoptosis and we propose that ABT-491 may be a novel approach in the treatment of HIBI.

Changes in self-reactive IgG antibody repertoire after treatment of experimental autoimmune encephalomyelitis with anti-allergic drugs

We reduced EAE severity by using two anti-allergic drugs. A control group of mice received i.p. injections of PBS as vehicle while a further two groups were treated either with pyrilamine, a histamine receptor 1 antagonist or with CV6209, a platelet activating factor receptor antagonist. Our results showed that the blockade of the responses to both histamine and PAF leads together to a decline in clinical signs of EAE and significant changes in the serum IgG recognition of some healthy brain antigenic targets. We characterized two discriminant antigens: internexin neuronal intermediate filament protein, and malate dehydrogenase 1, which were able to clearly distinguish untreated mice from treated mice. Their role as potent targets in pathogenic and/or neuroprotective processes is discussed.

Intracrine signaling through lipid mediators and their cognate nuclear G-protein-coupled receptors: a paradigm based on PGE2, PAF, and LPA1 receptors

Prostaglandins (PGs), platelet-activating factor (PAF), and lysophosphatidic acid (LPA) are ubiquitous lipid mediators that play important roles in inflammation, cardiovascular homeostasis, and immunity and are also known to modulate gene expression of specific pro-inflammatory genes. The mechanism of action of these lipids is thought to be primarily dependent on their specific plasma membrane receptors belonging to the superfamily of G-protein-coupled receptors (GPCR). Increasing evidence suggests the existence of a functional intracellular GPCR population. It has been proposed that immediate effects are mediated via cell surface receptors whereas long-term responses are dependent upon intracellular receptor effects. Indeed, receptors for PAF, LPA, and PGE(2) (specifically EP(1), EP(3), and EP(4)) localize at the cell nucleus of cerebral microvascular endothelial cells of newborn pigs, rat hepatocytes, and cells overexpressing each receptor. Stimulation of isolated nuclei with these lipids reveals biological functions including transcriptional regulation of major genes, namely c-fos, cylooxygenase-2, and endothelial as well as inducible nitric oxide synthase. In the present review, we shall focus on the nuclear localization and signaling of GPCRs recognizing PGE(2), PAF, and LPA phospholipids as ligands. Mechanisms on how nuclear PGE2, PAF, and LPA receptors activate gene transcription and nuclear localization pathways are presented. Intracrine signaling for lipid mediators uncover novel pathways to elicit their effects; accordingly, intracellular GPCRs constitute a distinctive mode of action for gene regulation.

Intracellular signaling of lipid mediators via cognate nuclear G protein-coupled receptors

Platelet-activating factor (PAF) and lysophosphatidic acid (LPA) are ubiquitous lipid mediators that play important roles in inflammation, cardiovascular homeostasis, and immunity and are also known to modulate gene expression of specific proinflammatory genes. The mechanism of action of these phospholipids is thought to be primarily dependent on their specific plasma membrane receptors belonging to the superfamily of G protein-coupled receptors (GPCRs). However, increasing evidence suggests the existence of a functional intracellular GPCR population. It has been suggested that immediate effects are mediated by cell surface receptors, whereas long-term responses are mediated by intracellular receptors. PAF and LPA(1) receptors localize at the cell nucleus of cerebral microvascular endothelial cells of newborn pig, rat hepatocytes, and cells overexpressing each receptor, and stimulation of isolated nuclei reveal biological functions, including transcriptional regulation of major genes, namely cylooxygenase-2 and inducible nitric oxide synthase. This mini review focuses on the nuclear localization and signaling of GPCRs, recognizing PAF and LPA phospholipids as ligands. Theories on how nuclear PAF and LPA1 receptors activate gene transcription and nuclear localization pathways are discussed. Intracrine signaling for lipid mediators uncover novel pathways to elicit their effects; moreover, intracellular GPCRs constitute a distinctive mode of action for gene regulation.

New insights into the retinal circulation: inflammatory lipid mediators in ischemic retinopathy

Ischemic proliferative retinopathy develops in various retinal disorders, including retinal vein occlusion, diabetic retinopathy and retinopathy of prematurity. Ischemic retinopathy remains a common cause of visual impairment and blindness in the industrialized world due to relatively ineffective treatment. Oxygen-induced retinopathy (OIR) is an established model of retinopathy of prematurity associated with vascular cell injury culminating in microvascular degeneration, which precedes an abnormal neovascularization. The retina is a tissue particularly rich in polyunsaturated fatty acids and the ischemic retina becomes highly sensitive to lipid peroxidation initiated by oxygenated free radicals. Consequently, the retina constitutes an excellent model for testing the functional consequences of membrane lipid peroxidation. Retinal tissue responds to physiological and pathophysiological stimuli by the activation of phospholipases and the consequent release from membrane phospholipids of biologically active metabolites. Activation of phospholipase A(2) is the first step in the synthesis of two important classes of lipid second messengers, the eicosanoids and a membrane-derived phospholipid mediator platelet-activating factor (PAF). These lipid mediators accumulate in the retina in response to injury and a physiologic role of these metabolites in retinal vasculature remains for the most part to be determined; albeit proposed roles have been suggested for some. The eicosanoids, in particular the prostanoids, thromboxane (TXA2) and PAF are abundantly generated following an oxidant stress and contribute to neurovascular injury. TXA2 and PAF play an important role in the retinal microvacular degeneration of OIR by directly inducing endothelial cell death and potentially could contribute to the pathogenesis of ischemic retinopathies. Despite these advances there are still a number of important questions that remain to be answered before we can confidently target pathological signals. This review focuses on mechanisms that precede the development of neovascularization, most notably regarding the role of lipid mediators that partake in microvascular degeneration.

Preterm fetal hypoxia-ischemia causes hypertonia and motor deficits in the neonatal rabbit: a model for human cerebral palsy?

Prenatal hypoxia-ischemia to the developing brain has been strongly implicated in the subsequent development of the hypertonic motor deficits of cerebral palsy (CP) in premature and full-term infants who present with neonatal encephalopathy. Despite the enormous impact of CP, there is no animal model that reproduces the hypertonia and motor disturbances of this disorder. We report a rabbit model of in utero placental insufficiency, in which hypertonia is accompanied by marked abnormalities in motor control. Preterm fetuses (67-70% gestation) were subjected to sustained global hypoxia. The dams survived and gave spontaneous birth. At postnatal day 1, the pups that survived were subjected to a battery of neurobehavioral tests developed specifically for these animals, and the tests were videotaped and scored in a masked manner. Newborn pups of hypoxic groups displayed significant impairment in multiple tests of spontaneous locomotion, reflex motor activity, and the coordination of suck and swallow. Increased tone of the limbs at rest and with active flexion and extension were observed in the survivors of the preterm insult. Histopathological studies identified a distinct pattern of acute injury to subcortical motor pathways that involved the basal ganglia and thalamus. Persistent injury to the caudate putamen and thalamus at P1 was significantly correlated with hypertonic motor deficits in the hypoxic group. Antenatal hypoxia-ischemia at preterm gestation results in hypertonia and abnormalities in motor control. These findings provide a unique behavioral model to define mechanisms and sequelae of perinatal brain injury from antenatal hypoxia-ischemia.

Brain injury and neurofunctional deficit in neonatal mice with hypoxic-ischemic encephalopathy

Birth asphyxia accounts for the majority of developmental motor and cognitive deficits. Studies were undertaken to develop a reproducible murine model of perinatal hypoxic-ischemic encephalopathy (HIE) which would permit both anatomic and neurofunctional quantification of injury. Short-term neurofunctional outcomes consisted of three developmental reflexes (righting, cliff aversion and geotaxis) assessed in 7-day-old mouse pups 24 h after unilateral carotid artery ligation followed by inhalation of 8% oxygen. Cerebral infarct volume was dependent on duration of hypoxia, being approximately 2.5-fold greater with longer (60 min) versus shorter (30 min) hypoxia exposure (P=0.001). All three sensorimotor neonatal reflexes assessed at 24 h after HIE injury correlated significantly with long-term neurofunction evaluated using a water-maze test of navigational learning and memory assessed 8 weeks later in the same animals. Cerebral atrophy, a delayed consequence of HIE in this model, also correlated strongly with water-maze performance (r=0.86, P=0.002). These data demonstrate for the first time that murine neonatal sensorimotor reflex performance can be rigorously quantified in the acute phase of perinatal HIE and has strong predictive value not only for anatomic extent of cerebral injury, but also for long-term neurofunctional outcome.

Pathogenesis of hypoxic-ischemic cerebral injury in the term infant: current concepts

Multiple, biochemical cascades contribute to the pathogenesis of neonatal hypoxic-ischemic brain injury. This article summarizes experimental evidence that supports the role of excitatory amino acids, calcium, free radicals, nitric oxide, proinflammatory cytokines, and bioactive lipids. Specific vulnerabilities that distinguish the response of the immature brain from that of the mature brain are highlighted. These include increased susceptibility to excitotoxicity and free radical injury, greater tendency to apoptotic death, and heightened vulnerability of developing oligodendrocytes. Available supportive evidence from human studies is also included. Implications for clinical neuroprotective strategies are discussed.

Proinflammatory gene induction by platelet-activating factor mediated via its cognate nuclear receptor

It has been postulated that intracellular binding sites for platelet-activating factor (PAF) contribute to proinflammatory responses to PAF. Isolated nuclei from porcine cerebral microvascular endothelial cells (PCECs) produced PAF-molecular species in response to H(2)O(2). Using FACS analysis, we demonstrated the expression of PAF receptors on cell and nuclear surfaces of PCECs. Confocal microscopy studies performed on PCECs, Chinese hamster ovary cells stably overexpressing PAF receptors, and isolated nuclei from PCECs also showed a robust nuclear distribution of PAF receptors. Presence of PAF receptors at the cell nucleus was further revealed in brain endothelial cells by radioligand binding experiments, immunoblotting, and in situ in brain by immunoelectron microscopy. Stimulation of nuclei with methylcarbamate-PAF evoked a decrease in cAMP production and a pertussis toxin-sensitive rise in nuclear calcium, unlike observations in plasma membrane, which exhibited a pertussis toxin-insensitive elevation in inositol phosphates. Moreover, on isolated nuclei methylcarbamate-PAF evoked the expression of proinflammatory genes inducible nitric oxide synthase and cyclooxygenase-2 (COX-2) and was associated with augmented extracellular signal-regulated kinase 1/2 phosphorylation and NF-kappaB binding to the DNA consensus sequence. COX-2 expression was prevented by mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 and NF-kappaB inhibitors. This study describes for the first time the nucleus as a putative organelle capable of generating PAF and expresses its receptor, which upon stimulation induces the expression of the proinflammatory gene COX-2.

Huperzine A attenuates cognitive deficits and brain injury in neonatal rats after hypoxia-ischemia

The protective effects of huperzine A, a novel acetylcholinesterase inhibitor, on hypoxic-ischemic (HI) brain injury were investigated in neonatal rats. A unilateral HI brain injury was produced by the ligation of left common carotid artery followed by 1 h hypoxia with 7.7% oxygen in 7-day-old rat pups. After 5 weeks, HI brain injury in rat pups resulted in working memory impairments shown by increased escape latency in a water maze and reduced time spent in the target quadrant. The combination of common carotid artery ligation and exposure to a hypoxic environment caused the damage in the striatum, cortex, and hippocampus in the ipsilateral hemisphere, and the neuronal loss in the CA1 region. Huperzine A was administrated daily at the dose of 0.05 or 0.1 mg/kg i.p. for 5 weeks after HI injury. The significant protection against HI injury on behavior and neuropathology was produced by huperzine A at the dose of 0.1 mg/kg. These findings suggest that huperzine A might be beneficial in the treatment of hypoxic-ischemic encephalopathy in neonates.