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

Cytotoxicity and molecular docking analysis of racemolactone I, a new sesquiterpene lactone isolated from Inula racemosa

CONTEXT

Traditionally, Inula racemosa Hook. f. (Asteraceae) has been reported to be effective in cancer treatment which motivated the authors to explore the plant for novel anticancer compounds.

OBJECTIVE

To isolate and characterize new cytotoxic phytoconstituents from I. racemosa roots.

MATERIALS AND METHODS

The column chromatography of I. racemosa ethyl acetate extract furnished a novel sesquiterpene lactone whose structure was established by NMR (1D/2D), ES-MS and its cytotoxic properties were assessed on HeLa, MDAMB-231, and A549 cell lines using MTT and LDH (lactate dehydrogenase) assays. Further, morphological changes were analyzed by flow cytometry, mitochondrial membrane potential, AO-EtBr dual staining, and comet assay. Molecular docking and simulation were performed using Glide and Desmond softwares, respectively, to validate the mechanism of action.

RESULTS

The isolated compound was identified as racemolactone I (compound 1). Amongst the cell lines tested, considerable changes were observed in HeLa cells. Compound 1 (IC50 = 0.9 µg/mL) significantly decreased cell viability (82%) concomitantly with high LDH release (76%) at 15 µg/mL. Diverse morphological alterations along with significant increase (9.23%) in apoptotic cells and decrease in viable cells were observed. AO-EtBr dual staining also confirmed the presence of 20% apoptotic cells. A gradual decrease in mitochondrial membrane potential was observed. HeLa cells showed significantly increased comet tail length (48.4 µm), indicating broken DNA strands. In silico studies exhibited that compound 1 binds to the active site of Polo-like kinase-1 and forms a stable complex.

CONCLUSIONS

Racemolactone I was identified as potential anticancer agent, which can further be confirmed by in vivo investigations.

Role of Ginkgolides in the Inflammatory Immune Response of Neurological Diseases: A Review of Current Literatures

The inflammatory immune response (IIR) is a physiological or excessive systemic response, induced by inflammatory immune cells according to changes in the internal and external environments. An excessive IIR is the pathological basis for the generation and development of neurological diseases. Ginkgolides are one of the important medicinal ingredients in Ginkgo biloba. Many studies have verified that ginkgolides have anti-platelet-activating, anti-apoptotic, anti-oxidative, neurotrophic, and neuroimmunomodulatory effects. Inflammatory immunomodulation is mediated by inhibition of the mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways. They also inhibit the platelet-activating factor (PAF)-mediated signal transduction to attenuate the inflammatory response. Herein, we reviewed the studies on the roles of ginkgolides in inflammatory immunomodulation and suggested its potential role in novel treatments for neurological diseases.

Ginkgo biloba extract and its diterpene ginkgolide constituents ameliorate the metabolic disturbances caused by recombinant tissue plasminogen activator in rat prefrontal cortex

INTRODUCTION

Although recombinant tissue plasminogen activator (rtPA) is a widely used therapy in patients with acute ischemic stroke, rtPA-induced toxicity or its adverse effects have been reported in our previous studies. However, Ginkgo biloba extract (GBE) may provide neuroprotective effects against rtPA-induced toxicity. Thus, in the present study, we investigated whether a single administration of rtPA caused neurotoxicity in the prefrontal cortex (PFC) of rats and determined whether GBE or its diterpene ginkgolide (DG) constituents were neuroprotective against any rtPA-induced toxicity.

MATERIALS AND METHODS

We randomly divided adult Sprague-Dawley rats into four groups that were intravenously administered saline, rtPA, rtPA+DG, or rtPA+GBE. The rats were sacrificed 24 hours later and the whole brain removed. A gas chromatography-mass spectrometry metabolomic approach was used to detect molecular changes in the PFC among the groups. Multivariate statistical and pathway analyses were used to determine the relevant metabolites as well as their functions and pathways.

RESULTS

We found 32 metabolites differentially altered in the four groups that were primarily involved in neurotransmitter, amino acid, energy, lipid, and nucleotide metabolism. Our results indicated that a single rtPA administration caused metabolic disturbances in the PFC. Both GBE and DG effectively ameliorated these rtPA-induced disturbances, although DG better controlled the rtPA-induced glutamate and aspartate excitotoxicity and the activation of NMDA receptor.

CONCLUSION

Our results provide important novel mechanistic insights into the adverse effects of rtPA and offer directions for future exploration on the thrombolytic effects of rtPA combined with the administration of DG or GBE for the treatment of acute ischemic stroke in humans.

Evaluation of in vitro inhibition and induction of cytochrome P450 activities by hydrolyzed ginkgolides

ETHNOPHARMACOLOGICAL RELAVANCE

The extracts of Ginkgo biloba leaves are effective in treating cerebral infarction, of which ginkgolides have been demonstrated to be the active ingredients. The purpose of this study was to determine whether hydrolyzed ginkgolides would cause potential drug-drug interactions (DDI) during its clinical use via inhibition or induction of the major human cytochrome P450s (CYPs).

MATERIALS AND METHODS

The inhibition (direct and metabolism-dependent inhibiton on CYP activities) and induction (mRNA expression level and activity of CYPs) by the hydrolyzed ginkgolides were evaluated in human liver microsomes and cryopreserved human hepatocytes, respectively.

RESULTS

Within 0.1 to 10μg/mL, the hydrolyzed ginkgolides showed negligible direct inhibition against CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4m (midazolam as substrate) and 3A4t (testosterone as substrate), with IC50 values determined to be >10μg/mL (concentrations expressed as the sum of equivalent concentrations of ginkgolide A, B and K). For the metabolism-dependent inhibition studies, the preincubation of 30min did not substantially alter the IC50 values when compared with the corresponding values in the direct inhibition studies. The activities and mRNA expression levels for CYP1A2 and 2B6 within each drug-treated group (0.1, 1 and 10μg/mL) were not affected after the 48-h incubation. For CYP3A4, the activity and mRNA expression level were not altered when incubated with 0.1 and 1μg/mL of hydrolyzed ginkgolides. When incubated with hydrolyzed ginkgolides at 10μg/mL, the relative activity and relative mRNA expression level of CYP3A4 remarkably increased to 4.59±3.67 and 17.2±9.16-fold of the corresponding vehicle control values, respectively.

CONCLUSIONS

The hydrolyzed ginkgolides is not likely to cause DDI via inhibition of the major human CYPs. However, the CYP3A4 induction might be clinically relevant.

Sesquiterpenoids lactones: benefits to plants and people

Sesquiterpenoids, and specifically sesquiterpene lactones from Asteraceae, may play a highly significant role in human health, both as part of a balanced diet and as pharmaceutical agents, due to their potential for the treatment of cardiovascular disease and cancer. This review highlights the role of sesquiterpene lactones endogenously in the plants that produce them, and explores mechanisms by which they interact in animal and human consumers of these plants. Several mechanisms are proposed for the reduction of inflammation and tumorigenesis at potentially achievable levels in humans. Plants can be classified by their specific array of produced sesquiterpene lactones, showing high levels of translational control. Studies of folk medicines implicate sesquiterpene lactones as the active ingredient in many treatments for other ailments such as diarrhea, burns, influenza, and neurodegradation. In addition to the anti-inflammatory response, sesquiterpene lactones have been found to sensitize tumor cells to conventional drug treatments. This review explores the varied ecological roles of sesquiterpenes in the plant producer, depending upon the plant and the compound. These include allelopathy with other plants, insects, and microbes, thereby causing behavioural or developmental modification to these secondary organisms to the benefit of the sesquiterpenoid producer. Some sesquiterpenoid lactones are antimicrobial, disrupting the cell wall of fungi and invasive bacteria, whereas others protect the plant from environmental stresses that would otherwise cause oxidative damage. Many of the compounds are effective due to their bitter flavor, which has obvious implications for human consumers. The implications of sesquiterpenoid lactone qualities for future crop production are discussed.

The pharmacokinetics and conversion of the lactone to the carboxylate forms of ginkgolide B in rat plasma

Ginkgolide B consists of three lactone groups, which may undergo hydrolysis, and lead to the rings opening in aqueous solution with different pHs. From mechanisms of pharmacological activity in vivo, the lactone appears to be the active form of the drug. Pharmacokinetics of lactone form (GB-lac) and the total of the lactone and carboxylate form (GB-tot) of ginkgolide B were investigated after intravenous administration of a dose of 4 mg/kg ginkgolide B. The rate of lactone hydrolysis was also studied in plasma in vitro. After intravenous administration, ginkgolide B in the original form was converted to its carboxylate form under simulated physiological conditions. The AUC0 - ∞ of GB-lac constituted 63.5 ± 17.4% of the AUC0 - ∞ of GB-tot. The ratio of average cumulation of excretion of lactone to carboxylate reached approximately 1 to 1 in urine. From the equilibrium of lactone hydrolysis in rat plasma in vitro, the k obs was - 0.0176 min(- 1) and t 1/2 was 39.38 min. In conclusion, the equilibrium existed between lactone of ginkgolide B and its carboxylate form in vivo at physiological pH, which suggested that more attention should be focused on the original and the ionization forms of ginkgolide B and the conversion of the lactone into carboxylate in vivo.

Identification of ginkgolide B metabolites in urine and rat liver cytochrome P450 enzymes responsible for their formation in vitro

AIM

To identify metabolites of ginkgolide B in rat urine, the predominant metabolism of ginkgolide B and the major cytochrome (CYP) P450 enzymes responsible for the metabolism of ginkgolide B in rat liver microsomes.

METHODS

A liquid chromatography quadrupole mass spectrometer and liquid chromatography ion-trap-time-of-flight mass spectrometer with electrospray ionization in negative-ion mode were used for the structure elucidation of metabolites in rat urine and liver microsome incubation. Various selective CYP450 inhibitors were applied to investigate their effects on the metabolism of ginkgolide B and the formation of the major metabolite in rat liver microsomes.

RESULTS

Three metabolites were identified in rat urine. One hydroxyl metabolite of ginkgolide B were identified in rat liver microsomes, and quinidine uncompetitively inhibited the formation of the metabolite; its inhibitor constant (Ki) value for the inhibition of hydroxyl metabolite was estimated to be 8 micromol/L, while alpha-naphthoflavone, ketoconazole, sulfaphenazole, and diethyldithiocarbamate had no inhibitory effects.

CONCLUSION

Ginkgolide B was metabolized to its hydroxyl metabolite in rats, and CYP2D6 was the major rat CYP isoform responsible for the ginkgolide B metabolism in rat liver microsomes.

Role of the pro-inflammatory cytokines TNF-alpha and IL-1beta in HIV-associated dementia

Human immunodeficiency virus-1 (HIV-1)-infected and immune-activated macrophages and microglia secrete neurotoxins. Two of these neurotoxins are the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), which are thought to play a major role in inducing neuronal death. Both TNF-alpha and IL-1beta increase the permeability of the blood-brain barrier, through which subsequently HIV-infected monocytes can enter the brain. They both induce over-stimulation of the NMDA-receptor via several pathways, resulting in a lethal neuronal increase in Ca(2+) levels. Additionally, TNF-alpha co-operates with several other proinflammatory mediators to enhance their toxic effects. Although most research has focused on the neurotoxic effects of TNF-alpha and IL-1beta in HAD, there is also evidence that these cytokines can be neuroprotective. In this paper the effect of TNF-alpha and IL-1beta on neuronal life and death in HAD is discussed.

Differential effect of PMS777, a new type of acetylcholinesterase inhibitor, and galanthamine on oxidative injury induced in human neuroblastoma SK-N-SH cells

In the search for highly selective and potent cholinesterase inhibitors (AChEI) being able to improve oxidative injury, PMS777, a tetrahydrofuran derivative, was designed as a novel dual PAF and acetylcholinesterase inhibitor. The aim of this study was to investigate the modulatory effects of PMS777 and galanthamine, another AChEI, on the oxidative injury induced in neuronal cells. The SK-N-SH cells stimulated with LPS+IL-(1beta) were selected to investigate the direct inhibitory effect of PMS777 and galanthamine. LPS+IL-(1beta) induced oxidative injury as assessed by ROS production (29%), GSH depletion (11%) and loss of mitochondrial activity (22%). GSH depletion was never decreased by either drug. In contrast, ROS production and mitochondrial activity were totally prevented by addition of PMS777 but not galanthamine. PMS777 also inhibits butylcholinesterase and it shows selectivity for acetylcholinesterase. Thus, this PAF antagonist inaugurates a new type of AChEI, able to fight oxidative injury. Therefore, PMS777 could be of interest on patients with cognitive impairments and inflammatory damage, as in AD.

Lipid signaling in neural plasticity, brain repair, and neuroprotection

The extensive networking of the cells of the nervous system results in large cell membrane surface areas. We now know that neuronal membranes contain phospholipid pools that are the reservoirs for the synthesis of specific lipid messengers on neuronal stimulation or injury. These messengers in turn participate in signaling cascades that can either promote neuronal injury or neuroprotection. Prostaglandins are synthesized as a result of cyclooxygenase activity. In the first step of the arachidonic acid cascade, the short-lived precursor, prostaglandin H2, is synthesized. Additional steps in the cascade result in the synthesis of an array of prostaglandins, which participate in numerous physiological and neurological processes. Our laboratory recently reported that the membrane polyunsaturated fatty acid, docosahexaenoic acid, is the precursor of oxygenation products now known as the docosanoids, some of which are powerful counter-proinflammatory mediators. The mediator 10,17S-docosatriene (neuroprotectin D1, NPD1) counteracts leukocyte infiltration, NF-kappa activation, and proinflammatory gene expression in brain ischemia-reperfusion and is an apoptostatic mediator, potently counteracting oxidative stress-triggered apoptotic DNA damage in retinal pigment epithelial cells. NPD1 also upregulates the anti-apoptotic proteins Bcl-2 and Bcl-xL and decreases pro-apoptotic Bax and Bad expression. Another biologically active messenger derived from membrane phospholipids in response to synaptic activity is platelet-activating factor (PAF). The tight regulation of the balance between synthesis (via phospholipases) and degradation (via acetylhydrolases) of PAF modulates the functions of this lipid messenger. Under pathological conditions, this balance is tipped, and PAF becomes a proinflammatory mediator and neurotoxic agent. The newly discovered docosahexaenoic acid signaling pathways, as well as other lipid messengers related to synaptic activation, may lead to the clarification of clinical issues relevant to stroke, age-related macular degeneration, spinal cord injury, Alzheimer's disease, and other diseases that include neuroinflammatory components.

N-PEP-12 – a novel peptide compound that protects cortical neurons in culture against different age and disease associated lesions

The neuroprotective potency of N-PEP-12, a novel, proprietary compound consisting of biopeptides and amino acids was investigated. Lesion models have been applied in neuronal cultures of embryonic chicken cortex, pre-treated with N-PEP-12 from the first day onwards. On day 8 in vitro neurons were lesioned and cell viability was measured 24 and 48 hours later. To simulate acute brain ischemia, cytotoxic hypoxia was induced by sodium cyanide or by iodoacetate and excitotoxicity by L-glutamate. Ionomycin for up to 48 hours induced calcium overload. The cytoskeleton was disrupted by addition of colchicine. N-PEP-12 shows dose-dependent neuroprotection in all different models. The effect size depends on the recovery time but also on the extent of the lesion. In cases of mild to moderate lesion pronounced dose-dependent effects could be demonstrated. This indicates that chronic exposure to N-PEP-12 is able to prevent neuronal cell death associated to conditions occurring during normal aging and neurological disorders like ischemic stroke, hypoxia, brain trauma, or AD.

Combination therapy in Alzheimer's disease: a review of current evidence

Treating dementia has become a major challenge in clinical practice. Presently, acetylcholinesterase inhibitors are the first-line drugs in the treatment of Alzheimer's disease (AD). These options are now complemented by memantine, which is approved for the treatment of moderate-to-severe AD. Altogether, a minimum of six agent classes already exist, all of which are approved for clinical use and are either already being tested or ready for phase III clinical trials for the treatment of AD. These include cholinesterase inhibitors, blockers of the NMDA receptor, antioxidants or blockers of oxidative deamination (including Gingko biloba), anti-inflammatory agents, neurotrophic factors (including hormone replacement therapy and drugs acting on insulin signal transduction) and antiamyloid agents (including cholesterol-lowering therapy). These approaches hold promise for disease modification and have a potential to be used as combination therapy for cognitive enhancement. Presently, only nine clinical studies have been published that have investigated the effects of a combination regimen on cognitive performance or AD. Among those, one study was conducted in elderly cognitively intact persons; the others involved patients with AD. Only five of the treatment studies followed a randomised, controlled design. Not all studies favoured the superior efficacy of combination therapy over monotherapy. Some studies, however, showed some evidence for synergistic combination effects of symptomatic therapy, including delay or prevention of disease progression in AD patients. In addition, six studies investigated the effects of AChE inhibitor in combination with antipsychotic or antidepressant therapy on behavioural aspects of AD symptomatology. In four of those studies there were indications that combination therapy had greater efficacy over monotherapy. The treatment of AD patients requires optimised options for all stages of illness based on the available drugs. There is a great need for further well designed studies on combination therapy in AD.

Platelet-activating factor receptor and respiratory and metabolic responses to hypoxia and hypercapnia

Activation of the platelet-activating factor receptor (PAFR) regulates neural transmission. A PAFR blocker reduced the peak hypoxic (pHVR) but not hypercapnic ventilatory (HCVR) responses in rats [Am. J. Physiol. 275 (1998) R604]. To further examine the role of PAFR in respiratory control, genotype-verified PAFR -/- and PAFR +/+ adult male mice underwent hypoxic and hypercapnic challenges. HCVR was similar in the two groups (p-NS). However, pHVR was significantly reduced in PAFR -/- mice (38 +/- 13% baseline [S.D.]) compared to PAFR +/+ mice (78 +/- 16% baseline; P < 0.001, ANOVA), with reduced tidal volume recruitments during pHVR. In addition, hypoxic ventilatory depression was attenuated in PAFR -/- mice (P < 0.01), and was primarily due to attenuation of the time-dependent decreases in oxygen consumption during sustained hypoxia (P < 0.01). Thus, PAFR expression/function modulates components of the acute ventilatory and metabolic adaptations to hypoxia but not to hypercapnia. Imbalances in PAFR activity may lead to maladaptive regulation of the tightly controlled metabolic-ventilatory relationships during hypoxia.

Microglial Calcium Responses to Platelet-Activating Factor are Inhibited by Analogue CAS 99103-16-9 and Dihydropyridine PCA 4248 but Not by Ginkgolide A

Calcium signals evoked in N9 microglial cells were monitored using the calcium indicator dye Fluo-4 in a fluorescence imaging plate reader. Platelet activating factor in the range 100 nM to 20 microM elicited graded calcium responses. The analogue CAS 99103-16-9 inhibited the evoked calcium rise with an apparent KB of 1.3 +/- 0.4 microM. The dihydropyridine PCA 4248 inhibited the evoked calcium rise with an apparent KB of 1.2 +/- 0.2 microM. Ginkgolide A at concentrations up to 18 microM had no effect on the evoked calcium rise. While CAS 99103-16-9 and PCA 4248 appear to be simple competitive inhibitors of platelet-activating factor responses, the efficacy of ginkgolide in more complex pharmacological situations may result from an action at a site other than the platelet-activating factor receptor.

Platelet-activating factor receptor modulates respiratory adaptation to long-term intermittent hypoxia in mice

During hypoxia, release of platelet-activating factor (PAF) and activation of its cognate receptor (PAFR) regulate neural transmission and are required for full expression of peak hypoxic ventilatory response (pHVR) but not hypercapnic ventilatory response. However, it is unclear whether PAFR underlie components of long-term ventilatory adaptations to hypoxia. To examine this issue, adult male PAFR(+/+) and PAFR(-/-) mice were exposed to intermittent hypoxia (IH) consisting of 90 s 21% O(2) and 90 s 10% O(2) for 30 days, and normoxic and hypoxic ventilatory patterns were assessed using whole body plethysmography. Starting at day 14 of IH, normoxic ventilation in PAFR(-/-) was reduced significantly compared with PAFR(+/+) mice (P < 0.001), the latter exhibiting a prominent long-term ventilatory facilitation (LTVF). However, IH-exposed PAFR(-/-) mice had markedly enhanced pHVR and hypoxic ventilatory decline that became similar to those of IH-exposed PAFR(+/+) mice. Thus we postulate that PAFR expression and/or function underlies critical components of IH-induced LTVF but does not play a role in the potentiation of the hypoxic ventilatory response after IH exposures.

Synaptic lipid signaling: significance of polyunsaturated fatty acids and platelet-activating factor

Neuronal cellular and intracellular membranes are rich in specialized phospholipids that are reservoirs of lipid messengers released by specific phospholipases and stimulated by neurotransmitters, neurotrophic factors, cytokines, membrane depolarization, ion channel activation, etc. Secretory phospholipases A2 may be both intercellular messengers and generators of lipid messengers. The highly networked nervous system includes cells (e.g., astrocytes, oligodendrocytes, microglial cells, endothelial microvascular cells) that extensively interact with neurons; several lipid messengers participate in these interactions. This review highlights modulation of postsynaptic membrane excitability and long-term synaptic plasticity by cyclooxygenase-2-generated prostaglandin E2, arachidonoyldiacylcylglycerol, and arachidonic acid-containing endocannabinoids. The peroxidation of docosahexaenoic acid (DHA), a critical component of excitable membranes in brain and retina, is promoted by oxidative stress. DHA is also the precursor of enzyme-derived, neuroprotective docosanoids. The phospholipid platelet-activating factor is a retrograde messenger of long-term potentiation, a modulator of glutamate release, and an upregulator of memory formation. Lipid messengers modulate signaling cascades and contribute to cellular differentiation, function, protection, and repair in the nervous system. Lipidomic neurobiology will advance our knowledge of the brain, spinal cord, retina, and peripheral nerve function and diseases that affect them, and new discoveries on networks of signaling in health and disease will likely lead to novel therapeutic interventions.

Prevention of age-related spatial memory deficits in a transgenic mouse model of Alzheimer's disease by chronic Ginkgo biloba treatment

Alzheimer's disease (AD) is characterized by cognitive decline and deposition of beta-amyloid (Abeta) plaques in cortex and hippocampus. A transgenic mouse AD model (Tg2576) that overexpresses a mutant form of human Abeta precursor protein exhibits age-related cognitive deficits, Abeta plaque deposition, and oxidative damage in the brain. We tested the ability of Ginkgo biloba, a flavonoid-rich antioxidant, to antagonize the age-related behavioral impairment and neuropathology exhibited by Tg2576 mice. At 8 months of age, 16 female Tg2576 and 15 female wild-type (wt) littermate mice were given ad lib access to tap water or Ginkgo biloba (70 mg/kg/day in water). After 6 months of treatment, all mice received Morris water maze training (4 trials/day for 10 days) to assess hippocampal dependent spatial learning. All mice received a 60-s probe test of spatial memory retention 24 h after the 40th trial. Untreated Tg2576 mice exhibited a spatial learning impairment, relative to wt mice, while Ginkgo biloba-treated Tg2576 mice exhibited spatial memory retention comparable to wt during the probe test. Spatial learning was not different between Ginkgo biloba-treated and untreated wt mice. There were no group differences in learning to swim to a visible platform. Soluble Abeta and hippocampal Abeta plaque burden did not differ between the Tg2576 groups. Brain levels of protein carbonyls were paradoxically elevated in Ginkgo biloba-treated mice. These data indicate that chronic Ginkgo biloba treatment can block an age-dependent decline in spatial cognition without altering Abeta levels and without suppressing protein oxidation in a transgenic mouse model of AD.

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.

Selective inflammatory stimulations enhance release of microglial response factor (MRF)-1 from cultured microglia

The mrf-1 gene has been isolated from microglia exposed to cultured cerebellar granule neurons undergoing apoptosis. We have shown that mrf-1 is upregulated in response to neuronal death and degeneration both in vitro and in vivo. However, the exact role of MRF-1 remains unknown. Here we show that MRF-1 is released from cultured rat microglia, and its release is greatly enhanced under inflammatory conditions. When microglia were treated with ATP, the amount of MRF-1 that was released increased 10-fold compared to the basal level of release. Enhanced MRF-1 release was induced within 10 min and peaked within 1 h; after approximately 4 h, the MRF-1 release had returned to normal. MRF-1 release was stimulated by 2-methyl-thio-ATP (five-fold) and a P2X(7) selective agonist, 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (ten-fold). Moreover, the ATP-stimulated MRF-1 release was inhibited by a P2X(7) selective antagonist, oxidized ATP (oATP), and also under a Ca(2+)-free condition. These results indicate that the effects of ATP are dependent on Ca(2+) influx through P2X(7) receptors. MRF-1 release was enhanced by Ca(2+)-ionophore A23187 (sixfold), thapsigargin (threefold); however, it was not enhanced by glutamate or lipopolysaccharide. Moreover, a platelet-activating factor enhanced microglial MRF-1 release in a dose-dependent manner. We also showed that a conditioned medium from cerebellar granule neurons undergoing apoptosis markedly increased MRF-1 release from microglia; that effect was significantly inhibited by oATP. These results indicate that selective inflammatory stimulations, including ATP and PAF, enhance MRF-1 release from microglia through a Ca(2+)-dependent mechanism and suggest that MRF-1 may play a role in cell-cell interactions under inflammatory conditions.

Effect of a platelet-activating factor antagonist, E5880, on cerebrovasospasm following subarachnoid hemorrhage in a canine double-hemorrhage model

We investigated the effects of a platelet-activating factor (PAF) antagonist, E5880 (1-ethyl-2-[N-(2-methoxy)benzoyl-N-[(2)-2-methoxy-3-(4-octadecycarbamoylox)piperidinocarbonyloxy-propyloxy]carbonyl]aminomethyl-pyridiniumchloride), on subarachnoid hemorrhage-induced prolongation of cerebral circulation time and decrease in the basilar artery diameter in a canine double-hemorrhage model. Animals were assigned to three groups, control (saline), E5880 1.2 mg/kg and E5880 2.4 mg/kg. For measurement of cerebral circulation time, regions of interest were chosen at the basilar artery and the straight sinus in order to obtain time-density curves. Cerebral circulation time was defined as the difference between the arterial and venous peaks. Cerebral circulation time and basilar artery diameter were assessed by intra-arterial digital subtraction angiography (IA-DSA) on Days 0, 2 and 7. The prolongation of cerebral circulation time following subarachnoid hemorrhage was significantly inhibited by intravenous administration of 2.4 mg/kg of E5880. Basilar artery constriction was also reduced by E5880. Thus, E5880 had preventive effects on the prolongation of cerebral circulation time and the vasoconstriction of basilar artery in this model. These results suggest that E5880 may have a preventive effect on neurological symptoms aggravated by cerebrovascular lesions following subarachnoid hemorrhage.

Influence of pharmaceutical quality on the bioavailability of active components from Ginkgo biloba preparations

To be effective, herbal medicinal products are expected to meet comparable standards concerning the assessment of efficacy, safety and biopharmaceutical quality as chemically defined synthetic drugs as food supplements. However, these requirements are often not fulfilled, particularly regarding the characterization of biopharmaceutical properties such as in-vitro dissolution and in-vivo bioavailability. With respect to the relevance of biopharmaceutical quality of herbal medicinal products, two different Ginkgo biloba brands (test product: Ginkgo biloba capsules; reference product: Ginkgold) were analysed for dissolution rates and bioavailability of the most relevant active ingredients. Dissolution rates at pH 1 and 4.5 were determined according to the USP 23. The relative bioavailability of ginkgolide A, ginkgolide B and bilobalide was investigated after single oral administration of 120 mg Ginkgo biloba extract as tablets or capsules. Bioavailability data (area under the curve and peak concentration in plasma) were clearly different and did not show bioequivalence of test and reference products. The slow in-vitro dissolution of the test product resulted in a large decrease in bioavailability. These results indicate for the first time that the pharmaceutical properties of a herbal medicinal product have a significant impact on the rate and extent of drug absorption, and very likely on efficacy in humans.

Ginkgolic acids induce neuronal death and activate protein phosphatase type-2C

The standardized extract from Ginkgo biloba (EGb 761) is used for the treatment of dementia. Because of allergenic and genotoxic effects, ginkgolic acids are restricted in EGb 761 to 5 ppm. The question arises whether ginkgolic acids also have neurotoxic effects. In the present study, ginkgolic acids caused death of cultured chick embryonic neurons in a concentration-dependent manner, in the presence and in the absence of serum. Ginkgolic acids-induced death showed features of apoptosis as we observed chromatin condensation, shrinkage of the nucleus and reduction of the damage by the protein synthesis inhibitor cycloheximide, demonstrating an active type of cell death. However, DNA fragmentation detected by the terminal-transferase-mediated ddUTP-digoxigenin nick-end labeling (TUNEL) assay and caspase-3 activation, which are also considered as hallmarks of apoptosis, were not seen after treatment with 150 microM ginkgolic acids in serum-free medium, a dose which increased the percentage of neurons with chromatin condensation and shrunken nuclei to 88% compared with 25% in serum-deprived, vehicle-treated controls. This suggests that ginkgolic acid-induced death showed signs of apoptosis as well as of necrosis. Ginkgolic acids specifically increased the activity of protein phosphatase type-2C, whereas other protein phosphatases such as protein phosphatases 1A, 2A and 2B, tyrosine phosphatase, and unspecific acid- and alkaline phosphatases were inhibited or remained unchanged, suggesting protein phosphatase 2C to play a role in the neurotoxic effect mediated by ginkgolic acids.

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

Platelet-activating factor (PAF) is a lipid derived from breakdown of cell membranes that is postulated to be a mediator of cerebral ischemic injury. PAF regulates CNS gene transcription via intracellular binding sites. To test the hypothesis that PAF mediates CNS injury in part by modulating gene transcription, we evaluated the neuroprotective efficacy of the drug BN 50730, an antagonist of the intracellular (microsomal) CNS PAF binding site, in the neonatal rat model of unilateral cerebral hypoxia-ischemia. Seven-day-old rats underwent right carotid ligation followed by a 2.5-h exposure to 8% O(2), and were then treated with BN 50730 (2.5 or 25 mg/kg per dose) or vehicle, at 0 and 2 h after the end of hypoxia. Ipsilateral cortical, striatal, and hippocampal damage was quantitated either 5 d later, or at 5 wk after the insult. Treatment with BN 50730 resulted in approximately 60- 80% reduction in ipsilateral tissue loss at both times. Learning and memory were evaluated 5 wk after insult using the Morris Watermaze place navigation task. Severity of cortical and striatal damage correlated significantly with learning and memory deficits. These results support the hypothesis that PAF is a pathogenetic mediator of hypoxic-ischemic damage in the immature brain. Accumulating evidence suggests that PAF mediates its deleterious effects in the immature CNS via multiple mechanisms.

Ginkgo biloba and the central nervous system

In this paper the main features of the pharmacological effects exerted by Ginkgo biloba leaf extracts on central nervous system functions are reviewed.

Neuronal cytoskeletal alterations evoked by a platelet-activating factor (PAF) analogue

Platelet-activating factor (PAF), a phospholipid signaling molecule found in brain, modulates several neural functions and is implicated in the human developmental brain disorder Miller-Dieker Lissencephaly (MDL). Exposure to PAF, and a non-hydrolyzable analogue, methyl carbamyl PAF (mc-PAF), produces the following rapid, reversible effects upon cultured hippocampal neurites: growth cone collapse, neurite retraction, and neurite varicosity formation. In this study, the cytoskeletal alterations that mediate these shape changes were investigated by comparing the effects of mc-PAF with other cytoskeletal-altering drugs, through the fluorescent labeling of cytoskeletal proteins and mitochondria, and by electron microscopy. Results indicate that rearrangements of microtubules (MTs), F-actin, and mitochondria underlie the neurite shape changes produced by mc-PAF. Evidence for MT alteration was obtained by comparing the effects of mc-PAF with nocodozole and taxol. Exposure to nocodazole, a MT-depolymerizing agent, produced growth cone collapse and neurite varicosity formation similar to mc-PAF, whereas pre-incubation of neurites in taxol, a MT-stabilizing drug, was effective in blocking mc-PAF-induced neurite effects. Immunofluorescent labeling and EM revealed MT splaying and unbundling within neurite varicosities following mc-PAF treatment. Immunofluorescent labeling also revealed that F-actin shifted from concentration in the growth cone to a diffuse distribution along the neurite shaft following mc-PAF exposure. Fluorescent labeling and EM also revealed retrograde movement and morphological alterations of mitochondria following mc-PAF exposure, resulting in mitochondrial aggregates within neurite varicosities. These cytoskeletal rearrangements may provide insights into the mechanisms by which PAF influences neuronal activity, and could have important implications for the impairment of neuronal motility observed in MDL.

The Ginkgo biloba extract (EGb 761) protects and rescues hippocampal cells against nitric oxide-induced toxicity: involvement of its flavonoid constituents and protein kinase C

An excess of the free radical nitric oxide (NO) is viewed as a deleterious factor involved in various CNS disorders. Numerous studies have shown that the Ginkgo biloba extract EGb 761 is a NO scavenger with neuroprotective properties. However, the mechanisms underlying its neuroprotective ability remain to be fully established. Thus, we investigated the effect of different constituents of EGb 761, i.e., flavonoids and terpenoids, against toxicity induced by NO generators on cells of the hippocampus, a brain area particularly susceptible to neurodegenerative damage. Exposure of rat primary mixed hippocampal cell cultures to either sodium nitroprusside (SNP; 100 microM) or 3-morpholinosydnonimine resulted in both a decrease in cell survival and an increase in free radical accumulation. These SNP-induced events were blocked by either EGb 761 (10-100 microg/ml) or its flavonoid fraction CP 205 (25 microg/ml), as well as by inhibitors of protein kinase C (PKC; chelerythrine) and L-type calcium channels (nitrendipine). In contrast, the terpenoid constituents of EGb 761, known as bilobalide and ginkgolide B, as well as inhibitors of phospholipases A [3-[(4-octadecyl)benzoyl]acrylic acid (OBAA)] and C (U-73122), failed to display any significant effects. Moreover, EGb 761 (50 microm) CP 205 (25 microg/ml), and chelerythrine were also able to rescue hippocampal cells preexposed to SNP (up to 1 mM). Finally, EGb 761 (100 microg/ml) was shown to block the activation of PKC induced by SNP (100 microM). These data suggest that the protective and rescuing abilities of EGb 761 are not only attributable to the antioxidant properties of its flavonoid constituents but also via their ability to inhibit NO-stimulated PKC activity.

Interaction between neurone and microglia mediated by platelet-activating factor

BACKGROUND

Platelet-activating factor (PAF) is a potent phospholipid mediator that plays various roles in neuronal function and brain development. The production and release of PAF in the brain has also been reported under various pathological conditions. However, neither the cell types and mechanism responsible for the synthesis of PAF nor its target cells have been fully identified.

RESULTS

Using primary culture cells derived from rat brain and a very sensitive assay method for PAF, we found that PAF was synthesized in neurones following stimulation with glutamic acid. PAF synthesis required activation of NMDA receptors and subsequent elevation of intracellular calcium ions. Microglia, which express functional PAF receptors to a high level, showed a marked chemotactic response to PAF. This chemotaxis is a receptor-mediated process, as microglia from PAF-receptor-deficient mice did not show such a response. The activation of a pertussis-toxin-sensitive G-protein and mitogen-activated protein kinase presumably plays a role in intracellular signalling leading to chemotaxis.

CONCLUSIONS

Considering the cytoprotective and cytotoxic roles of microglia, PAF functions as a key messenger in neurone-microglial interactions.

Experimental therapy of a platelet-activating factor antagonist (ginkgolide B) on photochemically induced thrombotic cerebral ischaemia in tree shrews

1. The aim of the present study was to investigate the effects of a platelet-activating factor (PAF) antagonist (ginkgolide B; GB) on brain oedema, ion homeostasis, monoamine neurotransmitter disturbances in ischaemic penumbra and the neuroprotective mechanisms of the PAF antagonist. 2. Photochemically induced thrombotic cerebral ischaemia in tree shrews was used as the experimental model and changes in histopathology and the content of monoamine neurotransmitters (measured by a spectrofluorometer), water content (measured by a specific gravimetric method), sodium and calcium (measured by an atomic absorption spectrophotometer) in the penumbra were observed. 3. Results show that content of noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) decreased in the penumbra, while 5-HT metabolite 5-hydroxyindole-3-acetic acid, sodium, calcium and water contents increased markedly (P < 0.01) after photochemical reaction. 4. In tree shrews treated with GB (5 mg/kg, i.v.) 6 h after photochemical reaction, cortical NA, DA and 5-HT contents recovered to control levels and water and calcium contents decreased significantly (P < 0.01). 5. The results suggest that PAF may play an important role in inducing calcium overload, brain oedema and secondary brain damage in penumbra and that GB produces its neuroprotective effects by inhibiting the pathological manifestation of PAF.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Dietary supplements and natural products as psychotherapeutic agents

Alternative therapies are widely used by consumers. A number of herbs and dietary supplements have demonstrable effects on mood, memory, and insomnia. There is a significant amount of evidence supporting the use of Hypericum perforatum (St. John's wort) for depression and Ginkgo biloba for dementia. Results of randomized, controlled trials also support the use of kava for anxiety and valerian for insomnia. Although evidence for the use of vitamins and amino acids as sole agents for psychiatric symptoms is not strong, there is intriguing preliminary evidence for the use of folate, tryptophan, and phenylalanine as adjuncts to enhance the effectiveness of conventional antidepressants. S-adenosylmethionine seems to have antidepressant effects, and omega-3 polyunsaturated fatty acids, particularly docosahexaenoic acid, may have mood-stabilizing effects. More research should be conducted on these and other natural products for the prevention and treatment of various psychiatric disorders.

Platelet-activating factor mediates ischemia-induced leukocyte-endothelial adherence in newborn pig brain

The authors examined the involvement of platelet-activating factor (PAF) in mediating leukocyte adherence to brain postcapillary pial venules and altering blood-brain barrier (BBB) permeability during basal conditions and during reoxygenation after asphyxia in newborn piglets. Intravital epifluorescence videomicroscopy, closed cranial windows, and labeling of leukocytes with rhodamine 6G allowed us to obtain serial measurements of adherent leukocytes within postcapillary venules. Blood-brain barrier breakdown was determined by optical measures of cortical extravascular fluorescence intensity after intravenous sodium fluorescein. Superfusion of PAF over the cortex induced a dose-dependent increase in leukocyte adherence to cerebral venules and leakage of fluorescein; with 1 micromol/L PAF, the magnitude of adherence and BBB breakdown was similar to that seen during reoxygenation after 9 minutes of asphyxia. Both adherence and loss of BBB integrity resulting from either exogenous PAF or asphyxia-reoxygenation could be significantly attenuated by intravenous administration of WEB 2086, a PAF receptor antagonist. Window superfusion of superoxide dismutase with PAF attenuated PAF-induced increases in adherence and associated fluorescein leakage. These findings indicate that PAF exhibits proinflammatory effects in piglet brain and that PAF contributes to leukocyte adherence and BBB breakdown after cerebral ischemia. These PAF effects are mediated by increases in superoxide radical generation.

Glutamate receptor signaling interplay modulates stress-sensitive mitogen-activated protein kinases and neuronal cell death

Glutamate receptors modulate multiple signaling pathways, several of which involve mitogen-activated protein (MAP) kinases, with subsequent physiological or pathological consequences. Here we report that stimulation of the N-methyl-D-aspartate (NMDA) receptor, using platelet-activating factor (PAF) as a messenger, activates MAP kinases, including c-Jun NH2-terminal kinase, p38, and extracellular signal-regulated kinase, in primary cultures of hippocampal neurons. Activation of the metabotropic glutamate receptor (mGluR) blocks this NMDA-signaling through PAF and MAP kinases, and the resultant cell death. Recombinant PAF-acetylhydrolase degrades PAF generated by NMDA-receptor activation; the hetrazepine BN50730 (an intracellular PAF receptor antagonist) also inhibits both NMDA-stimulated MAP kinases and neuronal cell death. The finding that the NMDA receptor-PAF-MAP kinase signaling pathway is attenuated by mGluR activation highlights the exquisite interplay between glutamate receptors in the decision making process between neuronal survival and death.

Modulation of hypoxic ventilatory response by systemic platelet-activating factor receptor antagonist in the rat

Platelet activating factor (PAF) has recently emerged as an important modulator of neuronal excitability by enhancing synaptic glutamate release. Since PAF receptors (PAFR) are ubiquitously distributed in the brain, we hypothesized that PAF may play a role in respiratory control. To examine this issue, hypoxic (10% O2 for 15 min, n = 14) and hypercapnic (5% CO2 for 30 min, n = 6) challenges were performed in chronically-instrumented, unrestrained adult rats following administration of the pre-synaptic PAFR antagonist BN52021 (i.p. 20 mg/kg in 0.5 ml) or vehicle (Veh). In normoxia, BN52021 elicited VT decreases and corresponding f increases such that minute ventilation (VE) was unaffected. During hypercapnia, peak VE increased similarly after both treatments (103+/-18% in BN52021 vs. 94+/-19% in Veh, p-NS). In contrast, significant reductions in the peak hypoxic VE response occurred after BN52021 (42+/-10% vs. 104+/-18% in Veh, P<0.002). BN52021 increased normoxic arterial blood pressure and decreased heart rate. However, hypoxia-induced chronotropic responses were attenuated and depressor responses were enhanced by BN52021. We further examined protein kinase C (PKC) translocation patterns during acute hypoxia after systemic BN52021 administration. Activation of PKC beta and delta was blocked by BN52021, PKC gamma was attenuated, with no effects on PKC alpha, epsilon, theta, iota, mu, and zeta. We conclude that systemic administration of a PAFR antagonist attenuates cardioventilatory recruitment to hypoxia and selectively attenuates activation of PKC in the rat brainstem. We speculate that enhanced regional PAF production and release during hypoxic conditions may contribute important excitatory inputs and signal transduction pathways within neuronal structures underlying cardiovascular and respiratory control.

Recombinant plasma-type platelet-activating factor acetylhydrolase attenuates NMDA-induced hippocampal neuronal apoptosis

The bioactive lipid platelet-activating factor (PAF) accumulates in brain during injury, seizures and ischemia and may, in addition, be significant in AIDS dementia and in other neurodegenerative diseases. We have used plasma-type recombinant PAF acetylhydrolase (rPAF-AH) to test the hypothesis that PAF accumulation is involved in early events leading to neuronal apoptosis during excitotoxic neuronal injury. Neuronal cultures were labeled with FITC-12-dUTP (TUNEL technique) and propidium iodide, digitized using fluorescence microscopy and a chilled 3CCD color camera, and analyzed with 2D graphics analysis software. N-methyl-D-aspartate (NMDA) (50 microM, 2 hr) induced a 2.5-fold increase in apoptosis of hippocampal neurons compared with controls when analyzed 24 hr after NMDA treatment. Hippocampal neurons receiving rPAF-AH (20 microg/ml) before, during, and after NMDA treatment demonstrated a concentration-dependent neuroprotective effect which resulted in 47% and 30% neuroprotection against 50 and 100 microM NMDA, respectively. The noncompetitive NMDA receptor antagonist MK-801(300 nM) completely inhibited apoptosis caused by NMDA. The neuroprotective effect of rPAF-AH against NMDA-induced apoptosis was confirmed using as additional criteria, histone release, electron microscopy, and DNA laddering. Neuroprotection elicited by rPAF-AH demonstrates that PAF is an injury mediator in NMDA-induced neuronal apoptosis and that the recombinant protein is potentially useful as a therapeutic approach.

Platelet-activating factor modulates cardiorespiratory responses in the conscious rat

Platelet-activating factor receptor (PAFR) activation is associated with increases in neuronal excitability. We hypothesized that PAF may play a role in cardiorespiratory control. Ventilatory responses to microinjection of a long-acting PAF analog (mc-PAF, 1 microg in 1 microl) within the dorsocaudal brain stem were measured in unrestrained adult rats. mc-PAF elicited significant minute ventilation (VE) enhancements that were primarily due to tidal volume increases and were accompanied by respiratory alkalosis, heart rate increase, and reduction of arterial blood pressure. Such cardiovascular and respiratory effects did not occur after administration of either vehicle or the inactive analog lyso-PAF. The effect was blocked when animals were coadministered the presynaptic PAFR antagonist BN-52021 or recombinant PAF acetyl hydrolase. To determine the relative contribution of PAF to hypercapnic and hypoxic ventilation, microinjections were performed in additional animals with either vehicle (CO, 1 microl) or with 5 microg in 1 microl of BN-52021. Hypercapnic challenges with 5% CO2 were unaffected by BN-52021. In contrast, although 10% O2 breathing increased VE from 120.4 +/- 7.5 to 204.6 +/- 11.4 ml/min in CO, after BN-52021, VE increased only from 118.7 +/- 6.9 to 137.3 +/- 8. 9 ml/min (CO vs. BN-52021, P < 0.001). We conclude that PAFR activation in the dorsocaudal brain stem exerts significant cardioventilatory effects during normoxia and appears to play an important modulatory role in the VE response to hypoxia in conscious rats.

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.

Cytokines and perinatal brain injury

A rapidly expanding body of data provides support for the hypothesis that pro-inflammatory cytokines including interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) are expressed acutely in injured brain and contribute to progressive neuronal damage. Little is known about the pathogenetic role of these cytokines in perinatal brain injury. Recent experimental studies have incorporated two closely related in vivo perinatal rodent brain injury models to evaluate the role(s) of pro-inflammatory cytokines in the progression of neuronal injury: a perinatal stroke model, elicited by unilateral carotid artery ligation and subsequent timed exposure to 8% oxygen in 7-day-old rats, and a model of excitotoxic injury, elicited by stereotactic intra-cerebral injection of the selective excitatory amino acid agonist NMDA. Each of these lesioning methods results in reproducible, quantifiable focal forebrain injury at this developmental stage. Acute brain injury, evoked by cerebral hypoxia-ischemia or excitotoxin lesioning, results in transient marked increases in expression of IL-1 beta, and TNF-alpha mRNA in brain regions susceptible to irreversible injury, and there is evidence that pharmacological antagonism of IL-1 receptors can attenuate injury in both models. Recent studies also suggest that complementary strategies, based on pharmacological antagonism of platelet activating factor and on neutrophil depletion can also limit the extent of irreversible injury. In summary, current data suggest that pro-inflammatory cytokines contribute to the progression of perinatal brain injury, and that these mediators are important targets for neuroprotective interventions in the acute post-injury period.

Signal transduction and gene expression in the eye: a contemporary view of the pro-inflammatory, anti-inflammatory and modulatory roles of prostaglandins and other bioactive lipids

Eye tissues respond to physiological and pathophysiological stimuli by the activation of phospholipases and the consequent release from membrane phospholipids of biologically active metabolites. These rapid events have profound effects on long-term ocular physiology. Activation of phospholipase A2 is the first step in the synthesis of two important classes of lipid second messengers, the eicosanoids and platelet-activating factor (PAF). PAF accumulates in the cornea in response to injury. It has been shown to stimulate metalloproteinase gene expression in the corneal epithelium, and is, thus, implicated in the extracellular matrix remodeling that accompanies wound healing and ulceration. PAF antagonists confer protection in animal models of acute and chronic anterior segment inflammation, and block the PAF-enhanced glutamate release from retina. The latter effect suggests a role for PAF in glaucomatous neuronal damage. The eicosanoids, in particular the prostaglandins, have long been implicated in the pathophysiology of ocular inflammation and there is pharmacological evidence for their role in the regulation of intraocular pressure. The induction by PAF of the inducible prostaglandin synthase in neurons and in the corneal epithelium provides a link between the actions of these two lipid second messengers. There may be thresholds of lipid second messenger concentrations which govern their activities as physiological, defensive, or harmful.

The platelet-activating factor antagonist BN 52021 attenuates hypoxic-ischemic brain injury in the immature rat

Platelet-activating factor (PAF) is overproduced in ischemic brain. Although postischemic PAF antagonist administration protects the mature brain in some models, little is known about the effects of PAF antagonists in the immature brain. We hypothesized that the PAF antagonist BN 52021 would attenuate perinatal cerebral hypoxic-ischemic injury. To elicit focal hypoxic-ischemic brain injury, 7-d-old (P7) rats (n = 111) underwent right carotid ligation, followed by 2.5-3.25 h of hypoxia (fractional concentration of inspired O2 = 0.08). BN 52021 neuroprotection was evaluated in three groups of experiments: 1) 25 mg/kg/dose, 0 and 2 h posthypoxia; 2), 25 mg/kg/dose immediately before and 1 h after hypoxia; and 3) posthypoxia-ischemia treatment with BN 52021 12.5, 25, or 50 mg/kg/dose in 2 doses 0 and 2 h after hypoxia. All experiments included concurrent vehicle-injected controls. To quantitate severity of injury, bilateral regional cross-sectional areas (groups 1 and 2) or hemisphere weights (group 3) were evaluated on P12. Both pre- and posthypoxic treatment with BN 52021 (25 mg/kg/dose, two serial doses) decreased the incidence of cerebral infarction from 90% to about 30% (p < 0.02, Fisher's exact test). Measurement of cross-sectional areas confirmed neuroprotection and indicated some benefit of pre- over posthypoxic-ischemic treatment in hippocampus and cortex. Over the dose range tested, the neuroprotective effect of BN 52021 administration was not dose-dependent. In contrast, BN 52021 did not attenuate N-methyl-D-aspartate-induced hippocampal excitotoxic injury in P7 rats. Either prophylactic or "rescue" administration of PAF antagonists decreases the incidence and severity of brain injury associated with an episode of perinatal cerebral hypoxia-ischemia.

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.

Nicardipine and MK-801 attenuate platelet-activating factor increases following cerebral ischemia-reperfusion in gerbils

The effects of pretreatment with nicardipine (dihydropyridine Ca2+ channel antagonist), Bay K8644 (dihydropyridine Ca2+ channel agonist), and MK-801 (N-methyl-D-aspartate-receptor antagonist) on changes of platelet-activating factor (PAF) concentrations in transient ischemic brain are reported. The tissue concentration of PAF increases significantly in hippocampus, cortex and thalamus by 210%, 169% and 168% of controls without ischemia-reperfusion, respectively after 1 h of reperfusion. Nicardipine (5 mg/kg) reduces the accumulation of PAF, the remaining increases in hippocampus, cortex and thalamus being 151%, 138% and 145% of the controls, respectively. In contrast, Bay K8644 (2.5 mg/kg) enhances the accumulation of PAF, its concentrations in hippocampus, cortex and thalamus being 376%, 233% and 204% of the controls, respectively. The Bay K8644 enhancement in hippocampus is completely inhibited by pretreatment of nicardipine (5 mg/kg). MK-801 (10 mg/kg) reduces the accumulation of PAF, the remaining increases in hippocampus, cortex and thalamus being 152%, 147% and 144% of the controls, respectively. Moreover, brain tissue from animals subjected to the combined pretreatment with nicardipine (5 mg/kg) and MK-301 (10 mg/kg) indicates there is greater inhibition of ischemia-induced PAF increases than with either drug alone. These results indicate that PAF production in the ischemic brain may be regulated by Ca2+ influx through voltage-sensitive Ca2+ channels which are antagonized and agonized by nicardipine and Bay K8644, respectively and receptor-operated Ca2+ channels which are antagonized by MK-801. Because it is known that increases of intracellular Ca2+ in the brain accompany ischemia and early periods of reperfusion and that PAF exhibits neurotoxicity, the present findings support the role of PAF as a mediator in ischemia-induced brain damage at early stages of reperfusion.

Platelet-activating factor in the modulation of excitatory amino acid neurotransmitter release and of gene expression

Selective phospholipids of synaptic membranes are reservoirs for lipid second messengers. 1-Alkyl-2 arachidonoyl glycero-3-phosphocholine is hydrolyzed by phospholipase A2 (PLA2) into two products: lyso-PAF, which is transacetylated to yield platelet-activating factor (PAF), and free arachidonic acid (20:4), which can undergo oxidative metabolism to eicosanoids. Alternative pathways of PAF synthesis, such as CoA-independent transacylase and the de novo route of synthesis, remain to be explored and compared to the PLA2-dependent route. At low concentrations, PAF is a retrograde messenger of LTP in CA1 hippocampal neurons, and is also a memory enhancer in inhibitor avoidance tasks. PAF enhances excitatory amino acid release in synaptic pairs from primary hippocampal cultures by a presynaptic mechanism. Ischemia and convulsions activate synaptic PLA2. Thus, increased concentrations of PAF promote massive glutamate exocytosis, glutamate receptor activation, and elevated intracellular calcium levels in target cells. As a result, calcium-sensitive cascades are affected. PAF thus had dual roles as a lipid mediator: under physiological conditions it modulates neurotransmitter release, but at high concentrations it becomes neurotoxic. Through an intracellular high affinity binding site, PAF activates the expression of immediate-early genes. Some of these genes encode transcription factors (e.g. zif-268, c-fos), and others encode enzymes (COX-2 or inducible prostaglandin synthase). PAF also activates the expression of metalloproteinases which participate in the remodeling of the extracellular matrix. These effects have been studied in cells in culture as well as in the brain. A PAF antagonist specific for the intracellular binding site inhibits COX-2 expression elicited by a single electroconvulsive shock or vasogenic edema. COX-1, the constitutive prostaglandin synthase, is not induced and is unaffected by the antagonist. Most of the cerebral induction occurs in the hippocampus and results from transcriptional activation. PAF mediated gene expression may be involved in neural plasticity as well as in pathophysiological conditions in which the neural tissue activates repair-injury pathways.

Predominant expression of platelet-activating factor receptor in the rat brain microglia

Cellular localization of platelet-activating factor (PAF) receptor in the rat brain was determined by (1) in situ hybridization, (2) Northern blot analysis in primary cell cultures of neurons, microglia, astrocytes, and fibroblasts, and (3) Ca2+ imaging in hippocampal culture. In situ hybridization revealed that the PAF receptor mRNA is expressed intensely in microglia and moderately in neurons. Northern blot analysis revealed that PAF receptor mRNA is the most abundant in microglia. In primary hippocampal cultures, PAF elevated intracellular Ca2+ concentration in microglia and also in neurons, but to a lesser extent. These results suggest predominant presence of PAF receptor in microglia. Cultured microglia also expressed cPLA2 mRNA the most intensely. PAF-activated microglia released arachidonic acid in a Ca(2+)-dependent manner and without conversion to its derivatives. We propose that microglia as well as neurons contribute to PAF-related events in the CNS by releasing arachidonic acid.

Structure-activity relationships in platelet-activating factor (PAF). 8. Tetrahydrofuran derivatives as dual PAF antagonists and acetylcholinesterase inhibitors: anti-acetylcholinesterase activity and comparative SAR

2,5-disubstituted tetrahydrofuran derivatives display a dual functionality: they are PAF antagonists and acetylcholinesterase (AChE) inhibitors. In vitro anti-AChE activity and in vivo trials are presented herein. These compounds are competitive and potent AChE inhibitors. Structure-activity relationships are described and compared with PAF-antagonist results. The presence of an onium group, a suitable distance supplied by a chain of 7 or 10 carbon atoms separating the function from the polar head and an appreciable chain hydrophobicity (4 < sigma f < 7) are the main features required for a dual activity. The derivatives are evaluated in a mouse passive avoidance model. Only compounds with both activities are able to reverse scopolamine-induced amnesia. In addition, they display a very weak toxicity.

Prevention of cerebrovasospasm following subarachnoid hemorrhage in rabbits by the platelet-activating factor antagonist, E5880

Recently, an important role of platelet-activating factor (PAF), an inflammation mediator, has been demonstrated in the genesis of cerebral vasospasm following subarachnoid hemorrhage (SAH). In the current study, the authors examined whether intravenous administration of the novel PAF antagonist, E5880, can prevent vasospasm following SAH in rabbits. A vasospasm model was produced in three groups of rabbits using two subarachnoid injections of autologous arterial blood, followed by intravenous administration of distilled water (control), a low dose of E5880 (0.1 mg/kg in distilled water), or a high dose of E5880 (0.5 mg/kg in distilled water). Neurological deterioration was largely prevented in the rabbits that received E5880. Basilar artery constriction was also reduced by both doses of E5880. Histological examination at autopsy predominantly showed ischemic changes in the brain. Animals in each E5880-treated group exhibited ischemic changes less frequently than those in the control group. Plasma thromboxane B2 concentrations were reduced in rabbits treated with E5880. Platelet-activating factor was immunolocalized in the intima and media of the basilar artery in the control group. The PAF immunoreactivity demonstrated in the basilar artery was decreased in the E5880 groups in a dose-dependent manner. Thus, this study provides evidence that PAF may play a role in the pathogenesis of vasospasm after SAH and that intravenous administration of E5880 is a promising approach in preventing vasospasm.

Activities of enzymes in platelet activating factor biosynthetic pathways in the gerbil model of cerebral ischemia

The activities of enzymes in platelet activating factor (PAF) biosynthetic pathways were analyzed in hippocampal and cerebral cortical regions of normal and ischemic gerbil brain to assess changes in enzyme activities and potential modulators that could explain the accentuated production of PAF seen in ischemia. Global forebrain ischemia was produced by bilateral carotid artery ligation, and the effectiveness of the ligation was shown by free fatty acid release and ATP depletion. Specific activities of 1-alkyl-2-acetyl-sn-glycerol (AAG) choline phosphotransferase, 1-alkyl-sn-glycero-3-phosphate (AGP) acetyl transferase, and 1-alkyl-sn-glycero-3-phosphocholine (lyso PAF) acetyl transferase in tissue homogenates were in the ratio 4:1:0.1, respectively. Sham-operated and ischemic or ischemic-reperfused tissues showed similar activities for individual enzymes, indicating that enzyme levels or activation states did not change in ischemic or reperfused tissues. However, small metabolites (relevant to ischemia) added to the in vitro assays did modify enzyme activities. Physiological concentrations of MgATP severely inhibited AGP acetyl transferase activity, and this resulted in the ratio of AGP acyl transferase to AGP acetyl transferase activities changing from 48:1 in the presence of 2.5 mM MgATP to 6:1 in the absence of MgATP. This suggests that falling ATP levels in cerebral ischemia may promote the de novo pathway of PAF biosynthesis by releasing inhibition of AGP acetyl transferase. Lyso PAF acetyl transferase was much less active than AGP acetyl transferase and was also inhibited by MgATP. AAG choline phosphotransferase was not inhibited by MgATP but was inhibited by calcium. However the superior specific activity of the choline phosphotransferase in comparison with the AGP acetyl transferase suggested that the lowered choline phosphotransferase activity in the presence of rising intracellular calcium would not seriously compromise the synthesis of PAF by the de novo route. Both acetyl transferase enzymes were also inhibited by oleoyl CoA.