Effectiveness and tolerability of CV-3988, a selective PAF antagonist, after intravenous administration to man

Particulate matter exposure promotes Pseudomonas aeruginosa invasion into airway epithelia by upregulating PAFR via the ROS-mediated PI3K pathway

Over exposure to particulate matter (PM) could irritate respiratory tract infection; while, Pseudomonas aeruginosa (P. aeruginosa) is one of the main common pathogens. Our study aims are to define whether PM exposure enhances the invasion of P. aeruginosa into the airway epithelia and to characterize the underlying mechanisms. Human bronchial epithelial cells (BEAS-2B) or BEAS-2B transfected by PAFR siRNA were challenged with PM and pretreated with N-acetylcysteine (NAC), LY294002 (PI3K inhibitor), BAY 11-7082 (NF-κB inhibitor), or CV-3988 (PAFR antagonist). P. aeruginosa invasion was evaluated using colony-forming units assay and confocal microscopy. Real-time RT-PCR, immunofluorescence, flow cytometry and western blotting were used to detect the genes or proteins expression. PM exposure promoted P. aeruginosa invasion into BEAS-2B cells through ROS-mediated PI3K pathway which enhanced the expression of PAFR, which could be alleviated by treatment with NAC, LY294002, and BAY 11-7082. Furthermore, NAC and PAFR siRNA attenuated PM-stimulated activation of PI3K pathway. Treatment with PAFR antagonist and siRNA also alleviated PM exposure-induced P. aeruginosa invasion into BEAS-2B cells. Our results demonstrated that PM exposure increased the PAFR expression and activated the PI3K pathway in a ROS-dependent manner. Upregulated PAFR and activated PI3K pathway formed a positive regulatory loop and promoted the invasion of P. aeruginosa into airway epithelia. These mechanisms may provide a novel approach against P.aeruginosa invasion.

Forty Years Since the Structural Elucidation of Platelet-Activating Factor (PAF): Historical, Current, and Future Research Perspectives

In the late 1960s, Barbaro and Zvaifler described a substance that caused antigen induced histamine release from rabbit platelets producing antibodies in passive cutaneous anaphylaxis. Henson described a ‘soluble factor’ released from leukocytes that induced vasoactive amine release in platelets. Later observations by Siraganuan and Osler observed the existence of a diluted substance that had the capacity to cause platelet activation. In 1972, the term platelet-activating factor (PAF) was coined by Benveniste, Henson, and Cochrane. The structure of PAF was later elucidated by Demopoulos, Pinckard, and Hanahan in 1979. These studies introduced the research world to PAF, which is now recognised as a potent phospholipid mediator. Since its introduction to the literature, research on PAF has grown due to interest in its vital cell signalling functions and more sinisterly its role as a pro-inflammatory molecule in several chronic diseases including cardiovascular disease and cancer. As it is forty years since the structural elucidation of PAF, the aim of this review is to provide a historical account of the discovery of PAF and to provide a general overview of current and future perspectives on PAF research in physiology and pathophysiology.

Temporal upregulation of host surface receptors provides a window of opportunity for bacterial adhesion and disease

Host surface receptors provide bacteria with a foothold from which to attach, colonize and, in some cases, invade tissue and elicit human disease. In this review, we discuss several key host receptors and cognate adhesins that function in bacterial pathogenesis. In particular, we examine the elevated expression of host surface receptors such as CEACAM-1, CEACAM-6, ICAM-1 and PAFR in response to specific stimuli. We explore how upregulated receptors, in turn, expose the host to a range of bacterial infections in the respiratory tract. It is apparent that exploitation of receptor induction for bacterial adherence is not unique to one body system, but is also observed in the central nervous, gastrointestinal and urogenital systems. Prokaryotic pathogens which utilize this mechanism for their infectivity include Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis and Escherichia coli. A number of approaches have been used, in both in vitro and in vivo experimental models, to inhibit bacterial attachment to temporally expressed host receptors. Some of these novel strategies may advance future targeted interventions for the prevention and treatment of bacterial disease.

Does upregulated host cell receptor expression provide a link between bacterial adhesion and chronic respiratory disease?

Expression of the platelet-activating factor receptor is upregulated in the respiratory epithelium of smokers and chronic obstructive pulmonary disease patients. We have recently determined that increased expression of PAFr correlates with higher levels of adhesion to human bronchial epithelial cells by non-typable Haemophilus influenzae and Streptococcus pneumoniae which are major bacterial pathogens in acute exacerbations of COPD. In addition, we found that a PAFr antagonist decreased the adhesion of both respiratory bacterial pathogens to non-cigarette exposure control levels. This highlights the possibility that epithelial receptors, that are upregulated in response to cigarette smoke, could be targeted to specifically block chronic bacterial infections of the lower respiratory tract. In this commentary, we explore the question of whether adhesion to a temporally-upregulated host receptor is a common event in chronic bacterial disease, and as such, could represent a putative therapeutic target for blocking infection by respiratory and other pathogens.

Screening of Pharmacologically Active Small Molecule Compounds Identifies Antifungal Agents Against Candida Biofilms

Candida species have emerged as important and common opportunistic human pathogens, particularly in immunocompromised individuals. The current antifungal therapies either have toxic side effects or are insufficiently effect. The aim of this study is develop new small-molecule antifungal compounds by library screening methods using Candida albicans, and to evaluate their antifungal effects on Candida biofilms and cytotoxic effects on human cells. Wild-type C. albicans strain SC5314 was used in library screening. To identify antifungal compounds, we screened a small-molecule library of 1,280 pharmacologically active compounds (LOPAC(1280TM)) using an antifungal susceptibility test (AST). To investigate the antifungal effects of the hit compounds, ASTs were conducted using Candida strains in various growth modes, including biofilms. We tested the cytotoxicity of the hit compounds using human gingival fibroblast (hGF) cells to evaluate their clinical safety. Only 35 compounds were identified by screening, which inhibited the metabolic activity of C. albicans by >50%. Of these, 26 compounds had fungistatic effects and nine compounds had fungicidal effects on C. albicans. Five compounds, BAY11-7082, BAY11-7085, sanguinarine chloride hydrate, ellipticine and CV-3988, had strong fungicidal effects and could inhibit the metabolic activity of Candida biofilms. However, BAY11-7082, BAY11-7085, sanguinarine chloride hydrate and ellipticine were cytotoxic to hGF cells at low concentrations. CV-3988 showed no cytotoxicity at a fungicidal concentration. Four of the compounds identified, BAY11-7082, BAY11-7085, sanguinarine chloride hydrate and ellipticine, had toxic effects on Candida strains and hGF cells. In contrast, CV-3988 had fungicidal effects on Candida strains, but low cytotoxic effects on hGF cells. Therefore, this screening reveals agent, CV-3988 that was previously unknown to be antifungal agent, which could be a novel therapies for superficial mucosal candidiasis.

Platelet-activating factor antagonism: a new concept in the management of regional myocardial ischemia-reperfusion injury

Reperfusion therapies for treatment of myocardial infarction successfully reduce patient mortality; however, regional myocardial ischemia-reperfusion (RMIR) causes its own expression of cardiovascular dysfunction, including myocardial depression, hemodynamic instability, and dysrhythmias, which have increased patient mortality within the first 24 h after starting reperfusion therapy. Current evidence suggests that the release of oxygen-derived reactive substances and subsequent inflammatory mediators during ischemia-reperfusion contribute toward this injury. Platelet-activating factor (PAF), a mediator released during RMIR, has been emphasized by many investigators as playing a central role in causing RMIR injury. Similar cardiovascular dysfunctions that occur during RMIR, including myocardial depression, hemodynamic instability, and dysrhythmias, occur after administration of PAF and are ameliorated with PAF antagonists. Further, PAF antagonists have been shown to be cardioprotective and improve survival when administered before onset of reperfusion. A variety of phospholipid analogues, naturally derived compounds, and synthetic compounds have been developed that form the different classes of PAF antagonists, each with unique antagonizing properties. Several of these compounds have successfully passed safety and efficacy testing in humans; however, to date, no clinical trials have investigated the protective effects of PAF antagonists against RMIR injury. A current theory in the pathogenesis of RMIR injury considers the ischemic and necrotic portion of the myocardium and regional dysfunction due to tissue necrosis to be solely responsible for global cardiac dysfunction leading to hemodynamic instability and death. Evidence now suggests, however, that the global dysfunction is also due to the effect of inflammatory mediators such as PAF, thromboxanes, leukotrienes, and endothelins that are released during RMIR and are distributed throughout the heart on reperfusion. Antagonizing a central inflammatory mediator such as PAF, as adjunct treatment with currently used reperfusion therapies, improves cardiovascular function and survival in animals and should be introduced into clinical trials to investigate if similar protective effects can be provided in humans.

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.

Comparative effects of tetrandrine and berbamine on guineapig airway microvascular leakage induced by platelet-activating factor and other allergic mediators

The bisbenzylisoquinoline analogues, tetrandrine and berbamine, were investigated for their effects on guineapig airway microvascular leakage, an animal model of asthma and allergic inflammation. Significant inhibition of microvascular leakage by tetrandrine was observed with all four allergic mediators used in these experiments. By contrast, berbamine was able to suppress microvascular leakage induced by platelet-activating factor and bradykinin, but not by leukotriene D4 or histamine. These results indicate that tetrandrine has broad-spectrum inhibitory activity on allergic mediators, and may have value for the therapy of diseases in which these mediators have a role in pathogenesis.

Inhibition of ex-vivo PAF-induced platelet aggregation by the PAF-antagonist RP 48740: relationship to plasma concentrations in healthy volunteers

RP 48740, 3-(3-pyridyl)-1H,3H-pyrrolo [1,2-c] thiazole-7-carboxamide, a specific competitive PAF-receptor antagonist in vitro, was given to 29 healthy male volunteers for 7 days. Plasma drug concentrations and ex-vivo PAF-induced platelet aggregation were assessed on Days 1, 4, and 7. RP 48740 had linear pharmacokinetics after single and repeated doses. It caused stable inhibition of PAF-induced platelet aggregation in a dose-dependent manner. The effect disappeared within 24 h, even after 7 days of repeated doses. The effect of RP 48740 displayed a sigmoidal relation to the plasma drug concentration; I50 2.3 (0.3) mg.l-1. There were no clinical or biological adverse reactions to RP 48740 during the study.

Determination of MK-287, a new platelet-activating factor antagonist, in plasma and serum by gas chromatography chemical ionization mass spectrometry

MK-287 is a novel platelet-activating factor antagonist. A sensitive and specific gas chromatographic/mass spectrometric assay has been developed for the determination of the drug in serum and plasma. The assay utilizes an extraction with methyl-t-butyl ether and subsequent trimethylsilylation of the hydroxyl function. The gas chromatographic/mass spectrometric determinations are carried out with temperature-programmed capillary gas chromatography and ammonia negative chemical ionization mass spectrometry. The method has sufficient sensitivity, precision, accuracy and selectivity for the analysis of drug concentrations in clinical samples.

Inhibition of cutaneous and platelet responses to platelet-activating factor by oral WEB 2086 in man

WEB 2086, an antagonist of platelet-activating factor (PAF), was assessed against the cutaneous response in vivo and the aggregation of platelets ex vivo induced by PAF in a double-blind, placebo-controlled, crossover study in 12 normal male volunteers. Wheal-and-flare responses to intradermal PAF (200 ng) and histamine (1 microgram) were measured 1 hour after placebo or control administration. Wheal volumes were significantly reduced by 66% +/- 8.7% (mean +/- SEM), 86% +/- 8.3%, and 90% +/- 6.0% after 10, 40, and 100 mg of WEB 2086 compared to placebo administration (p less than 0.005). Flare responses were correspondingly inhibited by 66% +/- 8.3%, 82% +/- 8.7%, and 84% +/- 7.8% at 10, 40, and 100 mg of WEB 2086, respectively. Cutaneous responses to histamine were unaffected. Ex vivo platelet responses to PAF were significantly inhibited at all three doses of WEB 2086. Oral WEB 2086 is a potent and specific inhibitor of cutaneous and platelet responses to PAF in man.

Inhibition of PAF-induced human platelet responses by newly synthesized ether phospholipids

A series of 10 analogues of platelet-activating factor (PAF) was evaluated for proaggregatory and inhibitory behaviour on human blood platelets in vitro. Most of the compounds did not activate platelets but inhibited the PAF-induced aggregation. The inhibition was concentration-dependent and selective for PAF. Platelet responses to ADP and collagen were not suppressed. Schild analysis of the aggregation data was consistent with a simple competitive antagonism. The pA2 of the most effective antagonist (1-O-hexadecyl-2-O-ethylglycero-3-phosphoric acid-6'-(1-chinuclidinium)-hexylester) was 5.96. There is also evidence for its ability to inhibit the high affinity binding of [3H]PAF to the platelet receptors.

Platelet-activating factor (PAF) inhibitory profile of KO-286011 on blood platelets in vitro and in vivo

A newly synthesised structural analogue of PAF, coded KO-286011 (1-O-hexadecyl-2-O-ethyl-rac-glycero-3-phosphoric acid 4-(N,N-dimethylamino)pyridinium butylester), was proved for its ability to inhibit PAF-mediated platelet responses in vitro and in vivo. The compound inhibited effectively the PAF-induced aggregation and secretion of human and rabbit platelets. In contrast, there was little influence on ADP-, collagen-, and arachidonic acid-triggered platelet responses. Schild-analysis of aggregation data ascertained in human platelet-rich plasma was consistent with a simple competitive antagonism and yielded a pA2 of 6.44. Proaggregatory activity of KO-286011 was excluded turbidimetrically as well as by means of a single cell counting technique. [3H]PAF binding studies provided evidence that KO-286011 exerts its inhibitory action at the PAF-receptor level. A significant inhibition of the ex vivo PAF-induced platelet aggregation was found after i.v. administration of 0.5 mg/kg KO-286011 to rabbits. The effect was most pronounced 5 min after dosing the inhibitor and detectable over a period of 30 min. Intravenous administration of 10 and 25 micrograms/kg KO-286011 to guinea pigs prevented dose-dependently the PAF-induced formation of thromboxane A2. The PAF-inhibitory action of KO-286011 was more potent than that of the ginkgolide BN 52021.

Determination of a platelet activating factor antagonist (CV-3988): methodology and clinical application

A high-performance liquid chromatographic method was developed for determination of the platelet activating factor antagonist CV-3988 in human plasma and urine. After development of a column extraction procedure without an internal standard, a more satisfactory organic extraction procedure was set up with amiodarone as internal standard. Linearity of the calibration curves was found in the range 0.0625-10 micrograms/ml CV-3988. Reproducibility was higher than 10% for the column extraction and lower than 10% for the organic extraction procedure. Recovery of CV-3988 from plasma averaged 81.7% for the column procedure and 40% for the organic extraction. Urine samples could be extracted only by the organic extraction procedure. The organic extraction procedure was applied to the determination of CV-3988 in plasma and urine samples after intravenous administration to normal volunteers.

The role of platelet activating factor in allergic respiratory disease

1. Platelet activating factor (PAF) is an ether-linked phospholipid capable of eliciting many of the factors of the allergic response including bronchoconstriction, mucosal oedema, eosinophil infiltration and bronchial hyperresponsiveness. 2. A wide range of selective PAF receptor antagonists have now been described which have been reported to reduce many aspects of allergen-induced inflammatory responses in experimental animals. 3. Early clinical studies have indicated that some of these drugs are also effective PAF antagonists in man, but no controlled studies have been reported using these compounds in patients with allergic asthma. 4. The gingkolide mixture BN 52063 has recently been reported to inhibit allergen-induced cutaneous inflammation in man; a response which has certain pathological similarities to allergen-induced late-onset airways obstruction in the lung. 5. Therefore, drugs antagonizing the actions of PAF may well lead to a better understanding of and may be a novel therapeutic approach for allergic respiratory disorders.

The role of platelet activating factor in allergic inflammation

It is becoming increasingly apparent that platelet activating factor (PAF) is an important mediator in allergic disease. It is synthesized by a variety of cells including those which are thought to participate in the inflammatory process. In turn, PAF may stimulate these cells which further propagates the inflammatory process. Furthermore, PAF can mimic most of the characteristics which are relevant in allergic inflammation and PAF can produce effects comparable to that produced by antigen in animal models of allergic inflammation and in man. Other evidence to support the involvement of PAF in allergic disease has also arisen with the advent of PAF antagonists. Many PAF-induced responses can be attenuated by these agents and many antigen-induced responses in both animal models and in man can also be attenuated by PAF antagonists. This review attempts to summarize the results from studies which have investigated the role of PAF in allergic inflammation and the effects of PAF antagonists against both PAF and allergic-induced responses.