Platelet-activating Factor Receptor Antagonist Research Articles

PAF, rather than Histamine, Participates in Mouse Anaphylactic Hypotension

We determined the roles of platelet-activating factor (PAF) and histamine in anaphylactic hypotension in ovalbumin-sensitized anesthetized BALB/c mice. The effects of PAF and histamine on hemodynamic variables were studied by measuring the systemic arterial (Psa), portal venous (Ppv) and central venous (Pcv) pressures. Intravenous PAF evoked a biphasic Psa response, an initial rapid and transient drop followed by marked hypotension, accompanied by a decrease in Pcv. Histamine caused only mild systemic hypotension. Both agents similarly increased Ppv by approximately 4 cm H₂O at high doses. After an injection of antigen, Psa initially increased slightly and then decreased from the baseline of 94 ± 1 mm Hg to 46 ± 1 mm Hg at 10 min after antigen administration, with Pcv decreasing by 2.5 cm H₂O. Ppv increased by 3.5 cm H₂O at 5 min after antigen injection. Pretreatment with either CV-6209 (PAF receptor antagonist, 1 mg/kg) or diphenhydramine (histamine H₁ receptor antagonist, 20 mg/kg) significantly attenuated an antigen-induced decrease in Psa. The inhibitory action of CV-6209 was greater than that of diphenhydramine, and the combination of these 2 antagonists almost completely inhibited the anaphylactic hypotension. In contrast, the antigen-induced increase in Ppv was attenuated by CV-6209 alone but augmented by diphenhydramine. It is concluded that anaphylactic hypotension is mainly mediated by PAF and, to a lesser extent, by histamine in anesthetized BALB/c mice.

Potential mechanism for recruitment and migration of CD133 positive cells to areas of vascular inflammation

Objective Mast cells are found in large numbers in atherosclerotic plaques. The present study was conducted to determine whether tryptase stimulation of human coronary artery endothelial cells (HCAEC) would lead to an increase in transmigration of CD133 positive cells (CD133+). In vitro these cells can differentiate into mast cells under the influence of specific cytokines and growth factors. Methods and Results CD133+ cells were isolated from umbilical cord blood. They express mRNA for several adhesion molecules that are also utilized in neutrophil migration and can migrate across an HCAEC monolayer. Migration increased significantly when HCAEC were stimulated with tryptase and decreased when CD133+ cells were pretreated with CV3988, a platelet activating factor receptor (PTAFR) antagonist. Following long-term cell culture, these cells stained positively for the presence of tryptase, a mast cell enzyme. Conclusion CD133+ cells can be utilized as a mast cell precursor population. The transendothelial migration is facilitated by the presence of tryptase and may utilize the PAF/PTAFR interaction in a manner similar to that involved in neutrophil transmigration. Following transmigration, a subset of these progenitor cells may mature into mast cells in the subendothelial space and play a role in propagation of the inflammatory process in atherosclerosis.

Inhibition of Photocarcinogenesis by Platelet-Activating Factor or Serotonin Receptor Antagonists

The UV radiation in sunlight is the primary cause of nonmelanoma skin cancer. Moreover, UV exposure induces immune suppression. Early steps in the cascade of events leading to immune suppression are the binding of UV-induced platelet-activating factor (PAF) to its receptor and the binding of cis-urocanic acid, a photoreceptor for UVB radiation, to the serotonin (5-HT(2A)) receptor. Here, we tested the hypothesis that blocking the binding of PAF and 5-HT(2A) to their receptors would also block skin cancer induction. Hairless mice were injected with PAF or serotonin receptor antagonists and then exposed to solar-simulated UV radiation. We noted a significant and substantial decrease in skin cancer incidence in mice treated with the PAF or 5-HT(2A) receptor antagonists. Also, the PAF and/or serotonin receptor antagonists blocked skin cancer progression. The PAF and serotonin receptor antagonists worked in a synergistic fashion to block skin cancer induction. We also measured the effect that injecting PAF and 5-HT(2A) receptor antagonists had on UV-induced skin damage after a single UV exposure. We noted a significant decrease in UV-induced hypertrophy, sunburn cell formation, and apoptosis when the mice were injected with PAF and/or 5-HT(2A) receptor antagonists. These data indicate that treating UV-irradiated mice with PAF and 5-HT(2A) receptor antagonists blocks skin cancer induction in vivo, in part by reversing UV-induced damage to the skin and by preventing the induction of immune suppression.

A cardioprotective role for platelet-activating factor through NOS-dependent S-nitrosylation

Controversy exists as to whether platelet-activating factor (PAF), a potent phospholipid mediator of inflammation, can actually protect the heart from postischemic injury. To determine whether endogenous activation of the PAF receptor is cardioprotective, we examined postischemic functional recovery in isolated hearts from wild-type and PAF receptor-knockout mice. Postischemic function was reduced in hearts with targeted deletion of the PAF receptor and in wild-type hearts treated with a PAF receptor antagonist. Furthermore, perfusion with picomolar concentrations of PAF improved postischemic function in hearts from wild-type mice. To elucidate the mechanism of a PAF-mediated cardioprotective effect, we employed a model of intracellular Ca2+ overload and loss of function in nonischemic ventricular myocytes. We found that PAF receptor activation attenuates the time-dependent loss of shortening and increases in intracellular Ca2+ transients in Ca2+ -overloaded myocytes. These protective effects of PAF depend on nitric oxide, but not activation of cGMP. In addition, we found that reversible S-nitrosylation of myocardial proteins must occur in order for PAF to moderate Ca2+ overload and loss of myocyte function. Thus our data are consistent with the hypothesis that low-level PAF receptor activation initiates nitric oxide-induced S-nitrosylation of Ca2+ -handling proteins, e.g., L-type Ca2+ channels, to attenuate Ca2+ overload during ischemia-reperfusion in the heart. Since inhibition of the PAF protective pathway reduces myocardial postischemic function, our results raise concern that clinical therapies for inflammatory diseases that lead to complete blockade of the PAF receptor may eliminate a significant, endogenous cardioprotective pathway.

Platelet-activating factor (PAF) increases NO production in human endothelial cells—real-time monitoring by DAR-4M AM

Background Platelet-activating factor (PAF) is a potent inflammatory lipid mediator that increases vascular permeability and vasodilation. Several studies have addressed the effect of PAF on nitric oxide (NO) production from microvessels in vivo. Objective The aim of present study was to evaluate the effect of PAF on NO production in primary cultured human vascular endothelial cells. Methods Human umbilical vein endothelial cells (HUVECs) were loaded with diaminorhodamine-4M acetoxymethyl ester (DAR-4MAM), and the cells were stimulated with PAF. Intracellular NO production was monitored as increase in fluorescence intensity. Also, NO production was visualized at cellular levels using DAR-4M AM and fluorescence imaging. Results Significant increases in NO production in HUVECs were soon after the PAF stimulation, reaching a plateau after 10 min of the stimulation. The increase of NO production at 10 min after the stimulation was statistically significant ( p<0.05) for 0.01–10 μM PAF. PAF-induced NO production was abolished by pretreatment of HUVECs with a NOS inhibitor N G-monomethyl- l-arginine ( l-NMMA) or PAF receptor antagonist BN 52021. LysoPAF, the inactive metabolite of PAF, did not exert a significant effect on intracellular NO levels. Conclusions These results provide direct evidence that PAF cause intracellular NO production via activation of PAF receptors in human vascular endothelial cells

High dose of lipopolysaccharide pre-treatment prevents OVA-induced anaphylactic decreases in rectal temperature in the immunized mice

It remains unclear whether lipopolysaccharide (LPS) pre-treatment, which prevents Th2-type responses via Toll-like receptor 4 (TLR4), inhibits anaphylaxis. To determine the dose-dependent effects of LPS pre-treatment on anaphylactic decreases in rectal temperature caused by ovalbumin (OVA) re-exposure in immunized mice, C3H/HeN mice were divided into vehicle/OVA (0mg/kg LPS), L-LPS/OVA (0.5mg/kg LPS), M-LPS/OVA (1.0mg/kg LPS) and H-LPS/OVA (3.0mg/kg LPS) groups. After receiving these treatments, the mice were systemically immunized with OVA. Negative control mice were not immunized with OVA (N-OVA). After measuring the serum levels of OVA-specific IgE and IgG1 antibodies, the mice were examined for changes in their rectal temperature and plasma histamine concentration after OVA re-exposure. The allergen-specific IgE and IgG1 concentrations in sera from L-LPS/OVA, M-LPS/OVA and H-LPS/OVA mice were significantly lower than those in sera from vehicle/OVA mice despite OVA immunization. However, the antibody levels in all OVA-immunized mice, with the exception of the IgG1 levels in H-LPS/OVA mice, were significantly higher than those in N-OVA mice. Interestingly, H-LPS/OVA mice were the only group that did not exhibit a decrease in rectal temperature, since the rectal temperatures in vehicle/OVA, L-LPS/OVA and M-LPS/OVA mice were significantly decreased by OVA re-exposure. Furthermore, the decrease in rectal temperature after OVA re-exposure in L-LPS/OVA mice, which did not exhibit an increase in the plasma histamine concentration, was significantly prevented by treatment with a platelet-activating factor (PAF) receptor antagonist alone. Taken together, the present results indicate that high-dose LPS pre-treatment may prevent anaphylaxis in OVA-immunized mice, and that this mechanism may depend on inhibition of the IgG-PAF pathway rather than the IgE-histamine pathway.

Thrombin activates calcium independent phospholipase A2 (iPLA2) in lung microvascular endothelial cells

The alveolar‐capillary barrier comprises of type 1 pneumocytes of the alveolar wall, endothelial cells of the capillaries and the basement membrane. Its function is to prevent blood entering the alveoli and to facilitate efficient gaseous exchange. Any disruption in the lining of the lung microveasculature is potentially deleterious. This study examines thrombin stimulation of human lung microvascular endothelial cells (HMVEC‐L) and the resultant increase in iPLA2 activity. Incubation of HMVEC‐L with thrombin resulted in a fourfold increase in iPLA2 activity that remained elevated for up to 60 minutes. Pretreatment of HMVEC‐L with bromoenol lactone (BEL, 2μM, 10 min, a selective iPLA2 inhibitor) but not with PX‐18 (2μM, 10 min, an sPLA2 inhibitor), or AACOCF3 (2μM, 10 min, a cPLA2 inhibitor) attenuated thrombin‐activated iPLA2. Activation of iPLA2 resulted in a rapid increase in arachidonic acid and PGI2 release that was also inhibited by BEL pretreatment. Thrombin stimulation also resulted in a four‐fold increase in neutrophil adherence to the apical surface of HMVEC‐L that was inhibited by BEL pretreatment of HMVEC‐L and pretreatment of the neutrophils with a PAF receptor antagonist. Taken together, these results demonstrate that iPLA2 inhibition has the potential to block the several inflammatory responses produced by thrombin in the lung microvasculature.Supported by AHA, Pre‐Doctoral Fellowship (PR)

PAF and H2O2 act synergistically to increase endothelial cell oxidant stress

We have previously shown that alveolar macrophages from septic mice can 1) induce an oxidant stress in pulmonary endothelial cells (PEC) and 2) promote neutrophil (PMN) transendothelial migration. Both of these responses can be blocked by catalase or a PAF receptor antagonist. In the present study, we assessed whether PAF and/or H2O2 can induce an oxidant stress in endothelial cells. PEC were isolated from murine lungs and exposed to different concentrations of H2O2 (25 – 200 μM) and PAF (10‐10 – 10‐7 M) for 1 hr. Subsequently, PEC oxidant stress was assessed using DHR 123 oxidation as an index. H2O2 increased PEC oxidant stress only when used at the highest concentration (200 μM), while PAF did not increase PEC oxidant stress at any of the concentrations tested. When PAF and H2O2 were added simultaneously to PEC there was a potentiation of PEC oxidant stress. Our findings indicate that PAF and H2O2 act synergistically to promote endothelial cell oxidant stress, most likely through the activation of NADPH oxidase.

Dermal Dendritic Cells, and Not Langerhans Cells, Play an Essential Role in Inducing an Immune Response

Langerhans cells (LCs) serve as epidermal sentinels of the adaptive immune system. Conventional wisdom suggests that LCs encounter Ag in the skin and then migrate to the draining lymph nodes, where the Ag is presented to T cells, thus initiating an immune response. Platelet-activating factor (PAF) is a phospholipid mediator with potent biological effects. During inflammation, PAF mediates recruitment of leukocytes to inflammatory sites. We herein tested a hypothesis that PAF induces LC migration. Applying 2,4-dinitro-1-fluorobenzene (DNFB) to wild-type mice activated LC migration. In contrast, applying DNFB to PAF receptor-deficient mice or mice injected with PAF receptor antagonists failed to induce LC migration. Moreover, after FITC application the appearance of hapten-laden LCs (FITC+, CD11c+, Langerin+) in the lymph nodes of PAF receptor-deficient mice was significantly depressed compared with that found in wild-type mice. LC chimerism indicates that the PAF receptor on keratinocytes but not LCs is responsible for LC migration. Contrary to the diminution of LC migration in PAF receptor-deficient mice, we did not observe any difference in the migration of hapten-laden dermal dendritic cells (FITC+, CD11c+, Langerin-) into the lymph nodes of PAF receptor-deficient mice. Additionally, the contact hypersensitivity response generated in wild-type or PAF receptor-deficient mice was identical. Finally, dermal dendritic cells, but not LCs isolated from the draining lymph nodes after hapten application, activated T cell proliferation. These findings suggest that LC migration may not be responsible for the generation of contact hypersensitivity and that dermal dendritic cells may play a more important role.

Effect of montelukast on platelet activating factor- and tachykinin induced mucus secretion in the rat

BackgroundPlatelet activating factor and tachykinins (substance P, neurokinin A, neurokinin B) are important mediators contributing to increased airway secretion in the context of different types of respiratory diseases including acute and chronic asthma. Leukotriene receptor antagonists are recommended as add-on therapy for this disease. The cys-leukotriene-1 receptor antagonist montelukast has been used in clinical asthma therapy during the last years. Besides its inhibitory action on bronchoconstriction, only little is known about its effects on airway secretions. Therefore, the aim of this study was to evaluate the effects of montelukast on platelet activating factor- and tachykinin induced tracheal secretory activity.MethodsThe effects of montelukast on platelet activating factor- and tachykinin induced tracheal secretory activity in the rat were assessed by quantification of secreted 35SO4 labelled mucus macromolecules using the modified Ussing chamber technique.ResultsPlatelet activating factor potently stimulated airway secretion, which was completely inhibited by the platelet activating factor receptor antagonist WEB 2086 and montelukast. In contrast, montelukast had no effect on tachykinin induced tracheal secretory activity.ConclusionCys-leukotriene-1 receptor antagonism by montelukast reverses the secretagogue properties of platelet activating factor to the same degree as the specific platelet activating factor antagonist WEB 2086 but has no influence on treacheal secretion elicited by tachykinins. These results suggest a role of montelukast in the signal transduction pathway of platelet activating factor induced secretory activity of the airways and may further explain the beneficial properties of cys-leukotriene-1 receptor antagonists.

Characterisation of the range of neutrophil stimulating mediators in cystic fibrosis sputum

Background:Most patients with cystic fibrosis (CF) die of respiratory failure due to chronic infection and destructive neutrophilic inflammation.Objective:To identify potential therapeutic targets by characterising the neutrophil stimulating mediators in the...

Novel Phosphorylcholine‐Containing Protein ofPseudomonas aeruginosaChronic Infection Isolates Interacts with Airway Epithelial Cells

Pseudomonas aeruginosa undergoes phase variation in the expression of the phosphorylcholine (ChoP) epitope, a structure crucial for the virulence of several respiratory pathogens. In this study, ChoP expression analysis comparing organisms from acute and chronic infections revealed that expression of ChoP at 37 degrees C was higher among strains from chronic infections. Coimmunoprecipitation experiments and mass spectrometry analysis demonstrated that ChoP was on the protein elongation factor Tu. The presence of ChoP at the surface was confirmed by immunofluorescence and flow cytometry analysis of intact bacteria. Pretreatment of bronchial epithelial cells or mice with a platelet-activating factor receptor (PAFR) antagonist reduced adhesion and invasion of the ChoP-positive P. aeruginosa isolates. Results of this study suggest that ChoP expression may represent a novel phenotype expressed by the chronic infection isolates that could mediate P. aeruginosa colonization of the epithelial airway by means of the interaction with the PAFR.

Involvement of endogenous leukotriene B4 and platelet‐activating factor in polymorphonuclear leucocyte recruitment to dermal inflammatory sites in rats

A critical role for leukotriene B(4) (LTB(4)) and/or platelet-activating factor (PAF) in regulating polymorphonuclear cell (PMN) trafficking to inflammatory sites has been reported in a number of experimental inflammatory models. In vitro, newly synthesized LTB(4) and PAF were shown to act in an autocrine/paracrine or intracrine fashion to enhance intracellular arachidonic acid availability and leukotriene biosynthesis. This suggested potentially cooperative effects of these lipid mediators in regulating PMN extravasation. The present study aimed to elucidate whether endogenous LTB(4) and PAF may both act to regulate plasma extravasation and PMN trafficking to inflammatory sites in experimental inflammation. With this aim, we have used selective and potent PAF and LTB(4) receptor antagonist pretreatments in dermal and pulmonary inflammation models in rats. Our results show additive inhibitory effects of dual LTB(4) and PAF receptor blockade in either PAF- or LTB(4)-elicited cutaneous PMN accumulation compared to single-drug administration. Furthermore, the combined administration of the drugs inhibited the PMN accumulation induced by the chemically unrelated soluble agonists tumour necrosis factor-alpha and C5a. Finally, in a model of pulmonary inflammation induced by the intravenous injection of Sephadex beads, lung neutrophilia was reduced by 63% following the administration of LTB(4) and PAF antagonists, in contrast with the lack of effect of single drug administration. Our results strongly support a role of both endogenous LTB(4) and PAF in regulating PMN trafficking to inflammatory sites in various experimental conditions.

Platelet Activating Factor as a Mediator and Therapeutic Approach in Bronchial Asthma

Platelet activating factor (PAF) is a potent phospholipid mediator involved in anaphylaxis and chronic inflammatory disorders, including bronchial asthma. PAF is able to act both, directly as a chemotactic factor and indirectly through the release of other inflammatory agents. Apart from its known potent ability to activate platelets, PAF influences other immune and inflammatory cells function involved in asthma, which may be of importance in the pathogenesis of the disease. In addition, PAF administration can mimic some of abnormalities observed in asthma, including bronchoconstriction, bronchial hyper responsiveness, and gas exchange impairment, which may be mediated by leukotrienes acting as secondary mediators of some PAF effects. Therefore, there has been an extensive interest in the role of PAF in human asthma and major efforts have been continued to discover drugs acting thorough inhibition of PAF effects in the disease. Surprisingly, PAF receptor antagonists have not clearly proven their clinical benefits. It may appear that the combined blockage of PAF effects and other mediators involved in asthma is a way to improve clinical efficacy and also an interesting approach to control inflammation in the disease. This review will focus on two main issues: the role of PAF and PAF antagonists in asthma.

Ginkgolides protect against amyloid-β1–42-mediated synapse damage in vitro

BackgroundThe early stages of Alzheimer's disease (AD) are closely associated with the production of the Aβ1–42 peptide, loss of synapses and gradual cognitive decline. Since some epidemiological studies showed that EGb 761, an extract from the leaves of the Ginkgo biloba tree, had a beneficial effect on mild forms of AD, the effects of some of the major components of the EGb 761 extract (ginkgolides A and B, myricetin and quercetin) on synapse damage in response to Aβ1–42 were examined.ResultsThe addition of Aβ1–42 to cortical or hippocampal neurons reduced the amounts of cell associated synaptophysin, a pre-synaptic membrane protein that is essential for neurotransmission, indicating synapse damage. The effects of Aβ1–42 on synapses were apparent at concentrations approximately 100 fold less than that required to kill neurons; the synaptophysin content of neuronal cultures was reduced by 50% by 50 nM Aβ1–42. Pre-treatment of cortical or hippocampal neuronal cultures with ginkgolides A or B, but not with myrecitin or quercetin, protected against Aβ1–42-induced loss of synaptophysin. This protective effect was achieved with nanomolar concentrations of ginkgolides. Previous studies indicated that the ginkgolides are platelet-activating factor (PAF) receptor antagonists and here we show that Aβ1–42-induced loss of synaptophysin from neuronal cultures was also reduced by pre-treatment with other PAF antagonists (Hexa-PAF and CV6209). PAF, but not lyso-PAF, mimicked the effects Aβ1–42 and caused a dose-dependent reduction in the synaptophysin content of neurons. This effect of PAF was greatly reduced by pre-treatment with ginkgolide B. In contrast, ginkgolide B did not affect the loss of synaptophysin in neurons incubated with prostaglandin E2.ConclusionPre-treatment with ginkgolides A or B protects neurons against Aβ1–42-induced synapse damage. These ginkgolides also reduced the effects of PAF, but not those of prostaglandin E2, on the synaptophysin content of neuronal cultures, results consistent with prior reports that ginkgolides act as PAF receptor antagonists. Such observations suggest that the ginkgolides are active components of Ginkgo biloba preparations and may protect against the synapse damage and the cognitive loss seen during the early stages of AD.

Therapy for acute pancreatitis with platelet-activating factor receptor antagonists

Acute pancreatitis (AP) causes release of platelet-activating factor (PAF), which induces systemic effects that contribute to circulatory disturbances and multiple organ failure. PAF is a cell surface secretion of bioactive lipid, which could produce physiological and pathological effects by binding to its cell surface receptor called platelet-activating factor receptor (PAF-R). Studies showed that PAF participate in the occurrence and development of AP and administration of platelet-activating factor receptor antagonists (PAF-RAs) could significantly reduce local and systemic events after AP. PAF has also been implicated as a key mediator in the progression of severe AP, which can lead to complications and unacceptably high mortality rates. Several classes of compounds show significant PAF-RAs, and significant local and systemic effects on reducing inflammatory changes. As a preventive treatment, PAF-RA could block a series of PAF-mediated inflammatory injury and thus improve the prognosis of AP. This review introduces the important role of PAF-RA in the treatment of AP.

Small bowel injury associated to allergy is triggered by platelet-activating factor, mast cells, neutrophils and protected by nitric oxide

Allergy to components of the diet is followed by gut inflammation which in children, sometimes progress to mucosal lesions and anaphylaxis. In newborns suffering of cow's milk allergy, bloody stools, rectal bleeding and ulcerations are found. The rat systemic anaphylaxis is a suitable model to study the intestinal lesions associated to allergy. In the present study we used this model to investigate some mechanisms involved. We found that 15 min after antigen challenge of sensitized rats, hemorrhagic lesions develop in the small intestine. The lesions were more severe in jejunum and ileum compared to duodenum. Pretreatment of the rats with a platelet-activating factor-receptor antagonist (WEB-2170) reduced the lesions whereas inhibition of endogenous nitric oxide by l-NAME, greatly increased the hemorrhagic lesions and mortality. Both, lesions and mortality were reversed by l-arginine. The hemorrhagic lesions were also significantly reduced by the mast cell stabilizers, disodium cromoglycate and ketotifen as well as by neutrophils depletion (with anti-PMN antibodies) or inhibition of selectin binding (by treatment with fucoidan). Thus, the intestinal hemorrhagic lesions in this model are dependent on platelet-activating factor, mast cell granule-derived mediators and neutrophils. Endogenous nitric oxide and supplementation with l-arginine has a protective role, reducing the lesions and preventing mortality. These results contributed to elucidate mechanisms involved in intestinal lesions which could be of relevance to human small bowel injury associated to allergy.

Platelet-activating factor (PAF) induced cytokine production and otitis media with effusion (OME) in the rat middle ear

Objectives We examined the effect of platelet-activating factor (PAF) on IL-8 production in cultured rat middle ear epithelial cells (RMECs), and the concentrations of cytokine, PAF, and PAF-acetylhydrolase (PAF-AH) were also examined in the PAF-induced experimental OME (otitis media with effusion) of rats. Methods Using an enzyme-linked immunospecific assay, we measured the levels of cytokines in the cultured RMECs and the PAF-induced OME of rats. The PAF was quantitated by the platelet-aggregating activity and the PAF-AH was measured by radioimmunoassay. Results Both PAF and C-PAF, which is a stable analogue of PAF, significantly induced production of IL-8 in the RMECs in a dose-dependent manner. The PAF-induced IL-8 production was abolished by co-incubation with WEB2170, a specific PAF receptor antagonist. The concentrations of the cytokines and PAF in the PAF-induced OME of rats were higher on day 1 and the PAF and cytokine levels seemed to correspond well with the persistence of OME. Conclusion PAF may stimulate the local production of cytokines and may induce OME in the middle ear.

Blockades of phospholipase A2 and platelet-activating factor receptors reduce the hemocyte phagocytosis in Rhodnius prolixus: In vitro experiments

The hemocytes phagocytosis in response to microorganisms may play an important role in the cellular immune responses of insects. Here, we have evaluated the effects of the platelet-activating factor (PAF) and eicosanoids in the phagocytosis of hemocyte monolayers of Rhodnius prolixus to the yeast Saccharomyces cerevisiae. Experiments showed that the phagocytosis of yeast cells by Rhodnius hemocytes is very efficient in both controls and cells treated with PAF and arachidonic acid. Phagocytosis of yeast particles is significantly blocked when the specific phopholipase A2 inhibitor, dexamethasone, is applied on the hemocytes. By contrast, dexamethasone-pretreated hemocyte monolayers exhibit a drastic increase in the quantity of yeast cell-hemocyte internalization when the cells are treated by arachidonic acid. In addition, phagocytosis presents significant reduction in hemocyte monolayers treated with a specific PAF receptor antagonist, WEB 2086. Nevertheless, inhibition of phagocytosis with WEB 2086 is counteracted by the treatment of the hemocyte monolayers with PAF. In conclusion, phagocytosis of yeast cells by hemocytes is related to the activation of PAF receptors and eicosanoid pathways in the bloodsucking bug, R. prolixus.

Platelet Activating Factor (PAF) Antagonism with Ginkgolide B Protects the Liver Against Acute Injury. Importance of Controlling the Receptor of PAF

Platelet activating factor (PAF) is an ubiquitous phospholipid that acts as a mediator of numerous pathophysiological conditions, including hepatotoxicity. The present study has been conducted to evaluate the eventual role of the platelet activating factor in post-acetaminophen intoxication of liver, using ginkgolide B, BN52021, a selective PAF receptor antagonist. One group of rats was treated with a toxic dose of acetaminophen (APAP) (3.5 g/kg b.w.) (control group) and a second one with the same dose of APAP followed by a dose of ginkgolide B, BN52021 (10 mg/kg b.w.) (BN52021-treated group). The animals were killed at 8, 16, 24, 32 and 40 h after treatment. APAP was found to cause an acute hepatic injury, evident by alterations of biochemical (serum enzymes: ALT, AST and ALP) and liver histopathological (degree of inflammation and apoptosis) indices, which was followed by liver regeneration evident by three independent indices ([3H] thymidine incorporation into hepatic DNA, liver thymidine kinase activity and hepatocyte mitotic index). Hepatic levels of malondialdehyde and serum cholesterol/HDL cholesterol fraction were also measured as parameters of oxidant-antioxidant balance. The protected effects of ginkgolide B were qualified during post treatment time by: (1) reduction of oxidative stress, (2) high decrease of hepatic injury, and (3) decrease of regenerating activity. These results indicate that PAF may play an important role in APAP-induced liver injury and regeneration, and that the use of ginkgolide B attenuates liver damage providing important means of improving liver function following acetaminophen intoxication.