α-Hederin inhibits the platelet activating factor-induced metastasis of HCC cells through disruption of PAF/PTAFR axis cascaded STAT3/MMP-2 expression.

Metastasis remains a crucial obstacle to the clinical treatment of hepatocellular carcinoma (HCC). Investigating the potential anti-tumor compounds from medicinal herb against HCC metastasis is of particular interest. As a triterpenoid saponin, α-Hederin has been reported to exhibit cytotoxicity for diverse cancer cell lines by inducing mitochondrial related apoptosis or autophagic cell death. Nevertheless, little is known about the inhibitory effect of α-Hederin on the metastasis of HCC and its underlying mechanisms. Here, we integrated well-established target prediction webtool and molecular docking methods to predict the potential targets for α-Hederin, and finally focused on PTAFR, the receptor for platelet-activating factor (PAF). Activation of PAF/PTAFR pathways has been reported to be contribution to the initiation and progression of cancer. We showed for the first time that non-cytotoxic concentration of α-Hederin inhibited cell migration and invasion induced by PAF in HCC cells, as well as lung metastasis in vivo. Moreover, we demonstrated α-Hederin reduced the PAF-induced matrix metalloproteinase-2 expression through inhibiting the activation of STAT3 in PAF stimulated HCC cells. These findings suggest that α-Hederin functions as a prospective inhibitor of PTAFR and may be utilized as an optional candidate for treatment of HCC.

Consumption of Enriched Yogurt with PAF Inhibitors from Olive Pomace Affects the Major Enzymes of PAF Metabolism: A Randomized, Double Blind, Three Arm Trial.

Platelet-activating factor (PAF), a proinflammatory lipid mediator, plays a crucial role in the formation of the atherosclerotic plaque. Therefore, the inhibition of endothelium inflammation by nutraceuticals, such as PAF inhibitors, is a promising alternative for preventing cardiovascular diseases. The aim of the present study was to evaluate the impact of a new functional yogurt enriched with PAF inhibitors of natural origin from olive oil by-products on PAF metabolism. Ninety-two apparently healthy, but mainly overweight volunteers (35-65 years) were randomly allocated into three groups by block-randomization. The activities of PAF's biosynthetic and catabolic enzymes were measured, specifically two isoforms of acetyl-CoA:lyso-PAF acetyltransferase (LPCATs), cytidine 5'-diphospho-choline:1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase (PAF-CPT) and two isoforms of platelet activating factor acetylhydrolase in leucocytes (PAF-AH) and plasma (lipoprotein associated phospholipase-A2, LpPLA2). The intake of the enriched yogurt resulted in reduced PAF-CPT and LpPLA2 activities. No difference was observed in the activities of the two isoforms of lyso PAF-AT. In conclusion, intake of yogurt enriched in PAF inhibitors could favorably modulate PAF biosynthetic and catabolic pathways.

Bioactive Lipids of Marine Microalga Chlorococcum sp. SABC 012504 with Anti-Inflammatory and Anti-Thrombotic Activities.

Microalgae are at the start of the food chain, and many are known producers of a significant amount of lipids with essential fatty acids. However, the bioactivity of microalgal lipids for anti-inflammatory and antithrombotic activities have rarely been investigated. Therefore, for a sustainable source of the above bioactive lipids, the present study was undertaken. The total lipids of microalga Chlorococcum sp., isolated from the Irish coast, were fractionated into neutral-, glyco-, and phospho-lipids, and were tested in vitro for their anti-inflammatory and antithrombotic activities. All tested lipid fractions showed strong anti-platelet-activating factor (PAF) and antithrombin activities in human platelets (half maximal inhibitory concentration (IC50) values ranging ~25-200 µg of lipid) with the highest activities in glyco- and phospho-lipid fractions. The structural analysis of the bioactive lipid fraction-2 revealed the presence of specific sulfoquinovosyl diacylglycerols (SQDG) bioactive molecules and the HexCer-t36:2 (t18:1/18:1 and 18:2/18:0) cerebrosides with a phytosphingosine (4-hydrosphinganine) base, while fraction-3 contained bioactive phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules. These novel bioactive lipids of Chlorococcum sp. with putative health benefits may indicate that marine microalgae can be a sustainable alternative source for bioactive lipids production for food supplements and nutraceutical applications. However, further studies are required towards the commercial technology pathways development and biosafety analysis for the use of the microalga.

Therapeutic promises of ginkgolide A: A literature-based review.

Ginkgolide A is a highly active platelet activating factor antagonist cage molecule which was isolated from the leaves of the Ginkgo biloba L. It is known for its inflammatory and immunological potentials. This review aims to sketch a current scenario on its therapeutic activities on the basis of scientific reports in the databases. A total 30 articles included in this review suggests that ginkgolide A has many important biological activities, including anti-inflammatory, anticancer, anxiolytic-like, anti-atherosclerosis and anti-atherombosis, neuro- and hepatoprotective effects. There is a lack of its toxicological (e.g. toxicity, cytotoxicity, genotoxicity and mutagenitcity) profile. In conclusion, ginkgolide A may be one of the potential therapeutic lead compounds, especially for the treatment of cardiovascular, hepatological, and neurological diseases and disorders. More studies are necessary on this hopeful therapeutic agent.

COVID-19, microthromboses, inflammation, and platelet activating factor.

Recent articles report elevated markers of coagulation, endothelial injury, and microthromboses in lungs from deceased COVID-19 patients. However, there has been no discussion of what may induce intravascular coagulation. Platelets are critical in the formation of thrombi and their most potent trigger is platelet activating factor (PAF), first characterized by Demopoulos and colleagues in 1979. PAF is produced by cells involved in host defense and its biological actions bear similarities with COVID-19 disease manifestations. PAF can also stimulate perivascular mast cell activation, leading to inflammation implicated in severe acute respiratory syndrome (SARS). Mast cells are plentiful in the lungs and are a rich source of PAF and of inflammatory cytokines, such as IL-1ß and IL-6, which may contribute to COVID-19 and especially SARS. The histamine-1 receptor antagonist rupatadine was developed to have anti-PAF activity, and also inhibits activation of human mast cells in response to PAF. Rupatadine could be repurposed for COVID-19 prophylaxis alone or together with other PAF-inhibitors of natural origin such as the flavonoids quercetin and luteolin, which have antiviral, anti-inflammatory, and anti-PAF actions.

Effect of Platelet-Activating Factor on Barrier Function of ARPE-19 Cells.

AIM: To examine the effects of platelet-activating factor (PAF) on the barrier functions of cultured retinal pigment epithelial (RPE) cells. METHODS: A human RPE cell line (ARPE-19) was cultured on microporous filter supports and treated with PAF and WEB 2086, a specific PAF-receptor (PAF-R) antagonist. The permeability of the RPE monolayer was measured using transepithelial electrical resistance (TER) and sodium fluorescein flux. The expression of the tight junction protein zonula occludens (ZO)-1 and the adherens junction protein N-cadherin was assessed using immunohistochemistry and Western blotting. We also measured the vascular endothelial growth factor (VEGF) concentrations in PAF-treated cultures and re-measured RPE monolayer permeability in the presence of VEGF-neutralizing antibodies. RESULTS: PAF significantly decreased the TER and enhanced the sodium fluorescein flux of the RPE monolayer and downregulated the expression of ZO-1 and N-cadherin. These effects were abolished by WEB 2086-mediated blockage of the PAF-R. PAF stimulation increased VEGF expression in RPE cells, and the antibody-mediated neutralization of VEGF caused a partial recovery of the barrier properties. CONCLUSION: The barrier functions of ARPE-19 cells were altered by PAF, and these effects were partly mediated by an upregulation of VEGF expression in these cells. Our results contribute to the growing body of evidence supporting the role of PAF in choroidal neovascularization. Our findings suggest that PAF is a novel target in the development of therapies for increased permeability of the RPE monolayer.

Structural Elucidation of Irish Ale Bioactive Polar Lipids with Antithrombotic Properties.

The structures of bioactive polar lipids (PLs) of Irish ale with potent antithrombotic and cardioprotective properties were elucidated. Ale PL was fractionated by preparative thin layer chromatography (TLC) into subclasses, and their antithrombotic effect was assessed against human platelet aggregation induced by the pro-inflammatory mediator, platelet-activating factor (PAF). The fatty acid content and the overall structures of ale PL were elucidated by liquid chromatography mass spectrometry (LC-MS). Phosphatidylcholines (PC) and molecules of the sphingomyelin (SM) family exhibited the strongest anti-PAF effects, followed by phosphatidylethanolamines (PE). PC contained higher amounts of omega-3 polyunsaturated fatty acids (n-3 PUFA) and thus the lowest n-6/n-3 ratio. Bioactive diacyl and alkyl-acyl PC and PE molecules bearing n-3 PUFA at their sn-2 position, especially docosahexaenoic acid (DHA) and α-linolenic acid (ALA) but mostly oleic acid (OA), were identified in both PC and PE subclasses. Eicosapentaenoic acid (EPA) was present only in bioactive PC molecules and not in PE, explaining the lower anti-PAF effects of PE. Bioactive sphingolipid and glycolipid molecules with reported anti-inflammatory and anti-tumour properties, such as specific ceramides and glucosylcerebrosides with sphingosine, phytosphingosine and dihydrosphingosine bases but also specific monogalactodiglycerides and SM species bearing ALA at their sn-2 position, were identified in the SM subclass, providing a rational for its strong bioactivities against the PAF pathway. Further studies are required on the health benefits of bioactive PL from beer and brewery by-products.

Rupatadine, a dual antagonist of histamine and platelet-activating factor (PAF), attenuates experimentally induced diabetic nephropathy in rats.

The role of histamine and platelet activating factor (PAF) as involved mediators in the pathophysiology of diabetic complications, in particular diabetic nephropathy (DN), has become a new focus of concern. Accordingly, the present study designed to explore the effect of rupatadine (RUP), a dual antagonist of histamine (H1) and PAF, on the progression of experimentally induced DN in rats. Rats were divided into five groups: control, RUP alone, streptozotocin (STZ)-diabetic model, STZ/RUP (3 mg/kg/day), and STZ/RUP (6 mg/kg/day). Treatment has continued for 4 weeks after diabetes confirmation. At the end of the study, serum was collected for measurement of glucose, insulin, urea, creatinine, histamine, and PAF. Renal tissue homogenates were prepared for measuring oxidative stress indices, tumor necrosis factor (TNF-α), cystatin C, and p21. Moreover, immunohistochemical expression of transforming growth factor-ß1 (TGF-ß1) and p53 along with histological pictures was also conducted. Antagonizing H1 and PAF receptors by RUP ameliorated the experimentally induced DN as evident by decreasing all serum parameters augmented by STZ together with improvement of the histopathological picture. RUP administration also improved oxidative-antioxidative agents with reduction in the anti-inflammatory marker, TNF-α. Additionally, the immunohistochemical expression of the fibrosis marker; TGF-ß1, was also decreased. STZ-induced DN showed a p21/p53-dependent induction of premature senescence and RUP administration decreased the expression of p21 and p53 levels in injured renal tissue. RUP represents a novel promising drug to prevent DN complicated diabetes probably via its inhibitory effect on H1 and PAF receptors. The renal protection was also related to the anti-inflammatory and antioxidant roles and PAF-facilitated senescence effect via p21/p53 signaling.

The therapeutic potential of ginkgolide K in experimental autoimmune encephalomyelitis via peripheral immunomodulation.

Multiple sclerosis is a T cell-mediated inflammatory, demyelinating disease of the central nervous system, accompanied by neuronal degeneration. Based on the anti-inflammatory effects of Ginkgolide K (GK), a platelet activating factor antagonist, we explored the possible application of GK in the treatment of MS. The results showed that GK effectively ameliorated the severity of experimental autoimmune encephalomyelitis. The intervention of GK inhibited the infiltration of inflammatory cells and demyelination in the spinal cord. At the same time, the expression of the inflammation-related molecules TLR4, NF-κB, and COX2 in the spinal cord was significantly lower in the GK-treated mice, indicating that GK intervention can inhibit the inflammatory microenvironment of the spinal cord in EAE mice. In mouse spleen lymphocytes, GK increased the proportion of regulatory T cells (Treg) and reduced the proportion of T helper 17 cells (Th17), modifying the imbalance between Th17/Treg cells. Additionally, GK shifted macrophage/microglia polarization from M1 to M2 cell type. Importantly, GK inhibited the expression of chemotactic molecules CCL-2, CCL-3 and CCL-5, thereby limiting the migration of inflammatory cells to the spinal cord. Our results provide the possibility that GK may be a promising naturally small molecule compound for the future treatment of MS.

The Potential Role of Dietary Platelet-Activating Factor Inhibitors in Cancer Prevention and Treatment.

Cancer is the second leading cause of mortality worldwide. The role of unresolved inflammation in cancer progression and metastasis is well established. Platelet-activating factor (PAF) is a key proinflammatory mediator in the initiation and progression of cancer. Evidence suggests that PAF is integral to suppression of the immune system and promotion of metastasis and tumor growth by altering local angiogenic and cytokine networks. Interactions between PAF and its receptor may have a role in various digestive, skin, and hormone-dependent cancers. Diet plays a critical role in the prevention of cancer and its treatment. Research indicates that the Mediterranean diet may reduce the incidence of several cancers in which dietary PAF inhibitors have a role. Dietary PAF inhibitors such as polar lipids have demonstrated inhibitory effects against the physiological actions of PAF in cancer and other chronic inflammatory conditions in vitro and in vivo. In addition, experimental models of radiotherapy and chemotherapy demonstrate that inhibition of PAF as adjuvant therapy may lead to more favorable outcomes. Although promising, there is limited evidence on the potential benefits of dietary PAF inhibitors on cancer prevention or treatment. Therefore, further extensive research is required to assess the effects of various dietary factors and PAF inhibitors and to elucidate the mechanisms in prevention of cancer progression and metastasis at a molecular level.

In vitro Anti-atherogenic Properties of N-Heterocyclic Carbene Aurate(I) Compounds.

The anti-atherogenic (anti-inflammatory) properties of various aurate(I) salts, of the general formula [NHC⋅H][AuCl2 ] (NHC=N-heterocyclic carbene) were investigated. The aurates were easily synthesized and obtained in analytically pure form. In addition, the biological activity of these compounds against atheromatosis via in vitro inhibition of platelet-activating factor (PAF)-induced platelet aggregation was probed. All complexes were found to possess anti-aggregatory properties in vitro with [IPr*⋅H][AuCl2 ] (6) being the most potent inhibitor of PAF at micromolar concentration. Based on our findings, we conclude that these simply assembled aurates are a very promising class of PAF inhibitors and anti-inflammatory drugs.

Human mesenchymal stem cells in the tumour microenvironment promote ovarian cancer progression: the role of platelet-activating factor.

BACKGROUND: The tumour microenvironment conferred by mesenchymal stem cells (MSCs) plays a key role in tumour development and progression. We previously determined that platelet-activating factor receptor (PAFR) was overexpressed in ovarian cancer cells (OCCs) and that PAF can promote ovarian cancer progression via PAF/PAFR-mediated inflammatory signalling pathways. Evidence suggests that MSCs can secrete high concentrations of PAF. Here, we investigated the role of PAF/PAFR signalling in the microenvironment mediated by MSCs and OCCs and its effect on cancer progression. METHODS: The PAF concentrations in the culture media of MSCs, OCCs and co-cultured MSCs and OCCs were determined by ELISA. The effects of MSCs on OCCs in vitro were assessed on cells treated with conditioned medium (CM). The expression and phosphorylation of key proteins in the PAF/PAFR signalling pathway were evaluated. In vivo, MSCs/RFP and SKOV3 cells were co-administered at different proportions to nude mice by interscapular injection. Mice in the WEB2086 group were intraperitoneally injected with the PAFR antagonist WEB2086 at a dose of 1 mg/kg.d for the duration of the animal experiments. Tumour progression was observed, and the weight and survival time of mice were measured. The PAF concentration in peripheral and tumour site blood was determined by ELISA. RESULTS: High concentrations of PAF were detected in CM from MSCs and MSCs co-cultured with OCCs. Both types of medium promoted non-mucinous OCC proliferation and migration but had no effect on mucinous-type OCCs. These effects could be blocked by PAFR inhibitors. The expression and phosphorylation of key proteins in the PAF/PAFR pathway significantly increased upon treatment with PAF and MSC-CM. In vivo, the tumour volume was larger following co-injection of SKOV3 cells and MSCs/RFP than following injection of SKOV3 cells alone. The tumour-promoting effect of MSCs/RFP was blocked by the PAFR antagonist WEB2086. Serum PAF concentrations significantly increased in co-injected mice. CONCLUSION: Our results suggest that the tumour-promoting effect of MSCs on OCCs via their cross-talk in the tumour microenvironment was, at least in part, mediated by the PAF/PAFR pathway, suggesting a new target for the treatment of ovarian cancer.

Tetrahydrobenzofuran-6(2 H)-one Neolignans from Ocotea heterochroma: Their Platelet Activating Factor (PAF) Antagonistic Activity and in Silico Insights into the PAF Receptor Binding Mode.

Three new tetrahydrobenzofuran-6(2 H)-one-type neolignans, heterochromins A-C (1-3), along with a bicyclo[3.2.1]octane neolignan, cinerin C (4), were isolated from an ethanol extract from the leaves of Ocotea heterochroma, a native plant growing in the Colombo-Ecuadorian region of the Andes. The chemical structures of 1-3 were elucidated by spectroscopic methods. The platelet activating factor (PAF) antagonistic activity was tested in vitro for these compounds. Additionally, their binding mode to the PAF receptor was studied by molecular docking and molecular dynamics simulations in order to rationalize such activity. Heterochromin A (1) was found to be a potent PAF antagonist with a favorable molecular profile for interacting with the PAF receptor binding site.

Human pharmacokinetics of ginkgo terpene lactones and impact of carboxylation in blood on their platelet-activating factor antagonistic activity.

Terpene lactones are a class of bioactive constituents of standardized preparations of Ginkgo biloba leaf extract, extensively used as add-on therapies in patients with ischemic cardiovascular and cerebrovascular diseases. This investigation evaluated human pharmacokinetics of ginkgo terpene lactones and impact of their carboxylation in blood. Human subjects received oral YinXing-TongZhi tablet or intravenous ShuXueNing, two standardized ginkgo preparations. Their plasma protein-binding and platelet-activating factor antagonistic activity were assessed in vitro. Their carboxylation was assessed in phosphate-buffered saline (pH 7.4) and in human plasma. After dosing YinXing-TongZhi tablet, ginkgolides A and B and bilobalide exhibited significantly higher systemic exposure levels than ginkgolides C and J; after dosing ShuXueNing, ginkgolides A, B, C, and J exhibited high exposure levels. The compounds' unbound fractions in plasma were 45-92%. Apparent oral bioavailability of ginkgolides A and B was mostly >100%, while that of ginkgolides C and J was 6-15%. Bilobalide's bioavailability was probably high but lower than that of ginkgolides A/B. Terminal half-lives of ginkgolides A, B, and C (4-7 h) after dosing ShuXueNing were shorter than their respective values (6-13 h) after dosing YinXing-TongZhi tablet. Half-life of bilobalide after dosing the tablet was around 5 h. Terpene lactones were roughly evenly distributed in various body fluids and tissues; glomerular-filtration-based renal excretion was the predominant elimination route for the ginkgolides and a major route for bilobalide. Terpene lactones circulated as trilactones and monocarboxylates. Carboxylation reduced platelet-activating factor antagonistic activity of ginkgolides A, B, and C. Ginkgolide J, bilobalide, and ginkgo flavonoids exhibited no such bioactivity. Collectively, differences in terpene lactones' exposure between the two preparations and influence of their carboxylation in blood should be considered in investigating the relative contributions of terpene lactones to ginkgo preparations' therapeutic effects. The results here will inform rational clinical use of ginkgo preparations.

Inflammation, not Cholesterol, Is a Cause of Chronic Disease.

Since the Seven Countries Study, dietary cholesterol and the levels of serum cholesterol in relation to the development of chronic diseases have been somewhat demonised. However, the principles of the Mediterranean diet and relevant data linked to the examples of people living in the five blue zones demonstrate that the key to longevity and the prevention of chronic disease development is not the reduction of dietary or serum cholesterol but the control of systemic inflammation. In this review, we present all the relevant data that supports the view that it is inflammation induced by several factors, such as platelet-activating factor (PAF), that leads to the onset of cardiovascular diseases (CVD) rather than serum cholesterol. The key to reducing the incidence of CVD is to control the activities of PAF and other inflammatory mediators via diet, exercise, and healthy lifestyle choices. The relevant studies and data supporting these views are discussed in this review.

Anti-platelet effects of vitamin supplements in age-related macular degeneration: an in vitro study.

OBJECTIVE: The purpose of this experimental study was to investigate the role of vitamin supplements (Ocuvite, Vitalux Omega, and Nutrof Total) as possible inhibitors of the onset of age-related macular degeneration (AMD). MATERIALS AND METHODS: The anti-aggregating effect of each vitamin was determined against four accumulative factors namely, platelet activating factor (PAF), adenosine diphosphate (ADP), thrombin receptor-activating peptide (TRAP), and arachidonic acid (AA) in the platelet rich plasma (PRP) of healthy volunteers. RESULTS: Ocuvite, Vitalux Omega, and Nutrof Total were more potent inhibitors against PAF and ADP compared to TRAP and AA. Among the three vitamins, Nutrof Total displayed more potent inhibitions against TRAP and AA, while against PAF and ADP all the three vitamins revealed similar IC50 values. CONCLUSIONS: The vitamins Ocuvite, Vitalux Omega, and Nutrof Total have anti-aggregating effects and therefore can be used against AMD in healthy volunteers.

Amiloride interferes with platelet- activating factor-induced respiratory burst and MMP-9 release in bovine neutrophils independent of Na+/H+ exchanger 1.

Cytoplasmic pH homeostasis is required for an appropriate response in polymorphonuclear neutrophils (PMNs). In these cells, chemotaxis and reactive oxygen species (ROS) production are reduced by the use of Na+/H+ exchanger (NHE-1) inhibitors, but these results are mainly obtained using amiloride, a non-selective NHE-1 inhibitor. In bovine PMNs, the role of NHE-1 in functional responses has not been confirmed yet. The aim of this study was to determine the role of NHE-1 using amiloride and zoniporide in pH regulation, ROS production, matrix metalloproteinase 9 (MMP-9) release and calcium flux in bovine PMNs induced by the platelet activation factor (PAF), additionally we evaluated the presence of NHE-1 and NHE-2 mRNA Our data show the presence only of NHE-1 but not NHE-2 in bovine PMNs. Amiloride or zoniporide inhibited the intracellular alkalization induced by PAF without affecting calcium flux. Amiloride diminished ROS production and MMP-9 release, while zoniporide enhanced ROS production without change the MMP-9 release induced by PAF. Our work led us to conclude that changes in intracellular pH induced by PAF are regulated by NHE-1 in bovine neutrophils, but the effects of amiloride on ROS production and MMP-9 release induced by PAF are not NHE-1 dependent.

Platelet-activating factor increases reactive oxygen species-mediated microbicidal activity of human macrophages infected with Leishmania (Viannia) braziliensis.

Platelet-activating factor (PAF) is produced by macrophages during inflammation and infections. We evaluated whether PAF is able to modulate the infection of human macrophages by Leishmania braziliensis, the main Leishmania sp. in Brazil. Monocyte-derived macrophages were incubated with promastigote forms in absence or presence of exogenous PAF. We observed that the treatment of macrophages with low concentrations of PAF prior to infection increased the phagocytosis of L. braziliensis. More importantly, exogenous PAF reduced the parasitism when it was added before, during or after infection. In addition, treatment with a PAF antagonist (PCA 4248) resulted in a significant increase of macrophage infection in a concentration-dependent manner, suggesting that endogenous PAF is important to control L. braziliensis infection. Mechanistically, while exogenous PAF increased production of reactive oxygen species (ROS) treatment with PCA 4248 reduced oxidative burst during L. braziliensis infection. The microbicidal effects of exogenous PAF were abolished when macrophages were treated with apocynin, an NADPH oxidase inhibitor. The data show that PAF promotes the production of ROS induced by L. braziliensis, suggesting that this lipid mediator may be relevant to control L. braziliensis infection in human macrophages.

Stereochemistry- and concentration-dependent effects of phosphatidylserine enrichment on platelet function.

Platelets are small (1-2µm in diameter), circulating anuclear cell fragments with important roles in hemostasis and thrombosis that provide an excellent platform for studying the role of membrane components in cellular communication. Platelets use several forms of communication including exocytosis of three distinct granule populations, formation of bioactive lipid mediators, and shape change (allowing for adhesion). This work explores the role of stereochemistry and concentration of exogenous phosphatidylserine (PS) on platelet exocytosis and adhesion. PS, most commonly found in the phosphatidyl-l-serine (l-PS) form, is exposed on the outer leaflet of the cell membrane after the platelet is activated. Knowledge about the impact of exogenous phosphatidylserine on cell-to-cell communication is limited (particularly concentration and stereochemistry effects). This study found that platelets incubated in l-PS or phosphatidyl-d-serine (d-PS) are enriched to the same extent with their respective incubated PS. All levels of l-PS enrichment also showed an increase in platelet cholesterol, but only the 50µM d-PS incubation showed an increase in cholesterol. The uptake of d-PS induced the secretion of granules and manufactured platelet activating factor (PAF) in otherwise unstimulated platelets. The uptake of l-PS had a greater impact on platelet stimulation by decreasing both the amount of δ-granule secretion and the amount of PAF that was manufactured.

In Vitro Effects of Anti-Glaucomatous Eye Drops on Platelet-Activating Factor and its Metabolism.

PURPOSE: The purpose of this study is to determine the effect of various commonly used antiglaucoma eye drops on inflammatory mediators such as the platelet activating factor (PAF). METHODS: Various intraocular pressure (IOP) lowering drops were tested to examine their inhibitory effect on PAF. Multiple eye drops were tested in washed rabbit platelets (WRPs) in order to determine the interaction between these eye drops and the inhibition of PAF in the PAF-induced platelet aggregation model. In addition, we examined the eyedrops' effect on PAF-metabolism, through in vitro analysis on PAF basic metabolic enzymes (PAF-CPT, lyso PAF-AT, and PAF-AH). RESULTS: Latanoprost (Xalatan) was found to be the most potent in inhibiting PAF, suggesting that it is the most effective in decreasing IOP amongst the eye drops tested. Conversely, dorzolamide hydrochloride-timolol (Cosopt) exhibited the least anti-PAF action. CONCLUSIONS: This is the first study examine the relationship between PAF activity and glaucoma medication. Potency in PAF inhibition may be related to drop efficacy.