Effects Of Platelet-activating Factor Research Articles

Platelet-activating Factor (PAF) in Urinary Bladder Smooth Muscle (UBSM): Its Novel Role as a Potential Inducer of Detrusor Overactivity and the Mechanisms Underlying Its Effects in Enhancing UBSM Mechanical Activities

Platelet-activating factor (PAF), a phospholipid mediator, was discovered in 1972 as an inducer of platelet aggregation. Subsequent studies have revealed that PAF has a variety of biological functions, such as its role as a potent proinflammatory mediator. Additionally, PAF regulates the contractile functions of various types of smooth muscle (SM), such as the (1) endothelium-dependent relaxation of vascular SM; (2) contraction and epithelium-dependent relaxation of airway SM; (3) contraction of gastrointestinal SM; and (4) contraction of uterine SM, which occurs more strongly in pregnant females. PAF is produced in platelets, monocytes, neutrophils, and macrophages, which are cells related to thrombus formation and inflammation/immune responses. Furthermore, PAF is produced in various other cells throughout the body. Interestingly, recent studies have focused on the urinary bladder (UB) as a PAF-producing organ since the accumulation of this phospholipid is enhanced in patients with bladder cancer and interstitial cystitis/bladder pain syndrome, especially those who smoke. Therefore, in UB tissue, PAF may play a substantial role as an inducer or enhancer of cancers and inflammatory diseases. However, the effects of PAF on the immediate mechanical activities of UBSM have not been investigated to date. In this regard, we recently discovered that PAF strongly enhances mechanical activities (muscle tone and spontaneous contractile activity) in UBSM tissues isolated from guinea pigs and mice. In this review article, we present our data on these PAF effects together with the possible underlying mechanisms. We also discuss the potential pathophysiological roles of this phospholipid in UB diseases and disorders.

Effects of Platelet-Activating Factor (PAF) on the Mechanical Activities of Lower Urinary Tract and Genital Smooth Muscles.

Since its first discovery as a bioactive phospholipid inducing potent platelet aggregation, platelet-activating factor (PAF) has been shown to be involved in a wide variety of inflammatory and allergic disease states. Many pharmacological studies in the 1980s and 1990s also showed that PAF induces endothelium-dependent vascular relaxation and contraction of various smooth muscles (SMs), including those in the airway, gastrointestinal organs, and uterus. However, since the late 1990s, there have been few reports on the SM contractions induced by PAF. The lower urinary tract (LUT), particularly the urinary bladder (UB) has attracted recent attention in SM pharmacology research because patients with LUT dysfunctions including overactive bladder are increasing as the population ages. In addition, recent clinical studies have implicated the substantial role of PAF in the inflammatory state in LUT because its production increases with smoking and with cancer. However, the effects of PAF on mechanical activities of LUT SMs including UBSM have not been investigated to date. Recently, we found that PAF very strongly increased mechanical activities of UBSM in guinea pigs and mice, and partly elucidated the possible mechanisms underlying these actions of PAF. In this review, we describe the effects of PAF on LUT SMs by introducing our recent findings obtained in isolated UBSMs and discuss the physiological and pathophysiological significance. We also introduce our data showing the effects of PAF on the SM mechanical activities of genital tissues (prostate and vas deferens).

Effect of platelet-activating factor on food intake, cloacal temperature, voluntary activity and crop emptying rate in chicks

Platelet-activating factor (PAF) plays a significant role in several leucocyte functions, including platelet aggregation and inflammation. Additionally, PAF has a role in the behavioral and physiological changes in mammals. However, the effect of PAF has not been well studied in birds. Therefore, the study aimed to determine if PAF affects feeding behavior, voluntary activity, cloacal temperature, and feed passage through the digestive tract in chicks (Gallus gallus). We also studied the involvement of PAF in the innate immune system induced by lipopolysaccharide (LPS), a cell wall component of gram-negative bacteria. Both intraperitoneal (IP) and intracerebroventricular (ICV) injections of PAF significantly decreased food intake. IP injection of PAF significantly decreased voluntary activity and slowed the feed passage from the crop, whereas ICV injection had no effect. Conversely, ICV injection of PAF significantly increased the cloacal temperature, but IP injection had no effect. The IP injection of LPS significantly reduced the mRNA expression of lysophosphatidylcholine acyltransferase 2, an enzyme responsible for PAF production in the heart and pancreas. On the other hand, LPS significantly increased the mRNA expression of the PAF receptor in the peripheral organs. The present study shows that PAF influences behavioral and physiological responses and is related to the response against bacterial infections in chicks.

Platelet-activating factor (PAF) strongly enhances contractile mechanical activities in guinea pig and mouse urinary bladder

In this study, we investigated the effects of platelet-activating factor (PAF) on the basal tone and spontaneous contractile activities of guinea pig (GP) and mouse urinary bladder (UB) smooth muscle (UBSM) tissues to determine whether PAF could induce UBSM tissue contraction. In addition, we examined the mRNA expression of the PAF receptor, PAF-synthesizing enzyme (lysophosphatidylcholine acyltransferase, LPCAT), and PAF-degrading enzyme (PAF acetylhydrolase, PAF-AH) in GP and mouse UB tissues using RT-qPCR. PAF (10−9–10−6 M) strongly enhanced the basal tone and spontaneous contractile activities (amplitude and frequency) of GP and mouse UBSM tissues in a concentration-dependent manner. The enhancing effects of PAF (10−6 M) on both GP and mouse UBSM contractile activities were strongly suppressed by pretreatment with apafant (a PAF receptor antagonist, GP: 10−5 M; mouse: 3 × 10−5 M). The PAF receptor (Ptafr), LPCAT (Lpcat1, Lpcat2), and PAF-AH (Pafah1b3, Pafah2) mRNAs were detected in GP and mouse UB tissues. These findings reveal that PAF strongly enhances the contractile mechanical activities of UBSM tissues through its receptor and suggest that the PAF-synthesizing and -degrading system exists in UBSM tissues. PAF may serve as both an endogenous UBSM constrictor and an endogenous mediator leading to detrusor overactivity.

Activation of canine neutrophils by platelet-activating factor

Neutrophils are essential for innate immunity as the first line of defence. Neutrophils act as phagocytic white blood cells to kill bacteria and other microorganisms. A strong respiratory burst of neutrophils, dependent on reactive oxygen species, is produced during phagocytosis. Platelet-activating factor (PAF) is a signalling molecule with several prominent roles in tissue injury, inflammation, and platelet aggregation. However, the detailed mechanisms and intracellular signalling pathways involved in PAF-mediated neutrophil activation remain unclear. Here, we investigated the effect of PAF on changes in calcium concentration ([Ca2+]i) and oxygen radical (O2−) generation in activating canine neutrophils. We further evaluated these effects of PAF with inhibition of G protein-coupled receptors using the specific inhibitor suramin. Blood samples were collected from a total of five dogs and neutrophils were isolated. PAF stimulation of canine neutrophils caused an increase in [Ca2+]i as well as the generation of O2−, and the PAF receptor was sensitive to suramin. The results suggested that PAF stimulation of canine neutrophils may cause Ca2+ influx from the endoplasmic reticulum into the cytoplasm (as the first wave) and then trigger store-operated Ca2+ entry (as the second wave), which is an important intracellular signal transduction pathway for neutrophil activation. Furthermore, O2− generation by PAF stimulation may depend on the intracellular signalling pathway, with increasing inositol trisphosphate levels and [Ca2+]i via G protein-coupled receptors. The finding that PAF-activating platelet aggregation is involved in canine neutrophil activation suggests a close relationship between haemostasis and neutrophil activation in dogs, offering new insight into the response to infection.

A novel receptor for platelet-activating factor and lysophosphatidylcholine in Trypanosoma cruzi.

The lipid mediators, platelet-activating factor (PAF) and lysophosphatidylcholine (LPC), play relevant pathophysiological roles in Trypanosoma cruzi infection. Several species of LPC, including C18:1 LPC, which mimics the effects of PAF, are synthesized by T. cruzi. The present study identified a receptor in T. cruzi, which was predicted to bind to PAF, and found it to be homologous to members of the progestin and adiponectin family of receptors (PAQRs). We constructed a three-dimensional model of the T. cruzi PAQR (TcPAQR) and performed molecular docking to predict the interactions of the TcPAQR model with C16:0 PAF and C18:1 LPC. We knocked out T. cruzi PAQR (TcPAQR) gene and confirmed the identity of the expressed protein through immunoblotting and immunofluorescence assays using an anti-human PAQR antibody. Wild-type and knockout (KO) parasites were also used to investigate the in vitro cell differentiation and interactions with peritoneal mouse macrophages; TcPAQR KO parasites were unable to react to C16:0 PAF or C18:1 LPC. Our data are highly suggestive that PAF and LPC act through TcPAQR in T. cruzi, triggering its cellular differentiation and ability to infect macrophages.

Prolonged Exposure to Platelet Activating Factor Transforms Breast Epithelial Cells.

Lipid species are known to have various biological functions owing to their structural differences, and each of them possesses a specific role to play depending upon their location and distribution in the cell. Some of these lipids interact with proteins on the cell membrane and acts as second messengers. The level of lipid mediators is generally maintained in the cell by feedback mechanisms; however, their improper degradation or enhanced production leads to their accumulation in the tumor microenvironment and disturbs the homeostasis of the cell. Platelet activating factor (PAF) is a known phospholipid mediator secreted upon immunological challenges by platelets, neutrophils, basophils, and macrophages. PAF, as a potent inflammatory molecule, is well studied, and its role in various cancers and cardiovascular diseases has also been investigated. Interestingly, increased levels of PAF have been found in the blood plasma of smokers, and breast cancer cells have shown the accumulation of PAF in presence of cigarette smoke extract. This accumulation was found to increase tumor cell motility that in turn could promote metastasis. Beyond this, however, the effect of PAF on tumorigenesis has not yet been well explored. Here, we show that the continuous exposure of 3D breast acinar cultures to PAF resulted in the activation of various oncogenic signaling pathways leading to transformation. We also found that the presence of PAF in the micro-environment increased the expression of PAF receptor (PAF-R), which corroborated with the higher expression of PAF-R detected in some epithelial cancers, as per literature. Thus, this study impresses on the fact that the presence of PAF alters the cellular microenvironment and eventually triggers irreversible effects that can cumulatively lead to transformation.

A Review of Platelet-Activating Factor As a Potential Contributor to Morbidity and Mortality Associated with Severe COVID-19.

The precise mechanisms of pathology in severe COVID-19 remains elusive. Current evidence suggests that inflammatory mediators are responsible for the manifestation of clinical symptoms that precedes a fatal response to infection. This review examines the nature of platelet activating factor and emphasizes the similarities between the physiological effects of platelet activating factor and the clinical complications of severe COVID-19.

Interplay Between EGFR and the Platelet-Activating Factor/PAF Receptor Signaling Axis Mediates Aggressive Behavior of Cervical Cancer.

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase widely expressed in cervical tumors, being correlated with adverse clinical outcomes. EGFR may be activated by a diversity of mechanisms, including transactivation by G-protein coupled receptors (GPCRs). Studies have also shown that platelet-activating factor (PAF), a pro-inflammatory phospholipid mediator, plays an important role in the cancer progression either by modulating the cancer cells or the tumor microenvironment. Most of the PAF effects seem to be mediated by the interaction with its receptor (PAFR), a member of the GPCRs family. PAFR- and EGFR-evoked signaling pathways contribute to tumor biology; however, the interplay between them remains uninvestigated in cervical cancer. In this study, we employed The Cancer Genome Atlas (TCGA) and cancer cell lines to evaluate possible cooperation between EGFR, PAFR, and lysophosphatidylcholine acyltransferases (LPCATs), enzymes involved in the PAF biosynthesis, in the context of cervical cancer. It was observed a strong positive correlation between the expression of EGFR × PAFR and EGFR × LPCAT2 in 306 cervical cancer samples. The increased expression of LPCAT2 was significantly correlated with poor overall survival. Activation of EGFR upregulated the expression of PAFR and LPCAT2 in a MAPK-dependent fashion. At the same time, PAF showed the ability to transactivate EGFR leading to ERK/MAPK activation, cyclooxygenase-2 (COX-2) induction, and cell migration. The positive crosstalk between the PAF-PAFR axis and EGFR demonstrates a relevant linkage between inflammatory and growth factor signaling in cervical cancer cells. Finally, combined PAFR and EGFR targeting treatment impaired clonogenic capacity and viability of aggressive cervical cancer cells more strongly than each treatment separately. Collectively, we proposed that EGFR, LPCAT2, and PAFR emerge as novel targets for cervical cancer therapy.

Platelet-Activating Factor Deteriorates Lysophosphatidylcholine-Induced Demyelination Via Its Receptor-Dependent and -Independent Effects.

Accumulating evidence suggests that platelet-activating factor (PAF) increases the inflammatory response in demyelinating diseases such as multiple sclerosis. However, PAF receptor (PAFR) antagonists do not show therapeutic efficacy for MS, and its underlying mechanisms remain poorly understood. In the present study, we investigated the effects of PAF on an ex vivo demyelination cerebellar model following lysophosphatidylcholine (LPC, 0.5mg/mL) application using wild-type and PAFR conventional knockout (PAFR-KO) mice. Demyelination was induced in cerebellar slices that were cultured with LPC for 18h. Exogenous PAF (1μM) acting on cerebellar slices alone did not cause demyelination but increased the severity of LPC-induced demyelination in both wild-type and PAFR-KO mice. LPC inhibited the expression of PAF-AH, MBP, TNF-α, and TGF-β1 but facilitated the expression of IL-1β and IL-6 in wild-type preparations. Of note, exogenous PAF stimulated microglial activation in both wild-type and PAFR-KO mice. The subsequent inflammatory cytokines TNFα, IL-1β, and IL-6 as well as the anti-inflammatory cytokine TGF-β1 demonstrated a diverse transcriptional profile with or without LPC treatment. PAF promoted TNF-α expression and suppressed TGF-β1 expression indiscriminately in wild-type and knockout slices; however, transcription of IL-1β and IL-6 was not significantly affected in both slices. The syntheses of IL-1β and IL-6 were significantly increased in LPC-induced demyelination preparations without PAF but showed a redundancy in PAF-treated wild-type and knockout slices. These data suggest that PAF can play a detrimental role in LPC-induced demyelination probably due to a redundant response of PAFR-dependent and PAFR-independent effects on inflammatory cytokines.

Platelet-Activating Factor-Induced Reduction in Contact Hypersensitivity Responses Is Mediated by Mast Cells via Cyclooxygenase-2-Dependent Mechanisms.

Platelet-activating factor (PAF) stimulates numerous cell types via activation of the G protein-coupled PAF receptor (PAFR). PAFR activation not only induces acute proinflammatory responses, but it also induces delayed systemic immunosuppressive effects by modulating host immunity. Although enzymatic synthesis and degradation of PAF are tightly regulated, oxidative stressors, such as UVB, chemotherapy, and cigarette smoke, can generate PAF and PAF-like molecules in an unregulated fashion via the oxidation of membrane phospholipids. Recent studies have demonstrated the relevance of the mast cell (MC) PAFR in PAFR-induced systemic immunosuppression. The current study was designed to determine the exact mechanisms and mediators involved in MC PAFR-mediated systemic immunosuppression. By using a contact hypersensitivity model, the MC PAFR was not only found to be necessary, but also sufficient to mediate the immunosuppressive effects of systemic PAF. Furthermore, activation of the MC PAFR induces MC-derived histamine and PGE2 release. Importantly, PAFR-mediated systemic immunosuppression was defective in mice that lacked MCs, or in MC-deficient mice transplanted with histidine decarboxylase- or cyclooxygenase-2-deficient MCs. Lastly, it was found that PGs could modulate MC migration to draining lymph nodes. These results support the hypothesis that MC PAFR activation promotes the immunosuppressive effects of PAF in part through histamine- and PGE2-dependent mechanisms.

Research progress of platelet activating factor(PAF) receptor antagonist

Platelet activating factor(PAF), an endogenous synthesized phospholipid transmitter, has widely biological activities. It has "signal transmission" effect in various life processes, but abnormality of concentration in vivo will promote or aggravate the diseases, such as, cerebral ischemia, myocardial injury, multi-organ failure, asthma, injury of liver and kidney, severely affecting the normal life activities of body. In recent years, with the development of medical science and technology, more and more attention has been paid to the research of platelet activating factor receptor antagonist. Components of animals, plants, microbial fermentation, and synthetic composition all can reflect such activity. Ginkgolide B and cytopone are the most representative herbal compositions at present. This paper referred to the research status of platelet activating factor receptor antagonist in recent years, made a summary of the researches on biological effect of platelet activating factor and platelet receptor antagonist of different sources, so as to provide a reference for the exploration of effective and safe platelet activating factor receptor antagonists.

Rho Kinase inhibitors and hypoxia modulate expression of platelet activating factor (PAF) receptor and gene expression in fetal ovine pulmonary vascular smooth muscle cells.

Hypoxia and PAF augment intracellular calcium flux in fetal ovine pulmonary vascular smooth muscle cells (PVSMC) indicating that high pulmonary vascular tone in fetal pulmonary vessels in utero is consequent on combined effects of hypoxia and PAF receptor (PAFR)‐linked vascular responses. PAFR internalization is said to inactivate PAF effects in PVSMC in vitro. Hypoxia increases PAFR expression, but Rho kinase (ROCK) inhibitors decrease the expression suggesting PAFR internalization may be one pathway to downregulate PAFR‐mediated responses in PVSMC. These findings also suggest that ROCK may act in synergy with PAF to modulate PAFR‐mediated pulmonary vascular responses. We studied effects of PAF, hypoxia and other modulators of pulmonary vascular reactivity in arterial (PA) and venous (PV) smooth muscle cells (SMC) to aid in understanding the signaling pathways of PAFR‐mediated fetal ovine pulmonary vascular reactivity in utero. We hypothesized that ROCK inhibitors attenuate PAFR expression in hypoxia leading to increased expression of the contractile proteins. Cells were cultured in normoxia or hypoxia, with and without 10 nM PAF or ROCK inhibitors (Y27632 and HA 1077, each 10 μM). Proteins were probed for PAFR, and Calponin, MLCK and Desmin, which are contractile protein modulators of PVSMC activity. PAF binding, PAFR protein and gene expression by qRT‐PCR were also determined. In normoxia, PAFR density (Bmax) in PA and PV SMC were 487±37 and 624±17 respectively, which increased by 30–35% in hypoxia, and higher in PV than PA in normoxia and hypoxia. The KD for PAF binding to PASMC was higher than for PVSMC, and then hypoxia decreased the KD of PAFR binding in both cell types. ROCK inhibitors attenuated PAFR binding with comparable effect to cycloheximide, but unlike PAFR inhibitor, CV3988, cycloheximide had no effect on pre‐synthesized proteins. ROCK inhibitors decreased PAFR expression, but increased expression of MLCK2, Calponin and Desmin in PASMC especially in hypoxia, with different effects in PVSMC. Generally, PAFR gene expression studied by qRT‐PCR was higher in PVSMC under all conditions. This study shows that hypoxia in conjunction with ROCK inhibitors modulate PAFR‐mediated signaling in PVSMC in vitro with different effects on cells from PA and PV. Increased expression of the contractive proteins in hypoxia indicates involvement of these proteins in PAF‐induced contractions in PVSMC.Support or Funding InformationLABiomedThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of Platelet-Activating Factor on Brain Microvascular Endothelial Cells

Platelet-activating factor (PAF) is a potent phospholipid mediator that exerts various pathophysiological effects by interacting with a G protein-coupled receptor. PAF has been reported to increase the permeability of the blood–brain barrier (BBB) via incompletely characterized mechanisms. We investigated the effect of PAF on rat brain microvascular endothelial cells (RBMVEC), a critical component of the BBB. PAF produced a dose-dependent increase in cytosolic Ca2+ concentration; the effect was prevented by the PAF receptor antagonist, WEB2086. The effect of PAF on cytosolic Ca2+ was abolished in Ca2+-free saline or in the presence of L-type voltage-gated Ca2+ channel inhibitor, nifedipine, indicating that Ca2+ influx is critical for PAF-induced increase in cytosolic Ca2+. PAF produced RBMVEC depolarization; the effect was inhibited by WEB2086. In cells loaded with [(4-amino-5-methylamino-2′,7′-difluoro-fluorescein)diacetate] (DAF-FM), a nitric oxide (NO)-sensitive fluorescent dye, PAF increased the NO level; the effect was prevented by WEB2086, nifedipine or by l-NAME, an inhibitor of NO synthase. Immunocytochemistry studies indicate that PAF reduced the immunostaining of ZO-1, a tight junction-associated protein, increased F-actin fibers, and produced intercellular gaps. PAF produced a decrease in RBMVEC monolayer electrical resistance assessed with Electric Cell-Substrate Impedance Sensing (ECIS), indicative of a disruption of endothelial barrier function. In vivo studies indicate that PAF increased the BBB permeability, assessed with sodium fluorescein and Evans Blue methods, via PAF receptor-dependent mechanisms, consequent to Ca2+ influx and increased NO levels. Our studies reveal that PAF alters the BBB permeability by multiple mechanisms, which may be relevant for central nervous system (CNS) inflammatory disorders.

The Effects of Platelet-Activating Factor on Uterine Contractility, Perfusion, Hypoxia, and Pain in Mice.

It is widely hypothesized that menstrual pain is triggered by prostaglandin synthesis that evokes high-pressure uterine contractions and ischemia. However, the effects of molecules implicated in menstrual pain on uterine contractility, perfusion, and oxygenation in vivo have been rarely demonstrated. Studies in women that do not respond to nonsteroidal anti-inflammatory drugs (NSAIDs) have reported elevated levels of platelet-activating factor (PAF). To establish in vivo evidence of PAF's capability to impair uterine homeostasis and to elicit visceral pain, we examined the effects of the PAF receptor agonist (carbamyl PAF [CPAF]) in comparison to other molecules hypothesized to play a role in uterine pain in mice. Uterine pressure was increased by oxytocin, prostaglandin F2α (PGF2α), and CPAF. Even in the absence of inflammatory molecules, uterine contractions reduced uterine oxygenation by 38%. CPAF reduced uterine perfusion by 40% ± 8% and elicited further oxygen desaturation approaching hypoxia (9.4 ± 3.4 mm Hg Pao2). Intraperitoneal injections of CPAF and PGF2α evoked visceral pain and pelvic hyperalgesia in awake wild-type mice. However, pain was not observed in identically injected PAF-receptor knockout mice. Thus, our model provides a demonstration that a molecule implicated in NSAID-resistant dysmenorrhea has a detrimental effect on uterine homeostasis and is capable of causing visceral pain. Our results support the general hypothesis that menstrual cramps are caused by uterine contractions, impaired perfusion, and reduced oxygenation. Since this study was limited to mice, confirmation of these results in humans would be valuable for development of novel therapeutics targeted at inflammatory precursors, contractility, perfusion, and tissue oxygenation.

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.

Modulation of Tumor-Associated Macrophages (TAM) Phenotype by Platelet-Activating Factor (PAF) Receptor.

Platelet-activating factor (PAF) plays an important role in the pathogenesis of several types of tumors. The biological effects of PAF are mediated by the PAF receptor (PAFR), which can be expressed by tumor cells and host cells that infiltrate the tumor microenvironment. In the present study, we investigated the role of PAFR expressed by leukocytes that infiltrate two types of tumors, one that expresses PAFR (TC-1 carcinoma) and another that does not express the receptor (B16F10 melanoma) implanted in mice that express the receptor or not (PAFR KO). It was found that both tumors grew significantly less in PAFR KO than in wild-type (WT) mice. Analysis of the leukocyte infiltration shown in PAFR KO increased the frequency of neutrophils (Gr1+) and of CD8+ lymphocytes in B16F10 tumors and of CD4+ lymphocytes in TC-1 tumors. PAFR KO also had a higher frequency of M1-like (CD11c+) and lower M2-like (CD206+) macrophages infiltrated in both tumors. This was confirmed in macrophages isolated from the tumors that showed higher iNOS, lower arginase activity, and lower IL10 expression in PAFR KO tumors than WT mice. These data suggest that in the tumor microenvironment, endogenous PAF-like activity molecules bind PAFR in macrophages which acquire an M2-like profile and this promotes tumor growth.

Platelet-activating factor and oxidized phosphatidylcholines do not suppress endotoxin-induced pro-inflammatory signaling among human myeloid and endothelial cells

Platelet-activating factor (PAF) and related phospholipid oxidation products termed oxidized phospholipids (OxPLs) promote inflammation. PAF is made in response to bacterial endotoxin-lipopolysaccharide (LPS) that is recognized by Toll-like receptor-4 (TLR-4) whose activation leads to translocation of transcription factor NF-ΚB to the nucleus—a key regulator of multiple pro-inflammatory genes including COX-2 and IL-8. Paradoxically, PAF and OxPLs are claimed to inhibit LPS-mediated signaling, questioning the very pro-inflammatory roles of PAF and OxPLs and anti-inflammatory nature of PAF-acetylhydrolase (PAF-AH), an enzyme that attenuates both PAF and OxPLs signaling. We investigated the effect of PAF and representative OxPLs: 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphocholine (POVPC), 1-palmitoyl-2-glutaroyl-sn- glycero-3-phosphocholine (PGPC) and 1-alkyl-2-butanoyl-sn-glycero-3-phosphocholine PAF (C4 PAF) on LPS-induced expression of NF-ΚB mediated inflammation in isolated human myeloid cells: polymorphonuclear leukocyte (PMNs), monocytes and human umbilical vein endothelial cells (HUVECs). Using intracellular calcium transients, we show that POVPC and PGPC dose-dependently activate the PAF-receptor (PAF-R) in PMNs, that can beblocked by the PAF-R antagonist WEB-2086 and rPAF-AH pre-treatment. All the three cell types express minute or no detectable COX-2 when stimulated with either PAF (0.1 µM) or OxPLs (0.1 µM) alone. While LPS (100 ng/mL) induced expression of COX-2 in all the cell types, pre-activation of PAF-R with PAF (0.1 µM) or OxPLs (0.1 µM) did not suppress LPS (100 ng/mL)-induced COX-2 expression and in fact we obresved incereased PGE2 levels in an NS-398 sensitive manner. In addition, pre-activation of PAF-R significantly augmented LPS (100 ng/mL)-induced IL-8 production in PMNs. Thus, PAF and OXPLs do not suppress the ability of LPS to exert its pro-inflammatory effects in isolated human vascular cells.

Platelet-activating factor receptor activation promotes prostate cancer cell growth, invasion and metastasis via ERK1/2 pathway.

Platelet-activating factor (PAF) and its receptor (PAFR), have been reported to participate in many cellular processes of cancer. However, little is known about their function in prostate cancer. In the present study, we found that PAFR was overexpressed in prostate cancer cells. PAF stimulation dose-dependently promoted the invasion, migration and growth of prostate cancer cells invitro, while knockdown of PAFR inhibited the effect of PAF on prostate cancer cells. We further found that PAFR promoted prostate cancer cell growth and metastasis invivo. Moreover, we found that PAFR activation increased MMP-3 expression and decreased E-cadherin expression of prostate cancer cells invitro and invivo. Finally, we found that PAFR time-dependently induced activation of ERK1/2, and ERK1/2 pathway contributed to PAFR-mediated prostate cancer cell invasion, migration and growth. Together, our findings demonstrate that PAFR can activate ERK1/2 pathway, and subsequently increase MMP-3 expression and decrease E-cadherin expression, which finally promote prostate cancer cell growth, invasion and metastasis. Thus, PAFR may act as a potential target for therapeutic use of prostate cancer.

Butyric acid stimulates bovine neutrophil functions and potentiates the effect of platelet activating factor

Increased short-chain fatty acid (SCFA) production is associated with subacute ruminal acidosis (SARA) and activation of inflammatory processes. In humans and rodents, SCFAs modulate inflammatory responses in the gut via free fatty acid receptor 2 (FFA2). In bovines, butyric acid is one of the most potent FFA2 agonists. Its expression in bovine neutrophils has recently been demonstrated, suggesting a role in innate immune response in cattle. This study aimed to evaluate if butyric acid modulates oxidative and non-oxidative functions or if it can potentiate other inflammatory mediators in bovine neutrophils. Our results showed that butyric acid can activate bovine neutrophils, inducing calcium (Ca2+) influx and mitogen-activated protein kinase (MAPK) phosphorylation, two second messengers involved in FFA2 activation. Ca2+ influx induced by butyric acid was dependent on the extracellular and intracellular Ca2+ source and phospholipase C (PLC) activation. Butyric acid alone had no significant effect on reactive oxygen species (ROS) production and chemotaxis; however, a priming effect on platelet-activating factor (PAF), a potent inflammatory mediator, was observed. Butyric acid increased CD63 expression and induced the release of neutrophil granule markers matrix metalloproteinase-9 (MMP-9) and lactoferrin. Finally, we observed that butyric acid induced neutrophil extracellular trap (NET) formation without affecting cellular viability. These findings suggest that butyric acid, a component of the ruminal fermentative process, can modulate the innate immune response of ruminants.