Platelet-activating Factor Production Research Articles

Lysophospholipid Acyltransferase 9 Promotes Emphysema Formation via Platelet-activating Factor.

Cigarette smoking is known to be the leading cause of chronic obstructive pulmonary disease (COPD). However, the detailed mechanisms have not been elucidated. Platelet-activating factor (PAF), a potent inflammatory mediator, is involved in the pathogenesis of various respiratory diseases, such as bronchial asthma or COPD. We focused on lysophospholipid acyltransferase 9 (LPLAT9), a biosynthetic enzyme of PAF, in the pathogenesis of COPD. LPLAT9 gene expression was observed in excised COPD lungs and single-cell RNA sequencing data of alveolar macrophage (AM). LPLAT9 was predominant and upregulated in AM, particularly monocyte-derived AM, in patients with COPD. To identify the function of LPLAT9/PAF in AM on the pathogenesis of COPD, we exposed cigarette smoke (CS) to systemic LPLAT9 knockout (LPALT9-/-) mice. CS increased the number of AM, especially monocyte-derived fraction, which secreted matrix metalloprotease 12 (MMP12). Also, CS augmented LPLAT9 phosphorylation/activation on macrophage and, subsequently, PAF synthesis in mice lung. LPLAT9-/- mice lung reduced PAF production after CS exposure. Intratracheal PAF administration accumulated AM by increasing monocyte chemoattractant protein-1 (MCP1). After CS exposure, AM accumulation and subsequent pulmonary emphysema, a primary pathologic change of COPD, were reduced in LPALT9-/- mice than in LPLAT9+/+ mice. Notably, these phenotypes got worsened again by LPLAT9+/+ bone marrow transplantation in LPALT9-/- mice. Thus, CS-induced LPLAT9 activation in monocyte-derived AM aggravated pulmonary emphysema via PAF-induced further AM accumulation. These results suggest that PAF synthesized by LPLAT9 has an important role in the pathogenesis of COPD.

PAFAH2 suppresses synchronized ferroptosis to ameliorate acute kidney injury.

Synchronized ferroptosis contributes to nephron loss in acute kidney injury (AKI). However, the propagation signals and the underlying mechanisms of the synchronized ferroptosis for renal tubular injury remain unresolved. Here we report that platelet-activating factor (PAF) and PAF-like phospholipids (PAF-LPLs) mediated synchronized ferroptosis and contributed to AKI. The emergence of PAF and PAF-LPLs in ferroptosis caused the instability of biomembranes and signaled the cell death of neighboring cells. This cascade could be suppressed by PAF-acetylhydrolase (II) (PAFAH2) or by addition of antibodies against PAF. Genetic knockout or pharmacological inhibition of PAFAH2 increased PAF production, augmented synchronized ferroptosis and exacerbated ischemia/reperfusion (I/R)-induced AKI. Notably, intravenous administration of wild-type PAFAH2 protein, but not its enzymatically inactive mutants, prevented synchronized tubular cell death, nephron loss and AKI. Our findings offer an insight into the mechanisms of synchronized ferroptosis and suggest a possibility for the preventive intervention of AKI.

The Interplay among Glucocorticoid Therapy, Platelet-Activating Factor and Endocannabinoid Release Influences the Inflammatory Response to COVID-19.

COVID-19 is associated with a dysregulated immune response. Currently, several medicines are licensed for the treatment of this disease. Due to their significant role in inhibiting pro-inflammatory cytokines and lipid mediators, glucocorticoids (GCs) have attracted a great deal of attention. Similarly, the endocannabinoid (eCB) system regulates various physiological processes including the immunological response. Additionally, during inflammatory and thrombotic processes, phospholipids from cell membranes are cleaved to produce platelet-activating factor (PAF), another lipid mediator. Nonetheless, the effect of GCs on this lipid pathway during COVID-19 therapy is still unknown. This is a cross-sectional study involving COVID-19 patients (n = 200) and healthy controls (n = 35). Target tandem mass spectrometry of plasma lipid mediators demonstrated that COVID-19 severity affected eCBs and PAF synthesis. This increased synthesis of eCB was adversely linked with systemic inflammatory markers IL-6 and sTREM-1 levels and neutrophil counts. The use of GCs altered these lipid pathways by reducing PAF and increasing 2-AG production. Corroborating this, transcriptome analysis of GC-treated patients blood leukocytes showed differential modulation of monoacylglycerol lipase and phospholipase A2 gene expression. Altogether, these findings offer a breakthrough in our understanding of COVID-19 pathophysiology, indicating that GCs may promote additional protective pharmacological effects by influencing the eCB and PAF pathways involved in the disease course.

Topical Photodynamic Therapy Generates Bioactive Microvesicle Particles: Evidence for a Pathway Involved in Immunosuppressive Effects

Although effective in treating actinic damage, topical photodynamic therapy (PDT) has been shown to be immunosuppressive through unknown mechanisms, which could potentially limit its effectiveness. Multiple types of environmental stressors, including PDT, can produce the immunosuppressive lipid mediator platelet-activating factor (PAF). Because PAF can produce subcellular microvesicle particles (MVPs), these studies tested whether PDT can generate PAF and MVP release and whether these are involved in PDT-induced immunosuppression. Previously, topical PDT using blue light and 5-aminolevulinic acid was found to be a potent stimulus for PAF production in mice and human skin explants and human patients, and we show that experimental PDT also generates high levels of MVP. PDT-generated MVPs were independent of the PAF receptor but were dependent on the MVP-generating enzyme acid sphingomyelinase. Patients undergoing topical PDT treatment to at least 10% of body surface area showed local and systemic immunosuppression as measured by inhibition of delayed-type hypersensitivity reactions. Finally, using a murine model of contact hypersensitivity, PDT immunosuppression was blocked by genetic and pharmacologic inhibition of acid sphingomyelinase and genetic inhibition of PAF receptor signaling. These studies describe a mechanism involving MVP through which PDT exerts immunomodulatory effects, providing a potential target to improve its effectiveness.

Compound Kushen Injection Induces Immediate Hypersensitivity Reaction Through Promoting the Production of Platelet-Activating Factor via de Novo Pathway.

Compound Kushen Injection (CKI) is a bis-herbal formulation extracted from Kushen (Radix Sophorae Flavescentis) and Baituling (Rhizoma Heterosmilacis Yunnanensis). Clinically, it is used as the adjuvant treatment of cancer. However, with the increased application, the cases of immediate hypersensitivity reactions (IHRs) also gradually rise. In this study, we investigated the underlying mechanism(s) and active constituent(s) for CKI-induced IHRs in experimental models. The obtained results showed that CKI did not elevate serum total IgE (tIgE) and mouse mast cell protease 1 (MMCP1) after consecutive immunization for 5 weeks, but could induce Evans blue extravasation (local) and cause obvious hypothermia (systemic) after a single injection. Further study showed that alkaloids in Kushen, especially matrine, were responsible for CKI-induced IHRs. Mechanism study showed that various platelet-activating factor (PAF) receptor antagonists could significantly counter CKI-induced IHRs locally or systemically. In cell system, CKI was able to promote PAF production in a non-cell-selective manner. In cell lysate, the effect of CKI on PAF production became stronger and could be abolished by blocking de novo pathway. In conclusion, our study identifies, for the first time, that CKI is a PAF inducer. It causes non-immunologic IHRs, rather than IgE-dependent IHRs, by promoting PAF production through de novo pathway. Alkaloids in Kushen, especially matrine, are the prime culprits for IHRs. Our findings may provide a potential approach for preventing and treating CKI-induced IHRs.

Cluster Analysis Identifies Phosphatidylcholine Species in the Liver and Heart as Prediction Hubs in Ossabaw Swine with Cardio‐Metabolic Heart Failure

We recently developed an Ossabaw swine model (Western Diet and aortic banding; WD-AB) that exhibits features consistent with cardio-metabolic heart failure (HF). This pre-clinical model has a pattern of findings possibly useful for enhancing our understanding of the interactions between metabolic syndrome and HF. The aim of this study is to use advanced quantitative methods to reveal novel relationships and candidate predictors we hypothesize may be important to cardio-metabolic HF. A large-scale data repository was created containing 142 hemodynamic, structural, and functional cardiovascular measures, 413 lipid species identified using shotgun lipidomics, and 28,386 mRNA-transcripts revealed by RNA-seq. Repository data was generated from heart, vascular, hepatic, and blood samples collected from 2 groups of intact female Ossabaw swine: 1) lean control (CON; N=5); and 2) WD-AB (N=4). Logistic regression models with AUC scores identified a subset of measurements predictive of HF status that included 1,237 measurements (4.3%). Log2 fold changes were then calculated and statistically significant changes (p<0.05) with absolute value log2 fold changes >1 were considered. Pearson correlations for these 153 measurements were analyzed to identify redundant information using k-medoids clustering analysis with an average silhouette approach. Twenty-eight left ventricle (LV) genes and 125 lipids in 2 clusters (Fig. 1 Circos plot) with center points were identified. Cluster 1 (7 mRNA-transcripts, 70 lipids) was composed of strong correlations with center point phosphatidylcholine (PC) alkyl ether (a) species 32 from the liver (LIVER_PC­_32.0a_754) that increased 10-fold in the WD-AB group (P<0.05; 25±4 CON vs. 277±56 WD-AB pmols/mg). Cluster 2 (21 mRNA-transcripts, 55 lipids) had center point PC species 38.4a from the LV (HEART_PC_38.4a_830) that increased ~3-fold in the WD-AB group (P<0.05; 37±3 CON vs. 102±3 WD-AB pmols/mg). Identified PCa species containing arachidonic acid are storage depots for bioactive oxylipids (eicosanoids) and a precursor for platelet activating factor production. Increased alkyl ether phospholipids may also indicate increased peroxisome proliferation (the site of alkyl ether biosynthesis) and the potential to increase unknown peroxisome proliferator-activated receptor (PPAR) endogenous ligands. In conclusion, PCa species identified from the heart and liver of WD-AB animals may be underappreciated and have predictive significance for cardio-metabolic HF. Ongoing work includes enrichment analysis to determine biological processes underlying clusters.

Thermal Burn Injury Generates Bioactive Microvesicles: Evidence for a Novel Transport Mechanism for the Lipid Mediator Platelet-Activating Factor (PAF) That Involves Subcellular Particles and the PAF Receptor.

Thermal burn injuries are an important environmental stressor that can result in considerable morbidity and mortality. The exact mechanism by which an environmental stimulus to skin results in local and systemic effects is an area of active research. One potential mechanism to allow skin keratinocytes to disperse bioactive substances is via microvesicle particles, which are subcellular bodies released directly from cellular membranes. Our previous studies have indicated that thermal burn injury of the skin keratinocyte in vitro results in the production of the lipid mediator platelet-activating factor (PAF). The present studies demonstrate that thermal burn injury to keratinocytes in vitro and human skin explants ex vivo, and mice in vivo generate microvesicle particles. Use of pharmacologic and genetic tools indicates that the optimal release of microvesicles is dependent upon the PAF receptor. Of note, burn injury-stimulated microvesicle particles do not carry appreciable protein cytokines yet contain high levels of PAF. These studies describe a novel mechanism involving microvesicle particles by which a metabolically labile bioactive lipid can travel from cells in response to environmental stimuli.

Lipids in ultraviolet radiation-induced immune modulation.

Ultraviolet (UV) radiation-mediated immune suppression is a key mechanism conferring both detrimental and beneficial impacts of sun exposure on human health. Suppression of anti-tumour responses promotes the development and progression of UV-induced skin cancers. In contrast, suppression of dysregulated immune responses facilitate the therapeutic success of phototherapy treatment for skin disorders and is postulated to be responsible for UV protection from autoimmune diseases. While some of the molecular and cellular mechanisms underlying UV-suppression of the immune system are known, a relatively unexplored area is immunomodulatory lipids. Cutaneous UV exposure changes lipids both locally in the skin, increasing platelet-activating factor (PAF) production and decreasing free triglyceride levels, and systemically reducing adipose tissue mass. There is growing recognition that bioactive lipids and lipid metabolism directly affect immune cell phenotype and function. Manipulation of immunomodulatory lipid pathways are effective strategies in modifying systemic immune responses. Indeed, the PAF pathway is a key initiator of UV-induced immune suppression and antagonism of PAF-receptors restores immune function and reduces skin cancer development in mice. This review focuses on the known effects of UV on lipids and proposes how this may in turn be involved in the modulation of the immune system.

MON-005 Inhibition of Glucocorticoid Signaling in SRC-1/-2 Double-Deficient Mice Results in Impaired Lung Maturation and Delayed Parturition

The mechanisms that lead to the initiation of parturition are incompletely defined. Parturition timing is mediated by signals from both mother and fetus. Our previous findings using mice that were double-deficient in steroid receptor coactivators (Src)1 and 2 (Src-1/-2d/d) suggest that the fetus signals its mother when it is ready to be born through fetal lung production of surfactant components, surfactant protein A (SP-A) and platelet-activating factor (PAF). Notably, mice that are double knockout for Src-1/-2 die at birth of respiratory distress, due to decreased surfactant lipoprotein production. Intriguingly, we observed that wild-type (WT) mothers carrying Src-1/-2d/d fetuses manifested a ~38 h delay in parturition compared to WT mothers carrying WT fetuses. This was associated with decreased production of SP-A and PAF by the Src-1/-2d/d fetal lungs. Our findings suggested that these effects of Src-1/-2d/d were caused by impaired glucocorticoid receptor (GR) transcriptional activity in fetal lung cells. To identify other genes in fetal lung that were affected by Src-1/-2d/d, we conducted RNA-seq analysis of lungs from 18.5 days post-coitum Src-1/-2d/dvs. WT fetuses. We observed that one of the genes most highly downregulated in Src-1/-2d/d fetal lungs was 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). 11β-HSD1 catalyzes the conversion of inactive cortisone or 11-dehydrocorticosterone into active cortisol or corticosterone, respectively, which are ligands for the glucocorticoid receptor (GR). We validated the RNA-seq results by RT-qPCR and immunoblotting and observed a striking reduction of 11β-HSD1 mRNA and protein in lungs of Src-1/2d/d fetuses, compared to WT. Others observed that glucocorticoids potently increased 11β-HSD1 expression in various cell types via activation of transcription factors C/EBPα and C/EBPβ, providing a potential positive feed-forward loop. Notably, we observed that C/EBPα and C/EBPβ mRNA and protein were markedly reduced in Src-1/-2d/d fetal lungs, compared to WT. Deletion of the Cebpa gene in respiratory epithelium of fetal mice caused respiratory failure at birth due to surfactant lipid and protein deficiency. This was associated with increased expression of TGF-β2, which inhibits fetal lung maturation. Notably, we observed that expression of TGF-β2 and TGF-β3 were increased in Src-1/-2d/d fetal lungs. Thus, impaired lung development, surfactant synthesis and delayed parturition in Src-1/-2d/d fetuses are likely caused by decreased 11β-HSD1 and GR signaling, resulting in decreased C/EBPα/β expression and increased TGF-β signaling.

Exposure to Cigarette Smoke is Linked to Platelet‐Activating Factor Accumulation in Myocardial Tissue

Smoking is a lifestyle risk factor for heart disease and is responsible for one‐third of all cardiovascular deaths. Although many studies have investigated the correlation between smoking and coronary artery disease, there are few studies examining the direct effect of smoking on the myocardium. In this study, we examined the effect of smoking on myocardial accumulation of platelet‐activating factor (PAF), a phospholipid mediator that causes a negative inotropic effect, arrhythmias, apoptosis and is involved in inflammation and atherosclerosis. Ventricular samples from mice exposed up to six months of cigarette smoke (48 min/day, 5 days/week), and human right atrial samples from smokers and nonsmokers scheduled for coronary artery bypass graft surgery were analyzed for biochemical and histochemical changes using activity assays, ELISA, immunoblot, and immunohistochemistry. Mice exposed to cigarette smoke showed a decrease in PAF‐acetylhydrolase (PAF‐AH, the enzyme responsible for PAF metabolism) activity that was significant after 1 month and decreased progressively over the 6 month period (5.8 ± 0.3 to 3.2 ± 0.5 nmol/mg protein/min, p&lt;0.01, n=6). This inhibition in PAF‐AH activity was accompanied by increased myocardial PAF content (0.23 ± 0.04 to 0.35 ± 0.03 at 6 months smoking, p&lt;0.05, n=6). In humans, smoking was associated with an increase in PAF content (3.19 ± 0.28 vs 4.29 ± 0.37 nmol/mg protein, p&lt;0.05, n=18) and inhibition of PAF‐AH activity (30.7 ± 2.0 vs 23.2 ± 1.8 nmol/mg protein/min, p&lt;0.01, n=18) when comparing atrial tissue from never smokers to current smokers. We did not detect a change in phospholipase A2 activity (the enzyme responsible for PAF production) in human or mouse myocardium exposed to cigarette smoke or room air. Thus, we hypothesize that the increase in PAF content in the myocardium is likely a result of smoking‐induced inhibition of PAF‐AH activity. The inhibition of PAF‐AH and subsequent accumulation of PAF in the myocardium of cigarette smokers may play a role in the pathogenesis of heart disease in this population.Support or Funding InformationLottie Caroline Hardy Foundation (to J.McH.)

Before platelets: the production of platelet-activating factor during growth and stress in a basal marine organism.

Corals and humans represent two extremely disparate metazoan lineages and are therefore useful for comparative evolutionary studies. Two lipid-based molecules that are central to human immunity, platelet-activating factor (PAF) and Lyso-PAF were recently identified in scleractinian corals. To identify processes in corals that involve these molecules, PAF and Lyso-PAF biosynthesis was quantified in conditions known to stimulate PAF production in mammals (tissue growth and exposure to elevated levels of ultraviolet light) and in conditions unique to corals (competing with neighbouring colonies over benthic space). Similar to observations in mammals, PAF production was higher in regions of active tissue growth and increased when corals were exposed to elevated levels of ultraviolet light. PAF production also increased when corals were attacked by the stinging cells of a neighbouring colony, though only the attacked coral exhibited an increase in PAF. This reaction was observed in adjacent areas of the colony, indicating that this response is coordinated across multiple polyps including those not directly subject to the stress. PAF and Lyso-PAF are involved in coral stress responses that are both shared with mammals and unique to the ecology of cnidarians.

Cigarette Smoke Regulates Calcium-Independent Phospholipase A2 Metabolic Pathways in Breast Cancer

Phospholipase A2 (PLA2)-dependent pathways are important in the regulation of cell proliferation, differentiation, motility, and immune responses, and can be dysregulated during tumor development and progression. We show herein, for the first time, that cigarette smoking leads to an increase in platelet-activating factor (PAF) content and PAF receptor expression in human breast cancer cells and tissue. PAF production could be abrogated in triple-negative breast cancer cells by inhibition of calcium-independent PLA2 (iPLA2). We also demonstrate that cigarette smoke induces the expression of cyclooxygenase-2 and microsomal prostaglandin E synthase-1 and reduces 15-hydroxyprostaglandin dehydrogenase, resulting in prostaglandin E2 release in human breast cancer. Increased cyclooxygenase-2 expression and prostaglandin E2 release could be abrogated in metastatic breast cancer cells by inhibition of iPLA2. These studies indicate that iPLA2-dependent metabolic pathways play an important role in tumor initiation or progression in smokers, representing novel therapeutic targets for breast cancer patients who smoke.

Pneumolysin mediates heterotypic aggregation of neutrophils and platelets in vitro

Platelets orchestrate the inflammatory activities of neutrophils, possibly contributing to pulmonary and myocardial damage during severe pneumococcal infection. This study tested the hypothesis that the pneumococcal toxin, pneumolysin (Ply), activates production of platelet-activating factor (PAF) and thromboxane A2 (TxA2) by neutrophils, these bioactive lipids being potential mediators of neutrophil:platelet (NP) networking. The effects of recombinant Ply (10-80ngmL-1) on the production of PAF and TxA2 by isolated neutrophils were measured using ELISA procedures, and NP aggregation by flow cytometry. Exposure of neutrophils to Ply induced production of PAF and, to a lesser extent, TxA2, achieving statistical significance at ≥20ngmL-1 of the toxin. In the case of NP interactions, Ply promoted heterotypic aggregation which was dependent on upregulation of P-selectin (CD62P) and activation of protease-activated receptor 1 (PAR1), attaining statistical significance at ≥10ngmL-1 of the toxin, but did not involve either PAF or TxA2. Ply induces synthesis of PAF and TxA2, by human neutrophils, neither of which appears to contribute to the formation of NP heterotypic aggregates invitro, a process which is seemingly dependent on CD62P and PAR1. These pro-inflammatory activities of Ply may contribute to the pathogenesis of pulmonary and myocardial injury during severe pneumococcal infection.

Cigarette smoke-induced urothelial cell damage: potential role of platelet-activating factor.

Cigarette smoking is an environmental risk factor associated with a variety of pathologies including cardiovascular disease, inflammation, and cancer development. Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic inflammatory bladder disease with multiple etiological contributors and risk factors associated with its development, including cigarette smoking. Previously, we determined that cigarette smoking was associated with bladder wall accumulation of platelet activating factor (PAF), a potent inflammatory mediator that facilitates transendothelial cell migration of inflammatory cells from the circulation. PAF has been shown to reduce expression of tight junctional proteins which could ultimately lead to increased urothelial cell permeability. In this study, we observed that cigarette smoke extract (CSE) treatment of human urothelial cells increases PAF production and PAF receptor expression and reduces wound healing ability. After exposure to cigarette smoke for 6 months, wild‐type C57BL/6 mice displayed urothelial thinning and destruction which was not detected in iPLA 2 β −/− (enzyme responsible for PAF production) animals. We also detected increased urinary PAF concentration in IC/BPS patients when compared to controls, with an even greater increase in urinary PAF concentration in smokers with IC/BPS. These data indicate that cigarette smoking is associated with urothelial cell damage that may be a result of increased PAF‐PAF receptor interaction. Inhibition of iPLA 2 β activity or blocking of the PAF‐PAF receptor interaction could serve as a potential therapeutic target for managing cigarette smoke‐induced bladder damage.

Lipopolysaccharide acts synergistically with the dengue virus to induce monocyte production of platelet activating factor and other inflammatory mediators

BackgroundPlatelet Activating Factor (PAF) has been shown to be an important mediator of vascular leak in acute dengue. Antibody dependent enhancement (ADE) and microbial translocation has also shown to contribute to severe dengue. Since monocytes are one of the primary targets of the dengue virus (DENV) we sought to investigate if monocytes were a source of PAF, and the effect of ADE and microbial endotoxin (LPS) on DENV infected monocytes. MethodsPAF and cytokine levels were evaluated in serial blood samples, in patients with acute dengue infection. The effect of ADE and LPS in production of PAF and cytokines from DENV infected primary human monocytes derived macrophages (MDMθ) was assessed. Gene expression analysis was undertaken to investigate mechanisms by which LPS potentiates PAF and cytokine production by DENV infected MDMθ. ResultsSerum PAF levels significantly correlated with both TNF-α (p < 0.0001) and IL-1β (p < 0.0001) in patients with acute DENV infection. Although primary human MDMθ produced inflammatory cytokines following infection with the DENV, they did not produce PAF following in vitro DENV infection alone, or in the presence of dengue immune serum. Levels of PAF produced by DENV infected MDMθ co-cultured with LPS was significantly higher than uninfected MDMθs co-cultured with LPS. Although TLR-4 was upregulated in uninfected MDMθs co-cultured with LPS, this upregulation was not significant in DENV infected MDMθ. Only expression of RIG-I was significantly up regulated (p < 0.05) when DENV infected MDMθ were co-cultured with LPS. ConclusionLPS acts synergistically with the DENV to induce production of PAF and other inflammatory cytokines, which suggests that microbial translocation that has shown to occur in acute dengue, could contribute to dengue disease severity.

Implications For Platelet Activating Factor Receptor Antagonism For Managing Bladder Cancer Progression

Cigarette smoking is the number one risk factor for bladder cancer development and epidemiological data suggests that nearly half of all bladder cancer patients have a history of smoking. In addition to stimulating growth of a primary tumor, it has been shown that there is a correlation between smoking and tumor metastasis. Platelet activating factor (PAF) is an inflammatory cell recruiter that is expressed on the endothelium during times of inflammation and through binding with the PAF‐receptor (PAFR) facilitates transendothelial migration of circulating inflammatory cells. PAF has been implicated in primary tumor growth and interactions with the PAFR have been shown to stimulate cellular growth. PAF is generated through hydrolysis of membrane phospholipids by the activity of calcium‐independent phospholipase A2 (iPLA2) which removes the sn‐‐2 fatty acid yielding a free fatty acid, arachidonic acid, and a lysophospholipid. Acetylation of the newly formed lysophospholipid results in PAF production. Under normal circumstances, PAF is maintained at a low concentration by PAF‐acetylhydrolase (PAF‐AH) resulting in the inactive lyso‐PAF. In the present study, we show that cigarette smoke extract (CSE) exposure of bladder cancer cells inhibits PAF‐AH activity and increases iPLA‐2 activity resulting in increased PAF accumulation. In addition to PAF accumulation, CSE increases PAFR expression. Furthermore, by immunohistochemical analysis of tumor biopsy samples from bladder cancer patients we detected increased PAF, iPLA2 and the PAFR in tumor regions when compared to surrounding tissue. This data highlights a pathway that is upregulated in tumor areas of bladder cancer patients and that is influenced by CSE which could facilitate primary tumor growth and increase metastatic potential. Targeting of the PAF‐PAFR interaction could serve as a beneficial therapeutic target for managing further growth of a developing tumor.

Mice with Genetic Deletion of Group VIA Phospholipase A2β Exhibit Impaired Macrophage Function and Increased Parasite Load in Trypanosoma cruzi-Induced Myocarditis.

Trypanosoma cruzi infection, which is the etiological agent of Chagas disease, is associated with intense inflammation during the acute and chronic phases. The pathological progression of Chagas disease is influenced by the infiltration and transmigration of inflammatory cells across the endothelium to infected tissues, which are carefully regulated processes involving several molecular mediators, including adhesion molecules and platelet-activating factor (PAF). We have shown that PAF production is dependent upon calcium-independent group VIA phospholipase A2β (iPLA2β) following infection of human coronary artery endothelial cells (HCAECs) with T. cruzi, suggesting that the absence of iPLA2β may decrease the recruitment of inflammatory cells to the heart to manage parasite accumulation. Cardiac endothelial cells isolated from iPLA2β-knockout (iPLA2β-KO) mice infected withT. cruzi demonstrated decreased PAF production compared to that by cells isolated from wild-type (WT) mice but demonstrated increases in adhesion molecule expression similar to those seen in WT mice. Myocardial inflammation in iPLA2β-KO mice infected with T. cruzi was similar in severity to that in WT mice, but the iPLA2β-KO mouse myocardium contained more parasite pseudocysts. Upon activation, macrophages from iPLA2β-KO mice produced significantly less nitric oxide (NO) and caused lessT. cruzi inhibition than macrophages from wild-type mice. Thus, the absence of iPLA2β activity does not influence myocardial inflammation, but iPLA2β is essential forT. cruzi clearance.

Increased susceptibility to bladder inflammation in smokers: targeting the PAF-PAF receptor interaction to manage inflammatory cell recruitment.

Chronic bladder inflammation can result in a significant reduction in quality of life. Smoking remains a leading preventable risk factor in many diseases. Despite the large amount of evidence supporting the risks of smoking, roughly 45 million people in the United States remain smokers. The impact of cigarette smoking on inflammation is well established, but how smoking promotes bladder inflammation is currently unknown. The aim of this study was to determine if cigarette smoke exposure impacts inflammatory cell adherence to bladder endothelial cells and if targeting the platelet-activating factor (PAF)-PAF receptor (PAFR) interaction could be beneficial in managing bladder inflammation. In response to cigarette smoke extract (CSE) incubation, bladder endothelial cells from human or mouse displayed increased PAF accumulation, decreased PAF-AH activity, and increased inflammatory cell adherence. Inhibition of endothelial cell calcium-independent phospholipase A2β (iPLA2β) with (S)-BEL, to block PAF production, prevented adherence of inflammatory cells. Pretreatment of inflammatory cells with PAFR antagonists, ginkgolide B or WEB2086 significantly reduced the number of adhered cells to bladder endothelium. Wild-type mice exposed to cigarette smoke displayed increased presence of inflammatory infiltration which was absent in iPLA2β(-/-) mice and those exposed to room air. In conclusion, cigarette smoke exposure increases endothelial cell PAF accumulation and increased inflammatory cell adherence. Inhibition of PAF accumulation or PAFR antagonism markedly attenuated inflammatory cell adherence to bladder endothelial cells. The results detailed in this study highlight to potential therapeutic targets for managing bladder inflammation.

Ginkgolide B Reduces the Degradation of Membrane Phospholipids to Prevent Ischemia/Reperfusion Myocardial Injury in Rats

Platelet-activating factor (PAF), a bioactive phospholipid, plays an important role in the integrity of the cellular membrane structure, and is involved in the pathogenesis of myocardial ischemia/reperfusion (IR) injuries. In this study, we tested the hypothesis that blockage of PAF receptor by BN 52021 (Ginkgolide B) can prevent IR-induced degradation of the myocardial membrane phospholipid, and deterioration of the cardiac function. Rat hearts in situ were subjected to 5 min ischemia and followed by 10 min reperfusion. Cardiac performances during periods of ischemia and reperfusion were monitored, and the amount of membrane phospholipids was analyzed. Myocardial total phospholipids, phosphatidylcholine, and phosphatidylethanolamine were decreased significantly in ischemia-reperfusion rat hearts compared with those of sham-operated rat hearts. Degradation of the membrane phospholipid was accompanied by the deterioration of cardiac functions and increase in serum lactate dehydrogenase (LDH) activity. BN 52021 (15 mg/kg), given by intravenous infusion 10 min prior to the left anterior descending coronary artery occlusion, reduced IR-related degradation of the myocardial phospholipids, the activity of serum LDH, and was concomitant with improvement of cardiac function. Furthermore, we demonstrated that the production of PAF was increased and BN 52021 decreased cellular damage in cultured anoxic cardiomyocytes. These results indicated that PAF antagonist BN 52021 has a protective effect against IR-induced myocardial dysfunction and degradation of the membrane phospholipids.

Steroid receptor coactivators 1 and 2 mediate fetal-to-maternal signaling that initiates parturition.

The precise mechanisms that lead to parturition are incompletely defined. Surfactant protein-A (SP-A), which is secreted by fetal lungs into amniotic fluid (AF) near term, likely provides a signal for parturition; however, SP-A-deficient mice have only a relatively modest delay (~12 hours) in parturition, suggesting additional factors. Here, we evaluated the contribution of steroid receptor coactivators 1 and 2 (SRC-1 and SRC-2), which upregulate SP-A transcription, to the parturition process. As mice lacking both SRC-1 and SRC-2 die at birth due to respiratory distress, we crossed double-heterozygous males and females. Parturition was severely delayed (~38 hours) in heterozygous dams harboring SRC-1/-2-deficient embryos. These mothers exhibited decreased myometrial NF-κB activation, PGF2α, and expression of contraction-associated genes; impaired luteolysis; and elevated circulating progesterone. These manifestations also occurred in WT females bearing SRC-1/-2 double-deficient embryos, indicating that a fetal-specific defect delayed labor. SP-A, as well as the enzyme lysophosphatidylcholine acyltransferase-1 (LPCAT1), required for synthesis of surfactant dipalmitoylphosphatidylcholine, and the proinflammatory glycerophospholipid platelet-activating factor (PAF) were markedly reduced in SRC-1/-2-deficient fetal lungs near term. Injection of PAF or SP-A into AF at 17.5 days post coitum enhanced uterine NF-κB activation and contractile gene expression, promoted luteolysis, and rescued delayed parturition in SRC-1/-2-deficient embryo-bearing dams. These findings reveal that fetal lungs produce signals to initiate labor when mature and that SRC-1/-2-dependent production of SP-A and PAF is crucial for this process.