Glucocorticoids prevent NF-kappaB activation by inhibiting the early release of platelet-activating factor in response to lipopolysaccharide

A natural Ala610Val substitution causing glucocorticoid receptor hypersensitivity aggravates consequences of endotoxemia

Despite the crucial role of glucocorticoid receptor (GR) in proper immune responses, the effect of GR hypersensitivity on inflammation is rarely reported. To fill this knowledge gap, we exploited the natural gain-of-function substitution in the porcine glucocorticoid receptor (GR_Ala610Val) and challenged pigs carrying normal or hypersensitive GR using 50 µg/kg lipopolysaccharide (LPS) following pretreatment with either saline or single bolus of 60 µg/kg dexamethasone (DEX). The GR_Ala610Val substitution reduced baseline cortisol, adrenocorticotropic hormone (ACTH), and triglyceride concentration and granulocyte proportion whereas baseline platelet counts were elevated. Val-carriers, i.e. AlaVal as well as ValVal pigs, showed less LPS-induced cortisol rise but the cortisol fold change was similar in all genotypes. Differently, ACTH response to LPS was most significant in GR_Ala610Val heterozygotes (AlaVal). LPS-induced disorders, including sickness behaviors, anorexia, thrombocytopenia, cytokine production, and metabolic alterations were more intense in Val-carriers. On the other hand, Val-carriers were more sensitive to DEX effect than wild types (AlaAla) during endotoxemia, but not under unchallenged conditions. This is the first report revealing aggravated responses to endotoxemia by GR gain-of-function. Together, these results imply that GR hypersensitivity is difficult to diagnose but may represent a risk factor for endotoxemia and sepsis.

Platelet-activating factor is a potent pyrogen and cryogen, but it does not mediate lipopolysaccharide fever or hypothermia

We examined whether platelet-activating factor (PAF) and its receptor mediate lipopolysaccharide (LPS)-induced fever and hypothermia in rats. Two highly potent, structurally distinct antagonists of the PAF receptor, CV6209 and WEB2086, were used. At a neutral ambient temperature (Ta) of 30ºC, administration of LPS at a low (10 μg/kg, i.v.) or high (1,000 μg/kg, i.v.) dose resulted in fever. The response to the high dose was turned into hypothermia at a subneutral Ta of 22ºC. Neither LPS-induced fever nor hypothermia was affected by pretreatment with CV6209 (5 mg/kg, i.v.) or WEB2086 (5 mg/kg, i.v.). However, both PAF antagonists were efficacious in blocking the thermoregulatory response caused by PAF (334 pmol/kg/min, 1 h, i.v.), regardless of whether the response was a fever (at 30ºC) or hypothermia (at 22ºC). Additional experiments showed that the thermoregulatory responses to LPS and PAF are also distinct in terms of their mediation by prostaglandins. Neither PAF fever nor PAF hypothermia was affected by pretreatment with the cyclooxygenase-2 inhibitor SC236 (5 mg/kg, i.p.), which is known to abrogate LPS fever. The responses to PAF were also unaffected by pretreatment with the cyclooxygenase-1 inhibitor SC560 (5 mg/kg, i.p.), which is known to attenuate LPS hypothermia. In conclusion, PAF infusion at a picomolar dose causes fever at thermoneutrality but hypothermia in a subthermoneutral environment, both responses being dependent on the PAF receptor and independent of prostaglandins. However, the PAF receptor does not mediate LPS-induced fever or hypothermia, thus challenging the dogma that PAF is an upstream mediator of responses to LPS.

Platelet-activating factor enhances tumour metastasis via the reactive oxygen species-dependent protein kinase casein kinase 2-mediated nuclear factor-κB activation

Platelet-activating factor (PAF) promotes tumour metastasis via activation of the transcription factor nuclear factor-κB (NF-κB). We here investigated the role of the protein kinase CK2 (formerly Casein Kinase 2 or II) in PAF-induced NF-κB activation and tumour metastasis, given that PAF has been reported to increase CK2 activity, and that CK2 plays a key role in NF-κB activation. PAF increased CK2 activity, phosphorylation and protein expression in vivo as well as in vitro. CK2 inhibitors inhibited the PAF-mediated NF-κB activation and expression of NF-κB-dependent pro-inflammatory cytokines and anti-apoptotic factors. Pre-treatment with the antioxidant N-Acetyl-L-Cysteine (NAC) resulted in a significant inhibition in PAF-induced enhancement of CK2 activity, phosphorylation and protein expression in vivo as well as in vitro. H2 O2 and known reactive oxygen species inducers, lipopolysaccharide (LPS) and tumour necrosis factor-α (TNF-α) enhanced CK2 activity, phosphorylation and protein expression, which was again inhibited by antioxidant. PAF, LPS and TNF-α induced increased CK2 activity, phosphorylationand protein expression, which were inhibited by p38 inhibitor. PAF, LPS or TNF-α increased pulmonary metastasis of B16F10, which was inhibited by antioxidants, CK2 inhibitor and p38 inhibitor. Our data suggest that (i) reactive oxygen species activate CK2 via p38, which, in turn, induces NF-κB activation, and (ii) PAF, LPS and TNF-α increase pulmonary tumour metastasis via the induction of the reactive oxygen species (ROS)/p38/CK2/NF-κB pathway.

The 15-deoxy-δ12,14-prostaglandin J2 inhibits LPS‑stimulated inflammation via enhancement of the platelet‑activating factor acetylhydrolase activity in human retinal pigment epithelial cells

A well-recognized natural ligand of PPARγ, 15-deoxy-δ(12,14)-prostaglandin J(2) (15d-PGJ(2)) possesses immunomodulatory properties. The aim of this study was to elucidate whether 15d-PGJ(2) was able to attenuate lipopolysaccharide (LPS)-induced inflammatory responses in human retinal pigment epithelial (RPE) cells, which are involved in ocular immune responses. In addition, we examined whether the platelet activating factor (PAF) is associated with the anti-inflammatory activity of 15d-PGJ(2). ARPE19 cells treated with varying concentrations of 15d-PGJ(2) and a PAF antagonist (CV3988) were used in this study. The activity of PAF-acetylhydrolase (PAF-AH) was assayed by treatment with 15d-PGJ(2) and CV3988 in the presence of LPS. 15d-PGJ(2) and CV3988 inhibited the LPS-induced mRNA expression and protein production of interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and intercellular adhesion molecule-1 (ICAM-1) in ARPE19 cells. These effects resulting from 15d-PGJ(2) were not abrogated by the PPARγ antagonist, indicating that the actions were PPARγ-independent. Furthermore, 15d-PGJ(2) and CV3988 enhanced the PAF-AH activity. Additionally, 15d-PGJ(2) inhibited the phosphorylation of the extracellular signal-regulated kinase (ERK) and the activation of nuclear transcription factor-κB (NF-κB). These results demonstrated that 15d-PGJ(2) reduced LPS-stimulated inflammatory responses in ARPE19 cells by enhancing the PAH-AH activity. These results suggest that 15d-PGJ(2) may have potent anti-inflammatory activity against ocular inflammation.

Lactobacillus acidophilus alleviates platelet-activating factor-induced inflammatory responses in human intestinal epithelial cells

Probiotics have been used as alternative prevention and therapy modalities in intestinal inflammatory disorders including inflammatory bowel diseases (IBD) and necrotizing enterocolitis (NEC). Pathophysiology of IBD and NEC includes the production of diverse lipid mediators, including platelet-activating factor (PAF) that mediate inflammatory responses in the disease. PAF is known to activate NF-κB, however, the mechanisms of PAF-induced inflammation are not fully defined. We have recently described a novel PAF-triggered pathway of NF-κB activation and IL-8 production in intestinal epithelial cells (IECs), requiring the pivotal role of the adaptor protein Bcl10 and its interactions with CARMA3 and MALT1. The current studies examined the potential role of the probiotic Lactobacillus acidophilus in reversing the PAF-induced, Bcl10-dependent NF-κB activation and IL-8 production in IECs. PAF treatment (5 µM×24 h) of NCM460 and Caco-2 cells significantly increased nuclear p65 NF-κB levels and IL-8 secretion (2-3-fold, P<0.05), compared to control, which were blocked by pretreatment of the cells for 6 h with L. acidophilus (LA) or its culture supernatant (CS), followed by continued treatments with PAF for 24 h. LA-CS also attenuated PAF-induced increase in Bcl10 mRNA and protein levels and Bcl10 promoter activity. LA-CS did not alter PAF-induced interaction of Bcl10 with CARMA3, but attenuated Bcl10 interaction with MALT1 and also PAF-induced ubiquitination of IKKγ. Efficacy of bacteria-free CS of LA in counteracting PAF-induced inflammatory cascade suggests that soluble factor(s) in the CS of LA mediate these effects. These results define a novel mechanism by which probiotics counteract PAF-induced inflammation in IECs.

PTEN/MAPK pathways play a key role in platelet-activating factor-induced experimental pulmonary tumor metastasis

In this study, we investigated the role of PTEN (phosphatase and tensin homolog deleted on chromosome 10) in a platelet-activating factor (PAF)-induced experimental pulmonary tumor metastasis model. An adenovirus carrying PTEN cDNA (Ad-PTEN) reversed PAF-induced increase in phosphorylation of AKT as well as pulmonary metastasis of B16F10. PAF-induced pulmonary metastasis was inhibited by MAPK inhibitors, but not by PI3K inhibitor. Ad-PTEN abrogated PAF-induced phosphorylation of MAPKs. These data indicate PTEN/MAPK pathways play a key role in PAF-induced tumor metastasis.

Protein kinase CK2/PTEN pathway plays a key role in platelet-activating factor-mediated murine anaphylactic shock

Platelet-activating factor (PAF) is a major mediator in the induction of fatal hypovolemic shock in murine anaphylaxis. This PAF-mediated effect has been reported to be associated with PI3K/Akt-dependent eNOS-derived NO. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is phosphatidylinositol phosphate phosphatase, which negatively controls PI3K by dephosphorylating the signaling lipid, phosphatidylinositol 3,4,5-triphosphate. In this study, we examined the possible involvement of PTEN in PAF-mediated anaphylactic shock. Induction of anaphylaxis or PAF injection resulted in a rapid decrease in PTEN activity, followed by increases in PI3K activity and phosphorylation of Akt and eNOS. Systemic administration of adenoviruses carrying PTEN cDNA (adenoviral PTEN), but not the control AdLacZ, not only attenuated anaphylactic symptoms, but also reversed anaphylaxis- or PAF-induced changes in PTEN and PI3K activities, as well as phosphorylation of Akt and eNOS. We found that the decreased PTEN activity was associated with PTEN phosphorylation, the latter effect being prevented by the protein kinase CK2 inhibitor, DMAT. DMAT also inhibited anaphylactic symptoms as well as the anaphylaxis- or PAF-mediated PTEN/PI3K/Akt/eNOS signaling cascade. CK2 activity was increased by PAF. The present data provide, as the key mechanism underlying anaphylactic shock, PAF triggers the upstream pathway CK2/PTEN, which ultimately leads to the activation of PI3K/Akt/eNOS. Therefore, CK2/PTEN may be a potent target in the control of anaphylaxis and other many PAF-mediated pathologic conditions.

Beyond thrombosis: the versatile platelet in critical illness

Sepsis, acute lung injury, and ARDS contribute substantially to the expanding burden of critical illness within our ICUs. Each of these processes is characterized by a myriad of injurious events, including apoptosis, microvascular dysfunction, abnormal coagulation, and dysregulated host immunity. Only recently have platelets--long considered merely effectors of thrombosis--been implicated in inflammatory conditions and the pathobiology of these disease processes. A growing body of evidence suggests a prominent role for maladaptive platelet activation and aggregation during sepsis and ARDS and has begun to underscore the pluripotential influence of platelets on outcomes in critical illness. Not only do platelets enhance vascular injury through thrombotic mechanisms but also appear to help orchestrate pathologic immune responses and are pivotal players in facilitating leukocyte recruitment to vulnerable tissue. These events contribute to the organ damage and poor patient outcomes that still plague the care of these high-risk individuals. An understanding of the role of platelets in critical illness also highlights the potential for both the development of risk stratification schema and the use of novel, targeted therapies that might alter the natural history of sepsis, acute lung injury, and ARDS. Future studies of adenosine, platelet polyphosphates, and the platelet transcriptome/proteome also should add considerably to our ability to unravel the mysteries of the versatile platelet.

Chylomicrons combined with endotoxin moderate microvascular permeability

Triglyceride-rich lipoprotein-bound endotoxin (CM-LPS) inhibits the host innate immune response to sepsis by attenuating the hepatocellular response to pro-inflammatory cytokine stimulation. This 'cytokine tolerance' in hepatocytes is a transient, receptor-dependent process that correlates with internalization of CM-LPS via low density lipoprotein (LDL) receptors. Since endothelial cells are integral to the immune response and similarly express LDL receptors, we hypothesized that CM-LPS could be internalized and ultimately attenuate the deleterious effects of pro-inflammatory molecules like tumor necrosis factor-α (TNF-α) and platelet activating factor (PAF) on endothelial permeability. Here, we show that CM-LPS complexes induce cytokine tolerance in endothelial cells. In rats, TNF-α increased hydraulic conductivity 2.5-fold over baseline and PAF increased it 5-fold; but, pretreatment with CM-LPS or an attenuated analog (CM-LPS*) inhibited these changes. Nuclear/cytoplasmic levels of p65 were reduced after TNF-α-stimulation in endothelial cell monolayers pretreated with CM-LPS, a finding consistent with inhibition of nuclear factor (NF)-κB translocation. Also consistent with inhibition was stabilized intercellular adhesion, as illustrated with antibody to VE-cadherin using confocal microscopy. These results provide additional support for the integral role of lipoproteins in the innate immune response to infection and lend further credence to developing lipid-based therapy for Gram-negative sepsis.

Platelet-activating factor-induced NF-kappaB activation and IL-8 production in intestinal epithelial cells are Bcl10-dependent

BACKGROUND

Platelet-activating factor (PAF), a potent proinflammatory phospholipid mediator, has been implicated in inducing intestinal inflammation in diseases such as inflammatory bowel disease (IBD) and necrotizing enterocolitis (NEC). However, its mechanisms of inducing inflammatory responses are not fully understood. Therefore, studies were designed to explore the mechanisms of PAF-induced inflammatory cascade in intestinal epithelial cells.

METHODS

Nuclear factor kappa B (NF-kappaB) activation was measured by luciferase assay and enzyme-linked immunosorbent assay (ELISA), and interleukin 8 (IL-8) production was determined by ELISA. B-cell lymphoma 10 (Bcl10), caspase recruitment domain-containing membrane-associated guanylate kinase protein 3 (CARMA3), and mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) mRNA and protein levels were assessed by real-time reverse-transcription polymerase chain reaction (RT-PCR) and Western blot, respectively. siRNA silencing of Bcl10 was used to examine its role in PAF-induced NF-kappaB activation and IL-8 production. The promoter region of the Bcl10 gene was cloned with the PCR method and promoter activity measured by luciferase assay.

RESULTS

The adaptor protein Bcl10 appeared to play an important role in the PAF-induced inflammatory pathway in human intestinal epithelial cells. Bcl10 was required for PAF-induced I kappaB alpha phosphorylation, NF-kappaB activation, and IL-8 production in NCM460, a cell line derived from normal human colon, and Caco-2, a transformed human intestinal cell line. PAF also stimulated Bcl10 interactions with CARMA3 and MALT1, and upregulated Bcl10 expression in these cells via transcriptional regulation.

CONCLUSIONS

These findings highlight a novel PAF-induced inflammatory pathway in intestinal epithelial cells, requiring Bcl10 as a critical mediator and involving CARMA3/Bcl10/MALT1 interactions. The proinflammatory effects of PAF play prominent roles in the pathogenesis of IBD and this pathway may present important targets for intervention in chronic inflammatory diseases of the intestine.

Evaluation of anti-allergic properties of caffeic acid phenethyl ester in a murine model of systemic anaphylaxis

Caffeic acid phenethyl ester (CAPE) is an active component of honeybee propolis extracts. It has several positive effects, including anti-inflammatory, anti-oxidation, anti-cancer, anti-bacterial, anti-viral, anti-fungal, and immunomodulatory effects. In particular, the suppressive effect of NF-kappaB may disrupt a component of allergic induction. The principal objective of this experimental study was to evaluate the effects of CAPE on the active systemic anaphylaxis induced by ovalbumin (OVA) challenge in mice. Mice were intraperitoneally sensitized and intravenously challenged with OVA. Histopathological analysis, nuclear factor (NF)-kappaB activation, and the plasma levels of histamine and total IgE after allergen challenge were evaluated. After challenges, all of the sham-treated mice developed anaphylactic symptoms, increased plasma levels of histamine and OVA-specific IgE, marked vascular leakage, NF-kappaB activation, platelet-activating factor (PAF) production, and histological changes including pulmonary edema and hemorrhage in the renal medullae within 20 min. By way of contrast, a reduction in the plasma levels of histamine and OVA-specific IgE and an inhibition of NF-kappaB activation and PAF release were observed in the CAPE-treated mice. In addition, a significant prevention of hemoconcentration and OVA-induced pathological changes were noted. These results indicate that CAPE demonstrates an anti-allergic effect, which may be the result of its protective effects against IgE-mediated allergy.

A Single Enzyme Catalyzes Both Platelet-activating Factor Production and Membrane Biogenesis of Inflammatory Cells

Platelet-activating factor (PAF) is a potent proinflammatory lipid mediator eliciting a variety of cellular functions. Lipid mediators, including PAF are produced from membrane phospholipids by enzymatic cascades. Although a G protein-coupled PAF receptor and degradation enzymes have been cloned and characterized, the PAF biosynthetic enzyme, aceyl-CoA:lyso-PAF acetyltransferase, has not been identified. Here, we cloned lyso-PAF acetyltransferase, which is critical in stimulus-dependent formation of PAF. The enzyme is a 60-kDa microsomal protein with three putative membrane-spanning domains. The enzyme was induced by bacterial endotoxin (lipopolysaccharide), which was suppressed by dexamethasone treatment. Surprisingly, the enzyme catalyzed not only biosynthesis of PAF from lyso-PAF but also incorporation of arachidonoyl-CoA to produce PAF precursor membrane glycerophospholipids (lysophosphatidylcholine acyltransferase activity). Under resting conditions, the enzyme prefers arachidonoyl-CoA and contributes to membrane biogenesis. Upon acute inflammatory stimulation with lipopolysaccharide, the activated enzyme utilizes acetyl-CoA more efficiently and produces PAF. Thus, our findings provide a novel concept that a single enzyme catalyzes membrane biogenesis of inflammatory cells while producing a prophlogistic mediator in response to external stimuli.

Impairment of p38 MAPK-mediated cytosolic phospholipase A2 activation in the kidneys is associated with pathogenicity of Candida albicans

In studying the mechanisms underlying the susceptibility of the kidney to candidal infection, we previously reported that the reduced production of cytokines [i.e. tumour necrosis factor-alpha (TNF-alpha)] via platelet-activating factor (PAF)-induced activation of nuclear factor-kappaB (NF-kappaB) renders the organ susceptible to the fungal burden. In this study, we investigated the possibility that pathogenic Candida albicans may evade clearance and perhaps even multiply by inhibiting elements in the signalling pathway that lead to the production of TNF-alpha. The fungal burden of pathogenic C. albicans in the kidneys was 10(4)-10(5)-fold higher than that of a non-pathogenic strain. PAF-induced early activation of NF-kappaB and TNF-alpha mRNA expression were both observed in the kidneys of mice infected with non-pathogenic strains of C. albicans, but not in mice infected with pathogenic strains. Impairment of PAF-mediated early NF-kappaB activation following infection with pathogenic C. albicans was associated with the prevention of activation of the enzyme cytosolic phospholipase A(2) (cPLA(2)) as well as the upstream pathway of cPLA(2), p38 mitogen-activated protein kinase. Collectively, these findings indicate that C. albicans exerts its pathogenicity through impairing the production of anticandidal cytokines by preventing cPLA(2) activity. This novel mechanism provides insight into understanding pathogenic C. albicans and perhaps identifies a target for its treatment.

Platelet-activating factor induces up-regulation of antiapoptotic factors in a melanoma cell line through nuclear factor-kappaB activation

In this study, we investigated the influence of platelet-activating factor (PAF) on the induction of apoptosis-regulating factors in B16F10 melanoma cells. PAF increased the expression of mRNA and the protein synthesis of antiapoptotic factors, such as Bcl-2 and Bcl-xL, but did not increase the expression of the proapoptotic factor, Bax. A selective nuclear factor-kappaB (NF-kappaB) inhibitor, parthenolide, inhibited the effects of PAF. Furthermore, PAF inhibited etoposide-induced increases in caspase-3, caspase-8, and caspase-9 activities, as well as cell death. p50/p65 heterodimer increased the mRNA expression of Bcl-2 and Bcl-xL and decreased etoposide-induced caspase activities and cell death. In an in vivo model in which Matrigel was injected s.c., PAF augmented the growth of B16F10 cells and attenuated etoposide-induced inhibition of B16F10 cells growth. These data indicate that PAF induces up-regulation of antiapoptotic factors in a NF-kappaB-dependent manner in a melanoma cell line, therefore suggesting that PAF may diminish the cytotoxic effect of chemotherapeutic agents.

Platelet-activating factor-induced NF-κB activation enhances VEGF expression through a decrease in p53 activity

We investigated the role of p53 in nuclear factor (NF)-kappaB dependent, platelet-activating factor (PAF)-induced vascular endothelial growth factor (VEGF) expression. Transfected NF-kappaB subunits in ECV304 cells increased the tumor necrosis factor-alpha promoter activity, which was completely inhibited by p53. Transfected p53 increased p53RE promoter activity, which was completely inhibited by NF-kappaB subunits, indicating that cross-regulation occurs between NF-kappaB and p53. PAF-induced increase in VEGF expression was correlated with decreased p53 activity. These data suggest that NF-kappaB-dependency of the PAF-induced increase in VEGF expression is due to decreased p53 activity, which is reciprocally regulated by increased NF-kappaB activity.

Platelet-activating factor induces matrix metalloproteinase-9 expression through Ca2+- or PI3K-dependent signaling pathway in a human vascular endothelial cell line

Platelet-activating factor (PAF) augments angiogenesis by promoting the synthesis of a variety of angiogenic factors, via the nuclear factor (NF)-kappaB activation. Recently, we reported that PAF upregulates MMP-9 expression in a NF-kappaB-dependent manner. In this study, we investigated the signaling pathway involved in PAF-induced MMP-9 expression in ECV304 cells. Our current data indicate that the Ca(2+)- or phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathway is necessary for PAF-induced MMP-9 expression. Furthermore, PAF-induced NF-kappaB activation was blocked by selective inhibitors of Ca(2+), PI3K, or extracellular signal-regulated kinase (ERK). Our results suggest that PAF-induced MMP-9 expression, in a NF-kappaB-dependent manner, is regulated by Ca(2+), PI3K and ERK signaling pathways.

Involvement of matrix metalloproteinase-9 in platelet-activating factor-induced angiogenesis

Platelet-activating factor (PAF) augments angiogenesis by promoting the synthesis of various angiogenic factors, via the activation of NF-kappaB. In this study, we investigated the role of the matrix metalloproteinase (MMP)-9, in PAF-induced angiogenesis. PAF increased mRNA expression, protein synthesis, and MMP-9 activity in ECV304 cells, in a NF-kappaB-dependent manner. PAF increased MMP-9 promoter activity in ECV304, which was inhibited by WEB2107, and NF-kappaB inhibitors. Transfected NF-kappaB subunits, p65 or/and p50, increased luciferase activity in the reporter plasmid MMP-9, resulting in an increase not only of MMP-9 luciferase activity, but also of mRNA expression in MMP-9. MMP-9 or NF-kappaB inhibitors significantly inhibited PAF-induced angiogenesis, in a dose-dependent manner, in an in vivo mouse Matrigel implantation model. In a parallel to the Matrigel implantation study, MMP-9 or NF-kappaB inhibitors inhibited PAF-induced sprouting of porcine pulmonary arterial endothelial cells. These data indicate that NF-kappaB-dependent MMP-9 plays a key role in PAF-induced angiogenesis.

Lack of effect of proteinase-activated receptor-2 (PAR-2) deletion on the pathophysiological changes produced by lipopolysaccharide in the mouse: comparison with dexamethasone

This study tested the hypothesis that activation of proteinase-activated receptor-2 (PAR-2) contributes towards the pathophysiology of lipopolysaccharide (LPS)-induced shock in the mouse. The effects of LPS on plasma glucose, biochemical markers of hepatic, renal and pancreatic exocrine function and lung content of myeloperoxidase (MPO) were examined in homozygous PAR-2 knockout mice (PAR-2 -/-) and genetically equivalent, homozygous PAR-2 +/+ mice. The effect of LPS was also examined in normal mice receiving dexamethasone (10 mg kg(-1), i. p.) or saline as a positive control. At six hours after intraperitoneal injection, LPS (40 mg kg(-1)) produced an increase in rectal temperature, hypoglycaemia and elevations in serum concentrations of alanine aminotransferase (ALT), creatinine and lipase, as well as an increase in lung MPO content. Dexamethasone treatment reduced LPS-induced hypoglycaemia and elevation of serum ALT concentrations but did not modify elevations in serum creatinine and lipase concentrations or the increase in lung MPO content. The changes in serum concentrations of glucose, ALT, creatinine and lipase produced by LPS in PAR-2 -/- mice were not different from those seen in wild-type or PAR-2 +/+ mice. These data suggest that activation of PAR-2 may not play a pivotal role in LPS-induced multi-organ dysfunction.

Estrogen enhances angiogenesis through a pathway involving platelet-activating factor-mediated nuclear factor-kappaB activation

In this study, we investigated the molecular events involved in estrogen-induced angiogenesis. Treatment of the human endometrial adenocarcinoma cells, HEC-1A, with estrogen up-regulated mRNA expression and protein synthesis of various angiogenic factors such as tumor necrosis factor-alpha, interleukin-1, basic fibroblast growth factor, and vascular endothelial growth factor. The estrogen-dependent induction of the expression was blocked by the platelet-activating factor (PAF) antagonists, WEB 2170. Estrogen treatment caused the activation of nuclear factor (NF)-kappaB in HEC-1A cells and was also blocked by PAF antagonist. Inhibitors of NF-kappaB activation inhibited estrogen-induced mRNA expression and protein synthesis of the angiogenic factors. Estrogen led to a pronounced angiogenesis as assessed by a mouse Matrigel model in vivo and endothelial cell sprouting in vitro. PAF antagonists or NF-kappaB inhibitors significantly inhibited this estrogen-dependent angiogenesis. Estrogen caused phospholipase A2 (PLA2) gene and protein expression. Estrogen-induced vascular endothelial growth factor mRNA expression and sprouting were significantly inhibited by PLA2 inhibitors, suggesting PLA2 expression is the upstream pathway in the estrogen-induced angiogenesis. Taken together, these results suggest that estrogen induces the production of angiogenic factors via a mechanism involving PAF-mediated NF-kappaB activation.

Platelet-activating factor: a previously unrecognized mediator of fever

Lipopolysaccharide (LPS)-induced systemic inflammation is accompanied by either hypothermia (prevails when the ambient temperature (Ta) is subneutral) or fever (prevails when Ta is neutral or higher). Because platelet-activating factor (PAF) is a proximal mediator of LPS inflammation, it should mediate both thermoregulatory responses to LPS. That PAF possesses hypothermic activity and mediates LPS-induced hypothermia is known. We asked whether PAF possesses pyrogenic activity (Expt 1) and mediates LPS fever (Expt 2). The study was conducted in Long-Evans rats implanted with jugular catheters. A complex with bovine serum albumin (BSA) was infused as a physiologically relevant form of PAF; free (aggregated) PAF was used as a control. In Expt 1, either form of PAF caused hypothermia when infused (83 pmol kg-1 min-1, 60 min, i.v.) at a subneutral Ta of 20 degrees C, but the response to the PAF-BSA complex (-4.5 +/- 0.5 degrees C, nadir) was ~4 times larger than that to free PAF. At a neutral Ta of 30 degrees C, both forms caused fever preceded by tail skin vasoconstriction, but the febrile response to PAF-BSA (1.0 +/- 0.1 degrees C, peak) was > 2 times higher than that to free PAF. Both the hypothermic (at 20 degrees C) and febrile (at 30 degrees C) responses to PAF-BSA started when the total amount of PAF infused was extremely small, < 830 pmol kg-1. In Expt 2 (conducted at 30 degrees C), the PAF receptor antagonist BN 52021 (29 micromol kg-1, i.v.) had no thermal effect of itself. However, it strongly (~2 times) attenuated the febrile response to PAF (5 nmol kg-1, i.v.), implying that this response involves the PAF receptor and is not due to a detergent-like effect of PAF on cell membranes. BN 52021 (but not its vehicle) was similarly effective in attenuating LPS (10 microg kg-1, i.v.) fever. It is concluded that PAF is a highly potent endogenous pyrogenic substance and a mediator of LPS fever.

Dexamethasone improves vascular hyporeactivity induced by LPS in vivo by modulating ATP-sensitive potassium channels activity

(1) Septic shock represents an important risk factor for patients critically ill. This pathology has been largely demonstrated to be a result of a myriad of events. Glucocorticoids represent the main pharmacological therapy used in this pathology. (2) Previously we showed that ATP-sensitive potassium (KATP) channels are involved in delayed vascular hyporeactivity in rats (24 h after Escherichia coli lipopolysaccharide (LPS) injection). In LPS-treated rats, we observed a significant hyporeactivity to phenylephrine (PE) that was reverted by glybenclamide (GLB), and a significant increase in cromakalim (CRK)-induced hypotension. (3) We evaluated the effect of dexamethasone (DEX 8 mg kg-1 i.p.) whether on hyporeactivity to PE or on hyperreactivity to CRK administration, in vivo, in a model of LPS (8 x 106 U kg-1 i.p.)-induced endotoxemia in urethane-anaesthetised rats. (4) DEX treatment significantly reduced, in a time-dependent manner, the increased hypotensive effect induced by CRK in LPS-treated rats. This effect was significantly (P<0.05) reverted by the glucocorticoid receptor antagonist RU38486 (6.6 mg kg-1 i.p.). (5) GLB-induced hypertension (40 mg kg-1 i.p.), in LPS-treated rats, was significantly inhibited by DEX if administered at the same time of LPS. (6) Simultaneous administration of DEX and LPS to rats completely abolished the hyporeactivity to PE observed after 24 h from LPS injection. (7) In conclusion, our results suggest that the beneficial effect of DEX in endotoxemia could be ascribed, at least in part, to its ability to interfere with KATP channel activation induced by LPS. This interaction may explain the improvement of vascular reactivity to PE, mediated by DEX, in LPS-treated rats, highlighting a new pharmacological activity to the well-known anti-inflammatory properties of glucocorticoids.

Corticosteroids in sepsis: from bench to bedside?

The use of corticosteroids in patients with septic shock has been recently revisited and the use of low dose corticosteroids led to very promising results, particularly in patients with corticosteroid insufficiency. We review the different mechanisms that can account for their beneficial effects in patients. Glucocorticoids display a wide spectrum of anti-inflammatory properties that have been identified in in vitro and in vivo experimental models (e.g., inhibition of production of pro-inflammatory cytokines, free radicals, prostaglandins and inhibition of chemotaxis, and adhesion molecule expressions.) In addition, glucocorticoids have profound effects on the cardiovascular system (e.g., increasing mean blood pressure, increasing pressor sensitivity, and therefore decreasing the duration of use of catecholamines during septic shock.) Through these anti-inflammatory and cardiovascular effects, low doses of glucorticoids may improve septic shock survival.

Expression of MIS in the testis is downregulated by tumor necrosis factor alpha through the negative regulation of SF-1 transactivation by NF-kappa B

The expression of Mullerian inhibiting substance (MIS), a key molecule in sex differentiation and reproduction, is tightly regulated. It has been suggested that meiotic germ cells repress MIS expression in testicular Sertoli cells, although the substance responsible for this cell-cell communication remains unknown. Here, we present the cytokine tumor necrosis factor alpha (TNF-alpha) as a strong candidate for such a substance and its downstream molecular events. TNF-alpha inhibited MIS expression in testis organ cultures, and TNF-alpha(-/-) testes showed high and prolonged MIS expression. Furthermore, in transient-transfection assays TNF-alpha suppressed the MIS promoter that was activated by steroidogenic factor 1 (SF-1), one of the major transcription factors that regulate MIS expression. The modulation of SF-1 transactivation by TNF-alpha is through the activation of NF-kappa B, which subsequently interacts with SF-1 and represses its transactivation. The physical association of NF-kappa B with SF-1 was shown by yeast two-hybrid protein interaction, glutathione S-transferase pull-down, and coimmunoprecipitation (ChIP) analyses. ChIP assays also revealed that endogenous NF-kappa B, as well as SF-1, is recruited to the MIS promoter upon TNF-alpha signaling. SF-1-bound NF-kappa B subsequently recruits histone deacetylases to inhibit the SF-1-activated gene expression. These results may identify, for the first time, the responsible substance and its action mechanism underlying the repression of MIS expression by meiotic germ cells in the testis.

The interplay between the glucocorticoid receptor and nuclear factor-kappaB or activator protein-1: molecular mechanisms for gene repression

The inflammatory response is a highly regulated physiological process that is critically important for homeostasis. A precise physiological control of inflammation allows a timely reaction to invading pathogens or to other insults without causing overreaction liable to damage the host. The cellular signaling pathways identified as important regulators of inflammation are the signal transduction cascades mediated by the nuclear factor-kappaB and the activator protein-1, which can both be modulated by glucocorticoids. Their use in the clinic includes treatment of rheumatoid arthritis, asthma, allograft rejection, and allergic skin diseases. Although glucocorticoids have been widely used since the late 1940s, the molecular mechanisms responsible for their antiinflammatory activity are still under investigation. The various molecular pathways proposed so far are discussed in more detail.

Platelet-activating factor-mediated NF-kappaB dependency of a late anaphylactic reaction

Anaphylaxis is a life-threatening systemic allergic reaction with the potential for a recurrent or biphasic pattern. Despite an incidence of biphasic reaction between 5 and 20%, the molecular mechanism for the reaction is unknown. Using a murine model of penicillin V-induced systemic anaphylaxis, we show an autoregulatory cascade of biphasic anaphylactic reactions. Induction of anaphylaxis caused a rapid increase in circulating platelet-activating factor (PAF) levels. In turn, the elevated PAF contributes to the early phase of anaphylaxis as well as the subsequent activation of the nuclear factor (NF)-kappaB, a crucial transcription factor regulating the expression of many proinflammatory cytokines and immunoregulatory molecules. The induction of NF-kappaB activity is accompanied by TNF-alpha production, which, in turn, promotes late phase PAF synthesis. This secondary wave of PAF production leads eventually to the late phase of anaphylactic reactions. Mast cells do not appear to be required for development of the late phase anaphylaxis. Together, this work reveals the first mechanistic basis for biphasic anaphylactic reactions and provides possible therapeutic strategies for human anaphylaxis.

Analysis of the antitumoral mechanisms of lipopolysaccharide against glioblastoma multiforme

Our objective was to analyze the lipopolysaccharide (LPS) antitumoral effect upon glioblastoma, including whether the lipid A subunit alone can elicit glioblastoma regression, whether dexamethasone suppresses this response to LPS, whether B and T lymphocytes factor in this response, and whether this antitumoral effect of LPS provides resistance against subsequent challenge with glioblastoma. Mice (BALB/c, nude or SCID) implanted with s.c. DBT glioblastomas were treated with LPS (with or without dexamethasone) or with lipid A. A subset of BALB/c mice in which s.c. DBT glioblastomas had previously been eradicated using LPS were re-implanted with s.c. or intracranial (i.c.) DBT cells. For mice with s.c. tumors, mean tumor masses (MTM) were compared between groups. Survival was compared for mice with i.c. tumors. Lipid A caused near complete tumor regression of DBT glioblastomas in BALB/c mice (p<0.0001). Dexamethasone did not alter the antitumoral effect of LPS (p=0.48). LPS reduced the MTM of s.c. glioblastomas in T lymphocyte-deficient nude mice, but not as effectively as in immunocompetent mice. The antitumoral response to LPS for T and B lymphocyte-deficient SCID mice bearing DBT glioblastomas was similar to that for nude mice. Eradication of s.c. DBT glioblastoma in BALB/c provided partial resistance to subsequent challenge with s.c. or i.c. glioblastoma. We conclude that the LPS-mediated antitumoral response against glioblastoma is dependent upon the lipid A subunit of LPS, partially dependent upon T lymphocytes, independent of B lymphocytes, unaffected by dexamethasone and provides partial protection against subsequent challenges with glioblastoma.

Platelet-activating factor modulates gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide

Platelet-activating factor (PAF) is a phospholipid messenger implicated in mediation of inflammatory events associated with the resolution of inflammation. We applied the animal model of Helicobacter pylori LPS-induced gastritis in conjunction with prophylactic and therapeutic administration of a specific PAF antagonist, BN52020, to investigate the role of PAF in gastric mucosal responses to H. pylori infection. Prophylactic BN52020 administration produced up to 73.6% reduction in the severity of the LPS-induced inflammatory changes, whereas up to 38.4% increase in the severity of mucosal involvement occurred with BN52020 administered therapeutically. The prophylactic effects of BN52020 were accompanied by a drop in apoptosis and the expression of TNF-alpha and NOS-2, while BN52020 administered therapeutically caused a marked upregulation in apoptosis, TNF-alpha, and NOS-2. The untoward therapeutic effects of BN52020, moreover, were potentiated further in the presence of COX-2 inhibitor, whereas NOS-2 inhibitor caused a reduction in the extent of inflammatory changes. Our findings point to PAF as a key mediator of gastric mucosal inflammatory responses to H. pylori and suggest its modulatory role in the expression of COX-2 derived anti-inflammatory prostaglandins that are involved in controlling the extent of NOS-2 induction.

In vivo platelet response to lipopolysaccharide in mice: proposed method for evaluating new antiplatelet drugs

We previously found evidence (based on the use of 5HT as a marker) that i.v. injection of a lipopolysaccharide (LPS) into mice induces a rapid accumulation of platelets in liver and lung. Our previous studies lacked measurement of the platelet count itself, but we have now compared the LPS-induced changes in 5HT levels with the change in platelet count. We also examined the effects on the platelet response of some drugs that act on platelets. In mice, sublethal doses of LPS induced parallel decreases in platelets and 5HT in the blood. The 5HT lost from the blood accounted well for the 5HT accumulated in liver and lung. Soon after this accumulation, the levels of platelets and 5HT in the blood recovered in parallel, and these recoveries corresponded well with the decreases in 5HT occurring in liver and lung. Aspirin and dexamethasone were effective at both reducing pulmonary platelet-accumulation and promoting their return to the circulation. By contrast, oestrogen tended to reduce the return of platelets from lung to circulation. Heparin did not inhibit pulmonary platelet-accumulation but it did decrease their return to the circulation. These results suggest that (i) in response to sublethal doses of LPS, platelets translocate into the liver and lung, then return to the circulation; (ii) this platelet response involves mechanisms that can be modified by drugs; and (iii) the use of this platelet response as a tool for drug evaluation might help identify new drugs with therapeutic potential.

Molecular mechanisms for lipopolysaccharide-induced biphasic activation of nuclear factor-kappa B (NF-kappa B)

The nuclear factor-kappaB (NF-kappaB) is an important transcription factor necessary for initiating and sustaining inflammatory and immune reactions. The inducers of NF-kappaB are well characterized, but the molecular mechanisms underlying multiple in vivo NF-kappaB activation processes are poorly understood. The injection of lipopolysaccharide resulted in a biphasic activation of NF-kappaB during the 18-h observation period in various organs of mice. The early and late phases of NF-kappaB activation occurred at 0.5-2 h and 8-12 h, respectively. Platelet-activating factor, which is released in response to lipopolysaccharide injection, was responsible for the activation of the early phase of NF-kappaB. The early NF-kappaB activity led to the induction of proinflammatory cytokines, tumor necrosis factor (TNF), and interleukin (IL)-1beta, which are known to be efficient inducers of NF-kappaB. Using the TNF knockout and IL-1 receptor knockout mice, we found that TNF and IL-1beta had a role in the second phase activation of NF-kappaB. These cytokines did promote the synthesis of platelet-activating factor, which in turn induced the secondary activation of NF-kappaB. These observations describe a novel autoregulatory molecular mechanism for the biphasic activation of NF-kappaB.

Nuclear factor κB activity in patients with acute severe cholangitis

AIM: To determine the NF-κB activity in peripheral blood mononuclear cells (PBMC) in patients with acute cholangitis of severe type (ACST) and correlate the degree of NF-κB activation with severity of biliary tract infection and clinical outcome.

METHODS: Twenty patients with ACST were divided into survivor group (13 cases) and nonsurvivor group (7 cases). Other ten patients undergoing elective gastrectomy or inguinal hernia repair were selected as control group. Peripheral blood samples were taken 24 h postoperatively. PBMC were separated by density gradient centrifugation, then nuclear proteins were isolated from PBMC, and Electrophoretic Mobility Shift Assay (EMSA) used determined. The results were quantified by scanning densitometer of a Bio-Image Analysis System and expressed as relative optical density (ROD). The levels of TNF-α, IL-6, and IL-10 in the plasma of patients with ACST and healthy control subjects were determined by using an enzyme-linked immunoassay (ELISA).

RESULTS: The NF-κB activity was 5.02 ± 1.03 in nonsurvivor group, 2.98 ± 0.51 in survivor group and 1.06 ± 0.34 in control group. There were statistical differences in three groups (P < 0.05). The levels of TNF-α and IL-6 in plasma were (498 ± 53) ng·L^-1 and (587 ± 64) ng·L^-1 in nonsurvivor group, (284 ± 32) ng·L^-1 and (318 ± 49) ng·L^-1 in survivor group and (89 ± 11) ng·L^-1 and (102 ± 13) ng·L^-1 in control group. All patients with ACST had increased levels of TNF-α and IL-6, which were manyfold greater than those of control group, and there was an evidence of significantly higher levels in those of nonsurvivor group than that in survivor group (P < 0.05). The levels of IL-10 in plasma were (378 ± 32) ng·L^-1, (384 ± 37) ng·L^-1 and (68 ± 11) ng·L^-1 in three groups, respectively. All patients had also increased levels of IL-10 when compared with control group (P < 0.05), but the IL-10 levels were not significantly higher in nonsurvivors than in survivors (P > 0.05).

CONCLUSION: NF-κB activity in PBMC in patients with ACST increases markedly and the degree of NF-κB activation is correlated with severity of biliary tract infection and clinical outcome.

Glucocorticoid receptor activation of the I kappa B alpha promoter within chromatin

The glucocorticoid receptor (GR) is a ligand-activated transcription factor that induces expression of many genes. The GR has been useful for understanding how chromatin structure regulates steroid-induced transcription in model systems. However, the effect of glucocorticoids on chromatin structure has been examined on few endogenous mammalian promoters. We investigated the effect of glucocorticoids on the in vivo chromatin structure of the glucocorticoid-responsive I kappa B alpha gene promoter, the inhibitor of the ubiquitous transcription factor, nuclear factor kappa B (NF kappa B). Glucocorticoids inhibit NF kappa B activity in some tissues by elevating the levels of I kappa B alpha. We found that glucocorticoids activated the I kappa B alpha promoter in human T47D/A1-2 cells containing the GR. We then investigated the chromatin structure of the I kappa B alpha promoter in the absence and presence of glucocorticoids with the use of micrococcal nuclease, restriction enzyme, and deoxyribonuclease (DNaseI) analyses. In untreated cells, the promoter assembles into regularly positioned nucleosomes, and glucocorticoid treatment did not alter nucleosomal position. Restriction enzyme accessiblity studies indicated that the I kappa B alpha promoter is assembled as phased nucleosomes that adopt an "open" chromatin architecture in the absence of hormone. However, glucocorticoids may be required for transcription factor binding, because DNaseI footprinting studies suggested that regulatory factors bind to the promoter upon glucocorticoid treatment.

Platelet-activating factor-induced early activation of NF-kappa B plays a crucial role for organ clearance of Candida albicans

In this study, we have investigated the mechanisms underlying organ susceptibility to candida infection. Infection of BALB/c mice with Candida albicans led to both an early (1-8 h) and late (24-48 h) activation of NF-kappaB in the organs resistant to C. albicans, including the lung and spleen. In susceptible organs such as the kidneys, early activation of NF-kappaB was not observed. The kinetics of TNF-alpha mRNA expression paralleled those of NF-kappaB activation in all organs examined. Blocking the effects of endogenous platelet-activating factor (PAF) by pretreatment with the PAF antagonist BN50739 or antioxidants significantly reduced the early activity of NF-kappaB and TNF-alpha mRNA expression, and increased the recovery of C. albicans in the lung and spleen. Importantly, administration of PAF 5 min prior to the infection resulted in the appearance of early activities of NF-kappaB and TNF-alpha mRNA expression, followed by a nearly complete clearance of the organisms in the kidneys. Pretreatment with anti-TNF-alpha Ab resulted in an enhanced susceptibility to C. albicans, and the PAF-mediated resistance was abrogated by anti-TNF-alpha in all organs examined. These data indicated that endogenously produced PAF in response to C. albicans is a key molecule involved in the early activation of NF-kappaB, which, in turn, renders the organ resistant to the fungus by promoting the production of anti-candidal proinflammatory cytokines such as TNF-alpha. Susceptible organs, including the kidneys, lack the capacity to generate a sufficient PAF-induced early NF-kappaB response.

Selective involvement of reactive oxygen intermediates in platelet-activating factor-mediated activation of NF-kappaB

Although it has been suggested that some biological activities of platelet-activating factor (PAF) are mediated by, at least in part, reactive oxygen intermediates (ROI), the precise mechanisms underlying the interaction between the two remains to be elucidated. Antioxidants, such as alpha-tocopherol acid succinate, N-acetyl-L-Cysteine, pyrrolidinedithiocarbamate failed to inhibit PAF-induced immediate systemic reactions such as lethality, symptoms of disseminated intravascular coagulation, and histological changes such as pulmonary edema and hemorrhage in renal medullae 10 min following PAF injection. In contrast. antioxidants significantly inhibited both the in vivo and in vitro PAF-induced NF-kappaB activation and NF-kappaB-dependent TNF-alpha expression. The effects of the antioxidants were due to their inhibition of PAF-induced degradation of IkappaBalpha, a protein responsible for keeping NF-kappaB in an inactive form. A protein tyrosine kinase and N-tosyl-L-phenylalanine chloromethyl ketone sensitive serine protease were involved in both PAF- and H2O2-induced NF-kappaB activation. Collectively, these data indicate that the PAF-induced NF-kappaB activation is selectively mediated through the generation of ROI.

Platelet activating factor (PAF) antagonists on cytokine induction of iNOS and sPLA2 in immortalized astrocytes (DITNC)

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and its receptor are known to play important roles in modulating neuronal plasticity and inflammatory responses, particularly during neuronal injury. PAF receptors are widespread in different brain regions and are present on the cell surface as well as in intracellular membrane compartments. Astrocytes are immune active cells and are responsive to cytokines, which stimulate signaling cascades leading to transcriptional activation of genes and protein synthesis. Our recent studies indicate the ability of cytokines, e.g., tumor necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) and interferon-gamma (IFNgamma), to induce the inducible nitric oxide (iNOS) and secretory phospholipase A2 (sPLA2) genes in immortalized astrocytes (DITNC) (Li et al., J. Interferon and Cytokine Res. 19: 121-127. 1999). The main objective for this study is to examine the effects of PAF antagonists on cytokine induction of iNOS and sPLA2 in these cells. Results show that BN50730, a synthetic PAF antagonist, but not BN52021, a natural PAF antagonist (ginkolide B) can dose-dependently inhibit cytokine induction of NO production and sPLA2 release. Inhibition of NO production by BN50730 corroborated well with the decrease in iNOS protein and mRNA levels as well as binding of NF-kappaB STAT- 1 to DNA, suggesting that BN50730 action is upstream of the transcriptional process. These results are in agreement with the role of intracellular PAF in regulating the cytokine signaling cascade in astrocytes and further suggest the possible use of BN50730 as a therapeutic agent for suppressing the inflammatory pathways elicited by cytokines.