Tumor necrosis factor/cachectin stimulates peritoneal macrophages, polymorphonuclear neutrophils, and vascular endothelial cells to synthesize and release platelet-activating factor

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.

BCAA-BCKA axis regulates WAT browning through acetylation of PRDM16

The link between branched-chain amino acids (BCAAs) and obesity has been known for decades but the functional role of BCAA metabolism in white adipose tissue (WAT) of obese individuals remains vague. Here, we show that mice with adipose tissue knockout of Bcat2, which converts BCAAs to branched-chain keto acids (BCKAs), are resistant to high-fat diet-induced obesity due to increased inguinal WAT browning and thermogenesis. Mechanistically, acetyl-CoA derived from BCKA suppresses WAT browning by acetylation of PR domain-containing protein 16 (PRDM16) at K915, disrupting the interaction between PRDM16 and peroxisome proliferator-activated receptor-γ (PPARγ) to maintain WAT characteristics. Depletion of BCKA-derived acetyl-CoA robustly prompts WAT browning and energy expenditure. In contrast, BCKA supplementation re-establishes high-fat diet-induced obesity in Bcat2 knockout mice. Moreover, telmisartan, an anti-hypertension drug, significantly represses Bcat2 activity via direct binding, resulting in enhanced WAT browning and reduced adiposity. Strikingly, BCKA supplementation reverses the lean phenotype conferred by telmisartan. Thus, we uncover the critical role of the BCAA-BCKA axis in WAT browning.

TNF-α in Uveitis: From Bench to Clinic

Uveitis is an inflammation of the iris, ciliary body, vitreous, retina, or choroid, which has been shown to be the first manifestation of numerous systemic diseases. Studies about the immunopathogenesis and treatment of uveitis are helpful to comprehend systemic autoimmune diseases, and delay the progression of systemic autoimmune diseases, respectively. Tumor necrosis factor-alpha (TNF-α), a pleiotropic cytokine, plays a pivotal role in intraocular inflammation based on experimental and clinical data. Evidence of the feasibility of using anti-TNF-α agents for uveitis management has increased. Although there are numerous studies on TNF-α in various autoimmune diseases, the pathological mechanism and research progress of TNF-α in uveitis have not been reviewed. Therefore, the objective of this review is to provide a background on the role of TNF-α in the immunopathogenesis of uveitis, as well as from bench to clinical research progress, to better guide TNF-α-based therapeutics for uveitis.

Thrombosis in Psoriasis: Cutaneous Cytokine Production as a Potential Driving Force of Haemostatic Dysregulation and Subsequent Cardiovascular Risk

Psoriasis (PsO) is a common T cell-mediated inflammatory disorder of the skin with an estimated prevalence of 2%. The condition manifests most commonly as erythematous plaques covered with scales. The aetiology of PsO is multifactorial and disease initiation involves interactions between environmental factors, susceptibility genes, and innate and adaptive immune responses. The underlying pathology is mainly driven by interleukin-17. In addition, various inflammatory mediators from specific T helper (T_H) cell subsets, namely T_H1, T_H17, and T_H22, are overexpressed in cutaneous lesions and may also be detected in the peripheral blood of psoriatic patients. Moreover, these individuals are also at greater risk, compared to the general population, of developing multiple comorbid conditions. Cardiovascular disease (CVD) has been recognised as a prominent comorbidity of PsO. A potential mechanism contributing to this association may be the presence of a hypercoagulable state in these individuals. Inflammation and coagulation are closely related. The presence of chronic, low-grade systemic inflammation may promote thrombosis – one of the major determinants of CVD. A pro-inflammatory milieu may induce the expression of tissue factor, augment platelet activity, and perturb the vascular endothelium. Altogether, these changes will result in a prothrombotic state. In this review, we describe the aetiology of PsO, as well as the pathophysiology of the condition. We also consider its relationship to CVD. Given the systemic inflammatory nature of PsO, we evaluate the potential contribution of prominent inflammatory mediators (implicated in PsO pathogenesis) to establishing a prothrombotic state in psoriatic patients.

Dissecting the Mechanism of Intracellular Mycobacterium smegmatis Growth Inhibition by Platelet Activating Factor C-16

Mycobacterium tuberculosis (M.tb) infection results in approximately 1.3 million human deaths each year. M.tb resides primarily inside macrophages, and maintains persistent infection. In response to infection and inflammation, platelet activating factor C-16 (PAF C-16), a phospholipid compound, is released by various cells including neutophils and monocytes. We have recently shown that PAF C-16 can directly inhibit the growth of two representative non-pathogenic mycobacteria, Mycobacterium bovis BCG and Mycobacterium smegmatis (M. smegmatis), by damaging the bacterial cell membrane. Here, we have examined the effect of PAF C-16 on M. smegmatis residing within macrophages, and identified mechanisms involved in their growth inhibitory function. Our results demonstrated that exogenous PAF C-16 inhibited the growth of M. smegmatis inside phagocytic cells of monocytic cell line, THP-1; this effect was partially blocked by PAF receptor antagonists, suggesting the involvement of PAF receptor-mediated signaling pathways. Arachidonic acid, a downstream metabolite of PAF C-16 signaling pathway, directly inhibited the growth of M. smegmatis in vitro. Moreover, the inhibition of phospholipase C and phospholipase A₂ activities, involved in PAF C-16 signaling pathway, increased survival of intracellular M. smegmatis. Interestingly, we also observed that inhibition of inducible nitric oxide synthase (iNOS) enzyme and antibody-mediated neutralization of TNF-α partially mitigated the intracellular growth inhibitory effect of PAF C-16. Use of a number of PAF C-16 structural analogs, including Lyso-PAF, 2-O-methyl PAF, PAF C-18 and Hexanolamino PAF, revealed that the presence of acetyl group (CH₃CO) at sn-2 position of the glycerol backbone of PAF is important for the intracellular growth inhibition activity against M. smegmatis. Taken together, these results suggest that exogenous PAF C-16 treatment inhibits intracellular M. smegmatis growth, at least partially, in a nitric oxide and TNF-α dependent manner.

Direct Growth Inhibitory Effect of Platelet Activating Factor C-16 and Its Structural Analogs on Mycobacteria

Mycobacterium tuberculosis, the causative agent of tuberculosis, is one of the leading causes of human deaths due to a single infectious agent. M. tuberculosis infection of the host initiates a local inflammatory response, resulting in the production of a range of inflammatory factors at the site of infection. These inflammatory factors may come in direct contact with M. tuberculosis and immune cells to activate different signaling pathways. One such factor produced in excess during inflammation is a phospholipid compound, Platelet Activating Factor C-16 (PAF C-16). In this study, PAF C-16 was shown to have a direct inhibitory effect on the growth of Mycobacterium bovis BCG (M. bovis BCG) and Mycobacterium smegmatis (M. smegmatis) in a dose- and time-dependent manner. Use of a range of PAF C-16 structural analogs, including the precursor form Lyso-PAF, revealed that small modifications in the structure of PAF C-16 did not alter its mycobacterial growth inhibitory properties. Subsequent experiments suggested that the attachment of aliphatic carbon tail via ether bond to the glycerol backbone of PAF C-16 was likely to play a vital role in its growth inhibition ability against mycobacteria. Fluorescence microscopy and flow cytometry using Propidium iodide (PI) indicated that PAF C-16 treatment had a damaging effect on the cell membrane of M. bovis BCG and M. smegmatis. Furthermore, the growth inhibitory effect of PAF C-16 was partially mitigated by treatment with membrane-stabilizing agents, α-tocopherol and Tween-80, which further suggests that the growth inhibitory effect of PAF C-16 was mediated through bacterial cell membrane damage.

Mechanisms of Fish Macrophage Antimicrobial Immunity

Overcrowding conditions and temperatures shifts regularly manifest in large-scale infections of farmed fish, resulting in economic losses for the global aquaculture industries. Increased understanding of the functional mechanisms of fish antimicrobial host defenses is an important step forward in prevention of pathogen-induced morbidity and mortality in aquaculture setting. Like other vertebrates, macrophage-lineage cells are integral to fish immune responses and for this reason, much of the recent fish immunology research has focused on fish macrophage biology. These studies have revealed notable similarities as well as striking differences in the molecular strategies by which fish and higher vertebrates control their respective macrophage polarization and functionality. In this review, we address the current understanding of the biological mechanisms of teleost macrophage functional heterogeneity and immunity, focusing on the key cytokine regulators that control fish macrophage development and their antimicrobial armamentarium.

In vivo neutralization of tumor necrosis factor attenuates the generalized Shwartzman reaction in the rabbit

A role for tumor necrosis factor (TNF) and TNF-induced tissue factor (TF) expression has been postulated in endotoxin (LPS)-induced diffuse intravascular coagulation (DIC). We studied the protective efficacy of goat polyclonal gammaglobulin (lgG) against recombinant human (rh)-TNF in the generalized Shwartzman reaction (GSR) in rabbits, a model of DIC. Administration of anti-rhTNF 2 h before the first, preparative, LPS injection afforded 95% neutralization of TNF released during the GSR. Compared to saline-pretreated controls, a modest attenuation of fibrin deposition in kidney, lung, liver and spleen was observed 4 h after the second provocative LPS injection. Except for the lung, fibrin deposition in the anti-rhTNF group was not attenuated compared to the non-immune goat IgG (ni-lgG)-pretreated group. Both ni-lgG and anti-rhTNF prevented LPS-induced TF expression by mononuclear cells, but not by isolated glomeruli. Other mediators than TNF and TF are involved as well in glomerular injury and fibrin deposition after LPS.

Mechanisms of immune evasion in leishmaniasis

Diseases caused by Leishmania present a worldwide problem, and current therapeutic approaches are unable to achieve a sterile cure. Leishmania is able to persist in host cells by evading or exploiting host immune mechanisms. A thorough understanding of these mechanisms could lead to better strategies for effective management of Leishmania infections. Current research has focused on parasite modification of host cell signaling pathways, entry into phagocytic cells, and modulation of cytokine and chemokine profiles that alter immune cell activation and trafficking to sites of infection. Immuno-therapeutic approaches that target these mechanisms of immune evasion by Leishmania offer promising areas for preclinical and clinical research.

IL-1β and TLR4 signaling are involved in the aggravated murine acute graft-versus-host disease caused by delayed bortezomib administration

It was shown that the proteasome inhibitor, bortezomib, administered immediately following allogeneic bone marrow transplantation resulted in marked inhibition of acute graft-versus-host disease (aGVHD), with retention of graft-versus-tumor effects. However, continuous bortezomib administration resulted in significant acceleration of graft-versus-host disease-dependent morbidity. We carried out studies to dissect the mechanisms of aggravated aGVHD caused by delayed bortezomib administration. First, we demonstrated that IL-1β was critically involved, and the subsequent aGVHD could be alleviated by IL-1β blockade. Bortezomib treatment after dendritic cell (DC) activation resulted in drastically elevated IL-1β production, whereas bortezomib treatment before DC activation inhibited IL-1β production, suggesting that the timing of bortezomib administration significantly affected IL-1β production by DCs. We further demonstrated that delayed administration of bortezomib accelerated aGVHD through TLR4 signaling. Because the LPS levels were much lower with reduced-intensity conditioning compared with high-dose irradiation, the accelerated graft-versus-host disease-dependent morbidity with delayed bortezomib administration could be rescued by reduced-intensity conditioning. Our studies suggested that TLR4 pathway activation and delayed bortezomib administration amplified the production of IL-1β and other inflammatory cytokines, which resulted in accelerated aGVHD-dependent morbidity. These results indicated that decreased toxicity of continuous bortezomib administration could be achieved by reduced-intensity conditioning or by inhibiting IL-1β.

Baseline and 6-Week follow-up levels of PAF and activity of its metabolic enzymes in patients with heart failure and healthy volunteers--a pilot study

This study aimed at evaluating the changes in platelet-activating factor (PAF) and its metabolic enzymes over a 6-week follow-up period in patients with newly diagnosed heart failure ([HF] n = 12) compared with age-, sex-, and BMI-matched apparently healthy volunteers (n = 10). The PAF, its key biosynthetic enzymes (lyso-PAF acetyltransferase [lyso-PAF-AT] and dithiothreitol [DTT]-insensitive CDP choline: 1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase [PAF-CPT]), and its catabolic isoenzymes (PAF-acetylhydrolase [PAF-AH] and lipoprotein-associated phospholipase A2 [Lp-PLA2]) were measured in serum and leukocytes of participants. At baseline, patients with HF had lower median activities of lyso-PAF-AT (P < .001) and PAF-CPT (P = .07) in parallel with PAF levels (P = .05) and higher activities of PAF-AH (P = .02) and Lp-PLA2 (P < .001) than controls. At follow-up, PAF-CPT and PAF levels marginally increased (P = .1), lyso-PAF-AT (P < .001) remained downregulated, while PAF-AH (P = .004) and Lp-PLA2 (P < .001) remained elevated compared with the controls. Newly diagnosed patients with HF under drug treatment have an affected profile of PAF biosynthetic enzymes and especially lyso-PAF-AT.

Cytokine gene regulation by PGE(2), LTB(4) and PAF

The initial response of the host to noxious stimuli produces a nonspecific inflammatory response. A more specific immune response is believed to be modulated by two classes of molecules: lipid mediators (PG, LT and PAF) and cytokines, synthesized by phagocytes and parenchyreal cells. In this review we discuss the increasing evidence of the interrelationship between eicosanoids, PAF and cytokines: IL-1 and TNF induce PG synthesis in various cells and PG, in turn, modulate cytokine production. We focused on the regulatory effects of LTB(4), PGE(2) and PAF on cytokine gene expression.

Association of IL-1β -511 polymorphism with severe veno-occlusive disease in pediatric-matched allogeneic hematopoietic stem cell transplantation

Single nucleotide polymorphisms (SNPs) of the interleukin 1 (IL-1) family have been implicated in acute graft-versus-host disease and mortality postallogeneic hematopoietic stem cell transplantation (HSCT) in adults. Hepatic veno-occlusive disease (VOD) is a well-known complication of HSCT and can result in an increased risk of mortality. In this study, we sought to investigate the association of both patient and donor genotypes at the IL-1β -511 cytidine/thymidine (C/T) polymorphic site with hepatic VOD and mortality in an exclusive pediatric cohort undergoing matched myeloablative allogeneic HSCT. Donor TT genotype was associated with higher cumulative incidence of grade III-IV hepatic VOD at 3 months after transplantation relative to donor CT and CC genotypes (25±13.1% in TT, 2.9±2.9% in CT, and 3.6±3.6% in CC; P=0.024). Neither recipient nor donor IL-1β -511 single nucleotide polymorphisms genotypes were associated with mortality or relapse. Our findings suggest that donor, rather than host, genotype at the IL-1β -511 polymorphic site may associate with higher risk for severe VOD after matched allogeneic HSCT. Our findings challenge the assumption that host factors are exclusively responsible for VOD and suggest a novel role for the donor inflammasome pathway in inducing injury and microvascular disease after HSCT, which merits further study in a larger cohort analysis.

Pentosan polysulfate inhibits atherosclerosis in Watanabe heritable hyperlipidemic rabbits: differential modulation of metalloproteinase-2 and -9

Pentosan polysulfate (PPS), a heparinoid compound essentially devoid of anticoagulant activity, modulates cell growth and decreases inflammation. We investigated the effect of PPS on the progression of established atherosclerosis in Watanabe heritable hyperlipidemic (WHHL) rabbits. After severe atherosclerosis developed on an atherogenic diet, WHHL rabbits were treated with oral PPS or tap water for 1 month. The aortic intima-to-media ratio and macrophage infiltration were reduced, plaque collagen content was increased, and plaque fibrous caps were preserved by PPS treatment. Plasma lipid levels and post-heparin hepatic lipase activity remained unchanged. However, net collagenolytic activity in aortic extracts was decreased, and the levels of matrix metalloproteinase (MMP)-2 and tissue inhibitor of metalloproteinase (TIMP) activity were increased by PPS. Moreover, PPS treatment decreased tumor necrosis factor α (TNFα)-stimulated proinflammatory responses, in particular activation of nuclear factor-κB and p38, and activation of MMPs in macrophages. In conclusion, oral PPS treatment prevents progression of established atherosclerosis in WHHL rabbits. This effect may be partially mediated by increased MMP-2 and TIMP activities in the aortic wall and reduced TNFα-stimulated inflammation and MMP activation in macrophages. Thus, PPS may be a useful agent in inhibiting the progression of atherosclerosis.

Platelet-activating factor receptor agonists mediate xeroderma pigmentosum A photosensitivity

To date, oxidized glycerophosphocholines (Ox-GPCs) with platelet-activating factor (PAF) activity produced non-enzymatically have not been definitively demonstrated to mediate any known disease processes. Here we provide evidence that these Ox-GPCs play a pivotal role in the photosensitivity associated with the deficiency of the DNA repair protein xeroderma pigmentosum type A (XPA). It should be noted that XPA-deficient cells are known to have decreased antioxidant defenses. These studies demonstrate that treatment of human XPA-deficient fibroblasts with the pro-oxidative stressor ultraviolet B (UVB) radiation resulted in increased reactive oxygen species and PAF receptor (PAF-R) agonistic activity in comparison with gene-corrected cells. The UVB irradiation-generated PAF-R agonists were inhibited by antioxidants. UVB irradiation of XPA-deficient (Xpa-/-) mice also resulted in increased PAF-R agonistic activity and skin inflammation in comparison with control mice. The increased UVB irradiation-mediated skin inflammation and TNF-α production in Xpa-/- mice were blocked by systemic antioxidants and by PAF-R antagonists. Structural characterization of PAF-R-stimulating activity in UVB-irradiated XPA-deficient fibroblasts using mass spectrometry revealed increased levels of sn-2 short-chain Ox-GPCs along with native PAF. These studies support a critical role for PAF-R agonistic Ox-GPCs in the pathophysiology of XPA photosensitivity.

Neutrophils reduce the parasite burden in Leishmania (Leishmania) amazonensis-infected macrophages

BACKGROUND

Studies on the role of neutrophils in Leishmania infection were mainly performed with L. (L) major, whereas less information is available for L. (L) amazonensis. Previous results from our laboratory showed a large infiltrate of neutrophils in the site of infection in a mouse strain resistant to L. (L.) amazonensis (C3H/HePas). In contrast, the susceptible strain (BALB/c) displayed a predominance of macrophages harboring a high number of amastigotes and very few neutrophils. These findings led us to investigate the interaction of inflammatory neutrophils with L. (L.) amazonensis-infected macrophages in vitro.

METHODOLOGY/PRINCIPAL FINDINGS

Mouse peritoneal macrophages infected with L. (L.) amazonensis were co-cultured with inflammatory neutrophils, and after four days, the infection was quantified microscopically. Data are representative of three experiments with similar results. The main findings were 1) intracellular parasites were efficiently destroyed in the co-cultures; 2) the leishmanicidal effect was similar when cells were obtained from mouse strains resistant (C3H/HePas) or susceptible (BALB/c) to L. (L.) amazonensis; 3) parasite destruction did not require contact between infected macrophages and neutrophils; 4) tumor necrosis factor alpha (TNF-α), neutrophil elastase and platelet activating factor (PAF) were involved with the leishmanicidal activity, and 5) destruction of the parasites did not depend on generation of oxygen or nitrogen radicals, indicating that parasite clearance did not involve the classical pathway of macrophage activation by TNF-α, as reported for other Leishmania species.

CONCLUSIONS/SIGNIFICANCE

The present results provide evidence that neutrophils in concert with macrophages play a previously unrecognized leishmanicidal effect on L. (L.) amazonensis. We believe these findings may help to understand the mechanisms involved in innate immunity in cutaneous infection by this Leishmania species.

Chronic alcohol exposure increases circulating bioactive oxidized phospholipids

Ethanol metabolism by liver generates short lived reactive oxygen species that damage liver but also affects distal organs through unknown mechanisms. We hypothesized that dissemination of liver oxidative stress proceeds through release of biologically active oxidized lipids to the circulation. We searched for these by tandem mass spectrometry in plasma of rats fed a Lieber-DeCarli ethanol diet or in patients with established alcoholic liver inflammation, steatohepatitis. We found a severalfold increase in plasma peroxidized phosphatidylcholines, inflammatory and pro-apoptotic oxidatively truncated phospholipids, and platelet-activating factor, a remarkably potent and pleiotropic inflammatory mediator, in rats chronically ingesting ethanol. Circulating peroxidized phospholipids also increased in humans with established steatohepatitis. However, reactive oxygen species generated by liver ethanol catabolism were not directly responsible for circulating oxidized phospholipids because the delayed appearance of these lipids did not correlate with ethanol exposure, hepatic oxidative insult, nor plasma alanine transaminase marking hepatocyte damage. Rather, circulating oxidized lipids correlated with steatohepatitis and tumor necrosis factor-alpha deposition in liver. The organic osmolyte 2-aminoethylsulfonic acid (taurine), which reduces liver endoplasmic reticulum stress and inflammation, even though it is not an antioxidant, abolished liver damage and the increase in circulating oxidized phospholipids. Thus, circulating oxidized phospholipids are markers of developing steatohepatitis temporally distinct from oxidant stress associated with hepatic ethanol catabolism. Previously, circulating markers of the critical transition to pathologic steatohepatitis were unknown. Circulating oxidatively truncated phospholipids are pro-inflammatory and pro-apoptotic mediators with the potential to systemically distribute the effect of chronic ethanol exposure. Suppressing hepatic inflammation, not ethanol catabolism, reduces circulating inflammatory and apoptotic agonists.

TNFalpha is a potent inducer of platelet-activating factor synthesis in adipocytes but not in preadipocytes. Differential regulation by PI3K

Tumour necrosis factor alpha (TNFalpha) induces platelet-activating factor (PAF) synthesis in many inflammatory cells. Here, we investigate the possibility that TNFalpha stimulates PAF synthesis in rat adipocytes and preadipocytes and that phosphoinositide 3-kinase (PI3K) and extracellular signal-regulated kinase 1/2 (ERK1/2) are implicated in this process. Primary cultures were incubated with [3H]lyso-PAF and stimulated by TNFalpha in the presence or absence of wortmannin. We found that, although both cultures synthesized PAF at a similar basal rate, TNFalpha-induced PAF synthesis in adipocytes was 7-fold higher than in preadipocytes. This suggested a maturation of PAF-TNFalpha interrelationship during adipocyte differentiation. Wortmannin enhanced TNFalpha-dependent PAF synthesis in adipocytes but not in preadipocytes, indicating the negative control by PI3K in mature cells. PAF increase was due to the regulation of its biosynthesis since PAF-acetylhydrolase (PAF-AH) activity was TNFalpha- and wortmannin-independent. Our hypothesis is that PAF mediates TNFalpha inflammatory effects in both adipocytes and preadipocytes and that this pathway is enhanced during adipocyte differentiation, a mechanism which is highly active during the development of obesity.

The fetal inflammatory response syndrome

The fetal inflammatory response syndrome (FIRS) is a condition characterized by systemic inflammation and an elevation of fetal plasma interleukin-6. This syndrome has been observed in fetuses with preterm labor with intact membranes, preterm prelabor rupture of the membranes, and also fetal viral infections such as cytomegalovirus. FIRS is a risk factor for short-term perinatal morbidity and mortality after adjustment for gestational age at delivery and also for the development of long-term sequelae such as bronchopulmonary dysplasia and brain injury. Multiorgan involvement in FIRS has been demonstrated in the hematopoietic system, thymus, adrenal glands, skin, kidneys, heart, lung, and brain. This article reviews the fetal systemic inflammatory response as a mechanism of disease. Potential interventions to control an exaggerated inflammatory response in utero are also described.

Role of micro-organisms in necrotizing enterocolitis

The frequency with which necrotizing enterocolitis occurs in outbreaks makes it likely that the illness can have an infective origin. Immunological and non-immunological defences of the gastrointestinal are impaired in early life. Consequently the gut of the preterm infant is predisposed to bacterial overgrowth. A wide range of pathogenic bacteria and viruses have been isolated from infants with necrotizing enterocolitis or detected histologically. The presence of bacterial metabolites in the breath, intestinal bullae (hydrogen) and urine (D-lactate) during the course of the illness is further confirmatory evidence. The presence of bacteria or bacterial products (such as exo- and endotoxin) in the circulation will lead to ischaemia of the intestine and other organs either directly or via mediators such as cytokines or platelet activating factor. Future studies in necrotizing enterocolitis should be directed to understanding and modulating inflammatory mediators in necrotizing enterocolitis and preventing the disease with breast milk and nutritional supplements (glutamine, short chain fatty acids), chemoprophylaxis, and antibodies.

Platelet-activating factor (PAF) is the effector of IFNγ-stimulated invasiveness and motility in a B16 melanoma line

In this study, we investigated whether PAF synthesized by F10-M3 cells (a clone of B16-F10 melanoma line) mediates the increased capacity of these cells to penetrate into Matrigel upon stimulation with IFN gamma. The determination of PAF synthesized by IFN gamma-stimulated tumor cells revealed that 70% of newly synthesized PAF was released into growth media, while the remaining 30% was associated with the cell bodies. An experimental protocol based on the use of WEB 2086, a PAF receptorial antagonist, was designed to explore which of the two fractions of PAF synthesized by IFN gamma-stimulated F10-M3 cells (released into the growth medium or associated with the cell bodies) is essential to their capacity to migrate through Matrigel. We found that the PAF secreted into growth medium is the fraction responsible for the enhanced invasiveness of melanoma cells stimulated with IFN gamma. We also investigated whether motility of melanoma cells is stimulated by IFN gamma, and, if so, whether PAF is involved in this effect. We found that WEB 2086 prevented the remodeling of stress fibers, examined as an index of cell motility, that we observed in F10-M3 cells stimulated with IFN gamma. Furthermore, the observation that PAF receptor is expressed in IFN gamma-stimulated melanoma cells suggests that the invasive phenotype (e.g. migration through a reconstituted basement membrane and motility) promoted by PAF is based on an autocrine mechanism. On the whole, these results might indicate that PAF contributes to the expression of properties typical of an invasive phenotype in tumor cells stimulated with cytokines.

Pentoxifylline reduces the incidence and severity of necrotizing enterocolitis in a neonatal rat model

Necrotizing enterocolitis (NEC) is a potentially fatal illness in premature neonates. Tumor necrosis factor alpha (TNF-alpha) has been shown to play a central role in the inflammatory cascade leading to the development of NEC. Published evidence points to a significant role of pentoxifylline in inhibition of TNF-alpha and in reducing mucosal injury and improving healing in ischemia-reperfusion experiments. Our aim was to investigate the effect of pentoxifylline on the incidence of NEC in a neonatal rat model. Newborn Sprague-Dawley rat pups originating from eight separate litters were delivered by cesarean section at 21.5 d and were formula fed from birth by orogastric gavage. The rat pups were randomized to receive either intraperitoneal pentoxifylline (15 mg/kg/dose) or placebo, given every 8 h beginning at 24 h of age, in a blinded fashion. Experimental NEC was induced by exposure to hypoxia for 60 s followed by cold stress at 4 degrees C for 10 min. The animals were euthanized at development of NEC or at 96 h and intestinal tissue was processed and examined for histologic changes of NEC. The incidence of NEC was significantly lower in the pentoxifylline group [pentoxifylline 5/38 versus placebo 15/36; p = 0.008, odds ratio (OR) = 0.21 95% confidence interval (CI) 0.07-0.67]. Among the pups developing NEC, significantly fewer rat pups treated with pentoxifylline had severe (>or=3) intestinal injury scores [pentoxifylline 1/5 versus placebo 10/15; p = 0.031, OR 0.06, 95% CI 0.01-0.79]. We conclude that intraperitoneal administration of pentoxifylline significantly reduced the incidence and severity of NEC in our experimental animal model.

Platelet activating factor and its metabolite promote sleep in rabbits

Platelet activating factor (PAF) is a key inflammatory mediator. PAF and its receptor are found in brain and PAF affects or is affected by the production of sleep promoting cytokines such as interleukin-1. PAF also interacts with several other sleep-regulatory substances such as nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, nitric oxide, prostaglandins, and prolactin. We thus hypothesized that PAF would increase sleep. In these experiments, each rabbit received an injection of 25 microl of 2% DMSO to obtain control values, and on a separate day received PAF or lyso-PAF, a metabolite of PAF. Ten, 100 and 500 nmol for each substance was injected intracerebroventricularly. Both PAF and lyso-PAF enhanced non-rapid eye movement (NREM) sleep but not REM sleep. Lyso-PAF, but not PAF, induced hyperthermia. Results are consistent with the hypothesis that the brain cytokine network is involved in physiological sleep regulation.

Impaired inflammatory angiogenesis, but not leukocyte influx, in mice lacking TNFR1

The majority of biological responses classically attributed to tumor necrosis factor alpha (TNF-alpha) is mediated by p55 receptor (TNFR1). Here, we aimed to clarify the biological role of TNFR1-mediated signals in an in vivo inflammatory angiogenesis model. Polyester-polyurethane sponges, used as a framework for tissue growth, were implanted in C57Bl/6 mice. These implants were collected at days 1, 7, and 14 post-implant for enzyme-linked immunosorbent assay or at days 7 and 14 for hemoglobin, myeloperoxidase, and N-acetylglucosaminidase measurements, used as indexes for angiogenesis, neutrophil, and macrophage accumulation, respectively. In TNFR1-deficient C57Bl/6 mice, there was a significant decrease in sponge vascularization but not in late inflammatory cell influx. It is interesting that levels of vascular endothelial growth factor were significantly lower in TNFR1-deficient than in wild-type mice at days 1 and 7. Levels of angiogenic chemokines, CC chemokine ligand 2/murine homologue of monocyte chemoattractant protein-1 and CXC chemokine ligand 1-3/keratinocyte-derived chemokine, were significantly lower in TNFR1-deficient mice at days 1 and 7 after implantation, respectively. These observations suggest that TNFR1-mediated signals have a critical role in sponge-induced angiogenesis, possibly by influencing the effector state of inflammatory cells and hence, modulating the angiogenic molecular network.

Pancreatic proteases and inflammatory mediators in peritoneal fluid during splanchnic arterial occlusion and reperfusion

Pancreatic enzymes in the ischemic intestine are involved in the production of in vivo inflammatory mediators. These mediators stimulate cells in the cardiovascular system during shock and initiate multiorgan failure. An important aspect that controls the extent of the inflammation is the dispersion of these mediators from the ischemic intestine. In the past, two pathways for dispersion of these inflammatory mediators have been identified, absorption into the intestinal venous circulation and uptake into the lymphatics. We hypothesize here that the inflammatory mediators produced by pancreatic digestive enzymes in the lumen of the intestine may also be released directly into the peritoneal space. To assess the presence of inflammatory mediators in the peritoneal cavity in response to splanchnic arterial occlusion (90 min) and reperfusion (SAO shock), we measured the ability of fluid collected from this cavity to activate naive donor granulocytes. After SAO in control rats, peritoneal lavage fluid caused activation of naive donor granulocytes when tested in vitro. In contrast, when the lumen of the small intestine was flushed with a broad-acting pancreatic enzyme inhibitor (6-amidino-2-naphtyl p-guanidinobenzoate dimethanesulfate), the fluid no longer caused leukocyte activation. Reduction of the levels of inflammatory mediators in the peritoneal fluid was associated with an attenuation in the fall of blood pressure after SAO shock. These results indicate that the inflammatory mediators, which are produced by pancreatic digestive enzymes, can be absorbed directly into the systemic circulation via a transperitoneal route and play a part in the development of multiorgan failure.

Vascular adhesion and transendothelial migration of eosinophil leukocytes

Tissues respond to injury with inflammation in an effort to protect and repair the damaged site. During inflammation, leukocytes typically accumulate in response to certain chemicals produced within the tissue itself. The passage of leukocytes through the vascular lumen into tissues occurs in several phases, including rolling, activation, firm adhesion, transendothelial migration, and subendothelial migration. Although infiltration of eosinophil leukocytes is one of the most important aspects of allergic inflammatory reactions, eosinophils also participate in nonallergic inflammation. Eosinophil accumulation is regulated not only by endothelial adhesion molecules, but also by interactions between eosinophil adhesion molecules and extracellular matrix elements. This review summarizes the regulation of eosinophil leukocyte adhesion and migration. A better understanding of eosinophil recruitment responses may lead to the development of novel therapeutics for chronic allergic diseases.

Dynamic contrast-enhanced MRI using macromolecular contrast media for monitoring the response to isolated limb perfusion in experimental soft-tissue sarcomas

The objective of this study was to evaluate the potential of dynamic contrast-enhanced MRI for quantitative characterization of tumor microvessels and to assess the microvascular changes in response to isolated limb perfusion with TNF-alpha and melphalan. Dynamic contrast-enhanced MRI was performed in an experimental cancer model, using a macromolecular contrast medium, albumin-(Gd-DTPA)45. Small fragments of BN 175, a soft-tissue sarcoma, were implanted in 11 brown Norway (BN) rats. Animals were assigned randomly to a control (Haemaccel) or drug-treated group (TNF-alpha/melphalan). MRI was performed at baseline and 24 h after ILP. The transendothelial permeability (K(PS)) and the fractional plasma volume (fPV) were estimated from the kinetic analysis of MR data using a two-compartment bi-directional model. K(PS) and fPV decreased significantly in the drug-treated group compared to baseline (p<0.05). In addition, K(PS) post therapy was significantly lower (p<0.05) in the drug-treated group than in the control group. There was no significant difference in fPV between the drug-treated and the control group after therapy. Tumor microvascular changes in response to isolated limb perfusion can be determined after 24 h by dynamic contrast-enhanced MRI. The data obtained in this experimental model suggest possible applications in the clinical setting, using the appropriate MR contrast agents.

Platelet-activating factor and normal or leukaemic haematopoiesis

Platelet-activating factor (PAF), a phospholipid mediator with a wide range of actions on mature leukocytes, acts directly during early human haematopoiesis by affecting the growth of haematopoietic progenitors and indirectly, by modulating cytokine synthesis by bone marrow stromal cells. At this time, its role during leukaemic diseases remains speculative. The lack of membrane PAF receptor (PAF-R) on leukaemic blasts suggest that this receptor represents a marker of mature cells and its membrane induction a consequence of cell maturation. While the couple PAF/PAF-R has been largely studied using B cell lines, few results are available using B cells of patients with haematopoietic malignancies casting some doubts concerning the potential role (if any) of this molecule during leukaemic diseases.

Platelet-activating factor synthesis by neutrophils, monocytes, and endothelial cells is modulated by nitric oxide production

Nitric oxide (NO) and platelet-activating factor (PAF) can modulate the interaction between endothelial lining and circulating leukocytes. Several studies implicated the production of PAF and NO in the pathogenesis of microcirculatory alterations occurring in septic shock. However, the reciprocal interaction between PAF and NO has not been fully elucidated. In the present study, we evaluated whether the basal synthesis of NO could modulate the production of PAF by neutrophils (PMN), monocytes (MO), and endothelial cells (EC) unstimulated or stimulated with lipopolysaccharides (LPS) or tumor necrosis factor (TNF). PMN, MO, and EC, when incubated with N(omega)-nitro-L-arginine methyl ester (L-NAME) spontaneously synthesized PAF, with an early peak at 30 min. The effective inhibition of NO production was visualized on MO cells as generation of fluorescence reactivity by cell-permeable NO reactive dye DAF-2 DA. Also, monomethyl-L-arginine (L-NMMA) induced PAF synthesis by PMN, whereas the biologically inactive D-enantiomers of NAME (D-NAME) and of NMMA (D-NMMA) did not. Stimulation of PMN with L-NAME in presence of the exogenous NO donor nitroprusside, of the NO secondary mediator cGMP, or of the NO synthase substrate L-arginine reduced PAF synthesis, suggesting the involvement of an NO-dependent pathway on the modulation of PAF synthesis. The synthesis of PAF was enhanced by combined treatment with L-NAME and TNF or LPS. These results indicate an inhibitor effect of NO on the spontaneous and TNF or LPS-induced synthesis of PAF by human PMN, MO, and EC.

The long pentraxin PTX3 is synthesized in IgA glomerulonephritis and activates mesangial cells

The long pentraxin PTX3 has been recently involved in amplification of the inflammatory reactions and regulation of innate immunity. In the present study we evaluated the expression and role of PTX3 in glomerular inflammation. PTX3 expression was investigated in the IgA, type I membranoproliferative, and diffuse proliferative lupus glomerulonephritis, which are characterized by inflammatory and proliferative lesions mainly driven by resident mesangial cells, and in the membranous glomerulonephritis and the focal segmental glomerular sclerosis, where signs of glomerular inflammation are usually absent. We found an intense staining for PTX3 in the expanded mesangial areas of renal biopsies obtained from patients with IgA glomerulonephritis. The pattern of staining was on glomerular mesangial and endothelial cells. Scattered PTX3-positive cells were also detected in glomeruli of type I membranoproliferative glomerulonephritis. The concomitant expression of CD14 suggests an inflammatory origin of these cells. Normal renal tissue and biopsies from patients with the other glomerular nephropathies studied were mainly negative for PTX3 expression in glomeruli. However, PTX3-positive cells were detected in the interstitium of nephropathies showing inflammatory interstitial injury. In vitro, cultured human mesangial cells synthesized PTX3 when stimulated with TNF-alpha and IgA and exhibited specific binding for recombinant PTX3. Moreover, stimulation with exogenous PTX3 promoted mesangial cell contraction and synthesis of the proinflammatory lipid mediator platelet-activating factor. In conclusion, we provide the first evidence that mesangial cells may both produce and be a target for PTX3. The detection of this long pentraxin in the renal tissue of patients with glomerulonephritis suggests its potential role in the modulation of glomerular and tubular injury.

Neonatal necrotizing enterocolitis: clinical considerations and pathogenetic concepts

Necrotizing enterocolitis (NEC), a disease affecting predominantly premature infants, is a leading cause of morbidity and mortality in neonatal intensive care units. Although several predisposing factors have been identified, such as prematurity, enteral feeding, and infection, its pathogenesis remains elusive. In the past 20 years, we have established several animal models of NEC in rats and found several endogenous mediators, especially platelet-activating factor (PAF), which may play a pivotal role in NEC. Injection of PAF induces intestinal necrosis, and PAF antagonists prevent the bowel injury induced by bacterial endotoxin, hypoxia, or challenge with tumor necrosis factor-a (TNF) plus endotoxin in adult rats. The same is true for lesions induced by hypoxia and enteral feeding in neonatal animals. Human patients with NEC show high levels of PAF and decreased plasma PAF-acetylhydrolase, the enzyme degrading PAF. The initial event in our experimental models of NEC is probably polymorphonuclear leukocyte (PMN) activation and adhesion to venules in the intestine, which initiates a local inflammatory reaction involving proinflammatory mediators including TNF, complement, prostaglandins, and leukotriene C4. Subsequent norepinephrine release and mesenteric vasoconstriction result in splanchnic ischemia and reperfusion. Bacterial products (e.g., endotoxin) enter the intestinal tissue during local mucosal barrier breakdown, and endotoxin synergizes with PAF to amplify the inflammation. Reactive oxygen species produced by the activated leukocytes and by intestinal epithelial xanthine oxidase may be the final pathway for tissue injury. Protective mechanisms include nitric oxide produced by the constitutive (mainly neuronal) nitric oxide synthase, and indigenous probiotics such as Bifidobacteria infantis. The former maintains intestinal perfusion and the integrity of the mucosal barrier, and the latter keep virulent bacteria in check. The development of tissue injury depends on the balance between injurious and protective mechanisms.

Divergent mechanisms of action of the inflammatory cytokines interleukin 1-beta and tumour necrosis factor-alpha in mouse cremasteric venules

1. Protein synthesis dependency and the role of endogenously generated platelet activating factor (PAF) and leukotriene B(4) (LTB(4)) in leukocyte migration through interleukin-1beta (IL-1beta)- and tumour necrosis factor-alpha (TNFalpha)-stimulated mouse cremasteric venules was investigated using established pharmacological interventions and the technique of intravital microscopy. 2. Based on previously obtained dose-response data, 30 ng rmIL-1beta and 300 ng rmTNFalpha were injected intrascrotally (4 h test period) to induce comparable levels of leukocyte firm adhesion and transmigration in mouse cremasteric venules. 3. Co-injection of the mRNA synthesis inhibitor, actinomycin D (0.2 mg kg(-1)), with the cytokines significantly inhibited firm adhesion (49+/-13.6%) and transmigration (67.2+/-4.2%) induced by IL-1beta, but not TNFalpha. 4. In vitro, TNFalpha (1-100 ng ml(-1)), but not IL-1beta, stimulated L-selectin shedding and increased beta(2) integrin expression on mouse neutrophils, as quantified by flow cytometry. 5. The PAF receptor antagonist, UK-74,505 (modipafant, 0.5 mg kg(-1), i.v.), had no effect on adhesion induced by either cytokine, but significantly inhibited transmigration induced by IL-1beta (66.5+/-4.5%). 6. The LTB(4) receptor antagonist, CP-105,696 (100 mg kg(-1), p.o.), significantly inhibited both IL-1beta induced adhesion (81.4+/-15.2%) and transmigration (58.7+/-7.2%), but had no effect on responses elicited by TNFalpha. Combined administration of the two antagonists had no enhanced inhibitory effects on responses induced by either cytokine. 7. The data indicate that firm adhesion and transmigration in mouse cremasteric venules stimulated by IL-1beta, but not TNFalpha, is protein synthesis dependent and mediated by endogenous generation of PAF and LTB(4). Additionally, TNFalpha but not IL-1beta, can directly stimulate mouse neutrophils in vitro. The findings provide further evidence to suggest divergent mechanisms of actions of IL-1beta and TNFalpha, two cytokines often considered to act via common molecular/cellular pathways.

Nitric oxide/platelet activating factor cross-talk in mesangial cells modulates the interaction with leukocytes

BACKGROUND

Platelet activating factor (PAF) and nitric oxide (NO) exert opposite effects on adherence and activation of circulating leukocytes to endothelium. Several studies have implicated the production of PAF and NO by mesangial cells in the regulation of glomerular filtration, permeability and inflammation. However, the reciprocal interaction between PAF and NO in mesangial cells and their role in leukocyte adhesion has not been investigated.

METHODS

We evaluated whether blockade of constitutive production of NO by two different NO synthase (NOS) inhibitors (L-NAME and L-NMMA) could modulate PAF synthesis, and conversely whether exogenous PAF could influence the production of NO by mesangial cells. We evaluated whether modulation of PAF synthesis by NOS inhibitors could affect leukocyte adhesion to mesangial cells. The effect of PAF-receptor antagonist WEB2170, of anti-beta(2) integrins and intracellular adhesion molecule-1 (ICAM-1) blocking antibodies and of soluble Sialyl-Lewis-a also was evaluated.

RESULTS

Blockade of NO synthesis by NOS inhibitors induced a spontaneous synthesis of PAF that was conversely inhibited by NO generation. On the other hand, PAF inhibited both the basal and l-arginine induced synthesis of NO by mesangial cells. Moreover, NOS inhibition promoted the adhesion of polymorphonuclear cells and monocytes to mesangial cells by a mechanism dependent on the synthesis of PAF and on the interaction of beta(2) integrins and ICAM-1.

CONCLUSIONS

These data indicate that PAF and NO exhibit a bi-directional effect on their respective synthesis in human mesangial cells, and suggest that their reciprocal regulation may be relevant for leukocyte adhesion to glomerular mesangial cells.

Involvement of platelet-activating factor in hepatic apoptosis and necrosis in chronic ethanol-fed rats given endotoxin

BACKGROUND/AIMS

Platelet-activating factor (PAF)-a potent activator of neutrophils-plays an important role in the pathogenesis of endotoxin-induced tissue injury. However, the role of PAF in hepatic damage during alcoholic hepatitis remains unclear. The aims of the present study were to test whether PAF contributes to hepatic injury in an animal model of alcoholic hepatitis and to investigate the involvement of the Fas-receptor/Fas-ligand system in this process.

METHODS

Male Sprague-Dawley rats were pair-fed with Lieber-DeCarli ethanol liquid diet or isocaloric control diet for 6 weeks. Liver injury was induced by the intravenous (i.v.) injection of lipopolysaccharide (LPS) (1 mg/kg). Rats were pretreated with a specific PAF receptor antagonist (TCV-309; 100 mg/kg i.v.) or vehicle 1 h before LPS treatment.

RESULTS

Chronic ethanol administration remarkably sensitized the rats to the effects of LPS, with resultant severe hepatocellular injury, accompanied by significant increases in serum levels of alanine aminotransferase (ALT), tumour necrosis factor (TNF)-alpha and interleukin (IL)-8 (CINC/gro). Histological examination of the damaged livers showed hepatocyte apoptosis and necrosis with extensive infiltration by neutrophils, whereas immunohistochemical studies revealed enhanced Fas-receptor expression on hepatocytes and hepatic accumulation of neutrophils expressing Fas-ligand. Pretreatment with the PAF receptor antagonist protected against hepatic injury, suppressing hepatocyte apoptosis and necrosis, infiltration of neutrophils, expression of Fas-receptor and Fas-ligand, and serum TNF-alpha levels.

CONCLUSIONS

Our study suggests that PAF is an important mediator of hepatic injury in the ethanol/endotoxin model of alcoholic hepatitis.

Synthesis of platelet-activating factor (PAF) in transformed cell lines of a different origin

Interest in the possible involvement of the platelet-activating factor (PAF) in tumor growth and invasiveness has been stimulated by the recognition that PAF influences various biological responses relevant to metastatic diffusion, such as angiogenesis, adhesiveness to endothelia and cellular motility. In the present study, we investigated the extent to which PAF is synthesized by a series of human and murine transformed cell lines of a different histotype. Synthesis of PAF was studied by combining the 14C-acetate incorporation into PAF with the quantitative analysis of PAF performed by a procedure based on gas chromatography-mass spectrometry with a negative ion chemical ionization. In the presence of the Ca2+ ionophore A23187, cultures of human melanoma (Hs294T), fibrosarcoma (HT1080) and colon carcinoma (LS180) cell lines synthesized conspicuous amounts of PAF, comparable to those produced by resident peritoneal macrophages. Substantial quantities of PAF were also synthesized by the murine melanoma (F10-M3 cells). PAF synthesis was rather limited in RSV-transformed Balb/c3T3 (B77-3T3) cells and in one of their high metastatic variants (B77-AA6 cells), although it was more abundant in the latter. We also investigated whether certain cytokines, such as TNFalpha and IFNgamma might induce PAF synthesis in our systems of cell lines which we found to express mRNAs encoding receptors for these cytokines. We observed that PAF synthesis was enhanced in human melanoma and colon carcinoma cell lines and in the murine B77-AA6 cells to levels comparable to those obtained with the Ca2+ ionophore. Synthesis of PAF was not inducible by TNFalpha in murine F10-M3 melanoma cells. IFNgamma also stimulated PAF synthesis in human and murine melanoma lines, and in human LS180 colon carcinoma line, but not in the B77-AA6 cells. PAF synthesis was also inducible by exogenous PAF in the human and murine melanoma lines, and in the human LS180 colon carcinoma line, all of which expressed cell surface PAF receptors. PAF synthesis was not inducible by exogenous PAF in the B77-AA6 cells, which do not express PAF receptors.

The role of tumour necrosis factor-alpha (TNF-alpha) and platelet-activating factor (PAF) interaction on murine candidosis

Tumour necrosis factor-alpha (TNF-alpha) is related to some other factors in addition to being the essential cytokine of the sepsis which results from Candida infections. In our study, we investigated serum TNF-alpha levels, measured by enzyme-linked immunosorbent assay (ELISA), and platelet-activating factor (PAF)-like activity, measured by high-pressure liquid chromatography (HPLC) of the mice infected with Candida species. The PAF antagonist, ginkgolide BN 52021 was used to evaluate the possible interaction between TNF-alpha and PAF. The average TNF-alpha levels were found to be 396, 489, 699 and 803 pg ml(-1) on the 4th, 5th, 6th and 19th days of Candida albicans infection, respectively (P<0.05). There was no statistically significant difference between the serum TNF-alpha levels of the groups infected with other Candida species, such as C. kefyr, C. krusei and C. tropicalis (P>0.05). Serum TNF-alpha levels were found to be more significantly different in mice with C. albicans infection that were injected with PAF antagonists on the 6th day (23 pg ml(-1)). It was therefore thought that PAF antagonists have an inhibitory effect on TNF-alpha production. No significant difference was found between PAF levels in the three groups: healthy control mice, C. albicans-infected mice and C. albicans-infected mice given PAF antagonists (466 milli-absorbance unit (mAU), 475 mAU and 329 mAU, respectively). It was noticed that the positive interaction between PAF and TNF-alpha was not important after the first 4 days of the infection had passed.

PAF antagonist treatment reduces pro-inflammatory cytokine mRNA after spinal cord injury

Platelet-activating factor (PAF) is a pro-inflammatory molecule which contributes to secondary damage after spinal cord injury (SCI). To test if PAF contributes to cytokine induction following SCI, female Long-Evans rats were pretreated with the PAF antagonist WEB 2170 prior to receiving a contusion injury at spinal cord level T10 using the NYU impactor. RNase protection assay (RPA) analysis revealed that IL-1alpha mRNA peaked at I h post-injury while IL-1beta and IL-6 mRNA levels were higher and peaked at 6 h.TNF-alpha mRNA was almost undetectable. All mRNA levels approached baseline by 24 h. Treatment with WEB 2170 (1 mg/kg, i.p.) 15 min prior to injury significantly decreased mRNA levels for all three cytokines at 6 h post-injury, but not at I h post-injury. These results demonstrate a role for PAF in proinflammatory cytokine induction after SCI.

Effect of corticosteroids and eicosapentaenoic acid/docosahexaenoic acid on pro-oxidant and anti-oxidant status and metabolism of essential fatty acids in patients with glomerular disorders

It is known that the concentrations of essential fatty acids and their metabolites including eicosanoids, free radicals and anti-oxidants are altered in glomerular disorders. Both corticosteroids and n-3 fatty acids--eicosapentaenoic acid and docosahexaenoic acid (EPA and DHA respectively)--are useful in the management of glomerular disorders. In the present study, the altered plasma concentrations of lipid peroxides, nitric oxide and the metabolites of essential fatty acids and anti-oxidants--superoxide dismutase, glutathione peroxidase and vitamin E--in the RBC membranes of patients with glomerular disorders (nephrotic syndrome) reverted to normalcy following corticosteroids or EPA/DHA administration. This suggests that the beneficial actions of corticosteroids and EPA/DHA in glomerular disorders can be attributed to their action on the pro-oxidant and anti-oxidant concentrations and metabolism of essential fatty acids.

Involvement of a serine protease, but not of neutrophil elastase, in tumor necrosis factor-induced lethal hepatitis and induction of platelet-activating factor

BACKGROUND/AIMS

Tumor necrosis factor (TNF) plays an essential role in several types of acute and chronic hepatitis. Our aims in the present study were to elucidate the mechanism by which TNF leads to acute lethal hepatitis, thereby focusing on the role of serine proteases and platelet-activating factor (PAF).

METHODS

All experiments were performed in a model of acute hepatitis, induced by TNF in combination with D-(+)-galactosamine (GalN). Neutrophil elastase (NE)-deficient mice, generated by gene targeting were used in the studies.

RESULTS

We found that a serine protease plays an essential mediating role in the in vivo TNF effect as alpha1-antitrypsin (alpha1-AT), soybean trypsin inhibitor (STI) and turkey trypsin inhibitor (TTI), confer complete protection. alpha1-AT and TTI, but not STI, reduce PAF blood levels, induced by TNF/GalN, which is compatible with an elastase-like serine protease involvement in PAF synthesis. In our search for relevant serine proteases we believed that NE was an excellent candidate protease. However, we found that TNF/GalN-induced lethality is not attenuated in mice deficient in NE.

CONCLUSIONS

The data suggest that TNF-induced lethal hepatitis is accompanied by increases in circulating PAF and plasma clotting time, and mediated by a serine protease, but not by NE.

Tat-induced platelet-activating factor synthesis contributes to the angiogenic effect of HIV-1 Tat

This study shows that human umbilical cord vein-derived endothelial cells (HUVEC) stimulated with HIV-1 Tat synthesized platelet-activating factor (PAF), a phospholipid mediator of inflammation that possesses angiogenic properties. The synthesis of PAF by HUVEC stimulated with Tat was dose and time dependent. Moreover, in vitro experiments were performed to evaluate whether migration of HUVEC induced by Tat was dependent on the synthesis of PAF. It was found that the cell motility induced by Tat was inhibited by WEB 2170, a specific PAF receptor antagonist. In vivo, the neoangiogenesis induced by Tat was also inhibited by WEB 2170 in a murine model, in which matrigel subcutaneously injected was used as substratum for angiogenesis. These results suggest that the synthesis of PAF by endothelial cells mediates, at least in part, the angiogenic activity of Tat by promoting the endothelial cell migration.

HIV-1 Tat protein stimulates in vivo vascular permeability and lymphomononuclear cell recruitment

HIV-1 Tat protein released by infected cells is a chemotactic molecule for leukocytes and induces a proinflammatory program in endothelial cells (EC) by activating vascular endothelial growth factor (VEGF) receptors expressed on both cell types. Its potential role in causing vascular permeability and leukocyte recruitment was studied in vivo following its s.c. injection in mice. Tat caused a dose-dependent early (15 min) and late (6 h) wave of permeability that were inhibited by a neutralizing Ab anti-VEGF receptor type 2. Tissue infiltration of lymphomononuclear cells, mainly monocytes (76%), was evident at 6 h and persisted up to 24 h. WEB2170, a platelet activating factor (PAF) receptor antagonist, reduced the early leakage by 70-80%, but only slightly inhibited the late wave and cell recruitment. In vitro, Tat induced a dose-dependent flux of albumin through the EC monolayer that was inhibited by Ab anti-vascular VEGF receptor type 2 and WEB2170, and PAF synthesis in EC that was blocked by the Ab anti-VEGF receptor type 2. Lastly, an anti-monocyte chemotactic peptide-1 (MCP-1) Ab significantly reduced the lymphomononuclear infiltration elicited by Tat. In vitro, Tat induced a dose-dependent production of MCP-1 by EC after a 24-h stimulation. These results highlighted the role of PAF and MCP-1 as secondary mediators in the onset of lymphomononuclear cell recruitment in tissues triggered by Tat.

Role of NO and PAF in the impairment of skeletal muscle contractility induced by TNF-alpha

The role of platelet-activating factor (PAF) and nitric oxide (NO) as mediators of the effects of tumor necrosis factor-alpha (TNF-alpha) on skeletal muscle contractility was studied in guinea pig extensor digitorum longus (EDL) muscle. TNF-alpha (5-10 ng/ml) reduced contractility at every stimulation frequency (1-200 Hz) and shifted the force-frequency relationship to the right. The role of NO and PAF as mediators of TNF-alpha was suggested by the protective effect of N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mM), but not of N(G)-nitro-D-arginine methyl ester (D-NAME; 1 mM), and by the inhibitory effect of the PAF-receptor antagonist WEB-2170 (3 microM). TNF-alpha increased the production of PAF and NO. Similar to TNF-alpha, both S-nitroso-N-acetylpenicillamine (0.5-1 microM), an NO-generating compound, and PAF (10-20 nM) reduced EDL contractility. L-NAME, but not D-NAME, blocked the negative effect of PAF. Blockade of phospholipase A(2), which is required for PAF synthesis, significantly reduced the effects of TNF-alpha. WEB-2170 inhibited NO synthesis induced by TNF-alpha and PAF-stimulated NO production. These results suggest that both PAF and NO contribute to the development of the mechanical alterations induced by TNF-alpha and that NO production is downstream to the synthesis of PAF.

Role of platelet-activating factor in cardiovascular pathophysiology

Platelet-activating factor (PAF) is a phospholipid mediator that belongs to a family of biologically active, structurally related alkyl phosphoglycerides. PAF acts via a specific receptor that is coupled with a G protein, which activates a phosphatidylinositol-specific phospholipase C. In this review we focus on the aspects that are more relevant for the cell biology of the cardiovascular system. The in vitro studies provided evidence for a role of PAF both as intercellular and intracellular messenger involved in cell-to-cell communication. In the cardiovascular system, PAF may have a role in embryogenesis because it stimulates endothelial cell migration and angiogenesis and may affect cardiac function because it exhibits mechanical and electrophysiological actions on cardiomyocytes. Moreover, PAF may contribute to modulation of blood pressure mainly by affecting the renal vascular circulation. In pathological conditions, PAF has been involved in the hypotension and cardiac dysfunctions occurring in various cardiovascular stress situations such as cardiac anaphylaxis and hemorrhagic, traumatic, and septic shock syndromes. In addition, experimental studies indicate that PAF has a critical role in the development of myocardial ischemia-reperfusion injury. Indeed, PAF cooperates in the recruitment of leukocytes in inflamed tissue by promoting adhesion to the endothelium and extravascular transmigration of leukocytes. The finding that human heart can produce PAF, expresses PAF receptor, and is sensitive to the negative inotropic action of PAF suggests that this mediator may have a role also in human cardiovascular pathophysiology.

Role of platelet-activating factor in leukocyte-independent plasma extravasation and mast cell activation during endotoxemia

BACKGROUND

Independently from leukocyte adherence, endothelial factors and mast cell activation seems to promote microvascular permeability. Platelet-activating factor (PAF) has been shown to play a significant role in endotoxin-induced leukocyte adherence. The aim of our study was to investigate if there is also a role for PAF in mediating leukocyte-independent microvascular permeability changes and activation of mast cells during endotoxemia. Therefore, during endotoxemia microvascular permeability and mast cell activation were determined after inhibition of L-selectin-mediated leukocyte adherence by fucoidin and after inhibition of PAF effects by the PAF receptor antagonist BN52021.

MATERIALS AND METHODS

In male Wistar rats, red cell velocity (V(RBC)), venular wall shear rate, microvascular permeability, leukocyte adherence, and mast cell activation were determined in mesenteric postcapillary venules using intravital microscopy at baseline and 60 and 120 min after start of a continuous infusion of endotoxin (ETX; 2 mg/kg/h, Escherichia coli O26:B6) (ETX group). Animals in the FUCO/ETX group received fucoidin (25 mg/kg body wt) in addition to the procedure described above. Animals in the FUCO/ETX/PAF-ANT group received fucoidin and the PAF receptor antagonist BN52021 (5 mg/kg body wt) prior to the continuous endotoxin infusion. Control animals (control group) received only equivalent volumes of NaCl 0.9%.

RESULTS

There were no microhemodynamic and macrohemodynamic differences between groups. In all endotoxin-challenged groups macromolecular leakage and mast cell activity increased significantly, starting at 60 min. Both macromolecular leakage and mast cell activity were significantly higher in the FUCO/ETX group than in the FUCO/ETX/PAF-ANT group and control group. Differences in macromolecular leakage between groups were significant at 120 min. Differences in mast cell activity between groups were significant at 60 and 120 min.

CONCLUSIONS

The results of our study demonstrate a leukocyte-independent plasma extravasation that can be inhibited by the PAF receptor antagonist BN52021, indicating the involvement of PAF in the pathophysiology of leukocyte-independent microvascular damage during early endotoxemia. Mast cell activity seems to precede leukocyte-independent macromolecular leakage.

Evidence for involvement of the epidermal platelet-activating factor receptor in ultraviolet-B-radiation-induced interleukin-8 production

Ultraviolet B radiation has been shown to generate cutaneous inflammation in part through inducing oxidative stress and cytokine production in human keratinocytes. Amongst the proinflammatory cytokines synthesized in response to ultraviolet B radiation is the potent chemoattractant interleukin-8. Though the lipid mediator platelet-activating factor (PAF) is synthesized in response to oxidative stress, and keratinocytes express PAF receptors linked to cytokine biosynthesis, it is not known whether PAF is involved in ultraviolet-B-induced epidermal cell cytokine production. These studies examined the role of the PAF system in ultraviolet-B-induced epidermal cell interleukin-8 biosynthesis using a novel model system created by retroviral-mediated transduction of the PAF-receptor-negative human epidermal cell line KB with the human PAF receptor. Treatment of PAF-receptor-expressing KB cells with the metabolically stable PAF receptor agonist carbamoyl-PAF resulted in increased interleukin-8 mRNA and protein, indicating that activation of the epidermal PAF receptor was linked to interleukin-8 production. Ultraviolet B irradiation of PAF-receptor-expressing KB cells resulted in significant increases in both interleukin-8 mRNA and protein in comparison to ultraviolet-B-treated control KB cells. Pretreatment with PAF receptor antagonists inhibited both carbamoyl-PAF-induced and ultraviolet-B-induced interleukin-8 production in the PAF-receptor-positive cells, but not in control KB cells. Similarly, treatment of the PAF-receptor-expressing primary cultures of human keratinocytes or the human epidermal cell line A-431 with carbamoyl-PAF or ultraviolet B radiation resulted in interleukin-8 production that was partially inhibited by PAF receptor antagonists. These studies suggest that the epidermal PAF receptor may be a pharmacologic target for ultraviolet B radiation in skin and thus may act to augment ultraviolet-B-mediated production of cytokines such as interleukin-8.