Oxidized LDL induces alternative macrophage phenotype through activation of CD36 and PAFR.

OxLDL is recognized by macrophage scavenger receptors, including CD36; we have recently found that Platelet-Activating Factor Receptor (PAFR) is also involved. Since PAFR in macrophages is associated with suppressor function, we examined the effect of oxLDL on macrophage phenotype. It was found that the presence of oxLDL during macrophage differentiation induced high mRNA levels to IL-10, mannose receptor, PPAR γ and arginase-1 and low levels of IL-12 and iNOS. When human THP-1 macrophages were pre-treated with oxLDL then stimulated with LPS, the production of IL-10 and TGF- ß significantly increased, whereas that of IL-6 and IL-8 decreased. In murine TG-elicited macrophages, this protocol significantly reduced NO, iNOS and COX2 expression. Thus, oxLDL induced macrophage differentiation and activation towards the alternatively activated M2-phenotype. In murine macrophages, oxLDL induced TGF- ß , arginase-1 and IL-10 mRNA expression, which were significantly reduced by pre-treatment with PAFR antagonists (WEB and CV) or with antibodies to CD36. The mRNA expression of IL-12, RANTES and CXCL2 were not affected. We showed that this profile of macrophage activation is dependent on the engagement of both CD36 and PAFR. We conclude that oxLDL induces alternative macrophage activation by mechanisms involving CD36 and PAFR.

Lung inflammation is induced by renal ischemia and reperfusion injury as part of the systemic inflammatory syndrome.

INTRODUCTION: Ischemia and reperfusion injury (IRI) are mainly caused by leukocyte activation, endothelial dysfunction and production of reactive oxygen species. Moreover, IRI can lead to a systemic response affecting distant organs, such as the lungs. AIM: The objective was to study the pulmonary inflammatory systemic response after renal IRI. METHODS: Male C57Bl/6 mice were subjected to 45 min of bilateral renal ischemia, followed by 4, 6, 12, 24 and 48 h of reperfusion. Blood was collected to measure serum creatinine and cytokine concentrations. Bronchoalveolar lavage fluid (BALF) was collected to determine the number of cells and PGE(2) concentration. Expressions of iNOS and COX-2 in lung were determined by Western blot. Gene analyses were quantified by real time PCR. RESULTS: Serum creatinine increased in the IRI group compared to sham mainly at 24 h after IRI (2.57 +/- 0.16 vs. 0.43 +/- 0.07, p < 0.01). The total number of cells in BAL fluid was higher in the IRI group in comparison with sham, 12 h (100 x 10(4) +/- 15.63 vs. 18.1 x 10(4) +/- 10.5, p < 0.05) 24 h (124 x 10(4) +/- 8.94 vs. 23.2 x 10(4) +/- 3.5, p < 0.05) and 48 h (79 x 10(4) +/- 15.72 vs. 22.2 x 10(4) +/- 4.2, p < 0.05), mainly by mononuclear cells and neutrophils. Pulmonary COX-2 and iNOS were up-regulated in the IRI group. TNF-alpha, IL-1beta, MCP-1, KC and IL-6 mRNA expression were up-regulated in kidney and lungs 24 h after renal IRI. ICAM-1 mRNA was up-regulated in lungs 24 h after renal IRI. Serum TNF-alpha, IL-1beta and MCP-1 and BALF PGE(2) concentrations were increased 24 h after renal IRI. CONCLUSION: Renal IRI induces an increase of cellular infiltration, up-regulation of COX-2, iNOS and ICAM-1, enhanced chemokine expression and a Th1 cytokine profile in lung demonstrating that the inflammatory response is indeed systemic, possibly leading to an amplification of renal injury.

Platelet-activating factor (PAF) receptor as a promising target for cancer cell repopulation after radiotherapy.

A major drawback of radiotherapy is the accelerated growth of the surviving tumor cells. Radiotherapy generates a variety of lipids that bind to the receptor for platelet-activating factor, expressed by cells in the tumor microenvironment. In the present study, using the TC-1 tumor cell line, we found that irradiation induced a twofold increase in receptor expression and generated agonists of receptor. Irradiated cells induced a 20-fold increase in live TC-1 proliferation in vitro. Furthermore, subcutaneous co-injection of irradiated TC-1 cells with TC-1 expressing luciferase (TC-1 fluc+) markedly increased TC-1 fluc+ proliferation in a receptor-dependent way. Moreover we used a human carcinoma cell line not expressing the PAF receptor (KBM) and the same cell transfected with the receptor gene (KBP). Following co-injection of live KBP cells with irradiated KBM in RAG mice, the tumor growth was significantly increased compared with tumor formed following co-injection of live KBM with irradiated KBM. This tumor cell repopulation correlated with increased infiltration of tumor-promoting macrophages (CD206+). We propose that receptor represents a possible target for improving the efficacy of radiotherapy through inhibition of tumor repopulation.

Effect of endothelins on human neutrophil activation by immune complexes.

Neutrophils are important effector cells of tissue injury in several pathological conditions, among them, immune complexes (IC)-induced inflammation and tissue injury. There is evidence that endothelins modulate IC-induced tissue injury in experimental models in vivo. In the present study we investigated the effect of endothelins on neutrophil activation by IC in vitro. To this purpose, pre-formed insoluble immune complexes were used to stimulate human neutrophils and production of leukotriene B(4) (LTB(4)) and hydrogen peroxyde (H(2)O(2)) were measured as indicative of phospholipase A(2) and oxidative burst activation and myeloperoxidase (MPO) release as indicative of cell degranulation. The effect of endothelins (ETs) in these events induced by IC was then examined. We found that IC stimulated all three events in human neutrophils. Addition of ET-1 but not ET-2 or ET-3 to the IC-stimulated neutrophils potentiated LTB(4) but not H(2)O(2) production. The endothelins added to resting neutrophils did not induce LTB(4) production but they were effective to stimulate H(2)O(2) production. The increased MPO activity induced by IC was not affected by endothelins nor did they stimulate the release of this enzyme in resting cells. These results show that endothelins are able to activate some neutrophil functions and to upregulate the IC-induced production of the pro-inflammatory molecule LTB(4). These data indicate that products of endothelial cells, such as endothelins, can be involved in the potentiation of neutrophil-dependent tissue injury.

Role of insulin on PGE2 generation during LPS-induced lung inflammation in rats.

Alterations in arachidonic acid (AA) metabolism have been reported to occur in diabetes mellitus. The present study was carried out to verify if these alterations are due to the relative lack of insulin or to high levels of blood glucose. Male Wistar rats were rendered diabetic by alloxan injection (42 mg/kg, i.v.), 10 or 30 days before the experiments. Some diabetic rats received a single dose (4 IU, s.c.) of NPH insulin 2 h before an intratracheal instillation of lipopolysaccharide (LPS, 750 microg) or saline. Six hours after LPS challenge, the following parameters were analysed: blood glucose levels, total and differential leukocyte counts in bronchoalveolar lavage (BAL) fluid; linoleic acid and AA content in blood neutrophils (HPLC), and levels of prostaglandin (PG)E(2) in BAL (ELISA). Relative to controls, a reduced number of neutrophils (18%) and decreased amounts of PGE(2) (40%) were observed in the BAL fluid of diabetic rats in response to LPS. A single dose of insulin was not able to reduce blood sugar levels to normal values, but instead resulted in the normalization of both leukocyte migration to the lungs and levels of PGE(2). Accordingly, these abnormalities might be primarily linked to a continuing insulin deficiency rather than to secondary hyperglycaemia occurring in the diabetic rat. In conclusion, data presented suggest that insulin might regulate neutrophil migration and generation of PGE(2) during the course of acute lung injury induced by LPS.

Mycoplasma arginini enhances cytotoxicity of thioglycollate-elicited murine macrophages toward YAC-1 tumor cells through production of NO.

Bacterial products stimulate macrophage tumoricidal activity through release of tumor necrosis factor (TNF) and nitric oxide (NO). We show here that thioglycollate-elicited macrophages acquire cytotoxic activity when cocultured with Mycoplasma arginini-infected YAC-1 tumor cells and release TNF and NO. Fixed mycoplasma-infected cells, supernatants from infected-cell cultures, or purified heat-killed mycoplasma obtained from cell-free cultures were all able to induce TNF and NO production. Thus, the mycoplasma per se and not a product of infected cells induce the release of these molecules. Addition of prostaglandin E2 (PGE2) to the cocultures, which reduced TNF release, or antibodies to TNF, did not affect macrophage cytotoxicity nor NO release. Inhibition of NO production by L-NAME or aminoguanidine reduced the cytotoxicity, and treatment with a NO donor was toxic to YAC-1 cells. These results indicate that M. arginini activates thioglycollate-elicited murine macrophages for NO and TNF release increasing their cytotoxic activity toward YAC-1 cells and that this activity is dependent on NO but not TNF release.

Discrimination between NK and LAK cytotoxic activities of murine spleen cells by MTT assay: differential inhibition by PGE(2) and EDTA.

In the present study we propose a mathematical approach to improve the analysis of NK and LAK activities measured by MTT assay adapted for murine cells. We found that to calculate NK activity, high E:T ratios should be used (up to 50:1) and the phenomenon fits to a linear least-squares analysis. However, 5-fold less effector cells (10:1, E:T) should be used to detect LAK activity and the phenomenon has a nonlinear exponential behavior. Using this approach, we showed that EDTA inhibits LAK but not NK activity whereas PGE(2) inhibits NK but not LAK activity. In conclusion, this analytical approach allowed the discrimination between NK and LAK activities and exposed differences between these two cytotoxic activities.

Prevention of lung eosinophilic inflammation by oral tolerance.

Airway inflammation plays a major role in human asthma. Increasing evidence points to a close correlation between eosinophil infiltration and allergic lung disease. A new murine model of eosinophilic lung inflammation has recently been developed; it consists of immunizing mice with small fragments of solidified hen egg white implanted (EWI) into the subcutaneous tissue. In this model, which is further characterized here, mice challenged with ovalbumin (OVA) present an intense and persistent lung eosinophilia, as well as histopathological findings that resemble human asthma. In the present work, the effect of oral tolerance on the development of allergic lung inflammation in B6 mice immunized with antigen plus adjuvant or with EWI is investigated. It was found that in mice rendered orally tolerant by previous exposure to antigen in the drinking water, the T-helper type 2 cell (Th2)-associated allergic responses in both protocols of immunization were almost completely abolished. The allergic responses were assessed by pulmonary and bone marrow eosinophilia, lung histopathology and antigen-specific IgE and IgG1 production. These findings provide the first indication that Th2-associated lung pathology can be prevented by oral tolerance.

Uptake and inactivation of prostaglandin E2 methyl analogues in the rat pulmonary circulation.

1 The fate of (15S)-15-methyl prostaglandin E(2) methyl ester and 16,16-dimethyl prostaglandin E(2) in the pulmonary circulation of rat isolated lungs was compared with that of prostaglandin E(2) by means of bioassay.2 Calculated on the basis of height of response of the assay tissues, the inactivation of prostaglandin E(2) was 96 +/- 1%, of 15-methyl prostaglandin E(2) methyl ester, 53 +/- 6% and of 16,16-dimethyl prostaglandin E(2), 50 +/- 4%.3 Responses of the hamster stomach strip to the prostaglandin E(2) analogues passing through the pulmonary circulation were prolonged and slower in onset than those to the analogue given directly to the tissue. No such difference was observed with prostaglandin E(2).4 Bromocresol green, bromothymol blue, bromocresol purple and thymol blue (10(-5) M) all inhibited the inactivation of the three prostaglandins studied, as did diphloretin phosphate (1.5 x 10(-6) M). All five inhibitors also reversed the shape change in response seen after transpulmonary injection of 16-16-dimethyl prostaglandin E(2).5 We conclude that the inactivation of the methyl analogues is due to uptake, as they are not substrates for prostaglandin dehydrogenase.6 The lung may act as a depot for some compounds taking them up from the pulmonary vessels and later releasing them slowly into the systemic circulation.

Paf-induced release of spasmogens from guinea-pig lungs.

1. The injection of platelet activating factor (Paf; 250 ng), leukotriene B4 (LTB4; 50 ng) and leukotriene D4 (LTD4; 10 ng) elicited contractions of strips of guinea-pig trachea, bronchus and lung parenchyma. 2. When the effluent of perfused guinea-pig lungs was superfused over strips of guinea-pig trachea, bronchus and parenchyma, the intra-arterial injection of Paf (250 ng) caused the release of spasmogen(s) which contracted all three tissues. 3. The infusion of indomethacin (10 micrograms ml-1) into the pulmonary artery and over the assay tissues inhibited the responses of the tissues to the effluent of the lungs stimulated by Paf (250 ng) and LTB4 (50 ng). However, treating only the assay tissues with indomethacin (10 micrograms ml-1) did not block the contractile responses to the effluent of the lungs stimulated with LTB4 or Paf. stimulated with Paf. 4. Pretreatment of the lungs with indomethacin (10 micrograms ml-1) or aspirin (30 micrograms ml-1) for 30 min, washing them out and suspending them over the assay tissues did not block the release of spasmogens elicited by Paf but appeared to inhibit the release of cyclo-oxygenase products. 5. The infusion of two lipoxygenase inhibitors, nordihydroguaiaretic acid (NDGA; 1 microgram ml-1) and L-655,240 (1 microgram ml-1), into the pulmonary artery completely blocked the release of spasmogen(s) from the perfused lungs. 6. The slow reacting substance of anaphylaxis (SRS-A) antagonist, FPL-55712 (10 ng ml-1), did not block the responses of the tissues to the spasmogen(s) release by Paf. 7. The infusion of the Paf antagonist BN-52021 (30 micrograms ml-1) into the pulmonary artery completely abolished the release of spasmogen(s) induced by Paf. 8. These data suggest that a lipoxygenase product, possibly LTB4, could be responsible for the spasmogenic activity released by the lungs following Paf stimulation. Cyclo-oxygenase products released following Paf stimulation appear to result from the initial LTB4 generation.

Impairment in connective tissue mast cells degranulation in spontaneously hypertensive rats: stimulus dependent resistance.

1. Microvascular permeability in the mesentery and consequent leakage of protein into the peritoneum of spontaneously hypertensive rats (SHR) and normotensive rats (NTR) was measured in vivo by the extravasation of Evans blue dye. 2. In sensitized NTR, challenge with antigen produced extensive increases in dye extravasation in the mesentery and in peritoneal lavage fluid within 10 min. 3. In sensitized SHR there was no increase in the permeability of the mesentery and a very weak increase in dye extravasation in the peritoneal cavity following challenge. 4. The glucocorticoid antagonist RU38486 did not change the permeability response induced by antigen in sensitized NTR and SHR. 5. However, compound 48/80 was equally effective in either NTR or SHR in causing increased vasopermeability. 6. Mesenteric mast cells in the NTR were degranulated after immunological challenge, whereas those in the SHR were resistant, as measured histologically. 7. Similarly, challenge ex vivo of mesentery from sensitized NTR induced contraction of guinea-pig ileum in co-incubation experiments, whereas SHR mesentery was unresponsive. 8. Plasma levels of antigen-specific IgE and IgG2a in sensitized NTR and SHR were identical. 9. Immune serum from SHR was unable to induce a passive cutaneous anaphylaxis (PCA) reaction in the skin of NTR and SHR did not develop a PCA reaction upon passive sensitization with NTR immune serum. 10. We conclude that the mast cells of SHR are resistant to degranulation following immunological challenge, although the relevant antibodies are present.

Release of eicosanoids in rat peritoneal cavity stimulated with platelet-activating factor (PAF). Effect of the PAF-antagonist BN-52021.

Platelet activating factor (PAF; 10 micrograms) was injected in the peritoneal cavity of rats in the absence or presence of the PAF antagonist BN-52021 (5 mg/kg). Thirty min later, the peritoneal cavity was washed with 3 ml of saline, the fluid was collected and the concentrations of selected eicosanoids were measured using novel enzyme immunoassays. PAF increased by 2.9, 2.8 and 1.7 fold the levels of thromboxane B2, prostaglandin E2 and leukotriene B4 respectively in the peritoneal fluid. The stimulatory effects of PAF was reduced by 42, 51, and 86% for thromboxane B2, prostaglandin E2 and leukotriene B4 respectively by the specific PAF antagonist. These results confirm the presence of specific PAF receptors in tissues and/or cells of rat peritoneal cavity and underline the complex interactions between PAF and eicosanoids.

Studies on the mechanism of PAF-induced vasopermeability in rat lungs.

The present study evaluated the effect of platelet activating factor (PAF) instilled into rat airways on vascular permeability assessed in isolated lung tissues by Evans blue (EB)-labelled plasma protein extravasation. It was found that intratracheal instillation of PAF induces a dose-dependent increase of EB extravasation in the bronchi (upper and inner) but not in the lung parenchyma. The contribution of eicosanoids to PAF-induced increase of vascular permeability was investigated by treating the animals with selected inhibitors prior to PAF administration. Mepacrine (5 mg/kg), L-663,536 (10 mg/kg), indomethacin (4 mg/kg) and dazoxiben (10 mg/kg) significantly reduced EB extravasation in the bronchi. The PAF antagonists BN-52021 (5 mg/kg), WEB-2086 (1 mg/kg), WEB-2170 (5 mg/kg) and PCA-4248 (3 mg/kg) were all effective in reducing the extravasation. These results suggest that PAF-induced increase of vascular permeability in rat bronchi is mediated by cyclooxygenase and lipoxygenase products of arachidonic acid metabolism.

The anti-oedematogenic effect of SRS as an additional factor in the mode of action of non-steroid anti-inflammatory drugs.

A partially purified preparation of SRS was obtained from peritoneal exudates induced by a non-anaphylactic immediate hypersensitivity reaction. This preparation injected in the rat skin caused vasoconstriction and when administered together with carrageenin reduced oedema formation. Injection of carrageenin into the peritoneal cavity progressively increased exudate formation. Pretreatment of the animals with anti-inflammatory doses of aspirin, indomethacin and salicylate significantly reduced exudate formation and this inhibition was correlated with the appearance of SRS in the exudates. It is suggested that, in some inflammatory exudates, stimulation of the synthesis of vasoconstrictor SRS might be an additional factor to the inhibition of prostaglandin synthesis induced by non-steroid anti-inflammatory drugs.

Immune-complex alveolitis in the rat: evidence for platelet activating factor and leukotrienes as mediators of the vascular lesions.

In the present study we investigated the involvement of lipid mediators in an experimental model of immune-complex alveolitis induced in rat lungs by intrabronchial instillation of rabbit antibodies to ovalbumin followed by i.v. injection of the antigen. It was found that the reaction did not induce detectable oedema, as measured by the dry:wet weight ratio. A marked influx of neutrophils was observed in the bronchoalveolar lavage fluid, progressing from 6 to 24 h in parallel with the development of haemorrhagic lesions in lung parenchyma. The intensity of these lesions, evaluated by the concentration of extravascular haemoglobin, was not significantly affected by pretreatment of the animals with a cyclo-oxygenase inhibitor (indomethacin), a thromboxane inhibitor (econazole) or a thromboxane antagonist (L-655,240). However, the antagonists of platelet activating factor (PAF), WEB-2086 and BN-52021, and the lipoxygenase inhibitors, nor-dihydroguaiaretic acid and L-663,536, all significantly inhibited the haemorrhagic lesions. A peptide leukotriene antagonist (L-660,711) had no effect. Furthermore, the PAF antagonists inhibited the levels of LTB4, but not of PGE2 and thromboxane, released into the bronchoalveolar space 1 h after induction of the reaction. These results suggest that the haemorrhagic lesions in this model of immune-complex alveolitis are mediated by PAF and leukotrienes, possibly LTB4.

Mechanisms of arachidonic acid-induced contractions of canine cerebral arteries.

The effects of arachidonic acid in cerebral blood vessels has been examined using rings of canine cerebral arteries. Arachidonic acid produced dose-dependent contractions of this preparation even after mechanical removal of the endothelium. The contractions were not blocked by indomethacin or acetylsalicylic acid, both of which inhibit cyclooxygenase, but were inhibited by nordihydroguaiaretic acid which is a lipoxygenase inhibitor, BW 755c which blocks both pathways, and FPL 55712 which is an antagonist at leukotriene receptors. These data imply that arachidonic acid-induced contractions are mediated by products of the lipoxygenase pathway. Leukotrienes and cyclooxygenase products are generated by this preparation as shown by HPLC and radioimmunoassay and both LTC4 and LTD4 produce contractions in cerebral arteries lending further evidence in support of this suggestion.

Modulation by lipid mediators of immune complex-induced lung inflammation in mice.

The present study characterized a murine model of immune complex-induced pneumonitis and investigated the role of platelet-activating factor (PAF) and eicosanoids as mediators of lung neutrophil infiltration and hemorrhagic lesions. Rabbit antibodies to bovine serum albumin were injected into the airways and bovine serum albumin was injected intravenously into C3H/HePas and BALB/c mice. After 24 h, a significant increase in neutrophil infiltration and hemoglobin concentration in the bronchoalveolar lavage fluid and lung parenchyma was observed in both strains despite the C3H/HePas strain being 10 times more sensitive to PAF. Neutrophil influx and vascular lesions were not affected by pre-treatment of the mice with the PAF receptor antagonist, WEB 2170 (5-(2-chlorphenyl)carbonyl)-3,4-dihydro- 10-methyl-3-((4-morpholinyl)-2H,7H-cyclopenta(4,5)thieno(3,2-f)(1,2,4)-t riazolo-(4,3-a)(1,4)-diazepine). In contrast, neutrophil influx and vascular lesions were increased by the cyclo-oxygenase inhibitor, indomethacin, and reduced by the inhibitor of leukotriene synthesis, MK 886 (3-[1-(4-chlorobenzyl-3-t-butyl-thio-t-isopropyl-indol-2y-1]-2-2-+ ++dimethylpropanoic acid) and by the leukotriene B4 receptor antagonist, RO 0254094 (2-[(5-carboxypentyl)-6-[6-[3,4-dihidro-4-oxo-8-propyl-2H-1-benzop yran-7-yl)hexyl] benzenepropanoic acid). Increased levels of leukotriene B4, leukotriene C4/D4, thromboxane B2 were found in bronchoalveolar lavage fluid 4 h after induction of the reaction. There is also a tendency to increased prostaglandins E2 levels. Neutrophil infiltration and vascular lesions in immune complex-induced pneumonitis in mice are mediated by leukotriene B4.

Lipid mediators, tumor necrosis factor and nitric oxide and their interactions in immune-complex-induced lung injury.

We investigated the contribution of eicosanoids, platelet-activating factor, tumor necrosis factor and nitric oxide to the neutrophil influx and development of pulmonary haemorrhagic lesions following immune-complex-induced pneumonitis in rats and possible interactions between these mediators. Increased levels of leukotriene B4 and tumor necrosis factor, measured by enzyme immunoassay and L-929 cytotoxicity assay, were found in the bronchoalveolar lavage 1 and 4 h after induction of the reaction, respectively, and their release was dependent on the previous generation of platelet activating factor. Antagonism of leukotriene B4 receptors by RO-0254094 (2-[(5-carboxypentyl])oxy]-6-[6-[3,4-dihydro-4-oxo-8-propyl-2H-1-benzopy ran-7-yl)oxy]hexyl] benzenepropanoic acid), inhibition of nitric oxide synthesis by L-NAME (Nw-nitro-L-arginine methyl ester) and antagonism of PAF-receptors by WEB-2170 (5-(2-chlorphenyl)-3-4-dihydro-10-methyl-3-((4-morpholinyl)carbony l)-2 H,7H-cyclopenta (4,5)thieno(3,2-f)(1,2,4)-triazolo-4,3,a)91,4)diazepine), significantly inhibited the intensity of haemorrhage, evaluated by the increased levels of extravascular hemoglobin in homogenates of lung tissues. Little evidence support the role of tumor necrosis factor in these lesions. The infiltration of neutrophils, evaluated by measuring myeloperoxidase in homogenates of lungs, was reduced by compounds L-663,536 (3-[1-(4 chlorobenzyl)-3-t-butyl thio-5-isopropylindol-2-yl]-2-2-dimethylpropanoic acid), WEB-2170 and L-NAME. These results indicate that neutrophil infiltration and haemorrhagic lesions in immune-complex-induced lung inflammation are mediated by platelet activating factor, leukotriene B4 and nitric oxide and point out to interesting interactions between these mediators.

Effect of platelet-activating factor antagonists (BN-52021, WEB-2170, and BB-882) on bacterial translocation in acute pancreatitis.

Bacterial translocation is an important source of pancreas infection in acute pancreatitis. The effect of platelet-activating factor (PAF) in the pathogenesis of acute pancreatitis has been proved in various studies. The aim of this study was to determine whether potent PAF antagonists influence bacterial translocation in acute pancreatitis. Acute pancreatitis was induced in 62 Wistar rats by injection of 2.5% sodium taurocholate into the biliopancreatic duct. The rats treated with PAF factor antagonists received intravenous injection of WEB-2170 (10 mg/kg), lexipafant (5 mg/kg), and BN-52021 (5 mg/kg) 30 minutes before induction of acute pancreatitis. Six hours after induction of acute pancreatitis, bacteriologic cultures and histologic scoring of tissues were performed. There was a statistically significant reduction in bacterial translocation to the mesenteric lymph nodes and liver but not to the pancreas of the rats treated with PAF antagonists. No significant increase in the intestinal bacterial population of any group was found. There were no statistical differences between the pancreatic histologic scores of the groups. PAF antagonists reduced bacterial translocation to distant sites other than the pancreas, preventing the bacterial dissemination that occurs in the early phase of acute pancreatitis and may have beneficial effects on the evolution of this disease.

Hyperalgesia induced by Bothrops jararaca venom in rats: role of eicosanoids and platelet activating factor (PAF).

In this study we investigated the ability of Bothrops jararaca venom (BjV) to induce hyperalgesia and the modulation of this effect by lipid mediators. It was found that intraplantar injection of BjV (1 to 25 micrograms) caused a dose and time-related hyperalgesia. The peak of the hyperalgesic response was 1 hr after injection of the venom and persisted for 24 hr with the higher dose. The BjV-induced hyperalgesia was markedly attenuated by dexamethasone. Dexamethasone blocks the generation of biologically active metabolites from arachidonic acid by inhibiting PLA2 activation. Inhibition of the cyclo-oxygenase pathway by indomethacin, or inhibition of lipoxygenases by NDGA both significantly inhibited BjV-induced hyperalgesia. Two antagonists of PAF, WEB2170 and BN52021, also significantly inhibited the initial phase of the hyperalgesia. These results suggest that hyperalgesia induced by BjV is, at least partially, mediated by lipid mediators such as prostaglandins, leukotrienes and PAF.