Platelet-activating factor type activity in plasma from patients with septicemia and other diseases

p38 MAP-kinase inhibitor protects against platelet-activating factor-induced death in mice

Platelet-activating factor (PAF) is a potent inflammatory agonist. In Swiss albino mice, intraperitoneal injection of PAF causes sudden death with oxidative stress and disseminated intravascular coagulation (DIC), characterized by prolonged prothrombin time, thrombocytopenia, reduced fibrinogen content, and increased levels of fibrinogen degradation products. However, the underlying mechanism(s) is unknown. The PAF-R antagonist WEB-2086 protected mice against PAF-induced death by reducing DIC and oxidative stress. Accordingly, general antioxidants such as ascorbic acid, α-tocopherol, gallic acid, and N-acetylcysteine partially protected mice from PAF-induced death. N-acetylcysteine, a clinically used antioxidant, prevented death in 67% of mice, ameliorated DIC characteristics and histological alterations in the liver, and reduced oxidative stress. WEB-2086 suppressed H₂O₂-mediated oxidative stress in isolated mouse peritoneal macrophages, suggesting that PAF signaling may be a downstream effector of reactive oxygen species generation. PAF stimulated all three (ERK, JNK, and p38) of the MAP-kinases, which were also inhibited by N-acetylcysteine. Furthermore, a JNK inhibitor (SP600125) and ERK inhibitor (SCH772984) partially protected mice against PAF-induced death, whereas a p38 MAP-kinase inhibitor (SB203580) provided complete protection against DIC and death. In human platelets, which have the canonical PAF-R and functional MAP-kinases, JNK and p38 inhibitors abolished PAF-induced platelet aggregation, but the ERK inhibitor was ineffective. Our studies identify p38 MAP-kinase as a critical, but unrecognized component in PAF-induced mortality in mice. These findings suggest an alternative therapeutic strategy to address PAF-mediated pathogenicity, which plays a role in a broad range of inflammatory diseases.

Endocarditis is not an Independent Predictor of Blood Transfusion in Aortic Valve Replacement Patients With Severe Aortic Regurgitation

OBJECTIVE

This study sought to evaluate if the presence of endocarditis was independently associated with increased perioperative blood transfusion in patients undergoing aortic valve replacements (AVR) with aortic regurgitation.

DESIGN

This was a retrospective study.

SETTING

Large Canadian tertiary care hospital.

PARTICIPANTS

Six hundred sixty-two consecutive patients with aortic regurgitation score of 3 or higher undergoing AVR from 1995 to 2012.

INTERVENTIONS

No interventions were performed in this retrospective study.

MEASUREMENTS AND MAIN RESULTS

After REB approval, data were obtained from a center-specific database. Univariate analysis was performed to identify variables that may be associated with transfusion of any allogeneic blood product perioperatively. A multivariate logistic regression was generated to identify independent predictors of perioperative transfusion. Unadjusted transfusion rates in patients with no endocarditis and with endocarditis were 32% and 70% (p<0.001), respectively. Independent predictors of any transfusion were moderate-to-severe preoperative anemia, preoperative renal failure, non-isolated AVR, age>70, urgent/emergent surgery, BMI<25, and female sex. Endocarditis was not an independent predictor of transfusion (OR = 0.748; 95% CI = 0.35-1.601).

CONCLUSIONS

In patients undergoing AVR, unadjusted perioperative transfusion rates were higher when endocarditis was present. However, after adjustment, aortic valve endocarditis was not independently associated with blood transfusion. The authors' observation could be explained by the higher prevalence of many independent predictors of transfusion, such as comorbidities or more complex surgery, within the endocarditis group. Thus, AV endocarditis, in the absence of other risk factors, was not associated with increased perioperative transfusion risk.

Procalcitonin (PCT) in patients with abdominal sepsis

BACKGROUND

To assess the accuracy of procalcitonin as a measure of severity in patients with septic abdominal illnesses and the sepsis syndrome, to compare measurements with those of other inflammatory mediators, and to predict outcome.

METHODS

We carried out a prospective clinical study from 246 patients with infective or septic episodes confirmed at laparotomy and 66 patients undergoing elective operations who acted as controls. Specimens of blood for measurement of cytokine concentrations determination were obtained daily from septic patients. In the control group specimens were obtained before operation, at the end of operation, and on each of the following days until normal recovery (day 10). Every two weeks up to 3 months for patients with metastases, who were being followed up.

RESULTS

Compared with other cytokines such as tumor necrosis factor alphaa and interleukin 6 procalcitonin was closely related to the development of infective and septic complications. 59 of 246 patients (24%) with sepsis died. Procalcitonin concentrations preoperatively [median 2.05 compared with 4.2 ng/ml (p=0.08)] (Mann-Whitney U-test) did not differ, but those on the days 1,4 and at the end differed significantly [day 1: 4.9 compared with 13.8 ng/ml (p<0.01); day 4: 4.8 compared with 13.0 ng/ml (p<0.01) and 0.4 compared with 13.25 ng/ml (p<0.01) at the end of the study]. In the control group only 7 (1.6%) of all blood samples, were detected outside the normal range (up to 0.8 ng/ml).

CONCLUSIONS

Procalcitonin is a new indicator of infection and sepsis. TNF and IL-6 concentrations always rise after major operations and fall in the absence of infection, indicating operative trauma. Procalcitonin is sensitive in detecting infective complications. Under routine conditions the procalcitonin concentrations seems to be valid, reproducible and detectable.

Cardiovascular properties of yangambin, a lignan isolated from Brazilian plants

Yangambin was initially selected from a number of lignans isolated from Brazilian plants for its ability to antagonize Platelet-Activating Factor (PAF, 1-O-hexadecyl-2-acetyl- sn-glyceryl-3-phosphorylcholine)-induced biological effects. Subsequently it was shown that, besides its antagonistic properties at PAF receptors, yangambin also prevents the cardiovascular collapse observed during anaphylactic and endotoxic/septic shocks, as well as the vascular and cardiac hyporesponsiveness to catecholamines in endotoxic shock. It is suggested that this naturally occurring compound could be of potential interest in the adjunctive management of the above mentioned pathologies. In the present article, we review the main studies investigating the pharmacological properties of yangambin related to the cardiovascular function.

Coupled plasma filtration-adsorption in a rabbit model of endotoxic shock

OBJECTIVE

To test the hypothesis that nonselective adsorption by a hydrophobic resin of cytokines and other proinflammatory mediators could improve 72-hr survival in a rabbit model of endotoxic shock.

DESIGN

Prospective, randomized, controlled animal trial.

SETTING

Animal care facility at a research institution.

SUBJECTS

A total of 109 New Zealand white male rabbits.

INTERVENTIONS

Anesthetized rabbits were cannulated with indwelling femoral arterial and venous lines. Septic shock was induced by a single intravenous injection of Escherichia coli lipopolysaccharide. The dose was experimentally assessed in 40 rabbits receiving 1.0, 0.5, 0.1, and 0.05 mg/kg body weight to determine LD80 at 72 hrs. Extracorporeal circulation consisted of plasma filtration coupled with passage of the plasma filtrate through a hydrophobic sorbent and reinfusion into the venous line. The extracorporeal treatment lasted for 3 hrs. Rabbits injected with endotoxin (0.05 mg/kg) were submitted to plasma filtration with (19 rabbits) or without (20 rabbits) sorbent adsorption. As controls, rabbits injected with vehicle alone were treated with plasma filtration (ten rabbits) or without (ten rabbits) sorbent adsorption. Ten rabbits were monitored under anesthesia to determine basal survival.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of endotoxin, bioactive tumor necrosis factor, resin-adsorbed platelet-activating factor, mean arterial pressure, base excess, and white cell count were assessed and a global severity score was established. At 72 hrs, cumulative survival was significantly (p = .0041) improved in septic rabbits treated with coupled plasma filtration-adsorption. Circulating tumor necrosis factor bioactivity remained similar in control and treated rabbits. Biologically significant amounts of platelet activating factor were eluted from the sorbent during the entire treatment time. The severity score inversely correlated with survival (p < .001).

CONCLUSIONS

Coupled plasma filtration-adsorption improved survival in a rabbit model of endotoxic shock. Coupled plasma filtration-adsorption may be an extracorporeal treatment capable of removing structurally different inflammatory mediators associated with sepsis.

Interaction of platelet-activating factor, spleen and atrial natriuretic peptide in plasma volume regulation during endotoxaemia in rats

1. We studied endotoxin (lipopolysaccharide, LPS)-induced platelet-activating factor (PAF) production in various visceral organs, and the effect of PAF antagonists or splenectomy on LPS-induced changes. 2. PAF production in response to LPS was highest in the spleen, followed by ileum, heart, lung and kidneys. None was found in the liver. The splenic response was rapid, reaching 10 times the basal level at 30 min. The increased PAF content in each organ was unrelated to the enzyme activity of either macrophages or neutrophils. 3. LPS-induced hypotension and haemoconcentration were largely prevented by PAF antagonists and splenectomy. 4. Plasma volume fell, and plasma atrial natriuretic peptide (ANP) rose, after LPS administration. Splenectomy or pretreatment with PAF antagonists almost completely prevented these LPS-induced changes at 30 min, but only partially reversed them at 90 min. 5. These results suggest that during endotoxaemia: (a) the spleen is the site of the highest endogenous PAF production; (b) the initial release of ANP is dependent on the production of endogenous PAF, and a PAF-ANP interaction mediates the early plasma volume reduction; (c) plasma volume reduction as well as ANP release depend on the spleen; (d) PAF mediated the hypotensive response and its action in the spleen; and (e) sequestered neutrophils are probably not the main source of PAF in the spleen.

Effect of platelet-activating factor-receptor antagonism on endotoxin-induced lung dysfunction in sheep

To further define the role of platelet-activating factor (PAF) in endotoxin-induced lung dysfunction, we examined the effect of ABT-299, a specific and potent PAF-receptor antagonist, on the response to endotoxemia in six chronically instrumented awake sheep. We administered Escherichia coli endotoxin (0.5 microg/kg) intravenously with or without pretreatment with ABT-299 while monitoring mean pulmonary arterial pressure (Ppa), mean systemic arterial pressure (Psa), dynamic compliance of the lungs (Cdyn), and functional residual capacity (FRC). Endotoxin administration caused pulmonary hypertension, reduced Cdyn, leukopenia, and hypoxemia while having no significant effect on Psa or FRC. Administration of ABT-299 did not affect any of the measured variables at baseline. Pretreatment with ABT-299 attenuated the peak Ppa seen after endotoxin administration but had minimal effects on endotoxin-induced changes in Cdyn, white blood cell count, or alveolar-to-arterial oxygen difference. ABT-299 was shown to completely block the pulmonary hypertension and reduction in Cdyn seen after intravenous administration of exogenous PAF. We conclude that PAF does not play an essential role in the sheep's response to endotoxin.

Presence of paf-acether in human blood after thin-layer chromatography, but not after high-performance liquid chromatography purification

After HPLC purification of human blood extracts, paf-acether (paf) was found exclusively as a lipoprotein-bound compound (lipopaf), whereas free-paf was absent. When the same samples (or lipopaf recovered from HPLC) were purified by TLC, both free-paf and lipopaf were detected. The free-paf detected in blood samples could thus result from lipopaf dissociation during TLC purification.

Endotoxin induces PAF production in the rat ileum: quantitation of tissue PAF by an improved method

PAF (platelet-activating factor) is an endogenous mediator of endotoxin (LPS) shock and intestinal injury. In the present study we used an improved method to quantitate intestinal PAF after LPS injection. Both column and thin layer chromatography (TLC) were used to purify PAF. We found that using C18 column eluted sequentially with 10% acetic acid, ethyl acetate and 70% ethanol, yielded consistent results. TLC yielded falsely high PAF values, possibly from an unknown tissue lipid which co-migrated with PAF, or from toxic ingredients in the silica gel. Moreover, addition of optimal amounts of Tween-20 or ethanol in the bioassay samples enhanced PAF solubility and markedly improved PAF recovery. Lastly, dilution and heparinization of platelet-rich plasma greatly improved the sensitivity of the bioassay. The overall PAF recovery under these optimal conditions was 70-80%. We found that LPS (2-10 mg/kg, iv, 90 min) stimulated PAF production in the rat ileum, but not in the jejunum and colon. The difference in PAF production did not correlate to the numbers of sequestered neutrophils (reflected by myeloperoxidase levels) after LPS injection. This selective PAF production may account for the special vulnerability of the ileum to develop injury during endotoxemia.

BB-882 is a potent antagonist of the haemodynamic changes induced by platelet-activating factor in pigs

The effects of bolus doses (0.2-2 micrograms) of platelet-activating factor (PAF) on systemic and pulmonary arterial pressures were tested in five juvenile pigs, and were demonstrated to have a biphasic effect. There was an initial drop in the mean systemic arterial pressure within seconds, followed by an increase within 1-2 min., whereas mean pulmonary arterial pressure only rose. The response was dose-related and did not include tachyphylaxis. The pressures returned to baseline within 10 min. After confirming these results a novel specific PAF receptor antagonist (BB-882) was given as a 1 mg/kg bolus followed by a continuous infusion of 2 mg/kg/hr, and a third dose response curve was repeated with ten-fold higher PAF doses (2-20 micrograms). BB-882 effectively counteracted these effects. Six pigs were given a continuous infusion of BB-882 33 mg/kg/hr for 5 hr and were compared with another group of five pigs given vehicle only. In this high dose BB-882 did not affect the intravascular pressures. These results indicate that BB-882 is a potent PAF receptor antagonist in juvenile pigs.

Endogenous bacterial toxins are required for the injurious action of platelet-activating factor in rats

BACKGROUND & AIMS

Platelet-activating factor (PAF), an endogenous mediator for experimental sepsis, has been shown to induce shock and intestinal necrosis in vivo. However, it is unclear whether PAF exerts its injurious effects on the intestinal tissue directly or via synergism with other endogenous products. The aim of this study was to examine the role of endogenous bacterial products, such as endotoxin, in PAF-induced intestinal injury.

METHODS

PAF (3 micrograms/kg) was injected intravenously into normally colonized rats, germfree rats, and normal rats pretreated with a combination of antibiotics, and the systemic response and intestinal injury were assessed.

RESULTS

PAF did not cause prolonged shock, leukopenia, hemoconcentration, and bowel necrosis in germfree rats. When germfree rats were primed with a low dose (0.5 mg/kg) of endotoxin, the protection was lost. Combined treatment of the normally colonized rats with neomycin, polymyxin B, and metronidazole for 7 days largely protected the animal from PAF-induced shock and intestinal necrosis.

CONCLUSIONS

PAF does not directly induce prolonged hypotension, hemoconcentration, persistent leukopenia, and gross intestinal necrosis but causes these changes via a synergism with endogenous bacterial toxins, presumably from the gut flora.

The production of experimental cholecystitis by endotoxin

Acute acalculous cholecystitis (AAC) is a severe inflammatory disorder of the gallbladder. It occurs primarily in patients acutely ill from other disorders and is related to sepsis and shock. We previously found that platelet-activating factor (PAF), a phospholipid autacoid purported to be a mediator of the shock response, produced AAC. This study was performed to determine the effect of intravenous lipopolysaccharide (LPS) on feline gallbladders. Anesthetized cats underwent LPS administration with and without administration of a cyclooxygenase inhibitor and PAF antagonist. Gallbladder inflammation was evaluated by quantitation of luminal water transport and tissue myeloperoxidase levels. In an attempt to understand the mechanisms of the response, gallbladder perfusate and tissue prostanoid and PAF levels were quantitated as were serum PAF levels. LPS administration resulted in alteration of the normal absorptive pattern of the gallbladder mucosa to exsorption of fluid into the gallbladder lumen, increased tissue myeloperoxidase levels and increased serum PAF levels. This was associated with increased gallbladder tissue and perfusate prostanoid levels and increased perfusate PAF levels. Indomethacin prevented the pro-inflammatory changes in the gallbladder produced by LPS. The PAF antagonist, alprazolam, increased gallbladder prostanoid production when administered alone and with LPS. The administration of LPS resulted in the production of acute changes in the gallbladder consistent with cholecystitis. These changes being prevented by a cyclooxygenase inhibitor suggests that development of AAC may be related to the release of systemic and local pro-inflammatory substances.

Effect of the hetrazepinoic platelet-activating factor antagonist Bepafant (WEB 2170) in models of active and passive anaphylaxis in mice and guinea pigs

The selective hetrazepinoic platelet-activating factor (PAF) antagonist WEB 2170 (Bepafant) was used to study the pathophysiological role of PAF in several models of anaphylaxis in mice and guinea pigs. In actively sensitized mice, the PAF antagonist WEB 2170 (1.0-10 mg/kg p.o.) protected mice from anaphylactic death in a dose-dependent manner when the anaphylactic response was potentiated by the beta-receptor antagonist propranolol. When active anaphylaxis in guinea pigs was induced intravenously by 100 mg/kg ovalbumin (OA) in the presence of small doses of the antihistamine mepyramine, additional treatment with oral or intravenous WEB 2170 protected the guinea pigs from anaphylactic death. Also, the remaining anaphylactic bronchoconstriction and blood pressure changes (including anaphylactic hypotension) were attenuated. When guinea pigs were passively sensitized with a heterologous antibody via the tracheal route and then challenged by ovalbumin (100 mg/kg i.v.) 24 hr after sensitization in the presence of 0.003 mg/kg i.v. mepyramine, additional treatment with tracheal WEB 2170 at 0.1-1 mg/kg protected the guinea pigs dose-dependently not only from anaphylactic death but also from a further decrease of respiratory flow and changes of blood pressure. Increased levels of PAF-like activity (20-50 ng PAF/whole lung) were detected in lungs removed from antigen-challenged animals. The results suggest a causative role for PAF in active and passive anaphylaxis.

Involvement of platelet-activating factor (PAF) in septic shock and priming as indicated by the effect of hetrazepinoic PAF antagonists

Pharmacological data obtained with hetrazepinoic platelet-activating factor (PAF) antagonists, such as apafant (WEB 2086) and bepafant (WEB 2170), indicate a role for PAF in septic shock and in the priming process. The effect of PAF antagonists in different models of shock states favors a role for PAF in endotoxin associated lethality, activation of inflammatory blood cells with release of mediators, cardiovascular failure and increased vascular permeability, and in the development of shock organs and organ failure. The priming process (e.g., by endotoxin or tumor necrosis factor) towards an increased susceptibility towards minute amounts of PAF has to be taken into account when considering the pathophysiological significance of PAF under in vivo conditions and in septic shock.