A clinical study on the significance of platelet-activating factor in the pathophysiology of septic disseminated intravascular coagulation in surgery

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.

Animal models of DIC and their relevance to human DIC: a systematic review

Disseminated intravascular coagulation (DIC) is a severe clinical condition with activation of coagulation and fibrinolysis. Its diagnosis is based on the International Society of Thrombosis and Haemostasis (ISTH) scoring system of DIC. Animal models of DIC, used to investigate pathophysiology and evaluate treatments, have not been developed in a standardized way, which impedes comparison between models and translation to the human setting. In the current review of animal models of DIC an overview of species, inducers, and dosing regimens is provided. Diagnostic approaches are compared in the light of the ISTH score and treatments tested in animal models of DIC are summarized. Systematic analysis revealed that the rat is by far the preferred species amongst animal models of DIC and lipopolysaccharides (LPS) the preferred inducer of DIC. An overview of the reporting of ISTH DIC score parameters elucidated that only about 25% of the studies measure all of the four parameters necessary for the implementation the ISTH scoring system. Furthermore, most therapeutic interventions tested in animal models of DIC are administered prophylactically, which may be irrelevant to the clinical setting and could explain why compounds effective in preclinical animal models often fail in clinical trials. It is concluded that Implementation of a scoring system in animal models of DIC may increase the ability to compare DIC amongst animal models and improve the translational aspect of treatment effect.

Signaling via platelet-activating factor receptors accounts for the impairment of neutrophil migration in polymicrobial sepsis

Sepsis is a systemic inflammatory response that results from the inability of the immune system to limit bacterial spread during an ongoing infection. Recently, we have documented an impaired neutrophil migration toward the infectious focus in severe sepsis. This impairment seems to be mediated by circulating cytokines, chemokines, and NO. Platelet-activating factor (PAF) plays an important role in the orchestration of different inflammatory reactions, including the release of cytokines, chemokines, and free radicals. Using a PAFR antagonist, PCA-4248, and PAFR-deficient mice, we investigated whether signaling via PAFR was relevant for the failure of neutrophils to migrate to the site of infection after lethal sepsis caused by cecum ligation and puncture in mice. In PAFR-deficient mice or mice pretreated with PCA-4248 (5 mg/kg) and subjected to lethal sepsis, neutrophil migration failure was prevented, and bacterial clearance was more efficient. There was also reduced systemic inflammation (low serum cytokine levels), lower nitrate levels in plasma, and higher survival rate. Altogether, the results firmly establish a role for PAFR in mediating the early impairment of neutrophil migration toward the infectious focus. Blockade of PAFR may prevent the establishment of severe sepsis.

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.

Disseminated intravascular coagulation current concepts of etiology, pathophysiology, diagnosis, and treatment

The pathophysiologic mechanisms and clinical and laboratory manifestations of DIC are complex, partly because of inter-relationships within the hemostasis system. Only by clearly understanding these extraordinarily complex pathophysiologic inter-relationships can the clinician and laboratory scientist appreciate the divergent and wide spectrum of often-confusing clinical and laboratory findings in patients with DIC. Many therapeutic decisions to be made are controversial and lack validation. Nevertheless, newer antithrombotic agents and agents that can block, blunt, or modify cytokine activity and the activity of vasoactive substances seem to be of value. The complexity and variable degree of clinical expression suggest that therapy should be individualized depending on the nature of DIC, the patient's age, etiology of DIC, site and severity of hemorrhage or thrombosis, and hemodynamics and other appropriate clinical parameters.

Disseminated intravascular coagulation: a review of etiology, pathophysiology, diagnosis, and management: guidelines for care

The pathophysiologic mechanisms, clinical, and laboratory manifestations of DIC are complex in part due to interrelationships within the hemostasis system. Only by clearly understanding these extraordinarily complex pathophysiologic interrelationships can the clinician and laboratory scientist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Many therapeutic decisions to be made are controversial and lack validation. Nevertheless, newer antithrombotic agents, and agents that can block, blunt, or modify cytokine activity and the activity of vasoactive substances appear to be of value. The complexity and variable degree of clinical expression suggests that therapy should be individualized depending on the nature of DIC, age, etiology of DIC, site and severity of hemorrhage or thrombosis and hemodynamics and other appropriate clinical parameters. At present, treatment of the triggering event, low-dose heparin or antithrombin concentrate and wise choice of components when indicated appear to be the most effective modes of therapy.

Experimental and emerging therapies for sepsis and septic shock

The underlying principles of sepsis therapy have remained unchanged for decades. These include: prompt institution of antimicrobial agents aimed at the inciting pathogen, source control directed at removal of the infection nidus whenever possible, and support of organ dysfunction. Despite advances in antibiotics, surgical techniques and organ support technology, the morbidity and mortality from sepsis-related diseases have remained substantially unchanged (30 - 50%). Immunomodulation of the inflammatory cascade has been suggested as a crucial but inadequately addressed element in the treatment of sepsis. The list of potential therapeutic targets has been growing as more and more mediators are identified in the pathogenesis of sepsis. To date, numerous anti-inflammatory agents, found to have favourable effects in animal models of septic shock, have been tested in a number of clinical trials on thousands of patients. In this first of a three part series, we go through some of the background and current strategies in sepsis therapy. In this review, we include the two novel therapies that have shown clear survival benefit in large, randomised, placebo-controlled, multi-centre trials, low-dose steroids and recombinant activated protein C. Also included in this review are studies on antithrombin III, platelet-activating factor antagonists, complement modulators, nitric oxide synthase inhibitors and caspase inhibitors (apoptosis inhibitors).

Syndromes of disseminated intravascular coagulation in obstetrics, pregnancy, and gynecology. Objective criteria for diagnosis and management

This article presents current understanding of the causes, pathophysiology, clinical, and laboratory diagnosis, and management of fulminant and low-grade DIC, as they apply to obstetric, pregnant, and gynecologic patients. General medical complications leading to DIC, which may often be seen in these patients, are also discussed. Considerable attention has been given to interrelationships within the hemostasis system. Only by clearly understanding these pathophysiologic interrelationships can the obstetrician/gynecologist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Objective clinical and laboratory criteria for diagnosis of DIC have been outlined to eliminate unnecessary confusion and the need to make empiric decisions regarding the diagnosis. Particularly in the obstetric patient, if a condition is observed that is associated with DIC, or if any suspicion of DIC arises from either clinical or laboratory findings, it is imperative to monitor the patient carefully with clinical and laboratory tools to assess any progression to a catastrophic event. In most instances of DIC in obstetric patients, the disease can be ameliorated easily at early stages. Many therapeutic decisions are straightforward, particularly in obstetric and gynecologic patients. For more serious and complicated cases of DIC in these patients, however, efficacy and choices of therapy will remain unclear until more information is published regarding response rates and survival patterns. Also, therapy must be highly individualized according to the nature of DIC, patient's age, origin of DIC, site and severity of hemorrhage or thrombosis, and hemodynamic and other clinical parameters. Finally, many syndromes that are often categorized as organ-specific disorders and are sometimes identified as independent disease entities, such as AFE syndrome, HELLP syndrome, adult shock lung syndrome, eclampsia, and many others, either share common pathophysiology with DIC or are simply a form of DIC. These entities represent the varied modes of clinical expression of DIC and illustrate the diverse clinical and anatomic manifestations of this syndrome.

Phase II multicenter clinical study of the platelet-activating factor receptor antagonist BB-882 in the treatment of sepsis

OBJECTIVE

To evaluate the safety and efficacy of the platelet-activating factor receptor antagonist BB-882 in the treatment of patients with sepsis.

DESIGN

Double-blind, placebo-controlled, randomized, multi-centered study.

SETTING

Thirty-four European intensive care units.

PATIENTS

One hundred fifty-two patients with clinical suspicion of infection and a mean APACHE II score between 15 and 35 in the 24 hrs before entry into the trial.

INTERVENTIONS

Patients received either a loading dose of 4 mg of BB-882 on the first day, followed by an intravenous infusion of 96 mg/24 hrs for up to 120 hrs, or placebo.

MEASUREMENTS

Hemodynamic, respiratory and oxygen transport variables, blood lactate concentrations, interleukin-6, interleukin-8, tumor necrosis factor (TNF)-alpha, soluble TNF receptor concentrations, organ failure score, 28-day mortality rate, Acute Physiology And Chronic Health Evaluation (APACHE) II score within 24 hrs of entry.

RESULTS

Sixty-nine patients (42 male, 27 female) received placebo and 83 (59 male, 24 female) received BB-882. Patients ranged in age from 16 to 89 yrs (mean, 60 yrs). No important differences existed between the two groups in terms of gender distribution, age, or initial APACHE II score. Sepsis was identified as Gram-positive in 49 patients, Gram-negative in 40, mixed in 37, and unknown in 26. No important differences were shown in hemodynamic, respiratory, or oxygen transport variables between groups during the study. Organ failure scores were similar in the two groups throughout the study. Cytokine concentrations were not significantly different in the two groups. Within 28 days of entering the study, 75 patients died, including 31 (45%) in the placebo group and 44 (53%) in the treatment group, p = .32. The median time to death in the placebo group was 6.0 days, and in the treatment group, it was 4.5 days (p = .30).

CONCLUSION

Treatment of sepsis with the platelet-activating factor antagonist BB-882 offers no advantage over placebo on survival, hemodynamic status, respiratory function, or organ failure scores.

The sepsis-coagulant axis: a review

Activation of coagulation is a normal component of the acute inflammatory response. Inflammatory cytokines initiate coagulation events locally at sites of inflammation by converting endothelium from an antithrombotic surface to a prothrombotic surface; by stimulating tissue factor production, which activates both the extrinsic and intrinsic coagulation systems; and by stimulating production of platelet-activating factors. The fibrinolytic system is initially activated but is subsequently inhibited. This results in a marked imbalance in coagulation and fibrinolysis resulting in a net procoagulant state. When thrombin generation and platelet activation exceed the body's capacity to inactivate or remove these factors, disseminated intravascular coagulation (DIC) results. DIC directly contributes to multiple organ failure and death associated with sepsis. Presently available treatments (i.e., heparin and aspirin) are relatively ineffective in treating DIC; however, newer, more potent drugs may soon be available for clinical use.

Disseminated intravascular coagulation: clinical and laboratory aspects

Disseminated intravascular coagulation (DIC) is a complex acquired coagulopathy resulting from excessive thrombin formation. Abnormal tissue factor (TF) expression is a major mechanism initiating DIC in many disorders, including obstetrical complications, sepsis, cancer, and trauma. Numerous laboratory tests are available to monitor DIC, but most patients are adequately managed using only routine hemostasis screening tests, and assays for fibrinogen and D-dimer. Treatment of DIC should focus on reversing the underlying disorder initiating the coagulopathy. Novel treatments are being investigated for treating DIC; many of these experimental modalities target the excessive TF activity that characterizes DIC.

The platelet-activating factor antagonist BB-882 does not improve tissue oxygen extraction in endotoxic shock

PURPOSE

We investigated whether BB-882, a novel potent PAF antagonist, could influence systemic and pulmonary hemodynamics and oxygen extraction capabilities during an acute reduction in blood flow induced by cardiac tamponade after endotoxin challenge.

MATERIALS AND METHODS

Twenty-one anesthetized, ventilated, and endotoxin-shocked (2 mg/kg i.v. Escherichia coli endotoxin) dogs were randomly divided in three groups. One group (N = 7) served as control. A second group (N = 7) received BB-882 as a single bolus dose of 5 mg/kg, 30 minutes before endotoxin administration. A third group (N = 7) received BB-882 as a continuous infusion of 5 mg/kg x h, started 30 minutes after endotoxin. Hemodynamic and gazometric measurements were obtained in all dogs 30 minutes after endotoxin injection and repeated 30 minutes after cardiac filling pressures were restored to baseline by generous saline infusion. Saline infusion rate was then set at 20 mL/kg x h and tamponade was induced by repeated bolus injections of warm saline into the pericardial sac.

RESULTS

Compared with controls, pretreatment with BB-882 attenuated the early endotoxin-induced decrease in arterial pressure (70 +/- 17 v 51 +/- 14 mm Hg, P < .05), cardiac index (118 +/- 29 v 91 +/- 15 mL/ kg x min, P < .05), stroke index (1.0 +/- 0.2 v 0.7 +/- 0.3 mL/kg, P < .05), and left ventricular stroke work index (0.9 +/- 0.3 v 0.4 +/- 0.2 g x m/kg, P < .05), but these effects were not sustained after fluid resuscitation. In contrast, BB-882 post-treatment maintained arterial pressure and improved cardiac performance at lower filling pressures in the later phase of endotoxic shock. BB-882 did not influence pulmonary hemodynamics. Treatment with BB-882 did not influence oxygen extraction at critical oxygen delivery (51.5 +/- 9.9% and 52.8 +/- 13.9% v 46.6 +/- 9.0%, respectively BB-882 pretreatment and post-treatment v control).

CONCLUSIONS

We conclude that in this model of endotoxic shock the administration of BB-882, either before or after endotoxin challenge, has time-related beneficial hemodynamic and cardiac effects but does not improve global oxygen extraction capabilities. The potential benefit of adjunctive treatment with a platelet-activating factor antagonist in sepsis remains doubtful.

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.