Treatment with the platelet-activating factor antagonist TCV-309 in patients with severe systemic inflammatory response syndrome: a prospective, multi-center, double-blind, randomized phase II trial

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.

Platelets in the immune response: Revisiting platelet-activating factor in anaphylaxis

Anaphylaxis is an acute, severe, life-threatening multisystem allergic reaction resulting from the sudden systemic release of biochemical mediators and chemotactic substances. Release of both preformed granule-associated mediators and newly generated lipid-derived mediators contributes to the amplification and prolongation of anaphylaxis. Platelet-activating factor (PAF) is a potent phospholipid-derived mediator the central role of which has been well established in experimental models of both immune-mediated and non-immune mediated anaphylaxis. It is produced and secreted by several types of cells, including mast cells, monocytes, tissue macrophages, platelets, eosinophils, endothelial cells, and neutrophils. PAF is implicated in platelet aggregation and activation through release of vasoactive amines in the inflammatory response, resulting in increased vascular permeability, circulatory collapse, decreased cardiac output, and various other biological effects. PAF is rapidly hydrolyzed and degraded to an inactive metabolite, lysoPAF, by the enzyme PAF acetylhydrolase, the activity of which has shown to correlate inversely with PAF levels and predispose to severe anaphylaxis. In addition to its role in anaphylaxis, PAF has also been implicated as a mediator in both allergic and nonallergic inflammatory diseases, including allergic rhinitis, sepsis, atherosclerotic disease, and malignancy, in which PAF signaling has an established role. The therapeutic role of PAF antagonism has been investigated for several diseases, with variable results thus far. Further investigation of its role in pathology and therapeutic modulation is highly anticipated because of the pressing need for more selective and targeted therapy for the management of severe anaphylaxis.

Animal models of sepsis

Sepsis remains a common, serious, and heterogeneous clinical entity that is difficult to define adequately. Despite its importance as a public health problem, efforts to develop and gain regulatory approval for a specific therapeutic agent for the adjuvant treatment of sepsis have been remarkably unsuccessful. One step in the critical pathway for the development of a new agent for adjuvant treatment of sepsis is evaluation in an appropriate animal model of the human condition. Unfortunately, the animal models that have been used for this purpose have often yielded misleading findings. It is likely that there are multiple reasons for the discrepancies between the results obtained in tests of pharmacological agents in animal models of sepsis and the outcomes of human clinical trials. One of important reason may be that the changes in gene expression, which are triggered by trauma or infection, are different in mice, a commonly used species for preclinical testing, and humans. Additionally, many species, including mice and baboons, are remarkably resistant to the toxic effects of bacterial lipopolysaccharide, whereas humans are exquisitely sensitive. New approaches toward the use of animals for sepsis research are being investigated. But, at present, results from preclinical studies of new therapeutic agents for sepsis must be viewed with a degree of skepticism.

The platelet activating factor (PAF) signaling cascade in systemic inflammatory responses

The platelet-activating factor (PAF) signaling cascade evolved as a component of the repertoire of innate host defenses, but is also an effector pathway in inflammatory and thrombotic diseases. This review focuses on the PAF signaling cascade in systemic inflammatory responses and, specifically, explores its activities in experimental and clinical sepsis and anaphylaxis in the context of the basic biochemistry and biology of signaling via this lipid mediator system.

Poly adenosine diphosphate-ribose polymerase inhibitor PJ34 abolishes systemic proinflammatory responses to thoracic aortic ischemia and reperfusion

BACKGROUND

Systemic inflammatory responses contribute to mortality after thoracoabdominal aneurysm repair. Poly adenosine diphosphate (ADP) ribose polymerase (PARP) activity is known to modulate inflammation in animal models of injury. The effect of the PARP inhibitor PJ34 and genetic deletion of PARP-1(PARP -/-) on the systemic inflammatory response after thoracic aortic ischemia reperfusion (TAR) is not known.

STUDY DESIGN

In one group, all mice were subject to TAR followed by 48 hours of reperfusion. Treated mice (PJ, n=24) were given PJ34 IP; untreated mice (UN, n=41) received normal saline intraperitoneally. The number of mice in each group was selected to have a similar number of survivors by 48 hours. In a second group, sham animals were subjected to mediastinotomy alone (sham, n=10) without TAR, and were compared with mice with deletion of the PARP-1 isoform (PARP-1 -/-, n=11) subjected to TAR. Tissue extracts were assayed for keratinocyte derived chemokine and granulocyte colony stimulating factor. Serum was assayed for interleukin-6.

RESULTS

PJ34 treatment decreased mortality throughout the experimental protocol. There were no mortalities in the sham operated mice or PARP -/- mice subjected to TAR. PJ34 treatment decreased serum levels of interleukin-6 (p=0.01) and hepatic levels of interleukin-6 mRNA when compared with untreated and PARP-/- mice (p < 0.01). Only liver and kidney cytokine levels were decreased by PJ34 treatment (p < 0.05). In PARP-/- mice subjected to TAR, tissue cytokine levels were not different from those in sham mice.

CONCLUSIONS

PARP inhibition may represent a novel therapeutic approach to minimizing inflammatory sequelae after TAR.

Lack of evidence for qualitative treatment by disease severity interactions in clinical studies of severe sepsis

INTRODUCTION

The design of clinical trials of interventions aimed at reducing mortality in patients with severe sepsis assumes that the relative treatment effect of the intervention is independent of the patients' risk for death. We reviewed published data from phase III clinical studies of severe sepsis to determine whether a relationship exists between risk for death and the relative benefit of the investigational agent. Such an interaction might warrant a change in the assumptions that underlie current trial designs.

METHODS

We conducted a systematic review of published phase III, randomized, placebo-controlled trials in adult patients with sepsis, severe sepsis, or septic shock up to November 2004. All studies enrolled patients with known or suspected infection, evidence of a systemic response to the infection, and one or more organ dysfunctions resulting from the systemic response.

RESULTS

Twenty-two publications, investigating 17 molecular entities, fulfilled criteria for phase III or equivalent studies aimed at reducing mortality in adult patients with severe sepsis or septic shock. Three studies achieved the prospectively defined primary end-point of a statistically significant reduction in 28-day all-cause mortality. The control group mortality rates for these studies were 31%, 43% and 61%, indicating that the beneficial effects of adjunct therapies could be demonstrated over a wide range of illness severity. Analysis of subgroup data from failed studies provided no evidence that the efficacy of the therapeutics being investigated varied by baseline placebo mortality rates. Among all studies, interventions with anticoagulant activity or anti-inflammatory activity did not appear to be harmful in patients with evidence of less coagulopathy or less inflammation.

CONCLUSION

Our review of published clinical data does not support the hypothesis that mortality risk of the population studied alters the relative treatment effect associated with anti-inflammatory or other agents used to treat severe sepsis. Clinical studies in severe sepsis should continue to enroll patients over a wide range of disease severity, as long as patients enrolled have evidence of sepsis-induced organ dysfunction(s), patients are at an appreciable risk for death (e.g. as evidenced by admission to an intensive care unit), and the potential for benefit outweighs the potential for harm.

Efficacy and Safety of the Platelet-Activating Factor Receptor Antagonist BN???52021 (Ginkgolide??B) in Patients with Severe Sepsis

OBJECTIVE

To evaluate the efficacy and safety of the natural platelet-activating factor receptor antagonist, BN 52021 (ginkgolide B) in the treatment of patients with severe sepsis related to Gram-negative and mixed bacterial infection.

DESIGN AND SETTING

Prospective, randomised, double-blind, placebo-controlled, multicentre study carried out in 13 academic medical intensive care centres in Germany with up to 14 patients per centre.

PATIENTS

88 patients with severe sepsis under standard medical and surgical care: nine patients with pure Gram-positive infection, 79 patients with Gram-negative or mixed bacterial infections (subgroup for which efficacy was to be established).

INTERVENTIONS

Patients were randomised to receive either placebo or BN 52021 1.25 mg/kg bodyweight intravenously every 12h over a 4-day period in addition to their standard medical and surgical care.

MAIN OUTCOME MEASURES AND RESULTS

The primary efficacy variable was the 28-day all-cause mortality rate. The treatment groups were similar with respect to demographic data and prognostic factors influencing the outcome except for bodyweight and adequacy of antibiotic therapy. Analysis of patients with Gram-negative or mixed bacterial infection, for which efficacy was to be established, resulted in a 28-day all-cause mortality of 42.5% in the placebo group (n = 40; 17 deaths) versus 38.5% in the BN 52021 group (n = 39; 15 deaths). Among all randomised patients, the 28-day all-cause mortality rate was 40.9% in the placebo group (n = 44; 18 deaths) and 38.6% in the BN 52021 group (n = 44; 17 deaths). There were no differences in frequency and severity of adverse events between the two treatment groups.

CONCLUSIONS

Four-day administration of BN 52021 failed to demonstrate a statistically significant reduction in mortality in patients with severe sepsis suspected or confirmed to be related to infections other than Gram-positive bacterial infection.

Such stuff as dreams are made on: mediator-directed therapy in sepsis

Sepsis, a life-threatening disorder that arises through the body's response to infection, is the leading cause of death and disability for patients in an intensive care unit. Advances in the understanding of the complex biological processes responsible for the clinical syndrome have led to the identification of many promising new therapeutic targets, including bacterial toxins, host-derived mediators, and downstream processes such as coagulation and the endocrine response. Diverse therapies directed against these targets have shown dramatic effects in animal models; however, in humans, their impact has been frustratingly modest, and only one agent--recombinant activated protein C--has achieved regulatory approval. This review summarizes the approaches that have been evaluated in clinical trials, explores the reasons for the discordance between biological promise and clinical reality, and points to approaches that may lead to greater success in the future.

Recent developments in the treatment of sepsis

Despite advances in supportive care, septic shock remains a major cause of morbidity and mortality. With the identification of the systemic inflammatory response as a major component in the pathogenesis of the septic shock syndrome, much of the recent work has focused on modulating this response. This includes antiendotoxin therapies in patients with Gram-negative sepsis, and therapies to modulate the pro-inflammatory mediators produced in response to infection, such as TNF-alpha, platelet-activating factor and complement. High-flow haemofiltration has the potential advantage of clearing both endotoxin and pro-inflammatory mediators. Antithrombotic strategies have been investigated and have yielded the first major success in the treatment of sepsis with activated protein C. Nitric oxide produces the cardiovascular features of sepsis and investigators have looked at both reducing its production and mopping up the excess. Attempts to reduce apoptosis have been a new focus in the treatment of sepsis. There have also been recent developments in supportive care suggesting a role for vasopressin and replacement corticosteroid therapy.

Nutrition in patients with acute pancreatitis

Acute pancreatitis is a disease with varying severity. Patients with the mild form do not require nutritional support because oral intake is resumed rapidly. Studies on nutritional support in acute pancreatitis have included patients with both mild and severe disease. In this heterogeneous group, total parenteral nutrition did not improve outcome compared with no nutrition at all. This is caused in part by an increase in septic complications during total parenteral nutrition. Likewise, no benefit from enteral nutrition was observed compared with no nutrition, probably because the group was heterogeneous or because nutritional goals were not achieved. Patients with severe acute pancreatitis become profoundly catabolic. This group undoubtedly requires nutritional support to treat undernutrition. The limited available data indicate that enteral nutrition, if well tolerated, is superior to parenteral nutrition for patients with severe acute pancreatitis. Based on current knowledge, a combination of early total parenteral nutrition and enteral nutrition is advisable as soon as enteral nutrition is tolerated. Monitoring of gut function is crucial in this situation.

An improved clinically relevant sepsis model in the conscious rat

OBJECTIVE

To develop an improved small animal experimental paradigm that more closely mimics human sepsis.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Medical school research laboratory.

SUBJECTS

Male Sprague-Dawley rats (280-320 g).

INTERVENTIONS

We monitored the hemodynamic, hematologic, and biochemical consequences of abdominal sepsis produced by intraperitoneal implantation of a fibrin clot containing Escherichia coli in conscious, antibiotic-treated, rats.

MEASUREMENTS AND MAIN RESULTS

Similar to human sepsis, the implanted, infected clot (LD50 = 5-7 x 10(8) colony forming units/mL, n = 6) elevated cardiac index (>7% vs. sterile clot, p < .05, at 4 hrs), whereas mean arterial pressure and heart rate remained unaffected. The total peripheral resistance index and stroke volume index tended to decrease and increase, respectively. In contrast, an intravenous bolus injection of endotoxin (LD50 of E. coli lipopolysaccharide = 5.6 mg/kg, n = 7), the most commonly used sepsis model, induced profound hypodynamic responses manifested by a 27% decrease (vs. endotoxin vehicle, p < .01) in cardiac index, a 28% increase in the total peripheral resistance index (p < .01), and a 33% decrease in the stroke volume index (P < .01). The infectious peritonitis model also displayed dose-dependent thrombocytopenia (<61%, p < .05), leukopenia (<60%, p < .05), and mortality rate (50% at 5-7 x 10(8) colony forming units/mL, p < .05) with a minimally elevated serum tumor necrosis factor-alpha level (145 vs. 12 +/- 6 pg/mL in controls, p < .05).

CONCLUSION

This rodent model of antibiotic-treated, intra-abdominal infection features key characteristics of clinical sepsis. Although the hyperdynamic response observed in septic patients undergoing resuscitation was not clearly elicited, this paradigm better mimics clinical sepsis compared with the commonly used endotoxin model. Thus, utilization of this paradigm may provide additional opportunities to explore mechanisms of sepsis and to examine novel therapeutics.

Lipid mediators in the pathophysiology of critical illness

Inflammatory lipid mediators are produced by the metabolism of membrane phospholipids following a number of different stimuli. These mediators lead to a variety of cellular and systemic responses which contribute to the manifestations of the systemic inflammatory response syndrome in the critically ill patient. These mediators include platelet-activating factor and the eicosanoids, including prostaglandins, thromboxanes, leukotrienes, and HETEs. This review seeks to evaluate the current role of these mediators in the pathophysiology of critical illness. We will focus on recent studies concerning the modulation of these pathways as a potential therapeutic strategy for management of these critically ill patients. This includes the gamut from nutritional strategies to alter the cellular membrane lipid composition, thereby effecting the substrate available to produce these lipid byproducts, to intracellular inhibitors to alter production of these mediators, to receptor blockage and enhanced clearance to inhibit their effects.

Platelet-activating factor (PAF) receptor and genetically engineered PAF receptor mutant mice

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active phospholipid mediator. Although PAF was initially recognized for its potential to induce platelet aggregation and secretion, intense investigations have elucidated potent biological actions of PAF in a broad range of cell types and tissues, many of which also produce the molecule. PAF acts by binding to a unique G-protein-coupled seven transmembrane receptor. PAF receptor is linked to intracellular signal transduction pathways, including turnover of phosphatidylinositol, elevation in intracellular calcium concentration, and activation of kinases, resulting in versatile bioactions. On the basis of numerous pharmacological reports, PAF is thought to have many pathophysiological and physiological functions. Recently advanced molecular technics enable us not only to clone PAF receptor cDNAs and genes, but also generate PAF receptor mutant animals, i.e., PAF receptor-overexpressing mouse and PAF receptor-deficient mouse. These mutant mice gave us a novel and specific approach for identifying the pathophysiological and physiological functions of PAF. This review also describes the phenotypes of these mutant mice and discusses them by referring to previously reported pharmacological and genetical data.

Lipid mediators in inflammatory disorders

During the past few decades, intensive collaborative research in the fields of chronic and acute inflammatory disorders has resulted in a better understanding of the pathophysiology and diagnosis of these diseases. Modern therapeutic approaches are still not satisfactory and shock, sepsis and multiple organ failure remain the great challenge in intensive care medicine. However, the treatment of inflammatory diseases like rheumatoid arthritis, ulcerative colitis or psoriasis also represents an unresolved problem. Many factors contribute to the complex course of inflammatory reactions. Microbiological, immunological and toxic agents can initiate the inflammatory response by activating a variety of humoral and cellular mediators. In the early phase of inflammation, excessive amounts of interleukins and lipid-mediators are released and play a crucial role in the pathogenesis of organ dysfunction. Arachidonic acid (AA), the mother substance of the pro-inflammatory eicosanoids, is released from membrane phospholipids in the course of inflammatory activation and is metabolised to prostaglandins and leukotrienes. Various strategies have been evaluated to control the excessive production of lipid mediators on different levels of biochemical pathways, such as inhibition of phospholipase A2, the trigger enzyme for release of AA, blockade of cyclooxygenase and lipoxygenase pathways and the development of receptor antagonists against platelet activating factor and leukotrienes. Some of these agents exert protective effects in different inflammatory disorders such as septic organ failure, rheumatoid arthritis or asthma, whereas others fail to do so. Encouraging results have been obtained by dietary supplementation with long chain omega-3 fatty acids like eicosapentaenoic acid (EPA). In states of inflammation, EPA is released to compete with AA for enzymatic metabolism inducing the production of less inflammatory and chemotactic derivatives.

Comparison of the reversed passive Arthus and local Shwartzman reactions of rabbit skin: effects of the long-acting PAF antagonist UK-74,505

1. By using the selective, potent and long acting platelet-activating factor (PAF) antagonist, UK-74,505, we investigated the role of PAF in a local Shwartzman reaction (LSR) and a reversed passive Arthus (RPA) reaction in rabbit skin. For comparison, we also studied the effect of the PAF antagonist on neutrophil aggregation in vitro and on acute inflammatory responses induced by intradermally (i.d.) injected lipopolysaccharide (LPS), PAF, bradykinin and zymosan-activated plasma. 2. Neutrophil aggregation was assessed photometrically. Haemorrhage, oedema formation, platelet deposition and neutrophil accumulation were quantified in rabbit skin by measuring the accumulation of i.v. injected 51Cr-labelled red blood cells (RBC), 125I-labelled human serum albumin, 111In-labelled platelets and 111In-labelled neutrophils respectively. 3. UK-74,505 inhibited in vitro neutrophil aggregation induced by PAF but not by leukotriene B4. When injected i.v. into rabbits UK-74,505 suppressed oedema formation in response to i.d. PAF for up to 4 h but had no effect on oedema induced by bradykinin or zymosan-activated plasma. 4. Oedema formation, but not neutrophil accumulation, produced during the RPA reaction was significantly inhibited by i.v. UK-74,505. The PAF antagonist also suppressed 111In-platelet but not 111In-neutrophil accumulation in response to i.d. LPS. UK-74,505 did not affect haemorrhage or oedema formation produced during the LPS-mediated LSR. 5. The results demonstrate that PAF is an important mediator of oedema formation, but not neutrophil accumulation, in the immune-complex mediated RPA reaction in rabbit skin. PAF also appears to be required for platelet, but not neutrophil, accumulation in response to locally injected LPS. Our studies do not suggest a role for PAF in the LPS-mediated LSR.