The metabolic effects of platelet-activating factor antagonism in endotoxemic man

Fever and hypothermia in systemic inflammation

Systemic inflammation-associated syndromes (e.g., sepsis and septic shock) often have high mortality and remain a challenge in emergency medicine. Systemic inflammation is usually accompanied by changes in body temperature: fever or hypothermia. In animal studies, systemic inflammation is often modeled by administering bacterial lipopolysaccharide, which triggers autonomic and behavioral thermoeffector responses and causes either fever or hypothermia, depending on the dose and ambient temperature. Fever and hypothermia are regulated changes of body temperature, which correspond to mild and severe forms of systemic inflammation, respectively. Mediators of fever and hypothermia are called endogenous pyrogens and cryogens; they are produced when the innate immune system recognizes an infectious pathogen. Upon an inflammatory challenge, hepatic and pulmonary macrophages (and later brain endothelial cells) start to release lipid mediators, of which prostaglandin (PG) E₂ plays the key role, and cytokines. Blood PGE₂ enters the brain and triggers fever. At later stages of fever, PGE₂ synthesized within the blood-brain barrier maintains fever. In both cases, PGE₂ is synthesized by cyclooxygenase-2 and microsomal PGE₂synthase-1. Mediators of hypothermia are not well established. Both fever and hypothermia are beneficial host defense responses. Based on evidence from studies in laboratory animals and clinical trials in humans, fever is beneficial for fighting mild infection. Based mainly on animal studies, hypothermia is beneficial in severe systemic inflammation and infection.

Delayed therapy with a polymyxin B-dextran conjugate (PMX-622) improves survival in rabbits with Gram-negative peritonitis

Polymyxin B (PMB) is an amphipathic nephrotoxic antibiotic, which has been shown to neutralize the effects of endotoxin both in vitro and in vivo. PMB-D70 (PMX-622), a covalent conjugate of PMB with dextran 70 (D70), is less nephrotoxic than the parent compound. We sought to determine whether therapy with PMB-D70, in addition to conventional antimicrobial chemotherapy, could improve survival in a model of Gram-negative peritonitis. At T = 0 h, New Zealand white rabbits were implanted intraperitoneally with 10 ml of a suspension containing hemoglobin (40 μg/ml), mucin (150 μg/ml), and 1.0 ± 0.2 x 104 cfu/kg of viable Escherichia coli (O18:K1). Beginning at T = 4 h, the rabbits were treated with gentamicin (5 mg/kg every 12 h) for five doses or until death, and infused for 24 h or until death with either D70 or PMB-D70. Two pairs of groups were studied (doses indicate cumulative amounts infused over 24 h). The PMB-D70 (low dose) group received PMB-D70 (5 mg/kg of the PMB component) and the D70 (low dose) group received an equivalent dose of D70. The PMB-D70 (high dose) group received PMB-D70 (10 mg/kg of the PMB component) and the D70 (high dose) group received an equivalent dose of D70. Results for the two PMB-D70 groups, on the one hand, and the two D70 group, on the other hand, were statistically indistiguishable and, accordingly, were pooled for all analyses. Survival at 7 days was 11/25 (44%) for rabbits treated with PMB-D70 as compared to 2/23 (9%) for animals treated with D70 ( P = 0.007). We conclude that adjuvant treatment with PMB-D70 improves survival in a clinically relevant model of Gram-negative sepsis.

Platelet-activating factor is a potent pyrogen and cryogen, but it does not mediate lipopolysaccharide fever or hypothermia

We examined whether platelet-activating factor (PAF) and its receptor mediate lipopolysaccharide (LPS)-induced fever and hypothermia in rats. Two highly potent, structurally distinct antagonists of the PAF receptor, CV6209 and WEB2086, were used. At a neutral ambient temperature (Ta) of 30ºC, administration of LPS at a low (10 μg/kg, i.v.) or high (1,000 μg/kg, i.v.) dose resulted in fever. The response to the high dose was turned into hypothermia at a subneutral Ta of 22ºC. Neither LPS-induced fever nor hypothermia was affected by pretreatment with CV6209 (5 mg/kg, i.v.) or WEB2086 (5 mg/kg, i.v.). However, both PAF antagonists were efficacious in blocking the thermoregulatory response caused by PAF (334 pmol/kg/min, 1 h, i.v.), regardless of whether the response was a fever (at 30ºC) or hypothermia (at 22ºC). Additional experiments showed that the thermoregulatory responses to LPS and PAF are also distinct in terms of their mediation by prostaglandins. Neither PAF fever nor PAF hypothermia was affected by pretreatment with the cyclooxygenase-2 inhibitor SC236 (5 mg/kg, i.p.), which is known to abrogate LPS fever. The responses to PAF were also unaffected by pretreatment with the cyclooxygenase-1 inhibitor SC560 (5 mg/kg, i.p.), which is known to attenuate LPS hypothermia. In conclusion, PAF infusion at a picomolar dose causes fever at thermoneutrality but hypothermia in a subthermoneutral environment, both responses being dependent on the PAF receptor and independent of prostaglandins. However, the PAF receptor does not mediate LPS-induced fever or hypothermia, thus challenging the dogma that PAF is an upstream mediator of responses to LPS.

Clinical aspects of plasma platelet-activating factor-acetylhydrolase

Plasma platelet-activating factor (PAF)-acetylhydrolase (PAF-AH), which is characterized by tight association with plasma lipoproteins, degrades not only PAF but also phospholipids with oxidatively modified short fatty acyl chain esterified at the sn-2 position. Production and accumulation of these phospholipids are associated with the onset of inflammatory diseases and preventive role of this enzyme has been evidenced by many recent studies including prevalence of the genetic deficiency of the enzyme in the patients and therapeutic effects of treatment with recombinant protein or gene transfer. With respect to the atherosclerosis, however, it is not fully cleared whether this enzyme plays an anti-atherogenic role or pro-atherogenic role because plasma PAF-AH also might produce lysophosphatidylcholine (LysoPC) and oxidatively modified nonesterified fatty acids with potent pro-inflammatory and pro-atherogenic bioactivities. These dual roles of plasma PAF-AH might be regulated by the altered distribution of the enzyme between low density lipoprotein (LDL) and high density lipoprotein (HDL) particles because HDL-associated enzymes are considered to contribute to the protection of LDL from oxidative modification. This review focuses on the recent findings which address the role of this enzyme in the human diseases especially including asthma, septic shock and atherosclerosis.

Defective glucose homeostasis during infection

Infection leads to profound alterations in whole-body metabolism, which is characterized by marked acceleration of glucose, fat and protein, and amino acid flux. One of the complications of infection, especially in the nutritionally supported setting, is hyperglycemia. The hyperglycemia is caused by peripheral insulin resistance and alterations in hepatic glucose metabolism. The defects in hepatic glucose metabolism include overproduction of glucose and a failure of the liver to appropriately adapt when nutritional support is administered. Investigators have suggested that multiple factors contribute to the observed defects. In this review, I focus primarily on alterations in carbohydrate metabolism, examining both the metabolic response to infection and inflammatory stress, the role of the accompanying neuroendocrine and inflammatory responses in the metabolic response, and the interaction between the endocrine response to infection and nutritional support.

Priming effect of lipopolysaccharide on acetyl-coenzyme A:lyso-platelet-activating factor acetyltransferase is MyD88 and TRIF independent

LPS has a priming effect on various stimuli. For instance, LPS priming enhances the production of platelet-activating factor (PAF), a proinflammatory lipid mediator that is induced by PAF itself. Among various enzymes responsible for PAF biosynthesis, acetyl-coenzyme A:1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine acetyltransferase is one of the enzymes activated by PAF receptor stimulation. In this study we investigated the priming effect of LPS on the acetyltransferase activation by PAF in TLR4-knockout (KO) mice, MyD88-KO mice, and Toll/IL-1R domain-containing adaptor inducing IFN-beta (TRIF)-KO mice. This enzyme was biphasically activated by LPS. Although the first peak occurred within 30 min in wild-type (WT), but not TLR4-KO or MyD88-KO, macrophages, the second phase reached a maximum within hours in WT, MyD88-KO, and TRIF-KO, but not in TLR4-KO, macrophages. Only in the second phase was the increase in acetyltransferase activity upon PAF receptor activation remarkably enhanced in WT, MyD88-KO, and TRIF-KO cells, but not in TLR4-KO cells. These data demonstrated that LPS exerted a priming effect on PAF receptor-mediated acetyltransferase activation through the TLR4-dependent, but MyD88- and TRIF-independent, pathway.

Recombinant human platelet-activating factor acetylhydrolase for treatment of severe sepsis: results of a phase III, multicenter, randomized, double-blind, placebo-controlled, clinical trial

OBJECTIVE

Platelet-activating factor (PAF) and structurally-related oxidized phospholipids are proinflammatory mediators in systemic inflammatory states such as severe sepsis. The enzyme platelet-activating factor acetylhydrolase (PAF-AH) rapidly degrades PAF and oxidized phospholipids into inactive metabolites. Reduced PAF-AH activity has been observed in patients with severe sepsis and may contribute to their systemic inflammatory response and organ dysfunction. A previous clinical trial with recombinant human PAF-AH (rPAF-AH, Pafase) suggested that this treatment may decrease 28-day all-cause mortality in patients with severe sepsis. The current study was undertaken to confirm this result.

DESIGN

A prospective, randomized, double-blind, placebo-controlled, multicenter, international trial.

SETTING

One hundred forty-six intensive care units from nine countries.

PATIENTS

Approximately 2,522 patients were planned to be enrolled < or =12 hrs after the onset of severe sepsis. Eligible patients were randomized to receive either rPAF-AH 1.0 mg/kg or placebo administered intravenously once daily for five consecutive days.

MEASUREMENTS AND MAIN RESULTS

The study was terminated based on the recommendation of an independent data and safety monitoring committee after the second of three planned interim analyses, and the enrollment of 1,425 patients. rPAF-AH treatment was well tolerated among the 1,261 patients included in the interim analysis (643 rPAF-AH and 618 placebo), but did not decrease 28-day all-cause mortality compared with placebo (25% for rPAF-AH vs. 24% for placebo; relative risk, 1.03; 95% confidence interval, 0.85-1.25; p =.80). There were no statistically significant differences between treatment groups in any of the secondary efficacy end points. The overall incidence of adverse events was similar among rPAF-AH and placebo-treated patients, and no rPAF-AH-treated patients developed antibodies to PAF-AH.

CONCLUSIONS

rPAF-AH was well tolerated and not antigenic, but did not decrease 28-day all-cause mortality in patients with severe sepsis.

A new model for inflammation-induced preterm birth: the role of platelet-activating factor and Toll-like receptor-4

Preterm birth is a leading cause of neonatal morbidity and mortality. Despite a growing body of evidence correlating inflammation with preterm birth, the signal transduction pathways responsible for the emptying of the uterus in the setting of intrauterine inflammation has not been elucidated. We now report a unique, reproducible mouse model of localized intrauterine inflammation. This model results in 100% preterm delivery with no maternal mortality. Using our model, we also show that platelet-activating factor is a crucial mediator of both inflammation-induced preterm birth and fetal demise. Using C3H/HeJ mice, we demonstrate that toll-like receptor-4 (TLR-4) plays a role in lipopolysaccharide-induced preterm birth but not in inflammation-induced fetal death. Immunohistochemistry studies demonstrate the presence of the platelet-activating factor receptor in both endometrial glands and smooth muscle in uterine tissues. Molecular studies demonstrate the differential expression of platelet-activating factor receptor and TLR-4 in uterine and cervical tissue throughout gestation. Quantitative polymerase chain reaction revealed an up-regulation of TLR-4 in the fundal region of the uterus in response to intrauterine inflammation. The use of this model will increase our understanding of the significant clinical problem of inflammation-induced preterm birth and will elucidate signal transduction pathways involved in an inflammatory state.

Cytokines in coagulation and thrombosis: a preclinical and clinical review

The cytokine network is a complex and dynamic system, involved in numerous biological responses in the human body. This review of the current literature describes the role of cytokines and their interaction with the coagulation system, specifically in the maintenance of the thrombo-hemorrhagic balance in vivo in human subjects and in animals. In general, cytokines are thrombogenic, but they are amenable to therapeutic manipulations and hence are a potentially attractive tool in the clinician's armamentarium. Studies of the effects of cytokines in vivo are difficult because cytokines act in a very finite microenvironment and, although their actions are significant, they are transient. Most of the available clinical data related to interactions between cytokines and the coagulation system focuses on the role of tumor necrosis factor-alpha and interleukin-1 in septicemia and septic shock. However, several other cytokines and related proteins, such as platelet activating factor and plasminogen activator inhibitor, are also known to influence coagulation and thrombosis. These factors interact closely with cytokines, and have been included in this review for a better understanding of their interactions with traditional cytokines. Studies that utilize cell culture systems do not accurately model the in vivo status of this complex system and, hence, this review has excluded such studies. The role of the cytokine network in coronary artery disease, angiogenesis, or neoplasia has been addressed elsewhere by other workers and is not discussed here. By emphasizing important in vivo interactions, the intention of this review is to serve as an impetus to further translational research, both clinical and in the laboratory.

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.

A pharmacophore for high affinity PAF antagonists. II. Hydrophobicity study using the molecular lipophilicity potential

Platelet-activating factor (PAF) is a powerful phospholipid-derived autacoid involved in many physiopathological mechanisms. Many PAF antagonists have been synthesized and evaluated as therapeutic candidates. In a previous report, we have described an electronic pharmacophore of PAF antagonists using the molecular electrostatic potential. In the present study, a molecular lipophilicity potential is used to compare the hydrophobic properties of 49 "heterocyclic sp2 nitrogen' highly potent PAF antagonists, belonging to six structurally different series (nine hetrazepines, five pyrrolo[1,2-c]thiazoles, 14 carboxamides, nine dihydropyridines, nine pyridinyl-thiazolidines and three imidazo[4,5-c]pyridines). Their common features consist of three hydrophilic (HYD2, HY14(3)B and HYD3) and two lipophilic zones (LIP3 and LIP4), defining the lipophilic pharmacophore of the antagonists. This pharmacophore is also characterized by several zone-to-zone distances: HYD3-HYD2 = 1.3 +/- 1.0 A, HY3B-HYD2 = 7.8 +/- 1.1, HYD3-HY3B = 5.1 +/- 1.1 A, LIP4-LIP3 = 5.4 +/- 1.1 A, LIP3-HYD2 = 11.3 +/- 1.6 A, LIP3-HY3B = 5.9 +/- 1.0 A, LIP3-HYD3 = 4.3 +/- 0.9 A, LIP4-HYD2 = 14.7 +/- 1.6 A, LIP4-HY3B = 8.1 +/- 1.2 A and LIP4-HYD3 = 3.9 +/- 1.1 A. These results represent a new step in the determination of a global pharmacophore for PAF antagonists.

Effects of UR-12633, a new antagonist of platelet-activating factor, in rodent models of endotoxic shock

1. The effects of the selective and potent novel platelet-activating factor (PAF) antagonist, UR-12633 (1-(3,3-diphenylpropionyl)-4-(3-pyridylcyanomethyl)piperidin e) on several markers of endotoxic shock syndrome were evaluated in rats and mice. 2. UR-12633, administered 60 min after E. coli lipopolysaccharide (LPS), reversed the LPS-induced sustained hypotension in rats at doses of 0.01 to 1 mg kg-1, i.v. The reference compound WEB-2086 (1 mg kg-1) also reversed the LPS-induced hypotension. UR-12633 (1 mg kg-1), administered 10 min before LPS, almost fully inhibited sustained hypotension. The immediate hypotension (within 1 min) caused by LPS was not prevented by either UR-12633 or WEB-2086. 3. Pretreatment with 10 mg kg-1, i.v. of either UR-12633 or WEB-2086 inhibited the increase in disseminated intravascular coagulation markers, such as activated partial thromboplastin time (55 and 74% inhibition, respectively), and prothrombin time (22 and 72% inhibition) and prevented the decrease in plasma fibrinogen content (100 and 29% inhibition). 4. Increases in acid phosphatase (ACP) plasma activity, a marker of lysosomal activation, and in lactate dehydrogenase (LDH), a marker of tissue damage, were inhibited by pretreatment with 10 mg kg-1, i.v. of either UR-12633 or WEB-2086 (100% and 69% inhibition, ACP; 62 and 48% inhibition, LDH). Hyperglycaemia (71 and 46%) and hyperlactacidaemia (92 and 56%) were also inhibited. 5. UR-12633, but not WEB-2086, inhibited the LPS-induced increase in vascular permeability in rats, as shown by prevention of haemoconcentration and, to a lesser degree, the increase in Evans blue dye extravasation. 6. In a series of nine reference compounds and UR-12633, we found a high correlation (P < 0.001) between PAF antagonist activity, measured as the inhibition of PAF-induced rabbit platelet aggregation or PAF-induced mortality in mice and the inhibition of LPS-induced mortality. 7. In spite of the multifactorial nature of endotoxic shock, in which many mediators may be involved, the new potent PAF antagonist, UR-12633, proved effective in protecting against changes in most shock markers. These data strongly suggest a key role for PAF in the pathogenesis of endotoxic shock in rodents.

A pharmacophore for high affinity PAF antagonists. I. Electronic model using molecular electrostatic potential

PAF is a powerful phospholipid-derived autacoid involved in many physio-pathological mechanisms. Many PAF antagonists have been synthesized and assayed for therapeutic purposes. In this study, molecular electrostatic potential is used to compare the electronic properties of 48 'heterocyclic sp2 nitrogen' highly potent PAF antagonists, belonging to six series (nine hetrazepines, five pyrrolo[1,2-c]thiazoles, 14 carboxamides, nine dihydropyridines, nine pyridinylthiazolidines and two imidazo[4,5-c]pyridines). Their common features consist of three main electronegative zones (A, B1 and B2) describing the electronic pharmacophore of these ligands. The high affinity of these PAF antagonists seems to be related to this electronegative system A-B(x), which is characterized by three distances A-B1 (9.3 +/- 1.0 A), A-B2 (13.4 +/- 0.7 A) and B1-B2 (4.9 +/- 0.9 A). Moreover, B1 and B2 may surround a common anchorage point in the binding site of the receptor.

Pattern of soluble TNF receptors I and II in sepsis

The serum levels of soluble TNF receptors I (sTNFR I) and sTNFR II were measured frequently in 14 patients with sepsis to evaluate the pattern of these TNF antagonists in relation to TNF alpha, Soluble TNFR I and II could be detected in all samples with significantly higher levels (p < 0.001) compared to healthy controls. The concentration of sTNFR I as well as sTNFR II was significantly higher in nonsurvivors compared to survivors during the first 36 h of sepsis (p < 0.001). Levels remained elevated throughout the evaluation with maximal values in patients who died. A positive correlation exists between both receptors and between soluble receptors and simultaneously obtained sepsis score (p < 0.01) while TNF immunoreactivity detected in 80% of all samples did not correlate to soluble receptor levels or sepsis score. Soluble receptors were constantly found in the circulation representing the inflammatory state throughout the evaluation even when TNF activity was undetectable.

Inflammatory mediator profile in urine and bladder wash fluid of patients with interstitial cystitis

Interstitial cystitis is a syndrome of urinary urgency, frequency and suprapubic pain. We investigated the role of inflammatory mediators in 96 patients with histories and symptoms consistent with interstitial cystitis, and 13 controls from The New York Hospital-Cornell Medical Center, University of Washington and University of California at San Diego. Patients were classified into either group A (meets all criteria of the National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases for inclusion in research studies), group B (meets all of these criteria but without glomerulations) or an "other" group. A small number of group A patients had detectable interleukin-6 in the urine. Urinary concentrations of tumor necrosis factor, prostaglandins E2, D2 and F2 alpha, and thromboxane B2 were not different among either patient groups or controls. Urine specimens contained inhibitors of the bioactivity of interleukin-6 and tumor necrosis factors but no differences between patients or controls were found. No factors chemotactic for human neutrophils were detected in a small patient sample. Bladder wash fluid concentrations of prostaglandins E2, D2 and F2 alpha, and thromboxane were much lower than urinary levels. Bladder wash fluid interleukin-6 and tumor necrosis factor were not detectable. The results suggest that while a small subset of patients may have elevated levels of interleukin-6 the majority of patients do not appear to have elevated levels of inflammatory mediators in the urine or bladder wash fluid. Evaluation of patient bladder tissue may indicate changes not detectable in urine or bladder wash fluid. Alternatively, other etiologies must be considered in those patients.

The role of bactericidal/permeability-increasing protein in the treatment of primate bacteremia and septic shock

Human neutrophil azurophilic granules contain an approximately 55-kDa protein, known as bactericidal/permeability-increasing protein (BPI), which possesses a high-affinity binding domain for the lipid A component of lipopolysaccharide (LPS). The in vivo LPS neutralizing activity of exogenous BPI was studied in a model of lethal Escherichia coli bacteremia. Five baboons were treated with BPI (5 mg/kg bolus injection followed by a 95 micrograms/kg/min BPI infusion over 4 hr), while four additional animals received a genetically engineered variant of BPI (NCY103). Five animals received a placebo treatment and served as controls. Both wild-type rhBPI and NCY103 significantly (P < 0.05) decreased blood levels of LPS throughout an 8-hr evaluation period following live bacterial challenge. Two hours following E. coli administration, LPS levels peaked in the controls, at 6.86 +/- 3.22 ng/ml, whereas LPS levels were 3.39 +/- 2.1 ng/ml in the BPI group and 2.04 +/- 1.18 ng/ml in the NCY103 group. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 levels likewise were attenuated in the treatment groups, whereas circulating sTNFR I was significantly (P < 0.05) reduced only in the BPI group. Leukocytopenia and granulocytopenia were significantly (P < 0.02) lessened in the BPI group, by an average of 59% leukocytopenia and 65% granulocytopenia, respectively. This study supports the concept of E. coli LPS neutralization by BPI in vivo and demonstrates that a moderate (70%) reduction in peak LPS-LAL activity is sufficient to alter some hematologic and cytokine manifestations of bacteremia.