Fletcher B. Taylor

Extracellular histones are major mediators of death in sepsis.

Hyperinflammatory responses can lead to a variety of diseases, including sepsis. We now report that extracellular histones released in response to inflammatory challenge contribute to endothelial dysfunction, organ failure and death during sepsis. They can be targeted pharmacologically by antibody to histone or by activated protein C (APC). Antibody to histone reduced the mortality of mice in lipopolysaccharide (LPS), tumor necrosis factor (TNF) or cecal ligation and puncture models of sepsis. Extracellular histones are cytotoxic toward endothelium in vitro and are lethal in mice. In vivo, histone administration resulted in neutrophil margination, vacuolated endothelium, intra-alveolar hemorrhage and macro- and microvascular thrombosis. We detected histone in the circulation of baboons challenged with Escherichia coli, and the increase in histone levels was accompanied by the onset of renal dysfunction. APC cleaves histones and reduces their cytotoxicity. Co-infusion of APC with E. coli in baboons or histones in mice prevented lethality. Blockade of protein C activation exacerbated sublethal LPS challenge into lethality, which was reversed by treatment with antibody to histone. We conclude that extracellular histones are potential molecular targets for therapeutics for sepsis and other inflammatory diseases.

Human Protein C Receptor Is Present Primarily on Endothelium of Large Blood Vessels Implications for the Control of the Protein C Pathway

BACKGROUND The protein C anticoagulant pathway is critical to the control of hemostasis. Thrombomodulin and a newly identified receptor for protein C/activated protein C, EPCR, are both present on endothelium. EPCR augments activation of protein C by the thrombin-thrombomodulin complex. METHODS AND RESULTS To gain a better understanding of the relationship between thrombomodulin and EPCR, we compared the cellular specificity and tissue distributions of these two receptors by using immunohistochemistry. EPCR expression was detected almost exclusively on endothelium in human and baboon tissues. In most organs, EPCR was expressed relatively intensely on the endothelium of all arteries and veins, most arterioles, and some postcapillary venules. EPCR staining was usually negative on capillary endothelial cells. In contrast, thrombomodulin was detected at high concentrations in both large vessels and capillary endothelium. Both thrombomodulin and EPCR were expressed poorly on brain capillaries. The liver sinusoids were the only capillaries in which EPCR was expressed at moderate levels and thrombomodulin was low. EPCR and thrombomodulin were both expressed on the endothelium of vasa recta in the renal medulla, the lymph node subcapsular and medullary sinuses, and some capillaries within the adrenal gland. Even in these organs the majority of capillaries were EPCR negative or stained weakly. CONCLUSIONS These studies suggest that EPCR may be important in enhancing protein C activation on large vessels. The presence of high levels of EPCR on arterial vessels may help explain why partial protein C deficiency is a weak risk factor for arterial thrombosis.

Lethal staphylococcus aureus-induced shock in primates : prevention of death with anti-TNF antibody

A successful experimental treatment for gram-positive sepsis to our knowledge has not been achieved. The objectives of this study were to develop a nonhuman primate model of lethal gram-positive sepsis employing the micro-organism Staphylococcus aureus and to determine the efficacy of treatment using monoclonal antibody (MAb) to tumor necrosis factor alpha (TNF). The antibody was administered intravenously, 15 mg/kg, 30 minutes after the beginning of a 2-hour infusion of S. aureus, 4 x 10(10) colony forming units/kilogram. The baboons infused with S. aureus demonstrated the release of the cytokines TNF and interleukin-6 (IL-6), but endotoxin was not observed in the plasma at any time. Treatment with antibody to TNF abolished the rise in serum TNF levels and reduced the increased levels of IL-6. Treatment with MAb to TNF prevented multiple organ failure and achieved permanent (> 7 day) survival of all baboons.

Complement inhibition decreases the procoagulant response and confers organ protection in a baboon model of Escherichia coli sepsis.

Severe sepsis leads to massive activation of coagulation and complement cascades that could contribute to multiple organ failure and death. To investigate the role of the complement and its crosstalk with the hemostatic system in the pathophysiology and therapeutics of sepsis, we have used a potent inhibitor (compstatin) administered early or late after Escherichia coli challenge in a baboon model of sepsis-induced multiple organ failure. Compstatin infusion inhibited sepsis-induced blood and tissue biomarkers of complement activation, reduced leucopenia and thrombocytopenia, and lowered the accumulation of macrophages and platelets in organs. Compstatin decreased the coagulopathic response by down-regulating tissue factor and PAI-1, diminished global blood coagulation markers (fibrinogen, fibrin-degradation products, APTT), and preserved the endothelial anticoagulant properties. Compstatin treatment also improved cardiac function and the biochemical markers of kidney and liver damage. Histologic analysis of vital organs collected from animals euthanized after 24 hours showed decreased microvascular thrombosis, improved vascular barrier function, and less leukocyte infiltration and cell death, all consistent with attenuated organ injury. We conclude that complement-coagulation interplay contributes to the progression of severe sepsis and blocking the harmful effects of complement activation products, especially during the organ failure stage of severe sepsis is a potentially important therapeutic strategy.

Description of compensated and uncompensated disseminated intravascular coagulation (DIC) responses (non-overt and overt DIC) in baboon models of intravenous and intraperitoneal Escherichia coli sepsis and in the human model of endotoxemia: toward a better definition of DIC.

ObjectiveWork toward a better definition of disseminated intravascular coagulation (DIC) by characterizing the difference between compensated and uncompensated responses of the hemostatic system to inflammatory stress in baboons and human subjects using global coagulation and molecular marker assays of hemostatic, inflammatory, and endothelial perturbation. DesignWe conducted prospective evaluation of the response of baboons to increasing concentrations of intravenous Escherichia coli, human subjects to intravenous endotoxin, and baboons to intraperitoneal E. coli. SettingAnimal laboratory and medical intensive care facilities, University of Oklahoma Medical School laboratories. SubjectsCynocephalus baboons; normal healthy male human subjects (age, 24–37 yrs). Measurements and Main ResultsGlobal coagulation assays, white blood cell counts, and molecular marker assays (ELISA) of components of the inflammatory and hemostatic systems, neutrophil release products, and endothelial injury. A fall in both fibrinogen concentration and platelet counts indicated a decompensated hemostatic response to inflammatory stress (ie, overt DIC). These responses were observed 2–6 hrs after intravenous infusion of 109 and 1010 colony-forming units (CFU)/g of E. coli and after implantation of 1011 CFU/g of E. coli into the peritoneal cavity. However, 6 hrs after E. coli challenge, these tests were much less reliable as markers of overt DIC because the fibrinogen underwent an acute phase response and the platelet count fell and remained depressed for 48 hrs in the face of a coagulopathic response that was already beginning to resolve, as reflected by a rising fibrinogen concentration. This lack of reliability was particularly evident in the E. coli peritonitis studies, in which one third of the animals recovered, one third remained sick for up to 14 days, and one third died.In contrast, fibrin degradation products and the molecular markers thrombin/antithrombin, soluble fibrin monomer, protein C, and activated protein C/inhibitor complexes responded consistently in a dose-dependent manner regardless of the length of time after challenge. These variables exhibited this dose response to 106 and 108 CFU/g of E. coli in absence of a fall in fibrinogen concentration. This was defined as a compensated hemostatic response to inflammatory stress (ie, non-overt DIC). The values of these variables correlated closely with rising concentrations of markers of neutrophil activation (elastase/∝ 1 antitrypsin) and endothelial injury (soluble thrombomodulin). This was particularly evident in the human response to endotoxin, in which there was abundant evidence of hemostatic marker response in absence of a fall in platelet or fibrinogen concentration, both immediately after endotoxin infusion (first stage, 0–8 hrs after endotoxin) and later (second stage, 12–48 hrs after endotoxin). ConclusionGlobal coagulation tests are most useful in detecting overt consumptive coagulopathy (overt DIC) near the time of challenge or injury (1 to 6 hrs). Molecular markers can detect and grade the degree of hemostatic stress of a non-overt consumptive coagulopathy (nonovert DIC). These markers correlate with degree of endothelial cell injury and reveal a reperfusion injury stage (second stage) in the human endotoxin model of compensated hemostatic stress after all clinical symptoms have subsided and the subjects have returned to work.

Staging of the pathophysiologic responses of the primate microvasculature to Escherichia coli and endotoxin: examination of the elements of the compensated response and their links to the corresponding uncompensated lethal variants.

ObjectiveReview of primate studies of Escherichia coli sepsis and endotoxemia with a reexamination of the rationale for diagnosis and treatment of these multistage disorders. SettingAnimal research and intensive care units in a university medical school. SubjectsCyanocephalus baboons (E. coli) and normal human subjects (endotoxin). InterventionsBaboon studies: anti-tissue factor, protein C, endothelial protein C receptor, and anti-tumor necrosis factor antibodies, and active site inhibited factor recombinant VIIa and factor Xa. Results and Conclusions This review concerns the primate microvascular endothelial response to inflammatory and hemostatic stress. Studies of the impact of inflammatory and hemostatic stress on this microvasculature have fallen into four categories. First, studies of pure hemostatic stress using factor Xa phospholipid vesicles showed that blockade of protein C as well as protein C plus tissue plasminogen activator produced a severe but transient consumptive and a lethal thrombotic coagulopathy, respectively. These studies showed that the protein C and fibrinolytic systems can work in tandem to regulate even a severe response if the endothelium is not rendered dysfunctional by metabolic or inflammatory factors. Second, studies of compensated (nonlethal) inflammatory stress using E. coli or endotoxin in baboon and human subjects showed that even under minimal stress in which there is no evidence of overt disseminated intravascular coagulation, injury of the endothelium and activation of neutrophils and hemostatic factors are closely associated. This showed that molecular markers of hemostatic activity could be used to detect microvascular endothelial stress (nonovert disseminated intravascular coagulation) in patients who are compensated but at risk. These studies also showed that the compensated response to inflammatory stress could exhibit two stages, each with its unique inflammatory and hemostatic response signature. The first is driven by vasoactive peptides, cytokines, and thrombin, followed 12 to 14 hrs later by a second stage driven by C-reactive protein/complement complexes, tissue factor, and plasminogen activator inhibitor 1 secondary to oxidative stress after reperfusion. Third, studies of uncompensated (lethal) inflammatory stress using E. coli showed that irreversible thrombosis of the microvasculature was not a link in the lethal chain of events even though inhibition of components of the protein C network (protein C and endothelial protein C receptor) converted compensated responses to sublethal E. coli into uncompensated lethal responses. Fourth, these studies also showed that there were variants of the lethal response ranging from capillary leak and shock to recurrent sustained inflammatory disorders. We believe that each of these variants arises from their sublethal counterparts, depending on underlying or modulating host factors operating at the time of challenge. Such underlying conditions range from preexisting microvascular ischemia, reperfusion, and oxidative stress to alteration or reprogramming of monocyte/macrophage responses (tolerance to hyperresponsiveness). Characterization of these underlying conditions in patients who are at risk should aid in identifying and optimizing management of these variants.

A model for thrombin protection against endotoxin

Infusion of dogs with thrombin (0.5 U/kg/min) for 90 minutes significantly increased percent survival following infusion of endotoxin (0.06 mg/kg/min) for 30 minutes. Nine of fourteen dogs infused with thrombin survived seven days (permanent survivors), whereas thirteen of fourteen dogs infused with saline died within 36 hours. Those dogs which survived responded immediately to endotoxin with enhanced anticoagulant and fibrinolytic activity as measured by the Xa one-stage and fibrin degradation product assays, respectively. Those dogs receiving saline instead of thrombin did not respond with anticoagulant or fibrinolytic activity until the end of the study. We concluded that thrombin in the correct amounts protected dogs from endotoxin and that this protection was associated with an early anticoagulant and fibrinolytic response to endotoxin infusion.

Staging of the Baboon Response to Group A Streptococci Administered Intramuscularly: A Descriptive Study of the Clinical Symptoms and Clinical Chemical Response Patterns

Group A streptococcal infections, ranging from necrotizing fasciitis and myositis to toxic shock syndrome, have increased over the last 10 years. We developed the first primate model of necrotizing fasciitis and myositis. Thirteen baboons were inoculated intramuscularly with group A streptococci (GAS). Eleven animals survived for > or = 11 days before sacrifice, and two animals died within 2 days. The site of inoculation of the survivors exhibited an intense neutrophilic influx (stage I), followed by a lymphoplasmacytic influx (stages II and III). This was accompanied by the appearance of markers of an acute and then a chronic systemic inflammatory response. In contrast, the site of inoculation of the two nonsurvivors exhibited intravascular aggregates of neutrophils at its margin with no influx of neutrophils and with extensive bacterial colonization. We conclude that GAS inoculation induces a local and systemic acute neutrophilia followed by a chronic lymphoplasmacytic response; failure, initially, of neutrophilic influx into the site of inoculation predisposes to systemic GAS sepsis and death; and this three-stage primate model approximates the human disease.

Two-stage response to endotoxin infusion into normal human subjects: Correlation of blood phagocyte luminescence with clinical and laboratory markers of the inflammatory, hemostatic response

ObjectiveTo characterize a two-stage response of normal human subjects to an intravenous bolus infusion of endotoxin by using phagocyte luminescence and molecular markers of hemostatic and inflammatory system, phagocyte, and endothelial cell perturbation. DesignProspective evaluation of the response of normal subjects to endotoxin. SettingMedical intensive care unit, university laboratories. SubjectsNormal healthy male subjects ranging in age from 24 to 37 yrs. MeasurementsLuminescence measurements of phagocyte oxidase, oxidase-myeloperoxidase, opsonin receptor expression, clinical chemical and molecular markers of hemostatic and inflammatory system activation, phagocyte activation, and endothelial cell injury. ResultsResponse to intravenous bolus endotoxin includes two stages. The symptomatic first stage (time [T]-0 to T + 8 hrs) included sharp rises in phagocyte oxidase, oxidase-myeloperoxidase, and opsonin receptor expression with the appearance of morphologic and molecular markers of hemostatic and inflammatory system activation, phagocyte activation, and endothelial cell injury. All variables with the exception of soluble thrombomodulin, soluble fibrin monomer, lactate, white cell count, and opsonin receptor expression returned to baseline by T + 8 hrs, by which time all acute clinical symptoms had disappeared. The asymptomatic second stage (T + 8–48 hrs) included a second peak of oxidase activity at T + 24 hrs with an elevated but declining lactate and opsonin receptor expression. This coincided with a second high peak of soluble fibrin monomer, sustained elevated concentrations of soluble thrombomodulin and plasma soluble tissue factor antigen, a decrease in factor VIIa concentration to 50% of baseline at T + 12–24 hrs, and an increase in C-reactive protein/C3d and C4d complexes, which peaked at T + 24 hrs. ConclusionsThe results suggest that the human response to endotoxin consists of a previously well-characterized, symptomatic, first stage acute inflammatory response followed by an asymptomatic second stage that is marked by a second peak of oxidase activity, a continued increase and sustained elevation of markers of hemostatic and complement system activation, and endothelial cell injury. We conclude that this second stage represents a recovery or reperfusion phase of a compensated response to endotoxin in which contact of the microvasculature perturbed during the first stage is reestablished with blood in a second asymptomatic stage.

Infection-induced Modulation Of M1 And M2 Phenotypes In Circulating Monocytes: Role In Immune Monitoring And Early Prognosis Of Sepsis

To monitor and better understand the immunoinflammatory sequelae in sepsis and septic shock, systemic and monocyte-related cytokine responses were evaluated in baboons with experimental peritonitis induced by an E. coli–laden fibrin clot. Despite similar bacterial inocula, considerable interindividual variability in clinical manifestation and outcome of infection was observed. Because monocytes and macrophages are a key component of innate immunity, we hypothesized that early polarization of distinct activation programs in circulating monocytes that culminates in the emergence of either classically (M1) or alternatively (M2) activated monocytes may underlie the observed susceptibility or resistance to infection. To test our hypothesis, we analyzed infection-induced expression of cytokine mRNAs in monocytes isolated from surviving and dead animals. Our data show that resistance to E. coli sepsis may well be associated with a mixed M1/M2 activation state of circulating monocytes, whereas M1 phenotype appeared to be prevailing in monocytes from animals that died. Together with data on systemic cytokine responses, the latter findings indicate that morbidity and mortality of animals with gram-negative sepsis may well result from an overwhelming proinflammatory response. Collectively, our data contribute to a better understanding of cytokine networking in the immunoinflammatory response to microbial infection and suggest M1/M2 immunophenotypic profiling of readily available circulatory monocytes for early prognosis of severe infections.