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

The role of thromboinflammation in acute kidney injury among patients with septic coagulopathy

Inflammation and coagulation are critical self-defense mechanisms for mitigating infection that can nonetheless induce tissue injury and organ dysfunction. In severe cases, like sepsis, a dysregulated thromboinflammatory response may result in multiorgan dysfunction. Sepsis-associated acute kidney injury (AKI) is a significant contributor to patient morbidity and mortality. The connection between AKI and thromboinflammation is largely due to unique aspects of the renal vasculature. Specifically, the interaction between blood cells with the endothelial, glomerular, and peritubular capillary systems during thromboinflammation reduces oxygen supply to tubular epithelial cells. Previous studies have focused on tubular epithelial cell damage due to hypoxia, oxidative stress, and nephrotoxins. Although these factors are pivotal in acute tubular injury or necrosis, recent studies have demonstrated that AKI in sepsis encompasses a mixture of tubular and glomerular damage subtypes. In cases of sepsis-induced coagulopathy, thromboinflammation within the glomerulus and peritubular capillaries is an important pathogenic mechanism for AKI. Unfortunately, and despite the use of renal replacement therapy, the development of AKI in sepsis continues to be associated with high morbidity, mortality, and clinical challenges requiring alternative approaches. This review introduces the important role of thromboinflammation in AKI pathogenesis and details innovative vascular-targeting therapeutic strategies.

Effect of high-dose intravenous ascorbic acid on microcirculation and endothelial glycocalyx during sepsis and septic shock: a double-blind, randomized, placebo-controlled study

Previous studies indicate supplemental vitamin C improves microcirculation and reduces glycocalyx shedding in septic animals. Our randomized, double-blind, placebo-controlled trial aimed to investigate whether a high dose of intravenous ascorbic acid (AA) might improve microcirculation and affect glycocalyx in septic patients. In our study, 23 septic patients were supplemented with a high dose (50 mg/kg every 6 h) of intravenous AA or placebo for 96 h. Sublingual microcirculation was examined using a handheld Cytocam-incident dark field (IDF) video microscope. A sidestream dark field video microscope (SDF), connected to the GlycoCheck software (GlycoCheck ICU®; Maastricht University Medical Center, Maastricht, the Netherlands), was employed to observe glycocalyx. We found a significantly higher proportion of perfused small vessels (PPV) 6 h after the beginning of the trial in the experimental group compared with placebo. As an indicator of glycocalyx thickness, the perfused boundary region was lower in capillaries of the 5-9 μm diameter in the AA group than placebo after the first dose of AA. Our data suggest that high-dose parenteral AA tends to improve microcirculation and glycocalyx in the early period of septic shock. The study was retrospectively registered in the clinicaltrials.gov database on 26/02/2021 (registration number NCT04773717).

Vascular Proteome Responses Precede Organ Dysfunction in a Murine Model of Staphylococcus aureus Bacteremia

Vascular dysfunction and organ failure are two distinct, albeit highly interconnected, clinical outcomes linked to morbidity and mortality in human sepsis. The mechanisms driving vascular and parenchymal damage are dynamic and display significant molecular cross talk between organs and tissues. Therefore, assessing their individual contribution to disease progression is technically challenging. Here, we hypothesize that dysregulated vascular responses predispose the organism to organ failure. To address this hypothesis, we have evaluated four major organs in a murine model of Staphylococcus aureus sepsis by combining in vivo labeling of the endothelial cell surface proteome, data-independent acquisition (DIA) mass spectrometry, and an integrative computational pipeline. The data reveal, with unprecedented depth and throughput, that a septic insult evokes organ-specific proteome responses that are highly compartmentalized, synchronously coordinated, and significantly correlated with the progression of the disease. These responses include abundant vascular shedding, dysregulation of the intrinsic pathway of coagulation, compartmentalization of the acute phase response, and abundant upregulation of glycocalyx components. Vascular cell surface proteome changes were also found to precede bacterial invasion and leukocyte infiltration into the organs, as well as to precede changes in various well-established cellular and biochemical correlates of systemic coagulopathy and tissue dysfunction. Importantly, our data suggest a potential role for the vascular proteome as a determinant of the susceptibility of the organs to undergo failure during sepsis. IMPORTANCE Sepsis is a life-threatening response to infection that results in immune dysregulation, vascular dysfunction, and organ failure. New methods are needed for the identification of diagnostic and therapeutic targets. Here, we took a systems-wide approach using data-independent acquisition (DIA) mass spectrometry to track the progression of bacterial sepsis in the vasculature leading to organ failure. Using a murine model of S. aureus sepsis, we were able to quantify thousands of proteins across the plasma and parenchymal and vascular compartments of multiple organs in a time-resolved fashion. We showcase the profound proteome remodeling triggered by sepsis over time and across these compartments. Importantly, many vascular proteome alterations precede changes in traditional correlates of organ dysfunction, opening a molecular window for the discovery of early markers of sepsis progression.

Nonhuman primate species as models of human bacterial sepsis

Sepsis involves a disordered host response to systemic infection leading to high morbidity and mortality. Despite intense research, targeted sepsis therapies beyond antibiotics have remained elusive. The cornerstone of sepsis research is the development of animal models to mimic human bacterial infections and test novel pharmacologic targets. Nonhuman primates (NHPs) have served as an attractive, but expensive, animal to model human bacterial infections due to their nearly identical cardiopulmonary anatomy and physiology, as well as host response to infection. Several NHP species have provided substantial insight into sepsis-mediated inflammation, endothelial dysfunction, acute lung injury, and multi-organ failure. The use of NHPs has usually focused on translating therapies from early preclinical models to human clinical trials. However, despite successful sepsis interventions in NHP models, there are still no FDA-approved sepsis therapies. This review highlights major NHP models of bacterial sepsis and their relevance to clinical medicine.

Treatment for bacterial sepsis remains limited beyond the use of antibiotics. Lingye Chen, Karen Welty-Wolf, and Bryan Kraft review nonhuman primate models of sepsis and highlight their advantages and limitations compared to other preclinical models.

Experimental Protocol for Cecal Ligation and Puncture Model of Polymicrobial Sepsis and Assessment of Vascular Functions in Mice

Sepsis is the systemic inflammatory response syndrome that occurs during infection and is exacerbated by the inappropriate immune response encountered by the affected individual. Despite extensive research, sepsis in humans is one of the biggest challenges for clinicians. The high mortality rate in sepsis is primarily due to hypoperfusion-induced multiorgan dysfunctions , resulting from a marked decrease in peripheral resistance. Vascular dysfunctions are further aggravated by sepsis-induced impairment in myocardial contractility. Circulatory failure in sepsis is characterized by refractory hypotension and vascular hyporeactivity (vasoplegia) to clinically used vasoconstrictors. To investigate the complex pathophysiology of sepsis and its associated multiple organ dysfunction, several animal models have been developed. However, cecal ligation and puncture (CLP) model of murine sepsis is still considered as 'gold standard' in sepsis research. In this protocol we have described the standard surgical procedure to induce polymicrobial sepsis by cecal ligation and puncture. Further, we have described the protocol to study the molecular mechanisms underlying vascular dysfunctions in sepsis.

In vivo-generated thrombin and plasmin do not activate the complement system in baboons

Sepsis concurrently activates both coagulation and complement systems. Although complement activation by bacteria is well documented, work in mice and in vitro suggests that coagulation proteases can directly cleave complement proteins. We aimed to determine whether generation of coagulation proteases in vivo can activate the complement cascade in 2 highly coagulopathic models. We compared temporal changes in activation biomarkers of coagulation (thrombin-antithrombin [TAT]), fibrinolysis (plasmin-antiplasmin [PAP]), and complement (C3b, C5a, C5b-9) in baboons infused with factor Xa (FXa) and phospholipids (FXa/phosphatidylcholine-phosphatidylserine [PCPS]) vs LD100 Escherichia coli We found that, albeit with different timing, both FXa/PCPS and E coli infusion led to robust thrombin and plasmin generation. Conversely, only E coli challenge activated the complement system, reaching a maximum at 2 hours postchallenge during the peaks of lipopolysaccharide and bacteremia but not of TAT and PAP. Despite inducing a strong burst of thrombin and plasmin, FXa/PCPS infusion did not produce measurable levels of complement activation in vivo. Similarly, ex vivo incubation of baboon serum with thrombin, plasmin, or FXa did not show noticeable complement cleavage unless supraphysiologic amounts of enzymes were used. Our results suggest that in vivo-generated thrombin and plasmin do not directly activate the complement in nonhuman primates.

Astilbin alleviates sepsis-induced acute lung injury by inhibiting the expression of macrophage inhibitory factor in rats

Sepsis is a systemic inflammatory response syndrome caused by severe infections. Astilbin is a dihydroflavonol derivative found in many medicinal and food plants with multiple pharmacological functions. To investigate the effects of astilbin on sepsis-induced acute lung injury (ALI), cecal ligation and puncture was performed on rats to establish a sepsis-induced ALI model; these rats were then treated with astilbin at different concentrations. Lung injury scores, including lung wet/dry ratio, protein leakage, myeloperoxidase activity, and inflammatory cell infiltration were determined to evaluate the effects of astilbin on sepsis-induced ALI. We found that astilbin treatment significantly attenuates sepsis-induced lung injury and improves survival rate, lung injury scores, lung wet/dry ratio, protein leakage, myeloperoxidase activity, and inflammatory cell infiltration. Astilbin treatment also dramatically decreased the production of inflammatory cytokines and chemokines in bronchoalveolar lavage fluid. Further, astilbin treatment inhibited the expression and production of macrophage inhibitory factor (MIF), which inhibits the inflammatory response. Collectively, these data suggest that astilbin has a protective effect against sepsis-induced ALI by inhibiting MIF-mediated inflammatory responses. This study provides a molecular basis for astilbin as a new medical treatment for sepsis-induced ALI.

Differential Paradigms in Animal Models of Sepsis

Sepsis is a serious clinical problem involving complex mechanisms which requires better understanding and insight. Animal models of sepsis have played a major role in providing insight into the complex pathophysiology of sepsis. There have been various animal models of sepsis with different paradigms. Endotoxin, bacterial infusion, cecal ligation and puncture, and colon ascendens stent peritonitis models are the commonly practiced methods at present. Each of these models has their own advantages and also confounding factors. We have discussed the underlying mechanisms regulating each of these models along with possible reasons why each model failed to translate into the clinic. In animal models, the timing of development of the hemodynamic phases and the varied cytokine patterns could not accurately resemble the progression of clinical sepsis. More often, the exuberant and transient pro-inflammatory cytokine response is only focused in most models. Immunosuppression and apoptosis in the later phase of sepsis have been found to cause more damage than the initial acute phase of sepsis. Likewise, better understanding of the existing models of sepsis could help us create a more relevant model which could provide solution to the currently failed clinical trials in sepsis.

Effects of sodium methyldithiocarbamate on selected parameters of innate immunity and clearance of bacteria in a mouse model of sepsis

AIMS

Sodium methyldithiocarbamate (SMD), the third most widely used conventional pesticide in the United States, has been reported to inhibit several parameters associated with inflammation and to decrease resistance to infection. In a previous study, survival time was markedly decreased when mice were treated orally with SMD shortly before challenge with a high dose of Escherichia coli (E. coli) that was lethal to most of the control mice. In the present study, we evaluated selected parameters of the innate immune system using a lower challenge dose of E. coli, to determine which (if any) of these parameters reflected continued changes through 24h.

MAIN METHODS

Bacterial clearance from the peritoneal cavity, production of chemokines and cytokines, and body temperature were measured.

KEY FINDINGS

All these parameters were reduced by SMD up to 12h after bacterial challenge, but the concentration of the anti-inflammatory cytokine IL-10 was increased. Even so, mice in the control and SMD-treated groups cleared most bacteria by 24h. Other parameters (cytokine concentrations and body temperature) were also normal or near normal by 24h. The same dosage of SMD administered intranasally also did not significantly decrease survival. Hypothermia from 16 to 28 h correlated with lethal outcome, but SMD significantly increased hypothermia only at 2 and 4h after challenge.

SIGNIFICANCE

In spite of substantial early inhibition by SMD of parameters known to be important for resistance to infection, bacterial clearance and survival were not altered, suggesting immunological reserve and/or rapid recovery after transient effects of SMD.

Compstatin: a C3-targeted complement inhibitor reaching its prime for bedside intervention

There is a growing awareness that complement plays an integral role in human physiology and disease, transcending its traditional perception as an accessory system for pathogen clearance and opsonic cell killing. As the list of pathologies linked to dysregulated complement activation grows longer, it has become clear that targeted modulation of this innate immune system opens new windows of therapeutic opportunity for anti-inflammatory drug design. Indeed, the introduction of the first complement-targeting drugs has reignited a vibrant interest in the clinical translation of complement-based inhibitors. Compstatin was discovered as a cyclic peptide that inhibits complement activation by binding C3 and interfering with convertase formation and C3 cleavage. As the convergence point of all activation pathways and a molecular hub for crosstalk with multiple pathogenic pathways, C3 represents an attractive target for therapeutic modulation of the complement cascade. A multidisciplinary drug optimization effort encompassing rational 'wet' and in silico synthetic approaches and an array of biophysical, structural and analytical tools has culminated in an impressive structure-function refinement of compstatin, yielding a series of analogues that show promise for a wide spectrum of clinical applications. These new derivatives have improved inhibitory potency and pharmacokinetic profiles and show efficacy in clinically relevant primate models of disease. This review provides an up-to-date survey of the drug design effort placed on the compstatin family of C3 inhibitors, highlighting the most promising drug candidates. It also discusses translational challenges in complement drug discovery and peptide drug development and reviews concerns related to systemic C3 interception.

Complement, thrombotic microangiopathy and disseminated intravascular coagulation

In the blurring boundaries between clinical practice and scientific observations, it is increasingly attractive to propose shared disease mechanisms that could explain clinical experience. With the advent of available therapeutic options for complement inhibition, there is a push for more widespread application in patients, despite a lack of clinically relevant research. Patients with disseminated intravascular coagulation (DIC) and thrombotic microangiopathies (TMA) frequently exhibit complement activation and share the clinical consequences of thrombocytopenia, microangiopathic hemolytic anemia, and microvascular thrombosis. However, they arise from very different molecular etiologies giving rise to cautious questions about inclusive treatment approaches because most clinical observations are associative and not cause-and-effect. Complement inhibition is successful in many cases of atypical hemolytic uremic syndrome, greatly reducing morbidity and mortality of patients by minimizing thrombocytopenia, microangiopathic hemolytic anemia, and microvascular thrombosis. But is this success due to targeting disease etiology or because complement is a sufficiently systemic target or both? These questions are important because complement activation and similar clinical features also are observed in many DIC patients, and there are mounting calls for systemic inhibition of complement mediators despite the enormous differences in the primary diseases complicated by DIC. We are in great need of thoughtful and standardized assessment with respect to both beneficial and potentially harmful consequences of complement activation in these patient populations. In this review, we discuss about what needs to be done in terms of establishing the strategy for complement inhibition in TMA and DIC, based on the current knowledge.

Acute lung injury and fibrosis in a baboon model of Escherichia coli sepsis

Sepsis-induced inflammation of the lung leads to acute respiratory distress syndrome (ARDS), which may trigger persistent fibrosis. The pathology of ARDS is complex and poorly understood, and the therapeutic approaches are limited. We used a baboon model of Escherichia coli sepsis that mimics the complexity of human disease to study the pathophysiology of ARDS. We performed extensive biochemical, histological, and functional analyses to characterize the disease progression and the long-term effects of sepsis on the lung structure and function. Similar to humans, sepsis-induced ARDS in baboons displays an early inflammatory exudative phase, with extensive necrosis. This is followed by a regenerative phase dominated by proliferation of type 2 epithelial cells, expression of epithelial-to-mesenchymal transition markers, myofibroblast migration and proliferation, and collagen synthesis. Baboons that survived sepsis showed persistent inflammation and collagen deposition 6-27 months after the acute episodes. Long-term survivors had almost double the amount of collagen in the lung as compared with age-matched control animals. Immunostaining for procollagens showed persistent active collagen synthesis within the fibroblastic foci and interalveolar septa. Fibroblasts expressed markers of transforming growth factor-β and platelet-derived growth factor signaling, suggesting their potential role as mediators of myofibroblast migration and proliferation, and collagen deposition. In parallel, up-regulation of the inhibitors of extracellular proteases supports a deregulated matrix remodeling that may contribute to fibrosis. The primate model of sepsis-induced ARDS mimics the disease progression in humans, including chronic inflammation and long-lasting fibrosis. This model helps our understanding of the pathophysiology of fibrosis and the testing of new therapies.

Synthetic ligand-coated magnetic nanoparticles for microfluidic bacterial separation from blood

Bacterial sepsis is a serious clinical condition that can lead to multiple organ dysfunction and death despite timely treatment with antibiotics and fluid resuscitation. We have developed an approach to clearing bacteria and endotoxin from the bloodstream, using magnetic nanoparticles (MNPs) modified with bis-Zn-DPA, a synthetic ligand that binds to both Gram-positive and Gram-negative bacteria. Magnetic microfluidic devices were used to remove MNPs bound to Escherichia coli , a Gram-negative bacterium commonly implicated in bacterial sepsis, from bovine whole blood at flows as high as 60 mL/h, resulting in almost 100% clearance. Such devices could be adapted to clear bacteria from septicemic patients.

Plasma bacterial and mitochondrial DNA distinguish bacterial sepsis from sterile systemic inflammatory response syndrome and quantify inflammatory tissue injury in nonhuman primates

Systemic inflammatory response syndrome (SIRS) is a fundamental host response common to bacterial infection and sterile tissue injury. Systemic inflammatory response syndrome can cause organ dysfunction and death, but its mechanisms are incompletely understood. Moreover, SIRS can progress to organ failure or death despite being sterile or after control of the inciting infection. Biomarkers discriminating between sepsis, sterile SIRS, and postinfective SIRS would therefore help direct care. Circulating mitochondrial DNA (mtDNA) is a damage-associated molecular pattern reflecting cellular injury. Circulating bacterial 16S DNA (bDNA) is a pathogen-associated pattern (PAMP) reflecting ongoing infection. We developed quantitative polymerase chain reaction assays to quantify these markers, and predicting their plasma levels might help distinguish sterile injury from infection. To study these events in primates, we assayed banked serum from Papio baboons that had undergone a brief challenge of intravenous Bacillus anthracis delta Sterne (modified to remove toxins) followed by antibiotics (anthrax) that causes organ failure and death. To investigate the progression of sepsis to "severe" sepsis and death, we studied animals where anthrax was pretreated with drotrecogin alfa (activated protein C), which attenuates sepsis in baboons. We also contrasted lethal anthrax bacteremia against nonlethal E. coli bacteremia and against sterile tissue injury from Shiga-like toxin 1. Bacterial DNA and mtDNA levels in timed samples were correlated with blood culture results and assays of organ function. Sterile injury by Shiga-like toxin 1 increased mtDNA, but bDNA was undetectable: consistent with the absence of infection. The bacterial challenges caused parallel early bDNA and mtDNA increases, but bDNA detected pathogens even after bacteria were undetectable by culture. Sublethal E. coli challenge only caused transient rises in mtDNA consistent with a self-limited injury. In lethal anthrax challenge (n = 4), bDNA increased transiently, but mtDNA levels remained elevated until death, consistent with persistent septic tissue damage after bacterial clearance. Critically, activated protein C pretreatment (n = 4) allowed mtDNA levels to decay after bacterial clearance with sparing of organ function and survival. In summary, host tissue injury correlates with mtDNA whether infective or sterile. Mitochondrial DNA and bDNA polymerase chain reactions can quantify tissue injury incurred by septic or sterile mechanisms and suggest the source of SIRS of unknown origin.

Quiescent complement in nonhuman primates during E coli Shiga toxin-induced hemolytic uremic syndrome and thrombotic microangiopathy

Enterohemorrhagic Escherichia coli (EHEC) produce ribosome-inactivating Shiga toxins (Stx1, Stx2) responsible for development of hemolytic uremic syndrome (HUS) and acute kidney injury (AKI). Some patients show complement activation during EHEC infection, raising the possibility of therapeutic targeting of complement for relief. Our juvenile nonhuman primate (Papio baboons) models of endotoxin-free Stx challenge exhibit full spectrum HUS, including thrombocytopenia, hemolytic anemia, and AKI with glomerular thrombotic microangiopathy. There were no significant increases in soluble terminal complement complex (C5b-9) levels after challenge with lethal Stx1 (n = 6) or Stx2 (n = 5) in plasma samples from T0 to euthanasia at 49.5 to 128 hours post-challenge. d-dimer and cell injury markers (HMGB1, histones) confirmed coagulopathy and cell injury. Thus, complement activation is not required for the development of thrombotic microangiopathy and HUS induced by EHEC Shiga toxins in these preclinical models, and benefits or risks of complement inhibition should be studied further for this infection.

Plasmin-dependent proteolysis of tissue factor pathway inhibitor in a mouse model of endotoxemia

BACKGROUND

The development of a procoagulant state in sepsis, owing to aberrant expression of tissue factor (TF) and a sharp decrease in the level of its major inhibitor, TF pathway inhibitor (TFPI), could lead to microthrombotic organ failure. The mechanism for the decline in TFPI activity in the lung could involve plasmin-mediated cleavage of the inhibitor.

OBJECTIVE

To investigate the effect of plasmin generation on lung-associated TFPI activity, in normal conditions and during infusion of endotoxin (lipopolysaccharide [LPS]) in mice.

METHODS

Plasmin generation and TFPI activity were assayed in the lungs of mice deficient in tissue-type plasminogen (Plg) activator (t-PA) or Plg, at 2 h after LPS or saline injection.

RESULTS

The sharp loss of lung-associated TFPI activity at 2 h after LPS challenge paralleled the abrupt increase in plasmin generation. TFPI activity was significantly retained in both t-PA(-/-) and Plg(-/-) mice, which are unable to generate plasmin.

CONCLUSION

The increased plasmin generation during the early stages of sepsis could cleave/inactivate TFPI and thus lead to thrombotic complications.

Pathophysiology, staging and therapy of severe sepsis in baboon models

We review our baboon models of Escherichia coli sepsis that mimic, respectively, the shock/disseminated intravascular coagulation (DIC) and organ failure variants of severe sepsis, and analyse the pathophysiologic processes that are unique to each. The multi-stage, multi-factorial characteristics of severe sepsis develop as a result of the initial insult, which - depending on its intensity - activates components of the intravascular compartment leading to overwhelming shock/DIC; or initiates a sequence of events involving both the intra- and extravascular (tissues) compartments that lead to organ failure. In the latter case, the disorder passes through two stages: an initial inflammatory/coagulopathic intravascular first stage triggered by E. coli, followed by an extravascular second stage, involving components unique to each organ and triggered by ischemia/reperfusion (oxidative stress and histone release). Although a myriad of overlapping cellular and molecular components are involved, it is the context in which these components are brought into play that determine whether shock/DIC or organ failure predominate. For example, inflammatory and thrombotic responses amplified by thrombin in the first case whereas similar responses are amplified by complement activation products in the second. Rather than blocking specific mediators, we found that attenuation of the thrombin and complement amplification pathways can effectively reverse the shock/DIC and organ failure exhibited by the LD(100) and LD(50) E. coli models of severe sepsis, respectively. Translation of these concepts to successful intervention in the respective baboon models of E. coli sepsis and the application to their clinical counterparts is described.

Preclinical sepsis models

BACKGROUND

A variety of sepsis models have been used to unravel pathophysiologic processes and to examine the effects of novel therapeutic interventions. The lack of therapeutic efficacy of numerous compounds in clinical sepsis trials, despite glorious results in animal models of sepsis, has raised doubt and debate about the usefulness of such models.

METHODS

Review of the pertinent literature.

RESULTS

Many sepsis models have been described, none of which is ideal. Clinical sepsis can originate from different sources, can be accompanied by many complicating conditions, and strikes human beings with strongly variable genetic backgrounds, co-morbidities, and drug usages. To provide answers to the three main objectives of research-insight into the regulation of normal host defense mechanisms in the early stages of infection; the mechanisms underlying dysregulation of the host response; and proof of principle for the mechanism of action of novel therapeutic agents and to establish their efficacy and potential harm-diverse models are required. The future of sepsis research lies in the systematic combination of models, together with in vitro studies and carefully designed and monitored Phase I/II clinical studies.

CONCLUSION

This review discusses the nature of various animal sepsis models and the way their results should be interpreted.

Evidence for anti-inflammatory effects of C5a on the innate IL-17A/IL-23 axis

There is growing evidence that the complement activation product C5a positively or negatively regulates inflammatory functions. The studies presented here report that C5a exerts anti-inflammatory effects by altering production of the cytokines IL-17A and IL-23 during endotoxic shock in young adult male C57BL/6J mice and has similar effects on macrophages from the same mice. IL-17A and IL-23 both appeared in plasma during endotoxemia, and their neutralization improved survival. The relevant sources of IL-17A during endotoxemia were not CD4(+) cells, γδ T cells, or NK cells but CD11b(+)F4/80(+) macrophages. The addition in vitro of C5a to lipopolysaccharide-activated peritoneal macrophages dose dependently antagonized the production of IL-17A (IC(50), 50-100 nM C5a) and IL-23 (IC(50), 10 nM C5a). This suppression required the receptor C5aR, but was independent of the second C5a receptor, C5L2. Genetic absence of C5aR was associated with much higher levels of IL-17A and IL-23 during endotoxic shock. Mechanistically, C5a mediated its effects on the IL-17A/IL-23 axis in a 2-step process. C5a caused activation of the PI3K-Akt and MEK1/2-ERK1/2 pathways, resulting in induction of IL-10, which powerfully inhibited production of IL-17A and IL-23. These data identify previously unknown mechanisms by which the anaphylatoxin C5a limits acute inflammation and antagonizes the IL-17A/IL-23 axis.

Polymicrobial sepsis and endotoxemia promote microvascular thrombosis via distinct mechanisms

BACKGROUND

We reported recently that endotoxemia promotes microvascular thrombosis in cremaster venules of wild-type mice, but not in mice deficient in toll-like receptor 4 (TLR4) or von Willebrand factor (VWF).

OBJECTIVE

To determine whether the clinically relevant model of polymicrobial sepsis induced by cecal ligation/perforation (CLP) induces similar responses via the same mechanisms as endotoxemia.

METHODS

We used a light/dye-injury model of thrombosis in the cremaster microcirculation of wild-type mice and mice deficient in toll-like receptor-4 (C57BL/10ScNJ), toll-like receptor 2 (TLR2), or VWF. Mice underwent CLP or sham surgery, or an intraperitoneal injection of endotoxin (LPS) or saline. In the CLP model, we assessed the influence of fluid replacement on thrombotic responses.

RESULTS

Both CLP and LPS enhanced thrombotic occlusion in wild-type mice. In contrast to LPS, CLP enhanced thrombosis in TLR4- and VWF-deficient strains. While TLR2-deficient mice did not demonstrate enhanced thrombosis following CLP, LPS enhanced thrombosis in these mice. LPS, but not CLP, increased plasma VWF antigen relative to controls. Septic mice, particularly those undergoing CLP, developed significant hemoconcentration. Intravenous fluid replacement with isotonic saline prevented the hemoconcentration and prothrombotic responses to CLP, though fluids did not prevent the prothrombotic response to LPS.

CONCLUSIONS

Polymicrobial sepsis induced by CLP and endotoxemia promote microvascular thrombosis via distinct mechanisms; enhanced thrombosis induced by CLP requires TLR2 but not TLR4 or VWF. The salutary effects of intravenous fluid replacement on microvascular thrombosis in polymicrobial sepsis remain to be characterized.

Histopathology of septic shock induced acute kidney injury: apoptosis and leukocytic infiltration

PURPOSE

Septic shock is one of the leading causes of acute kidney injury. The mechanisms of this injury remain mostly unknown notably because of the lack of data on renal histological lesions in humans.

METHODS

Kidney biopsy was performed immediately post-mortem in consecutive patients who died of septic shock. Comparisons were made with specimens from eight patients who died of trauma on scene and nine ICU patients that died of non-septic causes.

RESULTS

Nineteen septic patients were included, 11 were male, and age was 72 +/- 12 years. Anuria occurred in all patients 2.2 +/- 1.4 days before death. Seven patients had disseminated intravascular coagulation. In all patients we observed (1) acute tubular lesions whose intensity correlated with blood lactate concentration; (2) intense infiltration by leukocytes, mainly monocytic, in glomeruli and interstitial capillaries as compared to controls; (3) presence of tubular cell apoptosis proved by the presence of apoptotic bodies (2.9% of tubular cells) significantly more frequently than in controls and confirmed by TUNEL and activated caspase-3 staining. Arteriolar/arterial thromboses were observed in only 4 of 19 patients, without any association with presence of disseminated intravascular coagulation.

CONCLUSIONS

Kidney lesions in septic shock go beyond those associated with simple acute tubular injury, notably capillary leukocytic infiltration and apoptosis. Vascular thrombosis, however, did not appear to play a major role in the majority of patients. The extent to which these lesions are specific to sepsis or are common to all multi-organ failure independent of its cause is yet to be elucidated. Electronic supplementary material The online version of this article (doi:10.1007/s00134-009-1723-x) contains supplementary material, which is available to authorized users.

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.

Phase 2 trial of eritoran tetrasodium (E5564), a toll-like receptor 4 antagonist, in patients with severe sepsis

OBJECTIVES

Endotoxin is a potent stimulus of proinflammatory response and systemic coagulation in patients with severe sepsis. Endotoxin is a component of Gram-negative bacteria that triggers an innate immune response through Toll-like receptor 4 signaling pathways in myeloid cells. We evaluated safety and tolerability of two dose regimens of eritoran tetrasodium (E5564), a synthetic Toll-like receptor 4 antagonist, and explored whether it decreases 28-day mortality rate in subjects with severe sepsis.

DESIGN

Prospective, randomized, double-blind, placebo-controlled, multicenter, ascending-dose phase II trial.

SETTING

Adult intensive care units in the United States and Canada.

PATIENTS

Three hundred adults within 12 hrs of recognition of severe sepsis, with Acute Physiology and Chronic Health Evaluation (APACHE) II-predicted risk of mortality between 20% and 80%.

INTERVENTIONS

Intravenous eritoran tetrasodium (total dose of either 45 mg or 105 mg) or placebo administered every 12 hrs for 6 days.

MEASUREMENTS AND MAIN RESULTS

Prevalence of adverse events was similar among subjects treated with 45 mg or 105 mg of eritoran tetrasodium or with placebo. For modified intent-to-treat subjects, 28-day all-cause mortality rates were 26.6% (eritoran tetrasodium 105 mg), 32.0% (eritoran tetrasodium 45 mg), and 33.3% in the placebo group. Mortality rate in the eritoran tetrasodium 105-mg group was not significantly different from placebo (p = .335). In prespecified subgroups, subjects at highest risk of mortality by APACHE II score quartile had a trend toward lower mortality rate in the eritoran tetrasodium 105-mg group (33.3% vs. 56.3% placebo group, p = .105). A trend toward a higher mortality rate was observed in subjects in the lowest APACHE II score quartile for the eritoran 105-mg group (12.0% vs. 0.0% placebo group, p = .083).

CONCLUSIONS

Eritoran tetrasodium treatment appears well tolerated. The observed trend toward a lower mortality rate at the 105-mg dose, in subjects with severe sepsis and high predicted risk of mortality, should be further investigated.

Fetal inflammatory response and brain injury in the preterm newborn

Preterm birth can be caused by intrauterine infection and maternal/fetal inflammatory responses. Maternal inflammation (chorioamnionitis) is often followed by a systemic fetal inflammatory response characterized by elevated levels of proinflammatory cytokines in the fetal circulation. The inflammation signal is likely transmitted across the blood-brain barrier and initiates a neuroinflammatory response. Microglial activation has a central role in this process and triggers excitotoxic, inflammatory, and oxidative damage in the developing brain. Neuroinflammation can persist over a period of time and sensitize the brain to subinjurious insults in early and chronic phases but may offer relative tolerance in the intermediate period through activation of endogenous anti-inflammatory, protective, and repair mechanisms. Neuroinflammatory injury not only destroys what exists but also changes what develops.

Immunological response to (1,4)-alpha-D-glucan in the lung and spleen of endotoxin-stimulated juvenile rats

We investigated the effects of (1,4)-alpha-D-glucan (alpha-DG), a novel immune stimulatory drug from Tinospora cordifolia, on the concentration of pro- and anti-inflammatory cytokines (interleukin [IL]-1beta, IL-6, tumour necrosis factor-alpha [TNF-alpha], gamma-interferon [IFN-gamma] and IL-10) in the lung and spleen of endotoxin-stimulated juvenile rats. Experimental groups (n = 16/group) included controls with an intraperitoneal injection of saline, endotoxaemic rats with a non-lethal dose of 10 mg/kg Escherichia coli endotoxin, and endotoxaemic rats treated with two doses of 10 mg/kg alpha-DG, intraperitoneally, 2 and 4 hr after endotoxin injection. At 24 hr of treatment, rats were euthanized and lungs and spleen were removed for cytokines determination and lung injury. Endotoxaemia increased IL-1beta concentration by fivefold in both organs, while creating a moderate pulmonary hypercellularity (demonstrated by about 11% increase in the alveolar-septal thickening and 11% decrease in the alveolar-interstitial space ratio). In the lung, alpha-DG treatment reduced concentrations of IL-1beta by 30% (p > 0.05), IL-6 by 43% (p < 0.01), IFN-gamma by 46% (p < 0.01) and the anti-inflammatory cytokine, IL-10, by 31% (p > 0.05) compared to endotoxaemia. In the spleen, alpha-DG treatment decreased the ratio of IL-1beta to IL-10 by 55% (p < 0.05), demonstrating an anti-inflammatory trend. These data suggest that alpha-DG differentially modulates cytokine response in the lung and spleen and modifies the pro- and anti-inflammatory balance during an early period of endotoxaemia in juvenile rats.

Vascular and dendritic cell coagulation signaling in sepsis progression

The intrinsic signaling networks of the coagulation pathways have recently emerged as crucial determinants for survival in sepsis and systemic inflammatory response syndromes. Protease activated receptor (PAR) 1 is central to both lethality promoting and vascular protective signaling. In the vascular anticoagulant pathway, EPCR/aPC-PAR1 signaling prevents vascular leakage and genetic or acute deficiencies in this pathway promote lethality. In addition, coagulation signaling acts directly on cells of the innate immune system. Dendritic cell (DC) thrombin-PAR1 signaling is coupled to the migration promoting sphingosine 1 phosphate receptor 3 (S1P3). Thrombin generated in the lymphatic compartment perturbs DCs to promote systemic inflammation and disseminated intravascular coagulation in severe sepsis. Signaling-selective aPC variants and selective modulators of the S1P receptor system attenuate sepsis lethality, suggesting novel therapeutic approaches that can be employed to rebalance alterations in the coagulation signaling pathways in severe inflammatory disorders.

Differential role of von Willebrand factor and P-selectin on microvascular thrombosis in endotoxemia

OBJECTIVE

Endotoxin (lipopolysaccharide [LPS]) enhances microvascular thrombosis in mouse cremaster venules. Because von Willebrand factor (vWF) and P-selectin are suggested to mediate LPS-induced platelet-microvessel interactions, we determined whether vWF and P-selectin contribute to microvascular thrombosis in endotoxemia.

METHODS AND RESULTS

A light/dye-induced thrombosis model was used in cremaster microvessels of saline or LPS-injected mice (wild-type, P-selectin-deficient, vWF-deficient, or littermate controls). In each strain except vWF-deficient mice, LPS enhanced thrombosis in venules, resulting in approximately 30% to 55% reduction in times to thrombotic occlusion. LPS had no effect on thrombosis in vWF-deficient mice, although these mice had similar systemic responses to LPS (tachycardia, thrombocytopenia, and plasma coagulation markers). vWF-deficient mice demonstrated prolonged times to thrombotic occlusion relative to littermates. LPS increased plasma vWF in each strain studied. While immunofluorescence in wild-type mice failed to detect LPS-induced differences in microvascular vWF expression, it revealed markedly higher vWF expression in venules relative to arterioles.

CONCLUSIONS

vWF mediates light/dye-induced microvascular thrombosis and endotoxin-induced enhancement of thrombosis in mouse cremaster venules; P-selectin is not required for enhanced thrombosis in response to endotoxin. Enhanced vWF expression in venules relative to arterioles has potential implications for the differences in thrombotic responses among these microvessels.

Does activation of the blood coagulation cascade have a role in malaria pathogenesis?

Plasmodium falciparum infection is often associated with a procoagulant state. Recent identification of tissue factor in the brain endothelium of patients who have died from cerebral malaria casts new light on our understanding of the coagulation disorder found in P. falciparum infection. It has also been revealed that parasitized red blood cells support the assembly of multimolecular coagulation complexes. Tissue factor expression by the endothelium and amplification of the coagulation cascade by parasitized red blood cells and/or activated platelets (particularly at sequestration sites) have crucial roles in mounting and sustaining a coagulation-inflammation cycle which contributes to organ dysfunction and coma in falciparum malaria.

Blood coagulation, inflammation, and malaria

Malaria remains a highly prevalent disease in more than 90 countries and accounts for at least 1 million deaths every year. Plasmodium falciparum infection is often associated with a procoagulant tonus characterized by thrombocytopenia and activation of the coagulation cascade and fibrinolytic system; however, bleeding and hemorrhage are uncommon events, suggesting that a compensated state of blood coagulation activation occurs in malaria. This article (i) reviews the literature related to blood coagulation and malaria in a historic perspective, (ii) describes basic mechanisms of coagulation, anticoagulation, and fibrinolysis, (iii) explains the laboratory changes in acute and compensated disseminated intravascular coagulation (DIC), (iv) discusses the implications of tissue factor (TF) expression in the endothelium of P. falciparum infected patients, and (v) emphasizes the procoagulant role of parasitized red blood cells (RBCs) and activated platelets in the pathogenesis of malaria. This article also presents the Tissue Factor Model (TFM) for malaria pathogenesis, which places TF as the interface between sequestration, endothelial cell (EC) activation, blood coagulation disorder, and inflammation often associated with the disease. The relevance of the coagulation-inflammation cycle for the multiorgan dysfunction and coma is discussed in the context of malaria pathogenesis.

Dendritic cell PAR1-S1P3 signalling couples coagulation and inflammation

Defining critical points of modulation across heterogeneous clinical syndromes may provide insight into new therapeutic approaches. Coagulation initiated by the cytokine-receptor family member known as tissue factor is a hallmark of systemic inflammatory response syndromes in bacterial sepsis and viral haemorrhagic fevers, and anticoagulants can be effective in severe sepsis with disseminated intravascular coagulation. The precise mechanism coupling coagulation and inflammation remains unresolved. Here we show that protease-activated receptor 1 (PAR1) signalling sustains a lethal inflammatory response that can be interrupted by inhibition of either thrombin or PAR1 signalling. The sphingosine 1-phosphate (S1P) axis is a downstream component of PAR1 signalling, and by combining chemical and genetic probes for S1P receptor 3 (S1P3) we show a critical role for dendritic cell PAR1-S1P3 cross-talk in regulating amplification of inflammation in sepsis syndrome. Conversely, dendritic cells sustain escalated systemic coagulation and are the primary hub at which coagulation and inflammation intersect within the lymphatic compartment. Loss of dendritic cell PAR1-S1P3 signalling sequesters dendritic cells and inflammation into draining lymph nodes, and attenuates dissemination of interleukin-1beta to the lungs. Thus, activation of dendritic cells by coagulation in the lymphatics emerges as a previously unknown mechanism that promotes systemic inflammation and lethality in decompensated innate immune responses.

Thrombin-thrombomodulin connects coagulation and fibrinolysis: more than an in vitro phenomenon

Thrombin activatable fibrinolysis inhibitor (TAFI), when activated, forms a basic carboxypeptidase that can inhibit fibrinolysis. Potential physiologic activators include both thrombin and plasmin. In vitro, thrombomodulin and glycosaminoglycans increase the catalytic efficiency of TAFI activation by thrombin and plasmin, respectively. The most relevant (patho-) physiologic activator of TAFI has not been disclosed. Our purpose was to identify the physiologic activator of TAFI in vivo. Activation of protein C (a thrombin-thrombomodulin-dependent reaction), prothrombin, and plasminogen occurs during sepsis. Thus, a baboon model of Escherichia coli-induced sepsis, where multiple potential activators of TAFI are elaborated, was used to study TAFI activation. A monoclonal antibody (mAbTAFI/TM#16) specifically inhibiting thrombin-thrombomodulin-dependent activation of TAFI was used to assess the contribution of thrombin-thrombomodulin in TAFI activation in vivo. Coinfusion of mAbTAFI/TM#16 with a lethal dose of E coli prevented the complete consumption of TAFI observed without mAbTAFI/TM#16. The rate of fibrin degradation products formation is enhanced in septic baboons treated with the mAbTAFI/TM#16; therefore, TAFI activation appears to play a key role in the extent of fibrin(ogen) consumption during E coli challenge, and thrombin-thrombomodulin, in a baboon model of E coli-induced sepsis, appears to be the predominant activator of TAFI.

Activated protein C

Protein C is a vitamin K-dependent plasma protein zymogen whose genetic mild or severe deficiencies are linked with risk for venous thrombosis or neonatal purpura fulminans, respectively. Studies over past decades showed that activated protein C (APC) inactivates factors (F) Va and VIIIa to down-regulate thrombin generation. More recent basic and preclinical research on APC has characterized the direct cytoprotective effects of APC that involve gene expression profile alterations, anti-inflammatory and anti-apoptotic activities and endothelial barrier stabilization. These actions generally require endothelial cell protein C receptor (EPCR) and protease activated receptor-1. Because of these direct cytoprotective actions, APC reduces mortality in murine endotoxemia and severe sepsis models and provides neuroprotective benefits in murine ischemic stroke models. Furthermore, APC reduces mortality in patients with severe sepsis (PROWESS clinical trial). Although much remains to be clarified about mechanisms for APC's direct effects on various cell types, it is clear that APC's molecular features that determine its antithrombotic action are partially distinct from those providing cytoprotective actions because we have engineered recombinant APC variants with selective reduction or retention of either anticoagulant or cytoprotective activities. Such APC variants can provide relatively enhanced levels of either cytoprotective or anticoagulant activities for various therapeutic applications. We speculate that APC variants with reduced anticoagulant action but normal cytoprotective actions hold the promise of reducing bleeding risk because of attenuated anticoagulant activity while reducing mortality based on direct cytoprotective effects on cells.

Gene expression profiling identifies C/EBPdelta as a candidate regulator of endotoxin-induced disseminated intravascular coagulation

RATIONALE

A runaway inflammatory response to systemic infection or severe trauma is characterized by the activation of a diversity of pathways, ultimately resulting in the development of disseminated intravascular coagulation (DIC) and multiorgan failure.

OBJECTIVES

Despite increased fundamental knowledge of the pathogenesis of DIC, the exact molecular mechanisms remain elusive. We aimed therefore to improve our understanding of the molecular pathways underlying endotoxin-induced DIC.

METHODS

We performed large-scale gene expression profiling in the liver of mice during the onset of endotoxin-induced DIC. The relevance of an identified candidate gene involved in endotoxin-induced DIC was subsequently assessed in the generalized Shwartzman reaction.

MEASUREMENTS AND MAIN RESULTS

Approximately 5% of over 20,000 genes were differentially regulated. In addition to well-established sepsis-associated genes, such as macrophage inflammatory protein 1, plasminogen activator inhibitor 1, CD14, and A20, we identified several novel candidates for inflammatory disease of which the transcription factor C/EBPdelta (CAAT/enhancer binding protein delta) was studied further. Induction of DIC in C/EBPdelta-deficient mice decreased endotoxin-induced systemic inflammation as compared with wild-type mice, as evident from decreased plasma levels of tumor necrosis factor-alpha and IL-6. In addition, C/EBPdelta deficiency partly protected against DIC-induced mortality. Interestingly, C/EBPdelta deficiency seemed mainly protective by improving renal function. This latter notion was confirmed in an experimental model of renal ischemia/reperfusion injury in which C/EBPdelta deficiency reduced ischemia/reperfusion-induced creatinine and urea levels.

CONCLUSIONS

Our results endorse the usefulness of gene expression profiling in identifying novel mediators of DIC by showing that C/EBPdelta regulates specific pathologic features of this endotoxin-induced syndrome.

Temporal dynamics of gene expression in the lung in a baboon model of E. coli sepsis

Background

Bacterial invasion during sepsis induces disregulated systemic responses that could lead to fatal lung failure. The purpose of this study was to relate the temporal dynamics of gene expression to the pathophysiological changes in the lung during the first and second stages of E. coli sepsis in baboons.

Results

Using human oligonucleotide microarrays, we have explored the temporal changes of gene expression in the lung of baboons challenged with sublethal doses of E. coli. Temporal expression pattern and biological significance of the differentially expressed genes were explored using clustering and pathway analysis software. Expression of selected genes was validated by real-time PCR. Cytokine levels in tissue and plasma were assayed by multiplex ELISA. Changes in lung ultrastructure were visualized by electron microscopy. We found that genes involved in primary inflammation, innate immune response, and apoptosis peaked at 2 hrs. Inflammatory and immune response genes that function in the stimulation of monocytes, natural killer and T-cells, and in the modulation of cell adhesion peaked at 8 hrs, while genes involved in wound healing and functional recovery were upregulated at 24 hrs.

Conclusion

The analysis of gene expression modulation in response to sepsis provides the baseline information that is crucial for the understanding of the pathophysiology of systemic inflammation and may facilitate the development of future approaches for sepsis therapy.

Plasmodium falciparum-infected erythrocytes induce tissue factor expression in endothelial cells and support the assembly of multimolecular coagulation complexes

BACKGROUND

Plasmodium falciparum malaria infects 300-500 million people every year, causing 1-2 million deaths annually. Evidence of a coagulation disorder, activation of endothelial cells (EC) and increase in inflammatory cytokines are often present in malaria.

OBJECTIVES

We have asked whether interaction of parasitized red blood cells (pRBC) with EC induces tissue factor (TF) expression in vitro and in vivo. The role of phosphatidylserine-containing pRBC to support the assembly of blood coagulation complexes was also investigated.

RESULTS

We demonstrate that mature forms of pRBC induce functional expression of TF by EC in vitro with productive assembly of the extrinsic Xnase complex and initiation of the coagulation cascade. Late-stage pRBC also support the prothrombinase and intrinsic Xnase complex formation in vitro, and may function as activated platelets in the amplification phase of the blood coagulation. Notably, post-mortem brain sections obtained from P. falciparum-infected children who died from cerebral malaria and other causes display a consistent staining for TF in the EC.

CONCLUSIONS

These findings place TF expression by endothelium and the amplification of the coagulation cascade by pRBC and/or activated platelets as potentially critical steps in the pathogenesis of malaria. Furthermore, it may allow investigators to test other therapeutic alternatives targeting TF or modulators of EC function in the treatment of malaria and/or its complications.

The cytoprotective protein C pathway

Protein C is best known for its mild deficiency associated with venous thrombosis risk and severe deficiency associated with neonatal purpura fulminans. Activated protein C (APC) anticoagulant activity involves proteolytic inactivation of factors Va and VIIIa, and APC resistance is often caused by factor V Leiden. Less known is the clinical success of APC in reducing mortality in severe sepsis patients (PROWESS trial) that gave impetus to new directions for basic and preclinical research on APC. This review summarizes insights gleaned from recent in vitro and in vivo studies of the direct cytoprotective effects of APC that include beneficial alterations in gene expression profiles, anti-inflammatory actions, antiapoptotic activities, and stabilization of endothelial barriers. APC's cytoprotection requires its receptor, endothelial cell protein C receptor, and protease-activated receptor-1. Because of its pleiotropic activities, APC has potential roles in the treatment of complex disorders, including sepsis, thrombosis, and ischemic stroke. Although much about molecular mechanisms for APC's effects on cells remains unclear, it is clear that APC's structural features mediating anticoagulant actions and related bleeding risks are distinct from those mediating cytoprotective actions, suggesting the possibility of developing APC variants with an improved profile for the ratio of cytoprotective to anticoagulant actions.

Sepsis and pathophysiology of anthrax in a nonhuman primate model

Studies that define natural responses to bacterial sepsis assumed new relevance after the lethal bioterrorist attacks with Bacillus anthracis (anthrax), a spore-forming, toxigenic gram-positive bacillus. Considerable effort has focused on identifying adjunctive therapeutics and vaccines to prevent future deaths, but translation of promising compounds into the clinical setting necessitates an animal model that recapitulates responses observed in humans. Here we describe a nonhuman primate (Papio c. cynocephalus) model of B. anthracis infection using infusion of toxigenic B. anthracis Sterne 34F2 bacteria (5 x 10(5) to 6.5 x 10(9) CFU/kg). Similar to that seen in human patients, we observed changes in vascular permeability, disseminated intravascular coagulation, and systemic inflammation. The lung was a primary target organ with serosanguinous pleural effusions, intra-alveolar edema, and hemorrhagic lesions. This animal model reveals that a fatal outcome is dominated by the host septic response, thereby providing important insights into approaches for treatment and prevention of anthrax in humans.

Roles of protease-activated receptors in a mouse model of endotoxemia

Endotoxemia is often associated with extreme inflammatory responses and disseminated intravascular coagulation. Protease-activated receptors (PARs) mediate cellular responses to coagulation proteases, including platelet activation and endothelial cell reactions predicted to promote inflammation. These observations suggested that PAR activation by coagulation proteases generated in the setting of endotoxemia might promote platelet activation, leukocyte-mediated endothelial injury, tissue damage, and death. Toward testing these hypotheses, we examined the effect of PAR deficiencies that ablate platelet and endothelial activation by coagulation proteases in a mouse endotoxemia model. Although coagulation was activated as measured by thrombin-antithrombin (TAT) production and antithrombin III (ATIII) depletion, Par1(-/-), Par2(-/-), Par4(-/-), Par2(-/-):Par4(-/-), and Par1(-/-):Par2(-/-) mice all failed to show improved survival or decreased cytokine responses after endotoxin challenge compared with wild type. Thus, our results fail to support a necessary role for PARs in linking coagulation to inflammation or death in this model. Interestingly, endotoxin-induced thrombocytopenia was not diminished in Par4(-/-) mice. Thus, a mechanism independent of platelet activation by thrombin was sufficient to cause thrombocytopenia in our model. These results raise the possibility that decreases in platelet count in the setting of sepsis may not be caused by disseminated intravascular coagulation but instead report on a sometimes parallel but independent process.

Prognostic value of a simple evolving disseminated intravascular coagulation score in patients with severe sepsis

OBJECTIVE

We postulated that the coagulopathy initiated by the inflammatory response to severe sepsis would be reflected by changes in the platelet count and prothrombin time that convey prognostic information. To examine this hypothesis, we looked at the utility of a simple evolving disseminated intravascular coagulation (DIC) score that awarded 1 point for each of the following: a) an absolute platelet count <100 x 10/L; b) a prothrombin time >15.0 secs; c) a 20% decrease in platelets; and d) a >0.3-sec increase in prothrombin time in predicting outcome in patients with severe sepsis.

DESIGN

Prospective observational study.

SETTING

Intensive care units of university medical center.

PATIENTS

Patients were 163 critically ill severe sepsis patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were clinically classified as having capillary leak syndrome (n = 24), multiple organ failure with death from sepsis (n = 37), or multiple organ failure with recovery (n = 57) or as well (n = 45) if they showed rapid improvement in their modified Multiple Organ Dysfunction Syndrome (MODS) score (which did not score for thrombocytopenia). Patients with capillary leak syndrome had the highest Acute Physiology and Chronic Health Evaluation II score, modified MODS, and prothrombin time and the lowest platelet counts, whereas well patients had the most normal values. The simple evolving DIC score increased with worsening clinical class and was associated with worsening organ failure (increased modified MODS). Mortality rate increased from 10% for a simple evolving score of 0 to 73% for a score of 4 (p < .01). Overall, 86% of those with a score < or =1 survived, whereas 85% of those with a score of > or =2 developed multiple organ failure and half of them died from sepsis.

CONCLUSIONS

The simple evolving DIC score calculated in the first 48 hrs from two readily available global coagulation markers appears to reflect the severity of the underlying disorder. It can be easily calculated at the bedside and provides useful prognostic information for the patient with severe sepsis.

Tissue factor-dependent coagulation is preferentially up-regulated within arterial branching areas in a baboon model of Escherichia coli sepsis

Endothelium plays a critical role in the pathobiology of sepsis by integrating systemic host responses and local rheological stimuli. We studied the differential expression and activation of tissue factor (TF)-dependent coagulation on linear versus branched arterial segments in a baboon sepsis model. Animals were injected intravenously with lethal doses of Escherichia coli or saline and sacrificed after 2 to 8 hours. Whole-mount arterial segments were stained for TF, TF-pathway inhibitor (TFPI), factor VII (FVII), and markers for endothelial cells (ECs), leukocytes, and platelets, followed by confocal microscopy and image analysis. In septic animals, TF localized preferentially at branches, EC surface, leukocytes, and platelet aggregates and accumulated in large amounts in the subendothelial space. FVII strongly co-localized with TF on ECs and leukocytes but less so with subendothelial TF. TFPI co-localized with TF and FVII on endothelium and leukocytes but not in the subendothelial space. Focal TF increases correlated with fibrin deposition and increased endothelial permeability to plasma proteins. Biochemical analysis confirmed that aortas of septic baboons expressed more TF mRNA and protein than controls. Branched segments contained higher TF protein levels and coagulant activity than equivalent linear areas. These data suggest that site-dependent endothelial heterogeneity and rheological factors contribute to focal procoagulant responses to E. coli.

The endothelium in intensive care

This article reviews the major role that the vascular endothelium plays in pathophysiological processes related to metabolism, vascular function, and blood coagulation. Normally an antithrombotic surface, inflammation activates endothelium to become a prothrombotic and pro-inflammatory interface that is critically involved in multi-organ failure in patients with severe systemic diseases including sepsis. Improving endothelial functions in sepsis is a major therapeutic challenge.

In vitro evaluation of blood coagulation activation and microthrombus formation by a microchannel array flow analyzer

An in vitro assay system for evaluating microthrombus formation in whole blood has not yet been established. In this study, we characterized the relationship between coagulation activation and capillary occlusion in an in vitro assay system using a microchannel array flow analyzer (MC-FAN), which can evaluate microthrombus formation in whole blood as a function of blood flow rate. The flow rate of lipopolysaccharide (LPS)-treated whole blood decreased in a dose- and time-dependent manner. Addition of LPS-pretreated mononuclear cells (PBMCs) to whole blood also decreased the flow rate. Treatment with an anti-tissue factor (TF) antibody blocked the LPS-induced decrease in blood flow rate, suggesting that TF expressed on PBMCs is responsible for decreased blood flow in the microchannels. Known anticoagulants and anti-platelet agents also inhibited the LPS-induced decrease in blood flow rate. Thrombin-antithrombin complexes were increased in LPS-stimulated whole blood, and decreased by anticoagulants but not by anti-platelet agents. These findings suggest that occlusion in microchannels occurs mainly by formation of microthrombi composed of fibrin nets and platelet aggregates, which result from TF expression on activated PBMCs. In addition, the MC-FAN was found to be useful for in vitro evaluation of antithrombotic agents in the capillary.

Mechanisms underlying growth hormone effects in augmenting nitric oxide production and protein tyrosine nitration during endotoxin challenge

The present study defined the effects of GH administration on components of the nitric oxide (NO)-generating cascade to account for observed increases in NO production and protein nitration after an immune challenge. Calves were assigned to groups with or without GH treatment (100 microg GH/kg body weight or placebo im, daily for 12 d) and with or without low-level endotoxin [lipopolysaccharide (LPS), 2.5 microg/kg, or placebo, iv]. Plasma was obtained for estimation of NO changes as [NO(2)(-) + NO(3)(-)] (NO(x)). Transcutaneous liver biopsies were collected for measurement of protein tyrosine nitration, cationic amino acid transporter (CAT)-2 mRNA transporter, and constitutive NO synthase (cNOS), inducible NOS (iNOS), and arginase activity. Liver protein nitration increased more than 10-fold 24 h after LPS and an additional 2-fold in animals treated with GH before LPS. GH increased plasma NO(x) after LPS to levels 27% greater than those measured in non-GH-treated calves. LPS increased CAT-2 mRNA after LPS; GH was associated with a 24% reduction in CAT-2 mRNA content at the peak time response. cNOS activity was 3-fold greater than iNOS after LPS. NOS activities were increased 140% (cNOS) at 3 h and 169% (iNOS) at 6 h, respectively, after LPS; GH treatment increased cNOS activity and the phosphorylation of endothelial NOS after LPS more than 2-fold over that measured in non-GH-treated calves. The data suggest that an increased production of nitrated protein develops in the liver during low-level, proinflammatory stress, and nitration is increased by GH administration through a direct effect on the competing activities of NOS and arginase, modulatable critical control points in the proinflammatory cascade.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.