Effects of anticoagulant strategies on activation of inflammation and coagulation

Acute inflammatory events, such as those that occur in sepsis, lead to dysregulation of the coagulation cascade. The hemostatic imbalance in sepsis, characterized by the excessive activation of procoagulant pathways and the impairment of anticoagulant activity, leads to disseminated intravascular coagulation and results in microvascular thrombosis, tissue hypoperfusion and, ultimately, multiple organ failure and death. Furthermore, natural anti-inflammatory mechanisms of the endogenous anticoagulants are diminished by the impaired coagulation. Supportive strategies aiming at inhibiting activation of coagulation and inflammation by treatment with exogenous anticoagulants have been found to be beneficial in experimental and initial clinical studies. This review summarizes the available experimental and clinical data regarding the interaction between coagulation and inflammation, focusing on the two anticoagulants which are in clinical use, antithrombin and activated protein C. Identification of the different biological mechanisms of the two endogenous anticoagulants might help to determine target patient populations as well as to develop new anticoagulant analogs that differ in there respective effects in coagulation and inflammation.     

Anticoagulant modulation of inflammation in severe sepsis

Inflammation and coagulation are so tightly linked that the cytokine storm which accompanies the development of sepsis initiates thrombin activation and the development of an intravascular coagulopathy. This review examines the interaction between the inflammatory and coagulation cascades, as well as the role of endogenous anticoagulants in regulating this interaction and dampening the activity of both pathways. Clinical trials attempting to improve outcomes in patients with severe sepsis by inhibiting thrombin generation with heparin and or endogenous anticoagulants are reviewed. In general, these trials have failed to demonstrate that anticoagulant therapy is associated with improvement in mortality or morbidity. While it is possible that selective patients who are severelyill with a high expected mortality may be shown to benefit from such therapy, at the present time none of these anticoagulants are neither approved nor can they be recommended for the treatment of sepsis.     

New treatment strategies for disseminated intravascular coagulation based on current understanding of the pathophysiology

A variety of clinical conditions may cause systemic activation of coagulation, ranging from insignificant laboratory changes to severe disseminated intravascular coagulation (DIC). DIC consists of a widespread systemic activation of coagulation, resulting in diffuse fibrin deposition in small and midsize vessels. There is compelling evidence from clinical and experimental studies that DIC is involved in the pathogenesis of microvascular dysfunction and contributes to organ failure. In addition, the massive and ongoing activation of coagulation, may result in depletion of platelets and coagulation factors, which may cause bleeding. Recent understanding of important pathogenetic mechanisms that may lead to DIC has resulted in novel preventive and therapeutic approaches to patients with sepsis and a derangement of coagulation. Thrombin generation proceeds via the (extrinsic) tissue factor/factor VIIa route and simultaneously occurring depression of inhibitory mechanisms, such as antithrombin III and the protein C system. Also, impaired fibrin degradation, due to high circulating levels of the fibrinolytic inhibitor plasminogen activator inhibitor, type 1 (PAI-1), contributes to enhanced intravascular fibrin deposition. Interestingly, an extensive cross-talk between activation of inflammation and coagulation exists, where inflammatory mediators (such as cytokines) not only activate the coagulation system, but vice versa activated coagulation proteases and protease inhibitors may modulate inflammation through specific cell receptors. Supportive strategies aimed at the inhibition of coagulation activation may theoretically be justified and have been found beneficial in experimental and initial clinical studies. These strategies comprise inhibition of tissue factor-mediated activation of coagulation or restoration of physiological anticoagulant pathways, for example by means of the administration of recombinant human activated protein C.     

New treatment strategies for disseminated intravascular coagulation based on current understanding of the pathophysiology

A variety of clinical conditions may cause systemic activation of coagulation, ranging from insignificant laboratory changes to severe disseminated intravascular coagulation (DIC). DIC consists of a widespread systemic activation of coagulation, resulting in diffuse fibrin deposition in small and midsize vessels. There is compelling evidence from clinical and experimental studies that DIC is involved in the pathogenesis of microvascular dysfunction and contributes to organ failure. In addition, the massive and ongoing activation of coagulation, may result in depletion of platelets and coagulation factors, which may cause bleeding. Recent understanding of important pathogenetic mechanisms that may lead to DIC has resulted in novel preventive and therapeutic approaches to patients with sepsis and a derangement of coagulation. Thrombin gener‐ation proceeds via the (extrinsic) tissue factor/factor VIIa route and simultaneously occurring depression of inhibitory mechanisms, such as antithrombin III and the protein C system. Also, impaired fibrin degradation, due to high circulating levels of the fibrinolytic inhibitor plasminogen activator inhibitor, type 1 (PAI‐1), contributes to enhanced intravascular fibrin deposition. Interestingly, an extensive cross‐talk between activation of inflammation and coagulation exists, where inflammatory mediators (such as cytokines) not only activate the coagulation system, but vice versa activated coagulation proteases and protease inhibitors may modulate inflammation through specific cell receptors. Supportive strategies aimed at the inhibition of coagulation activation may theoretically be justified and have been found beneficial in experimental and initial clinical studies. These strategies comprise inhibition of tissue factor‐mediated activation of coagulation or restoration of physiological anticoagulant pathways, for example by means of the administration of recombinant human activated protein C.     

Clinical review: Molecular mechanisms underlying the role of antithrombin in sepsis

In disseminated intravascular coagulation (DIC) there is extensive crosstalk between activation of inflammation and coagulation. Endogenous anticoagulatory pathways are downregulated by inflammation, thus decreasing the natural anti-inflammatory mechanisms that these pathways possess. Supportive strategies aimed at inhibiting activation of coagulation and inflammation may theoretically be justified and have been found to be beneficial in experimental and initial clinical studies. This review assembles the available experimental and clinical data on biological mechanisms of antithrombin in inflammatory coagulation activation. Preclinical research has demonstrated partial interference of heparin – administered even at low doses – with the therapeutic effects of antithrombin, and has confirmed – at the level of cellular mechanisms – a regulatory role for antithrombin in DIC. Against this biological background, re-analyses of data from randomized controlled trials of antithrombin in sepsis suggest that antithrombin has the potential to be developed further as a therapeutic agent in the treatment of DIC. Even though there is a lack of studies employing satisfactory methodology, the results of investigations conducted thus far into the mechanisms of action of antithrombin allow one to infer that there is biological plausibility in the value of this agent. Final assessment of the drug's effectiveness, however, must await the availability of positive, prospective, randomized and placebo-controlled studies.     

Clinical review: Molecular mechanisms underlying the role of antithrombin in sepsis

In disseminated intravascular coagulation (DIC) there is extensive crosstalk between activation of inflammation and coagulation. Endogenous anticoagulatory pathways are downregulated by inflammation, thus decreasing the natural anti-inflammatory mechanisms that these pathways possess. Supportive strategies aimed at inhibiting activation of coagulation and inflammation may theoretically be justified and have been found to be beneficial in experimental and initial clinical studies. This review assembles the available experimental and clinical data on biological mechanisms of antithrombin in inflammatory coagulation activation. Preclinical research has demonstrated partial interference of heparin – administered even at low doses – with the therapeutic effects of antithrombin, and has confirmed – at the level of cellular mechanisms – a regulatory role for antithrombin in DIC. Against this biological background, re-analyses of data from randomized controlled trials of antithrombin in sepsis suggest that antithrombin has the potential to be developed further as a therapeutic agent in the treatment of DIC. Even though there is a lack of studies employing satisfactory methodology, the results of investigations conducted thus far into the mechanisms of action of antithrombin allow one to infer that there is biological plausibility in the value of this agent. Final assessment of the drug's effectiveness, however, must await the availability of positive, prospective, randomized and placebo-controlled studies.     

The Loss of Homeostasis in Hemostasis: New Approaches in Treating and Understanding Acute Disseminated Intravascular Coagulation in Critically Ill Patients

Disseminated intravascular coagulation (DIC) profoundly increases the morbidity and mortality of patients who have sepsis. Both laboratory and clinical research advanced the understanding of the biology and pathophysiology of DIC. This, in turn, gave rise to improved therapies and patient outcomes. Beginning with a stimulus causing disruption of vascular integrity, cytokines and chemokines cause activation of systemic coagulation and inflammation. Seemingly paradoxically, the interplay between coagulation and inflammation also inhibits endogenous anticoagulants, fibrinolytics, and antiinflammatory pathways. The earliest documented and best‐studied microbial cause of DIC is the lipopolysaccharide endotoxin of Gram‐negative bacteria. Extensive microvascular thrombi emerge in the systemic vasculature due to dysregulation of coagulation. The result of this unrestrained, widespread small vessel thromboses multiorgan system failure. Consumption of platelets and coagulation factors during this process can lead to an elevated risk of hemorrhage. The management of these patients with simultaneous hemorrhage and thrombosis is complex and challenging. Definitive treatment of DIC, and attenuation of end‐organ damage, requires control of the inciting cause. Currently, activated protein C is the only approved therapy in the United States for sepsis complicated by DIC. Further research is needed in this area to improve clinical outcomes for patients with sepsis. Clin Trans Sci 2012; Volume 5: 85–92     

Pulmonary coagulopathy as a new target in therapeutic studies of acute lung injury or pneumonia--a review

OBJECTIVES: To review the involvement of coagulation and fibrinolysis in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), pulmonary infection, and ventilator-induced lung injury (VILI). DATA SOURCE: Published articles on experimental and clinical studies of coagulation and fibrinolysis in ALI/ARDS, pneumonia, and mechanical ventilation. CONCLUSIONS: Alveolar fibrin deposition is an important feature of ALI/ARDS and pulmonary infection. The mechanisms that contribute to disturbed alveolar fibrin turnover are localized tissue factor-mediated thrombin generation and depression of bronchoalveolar urokinase plasminogen activator-mediated fibrinolysis, caused by the increase of plasminogen activator inhibitors. These effects on pulmonary coagulation and fibrinolysis are regulated by various proinflammatory cytokines and are similar to those found in the intravascular spaces during severe systemic inflammation. Some studies also suggest that pulmonary coagulopathy is a feature of VILI. Recent studies have demonstrated the beneficial effect of anticoagulant therapy in sepsis. Theoretical considerations suggest that this anticoagulant therapy will benefit patients with primary lung pathology including VILI, but clinical studies are needed to examine this hypothesis before such therapy is to be advocated as a standard of care in critically ill patients.     

Science review: Role of coagulation protease cascades in sepsis

Cellular signaling by proteases of the blood coagulation cascade through members of the protease-activated receptor (PAR) family can profoundly impact on the inflammatory balance in sepsis. The coagulation initiation reaction on tissue factor expressing cells signals through PAR1 and PAR2, leading to enhanced inflammation. The anticoagulant protein C pathway has potent anti-inflammatory effects, and activated protein C signals through PAR1 upon binding to the endothelial protein C receptor. Activation of the coagulation cascade and the downstream endothelial cell localized anticoagulant pathway thus have opposing effects on systemic inflammation. This dichotomy is of relevance for the interpretation of preclinical and clinical data that document nonuniform responses to anticoagulant strategies in sepsis therapy.     

Laboratory assessment of the anticoagulant effects of the next generation of oral anticoagulants

Summary. In contrast to vitamin K antagonists, which reduce the functional levels of several coagulation factors, the new oral anticoagulants specifically target either thrombin or factor Xa. These new agents have such predictable pharmacokinetics and pharmacodynamics that routine coagulation monitoring is unnecessary. However, there are still some situations in which measurement of anticoagulant effect may be required. The coagulation assays that are used to monitor heparin derivatives or vitamin K antagonists may not always accurately reflect the anticoagulant activity of the new oral anticoagulants, and specialized assays may be needed. In this article, we: (i) identify situations in which assessment of anticoagulant effect may aid treatment decisions; (ii) describe the effects of the new oral anticoagulants on the various coagulation tests; (iii) review the specialized coagulation assays that have been developed to measure the anticoagulant effects of the new oral anticoagulants; and (iv) provide a clinical perspective on the role of coagulation testing in the clinical management of patients treated with the new oral anticoagulants.     

The normal role of Activated Protein C in maintaining homeostasis and its relevance to critical illness

Thrombin is a multifunctional protein, with procoagulant, inflammatory and anticoagulant effects. Binding of thrombin to thrombomodulin results in activation of Protein C and initiation of the Activated Protein C anticoagulant pathway, a process that is augmented by the endothelial cell Protein C receptor (EPCR). Activated Protein C has demonstrated antithrombotic, anti-inflammatory, and profibrinolytic properties. Its antithrombotic activity is particularly important in the microcirculation, and Protein C deficiency is associated with microvascular thrombosis. Activated Protein C has also been shown to modulate inflammation. When the level of thrombomodulin or Protein C is reduced in sepsis there is a vicious cycle of coagulation and inflammation, with potentially lethal consequences. In vitro studies and animal models have shown that Activated Protein C blunts the inflammatory and coagulant response to sepsis through a variety of mechanisms.     

Individualized "minimal invasive" anticoagulation controlled with D-dimer-antigen testing - a concept

The aim of the proposed concept is to use anticoagulant therapy in prophylaxis and therapy of thromboembolic events only to an extent that the coagulation activation is just not any longer detectable. It results an individualized anticoagulation tailored to the coagulation activation of the patient (individualized "minimal invasive" anticoagulation). Intensity and control of efficiency are to be monitored by measurement of in vivo coagulation activation, e.g. by D-dimer-antigen measurement. Especially with the use of the new oral anticoagulants such a saver anticoagulant therapy - as far as possible from bleeding risk - could open up new indications, which so far are not used because of safety reasons. More patients at risk could be prevented from thromboembolic events. The proposed concept is based on pathophysiological considerations and own clinical experience. It should be evaluated for efficiency in clinical studies.     

Regulation of inflammatory responses by activated protein C: the molecular mechanism(s) and therapeutic implications.

Activated protein C (APC), a natural anticoagulant, is formed from protein C by the action of the thrombin-thrombomodulin (TM) complex on the endothelial cell surface. Endothelial protein C receptor augments the activation of protein C by the thrombin/TM system. APC inactivates the activated form of coagulation factors V and VIII in the presence of protein S. Administration of APC reduced the pulmonary vascular injury and hypotension as well as the coagulation abnormalities by inhibiting production of the tumor necrosis factor-alpha (TNF-alpha) in rats given endotoxin (ET). These therapeutic effects of APC could not be attributed to its anticoagulant effects. APC inhibited ET-induced TNF-alpha production in human monocytes by inhibiting activation of nuclear factor K-B and activator protein-1 in vitro. Administration of the human plasma-derived APC ameliorated coagulation abnormalities without any adverse effects in patients with disseminated intravascular coagulation (DIC). Recombinant APC was reported to reduce the mortality of patients with severe sepsis, and the therapeutic effect was more marked in such patients with overt DIC than those without it. These observations strongly suggest that APC plays important roles in the regulation of inflammation as well as coagulation. Both anti-inflammatory and anticoagulant properties of APC might contribute to the therapeutic usefulness in patients with severe sepsis.     

Coagulation in sepsis: all bugs bite equally

Sepsis almost invariably leads to hemostatic abnormalities, ranging from insignificant laboratory changes to severe disseminated intravascular coagulation. There is compelling evidence from clinical and experimental studies that disseminated intravascular coagulation is involved in the pathogenesis of microvascular dysfunction and contributes to organ failure. Data from the PROWESS phase III clinical trial of recombinant activated protein C in patients with severe sepsis confirm this notion and demonstrate that the vast majority of patients with severe sepsis have increased markers for systemic coagulation activation, decreased physiological anticoagulant proteins and depressed fibrinolysis. There is no correlation between the type of microorganism that has caused the infection and the presence or severity of the coagulation disorder.     

Nebulized anticoagulants for acute lung injury - a systematic review of preclinical and clinical investigations

ABSTRACT: BACKGROUND: Data from interventional trials of systemic anticoagulation for sepsis inconsistently suggest beneficial effects in case of acute lung injury (ALI). Severe systemic bleeding due to anticoagulation may have offset the possible positive effects. Nebulization of anticoagulants may allow for improved local biological availability and as such may improve efficacy in the lungs and lower the risk of systemic bleeding complications. METHOD: We performed a systematic review of preclinical studies and clinical trials investigating the efficacy and safety of nebulized anticoagulants in the setting of lung injury in animals and ALI in humans. RESULTS: The efficacy of nebulized activated protein C, antithrombin, heparin and danaparoid has been tested in diverse animal models of direct (for example, pneumonia-, intra-pulmonary lipopolysaccharide (LPS)-, and smoke inhalation-induced lung injury) and indirect lung injury (for example, intravenous LPS- and trauma-induced lung injury). Nebulized anticoagulants were found to have the potential to attenuate pulmonary coagulopathy and frequently also inflammation. Notably, nebulized danaparoid and heparin but not activated protein C and antithrombin, were found to have an effect on systemic coagulation. Clinical trials of nebulized anticoagulants are very limited. Nebulized heparin was found to improve survival of patients with smoke inhalation-induced ALI. In a trial of critically ill patients who needed mechanical ventilation for longer than two days, nebulized heparin was associated with a higher number of ventilator-free days. In line with results from preclinical studies, nebulization of heparin was found to have an effect on systemic coagulation, but without causing systemic bleedings. CONCLUSION: Local anticoagulant therapy through nebulization of anticoagulants attenuates pulmonary coagulopathy and frequently also inflammation in preclinical studies of lung injury. Recent human trials suggest nebulized heparin for ALI to be beneficial and safe, but data are very limited.     

Inflammation and hemostasis: a bidirectional interaction

There is increasing evidence that inflammation is a potent activator of coagulation pathways. In fact, inflammatory mediators upregulate procoagulant factors, inhibit endogenous anticoagulants and attenuate fibrinolytic response. In addition, systemic inflammation appears to increase platelet reactivity. However, the interaction between these two systems is bidirectional as coagulation is also capable of modulating inflammatory activity. This review focuses on the current understanding of the complex interactions between inflammation and coagulation.     

Anticoagulant therapy for sepsis‐associated disseminated intravascular coagulation: the view from Japan

The current management of disseminated intravascular coagulation (DIC) is based on aggressive treatment of the underlying condition and resuscitation with appropriate blood products. Anticoagulant therapy has appeared and disappeared in the different guidelines and important documents detailing the treatment of DIC. For example, Surviving Sepsis Campaign (SSC) guidelines, the ‘global standard’ for the management of severe sepsis, had recombinant activated protein C highly recommended in the original version, but this was withdrawn in the latest version due to the lack of evidence. In contrast, recent international guidance released from the International Society on Thrombosis and Haemostasis has introduced the potential efficacy of other agents. In sepsis‐related DIC, the basis for anticoagulant therapy comes from the mounting evidence for the anti‐inflammatory effects which these agents possess and can prove beneficial in septic situations. Several studies have clearly shown the important cross‐talk between coagulation and inflammation in patients with sepsis. More recently, neutrophil extracellular traps and damage‐associated molecular patterns (DAMPs), especially histones, have been demonstrated to play a crucial role in the coagulopathy of sepsis. Once again, the natural anticoagulants have an important function in neutralizing the effects of DAMPs and histones. In this review, in addition to examining the important role of anticoagulants in the septic milieu, the clinical studies examining antithrombin, recombinant thrombomodulin and plasma‐derived activated protein C are detailed. However, large‐scale randomized controlled trials are yet to be performed, with important consideration of the timing, dosage and duration of treatment.     

Acenocoumarol decreases tissue factor-dependent coagulation during systemic inflammation in humans

BACKGROUND: Coumarin derivatives are still widely used for prophylaxis of thromboembolic events and therefore represent important comparator substances for new anticoagulants. Measurement of the efficacy of such novel compounds in a human coagulation model with adequate biomarkers could be useful for early-phase clinical drug development. To evaluate the applicability of a well-established model of tissue factor-dependent coagulation for defining anticoagulant potency, we investigated the effects of acenocoumarol in experimental human endotoxemia. METHODS: In a randomized, controlled, 2-by-2 factorial design, healthy volunteers received an infusion of 2 ng/kg endotoxin or placebo after 18 days of pretreatment with acenocoumarol or placebo. Prothrombin fragment 1+2 (F(1+2)), soluble fibrin, and D-dimer were used as markers of thrombin and fibrin formation. RESULTS: As expected, pretreatment with acenocoumarol decreased vitamin K-dependent coagulation factors, but it also decreased spontaneous thrombin formation. Acenocoumarol inhibited endotoxin-induced thrombin generation as measured by F(1+2) levels: endotoxin infusion increased F(1+2) levels 8-fold-from 0.5 to 4.1 nmol/L-in the placebo group, whereas peak F(1+2) levels reached only 1.0 nmol/L in subjects after acenocoumarol pretreatment. This inhibition was also reflected in decreased formation of soluble fibrin and decreased D-dimer levels, showing that depletion of endogenous coagulation factors limits the propagation of nonovert disseminated intravascular coagulation. CONCLUSIONS: Human endotoxemia is a suitable tool for measurement of the efficacy of oral anticoagulants and therefore may become a valuable addition for expeditious pharmacodynamic characterization of lead compounds with anticoagulant potency.     

The role of ethylenediamine tetraacetic acid (EDTA) as in vitro anticoagulant for diagnostic purposes.

Anticoagulants are used to prevent clot formation both in vitro and in vivo. In the specific field of in vitro diagnostics, anticoagulants are commonly added to collection tubes either to maintain blood in the fluid state for hematological testing or to obtain suitable plasma for coagulation and clinical chemistry analyses. Unfortunately, no universal anticoagulant that could be used for evaluation of several laboratory parameters in a sample from a single test tube is available so far. Ethylenediamine tetraacetic acid (EDTA) is a polyprotic acid containing four carboxylic acid groups and two amine groups with lone-pair electrons that chelate calcium and several other metal ions. Calcium is necessary for a wide range of enzyme reactions of the coagulation cascade and its removal irreversibly prevents blood clotting within the collection tube. Historically, EDTA has been recommended as the anticoagulant of choice for hematological testing because it allows the best preservation of cellular components and morphology of blood cells. The remarkable expansion in laboratory test volume and complexity over recent decades has amplified the potential spectrum of applications for this anticoagulant, which can be used to stabilize blood for a variety of traditional and innovative tests. Specific data on the behavior of EDTA as an anticoagulant in hematology, including possible pitfalls, are presented. The use of EDTA for measuring cytokines, protein and peptides, and cardiac markers is described, with an outline of the protection of labile molecules provided by this anticoagulant. The use of EDTA in proteomics and in general clinical chemistry is also described in comparison with other anticoagulants and with serum samples. Finally, the possible uses of alternative anticoagulants instead of EDTA and the potential use of a universal anticoagulant are illustrated.