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

Biomarkers Predicting Tissue Pharmacokinetics of Antimicrobials in Sepsis: A Review

The pathophysiology of sepsis alters drug pharmacokinetics, resulting in inadequate drug exposure and target-site concentration. Suboptimal exposure leads to treatment failure and the development of antimicrobial resistance. Therefore, we seek to optimize antimicrobial therapy in sepsis by selecting the right drug and the correct dosage. A prerequisite for achieving this goal is characterization and understanding of the mechanisms of pharmacokinetic alterations. However, most infections take place not in blood but in different body compartments. Since tissue pharmacokinetic assessment is not feasible in daily practice, we need to tailor antibiotic treatment according to the specific patient’s pathophysiological processes. The complex pathophysiology of sepsis and the ineffectiveness of current targeted therapies suggest that treatments guided by biomarkers predicting target-site concentration could provide a new therapeutic strategy. Inflammation, endothelial and coagulation activation markers, and blood flow parameters might be indicators of impaired tissue distribution. Moreover, hepatic and renal dysfunction biomarkers can predict not only drug metabolism and clearance but also drug distribution. Identification of the right biomarkers can direct drug dosing and provide timely feedback on its effectiveness. Therefore, this might decrease antibiotic resistance and the mortality of critically ill patients. This article fills the literature gap by characterizing patient biomarkers that might be used to predict unbound plasma-to-tissue drug distribution in critically ill patients. Although all biomarkers must be clinically evaluated with the ultimate goal of combining them in a clinically feasible scoring system, we support the concept that the appropriate biomarkers could be used to direct targeted antibiotic dosing.

The role of endothelial shear stress on haemodynamics, inflammation, coagulation and glycocalyx during sepsis

Sepsis is a multifactorial syndrome primarily determined by the host response to an invading pathogen. It is common, with over 48 million cases worldwide in 2017, and often lethal. The sequence of events in sepsis begins with the damage of endothelium within the microvasculature, as a consequence of the inflammatory and coagulopathic responses to the pathogen that can progress to multiple organ failure and death. Most therapeutic interventions target the inflammation and coagulation pathways that act as an auto-amplified vicious cycle, which, if unchecked can be fatal. Normal blood flow and shear stress acting on a healthy endothelium and intact glycocalyx have anti-inflammatory, anticoagulant and self-repairing effects. During early stages of sepsis, the vascular endothelium and its glycocalyx become dysfunctional, yet they are essential components of resuscitation and recovery from sepsis. The effects of shear forces on sepsis-induced endothelial dysfunction, including inflammation, coagulation, complement activation and microcirculatory breakdown are reviewed. It is suggested that early therapeutic strategies should prioritize on the restoration of shear forces and endothelial function and on the preservation of the endothelial-glycocalyx barrier.

New considerations on pathways involved in acute traumatic coagulopathy: the thrombin generation paradox

Abstract

Background

An acute traumatic coagulopathy (ATC) is observed in about one third of severely traumatized patients. This early, specific, and endogenous disorder is triggered by the association of trauma and hemorrhage. The early phase of this condition is characterized by the expression of a bleeding phenotype leading to hemorrhagic shock and the late phase by a prothrombotic profile leading to multiple organ failure. The physiopathology of this phenomenon is still poorly understood. Hypotheses of disseminated intravascular coagulation, activated protein C-mediated fibrinolysis, fibrinogen consumption, and platelet functional impairment were developed by previous authors and continue to be debated. The objective of this study was to observe general hemostasis disorders in case of ATC to confront these hypotheses.

Method

Four groups of 15 rats were compared: C, control; T, trauma; H, hemorrhage; and TH, trauma and hemorrhage. Blood samples were drawn at baseline and 90 min. Thrombin generation tests, platelet aggregometry, and standard hemostasis tests were performed.

Results

Significant differences were observed between the baseline and TH groups for aPTT (17.9 ± 0.8 s vs 24.3 ± 1.4 s, p < 0.001, mean ± SEM), MAP (79.7 ± 1.3 mmHg vs 43.8 ± 1.3 mmHg, p < 0.001, mean ± SEM), and hemoglobin (16.5 ± 0.1 g/dL vs 14.1 ± 0.3 g/dL, p < 0.001, mean ± SEM), indicating the presence of an hemorrhagic shock due to ATC. Compared to all other groups, coagulation factor activities were decreased in the TH group, but endogenous thrombin potential was (paradoxically) higher than in group C (312 ± 17 nM/min vs. 228 ± 23 nM/min; p = 0.016; mean ± SEM). We also observed a subtle decrease in platelet count and function in case of ATC and retrieved an inversed linear relationship between fibrinogen concentration and aPTT (intercept, 26.53 ± 3.16; coefficient, − 3.40 ± 1.26; adjusted R²: 0.1878; p = 0.0123).

Conclusions

The clinical-biological profile that we observed, combining normal thrombin generation, fibrinogen depletion, and a hemorrhagic phenotype, reinforced the hypothesis of activated protein C mediated-fibrinolysis. The key role of fibrinogen, but not of the platelets, was confirmed in this study. The paradoxical preservation of thrombin generation suggests a protective mechanism mediated by rhabdomyolysis in case of major trauma. Based on these results, we propose a new conception concerning the pathophysiology of ATC.

Post-transcriptional, post-translational and pharmacological regulation of tissue factor pathway inhibitor

: Tissue factor (TF) pathway inhibitor (TFPI) is an endogenous natural anticoagulant that readily inhibits the extrinsic coagulation initiation complex (TF-FVIIa-Xa) and prothrombinase (FXa, FVa and calcium ions). Alternatively, spliced TFPI isoforms (α, β and δ) are expressed by vascular and extravascular cells and regulate thrombosis and haemostasis, as well as cell signalling functions of TF complexes via protease-activated receptors (PARs). Proteolysis of TFPI plays an important role in regulating physiological roles of the TF pathway in host defense and possibly haemostasis. Elimination of TFPI inhibition has therefore been proposed as an approach to improve haemostasis in haemophilia patients. In this review, we focus on posttranscription and translational modification of TFPI and its function in thrombosis and how pharmacological inhibitors and endogenous proteases interfere with TFPI and alter haemostasis.

Anticoagulant Therapy in Sepsis. The Importance of Timing

Sepsis associated coagulopathy is due to the inflammation-induced activation of coagulation pathways concomitant with dysfunction of anticoagulant and fibrinolytic systems, leading to different degrees of haemostasis dysregulation. This response is initially beneficial, contributing to antimicrobial defence, but when control is lost coagulation activation leads to widespread microvascular thrombosis and subsequent organ failure. Large clinical trials of sepsis-related anticoagulant therapies failed to show survival benefits, but posthoc analysis of databases and several smaller studies showed beneficial effects of anticoagulants in subgroups of patients with early sepsis-induced disseminated intravascular coagulation. A reasonable explanation could be the difference in timing of anticoagulant therapy and patient heterogeneity associated with large trials. Proper selection of patients and adequate timing are required for treatment to be successful. The time when coagulation activation changes from advantageous to detrimental represents the right moment for the administration of coagulation-targeted therapy. In this way, the defence function of the haemostatic system is preserved, and the harmful effects of overwhelming coagulation activation are avoided.

Activated factor XI increases the procoagulant activity of the extrinsic pathway by inactivating tissue factor pathway inhibitor

Activation of coagulation factor XI (FXI) may play a role in hemostasis. The primary substrate of activated FXI (FXIa) is FIX, leading to FX activation (FXa) and thrombin generation. However, recent studies suggest the hemostatic role of FXI may not be restricted to the activation of FIX. We explored whether FXI could interact with and inhibit the activity of tissue factor pathway inhibitor (TFPI). TFPI is an essential reversible inhibitor of activated factor X (FXa) and also inhibits the FVIIa-TF complex. We found that FXIa neutralized both endothelium- and platelet-derived TFPI by cleaving the protein between the Kunitz (K) 1 and K2 domains (Lys86/Thr87) and at the active sites of the K2 (Arg107/Gly108) and K3 (Arg199/Ala200) domains. Addition of FXIa to plasma was able to reverse the ability of TFPI to prolong TF-initiated clotting times in FXI- or FIX-deficient plasma, as well as FXa-initiated clotting times in FX-deficient plasma. Treatment of cultured endothelial cells with FXIa increased the generation of FXa and promoted TF-dependent fibrin formation in recalcified plasma. Together, these results suggest that the hemostatic role of FXIa may be attributed not only to activation of FIX but also to promoting the extrinsic pathway of thrombin generation through inactivation of TFPI.

Crosstalk between the coagulation and complement systems in sepsis

Sepsis is a potent activator of the hemostatic and complement systems. While local activation of these proteolytic cascades contributes to the host defense, their uncontrolled systemic activation has major tissue damaging effects that lead to multiple organ failure and death. We have extensively studied the activation of complement and coagulation cascades in experimental sepsis using baboons challenged with live bacteria, such as Gram-negative Escherichia coli or Gram-positive Staphylococcus aureus and Bacillus anthracis, or with the bacterial product peptidoglycan. We observed that these challenges rapidly induce disseminated intravascular coagulation and robust complement activation. We applied a potent C3 convertase inhibitor, compstatin, which prevented sepsis-induced complement activation, reduced thrombocytopenia, decreased the coagulopathic responses, and preserving the endothelial anticoagulant properties. Overall, our work demonstrates that live bacteria and bacterial products activate the complement and coagulation cascades, and that blocking formation of complement activation products, especially during the organ failure stage of severe sepsis could be a potentially important therapeutic strategy.