Effects of thrombomodulin alfa on hemostatic parameters in disseminated intravascular coagulation: Post hoc analysis of a phase 3 randomized controlled trial

New insight into the traditional model of the coagulation cascade and its regulation: illustrated review of a three-dimensional view

The coagulation process relies on an intricate network of three-dimensional structural interactions and subtle biological regulations. In the present review, we illustrate the state of the art of the structural biology of the coagulation cascade by surveying the Protein Data Bank and the EBI AlphaFold databases. Investigations performed in the last decade have provided structural information on essentially all players involved in the process. Indeed, the initial characterization of specific and rather canonical domains has been progressively extended to complicated multidomain proteins. Recently, the application of cryogenic electron microscopy techniques has unraveled the structural features of highly complex coagulation factors, which has led to enhanced understanding. This review initially focuses on the structure of the individual factors as a function of their involvement in intrinsic, extrinsic, and common pathways. A specific emphasis is given to what is known or unknown on the structural basis of each step of the cascade. Available data providing clues on the structural recognition of the factors involved in the functional partnerships of the pathways are illustrated. Recent structures of important complexes formed by these proteins with regulators are described, focusing on the drugs used as anticoagulants and on their reversal agents. Finally, we highlight the different roles that innovative biomolecules such as aptamers may have in the regulation of the cascade.

Coagulation Disorders in Sepsis and COVID-19-Two Sides of the Same Coin? A Review of Inflammation-Coagulation Crosstalk in Bacterial Sepsis and COVID-19

Sepsis is a major cause of morbidity and mortality worldwide. Sepsis-associated coagulation disorders are involved in the pathogenesis of multiorgan failure and lead to a subsequently worsening prognosis. Alongside the global impact of the COVID-19 pandemic, a great number of research papers have focused on SARS-CoV-2 pathogenesis and treatment. Significant progress has been made in this regard and coagulation disturbances were once again found to underlie some of the most serious adverse outcomes of SARS-CoV-2 infection, such as acute lung injury and multiorgan dysfunction. In the attempt of untangling the mechanisms behind COVID-19-associated coagulopathy (CAC), a series of similarities with sepsis-induced coagulopathy (SIC) became apparent. Whether they are, in fact, the same disease has not been established yet. The clinical picture of CAC shows the unique feature of an initial phase of intravascular coagulation confined to the respiratory system. Only later on, patients can develop a clinically significant form of systemic coagulopathy, possibly with a consumptive pattern, but, unlike SIC, it is not a key feature. Deepening our understanding of CAC pathogenesis has to remain a major goal for the research community, in order to design and validate accurate definitions and classification criteria.

Recombinant Human Thrombomodulin Reduces Mortality and Acute Lung Injury Caused by Septic Peritonitis in Rats

This study aimed to investigate the therapeutic effects of recombinant human thrombomodulin (rhTM) on acute lung injury (ALI) caused by sepsis in rats. Rats that underwent cecal ligation and puncture (CLP) were treated with or without rhTM, and then mortality was analyzed. In another set of experiments, ALI was assessed. Furthermore, microthrombosis in the lungs was investigated by immunohistochemistry. Moreover, plasma inflammatory and anti-inflammatory cytokines, such as TNF-α, high-mobility group box chromosomal protein 1 (HMGB-1), and IL-10, were evaluated by ELISA. Production of TNF-α and HMGB-1 by isolated tissue macrophages (Mφs) was assessed in vitro. Mortality after CLP was significantly improved by rhTM treatment. In addition, rhTM treatment improved the wet/dry weight ratio of the lungs, the pulmonary microvascular permeability, and the lung injury scores in animals that underwent CLP. Microthrombosis was detected in the lungs after CLP. These pathophysiological changes were blunted by rhTM treatment. Increased plasma TNF-α and HMGB-1 levels were blunted by rhTM treatment; however, the anti-inflammatory cytokine IL-10 was significantly greater in the rhTM(+) group than in the rhTM(-) group. Increased TNF-α and HMGB-1 production by the tissue Mφs stimulated with LPS were significantly blunted by rhTM treatment in vitro, but the production of IL-10 by the tissue Mφs was not changed in the cells incubated with rhTM. Overall, rhTM improved the mortality caused by septic peritonitis. The possible mechanisms are most likely anti-inflammatory and anticoagulant effects, which lead to the prevention of ALI.

Specific detection of high mobility group box 1 degradation product with a novel ELISA

BACKGROUND

During sepsis or sterile tissue injury, the nuclear protein high mobility group box 1 (HMGB1) can be released to the extracellular space and ultimately into systemic circulation, where it mediates systemic inflammation and remote organ failure. The proinflammatory effects of HMGB1 can be suppressed by recombinant thrombomodulin (rTM), in part through a mechanism involving thrombin-rTM-mediated degradation of HMGB1. Given that HMGB1 is proinflammatory but the HMGB1 degradation product (desHMGB1) is not, an analytical method that discriminates between these two molecules may provide a more in-depth understanding of HMGB1-induced pathogenicity as well as rTM-mediated therapeutic efficiency.

METHODS

A peptide that has a shared amino-terminal structure with desHMGB1 was synthesized. C3H/lpr mice were immunized with the desHMGB1 peptide conjugate, and antibody-secreting hybridoma cells were developed using conventional methods. The reactivity and specificity of the antibodies were then analyzed using antigen-coated enzyme-linked immunosorbent assay (ELISA) as well as antibody-coated ELISA. Next, plasma desHMGB1 levels were examined in a cecal ligation and puncture (CLP)-induced septic mouse model treated with rTM.

RESULTS

Through a series of screening steps, we obtained a monoclonal antibody that recognized desHMGB1 but did not recognize intact HMGB1. ELISA using this antibody specifically detected desHMGB1, which was significantly increased in CLP-induced septic mice treated with rTM compared with those treated with saline.

CONCLUSIONS

In this study, we obtained a desHMGB1-specific monoclonal antibody. ELISA using the novel monoclonal antibody may be an option for the in-depth analysis of HMGB1-induced pathogenicity as well as rTM-mediated therapeutic efficiency.

Endotheliopathy in septic conditions: mechanistic insight into intravascular coagulation

Endothelial cells play a key role in maintaining intravascular patency through their anticoagulant properties. They provide a favorable environment for plasma anticoagulant proteins, including antithrombin, tissue factor pathway inhibitor, and protein C. Under septic conditions, however, the anticoagulant properties of endothelial cells are compromised. Rather, activated/injured endothelial cells can provide a scaffold for intravascular coagulation. For example, the expression of tissue factor, an important initiator of the coagulation pathway, is induced on the surface of activated endothelial cells. Phosphatidylserine, a high-affinity scaffold for gamma-carboxyglutamate domain containing coagulation factors, including FII, FVII, FIX, and FX, is externalized to the outer leaflet of the plasma membrane of injured endothelial cells. Hemodilution decreases not only coagulation factors but also plasma anticoagulant proteins, resulting in unleashed activation of coagulation on the surface of activated/injured endothelial cells. The aberrant activation of coagulation can be suppressed in part by the supplementation of recombinant antithrombin and recombinant thrombomodulin. This review aims to overview the physiological and pathological functions of endothelial cells along with proof-of-concept in vitro studies. The pathophysiology of COVID-19-associated thrombosis is also discussed.