State of the art article

Cell biology of tissue factor, the principal initiator of blood coagulation

Sepsis is a systemic syndrome involving physiological, pathological, and biochemical abnormalities precipitated by infection and is a major global public health problem. Endothelial cells (ECs) dysfunction is a major contributor to sepsis-induced multiple organ failure. This bibliometric analysis aimed to identify and characterize the status, evolution of the field, and new research trends of ECs and sepsis over the past 20 years.

For this analysis, the Web of Science Core Collection database was searched to identify relevant publications on ECs in sepsis published between January 1, 2002, and December 31, 2022. Microsoft Excel 2021, VOSviewer software, CiteSpace software, and the online analysis platform of literature metrology (http://bibliometric.com) were used to visualize the trends of publications’ countries/regions, institutions, authors, journals, and keywords.

In total, 4200 articles were identified and screened, primarily originating from 86 countries/regions and 3489 institutions. The USA was the leading contributor to this research field, providing 1501 articles (35.74 %). Harvard University's scientists were the most prolific, with 129 articles. Overall, 21,944 authors were identified, among whom Bae Jong Sup was the most prolific, contributing 129 publications. Additionally, Levi Marcel was the most frequently co-cited author, appearing 538 times. The journals that published the most articles were SHOCK, CRITICAL CARE MEDICINE, and PLOS ONE, accounting for 10.79 % of the total. The current emerging hotspots are concentrated on "endothelial glycocalyx," "NLRP3 inflammasome," "extracellular vesicle," "biomarkers," and "COVID-19," among others.

In conclusion, this study provides a comprehensive overview of the scientific productivity and emerging research trends in the field of ECs in sepsis. The evidence supporting the significant role of ECs in both physiological and pathological responses to sepsis is continuously growing. More in-depth studies of the molecular mechanisms underlying sepsis-induced endothelial dysfunction and EC-targeted therapies are warranted in the future.

Blood coagulation is a self-repair process regulated by activated platelet surfaces, clotting factors, and inhibitors. Tissue factor pathway inhibitor (TFPI) is one such inhibitor, well known for its inhibitory action on the active enzyme complex comprising tissue factor (TF) and activated clotting factor VII. This complex forms when TF embedded in the blood vessel wall is exposed by injury and initiates coagulation. A different role for TFPI, independent of TF:VIIa, has recently been discovered whereby TFPI binds a partially cleaved form of clotting factor V (FV-h) and impedes thrombin generation on activated platelet surfaces. We hypothesized that this TF-independent inhibitory mechanism on platelet surfaces would be a more effective platform for TFPI than the TF-dependent one. We examined the effects of this mechanism on thrombin generation by including the relevant biochemical reactions into our previously validated mathematical model. Additionally, we included the ability of TFPI to bind directly to and inhibit platelet-bound FXa. The new model was sensitive to TFPI levels and, under some conditions, TFPI could completely shut down thrombin generation. This sensitivity was due entirely to the surface-mediated inhibitory reactions. The addition of the new TFPI reactions increased the threshold level of TF needed to elicit a strong thrombin response under flow, but the concentration of thrombin achieved, if there was a response, was unchanged. Interestingly, we found that direct binding of TFPI to platelet-bound FXa had a greater anticoagulant effect than did TFPI binding to FV-h alone, but that the greatest effects occurred if both reactions were at play. The model includes activated platelets’ release of FV species, and we explored the impact of varying the FV/FV-h composition of the releasate. We found that reducing the zymogen FV fraction of this pool, and thus increasing the fraction that is FV-h, led to acceleration of thrombin generation.

Tissue factor (TF) is a cellular receptor for coagulation factor VII (FVII), and its activated form, factor Vila (FVIIa). Exposure of TF to blood upon vascular injury leads to TF-FVIIa complex formation, which triggers blood coagulation cascade. In health, TF is constitutively expressed in many extravascular cells, including fibroblasts and pericytes in and surrounding blood vessel walls and lung epithelial cells, but absent from blood cells and endothelial cells that line blood vessel wall. Certain pathological conditions, such as sepsis, induce TF expression in monocytes, and increase the expression in lung, kidney, and other tissues. Such increased TF activity contributes to the procoagulant environment in both intravascular and extravascular compartments. Increased TF expression in parenchymal and recruited lung cells, coupled with transendothelial leakage of plasma proteins, leads to alveolar fibrin deposition. In addition, TF-FVIIa, and downstream coagulant proteases generated by TF-FVIIa amplify multiple steps of the inflammatory response through activation of proteinase-activated receptors (PARs). Both the TF pathway-induced fibrin deposition and cell signaling contribute to the pathogenesis of acute lung injury and organ dysfunction. Blockade of TF attenuates acute lung injury associated with Gram-negative sepsis in experimental animal model systems.

Proteases are essential enzymes involved in multiple biological processes, including the regulation of inflammation. They have been shown to modify cytokine and chemokine activity to initiate and terminate proinflammatory or antiinflammatory responses. The dichotomy in the biological roles that proteases exert is essential to drive acute inflammation toward the resolution phase to later return to homeostasis. However, when left unchecked, proteases can also promote inflammatory diseases. In acute inflammatory diseases, such as sepsis, proteases play key roles in the coagulation cascade, leading to a hypercoagulable state and cytokine storms. In chronic inflammatory diseases, such as Crohn’s disease, proteases can regulate leukocyte recruitment, tissue damage, and impact resistance to certain treatments. Importantly, proteases play both protective and detrimental roles in inflammatory diseases. Therefore, a better characterization of their roles in inflammation could result in new drug targets’ identification and more effective treatment plans for patients.

Monocytes are active at the crossroads between inflammation and coagulation processes since they can secrete pro-inflammatory cytokines and express tissue factor (TF), a major initiator of coagulation. Cobalt-chrome (CoCr), a metal alloy, used as a biomaterial for vascular stents, has been shown to be potentially pro-thrombotic and pro-inflammatory. Research work with a polymer from a family of degradable-polar hydrophobic ionic polyurethanes (D-PHI), called HHHI, has been shown to exhibit anti-inflammatory responses from human monocytes. We have generated multifunctional polyurethane thin films (MPTF) based on the HHHI chemistry, as a thin coating for CoCr and have evaluated the reactivity of blood with MPTF-coated CoCr. The results showed that the coating of CoCr with MPTF derived from HHHI prevents thrombin generation, reduces coagulation activation, and suppresses fibrin formation in whole blood. Activation of monocytes was also suppressed at the surface of MPTF-coated CoCr and specifically the decrease in thrombin generation was accompanied by a significant decrease in TF and pro-inflammatory cytokine levels. Mass spectroscopy of the adsorbed proteins showed lower levels of fibrinogen, fibronectin and complement C3, C4, and C8 when compared to CoCr. We can conclude that MPTFs reduce the pro-thrombotic and pro-inflammatory phenotype of monocytes and macrophages on CoCr, and prevent clotting in whole blood.