Blockade of GPIIb/IIIa by eptifibatide and tirofiban does not alter tissue factor induced thrombin generation in human endotoxemia

Thromboinflammation in acute injury: infections, heatstroke, and trauma

Tissue microcirculation is essential for the maintenance of organ homeostasis. Following acute infections, activation of coagulation and inflammation, which are critical interconnected responses, lead to thromboinflammation and microthrombosis, thereby contributing to multiorgan dysfunction. Sepsis is the most common underlying disease and has been extensively studied. However, the COVID-19 pandemic further illustrated the pathomechanisms of diseases in which thromboinflammation plays a critical role. During thromboinflammation, injury to monocytes, neutrophils, platelets, and endothelial cells, along with coagulation and complement activation, was further characterized. Thrombin is pivotal in orchestrating thrombosis and inflammation and has long been considered a potential therapeutic target in sepsis. Although thromboprophylaxis for venous thromboembolism with heparins is part of standard management for COVID-19, it also potentially attenuates organ dysfunction due to thrombotic sequela. In contrast, the effectiveness of anticoagulation with heparin, antithrombin, or thrombomodulin to reduce mortality has not conclusively been proven in sepsis. Nonetheless, thromboinflammation has also been reported as an important pathophysiologic mechanism in other critical illnesses, including heatstroke, trauma, and ischemia/reperfusion injury, and may provide a potential therapeutic target for future clinical studies.

Endothelial dysfunction and immunothrombosis in sepsis

Sepsis is a life-threatening clinical syndrome characterized by multiorgan dysfunction caused by a dysregulated or over-reactive host response to infection. During sepsis, the coagulation cascade is triggered by activated cells of the innate immune system, such as neutrophils and monocytes, resulting in clot formation mainly in the microcirculation, a process known as immunothrombosis. Although this process aims to protect the host through inhibition of the pathogen’s dissemination and survival, endothelial dysfunction and microthrombotic complications can rapidly lead to multiple organ dysfunction. The development of treatments targeting endothelial innate immune responses and immunothrombosis could be of great significance for reducing morbidity and mortality in patients with sepsis. Medications modifying cell-specific immune responses or inhibiting platelet–endothelial interaction or platelet activation have been proposed. Herein, we discuss the underlying mechanisms of organ-specific endothelial dysfunction and immunothrombosis in sepsis and its complications, while highlighting the recent advances in the development of new therapeutic approaches aiming at improving the short- or long-term prognosis in sepsis.

Targeting von Willebrand Factor in Ischaemic Stroke: Focus on Clinical Evidence

Despite great efforts in stroke research, disability and recurrence rates in ischaemic stroke remain unacceptably high. To address this issue, one potential target for novel therapeutics is the glycoprotein von Willebrand factor (vWF), which increases in thrombogenicity especially under high shear rates as it bridges between vascular sub-endothelial collagen and platelets. The rationale for vWF as a potential target in stroke comes from four bodies of evidence. (1) Animal models which recapitulate the pathogenesis of stroke and validate the concept of targeting vWF for stroke prevention and the use of the vWF cleavage enzyme ADAMTS13 in acute stroke treatment. (2) Extensive epidemiologic data establishing the prognostic role of vWF in the clinical setting showing that high vWF levels are associated with an increased risk of first stroke, stroke recurrence or stroke-associated mortality. As such, vWF levels may be a suitable marker for further risk stratification to potentially fine-tune current risk prediction models which are mainly based on clinical and imaging data. (3) Genetic studies showing an association between vWF levels and stroke risk on genomic levels. Finally, (4) studies of patients with primary disorders of excess or deficiency of function in the vWF axis (e.g. thrombotic thrombocytopenic purpura and von Willebrand disease, respectively) which demonstrate the crucial role of vWF in atherothrombosis. Therapeutic inhibition of VWF by novel agents appears particularly promising for secondary prevention of stroke recurrence in specific sub-groups of patients such as those suffering from large artery atherosclerosis, as designated according to the TOAST classification.

Review: From therapy to experimental model: a hundred years of endotoxin administration to human subjects

This article is a review of studies in which endotoxin has been administered to human subjects for experimental purposes. Data are presented in tabular form so the reader can better appreciate the objectives of individual studies. Although the original intention was to focus on the adverse events associated with these studies, unexpected serious adverse events rarely have been reported.

P2Y12 receptor inhibition and LPS-induced coagulation

Platelets play a major role in the complex interactions involved in blood coagulation via multiple mechanisms. As reported in this issue, Schoergenhofer et al. tested the hypothesis that platelet inhibition by prasugrel, a potent platelet P2Y12 ADP receptor antagonist, attenuates the effect of lipopolysaccharide (LPS) on the blood coagulation system in healthy human subjects. LPS, a bacterial product with potent pro-inflammatory and pro-thrombotic effects, plays a central role in sepsis. It activates monocytes and endothelial cells via Toll-like receptor (TLR) 4 and other TLRs to stimulate production of TF and other pro-coagulant molecules, chemokines and cytokines. Treatment with prasugrel did not decrease biomarkers of coagulaion. A better understanding of the relative roles of platelet and coagulation mechanisms in triggering the pro-thrombotic state may lead to more effective antithrombotic strategies.

Procoagulant microparticles promote coagulation in a factor XI-dependent manner in human endotoxemia

Essentials The procoagulant effects of microparticles (MPs) on coagulation in endotoxemia are not known. MPs from endotoxemia volunteers were evaluated for procoagulant activity in a plasma milieu. MPs from endotoxemia volunteers shortened clotting times and enhanced thrombin generation. MP procoagulant effects were mediated in a factor XI-dependent manner.

SUMMARY

Background Human endotoxemia is characterized by acute inflammation and activation of coagulation, as well as increased numbers of circulating microparticles (MPs). Whether these MPs directly promote coagulation and through which pathway their actions are mediated, however, has not been fully explored. Objectives In this study, we aimed to further characterize endotoxin-induced MPs and their procoagulant properties using several approaches. Methods Enumeration and characterization of MPs were performed using a new-generation flow cytometer. Relative contributions of the extrinsic and intrinsic pathways in MP-mediated procoagulant activity were assessed using plasmas deficient in factor (F) VII or FXI or with blocking antibodies to tissue factor (TF) or FXIa. Results Total MPs and platelet MPs were significantly elevated in plasma at 6 h after infusion of endotoxin in healthy human subjects. MPs isolated from plasma following endotoxin infusion also demonstrated increased TF activity in a reconstituted buffer system. When added to recalcified platelet-poor plasma, these MPs also promoted coagulation, as judged by a decreased clotting time with shortening of the lag time and time to peak thrombin using calibrated automated thrombography (CAT). However, the use of FVII-deficient plasma or blocking antibody to TF did not inhibit these procoagulant effects. In contrast, plasma clotting time was prolonged in FXI-deficient plasma and a blocking antibody to FXIa inhibited all MP-mediated parameters in the CAT assay. Conclusions The initiation of coagulation by cellular TF in endotoxemia is in contrast to (and presumably complemented by) the intrinsic pathway-mediated procoagulant effects of circulating MPs.

Potent irreversible P2Y12 inhibition does not reduce LPS-induced coagulation activation in a randomized, double-blind, placebo-controlled trial

Intake of prasugrel, a strong P2Y12 receptor inhibitor, does not affect LPS-induced activation of coagulation. Sterile inflammation by LPS increases histone-complexed DNA, a surrogate parameter of neutrophil extracellular trap formation.

The inflammatory response is influenced by FXIII VAL 34 LEU polymorphism in a human LPS model

BACKGROUND

In sepsis, activation of coagulation and inhibition of fibrinolysis lead to microvascular thrombosis. The Val34Leu polymorphism affects the function of FXIII by increasing the rate of FXIII activation by thrombin, which results in an increased and faster rate of fibrin stabilization. Sepsis and multi-organ failure cause disturbance of the normal balance of inflammation and coagulation, one of the most frequent causes of death in ICU patients. Research in polymorphism has shown the possible influence of FXIII in coagulation and inflammation.

METHODS

We analyzed the influence of the common FXIII Val34Leu polymorphism on inflammatory and coagulation parameters in human experimental endotoxinemia. Healthy volunteers (n = 62) received 2 ng endotoxin (LPS) per kg body weight as a bolus infusion over 2 min. We developed a new mutagenic separated PCR assay for determination of the FXIII promoter polymorphism.

RESULTS

FXIII levels were higher for homozygous carriers of the FXIII polymorphism in comparison with wild-type 34 Val/Val and heterozygous 34 Val/Leu. Interestingly, persons homozygous for the FXIII Val34Leu polymorphism had lower monocyte and neutrophil counts throughout the observation period, yet prothrombin fragment 1+2 and D-dimer levels did not differ after LPS challenge.

CONCLUSION

Our findings indicate that the common FXIII Val34Leu polymorphism is associated with differences in monocyte and neutrophil cell counts in response to systemic LPS infusion in humans.

The tumor necrosis factor alpha -308 G/A polymorphism does not influence inflammation and coagulation response in human endotoxemia

Tumor necrosis factor (TNF)-alpha plays a major role in the immune system. Release of proinflammatory cytokines, such as TNF-alpha and interleukin 6, by macrophages and other cells occurs in response to bacterial products. It has been reported that the TNF-alpha -308 G/A polymorphism in the TNF-alpha gene determines basal TNF-alpha levels. We hypothesized that it may also be associated with the degree of inflammatory response in a well-standardized model of systemic inflammation. Eighty-seven young men (age range, 19-35 years) received 2 ng/kg i.v. endotoxin (lipopolysaccharide [LPS]). The TNF-alpha promoter genotype was analyzed on a TaqMan genomic analyzer. Inflammation markers (interleukin 6, TNF-alpha), temperature, and coagulation markers (prothrombin fragment F1+2, D-dimer) were measured at 0, 2, 6, and 24 h after LPS infusion. Tumor necrosis factor-alpha plasma concentrations increased from a baseline 1.3 ng/L (range, 0.8-3.1 ng/L) before LPS infusion to a peak of 57.5 ng/L (range, 10.8-131.4 ng/L) at 2 h after LPS and then decreased continually to 10.8 ng/L (range, 4.7-16.5 ng/L) after 6 h and returned to baseline values after 24 h (1.9 ng/L [range, 1.1-3.9 ng/L]). We observed no significant differences in TNF-alpha baseline levels or in response to LPS after stratification of the data according to TNF-alpha genotype. Basal and peak values of selected inflammatory and coagulation markers were not different between wild-type TNF-alpha -308 individuals (GG) and carriers of the TNF-alpha -308 mutant allele (GA and AA). The TNF-alpha -308 G/A polymorphism does not contribute significantly to the individual variability of systemic TNF-alpha plasma concentrations after endotoxin challenge. Thus, if any, the impact of the TNF-alpha -308 G/A polymorphism on systemic endotoxin-triggered inflammation seems to be limited.

The C-reactive protein (+)1444C/T alteration modulates the inflammation and coagulation response in human endotoxemia

BACKGROUND

C-reactive protein (CRP) plays a major role in the immune system and is an independent risk marker of cardiovascular disease. However, CRP's role in atherogenesis as innocent bystander, causative, or even protective agent, remains unresolved. The (+)1444C/T alteration in the CRP gene has been reported to determine basal CRP concentrations. We hypothesized that this alteration may also be associated with the degree of inflammatory response and coagulation activation in a well-standardized model of systemic inflammation.

METHODS

We administered 2 ng/kg endotoxin [Escherichia coli bacterial lipopolysaccharide (LPS)] intravenously to stimulate inflammation in 91 healthy young Caucasian male paid volunteers (age range, 19-40 years). Participants were confined to bed rest and fasted for 8.5 h after LPS infusion. We collected blood samples before LPS infusion and at 0, 2, 6, and 24 h after LPS infusion to measure inflammation markers [interleukin 6 (IL6), tumor necrosis factor-alpha (TNFalpha)], temperature, and coagulation markers (prothrombin fragment F(1+2), D-dimer). We analyzed the CRP 3' untranslated variant with a mutagenic separated PCR assay.

RESULTS

Basal concentrations of high-sensitivity CRP were approximately 40% lower in (+)1444CC alteration carriers than in T homozygous (TT) allele carriers (P = 0.04). In contrast, basal IL6 concentrations were 2-fold higher in wild-type C homozygous (CC) than in TT individuals (P = 0.01). In response to the LPS challenge, CC individuals had 4-fold higher peak TNFalpha concentrations (P <0.01), >2.5-fold higher peak IL6 concentrations (P <0.01), and increased temperature (P <0.01). Twenty-four hours after LPS challenge, prothrombin fragment F(1+2) concentrations were 75% higher and D-dimer concentrations 50% higher in CC than in TT individuals (P <0.05).

CONCLUSIONS

Genetic factors regulating CRP concentrations also modulate the individual response to endotoxin-stimulated inflammation.

Polymorphism in the tissue factor region is associated with basal but not endotoxin-induced tissue factor-mRNA levels in leukocytes

OBJECTIVE

Tissue factor (TF) plays a central role during disseminated intravascular coagulation (DIC) in sepsis. We hypothesized that a frequent D/I polymorphism, at nucleotide position -1208 in the promoter region, could influence TF-mRNA and downstream coagulation.

METHODS

Basal- and lipopolysaccharide (LPS)-induced TF-mRNA expression, microparticle-associated TF-procoagulant activity and coagulation were determined in healthy men (n = 74) before and after endotoxin (LPS) infusion (2 ng kg(-1)). Basal values of TF-mRNA ranged between 34 and > 37.5 cycles.

RESULTS

Baseline TF-mRNA levels significantly differed between genotypes: I/I carriers had almost 2-fold higher TF-mRNA levels compared to D/D carriers at baseline (P < 0.01). In accordance, higher levels of microparticle-associated TF-procoagulant activity could be seen in I/I carriers. However, the genotype did not affect basal or LPS-induced levels of prothrombin fragment F1+2, D-dimer or cytokines including tumor necrosis factor and interleukin-6.

CONCLUSION

The TF-1208 polymorphism is functional in that it regulates basal TF-mRNA in circulating monocytes and circulating microparticle-associated TF-procoagulant activity in vivo, but does not influence the relative increase in TF-mRNA or coagulation activation during low-grade endotoxemia.

Validation of rotation thrombelastography in a model of systemic activation of fibrinolysis and coagulation in humans

BACKGROUND

Thrombelastography (TEG) is a whole blood assay to evaluate the viscoelastic properties during blood clot formation and clot lysis. Rotation thrombelastography (e.g. ROTEM) has overcome some of the limitations of classical TEG and is used as a point-of-care device in several clinical settings of coagulation disorders. Endotoxemia leads to systemic activation of the coagulation system and fibrinolysis in humans.

OBJECTIVES

We validated whether ROTEM is sensitive to endotoxin induced, tissue factor-triggered coagulation and fibrinolysis and if its measures correlate with biohumoral markers of coagulation and fibrinolysis.

PATIENTS AND METHODS

Twenty healthy male volunteers participated in this randomized placebo-controlled trial. Volunteers received either 2 ng kg(-1) National Reference Endotoxin or saline.

RESULTS

Endotoxemia significantly shortened ROTEM clotting time (CT) by 36% (CI 0.26-0.46; P < 0.05) with a strong inverse correlation with the peak plasma levels of prothrombin fragments (F(1 + 2)) (r = -0.83, P < 0.05). Additionally, endotoxin infusion enhanced maximal lysis (ML) 3.9-fold (CI: 2.5-5.2) compared with placebo or baseline after 2 h (P < 0.05). Peak ML and peak tissue plasminogen activator (t-PA) values correlated excellently (r = 0.82, P < 0.05). ROTEM parameters clot formation time and maximal clot firmness were not affected by LPS infusion, whereas platelet function analyzer (PFA-100) closure times decreased.

CONCLUSIONS

Rotation thrombelastography (ROTEM) detects systemic changes of in vivo coagulation activation, and importantly it is a point of care device, which is sensitive to changes in fibrinolysis in humans. The ex vivo measures CT and ML correlate very well with established in vivo markers of coagulation activation (F(1 + 2)) and fibrinolysis (t-PA), respectively.

The single nucleotide polymorphism Ser128Arg in the E-selectin gene is associated with enhanced coagulation during human endotoxemia

The single nucleotide polymorphism (SNP) Ser128Arg in the E-selectin gene is overrepresented in certain patient groups with atherosclerosis or restenosis. We hypothesized and tested whether it may affect cytokine-induced levels of soluble (s) E-selectin, or be associated with proinflammatory or procoagulant properties in a well-standardized inflammation model. Healthy male volunteers (n = 157) received a lipopolysaccharide (LPS) infusion and were genotyped for the S128R SNP, and outcome parameters were measured by enzyme immunoassays and real-time polymerase chain reaction (RT-PCR, Taqman). The S128R SNP had no pronounced effects on basal or inducible sE-selectin levels, or levels of tumor necrosis factor or interleukin-6. However, carriers of the S128R SNP had 20% higher monocyte counts at 24 hours after LPS infusion. Importantly, the S128R allele enhanced thrombin generation by 50% to 80%, as measured by prothrombin fragment F1+2 (P &lt; .01), and hence fibrin formation (D-dimer) 2-fold (P = .01 to P = .002). However, tissue factor (TF) mRNA levels were not affected. The S128R E-selectin genotype is associated with procoagulant effects in a human model of endotoxin-induced, TF-triggered coagulation. This could contribute to its linkage with various thrombotic cardiovascular disorders.