Tranexamic acid suppresses the release of mitochondrial DNA, protects the endothelial monolayer and enhances oxidative phosphorylation

Tranexamic acid reduces inflammation, edema and burn wound conversion in a rodent model

Burn wound conversion is the observed process where superficial partial thickness burns convert into deep partial or full thickness burn injuries. This conversion process often involves surgical excision to achieve timely wound healing. Unfortunately, the pathophysiology of this phenomenon is multifactorial and poorly understood. Thus, a therapeutic intervention that may prevent secondary progression and cell death in burn-injured tissue is desirable. Recent work by our group and others has established that tranexamic acid (TXA) has significant anti-inflammatory properties in addition to its well-known anti-fibrinolytic effects. This study investigates TXA as a novel therapeutic treatment to mitigate burn wound conversion and reduce systemic inflammation. Sprague-Dawley rats were subjected to a hot comb burn contact injury. A subset of animals underwent a similar comb burn with an adjacent 30%TBSA contact injury. The interspaces represent the ischemic zones simulating the zone of stasis. The treatment group received injections of TXA (100 mg/kg) immediately after injury and once daily until euthanasia. Animals were harvested for analyses at 6 h and 7 days after injury. Full-thickness biopsies from the ischemic zones and lung tissue were assessed with established histological techniques. Plasma was collected for measurement of damage associated molecular patterns (DAMPs), and liver samples were used to study inflammatory cytokines expression. Treatment with TXA was associated with reduced burn wound conversion and decreased burn-induced systemic inflammatory response syndrome (SIRS). Lung inflammation and capillary leak were also significantly reduced in TXA treated animals. Future research will elucidate the underlying anti-inflammatory properties of TXA responsible for these findings.

Fibrinogen Fragment X Mediates Endothelial Barrier Disruption via Suppression of VE-Cadherin

INTRODUCTION

Major traumatic injury is associated with early hemorrhage-related and late-stage deaths due to multiple organ failure (MOF). While improvements to hemostatic resuscitation have significantly reduced hemorrhage-related deaths, the incidence of MOF among trauma patients remains high. Dysregulation of vascular endothelial cell (EC) barrier function is a central mechanism in the development of MOF; however, the mechanistic triggers remain unknown. Accelerated fibrinolysis occurs in a majority of trauma patients, resulting in high circulating levels of fibrin(ogen) degradation products, such as fragment X. To date, the relationship between fragment X and EC dysregulation and barrier disruption is unknown. The goal of this study was to determine the effects of fragment X on EC barrier integrity and expression of paracellular junctional proteins that regulate barrier function.

METHODS

Human lung microvascular endothelial cells (HLMVECs) were treated with increasing concentrations of fragment X (1, 10, and 100 μg/mL), and barrier function was monitored using the xCELLigence live-cell monitoring system. Quantitative PCR (qPCR) was performed to measure changes in EC expression of 84 genes. Immunofluorescent (IF) cytostaining was performed to validate qPCR findings.

RESULTS

Fragment X treatment significantly increased endothelial permeability over time (P < 0.05). There was also a significant reduction in VE-cadherin mRNA expression in fragment X-treated HLMVECs compared to control (P = 0.01), which was confirmed by IF staining.

CONCLUSIONS

Fragment X may induce EC hyperpermeability by reducing VE-cadherin expression. This suggests that a targeted approach to disrupting EC-fragment X interactions could mitigate EC barrier disruption, organ edema, and MOF associated with major trauma.

Tranexamic acid for haemostasis and beyond: does dose matter?

Tranexamic acid (TXA) is a widely used antifibrinolytic agent that has been used since the 1960's to reduce blood loss in various conditions. TXA is a lysine analogue that competes for the lysine binding sites in plasminogen and tissue-type plasminogen activator impairing its interaction with the exposed lysine residues on the fibrin surface. The presence of TXA therefore, impairs the plasminogen and tPA engagement and subsequent plasmin generation on the fibrin surface, protecting fibrin clot from proteolytic degradation. However, critical lysine binding sites for plasmin(ogen) also exist on other proteins and on various cell-surface receptors allowing plasmin to exert potent effects on other targets that are unrelated to classical fibrinolysis, notably in relation to immunity and inflammation. Indeed, TXA was reported to significantly reduce post-surgical infection rates in patients after cardiac surgery unrelated to its haemostatic effects. This has provided an impetus to consider TXA in other indications beyond inhibition of fibrinolysis. While there is extensive literature on the optimal dosage of TXA to reduce bleeding rates and transfusion needs, it remains to be determined if these dosages also apply to blocking the non-canonical effects of plasmin.

Effect of tranexamic acid on endothelial von Willebrand factor/ADAMTS-13 response to in vitro shock conditions

BACKGROUND

Traumatic/hemorrhagic shock, sepsis and other inflammatory processes lead to endothelial activation and a loss of the endothelial glycocalyx. von Willebrand factor (vWF) is an acute phase reactant that is released from endothelial cells and megakaryocytes. Stimulated but not basal vWF leads to significant formation of ultralarge multimers (ultralarge vWF [ULvWF]) and risk for thrombotic complications. Ultralarge vWF is cleaved by a disintegrin and metalloproteinase with a thrombospondin type motif 13 (ADAMTS 13); alterations in ULvWF/ADAMTS 13 ratio may contribute to trauma-induced coagulopathy. Salutary effects of tranexamic acid (TXA) on trauma-induced coagulopathy have been described. These effects appear apart from antifibrinolytic actions of TXA and include protection of the endothelial glycocalyx. Ultralarge vWF is in part anchored to the glycocalyx layer of the endothelium. Tranexamic acid protected the endothelial glycocalyx layer from degradation using a microfluidic model of the microcirculation subjected to hypoxia-reoxygenation and catecholamine excess. We hypothesized that TXA administration following shock conditions would impact the vWF-ADAMTS-13 axis by protecting the glycocalyx from degradation. This was studied in a endothelial microfluidic flow study.

METHODS

Human umbilical vein endothelial cells were established under flow conditions and subjected to biomimetic shock. Tranexamic acid was added after 90 minutes of perfusion. von Willebrand factor antigen and ADAMTS-13 activity were measured. Western blot analysis was performed for vWF characterization from perfusion media.

RESULTS

Shock conditions increased vWF antigen and decreased ADAMTS 13 activity. Tranexamic acid ameliorated shock induced cleavage in the ADAMTS 13-vWF axis with a reduction of the thrombogenic ULvWF.

CONCLUSION

These results suggest another mechanism whereby administration of TXA early following traumatic/hemorrhagic shock mitigates microvascular perfusion abnormalities and subsequent organ failure. The resultant effects on platelet adhesion and aggregation require further study.

Tranexamic acid in pediatric hemorrhagic trauma

ABSTRACT

There is strong evidence in adult literature that tranexamic acid (TXA) given within 3 hours from injury is associated with improved outcomes. The evidence for TXA use in injured children is limited to retrospective studies and one prospective observational trial. Two studies in combat settings and one prospective civilian US study have found association with improved mortality. These studies indicate the need for a randomized controlled trial to evaluate the efficacy of TXA in injured children and to clarify appropriate timing, dose and patient selection. Additional research is also necessary to evaluate trauma-induced coagulopathy in children. Recent studies have identified three distinct fibrinolytic phenotypes following trauma (hyperfibrinolysis, physiologic fibrinolysis, and fibrinolytic shutdown), which can be identified with viscohemostatic assays. Whether viscohemostatic assays can appropriately identify children who may benefit or be harmed by TXA is also unknown.

Tranexamic acid: Beyond antifibrinolysis

Tranexamic acid (TXA) is a popular antifibrinolytic drug widely used in hemorrhagic trauma patients and cardiovascular, orthopedic, and gynecological surgical patients. TXA binds plasminogen and prevents its maturation to the fibrinolytic enzyme plasmin. A number of studies have demonstrated the broad life-saving effects of TXA in trauma, superior to those of other antifibrinolytic agents. Besides preventing fibrinolysis and blood loss, TXA has been reported to suppress posttraumatic inflammation and edema. Although the efficiency of TXA transcends simple inhibition of fibrinolysis, little is known about its mechanisms of action besides the suppression of plasmin maturation. Understanding the broader effects of TXA at the cell, organ, and organism levels are required to elucidate its potential mechanisms of action transcending antifibrinolytic activity. In this article, we provide a brief review of the current clinical use of TXA and then focus on the effects of TXA beyond antifibrinolytics such as its anti-inflammatory activity, protection of the endothelial and epithelial monolayers, stimulation of mitochondrial respiration, and suppression of melanogenesis.

Tranexamic acid and obstetric hemorrhage: give empirically or selectively?

Antifibrinolytic agents such as tranexamic acid (TXA) inhibit the fibrinolytic pathway and protect blood clots from being degraded, thereby promoting hemostasis. They have been used to reduce blood loss in various settings including obstetrics. Based on current evidence, TXA can be considered as a therapeutic adjunct to control postpartum hemorrhage (PPH) after vaginal and cesarean deliveries, with earlier administration preferred. This strategy has been demonstrated to reduce mortality due to bleeding (but not the incidence of transfusion) in developing countries. On the other hand, the benefit-risk ratio of TXA has not been fully assessed in developed countries which have much lower PPH-related mortality rates and better access to other management modalities. As a proposed prophylactic agent to prevent PPH, the level of evidence is currently insufficient to recommend the routine use of TXA to prevent blood loss after vaginal and cesarean deliveries. The results of large new multicenter studies assessing the impact of TXA on maternal blood loss-related outcomes after cesarean delivery are awaited. While most studies to date have focused on empirical and one-size-fit-all dosing of TXA, more selective and individualized treatment protocols (possibly guided by functional coagulation assays) are needed to pave the way for safer and more effective use of this inexpensive and widely used medication.

Trauma-induced coagulopathy

Uncontrolled haemorrhage is a major preventable cause of death in patients with traumatic injury. Trauma-induced coagulopathy (TIC) describes abnormal coagulation processes that are attributable to trauma. In the early hours of TIC development, hypocoagulability is typically present, resulting in bleeding, whereas later TIC is characterized by a hypercoagulable state associated with venous thromboembolism and multiple organ failure. Several pathophysiological mechanisms underlie TIC; tissue injury and shock synergistically provoke endothelial, immune system, platelet and clotting activation, which are accentuated by the 'lethal triad' (coagulopathy, hypothermia and acidosis). Traumatic brain injury also has a distinct role in TIC. Haemostatic abnormalities include fibrinogen depletion, inadequate thrombin generation, impaired platelet function and dysregulated fibrinolysis. Laboratory diagnosis is based on coagulation abnormalities detected by conventional or viscoelastic haemostatic assays; however, it does not always match the clinical condition. Management priorities are stopping blood loss and reversing shock by restoring circulating blood volume, to prevent or reduce the risk of worsening TIC. Various blood products can be used in resuscitation; however, there is no international agreement on the optimal composition of transfusion components. Tranexamic acid is used in pre-hospital settings selectively in the USA and more widely in Europe and other locations. Survivors of TIC experience high rates of morbidity, which affects short-term and long-term quality of life and functional outcome.

Tranexamic acid administration in the field does not affect admission thromboelastography after traumatic brain injury

BACKGROUND

No Food and Drug Administration-approved medication improves outcomes following traumatic brain injury (TBI). A forthcoming clinical trial that evaluated the effects of two prehospital tranexamic acid (TXA) dosing strategies compared with placebo demonstrated no differences in thromboelastography (TEG) values. We proposed to explore the impact of TXA on markers of coagulation and fibrinolysis in patients with moderate to severe TBI.

METHODS

Data were extracted from a placebo-controlled clinical trial in which patients 15 years or older with TBI (Glasgow Coma Scale, 3-12) and systolic blood pressure of ≥90 mm Hg were randomized prehospital to receive placebo bolus/placebo infusion (placebo), 1 g of TXA bolus/1 g of TXA infusion (bolus maintenance), or 2 g of TXA bolus/placebo infusion (bolus only). Thromboelastography was performed, and coagulation measures including prothrombin time, activated partial thromboplastin time, international ratio, fibrinogen, D-dimer, plasmin-antiplasmin (PAP), thrombin antithrombin, tissue plasminogen activator, and plasminogen activator inhibitor 1 were quantified at admission and 6 hours later.

RESULTS

Of 966 patients receiving study drug, 700 had laboratory tests drawn at admission and 6 hours later. There were no statistically significant differences in TEG values, including LY30, between groups (p > 0.05). No differences between prothrombin time, activated partial thromboplastin time, international ratio, fibrinogen, thrombin antithrombin, tissue plasminogen activator, and plasminogen activator inhibitor 1 were demonstrated across treatment groups. Concentrations of D-dimer in TXA treatment groups were less than placebo at 6 hours (p < 0.001). Concentrations of PAP in TXA treatment groups were less than placebo on admission (p < 0.001) and 6 hours (p = 0.02). No differences in D-dimer and PAP were observed between bolus maintenance and bolus only.

CONCLUSION

While D-dimer and PAP levels reflect a lower degree of fibrinolysis following prehospital administration of TXA when compared with placebo in a large prehospital trial of patients with TBI, TEG obtained on admission and 6 hours later did not demonstrate any differences in fibrinolysis between the two TXA dosing regimens and placebo.

LEVEL OF EVIDENCE

Diagnostic test, level III.

Systemic Inflammatory Response Syndrome After Surgery: Mechanisms and Protection

The immune system is an evolutionary hallmark of higher organisms that defends the host against invading pathogens and exogenous infections. This defense includes the recruitment of immune cells to the site of infection and the initiation of an inflammatory response to contain and eliminate pathogens. However, an inflammatory response may also be triggered by noninfectious stimuli such as major surgery, and, in case of an overshooting, still not comprehensively understood reaction, lead to tissue destruction and organ dysfunction. Unfortunately, in some cases, the immune system may not effectively distinguish between stimuli elicited by major surgery, which ideally should only require a modest inflammatory response, and those elicited by trauma or pathogenic infection. Surgical procedures thus represent a potential trigger for systemic inflammation that causes the secretion of proinflammatory cytokines, endothelial dysfunction, glycocalyx damage, activation of neutrophils, and ultimately tissue and multisystem organ destruction. In this review, we discuss and summarize currently available mechanistic knowledge on surgery-associated systemic inflammation, demarcation toward other inflammatory complications, and possible therapeutic options. These options depend on uncovering the underlying mechanisms and could include pharmacologic agents, remote ischemic preconditioning protocols, cytokine blockade or clearance, and optimization of surgical procedures, anesthetic regimens, and perioperative inflammatory diagnostic assessment. Currently, a large gap between basic science and clinically confirmed data exists due to a limited evidence base of translational studies. We thus summarize important steps toward the understanding of the precise time- and space-regulated processes in systemic perioperative inflammation.

[Inflammation and perioperative organ dysfunction]

The immune system is an effective defense against invading pathogens and is accompanied by recruitment of immune cells and initiation of an inflammatory reaction. This can also be triggered by noninfectious stimuli, e.g. a large surgical intervention and cause severe tissue destruction and organ dysfunction. The organism cannot distinguish many stimuli that are released during a large surgical intervention from exogenous pathogens. Therefore, there is a high risk for the occurrence of systemic inflammatory reactions, particularly in large surgical interventions. This excessive immune response leads to release of proinflammatory cytokines, endothelial dysfunction, damage to the glycocalyx, activation of leukocytes as well as tissue and organ destruction. This article summarizes the molecular principles of the surgery-associated inflammatory reaction, the differentiation from other inflammatory complications and treatment options.

Prolonged Cardiopulmonary Bypass is Associated With Endothelial Glycocalyx Degradation

BACKGROUND

The endothelial glycocalyx (EG) is involved in critical regulatory mechanisms that maintain endothelial vascular integrity. We hypothesized that prolonged cardiopulmonary bypass (CPB) may be associated with EG degradation. We performed an analysis of soluble syndecan-1 levels in relation to duration of CPB, as well as factors associated with cell stress and damage, such as mitochondrial DNA (mtDNA) and inflammation.

METHODS

Blood samples from subjects undergoing cardiac surgery with CPB (n = 54) were obtained before and during surgery, 4-8 h and 24 h after completion of CPB, and on postoperative day 4. Flow cytometry was used to determine subpopulations of white blood cells. Plasma levels of mtDNA were determined using quantitative polymerase chain reaction and plasma content of shed syndecan-1 was measured. To determine whether syndecan-1 was signaling white blood cells, the effect of recombinant syndecan-1 on mobilization of neutrophils from bone marrow was tested in mice.

RESULTS

CPB is associated with increased mtDNA during surgery, increased syndecan-1 blood levels at 4-8 h, and increased white blood cell count at 4-8 h and 24 h. Correlation analysis revealed significant positive associations between time on CPB and syndecan-1 (r_s = 0.488, P < 0.001) and level of syndecan-1 and neutrophil count (r_s = 0.351, P = 0.038) at 4-8 h. Intravenous administration of recombinant syndecan-1 in mice resulted in a 2.5-fold increase in the number of circulating neutrophils, concurrent with decreased bone marrow neutrophil number.

CONCLUSIONS

Longer duration of CPB is associated with increased plasma levels of soluble syndecan-1, a signal for EG degradation, which can induce neutrophil egress from the bone marrow. Development of therapy targeting EG shedding may be beneficial in patients with prolonged CPB.