Effects of tranexamic acid on fibrinolysis, fibrinogenolysis and amidolysis

Fibrin-Dextran Hydrogels with Tunable Porosity and Mechanical Properties

Hydrogels as scaffolds in tissue engineering have gained increasing attention in recent years. Natural hydrogels, e.g., collagen or fibrin, are limited by their weak mechanical properties and fast degradation, whereas synthetic hydrogels face issues with biocompatibility and biodegradation. Therefore, combining natural and synthetic polymers to design hydrogels with tunable mechanical stability and cell affinity for biomedical applications is of interest. By using fibrin with its excellent cell compatibility and dextran with controllable mechanical properties, a novel bio-based hydrogel can be formed. Here, we synthesized fibrin and dextran-methacrylate (MA)-based hydrogels with tailorable mechanical properties, controllable degradation, variable pore sizes, and ability to support cell proliferation. The hydrogels are formed through in situ gelation of fibrinogen and dextran-MA with thrombin and dithiothreitol. Swelling and nuclear magnetic resonance diffusometry measurements showed that the water uptake and mesh sizes of fabricated hydrogels decrease with increasing dextran-MA concentrations. Cell viability tests confirm that these hydrogels exhibit no cytotoxic effect.

A Multifunctional, Low-Volume Resuscitation Cocktail Improves Vital Organ Blood Flow and Hemostasis in a Pig Model of Polytrauma with Traumatic Brain Injury

The resuscitation of polytrauma with hemorrhagic shock and traumatic brain injury (TBI) is a balance between permissive hypotension and maintaining vital organ perfusion. There is no current optimal solution. This study tested whether a multifunctional resuscitation cocktail supporting hemostasis and perfusion could mitigate blood loss while improving vital organ blood flow during prolonged limited resuscitation. Anesthetized Yorkshire swine were subjected to fluid percussion TBI, femur fracture, catheter hemorrhage, and aortic tear. Fluid resuscitation was started when lactate concentration reached 3–4 mmol/L. Animals were randomized to one of five groups. All groups received hydroxyethyl starch solution and vasopressin. Low- and high-dose fibrinogen (FBG) groups additionally received 100 and 200 mg/kg FBG, respectively. A third group received TXA and low-dose FBG. Two control groups received albumin, with one also including TXA. Animals were monitored for up to 6 h. Blood loss was decreased and vital organ blood flow was improved with low- and high-dose fibrinogen compared to albumin controls, but survival was not improved. There was no additional benefit of high- vs. low-dose FBG on blood loss or survival. TXA alone decreased blood loss but had no effect on survival, and combining TXA with FBG provided no additional benefit. Pooled analysis of all groups containing fibrinogen vs. albumin controls found improved survival, decreased blood loss, and improved vital organ blood flow with fibrinogen delivery. In conclusion, a low-volume resuscitation cocktail consisting of hydroxyethyl starch, vasopressin, and fibrinogen concentrate improved outcomes compare to controls during limited resuscitation of polytrauma.

Effect of Tranexamic Acid Administration on Postoperative Ecchymosis and Edema in Excision of Lipomas

BACKGROUND

Previous studies have shown that systemic tranexamic acid reduces bleeding during soft tissue surgeries and reduces postoperative ecchymosis and edema experienced by surgical patients.

OBJECTIVE

To evaluate the effect of postoperative tranexamic acid administration on the reduction of ecchymosis and edema after lipoma surgery.

MATERIALS AND METHODS

A total of 40 patients who underwent lipoma excision were included in the comparative analysis. In the tranexamic acid group (n = 20), 1 g of tranexamic acid was administered daily for 5 consecutive postoperative days. Tranexamic acid was not administered to the control group (n = 20). The severity of ecchymosis and edema at the first visit after surgery was rated on a 4-point scale by 2 blinded dermatologists.

RESULTS

The mean interval of the initial visit after surgery was 1.1 ± 0.5 (range: 1-4) days. Mean ecchymosis scores were significantly lower in the tranexamic acid group (0.5 ± 0.8) than in the control group (1.2 ± 1.0) (p < .05). No statistical difference was seen in mean edema scores between groups (0.5 ± 0.6 in tranexamic acid vs 0.7 ± 0.8 in control).

CONCLUSION

We observed that postoperative administration of tranexamic acid significantly decreased ecchymosis in lipoma excision.

Fibrinolysis-resistant carbonylated fibrin detected in thrombi attached to the vascular wall of abdominal aortic aneurysms

In this study, we investigated how carbonylation of fibrinogen by acrolein modified its indispensable function to enhance fibrinolysis after being converted to fibrin and contributed to generating a fibrinolysis-resistant fibrin clot. Acrolein-treated fibrinogen was subjected to tissue plasminogen activator-induced fibrinolysis assay and the effect of lysine residue carbonylation in fibrinogen on fibrinolysis was analyzed. The acrolein-treated fibrinogen-derived fibrin clot appeared more resistant to fibrinolysis and the N-acetyl 3-formyl-3,4-dehydropiperidino (FDP)-Lysine levels in the lysed solution were positively correlated with the duration of clot lysis. The lysine analog 6-amino hexanoic acid (6AHA), which mimics the C-terminal lysine of fibrin, was carbonylated and its enhancing effect on Glu₁-plasminogen activation was evaluated. After incubation with acrolein, 6AHA was converted to N-acetyl FDP-6AHA, losing its ability to enhance Glu₁-plasminogen activation. These results suggest that fibrinogen carbonylation by acrolein to generate N-acetyl FDP-Lysine resulted in the generation of fibrinolysis-resistant fibrin by attenuating the C-terminal lysine-dependent activation of the Glu₁-plasminogen. In abdominal aortic aneurysms, fibrin(ogen) containing the acrolein adduct N-acetyl FDP-Lysine was detected in the vascular wall-attached thrombi. These results suggest that this mechanism is likely involved in the modification of fibrinolysis-resistant thrombi and to their persistence for a long period.

Clinical application of auricular point sticking in perioperative hemostasis for elderly patients with intertrochanteric fractures of the femur

We investigated the clinical application of auricular point sticking (APS) combined with tranexamic acid in perioperative hemostasis in elderly patients with intertrochanteric fractures of the femur.This is a prospective cohort study, and we analyzed 86 elderly patients with intertrochanteric fractures of the femur who underwent closed reduction and internal fixation with proximal femoral nail antirotation (PFNA) between January 2016 and December 2016. The patients were divided into auricular point combined with tranexamic acid group (APS group, n = 43) and tranexamic acid alone group (Control group, n = 43). APS was performed for patients using Vaccaria seeds 1 to 2 days before the operation. The 4 acupoints of hemostasis, including spleen, diaphragm, pituitary, and adrenal gland, as well as acupoint of hip joint, were selected. Routine treatment was performed using tranexamic acid alone in the control group. Blood transfusion, intraoperative, postoperative, and total blood loss were compared between the 2 groups.This study enrolled 36 males and 50 females aged 71 to 93 years (average age: 78.5 years). There were no significant differences in gender, age, height, weight, preoperative hematocrit level, fracture classification, operative time, and hospitalization stay (P > .05). Total blood loss was lower in the APS group than the control group (244.26, 197.87-258.50 ml vs 533.94, 424.00-598.09 ml, P < .01). The blood transfusion rate was 14.0% in the APS group and 34.9% in the control group (P = .02).APS can reduce perioperative bleeding and decrease the need for blood transfusion in elderly patients with intertrochanteric fractures of the femur. This noninvasive method can be applied clinically. Randomized trials may be needed to confirm the findings.

What concentration of tranexamic acid is needed to inhibit fibrinolysis? A systematic review of pharmacodynamics studies

: Intravenous tranexamic acid (TXA) reduces death because of bleeding in patients with trauma and postpartum haemorrhage. However, in some settings intravenous injection is not feasible. To find different routes of administration, we first need to determine the minimal concentration of TXA in the blood that is required to inhibit fibrinolysis.We conducted a systematic review of in-vitro and in-vivo pharmacodynamics studies. We searched MEDLINE, EMBASE, OviSP, and ISI Web of Science from database inception to November 2017 for all in-vitro (including simulated clotting models) or in-vivo studies reporting the relationship between the TXA concentration in blood or plasma and any reliable measure of fibrinolysis.We found 21 studies of which 20 were in vitro and one was in vivo. Most in-vitro studies stimulated fibrinolysis with tissue plasminogen activator and measured fibrinolysis using viscoelastic, optical density, or immunological assays. TXA concentrations between 10 and 15 mg/l resulted in substantial inhibition of fibrinolysis, although concentrations between 5 and 10 mg/l were partly inhibitory.TXA concentrations of 10-15 mg/l may be suitable targets for pharmacokinetic studies, although TXA concentrations above 5 mg/l may also be effective.

Increased urokinase and consumption of α2 -antiplasmin as an explanation for the loss of benefit of tranexamic acid after treatment delay

Essentials Delayed treatment with tranexamic acid results in loss of efficacy and poor outcomes. Increasing urokinase activity may account for adverse effects of late tranexamic acid treatment. Urokinase + tranexamic acid produces plasmin in plasma or blood and disrupts clotting. α2 -Antiplasmin consumption with ongoing fibrinolysis increases plasmin-induced coagulopathy. SUMMARY: Background Tranexamic acid (TXA) is an effective antifibrinolytic agent with a proven safety record. However, large clinical trials show TXA becomes ineffective or harmful if treatment is delayed beyond 3 h. The mechanism is unknown but urokinase plasminogen activator (uPA) has been implicated. Methods Inhibitory mechanisms of TXA were explored in a variety of clot lysis systems using plasma and whole blood. Lysis by tissue plasminogen activator (tPA), uPA and plasmin were investigated. Coagulopathy was investigated using ROTEM and activated partial thromboplastin time (APTT). Results IC50 values for antifibrinolytic activity of TXA varied from < 10 to > 1000 μmol L-1 depending on the system, but good fibrin protection was observed in the presence of tPA, uPA and plasmin. However, in plasma or blood, active plasmin was generated by TXA + uPA (but not tPA) and coagulopathy developed leading to no or poor clot formation. The extent of coagulopathy was sensitive to available α2 -antiplasmin. No clot formed with plasma containing 40% normal α2 -antiplasmin after short incubation with TXA + uPA. Adding purified α2 -antiplasmin progressively restored clotting. Plasmin could be inhibited by aprotinin, IC50 = 530 nmol L-1 , in plasma. Conclusions Tranexamic acid protects fibrin but stimulates uPA activity and slows inhibition of plasmin by α2 -antiplasmin. Plasmin proteolytic activity digests fibrinogen and disrupts coagulation, exacerbated when α2 -antiplasmin is consumed by ongoing fibrinolysis. Additional direct inhibition of plasmin by aprotinin may prevent development of coagulopathy and extend the useful time window of TXA treatment.

Linoleic and palmitoleic acid block streptokinase-mediated plasminogen activation and reduce severity of invasive group A streptococcal infection

In contrast to mild infections of Group A Streptococcus (GAS) invasive infections of GAS still pose a serious health hazard: GAS disseminates from sterile sites into the blood stream or deep tissues and causes sepsis or necrotizing fasciitis. In this case antibiotics do not provide an effective cure as the bacteria are capable to hide from them very quickly. Therefore, new remedies are urgently needed. Starting from a myxobacterial natural products screening campaign, we identified two fatty acids isolated from myxobacteria, linoleic and palmitoleic acid, specifically blocking streptokinase-mediated activation of plasminogen and thereby preventing streptococci from hijacking the host’s plasminogen/plasmin system. This activity is not inherited by other fatty acids such as oleic acid and is not attributable to the killing of streptococci. Moreover, both fatty acids are superior in their inhibitory properties compared to two clinically used drugs (tranexamic or ε-amino caproic acid) as they show 500–1000 fold lower IC₅₀ values. Using a humanized plasminogen mouse model mimicking the clinical situation of a local GAS infection that becomes systemic, we demonstrate that these fatty acids ameliorate invasive GAS infection significantly. Consequently, linoleic and palmitoleic acid are possible new options to combat GAS invasive diseases.

An in vitro study of the effects of t-PA and tranexamic acid on whole blood coagulation and fibrinolysis

AIMS

Acute traumatic coagulopathy is characterised by fibrinolysis and low fibrinogen. It is unclear how much fibrinogenolysis contributes to reduce fibrinogen levels. The study aim was to: investigate in vitro the effects of tissue-plasminogen activator (t-PA) and tranexamic acid (TXA) on coagulation and fibrinolysis.

METHODS

Whole blood was spiked with varying t-PA concentrations. Clauss fibrinogen levels and thrombelastography (TEG, Haemonetics) were performed, including functional fibrinogen level (FLEV). TXA effects were assessed using four TXA concentrations. Recorded parameters from kaolin activated TEG included maximal amplitude (MA), clot strength (G), percentage lysis (LY). Plasmin-antiplasmin complex (PAP), endogenous thrombin potential (ETP), prothrombin fragment 1+2 (PF1+2), factor V and factor VIII levels were all measured.

RESULTS

t-PA induced fibrinolysis: it increased PAP and LY, but decreased MA and G. t-PA induced fibrinogenolysis, with a concentration-dependant decrease in fibrinogen from 2.7 (2.6-3.1) to 0.8 (0.8-0.9) g/L with 60 nM t-PA. FLEV and fibrinogen levels were well correlated. High t-PA doses increased PF1+2, decreased ETP of 19% and FVIII of 63% but not FV. TXA had no effect on plasmin generation as evidenced by no change in PAP. It corrected LY, MA and G and partly protected fibrinogen against fibrinogenolysis: 0.03 mg/mL TXA reduced the fibrinogen fall induced by t-PA 20 nM from 43% to 14%. TXA halved the FVIII fall and increased ETP.

CONCLUSIONS

t-PA induced plasminogen activation and fibrinogenolysis in a concentration-dependant manner. TXA did not affect plasmin activation but reduced fibrinogenolysis. These results suggest that TXA given early in bleeding patients may prevent fibrinogenolysis.

Tranexamic acid in trauma: how should we use it?

Tranexamic acid (TXA) reduces blood loss by inhibiting the enzymatic breakdown of fibrin. It is often used in surgery to decrease bleeding and the need for blood transfusion. In 2011, results from a multi-center, randomized, and placebo-controlled trial (CRASH-2 trial) showed that TXA (1 g loading dose over 10 min followed by an infusion of 1 g over 8 h) safely reduces mortality in bleeding trauma patients. Initiation of TXA treatment within 3 h of injury reduces the risk of hemorrhage death by about one-third, regardless of baseline risk. Because it does not have any serious adverse effects, TXA can be administered to a wide spectrum of bleeding trauma patients. Limiting its use to the most severely injured or those with a diagnosis of 'hyperfibrinolysis' would result in thousands of avoidable deaths. A clinical trial (CRASH-3 trial) of TXA in patients with traumatic brain injury is now in progress.

Mechanism of action of θ-amino acids on plasminogen activation and fibrinolysis induced by staphylokinase

Stimulation of Lys-plasminogen (Lys-Pg) and Glu-plasminogen (Glu-Pg) activation under the action of staphylokinase and Glu-Pg activation under the action of preformed plasmin-staphylokinase activator complex (Pm-STA) by low concentrations and inhibition by high concentrations of omega-amino acids (>90-140 mM) were found. Maximal stimulation of the activation was observed at concentrations of L-lysine, 6-aminohexanoic acid (6-AHA), and trans-(4-aminomethyl)cyclohexanecarboxylic acid 8.0, 2.0, and 0.8 mM, respectively. In contrast, the Lys-Pg activation rate by Pm-STA complex sharply decreased when concentrations of omega-amino acids exceeded the above-mentioned values. It was found that formation of Pm-STA complex from a mixture of equimolar concentrations of staphylokinase and Glu-Pg or Lys-Pg is stimulated by low concentrations (maximal at 10 mM) of 6-AHA. Negligible increase in the specific activities of plasmin and Pm-STA complex was detected at higher concentrations of 6-AHA (to maximal at 70 and 50 mM, respectively). Inhibitory effects of omega-amino acids on the rate of fibrinolysis induced by staphylokinase, Pm-STA complex, and plasmin were compared. It was found that inhibition of staphylokinase-induced fibrinolysis by omega-amino acids includes blocking of the reactions of Pm-STA complex formation, plasminogen activation by this complex, and lysis of fibrin by forming plasmin as a result of displacement of plasminogen and plasmin from the fibrin surface. Thus, the slow stage of Pm-STA complex formation plays an important role in the mechanism of action of omega-amino acids on Glu-Pg activation and fibrinolysis induced by staphylokinase. In addition to alpha-->beta change of Glu-Pg conformation, stimulation of Pm-STA complex formation leads to increase in Glu-Pg activation rate in the presence of low concentrations of omega-amino acids. Inhibition of Pm-STA complex formation on fibrin surface by omega-amino acids is responsible for appearance of long lag phases on curves of fibrinolysis induced by staphylokinase.