Inhibitory effects of lysine analogues on t-PA induced whole blood clot lysis

Chemical Adjustment of Fibrinolysis

Fibrinolysis is the process of the fibrin-platelet clot dissolution initiated after bleeding has been stopped. It is regulated by a cascade of proteolytic enzymes with plasmin at its core. In pathological cases, the balance of normal clot formation and dissolution is replaced by a too rapid lysis, leading to bleeding, or an insufficient one, leading to an increased thrombotic risk. The only approved therapy for emergency thrombus lysis in ischemic stroke is recombinant tissue plasminogen activator, though streptokinase or urokinase-type plasminogen activators could be used for other conditions. Low molecular weight compounds are of great interest for long-term correction of fibrinolysis dysfunctions. Their areas of application might go beyond the hematology field because the regulation of fibrinolysis could be important in many conditions, such as fibrosis. They enhance or weaken fibrinolysis without significant effects on other components of hemostasis. Here we will describe and discuss the main classes of these substances and their mechanisms of action. We will also explore avenues of research for the development of new drugs, with a focus on the use of computational models in this field.

Transfusion rate using intravenous tranexamic acid in hip revision surgery

INTRODUCTION

Hip revision surgery is associated with a high probability of the necessity for a blood transfusion. Different studies support the use of tranexamic acid (TXA) to decrease the rate of transfusions in primary hip surgery. Nevertheless, the use of this drug in hip revision surgery has not yet been widely accepted. The aim of our study was to establish the rate of blood transfusion with and without TXA in hip revision surgery.

METHODS

We retrospectively studied 125 hip revision surgery patients operated on between 2011 and 2014. We divided our series into 2 groups: the TXA group with 61 patients (in which a 1000 mg dose of TXA was used before the skin incision and a second identical dose after skin closure) and a control group with 64 patients. We analysed the red blood cell (RBC) transfusion rates and their odds risk as well as the presence of collateral complications.

RESULTS

Average RBC transfusion was 2.7 units/patient (range 0-6) in the control group compared to 1.6 units/patient (range 0-6) in the TXA group. A 90.11% (odds ratio [OR] 0.098; confidence interval [CI] 0.02-0.04; p<0.0029) odds risk reduction for transfusion of at least 1 unit of erythrocyte blood cell was observed in the TXA group. Complications associated with the TXA were similar in both groups.

INTERPRETATION

The benefits of TXA have been shown in elective hip replacement. In this study, TXA proved to be safe and efficacious in reducing the need for transfusions following revision total hip arthroplasty.

Transfusion rate using intravenous tranexamic acid in hip revision surgery

INTRODUCTION

Hip revision surgery is associated with a high probability of the necessity for a blood transfusion. Different studies support the use of tranexamic acid (TXA) to decrease the rate of transfusions in primary hip surgery. Nevertheless, the use of this drug in hip revision surgery has not yet been widely accepted. The aim of our study was to establish the rate of blood transfusion with and without TXA in hip revision surgery.

METHODS

We retrospectively studied 125 hip revision surgery patients operated on between 2011 and 2014. We divided our series into 2 groups: the TXA group with 61 patients (in which a 1000 mg dose of TXA was used before the skin incision and a second identical dose after skin closure) and a control group with 64 patients. We analysed the red blood cell (RBC) transfusion rates and their odds risk as well as the presence of collateral complications.

RESULTS

Average RBC transfusion was 2.7 units/patient (range 0-6) in the control group compared to 1.6 units/patient (range 0-6) in the TXA group. A 90.11% (odds ratio [OR] 0.098; confidence interval [CI] 0.02-0.04; p<0.0029) odds risk reduction for transfusion of at least 1 unit of erythrocyte blood cell was observed in the TXA group. Complications associated with the TXA were similar in both groups.

INTERPRETATION

The benefits of TXA have been shown in elective hip replacement. In this study, TXA proved to be safe and efficacious in reducing the need for transfusions following revision total hip arthroplasty.

Detection and Characterization of Bacterial Proteinases Using Zymography

Proteinases play a crucial role in invasion and pathogenesis of bacteria, especially the extracellular and membrane-bound forms. Analysis of these proteinases demands the isolation by retaining the enzymatic activity. The isolation procedures maintaining the native structure of the enzyme in its soluble form are also of extreme importance. The qualitative analyses of these proteinases are carried out by electrophoresis and zymography. Enzymatic characterization based on the effect of inhibitors and activators on gelatinase activity also can be assessed using this zymography. The membrane-bound proteinases can be isolated in their native and soluble form, still retaining the activity using 6-aminocaproic acid and sodium deoxycholate; the procedure of which is explained in this chapter.

Penta-L-lysine Potentiates Fibrin-Independent Activity of Human Tissue Plasminogen Activator

The therapeutic action of tissue plasminogen activator (t-PA) is a two-step process: (1) binding to lysine-rich fibrin (Km event) and (2) converting local plasminogen into plasmin (Kcat event). Overcoming limitations of other structural biophysics methods, we wanted to employ small-angle X-ray scattering (SAXS) to visualize what shape changes occur/accompany t-PA activation, but the prime hurdle was the polydisperse nature of the fibrin, which occluded scattering information from t-PA. Earlier, larger polylysine peptides have been used to potentiate activation of t-PA, so while screening short polylysine peptides as alternatives to fibrin or larger peptides, we found that penta-polylysine (P5) specifically activates t-PA in a dose-dependent manner, averaging to almost 3-fold more than in the absence of any peptide. SAXS data analysis confirmed that P5 does not induce association of t-PA molecules, and a narrower peak profile of the Kratky plot indicated that P5 binding quenches inherent motion in t-PA. Shape reconstruction of t-PA ∓ P5 revealed that P5 closes the "gap" between the two gross domains of t-PA, viz. fused F/E, K1 and K2 domains, and the P domain. Docking experiments suggested that, while other polylysine peptides preferentially interacted with the surfaces of kringle domains, P5 "slipped into" the gap/groove between K2 and P domains, thereby mediating a substantial increase in the number of long-range interactions between the K2 domain and exosites in the P domain. We report here dissection of shape events involved in between Km/Kcat steps of t-PA activation, which can pave the way toward the search for small molecule function regulator(s) of t-PA.

Mechanism of the action of SMTP-7, a novel small-molecule modulator of plasminogen activation

SMTP-7 is a small molecule that promotes the proteolytic activation of plasminogen by relaxing its conformation. SMTP-7 has excellent therapeutic activities against thrombotic stroke in several rodent models. The objective of this study was to elucidate detailed mechanism of the action of SMTP-7 in vitro. We report here that the action of SMTP-7 requires a cofactor with a long-chain alkyl or alkenyl group, and that the fifth kringle domain (kringle 5) of plasminogen is involved in the SMTP-7 action. In this study, we found that the SMTP-7 action to enhance plasminogen activation depended on the presence of a certain type of surfactant, and we screened biologically relevant molecules for their cofactor activity for the SMTP action. As a result, phospholipids, sphingolipids, and oleic acid were found to be active in assisting the SMTP-7 action. On the contrary, stearic acid and bile acids were inactive. Thus, a certain structural element, not only the surface-activating potential, is required for a compound to act as a cofactor for the SMTP-7 action. The plasminogen molecule consists of a PAN domain, five kringle domains, and a serine protease domain. The cofactor-dependent effects of SMTP-7 was observed with plasminogen species including kringle 5 such as intact plasminogen (Glu-plasminogen), des-PAN plasminogen (Lys-plasminogen), and des-[PAN - (kringles 1-4)] plasminogen (mini-plasminogen). However, SMTP-7 effect was not observed with the smallest plasminogen species des-[PAN - (kringles 1-4) and a half of kringle 5)] plasminogen (micro-plasminogen). Thus, kringle 5 is crucial for the action of SMTP-7.

α(1,3)-Fucosyltransferases FUT4 and FUT7 control murine susceptibility to thrombosis

The α(1,3)-fucosyltransferases, types IV and VII (FUT4 and FUT7, respectively), are required for the synthesis of functional selectin-type leukocyte adhesion molecule ligands. The selectins and their ligands modulate leukocyte trafficking, and P-selectin and its ligand, P-selectin glycoprotein ligand-1, can modulate hemostasis and thrombosis. Regulation of thrombosis by FUT4 and/or FUT7 activity was examined in mouse models of carotid artery thrombosis and collagen/epinephrine-induced thromboembolism. Mice lacking both FUT4 and FUT7 (Fut(-/-) mice) had a shorter time to occlusive thrombus formation in the injured carotid artery and a higher mortality due to collagen/epinephrine-induced pulmonary thromboemboli. Mice lacking P-selectin or P-selectin glycoprotein ligand-1 did not have a prothrombotic phenotype. Whole blood platelet aggregation was enhanced, and plasma fibrinogen content, clot weight, and clot strength were increased in Fut(-/-) mice, and in vitro clot lysis was reduced compared with wild type. Fut4(-/-), but not Fut7(-/-), mice had increased pulmonary thromboembolism-induced mortality and decreased thromboemboli dissolution in vivo. These data show that FUT4 and FUT7 activity regulates thrombosis in a P-selectin- and P-selectin glycoprotein ligand-1-independent manner and suggest that FUT4 activity is important for thrombolysis.

Short-term high-dose effect of lovastatin on thrombolysis by rt-PA in a human whole-blood in vitro clot model

High-dose hydroxymethylglutaryl coenzyme. A reductase inhibitor (statin) administration reduces neuronal injury and improves outcomes in experimental models of acute ischemic stroke, and has been shown to be safe in a phase 1 dose-escalation study using lovastatin at doses higher than currently approved for daily use. Statins also affect the hemostatic system by upregulating t-PA expression and decreasing plasminogen activator inhibitor (PAI-1) expression, platelet adhesion and thrombus formation in animal models. Since a thrombolytic agent, recombinant tissue plasminogen activator (rt-PA), is currently the only FDA-approved therapy for use in ischemic stroke patients, it is important to ascertain whether high statin doses impact the efficacy of rt-PA. The main goal of this study was to evaluate the effect of a high dose of lovastatin and its active form, lovastatin hydroxy acid, on rt-PA thrombolysis in an in vitro model. Percentage clot lysis was measured in the presence and absence of rt-PA in three different treatment groups: lovastatin, lovastatin hydroxy acid, and ethanol. The effect of ethanol on clot lysis was studied since ethanol was used to disperse the highly hydrophobic lovastatin. The decrease in clot width over time was measured using microscopic imaging of an in vitro human whole blood clot model; an approximately 400 μm diameter clot was formed on suture silk, suspended in human fresh frozen plasma (hFFP) and exposed to treatment. In the absence of rt-PA, clot lysis did not show statistically significant differences in the percentage clot lysis between different treatment groups (p=0.103). In the presence of rt-PA, clot lysis was greater than in the absence of rt-PA for all groups, but there were no statistically significant differences between treatment groups (p=0.385). In this in vitro study, high doses of lovastatin neither impaired nor enhanced the lytic efficacy of rt-PA.

Duration of postoperative fibrinolysis after total hip or knee replacement: a laboratory follow-up study

INTRODUCTION

Hyperfibrinolysis is observed during and immediately after major orthopedic surgery. The kinetics and duration of this phase should be defined to adjust the duration of antifibrinolytic treatment with tranexamic acid (TXA).

OBJECTIVE

We aimed to quantify the duration of postoperative fibrinolysis and to assess the biological impact of TXA administration.

MATERIALS AND METHODS

Fourteen patients undergoing total hip replacement (THR) and 10 patients undergoing total knee replacement (TKR) with tourniquet were included in an observational, prospective, single-center study. Among these patients, 7 THR patients and 5 TKR patients received TXA (15mg/kg IV intraoperatively, followed by continuous infusion of 15mg/kg/h until end of surgery, then every 4hours until 16±2hours after surgery). D-dimers, euglobulin lysis time (ELT), and thrombin generation time (TGT) were measured prior to surgery as well as 6, 18 and 24hours (H) after.

RESULTS

No significant difference in ELT was observed between the groups. In contrast, D-dimers significantly increased postoperatively in patients not treated with TXA (p<0.001), while such an increase was prevented in patients receiving TXA, as measured at H0, H6, H18 and H24 after THR, and at H6 and H18 after TKR (p<0.001). No significant between-group change in TGT, was observed (peak thrombin and endogenous thrombin potential) all along the study.

CONCLUSION

This study shows that fibrinolysis peaked 6hours after end of surgery and maintained about 18hours after surgery, as evidenced by an increase in D-dimers. When administered for up to 16±2hours after surgery, TXA reduced postoperative fibrinolysis.

Plasmodium ookinetes coopt mammalian plasminogen to invade the mosquito midgut

Ookinete invasion of the mosquito midgut is an essential step for the development of the malaria parasite in the mosquito. Invasion involves recognition between a presumed mosquito midgut receptor and an ookinete ligand. Here, we show that enolase lines the ookinete surface. An antienolase antibody inhibits oocyst development of both Plasmodium berghei and Plasmodium falciparum, suggesting that enolase may act as an invasion ligand. Importantly, we demonstrate that surface enolase captures plasminogen from the mammalian blood meal via its lysine motif (DKSLVK) and that this interaction is essential for midgut invasion, because plasminogen depletion leads to a strong inhibition of oocyst formation. Although addition of recombinant WT plasminogen to depleted serum rescues oocyst formation, recombinant inactive plasminogen does not, thus emphasizing the importance of plasmin proteolytic activity for ookinete invasion. The results support the hypothesis that enolase on the surface of Plasmodium ookinetes plays a dual role in midgut invasion: by acting as a ligand that interacts with the midgut epithelium and, further, by capturing plasminogen, whose conversion to active plasmin promotes the invasion process.

Effects of tranexamic acid on blood loss during total hip arthroplasty

PURPOSE

To assess the effects of tranexamic acid (TA) in patients undergoing total hip arthroplasty (THA) for osteoarthritis.

METHODS

42 patients underwent primary THA for osteoarthritis by a single surgeon. 10 men and 11 women who did not receive TA were controls, whereas 9 men and 12 women who received TA constituted the treatment group. Both groups were matched for age, gender, body mass index, and American Society of Anesthesiologists grading. The type of prosthesis used (cemented or uncemented) was based on the surgeon's preference and patient age, activity level and demands. No hybrid prosthesis was used. 10 minutes prior to incision, a single dose of intravenous TA (10 mg per kg body weight) was given to patients in the treatment group. Comparison was made between both groups with regard to intra-operative blood loss, postoperative reduction in haemoglobin and haematocrit levels, blood transfusion, incidence of deep vein thrombosis, and the length of hospital stay.

RESULTS

The mean intra-operative blood loss (489 [SD, 281] vs. 339 [SD, 184] ml, p = 0.048) and the decrease in haemoglobin level (38 [SD, 12] vs. 29 [SD, 10] g/l, p=0.014) were significantly higher in the control than the treatment group. Two patients among the controls received a transfusion, compared to none in the TA group (p = 0.49, Fisher's exact test). The 2 patients who needed blood transfusion had blood losses of 600 and 690 ml, compared to a mean of 489 ml in the whole group. No patient in either group developed deep vein thrombosis or pulmonary embolism up to 3 months.

CONCLUSION

A single dose of intravenous TA (10 mg per kg body weight) given 10 minutes prior to THA is a cost-effective and safe means of minimising blood loss and reduction in haemoglobin concentrations as well as the need for allogenic blood transfusion, without increasing the risk of thromboembolic events.

Small-molecule modulators of zymogen activation in the fibrinolytic and coagulation systems

The coagulation and fibrinolytic systems are central to the hemostatic mechanism, which works promptly on vascular injury and tissue damage. The rapid response is generated by specific molecular interactions between components in these systems. Thus, the regulation mechanism of the systems is programmed in each component, as exemplified by the elegant processes in zymogen activation. This review describes recently identified small molecules that modulate the activation of zymogens in the fibrinolytic and coagulation systems.

The effect of an intravenous bolus of tranexamic acid on blood loss in total hip replacement

Tranexamic acid is a fibrinolytic inhibitor which reduces blood loss in total knee replacement. We examined the effect on blood loss of a standardised intravenous bolus dose of 1 g of tranexamic acid, given at the induction of anaesthesia in patients undergoing total hip replacement and tested the potential prothrombotic effect by undertaking routine venography. In all, 36 patients received 1 g of tranexamic acid, and 37 no tranexamic acid. Blood loss was measured directly per-operatively and indirectly post-operatively.

Tranexamic acid reduced the early post-operative blood loss and total blood loss (p = 0.03 and p = 0.008, respectively) but not the intraoperative blood loss. The tranexamic acid group required fewer transfusions (p = 0.03) and had no increased incidence of deep-vein thrombosis. The reduction in early post-operative blood loss was more marked in women (p = 0.05), in whom this effect was dose-related (r = −0.793).

Our study showed that the administration of a standardised pre-operative bolus of 1 g of tranexamic acid was cost-effective in reducing the blood loss and transfusion requirements after total hip replacement, especially in women.

The use of the Chandler loop to examine the interaction potential of NXY-059 on the thrombolytic properties of rtPA on human thrombi in vitro

BACKGROUND AND PURPOSE

Recombinant tissue-type plasminogen activator (rtPA) is the only globally approved treatment for acute ischaemic stroke. Other potential treatments might be administered with rtPA, making it important to discover whether compounds interfere with rtPA-induced lysis. We evaluated methods for examining the effect of the neuroprotectant NXY-059 on the lytic property of rtPA.

EXPERIMENTAL APPROACH

Plasma clot formation and lysis in the presence of rtPA and NXY-059 was measured as the change in plasma turbidity. The effect of NXY-059 on rtPA-induced lysis was similarly assessed on preformed clots. Lysis of the thrombus formed in a Chandler loop measured release of fluorescent-tagged fibrinogen that had been incorporated during thrombus formation. Thrombi were exposed to both rtPA and NXY-059 throughout lysis in the presence of 80% autologous plasma and the release of label during lysis was measured.

KEY RESULTS

Data interpretation is limited in the clot lysis experiments because either the rtPA was present during clot formation or the drug was added to a clot formed in static conditions. In contrast, thrombi were formed in dynamic flow conditions in the Chandler loop and the time course of lysis in plasma was examined. rtPA increased thrombolysis and the antifibrinolytic trans-4-(aminomethyl) cyclohexane carboxylic acid (AMCA) inhibited lysis. Lysis induced by rtPA was unaltered by NXY-059.

CONCLUSIONS AND IMPLICATIONS

The Chandler loop method provides a reliable technique for examining the effect of compounds on rtPA-induced lysis in vitro and demonstrated that NXY-059 does not alter rtPA-induced lysis at clinically relevant concentrations of either drug.

ε-Aminocaproic acid inhibition of fibrinolysis in vitro: should the ‘therapeutic’ concentration be reconsidered?

The therapeutic concentration of epsilon-aminocaproic acid (EACA) has been 130 microg/ml or greater for nearly 50 years. We tested the effects on clot growth/disintegration of EACA with a plasmatic model of hyperfibrinolysis in vitro. Human plasma was exposed to 1000 U/ml tissue-type plasminogen activator containing 0, 13, 65 or 130 microg/ml EACA, with clot growth/disintegration kinetics quantified via thrombelastography. Data were analyzed with one-way analysis of variance or Kruskal-Wallis analysis of variance as appropriate. Exposure of plasma to 1000 U/ml tissue-type plasminogen activator resulted in a brief-lived clot, lasting 2 min. EACA at all concentrations tested significantly increased the rate of clot growth compared with samples with 0 microg/ml EACA. Clot strength was significantly increased by EACA in a concentration-dependent fashion. Similarly, EACA significantly prolonged the time of onset of clot lysis and decreased the rate of lysis. Samples with 130 microg/ml EACA had no sign of lysis present for 30 min. Subtherapeutic to therapeutic concentrations of EACA significantly attenuated or abolished fibrinolysis in the presence of a concentration of tissue-type plasminogen activator more than 2000-fold that encountered systemically during cardiopulmonary bypass. Further clinical investigation is warranted to determine whether smaller concentrations of EACA could provide a reduction in bleeding with a concomitant decrease in thrombotic complications.

Tumor growth and metastasis are not affected in thrombin-activatable fibrinolysis inhibitor-deficient mice

Many studies have indicated that the plasminogen activation system may have a prominent role in cancer. Activation of the zymogen plasminogen into the serine protease plasmin by plasminogen activator is mediated by carboxyterminal basic amino acids in fibrin, including lysines and arginines. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating carboxypeptidase B-type proenzyme that, after activation, removes carboxyterminal lysine or arginine residues in fibrin, resulting in decreased plasminogen activation and attenuated fibrinolysis. To determine directly whether TAFI is involved in primary tumor growth and metastasis formation, we examined the effects of TAFI deficiency on subcutaneous growth and experimentally or spontaneously induced pulmonary metastasis formation of different tumor cell types in mice. In all tumor models TAFI deficiency did not affect the formation and growth of primary and metastasized tumors.

Blood conservation with tranexamic acid in total hip arthroplasty: a randomized, double-blind study in 40 primary operations

We performed a randomized, double-blind study on the effect of tranexamic acid on blood loss and blood transfusions in 40 primary total hip arthroplasties. Tranexamic acid, 10 mg/kg body weight, or placebo, was given intravenously just before the operation. Blood loss during the operation and postoperatively into the drains was recorded, as also were blood hemoglobin concentrations. Ultrasound examination 1 week postoperatively was done to estimate the blood loss due to remaining hematomas. Total (operation + drain) blood loss was 0.76 (95 CI 0.63-0.89) L in the tranexamic acid group as compared to 1.0 (CI 0.81-1.2) L in the placebo group (p = 0.03). The number of blood transfusions during the day of operation was 2 vs. 10 (p = 0.07) and the total number during the hospital stay was 5 vs. 13 (p = 0.2). 1 patient in each group had a pulmonary embolism.

A reconstituted dilute blood clot lysis assay for the medium throughput screening of thrombolytic compounds

Antithrombotic and clotting factors have long been targets for drug discovery, necessitating the development of blood assays to determine the efficacy of lead compounds prior to animal testing. We have developed a reconstituted blood clot lysis assay which eliminates the need for on-site donors. The assay uses whole blood stored at 4 degrees C obtained from a local blood bank, diluted 1:10 in phosphate buffer. This blood was supplemented with 125I-labeled fibrinogen and the release of radioactive fibrinopeptides from formed clots was measured. The whole blood used in this assay, which had been stored at 4 degrees C for several days, no longer formed solid or retracting clots. Thus, platelets 5-7 days ex vivo (165 x 10(6) platelets) were added to the whole blood in the presence of thrombin (0.80 IU/ml) to form clots. Solid clots formed within 2 min of thrombin addition and began retracting shortly thereafter. In the absence of any thrombolytic agent, clots fully retracted within 2.5 h and remained stable. Thrombin-stimulated clot formation was completely inhibited by heparin. Clots could be lysed in a dose-dependent fashion in the presence of tissue-type plasminogen activator. Clot lysis could be completely inhibited in a dose-dependent fashion with plasminogen activator inhibitor type 1. To demonstrate the utility of this assay as a screen for thrombolytic agents, a 14-amino-acid PAI-1-inhibitory peptide relieved the PAI-1 effect on tPA in a dose-dependent fashion. These data describe an assay for the screening of potential pro-fibrinolytic agents that target PAI-1 inhibition in a human plasma-based system that is versatile, cost-effective, and physiologically relevant and does not rely on the availability of on-site blood donors.