Influence of the fast-acting inhibitor of plasminogen activator on in vivo thrombolysis induced by tissue-type plasminogen activator in rabbits. Interference of tissue-derived components

D-dimer corrected for thrombin and plasmin generation is a strong predictor of mortality in patients with sepsis

BACKGROUND

D-dimer (DD) is the most used fibrin-related marker and has been proposed, either alone or in combination with other variables, as prognostic factor in patients with sepsis. However, DD generation depends on both coagulation and fibrinolysis, meaning that it may give false negative results in conditions associated with marked fibrinolytic inhibition such as sepsis. In this study, we tested whether correction of DD for thrombin and plasmin generation could improve its prognostic significance in septic patients.

MATERIAL AND METHODS

We performed a nested study in 269 septic patients from the ALBIOS trial. DD, prothrombin fragment 1+2 (F1+2) and plasmin-antiplasmin complex (PAP) were assayed at day 1. Corrected DD (DD_corr) was calculated by the formula DD×PAP/F1+2, such that the lower the DD_corr the greater the imbalance in favour of fibrin formation over fibrin lysis, and vice-versa. Primary outcome was 90-day mortality.

RESULTS

DD_corr showed a J-shaped relationship with mortality, which was highest in the first DD_corr tertile (low fibrinolysis), intermediate in the 3^rd (high fibrinolysis), and lowest in the 2^nd (balanced fibrinolysis), suggesting an increased risk whenever the coagulation-fibrinolysis balance is tilted (p<0.0001). Neither DD, nor PAP or F1+2 showed a comparable association with mortality. DD_corr was an independent prognostic factor in multivariable Cox models and significantly improved risk stratification (cNRI≥0.28). Finally, by combining DD_corr and SOFA tertiles, we developed a score with high discriminatory power.

DISCUSSION

DD_corr is a good marker of the in vivo coagulation-fibrinolysis balance and displays a prognostic value in sepsis much higher than DD.

Dabigatran enhances clot susceptibility to fibrinolysis by mechanisms dependent on and independent of thrombin-activatable fibrinolysis inhibitor

BACKGROUND

Anticoagulants are expected to promote fibrinolysis by counteracting the antifibrinolytic effects of thrombin, which include thrombin-activatable fibrinolysis inhibitor (TAFI) activation and clot structure enhancement. However, the efficiency of anticoagulants may vary remarkably, and the ability of direct thrombin inhibitors to facilitate clot lysis remains controversial.

OBJECTIVE

To evaluate the profibrinolytic effect of dabigatran, a new, direct thrombin inhibitor, using different in vitro models.

METHODS AND RESULTS

The resistance of tissue factor-induced plasma clots to fibrinolysis by exogenous tissue-type plasminogen activator (t-PA) (turbidimetric method) was reduced by dabigatran in a concentration-dependent manner, with > or = 50% shortening of lysis time at clinically relevant concentrations (1-2 microm). A similar effect was observed in the presence of low (0.1 and 1 nm) but not high (10 nm) concentrations of thrombomodulin. Acceleration of clot lysis by dabigatran was associated with a reduction in TAFI activation and thrombin generation, and was largely, although not completely, negated by an inhibitor of activated TAFI, potato tuber carboxypeptidase inhibitor. The assessment of the viscoelastic properties of clots showed that those generated in the presence of dabigatran were more permeable, were less rigid, and consisted of thicker fibers. The impact of these physical changes on fibrinolysis was investigated using a model under flow conditions, which demonstrated that dabigatran made the clots markedly more susceptible to flowing t-PA, by a mechanism that was largely TAFI-independent.

CONCLUSIONS

Dabigatran, at clinically relevant concentrations, enhances the susceptibility of plasma clots to t-PA-induced lysis by reducing TAFI activation and by altering the clot structure. These mechanisms might contribute to the antithrombotic activity of the drug.

Coagulation and fibrinolytic responses of human peritoneal fluid and plasma to bacterial peritonitis

Significantly higher (P < 0.05) thrombin-antithrombin III complex levels were found in the abdominal exudate of patients with peritonitis (median 5500 ng/ml) than in that of controls (median 89 ng/ml). In patients, peritoneal fluid concentrations of tissue and urokinase-type plasminogen activator were increased by factors of 65 and 10 respectively (P < 0.05). The concentration of plasminogen activator inhibitor (PAI) 1 was increased by a factor of about 800 (median 395 versus 0.5 ng/ml, P < 0.05). Despite markedly raised concentrations of PAI, peritoneal fluid displayed fibrinolytic activity as demonstrated by significantly increased (P < 0.05) concentrations of plasmin-alpha 2-antiplasmin complex (median 10,952 versus 57 ng/ml) and fibrin degradation products (median 40,360 versus 126 ng/ml). There was no correlation between plasma and peritoneal fluid concentrations. Intraabdominal coagulation and fibrinolysis are stimulated in the abdominal cavity of patients with bacterial peritonitis.

Fibrin generation and digestion in patients with angina pectoris

Fibrin generation and lysis were studied in 28 patients with angina pectoris (14 with active disease and 14 with inactive disease) and in 14 normal controls. The fibrinolytic response was evaluated by comparing the ratio between the plasma levels of fibrinopeptide A and fibrin degradation products. Levels of both were higher in patients than in controls (P < 0.001), with higher levels in active than in inactive disease (P < 0.001). The fibrinopeptide A/fibrin degradation products ratio was much higher (P < 0.001) in the active group than in other groups. Thus, in patients with angina pectoris, especially in the active state, the increased thrombin generation is not paralleled by an equivalent increase in fibrinolytic activity.

Direct effects of gemfibrozil on the fibrinolytic system. Diminution of synthesis of plasminogen activator inhibitor type 1

BACKGROUND

Platelet-associated epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) can augment synthesis of plasminogen activator inhibitor type 1 (PAI-1). Accordingly, exacerbation of atherogenesis may accompany release of platelet-associated growth factors (or mitogens) occurring in association with occult, repetitive thrombosis and thrombolysis. In the Helsinki primary prevention trial, gemfibrozil decreased coronary events but did so essentially only in initially hypertriglyceridemic subjects. Such subjects are known to exhibit high concentrations of PAI-1 in plasma.

METHODS AND RESULTS

To determine whether pharmacological concentrations of gemfibrozil directly affect PAI-1 synthesis, we characterized its effects on a human hepatoma cell line (Hep G2) in vitro. Gemfibrozil decreased basal PAI-1 secretion by 43% and attenuated the augmentation of PAI-1 synthesis over 24 hours induced by EGF and TGF-beta by 37% and 39% without altering overall protein synthesis. Furthermore, it blocked the EGF and TGF-beta-induced increases in PAI-1 mRNA over 6 hours by 65% and 60%. Increases in plasma PAI activity induced by infusion of purified growth factors or by autologous platelet lysates in rabbits were inhibited by gemfibrozil by more than 50%.

CONCLUSIONS

Beneficial effects of gemfibrozil in reducing coronary events in hypertriglyceridemic patients may depend, in part, on potentiation of fibrinolysis by direct diminution of synthesis of endogenous PAI-1.

Changes in the coagulation-fibrinolysis balance of endothelial cells and mononuclear phagocytes: role in disseminated intravascular coagulation associated with infectious diseases

Over the last few years, evidence has accumulated that the pathogenetic mechanism of disseminated intravascular coagulation encountered in patients with infectious diseases is extraordinarily complex and involves multiple interactions between the microorganism itself and/or a number of mediators, both microorganism derived and host manufactured, and multifunctional cellular systems, namely endothelial cells and mononuclear phagocytes. In particular, infectious agents and mediators shift the coagulation-fibrinolysis equilibrium of these cells towards fibrin formation and accumulation, via enhancement of procoagulant properties and reduction of both anticoagulant and fibrinolytic capacities. New insights into the pathogenetic mechanism may have important implications for the management of infected patients with disseminated intravascular coagulation.

Nonradical excited oxygen species induce selective thrombolysis in vivo

All the thrombolytic agents currently in clinical use act as plasminogen activators. In this study evidence is presented that also oxidants of the phagocyte type are of fibrinolytic efficiency in vivo. Activated phagocytes participate in physiologic fibrinolysis. The cells generate plasminogen activators and reactive oxidants of the nitrogen-chlorine type. Experimental mimicry of this oxidative inflammatory response induces selective thrombolysis in a rabbit jugular vein model. Intravenous bolus administration of sub-millimolar blood concentrations of chloramine-T resulted in thrombolysis after about 30 min without notable systemic toxicity; the coagulation parameters activated partial thromboplastin time (aPTT), thrombin time, fibrinogen, and alpha-2-antiplasmin were not influenced. Control experiments with 2000 IU of urokinase/kg induced thrombolysis after about 90 min with systemic changes of the hemostatic system. The fibrinolysis promoting effect of the oxidants of the phagocyte type could be inhibited by quenchers of singlet molecular oxygen and was not affected at all by inhibitors of oxygen radicals. The data gives evidence that nonradical excited oxygen species (NEOS) act as powerful pro-fibrinolytic and anti-coagulant agents in vivo. It might be suggested that NEOS could represent a novel class of regulators of the fibrinolytic system. The long lived and hydrophilic chloramine derivatives can either accumulate or diffuse far from their site of generation. Therefore, on the one hand oxidants in high (local) concentrations might be considered as direct pro-fibrinolytic agents due to their powerful protein modulating efficacy. On the other hand, oxidants at low concentrations may act as indirect pro-fibrinolytic compounds, i.e. as chemoattractants to concentrate phagocytes to the site of a thrombus. In this case the oxidants would play the role of signal elements faraway from the thrombus, a self amplifying mechanism possibly mediated by oxidation of blood arachidonat/lipid metabolites.

Studies on the mechanism of action of oral contraceptives with regard to fibrinolytic variables

Evidence is provided that the fibrinolytic capacity in plasma is strongly dependent on circulating concentrations of tissue plasminogen activator rather than on concentrations of plasminogen activator inhibitor. Thus a decrease in plasma tissue plasminogen activator concentrations, as is the case in oral contraceptive users, may result in a decrease in plasma fibrinolytic capacity despite a parallel decrease in plasminogen activator inhibitor levels. It is now clear that the presence of specific intracellular receptors and a given motif in the genome are essential to mediate hormone-dependent regulation of gene expression. A computer search revealed potential estrogen and glucocorticoid-progesterone-responsive elements in the genes coding for tissue plasminogen activator, plasminogen activator inhibitor, and some other fibrinolytic variables. No convincing evidence for the presence of sex steroid receptors in endothelial cells was found, but liver cells clearly contain estrogen and androgen receptors. However, neither endothelial cells nor hepatocytes cultured in vitro showed a change in tissue plasminogen activator or plasminogen activator inhibitor synthesis on incubation with sex steroids (10(-9) to 10(-6) mol/L) for 3 days. An alternative explanation for the observed decreases in tissue plasminogen activator and plasminogen activator inhibitor concentrations in the plasma of oral contraceptive users is discussed.

Purification and characterization of natural and recombinant human plasminogen activator inhibitor-1 (PAI-1)

Human plasminogen activator inhibitor-1 (PAI-1) was purified from the conditioned medium of endotoxin-stimulated umbilical vein endothelial cell cultures by combinations of zinc-chelate-Sepharose chromatography, gel filtration on Sephacryl S-300 and immunoadsorption on an insolubilized murine monoclonal antibody (MA-7D4). The final product was obtained with a recovery of approximately 20% from conditioned medium containing about 3 micrograms/ml PAI-1. The yield of PAI-1 was 15-100 micrograms/umbilical cord, depending on the culture and harvest conditions. SDS gel electrophoresis revealed a main band with Mr = 46,000 both under reducing and non-reducing conditions. On gel filtration on Sephacryl S-300, however, the material was separated in two fractions, one eluting at the void volume, which contains active PAI-1, and one with Mr = 46,000 containing inactive material that could be reactivated with 12 M urea. SDS gel electrophoresis of the isolated high-Mr fraction revealed several bands including a main 46,000-Mr component, which reacted with anti-(PAI-1) antibodies on immunoblotting and neutralized tissue-type plasminogen activator (t-PA). The active high-Mr fraction and the reactivated low-Mr fraction of PAI-1 inhibited t-PA very rapidly with an apparent second-order rate constant of (1.5-4) x 10(7) M-1 s-1. The cDNA of endothelial cell PAI-1 was cloned and expressed in Chinese hamster ovary cells. The translation product, purified from conditioned medium of transfected cells, also revealed a high-Mr and a low-Mr fraction on gel filtration, which were indistinguishable from the natural proteins by physicochemical, immunochemical and functional analysis. On reduced SDS gel electrophoresis, the high-Mr fraction was separated into the Mr-46,000 low-Mr PAI-1 and two other components with Mr 65,000 and one barely entering the gel. When reactivated low-Mr PAI-1 was added to plasma, PAI activity and PAI-1 antigen eluted with an apparent Mr greater than or equal to 300,000 on gel filtration, indicating that active PAI-1 complexes with one or more binding proteins in plasma.

Plasminogen activator inhibitor is associated with the extracellular matrix of cultured bovine smooth muscle cells

The extracellular matrix secreted by cultured bovine smooth muscle cells (BSMC) contains an endothelial type plasminogen activator (PA) inhibitor. When PA is incubated with the matrix, a high molecular weight complex containing a truncated PA inhibitor is released into the supernatant. The inhibitor also dissociates from the matrix by treatment with glycine, pH 2.7, in its intact, functionally active, 45-kD form, whereas treatment of the matrix with thrombin results in the release of a cleaved, inactive, 41 kD PA inhibitor. Bowes melanoma cells but not smooth muscle cells cultured on BSMC matrices decrease available matrix associated PA inhibitor. PA inhibitor incorporated into the extracellular matrix may serve an important role in the regulation of plasminogen activator mediated matrix degradation.

Synergism of thrombolytic agents in vivo

The existence of significant synergism between tissue-type plasminogen activator (t-PA) and single-chain urokinase-type plasminogen activator (scu-PA), and between t-PA and urokinase in thrombolysis in vivo is described. In a quantitative preparation of thrombolysis, consisting of rabbits in which a blood clot was induced in the jugular vein with 125I-labeled fibrin, intravenous infusion over 4 hr of t-PA, scu-PA, or urokinase in amounts of 0.5, 1.0, or 2.0 mg/kg body weight resulted in significant thrombolysis (30% to 60%). The simultaneous infusion of t-PA and scu-PA or of t-PA and urokinase had a significantly greater (p less than .001) thrombolytic effect than could be anticipated on the basis of the added effects of each agents alone. However, no synergism was observed between scu-PA and urokinase. The observed alpha 2-antiplasmin consumption and fibrinogen breakdown after urokinase at higher doses did not occur with the equivalent thrombolytic combinations of t-PA and urokinase. The combined use of synergic thrombolytic agents in patients may permit a significant reduction in total administered doses, probably with elimination of the systemic activation of the fibrinolytic system and the concomitant fibrinogen breakdown that is unavoidable with the currently used thrombolytic doses of each agent.