An Analysis of Mechanisms Underlying the Antifibrinolytic Properties of Radiographic Contrast Agents

Background: Radiographic contrast agents inhibit fibrinolysis, although by poorly defined pathways. The purpose of this study was to define specific mechanisms by which contrast agents inhibit clot lysis. Methods and Results: Diatrizoate (high osmolar ionic agent), ioxaglate (low osmolar ionic), and ioversol (nonionic) were studied in vitro. Diatrizoate inhibited clot lysis by 81.3±0.6% vs. control (p<0.001). Ioxaglate inhibited clot lysis by 41.7±11.9%, which was of borderline significance (p=0.07). Ioversol did not significantly inhibit clot lysis (14.9±11.5% decrease vs. control; p>0.3). Inhibition of fibrinolysis was not explained by the high osmolarities of contrast agents, by their iodine content, or by their effects on the amidolytic activities of t-PA, urokinase, or plasmin. However, plasminogen activation by t-PA, urokinase, or streptokinase was significantly inhibited by contrast agents. Diatrizoate, ioxaglate, and ioversol inhibited plasminogen binding to plasma clots by 51±4% (p<0.001), 30.1±4% (p<0.01), and 19.4±7% (p=0.07), respectively. Plasma clots formed in the presence of contrast agents were resistant to lysis by plasmin. Diatrizoate produced the most potent effect, inhibiting clot lysis by 40±5.7% (p<0.03). Contrast agents did not inhibit plasminogen binding to fibrin or plasmin-mediated fibrinolysis if they were added after clot formation. Contrast agents altered clot turbidity, an index of fibrin structure, if present during clot formation, but not if added to preformed clots. Contrast agents did not affect plasminogen activator inhibitor-1 or ₂-antiplasmin function. Conclusions: Contrast agents inhibit clot lysis by inhibiting plasminogen activation and by disrupting interactions of plasminogen and plasmin with fibrin by altering fibrin structure. Significant variation in antifibrinolytic properties exists between different contrast agents. Abbreviated Abstract. The purpose of this study was to define specific mechanisms by which contrast agents inhibit clot lysis. In both a purified clot lysis system and a plasma clot lysis system, diatrizoate, an ionic agent, produced the most potent inhibition of fibrinolysis. Contrast agents did not inhibit the active sites of plasminogen activators or plasmin, but did inhibit plasminogen activation. Binding of plasminogen to fibrin and lysis of fibrin by plasmin were inhibited by contrast agents if they were present during clot formation, but not if they were added after clot formation was complete. Contrast agents altered clot turbidity, an index of fibrin structure, if present during clot formation, but not if added to preformed clots. Contrast agents did not affect plasminogen activator inhibitor-1 or ₂-antiplasmin function. The effects of contrast agents on fibrinolytic parameters were not explained by their high osmolarities. These results suggest that contrast agents inhibit clot lysis by inhibiting plasminogen activation and by disrupting interactions of plasminogen and plasmin with fibrin by altering fibrin structure.     

Clot lysis by gastric juice: an in vitro study.

Gastric juice from patients with peptic ulcer disease and from patients with no upper gastrointestinal abnormality was studied in order to assess its effect on a formed fibrin clot. In both groups of patients gastric juice caused a marked increase in fibrinolysis as evidenced by a shortening of the euglobulin clot lysis time. This plasmin mediated fibrinolytic activity was found to be heat labile and only present in an acid environment. Addition of tranexamic acid or sucralfate to gastric juice almost completely reversed this effect, whereas pepstatin was only partially effective. It is probable that acid dependent proteases other than pepsin are responsible for the marked fibrinolysis. The ulcer healing agent sucralfate might be useful in those patients at risk of bleeding or rebleeding from active peptic ulcer disease.     

The fibrinogen Aalpha R16C mutation results in fibrinolytic resistance

The fibrinogen Aalpha R16C mutation is a common cause of dysfibrinogenaemia and has been previously associated with both bleeding and thrombosis. However, the mechanism underlying the thrombotic phenotype has not yet been elucidated. This report characterises the defect in fibrinolysis seen as a result of the Aalpha R16C mutation. A young patient with dysfibrinogenaemia (fibrinogen Hershey III) was found to be heterozygous for the Aalpha R16C mutation. Functional assays were performed on the purified fibrinogen to characterise clot formation and lysis with plasmin and trypsin. Consistent with previous results, clot formation was diminished. Unexpectedly, fibrinolysis was also delayed. Plasminogen activation was normal, ruling out decreased plasmin generation as the mechanism behind the fibrinolytic resistance. Western blot analysis showed no difference in the amount of bound alpha2-antiplasmin or albumin. When clot lysis was assayed with trypsin substituted for plasminogen, a significant delay was also observed, indicating that defective binding to plasminogen could not explain the fibrinolytic resistance. These results suggest that the defective fibrinolysis is due to increased proteolytic resistance, most likely reflecting changes in clot structure.     

β2‐glycoprotein i is a cofactor for tissue plasminogen activator–mediated plasminogen activation

Objective

Regulation of the conversion of plasminogen to plasmin by tissue plasminogen activator (tPA) is critical in the control of fibrin deposition. While several plasminogen activators have been described, soluble plasma cofactors that stimulate fibrinolysis have not been characterized. The purpose of this study was to investigate the effects of β₂‐glycoprotein I (β₂GPI), an abundant plasma glycoprotein, on tPA‐mediated plasminogen activation.

Methods

The effect of β₂GPI on tPA‐mediated activation of plasminogen was assessed using amidolytic assays, a fibrin gel, and plasma clots. Binding of β₂GPI to tPA and plasminogen was determined in parallel. The effects of IgG fractions and anti‐β₂GPI antibodies from patients with antiphospholipid syndrome (APS) on tPA‐mediated plasminogen activation were also measured.

Results

Beta₂‐glycoprotein I stimulated tPA‐dependent plasminogen activation in the fluid phase and within a fibrin gel. The β₂GPI region responsible for stimulating tPA activity was shown to be at least partly contained within β₂GPI domain V. In addition, β₂GPI bound tPA with high affinity (K_d ∼20 nM), stimulated tPA amidolytic activity, and caused an overall 20‐fold increase in the catalytic efficiency (K_cat/K_m) of tPA‐mediated conversion of Glu‐plasminogen to plasmin. Moreover, depletion of β₂GPI from plasma led to diminished rates of clot lysis, with restoration of normal lysis rates following β₂GPI repletion. Stimulation of tPA‐mediated plasminogen activity by β₂GPI was inhibited by monoclonal anti‐β₂GPI antibodies as well as by anti‐β₂GPI antibodies from patients with APS.

Conclusion

These findings suggest that β₂GPI may be an endogenous regulator of fibrinolysis. Impairment of β₂GPI‐stimulated fibrinolysis by anti‐β₂GPI antibodies may contribute to the development of thrombosis in patients with APS.

     

Molecular mechanisms involved in the resistance of fibrin to clot lysis by plasmin in subjects with type 2 diabetes mellitus

Aims/hypothesis The aim of this study was to determine the influence of type 2 diabetes on fibrinolysis by assessing interactions between the regulatory components of fibrinolysis and the fibrin clot, using fibrinogen purified from 150 patients with type 2 diabetes and 50 matched controls.Methods Clot lysis rates were determined by confocal microscopy. Plasmin generation was measured using a plasmin-specific chromogenic substrate. Surface plasmon resonance was used to determine the binding interactions between fibrin, tissue-type plasminogen activator (t-PA) and Glu-plasminogen; cross-linkage of plasmin inhibitor to fibrin by factor XIII was determined using a microtitre plate assay.Results Lysis of diabetic clots was significantly slower than that of controls (1.35 vs 2.92 μm/min, p<0.0001) and plasmin generation was significantly reduced. The equilibrium binding affinity between both t-PA and Glu-plasminogen and fibrin was reduced in diabetic subjects: t-PA, K _D=0.91±0.3 μmol/l (control subjects), 1.21±0.5 μmol/l (diabetic subjects), p=0.001; Glu-plasminogen, K _D=97±19 nmol/l (control subjects), 156±66 nmol/l (diabetic subjects), p=0.001. Cross-linkage of plasmin inhibitor to fibrin by factor XIII was enhanced in diabetic subjects, with the extent of in vitro cross-linkage correlating with in vivo glycaemic control (HbA_1c) (r=0.59, p=0.001).Conclusions/interpretation These results indicate that impairment of the fibrinolytic process in diabetic patients is mediated via a number of different mechanisms; these may be a consequence of post-translational modifications to fibrinogen molecules, resulting from their exposure to the abnormal metabolic milieu associated with diabetes.     

Measurements of plasmin-alpha 2 plasmin inhibitor complex and FDP.D dimer levels in the fibrinolytic therapy of acute pulmonary thromboembolism]

The key enzyme for fibrinolysis is plasmin, which is converted from plasminogen by plasminogen activator. Activated plasmin lyses fibrinogen and fibrin to make fibrin degradation products(FDPs) and plasmin is inactivated immediately by alpha 2 plasmin inhibitor. As FDP.D dimer is derived solely from insoluble fibrin, FDP.D dimer is thought of as an index for clot lysis. We measured plasmin-alpha 2 plasmin inhibitor complex(PIC) and FDP.D dimer plasma levels in 3 patients with acute pulmonary thromboembolism treated with recombinant tissue plasminogen activator(tPA). Fifteen million units of tPA(TD-2061) were infused in one hour on the first, second and third hospital days. PIC and FDP.D dimer before tPA infusion showed slightly elevated values as compared to normal ranges. They increased markedly after tPA infusion. These findings suggest that the fibrinolytic system is slightly activated in the acute phase of pulmonary thromboembolism and also strongly activated by tPA infusion. Increased FDP D dimer suggests that fibrin clots are dissolved by activated plasmin. Improvement of arterial oxygen tension was observed after tPA infusion. As sustained higher FDP.D dimer means the existence of fibrin clots, heparin treatment should be continued for prevention of clot formation as long as FDP.D dimer shows higher value. In conclusion, PIC and FDP.D dimer are useful indices not only to detect the activated state of the fibrinolytic system but also to know clot lysis in tPA treatment.     

Altered plasma fibrin clot properties in essential thrombocythemia

Patients with increased thromboembolic risk tend to form denser fibrin clots which are relatively resistant to lysis. We sought to investigate whether essential thrombocythemia (ET) is associated with altered fibrin clot properties in plasma. Ex vivo plasma fibrin clot permeability coefficient (K_s), turbidimetry and clot lysis time (CLT) were measured in 43 consecutive patients with ET (platelet count from 245 to 991?×?10³/µL) and 50 control subjects matched for age, sex and comorbidities. Fibrinolysis proteins and inhibitors together with platelet activation markers were determined. Reduced K_s (?38%, p?p?p?=?0.01) and higher maximum absorbency of the turbidimetric curve (+6%, p?p?p?p?p?K_s inversely correlated with fibrinogen, PF4 and C-reactive protein. CLT positively correlated only with PAI-1. Patients with ET display prothrombotic plasma fibrin clot phenotype including impaired fibrinolysis, which represents a new prothrombotic mechanism in this disease.     

Stabilization of fibrin clots by activated prothrombin complex concentrate and tranexamic acid in FVIII inhibitor plasma

Summary. Defective hemostasis in haemophilia patients with FVIII inhibitors results in a dramatic decrease in thrombin generation forming unstable fibrin clots that are susceptible to fibrinolyisis. In this study we tested whether the combination of plasma derived activated prothrombin complex concentrate (pd‐aPCC) with tranexamic acid (TXA) may improve fibrin clot stability in FVIII inhibitor plasma. A microplate assay for clot lysis time was used to assess clot stability in FVIII inhibitor plasma. The effect of pd‐aPCC on clot stability was first tested using the commercial FVIII inhibitor plasma. TXA (5 ～ 10 mg mL^?1) increased clot lysis time, but pd‐aPCC (0.25 ～ 1.0 U mL^?1) had no effect on it. The combination of pd‐aPCC and TXA significantly increased clot lysis time compared with TXA alone. The effect appeared to be limited to fibrin clot resistance to fibrinolysis, as TXA was found to have no effect on thrombin generation induced by pd‐aPCC. The effect of pd‐aPCC and TXA on clot stability was then tested and verified in plasma samples from ten patients with severe haemophilia A and inhibitors. The combination of TXA (10 mg mL^?1) and pd‐aPCC (0.5 U mL^?1) significantly increased clot lysis time compared to TXA alone. Our results suggest that the combination of pd‐aPCC with TXA improves clot stability in FVIII inhibitor plasma without additional increases in thrombin generation.     

α2‐Antiplasmin and its deficiency: fibrinolysis out of balance

Summary. Fibrinolysis serves an important role in the process of coagulation, ensuring that clots that are formed in response to injury resolve after the injured tissue is repaired. Fibrinolysis occurs because the protein plasminogen is converted to the active serine protease plasmin by its activating molecules (primarily tissue plasminogen activator). One of the inhibitors of fibrinolysis is α₂‐antiplasmin, which acts as the primary inhibitor of plasmin(ogen). Congenital deficiency of α₂‐antiplasmin causes a rare bleeding disorder because of increased fibrinolysis. Despite the rare nature of this disorder, understanding of the actions of α₂‐antiplasmin and the results of its deficiency has provided the opportunity for better understanding of the fibrinolytic system in both how it affects the risk of bleeding and its impact on other bodily systems. Here, we review the history of the discovery of α₂‐antiplasmin, our understanding of its genetics and function, and our current knowledge of its congenital deficiency. We also discuss some of the current avenues of investigation into its impact on other diseases and physiological states.     

Differential binding of plasminogen to crosslinked and noncrosslinked fibrins: its significance in hemostatic defect in factor XIII deficiency

In spontaneous fibrinolysis of an alpha 2-plasmin inhibitor-deficient plasma clot or tissue-type plasminogen activator-induced fibrinolysis in a purified system without alpha 2-plasmin inhibitor, the lysis was faster when factor XIII-mediated crosslinking of fibrin to fibrin did not occur. During the initial period, the binding of plasminogen to fibrin steadily increased with incubation time. The initial level and subsequent increase of the binding, which may be critical for the subsequent development of fibrinolysis, were more remarkable when fibrin was not crosslinked. The amount of glu- or lys-plasminogen bound to noncrosslinked fibrin was around 4 or 1.5 times larger than the amount of the respective plasminogen bound to crosslinked fibrin. Plasmin was also found to be bound to noncrosslinked fibrin twice as much as the amount bound to crosslinked fibrin. Structural changes induced by crosslinking of fibrin alpha-chain may reduce either the affinity or the number of available complementary sites to lysine binding sites of plasmin(ogen), thereby decreasing the binding of plasmin(ogen) to fibrin. These results suggest that an increased affinity of noncrosslinked fibrin for plasmin(ogen) is contributory to the accelerated fibrinolysis observed in factor XIII deficiency, in addition to an absence of crosslinking of alpha 2-plasmin inhibitor to fibrin.     

Use of global assays to understand clinical phenotype in congenital factor VII deficiency

Congenital factor VII (FVII) deficiency is characterized by genotypic variability and phenotypic heterogeneity. Traditional screening and factor assays are unable to reliably predict clinical bleeding phenotype and guide haemorrhage prevention strategy. Global assays of coagulation and fibrinolysis may better characterize overall haemostatic balance and aid in haemorrhagic risk assessment. We evaluated the ability of novel global assays to better understand clinical bleeding severity in congenital FVII deficiency. Subjects underwent central determination of factor VII activity (FVII:C) as well as clot formation and lysis (CloFAL) and simultaneous thrombin and plasmin generation (STP) global assay analysis. A bleeding score was assigned to each subject through medical chart review. Global assay parameters were analysed with respect to bleeding score and FVII:C. Subgroup analyses were performed on paediatric subjects and subjects with FVII ≥1 IU dL^?1. CloFAL fibrinolytic index (FI₂) inversely correlated with FVII:C while CloFAL maximum amplitude (MA) and STP maximum velocity of thrombin generation (V_T max) varied directly with FVII:C. CloFAL FI₂ directly correlated with bleeding score among subjects in both the total cohort and paediatric subcohort, but not among subjects with FVII ≥1 IU dL^?1. Among subjects with FVII ≥1 IU dL^?1, STP time to maximum velocity of thrombin generation and time to maximum velocity of plasmin generation inversely correlated with bleeding score. These preliminary findings suggest a novel potential link between a hyperfibrinolytic state in bleeding severity and congenital FVII deficiency, an observation that should be further explored.     

The pathogenesis of accelerated fibrinolysis in liver cirrhosis: a critical role for tissue plasminogen activator inhibitor

The pathogenesis of accelerated fibrinolysis in liver cirrhosis was investigated by comparing the results of specific assays for tissue plasminogen activator (tpa) antigen, tpa activity, tpa inhibitor, and alpha-2 plasmin inhibitor (a2PI) in 12 patients with cirrhosis and markedly accelerated fibrinolysis (dilute whole blood clot lysis time (DWBCLT) less than two hours), in nine patients with cirrhosis and moderately accelerated fibrinolysis (DWBCLT two to four hours), and in nine patients with cirrhosis and normal fibrinolysis (DWBCLT greater than four hours). Mean tpa antigen was markedly increased in all three groups, but no correlation was observed between overall fibrinolytic activity as measured by the DWBCLT and the level of tpa antigen. In contrast, there was a significant correlation between overall fibrinolytic activity and tpa activity and an equally significant correlation between fibrinolytic activity and decreased tpa inhibition. Mean a2PI activity was significantly lower than normal in groups 1 and 2 but was normal in group 3. The pathogenesis of accelerated fibrinolysis in liver cirrhosis thus appears to depend critically on the capacity of plasma inhibitors to inhibit increased circulating tpa antigen. Reduced a2PI also appears to play a role.     

A novel simultaneous clot-fibrinolysis waveform analysis for assessing fibrin formation and clot lysis in haemorrhagic disorders

Simultaneous evaluation of coagulation and fibrinolysis facilitates an overall understanding of normal and pathological haemostasis. We established an assay for assessing clot formation and fibrinolysis simultaneously using clot waveform analysis by the trigger of a mixture of activated partial thromboplastin time reagent and an optimized concentration of tissue-type plasminogen activator (0·63 μg/ml) to examine the temporal reactions in a short monitoring time (<500 s). The interplay between clot formation and fibrinolysis was confirmed by analysing the effects of argatroban, tranexamic acid and thrombomodulin. Fibrinogen levels positively correlated with coagulation and fibrinolytic potential and initial fibrin clot formation was independent of plasminogen concentration. Plasminogen activator inhibitor-1-deficient (-def) and α2-antiplasmin-def plasmas demonstrated different characteristic hyper-fibrinolytic patterns. For the specificity of individual clotting factor-def plasmas, factor (F)VIII-def and FIX-def plasmas in particular demonstrated shortened fibrinolysis lag-times (FLT) and enhanced endogenous fibrinolysis potential in addition to decreased maximum coagulation velocity, possibly reflecting the fragile formation of fibrin clots. Tranexamic acid depressed fibrinolysis to a similar extent in FVIII-def and FIX-def plasmas. We concluded that the clot-fibrinolysis waveform analysis technique could sensitively monitor both sides of fibrin clot formation and fibrinolysis, and could provide an easy-to-use assay to help clarify the underlying pathogenesis of bleeding disorders in routine clinical practice.     

Fibrinolysis in patients with diabetic nephropathy determined by plasmin-α2 plasmin inhibitor complexes in plasma

Activation of fibrinolysis in patients with diabetic nephropathy was determined by the plasma levels of plasmin-α₂ plasmin inhibitor complexes (α₂PIC) using a one-step sandwich enzyme immunoassay (EIA). Plasma levels of α₂PIC in diabetic patients with persistent proteinuria were significantly higher than those in diabetic patients without proteinuria, patients with chronic glomerulonephritis, and healthy adults. Plasma levels of α₂PIC in diabetic patients with intermittent proteinuria were also significantly higher than those of diabetic patients without proteinuria, patients with chronic glomerulonephritis, and healthy adults. Diabetic patients have been suggested to have a hypercoagulable state. The findings obtained from this study indicated that activation of fibrinolysis might counteract the hypercoagulable state in patients with diabetic nephropathy.     

Elastic modulus-based thrombelastographic quantification of plasma clot fibrinolysis with progressive plasminogen activation.

Thrombelastographic detection of fibrinolysis has been critical in the identification and treatment of coagulopathy in many perioperative settings. However, the fibrinolytic assessments have been at best non-parametric, amplitude-based determinations (e.g. estimated % lysis, clot lysis time or clot lysis rate). Recognizing this limitation, a methodology was developed to measure the onset, speed and extent of clot disintegration by changes in elastic modulus derived from the amplitude. Using this approach, our goal was to characterize the clot disintegration kinetics of progressive plasminogen activation with tissue plasminogen activator (tPA) and to determine the extent of inhibition of fibrinolysis mediated by tPA with aprotinin and activated factor XIII. While the estimated % lysis and clot lysis time were significantly affected by tPA (0-300 U/ml), elastic modulus-based analyses in a more activity-specific fashion demonstrated significantly decreased onset, increased rate and increased extent of fibrinolysis. Furthermore, aprotinin was found to inhibit the onset, rate and extent of fibrinolysis in an activity-dependent fashion, whereas activated factor XIII was noted to enhance the speed of onset of clot growth and delay the onset of fibrinolysis. In summary, our results serve as the rational basis to utilize this elastic modulus-based approach to quantify the extent of fibrinolysis in clinical and laboratory settings, as well as potentially guiding antifibrinolytic therapy.     

Aβ delays fibrin clot lysis by altering fibrin structure and attenuating plasminogen binding to fibrin

Alzheimer disease is characterized by the presence of increased levels of the β-amyloid peptide (Aβ) in the brain parenchyma and cerebral blood vessels. This accumulated Aβ can bind to fibrin(ogen) and render fibrin clots more resistant to degradation. Here, we demonstrate that Aβ(42) specifically binds to fibrin and induces a tighter fibrin network characterized by thinner fibers and increased resistance to lysis. However, Aβ(42)-induced structural changes cannot be the sole mechanism of delayed lysis because Aβ overlaid on normal preformed clots also binds to fibrin and delays lysis without altering clot structure. In this regard, we show that Aβ interferes with the binding of plasminogen to fibrin, which could impair plasmin generation and fibrin degradation. Indeed, plasmin generation by tissue plasminogen activator (tPA), but not streptokinase, is slowed in fibrin clots containing Aβ(42), and clot lysis by plasmin, but not trypsin, is delayed. Notably, plasmin and tPA activities, as well as tPA-dependent generation of plasmin in solution, are not decreased in the presence of Aβ(42). Our results indicate the existence of 2 mechanisms of Aβ(42) involvement in delayed fibrinolysis: (1) through the induction of a tighter fibrin network composed of thinner fibers, and (2) through inhibition of plasmin(ogen)-fibrin binding.     

Inhibition of fibrinolysis by recombinant factor VIIa in plasma from patients with severe hemophilia A.

Recombinant factor VIIa (rFVIIa) is a novel prohemostatic drug for patients with hemophilia who have developed inhibitory antibodies. The postulation has been made that hemophilia is not only a disorder of coagulation, but that hyperfibrinolysis due to a defective activation of thrombin activatable fibrinolysis inhibitor (TAFI) might also play a role. In this in vitro study, the potential of rFVIIa to down-regulate fibrinolysis via activation of TAFI was investigated. rFVIIa was able to prolong clot lysis time in plasmas from 17 patients with severe hemophilia A. The prolongation of clot lysis time by rFVIIa was completely abolished by addition of an inhibitor of activated TAFI. The concentration of rFVIIa required for half maximal prolongation of clot lysis time (C(lys 1/2)-VIIa) varied widely between patients (median, 73.0 U/mL; range, 10.8-250 U/mL). The concentration of rFVIIa required for half maximal reduction of clotting time (C(clot 1/2)-VIIa) was approximately 10-fold lower than the C(lys 1/2)-VIIa value (median, 8.4 U/mL; range, 1.7-22.5 U/mL). Inhibition of TFPI with a polyclonal antibody significantly decreased C(lys 1/2)-VIIa values (median, 2.6 U/mL; range, 0-86.9 U/mL), whereas C(clot 1/2)-VIIa values did not change (median, 7.2 U/mL; range, 2.2-22.5 U/mL). On addition of 100 ng/mL recombinant full-length TFPI, a nonsignificant increase of C(lys 1/2)-VIIa values was observed (median, 119.2 U/mL; range, 12.3-375.0 U/mL), whereas C(clot 1/2)-VIIa values did not change (median, 8.8 U/mL; range, 2.6-34.6 U/mL). In conclusion, this study shows that rFVIIa both accelerates clot formation and inhibits fibrinolysis by activation of TAFI in factor VIII-deficient plasma. However, a large variability in antifibrinolytic potential of rFVIIa exists between patients.     

Clinical significance of accelerated fibrinolysis in liver disease

We compared site and severity of bleeding in 46 patients with cirrhosis of the liver and accelerated fibrinolysis (defined as a dilute whole-blood clot lysis time less than 2 h) to 44 patients with cirrhosis of the liver and normal fibrinolysis (dilute whole-blood clot lysis time greater than 4 h). Patients with accelerated fibrinolysis had a significantly higher incidence of severe soft-tissue bleeding after trauma and a trend toward increased intracranial bleeding. Mucosal, postoperative, and gastrointestinal bleeding were equally frequent in the two groups. The median partial thromboplastin time was significantly longer, and the median bilirubin and fibrin/fibrinogen degradation product levels were significantly higher in the group with accelerated fibrinolysis, but median prothrombin time, platelet count, and levels of fibrinogen and serum albumin were comparable. The fibrinolytic inhibitor epsilon-aminocaproic acid successfully controlled bleeding in 4 of 6 cases used. Accelerated fibrinolysis may predispose patients with cirrhosis to soft-tissue and intracranial bleeding.     

DISCUSSION

The specific indication of intravascular fibrinolysis is the demonstration of fibrinogenfibrin degradation products. To evaluate the effect on fibrinolysis 48 patients were treated with clofibrate, metformin, tolazamide or testosterone for periods of one to fourteen weeks. Blood fibrinolytic activity was assessed before, during and after treatment by measurements of euglobulin clot lysis time, plasminogen and fibrinogen, and immunoassays of fibrinogen-fibrin degradation products. 17 normal persons, 23 patients with atherosclerotic vascular disease, and 11 patients with other diseases were exposed to physical exertion or injections of nicotinic acid. Fibrinolytic activity was assessed as above, before and after stimulation. Acceleration of euglobulin clot lysis was found in only 2 of 11 patients treated with metformin, but in 47 persons exposed to short-term stimulation. No fibrinolytic breakdown products were found in serum samples containing EACA. The significance of accelerated euglobulin clot lysis cannot be evaluated independently.     

Fibrinolysis and Coagulation. I.

The effect of various concentrations of calcium on lysis of euglobulin clots was studied. If clot lysis times exceeded 200 minutes, 0.5 mM CaCl₂ or less inhibited the process, whereas higher concentrations accelerated clot lysis. If clot lysis times were short, high calcium concentrations inhibited clot lysis. This happened if enhanced activity was obtained by removal of inhibitors or if it was obtained by a higher activator concentration. These effects of calcium were related to its procoagulant effect and disappeared on adsorbtion with BaSO₄. Euglobulin from patients with severe coagulopathies revealed a reduced accelerating effect of calcium. The calcium effect on clot structure was probably of minor importance.