Clinical disorders of fibrinolysis: a critical review

Thrombotic Disease in Hemophilic Patients: Is This a Paradox in a State of Hypocoagulability?

Hemophilia patients have a deficiency in or dysfunction of clotting factors, which can lead to a bleeding tendency. However, paradoxically, some hemophilia patients may also be at an increased risk of developing thrombotic events such as deep vein thrombosis or pulmonary embolism. The pathophysiology of thrombosis in hemophilia patients is not fully understood, but it is thought to involve a complex interplay of various factors, including the severity of the hemophilia, the presence of other risk factors such as obesity, smoking, or the use of hormonal therapies, and the presence of certain genetic mutations that increase the risk of thrombosis. In addition, it has been suggested that the use of clotting factor replacement therapy, which is a standard treatment for hemophilia, may also contribute to the development of thrombosis in some cases.

Computational modeling of hypercoagulability in COVID-19

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected more than 100 million people worldwide and claimed millions of lives. While the leading cause of mortality in COVID-19 patients is the hypoxic respiratory failure from acute respiratory distress syndrome, there is accumulating evidence that shows excessive coagulation also increases the fatalities in COVID-19. Thus, there is a pressing demand to understand the association between COVID-19-induced hypercoagulability and the extent of formation of undesired blood clots. Mathematical modeling of coagulation has been used as an important tool to identify novel reaction mechanisms and to identify targets for new drugs. Here, we employ the coagulation factor data of COVID-19 patients reported from published studies as inputs for two mathematical models of coagulation to identify how the concentrations of coagulation factors change in these patients. Our simulation results show that while the levels of many of the abnormal coagulation factors measured in COVID-19 patients promote the generation of thrombin and fibrin, two key components of blood clots, the increased level of fibrinogen and then the reduced level of antithrombin are the factors most responsible for boosting the level of fibrin and thrombin, respectively. Altogether, our study demonstrates the potential of mathematical modeling to identify coagulation factors responsible for the increased clot formation in COVID-19 patients where clinical data is scarce.

Fibrinolytic Serine Proteases, Therapeutic Serpins and Inflammation: Fire Dancers and Firestorms

The making and breaking of clots orchestrated by the thrombotic and thrombolytic serine protease cascades are critical determinants of morbidity and mortality during infection and with vascular or tissue injury. Both the clot forming (thrombotic) and the clot dissolving (thrombolytic or fibrinolytic) cascades are composed of a highly sensitive and complex relationship of sequentially activated serine proteases and their regulatory inhibitors in the circulating blood. The proteases and inhibitors interact continuously throughout all branches of the cardiovascular system in the human body, representing one of the most abundant groups of proteins in the blood. There is an intricate interaction of the coagulation cascades with endothelial cell surface receptors lining the vascular tree, circulating immune cells, platelets and connective tissue encasing the arterial layers. Beyond their role in control of bleeding and clotting, the thrombotic and thrombolytic cascades initiate immune cell responses, representing a front line, "off-the-shelf" system for inducing inflammatory responses. These hemostatic pathways are one of the first response systems after injury with the fibrinolytic cascade being one of the earliest to evolve in primordial immune responses. An equally important contributor and parallel ancient component of these thrombotic and thrombolytic serine protease cascades are the serine protease inhibitors, termed serpins. Serpins are metastable suicide inhibitors with ubiquitous roles in coagulation and fibrinolysis as well as multiple central regulatory pathways throughout the body. Serpins are now known to also modulate the immune response, either via control of thrombotic and thrombolytic cascades or via direct effects on cellular phenotypes, among many other functions. Here we review the co-evolution of the thrombolytic cascade and the immune response in disease and in treatment. We will focus on the relevance of these recent advances in the context of the ongoing COVID-19 pandemic. SARS-CoV-2 is a "respiratory" coronavirus that causes extensive cardiovascular pathogenesis, with microthrombi throughout the vascular tree, resulting in severe and potentially fatal coagulopathies.

Is clinical outcome of dengue-virus infections influenced by coagulation and fibrinolysis? A critical review of the evidence

Despite efforts to elucidate the pathogenesis of dengue fever, the progression into severe disease remains poorly understood. In-vitro findings suggest that coagulopathy and disturbances in fibrinolysis have a pivotal role in the pathophysiology. If disturbances in these processes are predictive of clinical outcome in this disease, there could be important consequences for both diagnosis and treatment. We have critically reviewed publications on this topic to assess whether there is an association between activation of coagulation and fibrinolysis and clinical outcome of dengue-virus infections. In general, the selected studies showed activation of both the coagulation and fibrinolytic systems in this infection. The activation was more pronounced in severe infections and in cases with a poor clinical outcome. However, the findings were not consistent, and owing to a lack of detailed information on characteristics of patients, disease, and study design, we could not ascertain whether inconsistencies were caused by differences in these characteristics, selection bias, or confounding factors. We conclude that an association between activation of coagulation and fibrinolysis and clinical outcome of dengue-virus infections is conceivable but has been inadequately assessed and that methodologically sound studies, complemented with complete and reliable reporting, are needed to show whether there is a true association.

Pediatric resuscitation in the operating room

The resuscitation of pediatric patients undergoing anesthesia involves appropriate administration of fluid and blood products and stabilization of vital signs. Crystalloid is first-line therapy for fluid resuscitation, and should be given with awareness of its potential dilution of the child's hematocrit. Many alternatives to homologous blood transfusions now exist, however, when necessary for increasing oxygen-carrying capacity or treating coagulopathy benefits likely outweight the risks. The risks for such transfusion include infectious, hemolytic, metabolic, and immunologic effects. When fluid and blood administration does not stabilize the patient, the differential diagnosis of hypotension, arrest, or arrhythmias must include medication errors, anesthetic overdose, electrolyte disturbances, hypoxemia, ventilatory problems, and surgical insults, including medications given in the operative field. Resuscitation should include treatment of hypocalcemia and hyperkalemia, chest compressions, and the administration of epinephrine when necessary.

Antithrombotic, procoagulant, and fibrinolytic mechanisms in cerebral circulation: implications for brain injury and protection

Maintaining a delicate balance among anticoagulant, procoagulant, and fibrinolytic pathways in the cerebral microcirculation is of major importance for normal cerebral blood flow. Under physiological conditions and in the absence of provocative stimuli, the anticoagulant and fibrinolytic pathways prevail over procoagulant mechanisms. Blood clotting is essential to minimize bleeding and to achieve hemostasis; however, excessive clotting contributes to thrombosis and may predispose the brain to infarction and ischemic stroke. Conversely, excessive bleeding due to enhanced anticoagulatory and fibrinolytic mechanisms could predispose the brain to hemorrhagic stroke. Recent studies in the author's laboratory indicate that brain capillary endothelium in vivo produces thrombomodulin (TM), a key cofactor in the TM-protein C system that is of major biological significance to the antithrombotic properties of the blood-brain barrier (BBB). The BBB endothelium also expresses tissue plasminogen activator (tPA), a key protein in fibrinolysis, and its rapid inhibitor, plasminogen activator inhibitor (PAI-1). The procoagulant tissue factor is normally dormant at the BBB. There is a vast body of clinical evidence to document the importance of hemostasis in the pathophysiology of brain injury. In particular, functional changes caused by major stroke risk factors in the TM-protein C, tPA/PAI-1, and tissue factor systems at the BBB may result in large and debilitating infarctions following an ischemic insult. Thus, correcting this hemostatic imbalance could ameliorate drastic CBF reductions at the time of ischemic insult, ultimately resulting in brain protection. Delineation of the molecular mechanisms of BBB-mediated hemostasis will likely contribute to future stroke prevention efforts and brain protection strategies.

Brain capillary tissue plasminogen activator in a diabetes stroke model

BACKGROUND AND PURPOSE

Tissue plasminogen activator (TPA) is normally expressed in rat brain capillaries. This study examines the expression of TPA in brain capillaries of diabetic rats in relation to focal ischemic brain injury.

METHODS

Diabetes type 1 was induced by streptozotocin for 7 days. Acute hyperglycemia was induced by 50% dextrose. Expression of TPA in brain capillaries was determined by Western blot and reverse transcription-polymerase chain reaction analyses. Focal stroke was produced by 1 hour of reversible middle cerebral artery occlusion. Physiological variables and cerebral blood flow were monitored during occlusion and within 1 hour of reperfusion. Neurological and neuropathologic examinations were performed after 24 hours of reperfusion.

RESULTS

All rats developed comparable hyperglycemia (approximately 15 mmol/L). A complete depletion of TPA protein and 6.5-fold decrease in TPA mRNA were found in brain capillaries of diabetic rats, in contrast to normal TPA capillary levels in hyperglycemic rats. The blood flow in the periphery of the ischemic core was significantly reduced during reperfusion by 52% to 62% (P<.001) in diabetic rats and by 23% to 25% (P<.05) in hyperglycemic rats. The neurological score was worsened by 3.2-fold (P<.0003) by diabetes and by 24% by hyperglycemia only. Significant 41% (P<.007) and 29% (P<.05) increases in infarct volume and 163% (P<.007) and 60% increases in edema volume were found in diabetic rats relative to control and hyperglycemic rats, respectively.

CONCLUSIONS

Diabetes type 1, but not acute hyperglycemia, produces downregulation of TPA in rat brain capillaries. This TPA reduction is associated with impaired restoration of blood flow after an ischemic insult, poor neurological outcome, and enhanced ischemic brain injury.

Expression of tissue plasminogen activator in cerebral capillaries: possible fibrinolytic function of the blood-brain barrier

Previous work has shown that tissue plasminogen activator (tPA) is a key enzyme in the control of fibrinolysis within the vascular system. The sources of brain tPA and the mechanisms by which tPA secretion and production occur within cerebral microcirculation are not well established. In this study, expression of tPA was investigated in cerebral capillaries and capillary-depleted brain isolated from cortices of 4- to 5-week-old rats and guinea pigs. In both species, a single tPA band of M(r) 67,000 was detected in cerebral capillaries by Western blot analysis. The tPA signal was absent from capillary-depleted brain. These results were corroborated at the messenger ribonucleic acid level. Reverse transcription-polymerase chain reaction analysis revealed the presence of tPA complementary deoxyribonucleic acid in samples derived from cerebral microvessels and demonstrated very low or undetectable tPA expression in capillary-depleted brain. Immunohistochemical analysis confirmed tPA localization in endothelial cells of brain capillaries. We conclude that microvascular endothelium, i.e., the blood-brain barrier, may have a role in promoting plasmin-dependent fibrinolysis in brain microcirculation. Delineation of the molecular mechanisms of blood-brain barrier-mediated fibrinolysis will likely contribute to future stroke prevention efforts.

Fibrinolysis and coagulation abnormalities in systemic lupus erythematosus. Relationship with Raynaud's phenomenon, disease activity, inflammatory indices, anticardiolipin antibodies and corticosteroid therapy

Endothelial cell damage in systemic lupus erythematosus (SLE) was evaluated by measuring fibrinolytic activity and von Willebrand factor levels. Tissue-type plasminogen activator (t-PA) antigen, plasminogen activator inhibitor (PAI) activity, and von Willebrand factor antigen (vWF:Ag) and activity (vWF:RCof) were measured in 21 SLE patients (12 of whom were therapy free) and 22 controls. In addition, the relationship between such parameters and Raynaud's phenomenon, disease activity [according to personal criteria, Systemic Lupus Activity Measure (SLAM) and European Consensus Lupus Activity Measurement (ECLAM) scores] inflammatory indices [ESR, C-reactive protein (CRP), alpha 2-globulin], anticardiolipin antibodies and corticosteroid therapy was investigated. Lower levels of t-PA antigen (P = 0.003) and higher levels of vWF:Ag (P = 0.001) were found in SLE patients in comparison with controls. Moreover, t-PA antigen was lower (P = 0.02) in steroid-free patients in comparison with those taking steroids. No relationship was found between fibrinolysis and coagulation abnormalities and Raynaud's phenomenon, disease activity, inflammatory indices and anticardiolipin antibodies. Endothelial cell damage is probably a common feature in SLE patients; nevertheless, we were unable to clarify the nature of such abnormality. It is worth noting that low doses of steroids seem to be effective in improving endothelial cell function in SLE patients.

Reduction of the plasma levels of tissue plasminogen activator after infusion of a lipid emulsion in humans

A lipid emulsion of soybean oil, egg lecithin, and glycerol, widely used as a standard component of parenteral nutrition regimens, has been reported to induce changes in some hemostatic parameters known to be associated with increased thrombotic risk. We studied the effect of a single infusion of this lipid emulsion (500 mL of a 10% emulsion, give over 5 to 6 hours) on the plasma levels of tissue plasminogen activator and plasminogen activator inhibitor 1 antigens in 12 patients with various diseases. Twelve matched patients, not treated with lipid, served as controls. In patients receiving the lipid emulsion, tissue plasminogen activator was markedly reduced at the end of the infusion (p < .001) and remained significantly lower than the basal levels 24 hours later (p < .05). By contrast, in control patients, the activator was slightly but significantly increased (p < .01) at the time interval corresponding to the postinfusion sample. Plasminogen activator inhibitor 1 was similar in control and treated patients at all intervals. The release of tissue plasminogen activator in response to 10 minutes of venous stasis, evaluated in six lipid-treated patients at the end of the infusion, was not different from that observed in six control patients. It is concluded that the lipid emulsion induces a marked decrease in the circulating levels of tissue plasminogen activator.

Hematogenous factors and prediction of delayed ischemic deficit after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Delayed ischemic deficits contribute to the high morbidity and mortality rates associated with subarachnoid hemorrhage. We evaluated the potential usefulness of measuring coagulation and hemorheological variables and cardiolipin antibodies for prediction of delayed ischemic deficit after subarachnoid hemorrhage.

METHODS

Consecutive patients with subarachnoid hemorrhage were studied. Coagulation and hemorheological variables and cardiolipin antibodies were measured on admission, within 7 days of subarachnoid hemorrhage. A subset of patients was studied on admission and at two subsequent occasions.

RESULTS

Sixty-nine patients were studied. Sixty-one of these were without clinical manifestations of vasospasm at admission, and 16 developed delayed ischemic deficit during their hospitalization. None of the laboratory variables measured were significantly different between patients with or without later development of delayed ischemic deficit. Elevation of the fibrin fragment D-dimer was found in the group of eight patients admitted with ischemic symptoms and in 49% (34 of 69) of all patients, but this was not associated with delayed ischemic deficit. Sixteen patients were studied on three occasions; this group showed a significant decrease in hematocrit, an increased white blood cell count, and no change in fibrinogen concentration. Fibrin D-dimer levels rose significantly after surgery (from 5.01 +/- 0.69 to 5.53 +/- 0.58 ln-ng/ml, p less than 0.025) and after onset of delayed ischemic deficit (from 4.71 +/- 0.64 to 5.84 +/- 0.34 ln-ng/ml, p less than 0.01).

CONCLUSIONS

Hemostatic measurements, hemorheological variables, and cardiolipin immunoreactivity did not predict delayed ischemic deficit in this population.

Fibrinolytic mechanisms in tumor growth and spreading

The high prevalence of hypercoagulative states in cancer patients has been known for more than a century. Venous thrombosis in gastric cancer was described by Trousseau in 1865 [55]. In 1878, Billroth observed intravascular thrombus formation in association with metastasis [4]. Thrombohemorrhagic complications regularly occur in patients with disseminated malignancy and are related to an increase in fibrinogen and fibrin turnover. During the past decade, clinicians have witnessed considerable advances in the understanding of fibrinolysis. Initially centered on the role as part of a dynamic, hemostatic balance, research began to unravel the pathophysiological contribution of fibrinolysis to tumor progression. The mechanisms of tumor invasion and metastasis formation in cancer are of critical importance, since metastasis is the major cause of treatment failure and death. It has been suggested that cell-associated proteolytic enzymes contribute to tumor aggressiveness [11, 22, 23]. Fibrinolytic mechanisms are involved in a number of physiological processes in which tissue degradation and remodeling occurs. These include disruption of the ovarian follicle during ovulation and blastocyst implantation. These events in part resemble the invasive growth of cancer [37, 47]. Inspired by this hypothesis, the role of fibrinolytic processes in tumor invasion is under intensive study.

Hemobiology, vascular disease, and diabetes with special reference to impaired fibrinolysis

This brief review is intended to emphasize the multiple interactions between diabetes and the pathophysiological processes that lead to ischemic cardiovascular events. The main pathogenetic pathways of atherothrombosis and their relationship with diabetes are largely and frequently analyzed. In this review, we will focus on a particular aspect of this pathological process, namely, the impairment in fibrinolysis, the importance of which has been recently recognized in cardiovascular disease. Fibrinolysis is frequently impaired in diabetic patients.

Immunocytochemical localization of platelets in baboon hepatic sinusoids using monoclonal mouse anti-human platelet glycoprotein IIIa following induction of thrombocytopenia

A commercially available mouse monoclonal antibody to human platelet glycoprotein IIIa was used to demonstrate sequestration of platelets in hepatic biopsies obtained from baboons following intravenous infusion of echistatin, a novel fibrinogen receptor antagonist derived from the venom of the snake Echis carinatus. Biopsies of liver and spleen were taken prior to administration of echistatin. The hepatic biopsies were either snap-frozen in Freon-22/liquid nitrogen or fixed in 10% neutral buffered formalin. Biopsies of spleen were snap-frozen. During infusion of echistatin (2.3 micrograms/kg/min), circulating platelet counts decreased from 331,000/mm3 to 167,000/mm3. Selective sequestration within the liver was confirmed using whole body gamma camera imaging to demonstrate 111Indium-oxine labeled platelet accumulation within the liver during the thrombocytopenic episode. Hepatic biopsies were again taken and either snap-frozen in Freon-22/liquid nitrogen or fixed in 10% neutral buffered formalin. Biopsies of spleen and inguinal lymph node were also snap-frozen. Platelet rich plasma smears, included as positive controls, dewaxed paraffin sections, and cryosections of liver, spleen, and lymph node were stained with monoclonal mouse anti-human platelet glycoprotein IIIa using an avidin biotinylated peroxidase complex (ABC) technique. Prior to infusion of echistatin, platelet staining within the liver was minimal. After echistatin infusion, hepatic cryosections showed prominent platelet staining within hepatic sinusoids. No localization was shown in lymph node, however, the spleen showed prominent platelet staining both before and after echistatin infusion. Platelet rich plasma smears were intensely positive. No prominent platelet staining was observed in formalin-fixed, paraffin-embedded material. Thus, this immunocytochemical technique may help localize platelets in cryosections of tissues from baboons and other primate species.

A critical review of the relationship between impaired fibrinolysis and myocardial infarction

To explore the relationship between impaired fibrinolysis and myocardial infarction, we conducted a literature search and reviewed the published data. The results indicate that myocardial infarction has a significant influence on fibrinolytic activity and that impaired fibrinolysis is more frequent in patients who have had a myocardial infarction than in healthy control subjects. Prospective cohort studies indicate that tests for global fibrinolytic activity are not of prognostic value for first or recurrent myocardial infarction. However, high levels of plasminogen activator inhibitor and low levels of tissue plasminogen activator activity were associated with an increased risk of reinfarction in survivors of a first myocardial infarction. Whether this relationship between impaired fibrinolysis and reinfarction is causal or coincidental is unclear. There is evidence that impairment of fibrinolytic activity is more marked in patients with myocardial infarction who have minimal coronary atherosclerosis than in those who have marked atherosclerosis, suggesting that impaired fibrinolytic activity might be of pathogenetic importance in this small subgroup of patients.

Disturbances in the tissue plasminogen activator/plasminogen activator inhibitor (TPA/PAI) system in systemic lupus erythematosus

Increased thrombogenesis observed in systemic lupus erythematosus (SLE) is derived from multiple mechanisms, including: Enhanced coagulation factor VIII:VWf activity, lupus anticoagulants, anti-phospholipid antibodies, acquired deficiencies of natural anti-thrombotic mechanisms (protein C, protein S, anti-thrombin III), and impaired fibrinolytic mechanisms. We studied the fibrinolytic mechanisms of 18 patients with systemic lupus erythematosus, selected carefully to avoid other possible causes of abnormalities in the fibrinolytic activity. Despite the fact that the euglobulin lysis time in steady state was normal in all instances, disturbances in the tissue plasminogen activator/plasminogen activator inhibitor (TPA/PAI) system were found in all SLE patients: TPA activity was undetectable in all cases, whereas it was above 0.4 IU/ml in a control group. In 72 percent of patients, the undetectable TPA activity was correlated with abnormally high PAI activity; PAI levels were normal in all members of the control group, their mean value being 0.74 versus 8.63 IU/ml for SLE patients (P less than .01). Coagulation protein C deficiency was found in 3 patients (17%). Even though within normal range, fibrinogen levels were significantly higher in SLE than in normal controls (219 versus 192 mg/dl, P less than .01) and plasminogen levels were significantly higher in SLE than in controls (117 versus 78.2%, P less than .01). Cross-linked fibrin derivatives (D-D dimers) were negative in all patients with SLE. Sixty-eight percent of SLE patients had high levels of antiphospholipid antibodies, but no correlation with the disturbances of the TPA/PAI system was found. It is concluded that most patients with SLE display severe abnormalities in the TPA/PAI anti-thrombotic system and that these abnormalities may be related to the lupus thrombophilia, apparently multifactorial in its origin.

The molecular genetics of familial venous thrombosis

Inherited defects of antithrombin III, protein C, protein S, heparin cofactor II, plasminogen and the fibrinogens are thought to be responsible for between 10 and 15% of all patients presenting with recurrent venous thrombosis. The structure, function and expression of these genes and the nature of the gene lesions underlying the deficiency states are reviewed in detail.

Neonatal bleeding in transgenic mice expressing urokinase-type plasminogen activator

Spontaneous intestinal and intra-abdominal bleeding was observed in a high percentage of newborn transgenic mice carrying the murine urokinase-type plasminogen activator (uPA) gene linked to the albumin enhancer/promoter. These hemorrhagic events were directly related to transgene expression in the liver and the development of high plasma uPA levels. Two lines were established from surviving founder mice that displayed multigenerational transmission of the bleeding phenotype. Fatal hemorrhaging developed between 3 and 84 hr after birth in about half of the transgenic offspring of these lines; transgenic pups that did not bleed nevertheless passed the phenotype to their young. The phenotypic variability could not be explained by differences in transgene expression. All transgenic neonates were severely hypofibrinogenemic and displayed loss of clotting function that extended beyond the risk period for bleeding. These mice provide a means of studying the pathophysiology of plasminogen hyperactivation and evaluating therapeutic protocols designed to prevent bleeding.