Congenital deficiency of alpha 2-plasmin inhibitor associated with severe hemorrhagic tendency

Plasmin Inhibitor in Health and Diabetes: Role of the Protein as a Therapeutic Target

The vascular obstructive thrombus is composed of a mesh of fibrin fibers with blood cells trapped in these networks. Enhanced fibrin clot formation and/or suppression of fibrinolysis are associated with an increased risk of vascular occlusive events. Inhibitors of coagulation factors and activators of plasminogen have been clinically used to limit fibrin network formation and enhance lysis. While these agents are effective at reducing vascular occlusion, they carry a significant risk of bleeding complications. Fibrin clot lysis, essential for normal hemostasis, is controlled by several factors including the incorporation of antifibrinolytic proteins into the clot. Plasmin inhibitor (PI), a key antifibrinolytic protein, is cross-linked into fibrin networks with higher concentrations of PI documented in fibrin clots and plasma from high vascular risk individuals. This review is focused on exploring PI as a target for the prevention and treatment of vascular occlusive disease. We first discuss the relationship between the PI structure and antifibrinolytic activity, followed by describing the function of the protein in normal physiology and its role in pathological vascular thrombosis. Subsequently, we describe in detail the potential use of PI as a therapeutic target, including the array of methods employed for the modulation of protein activity. Effective and safe inhibition of PI may prove to be an alternative and specific way to reduce vascular thrombotic events while keeping bleeding risk to a minimum. Key Points Plasmin inhibitor (PI) is a key protein that inhibits fibrinolysis and stabilizes the fibrin network.This review is focused on discussing mechanistic pathways for PI action, role of the molecule in disease states, and potential use as a therapeutic target.

Alpha2-Antiplasmin: The Devil You Don't Know in Cerebrovascular and Cardiovascular Disease

Alpha2-antiplasmin (α2AP), the fast-reacting, serine protease inhibitor (serpin) of plasmin, was originally thought to play a key role in protection against uncontrolled, plasmin-mediated proteolysis of coagulation factors and other molecules. However, studies of humans and mice with genetic deficiency of α2AP have expanded our understanding of this serpin, particularly in disease states. Epidemiology studies have shown an association between high α2AP levels and increased risk or poor outcome in cardiovascular diseases. Mechanistic studies in disease models indicate that α2AP stops the body's own fibrinolytic system from dissolving pathologic thrombi that cause venous thrombosis, pulmonary embolism, arterial thrombosis, and ischemic stroke. In addition, α2AP fosters the development of microvascular thrombosis and enhances matrix metalloproteinase-9 expression. Through these mechanisms and others, α2AP contributes to brain injury, hemorrhage and swelling in experimental ischemic stroke. Recent studies also show that α2AP is required for the development of stasis thrombosis by inhibiting the early activation of effective fibrinolysis. In this review, we will discuss the key role played by α2AP in controlling thrombosis and fibrinolysis and, we will consider its potential value as a therapeutic target in cardiovascular diseases and ischemic stroke.

Variability in international normalized ratio and activated partial thromboplastin time after injury are not explained by coagulation factor deficits

BACKGROUND

Conventional coagulation assays (CCAs), prothrombin time (PT)/international normalized ratio (INR) and activated partial thromboplastin time (aPTT), detect clotting factor (CF) deficiencies in hematologic disorders. However, there is controversy about how these CCAs should be used to diagnose, treat, and monitor trauma-induced coagulopathy. Study objectives were to determine whether CCA abnormalities are reflective of deficiencies of coagulation factor activity in the setting of severe injury.

METHODS

Patients without previous CF deficiency within a prospective database at an ACS-verified Level I trauma center had CF activity levels, PT/INR, aPTT, and fibrinogen levels measured upon emergency department arrival from 2014 to 2017. Linear regression assessed how CF activity explained the aPTT and PT/INR variation. Prolonged CCA values were set as INR greater than 1.3 and aPTT greater than 34 seconds. CF deficiency was defined as less than 30% activity, except for fibrinogen, defined as less than 150 mg/dL.

RESULTS

Sixty patients with a mean age of 35.8 (SD, 13.6) years and median New Injury Severity Score of 32 (interquartile range, 12-43) were included; 53.3% sustained blunt injuries, 23.3% required massive transfusion, and mortality was 11.67%. Overall, 44.6% of the PT/INR variance and 49.5% of the aPTT variance remained unexplained by CF activity. Deficiencies of CFs were: common pathway, 25%; extrinsic pathway, 1.7%; and intrinsic pathway, 6.7%. The positive predictive value for CF deficiencies were: (1) PT/INR greater than 1.3:4.4% for extrinsic pathway, 56.5% for the common pathway; (2) aPTT greater than 34 seconds:16.7% for the intrinsic pathway, 73.7% for the common pathway.

CONCLUSION

Almost half of the variances of PT/INR and aPTT were unexplained by CF activity. Prolonged PT/INR and aPTT were poor predictors of deficiencies in the intrinsic or extrinsic pathways; however, they were indicators of common pathway deficiencies.

LEVEL OF EVIDENCE

Prognostic, level III.

Hemorrhagic disorders of fibrinolysis: a clinical review

Hyperfibrinolytic bleeding can be caused by a deficiency of one of the inhibitors of fibrinolysis (plasminogen activator inhibitor type 1 [PAI-1] or α2-antiplasmin [α2-AP]), or an excess of one of the activators of fibrinolysis: tissue-type plasminogen activator or urokinase-type plasminogen activator. This review focuses on the clinical implications of these disorders. The bleeding phenotype of fibrinolytic disorders is characterized by delayed bleeding after trauma, surgery and dental procedures. Bleeding in areas of high fibrinolytic activity is also common, such as menorrhagia and epistaxis. Patients with α2-AP deficiency present with the most severe bleeding episodes. Recently, it was discovered that hyperfibrinolytic disorders are associated with a high rate of obstetric complications such as miscarriage and preterm birth, especially in PAI-1 deficient patients. Hyperfibrinolytic disorders are probably underdiagnosed because of lack of knowledge and lack of accurate diagnostic tests. A substantial part of the large group of patients diagnosed as 'bleeding of unknown origin' could actually have a hyperfibrinolytic disorder. In the case of a high index of suspicion (i.e. because of a positive family history, recurrent bleeding or uncommon type of bleeding such as an intramedullary hematoma), further testing should not be withheld because of normal results of standard hemostatic screening assays. Timely diagnosis is important because these disorders can generally be treated well with antifibrinolytic agents.

New clotting disorders that cast new light on blood coagulation and may play a role in clinical practice

Recently several variants of clotting factors have shown a peculiar behavior so that they appear as new defects. The factors involved are FII, FV and FIX. Prothrombin deficiency is usually associated with bleeding. Recently a few prothrombin abnormalities involving Arg396 mutations, have been demonstrated to show antithrombin resistance with the consequent appearance of a thrombophilic state and venous thromboses in young age. The same is true for an abnormal FIX (FIX Padua). The thrombotic manifestations in the latter condition are also venous. The abnormal FIX (FIX Padua) is characterized by a great increase in FIX activity whereas FIX antigen is only slightly increased. The condition is due to an Arg338Lys mutation. The increased intrinsic clotting activity of this abnormal FIX is being investigated as a useful therapeutic approach in homophile B patients. Another new clotting disorder is represented by two abnormal FV (FV East Texas and FV Amsterdam). These are characterized by a deletion of part of the B domain of FV resulting in a "short" FV. The condition is characterized by a mild bleeding tendency due to high levels of Tissue Factor pathway inhibitor. The "short" factor V is in fact resistant to the action of Tissue Factor pathway inhibitor which is sharply increased in these patients. These new clotting entities have again demonstrated that the study of patients who show a tendency to venous thrombosis or a mild bleeding condition that cannot be explained on the basis of our current concepts of blood coagulation, may represent "new" coagulation disorders. All persons interested in thrombotic or hemorrhagic disorders should be informed about these new clinical and laboratory conditions.

Hemostatic function to regulate perioperative bleeding in patients undergoing spinal surgery: A prospective observational study

Although bleeding is a common complication of surgery, routine laboratory tests have been demonstrated to have a low ability to predict perioperative bleeding. Better understanding of hemostatic function during surgery would lead to identification of high-risk patients for bleeding. Here, we aimed to elucidate hemostatic mechanisms to determine perioperative bleeding. We prospectively enrolled 104 patients undergoing cervical spinal surgery without bleeding diathesis. Blood sampling was performed just before the operation. Volumes of perioperative blood loss were compared with the results of detailed laboratory tests assessing primary hemostasis, secondary hemostasis, and fibrinolysis. Platelet aggregations induced by several agonists correlated with each other, and only two latent factors determined inter-individual difference. Platelet aggregability independently determined perioperative bleeding. We also identified low levels of plasminogen-activator inhibitor-1 (PAI-1) and α2-plasmin inhibitor to be independent risk factors for intraoperative and postoperative bleeding, respectively. Most important independent factor to determine postoperative bleeding was body weight. Of note, obese patients with low levels of PAI-1 became high-risk patients for bleeding during surgery. Our data suggest that bleeding after surgical procedure may be influenced by inter-individual differences of hemostatic function including platelet function and fibrinolysis, even in the patients without bleeding diathesis.

Bleeding related to disturbed fibrinolysis

The components and reactions of the fibrinolysis system are well understood. The pathway has fewer reactants and interactions than coagulation, but the generation of a complete quantitative model is complicated by the need to work at the solid‐liquid interface of fibrin. Diagnostic tools to detect disease states due to malfunctions in the fibrinolysis pathway are also not so well developed as is the case with coagulation. However, there are clearly a number of inherited or acquired pathologies where hyperfibrinolysis is a serious, potentially life‐threatening problem and a number of antifibrinolytc drugs are available to treat hyperfibrinolysis. These topics will be covered in the following review.

Fibrinolysis and Thrombosis: Pathways and Inhibitors

The mechanism of fibrinolysis has been reviewed taking into account its two pathways extrinsic and intrinsic and the important role of α 2plasmin inhibitor. A clear distinction is now well documented on the mechanism of fibrinolysis in a liquid phase and in a solid phase.

The role of fibrin as an important trigger of fibrinolysis in vivo is demonstrated.

Finally a relationship between hypofibrinolysis and thrombosis is highly probable.

Novel approaches in management of perioperative coagulopathy

PURPOSE OF REVIEW

The recent advances in hemostatic monitoring, and discussion of the clinical implications of hemostatic therapies based on different blood components and factor concentrates.

RECENT FINDINGS

Implementing suitable laboratory tests and transfusion protocols is highly recommended because the laboratory test guided, protocol-driven transfusion approach reduces blood component utilization, and possibly leads to improved outcomes. Timely assessment of coagulation has been difficult using conventional coagulation tests, but thrombocytopenia, fibrin polymerization defects, and fibrinolysis can be quickly assessed on thromboelastometry. The latter testing can be applied to guide the dosing of fibrinogen and prothrombin complex concentrate, which are selectively used to correct fibrinogen deficiency, and improve thrombin generation in acquired coagulopathy. These therapeutic approaches are novel, and potentially effective in reducing the exposure to allogeneic components (e.g., plasma and platelets) and side-effects of transfusion. Although the accessibility of different therapies among different countries, tranexamic acid is widely available, and is an effective blood conservation measure with a good safety profile in various surgical settings.

SUMMARY

Our understanding of perioperative coagulopathy, diagnostic tools, and therapeutic approaches has evolved in recent years. Additional multidisciplinary efforts are required to understand the optimal combinations, cost-effectiveness, and safety profiles of allogeneic components, and available factor concentrates.

Alpha II Antiplasmin Deficiency Complicating Pregnancy: A Case Report

Background. Alpha II antiplasmin is a protein involved in the inhibition of fibrinolysis. A deficiency in this protein leads to increased hemorrhage. It is inherited in an autosomal recessive fashion. Case. 30-year-old Gravida 1, Para 0, presented for prenatal care with her first and subsequently her second pregnancy. Her medical history was significant for a known deficiency in alpha II antiplasmin. Her first and second pregnancies were complicated by nonobstetrical hemorrhage requiring transfusions and severe preeclampsia requiring preterm deliveries. Conclusion. Alpha II antiplasmin deficiency resulted in multiple episodes of nonobstetrical hemorrhages requiring transfusion and ultimately preterm deliveries due to severe preeclampsia. Both infants and mother had a good outcome. The presence of this disorder may require a multidisciplinary team approach involving obstetricians, pediatricians, and hematologists. Precis. Alpha II antiplasmin deficiency is a rare autosomal recessive disorder leading to increased fibrinolysis and hemorrhage. We present a case report of a pregnancy complicated by this disorder.

Noncovalent interaction of alpha(2)-antiplasmin with fibrin(ogen): localization of alpha(2)-antiplasmin-binding sites

Covalent incorporation (cross-linking) of plasmin inhibitor alpha(2)-antiplasmin (alpha(2)-AP) into fibrin clots increases their resistance to fibrinolysis. We hypothesized that alpha(2)-AP may also interact noncovalently with fibrin prior to its covalent cross-linking. To test this hypothesis, we studied binding of alpha(2)-AP to fibrin(ogen) and its fragments by an enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance. The experiments revealed that alpha(2)-AP binds to polymeric fibrin and surface-adsorbed fibrin(ogen), while no binding was observed with fibrinogen in solution. To localize the alpha(2)-AP-binding sites, we studied the interaction of alpha(2)-AP with the fibrin(ogen)-derived D(1), D-D, and E(3) fragments, and the recombinant alphaC region and its constituents, alphaC connector and alphaC domain and its subdomains, which together encompass practically the whole fibrin(ogen) molecule. In the ELISA, alpha(2)-AP bound to immobilized D(1), D-D, alphaC region, alphaC domain, and its C-terminal subdomain. The binding was Lys-independent and was not inhibited by plasminogen or tPA. Furthermore, the affinity of alpha(2)-AP for D-D was significantly increased in the presence of plasminogen, while that to the alphaC domain remained unaffected. Altogether, these results indicate that the fibrin(ogen) D region and the C-terminal subdomain of the alphaC domain contain high-affinity alpha(2)-AP-binding sites that are cryptic in fibrinogen and exposed in fibrin or adsorbed fibrinogen, and the presence of plasminogen facilitates interaction of alpha(2)-AP with the D regions. The discovered noncovalent interaction of alpha(2)-AP with fibrin may contribute to regulation of the initial stage of fibrinolysis and provide proper orientation of the cross-linking sites to facilitate covalent cross-linking of alpha(2)-AP to the fibrin clot.

Haemodilution-induced profibrinolytic state is mitigated by fresh-frozen plasma: implications for early haemostatic intervention in massive haemorrhage

BACKGROUND

Fibrinolysis contributes to coagulopathy after major trauma and surgery. We hypothesized that progressive haemodilution is responsible, at least in part, for increased fibrinolytic tendency of blood clot.

METHODS

The study was performed in two parts. First, whole blood (WB) samples collected from six healthy, consented volunteers were diluted in vitro with either saline or fresh-frozen plasma (FFP) to 40% and 15% of baseline. We quantified factor levels related to coagulation and fibrinolysis, and measured endogenous thrombin generation in undiluted control plasma samples and in samples diluted with saline or FFP. Additionally, thromboelastometry was used to assess susceptibility to fibrinolysis after adding tissue plasminogen activator in undiluted WB samples and in samples diluted with saline before and after substitution of fibrinogen or FFP. Secondly, as a model of in vivo haemodilution, we evaluated the same parameters before and after operation in nine consented patients undergoing off-pump coronary artery bypass surgery.

RESULTS

The dilution with saline caused dose-dependent decreases in plasma levels of coagulation and antifibrinolytic factors, and in thrombin generation. In FFP-supplemented samples, factor levels and thrombin generation were maintained within normal ranges. Fibrinolytic tendency was significantly higher after haemodilution with saline independent of fibrinogen substitution compared with FFP. Similarly, increased tendency for fibrinolysis was also observed in the in vivo haemodilution.

CONCLUSIONS

We demonstrated in vitro and in vivo that progressive haemodilution decreases endogenous antifibrinolytic proteins including alpha(2)-antiplasmin and thrombin-activatable fibrinolysis inhibitor, resulting in increased fibrinolytic tendency. Therefore, early fluid replacement therapy with FFP might be advantageous after massive haemorrhage.

Blood coagulation: hemostasis and thrombin regulation

Perioperative bleeding is a major challenge particularly because of increasing clinical use of potent antithrombotic drugs. Understanding current concepts of coagulation is important in determining the preoperative bleeding risk of patients, and in managing hemostatic therapy perioperatively. The serine protease thrombin plays pivotal roles in the activation of additional serine protease zymogens (inactive enzymatic precursors), cofactors, and cell-surface receptors. Thrombin generation is closely regulated to locally achieve rapid hemostasis after injury without causing uncontrolled systemic thrombosis. During surgery, there are major disturbances in coagulation and inflammatory systems because of hemorrhage/hemodilution, blood transfusion, and surgical stresses. Postoperative bleeding often requires allogeneic blood transfusions, which support thrombin generation and hemostasis. However, procoagulant activity and inflammation are increased postoperatively; thus, antithrombotic therapy may be required to prevent perioperative thrombotic complications. There have been significant advances in the management of perioperative hemostasis and thrombosis because of the introduction of novel hemostatic and antithrombotic drugs. However, a limitation of current treatment is that conventional clotting tests do not reflect the entire physiological processes of coagulation making optimal pharmacologic therapy difficult. Understanding the in vivo regulatory mechanisms and pharmacologic modulation of thrombin generation may help control bleeding without potentially increasing prothrombotic risks. In this review, we focus on the regulatory mechanisms of hemostasis and thrombin generation using multiple, simplified models of coagulation.

Evidence that alpha2-antiplasmin becomes covalently ligated to plasma fibrinogen in the circulation: a new role for plasma factor XIII in fibrinolysis regulation

BACKGROUND

Plasma alpha2-antiplasmin (alpha2AP) is a rapid and effective inhibitor of the fibrinolytic enzyme plasmin. Congenital alpha2AP deficiency results in a severe hemorrhagic disorder due to accelerated fibrinolysis. It is well established that in the presence of thrombin-activated factor XIII (FXIIIa), alpha2AP becomes covalently ligated to the distal alpha chains of fibrin or fibrinogen at lysine 303 (two potential sites per molecule). Some time ago we showed that alpha2AP is covalently linked to plasma fibrinogen . That singular observation led to our hypothesis that native plasma factor XIII (FXIII), which is known to catalyze covalent cross-linking of fibrinogen in the presence of calcium ions, can also incorporate alpha2AP into fibrinogen in the circulation.

RESULTS AND CONCLUSIONS

We now provide evidence that FXIII incorporates I 125-labelled alpha2AP into the Aalpha-chain sites on fibrinogen or fibrin. We also measured the content of alpha2AP in isolated plasma fibrinogen fractions by ELISA and found that substantial amounts were present (1.2-1.8 moles per mole fibrinogen). We propose that alpha2AP becomes ligated to fibrinogen while in the circulation through the action of FXIII, and that its immediate presence in plasma fibrinogen contributes to regulation of in vivo fibrinolysis.

Haemorrhage associated with large abdominal aortic aneurysms

Two patients are described who each had a major haemorrhage after minor surgery and who additionally had large abdominal aortic aneurysms. Neither had depletion of platelets or coagulation factors sufficient to account for bleeding. Both had grossly enhanced fibrinolytic activity with evidence of plasmin generation in the circulation. In one patient insertion of an aortic graft was rapidly followed by resolution of the fibrinolytic abnormalities. Overactive fibrinolysis, rather than coagulation factor consumption may account for some of the bleeding syndromes complicating abdominal aortic aneurysms.

Haemostatic management of intraoral bleeding in patients with congenital deficiency of alpha2-plasmin inhibitor or plasminogen activator inhibitor-1

Haemostatic management of intraoral bleeding was investigated in patients with congenital alpha2-plasmin inhibitor (alpha2-PI) deficiency or congenital plasminogen activator inhibitor- 1 (PAI-1) deficiency. When extracting teeth from patients with congenital alpha2-PI deficiency, we advocate that 7.5-10 mg kg(-1) of tranexamic acid be administered orally every 6 h, starting 3 h before surgery and continuing for about 7 days. For the treatment of continuous bleeding, such as post-extraction bleeding, 20 mg kg(-1) of tranexamic acid should be administered intravenously, and after achieving local haemostasis 7.5 mg kg(-1) of tranexamic acid should be administered orally every 6 h for several days. In addition, when treating haematoma caused by labial or gingival laceration or buccal or mandibular contusion, haemostasis should be achieved by administering 7.5-10 mg kg(-1) of tranexamic acid every 6 h. Tranexamic acid can also be used for haemostatic management of intraoral bleeding in patients with congenital PAI-1 deficiency, but is less effective when compared with use in patients with congenital alpha2-PI deficiency. Continuous infusion of 1.5 mg kg(-1) h(-1) of tranexamic acid is necessary for impacted tooth extraction requiring gingival incision or removal of local bone.

A splicing donor site point mutation in intron 6 of the plasmin inhibitor (alpha2 antiplasmin) gene with heterozygous deficiency and a bleeding tendency

A new case of familial plasmin inhibitor (alpha2 antiplasmin) deficiency is reported. The bleeding symptoms are moderate, happening after surgery or trauma or consisting of abnormal uterine bleeding induced by hormone replacement therapy. It is easily corrected with tranexamic acid. Gene sequencing makes it possible to find a splicing donor site mutation of intron 6, leading to exon 6 skipping. Neither a shortened variant nor an abnormal plasmin interaction was found in plasma by immunoblotting, and fibrin binding is unaffected. The mutation is heterozygous, associated with an intermediate decrease of both antiplasmin activity and antigen levels, and was found in four other family members out of five tested. It is different from the five mutations previously reported. At the time of diagnosis, the patient was living in Artas, France, allowing the defect to be named plasmin inhibitor (alpha2 antiplasmin) Artas.

Implications of excessive fibrinolysis and alpha(2)-plasmin inhibitor deficiency in patients with severe head injury

OBJECTIVE

To evaluate the involvement of the fibrinolytic system, especially focused on alpha(2)-plasmin inhibitor, in patients with head injury.

METHODS

This study consisted of 47 patients with isolated blunt head trauma in whom blood sampling could be initiated within 3 hours after injury. Patients were divided into two groups according to Glasgow Outcome Scale score status at 3 months after injury. In Group 1 patients (n = 26), the outcome was characterized as good recovery or moderate disability; in Group 2 patients (n = 21), the outcome was characterized as severe disability, vegetative state, or death.

RESULTS

Concentrations of thrombin-antithrombin III complex were greater than 100 microg/L in 39 of 47 patients, and concentrations in Group 2 patients were elevated significantly beyond the concentrations in Group 1 patients. Activities of alpha(2)-plasmin inhibitor in Group 2 were significantly lower than in Group 1 (P < 0.0001). In Group 1 patients, alpha(2)-plasmin inhibitor activity was greater than 60%, while in all but four Group 2 patients, the inhibitor was reduced to less than 60% of normal activity within 3 hours of injury. All patients with alpha(2)-plasmin inhibitor activity less than 60% showed a marked bleeding tendency and/or severe brain edema. Using sandwich enzyme-linked immunosorbent assay, fibrinogen degradation product and fibrin degradation product were measured separately. A significant correlation was apparent between thrombin-antithrombin III complex and fibrinogen degradation product, as well as between the complex and fibrin degradation product. Marked decreases in alpha(2)-plasmin inhibitor were noted only in patients with thrombin-antithrombin III complex concentrations exceeding 500 microg/L.

CONCLUSION

Fibrinolysis and fibrinogenolysis may be involved according to the degree of coagulation activation in the pathophysiology of severe head injury. Decreased activity of alpha(2)-plasmin inhibitor indicated poor prognosis and may be an exacerbating factor in the acute phase of head trauma.

Epsilon-aminocaproic acid promotes the release of alpha2-antiplasmin during and after cardiopulmonary bypass

This double-blind, randomized study compared the mechanisms by which low-dose aprotinin and epsilon-aminocaproic acid (EACA) inhibited fibrinolysis during cardiopulmonary bypass surgery. D-dimer levels during and after bypass were similar, indicating an equivalent inhibition of fibrinolysis. Effects on tissue plasminogen activator release were not associated with the inhibition of fibrinolysis by either drug. Treatment with EACA was associated with a substantial release of endogenous alpha2-antiplasmin, particularly 1 h after bypass. Compared with the aprotinin group, higher levels of the plasmin-alpha2-antiplasmin complex in the EACA group confirmed an increased inhibition of plasmin by alpha2-antiplasmin. In conclusion, it is hypothesized that EACA inhibited fibrinolysis by stimulating the release of the patients' own alpha2-antiplasmin.

Effective lysis of model thrombi by a t-PA mutant (A473S) that is resistant to alpha2-antiplasmin

This study used two mutants of tissue-type plasminogen activator (t-PA) with resistance to inhibitors of fibrinolysis to define the contribution of plasminogen activator inhibitor (PAI)-1 and alpha2-antiplasmin (alpha2-AP) to the control of fibrin lysis. Wild-type t-PA was compared with KHRR296-299AAAA, which is resistant to PAI-1, and with A473S, which is resistant to alpha2-AP. We examined these forms of t-PA in model systems that are physiologically relevant. Neutralization of alpha2-AP was essential for lysis of plasma clots, irrespective of their platelet content, by either wild-type t-PA or KHRR296-299AAAA. In marked contrast, A473S lysed plasma clots without neutralization of alpha2-AP. Model thrombi, with structures similar to in vivo thrombi, were lysed slowly by wild-type t-PA; the rate and extent of lysis were enhanced by the addition of antibodies to alpha2-AP or PAI-1. A473S was more effective than wild-type t-PA without the addition of antibodies by virtue of its resistance to alpha2-AP. This resistance was remarkable, in that no complex formed between A473S t-PA and alpha2-AP, even after extended incubation, when 50% of wild-type t-PA could be converted to complex. Comparison of A473S and KHRR296-299AAAA mutants showed their similar effectiveness in lysis of platelet-rich model thrombi. Thus, PAI-1 and alpha2-AP contribute approximately equally to the inhibition of thrombus lysis. This study underlines the functional significance of alpha2-AP as a direct inhibitor of t-PA and further explains the basis of the accepted role of alpha2-AP as a regulator of fibrin persistence and thrombus resistance to lysis.

Mannose trimming targets mutant alpha(2)-plasmin inhibitor for degradation by the proteasome

We have previously characterized the molecular and cellular mechanisms of alpha(2)-plasmin inhibitor (alpha(2)PI) deficiency. The mutant alpha(2)PI-Nara and alpha(2)PI-Okinawa proteins were found to be retained and degraded in cells stably expressing these mutant forms of alpha(2)PI. Degradation of the two mutant alpha(2)PI proteins, mediated by proteasomes, occurred after a lag time of 1.5 h during which glucose trimming took place. The mutant alpha(2)PI proteins were not ubiquitinated. Inhibition of mannosidase activity blocked the degradation of the mutant alpha(2)PI proteins without resulting in any changes in their binding to calnexin. Inhibition of glucose removal completely blocked the interaction between the alpha(2)PI proteins and the molecular chaperone calnexin. Under these conditions, mannose residues were removed from the oligosaccharides even when glucose residues were not processed. With mannose removal, the glucose-untrimmed mutant forms of alpha(2)PI, which failed to bind to calnexin, were degraded by proteasomes. The initiation of mannose trimming was a prerequisite for their degradation. Our findings show that modification of oligosaccharides of the mutant forms of alpha(2)PI determines their recognition by the degradation apparatus and that mannose trimming is important for targeting the mutant alpha(2)PI proteins for the degradation pathway.

Solvent/Detergent-Treated Plasma Has Decreased Antitrypsin Activity and Absent Antiplasmin Activity

Solvent/detergent (S/D)-treated plasma is currently marketed by the American Red Cross as a virally inactivated alternative to fresh-frozen plasma (FFP). The serpin-type serine proteinase inhibitors have a flexible reactive site loop (RSL) that can convert from the active conformation to the inactive latent or polymerized conformations when exposed to heat and/or detergents. We have compared the conformational stability and inhibitory activity of 3 plasma serpins—antithrombin, antitrypsin, and antiplasmin—in S/D plasma and FFP. In S/D plasma, virtually 100% of the antiplasmin and approximately 50% of the antitrypsin are in either the latent or polymerized conformation and lack inhibitory activity, while in FFP only the active conformation is present. Interestingly, antithrombin is not affected by S/D treatment and remains fully active. These data demonstrate that S/D plasma is not simply a virally inactivated equivalent of FFP. The lack of antiplasmin activity and decreased antitrypsin activity in S/D plasma suggest that it may not be as effective as FFP for the treatment of bleeding in patients with systemic activation of proteolytic cascades, such as disseminated intravascular coagulation and sepsis, acquired fibrinolytic states, and large-volume transfusion. Although there has been extensive use of S/D plasma in several European countries with no reports of adverse effects, clinical studies directly comparing the efficacy of these 2 plasma products are needed to directly evaluate the relative therapeutic efficacy of FFP and S/D plasma for the treatment of these diseases.

Solvent/Detergent-Treated Plasma Has Decreased Antitrypsin Activity and Absent Antiplasmin Activity

Solvent/detergent (S/D)-treated plasma is currently marketed by the American Red Cross as a virally inactivated alternative to fresh-frozen plasma (FFP). The serpin-type serine proteinase inhibitors have a flexible reactive site loop (RSL) that can convert from the active conformation to the inactive latent or polymerized conformations when exposed to heat and/or detergents. We have compared the conformational stability and inhibitory activity of 3 plasma serpins—antithrombin, antitrypsin, and antiplasmin—in S/D plasma and FFP. In S/D plasma, virtually 100% of the antiplasmin and approximately 50% of the antitrypsin are in either the latent or polymerized conformation and lack inhibitory activity, while in FFP only the active conformation is present. Interestingly, antithrombin is not affected by S/D treatment and remains fully active. These data demonstrate that S/D plasma is not simply a virally inactivated equivalent of FFP. The lack of antiplasmin activity and decreased antitrypsin activity in S/D plasma suggest that it may not be as effective as FFP for the treatment of bleeding in patients with systemic activation of proteolytic cascades, such as disseminated intravascular coagulation and sepsis, acquired fibrinolytic states, and large-volume transfusion. Although there has been extensive use of S/D plasma in several European countries with no reports of adverse effects, clinical studies directly comparing the efficacy of these 2 plasma products are needed to directly evaluate the relative therapeutic efficacy of FFP and S/D plasma for the treatment of these diseases.

2-Antiplasmin Gene Deficiency in Mice Is Associated With Enhanced Fibrinolytic Potential Without Overt Bleeding

2-antiplasmin (2-AP) is the main physiologic plasmin inhibitor in mammalian plasma. Inactivation of the murine 2-AP gene was achieved by replacing, through homologous recombination in embryonic stem cells, a 7-kb genomic sequence encoding the entire murine protein (exon 2 through part of exon 10, including the stop codon) with theneomycin resistance expression cassette. Germline transmission of the mutated allele was confirmed by Southern blot analysis. Mendelian inheritance of the inactivated 2-AP allele was observed, and homozygous deficient (2-AP−/−) mice displayed normal fertility, viability, and development. Reverse transcription-polymerase chain reaction confirmed the absence of 2-AP mRNA in kidney and liver from 2-AP−/− mice, in contrast to wild-type (2-AP+/+) mice. Immunologic and functional 2-AP levels were undetectable in plasma of 2-AP−/− mice, and were about half of wild-type in heterozygous littermates (2-AP+/−). Other hemostasis parameters, including plasminogen activator inhibitor-1, plasminogen, fibrinogen, hemoglobin, hematocrit, and blood cell counts were comparable for 2-AP+/+, 2-AP+/−, and 2-AP−/− mice. After amputation of tail or toe tips, bleeding stopped spontaneously in 2-AP+/+, as well as in 2-AP+/− and 2-AP−/− mice. Spontaneous lysis after 4 hours of intravenously injected 125I-fibrin–labeled plasma clots was significantly higher in 2-AP−/− than in 2-AP+/+ mice when injecting clots prepared from 2-AP+/+ plasma (78% ± 5% v 46% ± 9%; mean ± SEM, n = 6 to 7; P = .02) or from 2-AP−/−plasma (81% ± 5% v 46% ± 5%; mean ± SEM, n = 5; P = .008). Four to 8 hours after endotoxin injection, fibrin deposition in the kidneys was significantly reduced in 2-AP−/− mice, as compared with 2-AP+/+ mice (P ≤ .005). Thus, 2-AP−/− mice develop and reproduce normally; they have an enhanced endogenous fibrinolytic capacity without overt bleeding.

2-Antiplasmin Gene Deficiency in Mice Is Associated With Enhanced Fibrinolytic Potential Without Overt Bleeding

2-antiplasmin (2-AP) is the main physiologic plasmin inhibitor in mammalian plasma. Inactivation of the murine 2-AP gene was achieved by replacing, through homologous recombination in embryonic stem cells, a 7-kb genomic sequence encoding the entire murine protein (exon 2 through part of exon 10, including the stop codon) with theneomycin resistance expression cassette. Germline transmission of the mutated allele was confirmed by Southern blot analysis. Mendelian inheritance of the inactivated 2-AP allele was observed, and homozygous deficient (2-AP−/−) mice displayed normal fertility, viability, and development. Reverse transcription-polymerase chain reaction confirmed the absence of 2-AP mRNA in kidney and liver from 2-AP−/− mice, in contrast to wild-type (2-AP+/+) mice. Immunologic and functional 2-AP levels were undetectable in plasma of 2-AP−/− mice, and were about half of wild-type in heterozygous littermates (2-AP+/−). Other hemostasis parameters, including plasminogen activator inhibitor-1, plasminogen, fibrinogen, hemoglobin, hematocrit, and blood cell counts were comparable for 2-AP+/+, 2-AP+/−, and 2-AP−/− mice. After amputation of tail or toe tips, bleeding stopped spontaneously in 2-AP+/+, as well as in 2-AP+/− and 2-AP−/− mice. Spontaneous lysis after 4 hours of intravenously injected 125I-fibrin–labeled plasma clots was significantly higher in 2-AP−/− than in 2-AP+/+ mice when injecting clots prepared from 2-AP+/+ plasma (78% ± 5% v 46% ± 9%; mean ± SEM, n = 6 to 7; P = .02) or from 2-AP−/−plasma (81% ± 5% v 46% ± 5%; mean ± SEM, n = 5; P = .008). Four to 8 hours after endotoxin injection, fibrin deposition in the kidneys was significantly reduced in 2-AP−/− mice, as compared with 2-AP+/+ mice (P ≤ .005). Thus, 2-AP−/− mice develop and reproduce normally; they have an enhanced endogenous fibrinolytic capacity without overt bleeding.

Increased tissue-type plasminogen activator antigen release is not accompanied by increased systemic fibrinolytic activity in severe neonatal respiratory distress syndrome

Intravascular and intraalveolar fibrin depositions in preterm infants with severe respiratory distress syndrome (RDS) have been attributed to activation of clotting. We questioned whether in the face of activated clotting, fibrinolysis is sufficient in these infants. We found, in infants with severe RDS within 6 to 12 h of birth, increased median thrombin-antithrombin III complex formation (11.1 versus 1.3 ng/mL in the group with mild-to-moderate RDS, p < 0.001), indicating activation of clotting. Simultaneously, we found increased tissue-type plasminogen activator antigen (t-PA) release in plasma of these infants represented by increased median t-PA plasma concentrations (8.3 versus 2.5 ng/mL in the group with mild-to-moderate RDS, p < 0.01). This increased t-PA release was not accompanied with more plasminogen and antiplasmin consumption and with more fibrin and fibrinogen degradation than in the infants with mild-to-moderate RDS because plasma plasminogen and antiplasmin activity and total fibrin and fibrinogen degradation product concentrations were similar in both groups. We have found that activated clotting and t-PA plasma concentrations are positively correlated with arterial-to-alveolar oxygen tension ratio and ventilator efficiency index values. Plasminogen and antiplasmin activity, and total fibrin and fibrinogen degradation product concentrations were not correlated with these continuous measures of RDS severity. In neonatal RDS, clotting activity contributes to disease severity. Insufficient fibrinolysis likely facilitates the deleterious effects of activated clotting.

The plasminogen activator inhibitor-2 gene is not required for normal murine development or survival

Plasminogen activator inhibitor-2 (PAI-2), a member of the serpin gene family, is thought to serve as a primary regulator of plasminogen activation in the extravascular compartment. High levels of PAI-2 are found in keratinocytes, monocytes, and the human trophoblast, the latter suggesting a role in placental maintenance or embryo development. The primarily intracellular distribution of PAI-2 also may indicate a unique regulatory role in a protease-dependent cellular process such as apoptosis. To examine the potential functions of PAI-2 in vivo, we generated PAI-2-deficient mice by gene targeting in embryonic stem cells. Homozygous PAI-2-deficient mice exhibited normal development, survival, and fertility and were also indistinguishable from normal controls in response to a bacterial infectious challenge or endotoxin infusion. No differences in monocyte recruitment into the peritoneum were observed after thioglycollate injection. Epidermal wound healing was equivalent among PAI-2 -/- null and control mice. Finally, crossing PAI-2 -/- with PAI-1 -/- mice to generate animals deficient in both plasminogen activator inhibitors failed to uncover an overlap in function between these two related proteins.

Heterozygote for plasmin inhibitor deficiency developing hemorrhagic tendency with advancing age

A heterozygote for congenital deficiency of plasma plasmin in inhibitor had hemorrhagic episodes repeatedly after the age of 79. Before the age of 79, he had not exhibited any hemorrhagic tendency and did not have abnormal bleeding even after surgical operations. Although heterozygotes for congenital deficiency of this inhibitor usually have no or only a mild hemorrhagic tendency, this case suggests that they may exhibit severe hemorrhagic tendency when they reach advanced ages because of age-related vascular changes producing hemostatic imbalance.

Enhancement of plasma fibrinolysis in vitro by jararhagin, the main haemorrhagic metalloproteinase in Bothrops jararaca venom

Jararhagin, a haemorrhagic metalloproteinase from Bothrops jararaca venom, plays an important role in systemic as well as local haemorrhage. In this study, the effect of jararhagin on the fibrinolytic system was investigated. The fibrinolytic activity of various kinds of animal plasmas was measured by the fibrin plate method. No activity was detected in plasma alone. However, after mixing plasma with jararhagin, strong fibrinolytic activity was recorded in guinea-pig, horse, dog, rabbit and human plasmas. The mechanism of the increase of firbinolytic activity by jararhagin was studied further in guinea-pig plasma. Fibrin-zymographic studies indicated that jararhagin increased tissue-type plasminogen activator (tPA) activity by the dissociation of a complex of tPA with type 1 plasminogen activator inhibitor (PAI-1). alpha 2-Plasmin inhibitor (alpha 2-PI) activity in the plasma was measured using a synthetic chromogenic substrate method after incubation with jararhagin. The alpha 2-PI activity in the plasma decreased in both time-dependent and dose-dependent manners. These in vitro results suggest that, in some animal plasmas, jararhagin increases plasma fibrinolytic activity by causing dissociation of the tPA/PAI-1 complex and by the inactivation of alpha 2-PI. It is possible that this direct action of jararhagin on the enhancement of plasma fibrinolytic activity may contribute to the aetiology of systemic haemorrhage frequently observed in human victims of B. jararaca envenoming.