Plasmin converts factor X from coagulation zymogen to fibrinolysis cofactor

Clinical effects of tranexamic acid on bleeding tendency due to fibrinolytic activation of AL amyloidosis

We report a case where tranexamic acid, which is an antifibrinolytic agent, was used to effectively treat bleeding tendency in a patient with immunoglobulin light chain (AL) amyloidosis. A male patient in his 80s without a history of bleeding disorders was admitted to our hospital for the examination of bleeding tendency and was diagnosed with a bleeding disorder due to AL amyloidosis. Blood tests revealed elevated plasmin-α2-plasmin inhibitor complex levels, suggesting fibrinolytic activation. Managing the bleeding was difficult; however, we suspected fibrinolytic activation associated with AL amyloidosis and initiated treatment with oral tranexamic acid, which markedly improved the bleeding disorder and abnormalities of the fibrinolytic system. Therefore, in cases of bleeding due to fibrinolytic activation of AL amyloidosis, tranexamic acid administration can be an effective treatment.

The Fibrinolytic System: Mysteries and Opportunities

The deposition and removal of fibrin has been the primary role of coagulation and fibrinolysis, respectively. There is also little doubt that these 2 enzyme cascades influence each other given they share the same serine protease family ancestry and changes to 1 arm of the hemostatic pathway would influence the other. The fibrinolytic system in particular has also been known for its capacity to clear various non-fibrin proteins and to activate other enzyme systems, including complement and the contact pathway. Furthermore, it can also convert a number of growth factors into their mature, active forms. More recent findings have extended the reach of this system even further. Here we will review some of these developments and also provide an account of the influence of individual players of the fibrinolytic (plasminogen activating) pathway in relation to physiological and pathophysiological events, including aging and metabolism.

Assessing Plasmin Generation in Health and Disease

Fibrinolysis is an important process in hemostasis responsible for dissolving the clot during wound healing. Plasmin is a central enzyme in this process via its capacity to cleave fibrin. The kinetics of plasmin generation (PG) and inhibition during fibrinolysis have been poorly understood until the recent development of assays to quantify these metrics. The assessment of plasmin kinetics allows for the identification of fibrinolytic dysfunction and better understanding of the relationships between abnormal fibrin dissolution and disease pathogenesis. Additionally, direct measurement of the inhibition of PG by antifibrinolytic medications, such as tranexamic acid, can be a useful tool to assess the risks and effectiveness of antifibrinolytic therapy in hemorrhagic diseases. This review provides an overview of available PG assays to directly measure the kinetics of plasmin formation and inhibition in human and mouse plasmas and focuses on their applications in defining the role of plasmin in diseases, including angioedema, hemophilia, rare bleeding disorders, COVID-19, or diet-induced obesity. Moreover, this review introduces the PG assay as a promising clinical and research method to monitor antifibrinolytic medications and screen for genetic or acquired fibrinolytic disorders.

Plasmin-mediated proteolysis of human factor IXa in the presence of calcium/phospholipid: Conversion of procoagulant factor IXa to a fibrinolytic enhancer

BACKGROUND

Factor (F) IX/IXa inactivation by plasmin has been studied; however, whether plasmin converts FIXa to a fibrinolytic enhancer is not known.

OBJECTIVE

Investigate plasmin proteolysis site(s) in FIXa that inactivates and transforms it into a fibrinolytic enhancer.

METHODS

NH2 -terminal sequencing, mass spectrometry analysis, and functional assays.

RESULTS

Plasmin in the presence of Ca2+ /phospholipid (PL) rapidly cleaved FIXaβ at Lys316↓Gly317 to yield FIXaγ followed by a slow cleavage at Lys413↓Leu414 to yield FIXaδ. FIXaγ/FIXaδ migrated indistinguishably from FIXaβ in nondenaturing gel system indicating that C-terminal residues 317-415/317-413 of heavy chain remain noncovalently associated with FIXaγ/FIXaδ. However, as compared with FIXaβ, FIXaγ or FIXaγ/FIXaδ (25-75 mixture, 8-hour/24-hour incubation analysis by mass spectrometry) was impaired ~ 10-fold in hydrolyzing synthetic substrate CBS 31.39 (CH3-SO2-D-Leu-Gly-Arg-pNA), ~ 30-fold (~ 5-fold higher Km , ~ 6-fold lower kcat ) in activating FX in a system containing Ca2+ /PL, and ~ 650-fold in a system containing Ca2+ /PL and FVIIIa. Further, FIXaγ or FIXaγ/FIXaδ bound FVIIIa with ~ 60-fold reduced affinity compared with FIXaβ. Additionally, in ligand blots, plasminogen or diisopropylfluorophosphate-inhibited plasmin (DIP-plasmin) bound FIXaγ and FIXaδ but not FIXaβ. This interaction was prevented by ε-aminocaproic acid or carboxypeptidase B treatment suggesting that plasminogen/DIP-plasmin binds to FIXaγ/FIXaδ through newly generated C-terminal Lys316 and Lys413. Importantly, FIXaγ/FIXaδ mixture but not FIXaγ enhanced tissue plasminogen activator (tPA)-mediated plasminogen activation in a concentration dependent manner. Similarly, FIXaγ/FIXaδ mixture but not FIXaγ enhanced tPA-induced clot lysis in FIX-depleted plasma.

CONCLUSION

Plasmin cleavage at Lys316↓Gly317 abrogates FIXaβ coagulant activity, whereas additional cleavage at Lys413↓Leu414 converts it into a fibrinolytic enhancer.

Coagulation and fibrinolytic features in AL amyloidosis with abnormal bleeding and usefulness of tranexamic acid

Abnormal bleeding is sometimes observed in patients with immunoglobulin light chain (AL) amyloidosis. Although several theories have been proposed regarding the pathological causes of the bleeding tendency in AL amyloidosis, many lacked sufficient evidence and full consensus. We conducted a retrospective survey at a single institution to assess bleeding manifestations, methods for evaluating hematological abnormalities, and treatments for bleeding in patients with systemic AL amyloidosis over the past 13 years. The participants were 10 men and 14 women, aged 39-84 years (mean 65 years). The prevalence of bleeding was 29%. Prolonged prothrombin time (PT), elevated plasmin-α2-antiplasmin complex, and factor X deficiency were distinctive to the bleeding group. Two case studies showed that tranexamic acid was effective for treating this hematological condition. However, two patients with normal PT and activated partial thromboplastin time (APTT) also had a bleeding manifestation. The rates of administration of coagulation and fibrinolytic tests were relatively low in the non-bleeding group. Therefore, a close investigation concerning coagulation and fibrinolysis should be performed in every patient with AL amyloidosis regardless of the PT/APTT values. A more careful, comprehensive, and large-scale study is required to reinforce these findings.

Structural studies of plasmin inhibition

Plasminogen (Plg) is the zymogen form of the serine protease plasmin (Plm), and it plays a crucial role in fibrinolysis as well as wound healing, immunity, tissue remodeling and inflammation. Binding to the targets via the lysine-binding sites allows for Plg activation by plasminogen activators (PAs) present on the same target. Cellular uptake of fibrin degradation products leads to apoptosis, which represents one of the pathways for cross-talk between fibrinolysis and tissue remodeling. Therapeutic manipulation of Plm activity plays a vital role in the treatments of a range of diseases, whereas Plm inhibitors are used in trauma and surgeries as antifibrinolytic agents. Plm inhibitors are also used in conditions such as angioedema, menorrhagia and melasma. Here, we review the rationale for the further development of new Plm inhibitors, with a particular focus on the structural studies of the active site inhibitors of Plm. We compare the binding mode of different classes of inhibitors and comment on how it relates to their efficacy, as well as possible future developments.

Rivaroxaban and apixaban induce clotting factor Xa fibrinolytic activity

Essentials Activated clotting factor X (FXa) acquires fibrinolytic cofactor function after cleavage by plasmin. FXa-mediated plasma fibrinolysis is enabled by active site modification blocking a second cleavage. FXa-directed oral anticoagulants (DOACs) alter FXa cleavage by plasmin. DOACs enhance FX-dependent fibrinolysis and plasmin generation by tissue plasminogen activator.

BACKGROUND

When bound to an anionic phospholipid-containing membrane, activated clotting factor X (FXa) is sequentially cleaved by plasmin from the intact form, FXaα, to FXaβ and then to Xa33/13. Tissue-type plasminogen activator (t-PA) produces plasmin and is the initiator of fibrinolysis. Both FXaβ and Xa33/13 enhance t-PA-mediated plasminogen activation. Although stable in experiments using purified proteins, Xa33/13 rapidly loses t-PA cofactor function in plasma. Bypassing this inhibition, covalent modification of the FXaα active site prevents Xa33/13 formation by plasmin, and the persistent FXaβ enhances plasma fibrinolysis. As the direct oral anticoagulants (DOACs) rivaroxaban and apixaban bind to the FXa active site, we hypothesized that they similarly modulate FXa fibrinolytic function.

METHODS

DOAC effects on fibrinolysis and the t-PA cofactor function of FXa were studied in patient plasma, normal pooled plasma and purified protein experiments by the use of light scattering, chromogenic assays, and immunoblots.

RESULTS

The plasma of patients taking rivaroxaban showed enhanced fibrinolysis correlating with FXaβ. In normal pooled plasma, the addition of rivaroxaban or apixaban also shortened fibrinolysis times. This was related to the cleavage product, FXaβ, which increased plasmin production by t-PA. It was confirmed that these results were not caused by DOACs affecting activated FXIII-mediated fibrin crosslinking, clot ultrastructure and thrombin-activatable fibrinolysis inhibitor activation in plasma.

CONCLUSION

The current study suggests a previously unknown effect of DOACs on FXa in addition to their well-documented anticoagulant role. By enabling the t-PA cofactor function of FXaβ in plasma, DOACs also enhance fibrinolysis. This effect may broaden their therapeutic indications.

Plasminogen-binding proteins as an evasion mechanism of the host's innate immunity in infectious diseases

Pathogens have developed particular strategies to infect and invade their hosts. Amongst these strategies’ figures the modulation of several components of the innate immune system participating in early host defenses, such as the coagulation and complement cascades, as well as the fibrinolytic system. The components of the coagulation cascade and the fibrinolytic system have been proposed to be interfered during host invasion and tissue migration of bacteria, fungi, protozoa, and more recently, helminths. One of the components that has been proposed to facilitate pathogen migration is plasminogen (Plg), a protein found in the host’s plasma, which is activated into plasmin (Plm), a serine protease that degrades fibrin networks and promotes degradation of extracellular matrix (ECM), aiding maintenance of homeostasis. However, pathogens possess Plg-binding proteins that can activate it, therefore taking advantage of the fibrin degradation to facilitate establishment in their hosts. Emergence of Plg-binding proteins appears to have occurred in diverse infectious agents along evolutionary history of host–pathogen relationships. The goal of the present review is to list, summarize, and analyze different examples of Plg-binding proteins used by infectious agents to invade and establish in their hosts. Emphasis was placed on mechanisms used by helminth parasites, particularly taeniid cestodes, where enolase has been identified as a major Plg-binding and activating protein. A new picture is starting to arise about how this glycolytic enzyme could acquire an entirely new role as modulator of the innate immune system in the context of the host–parasite relationship.

Effects of Plasmin on von Willebrand Factor and Platelets: A Narrative Review

Plasmin is the major fibrinolytic protease responsible for dissolving thrombi by cleavage of its primary substrate fibrin. In addition, emerging evidence points to other roles of plasmin: (1) as a back-up for ADAMTS13 in proteolysis of ultra-large von Willebrand factor (VWF) multimers and (2) as an activator of platelets. Although the molecular mechanisms of fibrinolysis are well defined, insights on the effects of plasmin on VWF and platelets are relatively scarce and sometimes conflicting. Hence, this review provides an overview of the literature on the effects of plasmin on VWF multimeric structures, on VWF binding to platelets, and on platelet activation. This information is placed in the context of possible applications of thrombolytic therapy for the condition thrombotic thrombocytopenic purpura.

Thrombolysis by chemically modified coagulation factor Xa

Essentials Factor Xa (FXa) acquires cleavage-mediated tissue plasminogen activator (tPA) cofactor activity. Recombinant (r) tPA is the predominant thrombolytic drug, but it may cause systemic side effects. Chemically modified, non-enzymatic FXa was produced (Xai-K), which rapidly lysed thrombi in mice. Unlike rtPA, Xai-K had no systemic fibrinolysis activation markers, indicating improved safety.

SUMMARY

Background Enzymatic thrombolysis carries the risk of hemorrhage and re-occlusion must be evaded by co-administration with an anticoagulant. Toward further improving these shortcomings, we report a novel dual-functioning molecule, Xai-K, which is both a non-enzymatic thrombolytic agent and an anticoagulant. Xai-K is based on clotting factor Xa, whose sequential plasmin-mediated fragments, FXaβ and Xa33/13, accelerate the principal thrombolytic agent, tissue plasminogen activator (tPA), but only when localized to anionic phospholipid. Methods The effect of Xai-K on fibrinolysis was measured in vitro by turbidity, thromboelastography and chromogenic assays, and measured in a murine model of occlusive carotid thrombosis by Doppler ultrasound. The anticoagulant properties of Xai-K were evaluated by normal plasma clotting assays, and in murine liver laceration and tail amputation hemostatic models. Results Xa33/13, which participates in fibrinolysis of purified fibrin, was rapidly inhibited in plasma. Cleavage was blocked at FXaβ by modifying residues at the active site. The resultant Xai-K (1 nm) enhanced plasma clot dissolution by ~7-fold in vitro and was dependent on tPA. Xai-K alone (2.0 μg g(-1) body weight) achieved therapeutic patency in mice. The minimum primary dose of the tPA variant, Tenecteplase (TNK; 17 μg g(-1) ), could be reduced by > 30-fold to restore blood flow with adjunctive Xai-K (0.5 μg g(-1) ). TNK-induced systemic markers of fibrinolysis were not detected with Xai-K (2.0 μg g(-1) ). Xai-K had anticoagulant activity that was somewhat attenuated compared with a previously reported analogue. Conclusion These results suggest that Xai-K may ameliorate the safety profile of therapeutic thrombolysis, either as a primary or tPA/TNK-adjunctive agent.

Procoagulant and fibrinolytic activity after polytrauma in rat

The purpose of this study was to determine whether trauma-induced coagulopathy is due to changes in 1) thrombin activity, 2) plasmin activity, and/or 3) factors that stimulate or inhibit thrombin or plasmin. Sprague-Dawley rats were anesthetized with 1-2% isoflurane/100% oxygen, and their left femoral artery and vein were cannulated. Polytrauma included right femur fracture, and damage to the small intestines, the left and medial liver lobes, and right leg skeletal muscle. Rats were then bled 40% of blood volume. Plasma samples were taken before trauma, and at 30, 60, 120, and 240 min. Polytrauma and hemorrhage led to a significant fall in prothrombin levels. However, circulating thrombin activity did not change significantly over time. Antithrombin III and α2 macroglobulin fell significantly by 2 h, then rose by 4 h. Soluble thrombomodulin was significantly elevated over the 4 h. Circulating plasmin activity, plasminogen, and D-dimers were elevated for the entire 4 h. Tissue plasminogen activator (tPA) was elevated at 30 min, then decreased below baseline levels after 1 h. Plasminogen activator inhibitor-1 was significantly elevated at 2-4 h. Neither tissue factor pathway inhibitor nor thrombin activatable fibrinolysis inhibitor changed significantly over time. The levels of prothrombin and plasminogen were 30-100 times higher than their respective active enzymes. Polytrauma and hemorrhage in rats lead to a fibrinolytic coagulopathy, as demonstrated by an elevation in plasmin activity, D-dimers, and tPA. These results are consistent with the observed clinical benefit of tranexamic acid in trauma patients.

The C-terminal sequence of several human serine proteases encodes host defense functions

Serine proteases of the S1 family have maintained a common structure over an evolutionary span of more than one billion years, and evolved a variety of substrate specificities and diverse biological roles, involving digestion and degradation, blood clotting, fibrinolysis and epithelial homeostasis. We here show that a wide range of C-terminal peptide sequences of serine proteases, particularly from the coagulation and kallikrein systems, share characteristics common with classical antimicrobial peptides of innate immunity. Under physiological conditions, these peptides exert antimicrobial effects as well as immunomodulatory functions by inhibiting macrophage responses to bacterial lipopolysaccharide. In mice, selected peptides are protective against lipopolysaccharide-induced shock. Moreover, these S1-derived host defense peptides exhibit helical structures upon binding to lipopolysaccharide and also permeabilize liposomes. The results uncover new and fundamental aspects on host defense functions of serine proteases present particularly in blood and epithelia, and provide tools for the identification of host defense molecules of therapeutic interest.

Plasmin-induced procoagulant effects in the blood coagulation: a crucial role of coagulation factors V and VIII

Plasminogen activators provide effective treatment for patients with acute myocardial infarction. However, paradoxical elevation of thrombin activity associated with failure of clot lysis and recurrent thrombosis has been reported. Generation of thrombin in these circumstances appears to be owing to plasmin (Plm)-induced activation of factor (F) XII. Plm catalyzes proteolysis of several coagulant factors, but the roles of these factors on Plm-mediated procoagulant activity remain to be determined. Recently developed global coagulation assays were used in this investigation. Rotational thromboelastometry using whole blood, clot waveform analysis and thrombin generation tests using plasma, showed that Plm (> or =125 nmol/l) shortened the clotting times in similar dose-dependent manners. In particular, the thrombin generation test, which was unaffected by products of fibrinolysis, revealed the enhanced coagulation with an approximately two-fold increase of peak level of thrombin generation. Studies using alpha2-antiplasmin-deficient plasma revealed that much lower dose of Plm (> or =16 nmol/l) actually contributed to enhancing thrombin generation. The shortening of clotting time could be observed even in the presence of corn trypsin inhibitor, supporting that Plm exerted the procoagulant activity independently of FXII. In addition, using specific coagulation-deficient plasmas, the clot waveform analysis showed that Plm did not shorten the clotting time in only FV-deficient or FVIII-deficient plasma in prothrombin time-based or activated partial thromboplastin time-based assay, respectively. Our results indicated that Plm did possess procoagulant activity in the blood coagulation, and this effect was likely attributed by multicoagulation factors, dependent on FV and/or FVIII.

Engineering kunitz domain 1 (KD1) of human tissue factor pathway inhibitor-2 to selectively inhibit fibrinolysis: properties of KD1-L17R variant

Tissue factor pathway inhibitor-2 (TFPI-2) inhibits factor XIa, plasma kallikrein, and factor VIIa/tissue factor; accordingly, it has been proposed for use as an anticoagulant. Full-length TFPI-2 or its isolated first Kunitz domain (KD1) also inhibits plasmin; therefore, it has been proposed for use as an antifibrinolytic agent. However, the anticoagulant properties of TFPI-2 or KD1 would diminish its antifibrinolytic function. In this study, structure-based investigations and analysis of the serine protease profiles revealed that coagulation enzymes prefer a hydrophobic residue at the P2' position in their substrates/inhibitors, whereas plasmin prefers a positively charged arginine residue at the corresponding position in its substrates/inhibitors. Based upon this observation, we changed the P2' residue Leu-17 in KD1 to Arg (KD1-L17R) and compared its inhibitory properties with wild-type KD1 (KD1-WT). Both WT and KD1-L17R were expressed in Escherichia coli, folded, and purified to homogeneity. N-terminal sequences and mass spectra confirmed proper expression of KD1-WT and KD1-L17R. Compared with KD1-WT, the KD1-L17R did not inhibit factor XIa, plasma kallikrein, or factor VIIa/tissue factor. Furthermore, KD1-L17R inhibited plasmin with ∼6-fold increased affinity and effectively prevented plasma clot fibrinolysis induced by tissue plasminogen activator. Similarly, in a mouse liver laceration bleeding model, KD1-L17R was ∼8-fold more effective than KD1-WT in preventing blood loss. Importantly, in this bleeding model, KD1-L17R was equally or more effective than aprotinin or tranexamic acid, which have been used as antifibrinolytic agents to prevent blood loss during major surgery/trauma. Furthermore, as compared with aprotinin, renal toxicity was not observed with KD1-L17R.

Does plasmin have anticoagulant activity?

The coagulation and fibrinolytic pathways regulate hemostasis and thrombosis, and an imbalance in these pathways may result in pathologic hemophilia or thrombosis. The plasminogen system is the primary proteolytic pathway for fibrinolysis, but also has important proteolytic functions in cell migration, extracellular matrix degradation, metalloproteinase activation, and hormone processing. Several studies have demonstrated plasmin cleavage and inactivation of several coagulation factors, suggesting plasmin may be not only be the primary fibrinolytic enzyme, but may have anticoagulant properties as well. The objective of this review is to examine both in vitro and in vivo evidence for plasmin inactivation of coagulation, and to consider whether plasmin may act as a physiological regulator of coagulation. While several studies have demonstrated strong evidence for plasmin cleavage and inactivation of coagulation factors FV, FVIII, FIX, and FX in vitro, in vivo evidence is lacking for a physiologic role for plasmin as an anticoagulant. However, inactivation of coagulation factors by plasmin may be useful as a localized anticoagulant therapy or as a combined thrombolytic and anticoagulant therapy.

Enhanced fibrinolysis by proteolysed coagulation factor Xa

We previously showed that coagulation factor Xa (FXa) enhances activation of the fibrinolysis zymogen plasminogen to plasmin by tissue plasminogen activator (tPA). Implying that proteolytic modulation occurs in situ, intact FXa (FXaalpha) must be sequentially cleaved by plasmin or autoproteolysis, producing FXabeta and Xa33/13, which acquire necessary plasminogen binding sites. The implicit function of Xa33/13 in plasmin generation has not been demonstrated, nor has FXaalpha/beta or Xa33/13 been studied in clot lysis experiments. We now report that purified Xa33/13 increases tPA-dependent plasmin generation by at least 10-fold. Western blots confirmed that in situ conversion of FXaalpha/beta to Xa33/13 correlated to enhanced plasmin generation. Chemical modification of the FXaalpha active site resulted in the proteolytic generation of a product distinct from Xa33/13 and inhibited the enhancement of plasminogen activation. Identical modification of Xa33/13 had no effect on tPA cofactor function. Due to its overwhelming concentration in the clot, fibrin is the accepted tPA cofactor. Nevertheless, at the functional level of tPA that circulates in plasma, FXaalpha/beta or Xa33/13 greatly reduced purified fibrin lysis times by as much as 7-fold. This effect was attenuated at high levels of tPA, suggesting a role when intrinsic plasmin generation is relatively low. FXaalpha/beta or Xa33/13 did not alter the apparent size of fibrin degradation products, but accelerated the initial cleavage of fibrin to fragment X, which is known to optimize the tPA cofactor activity of fibrin. Thus, coagulation FXaalpha undergoes proteolytic modulation to enhance fibrinolysis, possibly by priming the tPA cofactor function of fibrin.

The serine protease plasmin cleaves the amino-terminal domain of the NR2A subunit to relieve zinc inhibition of the N-methyl-D-aspartate receptors

Zinc is hypothesized to be co-released with glutamate at synapses of the central nervous system. Zinc binds to NR1/NR2A N-methyl-d-aspartate (NMDA) receptors with high affinity and inhibits NMDAR function in a voltage-independent manner. The serine protease plasmin can cleave a number of substrates, including protease-activated receptors, and may play an important role in several disorders of the central nervous system, including ischemia and spinal cord injury. Here, we demonstrate that plasmin can cleave the native NR2A amino-terminal domain (NR2A(ATD)), removing the functional high affinity Zn(2+) binding site. Plasmin also cleaves recombinant NR2A(ATD) at lysine 317 (Lys(317)), thereby producing a approximately 40-kDa fragment, consistent with plasmin-induced NR2A cleavage fragments observed in rat brain membrane preparations. A homology model of the NR2A(ATD) predicts that Lys(317) is near the surface of the protein and is accessible to plasmin. Recombinant expression of NR2A with an amino-terminal deletion at Lys(317) is functional and Zn(2+) insensitive. Whole cell voltage-clamp recordings show that Zn(2+) inhibition of agonist-evoked NMDA receptor currents of NR1/NR2A-transfected HEK 293 cells and cultured cortical neurons is significantly reduced by plasmin treatment. Mutating the plasmin cleavage site Lys(317) on NR2A to alanine blocks the effect of plasmin on Zn(2+) inhibition. The relief of Zn(2+) inhibition by plasmin occurs in PAR1(-/-) cortical neurons and thus is independent of interaction with protease-activated receptors. These results suggest that plasmin can directly interact with NMDA receptors, and plasmin may increase NMDA receptor responses through disruption or removal of the amino-terminal domain and relief of Zn(2+) inhibition.

Identification of plasmin-interactive sites in the light chain of factor VIII responsible for proteolytic cleavage at Lys36

We have recently reported that plasmin likely associates with the factor VIII light chain to proteolyze at Lys36 within the A1 domain. In this study, we determined that the rate of plasmin-catalyzed inactivation on the forms of factor VIIIa containing A1-(1-336) and 1722A3C1C2, reflecting Lys36 cleavage, was reduced by approximately 60%, compared with those containing 1649A3C1C2 and 1690A3C1C2. SDS-PAGE analysis revealed that Lys36 cleavage of factor VIIIa with 1722A3C1C2 was markedly slower than those with 1649A3C1C2 and 1690A3C1C2. Surface plasmon resonance-based assays, using active site-modified anhydro-plasmin (Ah-plasmin) showed that 1722A3C1C2 bound to Ah-plasmin with an approximately 3-fold lower affinity than 1649A3C1C2 or 1690A3C1C2 (Kd, 176, 68.2, and 60.3 nM, respectively). Recombinant A3 bound to Ah-plasmin (Kd, 44.2 nM), whereas C2 failed to bind, confirming the presence of a plasmin-binding site within N terminus of A3. Furthermore, the Glu-Gly-Arg active site-modified factor IXa also blocked 1722A3C1C2 binding to Ah-plasmin by approximately 95%, supporting the presence of another plasmin-binding site overlapping the factor IXa-binding site in A3. In keeping with a major contribution of the lysine-binding sites in plasmin for interaction with the factor VIII light chain, analysis of the A3 sequence revealed two regions involving clustered lysine residues in 1690-1705 and 1804-1818. Two peptides based on these regions blocked 1649A3C1C2 binding to Ah-plasmin by approximately 60% and plasmin-catalyzed Lys36 cleavage of factor VIIIa with A1-(1-336) by approximately 80%. Our findings indicate that an extended surface, centered on residues 1690-1705 and 1804-1818 within the A3 domain, contributes to a unique plasmin-interactive site that promotes plasmin docking during cofactor inactivation by cleavage at Lys36.

Alpha1-antitrypsin suppresses TNF-alpha and MMP-12 production by cigarette smoke-stimulated macrophages

We have previously observed that mice exposed to cigarette smoke and treated with exogenous alpha(1)-antitrypsin (A1AT) were protected against the development of emphysema and against smoke-induced increases in serum TNF-alpha. To investigate possible mechanisms behind this latter observation, we cultured alveolar macrophages lavaged from C57 mice. Smoke-conditioned medium caused alveolar macrophages to increase secretion of macrophage metalloelastase (MMP-12) and TNF-alpha, and this effect was suppressed in a dose-response fashion by addition of A1AT. Macrophages from animals exposed to smoke in vivo and then lavaged also failed to increase MMP-12 and TNF-alpha secretion when the animals were pretreated with A1AT. Because proteinase activated receptor-1 (PAR-1) is known to control MMP-12 release, macrophages were treated with the G protein-coupled receptor inhibitor, pertussis toxin; this suppressed both TNF-alpha and MMP-12 release, while a PAR-1 agonist (TRAP) increased TNF-alpha and MMP-12 release. Smoke-conditioned medium caused increased release of the prothrombin activator, tissue factor, from macrophages. Hirudin, a thrombin inhibitor, and aprotinin, an inhibitor of plasmin, reduced smoke-mediated TNF-alpha and MMP-12 release, and A1AT inhibited both plasmin and thrombin activity in a cell-free functional assay. These findings extend our previous suggestion that TNF-alpha production by alveolar macrophages is related to MMP-12 secretion. They also suggest that A1AT can inhibit thrombin and plasmin in blood constituents that leak into the lung after smoke exposure, thereby preventing PAR-1 activation and MMP-12/TNF-alpha release, and decreasing smoke-mediated inflammatory cell influx.

Mechanisms of Plasmin-catalyzed Inactivation of Factor VIII

Plasmin not only functions as a key enzyme in the fibrinolytic system but also directly inactivates factor VIII and other clotting factors such as factor V. However, the mechanisms of plasmin-catalyzed factor VIII inactivation are poorly understood. In this study, levels of factor VIII activity increased approximately 2-fold within 3 min in the presence of plasmin, and subsequently decreased to undetectable levels within 45 min. This time-dependent reaction was not affected by von Willebrand factor and phospholipid. The rate constant of plasmin-catalyzed factor VIIIa inactivation was approximately 12- and approximately 3.7-fold greater than those mediated by factor Xa and activated protein C, respectively. SDS-PAGE analysis showed that plasmin cleaved the heavy chain of factor VIII into two terminal products, A1(37-336) and A2 subunits, by limited proteolysis at Lys(36), Arg(336), Arg(372), and Arg(740). The 80-kDa light chain was converted into a 67-kDa subunit by cleavage at Arg(1689) and Arg(1721), identical to the pattern induced by factor Xa. Plasmin-catalyzed cleavage at Arg(336) proceeded faster than that at Arg(372), in contrast to proteolysis by factor Xa. Furthermore, breakdown was faster than that in the presence of activated protein C, consistent with rapid inactivation of factor VIII. The cleavages at Arg(336) and Lys(36) occurred rapidly in the presence of A2 and A3-C1-C2 subunits, respectively. These results strongly indicated that cleavage at Arg(336) was a central mechanism of plasmin-catalyzed factor VIII inactivation. Furthermore, the cleavages at Arg(336) and Lys(36) appeared to be selectively regulated by the A2 and A3-C1-C2 domains, respectively, interacting with plasmin.

Serine proteases regulating synaptic plasticity

A number of molecules have been postulated to be involved in long-term potentiation, an experimental model for learning and short-term memory. Although the molecular mechanisms of the long-term potentiation have been considerably well understood, it is not yet known why and how real memory can last very long with outstanding stability. A mechanical change of synaptic morphology at acquisition, consolidation and retention of memory is hypothesized to explain long-lasting memory. Changes in the synaptic morphology may be due, at least in part, to local extracellular proteolysis of cell adhesion and extracellular matrix molecules. Some extracellular serine proteases of the Clan PA family may modulate synaptic adhesion and associate with long-term potentiation and learning behavior. In the present review, candidate proteases that are involved in the hippocampal memory are overviewed.

Fish protein stimulated the fibrinolysis in rats

OBJECTIVE

We hypothesized that fish protein affects blood coagulation and/or fibrinolysis, and compared the activity and amounts of factors involved in blood coagulation and fibrinolysis in rats fed the fish protein, which was treated to remove water-soluble and ethanol-soluble elements, from sardine (sardine protein).

METHODS

In the first experiment, rats were fed for 21 days an AIN-93G-based control diet, and diets in which the casein of the control diet was exchanged for sardine protein at 5, 10 and 20% levels. In the second experiment, rats were fed an AIN-93G control diet and diets containing 5% fish oil, 10% sardine protein or both (5% fish oil + 10% sardine protein) for 21 days. At the end of the experiments, blood coagulation time, hemostatic parameters and fibrinolysis parameters were measured.

RESULTS

The activated partial thromboplastin time (APTT), which is an assay for blood coagulation time in the intrinsic blood coagulation pathway, of rats fed the 20% sardine protein diet was significantly prolonged compared to that of rats fed the control diet. The prolonged APTT by dietary sardine protein was due to a significant decrease of the activities of plasma blood coagulation factors VIII, IX, XI and XII. On the other hand, dietary sardine protein significantly increased the activity of tissue-type plasminogen activator, and the amount of plasma plasmin-alpha(2)-plasmin inhibitor complex, which are markers of activated plasmin. Moreover, we observed that the 20% sardine protein diet increased the amount of plasma D-dimer, which is a degraded product of the fibrin polymer by plasmin. In the second experiment, the APTT and PT of rats fed the F diet were prolonged compared to those of rats fed the control diet, however the concentration and amount of fibrinolytic parameters in the plasma were almost the same as those of rats fed the control diet. In contrast, the F+S diet not only prolonged APTT and PT, but also increased the concentration and amount of fibrinolytic parameters in plasma.

CONCLUSIONS

We consider that the beneficial effects to health and amelioration of cardiovascular and cerebrovascular diseases by fish consumption are caused by a combination of the suppressing effect on blood coagulation of n-3 polyunsaturated fatty acids and the promoting effect on fibrinolysis of fish protein.

Binding of perfluorooctanoic acid to rat and human plasma proteins

Perfluorooctanoic acid (PFOA) is a commercially important organic fluorochemical and is considered to have a long half-life in human blood. In this paper, PFOA binding to rat and human plasma proteins was investigated. On the basis of results from size-exclusion chromatography and ligand blotting, most PFOA was in protein-bound form in male and female rat plasma, and the primary PFOA binding protein in plasma was serum albumin. PFOA binding to rat serum albumin (RSA) in the gas phase was observed by electrospray ionization MS. (19)F NMR experiments revealed that binding to RSA caused peak broadening and chemical shift changes of PFOA resonances, and on the basis of this observation, the dissociation constant was determined to be approximately 0.3 mM. The dissociation constants for PFOA binding to RSA and human serum albumin (HSA) and the numbers of PFOA binding sites on RSA and HSA were also determined by a separation method using microdesalting columns. No significant difference was found between PFOA binding to RSA and PFOA binding to HSA. The dissociation constants for binding of PFOA to RSA or HSA and the numbers of PFOA binding sites were in the range of 0.3-0.4 mM and 6-9, respectively. On the basis of these binding parameters and the estimated plasma concentration of serum albumin, greater than 90% of PFOA would be bound to serum albumin in both rat and human blood.

Activation and inactivation of human factor X by proteases derived from Ficus carica

We investigated the effect of proteases derived from Ficus carica (common fig) on human blood coagulation. The milky sap (latex) of several Ficus (F.) species contain ficin, which is a mixture of proteases. Ficin derived from Ficus carica shortened the activated partial thromboplastin time and the prothrombin time of normal plasmas and plasmas deficient in coagulation factors, except plasma deficient in factor X (FX) and generated activated FX (FXa) in defibrinated plasma. Chromatographic separation of ficin from Ficus carica yielded six proteolytic fractions with a different specificity towards FX. We isolated two factor X activators with molecular masses of 23.2 and 23.5 kDa, and studied their action on purified human FX. Factor X was converted to activated FXbeta by consecutive proteolytic cleavage in the heavy chain between Leu178 and Asp179, Arg187 and Gly188, and Arg194and Ile195 (FX numbering system) with concomitant release of a carboxy-terminal peptide. The cleavage pattern of FXa degradation products in the light chain was influenced by Ca2+ and Mn2+. These data suggest the haemostatic potency of Ficus proteases is based on activation of human coagulation factor X.

Tissue factor is the receptor for plasminogen type 1 on 1-LN human prostate cancer cells

Tissue factor (TF), the initiator of the extrinsic pathway of coagulation, binds plasminogen (Pg) with high affinity through an interaction between kringles 1-3 of Pg and the extracellular domain of TF. We investigated the binding of Pg type 1 (Pg 1) and Pg type 2 (Pg 2) to highly invasive, TF-expressing, 1-LN human prostate tumor cells and to TF isolated from 1-LN cell membranes. Pg 1, containing both N-linked and O-linked oligosaccharide chains, bound to isolated TF with high affinity, whereas Pg 2, containing only one O-linked oligosaccharide chain, did not bind to TF. Although Pg 1 and Pg 2 bind to 1-LN cells, only anti-TF antibodies inhibited the binding of Pg 1, suggesting that TF functions as the receptor for Pg 1 on 1-LN cells. Binding of Pg 1 to isolated TF was inhibited by 6-aminohexanoic acid and alpha-methylmannoside, suggesting that Pg 1 L-lysine binding sites and the biantennary, mannose-containing N-linked oligosaccharide chain are involved in this interaction. Binding of Pg 1 to 1-LN cells promoted activation by receptor-bound urinary-type Pg activator (u-PA) and initiated a Ca(++) signaling cascade. In previous studies we demonstrated that the Pg 2 O-linked carbohydrate chain is essential for its binding to CD26 on 1-LN cells. The current studies suggest that Pg oligosaccharide chains regulate the binding of Pg 1 and Pg 2 to separate receptors on the cell surface.

Mechanism of factor Va inactivation by plasmin. Loss of A2 and A3 domains from a Ca2+-dependent complex of fragments bound to phospholipid

The coagulation cofactor Va (FVa) is a noncovalent heterodimer consisting of a heavy chain (FVaH) and a light chain (FVaL). Previously, the fibrinolytic effector plasmin (Pn) has been shown to inhibit FVa function. To understand this mechanism, the fragmentation profile of human FVa by Pn and the noncovalent association of the derived fragments were determined in the presence of Ca(2+) using anionic phospholipid (aPL)-coated microtiter wells and large (1 microm) aPL micelles as affinity matrices. Following Pn inactivation of aPL-bound FVa, a total of 16 fragments were observed and their NH(2) termini sequenced. These had apparent molecular weights and starting residues as follows (single letter abbreviation is used): 50(L1766), 48(L1766), 43(Q1828), 40(Q1828), 30(S1546), 12(T1657), and 7(S1546) kDa from FVaL; and 65(A1), 50(A1), 45(A1), 34(S349), 30(L94), 30(M110), and 3 small <5(W457, W457, and K365) kDa from FVaH. Of these, 50(L1766), 48(1766), 43(Q1828), and 40(Q1828) spanning the C1/C2 domains, and 30(L94), but not the similar 30(M110), positioned within the A1 domain remained associated with aPL. These were detected antigenically during Pn- or tissue plasminogen activator-mediated lysis of fibrin clot formed in plasma. Chelation by EDTA dissociated the 30(L94)-kDa fragment, which was observed to associate with intact FVaL upon recalcification, indicating that the Leu-94 to Lys-109 region of the A1 domain plays a critical role in the FVaL and FVaH Ca(2+)-dependent association. By using domain-specific monoclonal antibodies and an assay for thrombin generation, loss of FVa prothrombinase function was coincident with proteolysis at sites in the A2 and A3 domains resulting in their dissociation. Inactivation of FV or FVa by Pn was independent of the thrombophilic R506Q mutation. These results identify the molecular composition of Pn-cleaved FVa that remains bound to membrane as largely A1-C1/C2 in the presence of Ca(2+) and suggest that Pn inhibits FVa by a process involving A2 and A3 domain dissociation.

The role of the membrane in the inactivation of factor va by plasmin. Amino acid region 307-348 of factor V plays a critical role in factor Va cofactor function

The mechanism of inactivation of bovine factor Va by plasmin was studied in the presence and absence of phospholipid vesicles (PCPS vesicles). Following 60-min incubation with plasmin (4 nm) membrane-bound factor Va (400 nm) is completely inactive, whereas in the absence of phospholipid vesicles following a 1-h incubation period, the cofactor retains 90% of its initial cofactor activity. Amino acid sequencing of the fragments deriving from cleavage of factor Va by plasmin demonstrated that while both chains of factor Va are cleaved by plasmin, only cleavage of the heavy chain correlates with inactivation of the cofactor. In the presence of a membrane surface the heavy chain of the bovine cofactor is first cleaved at Arg(348) to generate a fragment of M(r) 47,000 containing the NH(2)-terminal part of the cofactor (amino acid residues 1-348) and a M(r) 42,000 fragment (amino acid residues 349-713). This cleavage is associated with minimal loss in cofactor activity. Complete loss of activity of the membrane-bound cofactor coincides with three cleavages at the COOH-terminal portion of the M(r) 47,000 fragment: Lys(309), Lys(310), and Arg(313). These cleavages result in the release of the COOH terminus of the molecule and the production of a M(r) 40,000 fragment containing the NH(2)-terminal portion of the factor Va molecule. Factor Va was treated with plasmin in the absence of phospholipid vesicles followed by the addition of PCPS vesicles and activated protein C (APC). A rapid inactivation of the cofactor was observed as a result of cleavage of the M(r) 47,000 fragment at Arg(306) by APC and appearance of a M(r) 39,000 fragment. These data suggest a critical role of the amino acid sequence 307-348 of factor Va. A 42-amino acid peptide encompassing the region 307-348 of human factor Va (N42R) was found to be a good inhibitor of factor Va clotting activity with an IC(50) of approximately 1.3 microm. These data suggest that plasmin is a potent inactivator of factor Va and that region 307-348 of the cofactor plays a critical role in cofactor function and may be responsible for the interaction of the cofactor with factor Xa and/or prothrombin.

Binding of Plasminogen and Tissue Plasminogen Activator to Plasmin-Modulated Factor X and Factor Xa

Previous work in our laboratory has suggested that the fibrinolytic enzyme plasmin (Pn) inactivates coagulation factors X (FX) and Xa (FXa) in the presence of Ca(2+) and anionic phospholipid (aPL), producing fragments which bind plasminogen (Pg) and accelerate tissue plasminogen activator (t-PA). Our goals here were to determine if the Pn-mediated fragments of FX or FXa remain associated, whether they directly bind t-PA, and to quantify their interaction with Pg. Binding to aPL, benzamidine-Sepharose, or the active-site inhibitor dansyl-Glu-Gly-Arg-chloromethyl ketone demonstrated that Pn cleavage yielded noncovalent heterodimers of a fragment containing the aPL-binding domain (FXgamma(47) or FXagamma(33)) and a 13-kDa fragment (FXgamma(13) or FXagamma(13)). Both ligand blotting and surface plasmon resonance (SPR) showed that Pn-cleaved FX and FXa bound t-PA directly when Pn-treatment was effected in the presence of aPL and Ca(2+). Using SPR, apparent K(d) values of 1-3 microM and 0.3-0.4 microM were measured directly and by competition for the FXgamma(47/13)-Pg and FXagamma(33/13)-Pg interactions, respectively. For the first time, Pg-binding to a receptor was shown to be Ca(2+) enhanced, although primarily mediated by C-terminal lysine residues. Mathematical modeling of kinetic data suggesting two Pg per FXgamma(47/13) or FXagamma(33/13) was consistent with our conclusion that each subunit of FXgamma(47/13) or FXagamma(33/13) contains a C-terminal lysine. Earlier X-ray structures show that these Lys residues are distal from each other and the membrane, supporting the model where each interacts with a separate Pg. t-PA acceleration by FXgamma(47/13) or FXagamma(33/13) may therefore involve simultaneous presentation of two substrate molecules.

Rapid and general profiling of protease specificity by using combinatorial fluorogenic substrate libraries

A method is presented for the preparation and use of fluorogenic peptide substrates that allows for the configuration of general substrate libraries to rapidly identify the primary and extended specificity of proteases. The substrates contain the fluorogenic leaving group 7-amino-4-carbamoylmethylcoumarin (ACC). Substrates incorporating the ACC leaving group show kinetic profiles comparable to those with the traditionally used 7-amino-4-methylcoumarin (AMC) leaving group. The bifunctional nature of ACC allows for the efficient production of single substrates and substrate libraries by using 9-fluorenylmethoxycarbonyl (Fmoc)-based solid-phase synthesis techniques. The approximately 3-fold-increased quantum yield of ACC over AMC permits reduction in enzyme and substrate concentrations. As a consequence, a greater number of substrates can be tolerated in a single assay, thus enabling an increase in the diversity space of the library. Soluble positional protease substrate libraries of 137, 180 and 6,859 members, possessing amino acid diversity at the P4-P3-P2-P1 and P4-P3-P2 positions, respectively, were constructed. Employing this screening method, we profiled the substrate specificities of a diverse array of proteases, including the serine proteases thrombin, plasmin, factor Xa, urokinase-type plasminogen activator, tissue plasminogen activator, granzyme B, trypsin, chymotrypsin, human neutrophil elastase, and the cysteine proteases papain and cruzain. The resulting profiles create a pharmacophoric portrayal of the proteases to aid in the design of selective substrates and potent inhibitors.

Synthesis of positional-scanning libraries of fluorogenic peptide substrates to define the extended substrate specificity of plasmin and thrombin

We have developed a strategy for the synthesis of positional-scanning synthetic combinatorial libraries (PS-SCL) that does not depend on the identity of the P1 substituent. To demonstrate the strategy, we synthesized a tetrapeptide positional library in which the P1 amino acid is held constant as a lysine and the P4-P3-P2 positions are positionally randomized. The 6,859 members of the library were synthesized on solid support with an alkane sulfonamide linker, and then displaced from the solid support by condensation with a fluorogenic 7-amino-4-methylcoumarin-derivatized lysine. This library was used to determine the extended substrate specificities of two trypsin-like enzymes, plasmin and thrombin, which are involved in the blood coagulation pathway. The optimal P4 to P2 substrate specificity for plasmin was P4-Lys/Nle (norleucine)/Val/Ile/Phe, P3-Xaa, and P2-Tyr/Phe/Trp. This cleavage sequence has recently been identified in some of plasmin's physiological substrates. The optimal P4 to P2 extended substrate sequence determined for thrombin was P4-Nle/Leu/Ile/Phe/Val, P3-Xaa, and P2-Pro, a sequence found in many of the physiological substrates of thrombin. Single-substrate kinetic analysis of plasmin and thrombin was used to validate the substrate preferences resulting from the PS-SCL. By three-dimensional structural modeling of the substrates into the active sites of plasmin and thrombin, we identified potential determinants of the defined substrate specificity. This method is amenable to the incorporation of diverse substituents at the P1 position for exploring molecular recognition elements in proteolytic enzymes.

Expression of factor X in both the rat brain and cells of the central nervous system

Prothrombin is expressed in the central and peripheral nervous systems. However, the mechanism responsible for the activation of prothrombin to thrombin by the activated form of factor X in the central and peripheral nervous systems remains to be explored. Here, we investigated the expression of factor X mRNA in the brain and some cell lines derived from the central nervous system. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated the expression of mRNA encoding factor X in the rat brain, A172 (human glioblastoma) and GOTO (human neuroblastoma) cells. The sequences of PCR-derived fragments were identical to those reported for rat and human factor X. These results indicated the synthesis of factor X in the cells of the central nervous system.