The effect of plasmin-mediated degradation on fibrinolysis and tissue plasminogen activator diffusion

We modify a three-dimensional multiscale model of fibrinolysis to study the effect of plasmin-mediated degradation of fibrin on tissue plasminogen activator (tPA) diffusion and fibrinolysis. We propose that tPA is released from a fibrin fiber by simple kinetic unbinding, as well as by "forced unbinding," which occurs when plasmin degrades fibrin to which tPA is bound. We show that, if tPA is bound to a small-enough piece of fibrin that it can diffuse into the clot, then plasmin can increase the effective diffusion of tPA. If tPA is bound to larger fibrin degradation products (FDPs) that can only diffuse along the clot, then plasmin can decrease the effective diffusion of tPA. We find that lysis rates are fastest when tPA is bound to fibrin that can diffuse into the clot, and slowest when tPA is bound to FDPs that can only diffuse along the clot. Laboratory experiments confirm that FDPs can diffuse into a clot, and they support the model hypothesis that forced unbinding of tPA results in a mix of FDPs, such that tPA bound to FDPs can diffuse both into and along the clot. Regardless of how tPA is released from a fiber, a tPA mutant with a smaller dissociation constant results in slower lysis (because tPA binds strongly to fibrin), and a tPA mutant with a larger dissociation constant results in faster lysis.

Synergism of red blood cells and tranexamic acid in the inhibition of fibrinolysis

BACKGROUND

Postpartum hemorrhage (PPH) is the leading cause of maternal death worldwide. The World Maternal Antifibrinolytic trial showed that antifibrinolytic tranexamic acid (TXA) reduces PPH deaths. Maternal anemia increases the risk of PPH. The World Maternal Antifibrinolytic-2 trial is now assessing whether TXA can prevent PPH in women with anemia. Low red blood cell (RBC) counts promote fibrinolysis by altering fibrin structure and plasminogen activation.

OBJECTIVES

We explored interactions between RBCs and TXA in inhibiting fibrinolysis.

METHODS

We used global fibrinolytic assays (ball sedimentation and viscoelasticity) to monitor the lysis of fibrin containing plasminogen and tissue-type plasminogen activator. We applied a fluorogenic kinetic assay to measure plasmin generation in fibrin clots and scanning electron microscopy to study fibrin structure.

RESULTS

According to parallel-line bioassay analysis of the fibrin lysis-time data, the antifibrinolytic potency of 4-128 μM TXA was increased in the presence of 10% to 40% (v/v) RBCs. Global fibrinolysis assays showed that the joint effect of RBCs and TXA was about 15% larger than the sum of their individual effects in the inhibition of fibrinolysis. In plasminogen activation, TXA added the same increment of inhibition to the effect of RBCs at any cell count in the fibrin clot. Regarding fibrin structure, TXA thickened fibrin fibers, which impaired plasminogen activation, whereas RBCs promoted fine fibers that were more resistant to plasmin.

CONCLUSIONS

The antifibrinolytic potency of TXA is enhanced in fibrin formed in the presence of RBCs through inhibition of plasminogen activation and fibrin lysis, which correlates with modifications of fibrin structures.

Monoclonal enolase-1 blocking antibody ameliorates pulmonary inflammation and fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic fatal disease with limited therapeutic options. The infiltration of monocytes and fibroblasts into the injured lungs is implicated in IPF. Enolase-1 (ENO1) is a cytosolic glycolytic enzyme which could translocate onto the cell surface and act as a plasminogen receptor to facilitate cell migration via plasmin activation. Our proprietary ENO1 antibody, HL217, was screened for its specific binding to ENO1 and significant inhibition of cell migration and plasmin activation (patent: US9382331B2).

METHODS

In this study, effects of HL217 were evaluated in vivo and in vitro for treating lung fibrosis.

RESULTS

Elevated ENO1 expression was found in fibrotic lungs in human and in bleomycin-treated mice. In the mouse model, HL217 reduced bleomycin-induced lung fibrosis, inflammation, body weight loss, lung weight gain, TGF-β upregulation in bronchial alveolar lavage fluid (BALF), and collagen deposition in lung. Moreover, HL217 reduced the migration of peripheral blood mononuclear cells (PBMC) and the recruitment of myeloid cells into the lungs. In vitro, HL217 significantly reduced cell-associated plasmin activation and cytokines secretion from primary human PBMC and endothelial cells. In primary human lung fibroblasts, HL217 also reduced cell migration and collagen secretion.

CONCLUSIONS

These findings suggest multi-faceted roles of cell surface ENO1 and a potential therapeutic approach for pulmonary fibrosis.

Absence of hyperfibrinolysis may explain lack of efficacy of tranexamic acid in hypoproliferative thrombocytopenia

The American Trial Using Tranexamic Acid (TXA) in Thrombocytopenia (A-TREAT, NCT02578901) demonstrated no superiority of TXA over placebo in preventing World Health Organization (WHO) grade 2 or higher bleeding in patients with severe thrombocytopenia requiring supportive platelet transfusion following myeloablative therapy for hematologic disorders. In this ancillary study, we sought to determine whether this clinical outcome could be explained on the basis of correlative assays of fibrinolysis. Plasma was collected from A-TREAT participants (n = 115) before the initiation of study drug (baseline) and when TXA was at steady-state trough concentration (follow-up). Global fibrinolysis was measured by 3 assays: euglobulin clot lysis time (ECLT), plasmin generation (PG), and tissue-type plasminogen activator (tPA)-challenged clot lysis time (tPA-CLT). TXA was quantified in follow-up samples by tandem mass spectrometry. Baseline samples did not demonstrate fibrinolytic activation by ECLT or tPA-CLT. Furthermore, neither ECLT nor levels of plasminogen activator inhibitor-1, tPA, plasminogen, alpha2-antiplasmin, or plasmin-antiplasmin complexes were associated with a greater risk of WHO grade 2+ bleeding. TXA trough concentrations were highly variable (range, 0.7-10 μg/mL) and did not correlate with bleeding severity, despite the fact that plasma TXA levels correlated strongly with pharmacodynamic assessments by PG (Spearman r, -0.78) and tPA-CLT (r, 0.74). We conclude that (1) no evidence of fibrinolytic activation was observed in these patients with thrombocytopenia, (2) trough TXA concentrations varied significantly between patients receiving the same dosing schedule, and (3) tPA-CLT and PG correlated well with TXA drug levels.

The suboptimal fibrinolytic response in COVID-19 is dictated by high PAI-1

BACKGROUND

Severe COVID-19 disease is associated with thrombotic complications and extensive fibrin deposition. This study investigates whether the hemostatic complications in COVID-19 disease arise due to dysregulation of the fibrinolytic system.

METHODS

This prospective study analyzed fibrinolytic profiles of 113 patients hospitalized with COVID-19 disease with 24 patients with non-COVID-19 respiratory infection and healthy controls. Antigens were quantified by Ella system or ELISA, clot lysis by turbidimetric assay, and plasminogen activator inhibitor-1 (PAI-1)/plasmin activity using chromogenic substrates. Clot structure was visualized by confocal microscopy.

RESULTS

PAI-1 and its cofactor, vitronectin, are significantly elevated in patients with COVID-19 disease compared with those with non-COVID-19 respiratory infection and healthy control groups. Thrombin activatable fibrinolysis inhibitor and tissue plasminogen activator were elevated in patients with COVID-19 disease relative to healthy controls. PAI-1 and tissue plasminogen activator (tPA) were associated with more severe COVID-19 disease severity. Clots formed from COVID-19 plasma demonstrate an altered fibrin network, with attenuated fiber length and increased branching. Functional studies reveal that plasmin generation and clot lysis were markedly attenuated in COVID-19 disease, while PAI-1 activity was elevated. Clot lysis time significantly correlated with PAI-1 levels. Stratification of COVID-19 samples according to PAI-1 levels reveals significantly faster lysis when using the PAI-1 resistant (tPA) variant, tenecteplase, over alteplase lysis.

CONCLUSION

This study shows that the suboptimal fibrinolytic response in COVID-19 disease is directly attributable to elevated levels of PAI-1, which attenuate plasmin generation. These data highlight the important prognostic potential of PAI-1 and the possibility of using pre-existing drugs, such as tenecteplase, to treat COVID-19 disease and potentially other respiratory diseases.

Cryoprecipitate transfusion in trauma patients attenuates hyperfibrinolysis and restores normal clot structure and stability: Results from a laboratory sub-study of the FEISTY trial

BACKGROUND

Fibrinogen is the first coagulation protein to reach critical levels during traumatic haemorrhage. This laboratory study compares paired plasma samples pre- and post-fibrinogen replacement from the Fibrinogen Early In Severe Trauma studY (FEISTY; NCT02745041). FEISTY is the first randomised controlled trial to compare the time to administration of cryoprecipitate (cryo) and fibrinogen concentrate (Fg-C; Riastap) in trauma patients. This study will determine differences in clot strength and fibrinolytic stability within individuals and between treatment arms.

METHODS

Clot lysis, plasmin generation, atomic force microscopy and confocal microscopy were utilised to investigate clot strength and structure in FEISTY patient plasma.

RESULTS

Fibrinogen concentration was significantly increased post-transfusion in both groups. The rate of plasmin generation was reduced 1.5-fold post-transfusion of cryo but remained unchanged with Fg-C transfusion. Plasminogen activator inhibitor 1 activity and antigen levels and Factor XIII antigen were increased post-treatment with cryo, but not Fg-C. Confocal microscopy analysis of fibrin clots revealed that cryo transfusion restored fibrin structure similar to those observed in control clots. In contrast, clots remained porous with stunted fibres after infusion with Fg-C. Cryo but not Fg-C treatment increased individual fibre toughness and stiffness.

CONCLUSIONS

In summary, our data indicate that cryo transfusion restores key fibrinolytic regulators and limits plasmin generation to form stronger clots in an ex vivo laboratory study. This is the first study to investigate differences in clot stability and structure between cryo and Fg-C and demonstrates that the additional factors in cryo allow formation of a stronger and more stable clot.

Urokinase plasminogen activator induces epithelial-mesenchymal and metastasis of pancreatic cancer through plasmin/MMP14/TGF-β axis, which is inhibited by 4-acetyl-antroquinonol B treatment

BACKGROUND

The current standard therapy for metastatic pancreatic cancer is ineffective, necessitating a new treatment approach for prognosis improvement. The urokinase-plasmin activator (uPA) is a critical factor in epithelial-mesenchymal transition (EMT) and cancer metastasis, but its underlying mechanisms in pancreatic cancer remains elusive.

METHODS

We investigated uPA expression in our pancreatic cancer cohort. A bioinformatics approach was used to further determine the role of uPA in pancreatic cancer. We employed MiaPaCa-2 and PANC-1 cell lines to investigate how uPA regulates EMT and metastasis in pancreatic cancer and present a novel approach aimed at inhibiting uPA in pancreatic cancer.

RESULTS

We observed that higher uPA mRNA expression was significantly associated with overall-poor survival and progression-free survival in pancreatic cancer. uPA was highly expressed in tumor tissue. Gene set enrichment analysis revealed a positive association between uPA mRNA expression and EMT and transforming growth factor β (TGF-β) signaling pathways. Moreover, shRNA-mediated uPA gene knockdown reduced plasmin, MMP14, and TGF-β activation, leading to the inhibition of PANC-1 cells' EMT marker expression, migration, invasion, and cell viability. Notably, 4-acetyl-antroquinonol B (4-AAQB) treatment suppressed MiaPaCa-2 and PANC-1 cell migratory and invasive abilities by inhibiting the uPA/MMP14/TGF-β axis through upregulation of miR-181d-5p. In the xenograft mouse model of orthotropic pancreatic cancer, 4-AAQB treatment has reduced tumor growth and metastasis rate by deactivating uPA and improving the survival of the mice model.

CONCLUSION

Accordingly, to extent of our knowledge and previous studies, we demonstrated that 4-AAQB is an anti Pan-Cancer drug, and may inhibit pancreatic cancer EMT and metastasis and serve as a new therapeutic approach for patients with late-stage pancreatic cancer.

Application of a plasmin generation assay to define pharmacodynamic effects of tranexamic acid in women undergoing cesarean delivery

Essentials Tranexamic acid (TXA) is an antifibrinolytic drug used to reduce bleeding. Assaying plasmin generation (PG) in plasma detects clinically relevant TXA levels in vitro and ex vivo. 3.1-16.2 µg/mL TXA half-maximally inhibits PG in plasma from women undergoing cesarean delivery. PG velocity shows the strongest dose-relationship at low TXA concentrations (≤10 µg/mL). ABSTRACT: Background Tranexamic acid (TXA) is used to reduce bleeding. TXA inhibits plasmin(ogen) binding to fibrin and reduces fibrinolysis. TXA antifibrinolytic activity is typically measured by clot lysis assays; however, effects on plasmin generation (PG) are unclear due to a lack of tools to measure PG in plasma. Aims Develop an assay to measure PG kinetics in human plasma. Determine effects of TXA on PG and compare with fibrinolysis measured by rotational thromboelastometry (ROTEM). Methods We characterized effects of plasminogen, tissue plasminogen activator, fibrinogen, and α2 -antiplasmin on PG in vitro. We also studied effects of TXA on PG in plasma from 30 pregnant women administered intravenous TXA (5, 10, or 15 mg/kg) during cesarean delivery. PG was measured by calibrated fluorescence. PG parameters were compared with TXA measured by mass spectrometry and ROTEM of whole blood. Results The PG assay is specific for plasmin and sensitive to tissue plasminogen activator, fibrin(ogen), and α2 -antiplasmin. Addition of TXA to plasma in vitro dose dependently prolonged the clot lysis time and delayed and reduced PG. For all doses of TXA administered intravenously, the PG assay detected delayed time-to-peak (≤3 hours) and reduced the velocity, peak, and endogenous plasmin potential (≤24 hours) in plasma samples obtained after infusion. The PG time-to-peak, velocity, and peak correlated significantly with TXA concentration and showed less variability than the ROTEM lysis index at 30 minutes or maximum lysis. Conclusions The PG assay detects pharmacologically relevant concentrations of TXA administered in vitro and in vivo, and demonstrates TXA-mediated inhibition of PG in women undergoing cesarean delivery.

Preferential Reactivity of Dipeptidyl Peptidase-IV Inhibitor-Associated Bullous Pemphigoid Autoantibodies to the Processed Extracellular Domains of BP180

Bullous pemphigoid (BP) is a common autoimmune blistering disease in which autoantibodies target the hemidesmosomal components BP180 and/or BP230 in basal keratinocytes. In BP, 80 to 90% of autoantibodies target the juxtamembranous extracellular non-collagenous 16th A (NC16A) domain of BP180. Recently, the administration of dipeptidyl peptidase-IV inhibitors (DPP4i), which are widely used as antihyperglycemic drugs, has been recognized to be a causative factor for BP. DPP4i-associated BP (DPP4i-BP) autoantibodies tend to target epitopes on non-NC16A regions of BP180, and the pathomechanism for the development of the unique autoantibodies remains unknown. To address the characteristics of DPP4i-BP autoantibodies in detail, we performed epitope analysis of 18 DPP4i-BP autoantibodies targeting the non-NC16A domains of BP180 using various domain-specific as well as plasmin-digested polypeptides derived from recombinant BP180. Firstly, Western blotting showed that only one DPP4i-BP serum reacted with the epitopes on the intracellular domain of BP180, and no sera reacted with the C-terminal domain of the molecule. In addition, only 2 DPP4i-BP sera reacted with BP230 as determined by enzyme-linked immunosorbent assay. Thus, DPP4i-BP autoantibodies were found to mainly target the non-NC16A mid-portion of the extracellular domain of BP. Interestingly, Western blotting using plasmin-digested BP180 as a substrate revealed that all of the DPP4i-BP sera reacted more intensively with the 97-kDa processed extracellular domain of BP180, which is known as the LABD97 autoantigen, than full-length BP180 did. All of the DPP4i-BP autoantibodies targeting the LABD97 autoantigen were IgG1, and IgG4 was observed to react with the molecule in only 7 cases (38.9%). In summary, the present study suggests that IgG1-class autoantibodies targeting epitopes on the processed extracellular domain of BP180, i.e., LABD97, are the major autoantibodies in DPP4i-BP.

Tissue plasminogen activator mediates deleterious complement cascade activation in stroke

The use of intravenous tissue plasminogen activator (tPA) in the treatment of ischemic stroke is limited by its propensity to exacerbate brain edema and hemorrhage. The mechanisms underlying these deleterious effects of tPA remain incompletely understood. The purpose of this study was to delineate a pathway of tPA-mediated complement cascade activation in stroke and to determine whether complement inhibition ameliorates the adverse effects of post-ischemic tPA administration. We found that tPA promotes C3 cleavage both in vitro and in ischemic brain through a plasmin-mediated extrinsic pathway. Using cell culture models, we then showed that the C3a-receptor is strongly expressed on ischemic endothelium and that exogenous C3a dramatically enhances endothelial cell permeability. Next, we assessed the effect of tPA administration on brain edema and hemorrhage in a transient model of focal cerebral ischemia in C57BL/6 mice. We found that intravenous tPA exacerbates brain edema and hemorrhage in stroke, and that these effects are abrogated by a small-molecule antagonist of the C3a receptor. These findings establish for the first time that intravenous tPA dramatically upregulates complement cascade activation in ischemic brain and that pharmacologic complement inhibition protects against the adverse effects of tPA-mediated thrombolysis in stroke.

Fibrinolysis inhibitors in plaque stability: a morphological association of PAI-1 and TAFI in advanced carotid plaque

Essentials Fibrinolysis inhibitors are localized in advanced atheroma by immunohistology of endarterectomies. Neovascular endothelium/neocapillaries show thrombin-activatable fibrinolysis inhibitor (TAFI). Macrophage areas show free plasminogen activator inhibitor (PAI-1), notably in the vulnerable part. Free PAI-1 and TAFI stabilize active plaque area by inhibition of fibrinolysis and inflammation.

SUMMARY

Background Fibrinolysis plays an important role in destabilization of atherosclerotic plaques and is tightly regulated by specific inhibitors. Objective The fibrinolysis inhibitors plasminogen activator inhibitor type-1 (PAI-1) and thrombin-activatable fibrinolysis inhibitor (TAFI) were quantified and described in the morphological context of advanced carotid plaques American Heart Association VI-VIII to elucidate their role in plaque stability. Methods Immunohistochemistry in serial sections along the longitudinal axis of endarterectomies from patients with symptomatic carotid stenosis (n = 19) were studied using an antibody specific for free PAI-1 (I205), an antibody with high affinity for TAFI/TAFIa (CP17) and established antibodies for smooth muscle cells (α-actin), endothelial cells (von Willebrand factor [VWF]), macrophages (CD68) and platelets (CD42). Results PAI-1 and TAFI show a specific distribution in these advanced plaques with a maximum corresponding to the internal carotid artery (ICA). Free PAI-1 was mainly detected in macrophages and in intravascular thrombi, and TAFI in endothelial cells (ECs) but also macrophages. The one-way ANOVA analysis with Bonferroni's correction showed a significant increase of macrophages and ECs, TAFI and PAI-1 in areas with high neovascularization in endarterectomy sections corresponding to ICA. High Spearman factors for TAFI, PAI-1 and VWF indicate neovascularization as the main source of plasma proteins, transported by platelets into the atheroma (PAI-1) or expressed by ECs (TAFI). CD68 was highly associated with VWF, PAI-1 and especially TAFI, underlining the role of macrophages in fibrinolytic activity and inflammation. Conclusion The abundance of free PAI-1 and TAFI in the plaque may inhibit plasmin generation and thereby counteract plaque destabilization by fibrinolysis, cell migration and inflammation.

α1 -antitrypsin Pittsburgh and plasmin-mediated proteolysis

Essentials Patients with α-1-antitrypsin (α1-AT) Pittsburgh exhibit a mild bleeding tendency. A new case of α1-AT Pittsburgh with suspected high antifibrinolytic potential was studied. We showed that α1-AT Pittsburgh inhibits tissue plasminogen activator and plasmin. The antifibrinolytic potential of the variant contributes to explaining the mild bleeding phenotype.

SUMMARY

α1 -Antitrypsin (α1 -AT) Pittsburgh has a Met358 to Arg substitution at the reactive Met-Ser site of α1 -AT, which enables the protein to act as a potent thrombin inhibitor. Four patients with α1 -AT Pittsburgh have been described to date. An additional young girl was recently diagnosed with α1 -AT Pittsburgh in our center after presenting with a large hematoma in the forearm. Interestingly, all of these patients showed a potent thrombin inhibitor in the plasma and a mild bleeding phenotype. This observation suggests that the in vivo consequences of the mutation may contribute to the maintenance of normal hemostatic balance. We assessed inhibition of the fibrinolytic system by the variant protein by evaluating the fibrinolysis inhibitory potential of the patient's plasma, purified wild-type α1 -AT and purified Pittsburgh α1 -AT with an electrophoretic zymography system, western blotting, and clot fibrinolysis. Our results indicate that the patient's plasma and purified α1 -AT Pittsburgh have strong potential to inhibit tissue-type plasminogen activator and plasmin.

Pathological von Willebrand factor fibers resist tissue plasminogen activator and ADAMTS13 while promoting the contact pathway and shear-induced platelet activation

BACKGROUND

Under severe stenotic conditions, von Willebrand factor (VWF) multimerizes into large insoluble fibers at pathological shear rates.

OBJECTIVE

Evaluate the mechanics and biology of VWF fibers without the confounding effects of endothelium or collagen.

METHODS

Within a micropost-impingement microfluidic device, > 100-μm long VWF fibers multimerized on the post within 10 min using EDTA-treated platelet-free plasma (PFP) perfused at wall shear rates > 5000 s(-1) .

RESULTS

von Willebrand factor fiber thickness increased to > 10 μm as a result of increasing the shear rate to 10,000 s(-1) . In a stress-strain test, fibrous VWF had an elastic modulus of ~50 MPa. The insoluble VWF fibers were non-amyloid because they rapidly dissolved in trypsin, plasmin or 2% SDS, but were resistant to 50 nm ADAMTS13 or 100 nm tissue plasminogen activator in plasma. Following fiber formation, perfusion of low corn trypsin inhibitor (CTI)-treated (4 μg mL(-1) ), recalcified citrated plasma at 1500 s(-1) caused fibrin formation on the VWF fibers, a result not observed with purified type 1 collagen or a naked micropost. During VWF fiber formation, contact pathway factors accumulated on VWF because the use of EDTA/D-Phe-Pro-Arg chloromethylketone (PPACK)/apixaban/high CTI-treated PFP during VWF fiber formation prevented the subsequent fibrin production from low-CTI, recalcified citrated PFP. VWF fibers displayed FXIIa-immunostaining. When PPACK-inhibited whole blood was perfused over VWF fibers, platelets rolled and arrested on the surface of VWF, but only displayed P-selectin if prevailing shear rates were pathological. Platelet arrest on VWF fibers was blocked with αIIb β3 antagonist GR144053.

CONCLUSIONS

We report VWF fiber-contact pathway crosstalk and mechanisms of thrombolytic resistance in hemodynamic settings of myocardial infarction.

Interplay between fibrinolysis and complement: plasmin cleavage of iC3b modulates immune responses

BACKGROUND

The plasmin(ogen) and complement systems are simultaneously activated at sites of tissue injury, participating in hemostasis, wound healing, inflammation and immune surveillance. In particular, the C3 proteolytic fragment, iC3b, and its degradation product C3dg, which is generated by cleavage by factor I (FI) and the cofactor complement receptor CR1, are important in bridging innate and adaptive immunity. Via a thioester (TE) bond, iC3b and C3dg covalently tag pathogens, modulating phagocytosis and adaptive immune responses.

OBJECTIVE

To examine plasmin-mediated proteolysis of iC3b, and to evaluate the functional consequences, comparing the effects with products generated by FI/CR1 cleavage of iC3b.

METHODS

Dose-dependent and time-dependent plasmin-mediated cleavage of iC3b were characterized by analytical gel electrophoresis. The properties of the resultant TE bond-containing fragments on phagocytosis and induction of pro-inflammatory cytokines were measured in cell culture systems.

RESULTS

At low concentrations, plasmin effectively cleaves iC3b, but at numerous previously undescribed sites, giving rise to novel C3c-like and C3dg-like moieties, the latter of which retain the TE bond. When attached to zymosan or erythrocytes and exposed to THP-1 macrophages, the C3dg-like proteins behave almost identically to the bona fide C3dg, yielding less phagocytosis as compared with the opsonin iC3b, and more macrophage secretion of the pro-inflammatory cytokine, IL-12.

CONCLUSION

Plasmin cleavage of iC3b provides a complement regulatory pathway that is as efficient as FI/CR1 but does not require a cellular cofactor.

Lens subluxation after plasmin and SF6 injections in rabbit eyes

Purpose

To investigate the rate of lens subluxation following plasmin and/or SF₆ injections in eyes, and whether a subsequent elevated level of vascular endothelial growth factor (VEGF) and vitreous tap would aggravate subluxation.

Methods

Four groups of rabbits were used. Group 1 received an intravitreal injection (IVI) of plasmin and SF₆ in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF₆ in the right eye; and group 4 received an IVI of balanced salt solution in the right eye. After treatment, IVIs of VEGF were given and vitreous tap was performed three times, followed by clinical observation of lens subluxation and scanning electronic microscope evaluation of the zonular fibers.

Results

After IVIs of plasmin and SF₆, and VEGF and vitreous tap had been performed one to three times, lens subluxation was noted in 0%, 43%, 71%, 71%, and 86% of the eyes in group 1. After IVIs of plasmin, VEGF, and vitreous tap had been performed one to three times, lens subluxation was noted in 11%, 22%, 44%, 44%, and 67% of the eyes in group 2. The eyes in group 3 and 4 did not show signs of lens subluxation after VEGF IVIs and vitreous tap. Histology confirmed zonular fiber damage in the eyes treated with plasmin.

Conclusions

The incidence of lens subluxation increased following plasmin injections in the eyes, and this was aggravated by the subsequent high VEGF level in the eyes and vitreous tapping. Zonular fibers were disrupted following plasmin treatment. These effects should be kept in mind when using plasmin enzymes in patients with vitreoretinal abnormalities.

Recruitment of CCR6-expressing Th17 cells by CCL20 secreted from plasmin-stimulated macrophages

In the present study, monocyte-derived human macrophages were differentiated from buffy coats. Naïve CD4⁺ T-cells enriched from peripheral blood mononuclear cells using anti-CD4 magnetic beads and the autoMACS separation system were polarized under T-helper 17 (Th17)-promoting conditions for 6 days to get Th17 cells. The frequency of Th17 cell differentiation and the expression of C-C chemokine receptor type 6 (CCR6) on Th17 cells were investigated by flow cytometry. Plasmin-triggered induction of macrophage inflammatory protein-3alpha/C-C chemokine ligand 20 (CCL20) genes in macrophages was assessed by reverse transcription-polymerase chain reaction, and secreted protein levels were measured by enzyme-linked immunosorbent assay. Th17 cell migration induced by CCL20 secreted from plasmin-stimulated macrophages was tested in vitro by chemotaxis using a transwell system. These results demonstrate that plasmin triggers the expression of chemokine CCL20 messenger RNA and the release of CCL20 protein in human monocyte-derived macrophages, which critically depend on the proteolytic activity of plasmin and activation of p38 mitogen-activated protein kinase and nuclear factor-kappaB signaling pathways. Expression of CCR6 was detected on 87.23 ± 8.6% of Th17 cells in vitro. Similar to chemotaxis triggered by recombinant human CCL20, supernatants collected from plasmin-stimulated macrophage-induced chemotactic migration of Th17 cells, which could be inhibited by an anti-CCL20 neutralizing antibody. These results suggest that plasmin generated in inflamed tissues might elicit production of chemokine CCL20 by human macrophages leading to the recruitment of CCR6 positive Th17 cells to the inflammatory sites.

Protective effect of plasmin in marginal donor lungs in an ex vivo lung perfusion model

BACKGROUND

Donor lung thrombi are considered an important etiology for primary graft dysfunction in lung transplantation. We hypothesized that thrombolysis before lung transplantation could alleviate ischemia-reperfusion injury. This study was designed to evaluate the effect of the fibrinolytic agent plasmin on lungs damaged by thrombi in an ex vivo lung perfusion (EVLP) system.

METHODS

Rats were divided into control, non-plasmin, and plasmin groups (n = 7 each). In the control and plasmin groups, cardiac arrest was induced by withdrawal of mechanical ventilation without heparinization. Ventilation was restarted 150 minutes after cardiac arrest. The lungs were flushed, and the heart and lungs were excised en bloc. The lungs were perfused in the EVLP system for 60 minutes, and plasmin or placebo was administered upon EVLP initiation.

RESULTS

Fibrin/fibrinogen degradation products in the perfusate were significantly higher in the plasmin group than in the control and non-control groups (p < 0.001 for both). Plasmin administration significantly decreased pulmonary vascular resistance (plasmin vs non-plasmin, p = 0.011) and inhibited the exacerbation of dynamic compliance (plasmin vs non-plasmin, p = 0.003). Lung weight gain was less in the plasmin group than in the non-plasmin group (p = 0.04).

CONCLUSIONS

Our results confirmed that plasmin administration in an EVLP model dissolved thrombi in the lungs, resulting in reconditioning of the lungs as assessed by various physiologic parameters.

Thrombin regulation of synaptic plasticity: implications for physiology and pathology

Thrombin, a serine protease involved in the coagulation cascade has been recently shown to affect neuronal function following blood-brain barrier breakdown. Several lines of evidence have shown that thrombin may exist in the brain parenchyma under normal physiological conditions, yet its role in normal brain functions and synaptic transmission has not been established. In an attempt to shed light on the physiological functions of thrombin and Protease Activated Receptor 1 (PAR1) in the brain, we studied the effects of thrombin and a PAR1 agonist on long term potentiation (LTP) in mice hippocampal slices. Surprisingly, different concentrations of thrombin affect LTP through different molecular routes converging on PAR1. High thrombin concentrations induced an NMDA dependent, slow onset LTP, whereas low concentrations of thrombin promoted a VGCCs, mGluR-5 dependent LTP through activated Protein C (aPC). Remarkably, aPC facilitated LTP by activating PAR1 through an Endothelial Protein C Receptor (EPCR)-mediated mechanism which involves intracellular calcium stores. These findings reveal a novel mechanism by which PAR1 may regulate the threshold for synaptic plasticity in the hippocampus and provide additional insights into the role of this receptor in normal and pathological conditions.

Formation and stability of interpenetrating polymer network hydrogels consisting of fibrin and hyaluronic acid for tissue engineering

Fibrin gel is widely used as a tissue engineering scaffold. However, it has poor mechanical properties, which often result in rapid contraction and degradation of the scaffold. An interpenetrating polymer network (IPN) hydrogel composed of fibrin and hyaluronic acid-tyramine (HA-Tyr) was developed to improve the mechanical properties. The fibrin network was formed by cleaving fibrinogen with thrombin, producing fibrin monomers that rapidly polymerize. The HA network was formed through the coupling of tyramine moieties using horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The degree of crosslinking of the HA-Tyr network can be tuned by varying the H₂O₂ concentration, producing IPN hydrogels with different storage moduli (G'). While fibrin gels were completely degraded in the presence of plasmin and contracted when embedded with cells, the shape of the IPN hydrogels was maintained due to structural support by the HA-Tyr networks. Cell proliferation and capillary formation occurred in IPN hydrogels and were found to decrease with increasing G' of the hydrogels. The results suggest that fibrin-HA-Tyr IPN hydrogels are a potential alternative to fibrin gels as scaffolds for tissue engineering applications that require shape stability.

Apolipoprotein(a) inhibits in vitro tube formation in endothelial cells: identification of roles for Kringle V and the plasminogen activation system

Elevated plasma concentrations of lipoprotein(a) are associated with increased risk for atherothrombotic diseases. Apolipoprotein(a), the unique glycoprotein component of lipoprotein(a), is characterized by the presence of multiple kringle domains, and shares a high degree of sequence homology with the serine protease zymogen plasminogen. It has been shown that angiostatin, a proteolytic fragment of plasminogen containing kringles 1–4, can effectively inhibit angiogenesis. Moreover, proteolytic fragments of plasminogen containing kringle 5 are even more potent inhibitors of angiogenesis than angiostatin. Despite its strong similarity with plasminogen, the role of apolipoprotein(a) in angiogenesis remains controversial, with both pro- and anti-angiogenic effects reported. In the current study, we evaluated the ability of apolipoprotein(a) to inhibit VEGF- and angiopoietin-induced tube formation in human umbilical cord endothelial cells. A 17 kringle-containing form of recombinant apo(a) (17K), corresponding to a well-characterized, physiologically-relevant form of the molecule, effectively inhibited tube formation induced by either VEGF or angiopoietin-1. Using additional recombinant apolipoprotein(a) (r-apo(a)) variants, we demonstrated that this effect was dependent on the presence of an intact lysine-binding site in kringle V domain of apo(a), but not on the presence of the functional lysine-binding site in apo(a) kringle IV type 10; sequences within in the amino-terminal half of the molecule were also not required for the inhibitory effects of apo(a). We also showed that the apo(a)-mediated inhibition tube formation could be reversed, in part by the addition of plasmin or urokinase plasminogen activator, or by removal of plasminogen from the system. Further, we demonstrated that apo(a) treated with glycosidases to remove sialic acid was significantly less effective in inhibiting tube formation. This is the first report of a functional role for the glycosylation of apo(a) although the mechanisms underlying this observation remain to be determined in the context of angiogenesis.

Plasmin triggers a switch-like decrease in thrombospondin-dependent activation of TGF-β1

Transforming growth factor-β1 (TGF-β1) is a potent regulator of extracellular matrix production, wound healing, differentiation, and immune response, and is implicated in the progression of fibrotic diseases and cancer. Extracellular activation of TGF-β1 from its latent form provides spatiotemporal control over TGF-β1 signaling, but the current understanding of TGF-β1 activation does not emphasize cross talk between activators. Plasmin (PLS) and thrombospondin-1 (TSP1) have been studied individually as activators of TGF-β1, and in this work we used a systems-level approach with mathematical modeling and in vitro experiments to study the interplay between PLS and TSP1 in TGF-β1 activation. Simulations and steady-state analysis predicted a switch-like bistable transition between two levels of active TGF-β1, with an inverse correlation between PLS and TSP1. In particular, the model predicted that increasing PLS breaks a TSP1-TGF-β1 positive feedback loop and causes an unexpected net decrease in TGF-β1 activation. To test these predictions in vitro, we treated rat hepatocytes and hepatic stellate cells with PLS, which caused proteolytic cleavage of TSP1 and decreased activation of TGF-β1. The TGF-β1 activation levels showed a cooperative dose response, and a test of hysteresis in the cocultured cells validated that TGF-β1 activation is bistable. We conclude that switch-like behavior arises from natural competition between two distinct modes of TGF-β1 activation: a TSP1-mediated mode of high activation and a PLS-mediated mode of low activation. This switch suggests an explanation for the unexpected effects of the plasminogen activation system on TGF-β1 in fibrotic diseases in vivo, as well as novel prognostic and therapeutic approaches for diseases with TGF-β dysregulation.

Inhibition of stromelysin-1 by caffeic acid derivatives from a propolis sample from Algeria

Stromelysin-1 (matrix metalloproteinase-3: MMP-3) occupies a central position in collagenolytic and elastolytic cascades, leading to cutaneous intrinsic and extrinsic aging. We screened extracts of a propolis sample from Algeria with the aim to isolate compounds able to selectively inhibit this enzyme. A butanolic extract (B (3)) of the investigated propolis sample was found to potently inhibit MMP-3 activity (IC (50) = 0.15 ± 0.03 µg/mL), with no or only weak activity on other MMPs. This fraction also inhibited plasmin amidolytic activity (IC (50) = 0.05 µg/mL) and impeded plasmin-mediated proMMP-3 activation. B (3) was fractionated by HPLC, and one compound, characterized by NMR and mass spectroscopy and not previously identified in propolis, i.e., (+)-chicoric acid, displayed potent IN VITRO MMP-3 inhibitory activity (IC (50) = 6.3 × 10 (-7) M). In addition, both caffeic acid and (+)-chicoric acid methyl ester present in fraction B (3) significantly inhibited UVA-mediated MMP-3 upregulation by fibroblasts.

[The research of thrombolytic and hemolysis effect from Eupolyphage fibrinolyric protein and its inhibitory effect on S180 ascites tumor of mice]

OBJECTIVE

Eupolyphage fibrinolyric protein (EFP) was isolated and purified from Eupolyphage sineses, and its thrombolytic effect, hemolysis effect and inhibitory effect on S180 ascites tumor were investigated.

METHODS

EFP was isolated and purified by ammonium precipitation and DEAE ion exchange chromatography. It's thrombolytic and hemolysis effect were determined. MTT method and Colony-forming method were used to determine the inhibitory effect on S180 ascites tumor.

RESULTS

the EFP was proved to have the effect of Thrombolytic and Hemolysis, and both increased dose-dependently, however at a lower concentration, the EFP had no hemocytolysis. The EFP was also proved the effect of inhibitory on cell proliferation and Colony-forming on S180 ascites tumor of Mice.

CONCLUSION

EFP has a strong thrombolytic activity and weak hemolytic, and has inhibitory effect on S180 ascites tumor of mice.

Pharmacologic vitreodynamics and molecular flux

Several enzymatic agents, such as autologous plasmin enzyme and recombinant microplasmin, are able to cause vitreous liquefaction and a complete posterior vitreous detachment (PVD). Advancements in research have helped to explain the complex interactions that occur in the vitreous cavity after a PVD is created. The development of a PVD is a dynamic process that is thought to have a larger impact on the vitreous cavity milieu than just a separation of the posterior cortical vitreous from the retina. Pharmacologic vitreodynamics attempts to explain the mechanical and biochemical changes that occur at the vitreoretinal junction after a PVD is formed. The flow of molecules into and out of the vitreous cavity and across the vitreoretinal junction is thought to be influenced by the presence or absence of a PVD. A microplasmin-induced PVD has been shown to alter the vitreous levels of several molecules, and a PVD may have a protective role in multiple diseases. Significant progress has been made in the field of pharmacologic vitreodynamics. As we improve our understanding of the molecular flux in the vitreous cavity, pharmacologic vitreodynamics will likely become more important as it may allow for improved manipulation of intravitreal molecules.

Surface-associated activation of plasminogen on gram-positive bacteria. Effect of plasmin on the adherence of Staphylococcus aureus

In this article we review a novel type of plasminogen activation on staphylococcal and streptococcal cells. The activation mechanism implies a specific binding of glu-plasminogen to bacterial surface via the lysine-binding sites of plasminogen. Association of plasminogen with bacterial surfaces greatly enhances the t-PA mediated activation which takes place only poorly in solution. The end product, surface-associated plasmin, is enzymatically active, protected against high molecular weight plasmin inhibitors and capable of converting itself from glu-plasmin to the lys-form. The modification is associated with an increased affinity of the bound lys-plasmin towards the binding molecules on bacterial surface. This novel way of retaining plasmin on the surface may be important for the bacteria to invade and penetrate surrounding tissues. Our data on the effect of plasmin on staphylococcal adherence indicate that plasmin is not very effective in cleaning bacteria from surfaces coated with extracellular matrix components, fibronectin and fibrinogen.

Functional analysis of mutant variants of thrombin-activatable fibrinolysis inhibitor resistant to activation by thrombin or plasmin

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) defines a pathway that functionally links the coagulation and fibrinolytic cascades. TAFI is activated by proteolytic cleavage, a reaction that can be performed by thrombin and plasmin, but most efficiently by thrombin in complex with the endothelial cofactor thrombomodulin (TM). The respective roles of these activators in regulating the TAFI pathway are largely unknown.

OBJECTIVE AND METHODS

In the present study, we constructed and expressed mutant variants of TAFI that have key substitutions in the amino acids surrounding the scissile Arg92-Ala93 bond.

RESULTS AND CONCLUSIONS

We identified variants that showed patterns of resistance to specific activators. For example, the P91S, R92K and S90P variants exhibited specific impairment of activation by thrombin or thrombin-TM, thrombin alone, and thrombin alone or plasmin, respectively. The variants that we tested also showed antifibrinolytic potentials that can be rationalized in terms of which enzymes are capable of activating them. On the other hand, certain predictions from peptide studies of mutations that would be expected to interfere with plasmin cleavage were not satisfied by our data, indicating that protein context, as well as the identity of amino acids at protease cleavage sites, dictates protease specificity.

Plasmin enhances cell surface tissue factor activity in mesothelial and endothelial cells

BACKGROUND

Mesothelial cells that line the thoracic cavity play an important role in maintaining the local balance between procoagulant and fibrinolytic activity, a role akin to the endothelial cells in blood vessels. The mechanism(s) responsible for increased tissue factor (TF) expression in mesothelial cells in response to injury are at present unclear.

OBJECTIVE

To investigate whether plasmin or thrombin, two major proteases that may be generated on the pleural surface upon injury, induce TF expression in human pleural mesothelial cells (HMC) and elucidate the underlying mechanism(s).

METHODS

Confluent monolayers of HMC and human umbilical vein endothelial cells (HUVEC) were exposed to plasmin or thrombin for varying time periods and TF expression was analyzed by measuring its activity in a factor Xa generation assay, TF antigen levels by immunoblot analysis and TF mRNA by Northern blot analysis.

RESULTS

Both plasmin and thrombin treatments increased cell surface TF activity in HMC by 3- to 4-fold. In contrast to thrombin, plasmin-induced TF activity is not dependent on the de novo synthesis of TF. In HUVEC, plasmin had a minimal effect on unperturbed HUVEC whereas it markedly increased TF activity of activated HUVEC. Plasmin treatment neither affected anionic phospholipid levels at the cell surface nor released protein disulfide isomerase, an oxidoreductase protein that was newly described to play a role in TF activation. Plasmin cleaved cell-associated TFPI.

CONCLUSION

Thrombin up-regulates TF activity in HMC through the transcriptional activation of TF whereas plasmin increases TF activity by inactivating the cell-associated TFPI by a limited proteolysis.

A first-in-human phase I trial of locally delivered human plasmin for hemodialysis graft occlusion

BACKGROUND

Hemodialysis (HD) grafts often fail because of stenosis at the venous anastomosis and thrombotic occlusion. Percutaneous management relies on thrombolysis with plasminogen activators, mechanical removal of thrombus, and angioplasty of the stenotic lesion.

OBJECTIVES

This report describes a phase I trial using Plasmin (Human) TAL 05-00018, a direct-acting fibrinolytic agent, to evaluate safety and, secondarily, to establish effective thrombolytic dosing.

PATIENTS/METHODS

Six cohorts of five patients with acute HD graft occlusion documented by angiography were treated with escalating dosages of plasmin (1, 2, 4, 8, 12, and 24 mg) infused over 30 min via criss-crossed pulse-spray catheters within the graft. The primary efficacy endpoint was > or =50% thrombolysis, as determined by comparison of pre-plasmin and 30-min post-plasmin fistulograms.

RESULTS

Of 31 subjects who received study drug (safety population), one withdrew and 30 completed the trial (evaluable for efficacy). There was no significant change in plasma alpha-2 antiplasmin or fibrinogen concentration, major bleeding did not occur, and there were no deaths. Serious adverse events in four patients were not related to the study drug. There was a dose-response relationship for the primary efficacy endpoint, all five subjects receiving 24 mg achieving >75% lysis.

CONCLUSIONS

This first phase I study of Plasmin (Human) TAL 05-00018, infused into thrombosed HD grafts, documents safety at dosages of 1-24 mg and an effective thrombolytic dosage of 24 mg. The results establish a foundation for further clinical study of catheter-based plasmin administration in thrombotic disorders.

Middle cerebral artery occlusion in the rabbit using selective angiography: application for assessment of thrombolysis

BACKGROUND AND PURPOSE

An animal model of selective middle cerebral artery (MCA) occlusion is needed for evaluation of intra-arterial (IA) delivery of thrombolytic agents. We describe a technique for MCA thrombo-occlusion in the rabbit with real-time angiographic documentation of occlusion and thrombolytic recanalization.

METHODS

After femoral artery cutdown, a microcatheter was advanced from the internal carotid artery to the MCA. MCA occlusion was achieved by IA thrombin and reperfusion by IA plasmin.

RESULTS

The terminal internal carotid artery was successfully catheterized in 12 of 13 animals. Stable (2-hour) MCA occlusion was induced and verified angiographically in all 12 animals; 2 animals also had distal internal carotid artery thrombus. Recanalization was achieved rapidly after IA plasmin in 3 of 3 animals.

CONCLUSIONS

We describe a new animal model of selective MCA occlusion documented by real-time angiography and used to demonstrate recanalization with IA plasmin.

[Effect of recombinant microplasmin on acute cerebral infarction in rats]

The effect of recombinant microplasmin (micro-plasmin) on acute cerebral infarction was evaluated in rats, and compared with recombinant tissue plasminogen activator (rt-PA). After the model of middle cerebral artery occlusion (MCAO) was established by autologous blood clots, different doses of micro-plasmin (2.5, 5, and 10 mg x kg(-1)) were administered into the thrombus intra-arterial. Twelve hours after administration of micro-plasmin, the neurological deficit score of rats was recorded and the infarct volumes were determined. Bleeding time (BT), fibrin degradation product (FDP) concentration in serum and thrombin time (TT), prothrombin time (PT) and fibrinogen (FIB) concentration in plasma were tested after administration. Intra-arterial administration of micro-plasmin could reduce significantly neurological deficit score and infarct volumes in MCAO rats. FDP concentration increased significantly as compared with model group. There were no significant differences in TT, PT and BT. FIB concentration reduced markedly as compared with model group, but had no significant difference as compared with sham group. The results suggest that micro-plasmin is effective in treatment of rat acute cerebral infarction, and has no significant influence on fibrinolytic system and blood clotting system, indicating that micro-plasmin may be useful for treatment of acute cerebral infarction, and not lead to hemorrhage. Micro-plasmin seems to be distinguished from clinical used rt-PA by its no hemorrhage effect.