Antiplasmin

Fibrinolysis-Mediated Pathways in Acute Liver Injury

Acute liver injury (ALI), that is, the development of reduced liver function in patients without preexisting liver disease, can result from a wide range of causes, such as viral or bacterial infection, autoimmune disease, or adverse reaction to prescription and over-the-counter medications. ALI patients present with a complex coagulopathy, characterized by both hypercoagulable and hypocoagulable features. Similarly, ALI patients display a profound dysregulation of the fibrinolytic system with the vast majority of patients presenting with a hypofibrinolytic phenotype. Decades of research in experimental acute liver injury in mice suggest that fibrinolytic proteins, including plasmin(ogen), plasminogen activators, fibrinolysis inhibitors, and fibrin(ogen), can contribute to initial hepatotoxicity and/or stimulate liver repair. This review summarizes major experimental findings regarding the role of fibrinolytic factors in ALI from the last approximately 30 years and identifies unanswered questions, as well as highlighting areas for future research.

A High-Throughput Small-Angle X-ray Scattering Assay to Determine the Conformational Change of Plasminogen

Plasminogen (Plg) is the inactive form of plasmin (Plm) that exists in two major glycoforms, referred to as glycoforms I and II (GI and GII). In the circulation, Plg assumes an activation-resistant "closed" conformation via interdomain interactions and is mediated by the lysine binding site (LBS) on the kringle (KR) domains. These inter-domain interactions can be readily disrupted when Plg binds to lysine/arginine residues on protein targets or free L-lysine and analogues. This causes Plg to convert into an "open" form, which is crucial for activation by host activators. In this study, we investigated how various ligands affect the kinetics of Plg conformational change using small-angle X-ray scattering (SAXS). We began by examining the open and closed conformations of Plg using size-exclusion chromatography (SEC) coupled with SAXS. Next, we developed a high-throughput (HTP) 96-well SAXS assay to study the conformational change of Plg. This method enables us to determine the Kopen value, which is used to directly compare the effect of different ligands on Plg conformation. Based on our analysis using Plg GII, we have found that the Kopen of ε-aminocaproic acid (EACA) is approximately three times greater than that of tranexamic acid (TXA), which is widely recognized as a highly effective ligand. We demonstrated further that Plg undergoes a conformational change when it binds to the C-terminal peptides of the inhibitor α2-antiplasmin (α2AP) and receptor Plg-RKT. Our findings suggest that in addition to the C-terminal lysine, internal lysine(s) are also necessary for the formation of open Plg. Finally, we compared the conformational changes of Plg GI and GII directly and found that the closed form of GI, which has an N-linked glycosylation, is less stable. To summarize, we have successfully determined the response of Plg to various ligand/receptor peptides by directly measuring the kinetics of its conformational changes.

Proteomic Approaches and Potential Applications in Autosomal Dominant Polycystic Kidney Disease and Fabry Disease

Although rare, hereditary diseases, such as autosomal dominant polycystic kidney disease (ADPKD) and Fabry disease (FD) may significantly progress towards severe nephropathy. It is crucial to characterize it accurately, predict the course of the illness and estimate treatment effectiveness. A huge effort has been undertaken to find reliable biomarkers that might be useful for an early prevention of the disease progression and/or any invasive diagnostic procedures. The study of proteomics, or the small peptide composition of a sample, is a field of study under continuous development. Over the past years, several strategies have been created to study and define the proteome of samples from widely varying origins. However, urinary proteomics has become essential for discovering novel biomarkers in kidney disease. Here, the extracellular vesicles in human urine that contain cell-specific marker proteins from every segment of the nephron, offer a source of potentially valuable urinary biomarkers, and may play an essential role in kidney development and kidney disease. This review summarizes the relevant literature investigating the proteomic approaches and potential applications in the regular studies of ADPKD and FD.

Serpin-loaded extracellular vesicles promote tissue repair in a mouse model of impaired wound healing

Chronic metabolic diseases such as diabetes are characterized by delayed wound healing and a dysregulation of the inflammatory phase of wound repair. Our study focuses on changes in the payload of extracellular vesicles (EVs) communicating between immune cells and stromal cells in the wound bed, which regulate the rate of wound closure. Adoptive transfer of EVs from genetically defined mouse models are used here to demonstrate a functional and molecular basis for differences in the pro-reparative biological activity of diabetic (db/db) vs. wildtype EVs in wound healing. We identify several members of the Serpin family of serine protease inhibitors that are absent in db/db EVs, then we overexpress Serpin A1, F2 and G1 in EVs to evaluate their effect on wound healing in db/db mice. Serpins have an important role in regulating levels of elastase, plasmin and complement factors that coordinate immune cell signaling in full thickness wounds in a diabetic model. Here, we establish a novel therapeutic approach by engineering the payload of EVs based on proteomic analysis. Serpin-loaded EVs were used to rescue the Serpin deficiency identified by proteomics and promote wound healing in db/db mice, as well as evaluated how EVs affected extracellular matrix remodeling and the resolution of tissue injury. Therefore, we propose that the identification of EV payloads that are downregulated in diabetic wounds can be systematically analyzed for their functional activity and potential as a therapeutic, based on whether their re-expression in engineered EVs restores normal kinetics of tissue repair in chronic wounds.

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

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

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

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

Prothrombotic clot properties can predict venous ulcers in patients following deep vein thrombosis: a cohort study

Venous ulcers are the most severe manifestation of post-thrombotic syndrome (PTS). We have previously demonstrated that formation of compact fibrin clots resistant to lysis is observed in patients following deep-vein thrombosis (DVT) who developed PTS. The current study investigated whether unfavourable fibrin clot properties can predict post-thrombotic venous ulcers. In a cohort study on 186 consecutive patients following DVT, we determined plasma fibrin clot characteristics, including clot permeability and lysability, inflammatory markers, thrombin generation, fibrinolysis proteins at 3 months since the index event. Occurrence of PTS and venous ulcers was recorded during follow-up (median, 53; range 24 to 76 months). Fifty-seven DVT patients (30.6%) developed PTS, including 12 subjects (6.45%) with a venous ulcer (4 individuals with recurrent ulcers). Patients who developed ulcers compared with the remainder had at enrolment 13.0% lower clot permeability (Ks), 17.4% longer clot lysis time (CLT), 13.1% longer lag phase of clot formation, and 5.0% higher maximum absorbance, with no difference in fibrinogen, C-reactive protein, and thrombin generation. The baseline prothrombotic fibrin clot phenotype (Ks ≤ 6.5 × 10-9 cm2 and CLT > 100 min) was associated with a higher risk of ulcers [hazard ratio (HR), 5.37; 95% confidence interval (CI), 1.3-21.5]. A multivariate model adjusted for age, sex, and fibrinogen showed that independent predictors of the ulcer occurrence were body mass index (HR 1.53; 95% CI 1.30-1.86), CLT (HR 1.43; 95% CI 1.04-2.05), and α2-antiplasmin (HR 0.95; 95% CI 0.90-0.99). This study suggests that formation of denser fibrin clots with impaired fibrinolysis predisposes to post-thrombotic venous ulcers.

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.

Genetic Regulation of Pigment Epithelium-Derived Factor (PEDF): An Exome-Chip Association Analysis in Chinese Subjects With Type 2 Diabetes

Elevated circulating levels of pigment epithelium-derived factor (PEDF) have been reported in patients with type 2 diabetes (T2D) and its associated microvascular complications. This study aimed to 1) identify the genetic determinants influencing circulating PEDF levels in a clinical setting of T2D, 2) examine the relationship between circulating PEDF and diabetes complications, and 3) explore the causal relationship between PEDF and diabetes complications. An exome-chip association study on circulating PEDF levels was conducted in 5,385 Chinese subjects with T2D. A meta-analysis of the association results of the discovery stage (n = 2,936) and replication stage (n = 2,449) was performed. The strongest association was detected at SERPINF1 (p.Met72Thr; P_combined = 2.06 × 10^-57; β [SE] -0.33 [0.02]). Two missense variants of SMYD4 (p.Arg131Ile; P_combined = 7.56 × 10^-25; β [SE] 0.21 [0.02]) and SERPINF2 (p.Arg33Trp; P_combined = 8.22 × 10^-10; β [SE] -0.15 [0.02]) showed novel associations at genome-wide significance. Elevated circulating PEDF levels were associated with increased risks of diabetic nephropathy and sight-threatening diabetic retinopathy. Mendelian randomization analysis showed suggestive evidence of a protective role of PEDF on sight-threatening diabetic retinopathy (P = 0.085). Our study provided new insights into the genetic regulation of PEDF and further support for its potential application as a biomarker for diabetic nephropathy and sight-threatening diabetic retinopathy. Further studies to explore the causal relationship of PEDF with diabetes complications are warranted.

Haemarthrosis stimulates the synovial fibrinolytic system in haemophilic mice

Recurrent joint bleeding is the most common manifestation of haemophilia resulting in haemophilic arthropathy (HA). The exact pathophysiology is unknown, but it is suggested that arthropathy is stimulated by liberation of fibrinolytic activators from the synovium during haemarthrosis. The aim of this study was to test the hypothesis that haemarthrosis activates the local synovial fibrinolytic system in a murine haemophilia model. The right knees of haemophilic and control mice were punctured to induce haemarthrosis. The left knees served as internal control joints. Synovial levels of urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor 1 (PAI-1), plasmin, and alpha-2-antiplasmin (A2AP) were compared between the punctured and control knees. In haemophilic mice, an increase in synovial cells expressing urokinase-type plasminogen activator (uPA) in the right punctured knee versus the left unaffected knee was observed: (47% vs 43%) (p=0.03). Additionally, in haemophilic mice, haemar-throsis induced an increase in uPA (0.016 ng/ml vs 0.01 ng/ml) (p=0.03) and plasmin (0.53 μg/ml vs 0.46 μg/ml) (p=0.01) as promoters of fibrinolysis. Synovial levels of PAI-1 (0.32 ng/ml vs 0.17 ng/ ml) (p<0.01) was also increased, whereas synovial levels of A2AP were unchanged: (0.021 μg/ml vs 0.021 μg/ml) (p=0.15). Enhanced uPA production was confirmed in human stimulated synovial fibroblast cultures and elevated levels of plasmin were confirmed harmful to human cartilage tissue explants. In this study we demonstrate that haemarthrosis in haemophilic mice induces synovial uPA expression and results in an increase in synovial plasmin levels, making the joint more vulnerable to prolonged and subsequent bleedings, and adding directly to cartilage damage.

Microbial serine protease inhibitors and their therapeutic applications

Serine protease inhibitors, inhibit serine proteases either partially or completely after forming complexes with their respective proteases. Protease actions are significant for many physiological pathways found in living forms and any anomalies may lead to numerous physiological complications. Each cell or organism has its own mechanism for controlling these protease actions. It is often regulated by the action of inhibitors or activators. Among the proteases, serine proteases are the most common that are involved in many life and death processes. Selective inhibitors of physiologically relevant proteases can be used as a lead compound for the drug development. Therefore, it is imperative to identify small peptides and proteins that selectively inhibit serine proteases from various sources. Microbes can be considered as a major source of diverse serine protease inhibitors since they have the prominent and diverse domain in nature. Most of the microbial serine protease inhibitors are intracellular and few are extracellular. Microbes produce protease inhibitors for protection against its own proteases or against other environmental factors. The status and future prospects of microbial serine protease inhibitors and their therapeutic benefits in treating cancer, blood coagulation disorders and viral infections, are reviewed here.

X-ray crystal structure of plasmin with tranexamic acid-derived active site inhibitors

The zymogen protease plasminogen and its active form plasmin perform key roles in blood clot dissolution, tissue remodeling, cell migration, and bacterial pathogenesis. Dysregulation of the plasminogen/plasmin system results in life-threatening hemorrhagic disorders or thrombotic vascular occlusion. Accordingly, inhibitors of this system are clinically important. Currently, tranexamic acid (TXA), a molecule that prevents plasminogen activation through blocking recruitment to target substrates, is the most widely used inhibitor for the plasminogen/plasmin system in therapeutics. However, TXA lacks efficacy on the active form of plasmin. Thus, there is a need to develop specific inhibitors that target the protease active site. Here we report the crystal structures of plasmin in complex with the novel YO (trans-4-aminomethylcyclohexanecarbonyl-l-tyrosine-n-octylamide) class of small molecule inhibitors. We found that these inhibitors form key interactions with the S1 and S3' subsites of the catalytic cleft. Here, the TXA moiety of the YO compounds inserts into the primary (S1) specificity pocket, suggesting that TXA itself may function as a weak plasmin inhibitor, a hypothesis supported by subsequent biochemical and biophysical analyses. Mutational studies reveal that F587 of the S' subsite plays a key role in mediating the inhibitor interaction. Taken together, these data provide a foundation for the future development of small molecule inhibitors to specifically regulate plasmin function in a range of diseases and disorders.

Plasminogen-receptor KT : plasminogen activation and beyond

The cell surface orchestrates plasminogen activation through the concomitant binding of plasminogen and plasminogen activators to specific receptors. In this issue, Miles and colleagues describe their detailed phenotypic characterization of mice deficient in Plg-RKT, a key plasminogen receptor expressed in numerous tissues, but highly expressed by proinflammatory macrophages. The analysis provides critical and surprising new insights into the biology of this receptor.

Egg serpins: The chicken and/or the egg dilemma

Twenty-seven serpins belonging to clade A, B, C, D, E, F, G, H and I serpins are currently referenced in chicken genome databases. Phylogenetic analysis of chicken serpins revealed that ovalbumin (Serpinb14) and its paralogs ovalbumin-related protein Y (Serpinb14b) and ovalbumin-related protein X (Serpinb14c) are found in bird species. These clade B serpins are specifically expressed in reproductive tissues and exported in the egg where they constitute major protein components. These data suggest that these three paralogs have probably appeared in birds to face new environments and ensure the extra-uterine development of an embryo in a shell egg. Twelve other serpins have been identified in the newly produced egg, some of them having a specific distribution in the respective egg structures (eggshell, egg white, vitelline membrane and egg yolk). The physiological role of these egg serpins remain largely unexplored, but there is increasing evidence in literature or by homologies with their mammalian counterparts, that some of them participate in cell proliferation, tissue remodeling and/or angiogenesis associated with folliculogenesis and development of extraembryonic structures, eggshell biomineralization, egg defense and nutrition of the embryo. A better knowledge of the phylogenetic evolution of these 15 serpins in other oviparous species, on their egg distribution, on their regulation during embryonic development (activation/degradation/transfer) and on their functional specificity, is needed to better appreciate their role and their bird-specificity. These review shed light on the multiple possibilities that offer the avian egg model to study the role of serpins in reproduction and developmental biology.

From the analysis of pharmacologic vitreolysis to the comprehension of ocriplasmin safety

INTRODUCTION

Pharmacologic vitreolysis is a strategy used to treat anomalous posterior vitreous detachment, by weakening vitreoretinal adhesion with an intravitreal drug. Pharmacologic vitreolysis facilitates surgery, and abnormalities of the vitreoretinal interface including vitreomacular traction (VMT) and early stage macular hole (MH) could be resolved. Ocriplasmin is a recombinant protease, active against fibronectin and laminin, which are important components of the vitreoretinal interface. Ocriplasmin has been approved for symptomatic treatment of VMT and MH with visible traction, and it functions by dissolving the proteins that link the vitreous to the macula, thereby creating a complete posterior vitreous detachment (PVD).

AREAS COVERED

This paper reviews the current knowledge and status of investigations regarding the use of ocriplasmin for pharmacologic vitreolysis and its safety.

EXPERT OPINION

Ocriplasmin is a non-specific enzyme; therefore, it dissolves vitreal proteins as well as possibly proteins associated with visual function in the retina, choroid, and lens. Ocular adverse events (OAEs) of ocriplasmin include transient visual loss, intraocular inflammation, vitreous floaters, lens opacification, zonular instability of the lens, and intraocular hemorrhage. The prevalence of the OAEs is very low; however, on rare occasions, they can result in widespread retinal dysfunction. Research into the acute and long-term safety of ocriplasmin is required.

Rapid Increases in proBDNF after Pilocarpine-Induced Status Epilepticus in Mice Are Associated with Reduced proBDNF Cleavage Machinery

Brain-derived neurotrophic factor (BDNF) levels are elevated after status epilepticus (SE), leading to activation of multiple signaling pathways, including the janus kinase/signal transducer and activator of transcription pathway that mediates a decrease in GABAA receptor α1 subunits in the hippocampus (Lund et al., 2008). While BDNF can signal via its pro or mature form, the relative contribution of these forms to signaling after SE is not fully known. In the current study, we investigate changes in proBDNF levels acutely after SE in C57BL/6J mice. In contrast to previous reports (Unsain et al., 2008; Volosin et al., 2008; VonDran et al., 2014), our studies found that levels of proBDNF in the hippocampus are markedly elevated as early as 3 h after SE onset and remain elevated for 7 d. Immunohistochemistry studies indicate that seizure-induced BDNF localizes to all hippocampal subfields, predominantly in principal neurons and also in astrocytes. Analysis of the proteolytic machinery that cleaves proBDNF to produce mature BDNF demonstrates that acutely after SE there is a decrease in tissue plasminogen activator and an increase in plasminogen activator inhibitor-1 (PAI-1), an inhibitor of extracellular and intracellular cleavage, which normalizes over the first week after SE. In vitro treatment of hippocampal slices from animals 24 h after SE with a PAI-1 inhibitor reduces proBDNF levels. These findings suggest that rapid proBDNF increases following SE are due in part to reduced cleavage, and that proBDNF may be part of the initial neurotrophin response driving intracellular signaling during the acute phase of epileptogenesis.

Natural heterogeneity of α2-antiplasmin: functional and clinical consequences

Human α2-antiplasmin (α2AP, also called α2-plasmin inhibitor) is the main physiological inhibitor of the fibrinolytic enzyme plasmin. α2AP inhibits plasmin on the fibrin clot or in the circulation by forming plasmin-antiplasmin complexes. Severely reduced α2AP levels in hereditary α2AP deficiency may lead to bleeding symptoms, whereas increased α2AP levels have been associated with increased thrombotic risk. α2AP is a very heterogeneous protein. In the circulation, α2AP undergoes both amino terminal (N-terminal) and carboxyl terminal (C-terminal) proteolytic modifications that significantly modify its activities. About 70% of α2AP is cleaved at the N terminus by antiplasmin-cleaving enzyme (or soluble fibroblast activation protein), resulting in a 12-amino-acid residue shorter form. The glutamine residue that serves as a substrate for activated factor XIII becomes more efficient after removal of the N terminus, leading to faster crosslinking of α2AP to fibrin and consequently prolonged clot lysis. In approximately 35% of circulating α2AP, the C terminus is absent. This C terminus contains the binding site for plasmin(ogen), the key component necessary for the rapid and efficient inhibitory mechanism of α2AP. Without its C terminus, α2AP can no longer bind to the lysine binding sites of plasmin(ogen) and is only a kinetically slow plasmin inhibitor. Thus, proteolytic modifications of the N and C termini of α2AP constitute major regulatory mechanisms for the inhibitory function of the protein and may therefore have clinical consequences. This review presents recent findings regarding the main aspects of the natural heterogeneity of α2AP with particular focus on the functional and possible clinical implications.

Bayesian phylogeny analysis of vertebrate serpins illustrates evolutionary conservation of the intron and indels based six groups classification system from lampreys for ∼500 MY

The serpin superfamily is characterized by proteins that fold into a conserved tertiary structure and exploits a sophisticated and irreversible suicide-mechanism of inhibition. Vertebrate serpins are classified into six groups (V1-V6), based on three independent biological features-genomic organization, diagnostic amino acid sites and rare indels. However, this classification system was based on the limited number of mammalian genomes available. In this study, several non-mammalian genomes are used to validate this classification system using the powerful Bayesian phylogenetic method. This method supports the intron and indel based vertebrate classification and proves that serpins have been maintained from lampreys to humans for about 500 MY. Lampreys have fewer than 10 serpins, which expand into 36 serpins in humans. The two expanding groups V1 and V2 have SERPINB1/SERPINB6 and SERPINA8/SERPIND1 as the ancestral serpins, respectively. Large clusters of serpins are formed by local duplications of these serpins in tetrapod genomes. Interestingly, the ancestral HCII/SERPIND1 locus (nested within PIK4CA) possesses group V4 serpin (A2APL1, homolog of α 2-AP/SERPINF2) of lampreys; hence, pointing to the fact that group V4 might have originated from group V2. Additionally in this study, details of the phylogenetic history and genomic characteristics of vertebrate serpins are revisited.

Microvascular thrombosis, fibrinolysis, ischemic injury, and death after cerebral thromboembolism are affected by levels of circulating α2-antiplasmin

OBJECTIVE

Ischemic stroke is primarily attributable to thrombotic vascular occlusion. Elevated α2-antiplasmin (a2AP) levels correlate with increased stroke risk, but whether a2AP contributes to the pathogenesis of stroke is unknown. We examined how a2AP affects thrombosis, ischemic brain injury, and survival after experimental cerebral thromboembolism.

APPROACH AND RESULTS

We evaluated the effects of a2AP on stroke outcomes in mice with increased, normal, or no circulating a2AP, as well as in mice given an a2AP-inactivating antibody. Higher a2AP levels were correlated with greater ischemic brain injury (rs=0.88, P<0.001), brain swelling (rs=0.82, P<0.001), and reduced middle cerebral artery thrombus dissolution (rs=-0.93, P<0.001). In contrast, a2AP deficiency enhanced thrombus dissolution, increased cerebral blood flow, reduced brain infarction, and decreased brain swelling. By comparison to tissue plasminogen activator (TPA), a2AP inactivation hours after thromboembolism still reduced brain infarction (P<0.001) and hemorrhage (P<0.05). Microvascular thrombosis, a process that enhances brain ischemia, was markedly reduced in a2AP-deficient or a2AP-inactivated mice compared with TPA-treated mice or mice with increased a2AP levels (all P<0.001). Matrix metalloproteinase-9 expression, which contributes to acute brain injury, was profoundly decreased in a2AP-deficient or a2AP-inactivated mice versus TPA-treated mice or mice with increased a2AP levels (all P<0.001). a2AP inactivation markedly reduced stroke mortality versus TPA (P<0.0001).

CONCLUSIONS

a2AP has profound, dose-related effects on ischemic brain injury, swelling, hemorrhage, and survival after cerebral thromboembolism. By comparison to TPA, the protective effects of a2AP deficiency or inactivation seem to be mediated through reductions in microvascular thrombosis and matrix metalloproteinase-9 expression.

Structural and functional characterization of cleavage and inactivation of human serine protease inhibitors by the bacterial SPATE protease EspPα from enterohemorrhagic E. coli

EspPα and EspI are serine protease autotransporters found in enterohemorrhagic Escherichia coli. They both belong to the SPATE autotransporter family and are believed to contribute to pathogenicity via proteolytic cleavage and inactivation of different key host proteins during infection. Here, we describe the specific cleavage and functional inactivation of serine protease inhibitors (serpins) by EspPα and compare this activity with the related SPATE EspI. Serpins are structurally related proteins that regulate vital protease cascades, such as blood coagulation and inflammatory host response. For the rapid determination of serpin cleavage sites, we applied direct MALDI-TOF-MS or ESI-FTMS analysis of coincubations of serpins and SPATE proteases and confirmed observed cleavage positions using in-gel-digest of SDS-PAGE-separated degradation products. Activities of both serpin and SPATE protease were assessed in a newly developed photometrical assay using chromogenic peptide substrates. EspPα cleaved the serpins α1-protease inhibitor (α1-PI), α1-antichymotrypsin, angiotensinogen, and α2-antiplasmin. Serpin cleavage led to loss of inhibitory function as demonstrated for α1-PI while EspPα activity was not affected. Notably, EspPα showed pronounced specificity and cleaved procoagulatory serpins such as α2-antiplasmin while the anticoagulatory antithrombin III was not affected. Together with recently published research, this underlines the interference of EspPα with hemostasis or inflammatory responses during infection, while the observed interaction of EspI with serpins is likely to be not physiologically relevant. EspPα-mediated serpin cleavage occurred always in flexible loops, indicating that this structural motif might be required for substrate recognition.

Plasmin-dependent modulation of the blood-brain barrier: a major consideration during tPA-induced thrombolysis?

Plasmin, the principal downstream product of tissue-type plasminogen activator (tPA), is known for its potent fibrin-degrading capacity but is also recognized for many non-fibrinolytic activities. Curiously, plasmin has not been conclusively linked to blood-brain barrier (BBB) disruption during recombinant tPA (rtPA)-induced thrombolysis in ischemic stroke. This is surprising given the substantial involvement of tPA in the modulation of BBB permeability and the co-existence of tPA and plasminogen in both blood and brain throughout the ischemic event. Here, we review the work that argues a role for plasmin together with endogenous tPA or rtPA in BBB alteration, presenting the overall controversy around the topic yet creating a rational case for an involvement of plasmin in this process.

Novel or expanding current targets in fibrinolysis

Globally the leading cause of long-term disability and mortality stems from cardiovascular diseases, which creates an enormous economic burden. Currently available treatments for intravascular thrombosis consist of a large repertoire of antithrombotic agents targeting coagulation and platelet function. However, the only agents available to enhance fibrinolysis are recombinant or modified forms of plasminogen activators. Their clinical use is limited by low efficacy, life-threatening side-effects (primarily caused by the high systemic dose required) and the inapplicability for prophylactic use. This review provides an update on the latest advances in targeting the antifibrinolytic proteins, plasminogen activator inhibitor-1 and thrombin-activatable fibrinolysis inhibitor, and will highlight novel therapeutic avenues to enhance fibrinolysis.

Characterization of a Kunitz-type protease inhibitor peptide (Rusvikunin) purified from Daboia russelii russelii venom

The snake venom may be considered as a potent source of untapped therapeutic proteins and peptides. The peptide mass fingerprinting and N-terminal sequence alignment of a 6.9kDa peptide named Rusvikunin from Daboia russelii russelii venom show the presence of putative conserved domains of the KU superfamily. Further, BLAST analysis of two of the de novo peptide sequences of Rusvikunin demonstrates significant sequence homology with serine proteases reported in the NCBI database. Rusvikunin possesses conserved cysteine residues and Arg15 at the P1 position. It inhibits amidolytic activity of trypsin (IC50=50nmol/l), plasmin (IC50=1.1μmol/l), and fibrinogen clotting as well as plasma clotting activity of thrombin (IC50=1.3μmol/l); however, it does not inhibit the amidolytic activity of chymotrypsin, thrombin, factor Xa, and tissue plasminogen activator. Rusvikunin is a glycoprotein, demonstrates dose-dependent BAEE-esterase activity. It does not show lethality in mice or in vitro cytotoxicity against mammalian cells but shows in vivo anticoagulant activity 6h after i.p. injection in the mouse model. The commercial polyvalent and monovalent antivenom failed to inhibit the functional properties of Rusvikunin. The possible biomedical applications of Rusvikunin in the treatment and/or prevention of cardiovascular disorders such as thrombosis and trypsin-induced inflammation are suggested.

[Advances on mechanisms of coagulation with non-small cell lung cancer]

Recently, researchers have been increasingly finding coagulation disorders are commonly the first sign of malignancy. It has now been established that cancer development leads to an increased risk of thrombosis, and conversely, excessive activation of blood coagulation profoundly influences cancer progression. In patients with lung cancer, a sustained stimulation of blood coagulation takes place. Cancer cells trigger coagulation through expression of tissue factor, and affect coagulation through expression of thrombin, release of microparticles that augment coagulation and so on. Coagulation also facilitates tumour progression through release of platelet granule contents, inhibition of natural killer cells and recruitment of macrophages. Non-small cell lung cancer (NSCLC) accounts for about 80%-85% of all lung malignancies. In the present review, we summarized the newly updated data about the physiopathological mechanisms of various components of the clotting system in different stages of carcinogenesis in NSCLC.

Endogenous α2-antiplasmin is protective during severe gram-negative sepsis (melioidosis)

RATIONALE

α2-Antiplasmin (A2AP) is a major inhibitor of fibrinolysis by virtue of its capacity to inhibit plasmin. Although the fibrinolytic system is strongly affected by infection, the functional role of A2AP in the host response to sepsis is unknown.

OBJECTIVES

To study the role of A2AP in melioidosis, a common form of community-acquired sepsis in Southeast Asia and Northern Australia caused by the gram-negative bacterium Burkholderia pseudomallei.

METHODS

In a single-center observational study A2AP was measured in patients with culture-proven septic melioidosis. Wild-type and A2AP-deficient (A2AP(-/-)) mice were intranasally infected with B. pseudomallei to induce severe pneumosepsis (melioidosis). Parameters of inflammation and coagulation were measured, and survival studies were performed.

MEASUREMENTS AND MAIN RESULTS

Patients with melioidosis showed elevated A2AP plasma levels. Likewise, A2AP levels in plasma and lung homogenates were elevated in mice infected with B. pseudomallei. A2AP-deficient (A2AP(-/-)) mice had a strongly disturbed host response during experimental melioidosis as reflected by enhanced bacterial growth at the primary site of infection accompanied by increased dissemination to distant organs. In addition, A2AP(-/-) mice showed more severe lung pathology and injury together with an increased accumulation of neutrophils and higher cytokine levels in lung tissue. A2AP deficiency further was associated with exaggerated systemic inflammation and coagulation, increased distant organ injury, and enhanced lethality.

CONCLUSIONS

This study is the first to identify A2AP as a protective mediator during gram-negative (pneumo)sepsis by limiting bacterial growth, inflammation, tissue injury, and coagulation.

Differential gene expression of serine protease inhibitors in bovine ovarian follicle: possible involvement in follicular growth and atresia

BACKGROUND

SERPINs (serine protease inhibitors) regulate proteases involving fibrinolysis, coagulation, inflammation, cell mobility, cellular differentiation and apoptosis. This study aimed to investigate differentially expressed genes of members of the SERPIN superfamily between healthy and atretic follicles using a combination of microarray and quantitative real-time PCR (QPCR) analysis. In addition, we further determined mRNA and protein localization of identified SERPINs in estradiol (E2)-active and E2-inactive follicles by in situ hybridization and immunohistochemistry.

METHODS

We performed microarray analysis of healthy (10.7 +/- 0.7 mm) and atretic (7.8 +/- 0.2 mm) follicles using a custom-made bovine oligonucleotide microarray to screen differentially expressed genes encoding SERPIN superfamily members between groups. The expression profiles of six identified SERPIN genes were further confirmed by QPCR analysis. In addition, mRNA and protein localization of four SERPINs was investigated in E2-active and E2-inactive follicles using in situ hybridization and immunohistochemistry.

RESULTS

We have identified 11 SERPIN genes expressed in healthy and atretic follicles by microarray analysis. QPCR analysis confirmed that mRNA expression of four SERPINs (SERPINA5, SERPINB6, SERPINE2 and SERPINF2) was greater in healthy than in atretic follicles, while two SERPINs (SERPINE1 and SERPING1) had greater expression in atretic than in healthy follicles. In situ hybridization showed that SERPINA5, SERPINB6 and SERPINF2 mRNA were localized in GCs of E2-active follicles and weakly expressed in GCs of E2-inactive follicles. SERPING1 mRNA was localized in both GCs and the theca layer (TL) of E2-inactive follicles and a weak hybridization signal was also detected in both GCs and TL of E2-active follicles. Immunohistochemistry showed that SERPINA5, SERPINB6 and SERPINF2 were detected in GCs of E2-active and E2-inactive follicles. SERPING1 protein was localized in both GCs and the TL of E2-active and E2-inactive follicles.

CONCLUSIONS

Our results demonstrate a characteristic expression of SERPIN superfamily member genes in bovine healthy and atretic follicles. The cell-type-and stage-specific expression of SERPINs may be associated with bovine follicular growth and atresia.

Contribution of conserved lysine residues in the alpha2-antiplasmin C terminus to plasmin binding and inhibition

α(2)-Antiplasmin is the physiological inhibitor of plasmin and is unique in the serpin family due to N- and C-terminal extensions beyond its core domain. The C-terminal extension comprises 55 amino acids from Asn-410 to Lys-464, and the lysine residues (Lys-418, Lys-427, Lys-434, Lys-441, Lys-448, and Lys-464) within this region are important in mediating the initial interaction with kringle domains of plasmin. To understand the role of lysine residues within the C terminus of α(2)-antiplasmin, we systematically and sequentially mutated the C-terminal lysines, studied the effects on the rate of plasmin inhibition, and measured the binding affinity for plasmin via surface plasmon resonance. We determined that the C-terminal lysine (Lys-464) is individually most important in initiating binding to plasmin. Using two independent methods, we also showed that the conserved internal lysine residues play a major role mediating binding of the C terminus of α(2)-antiplasmin to kringle domains of plasmin and in accelerating the rate of interaction between α(2)-antiplasmin and plasmin. When the C terminus of α(2)-antiplasmin was removed, the binding affinity for active site-blocked plasmin remained high, suggesting additional exosite interactions between the serpin core and plasmin.

Enhancement of fibrinolysis by inhibiting enzymatic cleavage of precursor α2-antiplasmin

BACKGROUND AND OBJECTIVE

Resistance of thrombi to plasmin digestion depends primarily on the amount of α(2)-antiplasmin (α(2)AP) incorporated within fibrin. Circulating prolyl-specific serine proteinase, antiplasmin-cleaving enzyme (APCE), a homologue of fibroblast activation protein (FAP), cleaves precursor Met-α(2)AP between -Pro12-Asn13- to yield Asn-α(2)AP, which is crosslinked to fibrin approximately 13× more rapidly than Met-α(2)AP and confers resistance to plasmin. We reasoned that an APCE inhibitor might decrease conversion of Met-α(2)AP to Asn-α(2)AP and thereby enhance endogenous fibrinolysis.

METHODS AND RESULTS

We designed and synthesized several APCE inhibitors and assessed each vs. plasma dipeptidyl peptidase IV (DPPIV) and prolyl oligopeptidase (POP), which have amino acid sequence similarity with APCE. Acetyl-Arg-(8-amino-3,6-dioxaoctanoic acid)-D-Ala-L-boroPro selectively inhibited APCE vs. DPPIV, with an apparent K(i) of 5.7 nm vs. 6.1 μm, indicating that an approximately 1000-fold greater inhibitor concentration is required for DPPIV than for APCE. An apparent K(i) of 7.4 nm was found for POP inhibition, which is similar to 5.7 nm for APCE; however, the potential problem of overlapping FAP/APCE and POP inhibition was negated by our finding that normal human plasma lacks POP activity. The inhibitor construct caused a dose-dependent decrease of APCE-mediated Met-α(2)AP cleavage, which ultimately shortened plasminogen activator-induced plasma clot lysis times. Incubation of the inhibitor with human plasma for 22 h did not lessen its APCE inhibitory activity, with its IC(50) value in plasma remaining comparable to that in phosphate buffer.

CONCLUSION

These data establish that inhibition of APCE might represent a therapeutic approach for enhancing thrombolytic activity.

The plasmin-antiplasmin system: structural and functional aspects

The plasmin-antiplasmin system plays a key role in blood coagulation and fibrinolysis. Plasmin and α(2)-antiplasmin are primarily responsible for a controlled and regulated dissolution of the fibrin polymers into soluble fragments. However, besides plasmin(ogen) and α(2)-antiplasmin the system contains a series of specific activators and inhibitors. The main physiological activators of plasminogen are tissue-type plasminogen activator, which is mainly involved in the dissolution of the fibrin polymers by plasmin, and urokinase-type plasminogen activator, which is primarily responsible for the generation of plasmin activity in the intercellular space. Both activators are multidomain serine proteases. Besides the main physiological inhibitor α(2)-antiplasmin, the plasmin-antiplasmin system is also regulated by the general protease inhibitor α(2)-macroglobulin, a member of the protease inhibitor I39 family. The activity of the plasminogen activators is primarily regulated by the plasminogen activator inhibitors 1 and 2, members of the serine protease inhibitor superfamily.

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

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

Alpha2-Antiplasmin Is a Critical Regulator of Angiotensin II–Mediated Vascular Remodeling

Objective— Alpha2-antiplasmin (α2-AP) is the major circulating inhibitor of plasmin, which plays a determining role in the regulation of intravascular fibrinolysis. We investigated the role of α 2 -AP on vascular remodeling in response to angiotensin II (Ang II).

Methods and Results— α2-AP–deficient mice were performed. Ang II and N ω -nitro- L-arginine methyl ester (L-NAME)–induced perivascular fibrosis was significantly decreased in α2-AP −/− mice compared with wild-type mice. In situ gelatinolytic activity analysis shows that perivascular gelatinolytic activity was increased in α2-AP −/− mice, which was responsible for decreased perivascular fibrosis in response to Ang II and L-NAME. Ang II–induced arterial wall thickening, vascular cell proliferation, apoptosis, c-Myc, and collagen Ι expression were significantly decreased in α2-AP −/− mice compared with wild-type mice. Further analysis shows that increased p53 and p21 expression were responsible for inhibition of Ang II–induced vascular remodeling in α2-AP −/− mice.

Conclusion— The results show that α2-AP is a critical regulator for vascular remodeling by inhibiting p53/p21 pathway, suggesting that α2-AP is proposed to be a potential therapeutic target for vascular remodeling.

Plasminogen-dependent internalization of soluble melanotransferrin involves the low-density lipoprotein receptor-related protein and annexin II

We investigated the effect of plasminogen (Plg) on the internalization of recombinant soluble melanotransferrin (sMTf) using U87 human glioblastoma cells and murine embryonic fibroblasts (MEF) deficient in the low-density lipoprotein receptor-related protein (LRP). Using biospecific interaction analysis, both Glu- and Lys-Plg were shown to interact with immobilized sMTf. The binding of sMTf at the cell surface increased in the presence of both forms of Plg in control and in LRP-deficient MEF cells, whereas the uptake was strongly stimulated only by Lys-Plg in control MEF and U87 cells. In addition, in the presence of Lys-Plg, the internalization of sMTf was a saturable process, sensitive to temperature and dependent on the integrity of lysine residues. The addition of the receptor-associated protein, lactoferrin and aprotinin, as well as a monoclonal antibody (mAb) directed against LRP, inhibited the Lys-Plg-dependent uptake of sMTf. These results suggest an important role for LRP in this process. In addition, using binding and uptake assays in the presence of anti-annexin II mAb, we showed that annexin II might be responsible for the initial binding of sMTf in the presence of Plg. Our results suggest a Plg-mediated internalization mechanism for the clearance of sMTf via annexin II and LRP.

Serpins in thrombosis, hemostasis and fibrinolysis

Hemostasis and fibrinolysis, the biological processes that maintain proper blood flow, are the consequence of a complex series of cascading enzymatic reactions. Serine proteases involved in these processes are regulated by feedback loops, local cofactor molecules, and serine protease inhibitors (serpins). The delicate balance between proteolytic and inhibitory reactions in hemostasis and fibrinolysis, described by the coagulation, protein C and fibrinolytic pathways, can be disrupted, resulting in the pathological conditions of thrombosis or abnormal bleeding. Medicine capitalizes on the importance of serpins, using therapeutics to manipulate the serpin-protease reactions for the treatment and prevention of thrombosis and hemorrhage. Therefore, investigation of serpins, their cofactors, and their structure-function relationships is imperative for the development of state-of-the-art pharmaceuticals for the selective fine-tuning of hemostasis and fibrinolysis. This review describes key serpins important in the regulation of these pathways: antithrombin, heparin cofactor II, protein Z-dependent protease inhibitor, alpha(1)-protease inhibitor, protein C inhibitor, alpha(2)-antiplasmin and plasminogen activator inhibitor-1. We focus on the biological function, the important structural elements, their known non-hemostatic roles, the pathologies related to deficiencies or dysfunction, and the therapeutic roles of specific serpins.

Genomic abnormalities of the murine model of Fabry disease after disease-related perturbation, a systems biology approach

Fabry disease is a disorder of alpha-D-galactosyl-containing glycolipids resulting from a deficiency of alpha-galactosidase A. Patients have a poorly understood vascular dysregulation. We hypothesized that disease-related perturbation by using enzyme replacement therapy in the murine model of Fabry disease would provide insight into abnormal biological processes in Fabry disease. Gene expression analyses of the heart, aorta, and liver of male alpha-galactosidase A knockout mice 28 weeks of age were compared with that of WT mice. Microarray analyses were performed before and after six weekly injections of alpha-galactosidase A. Alteration of Rpgrip1 ranked highest statistically in all three organs when knockout mice were compared with WT, and its splice variants responded in a unique way to alpha-galactosidase A. Enzyme replacement therapy tended to not only normalize gene expression, e.g., reduce the overexpression of securin, but also specifically modified gene expression in each tissue examined. Following multiple comparison analysis, gene expression correlation graphs were constructed, and a priori hypotheses were examined by using structural equation modeling. This systems biology approach demonstrated multiple and complex parallel cellular abnormalities in Fabry disease. These abnormalities form the basis for informed, in a Bayesian sense, sequential, hypothesis-driven research that can be subsequently tested experimentally.

Proteomics of specific treatment-related alterations in Fabry disease: a strategy to identify biological abnormalities

Fabry disease is inherited as an X-linked disorder secondary to deficiency of alpha-galactosidase A, resulting in abnormal metabolism of substances containing alpha-d-galactosyl moieties. As a consequence, a multisystem disorder develops, culminating in strokes, progressive renal, and cardiac dysfunction. Signs and symptoms of Fabry disease become manifest in childhood, but diagnosis is often delayed. Thirteen children with Fabry disease (age range, 6.5-17 years) were studied as part of a 6-month open-label study of enzyme replacement therapy (ERT) with agalsidase alfa. Paired serum samples were drawn at the start of the study and after 6 months of ERT. Global protein changes in paired samples were compared by using differential stable isotope labeling of peptide lysine residues with O-methylisourea and subsequent nanoHPLC-tandem MS. Statistically significant decreases were observed for five proteins following ERT: alpha(2)-HS glycoprotein, vitamin D-binding protein, transferrin, Ig-alpha-2 C chain, and alpha-2-antiplasmin. The presence of low levels of alpha-2-antiplasmin and plasminogen was confirmed by alternate means in 34 consecutive patients, including four of five ERT-naïve subjects. Decreased alpha-2-antiplasmin was associated with a parallel increase in circulating VEGF. Soluble VEGF receptor-2 was significantly elevated in plasma of patients compared with pediatric controls and decreased with ERT. These results suggest previously unknown abnormalities of fibrinolysis and angiogenesis factors in Fabry disease. We demonstrated the feasibility of identifying treatment-specific alterations in a small number of subjects that point to previously unsuspected disease-related biological abnormalities.