Thrombin physiology and pathophysiology

Probing naphthalene diimide and 3-hydroxypropylphosphate as end-conjugating moieties for improved thrombin binding aptamers: Structural and biological effects

The limitations associated with the in vivo use of the thrombin binding aptamer (TBA or TBA15) have dramatically stimulated the search of suitable chemically modified analogues in order to discover effective and reversible inhibitors of thrombin activity. In this context, we previously proposed cyclic and pseudo-cyclic TBA analogues with improved stability that proved to be more active than the parent aptamer. Herein, we have investigated a novel library of TBA derivatives carrying naphthalene diimide (NDI) moieties at the 3'- or 5'-end. In a subset of the investigated oligonucleotides, additional 3-hydroxypropylphosphate (HPP) groups were introduced at one or both ends of the TBA sequence. Evaluation of the G-quadruplex thermal stability, serum nuclease resistance and in vitro anticoagulant activity of the new TBA analogues allowed rationalizing the effect of these appendages on the activity of the aptamer on the basis of their relative position. Notably, most of the different TBA analogues tested were more potent thrombin inhibitors than unmodified TBA. Particularly, the analogue carrying an NDI group at the 5'-end and an HPP group at the 3'-end, named N-TBA-p, exhibited enhanced G-quadruplex thermal stability (ΔTm + 14° C) and ca. 10-fold improved nuclease resistance in serum compared to the native aptamer. N-TBA-p also induced prolonged and dose-dependent clotting times, showing a ca. 11-fold higher anticoagulant activity compared to unmodified TBA, as determined by spectroscopic methods. Overall, N-TBA-p proved to be in vitro a more efficient thrombin inhibitor than all the best ones previously investigated in our group. Its interesting features, associated with its easy preparation, make it a very promising candidate for future in vivo studies.

Complement and coagulation crosstalk - Factor H in the spotlight

The immune complement and the coagulation systems are blood-based proteolytic cascades that are activated by pathway-specific triggers, based on protein-protein interactions and enzymatic cleavage reactions. Activation of these systems is finely balanced and controlled through specific regulatory mechanisms. The complement and coagulation systems are generally viewed as distinct, but have common evolutionary origins, and several interactions between these homologous systems have been reported. This complement and coagulation crosstalk can affect activation, amplification and regulatory functions in both systems. In this review, we summarize the literature on coagulation factors contributing to complement alternative pathway activation and regulation and highlight molecular interactions of the complement alternative pathway regulator factor H with several coagulation factors. We propose a mechanism where factor H interactions with coagulation factors may contribute to both complement and coagulation activation and regulation within the haemostatic system and fibrin clot microenvironment and introduce the emerging role of factor H as a modulator of coagulation. Finally, we discuss the potential impact of these protein interactions in diseases associated with factor H dysregulation or deficiency as well as evidence of coagulation dysfunction.

Influence of a Physiologically Formed Blood Clot on Pre-Osteoblastic Cells Grown on a BMP-7-Coated Nanoporous Titanium Surface

Titanium (Ti) nanotopography modulates the osteogenic response to exogenous bone morphogenetic protein 7 (BMP-7) in vitro, supporting enhanced alkaline phosphatase mRNA expression and activity, as well as higher osteopontin (OPN) mRNA and protein levels. As the biological effects of OPN protein are modulated by its proteolytic cleavage by serum proteases, this in vitro study evaluated the effects on osteogenic cells in the presence of a physiological blood clot previously formed on a BMP-7-coated nanostructured Ti surface obtained by chemical etching (Nano-Ti). Pre-osteoblastic MC3T3-E1 cells were cultured during 5 days on recombinant mouse (rm) BMP-7-coated Nano-Ti after it was implanted in adult female C57BI/6 mouse dorsal dermal tissue for 18 h. Nano-Ti without blood clot or with blood clot at time 0 were used as the controls. The presence of blood clots tended to inhibit the expression of key osteoblast markers, except for Opn, and rmBMP-7 functionalization resulted in a tendency towards relatively greater osteoblastic differentiation, which was corroborated by runt-related transcription factor 2 (RUNX2) amounts. Undetectable levels of OPN and phosphorylated suppressor of mothers against decapentaplegic (SMAD) 1/5/9 were noted in these groups, and the cleaved form of OPN was only detected in the blood clot immediately prior to cell plating. In conclusion, the strategy to mimic in vitro the initial interfacial in vivo events by forming a blood clot on a Ti nanoporous surface resulted in the inhibition of pre-osteoblastic differentiation, which was minimally reverted with an rmBMP-7 coating.

Purification and characterization of thrombin from camel plasma: interaction with camel tick salivary gland thrombin inhibitor

BACKGROUND

Thrombin is the most important enzyme in the hemostatic process by permitting rapid and localized coagulation in case of tissue damage. Camel thrombin is the natural and proper target enzyme for the previously purified camel tick salivary gland thrombin inhibitor.

RESULTS

In this study, the camel thrombin was purified homogenously in a single affinity chromatographic step on the heparin-agarose affinity column with a specific activity of 3242 NIH units/mg proteins. On SDS-PAGE, the purified camel thrombin contained two forms, 37 kDa α-thrombin and 28 kDa β-thrombin, and the camel prothrombin was visualized as 72 kDa. The camel thrombin Km value was found out as 60 µM of N-(p-Tosyl)-Gly-Pro-Arg-p-nitroanilide acetate and displayed its optimum activity at pH 8.3. The PMSF was the most potent inhibitor of camel thrombin. Camel tick salivary gland thrombin inhibitor has two binding sites on camel thrombin and inhibited it competitively with Ki value of 0.45 µM.

CONCLUSIONS

The purified camel thrombin was found to be more susceptible toward the camel tick salivary gland thrombin inhibitor than bovine thrombin.

Application of InterCriteria Analysis to Assess the Performance of Scoring Functions in Molecular Docking Software Packages

(1) Background: In silico approaches to rational drug design are among the fastest evolving ones. Depending on the available structural information for the biomacromolecule and the small molecule, the in silico methods are classified as ligand- and structure-based. The latter predict ligand–receptor binding using 3D structures of both molecules, whose computational simulation is referred to as molecular docking. It aims at estimating the binding affinity (approximated by scoring function) and the ligand binding pose in the receptor’s active site, which postulates a key role of the scoring functions in molecular docking algorithms. This study focuses on the performance of different types of scoring functions implemented in molecular modelling software packages. (2) Methods: An InterCriteria analysis (ICrA) was applied to assess the performance of the scoring functions available in MOE, GOLD, SeeSAR, and AutoDock Vina software platforms. The InterCriteria analysis was developed to distinguish possible relations between pairs of criteria when multiple objects are considered. All 12 investigated scoring functions were tested by docking a set of protease inhibitors in the binding sites of two protein targets. The dataset consisted of 88 benzamidine-type compounds with experimentally measured inhibitory constants for thrombin and trypsin, which allows for the objective assessment of the scoring functions performance. The results generated by the molecular docking were subjected to ICrA in order to analyze both docking energies as approximations of the binding affinities and RMSDs (root-mean-square deviation) as measures of the experimental binding pose proximity between the compounds and the co-crystalized ligand, based on the atoms in the common scaffold. (3) Results: The results obtained for the best poses, the average of the best 5 or 30 poses retained after docking, were analyzed. A comparison with the experimentally observed inhibitory effects was also performed. The InterCriteria analysis application confirms that the performance of the scoring functions for the same dataset of ligands depends on the studied protein. The analysis reveals that none of the studied scoring functions is a good predictor of the compounds’ binding affinities for the considered protein targets. (4) Conclusion: In terms of this analysis, the investigated scoring functions do not produce equivalent results, which suggests the necessity for their combined use in consensus docking studies.

PI3K Isoform Signalling in Platelets

Platelets are unique anucleated blood cells that constantly patrol the vasculature to seal and prevent injuries in a process termed haemostasis. Thereby they rapidly adhere to the subendothelial matrix and recruit further platelets, resulting in platelet aggregates. Apart from their central role in haemostasis, they also kept some of their features inherited by their evolutionary ancestor-the haemocyte, which was also involved in immune defences. Together with leukocytes, platelets fight pathogenic invaders and guide many immune processes. In addition, they rely on several signalling pathways which are also relevant to immune cells. Among these, one of the central signalling hubs is the PI3K pathway. Signalling processes in platelets are unique as they lack a nucleus and therefore transcriptional regulation is absent. As a result, PI3K subclasses fulfil distinct roles in platelets compared to other cells. In contrast to leukocytes, the central PI3K subclass in platelet signalling is PI3K class Iβ, which underlines the uniqueness of this cell type and opens new ways for potential platelet-specific pharmacologic inhibition. An overview of platelet function and signalling with emphasis on PI3K subclasses and their respective inhibitors is given in this chapter.

Differential Internalization of Thrombin-Derived Host Defense Peptides into Monocytes and Macrophages

Proteolytic cleavage of thrombin generates C-terminal host defense peptides exerting multiple immunomodulatory effects in response to bacterial stimuli. Previously, we reported that thrombin-derived C-terminal peptides (TCPs) are internalized in monocytes and macrophages in a time- and temperature-dependent manner. In this study, we investigated which endocytosis pathways are responsible for the internalization of TCPs. Using confocal microscopy and flow cytometry, we show that both clathrin-dependent and clathrin-independent pathways are involved in the internalization of the prototypic TCP GKY25 in RAW264.7 and human monocyte-derived M1 macrophages, whereas the uptake of GKY25 in monocytic THP-1 cells is mainly dynamin-dependent. Internalized GKY25 was transported to endosomes and finally lysosomes, where it remained detectable for up to 10 h. Comparison of GKY25 uptake with that of the natural occurring TCPs HVF18 and FYT21 indicates that the pathway of TCP endocytosis is not only cell type-dependent but also depends on the length and composition of the peptide as well as the presence of LPS and bacteria. Finally, using neutron reflectometry, we show that the observed differences between HVF18 and the other 2 TCPs may be explained partially by differences in membrane insertion. Taken together, we show that TCPs are differentially internalized into monocytes and macrophages.

Charge-Transfer Interactions Stabilize G-Quadruplex-Forming Thrombin Binding Aptamers and Can Improve Their Anticoagulant Activity

In the search for optimized thrombin binding aptamers (TBAs), we herein describe the synthesis of a library of TBA analogues obtained by end-functionalization with the electron-rich 1,5-dialkoxy naphthalene (DAN) and the electron-deficient 1,8,4,5-naphthalenetetra-carboxylic diimide (NDI) moieties. Indeed, when these G-rich oligonucleotides were folded into the peculiar TBA G-quadruplex (G4) structure, effective donor-acceptor charge transfer interactions between the DAN and NDI residues attached to the extremities of the sequence were induced, providing pseudo-cyclic structures. Alternatively, insertion of NDI groups at both extremities produced TBA analogues stabilized by π-π stacking interactions. All the doubly-modified TBAs were characterized by different biophysical techniques and compared with the analogues carrying only the DAN or NDI residue and unmodified TBA. These modified TBAs exhibited higher nuclease resistance, and their G4 structures were markedly stabilized, as evidenced by increased Tm values compared to TBA. These favorable properties were also associated with improved anticoagulant activity for one DAN/NDI-modified TBA, and for one NDI/NDI-modified TBA. Our results indicated that TBA pseudo-cyclic structuring by ad hoc designed end-functionalization represents an efficient approach to improve the aptamer features, while pre-organizing and stabilizing the G4 structure but allowing sufficient flexibility to the aptamer folding, which is necessary for optimal thrombin recognition.

Dimeric and Multimeric DNA Aptamers for Highly Effective Protein Recognition

Multivalent interactions frequently occur in biological systems and typically provide higher binding affinity and selectivity in target recognition than when only monovalent interactions are operative. Thus, taking inspiration by nature, bivalent or multivalent nucleic acid aptamers recognizing a specific biological target have been extensively studied in the last decades. Indeed, oligonucleotide-based aptamers are suitable building blocks for the development of highly efficient multivalent systems since they can be easily modified and assembled exploiting proper connecting linkers of different nature. Thus, substantial research efforts have been put in the construction of dimeric/multimeric versions of effective aptamers with various degrees of success in target binding affinity or therapeutic activity enhancement. The present review summarizes recent advances in the design and development of dimeric and multimeric DNA-based aptamers, including those forming G-quadruplex (G4) structures, recognizing different key proteins in relevant pathological processes. Most of the designed constructs have shown improved performance in terms of binding affinity or therapeutic activity as anti-inflammatory, antiviral, anticoagulant, and anticancer agents and their number is certainly bound to grow in the next future.

Influence of dabigatran on pro-inflammatory cytokines, growth factors and chemokines - Slowing the vicious circle of coagulation and inflammation

AIMS

Blood coagulation is one of the most important host-defending mechanisms in vivo by maintaining the blood pressure after injury. However, besides maintaining homeostasis, blood coagulation and the contributing factors are directly linked to pathological conditions, such as thromboembolism and inflammation, leading to cardiovascular diseases, among others. As anti-inflammatory drugs may reduce cardiovascular events, we hypothesized in this study that the direct thrombin inhibitor dabigatran may reduce cytokine, growth factor and chemokine expression in vitro.

MAIN METHODS

Initially, human whole blood was incubated in tubes for serum, EDTA plasma, and heparinized plasma. Furthermore, human PBMCs were isolated and incubated under different culture conditions, including the treatment with human serum or thrombin, respectively. The effect of the oral anticoagulant dabigatran on pro-inflammatory cytokines, growth factors and chemokines was investigated by ELISA.

KEY FINDINGS

Conditioned serum resulted in a significant alteration of the secretome's protein levels after 24 h. However, solely ANG showed a dose-dependent increment by the addition of serum (79.8 ± 9.2 ng/mL) in comparison to baseline (0.2 ± 0.2 ng/mL), as it was in trend for thrombin treatment. Furthermore, the pre-treatment of PBMCs with different doses of dabigatran significantly lowered supernatant protein levels measured. Moreover, dabigatran was shown to decrease most notably the growth factor and chemokine levels in the PBMC's secretome that were treated with 200 ng/mL thrombin in a dose-dependent manner.

SIGNIFICANCE

In conclusion, novel oral anticoagulants, such as dabigatran, could help to reduce not only procoagulatory effects in inflammatory conditions but could also reduce proinflammatory stimuli via reduced expression of cytokines and chemokines.

G-quadruplex-based aptamers targeting human thrombin: Discovery, chemical modifications and antithrombotic effects

First studies on thrombin-inhibiting DNA aptamers were reported in 1992, and since then a large number of anticoagulant aptamers has been discovered. TBA - also named HD1, a 15-mer G-quadruplex (G4)-forming oligonucleotide - is the best characterized thrombin binding aptamer, able to specifically recognize the protein exosite I, thus inhibiting the conversion of soluble fibrinogen into insoluble fibrin strands. Unmodified nucleic acid-based aptamers, in general, and TBA in particular, exhibit limited pharmacokinetic properties and are rapidly degraded in vivo by nucleases. In order to improve the biological performance of aptamers, a widely investigated strategy is the introduction of chemical modifications in their backbone at the level of the nucleobases, sugar moieties or phosphodiester linkages. Besides TBA, also other thrombin binding aptamers, able to adopt a well-defined G4 structure, e.g. mixed duplex/quadruplex sequences, as well as homo- and hetero-bivalent constructs, have been identified and optimized. Considering the growing need of new efficient anticoagulant agents associated with the strong therapeutic potential of these thrombin inhibitors, the research on thrombin binding aptamers is still a very hot and intriguing field. Herein, we comprehensively described the state-of-the-art knowledge on the DNA-based aptamers targeting thrombin, especially focusing on the optimized analogues obtained by chemically modifying the oligonucleotide backbone, and their biological performances in therapeutic applications.

Design, Synthesis and Characterization of Cyclic NU172 Analogues: A Biophysical and Biological Insight

NU172—a 26-mer oligonucleotide able to bind exosite I of human thrombin and inhibit its activity—was the first aptamer to reach Phase II clinical studies as an anticoagulant in heart disease treatments. With the aim of favoring its functional duplex-quadruplex conformation and thus improving its enzymatic stability, as well as its thrombin inhibitory activity, herein a focused set of cyclic NU172 analogues—obtained by connecting its 5′- and 3′-extremities with flexible linkers—was synthesized. Two different chemical approaches were exploited in the cyclization procedure, one based on the oxime ligation method and the other on Cu(I)-assisted azide-alkyne cycloaddition (CuAAC), affording NU172 analogues including circularizing linkers with different length and chemical nature. The resulting cyclic NU172 derivatives were characterized using several biophysical techniques (ultraviolet (UV) and circular dichroism (CD) spectroscopies, gel electrophoresis) and then investigated for their serum resistance and anticoagulant activity in vitro. All the cyclic NU172 analogues showed higher thermal stability and nuclease resistance compared to unmodified NU172. These favorable properties were, however, associated with reduced—even though still significant—anticoagulant activity, suggesting that the conformational constraints introduced upon cyclization were somehow detrimental for protein recognition. These results provide useful information for the design of improved analogues of NU172 and related duplex-quadruplex structures.

Stability Is Not Everything: The Case of the Cyclisation of a Thrombin-Binding Aptamer

With the aim of developing a new approach to obtain improved aptamers, a cyclic thrombin-binding aptamer (TBA) analogue (cycTBA) has been prepared by exploiting a copper(I)-assisted azide-alkyne cycloaddition. The markedly increased serum resistance and exceptional thermal stability of the G-quadruplex versus TBA were associated with halved thrombin inhibition, which suggested that some flexibility in the TBA structure was necessary for protein recognition.

Enoxaparin pretreatment effect on local and systemic inflammation biomarkers in the animal burn model

Low-molecular weight heparins (LMWH) are anticoagulants that have shown anti-inflammatory activity in several experimental models. Hot water burn inflammatory model accurately simulates human clinical situations allowing its use for nociception test and evaluation of anti-inflammatory drugs. The present study aims to evaluate the enoxaparin pretreatment on local and systemic inflammation biomarkers in the animal burn model. Inflammation was induced by submersing the rat left hind paw in water at 60^o C for 60 s. C-reactive protein (CRP) and thrombin-antithrombin complex (TAT) were estimated by immunosorbent assay, fibrinogen (Fg) by the gravimetric method and paw oedema by orthogonal digital photography. Highest values of paw oedema, CRP and TAT were observed at 4 h post-burn while Fg peak occurs at 12 h post-burn; enoxaparin pretreatment decreased oedema (- 32.1%), and concentration of TAT (- 66.7%), PCR (- 37.9%) and Fg (- 8%). This study shows that enoxaparin has local and systemic anti-inflammatory effects and should be considered as a potential adjuvant drug for the treatment of burns.

Activities of Thrombin and Factor Xa Are Essential for Replication of Hepatitis E Virus and Are Possibly Implicated in ORF1 Polyprotein Processing

Hepatitis E virus (HEV) is a clinically important positive-sense RNA virus. The ORF1 of HEV encodes a nonstructural polyprotein of 1,693 amino acids. It is not clear whether the ORF1 polyprotein (pORF1) is processed into distinct enzymatic domains. Many researchers have attempted to understand the mechanisms of pORF1 processing. However, these studies gave various results and could never convincingly establish the mechanism of pORF1 processing. In this study, we demonstrated the possible role of thrombin and factor Xa in pORF1 processing. We observed that the HEV pORF1 polyprotein bears conserved cleavage sites of thrombin and factor Xa. Using a reverse genetics approach, we demonstrated that an HEV replicon having mutations in the cleavage sites of either thrombin or factor Xa could not replicate efficiently in cell culture. Further, we demonstrated in vitro processing when we incubated recombinant pORF1 fragments with thrombin, and we observed the processing of pORF1 polyprotein. The treatment of a liver cell line with a serine protease inhibitor as well as small interfering RNA (siRNA) knockdown of thrombin and factor Xa resulted in significant reduction in the replication of HEV. Thrombin and factor Xa have been well studied for their roles in blood clotting. Both of these proteins are believed to be present in the active form in the blood plasma. Interestingly, in this report, we demonstrated the presence of biologically active thrombin and factor Xa in a liver cell line. The results suggest that factor Xa and thrombin are essential for the replication of HEV and may be involved in pORF1 polyprotein processing of HEV.IMPORTANCE Hepatitis E virus (HEV) causes a liver disorder called hepatitis in humans, which is mostly an acute and self-limiting infection in adults. A high mortality rate of about 30% is observed in HEV-infected pregnant women in developing countries. There is no convincing opinion about HEV ORF1 polyprotein processing owing to the variability of study results obtained so far. HEV pORF1 has cleavage sites for two host cellular serine proteases, thrombin and factor Xa, that are conserved among HEV genotypes. For the first time, this study demonstrated that thrombin and factor Xa cleavage sites on HEV pORF1 are obligatory for HEV replication. Intracellular biochemical activities of the said serine proteases are also essential for efficient HEV replication in cell culture and must be involved in pORF1 processing. This study sheds light on the presence and roles of clotting factors with respect to virus replication in the cells.

Fluorescence Sensing Using DNA Aptamers in Cancer Research and Clinical Diagnostics

Among the various advantages of aptamers over antibodies, remarkable is their ability to tolerate a large number of chemical modifications within their backbone or at the termini without losing significant activity. Indeed, aptamers can be easily equipped with a wide variety of reporter groups or coupled to different carriers, nanoparticles, or other biomolecules, thus producing valuable molecular recognition tools effective for diagnostic and therapeutic purposes. This review reports an updated overview on fluorescent DNA aptamers, designed to recognize significant cancer biomarkers both in soluble or membrane-bound form. In many examples, the aptamer secondary structure switches induced by target recognition are suitably translated in a detectable fluorescent signal using either fluorescently-labelled or label-free aptamers. The fluorescence emission changes, producing an enhancement (“signal-on”) or a quenching (“signal-off”) effect, directly reflect the extent of the binding, thereby allowing for quantitative determination of the target in bioanalytical assays. Furthermore, several aptamers conjugated to fluorescent probes proved to be effective for applications in tumour diagnosis and intraoperative surgery, producing tumour-type specific, non-invasive in vivo imaging tools for cancer pre- and post-treatment assessment.

Targeting factor Xa and thrombin: impact on coagulation and beyond

Great advances have been made in recent years in understanding the haemostatic system and the molecular and cellular basis of thrombus formation. Although directly targeting factor Xa or thrombin (factor IIa) for effective anticoagulation is now well established, evidence has emerged suggesting that factor Xa and thrombin are involved in other physiological and pathophysiological cellular processes, including inflammation. These non-haemostatic activities of factor Xa and thrombin are predominantly mediated via the activation of proteinaseactivated receptors. Studies have indicated a potential role of coagulation proteins (including factor Xa and thrombin) in the progression of disease conditions such as atherothrombosis. Preclinical studies have provided evidence for the effects of direct factor Xa or direct thrombin inhibition beyond anticoagulation, including anti-inflammatory activities and atherosclerotic plaque stabilisation. In this article, the non-haemostatic activities of factor Xa and thrombin and the effects of direct inhibition of these coagulation factors on these activities are summarised. In addition, the potential roles of factor Xa and thrombin in atherosclerosis and atherothrombosis are explored and the cardiovascular profiles of rivaroxaban, apixaban and dabigatran etexilate observed in phase III clinical studies are discussed.

Venous and arterial thrombosis – pathogenesis and the rationale for anticoagulation

Thromboembolic disorders are major causes of morbidity and mortality. It is well-recognised that the pathogenesis is different for arterial and venous thrombosis; however, both involve coagulation activation. Anticoagulants are used for the prevention and treatment of a wide variety of thromboembolic and related conditions. Agents with anti-inflammatory properties in addition to anticoagulation may be particularly beneficial. Traditional anticoagulants, although effective, are associated with certain limitations. Understanding the pathological processes associated with thrombosis and the rational target for anticoagulation is essential, not only for the development of safer and more effective agents, but also for better clinical management of patients who require anticoagulation therapy. In recent years, new oral agents that target single enzymes of the coagulation cascade have been developed – some of those are in advanced stages of clinical development. Based on scientific rationale, both factor Xa and thrombin are viable targets for effective anticoagulation.

Fluorescent Thrombin Binding Aptamer-Tagged Nanoparticles for an Efficient and Reversible Control of Thrombin Activity

Progress in understanding and treatment of thrombotic diseases requires new effective methods for the easy, rapid, and reversible control of coagulation processes. In this framework, the use of aptamers, and particularly of the thrombin binding aptamer (TBA), has aroused strong interest, due to its enormous therapeutic potential, associated with a large number of possible applications in biotechnological and bioanalytical fields. Here, we describe a new TBA analogue (named tris-mTBA), carrying three different pendant groups: a dansyl residue at the 3'- and a β-cyclodextrin moiety at the 5'-end-providing a host-guest system which exhibits a marked fluorescence enhancement upon TBA G-quadruplex folding-and a biotin tag, allowing the attachment of the aptamer onto biocompatible streptavidin-coated silica nanoparticles (NPs) of 50 nm hydrodynamic diameter (Sicastar). The use of nanoparticles for the in vivo delivery of TBA, expected to induce per se increased nuclease resistance and improved pharmacokinetic properties of this oligonucleotide, offers as an additional advantage the possibility to exploit multivalency effects, due to the presence of multiple copies of TBA on a single scaffold. In addition, the selected fluorescent system allows monitoring both the presence of TBA on the functionalized NPs and its correct folding upon immobilization, also conferring enhanced enzymatic resistance and bioactivity. The anticoagulant activity of the new tris-mTBA, free or conjugated to Sicastar NPs, was evaluated by dynamic light scattering experiments. Highly effective and reversible inhibition of thrombin activity toward fibrinogen was found for the free tris-mTBA and especially for the tris-mTBA-conjugated NPs, demonstrating great potential for the biomedical control of blood clotting.

Structural Characterization of a Thrombin-Aptamer Complex by High Resolution Native Top-Down Mass Spectrometry

Native mass spectrometry (MS) with electrospray ionization (ESI) has evolved as an invaluable tool for the characterization of intact native proteins and non-covalently bound protein complexes. Here we report the structural characterization by high resolution native top-down MS of human thrombin and its complex with the Bock thrombin binding aptamer (TBA), a 15-nucleotide DNA with high specificity and affinity for thrombin. Accurate mass measurements revealed that the predominant form of native human α-thrombin contains a glycosylation mass of 2205 Da, corresponding to a sialylated symmetric biantennary oligosaccharide structure without fucosylation. Native MS showed that thrombin and TBA predominantly form a 1:1 complex under near physiological conditions (pH 6.8, 200 mM NH4OAc), but the binding stoichiometry is influenced by the solution ionic strength. In 20 mM ammonium acetate solution, up to two TBAs were bound to thrombin, whereas increasing the solution ionic strength destabilized the thrombin-TBA complex and 1 M NH4OAc nearly completely dissociated the complex. This observation is consistent with the mediation of thrombin-aptamer binding through electrostatic interactions and it is further consistent with the human thrombin structure that contains two anion binding sites on the surface. Electron capture dissociation (ECD) top-down MS of the thrombin-TBA complex performed with a high resolution 15 Tesla Fourier transform ion cyclotron resonance (FTICR) mass spectrometer showed the primary binding site to be at exosite I located near the N-terminal sequence of the heavy chain, consistent with crystallographic data. High resolution native top-down MS is complementary to traditional structural biology methods for structurally characterizing native proteins and protein-DNA complexes. Graphical Abstract ᅟ.

Identification of an active metabolite of PAR-1 antagonist RWJ-58259 and synthesis of analogues to enhance its metabolic stability

The discontinuation of PAR-1 antagonist RWJ-58259 beyond use as a biological probe is most likely due to it's short half-life in vivo. However, retention of significant in vivo activity beyond the point where most of the RWJ-58259 had been consumed implies the generation of an active metabolite. Herein we describe the biological activity of a predicted metabolite of RWJ-58259 and the synthesis of analogues designed to enhance the metabolic stability of RWJ-58259.

Angiopoietin-2 mediates thrombin-induced monocyte adhesion and endothelial permeability

Essentials Mechanism of thrombin-induced inflammation is not fully understood. Thrombin induced monocyte adhesion and barrier loss require Angiopoietin-2 (Ang-2). Ang-2 mediates vessel leakage and monocyte adhesion through SHP-2/p38MAPK pathway. Calcium dependent SHP2/p38MAPK activation regulates Ang-2 expression through a feedback loop.

SUMMARY

Background Thrombin imparts an inflammatory phenotype to the endothelium by promoting increased monocyte adhesion and vascular permeability. However, the molecular players that govern these events are incompletely understood. Objective The aim of this study was to determine whether Angiopoietin-2 (Ang-2) has a role, if any, in regulating inflammatory signals initiated by thrombin. Methods Assessment of vascular leakage by Miles assay was performed by intra-dermal injection on the foot paw. Surface levels of intercellular adhesion molecule-1 (ICAM-1) were determined by flow cytometry. Overexpression, knockdown and phosphorylation of proteins were determined by Western blotting. Results In time-course experiments, thrombin-stimulated Ang-2 up-regulation, peaked prior to the expression of adhesion molecule ICAM-1 in human umbilical vein-derived endothelial cells (HUVECs). Knockdown of Ang-2 blocked both thrombin-induced monocyte adhesion and ICAM-1 expression. In addition, Ang-2(-/-) mice displayed defective vascular leakage when treated with thrombin. Introducing Ang-2 protein in Ang-2(-/-) mice failed to recover a wild-type phenotype. Mechanistically, Ang-2 appears to regulate the thrombin-activated calcium spike that is required for tyrosine phosphatase SHP2 and p38 MAPK activation. Further, down-regulation of SHP2 attenuated both thrombin-induced Ang-2 expression and monocyte adhesion. Down-regulation of the adaptor protein Gab1, a co-activator of SHP2, as well as overexpression of the Gab1 mutant incapable of interacting with SHP2 (YFGab1), inhibited thrombin-mediated effects, including downstream activation of p38 MAPK, which in turn was required for Ang-2 expression. Conclusions The data establish an essential role of the Gab1/SHP2/p38MAPK signaling pathway and Ang-2 in regulating thrombin-induced monocyte adhesion and vascular leakage.

Popular naturally occurring antioxidants as potential anticoagulant drugs

Blood coagulation is a physiological process whose main task is prevention of blood loss from injured vessels. This process consists of a series of zymogens proteolytic activation leading to the generation of the main coagulation enzyme - thrombin. Besides its important role in blood coagulation process, thrombin is involved in many cardiovascular diseases, which are responsible for almost half of fatalities in economically developed countries. The evidence for the increased generation and in vivo activity of thrombin was observed in the plasma of individuals at high risk for clinically significant venous and arterial thromboembolic complications. Antioxidants activity of plants extracts has been well known for many years and was confirmed by many publications. However, during the last decade many research centers presented results suggesting anticoagulant potential of various plant extracts. Many researchers have also provided evidence that polyphenol compounds are able to inhibit the activity of many enzymes, including serine proteases. All research described in this review clearly indicate that polyphenols and polyphenol-rich extracts possess not only antioxidative but also anticoagulant properties and may be useful in creation of new therapeutic agents or dietary supplements. Based on described properties polyphenols would be very helpful with both prevention and treatment of thromboembolic complications associated with multiple failures of haemostasis, because the available therapeutic agents do not offer such double-effects (antioxidant and anticoagulant).

A novel nanosensor composed of aptamer bio-dots and gold nanoparticles for determination of thrombin with multiple signals

Thrombin is a crucial multifunctional enzyme involved in many physiological and pathological processes. Its detection is of great importance. In this work, a novel bio-dots nanosensor for detection of thrombin with colorimetric, fluorometric and light-scattering signals is developed. This nanosensor is composed of thrombin-binding aptamer bio-dots (TBA-dots) and gold nanoparticles (AuNPs), where TBA-dots serve as fluorometric reporter and AuNPs function as multiple roles as colorimetric reporter, light scattering reporter and fluorescence quencher. TBA-dots retain inherent structures of aptamer to specifically interact with thrombin and simultaneously induce the aggregation of AuNPs. The mechanism of the sensing system is based on distance-dependent aggregation of AuNPs and fluorescence resonance energy transfer (FRET). The nanosensor needs no further surface functionalization required for the as-prepared bio-dots and AuNPs, which provides a sensitive method for the selective detection of thrombin with a detection limit as low as 0.59nM. In addition, it provides a brand new perspective for bio-dots and its potential use in bioanalysis.

Expression of pro-inflammatory genes in human endothelial cells: Comparison of rivaroxaban and dabigatran

INTRODUCTION

In addition to its central role in coagulation, thrombin is involved in non-hemostatic activities such as inflammation. Direct inhibition of thrombin activity (e.g. with dabigatran) or reducing its generation by inhibition of Factor Xa (e.g. with rivaroxaban) may therefore have anti-inflammatory effects.

MATERIALS AND METHODS

Microarray experiments were performed to identify transcriptome-wide changes in mRNA expression levels induced by thrombin in the presence and absence of the PAR-1 antagonist vorapaxar in primary human umbilical vein endothelial cells (HUVECs). On this basis, HUVECs were incubated with recalcified plasma, with or without rivaroxaban (0.3-3000nM), dabigatran (0.3-10,000nM), or vorapaxar (0.3-10nM). Expression levels of preselected pro-inflammatory genes were quantified by real-time PCR.

RESULTS

Vorapaxar abolished 67 of the 69 transcripts altered by more than twofold on addition of thrombin to HUVECs. ELAM-1, VCAM-1, ICAM-1, MCP-1, IL-8, CXCL1, and CXCL2 were among the genes most strongly induced by thrombin. Inflammatory gene expression after stimulation of thrombin generation was concentration-dependently suppressed by vorapaxar, dabigatran, and rivaroxaban. However, dabigatran at low concentrations (3-300nM) increased significantly the expression levels of CXCL1, CXCL2, IL-8, ELAM-1, MCP-1, and tissue factor.

CONCLUSION

In HUVECs, plasma-induced transcriptional changes are mediated by thrombin-induced PAR-1 activation. Rivaroxaban downregulated the expression of pro-inflammatory markers and tissue factor to a similar extent to dabigatran.

Thrombin Activates Latent TGFβ1 via Integrin αvβ1 in Gingival Fibroblasts

Transforming growth factor β (TGFβ) regulates cell proliferation, differentiation, migration, apoptosis, and extracellular matrix production. It also plays a pivotal role in the pathogenesis of gingival overgrowth. Thrombin is a key player in tissue repair, remodeling, and fibrosis after an injury, and it exerts profibrotic effects by activating protease-activated receptors. Connective tissue growth factor (CTGF or CCN2) modulates cell adhesion, migration, proliferation, matrix production, and wound healing. It is overexpressed in many fibrotic disorders, including gingival overgrowth, and it is positively associated with the degree of fibrosis in gingival overgrowth. In human gingival fibroblasts, we previously found that TGFβ1 induced CCN2 protein synthesis through c-jun N-terminal kinase and Smad3 activation. Thrombin stimulates CCN2 synthesis through protease-activated receptor 1 and c-jun N-terminal kinase signaling. Curcumin inhibited TGFβ1- and thrombin-induced CCN2 synthesis. In this study, we demonstrated that thrombin and protease-activated receptor 1 agonist SFLLRN induced latent TGFβ1 activation and Smad3 phosphorylation in human gingival fibroblasts. Pretreatment with a TGFβ-neutralizing antibody, TGFβ type I receptor inhibitor SB431542, and Smad3 inhibitor SIS3 inhibited approximately 86%, 94%, and 100% of thrombin-induced CCN2 synthesis, respectively. Furthermore, blocking integrin subunits αv and β1 with antibodies effectively inhibited SFLLRN-induced Smad3 phosphorylation and CCN2 synthesis and increased activated TGFβ1 levels; however, similar effects were not observed for integrins αvβ3 and αvβ5. These results suggest that protease-activated receptor 1-induced CCN2 synthesis in human gingival fibroblasts is mediated through integrin αvβ1-induced latent TGFβ1 activation and subsequent TGFβ1 signaling. Moreover, curcumin dose dependently decreased thrombin-induced activated TGFβ1 levels. Curcumin-inhibited thrombin-induced CCN2 synthesis in human gingival fibroblasts is caused by the suppression of latent TGFβ1 activation.

Protective effect of Astragalus polysaccharide on endothelial progenitor cells injured by thrombin

Several studies have demonstrated that Astragalus polysaccharide (APS) has a protective effect on endothelial cells damaged by various factors. To examine the role of APS in the endothelial inflammatory response, rat bone marrow endothelial progenitor cells (EPCs) were isolated by density gradient centrifugation and identified by immunohistochemistry, then we established a model of inflammatory injury induced by thrombin and measured the effects of APS on EPC viability and proliferation by MTT assays. We also assayed the effect APS had on the inflammatory response, by examining the nuclear factor kappa B (NF-κB) signaling pathway, as well as the expression of intercellular adhesion molecule-1 (ICAM-1), vascular endothelial growth factor (VEGF) and its receptors Flt-1 and KDR. Results demonstrated that EPCs were damaged by thrombin, and APS appeared to inhibit this damage. APS suppressed thrombin-induced ICAM-1 expression by blocking NF-κB signaling in rat bone marrow EPCs, and up-regulating expression of VEGF and its receptors. We believed that APS may be used to treat and prevent EPC injury-related diseases.

Assessment of blood changes post-challenge with Corynebacterium pseudotuberculosis and its exotoxin (phospholipase D): A comprehensive study in goat

Aim:

There is very little information regarding blood changes during the challenge of phospholipase D (PLD) in goats. Therefore, this experiment was conducted to study the changes in blood after the challenge with Corynebacterium pseudotuberculosis and its exotoxin, PLD to fill in the gap of caseous lymphadenitis (CLA) research.

Materials and Methods:

Twenty-six crossbred Boer goats aged 12-14 months were divided into 3 groups; the first group n=6 was inoculated with 1 ml phosphate buffered solution s.c. as the control. The second group n=10 was inoculated with C. pseudotuberculosis 1 × 10⁹ cfu s.c. The third group n=10 was intravenous injected with PLD 1 ml/20 kg body weight. Serial blood collections were done at 1 h, 3 h, 5 h, 8 h, and 12 h then every 24 h post-inoculation for the first 30 days of the experiment. Subsequently, the blood collection continued twice a week till the end of the experiment (90 days post-challenge).

Results:

Both C. pseudotuberculosis and PLD treated groups showed significant changes (p<0.05) in red blood cell count, hemoglobin (Hb), packed cell volume, mean corpuscular volume, mean corpuscular Hb concentration, white blood cell count, neutrophils, lymphocytes, monocytes, eosinophils, basophils, globulin, and total plasma proteins. Similarly, both treated groups showed significant changes (p<0.05) in alanine transaminase, alkaline phosphatase, aspartate transaminase, total bilirubin, calcium concentration, creatine phosphokinase, creatinine, gamma-glutamyl transpeptidase, urea concentration, lactate dehydrogenase, prothrombin time, and activated partial thromboplastin time.

Conclusion:

It concluded that C. pseudotuberculosis and PLD have a negative impact on the goat’s health in general reflected by all those changes recorded in the hemogram, leukogram, and the blood chemistry.

A novel recombinant slow-release TNF α-derived peptide effectively inhibits tumor growth and angiogensis

RMP16, a recombinant TNF α-derived polypeptide comprising a specific human serum albumin (HSA)-binding 7-mer peptide identified by phage display screening (WQRPSSW), a cleavage peptide for Factor Xa (IEGR), and a 20-amino acid bioactive peptide P16 (TNF α segment including amino acid residues 75–94), was prepared by gene-engineering technology. RMP16 showed prolonged half-life, 13.11 hours in mice (half-lives of P16 and TNF α are 5.77 and 29.0 minutes, respectively), and obviously higher receptor selectivity for TNFRI than TNF α. RMP16 had significant inhibition effects for multiple tumor cells, especially prostate cancer Du145 cells, and human vascular endothelial cells but not for human mammary non-tumorigenic epithelial cells. RMP16 can more effectively induce apoptosis and inhibit proliferation for DU145 cells than P16 and TNF α via the caspase-dependent apoptosis pathway and G0/G1 cell cycle arrest. In nude mice with transplanted tumor of DU145 cells, RMP16 significantly induced apoptosis and necrosis of tumor tissues but causing less side effects, and tumor inhibitory rate reached nearly 80%, furthermore, RMP16 can potently inhibit tumor angiogenesis and neovascularization. These findings suggest that RMP16 may represent a promising long-lasting antitumor therapeutic peptide with less TNF α-induced toxicity.

A recombinant slow-release PACAP-derived peptide alleviates diabetes by promoting both insulin secretion and actions

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuroendocrine factor that activates both the receptor VPAC1 and VPAC2. Although PACAP possesses insulinotropic activity, its therapeutic application is limited by the extremely short acting half-life and the stimulatory effects on glucagon production via a VPAC1-dependent mechanism. Here we have generated a recombinant PACAP-derived peptide (named as MHDBAY) comprising a 7-mer albumin-binding peptide identified by phage display screening (WQRPSSW), a cleavage peptide for Factor Xa (FXa) and dipeptidyl peptidase IV (DPP IV), and a 31-amino acid PACAP-derived peptide (DBAY) that can specifically bind to the VPAC2 receptor. MHDBAY binds to albumin both in vitro and in animals, thereby leading to an orderly slow release of the active peptide DBAY via the protease cleavage. In db/db mice and New Zealand rabbits, the circulating half-life of MHDBAY is approximately 12.2 h, which is 146-fold longer than DBAY (∼5 min). A single injection of MHDBAY into db/db diabetic mice markedly increases insulin secretion, thereby leading to sustained alleviation of hyperglycemia. The potency and duration of MHDBAY in increasing insulin secretion and decreasing blood glucose levels is much greater than Exendin-4, an anti-diabetic drug via its insulinotropic actions. Furthermore, chronic administration of MHDBAY by daily injection for 8 weeks significantly improves both glucose and lipid profiles and also greatly increases insulin sensitivity in db/db mice. These findings suggest that serum albumin may act as a reservoir for slow-release of small bioactive peptides, and MHDBAY may represent a promising therapeutic peptide for diabetes.

Combining a loop-stem aptamer sequence with methylene blue: a simple assay for thrombin detection by resonance light scattering technique

Schematic illustration of the RLS aptasensor for selective detection of human thrombin.

Comparison of venous thromboembolism after total hip arthroplasty between ankylosing spondylitis and osteoarthritis

Objective. Ankylosing spondylitis (AS), an inflammatory rheumatic disease, will gradually lead to severe hip joint dysfunction. Total hip arthroplasty is a useful method to improve patients' quality of life. The aim of this study was to compare the incidence and risk factors of deep vein thrombosis (DVT) between AS and hip osteoarthritis. Methods. In a retrospective study, a total of 149 subjects who underwent cementless THA were studied. Clinical data, biochemical data, and surgery-related data were measured between AS and OA groups. Results. The incidence of DVT in AS group was lower than that of OA group, although no significant difference was detected (P = 0.89). The patients of AS group were much younger (P < 0.0001) and thinner (P = 0.018) compared with those of OA group. AS patients had higher ejection fraction (EF) (P = 0.016), higher platelet counts (P < 0.0001), and lower hypertension rate (P = 0.0004). The values of APTT, PT, and INR in AS patients were higher than those in OA patients (all P < 0.0001). The values of D-dimer and APTT were both significantly higher in DVT subjects than those in non-DVT subjects. Conclusion. AS patients potentially had a lower incidence of DVT compared with OA patients.

New antithrombotics for secondary prevention of acute coronary syndrome

Patients with acute coronary syndrome (ACS) usually receive acetylsalicylic acid plus an adenosine diphosphate (ADP) receptor inhibitor to reduce the long-term risk of recurrent events. However, patients receiving standard antiplatelet prophylaxis still face a substantial risk of recurrent events. Strategies involving 3 antithrombotic agents with different modes of action have now been tested. In Thrombin Receptor Antagonists for Clinical Event Reduction (TRA-CER), compared with standard care alone, bleeding complications including intracranial hemorrhage (ICH) were increased with the addition of vorapaxar, without efficacy benefit. In Trial to Assess the Effects of SCH 530348 in Preventing Heart Attack and Stroke in Patients With Atherosclerosis (TRA 2°P-TIMI 50), the addition of vorapaxar reduced recurrent events compared with standard care in stable patients with prior myocardial infarction. This study was terminated early in patients with prior stroke owing to excess ICH, though an increased risk of ICH or fatal bleeding was not detected in patients with prior myocardial infarction. The Apixaban for Prevention of Acute Ischemic and Safety Events 2 (APPRAISE-2) trial of standard-dose apixaban added to standard care in patients with ACS was also stopped early owing to excess serious bleeding. However, in Rivaroxaban in Combination With Aspirin Alone or With Aspirin and a Thienopyridine in Patients With Acute Coronary Syndromes (ATLAS ACS 2 TIMI 51), fatal bleeding or fatal ICH did not increase with low-dose rivaroxaban added to low-dose acetylsalicylic acid-based standard care compared with standard care alone. In that trial, a significant reduction of recurrent vascular events was shown with 3 antithrombotic regimens compared with standard care. Therefore, depending on drug dose and patient population, further reductions in recurrent vascular events after ACS may be possible in future clinical practice, with a favorable benefit-risk profile.

A colorimetric aptamer biosensor based on cationic polymer and gold nanoparticles for the ultrasensitive detection of thrombin

A colorimetric assay for the ultrasensitive determination of thrombin based on cationic polymer and gold nanoparticles was presented, in which unmodified gold nanoparticles (AuNPs) was used as probes and 21-mer thrombin-binding aptamer (TBA) as sensing elements. Upon the addition of thrombin, TBA interacted specifically with thrombin to form a G-quadruplex structure. As a result, the conformation change facilitated the cationic polymer, poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation. Thus, the visible change in color from wine-red to blue-purple was readily seen by the naked eye. The colorimetric sensor could detect thrombin down to 1 pM with high selectivity in the presence of other interferring proteins. Furthermore, the assay was successfully employed to determine thrombin in human serum sample, which suggested its great potential for diagnostic purposes.

Fluorescence enhancement upon G-quadruplex folding: synthesis, structure, and biophysical characterization of a dansyl/cyclodextrin-tagged thrombin binding aptamer

A novel fluorescent thrombin binding aptamer (TBA), conjugated with the environmentally sensitive dansyl probe at the 3'-end and a β-cyclodextrin residue at the 5'-end, has been efficiently synthesized exploiting Cu(I)-catalyzed azide-alkyne cycloaddition procedures. Its conformation and stability in solution have been studied by an integrated approach, combining in-depth NMR, CD, fluorescence, and DSC studies. ITC measurements have allowed us to analyze in detail its interaction with human thrombin. All the collected data show that this bis-conjugated aptamer fully retains its G-quadruplex formation ability and thrombin recognition properties, with the terminal appendages only marginally interfering with the conformational behavior of TBA. Folding of this modified aptamer into the chairlike, antiparallel G-quadruplex structure, promoted by K(+) and/or thrombin binding, typical of TBA, is associated with a net fluorescence enhancement, due to encapsulation of dansyl, attached at the 3'-end, into the apolar cavity of the β-cyclodextrin at the 5'-end. Overall, the structural characterization of this novel, bis-conjugated TBA fully demonstrates its potential as a diagnostic tool for thrombin recognition, also providing a useful basis for the design of suitable aptamer-based devices for theranostic applications, allowing simultaneously both detection and inhibition or modulation of the thrombin activity.

Platelet aggregation measurement for assessment of hemostasis failure mechanisms in patients with gastroduodenal ulcer bleeding

Background

The purpose of this study was to identify factors associated with the risk of unsustainable hemostasis in patients with gastric and duodenal ulcer bleeding by in vitro assessment of platelet reactivity using artificial neural networks.

Methods

Patients with gastroduodenal ulcers complicated by bleeding were studied. Platelet aggregation was measured using aggregometry with adenosine diphosphate 5 μM, epinephrine 2.5 μM, 5-hydroxytryptophan 10 μM, collagen 1 μM, and thrombin 0.06 NIH Unit/mL as agonists. Multiple logistic regression was used to evaluate the independent relationship between demographic, clinical, endoscopic, and laboratory data and in vitro assessment of platelet reactivity and local parameters of hemostasis in patients with ulcer bleeding.

Results

Analysis of platelet aggregation in patients with gastroduodenal ulcer bleeding allowed the variability of platelet response to different agonists used in effective concentration which induces 50% platelet aggregation (EC₅₀) to be established. The relationship between platelet aggregation and the spatial-temporal characteristics of ulcers complicated by bleeding was demonstrated. Adrenoreactivity of platelets was associated with time elapsed since the start of ulcer bleeding and degree of hemorrhage. The lowest platelet response to collagen and thrombin was detected in patients with active bleeding (P < 0.001) and unsustainable recent bleeding (P < 0.01). Decreased adenosine diphosphate-induced platelet aggregation in patients with ulcer bleeding was correlated with the platelet response to thrombin (r = 0.714, P < 0.001) and collagen (r = 0.584, P < 0.01).

Conclusion

Estimation of platelet reactivity in vitro indicates the key mechanisms of failure of hemostasis in patients with ulcer bleeding. In addition to gender, an important determinant of unsustainable hemostasis was a decreased platelet response to thrombin and adenosine diphosphate.

Thrombin has biphasic effects on the nitric oxide-cGMP pathway in endothelial cells and contributes to experimental pulmonary hypertension

Background

A potential role for coagulation factors in pulmonary arterial hypertension has been recently described, but the mechanism of action is currently not known. Here, we investigated the interactions between thrombin and the nitric oxide-cGMP pathway in pulmonary endothelial cells and experimental pulmonary hypertension.

Principal Findings

Chronic treatment with the selective thrombin inhibitor melagatran (0.9 mg/kg daily via implanted minipumps) reduced right ventricular hypertrophy in the rat monocrotaline model of experimental pulmonary hypertension. In vitro, thrombin was found to have biphasic effects on key regulators of the nitric oxide-cGMP pathway in endothelial cells (HUVECs). Acute thrombin stimulation led to increased expression of the cGMP-elevating factors endothelial nitric oxide synthase (eNOS) and soluble guanylate cyclase (sGC) subunits, leading to increased cGMP levels. By contrast, prolonged exposition of pulmonary endothelial cells to thrombin revealed a characteristic pattern of differential expression of the key regulators of the nitric oxide-cGMP pathway, in which specifically the factors contributing to cGMP elevation (eNOS and sGC) were reduced and the cGMP-hydrolyzing PDE5 was elevated (qPCR and Western blot). In line with the differential expression of key regulators of the nitric oxide-cGMP pathway, a reduction of cGMP by prolonged thrombin stimulation was found. The effects of prolonged thrombin exposure were confirmed in endothelial cells of pulmonary origin (HPAECs and HPMECs). Similar effects could be induced by activation of protease-activated receptor-1 (PAR-1).

Conclusion

These findings suggest a link between thrombin generation and cGMP depletion in lung endothelial cells through negative regulation of the nitric oxide-cGMP pathway, possibly mediated via PAR-1, which could be of relevance in pulmonary arterial hypertension.

Coagulation in hepatobiliary disease

OBJECTIVE

To review the pathogenesis and clinical consequences of coagulation abnormalities accompanying hepatobiliary disorders and to highlight the need for further studies to characterize these derangements and their treatment options in small animal patients.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent texts.

SUMMARY

The liver plays an important role in the production and clearance of many components of coagulation. A wide range of hemostatic derangements can occur in patients with hepatobiliary disease including alterations in platelet number and function, coagulation factor levels, anticoagulants, vascular endothelial function, and fibrinolysis. As these hemostatic alterations include both pro- and anticoagulation pathways, the net result is often a rebalanced hemostatic system that can be easily disrupted by concurrent conditions resulting in either clinical bleeding or thrombosis. Conventional coagulation tests are inadequate at identifying the spectrum of coagulation alterations occurring in patients with hepatobiliary disease, but their evaluation is necessary to assess bleeding risk and provide prognostic information. A paucity of information exists regarding the treatment of the coagulation derangements in small animals with hepatobiliary disease. Extrapolation from human studies provides some information about potential treatment options, but further studies are warranted in this area to elucidate the best management for coagulation abnormalities in dogs and cats with hepatobiliary disease.

CONCLUSION

Hepatobiliary disease can have profound effects on coagulation function leading to hypercoagulable or hypocoagulable states. Overall coagulation status with hepatobiliary disease depends on both the type and severity of disease and the presence of associated complications.

Antithrombin effect of polyphenol-rich extracts from black chokeberry and grape seeds

Thrombin is a serine protease that cleaves the peptide bonds in proteins located on the carboxyl side of arginine. Thrombin plays a central role in thromboembolic diseases, which are the major cause of mortality. The aim of the study was to estimate the effects of plant extracts on proteolytic properties of thrombin. Thrombin was incubated with polyphenol-rich extracts from berries of Aronia melanocarpa or seeds of Vitis vinifera (0.5, 5, 50 µg/mL) and with polyphenols ((+)-catechin, (-)-epicatechin, gallic acid, chlorogenic acid, procyanidin B1, cyanidin, cyanidin 3-glucoside, quercetin). The in vitro experiments showed that both extracts in all used concentrations inhibited proteolytic activity of thrombin observed as inhibition of thrombin-induced fibrinogen polymerization, stabilized fibrin formation, and platelet aggregation. Moreover, thrombin amidolytic activity was inhibited by polyphenols belonging to the flavonoid class. Results presented in this study indicate that polyphenol-rich extracts from berries of A. melanocarpa and seeds of V. vinifera may become promising dietary supplements in the prevention of thrombotic states.

Fibrinogen as a key regulator of inflammation in disease

The interaction of coagulation factors with the perivascular environment affects the development of disease in ways that extend beyond their traditional roles in the acute hemostatic cascade. Key molecular players of the coagulation cascade like tissue factor, thrombin, and fibrinogen are epidemiologically and mechanistically linked with diseases with an inflammatory component. Moreover, the identification of novel molecular mechanisms linking coagulation and inflammation has highlighted factors of the coagulation cascade as new targets for therapeutic intervention in a wide range of inflammatory human diseases. In particular, a proinflammatory role for fibrinogen has been reported in vascular wall disease, stroke, spinal cord injury, brain trauma, multiple sclerosis, Alzheimer's disease, rheumatoid arthritis, bacterial infection, colitis, lung and kidney fibrosis, Duchenne muscular dystrophy, and several types of cancer. Genetic and pharmacologic studies have unraveled pivotal roles for fibrinogen in determining the extent of local or systemic inflammation. As cellular and molecular mechanisms for fibrinogen functions in tissues are identified, the role of fibrinogen is evolving from a marker of vascular rapture to a multi-faceted signaling molecule with a wide spectrum of functions that can tip the balance between hemostasis and thrombosis, coagulation and fibrosis, protection from infection and extensive inflammation, and eventually life and death. This review will discuss some of the main molecular links between coagulation and inflammation and will focus on the role of fibrinogen in inflammatory disease highlighting its unique structural properties, cellular targets, and signal transduction pathways that make it a potent proinflammatory mediator and a potential therapeutic target.