[69] Hirudin as an inhibitor of thrombin

Cloning, characterization, and heterologous expression of a candidate Hirudin gene from the salivary gland transcriptome of Hirudo nipponia

Hirudin is a pharmacologically active substance in leeches with potent blood anticoagulation properties. Although recombinant hirudin production isolated from Hirudo medicinalis Linnaeus and Hirudinaria manillensis Lesson is known, to our knowledge, this study is the first to report recombinant hirudin expression and production from Hirudo nipponia Whitman. Thus, the present study aimed to clone and characterize the full-length cDNA of a candidate hirudin gene (c16237_g1), which is localized on the salivary gland transcriptome of H. nipponia, and further evaluate its recombinant production using a eukaryotic expression system. The 489-bp cDNA possessed several properties of the hirudin “core” motifs associated with binding to the thrombin catalytic pocket. A fusion expression vector (pPIC9K-hirudin) was constructed and successfully transformed into Pichia pastoris strain GS115 via electroporation. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis and western blot analysis confirmed hirudin expression. The recombinant protein was expressed with a yield of 6.68 mg/L culture. Mass spectrometry analysis further confirmed target protein expression. The concentration and antithrombin activity of purified hirudin were 1.67 mg/mL and 14,000 ATU/mL, respectively. These findings provide a basis for further elucidating the molecular anticoagulation mechanism of hirudin, and address China’s growing market demand for engineered H. nipponia-derived hirudin and hirudin-based drugs.

Make it double: identification and characterization of a Tandem-Hirudin from the Asian medicinal leech Hirudinaria manillensis

Haematophagous leeches express a broad variety of secretory proteins in their salivary glands, among them are hirudins and hirudin-like factors. Here, we describe the identification, molecular and initial functional characterization of Tandem-Hirudin (TH), a novel salivary gland derived factor identified in the Asian medicinal leech, Hirudinaria manillensis. In contrast to the typical structure of hirudins, TH comprises two globular domains arranged in a tandem-like orientation and lacks the elongated C-terminal tail. Similar structures of thrombin inhibitors have so far been identified only in kissing bugs and ticks. Expression of TH was performed in both cell-based and cell-free bacterial systems. A subsequent functional characterization revealed no evidence for a thrombin-inhibitory potency of TH.

The C-terminal acidic region in the A1 domain of factor VIII facilitates thrombin-catalyzed activation and cleavage at Arg372

BACKGROUND

Factor VIII (FVIII) is activated by thrombin-catalyzed cleavage at three sites. Previous reports indicated that the A2 domain contained thrombin-interactive sites responsible for cleavage at Arg372 . We have also found that the A1 domain of FVIII bound to the anion-binding exosite I of thrombin. The present study focused, therefore, on thrombin interaction with A1 residues 337-372 containing clustered acidic and hirugen-like sequences.

AIM

To identify specific thrombin-interactive site(s) within the A1 acidic region of FVIII.

METHODS AND RESULTS

The synthetic peptide of residues 337-353 with sulfated Tyr346 (337-353S) significantly blocked thrombin-catalyzed FVIII activation and cleavage at Arg372 , while a corresponding peptide of residues 354-372 had no significant effect. Treatment with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide to cross-link thrombin and 340-350S suggested that the 344-349 clustered acidic region was involved in thrombin interaction. Alanine-substituted FVIII mutants, Y346A and D347A/D348A/D349A, depressed thrombin-catalyzed activation and cleavage at Arg372 , with peak activation at ~ 50% and cleavage rates of ~ 10% to 20% compared to wild type (WT). The peak level of thrombin-catalyzed activation and the cleavage rate at Arg372 using FVIII mutants with 337-346 residues substituted with hirugen-sequences (MKNNEEAEDY337-346GDFEEIPEEY) were ~ 1.5- and ~ 2.5-fold of WT, respectively. Surface plasmon resonance-based analysis demonstrated that the Kd for active-site modified thrombin interactions using Y346A and D347A/D348A/D349A mutants was ~ 3- to 6-fold higher than that of WT, and that the hirugen-hybrid mutant facilitated association kinetics ~ 1.8-fold of WT.

CONCLUSION

Residues 346-349 with sulfated Tyr provided a thrombin-interactive site responsible for activation and cleavage at Arg372 . A hirugen-hybrid A1 mutant showed more efficient thrombin-catalyzed cleavage at Arg372 .

Recent Advances and Computational Approaches in Peptide Drug Discovery

BACKGROUND

Drug design and development is a vast field that requires huge investment along with a long duration for providing approval to suitable drug candidates. With the advancement in the field of genomics, the information about druggable targets is being updated at a fast rate which is helpful in finding a cure for various diseases.

METHODS

There are certain biochemicals as well as physiological advantages of using peptide-based therapeutics. Additionally, the limitations of peptide-based drugs can be overcome by modulating the properties of peptide molecules through various biomolecular engineering techniques. Recent advances in computational approaches have been helpful in studying the effect of peptide drugs on the biomolecular targets. Receptor - ligand-based molecular docking studies have made it easy to screen compatible inhibitors against a target.Furthermore, there are simulation tools available to evaluate stability of complexes at the molecular level. Machine learning methods have added a new edge by enabling accurate prediction of therapeutic peptides.

RESULTS

Peptide-based drugs are expected to take over many popular drugs in the near future due to their biosafety, lower off-target binding chances and multifunctional properties.

CONCLUSION

This article summarises the latest developments in the field of peptide-based therapeutics related to their usage, tools, and databases.

The Research Progress of Direct Thrombin Inhibitors

Blood coagulation is the process of changing the blood from the flowing state to the gel state. It is an important part of the hemostatic function. Coagulation is a process by which a series of coagulation factors are sequentially activated, and finally thrombin is formed to form fibrin clot. Direct thrombin inhibitors are important anticoagulant drug. These drugs can selectively bind to the active site of thrombin, inhibit thrombin activity, have strong action and high specificity, and have important significance in the clinical treatment of thrombus diseases. Some of them come from natural products of animals or plants, and many of them have been applied in the clinic. The other part is derived from the design, synthesis and activity studies of small molecule inhibitors. This review discusses the progress of direct thrombin inhibitors in recent years.

Transcriptomic Analysis of the Influence of Methanol Assimilation on the Gene Expression in the Recombinant Pichia pastoris Producing Hirudin Variant 3

Hirudin and its variants, as strong inhibitors against thrombin, are present in the saliva of leeches and are recognized as potent anticoagulants. However, their yield is far from the clinical requirement up to now. In this study, the production of hirudin variant 3 (HV3) was successfully realized by cultivating the recombinant Pichia pastoris GS115/pPIC9K-hv3 under the regulation of the promoter of AOX1 encoding alcohol oxidase (AOX). The antithrombin activity in the fermentation broth reached the maximum value of 5000 ATU/mL. To explore an effective strategy for improving HV3 production in the future, we investigated the influence of methanol assimilation on the general gene expression in this recombinant by transcriptomic study. The results showed that methanol was partially oxidized into CO₂, and the rest was converted into glycerone-P which subsequently entered into central carbon metabolism, energy metabolism, and amino acid biosynthesis. However, the later metabolic processes were almost all down-regulated. Therefore, we propose that the up-regulated central carbon metabolism, energy, and amino acid metabolism should be beneficial for methanol assimilation, which would accordingly improve the production of HV3.

Food-derived antithrombotic peptides: Preparation, identification, and interactions with thrombin

Thromboembolism and its sequelae have been the leading causes of morbidity and mortality throughout the world. Food-derived antithrombotic peptides, as potential ingredients in health-promoting functional foods targeting thrombus, have attracted increasing attention because of their high biological activities, low toxicity, and ease of metabolism in the human body. This review presents the conventional workflow of preparation, isolation and identification of antithrombotic peptides from various kinds of food materials. More importantly, to analyze the antithrombotic effects and mechanism of antithrombotic peptides, methods for interaction of anticoagulant peptides and thrombin, the main participant in thrombosis, were analyzed from biochemistry, solution chemistry and crystal chemistry. The present study is intended to highlight the recent advances in research of food-derived antithrombotic peptide as a novel vehicle in the field of food science and nutrition. Future outlooks are highlighted with the aim to suggest a research line to be followed in further studies with the introduced research approach.

Peptide therapeutics from venom: Current status and potential

Peptides are recognized as being highly selective, potent and relatively safe as potential therapeutics. Peptides isolated from the venom of different animals satisfy most of these criteria with the possible exception of safety, but when isolated as single compounds and used at appropriate concentrations, venom-derived peptides can become useful drugs. Although the number of venom-derived peptides that have successfully progressed to the clinic is currently limited, the prospects for venom-derived peptides look very optimistic. As proteomic and transcriptomic approaches continue to identify new sequences, the potential of venom-derived peptides to find applications as therapeutics, cosmetics and insecticides grows accordingly.

Identification and characterization of a novel neuropeptide (neuropeptide Y-HS) from leech salivary gland of Haemadipsa sylvestris

The present study was designed to identify immunomodulatory components from the leech salivary gland of Haemadipsa sylvestris. The Sephadex G-50, Resource(TM) S column chromatography and reverse-phase high performance liquid chromatography (RP-HPLC) were used to isolate and purify the salivary gland extracts (SGE). Structural analysis of isolated compounds was based on Edman degradation and matrix assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF-MS). The cDNA encoding the precursor of the compound was cloned from the cDNA library of the salivary gland of H. sylvestris. The levels of inflammatory mediators, including tumor necrosis factor-α (TNF-α), interferon γ (IFN-γ), interleukin-6 (IL-6), and monocyte chemotactic protein-1 (MCP-1) were assayed using an enzyme-linked immunosorbent assay (ELISA). The effects on cell proliferation and cell viability were observed using MTT assay. A novel neuropeptide Y (Neuropeptide Y-HS) from the leech salivary gland of H. sylvestris was purified and characterized. It was composed of 36 amino acid residues and the amino acid sequence was determined to be FLEPPERPAVFTSVEQMKSYIKALNDYYLLLGRPRF-NH2, containing an amidated C-terminus. It showed significant inhibitory effects on the production of inflammatory cytokines including TNF-α, IFN-γ, IL-6, and MCP-1. Neuropeptide Y was identified from leeches for the first time. The presence of neuropeptide Y-HS in leech salivary gland may help get blood meal from hosts and inhibit inflammation.

State-of-the-Art Review : Antithrombotic Agents from Hematophagous Animals

Bloodsucking animals produce anticoagu lantly effective substances that are a challenge to coagu lation studies. In the past 40 years efforts have been fo cused on the isolation and chemical characterization of such agents as well as on the clarification of their modes of action. Following the success in the development of the anticoagulant agent hirudin from medicinal leeches, these naturally occurring anticoagulants were recently in vestigated as a source of antithrombotics for pharmaceu tical use. These polypeptides or miniproteins were shown to be specific inhibitors of certain coagulation factors that block either the formation or the effect of thrombin or are supported by substances that inhibit the aggregation and adhesion of blood platelets and by proteolytic enzymes with fibrinolytic activity. By advances in biotechnology of protein-like substances, especially gene technology, these antithrombotics have been obtained in amounts suf ficient for preclinical and clinical studies. Thus, the in vestigation of the anticoagulant agents from hematopha gous animals offers a new line of research in antithrom botic drugs. Key Words: Bloodsucking animals— Naturally occurring anticoagulants—Fibrinolytics and platelet inhibitors.

Test of hirudin activity by tracking the binding of hirudin to thrombin in the presence of BS3 cross-linking

Hirudin has a great potential in inhibiting thrombin, and its antithrombin activity has direct bearing on its clinical application. Using bovine alpha-thrombin and recombinant hirudin of Poecilobdella javanica purified from Phichia pastoris as materials, this study introduced a novel method to testing antithrombin activity of hirudin visually and dynamically by tracking the binding of hirudin to thrombin. After incubating the mixture of thrombin and hirudin at 37 °C for 5 min, the binding of hirudin to thrombin was cross-linked by bis[sulfosuccinimidyl] suberate for 30 min and visualized by SDS-polyacrylamide gel electrophoresis. With the aid of image analysis on the basis of INRA-Noésis E1D analysis software, antithrombin activity of hirudin was calculated through intensity variations of protein bands of either thrombin-hirudin compound, unbound thrombin, or unbound hirudin. In this regard, activity of the given hirudin was tested to be 5625 ATU/mg based on a single reaction, and 5675.3 ATU/mg based on a series of reactions in a stepwise manner, close to the result of 6000 ATU/mg concluded by titration method. The superiorities of the method include good accuracy (the minimum testable concentration of hirudin is 1.5 μg/ml) and little sample consumption (sample consumption of hirudin is generally 1-11.5 μl using the apparatus of Mini Protean 3 Cell). Easy operation, low input, and equipment requirement also grant it as an effective way.

Anticoagulation activity of salivary gland extract of oriental blackfly Simulium indicum

OBJECTIVE

To study the morphology of the salivary gland of the female blackfly of the species Simulium indicum (S. indicum) along with protein profile and anticoagulant activity of the salivary gland extract.

METHODS

Sodium dodecyl sulphate polyacrylamide gel electrophoresis was used to analyze the protein profile of the salivary gland extract (SGE) and anticoagulant activities against thrombin, and the extrinsic and intrinsic coagulation pathways were found in S. indicum SGE in the TT, PT and APTT assays, respectively.

RESULTS

Results revealed that each gland consisted of a cylindrical U-shaped secretory lobe and a more or less spherical reservoir. The protein contents of whole salivary glands were also quantified and the amount of salivary gland proteins in the adult female S. indicum was found out to be approximately 1.12±0.13 µg/female. At least 16 major and several minor protein bands were detected in the female salivary glands. The molecular masses of these major protein bands were estimated at 69, 65, 61, 58, 44, 42, 39, 33, 30, 28, 27, 26, 23, 21, 18 and 16 kDa, consecutively. Anticoagulant activities were found in S. indicum SGE in all the assays. It was found that SGE prolonged human plasma clotting time in a dose-dependent manner. Factor Xa inhibition was shown by the SGE of S. indicum. Percent inhibition value was 93.8. A positive correlation (r=0.89) was observed between total protein and percent inhibition of factor Xa.

CONCLUSIONS

The present study demonstrated that the mode of action of the anticoagulant(s) is mainly on the inhibition of thrombin and factor Xa along with other target factors of the coagulation cascade.

Pharmacokinetics study of recombinant hirudin in the plasma of rats using chromogenic substrate, ELISA, and radioisotope assays

AIM

To compare the analytical methods used to study the pharmacokinetics of recombinant hirudin in the plasma of rats that had been injected with (125)I-recombinant hirudin.

METHODS

2.0 mg/kg (125)I-recombinant hirudin were injected intravenously into rats. The recombinant hirudins in the plasma was analyzed by chromogenic substrate assay, enzyme-linked immunosorbent assay (ELISA), total radioisotope assay (RA) and trichloroacetic acid pre-treated total radioisotope assay (TCA-RA).

RESULTS

The chromogenic substrate assay standard curve was linear over the concentration range from 3.12 to 40.00 ng/ml for the recombinant hirudin in plasma. The relative standard deviations (RSD) for the intra- and inter-day variation were 5.0 to 6.3% and 11.9 to 12.6%, respectively. The recoveries of recombinant hirudin was 89.8% to 100.7%. The limit of quantification (LOQ) was 3.12 ng/ml. The concentration-time curve of the recombinant hirudin in the plasma could be explained as a two-compartment model. Pharmacokinetic parameters, including the half-life of distribution phase (t1/2 α), the half-life of elimination phase (t1/2 β), volume of apparent distribution (Vd), and area under the concentration-time curve from zero to infinite time (AUC0-t) were 7.59 min, 46.99 min, 0.17 L/kg, and 204.5 mg/L/min, respectively, as determined by chromogenic substrate assay; 6.41 min, 47.28 min, 1.24 L/kg, and 575.18 mg/L/min, respectively, as determined by ELISA; 3.69 min, 701.90 min, 0.04 L/kg, and 4189 mg/L/min, respectively as determined by RA; and 4.57 min, 724.9 min, 0.09 L/kg, and 2329 mg/L/min, respectively, as determined by TCA-RA.

CONCLUSIONS

The chromogenic substrate assay on the concentration dynamics of the recombinant hirudin in the plasma is a specific, sensitive, and accurate analytical method for pharmacokinetic studies. Moreover, the pharmacokinetic parameters determined by the chromogenic substrate assay and ELISA are congruent except for AUC.

Evaluation of a multifunctional staphylokinase variant with thrombin inhibition and antiplatelet aggregation activities produced from salt-inducible E. coli GJ1158

Reocclusion is one of the major root causes for secondary complications that arise during thrombolytic therapy. A multifunctional staphylokinase variant SRH (staphylokinase (SAK) linked with tripeptide RGD and didecapeptide Hirulog) with antiplatelet and antithrombin activities in addition to clot specific thrombolytic function, was developed to address the reocclusion problem. We preferred to use Escherichia coli GJ1158 as the host in this study for economic production of SRH by osmotic (0.3 mol/L sodium chloride) induction, to overcome the problems associated with the yeast expression system. The therapeutic potential of SRH was evaluated in the murine model of vascular thrombosis. The SAK protein (1 mg/kg body mass) and SRH protein (1 mg/kg and 2 mg/kg) were administered intravenously to the different treatment groups. The results have shown a dose-dependent antithrombotic effect in carrageenan-induced mouse tail thrombosis. The thrombin time, activated partial thromboplastin time, and prothrombin time were significantly prolonged (p < 0.05) in the SRH-infused groups. Moreover, SRH inhibited platelet aggregation in a dose-dependent manner (p < 0.05), while the bleeding time was significantly (p < 0.05) prolonged. All of these results inferred that the osmotically produced multifunctional fusion protein SRH (SAK-RGD-Hirulog) is a promising thrombolytic agent, and one which sustained its multifunctionality in the animal models.

Expression, Purification and Characterization of the Recombinant Hirudin Variant iii in the Bacillus Subtilis

Hirudin is the most potent natural inhibitor of thrombin and a powerful anticoagulant. Large-scale production of recombinant hirudin is desirable for therapy. In this study, the gene encoding hirudin variant III was redesigned and synthesized by usingBacillus subtilispreferred codons, and the recombinant hirudin variant III (rHV3) was overexpressed inB. subtilisDB403 with strong anticoagulation activity for the first time. The hirudin activity from the supernatant of culture with optimized expression conditions could reach 210 ATU/ml. The protein in culture supernatant was precipitated by trichloroacetic acid, then desalted by ultrafiltration and purified by anion exchange chromatography. Strong anion Q F.F. performed better than weak anion DEAE F.F. The proper pH and conductivity was determined at pH 8 and 6 ms/cm, respectively. The maximum applied sample was 240 ATU/ml to medium of strong anion Q F.F. This optimized procedure was employed in strong anion exchange HiPrep 16/10Q with the 90% recovery rate and 70.2% purity. After gel filtration, the purity of rHV3 checked by HPLC could reach 95.1%, and the recovery rate was 93% for this step. The purified recombinant rHV3 showed a single band in SDS-PAGE. The rHV3 was stable at 100 °C and acidity condition, but was unstable under the condition of both heating and alkalinity. In conclusion, theses studies suggests thatB.subtilismight be useful for the production of biologically active medicine peptides in secretion facilitating purification procedures, and that this isolation method was suitable for scale-up purification process at a low cost.

The antithrombotic effect of a novel hirudin derivative after reconstruction of carotid artery in rabbits

INTRODUCTION

Hirudin is a direct thrombin inhibitor that has potential mechanistic advantages over indirect inhibitors. Peptides containing the RGD motif competitively inhibit binding of fibrinogen to glycoprotein IIb/IIIa on platelets, thus inhibiting platelet aggregation. A novel hirudin derivative, recombinant RGD-hirudin (r-RGD-hirudin), was engineered by fusing the tripeptide RGD sequence to the native hirudin. We tested the antithrombotic effect of r-RGD-hirudin using a carotid artery reconstruction model in rabbits.

MATERIALS AND METHODS

A fusion gene encoding r-RGD-hirudin was constructed and expressed at high levels in Pichia pastoris. Following traumatic injury and anastomosis, 42 New Zealand White rabbits were randomized to receive normal saline, abciximab, wild-type hirudin, or r-RGD-hirudin. Fibrinogen concentration, aPTT, TT, PT, and PAGm were measured prior to and following the operation. Carotid angiography and pathological examination of the anastomotic site were performed to compare patency rates among the groups.

RESULTS

The r-RGD-hirudin significantly prolonged aPTT, TT, PT and inhibited PAGm following carotid anastomosis in rabbits. The median dose of r-RGD-hirudin (0.5 mg/kg) had a therapeutic effect equal to that of wild-type hirudin (1.0 mg/kg) and higher than that of abciximab (0.2 mg/kg) with regard to patency rates.

CONCLUSIONS

Compared to wild-type hirudin or antiplatelet agent, the novel anticoagulant, r-RGD-hirudin was capable of inhibiting both thrombin activity and platelet aggregation, and was demonstrated to be effective in the prevention of thrombosis.

Screening of endophytic fungi with antithrombotic activity and identification of a bioactive metabolite from the endophytic fungal strain CPCC 480097

Fermentation extracts from 1,075 endophytic fungi were screened by the Markwardt method. The endophytic strain CPCC 480097 had the strongest antithrombotic activity and was identified as Fusarium sp. based on morphologic tests and internal transcriptional spacer sequence analysis. The target of the antithrombotic agent from the endophytic strain CPCC 480097 was identified by analysis of the fibrinogen clotting time, amidolytic activity, and fibrinolytic assay. The results showed that this antithrombotic agent is a 28-kDa single-chain fibrinolytic enzyme. The identification of this fibrinolytic enzyme was performed by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). The two internal sequences of this enzyme were obtained, and these showed no homology with those of other known fibrinolytic enzymes.

A novel hirudin derivative characterized with anti-platelet aggregations and thrombin inhibition

Background Hirudin is an anti-coagulative product of the salivary glands of the medicinal leech Hirudo medicinalis. It is a powerful and specific thrombin inhibitor. Peptides containing the RGD motif competitively inhibit the binding of fibrinogen to GP IIb/IIIa on the platelets, thus inhibiting platelet aggregation. Results We have constructed a recombinant RGD-hirudin (r-RGD-hirudin) by fusing the tripeptide RGD sequence to the native hirudin (wt-hirudin). The r-RGD-hirudin was expressed at high levels in Pichia pastoris, and was purified to ~97% homogeneity. The specific anti-thrombin activity of purified r-RGD-hirudin is 12,000 ATU/mg, which is equivalent to wt-hirudin, but only r-RGD-hirudin can inhibit platelet aggregation. The biological effects of r-RGD-hirudin on Thrombin Time (TT), Prothrombin Time (PT), Activated Partial Thromboplastin Time (APTT), Bleeding Time (BT), maximum platelet aggregation (PAGm) induced by ADP were studied in rabbit model and compared with that of wt-hirudin. The rabbits were infused r-RGD-hirudin had prolonged TT, PT, and aPTT which were similar to that of wt-hirudin; but only r-RGD-hirudin was capable of inhibiting PAGm. Histopathological analyses showed that r-RGD-hirudin was two to three times more effective than wt-hirudin in preventing thrombosis. Conclusions r-RGD-hirudin can potentially be used as a novel anti-coagulant for the prevention of thrombosis after carotid artery anastomosis or in other thrombotic events.

A rapid method for isolation and purification of an anticoagulant from Whitmania pigra

Whitmania pigra is common in China and has been used as a traditional Chinese anticoagulant medicine for years, but its effective components are unknown to scientists. In this article we report a rapid method for isolation and purification of an anticoagulant from W. pigra for the first time. An acetone-water extract of W. pigra was subjected to anion-exchange chromatography on a Sephadex DEAE A-50 column, and gel permeation chromatography on Sephadex G-25 and Sephadex LH-20 columns successively, which afforded a fraction with potent anticoagulant activity. An anticoagulant was isolated and purified from this fraction by reversed-phase high-performance liquid chromatography (RP-HPLC). It was identified as a single pure substance by RP-HPLC and sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). This component was named whitmanin and its molecular weight was determined as 8608 Da by matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI-TOF-MS).

Amidino-Containing Schiff Base Copper(II) and Iron(III) Chelates as a Thrombin Inhibitor

Four series of Schiff base copper(II) and iron(III) chelates were synthesized from 4-formyl-3-hydroxybenzamidine or 3-formyl-4-hydroxybenzamidine and various L- or D-amino acids. Their inhibitory activities for bovine alpha-thrombin (abbreviated as thrombin) were determined. The most potent thrombin inhibitor in this series is copper(II) chelate (1g') derived from 4-formyl-3-hydroxybenzamidine and D-Trp. Its Ki value, 2.7x10(-8) M, is comparable to that of Argatroban (MD-805), which is a clinically used compound. The iron(III) chelates derived from 4-formyl-3-hydroxybenzamidine and hydrophobic L-amino acids (Val, Ile, Leu, Phe, Trp, Met) also exhibited higher inhibitory potency. It appears that coordination geometry composed of metal ion, amidino group, amino acid side chain is well accommodated to the thrombin active site. From the Ki values of Schiff base metal chelates for thrombin, the structure-activity relationships between the chelates and active site of thrombin were discussed.

The thrombin–fibrinogen interaction

The thrombin-catalyzed conversion of fibrinogen (F) to fibrin consists of three reversible steps, with thrombin (T) being involved in only the first step which is a limited proteolysis to release fibrinopeptides (FpA and FpB) from fibrinogen to produce fibrin monomer. In the second step, fibrin monomers form intermediate polymers through noncovalent interactions. In the third step, the intermediate polymers aggregate to form the fibrin clot. The molecular mechanisms of the first two steps are elucidated.

Fibrinogenolytic and procoagulant activities in the hemorrhagic syndrome caused by Lonomia obliqua caterpillars

The hemorrhagic syndrome caused by accidents with caterpillars of the genus Lonomia has been the focus of several clinical and biochemical studies, since its venom is composed of many active principles that interfere with the hemostatic system. Whereas a fibrinolytic agent has been characterized in the venom of Lonomia achelous, in Lonomia obliqua, only a prothrombin activator activity has been reported so far, even though both species cause similar bleeding disorders, characterized by hemorrhage, disseminated intravascular coagulation (DIC), and acute renal failure. Considering the possibility that the hemorrhagic syndrome resulting from envenoming by L. obliqua may be due to fibrinolytic and procoagulant activities acting together, we decided to investigate the effects of bristle extract (BE) of this species upon blood coagulation and fibrin(ogen)olysis. This study shows that besides a procoagulant activity related to the activation of prothrombin, the venom contains at least one fibrin(ogen)olytic activity, as shown by fibrinolysis in a fibrin (F) plate assay, by interference in thrombin-catalyzed fibrinocoagulation, and by polyacrylamide gel electrophoresis profile of fibrin and fibrinogen (Fg) degradation. Considering that a recombinant prothrombin activator from L. obliqua has been suggested in other studies to be used as an anti-thrombotic agent, it is important in the first place to better characterize the different active principles of this venom.

Isolation of anticoagulant from the venom of tick, Boophilus calcaratus, from Uzbekistan

Boophilus calcaratus is a tick found in Central Asia and a common parasite to domestic animals. Venom from this tick was fractionated by two-step column chromatography, Sephadex G-75, and DEAE-Sephadex A-25. The homogeneity of the anticoagulant was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified component is named calcaratin and has a molecular weight of 14,500. The effect of the purified anticoagulant component (calcaratin) on various sites of the blood coagulation cascade scheme was examined and compared with crude venom. The chromogenic substrates S-2238 (H-D-Phe-Pip-Arg-pNA 2HCl) for thrombin and S-2765 (N-alpha-Z-D-Arg-Gly-Arg-pNA 2HCl) for factor Xa were also investigated. Activated partial clotting times were all prolonged, suggesting the anticoagulation nature of the purified component and crude venom. Prolongation of fibrinogen clotting time (FCT) is highly suggestive of the antithrombin property of the purified component and its original venom.

Gastrointestinal Absorption of Recombinant Hirudin-2 in Rats

To investigate the absorption of recombinant hirudin-2 (rHV2) after oral administration to rats and its possible absorption mechanism, a series of experiments were carried out. The degradation of (125)I-rHV2 in the luminal contents and variant mucosal subcellular fractions, as well as the effect of degradation inhibition of some adjuvant was investigated. The bioavailability of rHV2, with or without degradation inhibitor after oral administration to rats was estimated, whereas the in situ loop test and everted sac experiment were also conducted to understand more about the gastrointestinal absorption of rHV2 in rats. It was demonstrated that the rHV2 was not stable in the luminal contents and subfraction of the intestinal mucosa. Some enzyme inhibitor, such as bacitracin or casein, could inhibit the degradation to certain degrees. The intact rHV2 molecules were found in the rat plasma after oral administration, and the bioavailability varies obviously, dependent on the analytical method. Some of the enzyme inhibitor could enhance the rHV2 oral absorption. There is no site difference on rHV2 absorption in different segments of small intestine. The possible transport mechanism of rHV2 across the gastrointestinal tract is concerned with the endocytosis process.

Finding of an isoleucine derivative of a recombinant protein for pharmaceutical use

Protein modification generally occurs by addition to the amino acid side-chains of protein at the post-translational stage, for example, by enzymatic or chemical reactions after polypeptide synthesis. Recently, the recombinant hirudin analog CX-397, a potent thrombin inhibitor, was found to contain methylated Ile residues when it was overproduced by Escherichia coli in the absence of amino acids in the culture medium. The Ile derivatives, deduced to be beta-methylnorleucine [betaMeNle; (2S, 3S)-2-amino-3-methylhexanoic acid] by systematic chromatographic analysis, do not appear to be normal post-translational modifications of the protein because Ile has no functional group in its side-chain. We, therefore, propose that betaMeNle is biosynthesized by E. coli, activated by E. coli isoleucyl-tRNA synthetase (IleRS), then incorporated into the overproduced recombinant hirudin analog. The biosynthesis of betaMeNle in E. coli is thought to occur as follows: alpha-ketovalerate is synthesized from alpha-ketobutyrate by three Leu biosynthetic enzymes, alpha-isopropylmalate synthase (IPMS) (EC 4.1.3.12), alpha-isopropylmalate isomerase (ISOM) (EC 4.2.1.33) and beta-isopropylmalate dehydrogenase (IPMD) (EC 1.1.1.85), which have broad substrate specificities. alpha-Ketovalerate is then converted to alpha-keto-beta-methylcaproate by three Ile and Val biosynthetic enzymes, acetohydroxy acid synthase (AS) (EC 4.1.3.18), acetohydroxy acid isomeroreductase (IR) (EC 1.1.1.86) and dihydroxy acid dehydratase (DH) (EC 4.2.1.9). Finally, this is converted to betaMeNle by branched-chain amino acid transaminase (EC 2.6.1.42), one of the Ile and Val biosynthetic enzymes.

Evaluation of unfractionated heparin and recombinant hirudin on survival in a sustained ovine endotoxin shock model

OBJECTIVE

To compare and evaluate the potential benefit of two different anticoagulation regimens during endotoxemia in an ovine model.

DESIGN

Animal prospective randomized and controlled study following preliminary dose-range study conforming with the Guide for the Care and Use of Laboratory Animals as promulgated by the Council of the American Physiologic Society and reviewed by the Ethical Committee for Animal Research of our institution.

SETTING

Laboratories of anesthesiological investigations and hemostasis, primary care university medical center.

SUBJECTS

Twenty-two adult sheep of either sex, weighing 29-42 kg (mean 35.8 kg), surgically instrumented for chronic studies and randomly allocated to receive three different treatment groups: unfractionated heparin (40 units.kg.hr; n = 7), recombinant hirudin (500 units.kg.hr; n = 7), or saline (nonanticoagulated controls; n = 8).

INTERVENTIONS

Ovine model of severe endotoxin shock induced by a continuous intravenous endotoxin infusion over 72 hrs (10 ng.kg.min ).

MEASUREMENTS AND MAIN RESULTS

Endotoxin infusion alone produced a progressive hypotensive, hyperdynamic shock state with right ventricle failure leading to the death of all animals of the control group within 44 hrs (median, 12 hrs). Heparin profoundly improved survival rate in this model, whereas effective anticoagulation with hirudin did not significantly increase the survival rate compared with controls. Animals in the control group died from disseminated intravascular coagulation, metabolic acidosis, and hemorrhagic pulmonary edema, whereas sheep treated with hirudin died from severe pulmonary edema (hypoxemia, increased alveoloarterial oxygen gradient associated with an increased wet/dry lung weight ratio) in the absence of disseminated intravascular coagulation.

CONCLUSIONS

We conclude that systemic anticoagulation with the thrombin inhibitor hirudin is without benefit in this sheep model of lethal endotoxemia, whereas anticoagulation with heparin affords not only effective prevention of endotoxin-induced coagulation disorders but also global protection with prevention of respiratory decompensation and thus markedly improves survival rate in this situation.

Efficient expression and secretion of recombinant hirudin III in E. coli using the L-asparaginase II signal sequence

One of the hirudin variants HV3 was efficiently expressed in Escherichia coli using the L-asparaginase II signal sequence and the product was secreted into the culture medium. For the secretory manufacture of HV3, the L-asparaginase II signal sequence containing a single NheI restriction site at its 3' end was designed using the degenerate codons and PCR-amplified from E. coli chromosomal DNA. The synthetic HV3 coding sequence was fused to the signal sequence in-frame by its 5' NheI restriction site. The above signal-HV3 fusion gene was inserted into an expression vector pTA, which was derived from pkk223-3 such that its expression was under the control of the tac promotor. The resulting HV3 secretion expression vector pTASH thus constructed was introduced into an E. coli host cell AS1.357 with high L-asparaginase II producing level. After inducing with IPTG, the expression product was efficiently secreted into the culture medium and shake-flask culturing gave a yield of approximately 5 x 10(5)ATU/L (approximately 60mg/L). The secreted HV3 was easily purified from culture supernatant using ultrafiltration, ion-exchange column chromatography, and FPLC reverse-phase chromatography. The purified rHV3 from the culture supernatant had the expected N-terminal amino sequence and strong antithrombin activity, suggesting that the signal sequence was completely removed and the product was processed accurately during the secretion process.

Construction and characterization of trifunctional single-chain urokinase-type plasminogen activators

Two chimeric proteins have been constructed. One consists of four parts: a portion of the low molecular mass single-chain urokinase-type plasminogen activator (scu-PA-32K, residues 144-411), a 15-mer linker sequence, the C-terminal amino-acid sequence (residues 53-65) of hirudin (Hir), and an RGD sequence derived from the leech protein decorsin, i.e. scu-PA(32 k)-linker-Hir (residues 53-65)-RGD peptide. The other comprises two main segments: scu-PA(32 k) and hirudin into which RGDSP is inserted between its residues 33 and 34, i.e. hirudin (residues 1-33)-RGDSP-hirudin (residues 34-65)-scu-PA(32 k). These two chimeric genes were expressed in Escherichia coli, and the products were purified by Zn2+-chelating Sepharose 4B chromatography and benzamidine Sepharose 6B chromatography. Our results suggested that these two chimeric proteins not only had plasminogen-dependent fibrinolytic activity, but also possessed platelet aggregation inhibitory activity and antithrombin activity.

Biochemical evidence of specific trypsin-chymotrypsin inhibitors in the rhynchobdellid leech, Theromyzon tessulatum

The presence of two specific trypsin-chymotrypsin inhibitors from head parts of the rhynchobdellid leech Theromyzon tessulatum is reported. Two proteins, anti-trypsin chymotrypsin A (ATCA; 14636.6 +/- 131 Da) and anti-trypsin-chymotrypsin B (ATCB; 14368 +/- 95 Da) were purified by size exclusion and anion-exchange chromatography followed by reversed-phase HPLC. Based on amino-acid composition, N-terminal sequence determination (MELCELGQSCSRD-NPQPSNM), matrix assisted laser desorption-time of flight measurement (MALDI-TOF), trypsin mapping comparison, inhibition constant determination (Ki), and influence on amidolytic activity of different serine proteases, it is demonstrated that ATCA and ATCB are novel and highly potent serine-protease inhibitors of trypsin and chymotrypsin (ATCA: 350fM towards trypsin and chymotrypsin; ATCB: 400 and 75 fM towards trypsin and chymotrypsin, respectively). It is further surmised that ATCA and ATCB are linked, in that ATCB would lead to the formation of ATCA after loss of few amino acid residues.

Boophilus microplus anticoagulant protein: an antithrombin inhibitor isolated from the cattle tick saliva

An anticoagulant was isolated from saliva of the cattle tick Boophilus microplus. Crude saliva prolonged both recalcification time and prothrombin time in assays with bovine plasma. It also inhibited thrombin, but not fXa, amidolytic activity. We purified the antithrombin activity by a combination of gel filtration, anion exchange, and affinity chromatography. The purified inhibitor has a molecular weight of 60,000 Da, determined by SDS-PAGE. The anticoagulant IC50 varied from 100 nM to 1.1 microM, depending on the thrombin concentration and substrate used (fibrinogen or platelet receptor). The excess of inhibitor in relation to thrombin indicates that it is not a tight-binding inhibitor. Chromogenic assays using a panel of five serine-proteinases suggest that the inhibitor is specific against thrombin.

Inhibition of arterial thrombosis by a peptide ligand of the thrombin receptor

Thrombin plays an important role in promoting arterial thrombosis by platelet activation and by catalyzing fibrin formation. Use of thrombin inhibitors that block both the platelet-activating and fibrin formation properties of thrombin are associated with hemostasis. This problem might be overcome by developing agents that block only the platelet-activating property of thrombin. Because the platelet-activating property of thrombin is mediated by the thrombin receptor, antagonists of the thrombin receptor might be efficacious and potentially safer with regard to bleeding complications. We investigated whether a peptide ligand (AFLARAA) of the thrombin receptor that blocked alpha-thrombin and thrombin receptor activating peptide-induced platelet aggregation could inhibit thrombosis. A partially occlusive thrombus was generated by application of electric current in rabbit carotid artery. In control animals, the artery was completely occluded within 42+/-12 min after the current was discontinued. When the thrombin receptor activating peptide antagonist was given (100 micromol/kg as an IV bolus followed by 900 micromol/kg infusion for a period of 180 min) starting at the time the current was stopped, blood flow remained patent throughout the infusion period and for an additional 60 min after the infusion was stopped. The antithrombotic effect of the antagonist peptide was not associated with increased bleeding tendency, as judged by the amount of blood adsorbed by a gauze pad placed in a surgical incision extending to the muscle tissue and by a standard template bleeding time. These results indicate that thrombin receptor antagonist peptides can be used as antithrombotic agents.

Incorporation of an Asp-Ser sequence to form an RGDS-like motif in hirutonin: the effect on in vitro platelet function

We investigated the effect on in vitro platelet function of hirutonin, a modified hirutonin with an RGD-like motif, a pseudo-RGDS peptide and a linear RGDS peptide. Inhibition of expression of surface fibrinogen on ADP-activated platelets with 40 microM of the peptide was as follows: hirutonin 10+/-3%, modified chimeric peptide 26+/-5%, pseudo-RGDS 66+/-11% and linear RGDS 93+/-13%. Both hirutonin and the chimeric peptide significantly inhibited ADP-induced platelet activation as detected by CD62 expression. Unlike the RGDS and pseudo-RGDS controls, neither the chimeric peptide nor the parent hirutonin inhibited ADP-induced platelet aggregation even at 140 microM. The chimeric hirutonin peptide reduced ATP release from ADP-stimulated platelets by 40+/-4%. This inhibition was stronger than that caused by hirutonin (23+/-13%), but less than the RGDS (90+/-2%) and pseudo RGDS-peptides (59+/-11%). Primary platelet haemostasis was slightly but not significantly affected by the peptide at 40 and 80 microM. However, shear-induced platelet adhesion to vWF and especially subsequent aggregate formation was interrupted after the addition of the chimeric peptide. Similar results were obtained with hirutonin. This inhibition was not as marked as with the RGDS- and pseudo-RGDS peptides. Both the parent hirutonin and the chimeric peptide caused prolongation of the clinical coagulation assays aPTT and TT. In conclusion, the chimeric hirutonin peptide with introduction of the RGD motif retained its anticoagulant effect but had little formal disintegrin activity. Instead, it appeared to have novel anti-platelet effects that may be of therapeutic use.

New bivalent thrombin inhibitors with N(alpha)(methyl)arginine at the P1-position

A series of bivalent thrombin inhibitors was synthesized, consisting of a d-phenylalanyl-prolyl-N(alpha)(methyl)arginyl active site blocking segment, a fibrinogen recognition exosite inhibitor part, and a peptidic linker connecting these fragments. The methylation of the P1 amino acid led to a moderate decrease in affinity compared with the unmethylated analog. In addition, it prevented the thrombin catalyzed proteolysis, independent of the P1' amino acid used. This is a significant advantage compared to the original hirulogs, which strictly require a proline as P1' amino acid to reduce the cleavage C-terminal to the arginyl residue. Several analogs were prepared by incorporation of different P1' amino acids found in natural thrombin substrates. The most potent inhibitor was I-11 [dCha-Pro-N(Me)Arg-Thr-(Gly)5-DYEPIPEEA-Cha-dGlu] with a Ki of 37 pM. I-11 is highly selective and no inhibition of the related serine proteases trypsin, factor Xa and plasmin was observed. The stability of I-11 in human plasma in vitro was strongly improved compared to hirulog-1. In addition, a significantly reduced plasma clearance of I-11 was observed after intravenous injection in rats. Results from molecular modeling suggest that a strong reorganization of the hydrogen bonds in the active site of thrombin may result in the proteolytic stability found in this inhibitor series.