Indirect active-site titration of plasminogen activators

A method for the determination of the molar concentration of active tissue plasminogen activator (TPA) and urokinase (UK) has been developed. The method employs the principle of back-titration of a calibrated trypsin standard with a calibrated standard solution of a chloromethyl ketone inhibitor reactive with both trypsin and activator. Both trypsin and chloromethyl ketone standards are calibrated using a guanidinobenzoyl ester active-site titrant. Less than 20 ng of activator can be accurately determined by this method. The method is used to assay commercial samples of TPA and UK, to calculate the specific activity of such samples, and to determine kinetic constants of plasma activator inhibitor.     

Fibrinolysis standards: A review of the current status

Biological standards are used to calibrate measurements of components of the fibrinolytic system, either for assigning potency values to therapeutic products, or to determine levels in human plasma as an indicator of thrombotic risk. Traditionally WHO International Standards are calibrated in International Units based on consensus values from collaborative studies. The International Unit is defined by the response activity of a given amount of the standard in a bioassay, independent of the method used. Assay validity is based on the assumption that both standard and test preparation contain the same analyte, and the response in an assay is a true function of this analyte. This principle is reflected in the diversity of source materials used to prepare fibrinolysis standards, which has depended on the contemporary preparations they were employed to measure. With advancing recombinant technology, and improved analytical techniques, a reference system based on reference materials and associated reference methods has been recommended for future fibrinolysis standards. Careful consideration and scientific judgement must however be applied when deciding on an approach to develop a new standard, with decisions based on the suitability of a standard to serve its purpose, and not just to satisfy a metrological ideal.     

Fibrin-binding urokinase (or precursor form of urokinase) with a molecular weight of about 100,000 in fresh human urine

Fresh human urine was found to contain at least three different molecular forms of fibrin-binding urokinase (UK) or its precursor, all of which were absorbed on a fibrin/Celite column at neutral pH, and could be eluted with 0.3-1.0 mol/l NaCl in phosphate buffer, followed by 0.2 mol/l, Arg, 2 mol/l KSCN, and 2 mol/l urea, respectively. The main molecular form isolated revealed a molecular weight (MW) of approximately 100,000 (UK-100), and the minor ones were estimated to have MW of 150,000-200,000 and 45,000. In contrast, commercially obtained UK preparations contained mostly active enzymes with MW of 53,000 and 32,000, respectively, and the remaining high molecular forms represented less than 2.0% of the total amount. Rabbit monospecific antibody (IgG) against UK subcomponent (active heavy chain; H-chain UK) reacted and inhibited the fibrinolytic activity of all the active UK molecules. The UK-100 isolated was relatively stable in solution at neutral pH and resistant to mild reduction, without molecular change. Although the preparation had a very low specific activity (ca. 300 IU/mg protein), both the pyro-Glu-Gly-Arg-pNA amidolytic and plasminogen activating activities could be partially enhanced by the addition of trace amounts of plasmin. In this process, the appearance of two additional active enzymes of MW 53,000 and 32,000 was also confirmed by zymography.     

Plasma fibrinolysis after intraduodenal administration of urokinase in rats

Plasma fibrinolysis in rats rose above the level of physiological fluctuations in a curve with two peaks at 1 and 6 h, following intraduodenal administration of high-molecular-weight urokinase (HMW-UK; MW 53,000; 124,000 IU/mg protein). Activation of plasma fibrinolysis was also confirmed with insolubilized enzyme (glass-coupled UK), but lacked the first activity peak. Plasma fibrinolytic enzyme isolated by affinity chromatography revealed strong fibrinolytic (1,120 IU/dl), pyro-Glu-Gly-Arg-pNA amidolytic (3,200 nmol/dl) and Glu-plasminogen activating (24.5 IU/dl) activities. Using specific UK antibody, it appeared that the first peak originated from the administered UK, while the second one derived from endogenous plasminogen activator. Dose response of UK was not observed, and the maximal effect was at about 5,000 IU/kg body weight.     

Calibration and commutability assessment of the 1st International Standard for Diphtheria Antitoxin Human

The 1st International Standard for Diphtheria Antitoxin Human (coded 10/262) was established by the World Health Organization Expert Committee on Biological Standardization in 2012. This paper describes the production, characterization and calibration of the new standard which is intended for use in the standardization of assays used to measure diphtheria antibody responses in human serum. The new standard was calibrated in terms of the International Standard for Diphtheria Antitoxin Equine in an international collaborative study. A total of 8 participants from 8 different countries performed in vivo and/or in vitro toxin neutralization tests and returned data that was used to assign units to the proposed new standard. The new standard has a diphtheria antitoxin potency of 2 IU/ampoule and is predicted to be stable. A follow up study was performed to assess commutability of the new standard. The follow up study was an existing external quality assessment, modified to include the new standard. Results obtained suggest that the new standard is commutable, showing comparable behaviour to native human serum samples in the majority of the assays compared, and is therefore suitable for use as a reference preparation in assays used to measure the level of anti-diphtheria antibodies in human serum.     

一种新型海洋纤溶酶的分离纯化与性质鉴定(英文)

单环刺螠生活在近海泥沙地区的潮间带和低潮带,自1940年分类后曾归属于螠虫动物门,但是现在越来越认为它是多毛纲环节动物的一个分支。系统研究表明,单环刺螠的体腔液和内脏中含有高活性的溶栓物质,并从这两种组织中通过离心、过滤、硫酸铵盐析、超滤、Q.Sepharose Fast Flow、Sephadex G-75、Sephacry S-100等步骤分离到了一种纤溶酶UFE,SDS-PAGE聚丙烯酰胺凝胶电泳测得分子量为10.38kDa.利用尿激酶和PBS作对照的功能研究表明,UFE主要是直接降解纤维蛋白,但也表现部分激酶活性,这跟来自环节动物蚯蚓的蚓激酶一样,靠将纤维蛋白溶酶原转化为纤维蛋白溶酶降解纤维蛋白。研究表明,UFE是一种免疫原性小、纤溶能力强的具有潜在应用价值的溶栓剂。     

Purification and characterization of a novel low molecular weight form of single-chain urokinase-type plasminogen activator

A low Mr form (Mr 32,000) of single-chain urokinase-type plasminogen activator (scu-PA) was isolated from conditioned culture medium of a human lung adenocarcinoma cell line, CALU-3 (ATCC, HTB-55). The purified material (scu-PA-32k) consists of a single polypeptide chain and is immunologically similar to Mr 33,000 urokinase. Its NH2-terminal sequence is identical to that beginning at Leu-144 of Mr 54,000 urokinase. Whereas low Mr urokinase is derived from mature Mr 54,000 scu-PA by limited hydrolysis by plasmin first of the Lys-158-Ile-159 peptide bond and then of the Lys-136-Lys-137, scu-PA-32k is generated by specific hydrolysis of the Glu-143-Leu-144 peptide bond by an unidentified protease. scu-PA-32k resembles its Mr 54,000 scu-PA counterpart by its very low activity on chromogenic substrates for urokinase, by plasminogen-dependent fibrinolytic activity on fibrin plates, and by the lack of specific binding to fibrin. It activates plasminogen directly with high affinity, Km = 0.9 microM, but low turnover number, kcat = 0.0028 s-1. It is converted to fully active two-chain urokinase by plasmin with Km = 12 microM and kcat = 0.3 s-1. Like Mr 54,000 scu-PA, it causes significant lysis of a 125I-labeled fibrin clot in human plasma with relatively less fibrinogen breakdown as compared to urokinase. scu-PA-32k, which also has conserved fibrin specificity, represents a molecular variant which may be more suitable for large scale production as a fibrin-specific thrombolytic agent by recombinant DNA technology.     

血纤蛋白粘附肽与低分子量单链尿激酶融合产物活性分析

人工合成了血纤蛋白粘附肽基因,构建了粘附肽与低分子量单链尿激酶ｃＤＮＡ的融合基因,在大肠杆菌中表达了融合基因。融合基因表达产物的抗原性和天然尿激酶相同,并具有尿激酶的溶纤活性和粘附肽的抗纤维蛋白单体聚合的功能。     

Antibody-directed fibrinolysis: a bispecific (Fab')2 that binds to fibrin and tissue plasminogen activator

A bispecific (Fab')2 molecule was constructed by linking the monovalent Fab' from an anti-fibrin monoclonal antibody to the Fab' from an anti tissue plasminogen activator (tPA, single chain) monoclonal antibody by means of inter-heavy-chain disulfide bonds. An immunochemical complex composed of the bispecific (Fab')2 molecule bound to tPA [tPA-bispecific (Fab')2 complex] was then generated and purified. Its molecular weight was 170 kDa [less than half the molecular weight of a previously described tPA-bispecific antibody complex containing the entire anti-fibrin and anti-tPA immunoglobulin molecules; Runge, M. S., et al. (1987) Trans. Assoc. Am. Phys. 100, 250-255]. The tPA-bispecific (Fab')2 complex was 8.6-fold more efficient in fibrinolysis than tPA alone and 94-fold more potent than urokinase. This enhancement in the fibrinolytic potency of tPA compares favorably with that observed for the bispecific whole-antibody complex. These results suggest that this smaller, less immunogenic molecule is capable of binding both fibrin and tPA with high affinity and of enhancing the thrombolytic efficiency of exogenous and, perhaps, endogenous tPA.     

Characterization of plasminogen activator produced by an established cell line from human ovary

An established cell line (OC-1) was obtained from human ovarian tissue, which yielded a high concentration of plasminogen activator (PA) in the culture medium. The PA (OC-1-PA) produced by the cell line was purified and compared with urokinase (UK), proform of UK (pro-UK), and tissue-type PA (t-PA) purified from human melanoma cells (Bowes). OC-1-PA was purified by Zn chelate-Sepharose affinity chromatography followed by high-performance liquid chromatography with a Zn chelate-5PW column and with a p-amino-benzamidine-5PW column, giving a yield of 58.3% and a purification factor of 15,439. This purified material revealed a single band of Mr 55,000 on sodium dodecylsulfate polyacrylamide gel electrophoresis in the presence or absence of reducing agents. Electrophoretic enzymography demonstrated that the Mr 55,000 protein band had a plasminogen-dependent fibrinolytic activity. Treatment with plasmin did not change the Mr even in the presence of reducing agents. These results suggest that OC-1-PA has a single-chain structure protected from protease degradation, which is completely different from UK. The activator had higher affinities for lysine and fibrin than those of UK or pro-UK. An immunological study demonstrated that OC-1-PA cross-reacted with anti-UK IgG but not with anti-t-PA IgG. All these findings indicate that OC-1-PA belongs immunologically to the UK type, but its structure differs from that of UK.     

Biochemical and thrombolytic properties of a low molecular weight form (comprising Leu144 through Leu411) of recombinant single-chain urokinase-type plasminogen activator

The cDNA encoding a low Mr derivative (residues 144-411) of human single-chain urokinase-type plasminogen activator was cloned, the recombinant low Mr single-chain urokinase-type plasminogen activator (rscu-PA-32k) was expressed in Chinese hamster ovary cells, and the translation product was purified to homogeneity from conditioned cell culture medium. rscu-PA-32k is very similar to intact recombinant single-chain urokinase-type plasminogen activator in terms of its very low activity (120 IU/mg) on a chromogenic substrate for urokinase (pyroglutamylglycylarginine p-nitroanilide), its plasminogen-dependent fibrinolytic activity on fibrin plates (specific activity = 170,000 IU/mg), its plasminogen activating potential, and the lack of specific binding to fibrin. In a rabbit jugular vein thrombosis model, comparable thrombolysis was obtained with rscu-PA-32k as compared to low molecular weight two-chain urokinase (50% lysis at 2.1 and 1.6 mg/kg infused over 4 h). Thrombolysis was associated with much less extensive systemic fibrinogen breakdown with rscu-PA-32k than with two-chain urokinase (residual fibrinogen at 50% lysis of 71 and 10%, respectively). It is concluded that the functional properties of rscu-PA-32k, expressed with a high efficiency, are similar to those of its previously characterized natural counterpart.     

《中国药典》重组人干扰素注射剂质量标准浅析

本文剖析了现行版《中国药典》收载的重组人干扰素注射剂质量标准相关方法、检测限度和历史沿革;对比研究了与国外先进药典如欧洲药典的差距,包括相关物质、相关杂质分析、生物学活性测定结果的统计分析、比活性等方面;介绍了2015年版《中国药典》拟增修订主要内容,如增订报告基因法检测干扰素生物学活性、增订定量PCR法检测外源DNA残留量,加强"理化对照品"的管理,相关检定机构对国内生产企业的理化对照品进行了标定。本文还探讨了提高该类制品质量标准的主要方向。     

Measurement of human urokinase activity in plasma by using mono-specific antibody-conjugated paper disk

Human urokinase (HUK) was purified from commercial product by high performance liquid chromatography on TSK GEL-G3000SW and affinity chromatography on benzamidine-Sepharose 4B. The purified enzyme was of a high molecular weight form (molecular weight of 53,000). This preparation was utilized as an antigen to immunize rabbits; the obtained antibody showed a high specificity against HUK. The antibody was conjugated to CNBr-activated paper disks. The antibody-conjugated paper disk and a fluorogenic peptide substrate, glutaryl-Gly-Arg-4-methyl-coumarine-7-amide, were used to measure urokinase (UK) activity in plasma. The calibration curve obtained by the proposed method passed through the origin and was linear in the range of 0-0.16 IU of HUK. The incubation of HUK with an excess amount of alpha 2-macroglobulin at 37 degrees C for 3 h gave only about a 30% decrease of the activity assayed by the proposed method. After incubations of HUK with alpha 1-antitrypsin and antithrombin III, the activity was completely inhibited. The incubation of HUK with plasma at 37 degrees C decreased the activity as a function of time. However, when the antibody-conjugated paper disk was used for the immunoreaction to HUK in plasma at 4 degrees C, no decrease of UK activity was observed. The plasma decay curve of UK activity after a single intravenous (i.v.) injection of HUK into a rabbit (12,000 IU/kg) indicated bi-exponential kinetics by using this assay method. The rate constants of the alpha and beta phases were 0.120 +/- 0.020 and 0.021 +/- 0.002 min-1, respectively. These result suggest that the proposed method is useful for measuring UK activity in plasma of patients with intravascular coagulation after i.v. administration of UK.     

Synthesis and evaluation of tripeptidic plasmin inhibitors with nitrile as warhead

Plasmin is best known as the key molecule in the fibrinolytic system, which is critical for clot lysis and can initiate matrix metalloproteinase (MMP) activation cascade. Along with MMP, plasmin is suggested to be involved in physiological processes that are linked to the risk of carcinoma formation. Plasmin inhibitors could be perceived as a promising new principle in the treatment of diseases triggered by plasmin. On the basis of the peptidic sequence derived from the synthetic plasmin substrate, a series of peptidic plasmin inhibitors possessing nitrile as warhead were prepared and evaluated for their inhibitory activities against plasmin and other serine proteases, plasma kallikrein and urokinase. The most potent peptidic inhibitors with the nitrile warhead exhibit the potency toward plasmin (IC₅₀ = 7.7–11 μM) and are characterized by their selectivity profile against plasma kallikrein and urokinase. The results and molecular modeling of the peptidic inhibitor complexed with plasmin reveal that the P2 residue makes favorable contacts with the open binding pocket comprising the S2 and S3 subsites of plasmin. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Islet surface modification with urokinase through DNA hybridization

Transplantation of islets of Langerhans (islets) has been proposed as a safe, effective approach to treating patients with insulin-dependent diabetes mellitus (type I diabetes). It has been reported, however, that many islets are lost in the early phase after intraportal transplantation by instant blood coagulation-mediated inflammatory reactions. In this study, DNA hybridization was applied to conjugate the fibrinolytic enzyme urokinase on the islet surface. We synthesized amphiphilic polymers, PEG-lipids carrying oligo(dT)(20) (oligo(dT)(20)-PEG-lipid; PEG MW = 5000) and urokinase (UK) carrying oligo(dA)(20). The oligo(dT)(20)-PEG-lipid was spontaneously incorporated into the cell membrane through interactions between the hydrophobic parts of the PEG-lipids and the lipid bilayer, and UK was conjugated on the cell surface through DNA hybridization between oligo(dT)(20) on the cell and complementary oligo(dA)(20) on the UK. The activity of UK was maintained on the islet surface. The surface modification with UK did not influence islet morphology or islet ability to secrete insulin in response to changes in glucose concentration. No practical volume increase was observed with our method, indicating that islet graft loss could be suppressed at the early stage of intraportal islet transplantation.     

Isolation and characterization of plasminogen activators from hyperplastic and malignant prostate tissue

Plasminogen activators from prostate tissue were purified to apparent homogeneity by a procedure involving reverse ammonium sulfate gradient solubilization, chromatography on gelatine-Sepharose, gel filtration on Sephadex G-150, and chromatography on Con A-Sepharose as a final step. Two activators were obtained. The predominant one exhibited physicochemical, immunochemical and functional properties indistinguishable from human urinary high molecular weight urokinase. The other one, which amounted to about 20% was immunochemically related to tissue type plasminogen activator and its plasminogen activator activity was enhanced by addition of CNBr-fibrinogen fragments in a similar pattern as for the vascular plasminogen activator. The molecular weight, however, and enzymatic activities on the synthetic low molecular weight paranitroanilide substrates pyro-Glu-Gly-Arg-pNA and H-D-Ile-Pro-Arg-pNA were different to vascular plasminogen activator but similar to high molecular weight urinary urokinase.     

The matrix metalloproteinase pump-1 catalyzes formation of low molecular weight (pro)urokinase in cultures of normal human kidney cells.

The enzyme responsible for the metalloproteinase activity which cleaves the Glu143-Leu144 bond of (pro)urokinase has been isolated from the conditioned medium of cultured normal human kidney cells. Using S-Sepharose and Cibacron Blue-agarose chromatography, then C-4 reversed phase high pressure liquid chromatography, a protein of about 20,000 Da was isolated. Through an identical amino-terminal sequence, the protein was shown to be the matrix metalloproteinase previously referred to in the literature as "pump-1" (putative metalloproteinase). When aprotinin was added during the course of the purification, the major species isolated was the zymogen form (28,000 Da) of pump-1. Pump-1 has been shown to efficiently cleave the susceptible bond of both pro-urokinase (single-chain) and active (two-chain) urokinase and thereby produce the corresponding low molecular weight forms. The amino-terminal sequences of the A and B chains of low molecular weight urokinase prepared by action of pump-1 on recombinant high molecular weight urokinase are identical to those of the low molecular weight urokinase isolated from human kidney cell culture. Since the reaction of urokinase with this metalloproteinase results in separation of its serine proteinase region from the domain which mediates binding to the urokinase receptor, it may be of importance in the regulation of the functional activity of the plasminogen activator in cellular processes.     

Conformation of one- and two-chain high molecular weight urokinase analyzed by small-angle neutron scattering and vacuum ultraviolet circular dichroism

The structures of one- and two-chain high molecular weight human urokinase were analyzed by small-angle neutron scattering and vacuum ultraviolet circular dichroism. Both one- and two-chain high molecular weight urokinases exhibited a radius of gyration of 31 A and a maximum dimension of 90 A. Neither parameter was affected by the presence of lysine sufficient to saturate all the lysine-binding sites in human plasminogen. These physical parameters are consistent with the sedimentation coefficient of high molecular weight urokinase and indicate that both proteins are highly asymmetric. Neither protein contained much alpha-helix or parallel beta-sheet. Most of the secondary structure was in the form of antiparallel beta-sheet and beta-turns, very similar to the secondary structure of plasminogen. The macroscopic kinetic constants, Km and kcat, for the hydrolysis of (pyroGlu-Gly-Arg-NH)2-rhodamine by two-chain high molecular weight urokinase and low molecular weight urokinase which lacks the epidermal growth factor and kringle domains were similar. These structural and kinetic data are consistent with the domains in both forms of urokinase being independent structural and functional units.     

Interaction of urokinase A chain with the receptor of human keratinocytes stimulates release of urokinase-like plasminogen activator

On the basis of a fibrinolytic assay with 125I-fibrin, zymography, and immunoprobing with anti-human urokinase antibody, we have observed that the in vitro established NCTC human keratinocyte cell line releases into the culture medium a 54,000-Da plasminogen activator which is indistinguishable from human urokinase. Only the early release following the washing of keratinocyte monolayers is accounted for by secretion of preformed enzyme, while late secretory events require the de novo synthesis of urokinase. The released enzyme can interact by autocriny with its own receptor present on keratinocytes. The addition to the keratinocyte culture medium of the urokinase A chain can stimulate a concentration-dependent urokinase oversecretion, which is not paralleled by oversecretion of plasminogen activator inhibitor-1. Since stimulation of urokinase production can be obtained by an A chain concentration (5 ng/ml) which was previously shown to be efficient in inducing keratinocyte mobilization in an in vitro migration model system, we hypothesize that this mechanism may be important in vivo during the process of wound repair.     

Fish plasminogen activators: their identification and characterization

Immunoblots of proteins extracted from the skin of a small viviparous fish (Xiphophorus) showed that a monoclonal antibody against human urokinase recognizes multiple molecular weight species of antigens. The immunoaffinity-purified antigens had serine-protease activity for the hydrolysis of a chromogenic substrate and could convert human plasminogen to plasmin in a manner similar to that for human urokinase in vitro. Two antigens with apparent molecular weights of 55 and 50 kilodaltons that had been purified on a fibrin-Celite column were separable on SDS-polyacrylamide gels and were characterized as major plasminogen activators on fibrin-agar indicator plates. The 125I-tryptic peptide maps of both antigens were similar to that of human urokinase; therefore, the fish activators and human urokinase are structurally and functionally related.