Thrombin-binding substance and process for its preparation

Abstract: Thrombin-binding substances are obtained by fractionating human urine by ion-exchange chromatography, affinity chromatagraphy using a thrombin-bound carrier, immune adsorption column chromatography, gel filtration, and/or molecu­ lar-weight fractionation. One of the substances has a molecular weight of 46,500 ± 6,000 in reduced condition and 39,000 ± 10,000 in unreduced condition by SDS PAGE and an isoelectric point at pH 5,0-5,3, while the other has a molecular weight of 40,000 ± 8,000 in reduced condition and 31,000 ± 10,000 in unreduced condition by SDS PAGE and an isoelectric point at pH 4,9-5,7. They have strong affinity to thrombin. They are capable of promoting the thrombin catalyzed activation of protein C and prolong clotting time. They are stable to denaturing agents (urea and sodium dodecylsulfate).

Description: BACKGROUND OF THE INVENTION i) Field of the Invention: The present invention relates to a novel thrombin-binding substance, more particularly to a thrombin-binding substance useful as a medicine especially as a remedy for thrombosis and the like owing to its effects to the anticoagulation and fibrinolytic systems which control the coagulation of blood, and to a process for its preparation. ii) Description of the Prior Art: A great deal of work has been done regarding the role that thrombin plays as a proteolytic enzyme in the control mechanism of blood coagulation and the mechanism of the coagulation system has been elucidated for the most part. N.L. Esmon et al. have recently reported that thrombin activates in the organism Protein C which is said to act on the fibrinolytic and anticoagulant systems. They also reported the existence of a certain substance in extracts of rabbit lung tissue functioning as a coenzyme for the activation mechanism, and named it thrombomodulin [J.Biological Chemistry, 257(2) 859-864 (1982)]. Aoki, one of the present inventors, and others also reported human thrombomodulin separated from human placenta. The substance had similar properties to those reported by N.L. Esmon et al., with a molecular weight of about 71,000 in an unreduced condition [Thromb. Res. 37 , 353-364 (1985)]. Furthermore, I. Maruyama et al. reported that they compared the activities of human thrombomodulin separated from human placentae and having a molecular weight of about 75,000 with those of the above rabbit thrombomodulin and they had identical activities [J. Clin, Invest. 75 , 987-991, (March 1985)]. It has also been reported recently by H. Ishii et al. that human plasma and urine contain substances having the same activities as thrombomodulin and the molecular weights of such substances in plasma are about 63,000 and 54,000 [J. Clin. Invest. 76 , 2178-2181 (Dec. 1985)]. Earlier EP-A-0 230 945 describes a substance identified hereinafter as thrombin-binding substance A. SUMMARY OF THE INVENTION The present inventors have been working extensively with a view toward developing an advantageous method for isolating and purifying the above human thrombomodulin. In the course of the research, a novel type of thrombin-binding substance different from the above substance A and from human thrombomodulin has been found and separated from human urine. It has been found that this thrombin-binding substance is similar to the above substance A and that it is a novel compound having lower molecular weight compared with the human thrombomodulin, leading to completion of this invention. An object of this invention is therefore to provide a novel human thrombin-binding substance and a process for the preparation thereof. As a solution to this problem there is provided a process for preparing a thrombin-binding substance having the following characteristics: (a) molecular weight: 40,000 ± 8,000 in reduced condition by SDS PAGE 31,000 ± 10,000 in unreduced condition by SDS PAGE (b) isoelectric point: pH 4.9 - 5.7 (c) affinity: strong affinity to thrombin (d) activity: (1) capable of promoting the thrombin catalyzed activation of protein C (2) prolongs clotting time; and (e) stability: stable to denaturing agents (urea and sodium dodecylsulfate), which comprises fractionating human urine by ion-exchange chromatography, affinity chromatography using a thrombin-bound carrier, immune adsorption column chromatography, gel filtration, and/or molecular-weight fractionation. The thrombin-binding substance of this invention is useful as a fibrinolytic accelerator or as an anticoagulant since it binds thrombin and specifically enhances the activation of protein C and prolongs the clotting time. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS According to the present invention, the thrombin-binding substance can be prepared, for example, by fractionating fresh human urine or a human urine concentrate. The fractionation can be effected by suitably combining ion-exchange chromatography, affinity chromatography using a thrombin-bound carrier, immune adsorption column chromatography using a monoclonal antibody, gel filtration, molecular weight fractionation, etc. Among these methods, it is particularly preferred, for example, to conduct (1) ion-exchange chromatography, affinity chromatography, gel filtration and molecular weight fractionation successively or (2) immune adsorption column chromatography and ion-exchange chromatography successively. The method (1) may be practised, for example, in the following manner. Benzamidine hydrochloride, aprotinin or the like is added to fresh urine. The resultant mixture is subjected to ion-exchange chromatography on "DEAE-Sephadex A-50" (trade name, product of Pharmacia AB), "DEAE-TOYOPEARL 650C", "DEAE-TOYOPEARL 650M", "DEAE-TOYOPEARL 650S" (trade names, products of Toyo Soda Mfg. Co., Ltd.), "QAE-Sephadex A-50" (trade name, product of Pharmacia AB), or the like to adsorb active fractions, followed by elution with a Tris-HCl buffer containing sodium chloride and benzamidine hydrochloride. After concentration of the active fraction, the concentrate is caused to pass through a column packed with a thrombin-bound carrier such as diisopropylphosphorothrombin-agarose so as to adsorb the active fraction. The active fraction is thereafter eluted with a Tris-HCl buffer which contains sodium chloride and benzamidine hydrochloride, thereby obtaining the active fraction. The active fraction is concentrated further. Using "Sephadex G 150" (trade name, product of Pharmacia AB), "Ultrogel AcA34" (trade name, product of LKB Company) or the like, the resulting concentrate is subjected to gel filtration so as to collect the active fraction. The substance of the present invention can then be obtained by subjecting the active fraction to molecular weight fractionation by an electrophoretic technique making use of a sodium dodecylsulfate (SDS)-polyacrylamide gel and collecting fractions having the molecular weight of the below-described thrombin-binding substance of this invention, for example, in accordance with the Laemmli's method [see, Nature, 227 680-685, (1970)]. The method (2) may be practised, for example, in the following manner. After dialyzing fresh urine against a buffer having a high salt concentration and approximately neutral pH, active fractions are collected by immune adsorption column chromatography. The active fractions are then subjected to high performance liquid chromatography on an ion-exchange resin, whereby fractions corresponding to the molecular weight of the thrombin-binding substance of this invention are collected to obtain the substance of this invention. As an immunoadsorbent useful for the immune adsorption column chromatography, may be mentioned a monoclonal antibody bound carrier in which a monoclonal antibody for the thrombin-binding substance is bound on an insoluble carrier such as dextran gel, agarose gel or polyvinyl gel. The monoclonal antibody for the thrombin-binding substance may be obtained, for example, by fusing mouse spleen cells, which have been immunized with the above-described thrombin-binding substance extracted from human placentae and having the molecular weight of about 71,000, with mouse myeloma cells P3-Ag8-γ and then treating the resultant hybridomas in a manner known per se in the art. Of monoclonal antibodies available in the above-described manner, it is particularly preferred to use those capable of recognizing sites of the thrombin-binding substance which sites are not affected by calcium. The elution of the thrombin-binding substances from the immune adsorption column can be effected with a buffer containing potassium thiocyanate by way of example. As a column useful in the practice of the high performance liquid chromatography, a column packed with an anion-exchange resin is preferred. "TSK gel DEAE-5PW", "TSK gel DEAE-2SW", "TSK gel DEAE-3SW" (trade names, products of Toyo Soda Mfg. Co., Ltd.), "Mono Q HR5/5" (trade name, product of Pharmacia AB), etc. may be mentioned by way of example. The process of this invention is extremely efficient compared with the conventional placenta extraction process, since the process of this invention uses as a raw material human urine available in a large volume and the intended substance can be isolated and purified after separation of other useful substances such as urokinase. The thus-obtained thrombin-binding substance of this invention is a mixture of two types of substances identified by (A) and (B), which have the following properties respectively: (a) Molecular weight: (A) 46,500 ± 6,000 in reduced condition 39,000 ± 10,000 in unreduced condition (B) 40,000 ± 8,000 in reduced condition 31,000 ± 10,000 in unreduced condition Measuring method: Molecular weights were determined by an electrophoretic technique in accordance with the Laemmli's method (Nature, 227 , 680-685, 1970), which used a 7.5% sodium dodecylsulfate(SDS)-polyacrylamide gel containing 5% urea. "Bio-Rad SDS-PAGE Standard for High-Molecular Substances" (trade name, product of Nippon Bio-Rad Laboratories Inc.) was used as a standard protein. (b) Isoelectric point: (A) pH 5.0 - 5.3 (B) pH 4.9 - 5.7 Ampholite was used to determine an isoelectric point for each fraction in electrophoresis. (c) Affinity: The substance of the present invention has strong affinity to thrombin. Nearly 100% of the substance of this invention was adsorbed in a chromatographic treatment using diisopropylphosphoro-(DIP)-thrombin-agarose [See, J. Biological Chemistry, 245 , 3059-3065, (1970)]. (d) Activity: (1) The substance of the present invention binds thrombin to activate protein C. Measuring method: Dissolved in 35 µℓ of a 0.02 M Tris-HCℓ buffer (PH 7.5) containing 0.1 M sodium chloride and 5 mM calcium chloride were 5 µℓ of 7.32 µM protein C, 10 µℓ of the substance of this invention or human thrombomodulin extracted from placentae (0.5 µg/mℓ) and 50 µℓ of 5 U/mℓ thrombin. The solution was then incubated at 37°C for 0 - 30 minutes, followed by an addition of 100 µℓ of 2 units/mℓ anti-thrombin III. The resulting mixture was incubated at 37°C for 10 minutes, so that the reaction was terminated. To this solution, 200 µℓ of a buffer containing 0.02 mM Boc-Leu-Ser-Thr-Arg-MCA (product of Protein Research Foundation, Osaka, Japan) was added to effect a reaction at 37°C for 10 minutes. Thereafter, 600 µℓ of 20% acetic acid was added to terminate the reaction. The concentration of the dissociated AMC was measured by a spectro-fluorometer at an exciting light wavelength of 380 nm and an emitting light wavelength of 460 nm, whereby the concentration of activated protein C was determined. Results are shown in Table 1. Sample (0.5 µg/mℓ) Concentration of AMC (µmol/mℓ·min x 10⁻³) Invention substance (B) 9 Human thrombomodulin obtained from placentae 6 (2) The substance of the present invention prolongs the blood clotting time. Measuring method: Placed in a fibrocup were 100 µℓ of 1 U/mℓ cow thrombin (product of Mochida Pharmaceutical Co., Ltd.) and 100 µℓ of the substance of this invention or human thrombomodulin extracted from placentae (OD₂₈₀: 0.5), and the contents were heated at 37°C for 30 minutes. Then, 100 µℓ of 2 mg/mℓ human fibrinogen was added and a fibrometer manufactured by Becton-Dickinson Co. was turned on to measure the clotting time. The measurement was repeated twice. All samples were dissolved in 0.02 M imidazole-HCl buffer (pH 7.6) containing 0.15 M sodium chloride. The average of the resulting data is shown in Table 2. Sample (OD₂₈₀: 0.5) Clotting time (sec.) Invention substance (B) 144 Human thrombomodulin 120 Control (not added) 94 (e) Stability Conditions Residual Activity (%) (B) Reduction by 1% β-mercaptoethanol 0 Denaturing agent 1% SDS 140 Denaturing agent 8% urea 140 Denaturing agent 6M guanidium chloride 60 pH 2 40 pH 10 100 Pepsin treatment 50 Trypsin treatment 80 The substance of this invention (0.045OD) was separately treated at 37°C for 120 minutes under the conditions described above. After the treatment, the sample was separately diluted hundred-fold with a 0.02 M Tris-NaCl buffer to measure its activity. The residual activity was calculated relative to the activity data of the substance before treatment. The final concentration of pepsin and trypsin were 2.5 µg/mℓ (pH 2.5) and 2.5 µg/mℓ (pH 7.5), respectively and the treatments were both conducted at 37°C for eight hours. Having generally described the invention, a more complete understanding can be obtained by reference to certain specific examples, which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. Examples: The present invention will hereinafter be described by the following Referential Example and Examples. Referential Example: (1) Production of monoclonal antibody: The thrombin-binding substance (20 µg, molecular weight: 71,000) which had been extracted from human placentae and purified, was emulsified in the Freund's complete adjuvant and was then administered intraperitoneally to male BALB/c mice. The thrombin-binding substance was thereafter administered intraperitoneally in a dose of 20 - 100 µg at intervals of 2 - 4 weeks for 10 months, followed by a final intravenous administration of 100 µg. Three days later, the spleens were taken out of the mice. Spleen cells were loosened in the Iscove's modified Dulbecco's medium (IMDM). Discrete cells which had passed through a 100-mesh screen were collected. After adding a hypotonic solution (155 mM ammonium chloride) to the cells to hemolyze erythrocytes, the cells were washed three times with IMDM. Mouse myeloma cells (P3-Ag8-γ) were also washed three times with IMDM. The numbers of both cells were counted. The spleen cells and P3-Ag8-γ were mixed at a ratio of 3:1, followed by centrifugation. The supernatant was discarded. After thoroughly disintegrating the precipitated cells, 1 mℓ 50% polyethylene glycol (1500) was added dropwise to effect their fusion. After allowing the cells to stand for 30 minutes at room temperature, the cells were gently stirred while dropping 1 mℓ IMDM over 1 minutes and then 10 mℓ IMDM in the course of 5 minutes. The volume of the mixture reached 50 mℓ finally, followed by centrifugation at 1,000 rpm for 8 minutes. The precipitate was suspended in IMDM added with 10% FCS. Centrifugation was conducted again and the supernatant was discarded. The resultant cells were again suspended at 3 x 10⁵/mℓ in HAT-containing IMDM with 10% FCS added therein. The resulting suspension was poured 100µℓ by 100µℓ into the individual wells of a 96-well microplate. The culture medium was added in an amount of 50 µℓ with intervals of 3 - 4 days. Owing to the selection of the above culture medium, hybridomas alone were allowed to grow. Culture broths were collected separately from wells in which hybridomas had grown. Wells with the intended antibody produced therein were then determined by an enzyme immunoassay. Peritoneal cells (1 x 10⁵/mℓ), which had been collected by injecting IMDM into the abdominal cavities of normal mice, were suspended in IMDM added with 10% FCS and the resultant suspension were poured 100 µℓ by 100 µℓ into the individual wells of a 96-well microplate. On the following day, the antibody-producing hybridomas were diluted to 5 cells/mℓ and added in an amount of 100 µℓ per well into the wells. The culture medium was either added or replaced on the every third day. Supernatant was collected from each well in which cells had grown and the production of the antibody was confirmed by the enzyme immunoassay. Positive wells were subjected again to cloning so that cloned hybridomas TM-H54, TM-H59, TM-H60, TM-H65, TM-H73 and TM-H91, which were able to produce monoclonal antibodies, were obtained. BALB/c mice of at least 7 weeks of age were intraperitoneally administered with 0.5 mℓ pristane. About one week later, the above-described hybridoma TM-H59 was inoculated intraperitoneally at a rate of 1 x 10⁶ cells/mouse. Ten days later, ascites was collected from the mice and centrifuged at 3,000 rpm for 10 minutes, and the supernatant was separated. Added to 4.8 mℓ of this supernatant was the same volume of a 1.5 M glycine buffer (pH 8.9) containing 3 M sodium chloride. The resultant mixture was caused to pass through a column of 5 mℓ Protein A Sepharose CL-4B which had been equilibrated with the same buffer. After washing the column thoroughly with the buffer, the column was eluted with a 0.1 M citrate buffer (pH 4.0). The eluate was collected 3 mℓ by 3 mℓ in test tubes each of which contained 1 mℓ 1 M Tris-HCl buffer (pH 8.0). Their A₂₈₀ values were measured to collect protein fractions. After dialyzing the protein fractions against water, they were lyophilized to obtain 60 mg of a monoclonal antibody. The thus-obtained monoclonal antibody (TM-A59) had the following characteristics: Molecular weight: 190,000 ± 5,000 IgG subclass: IgGl Isoelectric point: 7.1 - 7.6 (2) Production of an immunoadsorbent: After washing 3 g of BrCN-activated Sepharose 4B successively with 1 mM hydrochloric acid and 0.1 M sodium carbonate buffer (pH 8.3) containing 0.1 M sodium chloride, it was converted into an 8 ml liquid mixture in the above buffer. To the liquid mixture, 20 mg of the monoclonal antibody (TM-A59) obtained in the above procedure (1) was added. The resultant mixture was shaken at room temperature for 2 hours, followed by removal of water through a glass filter. In addition, 40 mℓ of 1 M Tris-HCl buffer (pH 8.0) was added and the thus-obtained mixture was shaken for 2 hours, and added 40 mℓ of 0.1 M acetate buffer (pH 4.0). The obtained mixture was shaken for 2 hours followed by removal of water through a glass filter. The thus-obtained antibody-bound Sepharose was washed three times alternately with 0.1 M Tris-HCl buffer (pH 8.3) containing 0.5 M sodium chloride and 0.1 M acetate buffer (pH 4.0) containing 0.5 M sodium chloride. It was then equilibrated with 0.02 M Tris-HCl buffer (pH 7.6) containing 1 M sodium chloride and 0.05% Lubrol to obtain an immunoadsorbent. Example 1: Fresh human urine (1 ℓ) was dialyzed overnight against a 0.02 M Tris-HCl buffer (pH 7.6) which contained 1 M sodium chloride and 0.1% Lubrol. The thus-dialyzed solution was adsorbed on 10 mℓ the immunoadsorbent obtained in accordance with the Referential Example and packed in a column. After washing the column with the above buffer, the column was eluted with a Tris-HCl buffer (pH 7.6) which contained 2 M potassium thiocyanate and 0.1% Lubrol. The eluate was fractionated into 5 mℓ portions. Active fractions (Fraction Nos. 2 - 15) were combined together, followed by concentration to 3 mℓ with Millipore CX-10. The above concentrate was subjected to high performance liquid chromatography on DEAE-5PW, followed by elution in accordance with the gradient technique, using 0.02 M Tris-HCl buffer (pH 7.6) which contained 0 - 1 M sodium chloride and 0.1% Lubrol. The eluate was fractionated into 1 mℓ portions. Fraction Nos. 23 - 27 were combined together and concentrated to about 100 µℓ using Millipore CX-10, whereby the intended substance (A) having a protein concentration of 20 µg/mℓ was obtained. Fraction Nos. 15 - 19 were also combined together, followed by concentration to about 100 µℓ with Millipore CX-10 to obtain the intended substance (B) having a protein concentration of 15 µg/mℓ. Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, NL, SE A process for preparing a thrombin-binding substance having the following characteristics: (a) molecular weight: 40,000 ± 8,000 in reduced condition by SDS PAGE 31,000 ± 10,000 in unreduced condition by SDS PAGE (b) isoelectric point: pH 4.9 - 5.7 (c) affinity: strong affinity to thrombin (d) activity: (1) capable of promoting the thrombin catalyzed activation of protein C (2) prolongs clotting time; and (e) stability: stable to denaturing agents (urea and sodium dodecylsulfate), which comprises fractionating human urine by ion-exchange chromatography, affinity chromatography using a thrombin-bound carrier, immune adsorption column chromatography, gel filtration, and/or molecular-weight fractionation. A substance produced by the process of Claim 1. Claim for the following Contracting State : ES A process for preparing a thrombin-binding substance having the following characteristics: (a) molecular weight: 40,000 ± 8,000 in reduced condition by SDS PAGE 31,000 ± 10,000 in unreduced condition by SDS PAGE (b) isoelectric point: pH 4.9 - 5.7 (c) affinity: strong affinity to thrombin (d) activity: (1) capable of promoting the thrombin catalyzed activation of protein C (2) prolongs clotting time; and (e) stability: stable to denaturing agents (urea and sodium dodecylsulfate), which comprises fractionating human urine by ion-exchange chromatography, affinity chromatography using a thrombin-bound carrier, immune adsorption column chromatography, gel filtration, and/or molecular-weight fractionation.

Inventors: AOKI NOBUO, KIMURA SHIGERU, SHIRATSUCHI MASAMI, AOKI, NOBUO, KIMURA, SHIGERU, SHIRATSUCHI, MASAMI
Applicants: KOWA CO, KOWA CO. LTD.
Application year: 1987
Main classification: C07K15
IPC codes: C07K16, A61K38, C07K14