PEPTIDE

Abstract: A novel peptide possessing excellent antihypertensive activity is disclosed. The peptide has the formula: Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) and can be prepared by purifying a fluid extracted from fish tissues or by combining constituting amino acids by a peptide synthesis method. It exhibits excellent ACE inhibitory activity, low toxicity, and good stability, and is thus an extremely useful and effective antihypertensive substance.

Description: BACKGROUND OF THE INVENTION Field of the Invention : The present invention relates to a novel peptide possessing excellent antihypertensive activity and useful as a pharmaceutical. The invention also relates to a process for the preparation as well as the use of such a peptide. Description of the Background : Various active ingredients have been extracted and collected from the fish tissues. Although some of them have been put into practical use as pharmaceuticals and the like, it is believed that more physiologically active substances should be obtainable. This invention was achieved based on such contemplation. The present inventors have conducted research over a long period of time about the components of fish tissues, and found that a certain component extracted and isolated from fish tissues possessed a strong antihypertensive action. The inventors have undertaken investigations to identify such an active component and found that the component was a peptide represented by the following formula (I), Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a peptide represented by the following formula (I), Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) [Such a peptide is hereinafter referred to as Peptide (I)] As a preferred embodiment, the present invention provides Peptide (I) which is prepared by purifying an extract from fish tissues. As another preferred embodiment, the present invention provides Peptide (I) which is prepared by combining constituting amino acids by a peptide synthesis method. Another object of the present invention is to provide a process for preparing Peptide (I). Still another object of the present invention is to provide an antihypertensive agent which comprises as an active ingredient Peptide (I). Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elution pattern obtained when Fr. I (hereinafter defined) was purified using SP-Sephadex® C-25. Figure 2 shows a similar elution pattern obtained when Fr. II (hereinafter defined) was purified using Sephadex® G-25 column. Figure 3 is an elution pattern obtained when Fr. III (hereinafter defined) was run on an HPLC system using Develosil® ODS-7. Figure 4 presents an elution pattern obtained when Fr. IV (hereinafter defined) was run on an HPLC using Asahipak® GS-220. Figure 5 shows an ultraviolet absorption spectrum of Peptide (I) of the present invention. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The peptide of the present invention can be extracted, for example, from fish tissues according to the following methods. Fish tissue is added to an aqueous solution of acetic acid-HCl, heated for several minutes up to several tens of minutes at 100-150°C, and then extracted. This extracted fluid is adsorbed to a resin such as octadecyl silica gel (ODS) and then the fraction eluted with acetonitrile is collected (such a fraction is herein abbreviated as "Fr. I"). The Fr. I is further refined chromatographies on a SP-Sephadex C-25 and Sephadex G-25 column. The peptide of formula (I) is separated using high performance liquid chromatography (HPLC). Fish which can be used include the Thunus (tuna), Scomber (mackerel), Sadinops (sardines), Cololabis (saury), Lateolabrax (sea bass), Clupea (herring), Trachurus (horse mackerel), Paralichths (flounder), Suggrundus (flat head), doryteuthis (squid), Limanda (marbled sole), Sphyraene (barracuda), Trichiurus (cutlass fish), Ocycrius (Japanese butterfish), Anoplopoma (beshow), Pampus (harvest fish), and the like. Fish tissues from which the peptide having the amino acid sequence of formula (I) can be extracted include, for example, white muscle, heart, dark muscle, liver, testis, ovary, and the like. White muscle is the most desirable because it contains a lot of Peptide (I) and is readily available in large quantities. The peptide of the present invention can also be prepared by conventional peptide synthesis methods. Liquid phase methods and solid phase methods can both be used as peptide synthesis methods. Commercially available peptide synthesizing apparatus may be used for the synthesis. Peptide of formula (I) can be purified and isolated by reverse-phase column chromatography used in conventional peptide separation. The antihypertensive action of the peptide of the present invention was measured as Angiotensin I converting enzyme (ACE) inhibitory activity according to the method of Cushman and Cheung [Biochem. Pharmacol., 20 , 1637 (1971)]. A prescribed amount of sample was added to a solution composed of 1-10 mU ACE, 2.5 mM Hip-His-Leu substrate (produced by Peptide Research Institute), 100 mM potassium-phosphate buffer (pH 8.3), and 300 mM NaCl. 0.25 ml of this mixture was incubated at 37°C for 30 min, and the enzymatic reaction was stopped by adding 0.25 ml of 1N HCl. 1.5 ml of ethylacetate was then added and the mixture was vigorously shaken for 10 second, following which the hippuric acid produced was extracted. A 1 ml aliquot of the extract was evaporated to dryness and the residue was dissolved in 1 ml of distilled water to measure the hippuric acid concentration from the absorbance at 228 nm (ODs). A blank (ODsbl) was made by adding 1 N HCl prior to incubation, and the difference in absorbance, ODs-ODsbl, was determined. A control (ODc) to which no sample had been added was prepared and the difference ODc-ODcbl was determined in the same way. ACE inhibitory activity was calculated using the following equation: Table 1 shows comparison of ACE inhibitory activities of the peptide of the present invention [Peptide (I)], a porcine plasma tripeptide (Leu-Val-Leu), an 11 peptide viper toxin (Pyr-Gly-Pro-Pro-Pro-Arg-Pro-Lys-Ile-Pro-Pro), and the synthetic pharmaceutical Captopril. Sample Origin M.W. ACE Inhibitory Activity IC₅₀ (µM) Peptide (I) Fish 952 0.7 Peptide (I) Peptide Synthesis 952 0.6 Tripeptide Porcine plasma 343 1.7 11 Peptide Viper toxin 1,052 1.5 Captopril Chemical Synthesis 217 0.08 The peptide of formula (I) of the present invention, irrespective of its source, showed excellent ACE inhibitory activity, indicating that it is useful as an antihypertensive agent. Intravenous and oral administration are desirable as means of administration. Preparation forms which can be used include injections, and oral administration formulations such as capsules, tablets, powder preparations, granules, and the like. Normal daily therapeutic dose of Peptide (I) in adults is 0.1-1,000 mg, although an optimum dose will differ depending on the conditions of the patient, the means of administration, and the like. Peptide (I) can be made into pharmaceutical preparations together with conventional pharmaceutical components such as carriers, bases, and excipients according to commonly available methods. For oral administration preparations it is desirable to use them as oil-soluble capsules, tablets, powders, or granules, while for injections water-soluble injection preparations or freeze-dried powder preparations are preferable. Although it is possible to use conventional substances as excipients, the use of human serum albumin, sucrose, gelatin, starch, polyethylene glycol, or the like are preferable. Other features of the invention will become apparent in the course of the following description of the exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof. EXAMPLES Example 1 (i) Two (2) kg of white muscle of Neothunnus macropterus (Pacific yellow-finned tuna) minced and homogenized with 8 volumes of cold 1 M acetic acid - 20 mM HCl. The suspension was autoclaved at 120°C for 5 minutes, cooled and centrifuged at 16,000 rpm for 20 minutes. 80 g of activated ODS resin (55-105 µm) was added to the supernatant and stirred for 1 hour. The ODS recovered by filtration on a glass filter was washed with 800 ml of 4% acetic acid and eluted with 1 liter of 15% acetonitrile. The 15% acetonitrile fraction was evaporated under reduced pressure and 1,060 mg of Fr. I was obtained. The IC₅₀ value for the AEC of this fraction was 530 µM (ii) The eluate obtained in (i) above was passed through a column (1.8 x 50 cm) packed with SP-Sephadex C-25 and then eluted stepwise over the pH range of 3.1-5.0 using 0.2 M pyridine-acetic acid buffer. The elution pattern is shown in Figure 1. The fraction exhibiting ACE inhibitory activity was collected as Fr. II. The IC₅₀ value for the ACE of this fraction was 188 µM. (iii) Fr. II was passed through a column (2.5 x 93 cm) packed with Sephadex G-25 and eluted with 0.2 M acetic acid. The elution pattern is shown in Figure 2. The fraction exhibiting ACE inhibitory activity was collected as Fr. III. The IC₅₀ value for the ACE of this fraction was 100 µM. (iv) Fr. III was subjected to HPLC on a Deverosil ODS-7 column (0.8 x 25 cm, eluant: 10 - 20% CH₃CN in 0.05% HCl). The elution pattern is shown in Figure 3. The ACE inhibitory activity recovered in this fraction (Fr. IV) was 50 µM. (v) Fr. IV was subjected to HPLC on an Asahipak GS-220 column (0.76 x 50 cm, eluant: 50 mM sodium phosphate buffer, pH 7.0). The elution pattern is presented in Figure 4. The ACE inhibitory activity was recovered in a symmetrical peak (Fr. V). Finally, rechromatography by reverse-phase HPLC was necessary for desalting. The solvent was evaporated under reduced pressure and 0.8 mg of the octapeptide of the present invention was obtained. Amino acid composition: Hydrolysis was carried out for 20 hours at 110°C in 6 N HCl or 4 M methane sulfonic acid. The results obtained using the Pico-TAG amino acid analytical method are presented in Table 2. 6N HCl 4 M methane sulfonic acid Asp 1.1 (1) 1.1 (1) Gly 1.1 (1) 1.2 (1) His 1.0 (1) 1.0 (1) Thr 1.0 (1) 0.9 (1) Pro 1.0 (1) 1.1 (1) Ile 1.0 (1) 1.0 (1) Trp 0.8 (1) Lys 0.9 (1) 0.9 (1) Amino acid sequence: The amino acid sequence determined using a gas phase protein sequencer (Model 470A, made by Applied Biosystems Co. Ltd.) is shown in Formula (I) Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) C-terminal amino acid analysis: Asp was determined to be the C-terminal amino acid using the carboxypeptidase method [Biochemical Experiment Lecture 1, Chemistry of Proteins II, p 203]. This result was the same as that found by the gas phase protein sequencer. Ultraviolet absorption spectrum: The spectrum is shown in Figure 5. Example 2 Using a full automatic peptide synthesizer (Model 430-A, made by Applied Biosystems Co., Ltd.), the peptide of formula (I) was synthesized. Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) Elimination from the resin carrier and protective group removal were carried out using hydrogen fluoride, and then Peptide (I) of the present invention was purified by reversed-phase HPLC using an ODS column. As in Example 1, the result obtained by measuring the amino acid sequence was in agreement with the value expected from the amino acid sequence of Peptide (I). Example 3 The peptide of formula (I) prepared in Example 2 was dissolved in physiological saline. Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) Various concentrations of the peptide in physiological saline were intravenously administered to test animal groups each consisting of 6 week old male (10/group) or female 10/group) ICR mice, or 6 week old male (10/group) or female (10/group) Wistar rats. The LD₅₀ value was determined after a 2 week observation period. The LD₅₀ values for Peptide (I) of the present invention in both mice and rats were found to be greater than 10 mg/kg. As can be seen from the above examples, Peptide (I) of the present invention exhibits excellent ACE inhibitory activity, low toxicity, and safety, indicating that this compound is an extremely useful and effective antihypertensive substance. Below are further examples explaining specific medical uses of Peptide (I) of the present invention. Example 4 Water-soluble injection preparation 100 mg of peptide of formula (I) prepared in Example 2 was dissolved in 100 ml of 0.01 M phosphate buffer (pH 7.0) containing 0.14 M NaCl prepared using distilled water for injection use. The solution was filtered aseptically using a membrane filter. Each 1 ml sample of the filtrate was placed in a glass container and the container was tightly sealed to serve it as a water-soluble injection preparation. Example 5 Tablets 1,000 tablets each containing 100 mg of Peptide (I) were prepared from the following components. Peptide (I) prepared in Example 1 100.0 g Starch 50.0 g Gelatin 7.5 g Crystalline cellulose 25.0 g Magnesium stearate 2.5 g Total 185.0 g Peptide (I) and the starch were mixed together with an aqueous gelatin solution. The mixture was dried and pulverized to obtain a fine powder. The crystalline cellulose and magnesium stearate were then mixed with the powder. The resulting mixture was processed by a tablet machine to produce 1,000 tablets each containing 100 mg of the active ingredient. Example 6 Capsules Capsules were prepared by filling No. 1 gelatin capsules with the mixture consisting of the following components. Peptide (I) 50 mg Magnesium stearate 7 mg Lactose 393 mg Total 450 mg As fully illustrated above, the peptide of formula (I) possesses an excellent ACE inhibitive activity and is useful as an antihypertensive agent. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, NL, SE A peptide represented by the following formula (I), Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) A peptide according to Claim 1, which is obtained by purifying a fluid extracted from fish tissues. A peptide according to Claim 1, which is prepared by combining constituting amino acids by a peptide synthesis method. A process for the purification of a peptide represented by the following formula (I), Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) which comprises subjecting a fluid extracted from fish tissues to at least one of the processes selected from the group consisting of (1) ion-exchange chromatography, (2) gel-filtration chromatography, and (3) reverse-phase chromatography in any order. A process for preparing a peptide represented by the following formula (I), Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) which comprises combining constituting amino acids by a liquid phase or solid phase peptide synthesis method. An antihypertensive agent which comprises as an active ingredient a peptide represented by the following formula (I), Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) An antihypertensive agent according to Claim 6, wherein said peptide is obtained by purifying a fluid extracted from fish tissues. An antihypertensive agent according to Claim 6, wherein said peptide is prepared by combining constituting amino acids by a peptide synthesis method. Claims for the following Contacting States : ES, GR A process for preparing a peptide useful as an antihypertensive agent of general formula (I): Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) characterised becaue it comprises combining constituting amino acids, in the suitable sequence, by a liquid phase or solid phase peptide synthesis method. A process for the purification of a peptide useful as an antihypertensive agent of general formula (I): Pro-Thr-His-Ile-Lys-Trp-Gly-Asp (I) characterised because it comprises subjecting a fluid extracted from fish tissues to at least one of the processes selected from (1) ion-exchange chromatography, (2) gel-filtration chromatography, and (3) reverse-phase chromatography in any order desired then more than one of these processes is used.

Inventors: KOHAMA, YASUHIRO, MIMURA, TSUTOMU, NAGASE, YASUKAZU, SATAKE, MIKIO NIPPON SUISAN
Applicants: NIPPON SUISAN KAISHA, LTD.
Application year: 1989
Main classification: C07K7
IPC codes: C12N9, A61P29, C07K1, A61P9, C07K14, A61K38, C07K7