A HEAT-STABLE AQUEOUS SOLUTION OF HUMAN URINE KALLIKREIN

Abstract: Human urine kallikrein dissolved in water is made heat-­ stable by the addition of a citric acid salt such as sodium citrate, so that an aqueous solution containing the kallikrein and the citric acid salt can be sterilized at 60° to 70°C.

Description: This invention relates to a heat-stable aqueous solution of human urinary kallikrein and a process for treating the solution. Busby et al (J. Biol. Chem. Vol. 256 (1981) pp 12140-12147) have described the heat-stabilising effect of citrate, heparin and other compounds on the enzyme inhibitor Antithrombin III. However, there is neither disclosure nor implication of such heat stabilisation of any other proteins, such as enzymes themselves. Kallikrein is a kind of protease which is broadly distributed in the serum, urine and various organs, such as the pancreas, submandibular gland and kidney, of mammalian animals. It acts on kininogen in plasma to release kallidin which is a polypeptide and this kallidin displays such physiological activities as smooth muscle contracting, antihypertensive and blood flow increasing activities. Swine pancreatic kallikrein has for some time been utilized as a drug for the treatment of hypertension, arteriosclerosis, angina pectoris and climacteric disturbance. However, administration of such a drug, derived from a heterologous animal protein, to humans tends to cause immunological side effects. Although human urinary kallikrein is not being used as a drug today for the reason that its production cost is high because the material urine is not readily available and is lean in kallikrein, it is free from the antibody reaction which is encountered with swine kallikrein and, therefore, is expected to be useful as an injectable drug free from side effects. Human urinary kallikrein is not resistant to heat as are other glycoproteins and is inactivated at relatively low temperature under strongly acidic or strongly alkaline conditions. However, the present inventors have demonstrated that it is comparatively resistant to heat under weakly acid to weakly basic conditions (Japanese Patent Application No. 119000/1982 and No. 113364/1982). The present inventors further conducted research for developing an aqueous injection of human urinary kallikrein and for finding a stabilizer for such injection. As shown in Table 1, among various compounds tested, sodium citrate showed a remarkably great stabilizing effect and, thus, could be used as an effective thermal stabilizer for kallikrein. Thus, with sodium citrate as a candidate stabilizer, a detailed experimental study was conducted. Thus, as shown in the Examples that follow, the residual kallikrein activity in aqueous solutions of human urinary kallikrein in the presence or absence of sodium citrate was investigated at the accelerated storage temperatures of 60°, 65° and 70°C. The study showed very interesting findings (See the Examples) which may be summarized as below. When an aqueous solution of human urinary kallikrein was directly heated at 60° to 65°C, kallikrein activity in the solution dropped to 50 to 20% in about a week. However, when some amount of sodium citrate was added to the solution, more than 90% of the original kallikrein activity was retained under the same conditions. Thus, by adding sodium citrate to an aqueous injection of human urinary kallikrein, it was possible to carry out heat-treatments such as virucide and pasteurization. The above experiment can be considered to be an accelerated test on injections and the results suggest that the kallikrein injection can be stored at room temperature for a long time. Based on the above findings, this invention is directed to a process for preparing a heat-stable aqueous solution of human urinary kallikrein, by adding, at a concentration of 0.1 to 5 w/v %, a pharmaceutically acceptable citric acid salt to an aqueous solution of human urinary kallikrein. The citric acid salt is a water-soluble salt and when said aqueous solution is intended for use as an injection, for instance, the salt is a pharmaceutically acceptable salt. As examples of such salt may be mentioned sodium citrate and potassium citrate. The salt may be used in the form of a neutral salt or an acidic salt, and it is optional to add citric acid in the form of such salt to the aqueous solution or add free citric acid to the aqueous solution and then neutralize the solution so that the acid will form such a salt in the solution. The concentration of dissolved citric acid salt in the aqueous solution is preferably in the range of about 1 to 5 w/v %. In the following, all references to citric acid salt concentrations in percent represent w/v (weight/volume) percent. In addition to the citric acid salt, an osmotic pressure regulating agent such as sodium chloride may be added to the aqueous solution of human urinary kallikrein if necessary. The following examples are given to illustrate this invention in comparison with control (without addition of citric acid salt) for a better understanding of the invention. In the drawings, Fig. 1, 2 and 3 are graphs showing the residual kallikrein activities in aqueous solutions of human urinary kallikrein under the storage conditions of 60°C and 1 week, 65°C and 10 days, and 70°C and 6 hours, respectively. Example 1 1. Materials a) Sodium citrate (Na₃C₆H₅O₇·2H₂O) was dissolved in water to prepare 0, 1.2, 2.4, 3.6, 4.8 and 6.0% aqueous solutions. As the osmotic pressure ratios of the 0, 1.2 and 2.4% aqueous solutions of sodium citrate were less than 1.0, their ratios were adjusted to 1.0 by adding 0.68%, 0.37% and 0.09%, respectively, of sodium chloride. Sodium chloride was not added to the 3.6, 4.8 and 6.0% aqueous solutions, for their osmotic ratios were over 1.0. b) To 2.6 ml of an aqueous solution of human urinary kallikrein (173.4 KU/ml) was added 12.4 ml of one of the sodium citrate solutions prepared in a) above to give a solution containing 30 KU/ml of human urinary kallikrein and 0 to 5% of sodium citrate. Each of such solutions was distributed in 0.5 ml portions into 1 ml-ampules which were then sealed to provide samples. 2. Test method The experiment was performed at the different temperatures. The kallikrein activity of each sample was determined before and after the test and the residual activity rate was calculated with the activity before the test being taken as 100%. 3. Determination The determination of kallikrein activity was carried out by the MCA substrate hydrolytic activity method (note) using proline-phenylalanine-arginine coumarinylmethylamide as the substrate. To 850 µl of 0.01 M-phosphate buffer (pH 7.4) was added 50 µl of a 0.1 M solution of the above substrate and the mixture was preincubated at 37°C for 5 minutes. To this preincubated solution was added 100 µl of a 200-fold dilution of the sample and the mixture was incubated for 10 minutes. After cooling with ice, 20 µl of 10% acetic acid was added to the reaction mixture and using a spectrophotofluorometer (Shimadzu RF-510), the intensity of fluorescence at 460 nm was measured with an excitation wavelength of 380 nm. As a reference standard, 5 nM-aminomethylcoumarin was used as 100%. 4. Results The heat stabilities of human urinary kallikrein in the absence of sodium citrate and in the presence of 1 to 5% of sodium citrate are shown in Tables 2 to 4 and Figs. 1 to 3. The above results lead to the following conclusions. (1) Under the storage conditions of 60°C and 1 week, kallikrein activity in the absence of sodium citrate decreased to nearly 50% of the initial level, whereas the residual activity was 90 to 98% when 1 to 5% of sodium citrate was added. Thus, under the above conditions, the addition of sodium citrate was quite effective. (2) At the storage conditions of 65°C, residual kallikrein activity in the absence of sodium citrate was less than 60% after 1 day, 20% after 5 days, and close to 10% after 10 days. In the Presence of 1 to 5% of sodium citrate, residual kallikrein activity was 95 to 98% or more after 1 day, 75 to 88% after 5 days, and 60 to 85% after 10 days. Thus, sodium citrate had a very favorable effect. (3) At the storage temperature of 70°C, residual kallikrein activity in the absence of sodium citrate was about 70% after 2 hours, about 60% after 4 hours, and 50% after 6 hours. In the presence of sodium citrate, residual activity was 80 to 85% after 2 hours, 70-78% after 4 hours, and 70-75% after 6 hours, indicating that sodium citrate showed its expected effect. Example 2 Materials 1) A 4.0% aqueous solution of potassium citrate (K₃C₆H₅O₇·H₂O, Wako Pure Chemical Industries, Ltd.) was prepared. As the osmotic pressure ratio of this solution was approximately 1.0, sodium chloride was not added. To 2.6 ml of an aqueous solution of human urinary kallikrein (17.4 KU/ml) was added 12.4 ml of the above potassium citrate solution. This solution contained the same equivalent of citrate ion as the 3.0% solution of sodium citrate. This solution was distributed in 0.5 ml portions into 1-ml ampules which were then sealed to provide samples. 2) The kallikrein solution without addition of a citric acid salt and the kallikrein solution containing 3% of sodium citrate were prepared in the same manner as Example 1. The conditions of testing procedure and activity determination were the same as those used in the 70°C storage test of Example 1. The results are shown in Table 5. The sample prepared by adding 3.3% of potassium citrate to an aqueous solution of kallikrein showed a remarkable heat stability as did the sample containing 3.0% of sodium citrate in comparison the kallikrein solution containing no citric acid salt. Example 3 In accordance with Example 1, sodium citrate was added in a concentration of 0.1 to 1.0% to the solution of human urinary kallikrein for testing the heat stability and the variation per day of the kallikrein in the solution. 1. Materials To aqueous solutions of human urinary kallikrein (90 KU/ml), sodium citrate was added in a concentration of 0.1%, 0.25%, 0.5% and 1.0%, followed by adjusting the osmotic pressure ratio of the solution to 1.0 with sodium chloride. Each of these solutions was distributed in 0.5 ml portions into 1 ml-ampules which were then sealed to provide samples. 2. Test method Temperature conditions were set at room temperature, 50°C and 60°C and time conditions at 0 to 90 days. The kallikrein activity before the test was taken as 100% and the residual activity rate was determined after each set days. 3. Determination The determination of kallikrein activity was carried out by MCA substrate hydrolytic activity, as in Example 1. 4. Results Test for heat stability and variation per day with the solutions of human urinary kallikrein gave results as shown in Tables 6 to 8. The above-mentioned Tables lead to the following conclusions: (1) Under the storage conditions of room temperature for 90 days, residual kallikrein activity in the absence of sodium citrate is 92.4% after 30 days, 91.1% after 60 days and 92.3% after 90 days, showing considerable stability. While, when 0.1 to 1.0% of sodium citrate was added, residual kallikrein activities averaged 93.6% after 90 days, showing almost no effect by the addition of the stabilizer at room temperature. (2) At the storage conditions of 50°C for 90 days, residual kallikrein activity in the absence of sodium citrate decreased to 98.9% after 30 days, 83.9% after 60 days and 78.0% after 90 days. Whereas, in the presence of 0.1 to 1.0% of sodium citrate, residual kallikrein activity was not less than 98.5% after 30 days, not less than 93.8% after 60 days and 93.5 to 99.2% after 90 days, showing clearly the effect of sodium citrate. (3) At the storage conditions of 60°C for 60 days, residual kallikrein activity in the absence of sodium citrate was 76% after 7 days, 42% after 14 days, 39% after 30 days and 2.78% after 60 days, which indicates that the residual activity decreased day by day to almost no activity after 60 days. Whereas, in the presence of 0.1 to 1.0% of sodium citrate, residual activity was almost 100% after 14 days and 65 to 77% even after 30 days. As mentioned above, no significant difference was observed at room temperature for 90 days between the absence and presence of 0.1 to 1.0% of sodium citrate in the solution of human urinary kallikrein, however, in accelerated tests at 50°C and 60°C, the presence of sodium citrate in the solution clearly shows its stabilizing effect.

Claims: An aqueous solution of human urinary kallikrein, characterised in that it has dissolved therein a pharmaceutically acceptable citric acid salt in a concentration of 0.1 to 5 w/v % to heat-stabilize the kallikrein in the solution. A solution as claimed in Claim 1, wherein said concentration is 1 to 5 w/v %. A solution as claimed in Claim 1 or Claim 2, wherein the citric acid salt is sodium citrate or potassium citrate. A sterilized aqueous solution of human urinary kallikrein obtained by heating a solution as claimed in any one of the preceding claims. A sterilized solution as claimed in Claim 4, wherein the heating was at a temperature of 60°C to 70°C. A sterilized solution as claimed in Claim 4 or Claim 5, which is a solution for injection. A process of preparing a heat-stable aqueous solution of human urinary kallikrein as claimed in any one of Claims 1 to 3, which comprises dissolving human urinary kallikrein and the citric acid salt in water. A process of sterilizing an aqueous solution of human urinary kallikrein, characterised in that a citric acid salt is dissolved in the solution to provide a concentration of 0.1 to 5 w/v % and the resultant aqueous solution is heated to a sterilizing temperature. A process as claimed in Claim 8, wherein sodium or potassium citrate is dissolved to provide a concentration of 1 to 5 w/v % and the sterilizing temperature is 60° to 70°C.

Inventors: HIRATANI, HAJIME, NAKANISHI, KOICHIRO
Applicants: NIHON CHEMICAL RESEARCH KABUSHIKI KAISHA ALSO KNOWN AS JAPAN CHEMICAL RESEARCH CO., LTD
Application year: 1983
Main classification: A61K37
IPC codes: A61L2, C12N9, A61K38