Reagent for measuring creatine kinase activity and measuring method thereof

Abstract: The present invention provides such a measuring method of the ratio (MM₃/MM₁) and a reagent therefor. Accordingly, the present invention provides a reagent for measuring creatine kinase (CK) activity comprising an antibody, wherein said antibody inhibits CK-M subunit, but does not inhibit CK-M′ subunit. The present invention also provides a method for measuring CK activity comprising determining an inhibition of CK of body fluids using a reagent for measuring CK activity, wherein said reagent comprises an antibody which inhibits CK-M subunit, but does not inhibit CK-M′ subunit.

Description: FIELD OF THE INVENTION The present invention relates to a reagent for measuring creatine kinase activity of body fluids and a measuring method thereof. BACKGROUND OF THE INVENTION Measurement of creatine kinase (CK) activity of body fluids, such as serum is very significant for a diagnosis of muscle diseases, especially myocardial infarction. Creatine kinase (CK) has three isozymes based on a combination of two subunits, such as creatine kinase (CK) MM, creatine kinase (CK) MB and creatine kinase (CK) BB. Creatine kinase (CK) MM is mainly present in muscles, such as skeletal muscles, cardiac muscles and the like, creatine kinase (CK) MB is present in cardiac muscles and creatine kinase (CK) BB is in internal organs, such as a brain, the kidney and the like. Creatine kinase (CK) MB which is specifically present in cardiac muscles is important as a marker for a diagnosis of cardiac infarction. Accordingly, reagents which specifically measure creatine kinase (CK) MB are proposed. Japanese Patent Publications (examined) 19239/1981 and 20274/1983 disclose a method wherein an antibody, which specifically inhibits M subunits in creatine kinase (CK) MM and MB, is added and activity of the residual B subunit is then measured. The present inventors proposed to improve the above method by using a monoclonal antibody as an inhibiting antibody as disclosed in EP-A-0 261 781 (corresponding to Japanese Patent Application Ser. No. 191899/1986). These methods are very effective, but it takes more than 10 hours for CK-MB to excess normal range (see Clin., Chem. by Wu, 33 , p.358 (1987)). It is difficult to diagnose myocardial infarction early by measurement of CK-MB. It therefore is required to develop a new diagnostic method which enables early diagnosis of myocardial infarction. It has been recently elucidated that M subunits in creatine kinase (CK) MM and MB which is released from the heart or skeletal muscles due to myocardial infarction or a muscles disease is modified by carboxypeptitase N in blood plasma to M′ subunit (modified M subunit) (J. Biol. Chem. by George et al., 259 , p 2667 (1984). Thus, creatine kinase (CK) MM is converted from MM₃ (tissue type MM) through MM₂ (hybrid type MM′) to MM₁ (serum type M′M′). It is also made clear in Circulation by Hashimoto et al., 71 p 366 (1985) that in normal condition, a ratio of MM₃/MM₁ is approximately 0.3, but, in myocardial infarction, the ratio shows about 2 after 3 to 6 hours from after onset of myocardial infarction. Accordingly, the measurement of the ratio of MM₃/MM₁ makes possible an early diagnosis of myocardial infarction. Such early diagnosis of myocardial infarction is significant, because it is essential how early a intercoronary thrombolytic therapy is applied to a patient. Reattack of infarction is also easily and early detected. The measurement of the ratio of MM₃/MM₁ is presently carried out by an activity measuring method after separation by electrophoresis, a chromatofocusing method, an isoelctric point electrophoresis and the like. These methods are very complicated and time consuming. As mentioned above, since it is important that the measurement of the ratio of MM₃/MM₁ is made fast, these methods are not good. It is desired to develop a method which can measure the ratio in a short time. SUMMARY OF THE INVENTION The present invention provides such a measuring method of the ratio (MM₃/MM₁) and a reagent therefor. Accordingly, the present invention provides a reagent for measuring creatine kinase (CK) activity comprising an antibody, wherein said antibody inhibits creatine kinase (CK) M subunit, but does not inhibit creatine kinase (CK) M′ subunit. The present invention also provides a method for measuring creatine kinase (CK) activity comprising determining an inhibition of creatine kinase (CK) of body fluids using a reagent for measuring creatine kinase (CK) activity, wherein said reagent comprises an antibody which inhibits creatine kinase (CK) M subunit, but does not inhibit creatine kinase (CK) M′ subunit. DETAILED DESCRIPTION OF THE INVENTION The antibody of the present invention can be either polyclonal or monoclonal, but a monoclonal antibody is preferred. Physicochemical characteristics of the antibody are shown as follow; (1) Action The antibody acts on creatine kinase (CK) to raise an antigen-antibody reaction, then inhibits creatine kinase (CK) M subunit activity. (2) Reaction specificity The antibody inhibits only M subunit of creatine kinase (CK) M subunit, but does not inhibit M′ subunit. (3) Optimum pH 6 to 9 (4) Suitable pH range 3 to 11 (5) Measuring method of potency Measured by a dilution rate which is detected from the measurement of inhibition. (6) Suitable temperature range for action 0 to 40 °C (7) Condition of inactivation The antibody is inactivated at 100 °C for 30 minutes. (8) Molecular weight 130,000 to 210,000 For obtaining the monoclonal antibody, a hybridoma cell strain which can produce a monoclonal antibody inhibiting creatine kinase (CK) M activity is necessary. Such a hybridoma cell strain has the following cytological characteristics; (1) Derivation Fused cells of lymphocytes producing anti-CK-M antibody and myeloma cells. (2) Shape The fused cells have similar shape to myeloma cells. They have a size of 10 to 20 micrometer. (3) Function They constantly produce monoclonal antibodies inhibiting CK-M activity which recognize one antigenic determinant. (4) Growth ability They show proliferation ability similar to myeloma cells. Thus, they proliferate about ten times in number for 72 hours. (5) Storage stability They are stored for a long period of time at a temperature of not more than -120 °C. (6) Optimum proliferation conditions 37 °C, pH 7.2 (7) Proliferation range 32 to 42 °C, pH 6.5 to 7.8 For obtaining such cell strain, hybridomas which produce a monoclonal antibody inhibiting CK-M activity are obtained by, for example, a method described in EP-A-0 261 781 from which some hybridomas which do not inhibit M' subunit are selected in a similar manner mentioned above. The method disclosed in EP-A-0261 781 for producing the hybridoma cell line comprises fusing a sensitized lymphocyte obtained from a creatine kinase-immunised animal and a myeloma cell, said cell line being capable of producing a monoclonal antibody which is reactive with creatine kinase and which inhibit creatine kinase M subunit activity. As mentioned above, hybridomas producing antibodies which inhibit CK-MM₃ , but do not inhibit CK-MM₁ are obtained. One of hybridomas which is actually obtained by the above mentioned method is deposited on January 26,, 1988 at Fermentation Research Institute Agency of Industrial Science and Technology, Ibaraki-ken, Japan to assign a number of FERM P-9839. These hybridomas are named CKH-5 and can be permanently stored at -120° C. The hybridomas are cultured and an antibody is obtained therefrom. The obtaining method of the antibody is known to the art, especially a method described in Japanese Patent Application Ser. No. 191899/1986. The obtained antibodies may be used intact. They may be treated with proteolytic enzymes, such as pepsin, papain and the like to form Fab, Fab', F(ab')₂ fragments. The reagent for measuring creatine kinase activity is prepared and used as generally described in Japanese Patent Publications (examined) 19239/1981 and 20274/1983 and EP-A-0 261 781. For example, the reagent is generally composed of two packages. The first package generally contains 0.1 to 40 unit/ml of glucokinase (GlcK) or hexokinase (HK), 0.1 to 40 unit/ml of glucose-6 phosphate dehydrogenase (G6PDH), 0.001 to 5 mg/ml of M subunit inhibiting antibody (Ab), 0.1 to 20 mM of adenosine diphosphate (ADP), 0.05 to 20 mM of nicotinamide adenine dinucleotide (NAD⁺) or nicotinamide adenine dinucleotide phosphate (NADP⁺) 1 to 200 mM of glucose, 0.2 to 20 mM of adenosine monophosphate (AMP), 0.001 to 0.1 mM of diadenosine pentophosphate (Ap5A), 0.5 to 50 mM of N-acetylcysteine (NAC) or another thiol compound, 0.5 to 30 mM of magnesium salts (e.g. magnesium acetate), 0.5 to 50 mM of sodium azide, 0.1 to 20 mM of ethylenediamine tetraacetate (EDTA) and 5 to 50 mM of a buffer solution (pH 6.7). The second reagent contains 2 to 70 mM of creatine phosphate (CrP), 0.5 to 50 mM of sodium azide and 5 to 500 mM of a buffer solution. Preferably, in the first reagent, Glck or HK is present in an amount of 0.2 to 20 unit/ml, G6PDH is in an amount of 0.2 to 20 unit/ml, Ab is 0.005 to 2 mg/ml, ADP is 0.2 to 10 mM, NAD⁺ or NADP⁺ is 0.1 to 10 mM, glucose is 2 to 100 mM, AMP is 0.5 to 15 mM, Ap5A is 0.002 to 0.050 mM, NAC is 2 to 30 mM, magnesium salts are 1 to 15 mM, sodium azide is 1 to 30 mM, EDTA is 0.2 to 10 mM and the buffer solution (pH 6.7) is 10 250 mM. In the second reagent, preferably CrP is present in an mount of 5 to 40 mM, sodium azide is in an amount of 1 to 30 mM and the buffer solution 10 to 250 mM. As a measuring method, 0.5 ml of the first reagent is mixed with 0.001 to 0.02 ml of an enzyme solution (or serum) containing creatine kinase and kept at 25 to 37 °C for 5 to 10 minutes. Then, 0.125 ml of the second reagent is added to it and the residual creatine kinase activity is measured by an absorption change of 340 nm using a spectrometer. Thereafter, as a control, the first reagent which does not contain the antibody is added to the enzyme solution (or serum) and measured in a same manner as mentioned above. An inhibition rate is given by the following formula from the residual creatine kinase (CK) activity and the control creatine kinase (CK) activity; The antibody of the present invention does not inhibit creatine kinase (CK)-M′ subunit, but inhibits creatine kinase (CK)-M subunit. M subunit of creatine kinase which has been released from the heart by myocardial infarction is modified with carboxypeptidase of blood. Thus, CK-MM(MM₃) is modified through MM′(MM₂) to M′M′(MM₁), and CK-MB is modified to M′B(MB₁) with the passage of time. A large amount of creatine kinase just after released from the heart is modified very little so as to obtain a high inhibition. As proceeding the modification, the inhibition is lowered. Accordingly, by measuring an inhibition with the reagent of the present invention, myocardial infarction is early examined and a time when a patient fall in disease is estimated. EXAMPLES The present invention will be illustrated by the following Examples. Reference Example 1 An emulsion mixture of 50 microgram of pig CK-MM with complete Freund adjuvant (available from Nakarai Chemical Company) in a ratio of 1:1 was administered to 8 weeks mouse Balb/c (available from Nippon Clea Company). After three weeks, 50 microgram of pig CK-MM was intravenously injected. It was then fused with mouse myeloma X63.6.5.3 by a method by Oi, V.T., Selected Methods in Cellular Immunology, p. 351, W.H. Freeman and Co., 1980 and hybridoma grew in 54 wells / 96 wells. The supernatant was added to a reagent for measuring creatine kinase (CK) activity of the following Reference Example 2 and an inhibition of CK-MM was measured with respect to CK-MM₃ and CK-MM₁ to select antibodies which does not inhibit CK-MM₁ but inhibits CK-MM₃. The selected strain was cloned by a limit dilution method to obtain a hybridoma CKH-5 of monoclone. The CKH-5 shows the same cytological properties as mentioned before. The hybridoma CKH-5 was cultured on RPM11640 culture medium containing 10 % fetal bovine serum to a cell number of 2 X 10⁶ /ml, 300 ml of which was then subjected to centrifugal separation to collect the supernatant. It was then fractionated with ammonium sulfate to obtain crude antibody fraction, and absorbed to Protein A Cephalose (pH 8.0) after dialyzing. The absorbed fraction was eluted with a citric acid buffer solution to obtain a monoclonal antibody (CKA-5) of 3.2 mg. Reference Example 2 The antibody was added to reagents for measuring creatine kinase (CK) activity to determine inhibition of CK-MM₃, MM₂ and MM₁ in serum separated by a chromatofocusing. The first reagent was prepared by mixing 1.4 unit/ml of GlcK derived from Bacillus stearothermophilus (available from Seikagaku Kogyo Co., Ltd.), 1.2 unit/ml of G6PDH derived from Leuconostoc mesenteroides (available from Oriental Yeast Co., Ltd.), 1.2 mM of ADP, 0.75 mM of NADP, 25 mM of glucose, 6.25 mM of AMP, 125 micro M of Ap5A, 12.5 mM of N-acetylcystein, 12.5 mM of magnesium acetate, 10 mM of sodium azide, 2.5 mM of EDTA and 150 mM of an imidazole-acetate buffer solution (pH 6.7). The second reagent was prepared by mixing 100 mM of CP, 10 mM of sodium azide and 25 mM of a Tris-acetate buffer solution (pH 8.5). The monoclonal antibody CKA-5 inhibiting CK-M activity was added to the first reagent and CK-MM₃, then MM₂ or MM₁ was added to 0.5 ml of the mixture. It was then charged in a cell having a light length of 1 cm and incubated for 15 minutes. Next, 0.125 ml of the second reagent was added and the residual CK activity was measured by an absorption of 340 nm using a spectrometer which was kept at 30 °C. As control, CK-MM₃, MM₂ or MM₁ was added to the reagent which does not contain the antibody, and subjected to a same measuring. The result is shown in Table 1. Inhibition activity of CKA-5 Isoform Activity with no antibody (u/l) Activity with antibody (u/l) Inhibition (%) CK-MM₃ 221 1 100 CK-MM₂ 210 101 52 CK-MM₁ 197 195 1 Note: the values are an average of three samples. As shown in Table 1, CKA-5 does not inhibit CK-MM₁ of serum type, but inhibits CK-MM₃ of tissue type. It also inhibits a half of MM₂ of hybrid type. Thus, CKA-5 does not inhibit M′ subunit, but inhibits M subunit, and is inside of the physicochemical characteristics. Reference Example 3 and Comparative Example 1 CK-MM (800U/l) purified from cardiac muscles was added to blood plasma and incubated at 37 °C. Inhibition of CK-MM by CKA-5 was determined with time as generally described in Reference Example 2. A diagnostic reagent for measurement of CK-MB (CK-MB kit) which contains CK-MM inhibiting antibody (Boehringer Mannheim Company) was employed as a comparative example and inhibition was measured. The result is shown in Table 2. Change with time of inhibition by CKA-5 Incubation time (hours) Inhibition by CKA-5 (%) Inhibition by CK-MB kit (%) 0 97.3 100 1 57.6 100 2 38.9 100 3 23.5 100 4 16.1 97.0 5 8.2 96.7 6 0 100 As the purified CK-MM(MM₃) is modified by carboxy peptitase N in blood plasma to MM₂ and MM₁, inhibition of CK-MM by CKA-5 reduces with time and 6 hours later there is no inhibition. This is corresponded to the change of isoform. On the other hand, the inhibition of CK-MM by CK-MB kit does not change after 6 hours and therefore this can not trace the change of isoform. Example 1 and Comparative Example 2 As generally described in Reference Example 2, the CK activity and inhibition by CKA-5 of the serum from patient A who had onset of myocardial infarction was determined with time. For a comparison, the activity of CK-MB was determined using a reagent for CK-MB measurement kit which contains a CK-MM inhibiting antibody. The result is shown in Fig.1 and Fig.2. As shown in the figures, the inhibition by CKA-5 shows a peak after 6 hours from the onset, but CK-MB which has been used for a diagnosis of myocardial infarction shows a peak after 21 hours from the onset. Accordingly, it is very clear that the measurement of the inhibition by CKA-5 is very useful for an early diagnosis of myocardial infarction. Example 2 and Comparative Example 3 As generally described in Example 1, the CK activity and inhibition by CKA-5 of the serum from patient B who had a fit of myocardial infarction was determined with time. For a comparison, the activity of CK-MB was determined as generally described in Comparative Example 2. The result is shown in Fig.3 and Fig.4. As shown in the figures, the inhibition by CKA-5 shows a peak after 6 hours from the onset, but that of CK-MB which has been used for a diagnosis of myocardial infarction shows a peak after 16 hours from the onset. Accordingly, it is very clear that the measurement of the inhibition by CKA-5 is very useful for an early diagnosis of myocardial infarction. BRIEF EXPLANATION OF THE DRAWINGS Figs.1 and 3 show a relation of an inhibition by CKA-5 with time after onset of myocardial infarction. Figs.2 and 4 show a relation of a total CK activity (A) and CK-MB activity (B) with time after onset of myocardial infarction.

Claims: A reagent for measuring creatine kinase activity comprising an antibody, wherein said antibody inhibits creatine kinase M subunit, but does not inhibit creatine kinase M′ subunit. The reagent according to Claim 1 wherein said antibody is obtained from a hybridoma cell strain which can produce a monoclonal antibody inhibiting creatine kinase (CK) M activity. The reagent according to Claim 1 being composed of two packages, one of which comprises 0.1 to 40 unit/ml of glucokinase (GlcK) or hexokinase (HK), 0.1 to 40 unit/ml of glucose-6 phosphate dehydrogenase (G6PDH), 0.001 to 5 mg/ml of M subunit inhibiting antibody (Ab), 0.1 to 20 mM of adenosine diphosphate (ADP), 0.05 to 20 mM of nicotinamide adenine dinucleotide (NAD⁺) or nicotinamide adenine dinucleotide phosphate (NADP⁺), 1 to 200 mM of glucose, 0.2 to 20 mM of adenosine monophosphate (AMP), 0.001 to 0.1 mM of diadenosine pentophosphate (Ap5A), 0.5 to 50 mM of N-acetylcysteine (NAC) or another thiol compound, 0.5 to 30 mM of magnesium salts, 0.5 to 50 mM of sodium azide, 0.1 to 20 mM of ethylenediamine tetraacetate (EDTA) and 5 to 50 mM of a buffer solution (pH 6.7), and the other reagent comprises 2 to 70 mM of creatine phosphate (CrP), 0.5 to 50 mM of sodium azide and 5 to 500 mM of a buffer solution. A method for measuring creatine kinase activity comprising determining an inhibition of creatine kinase of body fluids using a reagent for measuring creatine kinase activity, wherein said reagent comprises an antibody which inhibits creatine kinase M subunit, but does not inhibit creatine kinase M′ subunit. The method according to Claim 4 wherein said antibody is obtained from a hybridoma cell strain which can produce a monoclonal antibody inhibiting creatine kinase (CK) M activity. The method according to Claim 4 wherein said reagent is composed of two packages, one of which comprises 0.1 to 40 unit/ml of glucokinase (GlcK) or hexokinase (HK), 0.1 to 40 unit/ml of glucose-6 phosphate dehydrogenase (G6PDH), 0.001 to 5 mg/ml of M subunit inhibiting antibody (Ab), 0.1 to 20 mM of adenosine diphosphate (ADP), 0.05 to 20 mM of nicotinamide adenine dinucleotide (NAD⁺) or nicotinamide adenine dinucleotide phosphate (NADP⁺), 1 to 200 mM of glucose, 0.2 to 20 mM of adenosine monophosphate (AMP), 0.001 to 0.1 mM of diadenosine pentophosphate (Ap5A), 0.5 to 50 mM of N-acetylcysteine (NAC) or another thiol compound, 0.5 to 30 mM of magnesium salts, 0.5 to 50 mM of sodium azide, 0.1 to 20 mM of ethylenediamine tetraacetate (EDTA) and 5 to 50 mM of a buffer solution (pH 6.7), and the other reagent comprises 2 to 70 mM of creatine phosphate (CrP), 0.5 to 50 mM of sodium azide and 5 to 500 mM of a buffer solution.

Inventors: ERA MIHOKO, KAMEI TOMOKO, SUZUKI TADAO, TSUBOTA HIROYUKI, ERA, MIHOKO, KAMEI, TOMOKO, SUZUKI, TADAO, TSUBOTA, HIROYUKI
Applicants: IATRON LAB, UNITIKA LTD, IATRON LABORATORIES INC., UNITIKA LTD.
Application year: 1989
Main classification: G01N33
IPC codes: D21H27, C12P21, G01N33, C07K16, C12N15