How many creatine kinase "isoenzymes" are there and what is their clinical significance?

Creatine Kinase-BB Activity in Malignant Tumors and in Sera from Patients with Malignant Diseases

Creatine kinase (CK EC 2.7.3.2) and CK-BB activity was analyzed in 41 malignant tumors of 6 different sites and different histological structures. The same analyses were done on 150 sera of patients with malignant diseases of various localizations. The rate of CK activity was determined kinetical-ly, whereas tissue and serum CK-BB were separated chromatographically (Mercer). Insofar as malignant tumor tissues are concerned, the highest average rate of CK-BB activity was detected in tumors of the prostate (mean 1450 IU/g), and the lowest in tumors of the parotid gland (mean 5.2 IU/g). CK-BB was detected by the Mercer technique in 56 (37.3 %) of 150 analyzed sera of patients with malignant diseases. The rate of CK activity in sera of patients with malignant diseases was 8 to 74 IU/I. In comparison with the site of the malignant process no significant CK serum activity differences were observed. T2-T3 tumors did not significantly influence the activity of either CK or CK-BB in the case of either tissues or sera (T1-T3). Enzyme activity was found to be much higher - both in tumoral tissue and in sera - with T4 tumors. The highest rate of CK-BB activity was found in sera of patients with malignant tumors of the stomach (mean 8.1 IU/I), and the lowest in malignant tumors of the rectum (mean 1.8 IU/I).

Serum creatine kinase isoenzymes in patients with advanced malignant disease

Serum creatine kinase (CK) B subunit (CK-B) activity, as estimated by the enzymatic anti-M immunoinhibition method, and the CK isoenzyme pattern after agarose gel electrophoresis, were studied in 28 patients with advanced, untreated malignant disease. CK-B was above the decision limit, i.e. the discrimination limit used in the diagnosis of acute myocardial infarction (AMI), in 14 patients (50%). Electrophoresis demonstrated, besides CK-MM, an atypical, cathodically migrating CK band in 10 of these patients. This band may represent mitochondrial CK. The CK-BB isoenzyme was detected in 9 and CK-MB in 3 subjects. Histopathologic findings indicated that the occurrence of these isoenzymes was related to tumour burden and the overall severity of the disease. Survival among patients with CK-B elevation was shorter than among other patients. The present findings are relevant to the enzyme diagnosis of AMI and of potential significance for the evaluation of patients with known or suspected malignant tumours.

Muscle damage induced by experimental hypoglycemia

To determine organ damage due to hypoglycemia, we studied the effects of insulin dose and hypoglycemia duration on serum enzyme activity in rabbits. Thirty rabbits were randomly divided into five groups according to hypoglycemia duration and insulin dose: A2, hypoglycemia for 30 minutes with 2 U/kg insulin; A10, hypoglycemia for 30 minutes with 10 U/kg insulin; B2, hypoglycemia for 60 minutes with 2 U/kg insulin; B10, hypoglycemia for 60 minutes with 10 U/kg insulin; and C, no hypoglycemia with 10 U/kg insulin and 50% glucose. Insulin-induced hypoglycemia was reversed by intravenous injection of glucose. Alterations in serum enzyme activity and creatine kinase (CK) isoenzyme distribution were determined before and after insulin injection. Serum CK activity increased significantly in all hypoglycemic groups compared with preinjection values, and tended to remain high for 24 hours in both groups A10 and B10. Serum activity of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) increased only in group B10. In addition, the level of band 4 of serum CK isoenzymes, which exists predominantly in skeletal muscle and myocardium, increased significantly in group B10. These results suggest that the increase in both serum enzyme and CK band 4 isoenzyme activities during hypoglycemia is primarily due to damage in muscle rather than liver, and that the hypoglycemia duration and insulin dosage may influence the extent of organ damage.

Isoforms of creatine kinase MM and MB in acute myocardial infarction: a clinical evaluation

Serum creatine kinase (CK, EC 2.7.3.2) isoenzymes MM and MB were resolved, respectively, into three (MM1, MM2, MM3) and two (MB1, MB2) isoforms (subforms derived from the same isoenzyme) by electrophoresis and the isoform patterns were determined in multiple sequential serum samples, timed from the onset of chest pain, from 58 patients with acute myocardial infarction (AMI). During the first 3 h after the onset of chest pain, the serum isoform activity resembled the pattern seen in normal volunteers. Specimens obtained 6 h after AMI showed predominantly MM3 and MB2 (45% and 11% of the total CK activity, respectively). Between 10 and 72 h, there was a gradual shift in which MM3, MM2 and MB2 decreased, while MM1 and MB1 increased. MB2 and MB1 disappeared from the pattern for samples collected after 24-48 h, while MM1 was always the most prominent band at the end of the observation period (66%, range 41-77%, at 48 h). These data suggest that a single determination of CK isoform pattern, drawn between 6 and 48 h after AMI, may provide an effective means of predicting the time of onset of necrosis. There were no significant differences in the CK isoform patterns according to infarct location and functional status of patients.

Cellulose acetate and electroendosmosis-low agarose electrophoresis: advanced methods for the separation and quantitative determination of serum creatine kinase isoenzyme levels

Two methods for the separation and demonstration of creatine kinase isoenzymes are described i.e. electrophoresis on cellulose acetate and on electroendosmosis-low agarose. The fluorescence of NADPH as an indicator for the creatine kinase bands was used in both methods. The methods proved to be specific, reliable and highly reproducible, and allow a rather large number of samples (12-18) to be analysed in one run within a relatively short time. The prominent advantage of the proposed methods over others is their extreme sensitivity. Both methods allow linear quantification of creatine kinase isoenzymes up to 700 U/l at 25 degrees C with a lower detection limit of 3 U/l, using a minute amount of sample (2 microliters). The diagnostic value of the methods was shown by their application to sera of patients with myocardial infarction or other diseases.

Macro serum CK-BB in a woman with severe primary hypothyroidism

We report the case of a woman with severe hypothyroidism and without concomitant myocardial damage, in whom elevated CK-MB values were measured by radioimmunological and enzymatic methods before and after thyroid replacement therapy. The patient's CK-MB activity was shown to be actually due to an atypical CK band between CK-MM and CK-MB (also termed "macro CK" or "idiopathic serum CK-BB").

Serum enzyme determinations in the diagnosis of acute myocardial infarction: an update

Serum CK-MB and LD-1 have proved extremely useful in the diagnosis and differential diagnosis of acute myocardial infarction. However, CK-MB is present in skeletal muscle and can be released during ischemic attacks; thus, abnormal serum CK-MB activities cannot be equated with myocardial injury. Even wider is the distribution of LD-1, which is found particularly in erythrocytes and renal cortex; hence, an abnormal LD-1 level also cannot be equated with myocardial injury. The method of choice and the final arbiter for the CK and LD isoenzymes is electrophoresis. The possibility of interpreting the results visually fulfills, in part, quality-control needs, and makes the technique suitable for small and large laboratories. Extreme analytic sensitivity is not needed, and electrophoresis provides clinically useful and acceptable results.

Mitochondrial creatine kinase as a tumor-associated marker

Sera from 167 patients with malignant tumor were examined with regard to mitochondrial creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2, CK). The CK (CKm) was detected in 66 cases (40%), in 42 of 96 men and in 24 of 71 women. Seventeen patients had hepatic carcinomas and 14 gastric carcinoma. CKm was also present in sera from patients with malignancy of the lung, the mammary gland etc. In the CKm positive group, about 85% had metastatic and/or infiltrating malignancy, and about 90% were undergoing chemotherapy. The figures resembled those in the CKm negative group. Mortality rates in the CKm positive group were 1.7 times higher than in the CKm negative group. CKm may be a marker of some biological factors leading to and/or resulting from a poor prognosis and not simply of primary or metastatic tumors. Most of the total serum CK activities in the CKm positive group were within normal limits. CKm activities in the gastric carcinoma group were higher than those in other groups, particularly in comparison to the liver carcinoma group.

The enzymology of skeletal muscle disorders

In myopathic disorders, abnormal serum enzyme activities are seen primarily in diseases of skeletal muscle where the condition involves the muscle fibers themselves. In denervation myopathies, serum enzyme activities are usually normal. The most dramatic increases of serum enzymes, particularly creatine kinase, are found in the dystrophic diseases, particularly Duchenne dystrophy. A review is given here of the many causes of abnormal serum enzyme activities where the source of enzymes is believed to be skeletal muscle. These include the dystrophies, various types of trauma, exercise, drug- and poison-induced causes including alcohol, malignant hyperthermia, inflammatory diseases, and miscellaneous causes. Tissue and serum activities are summarized for the commonly performed serum enzymes, i.e., CK, LD, AST, and aldolase. An extensive tabular and current description of the various types of dystrophies is given along with serum CK and pyruvate kinase activities.

Serum creatine kinase (CK) activity after M-subunit inhibition in patients with atypical CK isoenzymes--a comparison to findings in acute myocardial infarction

The serum levels of total creatine kinase (CK), and of CK-B, as estimated by the enzymatic anti-M-subunit immunoinhibition method, were studied in 14 patients with CK-B elevation associated with advanced malignant disease, in nine subjects with electrophoretically verified, immunoglobulin-bound CK-BB (macro CK) and in 28 patients with acute myocardial infarction (AMI). The range of CK-B activity was similar in all three groups. In AMI, the ratio CK-B/total CK at peak CK-B was less than 13% (mean 7%). In both the groups with atypical CK, the ratios varied from about 30% to nearly 100%, with a mean amounting to 2/3 of total CK activity. CK-B elevations in patients with untreated malignant tumours tended to increase with time, but occasionally remained fairly constant for months, like those in subjects with macro CK. Complementary CK isoenzyme separation, e.g. by electrophoresis, is needed to differentiate conditions with atypical CK activity, detected by routine use of CK-B determinations in the diagnosis of AMI.

Investigation of the heterogeneity of the MM isozyme of creatine kinase

MM creatine kinase (MM CK) from human skeletal muscle was resolved into 21 subspecies by isoelectric focusing. Rabbit and bovine MM CK's were also shown to have patterns of 21 bands. These results are compatible with the presence of six different M subunit forms in skeletal muscle, which by random association into dimers, could produce 21 different subspecies of creatine kinase. Two-dimensional isoelectric focusing of human MM CK yielded a diagonal pattern, indicating that the various enzyme subspecies were not induced by ampholyte-protein interaction. Heat inactivated serum appeared to stabilize various CK subspecies and also produced one further anodally migrating MM CK form. Fresh serum had combined inhibitory and stabilizing effects on the MM CK subforms, and allowed for the identification of four anodally migrating CK subspecies not present in tissue extract. These findings are of critical importance because of the widespread use of CK isoenzymes in serum for diagnostic purposes.

An assay for creatine kinase conversion factor

The M subunits of creatine kinase (CK) isoenzymes, MM and MB, are subject to a postsynthetic modification in serum. As a result of this modification three sub-bands of MM can be identified by agarose electrophoresis, called MM3, MM2 and MM1 in the order of increasing electrophoretic mobility towards the anode. An assay has been developed for the protein, called creatine kinase conversion factor, which catalyses the reaction leading to the sub-bands. The assay is based on the rate of conversion of MM3 to MM2 and MM1. The first order rate constant for the conversion, designated as kc, for sera of 24 apparently healthy adults ranges from 0.0221 to 0.0740 hr-1 with a mean of 0.0392 hr-1 under the conditions of the assay. Temperature and pH dependence of kc have been determined.

The origin of a cathode-migrating creatine kinase found in serum from a cancer patient

The origin of an atypical creatine kinase (CK, ATP:creatine N-phosphotransferase, EC 2.7,3.2) migrating cathodic to the MM position found in the serum of a cancer patient was studied. The electrophoretic mobility of the atypical CK is similar to that of the fast-moving cathodal mitochondrial CK. The relative molecular mass was estimated to be approximately 350000, and was similar to that of the fast-moving cathodal mitochondrial CK. The atypical CK reacted with anti-human mitochondrial CK antibody. It is therefore suggested that the atypical CK is of mitochondrial origin. After incubation in 2 mol/l urea, the enzyme was converted into a new form migrating to the MM position. The conversion was observed in liver mitochondrial CK but not heart mitochondrial CK. The residual CK activity after heating at 56 degrees C for 60 s was 77%, and the apparent Km value for creatine phosphate at 30 degrees C was about 0.27 mmol for the atypical CK. These characteristics were very similar to those of the liver mitochondrial CK, because the data from the enzyme determined at the same time were 75% for residual enzyme activity to heat, and 0.24 mmol for apparent Km value. Therefore liver mitochondria are suggested to be the source of the atypical CK.