Immunological identification in plasma of mitochondrial and cytoplasmic aspartate transaminase isoenzymes during experimental myocardial infarction

Aspartate aminotransferase isoenzymes

Aspartate aminotransferase (AST, EC 2.6.1.1) exists in human tissues as two distinct isoenzymes, one located in the cytoplasm (c-AST), and the other in mitochondria (m-AST). Striated muscle, myocardium, and liver tissues are the main sources of AST. A growing body of information suggests that determination of AST isoenzymes in human serum is useful in evaluating damage to some of these organs. In hepatic disease, the test is used to assess liver necrosis and for determining prognosis. It may also assist in identifying patients with active alcoholic liver disease. In patients with acute myocardial infarction, measurement of AST isoenzymes provides diagnostic information that differs from that obtained by determination of total creatine kinase and lactate dehydrogenase enzymes, and their isoenzymes.

Increase in mitochondrial GOT (m-GOT) activity after chronic alcohol consumption: clinical and experimental observations

In order to clarify the origin and the mechanism of increased serum activity of glutamic oxalacetic transaminase (GOT) in chronic alcoholics, clinical and experimental investigations were carried out. Mitochondrial (m-GOT) and cytosolic GOT (c-GOT) isoenzymes were separated chromatographically by using a mini-column packed with Sephadex A50. Sixty percent of 63 alcoholics had elevated serum GOT. The m-GOT activity in alcoholics with total serum GOT activity of over 50 Karmen Units was 17.2 +/- 1.6 K.U. and the m-GOT/GOT ratio was the highest when compared to those in non-alcoholic liver diseases. In in vitro study, six hours of incubation of isolated hepatocytes from rats fed ethanol chronically resulted in an increased leakage of m-GOT into the incubation medium and also showed a tendency of a higher m-GOT/GOT ratio than that from control rats. The m-GOT activity thus released into the medium showed a highly significant inverse correlation with the viability of hepatocytes. These data suggest that m-GOT substantially contributes to an increased serum GOT often observed in chronic alcoholics.

Prognostic value of mitochondrial aspartate aminotransferase in acute myocardial infarction

In 112 prospectively selected patients suffering from acute myocardial infarction (AMI), the serum CK, CK-MB, LD, HBD, AST and m-AST were determined from the time of admission to hospital and every 12 hours for three days in succession. Sixteen of the enrolled patients died due to complications which arose within the first four days of hospitalization while the rest had a favourable outcome. All enzyme activities were determined at 37 degrees C using routine methods; m-AST was measured using an immunochemical method. The statistical analysis of the results demonstrated that 12 hours after admission, serum m-AST and m-AST/AST ratio were significantly higher in the group of non-survivors compared with patients with a favourable prognosis. No significant differences in CK-MB were observed between survivors and non-survivors during the entire period. True and false positive rates were calculated for these and the other enzymes. An optimum decision level of 34 IU/L was chosen for m-AST and 10% for the m-AST/AST ratio. This gave a percentage of correctly classified patients, after 12 and 24 hours, of 74.9% and 91.9%, respectively. In conclusion, the immunochemical determination of m-AST in patients with AMI seems to be an early prognostic index which is able to distinguish patients with unfavourable outcome.

Blood level of mitochondrial aspartate aminotransferase as an indicator of the extent of ischemic necrosis of the rat liver

To assess the severity of ischemic liver injury, we examined release of mitochondrial aspartate aminotransferase (EC 2.6.1.1) and its cytoplasmic isozyme from the ischemic rat liver into the circulation. Their patterns of leakage were quite different: the level of cytoplasmic aspartate aminotransferase reached a peak soon after the circulation to the ischemic liver was restored, while that of mitochondrial aspartate aminotransferase increased slowly, reaching a maximum after more than 10 hr. On anoxic incubation of mitochondria isolated from the normal liver, oxidative phosphorylation capacity was lost within 2 hr, at which time no leakage of matrix enzymes was observed: more than 10 hr after-loss-of-oxidative phosphorylation were needed for the matrix enzymes to leak out of the mitochondrial membrane. Since the viability of cells is considered to depend on the capacity of oxidative phosphorylation, it is highly likely that the delayed appearance of mitochondrial aspartate aminotransferase in blood indicates the postmortem changes of injured cells. In fact, the cumulative activity of mitochondrial aspartate aminotransferase but not cytoplasmic aspartate aminotransferase in circulation after ischemic liver injury correlated fairly well with the decrease of total adenine nucleotides which were monitored to measure viable cells. The difference between mitochondrial aspartate aminotransferase and cytoplasmic aspartate aminotransferase as quantitative indices of hepatic necrosis may be due to the relative stability of the former and significant inactivation of the latter during hepatic ischemia. Therefore, the determination of mitochondrial aspartate aminotransferase in blood may be useful in the assessment of liver necrosis after ischemic injury.

Determination of mitochondrial aspartate aminotransferase in serum

Two specific and sensitive immunoassay methods for the determination of mitochondrial aspartate aminotransferase (m-AST) are described. One is a sandwich enzyme immunoassay which measures immunologically active m-AST using polystyrene balls coated with anti-m-AST antibody and peroxidase-labelled anti-m-AST antibody as the second antibody. The detection limit of this assay was 10 micrograms/l. The other is a paper disk method which measures catalytically active enzyme bound to anti m-AST antibody-conjugate paper disks. The calibration curve was linear up to 250 U/l. These assay methods were used to monitor the level of m-AST in serum. From measurements obtained by both methods, the correlation between the concentration of m-AST protein and its activity was poor (liver diseases, r = 0.539; myocardial infarction, r = 0.774) confirming that an inactive form of m-AST exists in serum, and that the specific activity of serum m-AST differs in individual diseases.

Systemic short-term fibrinolysis with high-dose streptokinase in acute myocardial infarction: time course of biochemical parameters

The course of plasma catalytic activities of total creatine kinase, creatine kinase isoenzyme MB, total, cytoplasmatic and mitochondrial aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alpha-hydroxybutyrate dehydrogenase, glutamate dehydrogenase and concentrations of myoglobin, urea, acidic alpha 1-glycoprotein and creatinine were followed in 33 patients suffering from acute myocardial infarction. All patients were randomized in a double-blind, prospective study. One group (18 patients) was infused with streptokinase 1.5 X 10(6) units/90 minutes; the control group received routine continuous i.v. heparin treatment (1000 units/h). Ten hours after completion of the study protocol, treatment of both groups of patients was continued with heparin, 1000 units/h and Aspisol, 1 g/day2). Streptokinase treatment induced earlier wash-out and therefore earlier peak levels of several enzymes: total creatine kinase (11 hours), creatine kinase isoenzyme MB (6 hours), total and cytoplasmatic aspartate aminotransferase (6 hours) and lactate dehydrogenase (9 hours). Total creatine kinase peak catalytic activity and myoglobin peak concentration were higher in the group receiving thrombolytic therapy. A significantly different course of catalytic activity between both treatment groups was found for total creatine kinase and creatine kinase isoenzyme MB, total and cytosolic aspartate aminotransferase, lactate dehydrogenase and alpha-hydroxybutyrate dehydrogenase. The course of mitochondrial aspartate aminotransferase catalytic activity was different only 12 hours after the beginning of treatment. The shift of several catalytic activities to an earlier peak level in plasma may indicate reperfusion of ischaemic myocardium due to thrombolytic therapy.

Mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase in sera of patients after myocardial infarction

Mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase (AST) were studied in the sera of 42 patients following acute myocardial infarction and compared to creatine kinase (CK), lactate dehydrogenase (LDH) and alanine aminotransferase (ALT). Mitochondrial AST( ASTm ) was detected in 93% (39/42) of patients. Maximum recorded ASTm activity was 59.5 +/- 8.8 U/l and was found 39.4 +/- 3.5 hours after the onset of symptoms (chest pain) of myocardial infarction. In contrast the maximum recorded cytoplasmic AST ( ASTc ) activity was greater (327 +/- 23 U/l) and it occurred earlier (33.5 +/- 2.2 hours) after onset of infarction compared to ASTm . ASTm correlated significantly (p less than 0.05) with ASTc , LDH and ALT but not with total CK or CK-MB. ASTc correlated significantly (p less than 0.05) with total CK, CK-MB and LDH but not ALT. Maximum recorded ASTm activity was significantly associated with the clinical assessment of left ventricular failure ( Killip classification) but not with ventricular arrhythmias. In a subset of 15 patients evaluated with invasive hemodynamic measurements of cardiac output and pulmonary capillary wedge pressure. ASTm correlated significantly (p less than 0.05) and better than CK-MB with the hemodynamic assessment of left ventricular dysfunction. Thus ASTSm can be readily identified in sera of patients after acute myocardial infarction and may be of value in the evaluation of patients with acute myocardial infarction.

Measurement of aminotransferases: Part 1. Aspartate aminotransferase

Aminotransferases are ubiquitous enzymes of mammalian cells and several are of important diagnostic use. The application of aspartate aminotransferase activity measurements in serum from individuals suffering from myocardial infarction brought about a new dimension in clinical laboratory testing in the 1950s. This review focuses on measurement techniques for aspartate aminotransferase and their application (a subsequent article will review other aminotransferases). Assay techniques measuring enzyme activity are direct spectrophotometric measurements, manometric techniques, assays using dye substances, coupled enzyme techniques, and radiometric procedures. Of these procedures, the one employing malate dehydrogenase and NADH is the most important and is covered in particular detail. The estimation of the mitochondrial isoenzyme of aspartate aminotransferase is also of clinical interest, in particular for estimating severity of disease or in specific applications (e.g., chronic alcoholism). Methods reviewed for estimation of this enzyme are electrophoresis, chromatography, differential kinetic behavior, and immunochemical separation. Determination of the enzyme protein by techniques independent of its catalytic activity are also reviewed.

Determination of aspartate aminotransferase isoenzymes in hepatic diseases--preliminary findings

The study sought to establish a relationship between the AST isoenzyme levels in serum and degree of hepatic damage, by using a new and simple immunochemical method for the differential determination of the isoenzymes. Sixty-nine patients with various hepatic diseases were studied. During hepatic damage, cytoplasmic isoenzyme (s-AST) is found in greater quantities than mitochondrial isoenzyme (m-AST), but the m-AST level increases to a greater extent in acute liver diseases. However, m-AST in alcoholic hepatitis is higher than expected from the total AST (t-AST) values. The ratio of m-AST to t-AST seems to discriminate alcoholic hepatitis from other liver diseases.

Immunological determination of serum m-AST activity in patients with acute myocardial infarction

Serum m-AST (mitochondrial isoenzyme of AST) activity in patients with acute myocardial infarction was determined quantitatively by a new immunological technique which is sensitive and easily available. All 31 patients with acute myocardial infarction showed abnormally high levels of serum m-AST (more than 5 KU/ml); the mean serum m-AST activity attained its peak (42.0 +/- 4.9 KU/ml) on the first day after the onset of infarction 5 hours later than that of serum t-AST (total AST) activity in 15 patients whose peak m- and t-AST activities were identified clearly. The individual peak m-AST activity correlated with the total CK released (r = 0.83, n = 15), indicating that the release of m-AST also reflects the infarct size. The ratio of serum m-AST/t-AST increased following myocardial infarction and showed the maximal value (average 25.7%) on the third to seventh day after onset. This ratio in the patients with acute myocardial ifarction was also greater than that in patients with liver disease or with heart failure from causes other than acute myocardial infarction. In the patients who had the additional complication of heart failure and/or cardiogenic shock the ratio was also greater than that is the patients without these hazards. These results indicate that the ratio of serum m-AST/t-AST reflects the severity of the myocardial cellular damage in acute myocardial infarction.