Abundance of Immunologically Active Alanine Aminotransferase in Sera of Liver Cirrhosis and Hepatocellular Carcinoma Patients

Background: Although alanine aminotransferase (ALT) is a widely used indicator of liver function, ALT enzymatic activity may not always reflect the degree of liver damage. Improved methods or approaches would be useful.

Methods: Monoclonal antibodies (mAbs) to ALT were generated to develop a sandwich enzyme immunoassay system. We used an immunoassay to measure ALT mass concentration and a common biochemical analyzer to assay ALT enzymatic activity in serum samples from patients with liver diseases and healthy individuals. The results from the 2 methods were compared and analyzed by ROC curve analysis.

Results: The ALT sandwich enzyme immunoassay system demonstrated reliable performance in linearity, recovery, and imprecision studies. The ALT activity assay exhibited a higher diagnostic accuracy in acute hepatitis (AH) patients, but the ALT immunoassay exhibited higher sensitivity and specificity in patients with chronic liver diseases. The areas under the ROC curve for ALT mass and enzymatic activity were 0.82 and 0.98, respectively, in AH, 0.99 and 0.52 in hepatocellular carcinoma (HCC), and 0.94 and 0.45 in liver cirrhosis (LC). Serum samples from HCC and LC patients had higher amounts of ALT–immunoglobulin complexes [median A450, 1.7 (interquartile range, 1.4–1.9)] than the other groups [1.3 (interquartile range, 0.9–1.6)].

Conclusions: Our analysis of sera from the HCC and LC patient groups revealed considerable amounts of immunologically active but catalytically inactive ALT. The amount of the ALT–immunoglobulin complex increased with the severity of the liver disease. The 2-site immunoassay method may be useful in the differential diagnosis of some causes of liver disease.

Electrophoretic analysis of enzyme-linked immunoglobulins and their clinical significance

The appearance of circulating enzyme-linked immunoglobulin complexes (E-Ig) is common for most enzymes used in clinical biochemical tests. The presence of E-Ig may result in altered enzyme activity in serum and interfere with the measurement of isoenzymes, and is thus of diagnostic importance. E-Ig can be identified by confirming that the binding protein is an immunoglobulin by its reaction with specific anti-human immunoglobulin antibodies. Currently, the presence of E-Ig in an individual is regarded as a benign phenomenon, not indicative of any particular disease process. However, it is becoming clear that E-IgG are closely associated with autoimmune states.

Laboratory and clinical features of lactate dehydrogenase subunit deficiencies

Heterozygous subjects with lactate dehydrogenase (LD) subunit deficiencies do not always show a low serum LD activity. Thus, it is necessary to examine the serum and erythrocyte LD isozyme patterns when screening for these conditions. We assessed patients with heterozygotes for H and M subunit deficiency by immunoblotting with anti-H subunit antibody. We could not find any protein or variant proteins in the heterozygous subjects with M subunit deficiency. On the other hand, the existence of variant protein was confirmed in the heterozygous subjects with H subunit deficiency. However, in one patient with homozygous for H subunit deficiency, no H subunit protein was observed. It is suggested that possibly many types of LD subunit deficiency may exist. Only patients with homozygous for M subunit deficiency show common patterns of clinical findings. All patients with LD subunit deficiencies have the risk of misdiagnosis of other clinical conditions from laboratory data because LD release is reduced. Thus it is important to detect them as a latent hereditary symptom poor disorders recognizing in laboratory medicine.

Lactate dehydrogenase isoenzymes

The analytical procedures for LD isoenzymes include electrophoresis, chromatography, immunochemical and kinetic methods. Electrophoretic methods are generally preferred because the resulting patterns are directly observable and all five isoenzymes are resolved in a single procedure. Chromatographic methods, with the introduction of HPLC, have recently been perfected in terms of speed, resolution, precision and accuracy. Immunochemical methods and kinetic methods are attractive because of their speed and simplicity. Therefore, the latter methods are used mainly for assaying acute myocardial infarction, where generally the determination of LD-1 and LD-2 is sufficient. In all other instances, however, electrophoretic separation is currently preferred. Ion-exchange high-performance procedures are useful prospects, particularly in view of their velocity in comparison with electrophoresis. In general, the LD isoenzymes assay contributes considerably to diagnosis, but the results must be used with an adequate knowledge of biochemistry, physiology and the advantages and drawbacks of the different assay methods used.