Mitochondrial aspartate aminotransferase linked to immunoglobulin G of the kappa-lambda type: report of a case

Transient human anti-mouse antibody generated with immune enhancement in a carbohydrate antigen 19-9 immunoassay after surgical resection of recurrent cancer

We report a case of transient human anti-mouse antibody from a 64-year-old man in a carbohydrate antigen 19-9 immunoassay using an AIA 1800 analyser that generated immune enhancement after surgical resection of recurrent cancer.

METHODS

The carbohydrate antigen 19-9 concentration was measured using an AIA 1800 analyser and a UniCel Dxl 800. Size-exclusion high-performance liquid chromatography was carried out on a Superose 12 column to estimate the carbohydrate antigen 19-9 elution profile using an AIA 1800 analyser. To determine whether IgM in the patient contributed to the carbohydrate antigen 19-9 immunoassay, immunoprecipitation was performed. Furthermore, mouse immunoglobulins were added to the patient's serum to verify that the patient's IgM reacted with it.

RESULTS

The carbohydrate antigen 19-9 concentration was >400 and 9.5 kU/L using an AIA 1800 analyser and using a UniCel Dxl 800, respectively. In the single carbohydrate antigen 19-9 peak, the molecular weight corresponded to IgM by size-exclusion high-performance liquid chromatography on a Superose 12 column. In the immunoprecipitation reaction and addition of mouse immunoglobulins, there was interference for anti-human IgM and mouse immunoglobulins whose recoveries were 3.2 and 14.2%, respectively. These results indicated that IgM in the patient's serum interfered with the carbohydrate antigen 19-9 immunoassay using an AIA 1800 analyser.

CONCLUSION

A novel transient human anti-mouse antibody generated with immune activation in a carbohydrate antigen 19-9 immunoassay using an AIA 1800 analyser was identified in a patient with rectal cancer after surgical resection. These findings demonstrate the importance of monitoring tumour markers in patients after treatment with mouse monoclonal antibody.

Development of macro-aspartate aminotransferase in a patient undergoing specific allergen injection immunotherapy

Macro-aspartate aminotransferase (macro-AST), a complex between normal AST and an immunoglobulin, is recognized as a cause of isolated elevation of AST. Though its pathogenesis is unknown, previous reports have been suggestive of an autoimmune process. We describe a case of macro-AST formation in a patient with previously normal liver enzymes in whom an isolated AST elevation was discovered after initiation of specific allergen injection immunotherapy (SIT) for allergic rhinitis. We propose that SIT in this otherwise healthy patient led to the formation of macro-AST as a consequence of antibody cross-reaction (molecular mimicry). Awareness of this possible mechanism of macroenzyme development may be helpful to physicians evaluating patients with isolated elevations in AST.

Macro-aspartate aminotransferase in a female with antibodies to hepatitis C virus

Persistent elevation of aspartate aminotransferase (AST) activity in serum due to the presence of a macroenzyme form of AST (macro-AST) may lead to diagnostic confusion in many clinical conditions, particularly those associated with chronic liver disease. We describe a case of macro-AST arising in an adult female with a false-positive hepatitis C virus (HCV) RNA test result that was not accompanied by other biochemical or histologic evidence of liver disease. The presence of macro-AST in serum was confirmed utilizing size-exclusion, high performance liquid chromatography (HPLC) and Protein G-agarose beads to precipitate immune complexes of AST and immunoglobulin G followed by centrifugation and AST activity measurements in the supernatant. A brief review of the clinical enzymology of AST and methods used to quantify serum macro-AST activity is provided.

Immunochemical study of immunoglobulins bound to lactate dehydrogenase

Immunochemical analysis of lambda type Bence Jones protein (BJP: designated as Suzuki-BJP) and IgG-lambda type M-protein (designated as Miki-IgG), lambda type BJP (designated as Miki-BJP) which showed non-specific binding with lactate dehydrogenase (LD, EC 1.1.1.27) was carried out in two cases. When the purified LD mixed with NADH was eluted through the CNBr-Sepharose 4B coupled to Suzuki-BJP or Miki-IgG, the affinity with these adsorbents was not demonstrated. The amino acid residue of the N-terminal in the Suzuki-BJP and lambda chain of the Miki-IgG was determined to be tyrosine by primary structure analysis, on the other hand, alanine was detected in the gamma chain of the Miki-IgG that did not have LD binding ability. By counter affinity electrophoresis, it was shown that LD bound to a synthetic peptide consisting of 15 amino acid residues of N-terminal which had the same beta-sheet structure as the Suzuki-BJP. It seems probable that LD combines with BJP (or IgG) molecule at the NAD+ binding site producing a three-dimensional structure similar to NAD+.

Macroaspartasemia as a cause of isolated elevation of aspartate aminotransferase--its biochemical and physiological characteristics

OBJECTIVES

The increase of serum aspartate aminotransferase (AST) is generally found in hepatic, cardiac, muscular disease and hemolytic disorders of the red blood cell (RBC). The elevation of its activity is suspected in pathological conditions of these organs. However, instances without any of those conditions rarely exist.

METHODS

The experimental samples were obtained from a normal person's hemolysed RBC, a hepatitis patient and a macroaspartatemic female's serum. They were studied with exclusion chromatography, electrophoresis of AST and changes of AST activity due to Polyethylene Glycol (PEG) and various conditions on storage.

RESULTS

1) The patterns of AST activity by exclusion chromatography are similar to the hemolysed RBC and the hepatitis's serum but differs by the isolated AST elevation. 2) The AST activity with addition of PEG and different anti-immunoglobulin subtypes to different serums are slightly decreased in hepatitis but markedly decreased with PEG and anti-IgG in macroaspartatemia. 3) The patterns of AST activity in electrophoresis are single band-cytosomal AST (cAST)-from hemolysed RBC and two bands-mitochondrial AST (mAST) and cAST-from hepatitis, the major being cAST and the minor mAST. Even though there are two bands, the major one is atypical and the minor corresponds to mAST in macroaspartatemia. 4) The changes of AST activity on storage according to time and temperature show to be stable over 4 weeks at room temperature and cooled condition, and 9 weeks under frozen state in macroaspartatase.

CONCLUSION

Concluding from the above findings, macroaspartatemia is an enzyme-immunoglobulin complex composed of cAST with IgG. MacroAST might be stabler than usual AST at physical conditions.

Aspartate aminotransferase-linked immunoglobulin complexes in serum of a patient with primary biliary cirrhosis

A 51-year-old woman who had been treated for primary biliary cirrhosis (PBC) was admitted to our hospital for evaluation of unexplained, isolated, persistently increased aspartate aminotransferase (AST) activity. Results of laboratory tests on admission showed: AST 171 KU, alanine aminotransferase 28 KU, and anti-mitochondrial titer 1/1280. Results of hepatitis B surface antigen (HBs Ag) and hepatitis C virus antibody (HCV Ab; C100-3) assays were negative. Histology of a liver biopsy specimen was compatible with a diagnosis of PBC (stage III of Scheuer's classification). The molecular size of serum AST was estimated to be more than 500,000 by high-performance size-exclusion liquid chromatography. Electrophoretic analysis showed an abnormal band of AST between supernatant AST (sAST) and mitochondrial AST (mAST), which band was characteristic of AST-immunoglobulin complexes (AST-Ig). Ouchterlony double-diffusion and immunoprecipitation tests identified the immunoglobulin component as IgM. The presence of AST-Ig appeared to be responsible for the elevated serum AST.

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.

Incidence and properties of aspartate aminotransferase-immunoglobulin complexes in patients with a high serum aspartate to alanine aminotransferase ratio

Sera of 260 patients with high serum aspartate aminotransferase (L-aspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1; AST)/alanine aminotransferase (L-alanine: 2-oxoglutarate aminotransferase, EC 2.6.1.2; ALT) ratio (greater than 2.0) and high serum AST (greater than 45 IU/1) were selected and tested for the presence of immunoglobulin complexed-AST, by using immunoprecipitation reaction and counterimmunoelectrophoresis. The macromolecular AST was confirmed by size-exclusion high-performance liquid chromatography (HPLC). 34 patients out of 260 were found to have AST-immunoglobulin complexes (13.1%). The classes of AST-linked immunoglobulins were identified to be alpha in 28 cases (82.4%, P less than 0.01), mixed type of alpha and gamma in 5 cases (14.7%) gamma in one case (2.9%). Positive frequency was the highest in liver malignancies, either primary (9/26, 34.6%) or metastatic (7/17, 42.2%), followed by other malignancies (6/55, 10.9%) and chronic liver diseases (4/22, 18.2%). Thus, it can be strongly suggested that the immunoglobulin A complexed-AST is frequently found in association with liver malignancies.

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.

Immunoglobulin-AST complex

A case of AST-IgG complex presenting as an isolated AST elevation is described. Measurement of elevated serum AST activity is dependent upon the inclusion of pyridoxal 5-phosphate in the substrate.