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

Abstract

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.

Fig. 1.

Gel exclusion chromatography (on Sephacryl G-300) of serum specimens from an acute viral hepatitis patient (○) 25 year-old-male, due to hepatitis B virus and isolated AST elevation female (●) described in this report and hemolysed RBC (◉). AST activity was determined in each of the fractions.

Fig. 2.

The electrophresis patterns of sampes [lane RH; from purified aspartate aminotransferase (c-AST) from hemolysed red blood cell (RBC), lane AVII; serum from acut viral hepatitis patient due to hepatitis B vivires, lane M; serum from macroaspartatemia patient] after AST stain by Sakakibara’s method. There is single band in RH lane(purified cytoplasmic-AST from RBC; 250IU). In lane AVH, there are two bands of which one is a major band corresponding to c-AST in RH lane and the other is a minor band suggested to mitochondrial-AST (m-AST). In M lane, there are two bands of which one is a minor band suggested to m-AST in AVH land and the other is a major band which is a new one. See text for further discussion.

Fig. 3.

Immunoglobulin electrophoresis patterns of macroaspartatemic patients. There is an atypical precipitin arc in the total anti-immunoglobulin (anti-Tig), anti-immunoglobulin G (anti-IgG) and anti-immunoglobulin GMA complex (anti-IgGMA). But there is not an atypical precipitin arc in the anti-immunoglobulin A and M. See text for further discussion.