LIVER-DISEASE AND SERUM HEXOSAMINIDASE LEVELS - STUDIES IN A HUMAN HEPATOMA CELL-LINE (HEP G2 CELLS)

In various forms of liver disease, increased levels of the lysosomal e nzyme beta-hexosaminidase (Hex) occur in serum. This may be caused by disturbances of the hepatocytic function, and we therefore studied the intracellular and extracellular isoenzyme pattern of Hex in a human h epatoma cell-line (Hep G2), using an immunoassay method, which separat es Hex A and Hex B isoforms. This cell-line synthesizes and secretes H ex. The cumulative release of extracellular activity was about 3-10% o f the intracellular activity. B-isoforms comprised one-third of intrac ellular activity but only 20% of extracellular activity. The proportio n of extracellular B-isoforms increased with time, presumably due to i nstability of A-isoforms at 37 degrees C. Cycloheximide inhibited the release of Hex activity, whereas NH4Cl increased the extracellular fra ction of Hex, even at a concentration of 1 mmol/l. We Speculate that t he increased concentration of NH4+ in patients with liver disease inte rferes with the distribution pathway of the lysosomal enzymes. This mi ght be one reason for the increased serum Hex activity found in patien ts with liver disease.