gamma-Glutamyl transpeptidase activity in liver disease: serum elevation is independent of hepatic GGTP activity.

gamma-Glutamyl transpeptidase activity was measured in liver and serum from 110 patients undergoing diagnostic liver biopsy, including patients with alcoholic liver disease, fatty liver not due to alcohol, primary biliary cirrhosis, persistent hepatic disease, chronic active hepatitis and normal livers. Serum gamma-glutamyl transpeptidase was markedly elevated in patients with alcoholic liver disease and primary biliary cirrhosis while mean hepatic gamma-glutamyl transpeptidase activity was significantly increased only in the alcoholic liver disease group. There was considerable overlap of individual enzyme values among the different disease groups. There was no inhibitors or activators of liver gamma-glutamyl transpeptidase in any of these disorders. The increased liver activity was not related to the degree of hepatic fibrosis or cirrhosis. There was no correlation between hepatic and serum gamma-glutamyl transpeptidase activity. Hepatic and serum gamma activities were equally increased in individuals with alcoholic liver disease whether or not they were drinking at the time of the study. The data suggest that increased hepatic gamma-glutamyl transpeptidase activity is neither specific for alcoholic liver disease nor essential for serum GGTP to be elevated.

The biology of SAA: identification of the inducer, in vitro synthesis, and heterogeneity demonstrated with monoclonal antibodies.

Continued studies of the macrophage-derived mediator of SAA synthesis (SAA Stimulating Factor) confirm our previous observations that SAASF copurified with leukocytic pyrogen (LP) and lymphocyte activating factor (LAF). Moreover, new data demonstrate three separate isoelectric points for human LP-LAF-SAASF each of which possess the three biological activities. During the purification of 15,000 MW LP from crude stimulated mononuclear cell supernatants, only those fractions with pyrogenic activity in rabbits caused augmented stimulation of lymphocytes (LAF) and induced SAA synthesis in mice. Purified human LP stimulated isolated mouse hepatocytes in vitro to synthesize SAA in a dose-responsive manner. Colchicine treatment of hepatocytes led to decreased secretion of SAA into the medium and to an intracellular accumulation of SAA. Messenger RNA was isolated from the livers of endotoxin-stimulated mice and translated in a wheat-germ cell-free system. A major product was identified at 13-14,000 MW. Immunoprecipitation with anti-mouse AA identified several bands on autoradiography of polyacrylamide gels. These larger SAA precursors may account for the previously noted heterogeneity of human SAA, comprising at least 6 SAA isomers, of similar molecular weight but different solubility and electrophoretic charge characteristics. Two monoclonal antibodies (IgM-K and IgG1-K) have been prepared using standard cell hybridization techniques. They are directed at the variable COOH terminal region of SAA since they detect differences between the 6 human SAAs but do not react with human, monkey, dog or mouse AA proteins, human AP, C-reactive protein, IgG nor albumin. These antibodies will be useful in examining the origin, structure and function of SAA.

Monokine-induced synthesis of serum amyloid A protein by hepatocytes.

Infection or inflammation triggers the rapid appearance in the blood of a group of proteins known as acute phase reactants. Serum amyloid A protein (SAA) is an acute phase protein which is believed to be the precursor for the secondary amyloid fibril protein, known previously as amyloid of unknown origin, and now as amyloid A protein (AA). The site of synthesis of SAA has been controversial, with previous evidence suggesting that AA related proteins arise in liver, connective tissues, polymorphonuclear neutrophil leukocytes and spleen. However, in none of these systems could SAA synthesis be induced in vitro and the evidence rested on studies of tissues or cells arising from pre-stimulated animals. Our aim in the present studies was to prove that the liver is capable of SAA production and to identify the specific cell responsible for synthesis. The experiments demonstrate that SAA is synthesized in the liver by hepatocytes. In addition, colchicine, currently used for the treatment of amyloidosis, blocks the secretion of SAA from the hepatocyte, as has been shown for another acute phase reactan, C-reactive protein.

Hepatic transaminase activity in alocholic liver disease.

Glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) activity were measured in precutaneous needle biopsy specimens of human liver tissue and compared with transaminase values in serum obtained on the day of biopsy. Hepatic GPT activity was significantly decreased in liver tissue of patients with alcoholic hepatitis and cirrhosis compared with the activity in individuals with normal livers (P less than 0.05) and individuals with primary biliary cirrhosis (P less than 0.05). The decreased hepatic GPT activity was not related to the presence of cirrhosis in biopsy specimens and was not increased by the addition of saturating amounts of pyridoxal phosphate to the assay mixture. Hepatic GOT was also slightly but significantly lowered in individuals with alcoholic liver disease (P less than 0.05). The GOT/GPT ratio in serum and liver tissue was increased only in individuals with alcoholic liver disease, but the increase did not reach statistical significance. The increased GOT/GPT ratio is due primarily to the low activity of GPT in liver and serum. The less than expected elevation of GPT in serum of patients with alcoholic hepatic reflects the diminished hepatic GPT activity and lesser amounts of this enzyme available to leak into serum from damaged hepatocytes.