[The determination of the recognition site of an antiserum detecting desialylation on O-glycosidic carbohydrates of hCG and its clinical applications. The relationship between the presence of asialo-hCG and malignant change in trophoblastic disease].

ABSTRACT

Human chorionic gonadotropin (hCG) is a specific tumor marker glycoprotein hormone for trophoblastic diseases. It contains 4 asparagine-linked and 4 serine-linked carbohydrate units. Recently, variations in the carbohydrate moieties of hCG in chorio-carcinoma have been suggested. However, the immunological method of detecting these malignant transformational changes of carbohydrate units in hCG have not been investigated. We therefore attempted to assess the possibility of establishing a radioimmunoassay system which can detect these transformational changes in serine-O-glycosidically linked carbohydrate units of hCG. HCG-specific hCG beta COOH-terminal portion contains all 4 O-glycosidically linked sugar chains (positions 121, 127, 132 and 138). An antiserum (R141) generated against the enzymatically cleaved, desialylated hCG beta COOH-terminal peptide (residue 123-145) by toepad immunization method was extensively characterized. This antiserum reacts with asialo-hCG better than with native hCG. It does not bind with synthetic COOH-terminal peptides nor monosaccharides such as N-acetyl-D-galactosamine and D-galactose, which are sugar components in O-glycosidic carbohydrate chains. The HF-treated asialo-hCG, in which galactose residues are further removed, still reacts with the antiserum. The antiserum requires both the peptide sequence and N-acetyl-D-galactosamine residues for its binding. Glycophorine and fetuin, which also contain the same O-glycosidic carbohydrate structure, do not react with the antiserum. Beta subunit gains its binding capability to the antiserum only upon desialylation, while native alpha and beta subunits do not react. The antiserum has high specificity toward asialo-hCG in which particularly O-glycosidic carbohydrate units are desialylated. With a specific radioimmunoassay system using this antiserum (R141), urinary hCG preparations from 29 patients with various trophoblastic diseases were analyzed. Asialo-hCG immunoactivity was insignificant in all patients with hydatidiform mole, invasive hydatidiform mole and persisted trophoblastic disease. However, asialo-hCG was found in 2 out of 6 cases of choriocarcinoma. The existence of asialo-hCG may be related to the advancement of disease.(ABSTRACT TRUNCATED AT 400 WORDS)