The biochemical properties of urinary human chorionic gonadotropin from the patients with trophoblastic disease

Abstract

Human chorionic gonadotropin (hCG) was extracted and purified from urine of normal pregnant women and patients with hydatidiform mole and choriocarcinoma using the sam methods. Both hCG-hydatidiform mole and hCG-choriocarcinoma as well as hCG-normal pregnancy was separated into alpha and beta subunits by SDS disc electrophoresis upon treatment with 2-mercaptoethanol and showed the same immunoreactivities against anti-hCG, -alpha hCG, and -beta hCG as hCG in each radioimmunoassay. In vivo bioassay, bioactivities of hCG- normal pregnancy and hCG-hydatidiform mole were approximately 7,000 IU/mg (2nd IS), while that of hCG--choriocarcinoma was only 400 IU/mg. Conversely, the receptor binding activities in vitro of hCG-chorio carcinoma was about 3 times more effective than the other 2. Although the amino acid composition of these hCG preparations were practically identical, a great difference in the carbohydrate composition was observed. The significant difference was that while sialic acid was undetectable in hCG-choriocarcinoma approximately 8.5% of sialic acid was found in hCG-normal pregnancy and hCG-hydatidiform mole. A parallel finding was that iodinated hCG-choriocarcinoma was taken up in large quantities by the liver in comparison to the ovary which differed from that observed with hCG-normal pregnancy and hCG-hydatidiform mole in Parlow rats. The present findings support the thesis that neoplastic or malignant transformation of trophoblasts may result in an alteration of the glycosylation process, especially the sialylation, in the biosynthesis of hCG rather than the translation steps.