The effect of galactose oxidase treatment on the hepatic binding and biological activity of desialylated human chorionic gonadotrophin

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Abstract
125I-labeled desialylated hCG [human chorionic gonadotropin] (asialo-hCG) was treated with galactose oxidase, to find out whether oxidation of the terminal galactosyl residues would diminish the hepatic uptake of asialo-hCG. Specific binding to the hepatic asialo-glycoprotein receptor was monitored in vitro by a rat liver radioligand receptor assay (RRA). Hormonal activities were compared by ovarian RRA and by in vitro bioassay. Uptake studies were done in superovulated immature rats. Galactose oxidase treatment had hardly any influence on the in vitro ovarian binding and biological activity of [125I]asialo-hCG. Binding in the liver RRA was virtually abolished. In vivo hepatic uptake was considerably above the level of [125I]hCG, as was the uptake in the kidneys. The hepatic uptake was inhibited by the administration of a high dose of asialo-fetuin. Oxidation of the terminal galactosyl residues apparently reduces the binding of asialo-hCG to the hepatic asialo-glycoprotein receptor, without affecting its hormonal properties. The ovarian uptake in vivo is still limited by the high hepatic and renal clearance.