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

Abstract. 125I labelled desialylated hCG (asialo-hCG) was treated with galactose oxidase, in order 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, however, 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. It is concluded that oxidation of the terminal galactosyl residues reduces the binding of asialo-hCG to the hepatic asialo-glycoprotein receptor, without affecting its hormonal properties. The ovarian uptake in vivo, however, is still limited by the high hepatic and renal clearance.