Hepatic Clearance and Metabolism in the Rat of a Human Breast Cancer Associated Glycoprotein (GCDFP-15)

Gross Cystic Disease Fluid Protein (GCDFP-15) is a 60,000 dalton glycoprotein isolated from human breast cyst fluid, composed of four 15,000 dalton monomers. Carbohydrate analysis indicates that each monomer has a single carbohydrate chain of the complex type. GCDFP-15 intravenously injected into rats showed a rapid circulatory clearance, the rate of clearance being faster in female animals [t1/2 = 12.8 (± 2.0) min. females, and 16.7 (± 2.6) min. males]. The major organs of clearance were the liver (70%) and kidneys (15%). Immunoperoxidase staining showed localization in Kupffer cells and the proximal convoluted tubules of the kidney. Removal of sialic acid from GCDFP-15 resulted in a more rapid clearance (t1/2 = 2.2 min) by the liver (85%). This clearance was inhibited by coinjection of asialo alpha1 acid glycoprotein. About 3% of GCDFP-15 was excreted in bile with a transit time through the liver of 38 min. Examination of the uptake of GCDFP-15 by isolated rat Kupffer cells showed that yeast mannan, fucosylated BSA, and carcinoembryonic antigen (CEA) failed to inhibit uptake, though the binding of GCDFP-15 was clearly saturable. This suggests that a novel receptor system on the rat Kupffer cell may be responsible for GCDFP-15 clearance.