Mechanism of clearance of circulating CA19-9 in rats

Molecules bearing the carbohydrate antigen 19-9 (CA19-9) epitope were prepared from serum and ascites of a patient with colon cancer or from the SW 1116 cell culture supernatant. Their plasma clearance mechanism was investigated in rats. The clearance curves of the molecules from three different sources showed a biphasic decrease. The coexistence of epitopes of CA19-9 and desialylated CA19-9 (Lea) in the same molecule was demonstrated by double-determinant enzyme immunoassays. CA19-9-bearing molecules with a low expression of Lea epitope, which were derived from the serum of a patient with colon cancer, showed mainly a slow disappearance, while the molecules with a high expression of Lea epitope from SW 1116 cells showed mainly a rapid disappearance. Thus, the clearance rate of the CA19-9-bearing molecules might be determined by their degrees of sialylation. This observation will be helpful for understanding the in vivo metabolism of CA19-9-bearing molecules.