ROLE OF ANTENNARY STRUCTURE OF N-LINKED SUGAR CHAINS IN RENAL HANDLING OF RECOMBINANT-HUMAN-ERYTHROPOIETIN

To elucidate the role of the branched structure of sugar chains of human erythropoietin (EPO) in the expression of in vivo activity, the pharmacokinetic profile of a less active recombinant human EPO sample (EPO-bi) enriched with bi-antennary sugar chains was compared with that of a highly active control EPO sample enriched with tetraantennary sugar chains. After an intravenous injection in rats, I-125-EPO-bi disappeared from the plasma with 3.2 times greater total body clearance (CItot) than control I-125-EPO. Whole-body autoradiography after 20 minutes of administration indicated that the overall distribution of radioactivity is similar, but I-125-EPO-bi showed a higher level of radioactivity in the kidneys than control I-125-EPO. Quantitative determination of radioactivity in the tissues also indicated that radioactivity of I-125-EPO-bi in the kidneys was two times higher than that of control I-125-EPO. The difference in plasma disappearance between (125)-EPO-bi and control I-125-EPO was not observed in bilaterally nephrectomized rats. The distribution of I-125-EPO-bi to bone marrow and spleen was similarly inhibited by simultaneous injection of excess amounts of either the nonlabeled EPO-bi or control EPO. These results indicate that the low in vivo biologic activity of EPO-bi results from rapid clearance from the systemic circulation by renal handling. Thus, the well-branched structure of the N-linked sugar chain of EPO is suggested to play an important role in maintaining its higher plasma level, which guarantees an effective transfer to target organs and stimulation of erythroid progenitor cells. (C) 1995 by The American Society of Hematology.