THE INVIVO METABOLISM OF RECOMBINANT HUMAN ERYTHROPOIETIN IN THE RAT

  • 1 January 1989
    • journal article
    • research article
    • Vol. 73  (1) , 90-99
Abstract
We compared the in vivo plasma clearance and organ accumulation in anesthetized rats of 125I-labeled, recombinant human erythropoietin and 125I-labeled, desialated recombinant erythropoietin. The immediate volume of distribution of 125I-labeled, recombinant erythropoietin approximated that of the plasma volume. Its plasma clearance was multiexponential, with an initial rapid distribution phase (t1/2 = 53 minutes) and a slower elimination phase (t1/2 = 180 minutes). Organ accumulation of labeled recombinant erythropoietin, as compared with 125I-labeled human albumin, was negligible until 30 minutes after injection when small amounts appeared in the kidneys and bone marrow. Only 24% of the 125I-labeled, desialated recombinant erythropoietin was recovered immediately after injection, and 96% of the hormone was cleared from the plasma with a t1/2 of 2.0 minutes. The bulk of the desialated hormone accumulated in the liver where it was rapidly catabolized and its breakdown products released back into the plasma. Significantly, in contrast to unmodified erythropoietin, there was also early accumulation of desalated hormone in the kidneys, marrow, and spleen. Desialated orosomucoid but not orosomucoid, yeast mannan, or dextran sulfate 500 inhibited the rapid plasma clearance and hepatic accumulation of desialated erythropoietin. Oxidation of the desialated hormone restored its plasma recovery and clearance to normal but rendered it biologically inactive, and accumulation in organs other than the kidney was negligible.