The in vivo metabolism of recombinant human erythropoietin in the rat

Abstract

We compared the in vivo plasma clearance and organ accumulation in anesthetized rats of 125I-labeled, recombinant human erythropoietin and 125I-labeled, desialylated 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, desialylated 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 desialylated 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 desialylated hormone in the kidneys, marrow, and spleen. Desialylated orosomucoid but not orosomucoid, yeast mannan, or dextran sulfate 500 inhibited the rapid plasma clearance and hepatic accumulation of desialylated erythropoietin. Oxidation of the desialylated hormone restored its plasma recovery and clearance to normal but rendered it biologically inactive, and accumulation in organs other than the kidney was negligible.

Erythropoietin after a century of research: younger than ever

“…Of major importance are the terminal sialic acid residues of these glycans (69). Like other asialo‐glycoproteins, asialo‐Epo is rapidly removed via galactose receptors of hepatocytes (70), because galactose is the preterminal sugar of the glycans. On the contrary, the introduction of additional N‐glycans into recombinant Epo by site‐directed mutagenesis results in a prolonged in vivo survival of the molecules (71, 72).…”

The enigma of the metabolic fate of circulating erythropoietin (Epo) in view of the pharmacokinetics of the recombinant drugs rhEpo and NESP

“…Epo isoforms having reduced sialic acids have a shortened plasma half‐life (71). In the latter case, an increased number of the preterminal galactose residues of the Epo molecules are exposed, resulting in rapid hepatic clearance (72–74). To some extent, native Epo as well as rhEpo or NESP may be desialylated by action of tissue and blood sialidases followed by galactose receptor‐mediated uptake through hepatocytes.…”

Optimization of anemia management in preterm infants

“…Information regarding the in vivo clearance of Epo remains incomplete. Some studies have shown that Epo is cleared by the liver (35,36) and the kidney (37) , however, their effects seem to be minimal (38). Receptor-mediated endocytosis in the bone marrow by erythroid progenitors followed by lysosomal degradation is the primary organ of Epo elimination from the body (17).…”

“…Identifying possible sources for the non-receptor mediated clearance mechanism of Epo is important for future characterization of the pathway. Some studies have shown that Epo is cleared by the liver (35,36) and the kidney (37) , however, their effects seem to be minimal (38). Buhrer et al determined the urinary losses of Epo in preterm infants confirming that clearance from the kidney is not a major contributor to Epo elimination (123).…”

“…Information regarding the in vivo clearance of Epo remains incomplete. Many studies have looked at the elimination of Epo in the liver (35,36,153) and the kidneys (37,154) , however, their effect seems to be minimal (38,67). Studies have shown that altered states of the bone marrow can significantly change the clearance of Epo suggesting that bone marrow is a significant source of Epo elimination (48,155).…”