Evidence of Receptor-Mediated Elimination of Erythropoietin by Analysis of Erythropoietin Receptor mRNA Expression in Bone Marrow and Erythropoietin Clearance During Anemia

Abstract

Erythropoietin (Epo) is the primary hormone that stimulates erythroid proliferation and differentiation through its cell surface receptor (EpoR) on erythroid progenitor cells. Previous studies have suggested that the bone marrow plays an important role in Epo's elimination. The changes in the EpoR mRNA levels and Epo's clearance in the bone marrow of 11 newborn lambs were studied to elucidate the role of EpoR in Epo's clearance under anemic conditions. Epo mRNA levels were measured by realtime polymerase chain reaction, and relative expression of EpoR was calculated by using the comparative CT method. The glyceraldehyde-3-phosphate dehydrogenase housekeeping gene was chosen as a control gene for the calculations. All lambs showed significant increase in bone marrow EpoR mRNA levels after phlebotomy-induced anemia. Epo's clearance determined from simultaneous pharmacokinetic studies with 125 I-recombinant human Epo showed a significant increase after phlebotomy-induced anemia that was similar to the increase in EpoR. By day 28 after phlebotomy, EpoR mRNA levels and Epo clearance had returned toward baseline. These results indicate that the changes in Epo's clearance are not caused by body growth but result from significant changes in the pool of EpoR. A linear mixed-effect model was used to evaluate the quantitative relationship between EpoR and Epo's clearance. This analysis demonstrated a highly significant positive linear correlation between EpoR and Epo clearance. Together, these findings provide strong evidence that receptormediated Epo clearance is an important route for Epo's elimination.

Receptor-Based Dosing Optimization of Erythropoietin in Juvenile Sheep after Phlebotomy

“…In addition, because the EpoRs are located primarily in the bone marrow, phlebotomy does not significantly change the EpoR pool. Our group recently showed that EpoR mRNA is up-regulated after the induction of anemia in sheep, which is consistent with the model used in this study (Nalbant et al, 2010). Because this study used the GAPDH gene as a control, it can be suggested that the number of EpoRs per cell increased rather than the total number of cells.…”

“…An additional study modeled the change in the EpoR level over time after the induction of anemia (Chapel et al, 2001). In a recent study by our group, we reported up-regulation of EpoR mRNA levels of 4.97 Ϯ 3.92 times baseline at 9 days after the induction of anemia (Nalbant et al, 2010). Although EpoR mRNA levels do not necessarily correlate directly with the number of receptors, an increase in the mRNA level is probably associated with an increase in the quantity of EpoRs.…”

Erythropoietin for Neuroprotection in Neonatal Encephalopathy: Safety and Pharmacokinetics

“…57 Similar to previous neonatal studies, 28,29,58,59 we found that high- Epo appears to be primarily eliminated by receptor-mediated clearance. 31,62 As in previous reports, 32,33,58,63 we found that Epo followed nonlinear pharmacokinetics. As the dose of Epo increased twofold, fourfold, and 10-fold, the overall exposure to circulating Epo (AUC) increased 2.7, 7.1, and 17.8 times, respectively.…”

Characterization of erythropoietin and hepcidin in the regulation of persistent injury-associated anemia

“…13–18, 33, 34 Nalbant et al 15 demonstrated the relationship between EPOr expression and anemia. They demonstrated a 12-fold increase in bone marrow EPOr levels nine days post phlebotomy (Hb: 3.7–4.2 g/dL) when compared to pre-phlebotomy (Hb: 9.7±1.1 g/dL).…”

“…13–18 Although EPOr is located on multiple cell types, it is mainly found within bone marrow on erythroid progenitor cells such as burst-forming unit erythroid (BFU-Es) and colony-forming unit erythroid cells (CFU-Es). 15 Specifically, the binding between EPOr and EPO is required for the proliferation and survival of CFU-Es to produce mature erythrocytes. 16–18 Previous work has shown that serum EPO levels are significantly elevated following burns and trauma.…”