Erythropoietin Induced Erythroid Precursor Pool Depletion Causes Erythropoietin Hyporesponsiveness

Erythropoietin (EPO) hyporesponsiveness is demonstrated by a persistence of anemia despite high dose of recombinant human erythropoietin (rHuEPO) or requirement of large doses to maintain the target hemoglobin concentration. The purpose of this study is to demonstrate that the bone marrow depletion induced by rHuEPO treatment may another contributing factor to hyporesponsiveness.

Healthy Wistar rats were given single dose (SD) or multiple doses (MD) of rHuEPO. In MD study, animals were challenged with thrice-weekly (100 IU/kg) over two weeks and the pharamcodynamic biomarkers included reticulocyte (RET) and red blood cells (RBC) counts, and hemoglobin (HGB) concentrations. In SD study, in addition to the biomarkers in the peripheral blood, the erythropoietic responses in bone marrow and spleen were also quantified using a flow cytometric immunophenotyping technique. The total marrow and spleen cellularity was quantitatively assessed using flow cytometry. A mathematical approach involving measuring RET age distribution was developed to evaluate the RET loss due to neocytolysis. The pharmacokinetics of rHuEPO was assessed by measuring serum concentrations over time using ELISA.

In MD study, a slow and oscillatory decline of RET response was observed before the administration of the last dose on day 11. The RET kept decreasing below the baseline and reached a nadir on day 22, followed by a slow return to the baseline on day 28. These observations demonstrated the tolerance and rebound phenomena. In SD study, the RET decreased below the baseline after day 6. A depletion of the bone marrow erythroid precursor cells was also observed. Meanwhile, neocytolysis of RET was only observed from day 3–5 after rHuEPO injection. These results suggested that the reduced levels of RET after day 6 resulted from the depletion in the erythroid precursor cells in bone marrow induced by rHuEPO treatment.

The EPO hyporesponsiveness is of clinical importance because it is associated with an increased risk of death or cardiovascular events. The findings in this study demonstrate that EPO-induced erythroid precursor depletion may contribute to the rHuEPO hyporesponsiveness. When the erythroid precursor cells are depleted, an increase of rHuEPO dose would not show much benefit, due to the smaller number of cells present to initiate the erythropoiesis. These findings provide additional justification for reducing the doses of erythropoietin stimulating agents in anemic patients demonstrating hyporesponsiveness.

No relevant conflicts of interest to declare.