Erythropoietin regulates endothelial progenitor cells.

Circulating bone marrow-derived endothelial progenitor cells (EPCs) promote vascular reparative processes and neoangiogenesis, and their number in peripheral blood correlates with endothelial function and cardiovascular risk. We tested the hypothesis that the cytokine erythropoietin (EPO) stimulates EPCs in humans. We studied 11 patients with renal anemia and 4 healthy subjects who received standard doses of recombinant human EPO (rhEPO). Treatment with rhEPO caused a significant mobilization of CD34(+)/CD45(+) circulating progenitor cells in peripheral blood (measured by flow cytometry), and increased the number of functionally active EPCs (measured by in vitro assay) in patients (week 2, 312% +/- 31%; week 8, 308% +/- 40%; both P <.01 versus baseline) as well as in healthy subjects (week 8, 194% +/- 15%; P <.05 versus baseline). The effect on EPCs was already observed with an rhEPO dose of about 30 IU/kg per week. Administration of rhEPO increased the number of functionally active EPCs by differentiation in vitro in a dose-dependent manner, assessed in cell culture and by tube formation assay. Furthermore, rhEPO activates the Akt protein kinase pathway in EPCs. Erythropoietin increases the number of functionally active EPCs in humans. Administration of rhEPO or EPO analogs may open new therapeutic strategies in regenerative cardiovascular medicine.

Endothelial progenitor cell proliferation and differentiation is regulated by erythropoietin.

BACKGROUND: Circulating bone marrow-derived endothelial progenitor cells (EPCs) promote vascular reparative processes. In humans, their number correlate with endothelial function and cardiovascular risk. We tested the hypothesis that darbepoetin alfa [i.e., a recombinant analogue of the cytokine erythropoietin (EPO)] stimulates proliferation and differentiation of EPCs. METHODS: We assessed CD34+ circulating stem cells (cSCs) in whole blood using flow cytometry and, in addition, proliferation/differentiation of EPCs in an in-vitro assay during 6 weeks of a standard darbepoetin therapy in eight patients with renal anemia. RESULTS: Darbepoetin treatment caused a significant increase in the number of CD34+ cSCs (week 2, 193%+/- 46%; and week 6, 298%+/- 90%; P < 0.05 vs. baseline). In addition, darbepoetin markedly increased the number of functionally active EPCs (week 2, 256%+/- 48%; and week 6, 299%+/- 59%; both P < 0.01 vs. baseline). The effect of darbepoetin on functional activity of EPCs assessed in a tube formation assay was dose dependent. Administration of darbepoietin caused activation of protein kinase B (Akt) in cultured EPCs. CONCLUSION: A standard treatment with darbepoetin markedly enhances EPC proliferation and differentiation in renal patients. The use of recombinant EPO analogues may be a novel and safe therapeutic approach in patients with vascular pathology.