Direct and Indirect Effects of Oxymetholone on Growth and Apoptosis of Hematopoietic Progenitor Cells In Vitro.

Despite a tarnished reputation, androgens remain a common treatment for aplastic anemia, especially in the Orient. Increased apoptosis of hematopoietic cells is characteristic of aplastic anemia; however, it has not been established whether androgens affect apoptosis of hematopoietic progenitor cells. In most previous studies regarding the in vitro effects of androgens on hematopoietic cells, whole bone marrow cells were used, rather than purified hematopoietic progenitor cells such as CD34+ cells. With these questions in mind, we investigated the direct and indirect effects of oxymetholone and other androgens on apoptosis and growth of normal hematopoietic progenitor cells (HPCs) in vitro. Oxymetholone did not rescue normal BM CD34+ cells and colony-forming cells (CFCs), other than mature erythroid CFCs, from apoptosis induced by growth factor deprivation. Unexpectedly, both testosterone and 5-dihydrotestosterone (5-DHT) at a concentration of 10⁻⁵ M, but not oxymetholone, increased the percentage of annexin-positive apoptotic cells (62.2 ± 5.9%, P < 0.05; 61.7 ± 6.4%, P < 0.05, respectively) compared with the controls (52.6 ± 5.6%). The addition of either stromal cell-derived factor-1 (SDF-1) or stem cell factor (SCF) partially relieved the increase in apoptosis induced by 5-DHT, and the addition of both SDF-1 and SCF completely reversed it. Oxymetholone did not rescue CFCs from interferon-gamma (IFN-g)-induced inhibition of clonal growth of BM CD34+ cells in methylcellulose cultures. Furthermore, oxymetholone did not mitigate IFN-g-induced suppression of CD34+ cell survival in the presence of growth factors. In a methylcellulose clonogenic assay, oxymetholone stimulated the clonal growth of colony-forming unit-erythroid at low concentrations, while not affecting colony-forming unit-granulocyte/macrophage or burst-forming unit-erythroid. Oxymetholone did not reverse the IFN-g-induced inhibition of colony formation by CD34+ cells. Interestingly, oxymetholone stimulated the production of SCF and thrombopoietin in normal human bone marrow stromal cells (BMSCs) through transcriptional regulation while inhibiting the production of interleukin-6. In agreement with this, oxymetholone-treated BMSCs better supported the survival and growth of HPCs. These results suggest that oxymetholone exerts most of its myelostimulatory effects via the regulation of cytokine production in BMSCs, rather than by direct action on hematopoietic progenitor cells.