[In vitro and in vivo studies of murine erythropoietic recovery after treatment with cyclophosphamide].

Abstract

Objectives: The aim of this study is to analyse functional changes in murine erythropoietic tissues over 20 days post cyclophosphamide (CY) treatment. The project was focused on the capability of femoral and splenic erythropoietic responsive cells (ERC) to proliferate with human recombinant erythropoietin (rh Epo) stimulation after cytotoxic treatment.

Materials and methods: CF-1 mice were injected i.p. with CY (200 mg/Kg). Individual lots were studied at 0, 2, 5, 7, 10, 14, 17 and 20 days post cytotoxic treatment. Haematologic parameters [packed red cells (PRC) reticulocytes, white blood cells] were scored. Erythropoietic differentiation was assessed by the 59Fe uptake assay and the proliferative profiles of erythropoietic progenitors were determined by 3H-thymidine incorporation assay with several doses of rh Epo (0-250 mU/mL). Total and differential cellularities were scored in bone marrow (BM) and spleen.

Results: A drastical decrease of total nucleated BM cells was noticed at 2 days post CY, although cellularity was restored by the 7th day. Spleen, however, failed in showing significant decrease. The maintenance of PRC was achieved through a deep erythropoietic reorganization. 59Fe uptake revealed changes in erythroid differentiation in both tissues. Spleen maturative contribution to whole erythropoiesis was always less than medullary supply, except on day 10 post CY when a transient compensatory red cell contribution was noticed. Proliferative assays revealed that erythropoietic recovery in BM post CY was delayed in comparison with myelopoietic restoration. Splenic erythroid proliferative pattern correlated with differentiation data.

Conclusions: Myelopoietic and erythropoietic progenitors showed different recovery patterns post CY administration in BM and spleen. Medullary hemopoietic lineages restoration described a particular sequence: myelopoiesis restitution was previous to the erythroid one. Medullary erythropoiesis occurred without drastic changes in erythropoietin sensitivity while the spleen showed a transient dramatic increment on 10 days post CY red proliferation. Experimental data strongly suggest that erythropoietic recovery after CY insult mainly depends on microenvironmental regulations rather than on hormone titers.