This study compares the effects of a high dose of methotrexate (HDMTX) to that of a high dose of methotrexate plus leucovorin protection on the hemopoietic stem cells in a murine model. C57BL × C3H F1 mice were treated with a single large bolus (500 mg/kg body weight) of methotrexate or with the same dose of the drug plus leucovorin administered in fractionated doses during the following 24 hr. At 1 to 2 days after the administration of HDMTX, there was a large bone marrow and spleen depopulation of pluripotent stem cells and of committed and recognizable progenitors. At 2 to 3 days, a severe fall of white blood cells and reticulocytes ensued. The recovery process of hemopoietic precursors followed alternate phases of overshooting and secondary falls. Leucovorin administration appeared to protect all stages of hemopoiesis and prevented the severe drops of bone marrow cellularity and stem cell content which followed the HDMTX bolus. However, the effect of leucovorin on peripheral blood cell reduction was less significant. After treatment with HDMTX, the recovery of bone marrow cells and the burst of splenic hemopoietic activity followed a pattern similar in both leucovorin-protected and unprotected animals, but in the former, the increase in stem cells and hemopoietic progenitors appeared to reach higher values and to last longer. In particular, the overshooting of colony-forming units, culture and erythroid, reached a higher peak in leucovorin-treated mice and was more prolonged. Our results indicate that, in HDMTX-treated mice, leucovorin protection involves the earliest stages of hemopoiesis, assuring the maintenance of a satisfactory endowment of stem and progenitor cells.
This investigation was supported in part by Contract 7900653, Progetto Finalizzato “Controllo Crescita Neoplastica” from the Consiglio Nazionale delle Richerche, Rome.