Flow cytometric detection of abnormal fetal erythropoiesis: application to 5-fluorouracil-induced anemia.

We sought to determine whether flow cytometric analysis of circulating fetal blood cells could be used to rapidly detect perturbations of fetal erythropoiesis. In addition, we wanted to determine whether this approach would allow sample collection by exsanguination instead of fetal cardiac puncture, a difficult technique used to prevent contamination of samples with maternal erythrocytes. To monitor fetal erythropoiesis from gestational day (GD) 14-20, we analyzed the cell size, RNA content, and percentage of circulating liver-derived reticulocytes relative to yolk-sac-derived erythroblasts. As a model toxicant, we chose 5-fluorouracil (5-FU), since we previously observed that maternal administration at 20-40 mg/kg on gestational day (GD) 14 produced fetal anemia on GD 16-17, as evidenced by dose-dependent decreases in the cell counts, hematocrit, and hemoglobin content of fetal blood obtained by cardiac puncture. We report herein that 48 hr after maternal 5-FU administration, both cardiac and peripheral blood samples exhibited a dose-dependent decrease in the relative percentage of reticulocytes, indicating a reduced rate of reticulocyte release from the fetal liver. Moreover, at 30 and 40 mg/kg, reticulocytes exhibited increased size and reduced RNA content on GD 16, but elevated RNA content (indicative of premature release) by GD 18. These data suggest that 5-FU inhibits both erythroid cell proliferation and RNA synthesis reversibly, resulting in an anemia that triggers compensatory release of immature reticulocytes.(ABSTRACT TRUNCATED AT 250 WORDS)