EFFECTS OF SUBCUTANEOUS RECOMBINANT-HUMAN-ERYTHROPOIETIN IN NORMAL SUBJECTS - DEVELOPMENT OF DECREASED RETICULOCYTE HEMOGLOBIN CONTENT AND IRON-DEFICIENT ERYTHROPOIESIS

The present study evaluates the properties of the reticulocytes produced in healthy volunteers after treatment with different regimens of recombinant human erythropoietin (r-HuEPO). Twenty-four subjects were randomly assigned to one of three different subcutaneous (SC) r-HuEPO (Protcrit; Ortho Biotech) administration protocols (1: 300 U/kg on days 1, 4, 7, 10; II: 400 U/kg on days 1, 5, 9; III: 600 U/kg on days 1, 10) with oral iron supplementation (Niferex; 150 mg, twice a day). The characteristics of the reticulocytes produced were examined with a flow cytometry method that allows measurements of individual reticulocyte cell volume, hemoglobin concentration, and hemoglobin content. Administration of SC r-HuEPO was associated with a significant increase in the production of reticulocytes. The hemoglobin content of reticulocytes (CHr, in picograms of hemoglobin per cell) in the three groups was 28.5+/-1.0, 28.2+/-0.5, and 28.5+/-1.3, respectively, at baseline, decreased to 24.6+/-1.6 (p < 0.001), 24.5+/-2.3 (p < 0.001), and 27.5+/-1.8 (not significant) at day 10, and returned to baseline after r-HuEPO was discontinued (28.8+/-0.9, 28+/-0.8, and 28.8+/-1.4, respectively, at day 22). The percentage of reticulocytes with cell hemoglobin content less than 23 pg was taken as an indicator of iron-deficient erythropoiesis. At baseline, 5.6%+/-2.7%, 6.9%+/-3.4%, and 8.3%+/-3.8% of reticulocytes had less than 23 pg hemoglobin in groups I, II, and III, respectively. In groups I and II, 39%+/-15% and 40%+/-21%, respectively, of reticulocytes had CHr values lower than 23 pg at day 10, versus 15%+/-11.5% in group III (p < 0.01). The different behavior of group III may be due either to the different r-HuEPO schedule or, more likely, to the significantly higher baseline serum ferritin values in group III, which occurred by chance. In fact, production of reticulocytes with reduced hemoglobin content was inversely correlated with the log value of baseline serum ferritin (r = -0.82, p < 0.001). In addition, the production of hypochromic reticulocytes on r-HuEPO therapy was associated with a marked decrease in transferrin saturation. Within 2 weeks of stopping r-HuEPO treatment, reticulocyte indices and transferrin saturation returned to normal. These data demonstrate that r-HuEPO-induced accelerated erythropoiesis may lead to the production of iron-deficient reticulocytes even in subjects with normal iron stores. Measurement of reticulocyte cell hemoglobin content can be a useful early indicator of iron-deficient erythropoiesis.