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 produc ed in healthy volunteers after treatment with different regimens of re combinant human erythropoietin (r-HuEPO). Twenty-four subjects were ra ndomly assigned to one of three different subcutaneous (SC) r-HuEPO (P rotcrit; 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 c haracteristics of the reticulocytes produced were examined with a flow cytometry method that allows measurements of individual reticulocyte cell volume, hemoglobin concentration, and hemoglobin content. Adminis tration of SC r-HuEPO was associated with a significant increase in th e 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, decre ased 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 w as discontinued (28.8+/-0.9, 28+/-0.8, and 28.8+/-1.4, respectively, a t day 22). The percentage of reticulocytes with cell hemoglobin conten t less than 23 pg was taken as an indicator of iron-deficient erythrop oiesis. At baseline, 5.6%+/-2.7%, 6.9%+/-3.4%, and 8.3%+/-3.8% of reti culocytes had less than 23 pg hemoglobin in groups I, II, and III, res pectively. 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, t o 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 p roduction of hypochromic reticulocytes on r-HuEPO therapy was associat ed with a marked decrease in transferrin saturation. Within 2 weeks of stopping r-HuEPO treatment, reticulocyte indices and transferrin satu ration returned to normal. These data demonstrate that r-HuEPO-induced accelerated erythropoiesis may lead to the production of iron-deficie nt reticulocytes even in subjects with normal iron stores. Measurement of reticulocyte cell hemoglobin content can be a useful early indicat or of iron-deficient erythropoiesis.