Erythropoietin and the anemia of chronic diseases

The red-cell mass is continuously adjusted to the optimal size for its function as an oxygen carrier by messages transmitted to the bone marrow from an oxygen sensor in the kidney. These messages are mediated by the hormone erythropoietin. Erythropoietin is a glycoprotein growth factor synthesized by cells adjacent to the proximal renal tubule in response to signals from a renal oxygen-sensing device, probably a heme protein (1). In the bone marrow, erythropoietin binds to and activates specific receptors on the erythroid progenitor cells (2). In the presence of this erythropoietin-receptor complex the progenitor cells continue their predestined development into mature erythrocytes. Erythropoietin was the first hemopoietic growth factor to be molecularly cloned in 1985 (3). Our understanding of the biology and physiology of erythropoietin has been considerably improved with the advent of recombinant human erythropoietin (rHuEpo). During the past 7 years, rHuEpo has undergone extensive testing in clinical trials. It has been approved for treatment of the anemia of chronic renal failure, both in progressive renal failure and endstage renal failure (ESRD). In these instances, the administration of rHuEpo has been used in effect as a substitutive therapy, since patients' erythropoietin levels are very low despite severe anemia, due to the failure of affected kidneys to produce adequate amounts of the hormone. However, the application of rHuEpo has now moved largely from the primitive indication of renal diseases, and the hormone is currently under study in a number of anemic states of different etiologies, even with relatively high serum erythropoietin levels. Among these, some of the best documented indications are the anemia associated with malignancies, either due to neoplastic bone marrow infiltration or to chemotherapy-related myelosuppression, the anemia of myelodysplastic syndromes and AIDS, the anemia of chronic inflammatory diseases, prematurity, and bone marrow transplantation (4). The purpose of this review is to provide a summary of our present knowledge regarding rHuEpo therapy for the anemia of renal failure. We provide some clues for the correct use of rHuEpo in the treatment of the anemia of chronic inflammatory diseases. In addition, we address a series of new issues in the attempt to better understand the relationship between erythropoietin and liver disease.