This minireview is an update of a 1997 review on erythropoietin (EPO) in this journal. EPO is a 30,400-dalton glycoprotein that regulates red cell production. In the human, EPO is produced by peritubular cells in the kidneys of the adult and in hepatocytes in the fetus. Small amounts of extra-renal EPO are produced by the liver in adult human subjects. EPO binds to an erythroid progenitor cell surface receptor that includes a p66 chain, and, when activated, the p66 protein becomes dimerized. EPO receptor activation induces a JAK2 tyrosine kinase, which leads to tyrosine phosphorylation of the EPO receptor and several proteins. EPO receptor binding leads to intracellular activation of the Ras/mitogen-activated kinase pathway, which is involved with cell proliferation, phosphatidylinositol 3-kinase, and STATS 1, 3, 5A, and 5B transcriptional factors. EPO acts primarily to rescue erythroid cells from apoptosis (programmed cell death) to increase their survival. EPO acts synergistically with several growth factors (SCF, GM-CSF, 1L-3, and IGF-1) to cause maturation and proliferation of erythroid progenitor cells (primarily colony-forming unit-E). Oxygen-dependent regulation of EPO gene expression is postulated to be controlled by a hypoxia-inducible transcription factor (HIF-1alpha). Hypoxia-inducible EPO production is controlled by a 50-bp hypoxia-inducible enhancer that is approximately 120 bp 3' to the polyadenylation site. Hypoxia signal transduction pathways involve kinases A and C, phospholipase A(2), and transcription factors ATF-1 and CREB-1. A model has been proposed for adenosine activation of EPO production that involves protein kinases A and C and the phospholipase A(2) pathway. Other effects of EPO include a hematocrit-independent, vasoconstriction-dependent hypertension, increased endothelin production, upregulation of tissue renin, change in vascular tissue prostaglandins production, stimulation of angiogenesis, and stimulation of endothelial and vascular smooth muscle cell proliferation. Recombinant human EPO (rHuEPO) is currently being used to treat patients with anemias associated with chronic renal failure, AIDS patients with anemia due to treatment with zidovudine, nonmyeloid malignancies in patients treated with chemotherapeutic agents, perioperative surgical patients, and autologous blood donation. A novel erythropoiesis-stimulating factor (NESP, darbepoetin) has been synthesized and when compared with rHuEPO, NESP has a higher carbohydrate content (52% vs 40%), a longer plasma half-life, the amino acid sequence differs from that of native human EPO at five positions, and has been reported to maintain hemoglobin levels just as effectively in patients with chronic renal failure as rHuEPO at less frequent dosing. The use of rHuEPO and darbepoetin to enhance athletic performance is officially banned by most sports-governing bodies because the excessive erythrocytosis can lead to increased thrombogenicity and can cause deep vein, coronary, and cerebral thromboses.

Erythropoietin: Physiology and pharmacology update

Effect of inflammatory cytokines on hypoxia-induced erythropoietin production

Many complications after renal transplantation can be prevented if they are detected early. Guidelines have been developed for the prevention of diseases in the general popu- lation, but there are no comprehensive guidelines for the pre- vention of diseases and complications after renal transplanta- tion. Therefore, the Clinical Practice Guidelines Committee of the American Society of Transplantation developed these guidelines to help physicians and other health care workers provide optimal care for renal transplant recipients. The guide- lines are also intended to indirectly help patients receive the access to care that they need to ensure long-term allograft survival, by attempting to systematically define what that care encompasses. The guidelines are applicable to all adult and pediatric renal transplant recipients, and they cover the outpa- tient screening for and prevention of diseases and complica- tions that commonly occur after renal transplantation. They do not cover the diagnosis and treatment of diseases and compli- cations after they become manifest, and they do not cover the pretransplant evaluation of renal transplant candidates. The guidelines are comprehensive, but they do not pretend to cover every aspect of care. As much as possible, the guidelines are evidence-based, and each recommendation has been given a subjective grade to indicate the strength of evidence that sup- ports the recommendation. It is hoped that these guidelines will provide a framework for additional discussion and research that will improve the care of renal transplant recipients.

Recommendations for the Outpatient Surveillance of Renal Transplant Recipients

Adenosine receptor subtypes

Use of recombinant human erythropoietin outside the setting of uremia

Background. Erythrocytosis occurs in 10 to 15 percent of renal-transplant recipients, and there is in vitro evidence that the production of erythropoietin is modulated by adenosine. Methods. We prospectively evaluated the effects of theophylline, a nonselective adenosine antagonist, in eight patients with erythrocytosis after renal transplantation and in five normal controls. Results. After an eight-week course of theophylline treatment, the mean (±SEM) serum erythropoietin levels were significantly reduced in both the renal-transplant recipients (from 60±14 units per liter at base line to 9±7 units after treatment; P<0.05) and the normal subjects (from 6.9±0.8 units per liter at base line to 4.7±0.5 units per liter after treatment; P<0.05). Similarly, the hematocrits were reduced in both the transplant recipients (from 0.58±0.04 at base line to 0.46±0.03 after treatment; P<0.05) and the normal subjects (from 0.43±0.01 at base line to 0.39±0.01; P<0.05). In the renal-transplant recipients, red-ce...

https://www.nejm.org/doi/pdf/10.1056/NEJM199007123230203

J W Fisher

Papers

Effects of Theophylline on Erythropoietin Production in Normal Subjects and in Patients with Erythrocytosis after Renal Transplantation