Frequent, Low-Dose Erythropoietin A Mechanistic Approach to Mitigate Adverse Cardiovascular Effects of Erythropoietin

Erythropoietin (EPO) is the most widely prescribed cytokine, yet the benefits and potential side effects of different dosing regimens are poorly understood. It is now recognized that erythropoietin administered at high doses to patients with chronic kidney disease, results in an increased risk of morbidity and mortality from heart disease and stroke. However, the mechanisms that mediate this increased risk of cardiovascular disease is not known. There are two receptors for erythropoietin the homodimeric EPO receptor (EPOR) and the heterodimeric beta common receptor ( CR)/EPOR. The investigators have demonstrated that activation of the heterodimeric CR/EPOR only occurs with high doses of EPO. Our exciting, published, preliminary data also demonstrates that the CR is in a complex with vascular endothelial growth factor receptor-2 (VEGFR-2) and that high doses of EPO activate VEGFR-2 through the CR, resulting in the deleterious effects of VEGFR-2 activation on the cardiovascular system. This is particularly important in patients with kidney disease since they are already at a high risk of cardiovascular disease. Moreover in advanced kidney disease cyanate derived from the high urea levels can non-enzymatically form an amide bond with EPO. This carbamylated EPO (cEPO) has no effect on hemoglobin, but still activates the heterodimeric CR/EPOR. To date there have been no studies that have directly measured levels of cEPO or activation of the CR/EPOR in patients with kidney disease. Our hypothesis is that the administration of low-doses of EPO more frequently will result in lower levels of total and carbamylated erythropoietin decreased activation of VEGFR-2 via the heterodimeric CR/EPOR and consequently decreased inflammation and atherosclerosis. The investigators will directly test this hypothesis by randomly allocating 120 patients with chronic kidney disease to either low- dose EPO given thrice weekly or the same cumulative dose, a high-dose, administered once every 2 weeks. Our hypothesis predicts that low-dose EPO will be as effective at correcting anemia, but will demonstrate less progression of carotid artery plaque, as assessed by non-contrast magnetic resonance imaging, as compared to the high-dose, EPO given every 2 weeks. To delineate how EPO affects blood vessels, the investigators will isolate endothelial cells from blood vessels in 20 patients who are assigned to low-dose EPO and 20 allocated to high-dose EPO. Within these cells the investigators will investigate the signaling pathways that are triggered by activation of CR/EPOR. In a substudy of 20 subjects with kidney disease randomized to low-dose EPO or to high-dose EPO, as well as 20 healthy controls receiving a single dose of high- or low-dose EPO, the investigators will determine how kidney function and dosing affects levels of total and carbamylated erythropoietin. The investigators' study will not only provide us with a thorough understanding of the mechanism by which EPO mediates the increased risk of atherosclerosis, but a clinical strategy to avoid the side effects of EPO therapy and a tool to quantify the cardiovascular risk of EPO and newer erythropoiesis stimulating agents by assessing activation of the heterodimeric CR/EPOR.