Erythropoietin (EPO) is a glycoprotein hormone that is a growth factor for erythrocyte (red blood cell) precursors in the bone marrow. It increases the number of red blood cells in the blood. Synthetic erythropoietin is available as a therapeutic agent produced by recombinant DNA technology. It is used in treating anemia resulting from chronic renal failure or from chemotherapy for the treatment of cancer. Its use is also believed to be common as a blood doping agent in endurance sports such as bicycle racing, triathlons and marathon running. more...
Discovery and Biological Role
The existence of a humoral factor regulating red blood cell production was first postulated in 1906 based on transfusion experiments in rabbits. In 1950, the still unidentified erythropoietic factor was found to be stimulated in rats breathing a low-oxygen atmosphere, thus establishing the elements of its biological regulation. In the 1960s its source was identified as the kidneys. The human hormone was first purified in 1977 from human urine and a small amount was used experimentally to treat patients with anemia.
EPO has now been identified as a glycoprotein with a molecular mass of about 30,000 Daltons. It has a 165 amino acid chain with four oligosaccharide side chains and circulates in the blood plasma at a very low concentration (about 5 pmol/L).
In adult humans, EPO is produced primarily by peritubular cells in the kidneys, where its production is stimulated by low oxygen levels in the blood. Some EPO is also produced by the liver, which is the primary source in the fetus.
EPO acts by binding to a specific erythropoietin receptor (EpoR) on the surface of red cell precursors in the bone marrow, stimulating them to transform into mature red blood cells. As a result the oxygen level in blood reaching the kidney rises and the amount of EPO produced decreases.
Because the kidneys are the primary source of erythropoietin, chronic kidney disease often results in a systemic deficiency of EPO and consequent anemia. Anemia can also occur in cancer patients, sometimes as a direct result of the malignancy but usually as a side effect of chemotherapy.
Also, in patients who may require a blood transfusion or undergo surgery where blood loss is expected, EPO is given in advance as a precaution. The bone marrow produces more red blood cells, and if blood is lost during the operation, there is still enough to sustain the patient.
EPO as a Therapeutic Agent
A portion of the human EPO isolated from urine in 1977 was acquired by Amgen, Inc., an American biotechnology company. In 1983, the gene coding for it was identified at Amgen just weeks ahead of a corporate rival, allowing the company to establish a dominant patent position in the field after an epic legal battle. Recombinant DNA technology was used to express the protein in Chinese hamster ovary cells, which allowed a synthetic form of EPO (rEPO) to be produced in commercial quantities for the first time.
Recombinant EPO was launched as a pharmaceutical product by Amgen for treatment of anemia resulting from chronic kidney disease in 1989 under the brand name Epogen. In 1991 it was also approved for treating anemia resulting from cancer chemotherapy. Johnson & Johnson (J&J), an American pharmaceutical company, markets EPO under license from Amgen for cancer chemotherapy under the brand name Procrit. Amgen’s patents have so far prevented other companies from entering the US market. Even though the patents are all based on work done in the early 1980s, the last of them will not expire until 2015, thirty-two years after the date of the original application.
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