Erythropoietin (EPO)

Updated: Oct 7, 2021


 

Erythropoietin (EPO) is a cytokine glycoprotein hormone, the main regulator of erythropoiesis, which stimulates the formation of erythrocytes from late progenitor cells (it binds to erythropoietin-sensitive receptors, which are mainly located on erythroblasts, and promotes the active proliferation of blast forms) and increases the release of reticulocytes from the bone marrow.


The production of erythropoietin is regulated at the level of transcription of its gene, and since the only physiological stimulus increasing the number of cells synthesizing erythropoietin is hypoxia, the production and metabolism of erythropoietin does not depend on its concentration in plasma. Approximately 90% of erythropoietin is synthesized in the cells of the capillaries of the renal glomeruli and up to 10% produce liver cells.


In recent years, it has been established that in small quantities erythropoietin is synthesized by astrocytes of the nervous tissue, where it performs a neuroprotective role in hypoxic and ischemic brain lesions.


Erythropoietin is an extremely active hormone that exerts its action in the body in picomolar concentrations. Small fluctuations of its concentration in the blood lead to significant changes in the rate of erythropoiesis, and the normal range of its concentration ranges from 4 to 26 IU / l. Therefore, until the hemoglobin concentration falls below 105 g / l, the concentration of erythropoietin does not exceed the specified range and it is almost impossible to identify its increase. Erythrocytosis leads to the suppression of the production of erythropoietin by the mechanism of negative feedback. The half-life of erythropoietin is 69 hours.

Thus, knowing the mechanism of action of erythropoietin, one can consider its use as doping.

Erythropoietin belongs to the group S2 - peptide hormones (the list of prohibited substances and methods). The expediency of its use lies in the fact that it can cause an increase in the number of red blood cells in the blood and increase the oxygen capacity of the blood. Accordingly, more oxygen can be delivered to the tissues (especially muscle tissue!), Which increases the efficiency of the body.


The active use of erythropoietin doping originates from the moment when it was possible to obtain it artificially. By the mid-1980s, the first recombinant erythropoietin was obtained by introducing the human EPO gene (localized in humans on the seventh chromosome in the 11q-12q region) into ovarian hamsters.

Recombinant human p-EPO (obtained by genetic engineering) Recormon is identical in amino acid composition to natural human EPO. However, there are minor differences in the composition of glycosidic residues that affect the physico-chemical properties of the entire hormone molecule.


Since 1988, alpha-EPO (Eralfon, Binocrit, Eprex) and beta-EPO (Vero epoetin, Erythropoietin (Binnopharm), Epostim) have been used. When subcutaneously, their bioavailability is about 25%, the maximum concentration in the blood - after 12-18 hours, the half-life - up to 24 hours (with intravenous administration - 5-6 hours). Erythropoietin retard (NESP) Aranesp has been used for the past few years, and is longer lasting than other EPO drugs.


In 2008, Roche Pharmaceuticals announced the appearance of a third generation of erythropoietin. The drug in this group was named Mircera (methoxy polyethylene glycol-epoetin beta). Due to polyethylene glycol attached to the structure of the drug, which contributes to a longer half-life, Mircera is 6 times longer in the body than darbpoetin-alpha and 20 times longer than epoetin, which creates the possibility of long breaks between injections of the drug.


All preparations of EPO are used according to the same type of scheme, dosages are 50-300 IU per kg of weight. The result becomes noticeable after two weeks of use. Most experts are inclined to believe that the drug should not be used for more than six weeks.



 

Erythropoietin doping is actively used in cyclic sports with a predominant manifestation of endurance (running, swimming, skiing, speed skating, all types of rowing, cycling, and others), when the same movement is repeated many times, a large amount of energy is consumed, and the work itself is performed with very high intensity.


All methods for the detection of erythropoietin doping are either very laborious or do not provide a definite answer. The modern arsenal of methods designed to determine erythropoietin includes direct and indirect approaches. The direct method is based on the identification of those minor differences that were found in the study of natural endogenous erythropoietin and EPO, obtained by the method of genetic engineering. In particular, some researchers tried to use the differences in the distribution of electric charge, which are established for these two types of EPO molecules.


Based on these differences, attempts were made to separate the two types of molecules using capillary electrophoresis. And although such a separation is possible in principle, this requires large volumes of urine (up to 1 liter, which for obvious reasons is unacceptable for practice).


Also a few months before the Sydney Summer Olympics, the French anti-doping lab developed a new method for detecting recombinant erythropoietin. This method is rather complicated and is based on the isoelectric focusing of samples with the subsequent use of double blotting (the method of determining the content of macromolecules in the samples by hybridizing the contents of the samples with probes, eg antibodies).


Preference is given to indirect methods that require only small volumes of blood or urine samples — by deviating from the normal level in the biomedia of the sample; by serum level of soluble transferrin receptor (sTfR), the level of which increases after the introduction of recombinant EPO; determination in urine of fibrin and fibrinogen breakdown products after administration of EPO. Currently, it is practically impossible to reliably identify cases of exogenous administration of erythropoietin in the body. Therefore, changes in the physiological parameters of blood that are detected after administration of EPO are used for control.


So, the International Cycling Union uses the criterion of the maximum hematocrit value (50% for men). The International Ski Federation as a criterion established the maximum permissible hemoglobin values ​​(165 g / l for women and 185 g / l for men), as well as the level of reticulocytes not more than 0.2%. In case of exceeding the specified limit values ​​set during the control procedure before the competition, the corresponding athlete will be suspended from participation in the competition in order to protect health.


However, both hemoglobin and hematocrit are indicators that are affected by many fact