Erythropoietin

Erythropoietin, also known as EPO, is a is_associated_with::glycoprotein is_associated_with::hormone that controls is_associated_with::erythropoiesis, or red blood cell production. It is a is_associated_with::cytokine (protein signaling molecule) for is_associated_with::erythrocyte (is_associated_with::red blood cell) precursors in the is_associated_with::bone marrow. Human EPO has a molecular weight of 34 kDa.

Also called hematopoietin or hemopoietin, it is produced by interstitial fibroblasts in the kidney in close association with is_associated_with::peritubular capillary and is_associated_with::proximal convoluted tubule. It is also produced in perisinusoidal cells in the is_associated_with::liver. While liver production predominates in the fetal and perinatal period, renal production is predominant during adulthood. In addition to erythropoiesis, erythropoietin also has other known biological functions. For example, it plays an important role in the brain's response to neuronal injury. EPO is also involved in the wound healing process.

is_associated_with::Exogenous erythropoietin is produced by is_associated_with::recombinant DNA technology in is_associated_with::cell culture. Several different pharmaceutical agents are available with a variety of is_associated_with::glycosylation patterns, and are collectively called erythropoiesis-stimulating agents (ESA). The specific details for labelled use vary between the is_associated_with::package inserts, but ESAs have been used in the treatment of is_associated_with::anemia in is_associated_with::chronic kidney disease, anemia in is_associated_with::myelodysplasia, and in anemia from is_associated_with::cancer is_associated_with::chemotherapy. Boxed warnings include a risk of death, myocardial infarction, stroke, venous thromboembolism, and tumor recurrence. Exogenous erythropoietin has been used illicitly as a is_associated_with::performance-enhancing drug; it can often be detected in blood, due to slight differences from the endogenous protein, for example, in features of is_associated_with::posttranslational modification.

Red blood cell production
The primary role of erythropoietin is an essential hormone for red blood cell production. Without it, definitive is_associated_with::erythropoiesis does not take place. Under hypoxic conditions, the kidney will produce and secrete erythropoietin to increase the production of red blood cells by targeting is_associated_with::CFU-E, prois_associated_with::erythroblast and basophilic erythroblast subsets in the differentiation. Erythropoietin has its primary effect on red blood cell progenitors and precursors (which are found in the bone marrow in humans) by promoting their survival through protecting these cells from is_associated_with::apoptosis.

Erythropoietin is the primary erythropoietic factor that cooperates with various other growth factors (e.g., IL-3, IL-6, is_associated_with::glucocorticoids, and SCF) involved in the development of is_associated_with::erythroid lineage from multipotent progenitors. The burst-forming unit-erythroid (is_associated_with::BFU-E) cells start is_associated_with::erythropoietin receptor expression and are sensitive to erythropoietin. Subsequent stage, the colony-forming unit-erythroid (is_associated_with::CFU-E), expresses maximal erythropoietin receptor density and is completely dependent on erythropoietin for further differentiation. Precursors of red cells, the proerythroblasts and basophilic erythroblasts also express erythropoietin receptor and are therefore affected by it.

Nonhematopoietic roles
Erythropoietin has a range of actions including is_associated_with::vasoconstriction-dependent is_associated_with::hypertension, stimulating is_associated_with::angiogenesis, and inducing proliferation of is_associated_with::smooth muscle fibers. It can increase iron absorption by suppressing the hormone is_associated_with::hepcidin.

EPO levels of 100 times the baseline have been detected in brain tissue as a natural response to hypoxic damage. In rats, pretreatment with erythropietin was associated with neuronal protection during induced cerebral hypoxia. Trials in humans have not been reported.

Multiple studies have suggested that EPO improves memory. This effect is independent of its effect on is_associated_with::hematocrit. Rather, it is associated with an increase in hippocampal response and effects on synaptic connectivity, neuronal plasticity, and memory-related neural networks. EPO may have effects on mood.

Mechanism of action
Erythropoietin has been shown to exert its effects by binding to the is_associated_with::erythropoietin receptor (EpoR).

EPO is highly glycosylated (40% of total molecular weight), with half-life in blood around five hours. EPO's half-life may vary between endogenous and various recombinant versions. Additional glycosylation or other alterations of EPO via recombinant technology have led to the increase of EPO's stability in blood (thus requiring less frequent injections). EPO binds to the erythropoietin receptor on the red cell progenitor surface and activates a JAK2 signaling cascade. Erythropoietin receptor expression is found in a number of tissues, such as bone marrow and peripheral/central nervous tissue. In the bloodstream, red cells themselves do not express erythropoietin receptor, so cannot respond to EPO. However, indirect dependence of red cell longevity in the blood on plasma erythropoietin levels has been reported, a process termed neocytolysis.

Synthesis and regulation
Erythropoietin levels in blood are quite low in the absence of anemia, at around 10 mU/ml. However, in hypoxic stress, EPO production may increase 1000-fold, reaching 10,000 mU/ml of blood. EPO is produced mainly by interstitial cells in the peritubular capillary bed of the is_associated_with::renal cortex. It is synthesized by renal peritubular cells in adults, with a small amount being produced in the liver. Regulation is believed to rely on a feedback mechanism measuring blood oxygenation. Constitutively synthesized transcription factors for EPO, known as is_associated_with::hypoxia-inducible factors, are hydroxylated and proteosomally digested in the presence of oxygen.

Medical uses
Erythropoietins available for use as therapeutic agents are produced by is_associated_with::recombinant DNA technology in is_associated_with::cell culture, and include Epogen/Procrit (epoetin alfa) and Aranesp (darbepoetin alfa); they are used in treating is_associated_with::anemia resulting from is_associated_with::chronic kidney disease, inflammatory bowel disease (Crohn's disease and ulcer colitis) and myelodysplasia from the treatment of is_associated_with::cancer (is_associated_with::chemotherapy and is_associated_with::radiation). The is_associated_with::package inserts include is_associated_with::boxed warnings of increased risk of death, myocardial infarction, stroke, venous thromboembolism, and tumor recurrence, particularly when used to increase the hemoglobin levels to more than 11 to 12 g/dl.

Available forms
Recombinant erythropoietin has a variety of is_associated_with::glycosylation patterns giving rise to alpha, beta, delta, and omega forms:

is_associated_with::Darbepoetin alfa, which early literature during its development often termed as novel erythropoiesis-stimulating protein (NESP), is a form created by five substitutions (Asn-57, Thr-59, Val-114, Asn-115 and Thr-117) that create two new N-glycosylation sites. This glycoprotein has a longer terminal half-life, meaning it may be possible to administer it less frequently.

Blood doping
is_associated_with::Erythropoiesis-stimulating agents (ESAs) have a history of use as is_associated_with::blood doping agents in endurance is_associated_with::sports, such as is_associated_with::horseracing, is_associated_with::boxing, is_associated_with::cycling, rowing, distance running, is_associated_with::race walking, is_associated_with::snowshoeing, is_associated_with::cross country skiing, is_associated_with::biathlon, is_associated_with::Mixed Martial Arts and is_associated_with::triathlon. The overall oxygen delivery system (blood oxygen levels, as well as heart stroke volume, vascularization, and lung function) is one of the major limiting factors to muscles' ability to perform endurance exercise. Therefore, the primary reason athletes may use ESAs is to improve oxygen delivery to muscles, which directly improves their endurance capacity. With the advent of recombinant erythropoietin in the 1990s, the practice of autologous and homologous blood transfusion has been partially replaced by injecting erythropoietin such that the body naturally produces its own red cells. ESAs increase hematocrit (% of blood volume that is red cell mass) and total red cell mass in the body, providing a good advantage in sports where such practice is banned. In addition to ethical considerations in sports, providing an increased red cell mass beyond the natural levels reduces blood flow due to increased viscosity, and increases the likelihood of thrombosis and stroke. Due to dangers associated with using ESAs, their use should be limited to the clinic where anemic patients are boosted back to normal hemoglobin levels (as opposed to going above the normal levels for performance advantage, leading to an increased risk of death).

Though EPO was believed to be widely used in the 1990s in certain sports, there was no way at the time to directly test for it, until in 2000, when a test developed by scientists at the French national antidoping laboratory (LNDD) and endorsed by the World Anti-Doping Agency (WADA) was introduced to detect pharmaceutical EPO by distinguishing it from the nearly identical natural hormone normally present in an athlete's urine. The first EPO-doping cases were found by the is_associated_with::Swiss Laboratory for Doping Analyses.

In 2002, at the Winter Olympic Games in Salt Lake City, Dr. is_associated_with::Don Catlin, the founder and then-director of the UCLA Olympic Analytical Lab, reported finding darbepoetin alfa, a form of erythropoietin, in a test sample for the first time in sports. At the is_associated_with::2012 Summer Olympics in London, is_associated_with::Alex Schwazer, the gold medalist in the 50-kilometer is_associated_with::race walk in the is_associated_with::2008 Summer Olympics in is_associated_with::Beijing, tested positive for EPO and was disqualified.

Since 2002, EPO tests performed by US sports authorities have consisted of only a urine or "direct" test. From 2000–2006, EPO tests at the Olympics were conducted on both blood and urine. However, several compounds have been identified that can be taken orally to stimulate endogenous EPO production. Most of the compounds stabilize the hypoxia-inducible transcription factors which activate the EPO gene. The compounds include oxo-glutarate competitors, but also simple ions such as cobalt(II) chloride.

Inhalation of a is_associated_with::xenon/oxygen mixture activates production of the transcription factor HIF-1-alpha, which leads to increased production of erythropoietin and improved performance. It has been used for this purpose in Russia since at least 2004.

Cycling
Synthetic EPO is believed to have come into use in cycling about 1990. In theory, EPO use can increase VO2max by a significant amount, making it useful for is_associated_with::endurance sports like cycling. Italian antidoping advocate is_associated_with::Sandro Donati has claimed that the history of doping in cycling can be traced to the Italian Dr is_associated_with::Francesco Conconi at the is_associated_with::University of Ferrara. Conconi had worked on the idea of giving athletes tranfusions of their own blood in the 1980s. Donati felt this work "opened the road to EPO . . . because blood doping was a trial to understand the role of EPO".

Dr is_associated_with::Michele Ferrari, a former student and mentee of Conconi, had a controversial interview mentioning the drug in 1994, just after his is_associated_with::Gewiss-Ballan team had a remarkable performance in the is_associated_with::La Flèche Wallonne race. Ferrari told l'Equipe journalist Jean-Michel Rouet that EPO had no "fundamental" effect on performance and that if his riders used it, it wouldn't "scandalize" himself. After the journalist pointed out several riders were suspected of dying from EPO, Ferrari said EPO was not dangerous, and only abuse of it was dangerous, saying, "It's also dangerous to drink 10 liters of orange juice." The 'orange juice' comment has been widely misquoted. Ferrari was fired shortly after, but continued to work in the industry with top riders that allegedly included is_associated_with::Lance Armstrong. That same year, is_associated_with::Sandro Donati, working for the is_associated_with::Italian National Olympic Committee, presented a report accusing Conconi of being linked to the use of EPO in the sport.

In 1997, the is_associated_with::Union Cycliste Internationale (UCI) instituted a new rule that riders testing above 50% is_associated_with::haematocrit were not only immediately disqualified, but banned from racing for two weeks. Robert Millar, former racer, later wrote for Cycling News that the 50% limit was "an open invitation to dope to that level", pointing out that normally haematocrit levels would start "around 40-42%" and drop during the course of a "grand tour", but after EPO, they were staying at 50% for "weeks at a time". By 1998, EPO use had become widespread, and the is_associated_with::Festina affair tarnished the is_associated_with::1998 Tour de France. One manager offered a 270,000-is_associated_with::franc-per-month raise to is_associated_with::Christophe Bassons if he would use EPO, but Bassons refused.

In the is_associated_with::1998 Tour de France is_associated_with::Stuart O'Grady won one stage, held the Tour de France is_associated_with::yellow jersey for three days, and came second in the points classification with the assistance of EPO. In 2010, is_associated_with::Floyd Landis admitted to using performance-enhancing drugs, including EPO, throughout his career as a professional cyclist. In 2012, the is_associated_with::USADA released a report on its investigation into massive doping by the is_associated_with::US Postal Service cycling team under the leadership of is_associated_with::Lance Armstrong. The report contained affidavits from numerous riders on the team, including is_associated_with::Frankie Andreu, is_associated_with::Tyler Hamilton, is_associated_with::George Hincapie, is_associated_with::Floyd Landis, is_associated_with::Levi Leipheimer, and others, outlining that they and Armstrong used a cocktail of performance-enhancing substances for the Tour de France, most notably EPO, during Armstrong's seven consecutive Tour wins. It detailed how Armstrong and the Postal manager, is_associated_with::Johan Bruyneel, forced other team members to dope as well. It also went to the root of their doping network, targeting the shadowy doctors and back room enablers who helped cyclists procure and administer drugs as well as highly placed executives who helped to avoid doping controls and hide positive test results. Armstrong was subsequently stripped of all of his victories from 1998 onward—including his Tour wins and his performance in the 2000 Summer Olympics. The UCI concurred with the decision. While several of the doping offenses took place outside the normal eight-year statute of limitations for doping offenses, USADA contended the statute of limitations did not apply due to Armstrong's "fraudulent concealment" of his doping. Longstanding precedent in U.S. law holds that the statute of limitations does not apply in cases of fraudulent conduct by a defendant. In accordance with this decision, Tour organizers removed Armstrong's name and results from the race's history. Witnesses testified that code words used for EPO included "Edgar", "Poe", "Edgar Allan Poe", and "Zumo" (Spanish for 'juice').

History
In 1905, is_associated_with::Paul Carnot, a professor of medicine in Paris, and his assistant, Clotilde Deflandre, proposed the idea that hormones regulate the production of red blood cells. After conducting experiments on rabbits subject to is_associated_with::bloodletting, Carnot and Deflandre attributed an increase in red blood cells in rabbit subjects to a hemotropic factor called hemopoietin. Eva Bonsdorff and Eeva Jalavisto continued to study red cell production and later called the hemopoietic substance 'erythropoietin'. Further studies investigating the existence of EPO by K.R. Reissman (unknown location) and Allan J. Erslev (Thomas Jefferson Medical College) demonstrated that a certain substance, circulated in the blood, is able to stimulate red blood cell production and increase is_associated_with::hematocrit. This substance was finally purified and confirmed as erythropoietin, opening doors to therapeutic uses for EPO in diseases such as is_associated_with::anemia.

is_associated_with::Haematologist John Adamson and nephrologist is_associated_with::Joseph W. Eschbach looked at various forms of renal failure and the role of the natural hormone EPO in the formation of red blood cells. Studying sheep and other animals in the 1970s, the two scientists helped establish that EPO stimulates the production of red cells in bone marrow and could lead to a treatment for anemia in humans. In 1968, Goldwasser and Kung began work to purify human EPO, and managed to purify milligram quantities of over 95% pure material by 1977. Pure EPO allowed the amino acid sequence to be partially identified and the gene to be isolated. Later, an NIH-funded researcher at Columbia University discovered a way to synthesize EPO. Columbia University patented the technique, and licensed it to is_associated_with::Amgen. Controversy has ensued over the fairness of the rewards that Amgen reaped from NIH-funded work, and Goldwasser was never financially rewarded for his work.

In the 1980s, Adamson, is_associated_with::Joseph W. Eschbach, Joan C. Egrie, Michael R. Downing and Jeffrey K. Browne conducted a clinical trial at the is_associated_with::Northwest Kidney Centers for a synthetic form of the hormone, is_associated_with::Epogen, produced by Amgen. The trial was successful, and the results were published in the is_associated_with::New England Journal of Medicine in January 1987.

In 1985, Lin et al isolated the human erythropoietin gene from a genomic phage library and were able to characterize it for research and production. Their research demonstrated the gene for erythropoietin encoded the production of EPO in mammalian cells that is biologically active in vitro and in vivo. The industrial production of recombinant human erythropoietin (RhEpo) for treating anemia patients would begin soon after.

In 1989, the is_associated_with::US Food and Drug Administration approved the hormone Epogen, which remains in use today.