Erythropoietin

Erythropoietin
Abbreviation	EPO
Molecular formula	Glycoprotein (~34 kDa, 165 amino acids)
Type	Glycoprotein hormone/cytokine
Administration	Subcutaneous/IV injection (recombinant epoetin)
Bioavailability	N/A, peptide, injection only
Synonyms	Hematopoietin
Source	Kidney (peritubular fibroblasts), some liver
Ray's verdict	Depends on context Stimulates red blood cell production; low oxygen and kidney disease change levels

Erythropoietin (EPO) is a kidney hormone that stimulates red blood cell production. Low oxygen and kidney disease change levels. Abuse in sport is a separate issue.

History

Etymology

The name combines Greek erythros ("red") with "poietin" ("maker"), describing its role in making red blood cells.

Paul Carnot and Clotilde Deflandre proposed the existence of a blood-borne factor controlling red cell production in 1906, coining the term. Eugene Goldwasser isolated erythropoietin in pure form in 1977, after decades of work, enabling later production of recombinant EPO as a drug.

The existence of a blood-borne factor controlling red blood cell production was proposed in the early 20th century, but erythropoietin itself wasn't isolated in pure form until 1977, from the urine of patients with severe anemia. The gene was cloned in 1985, work that made recombinant EPO (epoetin alfa) commercially available by the late 1980s, the first blockbuster biotechnology drug and a major source of both legitimate medical benefit and endurance-sport doping controversy.

Structure/Chemical properties

Erythropoietin is a glycoprotein of 165 amino acids (about 34 kDa including its carbohydrate side chains), produced mainly by peritubular fibroblast-like cells in the kidney, with a smaller contribution from the liver, particularly before birth.

Function/Mechanism of Action

Falling tissue oxygen levels stabilize the transcription factor HIF (hypoxia-inducible factor), which drives EPO gene expression in the kidney. Circulating EPO then binds receptors on bone marrow erythroid progenitor cells, promoting their survival and maturation into red blood cells. Levels rise with altitude, blood loss, and chronic hypoxia, and fall with kidney failure (the main cause of the anemia seen in chronic kidney disease) and with some hormonal states.

There is some evidence that estrogen slightly suppresses the formation of erythropoietin, the regulator of red blood cell formation, but most evidence indicates that it is estrogen's suppression of the bone marrow itself that accounts for most of the difference.

— Ray Peat

Medical uses/Effects

Recombinant EPO (epoetin alfa, darbepoetin, and related agents) is used clinically to treat anemia from chronic kidney disease, chemotherapy, and some other causes of reduced red cell production. It is also one of the most notorious doping agents in endurance sport, used to raise oxygen-carrying capacity, prompting the biological passport monitoring systems now used in professional cycling and other endurance sports.

Dosing

Clinical dosing is individualized to target hemoglobin, typically starting around 50-100 units/kg subcutaneously two to three times weekly for standard epoetin alfa, with longer-acting agents (darbepoetin) dosed less frequently. Overcorrection carries real risk (see below), so dosing is titrated to the lowest amount that avoids transfusion, not to a maximal hemoglobin target.

Side/Adverse effects

The main serious risk of EPO therapy is overcorrection: raising hemoglobin too high or too fast increases blood viscosity and has been linked to increased cardiovascular events, stroke, and thrombosis in clinical trials, which is why current guidelines target a moderate hemoglobin range rather than normalizing it fully. EPO can also raise blood pressure and, rarely, trigger pure red cell aplasia from antibody formation against the drug.

See also

• Kidney
• Anemia
• Iron