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EPO can be administered intravenously or, more commonly, by subcutaneous (s.c.) injection. Peak serum concentrations are witnessed 8-24 h after s.c. administration. Although they are lower than the values achieved by i.v. administration, the effect is more prolonged, lasting for several hours. In healthy individuals, less than 10% of administered EPO is excreted intact in the urine. This suggests that the kidneys play, at best, a minor role in the excretion of this hormone.
HAEMOPOIETIC GROWTH FACTORS 269
Figure 6.6. Proposed mechanism by which hypoxic conditions stimulate enhanced EPO synthesis (see text for details)
Table 6.6. Some additional regulatory factors that can promote increased EPO production. Other regulatory factors, including IL-3 and CSFs, which also influence the rate of erythropoiesis, are omitted as they have been discussed previously
Growth hormone Thyroxine
Androgens and anabolic steroids
Table 6.7. Diseases (and other medical conditions) for which anaemia is one frequently observed symptom
Bone marrow transplantation
Table 6.8. EPO preparations that have gained regulatory approval or are undergoing clinical trials
Product Status Company
Epogen (rhEPO) Approved Amgen
Procrit (rhEPO) Approved Ortho Biotech
Neorecormon (rhEPO) Approved Boehringer-Mannheim
Aranesp (rEPO analogue) Approved Amgen
Nespo (rEPO analogue) Approved Dompe Biotec
rEPO In clinical trials Aventis
More recently, an engineered form of EPO has gained marketing approval. Darbepoetin-a is its international non-proprietary name and it is marketed under the tradenames Aranesp (Amgen) and Nespo (Dompe Biotec, Italy). The 165 amino acid protein is altered in amino acid sequence when compared to the native human product. The alteration entails introducing two new N-glycosylation sites, so that the recombinant product, produced in an engineered CHO cell line, displays five glycosylation sites as opposed to the normal three. The presence of two additional carbohydrate chains confers a prolonged serum half-life on the molecule (up to 21 h as compared to 4-6 h for the native molecule).
EPO was first used therapeutically in 1989 for the treatment of anaemia associated with chronic kidney failure. This anaemia is largely caused by insufficient endogenous EPO production by the diseased kidneys. Prior to EPO approval, this condition could only be treated by direct blood transfusion. It responds well, and in a dose-dependent manner, to the administration of recombinant human EPO (rhEPO). The administration of EPO is effective in the case of both patients receiving dialysis and those who have not yet received this treatment.
Administration of doses of 50-150IU EPO/kg three times weekly is normally sufficient to elevate the patient’s haematocrit values to a desired 32-35% (haematocrit refers to ‘packed cell volume’, i.e. the percentage of the total volume of whole blood that is composed of erythrocytes). Plasma EPO concentrations generally vary between 5 and 25 IU/l in healthy individuals. One IU (international unit) of EPO activity is defined as the activity which promotes the same level of stimulation of erythropoiesis as 5 mmol cobalt.
In addition to enhancing erythropoiesis, EPO treatment also improves tolerance to exercise, as well as patients’ sense of well-being. Furthermore, reducing/eliminating the necessity for blood transfusions also reduces/eliminates the associated risk of accidental transmission of blood-borne infectious agents, as well as the risk of precipitating adverse transfusion reactions
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Cell culture Recovery of product-containing
Hydroxylapatite chromatography Blue-sepharose dye affinity
Reverse-phase HPLC Ion exchange
Fill and freeze-dry Excipient addition
Figure 6.7. Schematic overview of the production of the erythropoietin-based product Neorecormon. Refer to text for further details
in recipients. An American study calculated the average cost of rhEPO therapy to be of the order of $6000/patient/annum, compared to approx. $4600 for transfusion therapy. However, due to the additional benefits described, the cost:benefit ratio appears to favour EPO therapy. The therapeutic spotlight upon EPO has now shifted to additional (non-renal) applications (Table 6.9).