The chemistry and physiology of erythropoietin

Management of anemia of inflammation in the elderly

Anemia of any degree is recognized as a significant independent contributor to morbidity, mortality, and frailty in elderly patients. Among the broad types of anemia in the elderly a peculiar role seems to be played by the anemia associated with chronic inflammation, which remains the most complex form of anemia to treat. The origin of this nonspecific inflammation in the elderly has not yet been clarified. It seems more plausible that the oxidative stress that accompanies ageing is the real cause of chronic inflammation of the elderly and that the same oxidative stress is actually a major cause of this anemia. The erythropoietic agents have the potential to play a therapeutic role in this patient population. Despite some promising results, rHuEPO does not have a specific indication for the treatment of anemia in the elderly. Moreover, concerns about their side effects have spurred the search for alternatives. Considering the etiopathogenetic mechanisms of anemia of inflammation in the elderly population, an integrated nutritional/dietetic approach with nutraceuticals that can manipulate oxidative stress and related inflammation may prevent the onset of this anemia and its negative impact on patients' performance and quality of life.

Hematopoietic growth factor receptors

The formation of the cellular constituents of the blood is regulated by a series of endogenous polypeptides with largely paracrine function. A number of these hematopoietic growth factors (HGF's), which include colony stimulating factors, interleukins, and erythropoietin, have been purified to homogeneity and cloned, which in turn has led to extensive investigations of their biochemical properties and biological effects and functions. The HGF's act on target cells by binding to receptors. The kinetics and, to an even larger extent, dynamics of the factor/receptor associations display several intriguing characteristics, most of which are still poorly understood. Herein, the biochemical characteristics of HGF's receptors as well as the binding properties, post-receptor binding events and receptor modulation resulting from the association of HGF's and their target cells are reviewed.

The effect of erythropoietin on normal and neoplastic cells

Erythropoietin (Epo) is an essential hormone that binds and activates the Epo receptor (EpoR) resident on the surface of erythroid progenitor cells, thereby promoting erythropoiesis. Recombinant human erythropoietin has been used successfully for over 20 years to treat anemia in millions of patients. In addition to erythropoiesis, Epo has also been reported to have other effects, such as tissue protection and promotion of tumor cell growth or survival. This became of significant concern in 2003, when some clinical trials in cancer patients reported increased tumor progression and worse survival outcomes in patients treated with erythropoiesis-stimulating agents (ESAs). One of the potential mechanisms proffered to explain the observed safety issues was that functional EpoR was expressed in tumors and/or endothelial cells, and that ESAs directly stimulated tumor growth and/or antagonized tumor ablative therapies. Since then, numerous groups have performed further research evaluating this potential mechanism with conflicting data and conclusions. Here, we review the biology of endogenous Epo and EpoR expression and function in erythropoiesis, and evaluate the evidence pertaining to the expression of EpoR on normal nonhematopoietic and tumor cells.

Overexpression of human erythropoietin (EPO) affects plant morphologies: retarded vegetative growth in tobacco and male sterility in tobacco and Arabidopsis

Erythropoietin (EPO) is a glycoprotein used for curing human anemia by regulating the differentiation of erythroid progenitors and the production of red blood cells. To examine the expression of recombinant EPO in plants, pPEV-EP21, in which human epo cDNA under the control of the CaMV 35S promoter, was introduced into tobacco and Arabidopsis via Agrobacterium tumefaciens-mediated transformation. The RNA expression level of epo in the transgenic lines was initially estimated by Northern blot analysis. Two transgenic lines, which exhibited a high expression level of epo mRNA determined by Northern analysis, were chosen for Western blot analysis to examine the production of EPO proteins. Those two lines, EP21-12 and EP21-14, revealed detectable bands on the immunoblot. Interestingly, constitutive expression of the human epo gene affected the morphologies in transgenic plants such that vegetative growth of transgenic tobacco was retarded, and male sterility was induced in transgenic tobacco and Arabidopsis.

Oxygen-dependent regulation of erythropoietin gene expression in rat hepatocytes

The essential role of the glycoprotein hormone erythropoietin (Epo) in the control of red blood cell production is well established. Synthesis of Epo is induced in response to low oxygen (hypoxia). In response to stimulation, increases in serum Epo levels are paralleled by changes in the abundance of Epo mRNA. These changes indicate that the level of Epo mRNA is the major determinant of hormone production rate [1-3]. Studies of the organ distribution of Epo mRNA [4, 5] have confirmed the results of organ ablation studies, which demonstrated that in adults the kidney is the major organ responsible for the Epo production, but the liver is capable of Epo production as well [6, 7]. More sensitive detection methods of Epo mRNA have demonstrated small quantities in testis, brain, lung, and spleen of rodents [3, 8].

Treatment of anemia in inflammatory bowel disease with recombinant human erythropoietin: results in three patients

Inflammatory bowel disease (IBD) is often associated with anemia. Of 85 patients with IBD, 28 were anemic and had an inadequately low plasma erythropoietin (EPO) concentration. Three patients with a long-standing history of IBD and refractory chronic anemia (hemoglobin values < 10 g/dL, plasma EPO concentrations below 100 mU/mL) were treated with recombinant human EPO, which was administered subcutaneously three times per week at a dose of 200-300 U/kg of body weight. Bone marrow biopsy specimens taken before therapy showed slightly decreased erythropoiesis with a shift of erythroid precursors toward more immature stages. EPO treatment resulted in a marked increase in hemoglobin values in all 3 patients. Bone marrow biopsies after EPO therapy showed quantitatively and qualitatively normal erythropoiesis in all of them. Correction of anemia was followed by improved well-being, and all patients were able to cope much better with their IBD. In all three patients, there was an increase in body weight and their Karnofsky index improved. After a complete workup and exclusion of any other cause for anemia, erythropoietin treatment, although expensive, should be considered in patients with IBD and refractory anemia.

The detection of occult renal tumors in children by elevated hematocrit on routine complete blood count: a report of two cases

Wilms' tumor is a renal neoplasm usually found in young children and is rarely seen in teenagers. The production of erythropoietin by these tumors may result in secondary erythrocytosis, which should be reflected in complete blood counts (CBC). A search of the literature for reports of occult Wilms' tumors initially suspected on the basis of erythrocytosis was unrewarding. Two teenagers are reported in whom unexplained erythrocytosis was the initial indication of a Wilms' tumor. In both cases, a previous CBC showed elevations in hemoglobin and hematocrit that might have led to an earlier diagnosis. We conclude that unexplained erythrocytosis should sound the alert for further diagnostic studies to evaluate the possibility of occult renal neoplasia in older children.

Athletes' pseudoanaemia

To characterize the so-called pseudoanaemia of endurance-trained athletes, the plasma volume (PV), red cell volume (RCV) and total blood volume (TBV) of 12 male and 12 female athletes and 5 male and 5 female nonexercising controls were measured using 125I-labelled human serum albumin and 51Cr-labelled erythrocytes. The mean PV of the male athletes (52.8 ml.kg-1) was 37.5% higher than that of the controls (38.4 ml.kg-1), while the 18.1% increase measured in the female runners (51.5 ml.kg-1) over the controls (43.6 ml.kg-1) was a novel observation. Although the RCV was significantly greater (34.7%) in male athletes (32.6 ml.kg-1 vs 24.2 ml.kg-1 in the controls), a similar elevation (3.6%) was not found in the female athletes (25.9 ml.kg-1) compared to the sedentary women (22.8 ml.kg-1). This could have been due to iron-limited erythropoiesis because the RCV of the female athletes defined as clinically anaemic was markedly lower that of the nonanaemic women (P less than 0.05). The elevated plasma protein mass and concentration measured in the athletes partly accounted for their expanded PV. It was concluded that the decreased blood haemoglobin levels reported in the endurance athletes was largely a dilutional effect.

Receptors for recombinant erythropoietin in human bone marrow cells

Human recombinant erythropoietin, labelled with 125I, was saturably bound to high affinity receptors, ka = 1.5 X 10(9) M-1, of bone marrow cells from 10 patients with various haematological disorders. Binding of labelled erythropoietin was specific, with less than 0.01% cross-reactivities of TSH, hCG and renin substrate (angiotensinogen). Binding capacity averaged 3 X 10(-14) moles/10(6) cells. Binding was maximal within 30 min at 37 degrees C. Low binding, less than 15% of that to bone marrow cells, was found to peripheral blood buffy coat, while erythrocytes and BALL cells did not bind labelled erythropoietin. Autoradiography showed binding of label confined to 4-5% of the bone marrow cells.

Periodic changes in the organs involved in the erythropoiesis of anemic newts

In Triturus cristatus carnifex (Laurenti) newts rendered totally anemic by treatment with acetylphenylhydrazine (APH) diluted in their tank water (25 mg/liter for 48 hours, with four changes) the recovery of erythron occurs through periodic cycles of mitotic activity in the erythropoietic tissue. These cycles determine a marked increase in blood erythrocyte concentration at regular intervals of about 1 month. The consequence of this trend is the alternation of ferritin and hemosiderin accumulation phases during periods of stasis with iron mobilization phases during periods of erythropoietic activity, which is particularly evident in the Kupffer cells of the liver. Iron mobilization and erythropoietic activity are strictly related to the periodic hypertrophy of some Bowman's capsule cells in the renal corpuscle, which were previously denominated "lactate sensitive cells" (LSC). The histochemistry, location, and behavior of LSC indicate that they are probably the site of erythropoietin production in the newt.

The mechanism of action of erythropoietin

The proliferation and differentiation of committed erythroid progenitor cells is regulated by the glycoprotein hormone erythropoietin. Erythropoietin increases the number of developing erythroid precursors and accelerates the release of reticulocytes from the marrow without markedly altering the cell cycle length or number of mitotic divisions involved in the differentiation process. Although the hormone has been purified, molecularly cloned and sequenced, its secondary and tertiary structure and active site have not been defined. Erythropoietin has both mitogenic and differentiation functions, and whether an erythroid progenitor cell responds to the hormone by proliferating or differentiating appears to depend on its level of maturation. Erythroid progenitor cells are responsive to a variety of growth and developmental agents but only erythropoietin appears obligatory in vivo for terminal differentiation. Erythropoietin interacts with its target cells through specific high-affinity receptors and Ca2+ may be involved in the receptor-ligand interaction. Ca2+ may also be involved in the induction of differentiation by erythropoietin. An increase in RNA synthesis due to activation of transcription is one of the earliest recognized effects of the hormone and appears not to require protein or DNA synthesis but the initial sequence of biochemical events triggered by erythropoietin is still undefined.