Chromosomal assignment of the human erythropoietin gene and its DNA polymorphism

Challenges and recent advances in erythropoietin stability

Erythropoietin (EPO) is a pivotal hormone that regulates red blood cell production, predominantly synthesized by the kidneys and also produced by the liver. Since the introduction of recombinant human EPO (rh-EPO) in 1989 through recombinant DNA technology, the therapeutic landscape for anemia has been improved. rh-EPO's market expansion has been substantial, with its application extending across various conditions such as chronic kidney disease, cancer-related anemia, and other disorders. Despite its success, significant concerns remain regarding the stability of EPO, which is critical for preserving its biological activity and ensuring therapeutic efficacy under diverse environmental conditions. Instability issues, including degradation and loss of biological activity, challenge both drug development and treatment outcomes. Factors contributing to EPO instability include temperature fluctuations, light exposure, and interactions with other substances. To overcome these challenges, pharmaceutical research has focused on developing innovative strategies such as stabilizing agents, advanced formulation techniques, and optimized storage conditions. This review article explores the multifaceted aspects of EPO stability, examining the impact of instability on clinical efficacy and drug development. It also provides a comprehensive review of current stabilization strategies, including the use of excipients, lyophilization, and novel delivery systems.

Erythropoietin improve spatial memory impairment following methamphetamine neurotoxicity by inhibition of apoptosis, oxidative stress and neuroinflammation in CA1 area of hippocampus

OBJECTIVE

Methamphetamine (METH) is one of the most widely used addictive drugs, and addiction to it is on the rise all over the world. METH abuse has long-term damaging effects that reduce memory and impair cognitive functions. According to studies, the observed effects are strongly related to the nerve cell damage caused by METH, which leads to neurotoxicity. Some of these intra-neuronal events include dopamine oxidation, excitotoxicity, and oxidative stress. Erythropoietin (EPO) is a hormone produced primarily by the kidneys and, in small quantities, by the liver. Studies have shown that EPO exhibits considerable neuroprotective effects. This study aimed to investigate the protective effects of EPO on METH neurotoxicity.

METHODS

Initially, 48 male Wistar rats, weighing 250-300 g, were randomly assigned to four groups: control (n = 12), METH (n = 12), and METH+EPO (2500, 5000 IU/kg/IP- n = 12). METH was injected intraperitoneally at a dose of 40 mg per kg of body weight (four injections of 10 mg every two hours) to induce neurotoxicity. EPO was injected at doses of 2500 and 5000 IU/kg seven days after the last METH administration (ip). Morris water maze test was performed following EPO injection (1 day after the last dose) to assess spatial memory. The brains were removed after the behavioral test, biochemical evaluations and immunohistochemistry (caspase-3 and GFAP) was performed.

RESULTS

The results showed that EPO treatment significantly improved spatial memory impairment (P < 0.01), compared to the METH group, EPO was a significant reduction in malondialdehyde and TNF-α (P < 0.01), as well as an increase in superoxide dismutase (P < 0.05) and glutathione-PX (P < 0.01). Furthermore, EPO treatment significantly reduced the number of GFAP positive cells (P < 0.01) and caspase 3 (P < 0.001) in the hippocampus (CA1 region).

CONCLUSIONS

The study findings suggested that EPO may have great neuroprotective effects on METH neurotoxicity due to its anti-inflammatory, antioxidant, and antiapoptotic properties.

The prophylaxis and treatment potential of supplements for COVID-19

The global impact of the new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), infection that caused COVID-19 has been evident in the last few months from the unprecedented socioeconomic disruption to more than 600,000 deaths. The lack of vaccine and effective therapeutic agents for the disease prompted world-wide effort to test those antiviral therapeutics already in use for other diseases. Another interesting approach has been based on the pathological sequel of the disease that involve severe inflammatory reaction (or the cytokine storm) associated with pneumonia in critically ill patients. This article outlines the prophylaxis therapeutic potential of supplements vitamins and micronutrients in COVID-19. By ameliorating the inflammatory and oxidative stress associated with the disease and some direct antiviral effects, the application of these agents as adjuvants and other alternative approaches are discussed. Available clinical trials including those currently registered on these supplements are scrutinized.

Hypoxia-inducible factors not only regulate but also are myeloid-cell treatment targets

Hypoxia describes limited oxygen availability at the cellular level. Myeloid cells are exposed to hypoxia at various bodily sites and even contribute to hypoxia by consuming large amounts of oxygen during respiratory burst. Hypoxia-inducible factors (HIFs) are ubiquitously expressed heterodimeric transcription factors, composed of an oxygen-dependent α and a constitutive β subunit. The stability of HIF-1α and HIF-2α is regulated by oxygen-sensing prolyl-hydroxylases (PHD). HIF-1α and HIF-2α modify the innate immune response and are context dependent. We provide a historic perspective of HIF discovery, discuss the molecular components of the HIF pathway, and how HIF-dependent mechanisms modify myeloid cell functions. HIFs enable myeloid-cell adaptation to hypoxia by up-regulating anaerobic glycolysis. In addition to effects on metabolism, HIFs control chemotaxis, phagocytosis, degranulation, oxidative burst, and apoptosis. HIF-1α enables efficient infection defense by myeloid cells. HIF-2α delays inflammation resolution and decreases antitumor effects by promoting tumor-associated myeloid-cell hibernation. PHDs not only control HIF degradation, but also regulate the crosstalk between innate and adaptive immune cells thereby suppressing autoimmunity. HIF-modifying pharmacologic compounds are entering clinical practice. Current indications include renal anemia and certain cancers. Beneficial and adverse effects on myeloid cells should be considered and could possibly lead to drug repurposing for inflammatory disorders.

A Perspective on Erythropoietin as a Potential Adjuvant Therapy for Acute Lung Injury/Acute Respiratory Distress Syndrome in Patients with COVID-19

The novel coronavirus 2019-nCoV (SARS-CoV-2) infection that emerged in China in December 2019 has rapidly spread to become a global pandemic. This article summarizes the potential benefits of erythropoietin (EPO) in alleviating SARS-CoV-2 pathogenesis which is now called COVID-19. As with other coronavirus infection, the lethality of COVID-19 is associated with respiratory dysfunction due to overexpression of proinflammatory cytokines induced by the host immune responses. The resulting cytokine storm leads to the development of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Erythropoietin, well known for its role in the regulation of erythropoiesis, may have protective effects against ALI/ARDS induced by viral and other pathogens. EPO exerts antiapoptotic and cytoprotective properties under various pathological conditions. With a high safety profile, EPO promotes the production of endothelial progenitor cells and reduce inflammatory processes through inhibition of the nuclear factor-κB (NF-κB) and JAK-STAT3 signaling pathways. Thus, it may be considered as a safe drug candidate for COVID-19 patients if given at the early stage of the disease. The potential effects of erythropoietin on different aspects of ALI/ARDS associated with SARS-CoV-2 infection are reviewed.

Erythropoietin as a Neuroprotective Molecule: An Overview of Its Therapeutic Potential in Neurodegenerative Diseases

Erythropoietin (EPO) is a cytokine mainly induced in hypoxia conditions. Its major production site is the kidney. EPO primarily acts on the erythroid progenitor cells in the bone marrow. More and more studies are highlighting its secondary functions, with a crucial focus on its role in the central nervous system. Here, EPO may interact with up to four distinct isoforms of its receptor (erythropoietin receptor [EPOR]), activating different signaling cascades with roles in neuroprotection and neurogenesis. Indeed, the EPO/EPOR axis has been widely studied in the neurodegenerative diseases field. Its potential therapeutic effects have been evaluated in multiple disorders, such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, spinal cord injury, as well as brain ischemia, hypoxia, and hyperoxia. EPO is showing great promise by counteracting secondary neuroinflammatory processes, reactive oxygen species imbalance, and cell death in these diseases. Multiple studies have been performed both in vitro and in vivo, characterizing the mechanisms through which EPO exerts its neurotrophic action. In some cases, clinical trials involving EPO have been performed, highlighting its therapeutic potential. Together, all these works indicate the potential beneficial effects of EPO.

Erythropoiesis and chronic kidney disease-related anemia: From physiology to new therapeutic advancements

Erythropoiesis is triggered by hypoxia and is strictly regulated by hormones, growth factors, cytokines, and vitamins to ensure an adequate oxygen delivery to all body cells. Abnormalities in one or more of these factors may induce different kinds of anemia requiring different treatments. A key player in red blood cell production is erythropoietin. It is a glycoprotein hormone, mainly produced by the kidneys, that promotes erythroid progenitor cell survival and differentiation in the bone marrow and regulates iron metabolism. A deficit in erythropoietin synthesis is the main cause of the normochromic normocytic anemia frequently observed in patients with progressive chronic kidney disease. The present review summarizes the most recent findings about each step of the erythropoietic process, going from the renal oxygen sensing system to the cascade of events induced by erythropoietin through its own receptor in the bone marrow. The paper also describes the new class of drugs designed to stabilize the hypoxia-inducible factor by inhibiting prolyl hydroxylase, with a discussion about their metabolism, disposition, efficacy, and safety. According to many trials, these drugs seem able to simulate tissue hypoxia and then stimulate erythropoiesis in patients affected by renal impairment. In conclusion, the in-depth investigation of all events involved in erythropoiesis is crucial to understand anemia pathophysiology and to identify new therapeutic strategies, in an attempt to overcome the potential side effects of the commonly used erythropoiesis-stimulating agents.

Design and validation of a new method to detect and quantify residual host cell DNA in human recombinant erythropoietin (rEPO)

During the purification of human recombinant erythropoietin (rEPO) from host cells, residual DNA may remain in final products. This contamination is a risk factor for patients and may result in the inactivation of some tumor suppressor genes or activation of oncogenes if its concentration is more than the standard defined by WHO. Based on WHO's criteria, acceptable level of residual DNA in biopharmaceuticals is less than 10-100 pg/dose. In this study, we have designed a sensitive and specific quantitative real-time polymerase chain reaction (PCR) assay for the detection of residual DNA in human rEPO products. All reported sequences of CHO's GAPDH gene were retrieved from GenBank, and a multiple alignment was performed using Mega 6 software to find conserved regions of the gene. Primers and probe were designed by AlleleID7 software for the highly conserved region. Quantitative real-time PCR showed an R² value more than 0.99 and the efficiency equal to 101% indicating a highly accurate and efficiency of the reaction, respectively. Based on the standard curve, the limit of detection of the assay was determined to be 10 copies/µL (0.00967 fg/µL). In addition, the inter- and intra-assay of the test were determined to be 1.14% and 0.65%, respectively, which are in acceptable range according to the WHO's guidelines.

Role of Erythropoietin and Other Growth Factors in Ex Vivo Erythropoiesis

Erythropoiesis is a vital process governed through various factors. There is extreme unavailability of suitable donor due to rare phenotypic blood groups and other related complications like hemoglobinopathies, polytransfusion patients, and polyimmunization. Looking at the worldwide scarcity of blood, especially in low income countries and the battlefield, mimicking erythropoiesis using ex vivo methods can provide an efficient answer to various problems associated with present donor derived blood supply system. Fortunately, there are many ex vivo erythropoiesis methodologies being developed by various research groups using stem cells as the major source material for large scale blood production. Most of these ex vivo protocols use a cocktail of similar growth factors under overlapping growth conditions. Erythropoietin (EPO) is a key regulator in most ex vivo protocols along with other growth factors such as SCF, IL-3, IGF-1, and Flt-3. Now transfusable units of blood can be produced by using these protocols with their set of own limitations. The present paper focuses on the molecular mechanism and significance of various growth factors in these protocols that shall remain helpful for large scale production.

Epoetin alfa: basic biology and clinical utility in cancer patients

Anemia in cancer patients undergoing treatment is common and can cause debilitating symptoms such as fatigue and reduced exercise tolerance. The introduction of recombinant human erythropoietin represents a potential improvement in the treatment of this condition. Clinical studies in patients with solid tumors and nonmyeloid hematologic malignancies have convincingly shown an improvement in mean hemoglobin concentration, a reduction in transfusion requirement along with an improvement in quality of life scores, although an effect on survival is less clear. In myeloid disorders such as myelodysplasia, response to single-agent recombinant human erythropoietin is disappointing but significant synergism with granulocyte colony stimulating factor has been demonstrated and different dosing regimens may also improve response. Unfortunately, a significant proportion of patients remain refractory to treatment. Efforts have been made to identify treatable causes of erythropoietin refractoriness, such as functional iron deficiency, and concomitant intravenous iron supplementation does appear to improve response rates. The search for pretreatment factors that predict response has been largely disappointing, although a promising model for myelodysplasia has been developed that awaits large-scale evaluation. Recombinant human erythropoietin is well tolerated, although there were concerns in the late 1990s due to a rising incidence of pure red cell aplasia in chronic renal failure patients treated with subcutaneous Eprex (Ortho Biologics) in Europe. Since potentially contributory manufacturing processes have been identified and corrected, the incidence of this complication has been falling.

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.

Erythropoietin use and abuse

Recombinant human erythropoietin (rhEPO) is arguably the most successful therapeutic application of recombinant DNA technology till date. It was isolated in 1977 and the gene decoded in 1985. Since then, it has found varied applications, especially in stimulating erythropoiesis in anemia due to chronic conditions like renal failure, myelodysplasia, infections like HIV, in prematurity, and in reducing peri-operative blood transfusions. The discovery of erythropoietin receptor (EPO-R) and its presence in non-erythroid cells has led to several areas of research. Various types of rhEPO are commercially available today with different dosage schedules and modes of delivery. Their efficacy in stimulating erythropoiesis is dose dependent and differs according to the patient's disease and nutritional status. EPO should be used carefully according to guidelines as unsolicited use can result in serious adverse effects. Because of its capacity to improve oxygenation, it has been abused by athletes participating in endurance sports and detecting this has proved to be a challenge.

Review of the Role of Erythropoietin in Critical Leg Ischemia

There is a need to develop alternative treatment strategies for the 30% of patients with critical leg ischemia (CLI) for whom conventional modes of revascularization fail. The efficacy erythropoietin (EPO) in this regard has been verified in preclinical models. Erythropoietin receptors are expressed in the human skeletal muscle and possibly, upregulated in CLI. Furthermore, EPO induces angiogenesis and prevents apoptosis in the ischemic skeletal muscle. The use of EPO in conjunction with autologous bone marrow cells or gene-induced angiogenesis with vascular endothelial growth factor may be more effective in inducing angiogenesis and protecting the critically ischemic leg than EPO alone. The recently synthesized nonhemopoietic derivatives of EPO (eg, asialo erythropoietin and carbamylated erythropoietin) allow higher doses to be administered to achieve tissue protective effects, without an unwanted increase in hematocrit. This may allow translation of preclinical studies into clinical trials.

Granulocyte and erythropoietic stimulating proteins after high-dose chemotherapy for myeloma

High-dose chemotherapy is an established treatment for patients with myeloma. In randomized trials it has been shown to prolong disease-free survival by around 1 year compared to patients receiving chemotherapy alone. Physically and psychologically high-dose therapy takes its toll on the patient who may be in hospital for around 3 weeks and take some weeks or months to convalesce after discharge. Granulocyte colony stimulating factors and erythropoietic stimulating agents will speed neutrophil and red cell recovery, respectively, when used at an appropriate time after the high-dose chemotherapy. The clinical value of these laboratory findings is uncertain and the role of these agents after high-dose chemotherapy remains a subject for debate.

Erythropoietin after a century of research: younger than ever

In the light of the enthusiasm regarding the use of recombinant human erythropoietin (Epo) and its analogues for treatment of the anaemias of chronic renal failure and malignancies it is worth remembering that today's success has been based on a century of laborious research. The concept of the humoral regulation of haematopoiesis was first formulated in 1906. The term 'erythropoietin' for the erythropoiesis-stimulating hormone was introduced in 1948. Native human Epo was isolated in 1977 and its gene cloned in 1985. During the last 15 yr, major progress has been made in identifying the molecules controlling Epo gene expression, primarily the hypoxia-inducible transcription factors (HIF) that are regulated by specific O2 and oxoglutarate requiring Fe2+-containing dioxygenases. With respect to the action of Epo, its dimeric receptor (Epo-R) has been characterised and shown to signal through protein kinases, anti-apoptotic proteins and transcription factors. The demonstration of Epo-R in non-haematopoietic tissues indicates that Epo is a pleiotropic viability and growth factor. The neuroprotective and cardioprotective potentials of Epo are reviewed with a focus on clinical research. In addition, studies utilising the Epo derivatives with prolonged half-life, peptidic and non-peptidic Epo mimetics, orally active drugs stimulating endogenous Epo production and Epo gene transfer are reviewed.

Pathogenesis of renal anemia

Anemia is a common complication of chronic kidney disease. Although mechanisms involved in the pathogenesis of renal anemia include chronic inflammation, iron deficiency, and shortened half-life of erythrocytes, the primary cause is deficiency of erythropoietin (EPO). Serum EPO levels in patients with chronic kidney disease are usually within the normal range and thus fail to show an appropriate increase with decreasing hemoglobin levels, as found in nonrenal anemias. Studies elucidating the regulation of EPO expression led to the identification of the hypoxia inducible factor-hypoxia responsive element system. However, despite much progress in understanding the molecular mechanisms through which cells can sense oxygen availability and translate this information into altered gene expression, the reason why EPO production is inappropriately low in diseased kidneys remains incompletely understood. Both alterations in the function of EPO-producing cells and perturbations of the oxygen-sensing mechanism in the kidney may contribute. As with other anemias, the consequences of renal anemia are a moderate decrease in tissue oxygen tensions and counterregulatory mechanisms that maintain total oxygen consumption, including a persistent increase in cardiac output.

Amino acid and manganese supplementation modulates the glycosylation state of erythropoietin in a CHO culture system

The manufacture of secreted proteins is complicated by the need for both high levels of expression and appropriate processing of the nascent polypeptide. For glycoproteins, such as erythropoietin (EPO), posttranslational processing involves the addition of oligosaccharide chains. We initially noted that a subset of the amino acids present in the cell culture media had become depleted by cellular metabolism during the last harvest cycle in our batch fed system and hypothesized that by supplementing these nutrients we would improve EPO yields. By increasing the concentration of these amino acids we increased recombinant human erythropoietin (rHuEPO) biosynthesis in the last harvest cycle as expected but, surprisingly, we also observed a large increase in the amount of rHuEPO with a relatively low sialic acid content. To understand the nature of this process we isolated and characterized the lower sialylated rHuEPO pool. Decreased sialylation correlated with an increase in N-linked carbohydrates missing terminal galactose moieties, suggesting that beta-1,4-galactosyltransferase may be rate limiting in our system. To test this hypothesis we supplemented our cultures with varying concentrations of manganese (Mn(2+)), a cofactor for beta-1,4-galactosyltransferase. Consistent with our hypothesis we found that Mn(2+) addition improved galactosylation and greatly reduced the amount of rHuEPO in the lower sialylated fraction. Additionally, we found that Mn(2+) addition increased carbohydrate site occupancy and narrowed carbohydrate branching to bi-antennary structures in these lower sialylated pools. Surprisingly Mn(2+) only had this effect late in the culture process. These data indicate that the addition of Mn(2+) has complex effects on stressed batch fed cultures.

Regulation of erythropoietin production

The glycoprotein hormone erythropoietin (EPO) is an essential growth and survival factor for erythroid progenitor cells, and the rate of red blood cell production is normally determined by the serum EPO concentration. EPO production is inversely related to oxygen availability, so that an effective feedback loop is established, which controls erythropoiesis. Since recombinant EPO became available as an effective therapeutic agent, significant progress has also been made in understanding the basis of this feedback control. The main determinant of EPO synthesis is the transcriptional activity of its gene in liver and kidneys, which is related to local oxygen tensions. This control is achieved by hypoxia-inducible transcription factors (HIF), consisting of a constitutive beta-subunit and one of two alternative oxygen-regulated HIFalpha subunits (HIF-1alpha and HIF-2alpha). In the presence of oxygen (normoxia) the HIFalpha subunits are hydroxylated, which targets them for proteasomal degradation. Under hypoxia, because of the lack of molecular oxygen, HIF cannot be hydroxylated and is thereby stabilized. Although HIF-1alpha was the first transcription factor identified through its ability to bind to an enhancer sequence of the EPO gene, more recent evidence suggests that HIF-2alpha is responsible for the regulation of EPO. Although EPO is a prime example for an oxygen- regulated gene, the role of the HIF system goes far beyond the regulation of EPO, because it operates widely in almost all cells and controls a broad transcriptional response to hypoxia, including genes involved in cell metabolism, angiogenesis and vascular tone. Further evidence suggests that apart from its effect as an erythropoietic hormone EPO acts as a paracrine, tissue-protective protein in the brain and possibly also in other organs.

Recombinant erythropoietin in clinical practice

The introduction of recombinant human erythropoietin (RHuEPO) has revolutionised the treatment of patients with anaemia of chronic renal disease. Clinical studies have demonstrated that RHuEPO is also useful in various non-uraemic conditions including haematological and oncological disorders, prematurity, HIV infection, and perioperative therapies. Besides highlighting both the historical and functional aspects of RHuEPO, this review discusses the applications of RHuEPO in clinical practice and the potential problems of RHuEPO treatment.

Erythropoietin in human milk: physiology and role in infant health

Human milk contains substantial concentrations of erythropoietin, a hormone best known for its role in the regulation of erythropoiesis. Recent studies show that erythropoietin receptors are widely distributed in human tissues, including the gastrointestinal tract, endothelial cells, spinal cord, and brain, suggesting that erythropoietin plays a wider role in infant development. Mammary epithelial cells contribute to the production of erythropoietin in human milk, and erythropoietin concentrations appear to rise slowly in human milk during the first few months of lactation. Current data suggest that erythropoietin in human milk may play a pleiomorphic role in erythropoiesis, neurodevelopment, maturation of the gut, apoptosis, and immunity in the infant.

Biology and therapy of secondary leukaemias

Secondary leukaemias are common, accounting for more than 40% of all patients with acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS). A clinical history of exposure to haematotoxins or radiation is helpful; however, many older patients are diagnosed with leukaemia with no antecedent history of exposure. These patients' disease show a remarkably similar phenotype to classic therapy-related leukaemia. The specific cytogenetic abnormalities common to MDS, alkylating-agent-related AML and poor-prognosis AML (3q-, -5, 5q-, -7, 7q-, +8, +9, 11q-, 12p-, -18, -19,20q-, +21, t(1;7), t(2;11)), probably reflect a common pathogenesis distinct from that of other de novo AMLs, although the pathogenetic pathway has yet to be elucidated. Possibly, tumour suppressor genes are implicated and genomic instability may be a cause of multiple unbalanced chromosomal translocations or deletions. Typically, these patients are either elderly or have a history of exposure to alkylating agents or environmental exposure 5-7 years prior to diagnosis. Another distinct entity affects the mixed lineage leukaemia (MLL) gene located on 11q23. These account for about 3% of patients with therapy-related leukaemia and have a short latency period from exposure, usually to an inhibitor of topoisomerase II. Other therapy-related patients with t(8:21), inv16 or t(15;17) translocations should be treated as any other de novo AML with similar cytogenetics. In summary, the major prognostic factor is related to the pathogenetic mechanisms of the leukaemia. Cytogenetics and molecular features are a better predictor of outcome than patient history. Patients should receive standard induction therapy. However, the long-term outcome is relatively poor; the best results being obtained among patients undergoing allogeneic transplantation.

Erythropoietin

Maintenance of the red cell volume is a fundamental aspect of ensuring oxygen supply to the tissues. The balance between the very dynamic processes of erythropoiesis and erythrocyte loss is precarious and yet normal individuals experience a remarkably constant haematocrit. This is achieved by a very elegant and sensitive homeostatic mechanism which links tissue oxygen delivery to red cell production. The glycoprotein hormone erythropoietin (EPO) is the principle controller of this process. It is now clear that even minor underproduction of EPO will result in anaemia. The most widespread example of this is the anaemia of end-stage renal failure. The pharmacological use of recombinant human EPO (rHuEPO) in this setting is now well established and has had a dramatic impact on the quality of life of patients with renal disease. With the more widespread use of EPO in other clinical conditions and the advent of novel therapeutic approaches, this is an opportune moment to review the physiology and patho-physiology of this fascinating and essential hormone.

The production of recombinant human erythropoietin

Erythropoietin (EPO) is the glycoprotein hormone that promotes differentiation of erythroid progenitor cells in bone marrow. The normal kidney produces EPO to maintain erythrocyte for oxygen supply. This hormone activity was found in the serum of anemic animals in the 1890s. Renal failure results in severe anemia because of reduced EPO production, therefore anemia patients expected EPO treatment for long time. However, this was difficult due to the limited amount of EPO. Many researchers have tried to isolate EPO since the 1950s. Finally Miyake and Goldwasser purified highly active EPO from the urine of aplastic anemia patients. Since then, the characteristics and structural information from the purified material accelerated the cloning of the EPO gene. Mammalian cells were essential to produce EPO, because EPO contains 40% carbohydrate that plays some important roles in its activity, stability and biosynthesis. In 1984, two groups succeeded in cloning the EPO gene and expressing this gene in mammalian cells. Recombinant human EPO is currently available for anemia treatment. In this paper, we review production in mammalian cells, molecular characterization, especially carbohydrate moieties, and clinical applications of recombinant EPO.

IRS-PCR-based genetic mapping of the huntingtin interacting protein gene (HIP1) on mouse chromosome 5

Huntington's disease (HD) is a devastating central nervous system disorder. Even though the gene responsible has been positionally cloned recently, its etiology has remained largely unclear. To investigate potential disease mechanisms, we conducted a search for binding partners of the HD-protein huntingtin. With the yeast two-hybrid system, one such interacting factor, the huntingtin interacting protein-1 (HIP-1), was identified (Wanker et al. 1997; Kalchman et al. 1997) and the human gene mapped to 7q11.2. In this paper we demonstrate the localization of the HIP1 mouse homologue (Hip1) into a previously identified region of human-mouse synteny on distal mouse Chromosome (Chr) 5, both employing an IRS-PCR-based mapping strategy and traditional fluorescent in situ hybridization (FISH) mapping.

Congenital Polycythemia in Chuvashia

Familial and congenital polycythemia, not due to high oxygen affinity hemoglobin or reduced 2,3-diphosphoglycerate in erythrocytes, is common in the Chuvash population of the Russian Federation. Hundreds of individuals appear to be affected in an autosomal recessive pattern. We studied six polycythemic Chuvash patients <20 years of age from unrelated families and 12 first-degree family members. Hemoglobins were markedly elevated in the index subjects (mean ± standard deviation [SD] of 22.6 ± 1.4 g/dL), while platelet and white blood cell counts were normal. Although performed in only three of the index subjects, serum erythropoietin concentrations determined by both radioimmune and functional assays were significantly higher in polycythemic patients compared with first-degree family members with normal hemoglobin concentrations. Southern blot analysis of the Bgl 2 erythropoietin gene polymorphism showed that one polycythemic subject was a heterozygote, suggesting the absence of linkage of polycythemia with the erythropoietin gene, assuming autosomal recessive inheritance. Polymerase chain reaction (PCR) amplification of the GGAA and GA minisatellite polymorphic regions of the erythropoietin receptor gene showed no evidence of linkage of phenotype with this gene. We conclude that Chuvash polycythemia may represent a secondary form of familial and congenital polycythemia of as yet unknown etiology. This condition is the only endemic form of familial and congenital polycythemia described.

Monosomy 7 and 7q--associated with myeloid malignancy

An association between the complete or partial loss of chromosome 7 and preleukaemic myelodysplasia or acute myeloid leukaemia has been recognized from the early days of tumour cytogenetic analysis. Detection of such abnormalities usually heralds a poor prognosis. The loss of DNA on chromosome 7 has led to speculation that tumour-suppressor genes may play a significant role in this form of leukaemogenesis, although it may be part of a multistep process. A further association with leukaemia secondary to carcinogen exposure including previous chemotherapy or a number of congenital anaemias has increased the interest in discovering the gene or genes on chromosome 7. Banded chromosome analysis has suggested that there are two broad critical regions on the long arm of chromosome 7 at bands 7q22 and 7q34-q36 that may contain the relevant genes. Initial molecular analysis has confirmed these two regions to be of significance. The advent of fluorescence in-situ hybridization techniques has facilitated some definition of the 7q22 region, with identification of candidate genes for further functional analysis. It is becoming clear that there will be more than one gene on chromosome 7 involved in the leukaemic process and with the definition of these genes it may be possible to look for associations with different phenotypes and prognosis. As for the reason for chromosome 7 showing a particular predisposition to total or partial loss we may speculate that the DNA sequence and structure may confer a 'fragility' on the chromosome. A greater understanding of the DNA structure of the long arm may provide real insight into the mechanisms of leukaemia. We would like to speculate in the long term that this could lead to the ability to screen for leukaemia susceptibility and avoidance of 'inducers' in those at risk.

Mapping of the Active Site of Recombinant Human Erythropoietin

Recombinant human erythropoietin (rHuEPO) variants have been constructed to identify amino acid residues important for biological activity. Immunoassays were used to determine the effect of each mutation on rHuEPO folding. With this strategy, we could distinguish between mutations that affected bioactivity directly and those that affected bioactivity because the mutation altered rHuEPO conformation. Four regions were found to be important for bioactivity: amino acids 11 to 15, 44 to 51, 100 to 108, and 147 to 151. EPO variants could be divided into two groups according to the differential effects on EPO receptor binding activity and in vitro biologic activity. This suggests that rHuEPO has two separate receptor binding sites. Mutations in basic residues reduced the biologic activity, whereas mutations in acidic residues did not. This suggests that electrostatic interactions between rHuEPO and the human EPO receptor may involve positive charges on rHuEPO.

Chromosome 7 and Haematological Malignancies

Abnormalities of chromosome 7 are the most common clonal chromosomal changes observed in myelodysplasia (MDS) and the second most frequent in acute myeloid leukaemia (AML) [1-5]. These changes may consist of long arm deletion (7q-) or total loss of the whole chromosome (monosomy 7) from bone marrow cells [1, 4, 6-24] and was first reported in association with myeloid disease in 1964 with the report of 3 cases of refractory anaemia, granulocytic hyperplasia [25]. The association between chromosome 7 alterations, MDS and AML in children and adults is clear, however, a rare association with lymphoid malignancies has also been recently reported. The abnormalities may occur in de novo MDS/AML, secondary cases following exposure to drugs, radiotherapy and toxins and in addition in a range of constitutional disorders including Fanconi's anaemia, congenital neutropenia and neurofibromatosis type 1 (NF1). The broad spread of conditions in which this consistent genetic change can occur leads one to speculate that there is an underlying instability in chromosome 7 and that genes on this chromosome play a role in the development of malignancy. The loss of DNA associated with malignant progression suggests the presence of a tumour suppressor gene (or genes) [26, 27]. Patients with monosomy 7 usually present as classical MDS with abnormal erythroid, megakaryocyte and myeloid differentiation [7, 28]. From a mechanistic perspective, increased cell proliferation and apoptosis is a common feature possibly induced by the failure of normal haematopoietic maturation. In all groups the presence of chromosome 7 abnormalities defines a poor prognostic group [29]. The majority of patients with MDS transform to a form of acute leukaemia resistant to therapy, including bone marrow transplantation (BMT). Although fluorescence in situ hybridization (FISH) has accelerated the study of these disorders at the cytogenetic and molecular levels, [4, 30, 31, 32, 33] no gene has been clearly implicated. A few candidate genes are under investigation. While the loss of chromsome 7 material is crutial in the malignant process it is almost certainly not the primary molecular abnormality. An initiating event genetic event predisposing to chromosome breakage and loss probably occurs in haematopoietic cells permitting chromosome 7 loss and progression to clonal malignancy as a secondary event.

Erythropoietin in the control of red cell production

The understanding of the endocrine regulation of red cell production has been extended greatly since the erythropoietin gene was cloned and recombinant human erythropoietin has become available for experimental and clinical applications. Human erythropoietin is a 30 kDa glycoprotein. It is composed of 165 amino acids and 4 carbohydrate side chains. Studies in rodents have shown that blood-borne erythropoietin originates from peritubular cells, possibly fibroblasts, in the renal cortex and from parenchymal cells in the liver. In addition, erythropoietin mRNA has been demonstrated in spleen, lung and brain. Tissue hypoxia is the main stimulus for erythropoietin synthesis. Erythropoietin gene expression is controlled by DNA-binding proteins, primarily by hypoxia-inducible factor 1. Erythropoietin maintains red cell production by inhibiting apoptosis of erythrocytic progenitors, and by stimulating their proliferation and differentiation into normoblasts. The functional human erythropoietin receptor, a 484-amino acid glycoprotein, is member of the class I cytokine receptor superfamily. Lack of erythropoietin results in anaemia. Recombinant human erythropoietin is efficient for treatment of the anaemia of chronic renal failure. In addition, the drug is increasingly administrated to persons suffering from anaemia of chronic diseases and to surgical patients, thus abolishing the need for homologous red cell transfusion.

Molecular evidence that childhood monosomy 7 syndrome is distinct from juvenile chronic myelogenous leukemia and other childhood myeloproliferative disorders

The observation that juvenile chronic myelogenous leukemia (JCML) and childhood bone marrow monosomy 7 syndrome (Mo 7) are similar in many clinical and epidemiologic respects suggests a shared pathogenic basis and raises the possibility that the bone marrows of patients with JCML might lose chromosome 7 alleles by mechanisms that do not result in detectable cytogenetic deletions. We used a series of polymorphic markers mapped to chromosome 7 to test this hypothesis in 22 children with MPS and MDS, including 19 with JCML. All MPS and MDS samples demonstrated allelic heterozygosity with at least one chromosome 7 marker; 16 were heterozygous with probes from both 7p and 7q. Furthermore, the percentage of patient bone marrow samples heterozygous at each locus tested was similar to the frequency observed in the normal population. Whereas these data demonstrate that submicroscopic loss of large segments of chromosome 7 alleles is uncommon in children with MPS and MDS who do not have Mo 7, they do not exclude small deletions around an uncharacterized tumor-suppressor locus. Our results suggest that a number of distinct molecular events contribute to leukemogenesis, and we propose a multistep model to explain the similarities and differences between the major subtypes of childhood MPS and MDS.

Human thrombopoietin: gene structure, cDNA sequence, expression, and chromosomal localization

Thrombopoietin (TPO), a lineage-specific cytokine affecting the proliferation and maturation of megakaryocytes from committed progenitor cells, is believed to be the major physiological regulator of circulating platelet levels. Recently we have isolated a cDNA encoding a ligand for the murine c-mpl protooncogene and shown it to be TPO. By employing a murine cDNA probe, we have isolated a gene encoding human TPO from a human genomic library. The TPO locus spans over 6 kb and has a structure similar to that of the erythropoietin gene (EPO). Southern blot analysis of human genomic DNA reveals a hybridization pattern consistent with a single gene locus. The locus was mapped by in situ hybridization of metaphase chromosome preparations to chromosome 3q26-27, a site where a number of chromosomal abnormalities associated with thrombocythemia in cases of acute myeloid leukemia have been mapped. A human TPO cDNA was isolated by PCR from kidney mRNA. The cDNA encodes a protein with 80% identity to previously described murine TPO and is capable of initiating a proliferative signal to murine interleukin 3-dependent BaF3 cells expressing the murine or human TPO receptor.

The structure, biology and potential therapeutic applications of recombinant thrombopoietin

Platelets, an integral component of hemostasis, are produced by megakaryocytes derived from the differentiation of pluripotent stem cells in the bone marrow or spleen. After decades of study, the regulation of this process is still not well understood. However, the recent cloning and characterization of thrombopoietin, a ligand for the receptor encoded by the c-mpl proto-oncogene, provides new insights into the humoral regulation of megakaryocytopoiesis and platelet production. Consistent with the proposed role as a major physiological regulator of megakaryocytopoiesis, thrombopoietin has potent effects on megakaryocytopoiesis in vitro and in vivo. In addition to the original supposition that thrombopoietin functions as a late-acting megakaryocyte maturation factor, recombinant thrombopoietin proves also to be a potent stimulator of hematopoietic progenitor cells, inducing them to undergo proliferation and differentiation into megakaryocytic colonies. When administered to mice, thrombopoietin causes an increase in peripheral platelet numbers to previously unattainable levels within a few days. Studies of the efficacy of thrombopoietin are underway. It is envisaged that this new cytokine will have widespread applications as a therapeutic agent for the management of bleeding due to thrombocytopenias, in particular those resulting from cancer chemo- or irradiation therapy.

Fine mapping of the autosomal dominant split hand/split foot locus on chromosome 7, band q21.3-q22.1

Split hand/split foot (SHFD) is a human developmental defect characterized by missing digits, fusion of remaining digits, and a deep median cleft in the hands and feet. Cytogenetic studies of deletions and translocations associated with this disorder have indicated that an autosomal dominant split hand/split foot locus (gene SHFD1) maps to 7q21-q22. To characterize the SHFD1 locus, somatic cell hybrid lines were constructed from cytogenetically abnormal individuals with SHFD. Molecular analysis resulted in the localization of 93 DNA markers to one of 10 intervals surrounding the SHFD1 locus. The translocation breakpoints in four SHFD patients were encompassed by the smallest region of overlap among the SHfD-associated deletions. The order of DNA markers in the SHFD1 critical region has been defined as PON-D7S812-SHFD1-D7S811-ASNS. One DNA marker, D7S811, detected altered restriction enzyme fragments in three patients with translocations when examined by pulsed-field gel electrophoresis (PFGE). These data map SHFD1, a gene that is crucial for human limb differentiation, to a small interval in the q21.3-q22.1 region of human chromosome 7.

Direct selection: a method for the isolation of cDNAs encoded by large genomic regions

We have developed a strategy for the rapid enrichment and identification of cDNAs encoded by large genomic regions. The basis of this "direct selection" scheme is the hybridization of an entire library of cDNAs to an immobilized genomic clone. Nonspecific hybrids are eliminated and selected cDNAs are eluted. These molecules are then amplified and are either cloned or subjected to further selection/amplification cycles. This scheme was tested using a 550-kilobase yeast artificial chromosome clone that contains the EPO gene. Using this clone and a fetal kidney cDNA library, we have achieved a 1000-fold enrichment of EPO cDNAs in one cycle of enrichment. More significantly, we have further investigated one of the "anonymous" cDNAs that was selectively enriched. We confirmed that this cDNA was encoded by the yeast artificial chromosome. Its frequency in the starting library was 1 in 1 x 10(5) cDNAs and after selection comprised 2% of the selected library. DNA sequence analysis of this cDNA and of the yeast artificial chromosome clone revealed that this gene encodes the beta 2 subunit of the human guanine nucleotide-binding regulatory proteins. Restriction mapping and hybridization data position this gene (GNB2) to within 30-70 kilobases of the EPO gene. The selective isolation and mapping of GNB2 confirms the feasibility of this direct selection strategy and suggests that it will be useful for the rapid isolation of cDNAs, including disease-related genes, across extensive portions of the human genome.

The role of cytokines in oncology

The availability of sufficient quantities of recombinant human cytokines and promising preclinical data have led to their introduction into clinical trials. Cytokines have potential as new therapeutic agents in a variety of hematological disorders as well as in solid tumors. Only a few of the still increasing number of these glycoprotein hormones have been studied in humans so far, either as single agents or in combination with chemotherapy and other cytokines. Their clinical effects, beneficial role in supportive care, and use in the treatment of certain cancer patients are reviewed.

BglII polymorphism at the human erythropoietin gene

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Erythropoietin: its role in the regulation of erythropoiesis and as a therapeutic in humans

The application of recombinant DNA technology to the field of hematology has contributed greatly to our understanding of Epo gene structure and regulation, cellular expression and regulation of hormone production, pharmacokinetics, receptor biology, and ultimately, the value of this hormone as a therapeutic treatment. Areas that will undoubtedly prove fruitful for future research include the mechanisms by which hypoxia influences gene expression, structure/function relationships of the Epo molecule, mechanisms of transmembrane signaling and nuclear activation, and the application of rHuEpo in the treatment of other anemias. Epo is but one example of the contribution that modern biology has made to the understanding of hematopoietic regulation and to the availability of these regulators for the treatment of human disease.

Recombinant erythropoietin in pediatrics: a clinical perspective

Recombinant human erythropoietin represents a potential therapeutic alternative to red blood cell transfusions in a number of pediatric anemias. It is effective in correcting anemia associated with chronic renal failure and may significantly reduce the morbidity associated with childhood CRF. Most exposures to allogeneic blood products in pediatrics for treatment of anemia with blood transfusions occur in neonatal intensive care units. If proven effective in treating anemia in premature babies, r-HuEPO will be responsible for a major reduction in the use of blood transfusions in clinical neonatology. Carefully designed, placebo-controlled clinical trials will be required to establish the role of r-HuEPO in anemia of prematurity. Recombinant human erythropoietin also may be useful to increase the amount of blood that can be collected before elective surgical procedures. Another potential indication is to raise the hematocrits of infants with large intracardiac shunts who develop congestive heart failure coincident with the developmental fall in hemoglobin concentration after birth. Finally, r-HuEPO may one day play a role in modifying the expression of globin genes and, thereby, ameliorate the course of sickle cell disease and beta thalassemia. Many questions surrounding the use of r-HuEPO in infancy and childhood are being addressed in ongoing clinical trials.

The gene for the alpha 2 chain of the human fibrillar collagen type XI (COL11A2) assigned to the short arm of chromosome 6

A cosmid clone (CosHcol.11) containing the alpha 2(XI) collagen gene (COL11A2) has been isolated. The gene contains conserved DNA and amino-acid sequences characteristic of fibril forming collagen, which is in accordance with the classification of type XI collagen as a fibrillar collagen. The genomic clone containing the alpha 2(XI) gene has been used as probe in the Southern blot analysis of DNA from a panel of human/hamster somatic cell hybrids containing different numbers and combinations of human chromosomes. Synteny analysis revealed that only chromosome 6 showed complete concordant segregation with COL11A2. Furthermore, the gene was regionally mapped to the short arm of chromosome 6 by using a hybrid which contained only the long arm of the chromosome.

Serum immunoreactive erythropoietin in health and disease

The currently available radioimmunoassay for erythropoietin (Epo) using recombinant reagents is an accurate, reproducible, sensitive and specific assay which can be used to identify whether lack of Epo is contributing to anemia and, by extension, whether therapy with recombinant Epo might be appropriate. Elevation of the serum Epo level with anemia suggests that a marrow abnormality is the cause of the anemia, while a "high" Epo level in a non-anemic or plethoric patient suggests the presence of hypoxia or autonomous Epo production. Liver disease can elevate the serum Epo level, while modest degrees of anemia do not affect it appreciably. The lowest Epo levels occur in polycythemia vera, but in a particular patient this finding is not completely diagnostic.

Hematopoietic growth factors. Biology and clinical applications

The hematopoietic growth factors are potent regulators of blood-cell proliferation and development. The first phase of clinical trials suggests that they may augment hematopoiesis in a number of different conditions of primary and secondary bone marrow dysfunction. Future clinical use is likely to include combinations of these growth factors, in order to stimulate early marrow progenitors and obtain multilineage effects. An improved understanding of the biologic and clinical effects of hematopoietic growth factors promises future clinical applications for conditions of impaired function and reduced numbers of blood cells.

Familial bone marrow monosomy 7. Evidence that the predisposing locus is not on the long arm of chromosome 7

Loss of expression of a tumor-suppressing gene is an attractive model to explain the cytogenetic and epidemiologic features of cases of myelodysplasia and acute myelogenous leukemia (AML) associated with bone marrow monosomy 7 or partial deletion of the long arm (7q-). We used probes from within the breakpoint region on 7q-chromosomes (7q22-34) that detect restriction fragment length polymorphisms (RFLPs) to investigate three families in which two siblings developed myelodysplasia with monosomy 7. In the first family, probes from the proximal part of this region identified DNA derived from the same maternal chromosome in both leukemias. The RFLPs in these siblings diverged at the more distal J3.11 marker due to a mitotic recombination in one patient, a result that suggested a critical region on 7q proximal to probe J3.11. Detailed RFLP mapping of the implicated region was then performed in two additional unrelated pairs of affected siblings. In these families, DNA derived from different parental chromosome 7s was retained in the leukemic bone marrows of the siblings. We conclude that the familial predisposition to myelodysplasia is not located within a consistently deleted segment on the long arm of chromosome 7. These data provide evidence implicating multiple genetic events in the pathogenesis of myelodysplasia seen in association with bone marrow monosomy 7 or 7q-.