The enigma of the metabolic fate of circulating erythropoietin (Epo) in view of the pharmacokinetics of the recombinant drugs rhEpo and NESP

Change in erythropoietin pharmacokinetics following hematopoietic transplantation

Pre-clinical studies have demonstrated that bone marrow ablation has a profound effect in decreasing erythropoietin (EPO) elimination. The study's objective was to determine in humans if EPO pharmacokinetics (PKs) are perturbed following bone marrow ablation. EPO PK studies were performed in eight subjects, aged 4 to 61 years, undergoing fully myeloablative hematopoietic stem cell transplantation. Serial PK studies using intravenous injection of recombinant human EPO (92+/-2.0 U/kg) (mean+/-SEM) were carried out during four periods of altered marrow integrity: baseline pre-ablation, post-ablation pre-transplant, early post-transplant pre-engraftment, and late post-transplant full engraftment. Compared with baseline, post-ablation pre-transplant and early post-transplant EPO PKs demonstrated declines in clearance increases in terminal elimination half-life of 36 and 95%, respectively. Clearance and half-life returned to baseline following full engraftment. The association of EPO elimination with decreased bone marrow activity in patients undergoing transplantation conclusively establishes the bone marrow as a key determinant of EPO elimination in humans.

A statistical pattern recognition approach for determining cellular viability and lineage phenotype in cultured cells and murine bone marrow

BACKGROUND

Cellular binding of annexin V and membrane permeability to 7-aminoactinomycin D (7AAD) are important tools for studying apoptosis and cell death by flow cytometry. Combining viability markers with cell surface marker expression is routinely used to study various cell lineages. Current classification methods using strict thresholds, or "gates," on the fluorescent intensity of these markers are subjective in nature and may not fully describe the phenotypes of interest. We have developed objective criteria for phenotypic boundary recognition through the application of statistical pattern recognition. This task was achieved using artificial neural networks (ANNs) that were trained to recognize subsets of cells with known phenotypes, and then used to determine decision boundaries based on statistical measures of similarity. This approach was then used to test the hypothesis that erythropoietin (EPO) inhibits apoptosis and cell death in erythroid precursor cells in murine bone marrow.

METHODS

Our method was developed for classification of viability using an in vitro cell system and then applied to an ex vivo analysis of murine late-stage erythroid progenitors. To induce apoptosis and cell death in vitro, an EPO-dependent human leukemic cell line, UT-7(EPO) cells were incubated without recombinant human erythropoietin (rhEPO) for 72 h. Five different ANNs were trained to recognize live, apoptotic, and dead cells using a "known" subset of the data for training, and a K-fold cross validation procedure for error estimation. The ANNs developed with the in vitro system were then applied to classify cells from an ex vivo study of rhEPO treated mice. Tg197 (human tumor necrosis-alpha transgenic mice, a model of anemia of chronic disease) received a single s.c. dose of 10,000 U/kg rhEPO and femoral bone marrow was collected 1, 2, 4, and 8 days after dosing. Femoral bone marrow cells were stained with TER-119 PE, CD71 APC enable identification of erythroid precursors, and annexin V FITC and 7AAD to identify the apoptotic and dead cells. During classification forward and side angle light scatter were also input to all pattern recognition systems.

RESULTS

Similar decision boundaries between live, apoptotic, and dead cells were consistently identified by the neural networks. The best performing network was a radial basis function multi-perceptron that produced an estimated average error rate of 4.5% +/- 0.9%. Using these boundaries, the following results were reached: depriving UT-7(EPO) cells of rhEPO induced apoptosis and cell death while the addition of rhEPO rescued the cells in a dose-dependent manner. In vivo, treatment with rhEPO resulted in an increase of live erythroid cells in the bone marrow to 119.8% +/- 9.8% of control at the 8 day time point. However, a statistically significant transient increase in TER-119(+) CD71(+) 7AAD(+) dead erythroid precursors was observed at the 1 and 2 day time points with a corresponding decrease in TER-119(+) CD71(+) 7AAD(-) Annexin V(-) live erythroid precursors, and no change in the number of TER-119(+) CD71(+) annexin V(+) 7AAD(-) apoptotic erythroid precursors in the bone marrow.

CONCLUSIONS

A statistical pattern recognition approach to viability classification provides an objective rationale for setting decision boundaries between "positive" and "negative" intensity measures in cytometric data. Using this approach we have confirmed that rhEPO inhibits apoptosis and cell death in an EPO dependent cell line in vitro, but failed to do so in vivo, suggesting EPO may not act as a simple antiapoptotic agent in the bone marrow. Rather, homeostatic mechanisms may regulate the pharmacodynamic response to rhEPO.

Control of erythropoietin gene expression and its use in medicine

Erythropoietin (EPO) gene expression is under the control of inhibitory (GATA-2, NF-kappaB) and stimulatory (hypoxia-inducible transcription factor [HIF]-2, hepatocyte nuclear factor [HNF]-4alpha [alpha]) transcription factors. EPO deficiency is the main cause of the anemia in chronic kidney disease (CKD) and a contributing factor in the anemias of inflammation and cancer. Small, orally active compounds capable of stimulating endogenous EPO production are in preclinical or clinical trials for treatment of anemia. These agents include stabilizers of the HIFs that bind to the EPO enhancer and GATA inhibitors which prevent GATA from suppressing the EPO promoter. While HIF stabilizing drugs may prove useful as inexpensive second-line choices, at present, their side effects--particularly tumorigenicity--preclude their use as first-choice therapy. As an alternative, EPO gene therapy has been explored in animal studies and in trials on CKD patients. Here, a major problem is immunogenicity of ex vivo transfected implanted cells and of the recombinant protein produced after ex vivo or in vivo EPO complementary DNA (cDNA) transfer. Recombinant human EPO (rhEPO) engineered in Chinese hamster ovary (CHO) cell cultures (epoetin alpha and epoetin beta [beta]) and its hyperglycosylated analogue darbepoetin alpha are established and safe drugs to avoid allogeneic red blood cell transfusion. Gene-activated EPO (epoetin delta [delta]) from human fibrosarcoma cells (HT-1080) has recently been launched for use in CKD. It is important to know the basics of the technologies, production processes, and structural properties of the novel anti-anemic strategies and drugs.

Cost comparison of epoetin alpha, epoetin beta and darbepoetin alpha for cancer patients with anaemia in the clinical practice setting

BACKGROUND AND OBJECTIVE

Cost control is becoming an increasingly important consideration for clinicians when planning how to provide the best treatment for anaemic cancer patients. Administration of erythropoiesis stimulating agents (epoetin alpha, epoetin beta and darbepoetin alpha) has become the standard of care for treatment of anaemia in cancer patients. However, only limited information is available on the economic comparability of epoetin alpha, epoetin beta and darbepoetin alpha, and thus this study was conducted to compare cost per patient of each of these agents for anaemic cancer patients.

METHODS

All prescriptions of the agents over 1 year were analysed by two Austrian regional public health insurance associations and cost per patient for each agent was calculated from invoicing data. Data from the two regions were combined to obtain total mean drug costs per patient per year.

RESULTS AND DISCUSSION

Analyses showed significantly lower costs for epoetin alpha ( 2,743.27 euros) than for darbepoetin alpha (3,627.98 euros ) or epoetin beta ( 3,292.28 euros): epoetin alpha vs. darbepoetin alpha (P < 0.0001); epoetin beta vs. darbepoetin alpha (P = 0.0001); epoetin alpha vs. epoetin beta (P = 0.0009). As costs of the three agents in Austria are identical for therapeutically equivalent doses, the higher cost of darbepoetin alpha was believed to be due mainly to longer treatment duration to target haemoglobin level.

CONCLUSION

The finding of a cost difference favouring epoetin alpha over darbepoetin alpha suggests the need for prospective randomized studies comparing efficacy and cost effectiveness of all three agents to obtain more definitive data.

Urinary excretion of darbepoetin after intravenous vs subcutaneous administration to preterm neonates

OBJECTIVE

Previous studies suggest that darbepoetin might stimulate erythropoiesis in preterm neonates more effectively if injected subcutaneously (s.c.) than if infused intravenously (i.v.). It has been postulated that this is because very high plasma concentrations after i.v. dosing result in urinary loss of the drug. However, this theory has not been tested systematically, and no direct comparisons have been made between s.c. and i.v. dosing of darbepoetin in preterm neonates.

STUDY DESIGN

Preterm neonates were eligible for this pilot study if they were born at < or =32 weeks gestation with a weight of < or =1500 g, and had a hemoglobin < or =10.5 g/dl. The darbepoetin was given (4 microg/kg) i.v., over 4 h, if an i.v. was already in place and s.c. if no i.v. was in place. Urine was collected for drug quantification before dosing and for 48 h after. Blood was obtained for immature reticulocyte fraction (IRF), absolute reticulocyte count (ARC) and reticulocyte % before and 96 h after dosing.

RESULTS

Ten preterm neonates were studied: five received i.v. and five received s.c. darbepoetin. No adverse effects of the administrations were detected. IRF, ARC and reticulocyte % increased in the i.v. and s.c. recipients, and no difference in magnitude of increase was apparent between the groups. Before the darbepoetin was administered, none of the patients had any erythropoietin (Epo) detected in their urine. After i.v. dosing, no darbepoetin was detected in any of the samples, on any of the subjects, over the subsequent 48 h. After s.c. dosing, three of the patients had minimal urinary Epo detected. The patient with the largest urinary loss of drug had only 0.13% of the administered dose detected in the urine. Thus, essentially no urinary loss of drug was observed following either i.v. or s.c. darbepoetin dosing.

CONCLUSION

Darbepoetin loss into the urine was below detectable limits among seven patients, while three had minimally detectable urinary losses. i.v. and s.c. dosing resulted in approximately equivalent increases in reticulocyte response when measured 96 h after dosing. On this basis, we speculate that if a patient who is to receive darbepoetin has an i.v. in place, the drug can be given i.v., thus avoiding any discomfort associated with an s.c. injection.

Population pharmacokinetics of darbepoetin alfa in haemodialysis and peritoneal dialysis patients after intravenous administration

AIMS

To characterize the pharmacokinetics of darbepoetin alfa and covariate relationships in haemodialysis (HD) and peritoneal dialysis (PD) patients.

METHODS

Data were collected from 131 (63 HD and 68 PD) patients who received darbepoetin alfa intravenously. A total of 917 serum concentrations were available. The data were analysed by nonlinear mixed effect modelling using NONMEM with a model including endogenous erythropoietin production. In addition, the final model was evaluated using bootstrap resampling.

RESULTS

The selected basic model was a two-compartment model with a combination of additive and the constant coefficient of variation error models. The significant covariates were weight (WT) for clearance (CL) and the volume of central compartment (V(1)), and the dialysis technique (DIA) for V(1). The typical values of CL and V(1) were 0.0807 l h(-1) and 2.51 l, respectively. V(1) in PD patients was 17% higher than in HD patients. With the introduction of WT in CL and WT and DIA in V(1), interindividual variability decreased from 27.1% to 20.6% in CL and from 29.1% to 21.8% in V(1). The mean parameter estimates from the bootstrap datasets were similar to those from the original dataset. Evaluation by bootstrapping showed that the final model was stable.

CONCLUSIONS

The results of the present analysis suggest no dosage regimen change is warranted for darbepoetin alfa in HD and PD patients over the range of distribution of covariates included in this study.

Pharmacokinetics and pharmacodynamics of weekly epoetin beta in lung cancer patients

BACKGROUND

To assess the pharmacokinetic profile and time-course of trough concentrations and hemoglobin levels associated with subcutaneous weekly administration of epoetin beta in lung cancer patients with chemotherapy-induced anemia.

METHODS

Epoetin beta was subcutaneously administered to 15 anemic lung cancer patients once weekly for 8 weeks at doses of 9000, 18,000 and 36,000 IU. Pharmacokinetic parameters (C(max), AUC(inf) and T(1/2)) were determined after the first single dose administration on a model-independent basis, and the relationship between the dose and these parameters was examined for linearity.

RESULTS

Weekly administration of epoetin beta at 9000, 18,000 and 36,000 IU produced C(max) values of 308 +/- 117 (mean +/- standard deviation), 678 +/- 86.7 and 1316 +/- 766 mIU/ml, and AUC(inf) values of 15,300 +/- 9524, 54,574 +/- 16,265 and 88,501 +/- 55,687 hr mIU/ml, respectively, showing dose-proportional increases. Trough concentrations tended to increase in the presence of severe bone marrow suppression induced by chemotherapy or other factors. Extremely high values were seen in three patients, but there was no apparent trend toward an increase with repeated doses. After 8 weeks' administration at 9000, 18,000 and 36,000 IU, hemoglobin levels were changed by -0.37 +/- 1.26, 2.15 +/- 1.36 and 2.82 +/- 2.17 g/dl, respectively.

CONCLUSIONS

Epoetin beta exhibited linear pharmacokinetics when administered to anemic cancer patients at weekly doses of 9000-36,000 IU and did not cause drug accumulation. Hemoglobin levels increased with weekly doses of 18,000 or 36,000 IU.

Inducing Tolerance to a Soluble Foreign Antigen by Encapsulated Cell Transplants

The immune response to soluble antigens constitutes a current clinical problem impeding the development of protein therapeutics. We have developed an encapsulated-cell delivery system, which, transiently combined with an anti-CD154 antibody treatment, allows for the suppression of this immune response and the establishment of long-term secretion of a foreign antigen, human erythropoietin (huEPO). The chronic presence of antigen appears to be required to maintain this tolerance, as a 21-day gap in the exposure to huEPO is sufficient to restore the ability of mice to mount an antibody response. In contrast, chronic huEPO expression maintains tolerance even in the absence of further anti-CD154 treatment. These results suggest that a soluble antigenic protein can be continuously released, without inducing an antibody response, using encapsulated allogeneic cells. The temporary anti-CD154 treatment induces immune unresponsiveness to the delivered antigen, while the immunoprotected cell implant allows for chronic antigen release, favoring the establishment of tolerance.

Darbepoetin alfa: its use in anemia associated with chronic kidney disease

Darbepoetin alfa (Aranesp), Nespo) is an amino acid substituted analog of human erythropoietin (EPO) that promotes erythrocyte survival, proliferation, and differentiation. Approved in Europe and the US for the treatment of anemia associated with chronic kidney disease (CKD), it is characterized by delayed clearance and a more prolonged elimination half-life than recombinant human erythropoietin (rhEPO; epoetin alfa and beta), permitting an extended interval between doses. Darbepoetin alfa is generally well tolerated, and clinical trials of 20-52 weeks' duration have demonstrated the efficacy of subcutaneous and intravenous administration at 1- or 2-week intervals in the initial treatment of anemia associated with CKD both in dialysis patients and in patients not yet on dialysis. Trials of up to 52 weeks' duration demonstrated that in the majority of patients with CKD, treatment with darbepoetin alfa at up to 4-week intervals maintained hemoglobin (Hb) levels established by prior erythropoietic treatment, while in patients undergoing dialysis, intravenous or subcutaneous darbepoetin alfa administered at 1- or 2-week intervals was noninferior to rhEPO administered once, twice, or three times per week in maintaining established Hb levels.

Pharmacokinetics of Darbepoetin Alfa after Intravenous or Subcutaneous Administration in Patients with Non-myeloid Malignancies Undergoing Chemotherapy

BACKGROUND AND OBJECTIVE

The pharmacokinetics of darbepoetin alfa after intravenous (IV) administration in the oncology setting have not been previously reported. The objective of this study was to evaluate the pharmacokinetics of IV or subcutaneous (SC) darbepoetin alfa in patients with non-myeloid malignancies undergoing multicycle chemotherapy.

METHODS

Fifty-six patients (haemoglobin <or=13.0 g/dL) received weekly darbepoetin alfa 2.25 microg/kg administered either IV (n=27) or SC (n=29) during up to three cycles of chemotherapy. Noncompartmental pharmacokinetic analysis was performed, including analysis of intensive pharmacokinetic profiles collected over 168 hours during week 1 of both the first and third cycles of chemotherapy.

RESULTS

Darbepoetin alfa serum concentrations exhibited a biphasic profile (a rapid distributive phase followed by a slower terminal elimination phase) after IV administration, whereas darbepoetin alfa was slowly absorbed after SC administration. Darbepoetin alfa exhibited limited extravascular distribution after IV administration, with both initial and steady-state mean volumes of distribution (36.1 mL/kg and 55.2 mL/kg, respectively, after a single IV dose) approximating the plasma volume. After a single IV dose, darbepoetin alfa exhibited a mean clearance of 1.05 mL/h/kg, with a mean terminal half-life of 38.8 hours. Similar pharmacokinetic results were observed after single and multiple doses of darbepoetin alfa, for both SC and IV administration.

CONCLUSION

Darbepoetin alfa is cleared slowly after IV administration to patients with cancer receiving chemotherapy, resulting in a terminal half-life of 38.8 hours. No evidence of accumulation and no changes in pharmacokinetic profiles after repeated administration were observed in cancer patients undergoing cyclic chemotherapy, for both IV and SC dosing.

Cellular trafficking and degradation of erythropoietin and novel erythropoiesis stimulating protein (NESP)

Erythropoietin (Epo) is essential for the production of mature red blood cells, and recombinant Epo is commonly used to treat anemia, but how Epo is degraded and cleared from the body is not understood. Glycosylation of Epo is required for its in vivo bioactivity, although not for in vitro receptor binding or stimulation of Epo-dependent cell lines; Epo glycosylation actually reduces the affinity of Epo for the Epo receptor (EpoR). Interestingly, a hyperglycosylated analog of Epo, called novel erythropoiesis-stimulating protein (NESP), has a lower affinity than Epo for the EpoR but has greater in vivo activity and a longer serum half-life than Epo. We hypothesize that a major mechanism for degradation of Epo in the body occurs in cells expressing the Epo receptor, through receptor-mediated endocytosis of Epo followed by degradation in lysosomes, and therefore investigated the trafficking and degradation of Epo and NESP by EpoR-expressing cells. We show that Epo and NESP are degraded only by cultured cells that express the EpoR, and their receptor binding, dissociation, and trafficking properties determine their rates of intracellular degradation. Epo binds surface EpoR faster than NESP (k(on) = 5.0 x 10(8) m(-1) min(-1) versus 1.1 x 10(8) m(-1) min(-1)) but dissociates slower (k(off) = 0.029 min(-1) versus 0.042 min(-1)). Surface-bound Epo and NESP are internalized at the same rate (k(in) = 0.06 min(-1)), and after internalization 60% of each ligand is resecreted intact and 40% degraded. Our kinetic model of Epo and NESP receptor binding, intracellular trafficking, and degradation explains why Epo is degraded faster than NESP at the cellular level.

Efficacy prospective study of different frequencies of Epo administration by i.v. and s.c. routes in renal replacement therapy patients

BACKGROUND

The problem of pure red cell aplasia (PRCA) prompted nephrologists to revert to a wider intravenous (i.v.) utilization of erythropoeitin (Epo). Once weekly i.v. Epo administration has been suggested to be as effective as the twice/thrice weekly i.v. dose. The aim of the present study was to test whether once weekly i.v. Epo administration is equally as cost-effective as once weekly subcutaneous (s.c.) and 2-3 times weekly i.v. administration.

METHODS

We prospectively studied 41 patients (23 males, aged 28-82 years), on renal replacement therapy for 18-286 months, stabilized on twice or thrice weekly s.c. Epo-alpha (basal). The patients were treated for three consecutive 6 month periods with once weekly s.c. (OWSC), once weekly i.v. (OWIV) and twice/thrice weekly i.v. (TWIV) Epo-alpha. The initial dose for each period was equal to the final dose of the previous one; when necessary, the dose was adjusted according to DOQY guidelines. Iron, folic acid and vitamin B(12) supplementations were given throughout all the study periods. At the end of each of the four study periods, the following parameters were evaluated: haemoglobin, haematocrit, hypochromic red blood cells (RBCs), iron, serum ferritin, transferrin, folate, vitamin B(12), C-reactive protein (CRP), Kt/V, parathyroid hormone (PTH) and weekly dose of Epo-alpha.

RESULTS

Thirty-three out of 41 enrolled patients completed the study (there were five deaths, two renal transplants and one transfer). No significant changes were observed as regards iron, serum ferritin, transferrin, folate, vitamin B(12), CRP, Kt/V or PTH level. Haemoglobin levels were not different at the end of the basal (11.7+/-1.21), OWSC (11.8+/-0.86) and TWIV (12.1+/-1.04) periods, while significantly lower levels were observed after the OWIV period (11.0+/-0.97, P<0.01). Weekly Epo consumption (Epo U/week/kg body weight/g haemoglobin) was: basal 11.57+/-5.96; OWSC 10.22+/-4.53; OWIV 15.99+/-7.7*(a); and TWIV 11.89+/-6.3*(a) (*P<0.01 vs basal; (a)P<0.01 vs OWSC).

CONCLUSIONS

From our results, the OWIV schedule seems to have less efficacy in the control of anaemia of chronic renal failure patients on dialysis treatment than either OWSC or TWIV schedules.

Emerging biological roles for erythropoietin in the nervous system

Erythropoietin mediates an evolutionarily conserved, ancient immune response that limits damage to the heart, the nervous system and other tissues following injury. New evidence indicates that erythropoietin specifically prevents the destruction of viable tissue surrounding the site of an injury by signalling through a non-haematopoietic receptor. Engineered derivatives of erythropoietin that have a high affinity for this receptor have been developed, and these show robust tissue-protective effects in diverse preclinical models without stimulating erythropoiesis. A recent successful proof-of-concept clinical trial that used erythropoietin to treat human patients who had suffered a stroke encourages the evaluation of both this cytokine and non-erythropoietic derivatives as therapeutic agents to limit tissue injury.

Effects of chemotherapy on endogenous erythropoietin levels and the pharmacokinetics and erythropoietic response of darbepoetin alfa: a randomised clinical trial of synchronous versus asynchronous dosing of darbepoetin alfa

The introduction of longer-acting erythropoietic agents into the practice of oncology has demanded an understanding of the interaction of chemotherapy with the pharmacokinetics and haematological effects of these erythropoietins. We report results of a randomised trial comparing the haematological effects of darbepoetin alfa, 6.75 mug/kg, administered once every 3 weeks to anaemic cancer chemotherapy patients on either an asynchronous (day 15) or synchronous (day 1) schedule relative to their every-3-week chemotherapy. A total of 81 patients were randomised and received the study drug (43 asynchronous; 38 synchronous). No difference was observed between groups in the primary endpoint of mean haemoglobin change after 6 weeks of therapy (P=0.45) and change scores were similar to those observed with standard weekly darbepoetin alfa therapy. In a subset of patients evaluated with intensive pharmacokinetic sampling, an increase in endogenous erythropoietin concentration (up to 4-fold) lasting approximately 1 week following chemotherapy administration was observed in both groups. Synchronous administration of darbepoetin alfa was associated with a 1.3-fold increase in the area under the darbepoetin alfa concentration-time curve compared with asynchronous administration. Our data suggest that darbepoetin alfa is effective administered every 3 weeks regardless of timing of administration with respect to chemotherapy and that receptor-mediated uptake by the erythron may be an important clearance mechanism for erythropoietic proteins.

Capillary electrophoresis and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry for analysis of the novel erythropoiesis-stimulating protein (NESP)

NESP (novel erythropoiesis-stimulating protein) is a recently approved hyperglycosylated analogue of human erythropoietin (EPO) with a long-lasting effect. In this work, the capillary electrophoresis (CE) methodology proposed by the European Pharmacopoeia for the separation of EPO glycoforms has been modified for the separation of NESP glycoforms. Optimization of pH of the separation electrolyte has been fundamental in order to achieve baseline resolution of seven peaks corresponding to NESP glycoforms. Intact NESP has also been characterized by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). An accurate approximation to an average molecular mass of the NESP molecule has been obtained, taking into account the strong influence of laser intensity upon the MALDI-TOF mass spectra found.

Characterisation of intact recombinant human erythropoietins applied in doping by means of planar gel electrophoretic techniques and matrix-assisted laser desorption/ionisation linear time-of-flight mass spectrometry

Our experiments show that it is possible to detect different types of recombinant human erythropoietins (rhEPOs), EPO-alpha, EPO-beta and novel erythropoesis stimulating protein (NESP), based on exact molecular weight (MW) determination by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) applying a high-resolution time-of-flight (TOF) mass analyser in the linear mode. Detection limits for the highly purified, intact glycoproteins were achievable in the low fmol range (25-50 fmol) using a sample preparation method applying a hydrophobic sample support (DropStop) as MALDI target surface. These results are very promising for the development of highly sensitive detection methods for a direct identification of rhEPO after enrichment from human body fluids. During our investigation we were able to differentiate EPO-alpha, EPO-beta and NESP based on distinct molecular substructures at the protein level by specific enzymatic reactions. MW determination of the intact molecules by high resolving one-dimensional sodium dodecyl sulfate /polyacrylamide gel electrophoresis (1D SDS-PAGE) and isoform separation by planar isoelectric focusing (IEF) was compared with MALDI-MS data. Migration differences between the rhEPOs were observed from gel electrophoresis, whereby MWs of 38 kDa in the case of EPO-alpha/beta and 49 kDa for NESP could be estimated. In contrast, an exact MW determination by MALDI-MS based on internal calibration revealed average MWs of 29.8 +/- 0.3 kDa for EPO-alpha/beta and 36.8 +/- 0.4 kDa for NESP. IEF separation of the intact rhEPOs revealed the presence of four to eight distinct isoforms in EPO-alpha and EPO-beta, while four isoforms, which appeared in the more acidic area of the gels, were detected by immunostaining in NESP. A direct detection of the different N- or O-glycoform pattern from rhEPOs using MALDI-MS was possible by de-sialylation of the glycan structures and after de-N-glycosylation of the intact molecules. Thereby, the main glycoforms of EPO-alpha, EPO-beta and NESP could be characterised based on their N-glycan composition. A microheterogeneity of the molecules based on the degree of sialylation of the O-glycan was observable directly from the de-N-glycosylated protein.

Differentiating factors between erythropoiesis-stimulating agents: a guide to selection for anaemia of chronic kidney disease

Endogenous erythropoietin (EPO) consists of a central polypeptide core covered by post-translationally linked carbohydrates. Three of the four currently available erythropoiesis stimulating agents (ESA)--epoetin-alpha, epoetin-beta and epoetin-omega- are composed of an identical amino acid sequence, but glycosylation varies as a result of type- and host cell-specific differences in the production process. Epoetin-alpha and epoetin-beta resemble each other with respect to molecular characteristics and pharmacokinetic data, although epoetin-beta has a higher molecular weight, a lower number of sialylated glycan residues and possibly slight pharmacokinetic advantages such as a longer terminal elimination half-life. A serious adverse effect of long-term administration of ESA is pure red cell aplasia. This effect has been observed predominantly with subcutaneous use of epoetin-alpha produced outside the US after albumin was removed from the formulation. In comparison with the intravenous route, subcutaneous administration of epoetin has been reported to have a dose-sparing effect in some studies. Epoetin-beta has been the subject of studies aimed at proving efficacy with a reduced administration frequency but results are not unequivocal. Epoetin-omega is produced in a different host cell than all other erythropoietic agents, hence glycosylation and pharmacokinetics are different. Small-scale clinical studies found epoetin-omega to be slightly more potent than epoetin-alpha. Epoetin-delta is a recently approved agent produced by human cells that are genetically engineered to transcribe and translate the EPO gene under the control of a newly introduced regulatory DNA sequence. However, epoetin-delta is not yet on the market and few data are available. The erythropoietin analogue darbepoetin-alpha carries two additional glycosylation sites that permit a higher degree of glycosylation. Consequently, in comparison with the other epoetins, darbepoetin-alpha has a longer serum half-life and a higher relative potency, which further increases with extension of the administration interval. Dosage requirements of darbepoetin-alpha do not appear to differ between the intravenous and subcutaneous routes of administration. The less frequent administration of darbepoetin-alpha in comparison to the other epoetins may reduce drug costs in the long term, but the variability in dosage or dosage frequency required within a single patient is high. Further studies should be aimed at defining predictors of the individual demand for erythropoietic agents, thereby allowing nephrologists to prescribe a cost-effective, individualised regimen.

Molecular biology of erythropoietin

The glycoprotein hormone erythropoietin (EPO) is an essential viability and growth factor for the erythrocytic progenitors. EPO is mainly produced in the kidneys. EPO gene expression is induced by hypoxia-inducible transcription factors (HIF). The principal representative of the HIF-family (HIF-1, -2 and -3) is HIF-1, which is composed of an O2-labile alpha-subunit and a constant nuclear beta-subunit. In normoxia, the alpha-subunit of HIF is inactivated following prolyl- and asparaginyl-hydroxylation by means of alpha-oxoglutarate and Fe(2+)-dependent HIF specific dioxygenases. While HIF-1 and HIF-2 activate the EPO gene, HIF-3, GATA-2 and NFkappaB are likely inhibitors of EPO gene transcription. EPO signalling involves tyrosine phosphorylation of the homodimeric EPO receptor and subsequent activation of intracellular antiapoptotic proteins, kinases and transcription factors. Lack of EPO leads to anemia. Treatment with recombinant human EPO (rHuEPO) is efficient and safe in improving the management of the anemia associated with chronic renal failure. RHuEPO analogues with prolonged survival in circulation have been developed. Whether the recent demonstration of EPO receptors in various non-hemopoietic tissues, including tumor cells, is welcome or ominous still needs to be clarified. Evidence suggests that rHuEPO may be a useful neuroprotective agent.

Victor Ginsburg's influence on my research of the role of sialic acids in biological recognition

Sialic acids are monosaccharides with relatively strong acidity which belong to the most important molecules of higher animals and also occur in some microorganisms. They are bound to complex carbohydrates and occupy prominent positions, especially in cell membranes. Their structural diversity is high and, correspondingly, the mechanisms for their biosynthesis complex. Sialic acids are involved in a great number of cell functions. Due to their cell surface location these acidic molecules shield macromolecules and cells from enzymatic and immunological attacks and thus contribute to innate immunity. In contrast to this masking role, enabling, for example, blood cells and serum glycoproteins a longer life-time, sialic acids also represent recognition sites for various physiological receptors, such as the selectins and siglecs, as well as for toxins and microorganisms and thus allow their colonization. The recognition function of sialic acids can again be masked by O-acetylation, which modifies the interaction with receptors. Many viruses use sialic acids for the infection of cells. As sialic acids play also a decisive role in tumor biology, they prove to be rather versatile molecules that modulate biological and pathological cellular events in a sensitive way. Thus, they are most prominent representatives of mediators of molecular and cellular recognition.

Serum sTfR Levels May Indicate Charge Profiling of Urinary r-hEPO in Doping Control

PURPOSE

The aim of the study was to demonstrate whether changes in the charge pattern of urinary human erythropoietin (u-hEPO) from well-trained athletes before, during and after controlled administration of recombinant human EPO (r-hEPO) could be related to altered levels of hemoglobin (Hb), hematocrit (Hct), soluble transferrin receptor (sTfR) and maximal oxygen uptake (VO2max).

METHODS

Urinary samples from athletes in an EPO-receiving group and a control group were collected before, during and after r-hEPO administration. The samples were analyzed with respect to the charge pattern of hEPO by iso-electric focusing (IEF).

RESULTS

The charge of the u-hEPO variants shifted from an acidic to a more basic pattern after initiating r-hEPO administration. This shift appeared together with increased levels of sTfR, and appeared before increased levels of Hb, Hct and VO2max. Until three days after the last injection, the IEF profiles were similar to the charge profile of r-hEPO. Thereafter the levels of sTfR decreased and the charge profiles of the hEPO variants gradually became more acidic. In contrast, the levels of Hb, Hct and VO2max remained elevated for an extended period of time.

CONCLUSION

A significant correlation was found between the relative amount of basic u-hEPO variants and the relative levels of sTfR, demonstrating that the relative levels of sTfR may be used as a marker to select urinary samples for further analysis of r-hEPO by IEF in routine doping control.

Single intravenous injection of naked plasmid DNA encoding erythropoietin provides neuroprotection in hypoxia-ischemia rats

Hypoxic-ischemic (H-I) encephalopathy is a major contributor to morbidity and mortality in infants and children. To delineate the nature and mechanism(s) of neuroprotection via erythropoietin (EPO) gene therapy, we evaluated the effects of single intravenous injection of naked plasmid DNA encoding EPO in H-I infant rats. Single administration of naked plasmid containing EPO cDNA driven under cytomegalovirus promoter (pCMV-EPO) by rapid injection via the tail vein produced a remarkable level of human EPO protein in the circulation, peaking at one day and lasting for 14 days after injection. There were significant improvements of water maze task in H-I rats after EPO gene therapy. Our data showed that the mechanisms of EPO gene therapy were rescue of CA1 neurons from lethal H-I injury, prevention of neuronal apoptosis in CA1 region, and decrease of glial activation in corpus callosum. This could be the first report of successful treatment of H-I injury by a single intravenous infusion of EPO gene.

The Evolving Role of Epoetin Alfa in Cancer Therapy

Since its initial indication as hormone-replacement therapy in the anemia of chronic kidney disease, epoetin alfa has become a mainstay of therapy for chemotherapy-related anemia. Clinical studies have shown that epoetin alfa administered once weekly or three times weekly improves hemoglobin levels, decreases transfusion requirements, and improves quality of life independent of tumor response to chemotherapy. Ongoing research is now evaluating ways to improve the response rate to epoetin alfa, the potential benefits of alternative dosing regimens and early treatment intervention, and nonanemia-related indications (e.g., cognitive impairment, asthenia). In addition, scientists are exploring the role of epoetin alfa in preventing apoptosis and ischemic brain injury, as well as its activity in other nonerythroid tissues. Thus, the role of epoetin alfa is likely to expand in the cancer setting in the coming years.

Sugar coating extends half-lives and improves effectiveness of cytokine hormones

Recombinant human erythropoietin (rhEPO) is an effective and widely used therapeutic agent that is produced by bioengineering. Modification of the rhEPO protein by glycoengineering increased its already abundant N-glycosylation, which enhances its erythropoietic activity in vivo by decreasing its metabolic clearance. Elliott et al. recently reported increased in vivo activities of thrombopoietin (Mpl ligand) and leptin following carbohydrate addition to both, which suggests that such glycoengineering could be applied to a variety of hormones, cytokines and growth factors.

Separation of Recombinant Human Erythropoietin Glycoforms by Capillary Electrophoresis Using Volatile Electrolytes. Assessment of Mass Spectrometry for the Characterization of Erythropoietin Glycoforms

The separation of the glycoforms of erythropoietin (EPO) by capillary electrophoresis (CE) was recently published as a monograph by the European Pharmacopoeia (European Pharmacopoeia 4 2002, 1316, 1123-1128). Although the experimental CE conditions employed a background electrolyte containing additives suitable for on-line UV-absorption detection, they were not appropriate for on-line mass spectrometry (MS) detection. In this work, an attempt was made to investigate experimental conditions employing volatile electrolyte systems to achieve the separation and characterization of EPO glycoforms using CE and ESI-MS methodologies. The influence of several operating conditions, such as the coating of the internal walls of the capillary as well as the composition, concentration, and the pH of the separation buffer were investigated. The results demonstrated that when the internal walls of the capillaries were permanently coated with Polybrene and a buffer electrolyte containing 400 mM of HAc-NH4Ac (acetic acid-ammonium acetate), pH 4.75, was used, a significantly reproducible separation was achieved for EPO glycoforms. Intact EPO was characterized by two mass spectrometry techniques: electrospray ionization (ESI-MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF-MS). The data demonstrated that MALDI-TOF-MS provided a good approximation to an average molecular mass of the EPO molecule. However, it was still necessary to carry out further separation of the intact EPO glycoforms in order to obtain molecular mass information when ESI-MS was used.

A new principle suggested for detection of darbepoetin-alpha (NESP) doping

Doping with darbepoetin-alpha, also termed novel erythropoiesis stimulating protein (NESP), a hypersialylated, very effective analogue of erythropoietin, is a serious threat in sport. We report here on a new principle for the detection of darbepoetin-alpha in serum based upon increase in immunoactivity after desialylation with neuraminidase. The method is evaluated on sera from patients taken 2-14 days after last injection of darbepoetin-alpha. Thirty-two venous blood samples and 3 capillary samples taken from finger tips were obtained from 13 patients with end stage renal disease treated with intravenous or subcutaneous injections of Aranesp, 0.45 to 2.60 microg*kg(-1). Blood samples from 37 individuals with endogenous erythropoietin were used as controls. The sera were diluted 1:2 with acetate buffer pH 5.6 with or without neuraminidase and incubated at 37 degrees C for 1 or 24 h before immunoassay. The erythropoietin immunoactivity in serum volumes of 12.5-50 microL was measured with ELISA-kits from R&D Systems Inc and medac GmbH. The relative increase in immunoactivity after desialylation was in all cases higher for the darbepoetin-alpha samples than for any of the control samples assayed in parallel, varying incubation time with the enzyme, serum volumes and batches of both ELISA-kits. The mean relative increase in immunoactivity of endogenous erythropoietin after neuraminidase was 42% with the medac-kit and 117% with R&D-kit while the corresponding figures for darbepoetin-alpha were 282% and 231% with 1 h and 299% and 256% with 24 h enzyme incubation, respectively. Endogenous and recombinant human erythropoietin showed similar relative increase after desialylation. The method to detect darbepoetin-alpha in serum is simple to perform, robust, sensitive and requires a small amount of blood. The drug was detected in all patient sera taken 2-14 days after last injection. We suggest that the method should be evaluated for the detection of darbepoetin-alpha doping in sport.