New enzyme-linked immunosorbent assay methods for measurement of serum erythropoietin levels and erythropoietin antibodies

Time-dependent clearance and hematological pharmacodynamics upon erythropoietin multiple dosing in rats

The pharmacokinetics (PK) and pharmacodynamics (PD) of recombinant human erythropoietin (rHuEPO) upon its repeated administrations were investigated. Two groups (A and B) of normal Wistar rats received rHuEPO intravenously at 450 or 1350 IU/kg thrice weekly for 2 and 6 weeks. PK studies were conducted following days 0 and 4 for group (A) and days 0, 17 and 28 for group (B), then, washout PK were assessed on days 11 and 36 for both groups. Reticulocytes (RET), red blood cells (RBC) and hemoglobin (Hb) were evaluated daily until day 14, then every 2 days until day 30 for group (A) and 59 for group (B). The total clearance CL(Total) increased with the dose but decreased over time. Its decay reached 20% and 55% between the first and last full PK in both treatment arms. RET peaked on day 5 and were 77.6% and 87.3% higher than baselines for the two dosing regimen. Their nadirs occurred on days 22 and 55 and were 37.9% and 47.3% below normal values. Hb peaked on days 10 and 34 and was 28.9% and 38.6% above the baseline level, its nadirs occurred on days 25 and 57 and were 13.1% and 16% below baselines. Control animals showed stable baselines over the study but with moderate variability. In conclusion, rHuEPO exhibits a nonlinear PK with a time-dependent decrease of its CL(Total). During exposure, RET, RBC and Hb showed a tolerance effect. After exposure, the rebound was characterized for RET, RBC, but not Hb.

Simultaneous pharmacokinetics/pharmacodynamics modeling of recombinant human erythropoietin upon multiple intravenous dosing in rats

A pharmacokinetics (PK)/pharmacodynamics (PD) model was developed to describe the tolerance and rebound for reticulocyte (RET) and red blood cell (RBC) counts and the hemoglobin (Hb) concentrations in blood after repeated intravenous administrations of 1350 IU/kg of recombinant human erythropoietin (rHuEPO) in rats thrice weekly for 6 weeks. Drug concentrations were described by using a quasi-equilibrium model. The PD model consisted of a lifespan-based indirect response model (LIDR) with progenitor cells [burst colony-forming unit erythroblasts and colony-forming unit erythroblasts (CFUs)], normoblasts (NOR), RETs, and RBCs. Drug-receptor complex stimulatory effects on progenitor cells differentiation and RBC lifespan were expressed by using the E(max) model (S(max-epo) and SC(50-epo), E(max) and EC(50)). The Hb profile was indirectly modeled through a LIDR model for mean corpuscular hemoglobin (with a lifespan T(mch)) including a linear (S(max-mch)) drug stimulatory effect. The negative feedback from RBCs accounted for the time-dependent rHuEPO clearance decline. A simultaneous PK/PD fitting was performed by using MATLAB-based software. PK parameters such as equilibrium dissociation, erythropoietin receptor degradation, production, and internalization rate constants were 0.18 nM (fixed), 0.08 h(-1), 0.03 nM/h, and 2.51 h(-1), respectively. The elimination rate constant and central volume of distribution were 0.57 h(-1) and 40.63 ml/kg, respectively. CFU and NOR, RET, and RBC lifespans were 37.26 h, 17.25 h, and 30.15 days, respectively. S(max-epo) and SC(50-epo) were 7.3 and 0.47 10(-2) nM, respectively. E(max) was fixed to 1. EC(50) and SC(50-epo) were equal. S(max-mch) and T(mch) were 168.1 nM(-1) and 35.15 days, respectively. The proposed PK/PD model effectively described rHuEPO nonstationary PK and allowed physiological estimates of cell lifespans.

Determination of KRN321 in rat serum by ELISA and correlation between ELISA and in vitro bioassay

KRN321, darbepoetin alfa, is a hyperglycosylated analog of recombinant human erythropoietin (rHuEPO, epoetin alfa). We carried out the validation study by using a commercially available ELISA assay kit to establish the ELISA quantitation method for KRN321 in rat serum for the implementation of the pharmacokinetic studies with a lower limit of quantitation at 100 pg/mL and quantitation range from 100 to 4,000 pg/mL. We also established the in vitro bioassay method as an index of biological activity using UT-7/Epo, derived from a human leukemia cell line with a lower limit of quantitation, at 10 ng/mL. Furthermore, good correlation was observed between the two methods; it indicated that KRN321 concentration determined by the ELISA maintained biological activity.

The detection of anti-erythropoietin antibodies in human serum and plasma

Neutralizing antibodies to erythropoietin (EPO) can cause a loss of response to recombinant human EPO (rHuEPO) and lead to rare cases of sudden, unexplained, severe anemia in chronic renal failure patients treated with rHuEPO. An assay for neutralizing anti-EPO antibodies has been validated that is based on the inhibition of proliferation of human UT-7/EPO cells, an immortalized cell line, by neutralizing antibodies in serum test samples using 3H-thymidine as a marker for proliferation. The dependence of the human cell line on EPO for growth and proliferation in a concentration-dependent manner enabled the validation of a rHuEPO standard curve for cell proliferation that can be used to determine the presence of neutralizing anti-EPO antibodies in serum samples. Proliferation of the cells increases with increasing concentrations of EPO, forming an S-shaped standard curve, which is fit with a 4-parameter logistic model, between 2.5 and 50 mU/mL rHuEPO, with a percent coefficient of variation (% CV) from 8.7% to 22.1% and a % accuracy of 103.5% to 109.5%. Anti-EPO antibodies and serum with anti-EPO antibodies neutralize UT-7/EPO proliferation by 10 mU/mL rHuEPO in a concentration- or dilution-dependent manner with < or = 25% CV. Percent neutralization is calculated by determining the amount of EPO recovered from the original 10 mU/mL added using the formula [((10-concentration recovered)/10)x100%]. Stem cell factor (SCF) stimulated cell proliferation, but not as effectively as rHuEPO. Antibodies to SCF were not able to inhibit the proliferative response induced by EPO and vice versa, confirming the specificity of the assay for antibodies to EPO. High EPO levels can impact both the radioimmunoprecipitation and neutralization assays to produce a false negative result. However, the impact can be mitigated by the large dilutions used in the neutralization assay.

Recommendations on haematological criteria for the diagnosis of epoetin-induced pure red cell aplasia

Pure red cell aplasia (PRCA) is a rare condition characterised by an arrest in red blood cell production, which may be congenital or acquired. Recombinant human erythropoietin (epoetin) was introduced in 1989 for the treatment of anaemia of chronic kidney disease patients and has maintained an excellent therapeutic and safety record while treating hundreds of thousands of patients. A very rare, but serious adverse event associated with epoetin administration is a condition in which patients develop neutralising anti-erythropoietin antibodies and, consequently, PRCA. This condition is referred to as epoetin-induced PRCA (epo-PRCA). Since it is a rare condition, many haematologists and nephrologists around the world see the condition infrequently and may be uncertain about the diagnosis. For this reason, an ad hoc international working group of expert haematologists and nephrologists met together to derive new recommendations for the haematological diagnosis of epo-PRCA. These recommendations, which represent the consensus opinions of the working group, address haematological approaches to monitor and investigate suspected epo-PRCA and should help physicians differentiate between PRCA and other bone marrow diseases, as well as, between PRCA and epo-PRCA.

The detection of anti-erythropoietin antibodies in human serum and plasma

Rare cases of unexplained sudden severe anemia or red cell aplasia and resistance to recombinant human erythropoietin (rHuEPO) in patients with chronic renal failure (CRF) have been attributed to the development of anti-EPO antibodies. The development and validation of a radioimmunoprecipitation (RIP) assay to detect human anti-EPO antibodies in serum or plasma has been hampered by the lack of purified antibody to fully characterize and validate the assay. We have prepared an affinity-purified human antibody to EPO and used the antibody to characterize and validate a sensitive and reproducible RIP assay that can qualitatively measure anti-EPO antibody in serum or plasma samples. The lower limit of detection of the assay is 8 ng/ml of purified antibody. The threshold for detecting antibody is > or =0.9% cpm bound. The precision of the assay using purified antibody standards ranges from 5.8% to 15.3% and the precision of the assay using dilutions of the positive control ranges from 15.9% to 18.7%. EPO in the samples did not interfere with detection of the anti-EPO antibody except at high concentrations.