Optimization and qualification of capillary zone electrophoresis method for glycoprotein isoform distribution of erythropoietin for quality control laboratory.

The European Pharmacopoeia (Ph. Eur.) monograph for Erythropoietin Concentrated Solution describes a capillary zone electrophoresis method for identification of recombinant human erythropoietin. However, this method has shown poor reproducibility due to inadequate capillary conditioning. We have modified the Ph. Eur. method to make it more robust and suitable for the quality control laboratory for the analysis of epoetin alfa and epoetin alfa after formulation with polysorbate 80. This study qualified the modified method by showing improved robustness and reproducibility. The study also characterized and qualified a secondary standard of epoetin alfa as a substitute for the primary standard, Ph. Eur. erythropoietin Biological Reference Preparation, which is available in limited supply. Four sets of analyses were performed to assess repeatability, intermediate precision, and the secondary standard. The results showed that the modified method is suitable for its intended purpose to test epoetin alfa and formulated epoetin alfa samples. The epoetin alfa secondary standard is a suitable substitute for the primary standard. Further, we developed a procedure for the removal of polysorbate 80 from formulated epoetin alfa, allowing the material to be analyzed by the modified Ph. Eur. method.

Interaction of polysorbate 80 with erythropoietin: a case study in protein-surfactant interactions.

PURPOSE: The cause of antibody positive pure red cell aplasia associated with the subcutaneous administration of EPREX to patients with chronic kidney failure has been determined to be due to the leaching of weakly adjuvant compounds from the uncoated rubber stoppers that were formerly used in prefilled syringes. Other researchers have suggested that polysorbate 80 micelles containing erythropoietin may be a causative factor. The purpose of this work was to repeat previously published studies in a more controlled manner and to define the precise nature of the interactions between polysorbate 80 and erythropoietin. METHODS: The contents of EPREX prefilled syringes and laboratory-prepared, well-characterized formulations of EPREX were analyzed by size exclusion chromatography. Fractions were analyzed for the presence of erythropoietin by ELISA. EPREX formulations prepared with increasing amounts of polysorbate 80 were analyzed by light scattering. RESULTS: Well-controlled chromatographic studies showed that when EPREX formulations containing no aggregate were analyzed by high-performance liquid chromatography, erythropoietin monomer could not be detected under the polysorbate 80 peak. Dimer and oligomers of erythropoietin coeluted under the polysorbate 80 peak as the molecular weights overlapped on the size exclusion chromatogram. Solution light scattering indicated that polysorbate 80 associates with erythropoietin in a defined stoichiometric ratio of 1:12. CONCLUSIONS: Based on controlled studies, previous results suggesting that EPREX contains micelle-associated erythropoietin were incorrect. As with other surfactants and proteins, polysorbate 80 associates with erythropoietin in a defined stoichiometric ratio.