Erythropoietin (EPO) from sera obtained from anemic patients was successfully isolated using magnetic beads coated with a human EPO (hEPO)-specific antibody. Human serum EPO emerged as a broad band after sodium dodecyl sulfatepolyacrylamide gel electrophoresis, with an apparent molecular weight slightly smaller than that of recombinant hEPO (rhEPO). The bandwidth corresponded with microheterogeneity because of extensive glycosylation. Two-dimensional gel electrophoresis revealing several different glycoforms confirmed the heterogeneity of circulating hEPO. The immobilized anti-hEPO antibody was capable of binding a representative selection of rhEPO glycoforms. This was shown by comparing normal-phase high-performance liquid chromatography profiles of oligosaccharides released from rhEPO with oligosaccharides released from rhEPO after isolation with hEPO-specific magnetic beads. Charge analysis demonstrated that human serum EPO contained only mono-, di-, and tri-acidic oligosaccharides and lacked the tetra-acidic structures present in the glycans from rhEPO. Determination of charge state after treatment of human serum EPO with Arthrobacter ureafaciens sialidase showed that the acidity of the oligosaccharide structures was caused by sialic acids. The sugar profiles of human serum EPO, describing both neutral and charged sugar, appeared significantly different from the profiles of rhEPO. The detection of glycan structural discrepancies between human serum EPO and rhEPO by sugar profiling may be significant for diagnosing pathologic conditions, maintaining pharmaceutical quality control, and establishing a direct method to detect the misuse of rhEPO in sports. IntroductionHuman erythropoietin (EPO) is a glycoprotein that is synthesized mainly in the kidney and that stimulates erythropoiesis through actions on erythroid progenitor cells. [1][2][3] Human EPO (hEPO) was the first hematopoietic growth factor to be cloned. 4,5 Recombinant hEPO (rhEPO) has been available as a drug since 1988 and is used in the clinical treatment of anemia, especially anemia caused by renal failure. In sports the misuse of rhEPO has been suspected among athletes for several years. 6 Active hEPO consists of a single 165-amino acid polypeptide chain with three N-glycosylation sites at Asn24, Asn38, and Asn83, respectively, and one O-glycosylation site at Ser126. The average carbohydrate content is approximately 40%. 7-9 Glycosylation is important for the biologic activity of EPO. Removal or modification of the glycan chains results in altered in vivo and in vitro activity. [9][10][11][12][13][14] Furthermore, the number of sialic acid residues and the branching pattern of the N-linked oligosaccharides modify the pharmacodynamics, speed of catabolism, and biologic activity of hEPO. 11,15,16 Oligosaccharide units, or glycans, of glycoproteins serve a variety of functions, including folding of nascent polypeptide chains in the endoplasmic reticulum, protection of the protein moieties from the action of proteases, and modulation of biologic act...

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.

The large number of samples containing detectable amounts of darbepoetin alfa at 10 d into the washout period stipulate the possibility of a 7-d window of detection after administration, wherein a sample would be regarded as an adverse analytical finding. The marked variations in all examined blood parameters could be used for the targeting of urine samples. These preliminary findings open up for larger scale studies with more frequent urine sampling in the washout period on elite athletes.