Comparison of the Isoelectric Focusing Patterns of Darbepoetin Alfa, Recombinant Human Erythropoietin, and Endogenous Erythropoietin from Human Urine

摘要

Novel erythropoiesis-stimulating protein (AranespTM; darbepoetin alfa) is a glycoprotein hormone with a longer serum half-life than recombinant human erythropoietin (rHuEPO) (1). The polypeptide backbone of the human EPO molecule has an invariant amino acid sequence; however, the carbohydrate side chains exhibit microheterogeneity in sugar content and structure (2)(3)(4). A negatively charged sialic acid molecule typically caps the end of each arm of a carbohydrate chain. As a consequence, the variable nature of the sialic acid content gives rise to EPO isoforms with differences in charge (3). After purifying isoforms of rHuEPO, Egrie and coworkers (5)(6) discovered a direct correlation between the number of sialic acid groups on the carbohydrate part of rHuEPO and both its serum half-life and biological activity, as well as an inverse relationship with receptor binding. These data showed that pharmacokinetic factors have a greater influence on biological activity than receptor binding affinity. These principles explain the increased half-life and increased in vivo activity of darbepoetin alfa, which contains 5 N-linked carbohydrate chains and up to 22 sialic acids (5)(7). In contrast, rHuEPO has 3 N-linked carbohydrate chains and a maximum of 14 sialic acids (5)(7).Similar clinical responses can be achieved by administering darbepoetin alfa once a week or rHuEPO three times a week (8)(9). The efficacy of darbepoetin alfa in the treatment of anemia associated with chronic renal failure has been shown (10), and in 2001 it was approved by the US Food and Drug Administration for that indication. Darbepoetin alfa is under investigation for the treatment of anemia in cancer patients (11) and other applications. Although darbepoetin alfa was approved only recently, we detected darbepoetin alfa in the urine of three athletes competing in the 2002 Winter Olympic Games …