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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.