COMPARISONS OF HUMAN, RAT AND MOUSE ERYTHROPOIETINS BY ISOELECTRIC-FOCUSING - DIFFERENCES BETWEEN SERUM AND URINARY ERYTHROPOIETINS

Isoelectric focusing (IEF) in the pH range 2.5-5.0 has been used to compare the immunoreactive (ir) erythropoietin (Epo) in paired samples of serum and urine from three patients, two with idiopathic aplastic anaemia and one with paroxysmal nocturnal haemoglobinuria and also from three anaemic rats. Serum samples only were also examined from two further patients with aplastic anaemia and from three mice, made anaemic (like the rats) by irradiation and phenylhydrazine treatment. Most of the ir-Epo recovered after IEF was found in the pH range 2.5-3.9. For the sera, the proportion of more acidic ir-Epo with pI < 3.0 recovered after IEF increased from human to rat to mouse. Human sera contained a greater proportion of ir-Epo with pI > 3.4 than rat or mouse sera. For the urines, the distribution of ir-Epo by IEF was similar between human and rat. For both species, the proportion of ir-Epo with pI < 3.0 recovered after IEF was greater in urine than in the paired serum samples. The Second International Reference Preparation of Human Urinary Epo differed from the Epo in unextracted human urine in that there was a lower proportion of ir-Epo with pI < 3.0. The differences observed between serum and urinary Epo are of particular interest because only the urinary form of native human Epo has ever been purified, and because this was used to compare native with rDNA-derived Epo.