Inhibition of Erythrocyte Aminolevulinate Dehydratase by a 56.2-kD Peptide from Uremic Plasma

Abstract

Among the abnormalities in erythrocyte porphyrin metabolism already described in patients with chronic renal failure on hemodialysis, a decrease in blood aminolevulinate dehydratase activity has been reported, suggesting the presence in uremic plasma of an inhibitor of the enzyme. The aim of this work has been to isolate and characterize such an inhibitor. Blood samples from 105 patients with chronic uremia were collected; plasma was applied to Sephadex G-100 columns and the fraction with the highest inhibiting capacity was identified and purified by subsequent SDS-polyacrylamide gel electrophoresis, followed by electroelution and electroblotting. It was demonstrated that the factor present in plasma of uremic patients inhibited blood aminolevulinate dehydratase in a concentration-dependent manner; its inhibitory properties were abolished after heat, trypsin and TCA treatment indicating its peptidic nature. The purified inhibitor has an apparent molecular mass of 56.2 kD, it inhibits blood aminolevulinate dehydratase in a competitive way and the K_i value is 12×10^–6 M. The amino acid composition of the inhibitor has been determined and it has been found that its N-terminal amino acid is blocked. The isolated peptide may play a role in heme biosynthesis disturbances and in the pathogenesis of uremic anemia.

Does Parathyroid Hormone Affect Erythropoietin Therapy in Dialysis Patients?

“…The underlying mechanisms may include such various factors as reduced blood (and iron) loss and improved EPO production. Better clearance of middle molecule substance in CAPD [16] than with standard HD could in part explain the reduced requirement of rHuEPO in this dialysis modality. Inhibitors of aminolevulinate dehydrase, an enzyme involved in Hb metabolism [17] , and albumin-bound furancarboxylic acid, an inhibitor of erythropoiesis [18] , are possibly removed more efficiently by peritoneal dialysis.…”

Epoetin Responsiveness in Peritoneal Dialysis Patients: A Multi‐center Slovenian Study

“…We therefore expected a lower ERI in patients with higher RRF, but no such association was found. Other possible explanations for better epoetin responsiveness in PD patients compared to HD patients could be the superior removal of possible erythropoiesis inhibitors by the peritoneal membrane with the superior clearance of middle molecular weight solutes in PD (3,15).…”

Hemoglobin Content Is Increased in the Human Erythroleukemia K562 Cell Line by a 56.2-kD Peptide from Uremic Plasma

“…hypoactivity of ALAD and increased blood porphyrins, have been reported [1, 3, 4], as well as in experimental CRF [6, 7]and in a model of acute renal failure [2]. Decreased activity of erythrocyte ALAD was correlated with the presence of a protein-like factor in the uremic plasma and it was postulated that there might be a relationship between this heme biosynthesis abnormality and the pathogenesis of uremic anemia [1, 2, 3, 4, 5, 6, 7]. No correlation between the erythrocyte ALAD activity and hematocrit was found [1], likely because ALAD is not a rate-limiting enzyme.…”

“…Similar abnormalities in the heme pathway have also been observed in two experimental models where renal failure has been induced by nephrectomy or cyclosporin administration and in experimental acute renal failure. The hepatic heme pathway was never affected in any of these models [5, 6, 7]. …”

“…Plasma from these HD patients showed the ability to inhibit erythrocyte ALAD activity from healthy subjects [1, 3, 4, 5, 6, 7]and because the same inhibitory ability has been detected before and after dialysis, it was hypothesized [1, 5]that the inhibitor factor was not dialyzable.…”