(448g) Autocatalytic Release of Heme in Sickle and Normal Erythrocytes

Autocatalytic release of heme in sickle and normal erythrocytes

Anupam Aich^1,[1], Melissa Freundlich^{1,2, [1]}, Elena V. Petrova¹, Ye Li¹, Bogdan Dinu,³ Gladstone Airewele,³ and Peter G. Vekilov^1,4,*

¹ Department of Chemical and Biomolecular Engineering, University of Houston,
Houston, TX 77204, USA

² École Nationale Supérieure de Chimie de Paris, 11, rue Pierre et Marie Curie,
75231 PARIS Cedex 05 FRANCE

³ Texas Children’s Hospital, Baylor College of Medicine, 6621 Fannin St.
Houston, TX 77030, USA

⁴ Department of Chemistry, University of Houston, Houston, TX 77204, USA Abstract

The mutation responsible for sickle cell anemia has two main consequences: the mutant hemoglobin, HbS, polymerizes, and it partially releases its heme.  Here we determine the concentration of free heme in sickle, sickle trait, and normal erythrocytes.  We develop a novel assay for heme quantification, which is robust, sensitive to 100 pM, and accurate within 10%. We separate the free heme present in the red cells from the hemoglobin by dialysis.  We use the heme in the dialysate to reconstitute horse radish peroxidase in excess of the apoenzyme, and measure the rate of enzymatic decay of peroxide.   We find that the average concentration of free heme in sickle cell patients is 41±12 mM, in sickle trait individuals—35±4 mM, and in normal adults—22±9 mM. We find that the release of heme in both sickle cell patients and normal adults is autocatalytic, i.e., the presence of free heme induces stronger heme release. The found unexpectedly high concentration of free heme suggests that it may be an important factor in the pathology of sickle cell anemia.  The autocatalytic release may contribute to the known variability and unpredictability of the disease.