P-025: ABNORMAL MITOCHONDRIA RETENTION IN MATURE RED BLOOD CELLS OCCURS NOT ONLY IN SS BUT ALSO SC PATIENTS AND IS ASSOCIATED WITH HEMOLYTIC MARKERS

Abstract

Purpose: Sickle cell disease (SCD), the most frequent genetic disease worldwide, results from a unique point mutation leading to the synthesis of the abnormal hemoglobin S (HbS). Under hypoxic condition, HbS polymerization causes a mechanical distortion of red blood cells (RBCs) called sickling, which is accompanied by a decrease of their deformability and their life span. SCD is characterized by a wide variability of clinical expression and a complex pathophysiology including vaso-occlusive processes, intravascular hemolysis as well as pro-inflammation, pro-coagulant and vaso-constrictive states. Recently, the abnormal mitochondria retention in mature RBCs has been documented in small series of SS patients but the biological consequences of this abnormality have not been fully documented and not been documented in other sickle cell syndromes. In the present study, we analyzed mature RBC mitochondria retention in both SS and SC patients, the second most frequent sickle cell syndrome, taking into account the biological/clinical features associated with these abnormal RBCs. Materials and methods: Eighty-nine adult SCD patients were included: 35 SS patients treated with hydroxyurea (HU), 15 SS patients not treated with HU and 39 SC patients. All of them were at steady-state and regularly followed by the sickle center of Guadeloupe. Twenty-one Guadeloupean adult controls (AA) were also included. Mature RBCs containing mitochondria were identified by flow cytometry using MitoTracker® probe as well as thiazole orange and anti-CD71 antibody to discriminate total and stress reticulocytes respectively. Correlations between the percentage of mature mitochondria+-RBCs and the following parameters were then analyzed: RBC deformability (Ektacytometry), reticulocytes (both total and CD71+) counts and levels of hemoglobin, total bilirubin, aminotransferase aspartate and lactate dehydrogenase levels using routine procedures. The impact of splenic function was evaluated using Howell-Jolly bodies, assessed by classic May-Grünwald Giemsa smears, as a marker of splenic dysfunction. We also analyzed the relationships between mitochondria+-RBCs and HU treatment as well as the rates of hyper vaso-occlusive (painful vaso-occlusion, acute chest syndrome, osteonecrosis) and hyper hemolytic (micro/macro-albuminuria, leg ulcer) complications. Results: Abnormal mitochondria+ RBCs were detected not only in SS but also in SC patients, although at a less extend. In both sickle cell syndromes, positive correlations with mitochondria+ RBCs were detected with hemolysis markers (percentage of total and stress reticulocytes). In addition, a negative relationship with hemoglobin level was detected in SS patients. A negative correlation was also detected between these abnormal mitochondria+ RBCs and RBC deformability. In contrast, no association between the presence of this RBC sub-population and clinical manifestations, hydroxyurea treatment or Howell-Jolly bodies was detected. Conclusion: In the present report, we demonstrated that abnormal retention of mitochondria in mature RBCs occurred not only in SS but also in SC patients. We also presented evidence that this phenotype could be related to hemolysis rate. Further studies are warranted to reveal the molecular mechanisms involved. E. BERNIT declares a conflict of interest: Consultancy, Expert: for NOVARTIS PHARMA SAS