Iron Deficiency Induces Faster Sickling Kinetics in Transgenic Sickle Mice

Abstract

Sickle cell disease (SCD) is caused by polymerization of deoxygenated hemoglobin‐S (HbS) within the red blood cell (RBC). The kinetics of hemoglobin polymerization are dependent on the intra‐erythrocytic concentration of HbS; specifically, the time from deoxygenation to polymerization is inversely related to HbS concentration30. We hypothesized that iron‐deficient erythropoiesis would produce RBCs with decreased intracellular Hb concentration and prolonged sickling times which would reduce the severity of SCD.To interrogate this hypothesis, we studied Townes mice that express humanized alpha globin, gamma globin, and either beta‐S (Townes‐SCD) or normal beta globin (Townes‐Control). RBCs from these Townes‐SCD mice have similar sickling kinetics to RBCs from human volunteers with SCD. To induce iron deficiency, we fed mice either an iron‐restricted diet (3 ppm iron) or iron‐normal diet (48 ppm iron) introduced at the time of weaning. After two months on the experimental diets, we measured RBC parameters using an Advia 2120 hematology analyzer and measured in vitro RBC sickling kinetics at 3% oxygen. Analysis of RBC parameters revealed that SCD mice on the iron‐restricted diet had lower hematocrit (32% vs 42.2%, P <0.0001), and there were trends toward lower hemoglobin, mean corpuscular volume, mean cell hemoglobin, and mean corpuscular hemoglobin concentration. Surprisingly, the in vitro sickling kinetic assay showed a significantly shortened time to 50% sickled in the Iron Restricted group (t50: 96.6 vs 136.5 min., p<0.0001).At this two‐month time point, this study provides insights into the hematologic changes that occur during the initial onset of iron deficiency anemia in Townes‐SCD mice. We were surprised to find that the rate of sickling increased in the iron‐restricted mice; however, at two months of iron deficient diet, we have yet to see a substantial fall in the MCHC, a major determinant of the sickling delay time. Furthermore, these mice may have experienced compensatory changes in the red cell that adversely affected sickling such as a decrease in hemoglobin F levels, or a shift in the Hb‐ O2 dissociation curve that favors releasing oxygen at lower partial pressures. To address these questions, we will investigate the hemoglobin composition and the oxygen dissociation curve at the remaining four‐ and six‐month timepoints. We aim to determine the intermediate and long‐term potential of iron deficiency to delay sickling and reduce the severity of organ damage in the context of SCD. This may inform a strategy of optimizing iron intake as a potential treatment for SCD.Support or Funding InformationSupport from NIAID Intramural funding and NIH Division of Veterinary ResourcesScholarship Award from the Saudi Arabian Cultural Mission (SACM)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.