Iron Restriction Improves Markers of Disease Severity in the Townes Mouse Model of Sickle Cell Anemia

Introduction: Sickle cell anemia (SCA) is caused by mutations in β-globin that result in the production of the abnormal hemoglobin, HbS, with deleterious effects on erythrocyte shape and life span. Because the propensity of erythrocytes to sickle is inversely proportional to the concentration of HbS in the cell, decreasing the mean cellular hemoglobin concentration (MCHC) represents a potential therapeutic approach. Whereas iron restriction in healthy individuals does not alter MCHC, concomitant iron deficiency has been associated with decreased MCHC in SCA patients. Isolated case reports have linked iron restricted erythropoiesis with decreased hemolysis, increased red cell lifespan, and improvement in certain outcomes in SCA patients. We systematically examined the effects of iron restriction on erythropoietic outcomes in SCA utilizing the Townes murine model to investigate the hypothesis that mice with dietary iron deficiency will demonstrate a decreased MCHC, decreased erythrocyte sickling propensity, and improved anemia compared with mice on an iron sufficient diet.

Methods: Townes SCA mice were weaned to diets containing either 20 ppm iron (low) or 48 ppm iron (sufficient) and maintained on those diets until sacrifice at 2 months of age. Blood was collected for complete blood count by submandibular or cardiac puncture. Spleen weight was normalized to body weight for calculation of the splenic index. Red cell deformability, defined by the elongation index (EI), and the oxygen pressure at which sickling occurs (point of sickling) during deoxygenation were characterized by oxygenscan ektacytometry using a laser optical rotational red cell analyzer (Mechatronics, The Netherlands).

Results: SCA mice fed a 20 ppm low iron diet demonstrate a significant decrease in MCHC compared to SCA mice fed a 48 ppm iron sufficient diet (17.7+1.1 vs 22.7+5.5 g/dL; p <0.05). Mice fed the low iron diet produced more circulating RBCs (5.98+1.03 vs 4.61+0.84 x 10⁶ cells/uL; p <0.05) and a higher hematocrit (39.4+7.1 vs 24.6+4.6%; p <0.05) with a corresponding decrease in splenic index (0.074+0.14 vs 0.087+0.006 g/g body weight; p <0.05) compared to mice fed the iron sufficient diet. RBCs from mice fed the low iron diet showed a significant decrease in the oxygen pressure at the point of sickling compared to RBCs from mice fed the iron sufficient diet (31.9+4.7 vs 40.6+4.6 mmHg; p <0.01). The low iron diet also resulted in an overall improvement in deformability as evidenced by an increase in the EI minimum compared to the iron sufficient diet (0.25+.07 vs 0.12+.03 au; p <0.01). No significant differences between groups were found in maximum deformability (EI max). The improved EI minimum translates to a decreased change in elongation (Delta EI), defined as EI max minus EI min, in RBCs from mice fed the low iron diet compared to mice fed the iron sufficient diet (0.11+.08 vs .23+.02 au; p <0.01).

Conclusions: Decreased dietary iron intake is associated with a decrease in the MCHC in Townes SCA mice. The lower MCHC is accompanied by an amelioration of anemia, decreased extramedullary erythropoiesis, improved RBC deformability and a shift in the initiation of sickling to lower oxygen pressures during deoxygenation. We speculate that iron restriction may decrease the clinical complications arising from both hemolysis and sickling in SCA. Future studies will utilize this model system to further characterize the effects of manipulating iron homeostasis on erythropoietic outcomes in SCA.