Erythrocyte Deformability is Reduced and Fragility increased by Iron Deficiency

Pathologic mechanobiological interactions between red blood cells and endothelial cells directly induce vasculopathy in iron deficiency anemia

The correlation between cardiovascular disease and iron deficiency anemia (IDA) is well documented but poorly understood. Using a multi-disciplinary approach, we explore the hypothesis that the biophysical alterations of red blood cells (RBCs) in IDA, such as variable degrees of microcytosis and decreased deformability may directly induce endothelial dysfunction via mechanobiological mechanisms. Using a combination of atomic force microscopy and microfluidics, we observed that subpopulations of IDA RBCs (idRBCs) are significantly stiffer and smaller than both healthy RBCs and the remaining idRBC population. Furthermore, computational simulations demonstrated that the smaller and stiffer idRBC subpopulations marginate toward the vessel wall causing aberrant shear stresses. This leads to increased vascular inflammation as confirmed with perfusion of idRBCs into our "endothelialized" microfluidic systems. Overall, our multifaceted approach demonstrates that the altered biophysical properties of idRBCs directly lead to vasculopathy, suggesting that the IDA and cardiovascular disease association extends beyond correlation and into causation.

Marginally reduced maternal hepatic and splenic ferroportin under severe nutritional iron deficiency in pregnancy maintains systemic iron supply

The demand for iron is high in pregnancy to meet the increased requirements for erythropoiesis. Even pregnant females with initially iron‐replete stores develop iron‐deficiency anemia, due to inadequate iron absorption. In anemic females, the maternal iron supply is dedicated to maintaining iron metabolism in the fetus and placenta. Here, using a mouse model of iron deficiency in pregnancy, we show that iron recycled from senescent erythrocytes becomes a predominant source of this microelement that can be transferred to the placenta in females with depleted iron stores. Ferroportin is a key protein in the molecular machinery of cellular iron egress. We demonstrate that under iron deficiency in pregnancy, levels of ferroportin are greatly reduced in the duodenum, placenta and fetal liver, but not in maternal liver macrophages and in the spleen. Although low expression of both maternal and fetal hepcidin predicted ferroportin up‐regulation in examined locations, its final expression level was very likely correlated with tissue iron status. Our results argue that iron released into the circulation of anemic females is taken up by the placenta, as evidenced by high expression of iron importers on syncytiotrophoblasts. Then, a substantial decrease in levels of ferroportin on the basolateral side of syncytiotrophoblasts, may be responsible for the reduced transfer of iron to the fetus. As attested by the lowest decrease in iron content among analyzed tissues, some part is retained in the placenta. These findings confirm the key role played by ferroportin in tuning iron turnover in iron‐deficient pregnant mouse females and their fetuses.

Distinguishing iron deficiency anemia from thalassemia by the red blood cell lifespan with a simple CO breath test: a pilot study

BACKGROUND

Extant indices for distinguishing between iron deficiency anemia (IDA) and thalassemia (Thal) have substantial practical limitations. The aim of this pilot study was to assess the predictive value of red blood cell lifespan (RBCLS), as determined by an automated CO breath test analysis approach, in the differential diagnosis of these two common forms of microcytic hypochromic anemia (MHA).

METHODS

RBCLS measurements were conducted in 35 healthy controls (HCs) and 114 patients diagnosed with MHA (IDA, N = 59; and Thal, N = 55) with ELS TESTER that provides a direct RBCLS value read-out. RBCLS between IDA and Thal was compared and evaluated by referring to normal cut-off from the instrument.

RESULTS

Compared with that in HCs, RBCLS in IDA and Thal groups was shortened; and median RBCLS was shorter in the Thal group than that in IDA group (33 d versus 79 d, p < 0.001). The median RBCLS in IDA patients with chronic gastrointestinal (GI) bleeding was shorter than that those without GI bleeding (38 d versus 100 d, p < 0.001). Using 75 d as a cut-off, RBCLS had a sensitivity of 96.4% and a specificity of 50.8% for detecting Thal. When GI bleeding patients were excluded from the IDA group, discriminant efficiency of RBCLS was further improved.

CONCLUSIONS

MHA with a normal RBCLS is suggestive of IDA, whereas MHA with a significantly shortened RBCLS without signs of chronic GI bleeding is suggestive of Thal.

Measuring Deformability and Red Cell Heterogeneity in Blood by Ektacytometry

Decreased red cell deformability is characteristic of several disorders. In some cases, the extent of defective deformability can predict severity of disease or occurrence of serious complications. Ektacytometry uses laser diffraction viscometry to measure the deformability of red blood cells subject to either increasing shear stress or an osmotic gradient at a constant value of applied shear stress. However, direct deformability measurements are difficult to interpret when measuring heterogenous blood that is characterized by the presence of both rigid and deformable red cells. This is due to the inability of rigid cells to properly align in response to shear stress and results in a distorted diffraction pattern marked by an exaggerated decrease in apparent deformability. Measurement of the degree of distortion provides an indicator of the heterogeneity of the erythrocytes in blood. In sickle cell anemia, this is correlated with the percentage of rigid cells, which reflects the hemoglobin concentration and hemoglobin composition of the erythrocytes. In addition to measuring deformability, osmotic gradient ektacytometry provides information about the osmotic fragility and hydration status of erythrocytes. These parameters also reflect the hemoglobin composition of red blood cells from sickle cell patients. Ektacytometry measures deformability in populations of red cells and does not, therefore, provide information on the deformability or mechanical properties of individual erythrocytes. Regardless, the goal of the techniques described herein is to provide a convenient and reliable method for measuring the deformability and cellular heterogeneity of blood. These techniques may be useful for monitoring temporal changes, as well as disease progression and response to therapeutic intervention in several disorders. Sickle cell anemia is one well-characterized example. Other potential disorders where measurements of red cell deformability and/or heterogeneity are of interest include blood storage, diabetes, Plasmodium infection, iron deficiency, and the hemolytic anemias due to membrane defects.

The Effect of Iron Deficiency on Osmotic Sensitivity of Red Blood Cells from Neonatal Rats and Their Mothers

Iron deficiency during pregnancy has many effects on both the mother and her developing foetus. These can be both short and long term. One effect is an alteration in fatty acid metabolism and we hypothesised that these changes may result in alterations in membrane function and structure. In order to test this hypothesis, we measured osmotic sensitivity in red blood cells isolated from neonates and their mothers at different times following birth. We fed female rats control or iron-deficient diets for 4 weeks prior to mating and kept them on the same diet until term. At that time, we returned one group of deficient dams to the control diet. The others were kept on the same diet. We showed that iron deficiency results in a decrease in osmotic sensitivity in the mothers but not in their neonates. Returning the dams to the control diet resulted in a return of their red cell osmotic sensitivity to control levels. In the neonates, there was no recovery in haematocrit or in any other parameter, though they did not get any worse, in contrast to the pups being suckled by deficient mothers. The data show two things. The first is that following birth, the mother restores her own iron stores at the expense of the pups, and secondly, there are differences in properties and sensitivities between red cells from mothers and their neonates. This latter observation cannot be explained by differences in the membrane fatty acid profiles, which were not significantly different.

Hemorheological parameters in children with iron-deficiency anemia and the alterations in these parameters in response to iron replacement

AIM

Iron-deficiency anemia (IDA) is a common disorder in pediatric patients. There are a limited number of studies having controversial results in investigating red blood cell (RBC) deformability and aggregation in adult IDA patients. The aim of this study is to determine the change of hemorheological parameters, including RBC deformability, aggregation, and plasma and whole blood viscosity, in children with IDA following iron supplementation therapy.

MATERIALS AND METHODS

The study was performed on 20 children with IDA (average age 35.5 +/- 6.5 months) and 20 age-matched healthy children. The anemia group was treated with 5 mg/kg/day peroral iron for 2 months. Hematological and hemorheological parameters were determined before and after treatment. An ectacytometer was used for the assessment of RBC deformability and aggregation and a cone-plate rotational viscometer for plasma and whole blood viscosities. Hematological parameters were determined using an electronic hematology analyzer.

RESULTS

Although IDA resulted in a decrement in RBC deformability, aggregation, plasma, and whole blood viscosities, these parameters returned to control values after iron supplementation therapy. Serum ferritin levels and hematological parameters (Hb, MCV, MCH, MCHC) that were lower in IDA patients were also found to be increased after treatment.

CONCLUSION

Iron treatment not only reverses the symptoms of anemia but also may contribute to blood flow regulation by causing increments in the alterations observed in hemorheological parameters during anemia.

Targeting erythroblast-specific apoptosis in experimental anemia

Erythrocyte production is regulated by balancing precursor cell apoptosis and survival signaling. Previously, we found that BH3-only proapoptotic factor, Nix, opposed erythroblast-survival signaling by erythropoietin-induced Bcl-xl during normal erythrocyte formation. Since erythropoietin treatment of human anemia has limitations, we explored the therapeutic potential of abrogating Nix-mediated erythroblast apoptosis to enhance erythrocyte production. Nix gene ablation blunted the phenylhydrazine-induced fall in blood count, enhanced hematocrit recovery, and reduced erythroblast apoptosis, despite lower endogenous erythropoietin levels. Similar to erythropoietin, Nix ablation increased early splenic erythroblasts and circulating reticulocytes, while maintaining a pool of mature erythroblasts as erythropoietic reserve. Erythrocytes in Nix-deficient mice showed morphological abnormalities, suggesting that apoptosis during erythropoiesis not only controls red blood cell number, but also serves a "triage" function, preferentially eliminating abnormal erythrocytes. These results support the concept of targeting erythroblast apoptosis to maximize erythrocyte production in acute anemia, which may be of value in erythropoietin resistance.