Volumetric erythrocyte macrocytosis induced by hydroxyurea

EpoR stimulates rapid cycling and larger red cells during mouse and human erythropoiesis

The erythroid terminal differentiation program couples sequential cell divisions with progressive reductions in cell size. The erythropoietin receptor (EpoR) is essential for erythroblast survival, but its other functions are not well characterized. Here we use Epor-/- mouse erythroblasts endowed with survival signaling to identify novel non-redundant EpoR functions. We find that, paradoxically, EpoR signaling increases red cell size while also increasing the number and speed of erythroblast cell cycles. EpoR-regulation of cell size is independent of established red cell size regulation by iron. High erythropoietin (Epo) increases red cell size in wild-type mice and in human volunteers. The increase in mean corpuscular volume (MCV) outlasts the duration of Epo treatment and is not the result of increased reticulocyte number. Our work shows that EpoR signaling alters the relationship between cycling and cell size. Further, diagnostic interpretations of increased MCV should now include high Epo levels and hypoxic stress.

Mean corpuscular volume, hematocrit and polycythemia

Mean corpuscular volume (MCV) as a measure of the size of red blood cells (RBCs) has been pivotal in the diagnosis and morphologic classification of anemias for over a century. Despite its ubiquitous use and time-honored diagnostic value, one essential attribute of MCV has remained under the radar. It has been long underappreciated that the size of RBC correlates with the amount of hemoglobin (Hb) that it accommodates and, therefore, is an important determining factor of the total Hb level. By scrutinizing this basic principle, it has become possible to uncover a hitherto obscured relationship between MCV, hematocrit (Hct) and RBCs described as a dynamic equilibrium. This principle is shown to be invaluable in interpreting RBC parameters, particularly for the evaluation of patients with polycythemia.

Causes of macrocytic anemia among 628 patients: mean corpuscular volumes of 114 and 130 fL as critical markers for categorization

There have been no studies on the distribution of causes of macrocytic anemia with respect to mean corpuscular volume (MCV) cutoff values. We retrospectively investigated the causes of macrocytic anemia (MCV ≥100 fL) among 628 patients who visited the outpatient hematology clinic in Tohoku University Hospital. To ensure data validity, we also analyzed data from 307 patients in eight other hospitals in the Tohoku district. The leading causes of macrocytic anemia (number of patients, %) were myelodysplastic syndromes (121, 19.3 %), suspected bone marrow failure syndromes (BMF; 74, 11.8 %), aplastic anemia (51, 8.1 %), plasma cell dyscrasia (45, 7.2 %), and vitamin B12 deficiency (40, 6.4 %) in Tohoku University Hospital. We made three primary findings as follows. First, the most common cause of macrocytic anemia is BMF. Second, lymphoid and solid malignancies are also common causes of macrocytosis. Third, macrocytic anemia may be classified into three groups: Group 1 (megaloblastic anemia and medications), which can exceed MCV 130 fL; Group 2 (alcoholism/liver disease, BMF, myeloid malignancy, and hemolytic anemia), which can exceed MCV 114 fL; and Group 3 (lymphoid malignancy, chronic renal failure, hypothyroidism, and solid tumors), which does not exceed MCV 114 fL. These conclusions were supported by the results from eight other hospitals.

Macrocytosis as a potential parameter associated with survival after tyrosine kinase inhibitor treatment

AIM OF THE STUDY

As a rise in mean corpuscular volume (MCV) of the erythrocyte is frequently seen during treatment with imatinib and sunitinib, we investigated whether macrocytosis (MCV > 100 fl) also occurs as a class effect in other tyrosine kinase inhibitors (TKIs) and whether occurrence of macrocytosis is associated with outcome.

MATERIALS AND METHODS

In 533 patients, using 5 TKIs, we investigated if macrocytosis and an increase in MCV were associated with progression-free survival and overall survival (OS) in specific tumour-treatment combinations.

RESULTS

Macrocytosis as well as an increase in MCV from baseline of >10 fl (ΔMCV +10 fl), when included as a time-dependent covariate, were associated with improved OS in patients with renal cell cancer (RCC) treated with sunitinib (macrocytosis, hazard ratio [HR] = 0.61, p = 0.031, and ΔMCV +10 fl, HR = 0.58, p = 0.016).

CONCLUSION

In sunitinib-treated patients with RCC, the occurrence of macrocytosis, or a substantial increase in MCV levels after start of treatment, could potentially serve as a positive prognostic factor for survival, if validated prospectively.

[Macrocytosis without anaemia in an urban population]

OBJECTIVE

Observational study on a group of patients with macrocytosis without anaemia. The probable relationship of cause and effect between Helicobacter pylori and macrocytosis.

METHODS AND MATERIAL

An observational and cross-sectional study.

MAIN MEASUREMENTS

The measured variables were: personal data, medical and analytical history in relation to macrocytosis, alcohol and smoking habits and drug use. This information was taken from the medical history of the patient.

RESULTS

The prevalence of macrocytosis without anaemia was 7.12%. The main cause found was hypothyroidism in 37/234 (15.8%) patients, followed by alcoholism in 34/234 (14.5%) patients. The most frequent association was alcohol and tobacco in 9/234 (3.8%) patients. It was not possible to find a cause of the increased mean corpuscular volume (MCV) in 87/234 (37.18%) patients. Out of 37 tests conducted for Helicobacter pylori, 23 of them were positive.

DISCUSSION

Macrocytosis without anaemia has a high prevalence. Finding the most frequent causes could help in the early diagnosis and treatment. H. pylori currently appears to be associated to different digestive tract and non-digestive tract diseases.It could be a cause of increased MCV, but this study was unable demonstrate this.

Hydroxyurea therapy for management of secondary erythrocytosis in cyanotic congenital heart disease

Secondary erythrocytosis in cyanotic congenital heart disease (CCHD) causes substantial morbidity because of complications of hyperviscosity, including stroke and chronic end organ damage. Phlebotomy provides temporary improvement but leads to iron deficiency and can actually increase blood viscosity. We describe the successful use of hydroxyurea (hydroxycarbamide) in four patients with uncorrected CCHD and symptomatic secondary erythrocytosis. In all patients, hydroxyurea improved symptoms of hyperviscosity. Substantial decreases in the red blood cell (RBC) count were observed, along with increases in the mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), leading to only modest declines in the circulating hemoglobin concentration. Two patients experienced transient mild myelosuppression, which promptly resolved with dose reduction of hydroxyurea. Hydroyxurea provides a novel and useful therapeutic approach to reduce hyperviscosity from secondary erythrocytosis in patients with CCHD, while preserving oxygen carrying capacity and avoiding iron depletion by phlebotomy.

Treatment of Myeloproliferative Disorders With Hydroxyurea: Effects on Red Blood Cell Geometry and Deformability

Hydroxyurea (HU) is used in suppressing the bone marrow and producing fetal-like red blood cells (RBCs). These RBCs are large in size and may theoretically disturb the microcirculation. In five patients with myeloproliferative disorders (MPD), the RBC geometry and deformability were analyzed before and after 6 to 8 months of HU treatment. In untreated MPD, the RBC geometry and filterability was normal. After HU, the RBC membrane area increased 24% and the cell volume increased 39% (P < .005). This change resulted in a 12% increase in the minimum cylindrical diameter (MCD). From a static bending model of initial deformation, the RBC diametrical cross-section had a significantly increased section modulus. However, this increase in profile stiffness was compensated for by its larger projected cell area and, thus, pressure load on the RBC corpuscle. The resulting resistance to initial deformation therefore remained unchanged after HU. These findings were tested experimentally; with 3-μm filter membranes, HU treatment caused a significant increase in flow resistance (P < .02), in accordance with MCD. However, with 5-μm pores, no difference was seen, again in consonance with the theoretical findings of initial deformation. Because most capillaries are larger than 3 μm, we suggest that HU is acceptable from a perspective of cellular microrheology.

Treatment of Myeloproliferative Disorders With Hydroxyurea: Effects on Red Blood Cell Geometry and Deformability

Hydroxyurea (HU) is used in suppressing the bone marrow and producing fetal-like red blood cells (RBCs). These RBCs are large in size and may theoretically disturb the microcirculation. In five patients with myeloproliferative disorders (MPD), the RBC geometry and deformability were analyzed before and after 6 to 8 months of HU treatment. In untreated MPD, the RBC geometry and filterability was normal. After HU, the RBC membrane area increased 24% and the cell volume increased 39% (P < .005). This change resulted in a 12% increase in the minimum cylindrical diameter (MCD). From a static bending model of initial deformation, the RBC diametrical cross-section had a significantly increased section modulus. However, this increase in profile stiffness was compensated for by its larger projected cell area and, thus, pressure load on the RBC corpuscle. The resulting resistance to initial deformation therefore remained unchanged after HU. These findings were tested experimentally; with 3-μm filter membranes, HU treatment caused a significant increase in flow resistance (P < .02), in accordance with MCD. However, with 5-μm pores, no difference was seen, again in consonance with the theoretical findings of initial deformation. Because most capillaries are larger than 3 μm, we suggest that HU is acceptable from a perspective of cellular microrheology.

Hematologic responses of patients with sickle cell disease to treatment with hydroxyurea

Because fetal hemoglobin contains gammaglobin chains instead of beta chains, it is not affected by the genetic defect that causes sickle cell disease. Increased levels of fetal hemoglobin decrease the tendency toward intracellular polymerization of sickle hemoglobin that characterizes this disease. Hydroxyurea is one of several cytostatic agents that have been shown to increase the production of fetal hemoglobin in some patients with sickle cell disease. We studied the effects of hydroxyurea administration in 10 hospitalized patients with sickle cell disease, each of whom was treated for three months. Seven patients responded with a 2- to 10-fold increase in fetal hemoglobin, from a mean (+/- SD) of 1.6 +/- 1.6 percent of total hemoglobin to 6.8 +/- 4.7 percent; three patients had fetal-hemoglobin levels of 10 to 15 percent of total hemoglobin. Three did not respond to treatment. Four of the patients who responded were retreated with hydroxyurea after one to four months without treatment and were found to have larger increases in fetal-hemoglobin levels. In most patients, levels were still rising at the end of the study, even after 90 days of therapy. Fetal-hemoglobin levels tended to peak at dosages of hydroxyurea that were myelosuppressive. In the patients who responded to treatment, there were significant increases in the percentage of reticulocytes and erythrocytes containing fetal hemoglobin and in the amount of fetal hemoglobin within these cells. The percentage of dense red cells decreased in the patients who responded to treatment. The tendency toward intracellular polymerization at physiologic oxygen saturation was reduced by about 33 percent in the cells containing fetal hemoglobin, whereas there was no change in the other cells. We conclude that hydroxyurea is effective in increasing the production of fetal hemoglobin, which in this study was found to be associated with a small decrease in hemolysis and an increase in hemoglobin levels despite myelosuppression. Controlled, prospective trials are necessary to establish whether these effects will lead to clinical benefit.

Effect of hydroxyurea on the rheological properties of sickle erythrocytes in vivo

We have monitored the rheological effects of hydroxyurea (HU) on erythrocytes obtained from two patients with severe sickle cell anemia who were enrolled in a therapeutic trial of this drug. Erythrocyte membrane stability and whole cell and membrane deformability of red cells from treated and untreated patients and normal controls were determined in room air using an ektacytometer--a laser viscodiffractometer. The percentage of dense cells was quantitated by centrifugation on a discontinuous Stractan density gradient. F reticulocytes (FR), absolute F reticulocytes (AFR), and F cells (FC) were determined by single-cell radial immunolgic assays. After 1 year of treatment with HU, there was a significant increase in the level of hemoglobin (Hb) F, FR, AFR, and FC. The degree of anemia remained the same, but there was significant increase in the mean cell volume (MCV) and a significant decrease in the mean corpuscular Hb concentration (MCHC). Whole cell deformability improved by twofold, but membrane stability remained within normal limits. The hydration status of sickle erythrocytes improved as was indicated by a change toward normal in gradient osmotic ektacytometry, an increase in RBC K+ content, a decrease in percent of dense cells, and a decrease in the MCHC. The data indicate that, in addition to its effect on the production of Hb, F, HU has a salutary effect on whole cell deformability and on the hydration status of sickle erythrocytes. Determination of the rheological properties of erythrocytes may be of value in monitoring the response to HU.