Hereditary stomatocytosis: membrane and metabolism studies.
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A defect in the protein kinase-mediated phosphorylation of erythrocyte membrane proteins, previously unrecognized in stomatocytosis, was discovered in a boy with hereditary stomatocytosis and severe hemolytic anemia. The high-sodium, low-potassium erythrocytes of this patient were remarkably permeable to both sodium and potassium. The rate of ouabain-inhibitable active cation transport was more than ten times normal and was sustained by an increase of similar magnitude in glycolysis. The deformability in vitro of fresh stomatocytes was reduced and deteriorated further after a brief period of incubation with glucose. Ferrokinetic studies showed that these rigid cells were sequestered by the spleen. When stomatocytes were deprived of glucose in vitro, ATP depletion and ATPase cation pump failure rapidly ensued. Because of their permeability defect, such depleted cells rapidly became swollen and lysed. Prolonged entrapment in acidic, hypoglycemic regions of the spleen would recapitulate these unfavorable events in vivo. In this regard, splenectomy was followed by an improvement in erythrocyte survival, although evidence of continuing hemolysis was obtained. (+info)
A new form of hereditary persistence of fetal hemoglobin in blacks and its association with sickle cell trait.
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A new form of hereditary persistence of fetal hemoglobin (HPFH) producing 3%-8% Hb F in heterozygotes and an elevation of F-cell counts as measured by both the Kleihauer test and an antibody fluorescent procedure was found during the study of a black family. Individuals with this anomaly also had sickle cell trait. A sickle cell homozygote who had apparently inherited the HPFH determinant had 20.3% Hb F. Both types of gamma-chains were present in equal proportions in the Hb F of these individuals. A population study revealed other AS individuals with increased Hb F synthesis, three of whom were sibs. The presence of this previously unrecognized form of HPFH might explain the mild clinical manifestations and the hemoglobin phenotypes of sickle cell homozygotes with unusual elevations of Hb F. (+info)
Modulation of Gardos channel activity by cytokines in sickle erythrocytes.
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It has recently been shown that the Gardos channel activity of mouse erythrocytes can be modified by endothelins, suggesting a functional linkage between endothelin receptors and the Gardos channel. Using (86)Rubidium ((86)Rb) influx, effects were estimated of proinflammatory molecules such as platelet activator factor (PAF), endothelin-1 (ET-1), interleukin-10 (IL-10), and regulated on activation normal T cells expressed and secreted (RANTES) on the Gardos channel activity in human normal and sickle red cells. It was found that PAF (EC(50): 15 +/- 7 nM), RANTES (EC(50), 9 +/- 6 ng/mL [1.2 +/- 0.8 nM]), IL-10 (EC(50), 11 +/- 8 ng/mL [204 +/- 148 nM]), and ET-1 (EC(50), 123 +/- 34 nM) induce a significant increase in Gardos channel activity-between 28% and 84%-over the control. In addition, these agents modify the Gardos channel affinity for internal Ca(++) (K(0.5)) by 2- to 6-fold. Biochemical evidence is provided for the presence of ET receptor subtype B in sickle and normal red cells. Furthermore, it was found that ET-1, PAF, RANTES, and IL-10 induce a significant increase in red cell density (P <.05). These data suggest that activation of the Gardos channel is functionally coupled to receptor motifs such as C-X-C (PAF), C-C (RANTES), and ET receptor subtype B. Thus, cell volume regulation or erythrocyte hydration states might be altered by activation of the Gardos channel by cytokines in vivo. The role of these mediators in promoting sickle cell dehydration in vivo is under investigation. (+info)
Different substitutions at residue D218 of the X-linked transcription factor GATA1 lead to altered clinical severity of macrothrombocytopenia and anemia and are associated with variable skewed X inactivation.
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GATA1 is the X-linked transcriptional activator required for megakaryocyte and erythrocyte differentiation. Missense mutations in the N-terminal zinc finger (Nf) of GATA1 result in abnormal hematopoiesis, as documented in four families: the mutation V205M leads to both severe macrothrombocytopenia and dyserythropoietic anemia, D218G to macrothrombocytopenia and mild dyserythropoiesis without anemia, G208S to macrothrombocytopenia and R216Q to macrothrombocytopenia with beta-thalassemia. The three first GATA1 mutants display a disturbed binding to their essential transcription cofactor FOG1, whereas the fourth mutant shows an abnormal direct DNA binding. In this study, we describe a new family with deep macrothrombocytopenia, marked anemia and early mortality, if untreated, due to a different GATA1 mutation (D218Y) in the same residue 218 also implicated in the above mentioned milder phenotype. Zinc finger interaction studies revealed a stronger loss of affinity of D218Y-GATA1 than of D218G-GATA1 for FOG1 and a disturbed GATA1 self-association. Comparison of the phenotypic characteristics of patients from both families revealed that platelet and erythrocyte morphology as well as expression levels of the platelet GATA1-target gene products were more profoundly disturbed for the hemizygote D218Y mutation. The D218Y allele (as opposed to the D218G allele) was not expressed in the platelets of a female carrier while her leukocytes showed a skewed X-inactivation pattern. We conclude that the nature of the amino acid substitution at position 218 of the Nf of GATA1 is of crucial importance in determining the severity of the phenotype in X-linked macrothrombocytopenia patients and possibly also in inducing skewed X inactivation. (+info)
Heme redox properties of S-nitrosated hemoglobin A0 and hemoglobin S: implications for interactions of nitric oxide with normal and sickle red blood cells.
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S-Nitrosated hemoglobin is remarkably stable and can be cycled between deoxy, oxygenated, or oxidized forms without significant loss of NO. Here we show that S-nitrosation of adult human hemoglobin (Hb A(0)) or sickle cell Hb (Hb S) results in an increased ease of anaerobic heme oxidation, while anions cause redox shifts in the opposite direction. The negatively charged groups of the cytoplasmic domain of Band 3 protein also produce an allosteric effect on S-nitrosated Hb. Formation and deoxygenation of a SNO-Hb/Band 3 protein assembly does not in itself cause NO release, even in the presence of glutathione; however, this assembly may play a role in the migration of NO from the red blood cells to other targets and may be linked to Heinz body formation. Studies of the anaerobic oxidation of Hb S revealed an altered redox potential relative to Hb A(0) that favors met-Hb formation and may therefore underlie the increased rate of autoxidation of Hb S under aerobic conditions, the increased formation of Heinz bodies in sickle cells, and the decreased lifetime of red cells containing Hb S. A model for the interrelationships between the deoxy, oxy, and met forms of Hb A(0) and Hb S, and their S-nitrosated counterparts, is presented. (+info)
Acute erythroid neoplastic proliferations. A biological study based on 62 patients.
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BACKGROUND AND OBJECTIVES: The terms acute erythroleukemia and AML-M6 are defined in the FAB classification as proliferations of dysplastic erythroid elements mixed with blasts of myeloid origin, but pure erythroid leukemias are not included. The recent WHO classification has a category of acute myeloid leukemia not otherwise categorized, which includes acute erythroid leukemia (M6) of two subtypes: M6a-erythroleukemia (erythroid/myeloid) and M6b-pure erythroid leukemia. The aims of this co-operative study were to discover the incidences of these different subtypes, and pay special attention to the morphology of these entities. DESIGN AND METHODS: We reviewed a series of 62 patients with erythroid neoplastic proliferations. Previous medical history, age, sex, peripheral blood and bone marrow cell counts, cytochemical stains, immunophenotype, and cytogenetics were evaluated at presentation. We analyzed the incidence of erythrocyte, leukocyte and platelet abnormalities in the peripheral blood. In bone marrow we analyzed dysplastic features of erythroblasts, granulocytic elements and the megakaryocytic lineage. RESULTS: Fifty-three patients met the criteria of M6a subtype of the WHO classification, and 2 were classified as having pure erythremia (M6b); 7 cases could not be classified according to the WHO criteria. Fifty-five patients presented with de novo acute leukemia, and seven patients had secondary acute leukemia. The most frequent dysplastic features in blood smears were: schistocytes, tear-drop and pincered cells in erythrocytes; hypogranulation and hyposegmentation in leukocytes; gigantism and hypogranulation in platelets. In bone marrow, megaloblastic changes, multinuclearity, karyorrhexis and basophilic stippling in erythroblasts; hypogranulation and gigantism in granulocytic series, and micromegakaryocytes and unconnected nuclei in megakarocytes were the most dysplastic features. A positive PAS reaction and increase of bone marrow iron with ring sideroblasts were common features. Trilineage dysplasia was present in 54% of cases. Dysplastic features in granulocytic elements were absent in 26% of patients and minimal erythroblastic dysplasia was observed in seven patients. A complex karyotype was seen in 27% of patients; chromosomes 5 and 7 were the most frequently involved. INTERPRETATION AND CONCLUSIONS: De novo acute erythroid leukemia was more frequent than secondary cases in our series. The most frequent type of acute erythroid proliferation was the WHO M6a subtype and the least the pure erythroid leukemia. We found a group of seven patients (11%) who could not be classified according to the WHO criteria. Morphologic findings of erythrocytes in peripheral blood, such as schistocytes, tear-drop and pincered cells, were outstanding features. Morphologic aspects remain one of the most important tools for diagnosing these entities. (+info)
Megaloblastic erythropoiesis and macrocytosis in patients on anticonvulsants.
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The results of deoxyuridine suppression tests on the bone marrow cells of 14 patients on anticonvulsant drugs, 11 of whom had evidence of megaloblastic erythropoiesis, indicated that the megaloblastic changes and macrocytosis encountered in treated epileptics are often not caused either by folate deficiency or by drug-induced impairment of the 5, 10-methylenetetrahydrofolate-dependent methylation of deoxyuridylate to thymidylate. A folate-related abnormality in the methylation of deoxyuridylate was found in only two of the 11 patients with megaloblastic erythropoiesis. (+info)
Heparin inhibits the flow adhesion of sickle red blood cells to P-selectin.
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The adhesion of sickle erythrocytes to vascular endothelium is important to the generation of vascular occlusion. Interactions between sickle cells and the endothelium use several cell adhesion molecules. We have reported that sickle cell adhesion to endothelial cells under static conditions involves P-selectin. Others have shown that sickle cell adhesion is decreased by unfractionated heparin, but the molecular target of this inhibition has not been defined. We postulated that the adhesion of sickle cells to P-selectin might be the pathway blocked by unfractionated heparin. In this report we demonstrate that the flow adherence of sickle cells to thrombin-treated human vascular endothelial cells also uses P-selectin and that this component of adhesion is inhibited by unfractionated heparin. We also demonstrate that sickle cells adhere to immobilized recombinant P-selectin under flow conditions. This adhesion too was inhibited by unfractionated heparin, in a concentration range that is clinically attainable. These findings and the general role of P-selectin in initiating adhesion of blood cells to the endothelium suggest that unfractionated heparin may be useful in preventing painful vascular occlusion. A clinical trial to test this hypothesis is indicated. (+info)