Molecular mechanism of hemolytic anemia in homozygous hemoglobin C disease. Electron microscopic study by the freeze-etching technique.

Erythrocytes from a patient with homozygous hemoglobin C disease were subjected to gradual osmotic dehydration by incubation in hypertonic saline. Serial observations of these cells before and after 4 and 12 hr incubation were carried out by means of interference, Soret absorption, polarization microscopy, and the electron microscope employing the freeze-etching technique. Light microscopic studies showed a progressive contraction of cellular contents into central masses which, after 12 hr dehydration, formed birefringent intracellular hemoglobin crystals in 50-75% of the cells. Electron microscopic study of freeze-etched replicas of these cells at 0, 4, and 12 hr of dehydration reveals progressive aggregation, alignment, and crystallization of hemoglobin molecules. Molecular aggregation found in C-C cells prior to osmotic dehydration was not seen in normal erythrocytes. Aggregation and packing varied from cell to cell. Reticulocytes showed a loosely packed aggregate mesh-work; older cells showed variation of molecular packing, which appeared tightest in cells corresponding to microspherocytes. With further loss of intracellular water, aggregates coalesced into patterns of tighter molecular packing with small regions of alignment, and, finally, crystallization occurred. Hemoglobin molecules measuring 70 A in diameter were readily identified within the period patterns of intracellular crystals. These findings suggest that the hemoglobin C molecules within C-C erythrocytes exist in an aggregated state. As the cell ages, intracellular water is lost and intermolecular distance decreases, hemoglobin C molecules polymerize into intracellular crystals. This pathological behavior of hemoglobin C is associated with a charge alteration conferred by the substitution of beta-6-lysine for glutamic acid on the external surface in the A-helix region of the beta-chain of the molecule, possibly increasing intermolecular attraction. Molecular aggregation accounts for the increased rigidity of C-C cells which leads to accelerated membrane and water loss with resultant microspherocyte formation. The microspherocyte, with highest intracellular hemoglobin concentration, rapidly undergoes intracellular crystallization, and is sequestered and destroyed by reticuloendothelial elements.

Inhibition of erythrocyte sickling in vitro by pyridoxal.

To test the antisickling activity of pyridoxal, we compared the oxygen affinity and the percent sickling at low PO2 of untreated erythrocytes with values for cells from the same blood sample incubated with pyridoxal, glyceraldehyde, or pyridoxine. Pyridoxal increased oxygen affinity much more than glyceraldehyde. 20 mM pyridoxal and glyceraldehyde had equivalent antisickling activity. At PO2 levels above 20 mm Hg, both agents reduced sickling to less than 2%. In samples examined by electron microscopy, pyridoxal reduced the percent sickled cells and the percent cells that contain hemoglobin S fibers by the same amount (from 74 to 3%). Pyridoxine had no effect on oxygen affinity or sockling. Pyridoxal reacts with intracellular hemoglobin to increase oxygen affinity, which inhibits hemoglobin S polymerization and sickling.

Aggregation of intramembrane particles in erythrocyte membranes treated with diamide.

Treatment of erythrocytes with diamide (diazene dicarboxylic acid bis-(N,N-dimethylamide)) results in oxidation of sulfhydryl groups of the membrane, and cross-linking of membrane proteins into high molecular weight complexes. Concomitant freeze-etching studies show aggregation of intramembrane particles on the protoplasmic fracture face of erythrocyte ghost membranes treated with the oxidant. Furthermore, after a 3 h incubation of erythrocytes with 10 mM diamide at 37 degrees C, cellular energy levels declined to about 70% of control values. The data suggest that disulfide cross-linking of the major membrane proteins releases the apparent physical occlusion of the band 3 proteins within the interstices of the cytoskeletal shell. This results in the translational mobility of band 3 proteins which is reflected ultra-structurally in the freeze-etch images.

Drug-associated "bite cell" hemolytic anemia.

PURPOSE: "Bite cell" hemolytic anemia is a variant of drug-related hemolysis usually associated with methemoglobinemia and Heinz body inclusions in red blood cells secondary to oxidant drug injury. Bite cells are morphologically characterized as poikilocytes with one or more semicircular portions removed from the cell margin. The purpose of this report is to emphasize the importance of peripheral smear examination in patients with possible drug-associated hemolytic anemia. The morphologic characteristics of bite cells by light microscopy and scanning electron microscopy are detailed in this study, and the pathophysiologic mechanism is discussed. PATIENTS AND METHODS: Clinical and laboratory data were retrospectively studied on eight patients (two men and six women, aged 29 to 85 years) who showed evidence of bite cell hemolytic anemia associated with drug exposure. Multiple standard hematologic laboratory evaluations for hemolytic anemia were performed. Five hundred red blood cells were counted from randomly selected peripheral smear fields for the calculation of bite cell percentage. RESULTS: Peripheral smears showed predominantly normochromic normocytic red cells with prominent bite cells and occasional blister cells. Bite cell counts ranged from 5.5% to 13.6% (mean, 8.7 +/- 3.0% SD) associated with a hematocrit reduction of 3.0% to 13.2% (mean, 8.5 +/- 3.8% SD) and concomitant reticulocytosis of varying degree from 2.3% to 15.4% (mean, 7.3 +/- 4.9% SD). Withdrawal of the offending drug(s) and treatment of underlying diseases resulted in improvement of hemolytic anemia and eventual disappearance of bite cells. A close correlation between hematocrit reduction, reticulocyte response, and bite cell percentage increase was seen. The usual biochemical markers of hemolysis were not consistently observed. Scanning electron microscopy confirmed the light microscopic evidence of bite cell morphology and revealed a keratocytic variant. CONCLUSION: This study emphasizes the importance of peripheral smear examination for early diagnosis and management of bite cell hemolytic anemia. Withdrawal of the putative offending drug(s) and treatment of underlying disorders should result in improvement of this form of drug-associated hemolysis.

Bone marrow mast cell content in preleukemic syndrome.

Bone marrow mast cell content was evaluated by a semiquantitative method in 22 marrow specimens from 20 patients with preleukemic syndrome and was compared with 21 marrow specimens from iron-deficient control subjects. Results indicate a statistically significant increase of bone marrow mast cell content in patients with preleukemic syndrome in comparison to control subjects (p less than or equal to 0.0005). Two of 20 preleukemic patients converted to acute myeloblastic leukemia and conversion was accompanied by a significant decrease of bone marrow mast cell content. Our findings indicate that bone marrow mast cell content can be reproducibly quantitated and represents an additional morphologic criterion for diagnosis of the preleukemic syndrome.

Multiple myeloma in a patient with sickel cell anemia. Interacting effects on blood viscosity.

Described here is a case of multiple myeloma in a patient with sickle cell anemia. Viscometric studies were made by comparing the patient's whole blood, plasma and washed red blood cells with those of a normal control subject and a patient with sickle cell anemia. Results showed that the increased viscosity of the patient's whole blood as compared with that of the control patient with sickle cell anemia was mainly due to erythrocytic interaction with the circulating abnormal immunoglobulin. It is postulated that the increased frequency of vaso-occlusive crisis that occurred in our patient in the months before the diagnosis and treatment of multiple myeloma, was due to this cell-protein interaction with the resulting enhancement of whole blood viscosity and the sickling phenomena.

Clinical application of recombinant erythropoietin in myelodysplasia.

This article attempts to summarize the current information regarding the clinical application of recombinant human erythropoietin in patients with myelodysplastic syndromes (MDS). To date, more than 300 MDS patients have been reported to be treated with recombinant human erythropoietin. The response patterns have been variable, but in general they range from 20% to 30%. The hormone has been shown to be safe and nontoxic.

Cellular and rheological factors contributing to sickle cell microvascular occlusion.

Sickle (HbSS) erythrocytes contain subpopulations that are heterogeneous in shape, size, and density and exhibit abnormal microcirculatory behavior. Their phthalate esters density distributions quantitatively distinguish subpopulations of HbSS cells from density profiles of normal (HbAA) erythrocytes. Filtration of HbSS cell suspensions, devoid of leukocytes, through 5-microns Nucleopore filters at constant flow rate (29.5 microliters/s) yields pressure-time curves that demonstrate deformability of the sickle cells to be several-fold less than equivalent suspensions of normal (HbAA) cells. For a cell flux of 6.43 X 10(5) cells/s, the rate of the rise of the pressure (Pi/t) following 1-2 s of the initial pressure reading indicates occlusion of the filter pores by the dense cell fraction. Rats exchange-transfused with human sickle (HbSS), normal (HbAA), or autologous rat erythrocytes were used to investigate the flow dynamics of these cells in the mesenteric microcirculation by intravital videomicroscopy. Time-averaged velocities of the autologous rat red cells in 16-30 microns (i.d.) arterioles ranged from 1.10 to 1.25 mm/s with varying flux and wall shear rates. Time-averaged velocities of the HbAA cells in single 15-35-microns arterioles ranged from 1.16 to 1.24 mm/s with wall shear rates similar to the estimates for the autologous cells. In contrast, sickle cells exhibited time-averaged velocities of 0.38-0.45 mm/s with lower wall shear rates in 10-35 microns single unbranched arterioles with three times less volumetric flux. In some arterioles, sickle RBCs with a high axial ratio of 3-4 and low deformability showed apparent adhesion to endothelial surfaces and occluded precapillary junctions or entry points for several seconds until dislodged by the higher flow velocity. Within single unbranched vessels or at microvascular bifurcations, sickle elliptocytes and sickle echinocytes with low deformability and axial ratios of 3-4 obstructed flow and exhibited residence times of 6-75 s at the sites of occlusion, thereby causing stasis and increasing the local apparent viscosity. Thus, both the in vitro and in vivo data demonstrate the rheological disequilibrium state induced by HbSS cells as they traverse artificial micropores or course through successive segments of the microcirculation. The specific tendency of dense cells with high axial ratio (ISCs) to manifest precapillary junctional blockade and prolonged residence times implicates this cell fraction in the initiation of microvascular occlusion.

Rheological assessment of antisickling effects of pyridoxine and pyridoxal.

The antisickling effects of pyridoxine and pyridoxal on intact sickle erythrocytes (SRBCs) were assessed by microviscometry of cell suspensions at shear rates of 1.15 to 230.0/s, measurement of cellular deformability by cell filtration and scanning and transmission electron microscopy (EM). Incubation of fresh SRBCs in albuminated (0.1%) phosphate buffered saline, pH 7.4, with 5 to 30 mM, pyridoxine or pyridoxal at 37 degrees C for 90 min followed by deoxygenation to pO2 = 25 mmHg, decreased the percentage of sickled cells observed as a function of vitamin concentration. EM of fresh SRBCs incubated with 20 mM pyridoxine or pyridoxal at 25 mmHg pO2 showed mostly discocytes without intracellular fibers indicating absence of hemoglobin polymerization. Determination of fluidity (viscosity-1) versus shear stress showed that both pyridoxine and pyridoxal significantly (P less than 0.01) increased the fluidity of a deoxygenated suspension of SRBCs. The estimated apparent yield stress from Casson plots for the vitamin-treated deoxygenated cells and the deoxygenated control cells were 0.11 and 0.18 dynes/cm2 respectively. The relative resistance of 0.2% cell suspension to flow through 5 microns Nuclepore filters indicated a significant increase (greater than 75%) in the deformability of the vitamin-treated deoxygenated sickle cells. The ultrastructure of the SRBCs through the filter pores further suggested that the fluidity of the intracellular milieu of the vitamin-treated deoxygenated cells was higher than that of the deoxygenated controls. These data support the hypothesis that pyridoxylation of sickle hemoglobin inhibits sickling, increases the fluidity of sickle hemoglobin under low pO2, and thereby enhances the deformability of SRBCs in models of capillary blood flow.

Freeze-etching and biochemical analysis of human fetal erythrocyte membranes.

In order to test the hypothesis that there are ultrastructural and supramolecular differences between fetal and adult erythrocyte membranes that are manifested in their functional characteristics, the cells were studied by freeze-etching and transmission microscopy and biochemical methods. Freeze-etching and transmission electron microscopy of fetal erythrocyte membranes showed that the protoplasmic and exoplasmic fracture faces have 24% and 45% greater intramembrane particles respectively compared to adult cells (p less than 0.01). The apparent diameters of the intramembrane particles estimated on the exoplasmic fracture face averaged as follows: 4.84, 7.74, 11.42, and 15.64 nm, which are similar to estimates in adult cell membranes, suggesting similar dimensions for the presumptive glycoprotein structures in the fluid mosaic complex of the cell membranes. The average total cholesterol, phospholipid, and protein content per fetal erythrocyte ghost as well as ratios of protein/lipid, protein/cholesterol, and protein/phospholipids were all significantly greater than in the adult ghost (p less than 0.01). Analysis of fetal and adult ghost proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed similar qualitative and quantitative polypeptide and glycopeptide bands except for the intense appearance of bands 4.5 and 8 in the fetal samples. Polypeptide chains per ghost membrane were significantly greater in fetal ghosts than in adult ghosts. However, the molar ratios of the major polypeptides relative to band 3, the predominant protein in the ghost membrane, are comparable for the two cell types except for bands 4.5 and 8. These findings suggest that the molecular characteristics of the erythroid plasma membrane vary with the developmental age.

Erythrocyte density distribution in sickle cell anemia.

Density distributions were determined for sickle cell erythrocytes from 27 patients with HbSS genotype using the phthalate ester microcapillary differential flotation method of Danon and Marikovsky. Mean density distribution curves showed HbSS erythrocytes to have trimodal populations with significant increases in both dense and light cell fractions when compared to 20 normal controls of HbAA genotype (p less than 0.05). Irreversibly sickled cell (ISC) and reticulocyte counts were compared with density distributions. Integrated unit areas under the dense cell population curves correlated with ISC percentages, while corresponding unit areas for light populations correlated to a lesser extent with reticulocyte percentages. Mean cell density, D50, varied widely among patients and correlated poorly with the ISC or reticulocyte percentage; however, D50 did correlate with the net change in integrated unit areas. Several patients had repeated density distributions over a 2-year time period. All HbSS patients showed increased but variable dense cell fractions which could not be definitively correlated with the clinical state of the patient. Transfusion reproducibly resulted in a lowering of the dense cell fraction. Erythrocytes from the HbSC patients showed a uniform increase in density and absence of the large dense cell fraction seen in most HbSS patients. This method provides a simple means for quantitation of the light and dense cell fraction in blood of patients with sickling disorders and displays the profile of erythrocyte density heterogeneity for the individual sickle cell patient.

Vaso-occlusion in sickle cell disease: pathophysiology of the microvascular circulation.

Microvascular dysfunction accounts for the major morbidity and contributes to the mortality among patients with sickle cell hemoglobinopathies. We summarize the microcirculatory dynamics of red cells in sickle cell disease. An overview of the physiological attributes of the microcirculation is presented. The microcirculatory module is a unique organic entity within the tissue domain, which is concerned with the functional exchange of substances between the blood and the tissue environment. The impairment in deformability of sickle red cells and their heterogeneity cause them to show abnormal microvascular flow dynamics that, in turn, contribute to derangement of the microvascular bed. Studies of experimental models in animals have employed the microcirculation of the mesentery, the cremaster muscle, and the mesoappendix. These studies showed the rheological disequilibrium that results as sickle cells course through successive segments of the arterioles, capillaries, and venules. Direct in vivo microscopic observations in human subjects, with analysis and quantitation of the nailfold and bulbar conjunctival capillaries, have also provided useful information as to the adverse effects of sickling on the microcirculation. Sickle cell vaso-occlusion has three phases--initiation, propagation, and resolution. This framework provides a basis for testable hypotheses for verification in appropriately designed experiments. In this context, the determinants of the microvascular flow of erythrocytes in sickle cell disease are emphasized.

Irreversible erythrocyte volume expansion induced by tellurite.

Tellurite (K2TeO3) has been suggested as a potential anti-sickling compound because it causes a selective increase in the water content of RBC. To investigate the conditions underlying the increase in RBC volume due to tellurite, normal RBCs were incubated with the compound in a physiological medium and the cells washed with a 10-fold volume of the medium. The washed cells were then incubated at 24 degrees C for periods up to 4 h and the following parameters were determined: MCV, MCH, MCHC and supernatant haemoglobin concentration by standard methods, the density distribution profile by phthalate esters and cell morphology by scanning electron microscopy (SEM). The effect of hypertonic PBS on the tellurite-treated cells was also tested. K2TeO3 induced concentration and time dependent increases in MCV and decreases in MCHC without any apparent change in MCH. The median density and the transitional 60% density range of the cell distribution profile respectively decreased and increased in proportion to [K2TeO3] and time. Hypertonic PBS did not inhibit or reverse the tellurite-induced changes in MCV and MCHC. SEM and photovolumetric measurements demonstrated tellurite-induced large vesicles ranging in size from 24 to 32 micron 3. The proportion of these vesicles increased with time and K2TeO3 concentration. Since tellurite is an oxidant, these findings suggest that its influx into the red cell results in irreversible reactions that disrupt the ion and water regulatory properties of the membrane.

Assessment of the hydration state of sickle cells by phthalate ester density distribution.

Intracellular hemoglobin S (Hb SS) concentration, a function of cell hydration, has a major influence on the rate of Hb SS polymerization and, therefore, cellular sickling. To determine the density distribution of homozygous sickle hemoglobin cells as a function of cell hydration, cells were incubated in autologous plasma buffer mixtures with final osmolalities ranging from 195 to 490 mosm/kg at ambient Po2. The density distribution of the cells was determined by differential flotation on 20 mixtures of di-n-butyl and dimethyl phthalates with specific gravities of 1.062 to 1.142. Mean cell hemoglobin concentration (MCHC) and mean cell volume (MCV) were determined by standard manual procedures. Cell shape was assessed by scanning electron microscopy (SEM), and the axial ratio (L/W) of the elliptical dense cell fraction measured by an image analyzer interfaced with a computer. The density distribution of normal red blood cells lies within a narrow 1.090 to 1.118 gm/ml density band with the middle or transitional 60% (T60) of the cells occupying a density range of 0.0067 +/- 0.0007 gm/ml (+/- SD). The density distribution of sickle cells shows a broader density band of 1.064 to 1.134 gm/ml, and the T60 was 0.0139 +/- 0.0022 gm/ml. The mean T60 did not change with osmotic variation but the mean T60 of Hb SS cells was significantly greater (P less than 0.005). MCHC and 1/MCV varied directly with the median density of the density distribution. By linear regression analysis and Ponder's osmotic equation, it is evident that sickle cells exhibit restricted volume increases in hypotonic media.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol-induced vacuolization in bone marrow cells: ultrastructure and mechanism of formation.

Vacuolization has been known for two decades to occur in the cytoplasm and over the nuclei of the erythroid and myeloid precursors in bone marrows of patients with acute alcoholism. Electron microscopic examination of the marrows from four acute alcohol-intoxicated subjects disclosed that the vacuoles are present only in the cytoplasm and free of organized structure. Surface invagination of the cell membrane of erythroblasts leads to endocytosis and consequent vacuole formation. Cytoplasmic vacuolization of bone marrow cells was reproduced in vitro in 8 of 12 bone marrows from normal individuals when incubated for 6 hours or more in nutrient medium containing alcohol. The critical alcohol concentration for vacuolization was 62.5 mg/dl. The proportion of cells developing vacuoles appeared to correlate with the concentration of alcohol particularly above levels of 250 mg/dl.