Relationship of clinical severity to packed cell rheology in sickle cell anemia

There is wide variation in the clinical manifestations of sickle cell disease (SCD) from one affected individual to another. Many investigators have sought to discern parameters that would explain this variability. In the present studies we have attempted to correlate the frequency of painful events and the extent of end organ failure in SCD with rheologic properties of packed suspensions of sickle cells, using a magneto-acoustic ball microrheometer developed in our laboratory. Using this device we have measured the steady-state viscosity, and the viscous and elastic moduli of cell suspensions in 16 individuals with hemoglobin SS disease who were untransfused and in their steady state. The rheologic parameters were then correlated with clinical parameters. The clinical parameters measured were emergency department visits, hospitalizations, hemoglobin, reticulocyte count, age, and end organ failure (nephropathy, avascular necrosis of bone, stroke, retinopathy, resting hypoxemia after acute chest syndrome(s), leg ulcer, and priapism with impotence). The P value for the correlation between the steady state viscosity and end organ failure was .001 with a correlation coefficient (R value) of .73. The P value for the correlation between the viscous modulus of viscosity and end organ failure was .00006 with an R value of .83. The P value for the correlation between the elastic modulus of viscosity and end organ failure was .0006 with an R value of .76. However, there was no significant correlation between any component of packed cell rheology and emergency department visits or hospitalizations for pain.

Okadaic acid inhibits activation of K-Cl cotransport in red blood cells containing hemoglobins S and C

The sensitivity of red blood cells containing hemoglobins S and C to activation of K-Cl cotransport by osmotic swelling and acidification was reduced by okadaic acid, a specific protein phosphatase inhibitor. The dose-response curve for okadaic acid suggests its action is on a type 1 protein phosphatase. Okadaic acid has been previously shown to inhibit swelling-induced activation of K-Cl cotransport in red blood cells from rabbits, normal humans, and dogs. The present work confirms the observation that okadaic acid blunts the stimulation of K-Cl cotransport by cell swelling. The new information is that okadaic acid reduces the effects of hemoglobins S and C on the volume and pH sensitivity of K-Cl cotransport. Thus the influences of cell volume, pH, and mutant hemoglobins may all be mediated via a common mechanisms that affects the phosphorylation state, either of the K-Cl. cotransporter itself or of a protein that regulates its function.

Effects of hydroxyurea on hemoglobin F and water content in the red blood cells of dogs and of patients with sickle cell anemia

A rationale for clinical trials of hydroxyurea (HU) treatment in sickle cell disease is that the agent increases red blood cell (RBC) fetal hemoglobin content. However, an additional effect of HU is to raise the mean corpuscular volume (MCV). To investigate the action of HU in a species that makes no electrophoretically distinguishable fetal hemoglobin, we treated dogs with the drug and compared their response to that of five patients with sickle cell anemia. Both dogs and patients had an increase in MCV, but the effect of HU treatment on the mean corpuscular hemoglobin concentration (MCHC), density, and water content of the RBCs differed in the two species. The dog RBCs became low in MCHC, high in ion and water content, and low in mean density. Thus, HU can raise MCV and lower MCHC without influencing fetal hemoglobin synthesis. A different pattern was seen in the sickle cell patients during HU treatment. Although the MCV of their RBCs increased, there was no change in MCHC, ion content, or mean density. A notable change in the sickle cell patients' blood was that two subpopulations of cells were nearly eliminated during HU treatment; the hypodense reticulocyte fraction and the hyperdense fraction that contains irreversibly sickled cells. These findings lead us to suggest that trials of HU in sickle cell disease must recognize the possibility that any beneficial effect of this agent might be due not only to an increase in hemoglobin F alone, but perhaps also to the associated increase in MCV or the altered RBC density profile.

Vanillin, a potential agent for the treatment of sickle cell anemia

Vanillin, a food additive, has been evaluated as a potential agent to treat sickle cell anemia. Earlier studies indicated that vanillin had moderate antisickling activity when compared with other aldehydes. We have determined by high performance liquid chromatography that vanillin reacts covalently with sickle hemoglobin (HbS) both in solution and in intact red blood cells. Hemoscan oxygen equilibrium curves show a dose-dependent left shift, particularly at low oxygen tensions. Rheologic evaluation (pO2 scan Ektacytometry) of vanillin-reacted HbS erythrocytes shows a dose-dependent inhibition of deoxygenation-induced cell sickling. Ektacytometry also suggests that vanillin may have a direct inhibitory effect on HbS polymer formation. Vanillin has no adverse effects on cell ion or water content. X-ray crystallographic studies with deoxyhemoglobin (HbA)-vanillin demonstrate that vanillin binds near His 103 alpha, Cys 104 alpha, and Gln 131 beta in the central water cavity. A secondary binding site is located between His 116 beta and His 117 beta. His 116 beta has been implicated as a polymer contact residue. Oxygen equilibrium, ektacytometry, and x-ray studies indicate that vanillin may be acting to decrease HbS polymerization by a dual mechanism of action; allosteric modulation to a high-affinity HbS molecule and by stereospecific inhibition of T state HbS polymerization. Because vanillin is a food additive on the GRAS (generally regarded as safe) list, and because it has little or no adverse effects at high dosages in animals, vanillin is a candidate for further evaluation as an agent for the treatment of sickle cell disease.

Inhibition of erythrocyte calcium transport by cetiedil

The elevated calcium content found in red cells from patients with sickle cell anemia may be of pathophysiologic importance in the hemolysis and vasoocclusion which characterize this disorder. Cetiedil, an antisickling agent, has been reported to inhibit the activity of enzymes that are stimulated by the calcium regulatory protein calmodulin. To investigate the mechanism by which cetiedil modifies calcium-mediated erythrocyte function, the effect of the drug on the active transport of calcium into inside-out erythrocyte vesicles was examined and its influence on the activities of phosphodiesterase and Ca-ATPase studied. Cetiedil, in the presence of calmodulin, significantly inhibited calcium transport into inside-out vesicles that were prepared with erythrocytes from normal controls and from patients with sickle cell anemia. However, in the absence of calmodulin, no inhibition was observed. Likewise, cetiedil inhibited calmodulin-stimulated, but not basal, activities of phosphodiesterase and Ca-ATPase. These data, along with previous reports, suggest that cetiedil does not act by lowering the intracellular calcium content. It is, therefore, likely that the beneficial effect of cetiedil is due to its ability to protect the red cell from the deleterious consequences of an elevated concentration of intracellular calcium.

Granulocytic sarcoma presenting as pulmonary nodules and lymphadenopathy

A patient presented with anterior and posterior cervical lymphadenopathy as well as widespread intrapulmonary nodules. Histologic sections of both lymph node and lung revealed dense infiltration by sheets of cells which were cytochemically positive for chloroacetate esterase and myeloperoxidase, thus suggesting a diagnosis of granulocytic sarcoma. The patient was initially treated with daily hydroxyurea. After 6 weeks, when progression of the disease was apparent, hydroxyurea was discontinued and the patient was placed on mithramycin, an agent reported to induce differentiation of myeloid precursor cells both in vitro and in vivo. On this latter agent, a dramatic response has been noted with a decrease in the pulmonary symptoms, and a marked reduction in the size of the lymph nodes and lung nodules. The authors report this case because it represents a rare presentation of an uncommon disease and because of the striking improvement that followed the initiation of a novel therapeutic modality.

Effect of N-ethylmaleimide on K transport in density-separated human red blood cells

N-ethylmaleimide (NEM) is a sulfhydryl-reacting agent known to stimulate chloride-dependent K transport in a variety of red cells. In high K sheep red cells, NEM-induced K movements are greater in magnitude in young cells compared with old cells. We hypothesized that human red cells might respond to NEM like high K sheep red cells. To test this idea, cells of various age were exposed to 0.5 mM NEM. We found that, after a 4-h incubation, young cells lost 50% of cell K, compared with 10% K loss in older cells. K loss in all fractions was inhibited by chloride replacement or furosemide.

Nutrition and sickle cell disease

The role of protein and calorie deficiency in sickle cell disease remains poorly defined. While such features as growth retardation, impaired immune function, and delayed menarche do suggest a relationship between sickle cell disease and undernutrition, measurement of more direct nutritional parameters in these patients have yielded mixed results. Anthropometric measurements such as skinfold thickness are subnormal in many but not all reports. Serum protein levels are normal, but low values for serum lipids have been reported. Finally, one small study shows an improvement in both growth parameters and clinical course following caloric supplementation. A variety of micronutrient deficiencies have been suggested in sickle cell disease. Numerous case reports describing an exacerbation of the chronic anemia that was reversed by folic acid therapy led to routine folate supplementation. More recent studies have shown, however, that clinically significant folic acid deficiency occurs only in a small minority of sickle cell patients. Clearly, more work is necessary to define the cost/benefit ratio of routine folic acid supplementation. Pharmacological amounts of vitamin B6 and certain of its derivatives possess in vitro antisickling activities. Nevertheless, a small clinical trial failed to demonstrate any consistent hematologic effects of B6 supplementation. Several reports indicate that vitamin E levels are low in sickle erythrocytes. Since these abnormal red cells both generate excessive oxidation products and are more sensitive to oxidant stress, and because oxidants appear to play a role in ISC formation, vitamin E deficiency could well be linked to ISC formation and hemolysis. Small clinical trials, however, have again failed to produce a clear hematological response in sickle cell anemia. The role of zinc in sickle cell disease has received considerable attention. Though studies are generally small, most do support a relationship between sickle cell disease and zinc deficiency. Etiologic associations between zinc deficiency and such complications of sickle cell disease as poor ulcer healing, growth retardation, delays in sexual development, immune deficiencies, and high ISC counts have all been suggested. Most of these studies need further corroboration. Iron deficiency is now known to be a relatively common occurrence in sickle cell anemia, especially in children and pregnant women. The theoretical benefits of concomitant iron deficiency and sickle cell anemia remain to be proven in a controlled clinical trial.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell volume regulation in hemoglobin CC and AA erythrocytes

Swelling hemoglobin CC erythrocytes stimulates a ouabain-insensitive K flux that restores original cell volume. This volume regulatory pathway was characterized for its anion dependence, sensitivity to loop diuretics, and requirement for Na. The swelling-induced K flux was eliminated if intracellular chloride was replaced by nitrate and both swelling-activated K influx and efflux were partially inhibited by 1 mM furosemide or bumetanide. K influx in swollen hemoglobin CC cells was not diminished when Na in the incubation medium was replaced with choline, indicating Na independence of the swelling-induced flux. Identical experiments with hemoglobin AA cells also demonstrated a swelling-induced increase in K flux, but the magnitude and duration of this increase were considerably less than that seen with hemoglobin CC cells. The increased K flux in hemoglobin AA cells was likewise sensitive to anion replacement and to loop diuretics and did not require the presence of Na. These data indicate that a volume-activated K pathway with similar transport characteristics exists in both hemoglobin CC and AA red cells.

Nuclear magnetic resonance measurement of cytosolic free calcium levels in human red blood cells

Red blood cells were loaded with 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (FBAPTA) by incubation with 50 microM of the acetoxymethyl ester (FBAPTA-AM), and cytosolic free Ca2+ was monitored with 19F-nuclear magnetic resonance (NMR). Loading with 50 microM FBAPTA-AM, which results in a final FBAPTA level of approximately 0.5 mM, caused only a 25-30% fall in cell ATP as measured by 31P-NMR when 5 mM pyruvate was present. Leakage of the NMR active Ca2+ indicator, which results from cell lysis, was corrected for with the addition of extracellular Eu3+ ions, extracellular ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA), or washing. With this method, we have found basal levels of cytosolic free Ca2+ averaging 61 +/- 6 nM (means +/- SE, n = 19). When the intracellular level of FBAPTA was varied from 0.1 to 1.0 mM, there was no correlation between the level of cytosolic free Ca2+ and the level of loading with FBAPTA. Addition of 10 microM of the Ca2+ ionophore A23187 with extracellular Ca2+ set at different levels by Ca2+-EGTA buffers caused an increase in cytosolic free Ca2+ as expected. Furthermore, ATP depletion caused a two- to three-fold increase in cytosolic free Ca2+, consistent with inhibition of Ca2+ efflux via that Ca2+-ATPase.

A single-dose pharmacokinetic study of the antisickling agent cetiedil

Cetiedil citrate is an antisickling agent shown to be effective in reducing the severity and duration of acute sickle cell crisis. With the use of a sensitive GC/MS assay, the pharmacokinetic profile of cetiedil was studied in normal men and in men with sickle cell anemia who were not in crisis at the time of study. A peak cetiedil concentration of 70 to 200 ng/ml was found immediately after a 30-minute drug infusion. The plasma level then gradually declined to approximately 10 ng/ml during a 3-hour distributive phase. Computer analysis of the data was most consistent with a three-compartment model. No pharmacokinetic differences were found between the normal men and the subjects with sickle cell. Because the cetiedil plasma levels achieved during this in vivo study are well below concentrations that exhibit antisickling activity in vitro, additional clinical studies will be necessary before an optimal dosing regimen can be established.

Hereditary spherocytosis. Recent experience and current concepts of pathophysiology

Hereditary spherocytosis is a clinically heterogeneous, genetically determined red blood cell membrane disorder resulting in hemolytic anemia. A deficiency of spectrin, the largest and most abundant structural protein of the erythrocyte membrane skeleton, results in the formation of spherocytes which lack the strength, durability, and flexibility to withstand the stresses of the circulation. Clinical manifestations of the disease are primarily dependent on the severity of hemolysis, which additionally results in an increased incidence of pigment gallstones. The likelihood of cholelithiasis is directly related to patient age and is uncommon before 10 years of age. Splenectomy is indicated in virtually every patient. When the disease is diagnosed in early childhood, the risk of overwhelming postsplenectomy sepsis makes it advisable to delay splenectomy until after 6 years of age if possible. At the time of splenectomy, it is important to identify and remove any accessory spleens. If gallstones are present, cholecystectomy should be performed. Although spherocytosis persists following splenectomy, hemolysis is alleviated and clinical cure of the anemia is achieved for most patients. Patients with recessively inherited spherocytosis are exceptions. Although they are significantly benefited by splenectomy, their anemia is not completely corrected. Splenectomy reduces hemolysis in all patients and thereby decreases the risk for development of pigment gallstones. Excision of an enlarged spleen removes the danger of traumatic rupture.

Cholelithiasis in sickle cell anemia: surgical considerations

Gallstones are frequently found in patients with sickle cell anemia. The differentiation between acute calculous biliary tract disease and sickle cell crisis can be difficult and should be based on the clinical presentation, comparison with previous episodes of abdominal pain, and judicious use of hepatobiliary radionuclide scanning. Emergency cholecystectomy is associated with a high morbidity and should be avoided if possible. Elective cholecystectomy is associated with a lower but still significant risk of complications. We believe patients with sickle cell anemia and symptomatic cholelithiasis should have elective cholecystectomy. Careful management is essential to minimize the danger of postoperative complications.

Passive sodium and potassium movements in sickle erythrocytes

Deoxygenation causes an increase in passive Na and K movements across the membrane of the sickle erythrocyte. Some investigators find that these ion movements are accompanied by cell dehydration, while others find no evidence for cell water loss with sickling. Because gelation of hemoglobin S would be enhanced by cell water loss, we reinvestigated Na and K movements in sickle cells to define further the role that ion movements might play in the pathogenesis of sickling. With deoxygenation, we found that sickle cells gained Na and lost K without losing cell water. These net ion movements were not seen in control red blood cells. For sickle cells, deoxygenation also increased passive unidirectional influxes of Na and K, effects not observed when control red blood cells were deoxygenated. The deoxygenation-induced passive influxes of Na and K in sickle cells were not diminished by anion substitution or by the addition of the diuretic furosemide. We also found differences in passive Na and K fluxes between oxygenated sickle cells and normal red blood cells. The addition of furosemide or replacement of Cl with NO3 or SCN, maneuvers that largely reduced passive Na and K movements in oxygenated normal cells, had no effect on Na and K movements in oxygenated sickle cells. These findings militate against the idea that solute and water loss occur as a consequence of deoxygenation but do indicate that there are acquired membrane abnormalities in sickle red blood cells.

An analysis of the mechanism by which cetiedil inhibits the Gardos phenomenon

Energy depletion in the human erythrocyte causes a rise in intracellular calcium. This in turn accelerates the transmembrane movement of potassium and chloride, resulting in cell dehydration. This process, known as the Gardos phenomenon, is inhibited by cetiedil. The present study examines the mechanism by which cetiedil inhibits the Gardos phenomenon. The ability of cetiedil to retard the initial step in the Gardos phenomenon, a rise in intracellular calcium, was first tested. Cetiedil did not prevent calcium accumulation. Cetiedil's ability to inhibit anion movement was next evaluated, as cetiedil could appear to be blocking K movement when in fact it was preventing the movement of its accompanying anion. No inhibitory effect on anion movement was seen. Since cetiedil prevented neither calcium accumulation nor anion movement, it must inhibit the Gardos phenomenon by preventing the opening of the K-specific gate in the erythrocyte membrane. The fact that cetiedil's effect on the Gardos phenomenon could not be removed with repeated cell washing indicates that this effect is irreversible.

A further characterization of the selective K movements observed in human red blood cells following acetylphenylhydrazine exposure

Following brief exposure to acetylphenylhydrazine, the potassium permeability of the human erythrocyte membrane is selectively augmented. While a similar increase in potassium permeability results from the intracellular accumulation of calcium (the Gardos phenomenon), we have found a number of features that allow these two pathways to be distinguished from one another. The acetylphenylhydrazine pathway does not require calcium for its activation, and can be seen even in the presence of a molar excess of the calcium chelator EGTA. The transmembrane potassium movement via this channel has a specific requirement for the anion chloride, and it can be inhibited by furosemide. The potassium that moves through the Gardos pathway, on the other hand, can be accompanied by any permeant anion, and is inhibitable by quinidine or cetiedil. Thus, acetylphenylhydrazine exposure seems to promote K + Cl cotransport, whereas the Gardos pathway represents a potassium conductive channel. While full demonstration of both these pathways requires harsh in vitro manipulation, the large electrochemical potassium gradient favoring the movement of this cation out from the erythrocyte suggests that even a partial activation of either pathway could cause intracellular dehydration and thus contribute importantly to the pathophysiology of in vivo red cell destruction.

Cetiedil inhibition of calmodulin-stimulated enzyme activity

Cetiedil, an in vitro anti-sickling agent, inhibited calmodulin-stimulated cyclic 3':5'-nucleotide phosphodiesterase (EC 3.1.4.17) and Ca2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3) activities. The drug had no effect on basal enzyme activities in the absence of calmodulin. The inhibition of phosphodiesterase was competitive with respect to the concentrations of both cAMP and calmodulin. Cetiedil did not inhibit calmodulin-stimulated enzyme activities by acting as a calcium chelator, since increasing the concentration of calcium did not reverse the inhibitory effect.

Polyarteritis nodosa in hairy cell leukemia

A patient with polyarteritis nodosa (PAN) developing after splenectomy and previously diagnosed hairy cell leukemia is presented. This rare association may provide an insight into the nature of PAN.

The effect of cell hydration on the deformability of normal and sickle erythrocytes

The deformability of the erythrocyte (RBC) is greatly influenced by its state of hydration. The purpose of this investigation is to quantitate this relationship by measuring the deformability of an RBC population over a broad range of cell water content. By manipulation of the ion content of the RBC, we performed all of the experiments in media which were isotonic with plasma. To raise ion and water content, RBC were incubated in a Li2CO3 medium. To lower cell ion and water content, RBC were exposed to the K ionophore, valinomycin. The range of cell water content achieved during the entire experiment was 900-3200 g/kg cell solid (normal in vivo cell water content being 1800-1950 g/kg cell solid). By using the Ektacytometer, an automated cylindrical viscometer, we were able to measure deformability of the RBC sampled at various points along this range of cell water content. We found that optimal rheologic behavior was exhibited by normal RBC when their water content was in the normal range. A rise or a fall in cell hydration resulted in a decrease in cell deformability. By contrast, the deformability of freshly drawn, well-oxygenated sickle RBC was well below that found for normal RBC. Upon volume expansion, however, the deformability of these sickle RBC improved markedly. This observation suggests that sickle RBC are suboptimally hydrated and that their abnormal rheology is at least in part a consequence of cell dehydration.

Pulmonary hypertension and cor pulmonale in the sickle hemoglobinopathies

Although pulmonary hypertension is frequently mentioned as a complication of the sicklemic state, careful review of the medical literature revealed only a single subject in whom cardiac catheterization data substantiated this diagnosis. In two additional patients, both clinical and autopsy findings of pulmonary vascular disease and cor pulmonale were described, although no hemodynamic studies had been performed. We have therefore detailed the clinical history, cardiac catheterization results, and autopsy findings in three previously undescribed patients. These three patients, along with the three case reports culled from the medical literature, from the substance of this review. Pulmonary hypertension should be suspected in patients with sickle hemoglobinopathy in whom either fixed dyspnea or unexplained syncope develops. Early in the course of the disease, right heart catheterization remains the only way to establish the diagnosis with certainty. Noninvasive studies such as chest x-ray, electrocardiography, and echocardiography tend to be nondiagnostic until late in the course of right ventricular failure. Although specific therapy has yet to be defined, the ominous prognosis of this complication of sickle hemoglobinopathy supports the application of experimental modalities such as continuous oxygen therapy, partial exchange transfusion, or even limited phlebotomy.

A molecular defect in two families with hemolytic poikilocytic anemia: reduction of high affinity membrane binding sites for ankyrin

Patients from two families with chronic hemolytic anemia have been studied. The erythrocytes are very fragile and appear microcytic with a great variety of shapes. Clinical evaluation failed to identify traditionally recognized causes of hemolysis. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed no significant abnormality of the major polypeptide bands. Erythrocytes spectrin-ankyrin and ankyrin-membrane interactions were analyzed with 125I-labeled spectrin, 125I-labeled ankyrin, and inside-out vesicles. Patients' vesicles bound 125I-spectrin normally. Likewise, patients' spectrin and ankyrin competed normally for the binding sites on control membranes. None of the individual components appeared to have abnormal thermal sensitivity. Ankyrin-stripped, inside-out vesicles prepared from the patients bound less 125I-ankyrin than did vesicles prepared from normals (P less than 0.05 for all corresponding points in the high-affinity region). Scatchard analysis showed the most significant abnormality to be a 50% reduction in the high affinity ankyrin binding sites. Similar experiments were performed with blood from patients with spherocytosis and splenectomized controls, but no abnormalities were detected. The water soluble 43,000-dalton fragments of band 3 (the high-affinity ankyrin binding sites) were prepared from one of the patients and competed normally for 125I-ankyrin binding in solution. This suggests that the primary structural defect is a reduction in the number of high affinity membrane binding sites for ankyrin, and is consistent with an abnormal organization of band 3 in the membrane.

Effect of cetiedil, an in vitro antisickling agent, on erythrocyte membrane cation permeability

Cetiedil has been reported to relieve painful crises in sickle cell anemia and to have antisickling properties in vitro. The drug alters neither oxygen affinity nor the solubility of deoxyhemoglobin S. Because the viscosity of the erythrocyte interior and the kinetics of gelation are dependent on the concentration of hemoglobin, we postulated that cetiedil might inhibit sickling by modifying erythrocyte sodium or potassium movements in a manner that would increase cell water content and thus dilute the cell hemoglobin. The drug has two such effects: it inhibits the specific increase in potassium permeability that follows a rise in cytoplasmic calcium concentration and it causes a rise in passive sodium movements. These effects are further evidence that cell ion and water movements may be important in the process of sickling and suggest a mechanism for the results reported with cetiedil.