Erythrocyte dehydration in pathophysiology and treatment of sickle cell disease

A prominent feature of sickle cell disease is the presence of cells with markedly increased sickle cell hemoglobin concentration, as a consequence of the loss of potassium, chloride, and water from the erythrocyte. Because of the extreme dependency of the kinetic of polymerization on sickle cell hemoglobin concentration, these dehydrated erythrocytes have an increased tendency to polymerize and sickle. Thus blockade of the loss of potassium from the erythrocyte should prevent the increase in sickle cell hemoglobin concentration and reduce sickling. The availability of this potential therapeutic option is based on a detailed knowledge of the mechanisms leading to cell dehydration. Two ion transport pathways, the K-Cl cotransport and the Ca(2+)-activated K+ channel, play a prominent role in the dehydration of sickle erythrocytes. Possible therapeutic strategies include inhibition of K-Cl cotransport by increasing erythrocyte Mg2+ content and inhibition of the Ca(2+)-activated K channel by oral administration of clotrimazole.     

Methylisocyanate as an antisickling agent and its reaction with hemoglobin S

Reviewing the reaction of potassium cyanate, an antisickling agent, with alpha-amino groups of hemoglobin, it was found that the reaction was a slow process and requires a large excess of the reagent. The reason for the slow reaction rate of carbamylation of hemoglobin by cyanate is that cyanate itself does not react with hemoglobin. It is rather isocyanic acid, the reactive species, that reacts with hemoglobin. Since the pK of isocyanic acid is 3.8, only one out of 4,000 cyanate ions is present as isocyanic acid at physiological pH. Therefore, it appears that a large excess of cyanate ions is required to achieve the carbamylation of hemoglobin S, both in vivo and in vitro. Furthermore, the pH optimum for carbamylation of carboxyhemoglobin and deoxyhemoglobin is 5.5 and, at pH 7.4, the reaction velocity drops to one-third for carboxyhemoglobin and one-half for deoxyhemoglobin. To seek an approach to reduce the dosage of cyanate and to increase the reaction velocity, an isocyanate derivative, methylisocyanate which is already in the reactive form, was tested for its antisickling activity and its reaction with hemoglobin S. It was found that methylisocyanate had antisickling activity and that only a stoichiometric amount to 2-fold excess of the reagent over hemoglobin S alpha-amino groups was required to prevent the sickling of erythrocytes. Methylisocyanate-treated sickle erythrocytes showed an increased oxygen affinity compared to untreated methylisocyanate reacted with alpha-amino groups of hemoglobin S and the reaction was complete in less than 1 min. Methylcarbamylated hemoglobin S had a higher minimum gelling concentration than the untreated hemoglobin S. There was no detectable reaction of free sulfhydryl and epsilon-amino groups of hemoglobin S with methylisocyanate. These results indicate that methylisocyanate, and probably other isocyanate derivatives, possesses powerful antisickling activity.     

Effect of cholecystokinin-pancreozymin (CCK-PZ) on glycoprotein secretion from mouse gallbladder epithelium: an ultrastructural and cytochemical study

L-Azetidine-2-carboxylic acid, the naturally occurring lower homologue of L-proline, is incorporated into hemoglobin S (sickle hemoglobin) in vitro. Sickle erythrocytes from patients with sickle cell anemia incubated with L-[3H] azetidine-2-carboxylate synthesized radiolabeled hemoglobin which when isolated from cell lysates, co-chromatographed with hemoglobin S on DEAE-cellulose columns. The alpha/beta ratio of azetidine carboxylate incorporation into the globin chains of sickle hemoglobin was 0.94, which is consistent with the presence of four proline residues in each polypeptide chain. Incorporation of azetidine carboxylate into hot trichloroacetic acid-insoluble material in sickle erythrocytes indicated that the homologue was present in the polypeptide backbone of the globin chains of sickle hemoglobin. Amino acid analysis of the hot trichloroacetic acid-insoluble material from sickle erythrocytes which had been incubated with radiolabeled azetidine carboxylate indicated that 75% of the radioactivity could be accounted for as intact homologue while 20% of the radioactivity co-chromatographed with alanine. These results suggest that azetidine carboxylate is incorporated unaltered into hemoglobin S in addition to being metabolized to alanine in sickle erythrocytes prior to incorporation into protein. The kinetics of thermal precipitation of hemoglobin S (oxygen ligand) into which radioactive azetidine carboxylate or radioactive proline had been incorporated in vitro is identical. This observation, together with the behavior of hemoglobin S and the globin chains from hemoglobin S containing azetidine carboxylate during ion-exchange chromatography, indicates that homologue replacement of prolyl residues does not significantly alter the overall charge or stability of the hemoglobin S tetramer. Azetidine carboxylate did not inhibit uptake of radiolabeled proline by sickle erythrocytes suggesting that the homologue does not adversely affect amino acid transport in these cells.     

Septic arthritis and Reiter's syndrome in sickle cell disorders: case reports and implications for management

Two patients with sickle cell disorders developed gram-negative septic arthritis and responded poorly to conventional managment. Unfavorable factors included (1) confusion with the nonseptic arthropathy of a sickle crisis; (2) impaired articular perfusion, perhaps related to local sickling; (3) conversion of an infecting organism to an L-form in the presence of cell-wall inhibitors; and (4) interference with cultures and antibacterial titrations of synovial fluid caused by intro-articular administration of antibiotics. Prolonged treatment with very high doses of antibiotics was required to eradicate infection in both patients. Because sickling and local hypoxia apparently interfere with defenses against infection, anemia should be corrected by transfusion. One patient had had Reiter's syndrome; the dysenteric form of this disease may be a cause of arthritis in some sicklemic patients.     

Isolation and partial characterization of elastase from dog granulocytes

Hemoglobin Hope (beta(H14)136gly leads to asp), a mildly unstable variant, was found to have decreased oxygen affinity, a normal Bohr effect and diminished cooperativity. Decreased oxygen affinity of hemoglobin Hope may explain the previous failure to find an appropriate response to hemolysis in individuals studied who were heterozygous for both hemoglobin Hope and sickle hemoglobin. Salt bridge formation between NA1 valine and H14 aspartic acid may stabilize the beta Hope subunit in its deoxy form thus producing intrinsically low oxygen affinity and reduced cooperativity.     

Immunohistochemical localization of hepatic nitric oxide synthase in normal and transgenic sickle cell mice: the effect of hypoxia

Nitric oxide (NO) generated from L-arginine and molecular oxygen by nitric oxide synthase (NOS) has been shown to influence hepatocellular function and pathology in response to ischemia and certain hepatotoxins. In the present study, we examined the liver of a transgenic line of sickle cell mice for hepatocellular injury and localization of two isoforms of NOS, the endothelial constitutively expressed isoform (EcNOS) and the inducible isoform (iNOS) by immunohistochemistry. Diffuse expression of EcNOS was observed in hepatocytes of control and sickle cell animals maintained under room air conditions. In contrast, iNOS was observed only in the sickle cell mice, well-localized to hepatocytes surrounding the central veins of the lobules. When normal mice were exposed to hypoxic conditions for 4 to 5 days, iNOS immunostaining appeared de novo in a patchy distribution throughout the liver lobules. In the sickle cell mice, hypoxia appeared to increase the subjective intensity of pericentral staining of iNOS. Liver histology was normal in the sickle cell mice maintained under room air conditions, but showed multifocal areas of necrosis when sickling was exacerbated by chronic hypoxic conditions. However, a pericentral zone of preserved architecture was present, corresponding to the region of iNOS staining. We postulate that pericentral induction of iNOS under ambient conditions occurs in transgenic sickle cell mice in response to particularly intense hypoxic conditions near the central veins of the liver. Increases in NO synthesis may occur in this region, which would serve to protect these cells from ischemic damage either directly or by maintaining blood flow. These findings could be relevant to liver pathophysiology in patients with sickle cell disease.     

Carbonyl reductase activity exhibited by pig testicular 20 beta-hydroxysteroid dehydrogenase

The carbonyl reductase activity exhibited by pig testicular 20 beta-hydroxysteroid dehydrogenase (20 beta-HSD) was examined using a recombinant enzyme. Kinetic parameters were obtained for 48 carbonyl group-containing substrates, including aromatic aldehydes, aromatic ketones, cycloketones, quinones, aliphatic aldehydes and aliphatic ketones. 20 beta-HSD showed a high affinity towards quinones, such as 9,10-phenanthrenequinone, alpha-naphthoquinone and menadione (Km values of 4, 2 and 5 microM, respectively), and the substrate utilization efficiency (Vmax/Km) of the enzyme against these quinones was very high. Cyclohexanone and 2-methylcyclohexanone were also reduced with a high Vmax/Km value, but not cyclopentanone or 2-methylcyclopentanone. Various aromatic aldehydes and ketones including benzaldehyde- and acetophenone-derivatives were reduced by 20 beta-HSD. Especially, 4-nitrobenzaldehyde and 4-nitroacetophenone were reduced with high Vmax/Km values in the related compounds. The enzyme also reduced the pyridine-derivatives, 2-, 3-, and 4-benzoylpyridine, with the Vmax/Km value for 2-benzoylpyridine being the highest. 20 beta-HSD reduced aliphatic aldehydes and aliphatic ketones, but was more effective on the former. The correlation between the structure of carbonyl compounds and their substrate Vmax/Km is discussed.     

Chlorophyll a fluorescence: a tool for the investigation of toxic effects in the photosynthetic apparatus

The effects of environmental pollutants, such as triazines, urea herbicides, phenols, nitro aromatic compounds, aldehydes, hydrogen sulfide, volatile halogenated aliphatic and aromatic compounds, and alkylbenzenes, the photosynthesis of green algae were investigated by using detailed analysis of chlorophyll a fluorescence. Application of quenching analysis by means of a pulse amplitude-modulated fluorometer allows the discrimination of different modes of action. Blocks of the electron-transport chain, the action of uncouplers, and fluorescence quenching by nitroaormatic compounds could be distinguished. Hydrogen sulfide and short-chain aldehydes seem to react in the same way, probably by reaction with components of the electron-transport chain. Nonreactive volatile compounds affect chlorophyll fluorescence in a strictly hydrophobicity-dependent manner. The quenching analysis suggests an inhibition of utilization of proton-motive force for ATP synthesis. Detailed analysis of fluorescence patterns may be of great help for identification of toxic pollutants and their sources.     

Mg-dependent ecto-ATPase activity in Leishmania tropica

Variation in the level of fetal hemoglobin (HbF) accounts for much of the clinical heterogeneity observed in patients with sickle cell disease (SCD). The HbF level has emerged as an important prognostic factor in both sickle cell pain and mortality, and a % HbF of 10-20% has been suggested as a threshold level for diminished clinical severity. The number of erythrocytes that contain HbF (termed F cells) may also be critically important, as F cells resist intravascular sickling and have preferential in vivo survival. Since F cells can be enumerated with high accuracy using flow cytometry methods, we prospectively studied a cohort of 242 children with SCD. Children with HbS and hereditary persistence of fetal hemoglobin (S/HPFH) had essentially 100% F cells. In contrast, children with homozygous sickle cell anemia (HbSS), HbS/beta0 thalassemia, or HbS/beta+ thalassemia had significantly lower mean % F cell values (55.9, 61.6, and 51.3%, respectively; P < 0.001), and children with HbSC had even fewer F cells (27.0%; P < 0.001). There was a highly significant correlation between the % F cells and the log (% HbF), which was observed for the total population of children (r = 0.95, P < 0.001), as well as for each of the individual subgroups of children with HbSS (r = 0.94, P < 0.001), HbSC (r = 0.89, P < 0.001), or HbS/beta0 thalassemia and HbS/beta+ thalassemia (r = 0.95, P <0.001). This logarithmic correlation between % F cells and % HbF has not been previously described and has important implications for the pharmacologic manipulation of HbF in patients with SCD.     

Radionuclide (MUGA) studies of left ventricular functional abnormalities in asymptomatic patients with sickle cell anemia

Radionuclide ventriculography was performed on 10 normal subjects and 39 patients with sickle cell anemia (10 homozygous and 29 heterozygous sicklers) at rest and after exercise. Their left ventricular (LV) function was assessed in both these situations. The results were then compared within the subgroups. The reduction in ejection fraction (EF) response (47.5 +/- 7 at rest and 46.4 +/- 8 at exercise in homozygous patients, and 52.4 +/- 8 at rest and 54.3 +/- 8 at exercise in heterozygous patients) was significant in both the homozygous and the heterozygous groups but more so in the former group. The diastolic filling was also significantly impaired in the homozygous group (PER 2.64 +/- 0.74, PFR 2.13 +/- 0.42 and PFR/HR 0.014 +/- 0.001). The study statistically demonstrates, that LV filling patterns are altered in the sickle cell patients, even in the absence of clinical symptoms relating to LV dysfunction. This fact may prove to be a marker of sickle cell heart disease. Frequent and significant sickling is probably the cause of more pronounced LV functional abnormalities in homozygous sicklers.     

Significance of elevated hemoglobulin A1c for the pathogenesis of diabetic retinopathy

The hemoglobin of 70 diabetics with retinopathy was analysed. 56 patients had pathologically elevated values, 12 values were within the upper normal limit and in 2 cases the findings were normal. This hemoglobin variant is characterized by an increased affinity of oxygen. Clinically and pathologically speaking the elevated HbA1c value could be a causal factor in diabetic retinopathy. Comparisons with sickle cell anemia and thalassemia seem to indicate that hemoglobinopathy and retinopathy are pathogenetically related.     

Transthoracic forequarter amputation and left pneumonectomy

As survival improves in patients with sickle cell anemia, the prospects of performing cardiac surgical procedures on older patients with this genetic defect increase. We describe the successful management of a 52-year-old patient with sickle cell disease (homozygous for hemoglobin S) and a history of multiple sickle crisis undergoing cardiopulmonary bypass for mitral valve repair. Preoperative partial exchange transfusion followed by total exchange transfusion at the time of operation was performed to reduce the level of hemoglobin S to 5.4% during bypass. Other management strategies included high-flow normothermic bypass with aortic crossclamping, topical hypothermia, and cold crystalloid cardioplegia.     

Assessing the validity of serodiagnostic test results

Abnormal adhesion of sickle cells to vascular endothelium may be a factor in the initiation of painful vaso-occlusive crisis. The sickle cell population contains an unusually large number of less dense reticulocytes that are known to be more adhesive than mature red cells, but there is contradictory evidence regarding the adhesiveness of dense sickle cells. We used a flow-based assay of adhesion to cultured human umbilical vein endothelial cells to test the properties of density fractions of sickle cells, prepared either by density gradient or by centrifugation of packed cells. We also examined the effects of incubating sickle cells with or without cyclical deoxygenation on their adhesion. After fractionation on a Percoll-isopaque gradient, the less dense 10% (reticulocyte-rich) cells and the most dense 10% cells adhered in greater number than the remainder (by about twofold). However, after centrifugation of packed cells, the less dense 10% were again more adhesive than the "middle" cells, but the most dense were not. Exposing sickle cells to constituents of the gradient had no consistent effect on adhesion, while centrifugal packing induced a degree of hemolysis, and tended to reduce adhesiveness of the dense fraction previously obtained from a gradient. Incubation in air at 37 degrees C for 15 hr reduced the number of reticulocytes and the adhesiveness of less dense sickle cells compared to those held at 4 degrees C. On the other hand, incubation at 37 degrees C for 15 hr with cyclical deoxygenation caused formation of dense cells and increased adhesiveness compared to incubation without cyclical deoxygenation. We conclude that young, less dense sickle cells are unusually adhesive, but that this adhesiveness is reduced during maturation. However, repeated sickling in vivo causes formation of an abnormally dense subpopulation of cells which either redevelop an increased tendency to adhere to endothelial cells or preserve their initial adhesiveness. Both adhesive cell populations may be implicated in promoting vascular obstruction.     

Reversible splenic hypofunction in hypertransfused children with homozygous sickle cell disease

Functional hyposplenism, as documented by technetium 99 metastable sulfur colloid spleen scan and increased pocked erythrocyte count (also known as a pit count), is well described in children under 2 years of age with homozygous sickle cell anemia. We evaluated the clinical course and splenic function of 16 patients with sickle cell anemia (ages 3 to 20 years) on a hypertransfusion program for more than 6 months following a cerebrovascular accident. Patients were followed with simultaneous spleen scan and pitted erythrocyte count using direct interference contrast microscopy. Pit counts were taken prior to each transfusion and hemoglobin S level maintained at less than 20%. With the exception of two patients, splenic function was recovered only in those patients who were younger than 10 years of age at the time transfusion was initiated. There were no serious bacterial infections or other complications of sickle cell anemia documented in the hypertransfused group. Based on our results and the literature review, we conclude that some patients with sickle cell anemia receiving intensive hypertransfusion therapy for a cerebrovascular accident recover a normal splenic phagocytic function. Age and level at which the hemoglobin S is maintained are important factors in reestablishing splenic phagocytic function.     

Sickle cell anemia

Sickle cell disease is a hereditary chronic hemolytic anaemia mostly found in negroes. The blood of these patients contains hemoglobin S. Absence of oxygen determines the sickling to the red blood cells. In the heterozygous state clinical manifestations usually are absent. The homozygous form shows different symptoms. The progressive course with hemolytic, aplastic or thrombotic crises mostly ends in an early death in infancy or childhood. Treatment is largely palliative. Transfusions, treatment of the crises and general measures play the most essential role.     

Oxygen-dependent circulation of sickle erythrocytes

The effects of in vivo hyperoxia and hypoxia on the intravascular survival of 51Cr-labeled human sickle erythrocytes (SS RBS's) were studied after transfusion into rats and guinea pigs. The function of these animals' reticuloendothelial and complement systems had been previously inhibited by ethyl palmitate and cobra venom factor, thus allowing extension of the survival of the heterologous human RBC's. In the blood of rats breathing ambient air the 51Cr half-life survival of RBC's from 11 patients with sickle-cell anemia (mean, 7.1 hours; range, 2.0 to 16.5 hours) was significantly shorter (p less than 0.001) than that of five control subjects (mean, 17.5 hours; range, 12.0 to 26.5 hours). When rats transfused with sickle RBC's were exposed to 100 per cent O2, a mean increment of 16.5 per cent blood 51Cr activity was observed within the first 15 to 60 minutes of hyperoxia. Subsequent oxygen deprivation (7 to 8 per cent O2) resulted in an equally rapid decrease (mean, 35.6 per cent) in blood 51Cr activity. Continuation of hypoxia for up to 17 hours did not cause further acceleration of 51Cr activity. Continuation of hypoxia for up to 17 hours did not cause further acceleration of 51 Cr RBC clearance. Under these conditions the slope of the sickle RBC survival curve was similar to that in animals kept in ambient air. After hypoxic rats were allowed to breate room air again, mean 51Cr blood activity increased by 41.7 per cent. Sickle RBC's transfused to guinea pigs exhibited similar oxygen-dependent survival characteristics. The survival of 51Cr RBC's from four adult control subjects and of unlabeled fetal RBC's from three human cord blood samples was unaffected by oxygen changes. When rats that had been transfused with sickle reticulocytes labeled in vitro with 59Fe were made hypoxic, a decrease in blood 59Fe activity was observed. The extent of this decrease was comparable to that in rats transfused with 51Cr labeled RBC's from the same patients. There was increased liver and spleen 51Cr activity in animals transfused with 51Cr SS RBC's and killed during hypoxia when compared to that of hyperoxic animals. These studies suggest that a minor population of sickle cells is removed from circulation during hypoxia and circulates again upon reoxygenation of the animals. Erythrocyte aging does not appear to be responsible for this phenomenon. The oxygen-depdendent circulation of a population of SS RBC's in this animal system is probably due to reversible sickling and trapping of sickled cells in the microcirculation.     

Oxygen tension modulates beta-globin switching in embryoid bodies

Little is known about the factors influencing the hemoglobin switch in vertebrates during development. Inasmuch as the mammalian conceptus is exposed to changing oxygen tensions in utero, we examined the effect of different oxygen concentrations on beta-globin switching. We used an in vitro model of mouse embryogenesis based on the differentiation of blastocyst-derived embryonic stem cells to embryoid bodies (EBs). Cultivation of EBs at increasing oxygen concentrations (starting at 1% O2) did not influence the temporal expression pattern of embryonic (betaH1) globin compared to the normoxic controls (20% O2). In contrast, when compared to normoxically grown EBs, expression of fetal/adult (betamaj) globin in EBs cultured at varying oxygen concentrations was delayed by about 2 days and persisted throughout differentiation. Quantitation of hemoglobin in EBs using a 2,7-diaminofluorene-based colorimetric assay revealed the appearence of hemoglobin in two waves, an early and a late one. This observation was verified by spectrophotometric analysis of hemoglobin within single EBs. These two waves might reflect the switch of erythropoiesis from yolk sac to fetal liver. Reduced oxygenation is known to activate the hypoxia-inducible factor-1 (HIF-1), which in turn specifically induces expression of a variety of genes among them erythropoietin (EPO). Although EBs increased EPO expression upon hypoxic exposure, the altered beta-globin appearance was not related to EPO levels as determined in EBs overexpressing EPO. Since mRNA from both mouse HIF-1alpha isoforms was detected in all EBs tested at different differentiation stages, we propose that HIF-1 modulates beta-globin expression during development.     

Morphological evaluation of intercellular junctions in the ovary of chick embryos: action of steroid and gonadotropic hormones in vitro

Synthesis and physico-chemical properties of nine 3-(4-fluoro or chlorobenzyl)-5-arylidène-imidazolidine-2,4-diones, four 3-(4-fluoro or bromobenzyl)-5-arylidène-thiazolidine-2,4-diones and three 3-)4-bromophénacyl)-5-arylidène-thiazolidine-2,4- diones has been described. These compounds were synthesized by aldolisation-crotonisation reaction from aromatic aldehydes and 3-substituted imidazolidine-2,4-diones or thiazolidine-2,4-diones. In vitro cytotoxic activity was determined for compounds 8, 17, 18, 21 and 22.     

Effect of 2, 3-diphosphoglycerate on the solubility of deoxy-sickle hemoglobin

We have examined the effect of 2, 3-diphosphoglycerate (DPG) on the solubility of deoxy-sickle hemoglobin (deoxy-Hb S) under conditions such that concentration, pH, and osmolarity of deoxy-Hb S solutions approached physiological. The range of DPG/Hb molar ratios encompassed the extremes found for this ratio in erythrocytes from individuals with sickle cell anemia. After monomer-polyer equilibrium had been established, the phases were separated by centrifugation and assayed for concentrations of Hb and DPG. DPG had no effect on the solubility of deoxy-Hb S. Furthermore, at DPG/Hb molar ratios less than one, there was no preferential incorporation of deoxy-Hb S containing bound DPG into polymers. At DPG/Hb molar ratios greater than one, concentrations of free DPG in monomer and polymer phases were virtually identical. Thus, under the specified equilibrium conditions, DPG is not a determining factor in the polymerization of deoxy-Hb S.