Sickling rates of human AS red cells infected in vitro with Plasmodium falciparum malaria.

The kinetics of sickling of malaria-infected red cells from humans with sickle cell trait were studied in vitro in an attempt to obtain direct experimental evidence for a selective advantage of the hemoglobin S heterozygote in a malarious region. The sickling rates of cells infected with Plasmodium falciparum and of non-infected cells were studied both in the total absence of oxygen (by dithionite addition) and at several different concentrations of oxyhemoglobin which might obtain in vivo. In all cases, red cells containing small plasmodium parasite forms (ring forms) sickled approximately eight times as readily as uninfected cells. Cells containing large parasitic forms (trophozoites and schizonts) appeared to sickle less readily than uninfected cells, by light microscopy criteria, but electron micrographs demonstrated the presence of polymerized deoxyhemoglobin S with a high frequency. It is concluded that enhanced sickling of plasmodium-infected AS cells may be one mechanism whereby the hemoglobin S polymorphism is balanced in favor of the heterozygote.

Correction of sickle cell disease in transgenic mouse models by gene therapy.

Sickle cell disease (SCD) is caused by a single point mutation in the human betaA globin gene that results in the formation of an abnormal hemoglobin [HbS (alpha2betaS2)]. We designed a betaA globin gene variant that prevents HbS polymerization and introduced it into a lentiviral vector we optimized for transfer to hematopoietic stem cells and gene expression in the adult red blood cell lineage. Long-term expression (up to 10 months) was achieved, without preselection, in all transplanted mice with erythroid-specific accumulation of the antisickling protein in up to 52% of total hemoglobin and 99% of circulating red blood cells. In two mouse SCD models, Berkeley and SAD, inhibition of red blood cell dehydration and sickling was achieved with correction of hematological parameters, splenomegaly, and prevention of the characteristic urine concentration defect.

Ligand kinetics in hemoglobin Hiroshima.

Hemoglobin Hiroshima is an electrophoretically fast-moving variant with a fourfold increase in oxygen affinity and a decreased Bohr effect. Based on a decreased rate of dissociation of O(2) in the presence of dithionite and an increased rate of binding of CO by the deoxy form, we have concluded that the kinetic basis of the high affinity exhibited by Hb Hiroshima is the concurrence of a faster combination rate and a slower dissociation rate for ligands.

Erythrocytes in sickle cell anemia are heterogeneous in their rheological and hemodynamic characteristics.

To understand the contribution to the pathophysiology of sickle cell anemia of the different erythrocyte density types present in the blood of these patients, we have studied the viscosimetric and hemodynamic characteristics of four major classes of hemoglobin SS erythrocytes. We have isolated reticulocytes, discocytes, dense discocytes, and irreversibly sickled cells (fractions I-IV) on Percoll-Renografin density gradients. Bulk viscosity was studied in a coneplate viscosimeter and the hemodynamic studies were performed on the isolated, artificially perfused mesoappendix vasculature of the rat (Baez preparation). Bulk viscosity measurements at shear rates of 230 S-1 demonstrate that when the cells are oxygenated, fraction I (reticulocyte rich) has a higher viscosity than expected from its low intracellular hemoglobin concentration. The rest of the fractions exhibit moderate increases in bulk viscosity pari-passu with the corresponding increases in density (mean corpuscular hemoglobin concentration). When deoxygenated, all cell fractions nearly doubled their bulk viscosity and the deoxy-oxy differences remained constant. The Baez preparation renders a different picture: oxygenated fractions behave as predicted by the viscosimetric data, but, when deoxygenated, cell fractions exhibit dramatically increased peripheral resistance and the deoxy-oxy difference are directly proportional to cell density, thus, the largest increases were observed for fractions III and IV. The differences between the rheological and the hemodynamic measurements are most probably due to the different sensitivity of the two methods to the extent of intracellular polymerization. These results also demonstrate that the hitherto unrecognized fraction III cells (very dense discocytes that change shape very little on deoxygenation) are as detrimental to the microcirculation as the irreversibly sickled cell-rich fraction IV. They may, however, induce obstruction by a different mechanism. As the extent to which these fractions are populated by erythrocytes varies considerably from patient to patient, the distribution function of cell densities in each sickle cell anemia patient might have consequences for the type of pathophysiological events occurring in their microcirculation.

A gene conversion located 5' to the A gamma gene in linkage disequilibrium with the Bantu haplotype in sickle cell anemia.

Cloning and sequencing of the gamma-globin gene of a sickle cell anemia patient homozygous for the Bantu haplotype has revealed a gene conversion that involves the replacement of an A gamma sequence by a G gamma sequence in the promoter area of the A gamma gene. This event is similar to another gene conversion believed to be responsible for the very high homology between gamma-globin genes, suggesting that the promoter area of these genes is prone to this type of genetic rearrangement. Further analysis demonstrated that the chromosome bearing this gene conversion has a very high frequency among Bantu chromosomes and a very low or nil frequency in other haplotypes linked to the beta s gene. No correlation was found between the G gamma/A gamma ratio and the presence of the gene conversion among Bantu haplotype patients, thus excluding a portion of the gamma gene sequence in the determination of this ratio.

In vivo demonstration of red cell-endothelial interaction, sickling and altered microvascular response to oxygen in the sickle transgenic mouse.

Intravascular sickling, red cell-endothelium interaction, and altered microvascular responses have been suggested to contribute to the pathophysiology of human sickle cell disease, but have never been demonstrated under in vivo flow. To address this issue, we have examined a transgenic mouse line, alphaHbetaSbetaS-Antilles [betaMDD] which has a combined high (78%) expression of beta S and beta S-Antilles globins. In vivo microcirculatory studies using the cremaster muscle preparation showed adhesion of red cells, restricted to postcapillary venules, in transgenic mice but not in control mice. Electron microscopy revealed distinct contacts between the red cell membrane and the endothelium surface. Some red cells exhibiting sickling were regularly observed in the venular flow. Infusion of transgenic mouse red cells into the ex vivo mesocecum vasculature also showed adhesion of mouse red cells exclusively in venules. Under resting conditions (pO2, 15-20 mmHg), there were no differences in the cremaster microvascular diameters of control and transgenic mice; however, transgenic mice showed a drastic reduction in microvascular red cell velocities (Vrbc) with maximal Vrbc decrease (> 60%) occurring in venules, the sites of red cell adhesion and sickling. Local, transient hyperoxia (pO2, 150 mmHg) resulted in striking differences between control and transgenic mice. In controls, oxygen caused a 69% arteriolar constriction, accompanied by 75% reduction in Vrbc. In contrast, in transgenic mice, hyperoxia resulted in only 8% decrease in the arteriolar diameter and in 68% increase in VrBC; the latter is probably due to an improved flow behavior of red cells as a consequence of unsickling. In summary, the high expression of human sickle hemoglobin in the mouse results not only in intravascular sickling but also red cell-endothelium interaction. The altered microvascular response to oxygen could be secondary to blood rheological changes, although possible intrinsic differences in the endothelial cell/vascular smooth muscle function in the transgenic mouse may also contribute. These sickle transgenic mice could serve as a useful model to investigate vasoocclusive mechanisms, as well as to test potential therapies.

Magnetic resonance evidence of hypoxia in a homozygous alpha-knockout of a transgenic mouse model for sickle cell disease.

All transgenic mouse models for sickle cell disease express residual levels of mouse globins which complicate the interpretation of experimental results. We now report on a mouse expressing high levels of human betaS and 100% human alpha-globin. These mice were created by breeding the alpha-knockout and the mouse beta(major)-deletion to homozygosity in mice expressing human alpha- and betaS-transgenes. These betaS-alpha-knockout mice have accelerated red cell destruction, altered hematological indices, ongoing organ damage, and pathology under ambient conditions which are comparable with those found in alphaH betaS-Ant[betaMDD] mice without introduction of additional mutations which convert betaS into a "super-betaS" such as the doubly mutated betaS-Antilles. This is of particular importance for testing strategies for gene therapy of sickle cell disease. Spin echo magnetic resonance imaging at room air and 100% oxygen demonstrated the presence of blood hypoxia (high levels of deoxygenated hemoglobin) in the liver and kidneys that was absent in control mice. We demonstrate here that transgenic mice can be useful to test new noninvasive diagnostic procedures, since the magnetic resonance imaging technique described here potentially can be applied to patients with sickle cell disease.

Some aspects of the pathophysiology of homozygous Hb CC erythrocytes.

We have studied erythrocytes from homozygous CC patients in vitro and in perfused rat mesoappendix vasculature to answer some long-standing questions. By examination of wet whole blood preparations, and by comparing the cell distribution on isopycnic continuous density gradients of whole blood samples from a splenectomized CC patient with those from three intact CC patients, we have demonstrated the presence of a distinct crystal-containing band of cells that is present in the former, but totally absent from the latter. We conclude that Hb CC cells containing crystals circulate in Hb CC individuals, but in intact patients they are effectively removed by the spleen. By use of 31P nuclear magnetic resonance and viscosity measurements on cells, we have demonstrated that intracellular aggregation of hemoglobin C occurs on deoxygenation even when no crystal formation is detectable by morphological methods. These two observations are in apparent contradiction with the absence of clinical microcirculatory impairment found in both intact and splenectomized CC patients. The contradiction was resolved by rheological studies on isolated rat mesoappendix preparations and erythrocyte diameter measurements that lead to the conclusion that the hemorheological properties of CC cells in the microcirculation are nearly normal because their increased viscosity is offset by their smaller diameter and size.

SC erythrocytes have an abnormally high intracellular hemoglobin concentration. Pathophysiological consequences.

We have examined 20 SC patients on Percoll-Stractan continuous density gradients and find that they have an elevated mean corpuscular hemoglobin concentration (MCHC). Reduction of the MCHC to normal values results in amelioration of four physiologically important blood abnormalities: decreased oxygen affinity, viscosity of deoxygenated erythrocyte suspensions, rate of sickling, and deoxygenation induced K+ efflux. These observations suggest that the rehydration of SC cells to normal values should be considered a potential approach in the therapeutic manipulation of this disease.

Sickle gene. Its origin and diffusion from West Africa.

Linked DNA polymorphisms can be used to study the evolution of structural gene mutations. Both the beta S-(beta 6Glu leads to Val) and beta C-(beta 6Glu leads to Lys) genes are common in West Africa. We have analyzed their linkage to a polymorphic Hpa 1 site appearing 3' to the beta-globin gene locus in selected populations from Wes Africa. A large reservoir of beta A-genes linked to 13-kilobase Hpa 1 fragments with a frequency of 17-18% has been identified. In addition, the beta S- and beta C-genes in Togo are found to be tightly linked to the 13-kilobase Hpa 1 fragment, whereas 72% of the beta S-genes in the Ivory Coast reside on the 7.6-kilobase Hpa 1 fragment. These studies are consistent with the selection and expansion of two different chromosomes bearing beta S-genes in at least two physically close, but ethnically separate regions of West Africa, with subsequent diffusion to North, Equatorial, and East Africa.

Impairment of the growth of Plasmodium falciparum in HbEE erythrocytes.

HbE is a beta-chain mutant frequently found among inhabitants of Southeast Asia and surrounding territories. We find that Plasmodium falciparum multiplies more slowly in erythrocytes from individuals homozygous for HbE than in cells from HbA individuals. In contrast, this parasite grows normally in erythrocytes heterozygous for HbE. This is the first direct evidence that suggests what has been suspected on the basis of circumstantial data, that HbE-containing erythrocytes might be advantageous to the carrier in regions with endemic malaria.

High levels of human gamma-globin gene expression in adult mice carrying a transgene of deletion-type hereditary persistence of fetal hemoglobin.

Persistent expression of the gamma-globin genes in adults with deletion types of hereditary persistence of fetal hemoglobin (HPFH) is thought to be mediated by enhancer-like effects of DNA sequences at the 3' breakpoints of the deletions. A transgenic mouse model of deletion-type HPFH was generated by using a DNA fragment containing both human gamma-globin genes and HPFH-2 breakpoint DNA sequences linked to the core sequences of the locus control region (LCR) of the human beta-globin gene cluster. Analysis of gamma-globin expression in six HPFH transgenic lines demonstrated persistence of gamma-globin mRNA and peptides in erythrocytes of adult HPFH transgenic mice. Analysis of the hemoglobin phenotype of adult HPFH transgenic animals by isoelectric focusing showed the presence of hybrid mouse alpha2-human gamma2 tetramers as well as human gamma4 homotetramers (hemoglobin Bart's). In contrast, correct developmental regulation of the gamma-globin genes with essentially absent gamma-globin gene expression in adult erythroid cells was observed in two control non-HPFH transgenic lines, consistent with autonomous silencing of normal human gamma-globin expression in adult transgenic mice. Interestingly, marked preferential overexpression of the LCR-distal (A)gamma-globin gene but not of the LCR-proximal (G)gamma-globin gene was observed at all developmental stages in erythroid cells of HPFH-2 transgenic mice. These findings were also associated with the formation of a DNase I-hypersensitive site in the HPFH-2 breakpoint DNA of transgenic murine erythroid cells, as occurs in normal human erythroid cells in vivo. These results indicate that breakpoint DNA sequences in deletion-type HPFH-2 can modify the developmentally regulated expression of the gamma-globin genes.

On the mechanism for the red-cell accumulation of mefloquine, an antimalarial drug.

The accumulation of the antimalarial drug mefloquine by human red blood cells has been studied by 19F-NMR spectroscopy. The uptake process was nonlinearly dependent on the external drug concentration. Concentrations inside cells as high as 60-times greater than those in the extracellular phosphate-buffered-saline were observed. Red-cell ghosts were also found to accumulate mefloquine with high-affinity binding sites for the drug. Hemoglobin was found to bind mefloquine with low affinity, but due to the high concentration of this protein it is a significant drug compartment in the red cell. Analysis of the 19F-NMR chemical shifts and linewidths of mefloquine in the presence of red cells, red-cells ghosts and hemoglobin indicates restricted mobility of the drug in the membrane-bound state and slow exchange with the extracellular medium. This is a significant characteristic of the reaction in connection with the prophylactic activity of the drug. Exchange of the drug between hemoglobin and the red-cell membrane, however, is fast and may play an important role in the bioavailability of the drug to the parasite.

Surface activity of hemoglobin S and other human hemoglobin variants.

The kinetics of surface pressure change (deltapi vs. t isotherms) were determined for several single point mutations of the human hemoglobin system. It was observed that hemoglobin S and hemoglobin CHarlem (both containing beta6 Glu leads to Val substitutions) have a specific behavior at the water-air interface: their extent of surface pressure change is larger than for hemoglobin A, hemoglobin C and hemoglobin Korle Bu (beta73 Asp leads to Asn). In addition, hemoglobin S seems to occupy a larger area per molecule than hemoglobin A. The conformational requirements for this property, in addition to the beta6 Val substitution, appear to be the liganded state of the betas chain in the tetramer. Electrostatic, hydrogen bonding and hydrophobic interactions are involved in determining the surface activity of a hemoglobin molecule. The differences between the surface activity of oxyhemoglobin S and oxyhemoglobin A could be the basis for their differences in mechanical precipitability, although other factors may play a role.

Kinetics of HB S gelation. Effect of alkylureas, ionic strength and other hemoglobins.

Using a light scattering (turbidity) method to estimate the delay time of gelation of deoxy hemoglobin S hemolysates, we have examined the effects of various alkylureas, variations in ionic strength by addition of NaCl, and admixture with other hemoglobins on gelation kinetics. Each of these factors substantially prolonged the delay times to different extents, but the dependence of the delay times on a high power of the hemoglobin concentration varied only slightly. These findings suggest that the events preceding gelation, most likely the formation of nuclei, are affected by these factors, but the critical nuclear size for gelling is fairly constant. Parallel changes indicated good qualitative correlation between gelation, delay times, minimum gelling concentrations of solutions of mixed hemoglobins and kinetics of sickling of red cells containing these mixtures, with the exception of hemoglobin Charlem trait cells the sickling kinetics of which were slower than predicted by the solution properties.

The binding of hemoglobin to membranes of normal and sickle erythrocytes.

The binding of hemoglobins A, S, and A2 to red cell membranes prepared by hypotonic lysis from normal blood and blood from persons with sickle cell anemia was quantified under a variety of conditions using hemoglobin labelled by alkylation with 14C-labelled Nitrogen Mustard. Membrane morphology was examined by electron microscopy. Normal membranes were found capable of binding native hemoglobin A and hemoglobin S in similar amounts when incubated at low hemoglobin: membrane ratios, but at high ratios hemoglobin saturation levels of the membranes increased progressively for hemoglobin A, hemoglobin S and hemoglobin A2, respectively, in order of increasing electropositivity. Binding was unaffected by variations in temperature (4-22 degrees C) and altered little by the presence of sulfhydryl reagents, but was inhibited at pH levels above 7.35; disrupted at high ionic strength; and dependent on the ionic composition of the media. These findings suggest that electrostatic, but not hydrophobic or sulfhydryl bonds are important in membrane binding of the hemoglobin under the conditions studied. An increased retention of hemoglobin in preparations of membranes from red cells of patients with sickle cell anemia (homozygote S) was attributable to the dense fraction of homozygote S red cells rich in irreversibly sickled cells, and the latter membranes had a smaller residual binding capacity for new hemoglobin. This suggests that in homozygote S cells which have become irreversibly sickled cells in vivo, there are membrane changes which involve alteration and/or blockade of hemoglobin binding sites. These findings support the notion that hemoglobin participates in the dynamic structure of the red cell membrane in a manner which differs in normal and pathological states.

Oxidation of spectrin and deformability defects in diabetic erythrocytes.

We reasoned that de novo oxidative damage, as a result of increased protein glycosylation, could participate in the mechanisms whereby diabetic erythrocytes acquire membrane abnormalities. To examine this hypothesis, the extent of erythrocyte membrane protein glycosylation and the oxidative status of spectrin, the major component of the erythrocyte membrane skeleton, were examined. Labeling erythrocyte membranes with [3H]borohydride, which labels glucose residues bound to proteins, revealed that several proteins were heavily glycosylated compared with nondiabetic erythrocyte membranes. In particular, the proteins beta-spectrin, ankyrin, and protein 4.2 were the most glycosylated. Although sodium dodecyl sulfate-polyacrylamide gel electrophoresis of diabetic erythrocyte membranes did not reveal any quantitative or qualitative abnormalities in spectrin or other membrane proteins, examination of spectrin oxidative status by amino acid analysis and with cis-dichlorodiammineplatinum(II) (cDDP), a chemical probe specific for protein methionine and cysteine residues, demonstrated that the diabetic spectrin was oxidatively damaged: spectrin from diabetic subjects contained 35% less methionine (P less than 0.002), 15% less histidine (P less than 0.006), and a twofold increase in cysteic acid (P less than 0.001) compared with normal spectrin. Diabetic spectrin bound 32% less cDDP than normal spectrin (P less than 0.001); the lowest cDDP binding was observed with spectrin from insulin-dependent diabetic subjects. The extent of cDDP binding to diabetic spectrin correlated moderately and inversely with glycosylated hemoglobin (GHb) levels (n = 12, r = -0.727). Erythrocyte deformability, measured by ektacytometry, was decreased between 5 and 23% of control measurements (average of approximately 10%) in 21 of 32 diabetic subjects surveyed.(ABSTRACT TRUNCATED AT 250 WORDS)

Interspecies hybrid HbS: complete neutralization of Val6(beta)-dependent polymerization of human beta-chain by pig alpha-chains.

Interspecies hybrid HbS (alpha(2)(P)beta(2)(S)), has been assembled in vitro from pig alpha-globin and human beta(S)-chain. The alpha(2)(P)beta(2)(S) retains normal tetrameric structure (alpha(2)beta(2)) of human Hb and an O(2) affinity comparable to that of HbS in 50 mM Hepes buffer; but, its O(2) affinity is slightly higher than that of HbS in the presence of allosteric effectors (chloride, DPG and phosphate). The (1)H-NMR spectroscopy detected distinct differences between the heme environments and alpha(1)beta(1) interfaces of pig Hb and HbS, while their alpha(1)beta(2) interfaces appear very similar. The interspecies hybrid alpha(2)(H)beta(2)(P) resembles pig Hb; the pig beta-chain dictated the conformation of the heme environment of the human alpha-subunit, and to the alpha(1)beta(1) interfaces of the hybrid. In the alpha(2)(P)beta(2)(S) hybrid, beta(S)-chain dictated the conformation of human heme environment to the pig alpha-chain in the hybrid; but the conformation of alpha(1)beta(1) interface of this hybrid is close to, but not identical to that of HbS. On the other hand, the alpha(1)beta(2) interface conformation is identical to that of HbS. More important, the alpha(2)(P)beta(2)(S) does not polymerize when deoxygenated; pig alpha-chain completely neutralizes the beta(S)-chain dependent polymerization. The polymerization inhibitory propensity of pig alpha-chain is higher when it is present in the cis alpha(P)beta(S) dimer relative to that in a trans alpha(P)beta(A) dimer. The semisynthetically generated chimeric pig-human and human-pig alpha-chains by exchanging the alpha(1-30) segments of human and pig alpha-chains have established that the sequence differences of pig alpha(31-141) segment can also completely neutralize the polymerization. Comparison of the electrostatic potential energy landscape of the alpha-chain surfaces of HbS and alpha(2)(P)beta(2)(S) suggests that the differences in electrostatic potential energy surfaces on the alpha-chain of alpha(2)(P)beta(2)(S) relative to that in HbS, particularly the ones involving CD region, E-helix and EF-corner of pig alpha-chain are responsible for the polymerization neutralization activity. The pig and human-pig chimeric alpha-chains can serve as blueprints for the design of a new generation of variants of alpha-chain(s) suitable for the gene therapy of sickle cell disease.

Roles of alpha 114 and beta 87 amino acid residues in the polymerization of hemoglobin S: implications for gene therapy.

Three novel recombinant mutants of sickle hemoglobin (Hb S, beta 6Glu-->Val) have been constructed to assess the role of proline at alpha 114 and threonine at beta 87 in the polymerization of deoxygenated Hb S. Using the hemoglobin expression system (pHE2) designed in our laboratory, four plasmids were expressed separately in Escherichia coli to produce the four recombinant hemoglobins: r Hb S (beta 6Glu-->Val); r Hb S-Chiapas (beta 6Glu-->Val, alpha 114Pro-->Arg); r Hb S-D-Ibadan (beta 6Glu-->Val, beta 87Thr-->Lys); and r Hb S-Chiapas-D-Ibadan (beta 6Glu-->Val, alpha 114Pro-->Arg, beta 87Thr-->Lys). The structural features of these four recombinant hemoglobins were analyzed by proton nuclear magnetic resonance spectroscopy, and were found to be similar to those of human normal adult hemoglobin (Hb A) under identical conditions. The recombinant hemoglobins were further investigated by measuring the oxygen-binding properties, which were found to be comparable to those of Hb A. Delay-time gelation studies of the three mutants of r Hb S were carried out in 1.8 M potassium phosphate (pH 7.34) by a temperature jump from 4 degrees C to 30 degrees C and an increase in delay time over that of r Hb S was observed, as well as an overall decrease in the polymerization of these three mutants of Hb S. A more detailed and quantitative investigation has also been carried out to determine the equilibrium solubility (Csat) in 0.1 M potassium phosphate (pH 7.35) at 25 degrees C of the three Hb S mutants as well as of mixtures of these mutants with Hb S versus mixtures of fetal hemoglobin (Hb F) and Hb A with Hb S. The inhibition of polymerization demonstrated in these experiments suggests that the interactions involving the two amino acid residues alpha 114Pro and beta 87Thr are very important to the formation of Hb S polymer, and modification of these amino acids results in an anti-sickling potential. Of particular interest is the inhibitory effect of alpha 114Pro-->Arg, which offers a novel opportunity to use an alpha-chain construct, in addition to a beta-chain construct in the same vector, in gene therapy for sickle cell anemia, with the objective of modifying a larger number of hemoglobin tetramers at a given level of expression.

Circulating BFU-E in sickle cell anemia: relationship to percent fetal hemoglobin and BPA-like activity.

Circulating 14-day erythroid progenitors (BFU-E) from sickle cell anemia (SS) patients were studied in culture to determine their frequency and their sensitivity to erythropoietin (Epo). Increased numbers of circulating BFU-E were found in half of the patients studied, whereas the remainder had a normal count. Patients with high circulating BFU-E counts had lower fetal hemoglobin (HbF) percentages (congruent to 4.5%) than patients with low circulating BFU-E counts (HbF congruent to 13%). This difference was highly significant (p less than 0.0001). In addition, SS circulating BFU-E expressed increased sensitivity to Epo due, at least partially, to an increased production of burst-promoting activity-like factor(s) generated by light-density mononuclear cells. These findings emphasize the possible role of the HbF level (and the extent of sickling) in BFU-E regulation under the continuous hemopoietic stress of SS disease.