Gelation Of Hemoglobin Research Articles

Interactions of unstable hemoglobin Rush with thalassemia and hemoglobin E result in thalassemia intermedia

ABSTRACTBackground: The clinical consequences and significance of many unstable hemoglobins interacting with other hemoglobinopathies remain unrecognized. Here we first explore molecular and hematological characterizations of previously undescribed compound heterozygosity states for unstable hemoglobin Rush (Hb Rush, Beta 101 Glu > Gln, HBB:c.304G > C) with Hb E and different forms of thalassemia.Methods: Hematological assays, globin gene mutation assays and β-globin gene cluster haplotype were conducted in 11 patients from 8 unrelated Chinese ethnic families with unexplained hemoglobin separation fraction in hemoglobin gel electrophoresis.Results: Hb Rush in various combinations with Hb E, β0-thalassemias and α+-thalassemia were identified. Hb Rush simple heterozygote was generally associated with mild hemolytic anemia, and the compound heterozygotes of Hb Rush and the other β-globin variants led to thalassemia intermedia phenotypes with moderate anemia. Hemoglobin electrophoreses showed that the co-presence of Hb Rush with either Hb E or β0-thalassemias increased proportion of Hb Rush due to relative decrease of other globin chain synthesis. Beta-globin gene cluster haplotype analysis suggested a common origin of the Hb Rush variant in the Chinese families of different ethnic ancestry.Conclusions: Unstable Hb Rush interacting with β-thalassemia result in thalassemia intermedia phenotypes, which demonstrated the clinical significance of Hb Rush and new insights into complex mechanism of clinical heterogeneity of thalassemia.

Description of criteria for near miss in high-complexity obstetric population with sickle cell anemia: an observational study

Introduction: Sickle cell disease (SCD) is one of the most common monogenic diseases worldwide, affecting approximately 30 million people across the globe. It is one of the most common hemoglobinopathies affecting pregnancy, particularly in the black population. Pregnant women with SCD, in conjunction with the physiological changes of pregnancy, have an increased risk of developing severe maternal and fetal complications.Materials and methods: A descriptive, observational study was conducted retrospectively to determine the maternal and neonatal disease burden of pregnant women with SCD between 2011 and 2016. The study included pregnant patients with SCD admitted to the hospital, with confirmed diagnosis through hemoglobin electrophoresis. Patients having no confirmatory testing of the disease were excluded.Results: In all, 54% (34 patients) had no previous diagnosis of sickle cell anemia or presence of sickle cell trait, and so an in-hospital diagnosis was carried out through hemoglobin gel electrophoresis, whereas the remaining 46% (28 patients) had already a peripheral diagnosis. In total, the following profiles were obtained: Hb AS 62.9% (39 patients), Hb SC 17.7% (11 patients), Hb SS 16.1% (10 patients), Hb AC 3.2% (2 patients), and Hb CC 0% (0 patients). Vaso-occlusive pain crises constituted the most common cause of hospital admission antepartum (54.8% of the general population), occurring in 100% of the patients with Hb SS and Hb AC, in 45% of the Hb SC group and in 43% of those with the Hb AS trait. The second cause of hospital admission encompassed infectious processes, which affected 45% of the general population, 30% of the Hb AS group, 60% of the Hb SS group, 77% of the Hb SC group, and 100% of the Hb AC group. The method of termination of pregnancy of 44% (27 patients) was C-section. The most common perinatal complication was preterm birth, occurring in 26% (16 patients), with the highest incidence in the Hb AC group. The second most common complication was the intrauterine growth restriction, reported in 6% (4 patients) of all patients, being most frequently in the Hb SS group.Conclusion: Pregnant women having SCD should be assessed and managed by a multidisciplinary team composed of hematology, perinatology, and intensive care. Management should be conducted preferably in high-quality centers experienced in treating this entity, thereby decreasing the great impact of morbidity and mortality associated with SCD in the pregnant population.

The Physical Foundation of Vaso-Occlusion in Sickle Cell Disease

The pathology of sickle cell disease arises from the occlusion of small blood vessels because of polymerization of the sickle hemoglobin within the red cells. We present measurements using a novel microfluidic method to determine the pressure required to eject individual red cells from a capillary-sized channel after the cell has sickled. We find that the maximum pressure is only around 100 Pa, much smaller than typically found in the microcirculation. This explains why experiments using animal models have not observed occlusion beginning in capillaries. The magnitude of the pressure and its dependence on intracellular concentration are both well described as consequences of sickle hemoglobin polymerization acting as a Brownian ratchet. Given the recently-determined stiffness of sickle hemoglobin gels (Zakharov, Aprelev, Turner & Ferrone, Biophys J, 99:1149-1156, 2010), the observed obstruction seen in sickle cell disease as mediated by adherent cells can now be rationalized, and surprisingly suggests a window of maximum vulnerability to occlusion during the circulation of sickle cells.

The Physical Foundation of Vasoocclusion in Sickle Cell Disease

The pathology of sickle cell disease arises from the occlusion of small blood vessels because of polymerization of the sickle hemoglobin within the red cells. We present measurements using a microfluidic method we have developed to determine the pressure required to eject individual red cells from a capillary-sized channel after the cell has sickled. We find that the maximum pressure is only ∼100 Pa, much smaller than typically found in the microcirculation. This explains why experiments using animal models have not observed occlusion beginning in capillaries. The magnitude of the pressure and its dependence on intracellular concentration are both well described as consequences of sickle hemoglobin polymerization acting as a Brownian ratchet. Given the recently determined stiffness of sickle hemoglobin gels, the observed obstruction seen in sickle cell disease as mediated by adherent cells can now be rationalized, and surprisingly suggests a window of maximum vulnerability during circulation of sickle cells.

Bone-Marrow Derived Cells Can Reconstitute GCLM Function in the Sickle Lung

Abstract 4836Sickle cell disease (SCD) is a chronic hemolytic and inflammatory disorder characterized by repeated episodes of vaso-occlusion and hemolysis, resulting in oxidative stress and endothelial dysfunction. We have recently demonstrated that the heme scavenging capacity in SCD is severely impaired, highlighting the danger posed by excess heme in this disorder. Paradoxically, heme induces expression of several cyto-protective enzymes including the modifier subunit of glutamate cysteine ligase (GCLM), the rate-limiting enzyme in glutathione (GSH) synthesis, which is a crucial antioxidant in the lung. While the induction of cytoprotective enzymes is thought to attenuate the deleterious effects of heme in SCD the somatic origin of this protection has not previously been defined. Using transgenic mouse models we show for the first time that the level of GCLM in the sickle lung is markedly up-regulated due primarily to enhanced expression of the enzyme in the epithelium and blood mononuclear cells, but not in the endothelium. Based on these findings, we tested the hypothesis that leukocyte-derived GCLM was sufficient to protect the sickle lung from oxidative stress. Thus, bone marrow chimeric SCD mice with GCLM deficiency were generated by transplanting bone marrow from Berkeley SCD transgenic mice into GCLM null mice recipients. We confirmed that the chimeric GCLM-null-SCD mice had a SCD phenotype as determined by >95% engraftment of donor white blood cells, reticulocyte counts, urine osmolality and hemoglobin gel electrophoresis. Whole lung GCLM and total GSH levels in the chimeric mice were identical to the levels in the wild-type SCD mice. Moreover, lung function, as determined by oxygen saturation and breath rate, were identical in the two mouse strains. These results show that loss of GCLM expression in resident lung cells does not compromise production of GSH or the function of the lung in SCD. Disclosures:Ofori-Acquah:Emory University: Patents & Royalties.

ChemInform Abstract: N-1 and C-2 Substituted Tryptophans as Potential Inhibitors of Sickle Cell Hemoglobin Gelation.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Microrheology of Sickle Hemoglobin Gels

Sickle cell disease is a rheological disease, yet no quantitative rheological data exist on microscopic samples at physiological concentrations. We have developed a novel method for measuring the microrheology of sickle hemoglobin gels, based on magnetically driven compression of 5- to 8-μm-thick emulsions containing hemoglobin droplets ∼80 μm in diameter. Using our method, by observing the expansion of the droplet area as the emulsion is compressed, we were able to resolve changes in thickness of a few nanometers with temporal resolution of milliseconds. Gels were formed at various initial concentrations and temperatures and with different internal domain structure. All behaved as Hookean springs with Young's modulus from 300 to 1500 kPa for gels with polymerized hemoglobin concentration from 6 g/dl to 12 g/dl. For uniform, multidomain gels, Young's modulus mainly depended on the terminal concentration of the gel rather than the conditions of formation. A simple model reproduced the quadratic dependence of the Young's modulus on the concentration of polymerized hemoglobin. Partially desaturated samples also displayed quadratic concentration dependence but with a smaller proportionality coefficient, as did samples that were desaturated in steps; such samples were significantly less rigid than gels formed all at once. The magnitude of the Young's modulus provides quantitative support for the dominant models of sickle pathophysiology.

Miccrorheology of Sickle Hemoglobin Gels

Sickle cell disease is a rheological disease, yet no quantitative rheological data exists on microscopic samples. We have developed a novel method for probing the microrheology of sickle hemoglobin gels, based on magnetically driven compression of 5-8 μm thick emulsions containing hemoglobin droplets of ∼100 μm diameter. By observing the expansion of the droplet area as the emulsion is compressed, our method can resolve changes in thickness of a few nm with temporal resolution of ms. Carbon monoxide bound to sickle hemoglobin was dissociated by laser illumination allowing the resulting deoxyhemoglobin to form gels in target droplets. The amount of polymer formed was determined by observing, in the target droplet, the residual concentration in a small region that was unilluminated by the laser. Thickness was monitored by observing a non-photolyzed reporter droplet adjacent to the target droplet.Gels were formed at different initial concentrations, temperatures and fractional saturation with CO. In addition, some gels were formed in small spatial regions which then were allowed to grow to the full extent of the target droplet, to contrast with the same sample gelled completely in the target droplet ab initio, thereby creating a different domain structure in the gel. We find that all the gels behave as Hookean springs with linear and repeatable dependence of thickness on force. This allowed us to determine Young's modulus, which ranged from 300 to 1500 kPa for the gels which varied in polymerized hemoglobin concentration from 6 g/dl to 12 g/dl. A highly simplified model for the gel, treating it as a simple lattice with fixed junctions, describes the observed quadratic concentration dependence of Young's modulus data. These measurements provide a quantitative rationale for pathophysiology in the disease.

Interactions between sickle hemoglobin fibers.

We report on observations of "zippering" that occurs when two sickle hemoglobin fibers come together side by side. A transient Y-shaped object is formed which "zips " closed. We have been able to show how the strength of the interactions that drive this may be estimated by studying the frustrated structures sometimes formed between several fibers. Our measurements, when combined with mechanical constants determined by an analysis of bending fluctuations, allow us to make the first estimate of the magnitude of these interactions, of the order of 7kBT microm(-1). Hemoglobin volume fractions of tens of %, lead to significant depletion forces. We estimate the magnitude of both the depletion and Van der Waals forces between pairs of single fibers. We study how these are effected by the helical nature of the fibers and renormalised by bending fluctuations, calculations that could have wider applications beyond sickle hemoglobin fibers. Our theoretical analysis of single fibers is in encouraging, although not fully quantitative, agreement with our measurements. We conclude that the physics and rheology of the hemoglobin gel, as well as the pathology of sickle cell anemia itself, may be influenced by depletion interactions.

High and low oxygen affinity conformations of T state hemoglobin.

To understand the interplay between tertiary and quaternary transitions associated with hemoglobin function and regulation, oxygen binding curves were obtained for hemoglobin A fixed in the T quaternary state by encapsulation in wet porous silica gels. At pH 7.0 and 15 degrees C, the oxygen pressure at half saturation (p50) was measured to be 12.4 +/- 0.2 and 139 +/- 4 torr for hemoglobin gels prepared in the absence and presence of the strong allosteric effectors inositol hexaphosphate and bezafibrate, respectively. Both values are in excellent agreement with those found for the binding of the first oxygen to hemoglobin in solution under similar experimental conditions. The corresponding Hill coefficients of hemoglobin gels were 0.94 +/- 0.02 and 0.93 +/- 0.03, indicating, in the frame of the Monod, Wyman, and Changeux model, that high and low oxygen-affinity tertiary T-state conformations have been isolated in a pure form. The values, slightly lower than unity, reflect the different oxygen affinity of alpha- and beta-hemes. Significantly, hemoglobin encapsulated in the presence of the weak effector phosphate led to gels that show intermediate oxygen affinity and Hill coefficients of 0.7 to 0.8. The heterogeneous oxygen binding results from the presence of a mixture of the high and low oxygen-affinity T states. The Bohr effect was measured for hemoglobin gels containing the pure conformations and found to be more pronounced for the high-affinity T state and almost absent for the low-affinity T state. These findings indicate that the functional properties of the T quaternary state result from the contribution of two distinct, interconverting conformations, characterized by a 10-fold difference in oxygen affinity and a different extent of tertiary Bohr effect. The very small degree of T-state cooperativity observed in solution and in the crystalline state might arise from a ligand-induced perturbation of the distribution between the high- and low-affinity T-state conformations.

The entropically favored osmotic ?compression? of sickle cell hemoglobin gels

Contrary to the accurate, hard-sphere depiction of monomeric hemoglobin in solution, sickle cell hemoglobin (HbS) polymerization/gelation requires attention to molecular interactions. From the temperature dependence of the osmotic compressibility of HbS gels, we were able to extract the entropy increase for concentrating HbS in this phase. Normalized per mole of water removed, the entropy increase from gel compression DeltaS(gel) is four times the previously measured DeltaS(trans), for the transition from monomeric HbS solution to HbS gel. The positive entropy change cannot emerge from the assembly of hard spheres but can indicate remodeling of HbS fibers driven by release of ordered water. The fourfold difference in DeltaS(gel) and DeltaS(trans) suggests that the act of initial fiber/gel formation from monomeric solution differs from the process of further polymerization due to tighter packing within the gel phase.

N-1 and C-2 substituted tryptophans as potential inhibitors of sickle cell hemoglobin gelation

A series of N-1 or C-2 phenylalkyl substituted tryptophans and C-1 phenylalkyl substituted 3,4-dihydro-β-carbolines were prepared from the apropriate aniline, 1b or 1e, or tryptophan, 8 or 11, by ring closure methods. None of the compounds prepared were more potent than 5-bromotryptophan (11) as inhibitors of sickle cell hemoglobin gelation.

Hemoglobin S antigelation agents based on 5-bromotryptophan with potential for sickle cell anemia

5-Bromotryptophan (5-BrTrp) is the most potent amino acid derivative reported in the literature to inhibit the gelation of hemoglobin S (from sickle cell anemia patients). Trp-Trp is also more potent than Trp as an antigelation agent. Therefore, we have prepared a series of dipeptides containing 5-BrTrp and evaluated the antigelation activity. 5-BrTrp-5-BrTrp is the most potent, i.e., 5.9 times the activity of Trp, followed by 5-BrTrp-Trp and then Trp-5-BrTrp. This improved antigelation potency for 5-BrTrp-5-BrTrp and 5-BrTrp-Trp is very significant and will be pursued further as lead compounds with potential for sickle cell anemia.

Solidity of sickle hemoglobin gels: relevance to pathophysiology of sickling disorders.

The physical properties of hemoglobin (Hb) S gels formed under conditions relevant to in vivo conditions have been characterized using viscometry. Mixed Hb SF and Hb AS gels of hemoglobin concentrations and compositions found in patients with Hb S-HPFH (mild sickle-cell disease) and Hb AS (sickle-cell trait) have been compared to those of pure Hb S. The results may explain why red cells containing gels occlude the microcirculation and/or undergo hemolysis in patients with sickle-cell anemia, why patients with Hb S-HPFH are mildly affected with red-cell sickling, and why individuals with Hb AS have no clinical manifestations of the Hb abnormality.

Kinetics of domain formation by sickle hemoglobin polymers

We have monitored the growth of domains of sickle hemoglobin polymers by using temporally and spatially resolved light scattering and birefringence measured pseudosimultaneously on a 50-microns square area. Polymerization was induced and indefinitely maintained by photolysis of the carbonmonoxy derivative using an argon ion laser. Intensity of scattering and birefringence (measured as intensity transmitted through crossed polarizers) were measured using a silicon-intensified target vidicon interfaced to a computer. Polymer concentration, as inferred by light scattering, grew with primarily circular symmetry, with approximately 20% of the signal initially in a twofold symmetric pattern. In time the circular symmetry increased. A distinct decrease in the scattering signal developed which spread outward from the center of the domain. Birefringence lagged the scattering and initially grew in a twofold pattern, with the formation of a characteristic Maltese cross only appearing much later, and well after the scattering signal had peaked. Radial profiles of the domain scattering and birefringence were both approximately gaussian. We successfully modeled the decrease in scattering by fitting the profiles to a large gaussian from which a second smaller gaussian was subtracted. This second gaussian had the width of the birefringence gaussian. The width of the birefringence gaussian grew linearly in time, while the width of the scattering gaussian showed a notable acceleration. We conclude that domains form primarily as disordered arrays which align at later times. We explain the above observations, including the shape of the birefringence progress curves, as the result of an alignment transition which is solely due to a redistribution of monomers from short to long, and from entangled to radial, polymers. We present a theoretical justification for this process in an appendix. In a separate paper (Zhou, H. X., and F. A. Ferrone, manuscript submitted for publication) we show that the gaussian shapes and acceleration of the width naturally arise from a generalization of the double nucleation mechanism for sickle hemoglobin gelation (Ferrone, F. A., J. Hofrichter, H. Sunshine, and W. A. Eaton 1980. Biophys. J. 32:361-377; Ferrone, F. A., J. Hofrichter, and W. A. Eaton. 1985. J. Mol. Biol. 183:611-631).

The effect of anisotropic properties of randomly oriented particles on polarized light: an operational calculus for spatially heterogeneous distributions.

AbstractRecent publication of the application of Mueller–Stokes calculus to a model of optical microdomains by Hjelm et al. [(1986) Biopolymers 25, 1359–1378] states that the CD of randomly orientated microdomains show apparent CD due to the linear dichroism components. In this paper we show that these conclusions are erroneous due to a misapplication of the Mueller calculus to the model proposed by Hjelm et al. We show in detail where the errors were committed, and prove that the ordinary Mueller matrices cannot be used to compute the interaction of light with heterogeneous distributions of optical microdomains that lay in a plane perpendicular to the direction of the irradiation of light. We further prove that ordinary Stokes vectors do not represent the polarization properties of light in systems that are a heterogeneous distribution of optical microdomains in the plane perpendicular to the light beam. A modified optical calculus is proposed, in which extended space matrices and extended space polarization vectors will give the correct formulation for the heterogeneous distribution of microdomains. We prove that, for randomly orientated microdomains in space, the linear dichroism and linear birefringence components cancel, and the only remaining terms are those due to the intrinsic CD and circular birefringence. This result negates the explanation of Hjelm et al. about the induced CD in the Soret region of sickle hemoglobin gels.

Inhibition of the gelation of extracellular and intracellular hemoglobin S by selective acetylation with methyl acetyl phosphate.

Methyl acetyl phosphate binds to the 2,3-diphosphoglycerate (2,3-DPG) binding site of hemoglobin and selectively acetylates three amino groups at or near that site. The subsequent binding of 2,3-DPG is thus impeded. When intact sickle cells are exposed to methyl acetyl phosphate, their abnormally high density under anaerobic conditions is reduced to the density range of oxygenated, nonsickling erythrocytes. This change is probably due to a combination of direct and indirect effects induced by the specific acetylation. The direct effect is on the solubility of deoxyhemoglobin S, which is increased from 17 g/dL for unmodified hemoglobin S to 22 g/dL for acetylated hemoglobin S at pH 6.8. Acetylated hemoglobin S does not gel at pH 7.4, up to a concentration of 32 g/dL. The indirect effect could be due to the decreased binding of 2,3-DPG to deoxyhemoglobin S within the sickle erythrocyte, thus hindering the conversion of oxyhemoglobin S to the gelling form, deoxyhemoglobin S.

Saturation-transfer electron paramagnetic resonance detection of anisotropic motion by sickle hemoglobin molecules in the polymer state

The motional behavior of spin-labeled deoxygenated sickle hemoglobin has been studied by using both 9- and 35-GHz saturation-transfer electron paramagnetic resonance (EPR). Using spectral subtraction techniques and saturation-transfer EPR parameter correlation plots, we find that the saturation-transfer EPR spectra for the sickle hemoglobin gel state at high temperature and high hemoglobin concentration cannot be described as a simple superposition of spectra from immobilized hemoglobin plus solution-state hemoglobin but instead suggest that the individual sickle hemoglobin molecules exhibit limited, anisotropic, rotational oscillation within the polymer fiber. The spectra also imply that the symmetry axis for sickle hemoglobin rotational oscillation is approximately coincident with the nitroxide z axis of the covalently attached spin-label. We suggest that this anisotropic rotational motion may be produced by one or two of the known intermolecular contact sites within the sickle hemoglobin fiber acting as strong intermolecular binding sites, and producing "motional alignment" within the fiber; determining the location of the strong binding site should be important in focusing the future development of antisickling agents.

CD of gels and suspensions: apparent CD in the soret region of sickle hemoglobin gels.

AbstractCD spectra in the soret region of sickle‐cell deoxyhemoglobin (deoxy‐HbS) fiber gels are radically different from the CD of deoxy‐HbS in solution. An explanation is found using the Stokes–Mueller representation of the interaction of a polarized beam with the instrument optical train and sample to derive expressions for the apparent CD of gels and suspensions of optically active molecules that consist of randomly oriented domains or particles that are linearly dichroic and linearly birefringent. These theoretical considerations show that the apparent CD spectra from such systems have contributions from the LD and birefringence of each domain even if no net linear birefringence and dichroism is apparent in the sample. Thus, the interpretation of the CD from gels and suspensions is problematic, unless it can be demonstrated that each domain or particle has extremely small absorbance or that the LD and birefringence of each is a very small fraction of the total absorbance. As a result, we conclude that the spectra of HbS gels are not due to the CD of the heme per se; rather, they also reflect the randomly oriented domain structure of the gels and the LD and linear birefringence associated with each domain.

Effects of red blood cell potassium and hypertonicity on the growth of Plasmodium falciparum in culture.

Malarial parasites reproduce asexually inside the erythrocytes of their vertebrate host. Relatively little is known about the interaction between host cell and parasite metabolism. In the present study the effect of host cell cation composition and osmotic shrinkage on in vitro growth and propagation of Plasmodium falciparum in human erythrocytes was investigated. It is shown that throughout the parasite cell cycle, infected cells lose potassium and gain sodium. Compartment analysis of infected cells revealed that host cell cytosol is poor in potassium and rich in sodium while in the parasite this relationship is reversed, indicating that the parasite is able to regulate its ionic composition independently. Parasites proceeded normally through their cell cycle in the presence of the sodium-pump inhibitor ouabain, although host cells lost up to 75-80% of their normal potassium content. Potassium-depleted erythrocytes harboring trophozoites and schizonts also display normal rates of protein synthesis as measured by isoleucine incorporation. Parasite growth was inhibited when infected cells were osmotically shrunken in hypertonic media, but this was not due to parasite dehydration. It is suggested that increased viscosity of host cell cytosol and/or hemoglobin gelation, are responsible for the effect, probably through interference with parasite feeding. The relevance of these results to understanding of the cellular mechanism involved in the inhibiton of parasite growth in deoxygenated sickle-trait erythrocytes is discussed.