Hemoglobin Syracuse (alpha2beta2-143(H21)His leads to Pro), a new high-affinity variant detected by special electrophoretic methods. Observations on the auto-oxidation of normal and variant hemoglobins

Rare coinheritance of hemoglobin vancleave with severe beta-thalassemia mutation in a patient with secondary erythrocytosis

Hemoglobin (Hb) Vancleave (NM_000518.5:c.431 A > T; dbSNP: rs33918338) is an extremely rare structural hemoglobin variant worldwide, and studies are limited. This report describes the case of a 16-year-old male patient who presented with secondary erythrocytosis. The diagnosis of Hb Vancleave, in combination with codon 41/42 (-TTCT) (NM_000518.5:c.126_129del; dbSNP: rs80356821), was confirmed by direct sequencing. This report highlights the importance of sequencing in the differential diagnosis of beta-thalassemia syndrome in Malaysia.

Syracuse Hemoglobinopathy Presenting With Tophaceous Gout: A Case Report

Background

Hemoglobinopathies are inherited disorders of hemoglobin that alter oxygen binding capacity by affecting the production of a specific subset of globin chains or their entire structure. A lesser-known subtype, Syracuse hemoglobinopathy, was first identified in 4 generations of a family in the 1970s. Gout has been reported in several forms of hemoglobinopathy, such as thalassemia and hemoglobin C disorder.

Case Presentation

A 44-year-old man with a known history of Syracuse hemoglobinopathy, tobacco use disorder, and shoulder osteoarthritis presented with diffuse nodular masses on his joints along with joint pain. His laboratory tests and imaging showed elevated uric acid, urate crystals in his synovial fluid, and bony erosions. These findings were concerning for gout, which was treated with allopurinol, prednisone, and colchicine, resulting in improvement in his symptoms.

Conclusions

Syracuse hemoglobinopathy, a rare disorder of high oxygen affinity hemoglobin, can present itself with findings of elevated serum uric acid and tophaceous gout. Most patients with hyperuricemia never go on to develop gout. However, having a condition that increases serum levels of uric acid should raise an astute clinician's suspicion when a patient presents with a history of hemoglobinopathy and joint pain.

Muscle oxygenation during normoxic and hypoxic cycling exercise in humans with high affinity haemoglobin

NEW FINDINGS

What is the central question of this study? Do humans with high affinity haemoglobin (HAH) demonstrate attenuated skeletal muscle deoxygenation during normoxic and hypoxic exercise? What is the main finding and its importance? Examination of NIRS-derived muscle oxygenation profiles suggests that fractional oxygen extraction is blunted during hypoxic exercise in humans with HAH compared to controls. However, muscle tissue oxygen saturation levels were higher in humans with HAH during exercise in normoxia compared to controls. These alterations in fractional oxygen extraction in humans with HAH may influence blood flow regulation and exercise capacity during hypoxia.

ABSTRACT

Recently, our lab has shown that humans with genetic mutations resulting in high affinity haemoglobin (HAH) demonstrate better maintained aerobic capacity and peak power output during hypoxic exercise versus normoxic exercise compared to humans with normal affinity haemoglobin. However, the influence of HAH on tissue oxygenation within exercising muscle during normoxia and hypoxia is unknown. Therefore, we examined near-infrared spectroscopy (NIRS)-derived oxygenation profiles of the vastus lateralis during graded cycling exercise in normoxia and hypoxia among humans with HAH (n = 5) and controls with normal affinity haemoglobin (n = 12). The HAH group elicited a blunted increase of deoxygenated haemoglobin+myoglobin during hypoxic exercise compared to the control group (P = 0.03), suggesting reduced fractional oxygen extraction in the HAH group. In addition, the HAH group maintained a higher level of muscle tissue oxygen saturation during normoxic exercise (HAH, 75 ± 4% vs. controls, 65 ± 3%, P = 0.049) and there were no differences between groups in muscle tissue oxygen saturation during hypoxic exercise (HAH, 68 ± 3% vs. controls, 68 ± 2%, P = 0.943). Overall, our results suggest that humans with HAH may demonstrate divergent patterns of fractional oxygen extraction during hypoxic exercise and elevated muscle tissue oxygenation during normoxic exercise compared to controls. This article is protected by copyright. All rights reserved.

Hemoglobin: Structure, Function and Allostery

This chapter reviews how allosteric (heterotrophic) effectors and natural mutations impact hemoglobin (Hb) primary physiological function of oxygen binding and transport. First, an introduction about the structure of Hb is provided, including the ensemble of tense and relaxed Hb states and the dynamic equilibrium of Hb multistate. This is followed by a brief review of Hb variants with altered Hb structure and oxygen binding properties. Finally, a review of different endogenous and exogenous allosteric effectors of Hb is presented with particular emphasis on the atomic interactions of synthetic ligands with altered allosteric function of Hb that could potentially be harnessed for the treatment of diseases.

High oxygen affinity hemoglobins

High oxygen affinity hemoglobins are responsible for rare and heterogeneous autosomic dominant genetic diseases. They cause pure erythrocytosis, sometimes accountable for hyperviscosity and thrombosis, or hemolysis. Differential diagnoses must be first ruled out. The diagnosis is based on the identification of a decreased P50, and their possible characterization by cation exchange-high performance liquid chromatography and capillary electrophoresis. Finally, genetic studies of the responsible globin chain gene will confirm the mutation. The prognosis mainly relies on the P50 decrease rate and on the hemoglobin cooperativity impairment. Disease management should be personalized, and it should primarily depend on smoking cessation and physical activity. Phlebotomy and platelet aggregation inhibitors' prescriptions can be discussed. There is no contraindication to flights, high-altitude conditions, or pregnancy. Nevertheless, blood donation must be prohibited.

Symptomatic Erythrocytosis Due to Homozygosity for Hb Luton [HBA2: c.269A>T (or HBA1)] and α-Thalassemia: A Clinical Update

A female proband homozygous for both Hb Luton [α89(FG1)His→Leu (CAC>CTC), HBA2: c.269A>T (or HBA1)], a high oxygen affinity hemoglobin (Hb), and for α(+)-thalassemia (α-thal), (-α(4.2), leftward deletion) was first described in 2012. This is a follow-up report of the same case. At the age of 18, the described patient presented with progressively worsening lethargy, headaches, dizziness, syncope and Raynaud's phenomenon. Following extensive cardiological and neurological investigation, it was felt that significant erythrocytosis was the most likely cause. Venesection followed by regular exchange transfusions were arranged with marked amelioration in symptomatology. In the vast majority of cases of high oxygen affinity Hbs, venesection is not recommended due to the asymptomatic phenotype and reduced oxygen delivery resulting from venesection. This update describes the evolving phenotype of this unique proband and, to the best of our knowledge, the first use of regular, long-term therapeutic red cell exchange transfusions in a case of high affinity Hb.

Structure-function relations of human hemoglobins

In 1949 Pauling and his associates showed that sickle cell hemoglobin (HbS) belonged to an abnormal molecular species. In 1958 Ingram, who used a two-dimensional system of electrophoresis and chromatography to break down the hemoglobin molecule into a mixture of smaller peptides, defined the molecular defect in HbS by showing that it differed from normal adult hemoglobin by only a single peptide. Since then, more than 200 variant and abnormal hemoglobins have been described. Furthermore, the construction of an atomic model of the hemoglobin molecule based on a high-resolution x-ray analysis by Dr. Max Perutz at Cambridge has permitted the study of the stereochemical part played by the amino acid residues, which were replaced, deleted, or added to in each of the hemoglobin variants. Some of the variants have been associated with clinical conditions. The demonstration of a molecular basis for a disease was a significant turning point in medicine. A new engineered hemoglobin derived from crocodile blood, with markedly reduced oxygen affinity and increased oxygen delivery to the tissues, points the way for future advances in medicine.

Haemoglobinopathies with high oxygen affinity. Experience of Erythropathology Cooperative Spanish Group

Haemoglobinopathies are the world's most frequently found monogenic disorders. In the cases with high oxygen affinity, the decrease in the liberation of the oxygen determines a secondary erythrocytosis. In this work, we present 17 unrelated families of Caucasian race and of Spanish origin, with ten variants of haemoglobin or haemoglobinopathies with high oxygen affinity which were diagnosed in our laboratory. Of the ten haemoglobinopathies, in four (the Hb San Diego, the Hb Johnstown, the Hb Malmö and the Hb Columbia-Missouri), the change of amino acid affects zones of the contact alpha(1)beta(2); in two variants (the Hb Strasbourg and the Hb Syracuse), it affects the unions with 2,3-DPG in the central cavity; in the other two (the Hb Badalona and the Hb La Coruña), the cavity of contact with the group haem is affected; in one (Hb Bethesda), it affects the zone of contact alpha(1)beta(1;) and in one (Hb Olympia), the position 20 of the chain in the helix B in the surface of the protein is affected. In all cases, the change of amino acid, though of different form, facilitates that the quaternary structure of the haemoglobin becomes stable in its relaxed configuration so the transfer of oxygen and the P(50) value are decreased. All cases were sent to our laboratory because of shown erythrocytosis. In the majority of them, the diagnosis was done during an analysis of routine or for being relatives of the first ones.

Hb Rancho Mirage [beta 143(H21)His----Asp]; a variant in the 2,3-DPG binding site showing normal oxygen affinity at physiological pH

Hb Rancho Mirage was detected in a 17-year-old male in association with a mild anemia. Hemoglobin electrophoresis revealed the variant had a mobility between Hbs A and J on cellulose acetate (pH 8.6) and a mobility like Hb F on citrate agar (pH 6.4). A substitution of His----Asp was found at position 143 in the beta chain, a residue that contributes to the anionic 2,3-DPG binding site in Hb. This variant exhibited normal oxygen affinity at physiologic pH and reduced affinity at alkaline pH. This suggested a subtle shift in the allosteric equilibrium due most likely to the introduction of a negative charge that stabilized the 2,3-DPG pocket. Both homotrophic (heme-heme) and heterotropic (2,3-DPG and protons) effects were reduced; this might be a consequence of an alteration in the carboxyl terminal region of the beta-subunits. Although a His----Asp substitution would be considered to cause reasonable disruption of the 2,3-DPG and C-terminal conformation of the beta- subunits, the properties of Hb Rancho Mirage suggest that, in fact, there appear to be no major perturbation of the critical C-terminal residues.

Hb Fukutomi [alpha 126(H9)Asp----Val]: a new hemoglobin variant with high oxygen affinity

Hb Fukutomi [alpha 126(H9)Asp----Val], a new hemoglobin variant with a high affinity for oxygen (log P50 = 0.201 at pH 7.0, normal = 1.087) was detected in a Japanese male during a screening survey. The amino acid substitution is located in the alpha 1 beta 1 contact of the tetramic molecule. Like other variants of the high oxygen affinity type Hb Fukutomi showed increased resistance to auto-oxidation. The tryptic peptide alpha T-13, that usually forms part of the trypsin-resistant core of the alpha chain, was cleaved off by trypsin in the new variant and released into the soluble fraction.

Some properties of hemoglobin mobile (alpha 2 beta 2 73 Asp----Val)

A hemoglobin variant was identified as hemoglobin Mobile in which valine replaces the normal aspartic acid at beta 73. Studies of its oxygen equilibria and of its interactions in gelation when mixed with hemoglobin S were carried out. Hemoglobin Mobile had an oxygen affinity lower than that of hemoglobin A, as observed by others. However, in mixtures with hemoglobin S, hemoglobin Mobile appeared to impair gelation or increase solubility to a slightly greater extent than did hemoglobin A. Beta 73 is a known site of intermolecular interactions in polymers of hemoglobin S. Our studies suggest that the impairment of hemoglobin S polymer formation by altered intermolecular interactions is significantly less in Hb Mobile than in Hb Korle-Bu in which beta 73 is asparagine.

Oxidation and cross-linking of human hemoglobins by activated oxygen species

The effect of activated oxygen species on human hemoglobins was studied. All radicals induced polymerization in Hb A both intermolecular and by cross-linking of subunits (intramolecular). However, a system producing mainly superoxide ion gave the most important changes. An oxidation step is necessary to produce polymerization since in the case of cyanmet Hb A (where there is no possible oxidation) no polymerization occurs. The effect of O2- on blocked SH beta 93 Hbs or on the abnormal Hbs tested was practically identical to that on Hb A although their autoxidation rates were modified. Consequently the action of radicals is different from autoxidation processes and the modified residues in the abnormal hemoglobins are not involved in the action of superoxide ion on Hb. The kinetics of oxidation of Hb by H2O2 followed two steps: the first is the oxidation of oxy Hb to ferri Hb and the second is hemichrome formation. This last step is independent of the presence of H2O2 since it is not inhibited by catalase. The kinetics of oxidation to ferri Hb were of second order and the rate constant was found to be 16 M-1 sec-1.

Structure and function of Hb Saint-Jacques (α2β2 140 (H18) Ala → Thr): A new high-oxygen-affinity variant with altered bisphosphoglycerate binding

A low P50 value in a fresh red blood cell suspension was discovered in a polycythemic patient (Hb 19 g X dl-1). Routine acid and alkaline electrophoreses of the hemolysate were identical to normal hemolysate. Isoelectrofocusing (pH gradient 6-8) did not reveal any abnormal band whether performed with the fully liganded or deoxygenated samples. Precise analyses of the oxygen dissociation curves of the propositus' red cells demonstrated a biphasic Hill plot, a normal Bohr effect and low interaction with 2,3-bisphosphoglycerate (2,3-DPG). Studies on the unfractionated hemolysate confirmed these observations and the inhibition of the effect of organic phosphates. Structural studies were carried out on the mixture of beta A + beta X chains and revealed the presence of two beta Tp14 peptides. Sequencing the abnormal beta Tp14 peptide showed the substitution Ala----Thr of the beta 140 (H18) residue. This new variant was named Hb Saint-Jacques. Examination of the three dimensional model of HbAo indicates that the substitution beta 140 (H18) Ala----Thr induces van der Waals interactions with the nearby lysine-82 (EF6) and leucine-81 (EF5) and a displacement of the EF corner of the beta chains. This is likely to change the normal position of the lysine-82 (EF6), a major anionic binding site in the central cavity between the two beta chains. Functional studies confirm the interpretation of a steric hindrance inhibiting the binding of large organic phosphates to Hb Saint-Jacques.

Characterization and properties of Hb York (beta 146 His leads to Pro)

A second case of Hb York (beta 146 His leads to Pro), was discovered in a patient with polycythemia. The oxygen equilibrium curves (OEC) of red cell suspensions in a buffer (pH 7.4) at 37 degrees C revealed a biphasic curve with a P50 of only 12.5 mm Hg (normal value: 26.5 +/- 1.0 mm Hg). The purified Hb York had an extremely high affinity for oxygen with diminished cooperativity and decreased Bohr effect. The oxygen affinity was significantly reduced by inositol hexaphosphate. Molecular stability studies by mechanical shaking of various liganded forms of Hb York revealed stabilities between those of Hb A and Hb S. Isolated beta Y-subunits were more unstable than beta A-subunits at every pH examined. Hb York was 1.4 times more unstable than Hb A in 18.9% isopropanol.

Effects of anions on the ligand-linked subunit assembly of human hemoglobin: the mutual effects of Cl- and EDTA

We have studied the mutual effects of chloride ion and EDTA on the dimer-tetramer assembly of human deoxyhemoglobin and oxyhemoglobin. It is found that these two anions have similar but interdependent effects. In low C1- (.01 M) increasing concentrations of EDTA are found to decrease both forward and reverse rate constants for deoxyhemoglobin, whereas no effect is observed at 0.1 M C1-. These results suggest that binding of anions at the alpha 1 beta 2 intersubunit contact may stabilize both the dimeric and tetrameric forms of the deoxy molecule, thus inhibiting both the dissociation and reassociation reactions. The overall effects of EDTA and low C1- on the dimer-tetramer equilibrium constants are found to be distinctly different in deoxy and oxyhemoglobins with a major effect on the oxy form. These findings establish validity of the results from previous thermodynamic studies carried out in approximately physiological C1- concentrations along with the small amounts of EDTA which are used to minimize artifacts of oxidation. As observed for deoxyhemoglobin, it is found that in 0.1 M C1- ion there is no further effect of EDTA on the oxyhemoglobin dimer-tetramer equilibrium.

Novel studies on a "silent" high affinity mutant hemoglobin (San Diego, beta 109 Val replaced by Met)

A patient with a "silent" mutant hemoglobin characterized by high oxygen affinity and erythrocytosis is described. A novel approach was used to identify the mutant chain. Functionally active alpha and beta chains were prepared from hemolysates of the patient and a normal control. Hybrid tetramers of patient's beta chain were prepared. Functional studies revealed that the patient's beta chains had a higher oxygen affinity (P50, 1.1 torr) than normal beta chains (P50, 1.7 torr) and the hybrid containing the patient's beta chains had a P50 similar to the patient's "stripped" hemolysate. It was assumed therefore that the mutation was in the beta chain; structural studies using cyanogen bromide cleavage revealed that the patient had Hb San Diego, beta 109 Val replaced by Met, and that the patient's cells contained approximately 50 percent mutant hemoglobin.

Structural analysis of the minor human hemoglobin components: Hb AIa1, Hb AIa2 and Hb AIb

Human hemolysate contains several minor hemoglobin components, including Hb AIa1, Hb AIa2, Hb AIb and Hb AIc which are post-translational modifications of the major component, Hb A0. Hb AIc is known to contain glucose attached to the N terminus of the beta chains by a ketoamine linkage. We separated the alpha and beta globin chains from purified Hb AIa1, Hb AIa2 and Hb AIb by ion-exchange chromatography. The beta chains were reducible by sodium borohydride and gave a positive thiobarbituric acid test. These results indicated that they are modified by ketoamine-linked carbohydrate. In addition, phosphate analysis revealed 1.5 phosphate residue associated with each beta AIa1 chain and 1 phosphate residue with each beta AIa2 chain. Hb AIa1, Hb AIa2 and Hb AIb were all found to be contaminated by non-globin proteins. Protein-sequencing approaches demonstrated that the N termini of beta AIa1, beta AIa2 and beta AIb were blocked. In support of this conclusion, analysis of tryptic digests of beta AIa2 and B AIb revealed modified N-terminal peptides. We conclude that, like Hb AIc, components Hb AIa1, Hb AIa2 and Hb AIb also contain a sugar moiety linked to the N terminus of the beta chain.

Hemoglobin Bougardirey-Mali beta 119 (GH2) Gly replaced by Val. An electrophoretically silent variant migrating in isoelectrofocusing as Hb F

Hemoglobin Bougardirey-Mali was detected by isoelectrofocusing during a screening in a 32 years old African, a native of Mali. This abnormal Hb, representing 35% of the total, exhibited the same pI as that of Hb F. In contrast, it was indistinguishable from Hb A in all the electrophoretic systems tested, and equally by its resistance to alkaline denaturation. Structural studies have shown that the abnormality was localized on the beta chain. A fingerprint of the tryptic digest of the aminoethylated beta chain indicated the absence of the beta T12 b. The presence of an abnormal beta T12 b was suspected in the T14-15 spot, as indicated by the intensity of staining and its amino acid composition. beta T12 b was isolated by chromatography on PA 35. Its sequential analysis by manual Edman-dansyl degradation showed that glycine 119 was replaced by a valine residue. This mutation is localized in a alpha 1 beta 1 contact, which makes the molecules slightly unstable. The clinical consequences of this mutation seem to be minor; similar observations have been reported for the other Hb mutated at the same locus, i.e. Hb Fannin-Lubbock beta 119 Gly leads to Asp.

2,3-Diphosphoglycerate: its role in health and disease

2,3-Diphosphoglycerate (2,3-DPG) was first discovered and isolated in 1925. However, it was not until 1967 that the function of 2,3-DPG was explained. This resulted in multiple research projects devoted to elucidating the mechanism by which 2,3-DPG exerts it effect on the oxygen affinity of hemoglobin. In addition, a vast amount of research has been devoted to assessing the role of 2,3-DPG in oxygen transport in various physiological and pathophysiological states. In many instances, the results of this research have produced conflicting data which have dampened the initial enthusiasm which followed the discovery of the function of 2,3-DPG. However, much of this conflicting data can be explained by the fact that 2,3-DPG is only one of a number of factors influencing the transport of oxygen to the tissues. Several of these factors influence oxygen transport independently as well as by altering the synthesis of 2,3-DPG and modifying its effect on hemoglobin. In spite of the conflicting results, the overall data gathered thus far appears to be sound enough to warrant the extensive research now being done, particularly in the area of blood storage and transfusion therapy.

Hemoglobins Aida (alpha 64 Asp leads to Asn) and D-Los Angeles (beta 121 Glu leads to Gln) in an Asian-Indian family

Hemoglobins D-Los Angeles (beta 121 Gln) and Aida (alpha 64 Asn) were encountered in an Asian Indian, unassociated with any clinical manifestations. These hemoglobins had normal oxygen affinities and were stable to heat and isopropanol. The ratio of alpha chain synthesis to beta chain synthesis was close to unity. The identical change in isoelectric points of the two variants produced an interesting electrophoretic pattern.

Hemoglobin S Travis: a sickling hemoglobin with two amino acid substitutions [beta6(A3)glutamic acid leads to valine and beta142 (h20) alanine leads to valine)

Hb S Travis is a previously undescribed sickling hemoglobin with two amino acid substitutions in the beta chain: beta6 Glu leads to Val and beta142 Ala leads to Val. The beta6 Glu leads to Val mutation imparts to Hb S Travis the characteristic properties of sickling hemoglobin, namely its association with erythrocyte sickling, the insolubility of the hemoglobin in the reduced form, and a minimum gelling concentration value identical to Hb S. Unlike Hb S, Hb S Travis exhibits an increased oxygen affinity and a decreased affinity for 2,3-bisphosphoglycerate and inositol hexakisphosphate. In addition, the variant hemoglobin's tendency to autoxidize and its mechanical precipitability suggest that there are conformational differences between Hb S and Hb S Travis.