Low Oxygen Affinity Hemoglobin Research Articles

A Failed CCHD Screen.

A Failed CCHD Screen.

Crystal Structure Analysis of Great Cormorant (Phalacrocorax carbo) Hemoglobin to Understand its High Oxygen Affinity Characteristics by Special Structural Features.

Hemoglobin (Hb) subunits are composed of the specific functional prosthetic group "heme'' and a protein moiety "globin". Bird Hbs are functionally similar to mammalian Hbs but they are structurally dissimilar with mammalian. The insufficient structural studies on avian Hbs limit us to understand their degree of adaptation to such critical environments. The Great Cormorant (GCT) can fly and swim, the dual characteristic of GCT leads to study the sturcture of hemoglobin. To determine the crystal structure of Great Cormorant Hemoglobin and to compare its three dimensional structure with other high and low oxygen affinity hemoglobin species to understand its characteristic features of high oxygen affinity. The GCT hemoglobin has been purified, crystallized and data sets were processed using iMosflm. The integrated data has been solved using Molecular replacement method using Graylag hemoglobin (1FAW) as the template. The structure has been deposited in Protein Data Bank with PDB code: 3WR1. In order to characterize the tertiary and quaternary structural differences, the structure of cormorant hemoglobin is compared with GLG, BHG and human Hb. The larger variation observed between GCT and human Hb indicates that GCT Hb differs remarkably from human. The α1β1 interface of Great cormorant Hb is similar to bar-headed goose Hb with few amino acid substitutions. It has been found that the interaction which is common among avian hemoglobins (α119 Pro- β55Leu) is altered by Ala 119 in GCT. This intra-dimer contact (α119 Pro - β 55 Leu) disruption leads to high oxygen affinity in BGH Hb. In cormorant, GLG and human the proline is unchanged but interestingly, in cormorant Hb, the β55 position was found to be Thr instead of Leu. Similar kind of substitutions (β 55 Leu - Ser) observed in Andean goose Hb structure leads to elevated oxygen affinity between Hb-O2. To our surprise, such type of substitution at β 55 (Thr) in cormorant Hb confirms that it is comparable with Andean goose Hb structure. Thus the sequence, structural differences at alpha, beta heme pocket and interface contacts confirms that GCT adopts high oxygen affinity conformation. The three dimensional structure of Great cormorant hemoglobin has been investigated to understand its unique structural features to adopt during hypoxia condition. By comparing the sequence and overall structural similarities with high and low oxygen affinity species, it appears that GCT has more possibilities to subsist with low oxygen demand.

Detection of Hb Rothschild HBB: c.[112T>A or 112T>C], Through High Index of Suspicion on Abnormal Pulse Oximetry

We describe a case with a low oxygen affinity hemoglobin (Hb) variant who presented with cyanosis in the absence of cardiopulmonary disease. The patient, a 27-year-old pregnant female (P1G2), complained of a productive cough and bluish discoloration of the lips that started 3 days prior to seeking attention. She had no previous episodes and has generally been in good health. A positive family history of cyanosis was obtained in one sibling. Systematic examination, notably the cardiorespiratory system, revealed no abnormalities. The arterial Hb oxygen saturation (SpO2) on pulse oximetry was 81.0% and Hb separation studies revealed an Hb variant identified as Hb Rothschild [β37(C3)Trp→Arg] (HBB: c.[112 T>A or 112 T>C]) by gene sequencing. The amino acid substitution (Trp→Arg) is an important contact point at the α1β2 interface and favors a T-quaternary state of the Hb tetramer. This leads to a low oxygen affinity state, which results in premature release of oxygen and drop in oxygen saturation. In the absence of cardiopulmonary disease, a decreased oxygen saturation reading, with or without cyanosis, should arouse suspicion for a possible dysHb.

Structural studies on a low oxygen affinity hemoglobin from mammalian species: Sheep (Ovis aries)

Hemoglobin (Hb) is in equilibrium between low affinity Tense (T) and high affinity Relaxed (R) states associated with its unliganded and liganded forms, respectively. Mammalian species can be classified into two groups on the basis of whether they express ‘high’ and ‘low’ oxygen affinity Hbs. Although Hbs from former group have been studied extensively, a limited number of structural studies have been performed for the low oxygen affinity Hbs. Here, the crystal structure of low oxygen affinity sheep methemoglobin (metHb) has been determined to 2.7Å resolution. Even though sheep metHb adopts classical R state like quaternary structure, it shows localized quaternary and tertiary structural differences compared with other liganded Hb. The critical group of residues in the “joint region”, shown as a major source of quaternary constraint on deoxyHb, formed unique interactions in the α1β2/α2β1 interfaces of sheep metHb structure. In addition, the constrained β subunits heme environment and the contraction of N-termini and A-helices of β subunits towards the molecular dyad are observed for sheep metHb structure. These observations provide the structural basis for a low oxygen affinity and blunt response to allosteric effector of sheep Hb.

Low oxygen affinity hemoglobin solution increases oxygenation of partially ischemic tissues during acute anemia

Maintenance of post‐surgical tissue oxygenation depends on the ability of the specific tissue to recruit perfusion and oxygen (O2) supply. However, when native O2 carrying capacity is lacking, fluids to improve O2 carrying capacity based in hemoglobin (Hb) could prevent partially ischemic tissue hypoxia by increasing O2 release from the remaining red blood cells. Responses to facilitated O2 transport after exchange transfusion with polymerized bovine Hb (PBH) were studied in a chronic partially ischemic tissue model, induced by large feeding arterioles ligation during hamster window chamber model implantation. PBH affects in microvascular perfusion and tissue oxygenation were studied after exchange transfusion of 40% of animal's blood volume. Experimental groups were defined by the concentration of PBH used, namely: PBH at 13g/dl [PBH13], PBH at 4 g/dl in albumin solution to matching colloidal osmotic pressure (COP) [PBH4], and no PBH only albumin solution at matching COP [PBH0]. Restitution of O2 carrying capacity with PBH13 increased blood pressure and produced vasoconstriction compared to PBH4 and PBH0. On the other hand, PBH4 maintained blood pressure without significant vasoconstriction, increased tissue pO2, arteriolar O2 supply and extraction to the partially ischemic tissue compared to PBH0 and PBH13. Results suggest the existence of an optimal concentration of low O2 affinity acellular Hb to increase oxygenation of partially ischemic tissue during anemic conditions. This work was supported by BRP R24‐HL64395 and P01 HL071064.

Low Oxygen-Affinity Hemoglobin Solution Increases Oxygenation of Partially Ischemic Tissue During Acute Anemia

Maintenance of postsurgical tissue oxygenation depends on the ability of the specific tissue to recruit perfusion and oxygen (O(2)) supply. When native O(2)-carrying capacity is lacking, fluids to improve O(2)-carrying capacity based in hemoglobin (Hb) could prevent partially ischemic tissue hypoxia by increasing O(2) release from the remaining red blood cells. Responses to facilitated O(2) transport after exchange transfusion with polymerized bovine Hb (PBH) were studied in a chronic partially ischemic tissue model, induced by large feeding arteriole ligation during hamster window chamber model implantation. PBH effects in microvascular perfusion and tissue oxygenation were studied after exchange transfusion of 40% of animal's blood volume. Experimental groups were defined by the concentration of PBH used, ie, PBH at 13 g/dL (PBH13); PBH at 4 g/dL in albumin solution to matching colloidal osmotic pressure (COP) (PBH4); and no PBH, only albumin solution at matching COP (PBH0). Restitution of O(2)-carrying capacity with PBH13 increased blood pressure and produced vasoconstriction compared with PBH4 and PBH0. On the other hand, PBH4 maintained blood pressure without substantial vasoconstriction, increased tissue partial pressure of O(2), arteriolar O(2) supply, and extraction to the partially ischemic tissue compared with PBH0 and PBH13. Results suggest the existence of an optimal concentration of low O(2)-affinity acellular Hb to increase oxygenation of partially ischemic tissue during anemic conditions.

Isovolemic exchange transfusion with increasing concentrations of low oxygen affinity hemoglobin solution limits oxygen delivery due to vasoconstriction

O2-carrying fluids based on hemoglobin (Hb) are in various stages of clinical trials to determine their suitability as O2-carrying plasma expanders. Polymerized Hb solutions are characterized by their vasoactivity, low O2 affinity, oncotic effect, prolonged shelf life, and stability. Physiological responses to facilitated O2 transport after exchange transfusion with polymerized bovine Hb (PBH) were studied in the hamster window chamber model during acute moderate anemia to determine how PBH affects microvascular perfusion and tissue oxygenation. The anemic state [29% hematocrit (Hct)] was induced by hemodilution with a plasma expander (70 kDa dextran). After hemodilution, animals were randomly assigned to different exchange transfusion groups. Study groups were based on the concentration of PBH used, namely: PBH at 13 g Hb/dl [PBH13], PBH diluted to 8 (PBH8) or 4 (PBH4) g Hb/dl in albumin solution at matching colloidal osmotic pressure (COP), and no PBH (only albumin solution) at matching COP (PBH0). Measurement of systemic parameters, microvascular hemodynamics, capillary perfusion, and intravascular and tissue O2 levels was performed at 18% Hct. Restitution of O2-carrying capacity with PBH13 increased arterial pressure and triggered vasoconstriction, low perfusion, and high peripheral resistance. PBH4 and PBH0 exhibited lower arterial pressures compared with PBH13. Exchange transfused animals with PBH8 and PBH4 better maintained perfusion and functional capillary density than PBH13. Blood gas parameters and acid-base balance were recovered proportional to microvascular perfusion. Arterial O2 tensions were improved with PBH4 and PBH8 by preventing O2 precapillary release and increasing O2 reserve. Further studies to establish PBH optimal dosage, efficacy, safety, and its effect on outcome are indicated before Hb-based O2-carrying blood substitutes are implemented in routine practice.

Low Oxygen Saturation by Pulse Oximetry May Be Associated With a Low Oxygen Affinity Hemoglobin Variant, Hemoglobin Titusville

The authors describe a 10-year-old Caucasian boy who presented with abnormally low oxygen saturation values on pulse oximetry after a routine tonsillectomy. He was asymptomatic and there was no personal or family history of respiratory, cardiac, or hematologic disorders. Multiple initial investigations were completed without diagnostic yield. Eventually, hemoglobinopathy studies identified the presence of a low oxygen affinity hemoglobin variant, characterized as hemoglobin Titusville. Hemoglobinopathies remain highly prevalent worldwide, with more than 65 low oxygen affinity hemoglobin variants identified to date. Early recognition of abnormal hemoglobin variants in asymptomatic patients may avoid extensive, unnecessary medical investigations.

Oxygen transport by low and normal oxygen affinity hemoglobin vesicles in extreme hemodilution

The oxygen transport capacity of phospholipid vesicles encapsulating purified Hb (HbV) produced with a Po(2) at which Hb is 50% saturated (P 50 ) of 8 (HbV(8)) and 29 mmHg (HbV(29)) was investigated in the hamster chamber window model by using microvascular measurements to determine oxygen delivery during extreme hemodilution. Two isovolemic hemodilution steps were performed with 5% recombinant albumin (rHSA) until Hct was 35% of baseline. Isovolemic exchange was continued using HbV suspended in rHSA solution to a total [Hb] of 5.7 g/dl in blood. P(50) was modified by coencapsulating pyridoxal 5'-phosphate. Final Hct was 11% for the HbV groups, with a plasma [Hb] of 2.1 +/- 0.1 g/dl after exchange with HbV(8) or HbV(29). A reference group was hemodiluted to Hct 11% with only rHSA. All groups showed stable blood pressure and heart rate. Arterial oxygen tensions were significantly higher than baseline for the HbV groups and the rHSA group and significantly lower for the HbV groups compared with the rHSA group. Blood pressure was significantly higher for the HbV(8) group compared with the HbV(29) group. Arteriolar and venular blood flows were significantly higher than baseline for the HbV groups. Microvascular oxygen delivery and extraction were similar for the HbV groups but lower for the rHSA group (P < 0.05). Venular and tissue Po(2) were statistically higher for the HbV(8) vs. the HbV(29) and rHSA groups (P < 0.05). Improved tissue Po(2) is obtained when red blood cells deliver oxygen in combination with a high- rather than low-affinity oxygen carrier.

Characteristic of Aromatic Amino Acid Substitution at α96 of Hemoglobin

Replacement of valine by tryptophan or tyrosine at position alpha96 of the alpha chain (alpha96Val), located in the alpha(1)beta(2) subunit interface of hemoglobin leads to low oxygen affinity hemoglobin, and has been suggested to be due to the extra stability introduced by an aromatic amino acid at the alpha96 position. The characteristic of aromatic amino acid substitution at the alpha96 of hemoglobin has been further investigated by producing double mutant r Hb (alpha42Tyr --> Phe, alpha96Val --> Trp). r Hb (alpha42Tyr --> Phe) is known to exhibit almost no cooperativity in binding oxygen, and possesses high oxygen affinity due to the disruption of the hydrogen bond between alpha42Tyr and beta99Asp in thealpha(1)beta(2) subunit interface of deoxy Hb A. The second mutation, alpha96Val -->Trp, may compensate the functional defects of r Hb (alpha42Tyr --> Phe), if the stability due to the introduction of trypophan at the alpha 96 position is strong enough to overcome the defect of r Hb (alpha42Tyr --> Phe). Double mutant r Hb (alpha42Tyr --> Phe, alpha96Val --> Trp) exhibited almost no cooperativity in binding oxygen and possessed high oxygen affinity, similarly to that of r Hb (alpha42Tyr --> Phe). (1)H NMR spectroscopic data of r Hb (alpha42Tyr --> Phe, alpha96Val --> Trp) also showed a very unstable deoxy-quaternary structure. The present investigation has demonstrated that the presence of the crucible hydrogen bond between alpha 42Tyr and beta 99Asp is essential for the novel oxygen binding properties of deoxy Hb (alpha96Val --> Trp) .

Additive Effects of β Chain Mutations in Low Oxygen Affinity Hemoglobin βF41Y,K66T

In order to decrease significantly the oxygen affinity of human hemoglobin, we have associated the mutation betaF41Y with another point mutation also known to decrease the oxygen affinity of Hb. We have synthesized a recombinant Hb (rHb) with two mutations in the beta chains: rHb betaF41Y,K66T. In the absence of 2, 3-diphosphoglycerate, additive effects of the mutations are evident, since the doubly mutated Hb exhibits a larger decrease in oxygen affinity than for the individual single mutations. In the presence of 2,3-diphosphoglycerate, the second mutation did not significantly increase the P(50) value relative to the single mutations. However, the kinetics of CO binding still indicate combined effects on the allosteric equilibrium, as evidenced by more of the slow bimolecular phase characteristic of binding to the deoxy conformation. Dimer-tetramer equilibrium studies indicate an increase in stability of the mutants relative to rHb A; the double mutant rHb betaF41Y, K66T at pH 7.5 showed a K(4,2) value of 0.26 microM. Despite the lower oxygen affinity, the single mutant betaF41Y and double mutant betaF41Y,K66T show only a moderate increase of 20% in the autoxidation rate. These mutations are thus of interest in developing a Hb-based blood substitute.

A New Unstable and Low Oxygen Affinity Hemoglobin Variant: HB Stanmore [B111 (G13)VAL→ALA

Hb Stanmore is a new hemoglobin variant with the amino acid substitution beta 111(G13)Val----Ala. It is unstable and has a low oxygen affinity. The propositus (of Italian nationality) is a double-heterozygote for Hb Stanmore and beta(0)-thalassemia.

Measurement of regional cerebral blood flow, blood volume and oxygen metabolism in patients with sickle cell disease using positron emission tomography.

Regional cerebral blood flow, blood volume, fractional oxygen extraction and oxygen consumption were measured by positron emission tomography in six patients with sickle cell disease to see how oxygen delivery to the brain is maintained in the presence of both anemia and a low oxygen affinity hemoglobin. Both regional cerebral blood flow and blood volume were found to be markedly increased compared to values obtained from 14 normal subjects in the same age range. The mean fractional oxygen extraction was not significantly different in the two groups. Mean oxygen consumption in the two groups was also not significantly different but low values in individual patients with sickle cell disease and the presence of atrophy on the CT-scans of three of them were suggestive of some neuronal loss in patients without any history of nervous system involvement. In view of the known high values of cerebral blood flow and metabolism in childhood, it is suggested that when compounded by anemia and abnormal red cells, a hypercirculatory state may make patients in this age-group particularly prone to ischemic infarction.

Abnormal functional properties of Hb hope αC A2β 2 (H14) Gly → Asp: A low oxygen affinity hemoglobin with decreased DPG effect

Abnormal functional properties of Hb hope αC A2β 2 (H14) Gly → Asp: A low oxygen affinity hemoglobin with decreased DPG effect