Hb Doha or alpha 2 beta 2[X-N-Met-1(NA1)Val----Glu]; a new beta-chain abnormal hemoglobin observed in a Qatari female

MetAP2 inhibition modifies hemoglobin S to delay polymerization and improves blood flow in sickle cell disease

Sickle cell disease (SCD) is associated with hemolysis, vascular inflammation, and organ damage. Affected patients experience chronic painful vaso-occlusive events requiring hospitalization. Hypoxia-induced polymerization of sickle hemoglobin S (HbS) contributes to sickling of red blood cells (RBCs) and disease pathophysiology. Dilution of HbS with nonsickling hemoglobin or hemoglobin with increased oxygen affinity, such as fetal hemoglobin or HbS bound to aromatic aldehydes, is clinically beneficial in decreasing polymerization. We investigated a novel alternate approach to modify HbS and decrease polymerization by inhibiting methionine aminopeptidase 2 (MetAP2), which cleaves the initiator methionine (iMet) from Val1 of α-globin and βS-globin. Kinetic studies with MetAP2 show that βS-globin is a fivefold better substrate than α-globin. Knockdown of MetAP2 in human umbilical cord blood-derived erythroid progenitor 2 cells shows more extensive modification of α-globin than β-globin, consistent with kinetic data. Treatment of human erythroid cells in vitro or Townes SCD mice in vivo with selective MetAP2 inhibitors extensively modifies both globins with N-terminal iMet and acetylated iMet. HbS modification by MetAP2 inhibition increases oxygen affinity, as measured by decreased oxygen tension at which hemoglobin is 50% saturated. Acetyl-iMet modification on βS-globin delays HbS polymerization under hypoxia. MetAP2 inhibitor-treated Townes mice reach 50% total HbS modification, significantly increasing the affinity of RBCs for oxygen, increasing whole blood single-cell RBC oxygen saturation, and decreasing fractional flow velocity losses in blood rheology under decreased oxygen pressures. Crystal structures of modified HbS variants show stabilization of the nonpolymerizing high O2-affinity R2 state, explaining modified HbS antisickling activity. Further study of MetAP2 inhibition as a potential therapeutic target for SCD is warranted.

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.

Pathology consultation on HbA(1c) methods and interferences

OBJECTIVES

To review the various hemoglobin (Hb) A1c methods, with a focus on interferences resulting from Hb variants.

METHODS

HbA1c is a marker used for the diagnosis and management of diabetes. Each available HbA1c method has advantages and challenges, such as its susceptibility to interferences.

RESULTS

The presence of Hb variants and/or abnormalities in RBC turnover cannot only interfere analytically with HbA1c measurements but also may affect the clinical interpretation of HbA1c values.

CONCLUSIONS

Familiarity with the advantages and challenges of the various methods used for HbA1c testing is essential when establishing therapeutic management and goals based on HbA1c results, especially in populations with a high prevalence of Hb variants.

Structure-function of Hb Marseille-Long Island [alpha 2 beta 2 N-methionyl-2(NA2) His----Pro]

Suspensions of red cells containing Hb Marseille-Long Island showed decreased oxygen affinity and low interaction with 2,3-diphosphoglycerate. Oxygen equilibrium studies of the purified component confirmed these abnormalities. Oxidation rate measurements of carbonmonoxy-Hb Marseille and carbonmonoxy-Hb A by ferricyanide showed an increased rate for the former, suggesting an increased dissociation constant for carbon monoxide. Nuclear Magnetic Resonance spectra in the high field region revealed small changes in the proximal region of the heme pocket. These results indicated that the mutation causes a perturbation at a distance from the mutation site.

Separation of normal and abnormal hemoglobin chains by reversed-phase high-performance liquid chromatography

A review is presented of the elution patterns on reversed-phase columns of the normal and abnormal globin chains of different hemoglobin types, including 16 beta-chain variants, 7 alpha-chain variants, 9 gamma-chain variants, and 4 variants with fusion or hybrid chains. Separations appear to be based primarily on differences in hydrophobicity. The method is ideally suited for the detection of abnormal globin chains, their quantitation and their isolation. Semi-quantitative data based on the calculation of the delta/non-alpha ratios allow the detection of beta-thalassemic conditions in situations where the quantitation of hemoglobin A2 by other procedures is impossible or complicated.