Globin chain analysis by reversed phase high performance liquid chromatography: recent developments

Hemoglobin fractionation by Sebia Capillarys 2 Flex Piercing System as primary method for evaluation of hemoglobinopathies

BACKGROUND

Hemoglobin fractionation by capillary zone electrophoresis (CE) is becoming a popular method for the identification of hemoglobin variants that can cause hemoglobinopathies. The goal of this study was to compare the performance of capillary electrophoresis using Sebia Capillarys 2 Flex Piercing system (CE-S) with high-pressure liquid chromatography (HPLC) using Primus Ultra2 Resolution Variants System (HPLC-P) as a primary method in hemoglobinopathy work-up.

METHODS

A total of 306 blood specimens submitted for evaluation of hemoglobinopathies were studied using HPLC-P and CE-S.

RESULTS

The reference ranges for Hb A, A₂ and F agreed well between methods. All common variants containing Hb S and Hb C were detected by both methods. Quantification of Hb A₂ with HPLC-P required a correction in the presence of Hb S, while quantification of Hb A₂ was slightly overestimated by CE-S in the presence of Hb C. Of 41 samples containing other variants, 2 were not identified by HPLC-P and 3 were not identified by CE-S.

CONCLUSION

CE-S provides comparable information to that obtained by HPLC-P and it is a reliable primary method for the evaluation of hemoglobin variants.

Rapid and Sensitive Assessment of Globin Chains for Gene and Cell Therapy of Hemoglobinopathies

The β-hemoglobinopathies sickle cell anemia and β-thalassemia are the focus of many gene-therapy studies. A key disease parameter is the abundance of globin chains because it indicates the level of anemia, likely toxicity of excess or aberrant globins, and therapeutic potential of induced or exogenous β-like globins. Reversed-phase high-performance liquid chromatography (HPLC) allows versatile and inexpensive globin quantification, but commonly applied protocols suffer from long run times, high sample requirements, or inability to separate murine from human β-globin chains. The latter point is problematic for in vivo studies with gene-addition vectors in murine disease models and mouse/human chimeras. This study demonstrates HPLC-based measurements of globin expression (1) after differentiation of the commonly applied human umbilical cord blood-derived erythroid progenitor-2 cell line, (2) in erythroid progeny of CD34+ cells for the analysis of clustered regularly interspaced short palindromic repeats/Cas9-mediated disruption of the globin regulator BCL11A, and (3) of transgenic mice holding the human β-globin locus. At run times of 8 min for separation of murine and human β-globin chains as well as of human γ-globin chains, and with routine measurement of globin-chain ratios for 12 nL of blood (tested for down to 0.75 nL) or of 300,000 in vitro differentiated cells, the methods presented here and any variant-specific adaptations thereof will greatly facilitate evaluation of novel therapy applications for β-hemoglobinopathies.

Diagnostic Dilemma of Hb Perth [β32(B14)Leu→Pro; HBB: c.98T > C] in Mainland China

Unstable hemoglobin (Hb) variants represent a rare etiology of congenital hemolytic anemia. Correct diagnosis can be a challenge due to the relative rarity or lack of awareness of this disorder. We report an 18-month-old girl, who presented with a long-standing hemolytic anemia. Her diagnosis of unstable Hb Perth [β32(B14)Leu→Pro, HBB: c.98T > C] had not been made until gene sequencing of the β-globin gene was performed.

Rapid determination of human globin chains using reversed-phase high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography (RP-HPLC) of human globin chains is an important tool for detecting thalassemias and hemoglobin variants. The challenges of this method that limit its clinical application are a long analytical time and complex sample preparation. The aim of this study was to establish a simple, rapid and high-resolution RP-HPLC method for the separation of globin chains in human blood. Red blood cells from newborns and adults were diluted in deionized water and injected directly onto a micro-jupiter C18 reversed-phase column (250 mm × 4.6 mm) with UV detection at 280 nm. Under the conditions of varying pH or the HPLC gradient, the globin chains (pre-β, β, δ, α, (G)γ and (A)γ) were denatured and separated from the heme groups in 12 min with a retention time coefficient of variation (CV) ranging from 0.11 to 1.29% and a peak area CV between 0.32% and 4.86%. Significant differences (P<0.05) among three groups (normal, Hb H and β thalassemia) were found in the area ratio of α/pre-β+β applying the rapid elution procedure, while P≥0.05 was obtained between the normal and α thalassemia silent/trait group. Based on the ANOVA results, receiver operating characteristic (ROC) curve analysis of the δ/β and α/pre-β+β area ratios showed a sensitivity of 100.0%, and a specificity of 100.0% for indicating β thalassemia carriers, and a sensitivity of 96.6% and a specificity of 89.6% for the prediction of hemoglobin H (Hb H) disease. The proposed cut-off was 0.026 of δ/β for β thalassemia carriers and 0.626 of α/pre-β+β for Hb H disease. In addition, abnormal hemoglobin hemoglobin E (Hb E) and Hb Westmead (Hb WS) were successfully identified using this RP-HPLC method. Our experience in developing this RP-HPLC method for the rapid separation of human globin chains could be of use for similar work.

Hb Marineo [β70(E14)Ala→Val]: A Silent Hemoglobin Variant with a Mutation Within the Heme Pocket

We report a new hemoglobin (Hb) variant, Hb Marineo [beta70(E14)Ala --> Val], found in three generations of a family from West Sicily. The mutation is due to a GCC --> GTC substitution at codon 70 of the beta-globin gene. To date, three mutations at codon 70 of the beta-globin gene have been described, presenting with hemolytic anemia. In our case, no anemia or other alteration of hematological indices were found. Cation exchange high performance liquid chromatography (HPLC) showed a peak in the P2 window (VARIANT I), while a peak was detected by VARIANT II HPLC in the P3 window. Reversed phase HPLC analysis showed an abnormal chain amounting to about 40% of the total beta chains.

Hb Zoetermeer: A New Mutation on the α2 Gene Inducing an Ala→Ser Substitution at Codon 21 is Possibly Associated with a Mild Thalassemic Phenotype

A 52-year-old Dutch male was referred to our laboratory for hemoglobinopathy analysis because of persistent microcytic hypochromic parameters and moderate erythrocytosis in the absence of iron deficiency. The hemoglobin (Hb) pattern was normal and breakpoint polymerase chain reaction (PCR) excluded the six common deletion defects of the alpha gene cluster. Direct sequencing revealed a GCT-->TCT transversion at codon 21 of the alpha2 gene generating an Ala-->Ser single amino acid substitution. The hematological parameters observed in the presence of this mutation are consistent with a compensated heterozygous alpha(+)-thalassemia (thal). However, the neutral mutation and the external position of the residue do not explain an association with this phenotype. Nevertheless, we cannot exclude that the mutation could induce the observed hematological abnormalities and could eventually be considered as a mutation associated with a mild alpha-thalassemic phenotype.

Disorders of the synthesis of human fetal hemoglobin

Fetal hemoglobin (HbF), the predominant hemoglobin in the fetus, is a mixture of two molecular species (alpha(2)(G)gamma(2) and alpha(2)(A)gamma(2)) that differ only at position 136 reflecting the products of two nonallelic gamma-globin genes. At the time of birth, HbF accounts for approximately 70% of the total Hb. The (G)gamma:(A)gamma globin ratio in the HbF of normal newborn is 70:30 whereas in the trace amounts of HbF that is found in the adult it reverses to 40:60 because of a gamma- to beta-globin gene switch. Alterations of these ratios are indicative of a molecular defect at the level of the HbF synthesis. Qualitative hemoglobinopathies due to (G)gamma and (A)gamma chain structural variants, and quantitative hemoglobinopathies affecting the synthesis of HbF such as gamma-thalassemias, duplications, triplications, and even sextuplications of the gamma-globin genes, which may be detected in newborn blood lysates, have been described. Moreover, several pathological and nonpathological conditions affecting the beta-globin gene cluster, such as beta-thalassemia, sickle cell disease, deltabeta-thalassemia, and hereditary persistence of HbF syndromes, are characterized by the continued synthesis of gamma-globin chains in the adult life. Studies of these natural mutants associated with increased synthesis of HbF in adult life have provided considerable insight into the understanding of the control of globin gene expression and Hb switching.

Detection of a thalassemic alpha-chain variant (Hemoglobin Groene Hart) by reversed-phase liquid chromatography

BACKGROUND

Hemoglobin (Hb) Groene Hart [alpha119 (H2)Pro-->Ser (alpha1)], also known as Hb Bernalda, is a nondeletional alpha-thalassemic Hb variant that is frequent in southern Italy and North Africa. This variant is not supposed to be produced in the erythrocytes of carriers. The alpha-thalassemic behavior of this variant has been explained as an impaired interaction between the alpha-globin chain and the alpha-Hb-stabilizing protein.

METHODS

To separate globin chains, we developed a modified reversed-phase liquid chromatography (RPLC) procedure that uses acetonitrile-water solvents containing up to 3 mL/L trifluoroacetic acid. After RPLC, we characterized the isolated globin chains by electrospray ionization (ESI) mass spectrometry (MS) and analyzed their tryptic peptides with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS and nano-LC-ESI-MS/MS.

RESULTS

RPLC detected an abnormal peak with a retention time substantially greater than that of the wild-type alpha(A)-globin chain. We identified this variant as Hb Groene Hart and found it in the hemolysates of 11 unrelated patients (1 homozygote, 9 heterozygotes, and 1 heterozygote associated with the -alpha(3.7) deletion). These patients possessed abnormal hematologic features suggesting an alpha-thalassemia phenotype. Molecular modeling suggested that the increase in hydrophobicity was due to opening of the GH interhelical segment following replacement of amino acid residue 119 with a nonhelix breaker residue.

CONCLUSIONS

This method allows the detection of Hb variants at low concentrations, and adjusting the composition of the organic solvents enables the method to identify Hb variants with large changes in hydrophobicity.

HPLC studies in hemoglobinopathies

An accurate diagnosis of beta -thalassemia carriers, homozygous patients and identification of different structural hemoglobin variants is important for epidemiological studies as well as for management and prevention of the major hemoglobin disorders. There are many electrophoretic and chromatographic approaches for estimation of HbA2 and Hb F but cation exchange HPLC (CE-HPLC)using automated dedicated machines like the Variant Hb testing system have become the method of choice for these investigations. CE-HPLC also helps in the presumptive identification of many abnormal hemoglobin variants and has been useful for both neonatal screening of sickle cell disease as well as second trimester prenatal diagnosis of thalassemia by fetal blood analysis. Other applications of HPLC in hemoglobinopathies include separation of globin chains, measuring the ratio of gamma globin chains (Ggamma/Agamma) and the recently described denaturing HPLC for detecting mutations in both alpha and beta globin genes.

A New Silent β Chain Variant: Hb Hounslow [β80(EF4)Asn→Tyr]

We report a new neutral hemoglobin (Hb) variant, found, during neonatal screening, in a child originating from Afghanistan. This variant was revealed by cation exchange and reversed phase high performance liquid chromatography (HPLC), but was silent in electrophoretic methods except for globin chain electrophoresis in the presence of urea and Triton X-100. The structural modification was determined by protein structure studies and the substitution established by tandem mass spectrometry (MS/MS). The mutation, located near to the 2,3-diphosphoglycerate (2,3-DPG) binding site, was without any hematological consequences. The pitfalls presented by the presence of neutral Hb variants as modulator factors of the main hemoglobinopathies is discussed.

Hb Barika [alpha42(C7)Tyr-->His (alpha2)] leads to an alpha+ -Thalassemia-like syndrome

In human deoxyhemoglobin (deoxyHb), the hydrogen bond between Aspbeta99(G1) and Tyralpha42(C7), located in the alpha1beta2 interface, is crucial for the stability of the T structure. All the variants that could arise from a single point mutation affecting codon beta99 have already been observed, leading always to erythrocytosis. Conversely, up to now, Hb Barika is the only example found in a patient in whom the alpha42 is mutated. From a biochemical point of view, for theoretical reasons, this substitution has already been extensively studied on recombinant hemoglobin (rHb). In the patient, Hb Barika is expressed at a level lower than expected for an alpha2 gene variant and leads to an alpha+-thalassemic-like syndrome.

Structure and function of sheep hemoglobin Chios: A novel allele at the HBBB locus with two Lys-->Arg substitutions at positions beta66(E10) and beta144(HC1)

A novel hemoglobin variant was observed in pure sheep (Ovis aries) breeds of the island of Chios (Greece), Egypt and Hungary. This silent variant was identified by gel electrophoresis and RP-HPLC of dissociated globin chains. Two Arg for Lys substitutions were detected, by means of MALDI TOF electrospray mass spectrometric analysis for the intact globins, at positions beta66(E10) and beta144(HC1) of a globin chain having the sequence of the beta(B) chain. Sequencing of the beta-globin gene confirmed the variant gene as being an allele of the HBBB locus having the AAG-->AGG and the AAA-->AGA mutations at codons 66 and 144, respectively, both corresponding to the Lys-->Arg substitution. The intrinsic oxygen affinity of the variant Hb (logP(50)=0.79 at pH 7.0) was found to be intermediate between that of the sheep Hb B (logP(50)=0.92) and that of Cypriot mouflon (O. a. ophion) Hb (logP(50)=0.53), the latter having only the Lys-->Arg change at beta144, whereas nearly no differences were observed in the presence of the Cl(-) physiological effector. Result supports the indication that Arg at beta144 enhances the role of the ligand in decreasing oxygen affinity, this effect being partially counteracted when Arg is at beta66. Data also shows that the Lys-->Arg change at beta66 is responsible for 1.49 fold reduction in the intrinsic oxygen affinity. This hitherto undescribed variant increases to seven the number of alleles at the sheep HBBB locus. Following the nomenclature used for human Hb variants, the new allele was termed as the Hb Chios or [beta(B)66(E10) Lys-->Arg, 144(HC1)Lys-->Arg], whereas the proposed genetic nomenclature of the locus is HBBK.

Observation of a rare hemoglobin variant [Hb Lulu island, beta107(G9)Gly-->Asp, GGC-->GAC] co-inherited with a beta+-thalassemia mutation [IVS-I-110 (G-->A)] or in the heterozygous state in a Greek-Albanian family

We report clinical, hematological, biochemical, functional and molecular studies carried out on two first cousins from a Greek-Albanian family who have clinical and hematological findings consistent with the diagnosis of thalassemia intermedia. DNA studies determined that they had co-inherited a common Mediterranean beta-thalassemia (thal) mutation, IVS-I-110 (G-->A), in trans to a beta-globin gene mutation at codon 107 (GGC-->GAC), predicted to give rise to a rare unstable beta chain variant Hb Lulu Island or beta107(G9)Gly-->Asp.

Hb Calais [beta76(E20)Ala --> Pro]: a family study of a variant with decreased oxygen affinity

Secondary to the detection of a chronic anemia with a slightly increased Hb F level in a 7-year-old boy carrying a hemoglobin (Hb) variant, we investigated the members of his family and found that they were related to the original case of Hb Calais. In the present study, we report the clinical and biological impacts of this Hb variant in various members of three generations of this family.

The homozygous state for Hb Crete [β129 (H7) Ala→Pro] is associated with a complex phenotype including erythrocytosis and functional anemia

Hb Crete, an electrophoretically neutral, unstable, high oxygen affinity variant, was characterized by protein and DNA analyses in the homozygous state in a 32-year-old woman from Crete, with erythrocytosis and microcytosis. The proband and members of her family over 3 generations, including 5 carriers of Hb Crete, were subject to clinical, hematological and biochemical investigations, and DNA, RNA and protein studies were carried out. The proband demonstrated features associated with disturbed hemoglobin (Hb) structure and function, including erythrocytosis and additionally a state of functional anemia, the latter reflected by increased erythropoetin levels and cardiac output. In addition, all the carriers surprisingly had hematological and biosynthetic findings more usually associated with thalassemia trait. The structural change in Hb Crete only partly explains all the pathological manifestations of this variant, and other mechanisms are discussed.

Hb Montfermeil [β 130(H8) Tyr→Cys]: suggests a key role for the interaction between helix A and H in oxygen affinity of the hemoglobin molecule

Hb Montfermeil [beta130(H8) Tyr-->Cys] is a high oxygen affinity variant causing erythrocytosis. The cysteine replacement is buried in the inside of the beta chain where it alters the interactions between helix A and H, with a further effect on helix E. This position has already been proposed to contribute to the difference in oxygen affinity between human and bovine hemoglobins. Three dimensional structural considerations and comparison of the functional behavior of other variants suggest that this region is an important determinant of the intrinsic oxygen affinity of the hemoglobin molecule.