Haemoglobin I toulouse: beta-66 (E 10) lys glu: a new abnormal haemoglobin with a mutation localized on the E 10 porphyrin surrounding zone

Hemoglobin I-Toulouse: A rare hemoglobinopathy presenting with low oxygen saturations

We report a child with persistently low oxygen saturations (SpO2 90%-92%) [normal SpO2 > 98%], with delayed diagnosis due to the co-existing congenital pulmonary airway malformation with possible arterio-venous malformation. The diagnosis was only achieved after low oxygen saturations incidentally discovered from the child's father. The eventual cause was Hemoglobin I-Toulouse, making both patients the first reported cases with low oxygen saturations.

Glycation of Host Proteins Increases Pathogenic Potential of Porphyromonas gingivalis

The non-enzymatic addition of glucose (glycation) to circulatory and tissue proteins is a ubiquitous pathophysiological consequence of hyperglycemia in diabetes. Given the high incidence of periodontitis and diabetes and the emerging link between these conditions, it is of crucial importance to define the basic virulence mechanisms employed by periodontopathogens such as Porphyromonas gingivalis in mediating the disease process. The aim of this study was to determine whether glycated proteins are more easily utilized by P. gingivalis to stimulate growth and promote the pathogenic potential of this bacterium. We analyzed the properties of three commonly encountered proteins in the periodontal environment that are known to become glycated and that may serve as either protein substrates or easily accessible heme sources. In vitro glycated proteins were characterized using colorimetric assays, mass spectrometry, far- and near-UV circular dichroism and UV-visible spectroscopic analyses and SDS-PAGE. The interaction of glycated hemoglobin, serum albumin and type one collagen with P. gingivalis cells or HmuY protein was examined using spectroscopic methods, SDS-PAGE and co-culturing P. gingivalis with human keratinocytes. We found that glycation increases the ability of P. gingivalis to acquire heme from hemoglobin, mostly due to heme sequestration by the HmuY hemophore-like protein. We also found an increase in biofilm formation on glycated collagen-coated abiotic surfaces. We conclude that glycation might promote the virulence of P. gingivalis by making heme more available from hemoglobin and facilitating bacterial biofilm formation, thus increasing P. gingivalis pathogenic potential in vivo.

Hb I-Toulouse in Association with Homozygosity for the α3.7 Deletion in a Pacific Island Woman

Only four cases of Hb I-Toulouse have been reported to date. Current literature associates Hb I-Toulouse in the heterozygote with a mild chronic hemolytic anemia. The variant is mildly unstable with a tendency to form metHb. The quantity of the variant in heterozygotes has been reported as varying between 33 to 40%. This report confirms the finding from a single case, that a reduced percentage of Hb IToulouse along with microcytosis can be attributed to the co-inheritance of an abnormal α globin genotype. This current case was found in a woman of Pacific People ethnicity residing in New Zealand. There is a high prevalence of α thalassemia in this ethnic group and New Zealand has the highest Pacific population in the world. Therefore, if a reduced percentage of Hb I-Toulouse is found with microcytosis and normal iron studies, co-inheritance with α thalassemia should be considered.

Case-control studies of novel hemoglobin anomalies as differential diagnosis in sleep apnea syndrome

PURPOSE

Pulse oximetry plays an essential role in the diagnosis of sleep apnea syndrome. We discovered two novel hemoglobin anomalies, Hb Bonn and Hb Venusberg, which initially resulted in avoidable sleep disorder examinations and therapeutic consequences due to their low oxygen saturation levels as measured by pulse oximetry.

METHODS

Hematological as well as clinical chemical diagnosis was carried out. Hemoglobin anomalies were detected through electrophoresis, chromatography, spectrophotometry, and pulse oximetry as well as hemoglobin gene sequencing.

RESULTS

Hb Bonn is a novel hemoglobin mutation of the proximal α1 globin with an additional absorption maximum of the oxyhemoglobin at 668 nm. This results in pulse oximetry measurements of false low oxygen saturation due to incorrect calculations at the pulse oximetry measuring point 660 m. Hb Venusberg is a novel oxygen-affine hemoglobin mutation of the β-globin which is electrophoretically silent. Clinical symptoms include intermittent low oxygen saturation levels, cyanosis of lips and nail beds, and limited physical resistance to stress.

CONCLUSIONS

Hemoglobin anomalies, such as Hb Bonn and Hb Venusberg, should be included in differential diagnosis as potential causes of low oxygen saturation especially in case of nonspecific or conflicting findings.

Fructose-induced structural and functional modifications of hemoglobin: implication for oxidative stress in diabetes mellitus

Increased fructose concentration in diabetes mellitus causes fructation of several proteins. Here we have studied fructose-induced modifications of hemoglobin. We have demonstrated structural changes in fructose-modified hemoglobin (Fr-Hb) by enhanced fluorescence emission with excitation at 285 nm, more surface accessible tryptophan residues by using acrylamide, changes in secondary and tertiary structures by CD spectroscopy, and increased thermolability by using differential scanning calorimetry in comparison with those of normal hemoglobin, HbA(0). Release of iron from hemoglobin is directly related with the extent of fructation. H2O2-induced iron release from Fr-Hb is significantly higher than that from HbA(0). In the presence of H2O2, Fr-Hb degrades arachidonic acid, deoxyribose and plasmid DNA more efficiently than HbA(0), and these processes are significantly inhibited by desferrioxamine or mannitol. Thus increased iron release from Fr-Hb may cause enhanced formation of free radicals and oxidative stress in diabetes. Compared to HbA(0), Fr-Hb exhibits increased carbonyl formation, an index of oxidative modification. Functional modification in Fr-Hb has also been demonstrated by its decreased peroxidase activity and increased esterase activity in comparison with respective HbA(0) activities. Molecular modeling study reveals Lys 7alpha, Lys 127alpha and Lys 66beta to be the probable potential targets for fructation in HbA(0).

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.

Additive effects of beta chain mutations in low oxygen affinity hemoglobin betaF41Y,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.

Hemoglobin Chico [beta 66(E10)Lys----Thr]: a new variant with decreased oxygen affinity

Hemoglobin Chico was discovered in an asymptomatic 3-year-old boy when a mild anemia was detected by a routine blood count. Affected individuals in three generations are also mildly anemic. The abnormal hemoglobin amounts to about 45% of the total. It separates from Hb A by cellulose acetate electrophoresis at pH 8.5 with a mobility similar to Hb J but does not separate in citrate agar at pH 6.2. Stability in isopropanol is slightly decreased. Its structure differs from the normal by the substitution of a threonyl residue for lysyl residue at position 66(E10) of the beta chain. The P50 of the oxygen equilibrium curve of whole blood at 37 degrees C was 38 torr compared with controls of 27 +/- 2 torr. The P50 binding studies of the isolated Hb Chico revealed a unique right shift of the equilibrium curve with an oxygen binding constant (1/P50) about half of normal. The remaining allosteric properties were essentially normal. This significant decrease in oxygen affinity appears to be due to changes in the heme region which result from the substitution of the normal beta 66 lysyl by the threonyl residue.

-G gamma A gamma-Thalassemia and gamma-chain variants in Chinese newborn babies

The occurrence of gamma-chain abnormal hemoglobins and of gamma-thalassemia in Chinese newborns was evaluated through analyses of the Hb F of over 1,100 babies and of the DNA from one baby and his parents. Gene mapping data identified this baby as a homozygote for -G gamma A gamma-thalassemia, which is caused by a deletion of about 5 kb due to an unequal crossing-over between the -G gamma- and -A gamma- genes. This condition is the same as that observed in Indian and Japanese babies [2,3]. Its gene frequency among babies from the Shanghai area was 0.012. A previously unrecognized G gamma chain variant, Hb F-Shanghai or alpha 2 G gamma 266(E10)Lys----Arg, was observed in one newborn. This variant was not detected by conventional techniques but only by high performance liquid chromatography, as the G gamma 66 Lys and G gamma 66 Arg chains had slightly different chromatographic mobilities. Lys at position gamma 66 participates in contacts with the heme group, and its substitution by another amino acid residue might interfere with physiochemical and/or functional properties. No other gamma-chain variants have been detected except the well-known A gamma T or F-Sardinia chain (f.A gamma T = 0.076).

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.

An unstable haemoglobin, Hb Tacoma beta30 (B12) arg leads to ser, detected at birth by the demonstration of red cell inclusions

Incomplete expression of human haemoglobin beta-chains at birth may lead to difficulty in the early demonstration of an inherited beta-chain variant. In this case, the rare unstable variant, Hb Tacoma beta30 (B12) arg leads to ser, although not present in cord blood in sufficient amounts to be easily detected by routine electrophoretic techniques, was readily shown to be present by the striking inclusions provoked by prolonged incubation of the neonatal red cells with new methylene blue.

Recent developments in foetal haemoglobin research

There have been numerous new contributions to the knowledge of foetal haemoglobin over the last few years. It is, therefore, timely to review them together. They throw light on the arrangement on the chromosome of non-alpha chain genes, and on the condition generally known as Hereditary Persistence of Foetal Haemoglobin (HPFH) and have contributed to other aspects of human ontogeny and physiology.