Clinical, hematologic and biosynthetic studies in sickle cell-betao-thalassemia: a comparison with sickle cell anemia

Diminished cerebral oxygen extraction and metabolic rate in sickle cell disease using T2 relaxation under spin tagging MRI

PURPOSE

T2 MRI oximetry can noninvasively determine oxygen saturation (Y) but requires empirical MR calibration models to convert the measured blood transverse relaxation (T2b ) into Y. The accuracy of existing T2b models in the presence of blood disorders such as sickle cell disease (SCD) remains unknown.

METHODS

A Carr Purcell Meiboom Gill T2 preparation sequence was used to make 83 whole blood measurements from 11 subjects with SCD to derive an ex vivo sickle hemoglobin (HbS) T2b model. Forearm venous blood gas, sagittal sinus T2 (T2 Relaxation Under Spin Tagging) and total brain blood flow (phase contrast MRI) were measured in 37 healthy controls and 33 SCD subjects (age 24.6 ± 10.2 years). Cerebral oxygen saturation, extraction fraction, and metabolic rate estimates were calculated using three separate T2b models. Cerebral and forearm oxygen extraction fraction were compared.

RESULTS

Ex vivo, SCD blood had greater saturation dependent relaxivity than control blood, with a weak dependence on HbS and no dependence on hematocrit. In vivo, the HbS T2b model predicted Yv values with lowest coefficient of variation (compared with existing T2b models) and the strongest correlation with peripheral venous oximetry (r2  = .29). The HbS T2b model predicted systematically higher Yv measurements in SCD patients (73 ± 5 and 61 ± 6; P < 0.0001) which was mirrored by peripheral venous measurements (75 ± 20 and 45 ± 20; P < 0.0001).

CONCLUSION

Cerebral and peripheral oxygen extraction are decreased in SCD patients, suggesting either blood flow is increased beyond metabolic demands or the presence of physiological arterial-venous shunting. Magn Reson Med 80:294-303, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Subclassification of HbS syndrome: is it necessary?

Sickle beta-thalassaemia (S beta-thalassaemia) is a condition, which results from coinheritance of a sickle cell gene and a beta-thalassaemia gene. The clinical phenotype depends on the type of beta-thalassaemia gene (beta+ or beta(o)). There are several similarities in clinical and haematological features, which sometimes pose a difficulty in correct diagnosis. A definitive diagnosis is required in order to initiate early supportive treatment in patients with homozygous sickle cell disease (SS disease) and to define the later clinical course. Forty-seven cases of haemoglobin sickle syndrome (HbS syndrome) were studied. The clinico-haematological features and high-performance liquid chromatography (HPLC) results from 17 patients with S beta-thalassaemia were compared with those of SS disease (10 patients). Splenomegaly was more commonly found in patients with S beta-thalassaemia. Among the haematological features, red blood cell counts and HbA2 levels were significantly higher in patients with S beta-thalassaemia, while red cell indices, such as MCV, MCH were significantly lower than those seen SS disease. MCHC, PCV total haemoglobin (Hb), HbS, A and HbF were similar in the two groups.

Peptide nucleic acid (PNA) binding-mediated induction of human gamma-globin gene expression

Peptide nucleic acids (PNAs) can bind to homopurine/homopyrimidine sequences of double-stranded DNA targets in a sequence-specific manner and form [PNA]2/DNA triplexes with single-stranded DNA D-loop structures at the PNA binding sites. These D-loop structures have been found to have a capacity to initiate transcription in vitro. If this strategy can be used to induce transcription of endogenous genes, it may provide a novel approach for gene therapy of many human diseases. Human [beta] globin disorders such as sickle cell anemia and beta-thalassemia are very common genetic diseases that are caused by mutations in the beta-globin gene. When gamma-globin genes are highly expressed in sickle cell patients, the presence of high levels of fetal hemoglobin (HbF, alpha2gamma2) can compensate for the defective beta-globin gene product and such patients have much improved symptoms or are free of disease. However, the gamma-globin genes are developmentally regulated and normally expressed at very low levels (>1%) in adult blood cells. We have investigated the possibility of inducing gamma-globin gene expression with PNAs. Using PNAs designed to bind to the 5' flanking region of the gamma-globin gene, induction of expression of a reporter gene construct was demonstrated both in vitro and in vivo. More importantly, PNA-mediated induction of endogenous gamma-globin gene expression was also demonstrated in K562 human erythroleukemia cells. This result suggests that induction of gamma-globin gene expression with PNAs might provide a new approach for the treatment of sickle cell disease. PNA-induced gene expression strategy also may have implications in gene therapy of other diseases such as genetic diseases, cancer and infectious diseases.

Nomegestrol acetate contraceptive implant use by women with sickle cell disease

OBJECTIVE

To assess the contraceptive effectiveness, safety, and potential health benefits of nomegestrol acetate contraceptive implant use by women with homozygous sickle cell disease (hemoglobin SS).

METHODS

This was a prospective observation before and after insertion of nomegestrol acetate of 20 women with sickle cell disease (test group) compared with 10 women with similar sociodemographic backgrounds. Changes in hematologic and biochemical parameters and symptoms of sickle cell crisis were measured during 12 months of observation.

RESULTS

After use of nomegestrol acetate for 1 to 9 months, the women in the test group had symptomatic improvement, with no crisis that required hospitalization and no deaths. Sickle cell symptoms persisted in the women in the control group, with 1 recorded death. Increases in F-cell and fetal hemoglobin parallel the observed clinical improvement in the treated women. There were no adverse hematologic or biochemical changes associated with the use of nomegestrol acetate implants.

CONCLUSION

Nomegestrol acetate appears to be a safe and appropriate contraceptive for women with sickle cell disease, showing evidence of being a "stimulant" for F-cell reactivation, independent of F hemoglobin total production increase.

Fetal Hemoglobin and F-Cell Responses to Long-Term Hydroxyurea Treatment in Young Sickle Cell Patients

We have studied the cellular and molecular responses to long-term hydroxyurea (HU) treatment in 29 severely affected young patients with sickle cell disease (mean age, 10.9 ± 4.1 years). Patients received HU at 20 mg/kg/d on 4 consecutive days per week initially, with a monthly escalated dose avoiding marrow-toxicity (mean steady-state dose, 34.2 ± 4.6 mg/kg/d) for 12 to 36 months (mean duration, 22 months). The studied parameters were hemoglobin F (HbF), F reticulocytes (F retics), F cells, the amount of HbF per F cell (F/F cell), polymer tendency at 40% and 70% oxygen saturation, and hemolysis. Initial HbF (Fi) was dispersed (from 0.85% to 13.9%). HbF increased in all patients but 1. HbF at maximal response (Fmax) reached a sustained level varying from a 1.5-fold to a 16-fold Fi after a variable delay (6 to 24 months). Fmax was not related to HU dosage, but ▵F (Fmax − Fi) was strongly correlated to ▵MCV (MCVmax − MCVi). HbF increase resulted from the increase of both F cells and F/F cell. In this rather short series, Fi and Fmax were not significantly associated with age, gender, or β-globin haplotype. Neither Fmax nor ▵F was related to bone marrow reserve, as measured by baseline reticulocyte or neutrophil counts. However, Fmax was highly dependent on Fi. When patients are individualized into three groups according to Fmax (group 1, Fmax >20% [12 patients]; group 2, 10% < Fmax < 20% [11 patients]; group 3, Fmax <10% [5 patients]), Fi is significantly different between groups, being the highest in group 1. In addition, the best responders (group 1) were significantly different from patients in the two other groups with higher levels of total hemoglobin, decreased bilirubin, and decreased polymer tendency.

Fetal Hemoglobin and F-Cell Responses to Long-Term Hydroxyurea Treatment in Young Sickle Cell Patients

We have studied the cellular and molecular responses to long-term hydroxyurea (HU) treatment in 29 severely affected young patients with sickle cell disease (mean age, 10.9 ± 4.1 years). Patients received HU at 20 mg/kg/d on 4 consecutive days per week initially, with a monthly escalated dose avoiding marrow-toxicity (mean steady-state dose, 34.2 ± 4.6 mg/kg/d) for 12 to 36 months (mean duration, 22 months). The studied parameters were hemoglobin F (HbF), F reticulocytes (F retics), F cells, the amount of HbF per F cell (F/F cell), polymer tendency at 40% and 70% oxygen saturation, and hemolysis. Initial HbF (Fi) was dispersed (from 0.85% to 13.9%). HbF increased in all patients but 1. HbF at maximal response (Fmax) reached a sustained level varying from a 1.5-fold to a 16-fold Fi after a variable delay (6 to 24 months). Fmax was not related to HU dosage, but ▵F (Fmax − Fi) was strongly correlated to ▵MCV (MCVmax − MCVi). HbF increase resulted from the increase of both F cells and F/F cell. In this rather short series, Fi and Fmax were not significantly associated with age, gender, or β-globin haplotype. Neither Fmax nor ▵F was related to bone marrow reserve, as measured by baseline reticulocyte or neutrophil counts. However, Fmax was highly dependent on Fi. When patients are individualized into three groups according to Fmax (group 1, Fmax &gt;20% [12 patients]; group 2, 10% &lt; Fmax &lt; 20% [11 patients]; group 3, Fmax &lt;10% [5 patients]), Fi is significantly different between groups, being the highest in group 1. In addition, the best responders (group 1) were significantly different from patients in the two other groups with higher levels of total hemoglobin, decreased bilirubin, and decreased polymer tendency.

DNA methylation: biology and significance

The modification of DNA by cytosine methylation is crucial for normal development. DNA methylation patterns are distinctive between tissues and are maintained with high fidelity during cell division. DNA methylation probably exerts its effects through alterations in chromatin structure, with a resultant effect on genetic transcription. 5-methylcytosine is also prone to spontaneous hydrolytic deamination to thymine. Whilst most G:T mismatches so produced are repaired, failure of mismatch repair leads to established mutation. Indeed, mutations that are the result of 5-methylcytosine transitions account for a disproportionate number of genetic mutations described in malignant and non-malignant disease. There is also evidence for substantial deregulation of DNA methylation in malignancy. Whether this deregulation is crucial for the transformation process, or simply an epiphenomenon associated with it, is still not established.

Hydroxyurea therapy in children severely affected with sickle cell disease

HYPOTHESIS

The major clinical manifestations of sickle cell disease (SCD) are hemolytic anemia, predisposition to infection, and recurrent vaso-occlusive episodes resulting in pain, organ dysfunction, or both. There has been no satisfactory treatment for children with recurrent severe painful episodes caused by SCD. Hydroxyurea is an antimetabolite drug shown in adults with SCD to increase fetal hemoglobin levels and reduce the symptoms of SCD. We hypothesized that hydroxyurea therapy in children with severe (defined as > or = 3 vaso-occlusive events per year) SCD could improve hematologic parameters and reduce vaso-occlusive events.

OBJECTIVE

To assess the safety and efficacy of hydroxyurea for the treatment of severe SCD in children.

STUDY DESIGN

After obtaining informed consent, we initiated hydroxyurea therapy at a dosage of 10 to 20 mg/kg per day in 15 patients with severe SCD (hemoglobin SS, hemoglobin SS-alpha thalassemia, or hemoglobin S-beta0-thalassemia). Doses were escalated as tolerated. Patients were monitored with bimonthly physical examinations and monthly laboratory measures. To assess the impact of hydroxyurea on clinical symptoms, we recorded the number of inpatient days for each patient during the period of treatment and compared it with the number of inpatient days for the 12- to 24-month period before institution of hydroxyurea therapy, using the subject as his or her own control subject.

RESULTS

Thirteen patients received hydroxyurea for a median of 24 months (range, 6 to 39 months). The mean dose of hydroxyurea was 21.4 +/- 5.2 mg/kg. Treatment with hydroxyurea induced statistically significant increases in the total hemoglobin concentration, mean corpuscular volume, and percentage of hemoglobin F, and a decrease in the serum concentration of bilirubin. Toxic effects included three episodes of a reversible myelotoxic reaction, two of which required transfusion of packed erythrocytes. For the entire group, hospitalization decreased from a prehydroxyurea median of 3.9 +/- 2.0 days per month to 1.1 +/- 2.1 days per month of therapy (p = 0.09). For those subjects (n = 10) completing at least 1 year of treatment, the decrease in hospitalization from 4.1 +/- 2.2 to 1.0 +/- 1.7 days per month was significant (p = 0.03).

CONCLUSIONS

In this pilot trial, hydroxyurea treatment of severe SCD in children was associated with improved hematologic parameters, acceptable toxic effects, and a trend to reduced hospitalization. Hydroxyurea appears to be a safe and potentially effective agent for the treatment of severe SCD in children. A prospective, controlled trial to investigate the efficacy of hydroxyurea in children is therefore warranted.

Interaction between HBS-beta-o-thalassemia and alpha-thalassemia

We have defined the clinical and laboratory characteristics of a group of patients with HbS-beta o-thalassemia plus alpha-thalassemia, by analysis of erythrocyte indices, hemoglobin A2 and F levels, globin biosynthesis studies and alpha-globin gene mapping. Patients with HbS-beta o + alpha-thalassemia closely resembled individuals with HbS-beta o-thalassemia except for balanced globin synthesis ratios and a lower HbF level. The frequency of painful crises, leg ulceration, aseptic necrosis of bone and acute chest syndrome was similar in HbS-beta o + alpha-thalassemia patients and controls with sickle cell anemia (HbSS), HbSS-alpha-thalassemia and HbS-beta o-thalassemia. These findings are consistent with previous work which failed to show a reduction in the vaso-occlusive severity of sickle cell disease by the coexistence of alpha-thalassemia.

Sickle cell beta-thalassaemia compared with sickle cell anaemia in Algeria

Clinical, haematological and biochemical features in 42 subjects with S-beta thalassaemia (31 subjects with S-beta thalassaemia and 11 subjects with S-beta+ thalassaemia); and in 42 with homozygous sickle cell disease were compared. Persistent splenomegaly was more common and painful crises less common in the S-beta thalassaemia group. Total Hb was higher and reticulocyte count lower in S-beta+ thalassaemia than in S-beta thalassaemia or SS disease. Microcytosis was marked in the S-beta thalassaemia group while the MCV was normal in sickle cell anaemia. Hb F was significantly higher in the S-beta thalassaemia group, without any influence on the severity of the disease. Many features suggest that sickle cell thalassaemia is more severe in Algeria than in Negro subjects and similar to the disease in Italian patients.

The effects of alpha-thalassaemia in HbSC disease

In HbSC disease, as in sickle cell anaemia, there is a spectrum of clinical severity. A reduced mean corpuscular volume and haemoglobin concentration, traits typical of thalassaemia, might retard sickling. We therefore ascertained the prevalence of alpha-thalassaemia in 53 adults with HbSC disease and related alpha-globin gene deletion to the haematologic and clinical findings. Alpha-globin genotype was identified by restriction endonuclease gene mapping. Indirect ophthalmoscopy and fluorescein angiography were used to document the presence of proliferative retinopathy. Bone necrosis and infarction were determined roentgenographically or by radionuclide scanning. Either heterozygous or homozygous alpha-thalassaemia-2 was present in 26% of patients. There was no relationship between alpha-globin genotype and haematocrit, pain crises, bone lesions, proliferation retinopathy or clinical severity score.

Molecular analysis of the beta-thalassemia phenotype associated with inheritance of hemoglobin E (alpha 2 beta2(26)Glu leads to Lys)

Inheritance of the gene for betaE-globin is associated with hypochromia and microcytosis, reminiscent of typical heterozygous beta-thalassemia. Patients with hemoglobin (Hb)E-beta-thalassemia exhibit clinical phenotypes of severe beta-thalassemia, a circumstance not encountered in other compound heterozygous states for structural beta-chain mutations and beta-thalassemia. We have analyzed the kinetics of globin synthesis and the levels of globin messenger (m) RNA accumulation in patients with Hb E-beta-thalassemia and Hb E trait. The initial rate of beta-globin synthesis (betaE/alpha=0.20-0.34) was less than expected on the basis of gene dosage, or comparable studies of other compound heterozygous states for beta-thalassemia and structurally abnormal beta-chains. betaE-globin synthesis was not only reduced during short-term incubations (1-5 min), but also remained relatively unchanged during long-term pulse or chase incubations up to 5h. Analysis of globin mRNA by cell-free translation and molecular hybridization confirmed that the unexpectedly low levels of betaE-globin synthesis were associated with comparable reduction in the levels of beta-globin mRNA. In Hb E-beta-thalassemia the betaA + betaE (alpha globin nRNA ratio observed were substantially lower than those obtained from reticulocytes of patients with heterozygous beta-thalassemia, or Hb S-betaO-thalassemia, while in Hb E trait, the betaA + betaE/alpha mRNA ratio was in the ranged observed for beta-thalassemia trait. The betaE-globin gene specifies reduced accumulation of betaE-globin mRNA, a property characteristic of other forms of beta-thalassemia. The beta-thalassemia phenotype associated with inheritance of Hb E is thus determined at the level of beta-globin mRNA metabolism.

Sickle cell anemia as a syndrome: a review of diagnostic features

Sickle cell (SS) disease is a complex of various genetic conditions. In some, homozygosity for the beta S gene may be present alone or in combination with the heterozygous or homozygous alpha-thalassemia-2 condition. Such combinations might ameliorate the clinical and hematological condition of the patient. The same may be true for the high levels of Hb F and F-cells observed in many Hb S homozygotes. Howeever, the chemical heterogeneity of Hb F appears not to be related to the clinical status of the Hb S homozygote. Combinations of a Hb S heterozygosity with a heterozygosity for a Hb D-type of variant, for either one of two types of beta-thalassemia, two types of alpha beta- thalassemia, and five types of HPFH are discussed, and data are compared with those obtained for Hb S homozygotes. The use of advanced laboratory procedures and family studies is often necessary for an accurate diagnosis.

Comparison of sickle cell-beta0 thalassaemia with homozygous sickle cell disease

Clinical and haematological features in 41 patients with sickle cell-beta0 thalassaemia (Sbeta0 thalassemia) and in 123 age--sex matched controls with homozygous sickle cell (SS) disease were compared. Persistence of splenomegaly was more common and fetal loss less common in Sbeta0 thalassemia but other clinical features were similar in the two genotypes. Total haemoglobin, Hb A2, PCV, CCV, and red cell count were significantly higher and MCV, MCH, MCHC, and ISC counts significantly lower in Sbeta0 thalassaemia. Proportional reticulocyte counts were significantly lower in Sbeta0 thalassaemia but there was no difference in absolute reticulocyte counts. Persistence of splenomegaly and low ISC counts are compatible with decreased intravascular sickling which may result from the lower mean cell haemoglobin S concentration in Sbeta0 thalassaemia. If beneficial effects of a low MCHC can be confirmed then a carefully monitored trial of iron deficiency in SS disease may be a logical experimental procedure.

Erythrocyte calcium abnormalities and the clinical severity of sickling disorders

We studied erythrocyte calcium levels and uptake in a group of patients with sickle haemoglobinopathies of different clinical severity in an attempt to relate these measurements to the production of irreversibly sickled cells and disease severity. Erythrocyte calcium levels were measured by atomic absorption spectroscopy and calcium uptake by isotopic means. In sickle cell anaemia, erythrocyte calcium content was elevated and the uptake of isotopic calcium increased under both oxygenated and deoxygenated conditions. There was a direct correlation between the numbers of irreversibly sickled cells and calcium uptake and an inverse relationship between calcium uptake and red cell potassium level. The clinical course of disease was milder in patients with high fetal haemoglobin levels, but there was no relationship between clinical course and calcium levels, calcium flux or irreversibly sickled cells. Our observations suggest that calcium accumulation and irreversibly sickled cell formation are related processes. The absence of good correlation between various biochemical and clinical parameters emphasizes the complexity of factors which modify the clinical course of this disorder.

Variations in globin synthesis in delta-beta-thalassaemia

Peripheral blood globin synthesis studies were done in 11 patients with delta beta-thalassaemia trait, Hb S-delta beta-thalassaemia or delta beta/betao-thalassaemia from two black and two Caucasian families. All patients had elevated Hb F and normal or decreased Hb A2 levels and 10 had family studies confirming the diagnosis. In addition, four unrelated non-thalassaemic patients with elevated Hb F levels also had peripheral blood globin synthesis studies. The beta/alpha specific activity globin synthesis ratios in the three blacks with delta beta-thalassaemia trait were 0.60--1.04. In the four Caucasians with delta beta-thalassaemia traint, the beta/alpha ratios were 0.58--1.02. These results demonstrate a wide range of ratios overlapping those of normal controls (0.99 +/- 0.06). The betas/alpha ratios in three blacks with Hb S-delta beta-thalassaemia ranged from 0.66 to 1.00, similar to those of patients with delta beta-thalassaemia trait. In the black patient with delta beta/betao-thalassaemia, the gamma/alpha ratio was 0.67. The beta/alpha peripheral blood ratios in the four non-thalassaemia patients with elevated Hb F ranged from 1.00 to 1.11, similar to those of normal controls. These studies indicate that a decreased beta/alpha ratio is not an invariable finding in delta beta-thalassaemia in blacks or Caucasian patients and that globin synthesis data alone is insufficient to diagnose definitively heterozygotes for delta beta-thalassaemia or to distinguish this trait from non-thalassaemic haematological disorders associated with a normal percentage of Hb A2 and an elevated level of Hb F.

Globin biosynthesis in sickle cell, Hb SC, and Hb C diseases

The wide range of globin synthesis ratios reported in patients with sickle cell disease casts doubt on whether the presence of genes for alpha- or beta-thalassemia in combination with Hb S can be detected by globin synthesis studies. We have studied globin synthesis in 20 patients with Hb SS who had a mean betaA/alpha ratio of 1.05+/-0.04, similar to that of 28 control children. In nine of these patients the percentage of newly synthesized radioactive alpha-chains in dimer or monomer forms was 16.3%+/-1.3, also similar to the control subjects. The remainder of alpha-chain was in hemoglobin tetramer. In nine patients with Hb SC, the (non-alpha)/alpha ratio was 0.97+/-0.04, and the free alpha-chain pool radioactivity in four patients was 14.1%+/-4.2. In three patients with Hb CC, betac/alpha ratios were 0.99, 1.07, and 1.10. These results indicate that globin synthesis ratios and alpha-chain radioactivity in the free alpha-chain pool of peripheral blood of patients with Hb SS, Hb SC, and Hb CC have narrow ranges, close to those of nonthalassemic controls. The data provide a basis for detecting syndromes with Hb S or Hb C associated with alpha- or beta-thalassemia. This precise differentiation is important for clinical studies of severity in sickle cell disease and for genetic counseling.

Sickle cell anemia: erythrokinetics, blood volumes, and a study of possible determinants of severity

The variability in the clinical expression of sickle cell anemia led us to study factors which might influence the course of this disease. We examined erythrokinetics, blood volumes, and variables which influence hemoglobin function in a group of adults with sickle cell anemia of varying degrees of clinical severity. We were unable to correlate any single measurement with the clinical course; however, our patient sample was small and the data suggested areas for further study. An expansion of plasma volume noted in all patients. This made it difficult to predict red cell mass from the hemoglobin level, which consistently underestimated its magnitude. The red cell production index and iron turnover values indicated that there is often a suboptimal erythropoietic response to anemia in sickle cell disease.