Effect of Age on Blood Rheology in Sickle Cell Anaemia and Sickle Cell Haemoglobin C Disease: A Cross-Sectional Study.

OBJECTIVES: Blood rheology plays a key role in the pathophysiology of sickle cell anaemia (SS) and sickle cell haemoglobin C disease (SC), but its evolution over the lifespan is unknown. MATERIALS AND METHODS: Blood viscosity, red blood cell (RBC) deformability and aggregation, foetal haemoglobin (HbF) and haematocrit were measured in 114 healthy individuals (AA), 267 SS (161 children + 106 adults) and 138 SC (74 children + 64 adults) patients. RESULTS: Our results showed that 1) RBC deformability is at its maximal value during the early years of life in SS and SC populations, mainly because HbF level is also at its peak, 2) during childhood and adulthood, hydroxycarbamide treatment, HbF level and gender modulated RBC deformability in SS patients, independently of age, 3) blood viscosity is higher in older SS and SC patients compared to younger ones and 4) haematocrit decreases as SS patients age. CONCLUSION: The hemorheological changes detected in older patients could play a role in the progressive development of several chronic disorders in sickle cell disease, whose prevalence increases with age. Retarding these age-related haemorheological impairments, by using suitable drugs, may minimize the risks of vaso-occlusive events and chronic disorders.

Neonatal haemoglobinopathy screening: review of a 10-year programme in Brussels.

Since 1994, a neonatal screening programme for major haemoglobinopathies has been conducted in Brussels. We performed a 10-year re-evaluation of the incidence of haemoglobinopathies in Brussels and found that of the 118,366 newborns screened, 64 were diagnosed with a sickle cell syndrome, six had beta-thalassaemia major, four had a haemoglobin C disease and three had a haemoglobin H disease. Of the 64 babies with a sickle cell disease, two died before the age of two years and two did not present at the first neonatal visit. Of the six babies suffering from beta-thalassaemia major, all are alive and two have undergone a haematopoietic stem cell transplantation. The universal neonatal screening programme for haemoglobinopathies should be maintained in Brussels.

K:Cl cotransport activity is inhibited by HCO3- in knockout mouse red cells expressing human HbC.

K:Cl cotransport (KCl) was examined in transgenic mice expressing exclusively human hemoglobin C. In contrast to previous studies in early transgenic mice expressing human alpha and beta(S) and residual mouse globins, we found significant volume and pH stimulation and sensitivity to. Exposure to physiological levels of also blocked a significant fraction of KCl cotransport.

Crystallization of recombinant hemoglobins with basic amino acid substitutions (Lys and Arg) at the beta 6 position.

We have produced recombinant hemoglobins (rHbs) alpha 2 beta 2(6Glu-->Lys) (rHb beta E6K) and alpha 2 beta 2(6Glu-->Arg) (rHb beta E6R) using a yeast expression system coupled with a polymerase chain reaction (PCR)-based mutagenesis strategy for studies focused on defining determinants that facilitate crystallization of Hb C (alpha 2 beta 2(6Lys)). rHb beta E6K had the same electrophoretic mobility as native human Hb C, whereas rHb beta E6R migrated slightly slower than Hb C on cellulose acetate electrophoresis. The carbonmonoxy (CO) forms of rHb beta E6K and rHb beta E6R formed tetrahedral crystals in vitro in 2.3 mol/L phosphate buffer just like native Hb C. The Hb concentration required for crystallization of CO-rHb beta E6R was lower than that of CO-rHb beta E6K, suggesting that stronger basic amino acids at the beta 6 position accelerate crystallization of Hb. However, the size of rHb beta E6R crystals was smaller than that of rHb beta E6K. Crystallization of native Hb C and both rHbs was inhibited by Hb F. These results suggest that alpha 2 beta gamma-heterohybrids that have basic amino acids at the beta 6 position behave similarly and are unable to crystallize like Hb C.

Kinetics of the Hb A to Hb C switch and erythropoietin plasma levels in sheep.

The induction of Hb A (alpha 2 beta A2) and Hb C (alpha 2 beta C2) synthesis in three adult sheep has been sequentially analysed, in relation to the reduction of the haematocrit (Ht) and to the changes of erythropoietin (Epo) concentration in plasma. Hb A production is detected in peripheral reticulocytes when the Ht approaches 70% of its initial value in correspondence with the first rise of EPO plasma level, whereas HB C synthesis appears when the Ht is further reduced to about 50%, at an Epo concentration two to three times higher. The assumption that the cell committed to HB C synthesis is close to the erythroid colony-forming unit (CFU-e) progenitor is also discussed.

Fetal and adult hemoglobin in the chronically catheterized sheep fetus.

The switch from fetal to adult hemoglobin (Hb) has been investigated in fetal and newborn lambs. In the period between 125 and 145 days gestation, the proportion of fetal cells containing adult Hb increased significantly in catheterized fetuses. This increase paralleled the rise in fetal plasma cortisol under several different experimental conditions. However, infusion of synthetic adrenocorticotropin (ACTH1-24) into the fetus, which increased fetal plasma cortisol concentrations to levels slightly higher than observed at term, did not bring about any increase in the proportion of cells containing adult Hb. Increasing fetal plasma prolactin (PRL) concentration either by infusion of PRL or by stimulating endogenous PRL release with thyrotropin-releasing hormone (TRH) did not influence the time or rate of the switch. The fetal reticulocyte count was significantly higher in blood samples taken at the time of catheterization in fetuses of 103-115 days gestation than at 116-128 days gestation. In one repeatedly sampled fetus of adult type Hb AB, Hb C was observed at the time when the fetus was anemic. At birth the number of cells containing adult Hb was significantly higher in catheterized lambs than in nonoperated controls.

Hemoglobin switching in sheep: a comparison of the erythropoietin-induced switch to HbC and the fetal to adult hemoglobin switch.

Stimulation of sheep erythropoietic progenitor cells by erythropoietin (epo) has been studied with regard to its effect on the pattern of hemoglobin production. An analysis of hemoglobin (Hb) synthesis in BFU-E- and CFU-E-derived colonies from fetuses either homozygous for HbA (AA) (homozygous also for the beta c gene responsible for HbC production) or HbB (BB) (lacking the beta c gene) indicated the following. Colonies derived from precursor cells from 51- and 89-day fetuses exhibited small but detectable increments of HbB synthesis with prolonged incubation in vitro. This response was not dependent on the epo concentration. Erythropoietic precursor cells from a 124-day BB fetus were already committed to HbB synthesis, since HbF production was replaced by HbB on successive days in vitro as erythroid colonies matured; this switch was not affected by varying the epo concentration. In contrast, progenitor cells from a 124-day AA fetus responded to higher doses of epo by forming colonies in which more HbC was made at the expense of both HbF and HbA. Erythropoietic stress did not result in induction of HbF in vivo or in erythroid colonies derived from CFU-E in young adult BB sheep, whereas our prior studies had shown induction of HbC synthesis under analogous conditions in colonies derived from young adult AA sheep. We conclude that the epo-induced HbF (or HbA) to HbC switch and the fetal to adult hemoglobin switch are regulated by different mechanisms.

Hemoglobin switching in sheep: characteristics of BFU-E-derived colonies from fetal liver.

Two types of erythroid colonies were generated in vitro from sheep fetal liver cells. The first type consisted of single colonies of 8-256 cells that were well hemoglobinized by 4 days; these are thought to originate from CFU-E. The second type consisted of macroscopic colonies composed of several subcolonies that matured between days 3 and 8 in vitro. At maturity, each contained 256 to > 1000 cells that formed a discrete macroscopic cluster. The macroscopic colonies, not previously described in sheep, are thought to be derived from BFU-E. The characteristics of sheep BFU-E were defined and the production of fetal hemoglobin (HbF, alpha 1, gamma 2) and HbC (alpha 2 beta 2) was compared in colonies derived from CFU-E or BFU-E. Bursts developed at erythropoietin (epo) concentrations as low as 0.1 U/ml, although the number observed increased with epo concentration up to 10 U/ml. The number of bursts observed was approximately proportional to the number of cells plated. As shown by thymidine suicide, approximately 50% of both the BFU e and CFU-E were in S-phase when obtained from the fetus. BFU-E were smaller and partially separable from CFU-E after sedimentation at unit gravity. The beta c/gamma synthetic ratio in colonies derived from BFU-E was greater than in CFU-E-derived colonies. These data suggest that the capacity for generation of erythroblasts making HbC is greater in the earlier or more primitive erythroid stem cells in fetal liver.

Overview: mechanisms of the regulation of hemoglobin synthesis at the cellular level.

The concept that has emerged from our experiments and those of others is that erythroid stem cells are committed to undergo a program of erythroid differentiation with respect to the ultimate hemoglobin phenotype of their progeny erythrocytes. A clear distinction can be drawn between the switch from Hb A (or Hb F) to Hb C in sheep and the switch from Hb F to adult hemoglobin in humans. The former appears to be regulated in a relatively late erythroid stem cell with characteristics of CFU-E. In contrast, the CFU-E found in adult sheep bone marrow from animals that lack the beta C gene appear to be preprogrammed to produce only adult hemoglobin. Fetal stem cells may be induced to synthesize Hb C within a time frame that is similar to that seen in cultures of adult bone marrow. Thus, a common mechanism modulating the potential for expression of this gene and commitment of erythroid stem cells with respect to Hb C production in progeny erythroblasts seems quite likely. Again fetal CFU-E and BFU-E in animals lacking the beta C gene appear to be, for the most part, committed toward producing erythroblasts making Hb F. Further analysis will be required to determine at exactly which stage of stem cell differentiation this programming occurs and also the factors that are important in modulating the potential for fetal and adult hemoglobin synthesis.

Hemoglobin switching in sheep. Synthesis, cloning, and characterization of DNA sequences coding for the beta B, beta C, and gamma-globin mRNAs.

Synthetic double-stranded DNAs (sDNAs) were prepared from sheep globin mRNA templates isolated from reticulocytes producing either hemoglobin B (HbB) (alpha 2 beta B2), HbC (alpha 2 beta C2), or HbF (alpha 2 gamma 2). These DNAs were inserted into the Eco RI site of plasmid pMB9 by the homopolymer tailing method and used to transform Escherichia coli X1776 to tetracycline resistance. Recombinant clones were identified by colony hybridization and further characterized by molecular hybridization and restriction endonuclease analysis. All plasmids analyzed thus far contained either beta- or gamma-globin DNA sequences. Moreover, sDNAs used for cloning yielded restriction endonuclease fragments consistent with the presence of predominantly beta- or gamma-sDNA, indicating that formation of double-stranded alpha-sDNA proceeds much less efficiently under our conditions than the formation of non-alpha-sDNAs. Three recombinant plasmids, pS beta B2, pS beta C69, and pS gamma 56, were selected for detailed study. These were shown to contain, respectively, beta B-, beta C-, and gamma-DNA sequences by molecular hybridization and by protection of the appropriate cDNAs from S1 nuclease digestion. Each contained all of the restriction endonuclease sites defined for the synthetic sDNAs and protected at least 90% of the sequence length of homologous cDNA. Restriction endonuclease maps of the beta B- and beta C-globin genes were identical at all 12 sites that were mapped, whereas four differences were identified in the gamma gene compared to the two others; three of these corresponded to differences in amino acid sequence of the globins. A method was developed to isolate the anti-mRNA strand of the insert for use as a specific molecular hybridization probe analogous to complementary DNA.

Regulation of hemoglobin synthesis during the development of the red cell (third of three parts).

In this article we have surveyed the current state of knowledge regarding the accumulation of globin mRNA and hemoglobin in red cells. We have attempted to examine the interplay of numerous processes that seem to be necessary to achieve this highly differentiated state. Finally, we have made an effort to formulate some of the mechanisms whereby individual red cells may come to contain varying proportions of specific hemoglobins. The past several years have been characterized by a veritable explosion of knowledge concerning the globin structure genes, and the structure, transcription, processing and function of globin mRNA in erythroid cells. It now seems possible to analyze the earlier stages of erythropoiesis by cultivation and examination of erythroid colonies in vitro. The primary differentiation events leading to the production of specific globins, especially for hemoglobin F production in man, are now experimentally accessible. There is good reason to hope that these advances will soon permit achievement of the long desired therapeutic goal of enhancing hemoglobin F synthesis in patients with severe beta-chain hemoglobinopathies. Our aim has been to review the scientific information that might provide the rationable for amelioration of the clinical phenotypes in patients inheriting abnormal globin genes.

Hemoglobin switching in sheep and goats: induction of hemoglobin C synthesis in cultures of sheep fetal erythroid cells.

Synthesis of HbF (alpha2gamma2) is replaced by synthesis of Hb A (alpha2betaA2) shortly before birth in sheep homozygous for the betaA globin chain whereas Hb C (alpha2betaC2) is produced transiently during the neonatal period. We have obtained a Hb F-to-Hb C switch by generating erythroid colonies at high erythropoietin concentration in plasma clot cultures of mid-gestation fetal bone marrow or liver. Furthermore, high erythropoietin concentration appeared specifically to activate the gene for betaC and not those for betaA or betaB globin in colonies grown from cells of an animal heterozygous for the betaA and betaB genes. Erythropoietic stress in the form of periodic bleeding or erythropoietin injection in utero did not stimulate production of Hb C (alpha2betaC2) in fetal sheep until shortly before birth, and then only in two of six animals. Thus, factors other than erythropoietin may influence the potential for betaC globin synthesis in vivo in fetal sheep.

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.

Stability of the individual globin genes during erythroid differentiation.

The genes of sheep betaA, betaC, and gamma globin were all present in DNA from erythroid cells which synthesized only betaC globin. Similarly, selective excision of non-expressed genes was shown not to occur during human erythroid differentiation. In contrast, evolutionary deletion of the betaC gene accounts for the inability of many sheep to make this globin.

Hemoglobin ontogenesis: test of the gene excision hypothesis.

The gene excision hypothesis of hemoglobin ontogenesis was tested in persons with HbSC disease, with the use of monospecific fluorescent antibodies for the identification of hemoglobins S, C, and F in individual erythrocytes. The results are incompatible with the prediction that only one gamma- or beta-globin gene may be active in any single chromosome and provide further evidence for incomplete repression of gamma-globin genes lying cis to active beta-globin genes.

Haemoglobin synthesis in 28 obligatory cases for alpha-thalassemia traits.

In the Far East two types of alpha-thalassemia genes, namely alpha-thalassemia, (alpha-thal1), and alpha-thalassemia2 (alpha-thal2) exist. Definite diagnosis of the alpha-thal1 and alpha-thal2 traits is very difficult because their hematological findings are minimally abnormal or normal. This study attempts to characterize the heterozygotes by hemoglobin chain synthesis in reticulocytes from obligatory cases of the alpha-thal1 and alpha-thal2 traits. Twelve parents of babies with hemoglobin Bart's hydrops fetalis (obligatory alpha-thal1 trait) had the mean total radioactivity alpha/beta ratio of 0.76 +/- SD 0.04, while that of 7 normal controls was 1.06 +/- SD 0.04. The alpha/beta globin chain ratios of 16 cases, who were either parents or offspring of patients with hemoglobin H disease, were found to segregate into 2 groups, i.e. 0.78 +/- SD 0.03 (10 cases) and 0.9l1 and alpha-thal2 traits respectively. The hematological data of the first group showed definite hypochromic microcytic red cells, similar to those of the parents of the hydrops. The second group had significantly higher mean corpuscular hemoglobin than the first group, compatible with alpha-thal2 trait. Our globin chain synthesis study thus appears to be capable of discriminating normal, alpha-thal1 and alpha-thal2 traits.

Lipodystrophy of the extremities. A dominantly inherited syndrome associated with lipatrophic diabetes.

A female patient with the following symptoms has been observed: complete absence of subcutaneous fat on the arms and legs, well developed adipose tissue on the trunk and face, severe hyperlipidemia, eruptive xanthomas, insulin resistant diabetes mellitus with lack of ketoacidosis, hepatomegaly and elevated basal metabolic rate. The patient thus exhibited all characteristics of lipatrophic diabetes (Lawrence type of diabetes). The mother and a sister of the patient were found to have the same peculiar appearance and a slight hyperlipidemia but no diabetes mellitus. The combination of this type of partial lipodystrophy with severe hyperlipidemia, insulin resistant diabetes mellitus without ketoacidosis and elevated basal metabolic rate was further observed in 2 unrelated patients without known familial occurrence. Thus partial lipodystrophy of the extremities is another, previously undescribed, syndrome associated with the Lawrence type of diabetes mellitus. In the 1 family the syndrome of lipodystrophy and hyperlipidemia is dominantly inherited. Besides the autosomal recessively inherited syndrome of congenital generalized lipodystrophy there is a heterogenous group of dominantly inherited syndromes with various types of lipodystrophy.

Haemoglobin C/alpha thalassaemia: haematological and biosynthetic studies.

A family with genes for haemoglobin C (Hb C) and alpha thalassaemia was studied. The mother had Hb-C trait. The father also had Hb-C trait but in addition displayed microcytosis, elevated Hb-F levels and a concentration of Hb-C less than usual for heterozygotes. The proband was homozygous for Hb-C but had Hb-F levels far exceeding those present in Hb-C disease. Biosynthetic studies of globin synthesis in both father and daughter showed a deficit of alpha chains relative to non-alpha chains, confirming the presence of alpha thalassaemia. The coexistence of alpha thalassaemia influences the level of mutant haemoglobin in haemoglobinopathies in which Hb C is present, in a fashion similar to that observed in sickle-cell trait.