PubMed Health⌕ Search

Biomedical subjects

J DeSimone

Publications and source records attributed to J DeSimone.

At least 37 records · Page 2Linked to original sources
PubMed1986

Effect of lead and ethanol upon gamma-globin synthesis in sickle reticulocytes.

There is evidence from both in vivo and in vitro studies that the synthesis of hemoglobin can be modified by posttranslational alterations in the assembly of the tetrameric molecule. Globin biosynthesis in reticulocytes of patients with sickle cell disease was studied to ascertain the effects of lead and ethanol on gamma-globin chain synthesis and hemoglobin assembly. In incubations containing lead (400 micrograms/dl) or ethanol (1.0 M) there were 86.7 +/- 139.7% and 542.7 +/- 397.0% increases in the relative synthesis of the gamma-globin chain. This was associated with a relative reduction in alpha-chain synthesis, as estimated by changes in the alpha/gamma + beta S synthesis ratio, as well as a marked reduction in total globin synthesis.

Anemia, Sickle Cell↗
PubMed1986

On the mechanism of Hb F elevations in the baboon by erythropoietic stress and pharmacologic manipulation.

Maximal fetal hemoglobin (Hb F) elevations in the baboon subsequent to phenyl hydrazine-induced hemolytic anemia, bleeding, bleeding plus hydroxyurea (HU), or cytosine arabinoside were two to three times lower than those achieved with bleeding plus 5-azacytidine (azaC). Because, in the baboon, maximal elevations in F cell numbers occurred with bleeding alone, changes in the levels of Hb F in hemolysates and in Hb F per F cell could be considered to be due to the administered drugs. Erythropoietic toxicity of azaC was minimal, making it unlikely that the marked elevations of Hb F were due to shifts in the population of erythroid progenitors and precursors and more likely that they were related to a biochemical effect of the drug on DNA. The data indicate marked DNA hypomethylation. This was also found to be associated, but to a much lesser extent, with the modest Hb F elevations after bleeding, hemolysis, and treatment with HU. This drug had greater erythroid toxicity than azaC, and it appeared that the Hb F elevations occurred mainly on the rebound from the early cytotoxicity. The explanation of the molecular DNA changes with this drug and in erythropoietic stress alone remains unknown.

Anemia, Hemolytic↗
PubMed1985

Tetrahydrouridine, cytidine analogues, and hemoglobin F.

5-Azacytidine (azaC) has previously been shown to raise Hb F levels in the repeatedly phlebotomized baboon (PCV: around 20%). The administration of tetrahydrouridine (THU), an inhibitor of the enzymatic conversion of azaC to 5-azauridine, made it possible to reduce the amount of azaC and also of 2-deoxy-5-azacytidine (d-azaC) by more than 90% and still achieve maximal Hb F elevations. However, the granulocytopenia, usually occurring after 5-azaC, was not altered by the lowering of the dosages in the presence of THU. Thus, the granulocytopenia is not due to 5-azauridine or other catabolic products resulting from deamination. It is also unlikely that it is caused by a direct influence of azaC on RNA since d-azaC also causes granulocytopenia. The persistence of reticulocytosis throughout the treatment with azaC or d-azaC makes it appear likely that the observed increase in Hb F levels to more than 60% of total hemoglobin is not due to a cytotoxic effect on erythropoiesis resulting in a shift of cell populations toward greater immaturity, but to a direct influence of the drug on the regulation of gamma globin chain production.

Agranulocytosis↗
PubMed1984

5-Azacytidine and fetal hemoglobin.

The evidence that 5-azacytidine stimulates the production of Hb F and F cells in baboon and man is reviewed. The mechanism of this effect is not entirely clear, but 5-azacytidine produces hypomethylation of the gamma gene at certain sites, and gene expression and DNA hypomethylation are related phenomena in many other systems. Other mechanisms have been postulated by other investigators. The therapeutic significance of increased Hb F levels in homozygous beta thalassemia and sickle cell anemia is exemplified. The potential risk of carcinogenicity has delayed more extensive clinical trials.

Adult↗
PubMed1984

Speciation in the baboon and its relation to gamma-chain heterogeneity and to the response to induction of HbF by 5-azacytidine.

In the baboon (Papio species), the two nonallelic gamma-genes produce gamma-chains that differ at a minimum at residue 75, where isoleucine (I gamma-chain) or valine (V gamma) may be present. This situation obtains in baboons that are sometimes designated as Papio anubis, Papio hamadryas, and Papio papio. However, in Papio cynocephalus, although the I gamma-chains are identical with those in the above mentioned types, the V gamma-chains have the substitutions ala----gly at residue 9 and ala----val at residue 23. The V gamma-chains of P. cynocephalus are called V gamma C to distinguish them from the V gamma A-chains of P. anubis, etc. A single cynocephalus animal has been found to have only normal I gamma-chains and I gamma C-chains (that is, glycine in residue 9, valine in 23, and isoleucine in 75). When HbF is produced in response to stress with 5-azacytidine, P. anubis baboons respond with greater production than do P. cynocephalus, and hybrids fall between. Minimal data on P. hamadryas and P. papio suggest an even lower response than P. cynocephalus. As HbF increases under stress, the ratio of I gamma to V gamma-chains changes from the value in the adult or juvenile baboon toward the ratio in the newborn baboon. However, it does not attain the newborn value. The V gamma A and V gamma C-genes respond differently to stress. In hybrids, the production of V gamma A-chains exceeds that of V gamma C-chains. A controlling factor in cis apparently is present and may be responsible for the species-related extent of total HbF production. It may be concluded that the more primitive the cell in the erythroid maturation series that has been subjected to 5-azacytidine, the more active is the I gamma-gene.

Amino Acid Sequence↗
PubMed1983

Changes in the gamma chain heterogeneity of hemoglobin F of the baboon (Papio cynocephalus) postnatally and after partial switching to hemoglobin F production by various stimuli.

The postnatal switch from hemoglobin (Hb) F to Hb A in the baboon (Papio cynocephalus) occurs somewhat more rapidly than in humans. Minor components which are related to Hb F and Hb A are also present and show reciprocal rise and fall. The baboon produces two types of gamma chain presumably from nonallelic genes. These have either an isoleucyl (I gamma) or a valyl (V gamma) residue in position 75. As in the human case with G gamma and A gamma chains, the ratio I gamma to V gamma chains changes during the postnatal switch. Production of Hb F in the baboon may be stimulated by phenylhydrazine or more effectively by 5-azacytidine. With phenylhydrazine, the ratio of I gamma to V gamma chains in the Hb F is the same as in the traces of Hb F in the juvenile or adult baboon. However, with 5-azacytidine, at least some of the Hb F that is produced probably has been synthesized with an I gamma to V gamma ratio that is present prenatally and in the newborn baboon.

Aging↗
PubMed1983

5-Azacytidine increases gamma-globin synthesis and reduces the proportion of dense cells in patients with sickle cell anemia.

We previously demonstrated that 5-azacytidine can selectively increase gamma-globin synthesis in a patient with beta +-thalassemia, prompting us to treat two patients with sickle cell anemia and two additional patients with beta + thalassemia. 5-Azacytidine (2 mg/kg/day) was continuously infused for 7 days with no apparent clinical toxicity. The gamma/beta-globin biosynthetic ratio increased fourfold to sixfold in the bone marrow cells of each patient after treatment and remained elevated for 7-14 additional days. Hypomethylation of DNA near the gamma-globin genes in bone marrow cells was demonstrated 2 days after beginning the 5-azacytidine infusion. The peripheral blood fetal hemoglobin (HbF) level increased from 6.0% to 13.7% in one patient with sickle cell anemia and from 1.6% to 8.9% in the second. Stractan gradient analyses of peripheral blood from patients with sickle cell anemia revealed a marked decrease in the percentage of dense cells (cells that contain increased amounts of HbS polymer when deoxygenated) following treatment. These observations provide an impetus to investigate the effects of repeated courses of 5-azacytidine in a small group of severely ill patients to determine whether this drug may have a role in the treatment of patients with sickle cell anemia and beta-thalassemia.

Adult↗
PubMed1983

DNA methylation and globin gene expression in patients treated with 5-azacytidine.

5-Azacytidine, a cytidine analog, stimulated fetal hemoglobin synthesis in five patients who had either severe beta-thalassemia or sickle cell anemia. After treatment, a reduction in the frequency of methylated cytosine residues was observed at all Hpa II sites examined. Despite causing "global" hypomethylation, 5-azacytidine augmented the synthesis of gamma-globin only. Although gamma-gene hypomethylation and increased gamma-gene expression seem to be linked, hypomethylation near other genes was not sufficient to activate transcription. These data suggest that the gamma genes lie in a unique "preactivational" state responsive to hypomethylation, and that other genes are repressed in bone marrow cells by different mechanisms. DNA hypomethylation and an increased concentration of gamma-mRNA were observed in bone marrow cells 2 days after initiation of treatment, indicating that 5-azacytidine may act directly on differentiated erythroid precursors. This compound probably affects early erythroid progenitors as well, since an increased level of gamma-globin synthesis persists for 1-2 weeks after the drug is stopped. A direct effect on erythroid progenitors was also suggested by in vitro assays: Erythroid colonies derived from progenitor cells obtained on day 2 of treatment produced more Hb F than colonies derived from progenitors obtained before 5-azacytidine was given.

Azacitidine↗
PubMed1983

Fetal hemoglobin production in adult baboons by 5-azacytidine or by phenylhydrazine-induced hemolysis is associated with hypomethylation of globin gene DNA.

Nucleoside analog were used to stimulate fetal hemoglobin synthesis in baboons. Only those nucleoside analogs (5-azacytidine and 2'-deoxy-5-azacytidine) that blocked DNA methylation caused large increases in Hb F levels. DNA extracted from bone marrow samples of these animals was cleaved with MspI or HpaII restriction enzymes and analyzed by Southern blot hybridization. Results of these experiments strongly support the hypothesis that hypomethylation of CCGG sequences in the gamma-gene region is a condition of gamma-gene expression. This also applies to Hb F elevations resulting from erythropoietic stress due to phenylhydrazine-induced hemolytic anemia.

Animals↗
PubMed1982

5-azacytidine selectively increases gamma-globin synthesis in a patient with beta+ thalassemia.

5-Azacytidine is a cytidine analogue that is capable of activating repressed genes in tissue-culture cells and has been shown to increase hemoglobin-F production in anemic baboons. This drug was administered to a patient with severe beta-thalassemia in an attempt to stimulate hemoglobin-F production. After seven days of 5-azacytidine treatment, gamma-globin synthesis increased approximately sevenfold, temporarily normalizing the patient's unbalanced globin synthesis. Erythropoiesis became more effective, leading to a temporary increase in the absolute reticulocyte count (from 5000 to 22,000 per cubic millimeter) and in hemoglobin concentration (from 8.0 to 10.8 g per deciliter). Hypomethylation of bone-marrow DNA near both the gamma-globin and epsilon-globin genes was directly demonstrated. At the time of peak drug effect, about 7000 gamma-globin messenger RNA molecules were present per erythroid bone-marrow cell, in contrast to 10 to 15 epsilon-globin messenger RNA molecules per cell. 5-Azacytidine selectivity increases gamma-globin synthesis and therefore provides a new approach to the treatment of severe beta-thalassemia. Further studies will be required to evaluate the efficacy, risks, and long-term toxicity of 5-azacytidine (or related compounds) before this approach can be used as a therapy for patients with disorders of hemoglobin synthesis.

Adult↗
PubMed1982

5-Azacytidine stimulates fetal hemoglobin synthesis in anemic baboons.

In an attempt to stimulate Hb F synthesis in baboons by means other than erythropoietic stress, we considered the possibility that an agent that inhibits methylation of CpG sequences in DNA may be effective. 5-Azacytidine, a cytosine analogue that cannot be methylated, is such an agent. Animals whose packed red cell volume was maintained at approximately 20% by bleeding were given 10 daily intravenous injections of the drug (6 mg/kg) in 12 days. Hb F levels in these animals started to increase on day 5 of this regimen and peak levels, which were 6-30 times higher than those produced by bleeding alone, occurred 5-7 days after the last dose of the drug. In animals previously identified as genetically "high" or "low" Hb F responders, the maximal Hb F levels were 70-85% and 35-40% respectively. In dose-response studies 5-azacytidine given daily at 3-4 mg/kg produced maximal Hb F increases. The drug did not correlate the percentage (number) of Hb F-containing cells (F cells) beyond the maximal number achieved by bleeding alone and thus its main effect was to increase Hb F per F cell. The finding that Hb F synthesis can be modulated to such a high degree by a drug may have therapeutic implications--e.g., in sickle cell anemia, in which stimulation of Hb F synthesis may prevent sickling.

Animals↗
PubMed1982

Maintenance of fetal hemoglobin (HbF) elevations in the baboon by prolonged erythropoietic stress.

We have previously shown that acute erythropoietic (Ep) stress by hemolysis or hypobaric hypoxia causes elevations of HbF in the baboon. The magnitude of these elevations is genetically determined, ranging from 3% to 60% (low, intermediate, and high responders). These genetic differences in HbF levels among animals are mainly due to differences in the number of HbF-containing cells ("F-cells"). The present study was undertaken to study the influence of prolongation and of the severity of Ep stress on HbF levels and the number of F-cells. The packed cell volume (PCV) of the blood of 4 animals, approximately 3 yr old, was maintained at 20% by daily phlebotomies, and the animals were exposed to varying degrees of hypobaric hypoxia for up to 40 days. In these experiments, the number of F-cells increased rapidly and reached individually constant levels ranging from 60% to 80%, when the PCV reached 20%, and no further increase was observed regardless of the subsequent degree of hypoxia. On the other hand, HbF levels, and with it the values for HbF per F-cell, increased proportionally to the severity of the Ep stress and could be maintained at a constant level dependent on the degree of the hypoxia, e.g., at 19,000 feet HbF levels of one animal remained 20%-25% throughout the duration of the exposure of 14 days. These data are indicative of separate control of F-cell numbers and of the levels of HbF per F-cell. It appears that with the increase of Ep stress, those Ep stem cells that have retained the HbF program are mobilized into maturation. A model, attempting to explain this phenomenon is presented.

Anemia, Hemolytic↗
PubMed1982

Failure of D-thyroxine to increase fetal hemoglobin levels in normal and anemic baboons.

The synthesis of Hb F in baboons after erythropoietic stress is markedly increased. The mechanism of this "reverse switch" is unknown, but erythropoietin is not directly responsible for it. Since D-thyroxine has been reported to cause Hb F increases in marmosets, we determined its effect in normal and anemic baboons whose erythropoiesis, hemoglobin fractions and regulation of hemoglobin synthesis are similar to those of man. No effect was demonstrated in the normal baboons. In the anemic animal the Hb F level did not increase beyond the elevation attributable to the erythropoietic stress itself. It is therefore, unlikely that D-thyroxine will increase Hb F levels in man.

Anemia↗