The synthesis of fetal hemoglobin types in red blood cells and in BFU-E derived colonies from peripheral blood of patients with sickle cell anemia, beta+ - and delta beta-thalassemia, various forms of hereditary persistence of fetal hemoglobin, normal adults and newborn

Cell-free fetal DNA levels in maternal plasma after elective first-trimester termination of pregnancy

OBJECTIVE

To determine if first-trimester elective termination of pregnancy affects cell-free fetal DNA (fDNA) levels in maternal plasma.

DESIGN

Prospective cohort study.

SETTING

Clinical and academic research centers.

PATIENT(S)

One hundred thirty-four women who underwent first-trimester elective termination procedures.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Real-time polymerase chain reaction (PCR) amplification and measurement of DYS1, a Y-chromosome sequence, was used as a marker of fDNA.

RESULT(S)

We detected fDNA in pretermination samples from 27 out of 71 patients in the surgical arm, and 29 out of 63 patients in the medical arm. Based on confirmation of male gender in placental tissue, the sensitivity of fDNA detection is 92.6%. We detected fDNA as early as 32 days of gestation, which increased 4.2 genome equivalents/mL/week. In the surgical arm, the mean level of posttermination fDNA, adjusted for the clearance of fDNA in maternal blood, was higher than projected based on an expected increase with gestational age. In the medical arm, six patients had increased fDNA levels up to 11 days following termination.

CONCLUSION(S)

We found that fDNA can be reliably quantified in the early first trimester; fDNA elevation that occurs shortly after surgical termination may reflect fetomaternal hemorrhage or destruction of trophoblastic villi. Continued elevation of fDNA for several days may occur following medical termination.

Synthesis of the minor fetal hemoglobin Fic in colonies of erythropoietic precursors isolated from human umbilical cord blood

The biosynthesis of the minor hemoglobin FIc, which contains acetylated gamma chains, and the major hemoglobin Fo was studied during erythroid cell differentiation and maturation in cultures of erythroid precursors isolated from five human umbilical cord blood samples. A gradual decrease in the synthesis of Hb FIc was observed during the maturation of the erythroid cells when cultured from 7 to 15 days. The synthesis of Hb Fo did not show a consistent change; however, the relative synthesis of Hb FIc was the highest in the 7-day-old colonies and decreased at day 15 to levels observed in the reticulocytes. The addition of sodium butyrate, which is known to promote histone acetylation, significantly increased the synthesis of Hb FIc in 7-day-old colonies.

Greek (A gamma) variant of hereditary persistence of fetal haemoglobin: globin gene organization and studies of expression of fetal haemoglobins in clonal erythroid cultures

Individuals heterozygous for the Greek (A gamma) variant of hereditary persistence of fetal haemoglobin (HPFH) synthesize Hb F whose gamma-globin chains are predominantly of the A gamma type. DNA obtained from Greek HPFH heterozygotes was used to test for abnormalities in the organization of non alpha-globin genes. In addition, gamma- and beta-globin expression was studied in BFUe cultures. Restriction endonuclease mapping showed that the G gamma, delta and beta genes in cis to the Greek HPFH determinant are intact. Overproduction of gamma-globin chains synthesis was observed in the BFUe cultures. A significant portion of the gamma chain synthesis was of the G gamma type, suggesting that the G gamma genes cis and trans to the HPFH chromosome are active in culture. DNA mapping data indicate that in contrast to G gamma A gamma HPFH and the G gamma (delta beta) thalassaemia, the Greek (A gamma) HPFH is not due to a large deletion in the non-alpha globin gene region. It is possible that the anomaly may result either from a small deletion or point mutation which influences non alpha-globin transcription. The in vitro synthesis data suggest that the low level of G gamma-globin chain synthesis in vivo is not the result of transcriptional inactivation of the G gamma gene, since this gene appears to be expressed in erythroid cell cultures. We speculate that the genetic lesion in Greek (A gamma) HPFH is in regulatory sequences which control the level of G gamma and A gamma expression during development.

The percentages of Hb F and of G gamma and A gamma chains in the Hb F synthesized by reticulocytes and BFUe-derived colonies of patients with sickle cell anemia

The synthesis of Hb F was studied in the BFUe-derived colonies of 20 SS patients after incubation with 35S methionine for 24 hours, 13 days after the start of the experiments. Similar analyses were made for isolated reticulocytes from 28 SS patients; these cells were incubated for 2 hours and occasionally for 24 hours. The G gamma and A gamma percentages were determined in these two Hb F preparations and in the Hb F of circulating red cells using two different HPL chromatographic procedures. The data show an increased production of Hb F in the colonies mainly of patients with low blood Hb F values. A close correlation was present between the % G gamma chain in peripheral red cells and the G gamma percentages observed for the Hb F synthesized in the BFUe-derived colonies and that in reticulocytes. However, the values for the reticulocytes were significantly higher than those for the colonies. These data indicate a considerable variability among SS patients in their ability to produce Hb F in in vitro colonies which may in part be due to differences in the numbers of BFUe types in circulation. The variation in G gamma and A gamma levels in Hb F synthesized in reticulocytes and BFUe-derived colonies could be the result of slight differences in the stability of the corresponding mRNA's.

In vitro synthesis of hemoglobin and hemoglobin chains in the BFUe-derived colonies form person with alpha- or beta-thalassemia

The synthesis of alpha and non-alpha chains of human hemoglobin (Hb) was studied in reticulocytes and in BFUe-derived cell colonies from patients with alpha chain or beta chain deficiencies. The subjects included normal adults (alpha alpha/alpha alpha) with or without a beta chain variant (Hb S, Hb Leslie) or an alpha chain variant (Hb G-Georgia); alpha-thalassemia-2 heterozygotes (alpha 0 alpha/alpha alpha) with an alpha chain variant (G-Georgia or G-Philadelphia); an alpha-thalassemia-1 heterozygote (alpha 0 alpha 0/alpha alpha); alpha-thalassemia-2 homozygotes (alpha 0 alpha 0/alpha 0 alpha) with a beta chain variant (Hb S), an alpha chain variant (G-Philadelphia), a Hb S homozygosity with Hb G-Philadelphia, or a Hb G-Philadelphia homozygosity; and three black beta +-thalassemia homozygotes. Data from reticulocyte in vitro synthesis analysis showed the expected deficiencies. However, similar analyses of the Hb synthesized in cell colonies (even from the black beta-thalassemia homozygotes) gave (nearly) balanced sigma alpha/sigma non-alpha ratios. It is speculated that this balanced synthesis is due to a most effective proteolysis in the immature erythroblast which rapidly removes free alpha or beta chains. The levels of Hb F and Hb A2 were considerably increased in these proerythroblasts; a two- to threefold increase in the synthesis of Hb A2 was observed over that seen in the reticulocytes.

Control of the simian fetal hemoglobin switch at the progenitor cell level

This investigation was designed to define the cellular level at which the gamma to beta globin switch is established in the developing simian fetus in order to determine whether the switch is controlled by environmental influences within differentiating erythroid precursors or predetermined by the genetic program of erythroid progenitors. Samples of marrow and liver were obtained from rhesus fetuses throughout the switch period, and marrow was obtained from adult rhesus monkeys. Globin chain synthesis was then measured in differentiated erythroblasts and in erythroid progenitor-derived colonies grown in semisolid media. The relative rates of synthesis of gamma and beta chains were determined by the uptake of [(3)H]leucine into the respective chains separated by Triton gel electrophoresis and in some cases by urea carboxymethyl cellulose chromatography. Four periods of the switch were defined during fetal development. In the preswitch period both erythroblasts and progenitor-derived colonies produced <5% beta globin. In the early switch erythroblasts produced 5-15% beta globin, while progenitor-derived colonies produced 10-35% beta globin. In mid-switch erythroblasts synthesized 50% beta globin, whereas progenitor-derived colonies produced only 15-35% beta. At the completion of the switch erythroblasts produced 100% beta globin, while progenitor-derived colonies produced as little as 40% beta chains. We conclude that the program of globin synthesis that characterizes the fetal switch is established at the level of erythroid progenitors. Fetal erythroid burst-forming units (BFU-E) dominate the marrow prior to the switch. The early switch period is heralded by the appearances of adult erythroid burst-forming units programmed to express increasing beta chain synthesis in colonies. By mid-switch a second class of adult erythroid progenitors capable of giving rise to fetal and adult hemoglobin synthesis in in vitro colonies becomes apparent. These shifting populations of erythroid progenitors with unique globin synthesis programs give rise to the erythroblasts that create the sigmoid pattern of the fetal to adult hemoglobin switch in the developing simian fetus.

Effects of dexamethasone on fetal hemoglobin synthesis in peripheral blood erythroid burst-forming units

Colonies derived from erythroid burst-forming units (BFU-E) synthesize fetal hemoglobin (HbF) in amounts that far exceed in vivo levels. There is some evidence that HbF synthesis is controlled at the level of a primitive erythroid precursor cell. Dexamethasone may potentiate the development of BFU-E. Since a means of augmenting HbF production in sickle cell anemia or severe beta-thalassemia would be of great therapeutic value, we studied the effects of dexamethasone on HbF and gamma-globin chain synthesis in BFU-E from patients with sickle cell anemia and controls. HbF was measured by radioimmunoassay of BFU-E lysate and gamma-chain synthesis by the incorporation of 3H-leucine into globin, which was then purified by gel filtration and column chromatography. Dexamethasone (10(-9) M) produced an increase in the number of BFU-E in 16 of 19 subjects when compared with numbers of BFU-E cultured with only erythropoietin. The individual BFU-E were larger and contained more subcolonies. Dexamethasone did not increase HbF or gamma-chain synthesis, and there was no relationship between proliferation of BFU-E and augmented HbF production. Thus, although dexamethasone augmented the development of erythroid bursts, there was no increment in HbF.

Globin biosynthesis in erythroid bursts of heterozygous alpha or beta thalassaemia

We examined globin chain synthesis in erythroid bursts (BFU-E) of patients with heterozygous alpha or beta thalassaemia. BFU-E were cloned from circulating mononuclear cells, labelled with [3H]leucine and globin chains purified by gel filtration and column chromatography. In six patients heterozygous for beta thalassaemia, globin synthesis in BFU-E was nearly balanced, with an alpha/non alpha ratio of 1.05 +/- 0.12. These BFU-E produced 33.8 +/- 12.7% gamma globin chain, an amount similar (P > 0.05) to that found in 10 controls with sickle cell anaemia (25.6 +/- 6.7) but greater (P > 0.05) than that of five normal controls (17.2 +/- 2.2). The balanced globin synthesis appeared due to the large amounts of gamma chain made by BFU-E. In two alpha thalassaemia carriers, who also had sickle cell trait, the BFU-E alpha/non-alpha ratio was 0.67 and 0.79. These BFU-E produced 15% and 20% gamma chain and 39% and 45% betaS globin. The synthesis of betaS globin in BFU-E exceeded the erythrocyte levels of 20% and 29% HbS and indicated nearly equal expression of betaA and betaB globin genes in these proliferating erythroid precursors. This provides further evidence that the low levels of HbS in sickle cell carriers with alpha thalassaemia are due to post-translational events resulting from the differing affinity of betaS and betaA globin for alpha chain and the destruction of excessive betaS chain.

Adult and fetal hemoglobin production in erythroid colonies from subjects with beta-thalassemia or with hereditary persistance of fetal hemoglobin (HPFH)

The synthesis of alpha and non-alpha chains (beta, delta, G gamma, and A gamma) was studied in cultures of peripheral blood mononuclear cells from eleven beta-thalassemia heterozygotes, two HPFH heterozygotes, and one HPFH homozygote. The synthesis of Hb F in the thalassemia colonies (average value: 12.6%) was comparable to that in normal adult colonies (average value: 12.6%) was comparable to that in normal adult colonies (average value: 12.2%). The percent G gamma chain in the Hb F varied greatly but a relationship between the G gamma chain percentage in the Hb F from colonies and that from peripheral blood was established. The relative synthesis of Hb A2 in colonies of beta-thalassemia heterozygotes (average value: 5.8%) was 1.6 times as much as that in colonies of normal adults (average value: 3.6%). Hb A2 and Hb A were absent in the colonies of the HPFH homozygote. The alpha/non-alpha (i.e., beta, gamma, and delta) ratio of the hemoglobins in the cultured cells of the beta-thalassemia heterozygotes and the alpha/beta and alpha/beta ratios of isolated Hb A and Hb A2 were about one (range 0.74 to 1.38). The alpha/gamma ratio of the Hb F synthesized in BFUe-derived colonies of the HPFH homozygote, however, was 1.5. These results suggest a deficiency in the in vitro culture system resulting in decreased levels of alpha-mRNA or in a partial inhibition of initiation of protein synthesis which is known to reduce the synthesis of alpha chains more than that of the beta chains.

Separation of tryptic peptides of normal and abnormal alpha, beta, gamma, and delta hemoglobin chains by high-performance liquid chromatography

High-performance liquid chromatography (HPLC) was used to separate tryptic peptides of the normal alpha, beta, gamma, and delta chains of human hemoglobins A, F, and A2 and of the abnormal chains of 25 hemoglobin variants. In addition, the separation of chymotryptic peptides of the oxidized core of the normal alpha chain by HPLC was evaluated. HPLC has several advantages over conventional methods used for the separation of proteolytic fragments of hemoglobin chains. The method is fast, and reproducible, and requires only small quantities of material. Several peptides are eluted as single zones, thus eliminating the need of rechromatography for further purification. Characteristic changes in the elution pattern of the peptides often indicate specific modifications.