Increased response of erythroid progenitors to interleukin-3 in sickle cell anemia: CFU-E-like behavior of circulating erythroid progenitors in liquid culture

Bone marrow progenitor cells from chemically exposed workers display an intrinsic ability for autonomous proliferation

In this study, the autonomous proliferation of bone marrow progenitor cells (CFU-C), a pathological phenomenon observed in many hematological abnormalities, was investigated in 31 individuals who had been diagnosed as having neutropenia. Of these subjects, 18 had been chronically exposed (range of exposure 5-30 years) to a variety of petroleum distillates. We observed that the group of exposed individuals presented higher numbers of autonomous CFU-C when compared with those unexposed subjects. In addition, follow-up data demonstrated that 20% of the exposed population (4 of the 18) developed malignant hematological diseases. The autonomous CFU-C obtained from all individuals studied was composed predominantly of macrophages. This suggests an involvement of these cells in the development of hematological abnormalities, probably as a result of increased production of chemical myelotoxic metabolites.

Hydroxyurea promotes the reduction of spontaneous BFU-e to normal levels in SS and S/beta thalassemic patients

We have studied the effects of hydroxyurea on growth and differentiation of early erythroid progenitor cells (BFU-e) from peripheral blood of sickle cell disease patients (five SS and two Hb S/beta-thalassemia) in the presence or absence of exogenous stimulating factors. When the mononuclear cells from the sickle cell disease patients were cultured at diagnosis (before hydroxyurea treatment), there was an increased number of BFU-e in relation to controls (p < 0.05, Wilcoxon test) when cells were grown in the presence or absence of 5637 conditioned medium and erythropoietin. Colonies that developed in the absence of added growth factors were considered "spontaneous". A significant difference was observed after hydroxyurea treatment in the number of BFU-e obtained in the presence and absence of stimulus, with a higher reduction in the spontaneous BFU-e number. As expected, there was an increased Hb F level in these patients when compared with their pretreatment levels. There was no correlation between spontaneous BFU-e and hemoglobin levels in all patients studied.

Spontaneous erythroid colony formation in Brazilian patients with sickle cell disease

The ability of circulating progenitor cells to develop erythroid colonies was studied in vitro in the presence or absence of growth factors (5637-CM and erythropoietin) in 63 patients with sickle cell disease (SCD) (36 homozygotes for hemoglobin [Hb] S, 13 double heterozygotes for Hb S and beta thalassemia, and 14 SC patients) in Southeast Brazil. In the presence of growth factors, SCD patients (all genotypes) presented significantly higher numbers of circulating burst-forming unit-erythroid (BFU-E/5 x 10(5) MNC), when compared with control subjects. However, when the progenitor cells were cultured in the absence of added stimulus, high numbers of BFU-E were observed only in the genotypes SS and S/beta thalassemia. SC patients presented a similar response to the control subjects. Moreover, there was an inverse correlation between spontaneous (without stimulus) BFU-E and Hb levels in SCD patients. These results suggest that the formation of spontaneous BFU-E observed in SCD may be due to an expanded erythropoiesis secondary to hemolysis.

Early circulating erythroid progenitor cells and expression of erythropoietin receptors in sickle cell disease

The ability of circulating progenitor cells from 22 patients with sickle cell disease (SCD) to develop erythroid colonies was studied in vitro in the presence or absence of growth factors (5637-CM and erythropoietin). In both conditions, SCD patients presented significantly higher numbers of circulating burst-forming unit-erythroid (BFU-E/5x10[5]MNC) when compared to control subjects. The study of the expression of erythropoietin receptors revealed an increased level in SCD patients. Moreover, there was a correlation between both stimulated and autocrine (without stimulus) BFU-E and the expression of erythropoietin receptors. These results are of particular interest since they indicate that the phenomenon of spontaneous BFU-E-derived colonies observed in SCD patients may be due to an increased expression of erythropoietin receptors.

Mechanism of differentiation of human erythroleukaemic cell line K562 by hemin

The human erythroleukaemic cell line K562, in response to various chemical agents, undergoes differentiation and exhibits exclusive production of fetal and embryonic haemoglobins. In this study we have compared the efficiency of natural growth factors interleukin-3 and erythropoietin and three chemical inducers such as dimethyl sulfoxide (DMSO, 1.9%), phorbol-12-myristate-13-acetate (PMA, 50 ng/ml) and hemin (25 microM) on growth and differentiation of these cells. Erythropoietin significantly stimulated the growth of K562 cells (P<0.0001), while interleukin-3 did not (P = 0.2783). However, neither of these growth factors individually or together induced differentiation of K562 cells. Hemin appears to be more efficient than DMSO or PMA in differentiation of K562 cells as measured by benzidine positive cells (70% or more). The differentiation of K562 cells by hemin occurs independently of protein kinase-C activation and the arrest of DNA synthesis. In contrast, hemin significantly stimulated RNA and protein synthesis (P<0.0001) as measured by [3H]-uridine and [3H]-leucine incorporation respectively. Analysis of hemin-treated K562 nuclear extract on sodium dodecylsulphate gel electrophoresis showed that one protein band of molecular weight 70 kDa decreased after 48 h of incubation in the presence of 25 microM hemin. The disappearance of this protein can be prevented by cycloheximide (100 microg/ml) and actinomycin D (0.1 microg/ml) and thus indicating that the removal of 70 kDa protein seems to be dependent on RNA and protein synthesis. The regulatory role of 70 kDa protein in hemin-induced differentiation of K562 cells is discussed.