Fetal erythropoiesis and the diagnosis and treatment of hemoglobin disorders in the fetus and child

Very preterm birth results in later lower platelet activation markers

BACKGROUND

Premature birth entails an adverse cardiovascular risk profile, but the underlying mechanisms are insufficiently understood. Here, we employed an unbiased cardiovascular proteomics approach to profile former very preterm-born preschoolers.

METHODS

This observational study investigated differences in plasma concentrations of 79 proteins, including putative cardiovascular biomarkers between very preterm- and term-born children on average 5.5 years old (53.1% male) using multiple-reaction monitoring mass spectrometry.

RESULTS

Very preterm-born (n = 38; median gestational age 29.6 weeks) compared to term-born (n = 26; 40.2 weeks) children featured lower plasma concentrations of platelet factor 4 (PLF4; -61.6%, P < 0.0001), platelet basic protein (CXCL7; -57.8%, P < 0.0001), and hemoglobin subunit beta (-48.3%, P < 0.0001). Results remained virtually unchanged when adjusting for complete blood count parameters, including platelet count. Conversely, whole blood hemoglobin was higher (+7.62%, P < 0.0001) in preterm-born children.

CONCLUSIONS

Very preterm birth was associated with decreased markers of platelet activation among preschoolers. These findings are consistent with reduced platelet reactivity persisting from very preterm birth to a preschool age.

IMPACT

Former very preterm-born preschoolers featured reduced levels of platelet activation markers. While lower platelet reactivity in very preterm-born compared to term-born infants in the first days of life was established, it was unknown when, if at all, reactivity normalizes. The current study suggests that platelet hyporeactivity due to very preterm birth persists at least up to a preschool age. "Immaturity of the hemostatic system" may be a persistent sequel of preterm birth, but larger studies are needed to investigate its potential clinical implications.

Mutations in the zebrafish hmgcs1 gene reveal a novel function for isoprenoids during red blood cell development

Erythropoiesis is the process by which new red blood cells (RBCs) are formed and defects in this process can lead to anemia or thalassemia. The GATA1 transcription factor is an established mediator of RBC development. However, the upstream mechanisms that regulate the expression of GATA1 are not completely characterized. Cholesterol is 1 potential upstream mediator of GATA1 expression because previously published studies suggest that defects in cholesterol synthesis disrupt RBC differentiation. Here we characterize RBC development in a zebrafish harboring a single missense mutation in the hmgcs1 gene (Vu57 allele). hmgcs1 encodes the first enzyme in the cholesterol synthesis pathway and mutation of hmgcs1 inhibits cholesterol synthesis. We analyzed the number of RBCs in hmgcs1 mutants and their wild-type siblings. Mutation of hmgcs1 resulted in a decrease in the number of mature RBCs, which coincides with reduced gata1a expression. We combined these experiments with pharmacological inhibition and confirmed that cholesterol and isoprenoid synthesis are essential for RBC differentiation, but that gata1a expression is isoprenoid dependent. Collectively, our results reveal 2 novel upstream regulators of RBC development and suggest that appropriate cholesterol homeostasis is critical for primitive erythropoiesis.

Hydroxycarbamide-induced changes in E/beta thalassemia red blood cells

In thalassemia, fetal hemoglobin (HbF) augmentation with hydroxycarbamide (also known as hydroxyurea) is not always successful. The expected parallel effects on red cell (RBC) membrane deformability, cell hydration, and membrane phospholipid organization, all important for extending RBC life span and increasing Hb, have been infrequently examined. We analyzed these characteristics in 15 nontransfused E/beta(0) thalassemia patients treated with HU (mean 10.2 months). Membrane deformability and cell hydration mildly improved in association with increased HbF levels approaching statistical significance (r = 0.51, P = 0.06). All measures improved considerably in splenctomized patients. These findings underscore the disappointing results of hydroxyurea treatment in clinical trials and the importance of examining the effect on RBC characteristics for the development and understanding of HbF-enhancing agents.

Single and combination drug therapy for fetal hemoglobin augmentation in hemoglobin E-beta 0-thalassemia: Considerations for treatment

Patients with hemoglobin E (Hb E)-beta 0-thalassemia, one of the most common hemoglobinopathies worldwide, could benefit from drugs that increase fetal and total hemoglobin levels and thereby decrease the need for transfusions. The long-term clinical outcome of such therapy, its hematologic effects, and which patients are likely to benefit from treatment are unknown. Consequently, the use of such drugs for Hb E-beta 0-thalassemia is limited, and countries where resources for safe and regular transfusion are scarce cannot benefit from them. In a multicenter trial of 42 patients treated with hydroxyurea for two years, almost half the patients demonstrated a significant increase in steady-state hemoglobin level. Drug toxicity was minimal. Combined treatment of hydroxyurea with erythropoietin benefited selected patients, but the addition of sodium phenyl butyrate was ineffective. After 5 years of follow-up, a subset of patients remained off transfusions. Hydroxyurea should be considered for a subset of Hb E-beta 0-thalassemia patients.

Fetal haemoglobin augmentation in E/beta(0) thalassaemia: clinical and haematological outcome

Patients with E/beta(0) thalassaemia, the most common haemoglobinopathy in many Asian countries, might benefit from drugs that increase fetal and total haemoglobin and thereby decrease the need for transfusions. The long-term clinical efficacy and safety of such therapy is unknown, limiting its use in countries where resources for safe and regular transfusion are scarce. In this study, 45 patients were treated with hydroxyurea (18-20 mg/kg) for 24+/-9 months, hydroxyurea with sodium phenyl butyrate (n=8) and hydroxyurea with erythropoietin (n=9), each for approximately 6 months, and followed for 3 years from study exit. Hydroxyurea had minimal toxicity, resulted in a mean 1.3 g/dl steady-state increase in haemoglobin in 40% of patients, and a milder response (<OR=1 g/dl) in the others. Baseline haemoglobin F was significantly associated with an increase in haemoglobin (P<0.001). Combined treatment with erythropoietin benefited selected patients, but the addition of sodium phenyl butyrate had no effect. Of the 27/45 patients who discontinued regular transfusions before the study, 13 remained transfusion independent during long-term follow-up, 6/13 continued hydroxyurea. Hydroxyurea moderately increased steady-state haemoglobin in a sub-group of E/beta(0) thalassaemia patients and can be considered for patients with intermediate severity disease, thus delaying or avoiding the need for life-long transfusions. Continuous monitoring of toxicity and growth is required.

Developmental biology of erythropoiesis

A newborn infant represents the culmination of developmental events from conception through organogenesis. Red cells are critically important for survival and growth of the embryo. During development, erythropoiesis occurs in two distinct forms. The first 'primitive' form consists of nucleated erythroblasts that differentiate within the blood vessels of the extraembryonic yolk sac. The second 'definitive' form consists of anucleate erythrocytes that differentiate within the liver and third trimester bone marrow of the fetus. While adult bone marrow and cord blood now serve as sources of stem cells for the treatment by transplantation of genetic and malignant diseases, the developmental origin of hematopoietic stem cells has not been determined. During the third trimester the fetus grows rapidly and the production of red cells is approximately 3-5 times that of adult steady state levels. Birth brings dramatic changes in oxygenation and erythropoietin production that result in a tenfold drop in red cell production and in a transient 'physiologic' anemia. Other causes of fetal and infant anemias have their origins in development processes. These include globin gene switching in alpha and beta thalassemia, the expression of red cell antigens in alloimmune hemolytic disease, and the poorly understood defects in the regulation of erythropoiesis in Diamond Blackfan anemia. Even in the adult, vestiges of fetal erythropoiesis are evident during transient states of accelerated erythroid expansion. A better understanding of the development of erythropoiesis will bring improvements in the treatment of anemia, not only in the newborn, but also in the fetus and the adult.