Regulation of iron homeostasis through the erythroferrone-hepcidin axis in sickle cell disease.

Sickle cell disease (SCD) has a distinct pattern of transfusional iron overload (IO) when compared to transfusion-dependent ß-thalassaemia major (TDT). We conducted a single institution prospective study to evaluate plasma biomarkers of iron regulation and inflammation in patients with SCD with IO (SCD IO cases, n = 22) and without IO (SCD non-IO cases, n = 11), and non-SCD controls (n = 13). Hepcidin was found to be inappropriately low, as evidenced by a significantly higher median hepcidin/ferritin ratio in non-SCD controls compared to SCD IO cases (0·3 vs. 0·02, P < 0·0001) and SCD non-IO cases (0·3 vs. 0·02, P < 0·0001), suggesting that certain inhibitory mechanism (s) work to suppress hepcidin in SCD. As opposed to the SCD non-IO state, where hepcidin shows a strong significant positive correlation with ferritin (Spearman ρ = 0·7, P = 0·02), this correlation was lost when IO occurs (Spearman ρ = -0·2, P = 0·4). Although a direct non-linear correlation between erythroferrone (ERFE) and hepcidin did not reach statistical significance both in the IO (Spearman ρ = -0·4, P = 0·08) and non-IO state (Spearman ρ = -0·6, P = 0·07), patients with highest ERFE had low hepcidin levels, suggesting that ERFE contributes to hepcidin regulation in some patients. Our results suggest a multifactorial mechanism of hepcidin regulation in SCD.

The proinflammatory cytokine GM-CSF downregulates fetal hemoglobin expression by attenuating the cAMP-dependent pathway in sickle cell disease.

Although reduction in leukocyte counts following hydroxyurea therapy in sickle cell disease (SCD) predicts fetal hemoglobin (HbF) response, the underlying mechanism remains unknown. We previously reported that leukocyte counts are regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) in SCD patients. Here we examined the roles of GM-CSF in the regulation of HbF expression in SCD. Upon the analysis of retrospective data in 372 patients, HbF levels were inversely correlated with leukocyte counts and GM-CSF levels in SCD patients without hydroxyurea therapy, while HbF increments after hydroxyurea therapy correlated with a reduction in leukocyte counts, suggesting a negative effect of GM-CSF on HbF expression. Consistently, in vitro studies using primary erythroblasts showed that the addition of GM-CSF to erythroid cells decreased HbF expression. We next examined the intracellular signaling pathway through which GM-CSF reduced HbF expression. Treatment of erythroid cells with GM-CSF resulted in the reduction of intracellular cAMP levels and abrogated phosphorylation of cAMP response-element-binding-protein, suggesting attenuation of the cAMP-dependent pathway, while the phosphorylation levels of mitogen-activated protein kinases were not affected. This is compatible with our studies showing a role for the cAMP-dependent pathway in HbF expression. Together, these results demonstrate that GM-CSF plays a role in regulating both leukocyte count and HbF expression in SCD. Reduction in GM-CSF levels upon hydroxyurea therapy may be critical for efficient HbF induction. The results showing the involvement of GM-CSF in HbF expression may suggest possible mechanisms for hydroxyurea resistance in SCD.

Acute splenic complications and implications of splenectomy in hemoglobin SC disease.

Splenectomy indications and outcome were evaluated in 124 adults with hemoglobin SC disease (Hb SC). Twelve patients (9.6%) required splenectomy. There was a significant difference between the splenectomy group and the non-splenectomy group, respectively, regarding Hb levels (median 7.2 g/dL vs. 12.5 g/dL, P < 0.0001), platelet counts (median 146 x 10(6)/L vs. 275 x 10(6)/L, P = 0.031), palpable spleen rate (66% vs. 16%, P = 0.0003%), acute chest syndrome frequency (75% vs. 12%P = 0.0004) and cholecystectomy rate (66% vs. 13%, P = 0.0004). No significant morbidity or mortality occurred postsplenectomy. There is a subgroup of Hb SC patients requiring splenectomy, in which splenectomy is effective. Although it appears to be safe regarding short-term complications of surgery, long-term adverse effects such as infections have to be evaluated cautiously.

Mortality in sickle cell patients on hydroxyurea therapy.

The efficacy of hydroxyurea (HU) and its role in the reduction in mortality in sickle cell patients has been established. Nevertheless, many patients still die of complications of this disease while on HU. Of the 226 patients treated with HU at our center, 38 died (34 of sickle cell-related causes). Acute chest syndrome (ACS) was the most common (35%) cause of death. Deceased and surviving patients did not differ significantly in average HU dose, baseline fetal hemoglobin (Hb F), or maximum Hb F response. However, the deceased patients were significantly older when HU was instituted, were more anemic, and more likely to have BAN or CAM haplotypes. They also had significantly higher serum blood-urea-nitrogen (BUN) and creatinine levels. Sickle cell patients who die while on HU therapy may represent a subgroup of older patients, possibly with more severe disease and more severe organ damage. Such patients need early identification and prompt HU institution.

A novel approach to rapid determination of betaS-globin haplotypes: sequencing of the Agamma-IVS-II region.

beta-Globin gene cluster haplotypes were originally determined by restriction endonuclease mapping with Southern blots of polymorphic sites around the gene cluster. Over the years, haplotyping has been found to be useful, not only in population genetics but also in predicting the severity of hemoglobinopathies such as sickle cell disease. The sickle mutation occurs on five distinct haplotypes. The hitherto used methods are cumbersome and time-consuming, making haplotype determination a tedious procedure. We report our experience with a novel, rapid approach to haplotyping based on sequence polymorphisms in the Agamma-IVS-II region. We provide an algorithm that allows rapid assignment of the four African haplotypes carrying the sickle mutation.

Genetic risk factors for cerebrovascular disease in children with sickle cell disease: design of a case-control association study and genomewide screen.

BACKGROUND: The phenotypic heterogeneity of sickle cell disease is likely the result of multiple genetic factors and their interaction with the sickle mutation. High transcranial doppler (TCD) velocities define a subgroup of children with sickle cell disease who are at increased risk for developing ischemic stroke. The genetic factors leading to the development of a high TCD velocity (i.e. cerebrovascular disease) and ultimately to stroke are not well characterized. METHODS: We have designed a case-control association study to elucidate the role of genetic polymorphisms as risk factors for cerebrovascular disease as measured by a high TCD velocity in children with sickle cell disease. The study will consist of two parts: a candidate gene study and a genomewide screen and will be performed in 230 cases and 400 controls. Cases will include 130 patients (TCD > or = 200 cm/s) randomized in the Stroke Prevention Trial in Sickle Cell Anemia (STOP) study as well as 100 other patients found to have high TCD in STOP II screening. Four hundred sickle cell disease patients with a normal TCD velocity (TCD < 170 cm/s) will be controls. The candidate gene study will involve the analysis of 28 genetic polymorphisms in 20 candidate genes. The polymorphisms include mutations in coagulation factor genes (Factor V, Prothrombin, Fibrinogen, Factor VII, Factor XIII, PAI-1), platelet activation/function (GpIIb/IIIa, GpIb IX-V, GpIa/IIa), vascular reactivity (ACE), endothelial cell function (MTHFR, thrombomodulin, VCAM-1, E-Selectin, L-Selectin, P-Selectin, ICAM-1), inflammation (TNFalpha), lipid metabolism (Apo A1, Apo E), and cell adhesion (VCAM-1, E-Selectin, L-Selectin, P-Selectin, ICAM-1). We will perform a genomewide screen of validated single nucleotide polymorphisms (SNPs) in pooled DNA samples from 230 cases and 400 controls to study the possible association of additional polymorphisms with the high-risk phenotype. High-throughput SNP genotyping will be performed through MALDI-TOF technology using Sequenom's MassARRAY system. DISCUSSION: It is expected that this study will yield important information on genetic risk factors for the cerebrovascular disease phenotype in sickle cell disease by clarifying the role of candidate genes in the development of high TCD. The genomewide screen for a large number of SNPs may uncover the association of novel polymorphisms with cerebrovascular disease and stroke in sickle cell disease.