Response to hydroxyurea among Kuwaiti patients with sickle cell disease and elevated baseline HbF levels

Abstract

the tyrosine kinase activity that is supposed to be the cause of the disease and its complications.JAK2V617F mutation primarily affects the proliferation of the red cell lineage but its impact on the phenotype of circulating RBCs is poorly documented. Our group showed increased adhesion of PV RBCs to endothelial cells mediated by erythroid Lu/BCAM and endothelial laminin a5 chain [4]. Recently, we showed that this abnormal adhesion stems from JAK2V617F-mediated Lu/BCAM activation through a Rap1/Akt signaling pathway [5]. Blocking this pathway by JAK2 specific inhibitors led to significant decrease of PV RBC adhesion [5]. Here, we extended our findings by a quantitative analysis to determine the relationship between the rate of RBC adhesion to laminin and the JAK2V617F allele burden.We first asked whether variation between patients in RBC adhesion was related to Lu/BCAM expression on the surface of PV RBCs. Indeed, Lu/BCAM erythroid expression is heterogeneous within the same individual, including a variable surface expression level and a proportion of Lu/BCAM-negative RBCs. We performed adhesion assays with blood samples from 17 JAK2V617F-positive PV patients, with no cytotoxic antiproliferative treatment, and determined the number of RBCs adhering to laminin at 3 dyn/cm 2 .The adhesion values were variable, ranging from 14 to 1021 RBCs/mm 2 (Supporting Information Table S1). The percentage of Lu/BCAM-positive RBCs as assessed by flow cytometry ranged from 38% to 90%, and the expression level, estimated by the mean fluorescence intensity (MFI), from 1249 to 3153 (Supporting Information Table S1). Because Lu/BCAM phosphorylation is driven by a JAK2V617F-dependent pathway in PV RBCs [5], we asked whether RBC adhesion was influenced by JAK2V617F expression level. To date the most commonly used tool for evaluating the mutational load in one individual is by measuring the mutant allele burden in blood cell DNA. The JAK2V617F allele burden was determined for the 17 PV patients using an allele specific quantitative PCR (MutaquantV R , Qiagen) and ranged from 20 to 68% (Supporting Information Table S1). RBC adhesion values were plotted against the percentage of JAK2V617F. Statistical analysis showed a significant correlation between RBC adhesion and JAK2V617F percentage (r 5 0.571 and P 5 0.016, Fig. 1C) that was improved when the interval of Lu/ BCAM-positive RBCs was restricted to 65-90% (r 5 0.849 and P 5 0.0009, n 5 11 patients), indicating that for equivalent Lu/BCAM expression, higher JAK2V617F levels would drive higher RBC adhesion to laminin (Fig. 1D).As RBCs are enucleated, it is not possible to estimate the level of JAK2V617F using DNA or RNA based PCR assays. However, clonogenic assays showed that patients with higher JAK2V617F mutant allele burden in blood DNA carried more mutated erythroid progenitor cells [6]. Our study revealed RBC adhesion as a biological marker to estimate the V617F mutational load at the protein level in PV RBCs; although indirect, this marker has the potential of informing about the ...

Risk of avascular necrosis of the femoral head in children with sickle cell disease on hydroxyurea: MRI evaluation

“…Two reports have implicated HU therapy as a risk factor for AVNFH among children and adolescents with SCD, but others have not found this association . The latter is also in agreement with previous reports from our center …”

“…[18][19][20] The latter is also in agreement with previous reports from our center. 7,21 The present study was designed to study the effect of HU on the prevalence and/or course of AVNFH in a cohort of Kuwaiti patients with SCD who have been on prolonged HU therapy, who had MRI of the hips done before commencing the drug and at the end of the study.…”

Additive effect of sirolimus and hydroxycarbamide on fetal haemoglobin level in kidney transplant patients with sickle cell disease

“…Our patients are from eastern Saudi Arabia and are expected to have the Arab‐Indian β‐globin haplotype (Padmos et al , ). SCD patients with this haplotype have higher baseline HbF level (Padmos et al , ) and can raise HbF further in response to HC therapy (Adekile et al , ). The additive effect of HC to other agents was first reported in an animal model treated with HC and recombinant erythropoietin (Al‐Khatti et al , ) and a similar observation was made in SCD patients (Rodgers et al , ).…”

Hydroxyurea: Pattern of Use, Patient Adherence, and Safety Profile in Patients with Sickle Cell Disease in Oman

“…14-16 Studies conducted within the Middle East region assessing the beneficial effects of HU in patients with SCD have also shown promising results as seen elsewhere. 9,13,17,18 Unfortunately, underutilization or suboptimal use of HU is a serious problem among patients with SCD. 6,19-24 Side effects and lack of patient adherence to treatment is a major concern associated with its use.…”