Therapy with hydroxyurea is associated with reduced adhesion molecule gene and protein expression in sickle red cells with a concomitant reduction in adhesive properties

Abstract

Propagation of the vaso-occlusive process in sickle cell anaemia (SCA) is a complex process involving the adhesion of steady-state SCA patients red cells and reticulocytes to the vascular endothelium. The effect of hydroxyurea therapy (HUT) on the adhesive properties of sickle cells and the expression of adhesion molecule genes by erythroid cells of SCA individuals is not yet fully understood. The expressions of the CD36 gene and the VLA-4-integrin subunit genes, CD49d (alpha-subunit) and CD29 (beta-subunit), were compared in the reticulocytes of steady-state SCA patients and patients on HUT using real-time PCR. Basal adhesion of red cells from these subjects was also compared using static adhesion assays, as was surface protein expression, using flow cytometry. Basal sickle red cell adhesion to fibronectin was significantly greater than that of normal cells (P < 0.01); in contrast, HUT was associated with significantly lower levels (P < 0.01) of red cell adhesion that were similar to those of control cells; this decrease could not be justified solely by altered reticulocyte numbers in this population. Accordingly, flow cytometry demonstrated that reticulocytes from patients on HUT had significantly lower CD36 and CD49d surface expressions (P < 0.01) and, importantly, significantly lower expressions of the CD36, CD49d and CD29 genes (P < 0.05) than reticulocytes of SCA patients not on HUT. Taken together, data support the hypothesis that HUT reduces the adhesive properties of sickle cells and that this decrease appears to be mediated, at least in part, by a decrease in the gene and, consequently, surface protein expression of adhesion molecules such as VLA-4 and CD36.

Hydroxyurea responsiveness in -thalassemic patients is determined by the stress response adaptation of erythroid progenitors and their differentiation propensity

“…23 The expression profile of these cells is, therefore, not informative for the HbF response to HU in erythroid progenitor cells. Other studies on the effect of HU in SCD patients show decreased expression of adhesion molecules in vascular endothelial and red cells, [24][25] its stimulating effect on proinflammatory gene expression, 26 and several other pathways. [27][28] To our knowledge, none of these studies address the differential HU response in β-thalassemia.…”

Intercellular adhesion molecule-4 and CD36 are implicated in the abnormal adhesiveness of sickle cell SAD mouse erythrocytes to endothelium

“…However, the expression of α4b1 integrins is increased on reticulocytes of subjects with sickle cell disease. 8,24 We could not detect α4b1 integrins on either mature or young mouse RBC (data not shown). ICAM-4 is an erythrocyte-specific intercellular adhesion molecule which binds to αVb3 integrins on endothelial cells.…”

“…For instance, Lu/BCAM was found to be over-expressed on RBC of sickle cell patients treated with hydroxyurea 8 when adhesive properties of sickle cells were reduced. 24 It is, therefore, conceivable that ICAM-4 and CD36 of SAD RBC, although present in reduced amounts, might be activated by a state of abnormal constitutive phosphorylation. Under our experimental conditions, we did not detect phosphorylation on tyrosine or threonine residues of ICAM-4, either from SAD or wild-type mice.…”

Venous sinus thrombosis leading to stroke in a patient with sickle cell disease on hydroxyurea and high hemoglobin levels: Treatment with thrombolysis

“…This syndrome can be explained by increases in viscosity leading to essentially stationary blood flow despite elevated blood pressure [12]. While treatment with hydroxyurea leads to increased hemoglobin in most patients, this is not associated with hyperviscosity or complications probably because of the effects of hydroxyurea in improving the rheologic and adhesive features of sickle erythrocytes [14][15][16]. Unlike the other reported cases our patient had not received transfusions; however, the high hemoglobin levels reached on hydroxyurea therapy may have played a role in the development of DVST and AVN.…”