Hydroxycarbamide stimulates the production of proinflammatory cytokines by endothelial cells: relevance to sickle cell disease.

Background And Objective: The clinical hallmarks of sickle cell disease (SCD) are vaso-occlusive crises (VOC) triggered by red blood cells (RBC) stiffening and abnormal adhesion to vascular endothelial cells (VEC) in the context of chronic inflammation, cell activation, and vascular tone abnormalities. Hydroxycarbamide (HC) is the only drug with a proven efficacy in decreasing VOC frequency. HC decreases RBC stiffening, modulates adhesion protein expression by RBC and VEC, and reduces endothelin-1 production by VEC. Our objective was to test whether HC could also affect inflammation through its action on VEC.

Methods: We used microarrays to study the effect of HC on the transcriptome of transformed human bone marrow endothelial cell, a cell line derived from bone marrow microcirculation (the predilection site of VOC), in basal and proinflammatory conditions. Microarray results were confirmed by real-time quantitative PCR and protein analysis on transformed human bone marrow endothelial cell (TrHBMEC) and on two other VEC types in the primary culture: human pulmonary microcirculation endothelial cell (HPMEC) and human umbilical vein endothelial cell (HUVEC a classical model for the macrocirculation).

Results: HC had a significant effect on the expression of genes of the 'inflammation pathway'. Strikingly, it stimulates the expression of proinflammatory genes such as IL1A, IL1B, IL6, IL8, CCL2, CCL5, CCL20, and CCL8 in all the tested VEC types.

Conclusion: Our study confirms that VECs are significant targets of HC in the context of SCD and identifies its earlier unsuspected action on another major component of SCD pathophysiology, that is, the 'inflammation pathway'.