A randomized, controlled clinical trial established the efficacy and safety of short-term use of hydroxyurea in adult sickle cell anemia. To examine the risks and benefits of long-term hydroxyurea usage, patients in this trial were followed for 17.5 years during which they could start or stop hydroxyurea. The purpose of this follow-up was to search for adverse outcomes and estimate mortality. For each outcome and for mortality, exact 95% confidence intervals were calculated, or tests were conducted at a 5 0.05 level (P-value <0.05 for statistical significance). Although the death rate in the overall study cohort was high (43.1%; 4.4 per 100 person-years), mortality was reduced in individuals with long-term exposure to hydroxyurea. Survival curves demonstrated a significant reduction in deaths with long-term exposure. Twenty-four percent of deaths were due to pulmonary complications; 87.1% occurred in patients who never took hydroxyurea or took it for <5 years. Stroke, organ dysfunction, infection, and malignancy were similar in all groups. Our results, while no longer the product of a randomized study because of the ethical concerns of withholding an efficacious treatment, suggest that long-term use of hydroxyurea is safe and might decrease mortality. Am. J. Hematol. 85:403-408, 2010. V

Osteonecrosis of the femoral head is common in patients with sickle cell disease, with an incidence ranging from about 2 to 4.5 cases per 100 patient-years. Patients with the hemoglobin SS genotype and alpha-thalassemia and those with frequent painful crises are at highest risk. The overall prevalence is about 10 percent. The results of hip arthroplasty are poor.

The adherence of sickle red blood cells (RBCs) to the vascular endothelium may contribute to painful vaso-occlusion in sickle cell disease. Sickle cell adherence involves several receptor-mediated processes and may be potentiated by the up-regulated expression of adhesion molecules on activated endothelial cells. Recent results showed that thrombin rapidly increases the adhesivity of endothelial cells for sickle erythrocytes. The current report presents the first evidence for the novel adhesion of normal and, to a greater extent, sickle RBCs to endothelial Pselectin. Studies of the possible interaction of erythrocytes with P-selectin revealed that either P-selectin blocking monoclonal antibodies or sialyl Lewis tetrasaccharide inhibits the enhanced adherence of normal and sickle cells to thrombin-treated endothelial cells. Both RBC types also adhere to immobilized recombinant P-selectin. Pretreating erythrocytes with sialidase reduces their adherence to activated endothelial cells and to immobilized recombinant P-selectin. Herein the first evidence is presented for the binding of normal or sickle erythrocytes to P-selectin. This novel finding suggests that P-selectin inhibition be considered as a potential approach to therapy for the treatment of painful vasoocclusion in sickle cell disease. IntroductionThe interaction of P-selectin and its ligands contributes to the specificity of interactions among endothelial cells, platelets, and leukocytes during inflammation, coagulation, and atherosclerosis. [1][2][3][4][5][6][7][8] The expression of P-selectin on endothelial cells and platelets requires activation of these cells by specific biologic response modifiers, such as thrombin, which has the capacity in both cell types to trigger rapid translocation of P-selectin from intracellular storage granules to the membrane surface and in endothelial cells to induce also slower transcriptional up-regulation of the P-selectin gene. [9][10][11] Another requisite for P-selectin-mediated adhesive interactions is a P-selectin ligand whose specificity is conferred by the particular transferases that generate its unique carbohydrate composition. 1,4,[6][7][8]12,13 Erythrocytes are not considered to participate in these receptor-mediated processes, 8 because normal red blood cells (RBCs) are not known to bear selectin ligands or to bind to P-selectin. 14 The conventional view that erythrocyte sickling in small blood vessels causes the painful vaso-occlusion of sickle cell disease does not explain why only 5% of patients account for 30% of pain crises in this common debilitating genetic condition. 15,16 An emerging hypothesis is that vaso-occlusion involves factors besides erythrocyte sickling. The adherence of sickle cells to vascular endothelium may be particularly important to vaso-occlusion. 17 Hebbel and colleagues found that sickle erythrocytes are abnormally adherent to endothelial cells in vitro 18 and that the adhesivity of sickle RBCs in vitro correlates with vaso-occlusive severity. 19 Kaul and associates determined t...