Hydroxyurea corrects the dysregulated L-selectin expression and increased H2O2 production of polymorphonuclear neutrophils from patients with sickle cell anemia

Abstract

Impaired polymorphonuclear neutrophil (PMN) functions during sickle cell anemia (SCA) may have a pathogenic role in the onset of vasoocclusive events. We used flow cytometry to study, in whole blood, the adhesion molecule expression and respiratory burst of PMNs from children with SCA. Three different clinical groups were studied: (1) patients with no history of vasoocclusive events (n ‫؍‬ 15); (2) patients with a history of vasoocclusive events (n ‫؍‬ 17); and (3) patients receiving hydroxyurea therapy for severe vasoocclusive events (n ‫؍‬ 9). Unstimulated PMNs showed decreased L selectin expression and increased H 2 O 2 production whatever the severity of the disease, reflecting PMN activation. This could contribute to endothelial activation reflected by abnormal plasma levels of soluble adhesion molecules (soluble intercellular adhesion molecule-1, sE selectin, and sL selectin). After stimulation with bacterial N-formyl peptides (N-formyl-methionylleucyl-phenylalanine [fMLP]), PMNs from untreated patients with a history of vasoocclusive events showed dysregulated L selectin shedding and increased H 2 O 2 production. Furthermore, in these patients, tumor necrosis factor priming followed by fMLP stimulation induced an H 2 O 2 production significantly higher than in the other patient groups and controls. These impairments could immobilize PMNs on the endothelium, thereby inducing reduced blood flow and fostering microvascular occlusion and vascular damage. In contrast, children treated with hydroxyurea showed near-normal basal and poststimulation H 2 O 2 production as well as normal L selectin shedding after stimulation but no change in plasma levels of soluble adhesion molecules. To our knowledge, this is the first report showing major qualitative changes of PMN abnormalities upon hydroxyurea treatment in SCA patients. This strongly suggests that PMNs are a primary target of this drug. IntroductionSickle cell anemia (SCA) results from a single point mutation that substitutes valine for glutamic acid at the sixth position in the ␤-globin chain and produces hemoglobin S (Hb S). 1,2 The basic pathophysiologic mechanism, based upon the polymerization of deoxy-Hb S and the ensuing deformation, rigidification, and fragilization of the red cells, explains the 3 hallmarks of the disease: hemolytic anemia, vasoocclusive events, and progressive functional asplenia leading to increased susceptibility to infection. Even though all SCA patients have the same biochemical defect, they show wide variability in the frequency and clinical severity of vasoocclusive crises and remain asymptomatic for long periods, indicating that additional factors must contribute to the pathophysiology of vasoocclusion. 3 Abnormal red blood cell (RBC) adhesion to the endothelium has recently been forwarded as the probable initiating event of vasoocclusion, while variations in the endothelium activation state may modulate the unpredictable occurrence of the major complications. 4 Inflammation plays a major role in this process. 5 To date, hydrox...

Increased levels of soluble ICAM‐1 in the plasma of sickle cell patients are reversed by hydroxyurea

“…Plasma levels of sVCAM-1 and sICAM-1 were significantly increased in steady-state SCD patients, confirming previous reports of increased sVCAM-1 levels in SCD patients [7] and clarifying conflicting reports regarding changes in sICAM-1 levels in patients [7,8]. sVCAM-1 levels in SCD patients were reduced by HU.…”

“…A study by Duits et al [7], relating increases in plasma sVCAM-1 in a small sample of sickle cell patients, failed to demonstrate any difference in sICAM-1 levels in the same patients. In contrast, a more recent study by Benkerrou et al [8] demonstrated increased sICAM-1 levels in steadystate SCD patients and in vaso-occlusive patients but were unable to show any effect of HU therapy upon these levels.…”

Hydroxyurea downregulates endothelin-1 gene expression and upregulates ICAM-1 gene expression in cultured human endothelial cells

“…sICAM-1 levels are higher (two-to three-fold) in children with SCA than in ethnically matched controls. 39 Our in vitro experimental finding that HU enhances the expression of mbICAM-1 by endothelial cells in culture (Figure 6a and b) does not appear to be consistent with the significant clinical benefits conferred by this drug in SCA patients. The strongest correlation was found between total white cell count and severity of crisis rather than with erythrocyte-related parameters.…”

“…38 Elevated serum sICAM-1 levels have been noted in various immune and inflammatory disorders including SCA. 39 Indeed, sickle RBCs have been shown to induce mbICAM-1 expression by endothelial cells in culture both in stationary and flow studies. 40 Under flow conditions, upregulation of mbICAM-1 involves both transcriptional and translational control.…”

Sodium phenyl butyrate downregulates endothelin‐1 expression in cultured human endothelial cells: Relevance to sickle‐cell disease

“…ICAM-1 is an EC surface glycoprotein implicated in leukocyte adhesion. sICAM-1 is elevated in SCD patients but not modified by HU treatment in vivo [25,26]. VCAM-1 is the endothelial receptor for the very late activation antigen 4 (VLA-4) at the surface of sickle erythrocytes [27].…”