Relationship of Thrombospondin 1 to von Willebrand Factor and ADAMTS-13 in Sickle Cell Disease Patients of Arab Ethnicity

Abstract

<b><i>Background:</i></b> Thrombospondin 1 (TSP-1) is a multifunctional glycoprotein secreted by platelets. In sickle cell disease (SCD), TSP-1 promotes red cell adhesion to the endothelium by binding to von Willebrand factor (vWF) and inhibiting its degradation by the protease ADAMTS-13. We investigated a possible correlation between TSP-1, vWF and ADAMTS-13 in adult and pediatric SCD patients. <b><i>Methods:</i></b> Using commercially available ELISA kits, TSP-1, vWF and ADAMTS-13 levels were measured in 59 SCD patients (20 children and 39 adults) and compared with 59 age- and sex-matched controls. Associations between TSP-1 and parameters of interest were analyzed using Pearson’s correlation coefficient. <b><i>Results:</i></b> Although TSP-1 levels were higher in adult and pediatric SCD patients than in controls, the increase was not statistically significant (<i>p</i> &#x3e; 0.05). We found a significant positive correlation between TSP-1 and platelet count in both adult (<i>r</i> = 0.402, <i>p</i> = 0.01) and pediatric (<i>r</i> = 0.589, <i>p</i> = 0.01) patients, which is expected due to increased platelet activation in SCD. There was a positive correlation between TSP-1 and vWF in normal adults (<i>r</i> = 0.305, <i>p</i> = 0.049) and children (<i>r</i> = 0.633, <i>p</i> = 0.005) but not in patients (<i>p</i> &#x3e; 0.05). A significant negative correlation between TSP-1 and ADAMTS-13 activity (<i>r</i> = –0.41, <i>p</i> = 0.01) was found in adult patients. Also, a significant negative correlation between TSP-1 and ADAMTS-13/vWF antigen ratio in both normal controls (<i>r</i> = –0.595, <i>p</i> = 0.009) and patients (<i>r</i> = –0.493, <i>p</i> = 0.032) is reported for the pediatric group. <b><i>Conclusions:</i></b> Our findings confirm the inhibitory effects of TSP-1 on ADAMTS-13 activity in adult SCD patients. The negative correlation reported between TSP-1 and ADAMTS-13/vWF antigen ratio in pediatric subjects suggests a possible protective mechanism in younger individuals, although this is not related to the presence of SCD. This work emphasizes the impact of age on interpreting results related to the regulation of vWF expression and interaction with TSP-1 and ADAMTS-13 in SCD.