Elevated Endothelial Progenitor Cells during Painful Sickle Cell Crisis

Background: Sickle Cell Disease (SCD) is characterized by microvascular occlusion leading to an ischemia-induced pro-angiogenic response. Circulating endothelial progenitor cells (EPCs) play an important role in neovascularisation and decreased EPC numbers are associated with poor outcome in cardiovascular disease.

Aims: To determine the numbers of circulating EPCs in patients with SCD during steady state and painful crisis and to assess the association of EPC numbers with serum levels of humoral growth factors (stromal derived growth factor-1α (SDF-1α), erythropoietin (EPO), vascular endothelial growth factor (VEGF), placenta-induced growth factor (PIGF), interleuking-8 (IL-8), soluble vascular adhesion molecule-1 (sVCAM-1)).

Methods: Numbers of circulating EPCs, defined as CD45^dim/CD34⁺ cells expressing vascular endothelial growth factor receptor-2 (VEGF-R2), and serum levels of humoral factors were measured consecutively in 66 patients in steady state, 23 patients during painful sickle cell crisis and 13 age- and race-matched healthy controls.

Results: While circulating EPC numbers were comparable between healthy controls and sickle cell patients in steady state, they were significantly increased in patients during sickle cell crisis. EPC numbers correlated significantly only to serum SDF-1α levels during painful crisis.

Conclusion: Sickle cell crisis is characterized by elevated circulating EPC numbers further supporting a pro-angiogenic state in SCD. SDF-1 may play a role of importance in EPC mobilisation during sickle cell crisis.