Circulating Endothelial Cells: A Potential Parameter of Organ Damage in Sickle Cell Anemia?

Traditional laboratory markers of disease severity (Hb concentrations, HbF%, LDH concentrations and leukocyte counts) are not powerful enough to identify individuals with sickle cell disease (SCD) at high risk of complications. In several disease states, the number of circulating endothelial cells (CEC) is indicative of the extent of vascular disease and several small studies employing cumbersome techniques have shown increased CEC to occur in SCD as well. In this pilot study we determined if, by employing the CellSearch system, elevated CEC can be detected in SCD and whether the CEC count is related to the presence of organ damage, painful crisis frequency, traditional laboratory markers of disease severity as well as markers of endothelial activation. Peripheral blood was collected from 15 sickle cell patients and 15 healthy sex, age and race matched HbAA controls. Cells positive for CD146 (present on endothelial cells) are immuno-magnetically isolated and stained with nuclear DAPI and anti-CD105 (present on endothelial cells) and anti-CD45 (pan-leukocyte marker). Within the CD146 enriched cell suspension, cells meeting the DAPI+/CD146+/CD105+/CD45− criteria after image cytometry are designated CEC. CEC counts were significantly higher in sickle cell patients (12 cells/mL, IQR 8–29) as compared to controls (4 cells/mL, 3–10) (p=0.007). CEC counts were significantly higher in patients with pulmonary hypertension (PHT) (p=0.02), and increased with the presence of number of affected organs as well (0–4 involved organs, p=0.03), with the number of affected organs being the most important determinant of increased CEC numbers in SCD (R2=0.72, P=0.001). No statistically significant correlation was detected between CEC counts and markers of endothelial activation (serum sVCAM-1 and plasma VWF:Ag levels). CEC counts did not differ between patients on hydroxyurea and those who did not use hydroxyurea. No statistically significant correlations were detected between CEC counts and painful crisis frequency, Hb, HbF%, leukocyte counts, LDH concentrations. In conclusion, elevated CEC’s can be demonstrated in the clinically asymptomatic state in patients with sickle cell anemia with a validated and automated technique and, for the first time, a relation of CEC counts to SCD related organ damage is demonstrated. Furthermore, the extent of EC activation (as assessed by sVCAM-1 and VWF:Ag levels) is not necessarily related to the extent of EC damage (as assessed by CEC counts).