Hemoglobin-Bound Platelets Correlate With The Increased Platelet Activity In Hemoglobin E/Beta-Thalassemia

Introduction An increase in platelet activity is a contributing factor to vascular complications in hemoglobin E/beta-thalassemia (HbE/beta-thal). Plasma-free hemoglobin (Hb) increases in HbE/beta-thal patients and correlates with platelet activation, but the levels of Hb-bound platelets have never been reported. In this study, we aimed to investigate the levels of Hb-bound platelets and its association with platelet activity in HbE/beta-thal patients. Methods Hb-bound platelets were measured by flow cytometry in 22 healthy subjects and 26 HbE/beta-thal patients (16 nonsplenectomized and 10 splenectomized HbE/beta-thal patients). Plasma Hb was measured by the chemiluminescence method based on the consumption of nitric oxide (NO) by Hb. Expression of P-selectin and activated glycoprotein (aGP) IIb/IIIa on platelets was measured by flow cytometry as a marker of platelet activity. Results Both nonsplenectomized and splenectomized HbE/beta-thal patients had higher levels of Hb-bound platelets and plasma Hb than healthy subjects. In vitro incubation of dialyzed Hb from patients with platelets of healthy subjects caused an increase in Hb-bound platelets, which was partially inhibited by anti-GPIb alpha antibody. Plasma Hb positively correlated with Hb-bound platelets. Platelet P-selectin expression at baseline and in response to adenosine diphosphate (ADP, 1 mu M) stimulation was higher in nonsplenectomized and splenectomized HbE/beta-thal patients than healthy subjects. The ADP-induced aGPIIb/IIIa expression on platelets was also higher in HbE/beta-thal patients than healthy subjects. Hb-bound platelets correlated with baseline P-selectin expression and ADP-induced P-selectin expression. Conclusion HbE/beta-thal patients have increased Hb-bound platelets, which is associated with increased baseline platelet activation and reactivity.