Submitted on September 14, 2007
Accepted on November 9, 2007
Hydroxyurea Attenuates Activated Neutrophil-Mediated Sickle Erythrocyte Membrane Phosphatidylserine Exposure and Adhesion to Pulmonary Vascular Endothelium
Johnson Haynes, Jr.1*, Boniface Obiako2, Raymond B. Hester3, B. Surendra Baliga4, and Troy Stevens5
1 Comprehensive Sickle Cell Center, University of South Alabama College of Medicine, Mobile, Alabama, United States; Internal Medicine, University of South Alabama, Mobile, Alabama, United States; Center of Lung Biology, University of South Alabama College of Medicine, Mobile, Alabama, United States
2 Comprehensive Sickle Cell Center, University of South Alabama College of Medicine, Mobile, Alabama, United States; Center of Lung Biology, University of South Alabama College of Medicine, Mobile, Alabama, United States
3 Pathology, University of South Alabama College of Medicine, m, Alabama, United States; Microbiology, University of South Alabama College of Medicine, Mobile, Alabama, United States
4 Pediatrics, University of South Alabama College of Medicine, Mobile, Alabama, United States
5 Center of Lung Biology, University of South Alabama College of Medicine, Mobile, Alabama, United States; Pharmacology, University of South Alabama College of Medicine, Mobile, Alabama, United States
* To whom correspondence should be addressed. E-mail: jhaynes{at}usouthal.edu.
Abstract
Activated neutrophils increase erythrocyte phosphatidylserine (PS) exposure. PS-exposed sickle erythrocytes (SSRBC) are more adhesive to vascular endothelium than non-PS exposed cells. An increase in SSRBC fetal hemoglobin (Hb F) concentration has been associated with improved rheology and decreased numbers of vaso-occlusive episodes. This study examined the effects of Hb F, PS-exposed SSRBCs, and chronic hydroxyurea treatment on activated neutrophil-mediated SSRBC retention/adherence in isolated- perfused rat lungs. Lungs were perfused with erythrocyte suspensions from: (1) individuals homozygous for hemoglobin S with 0-7% Hb F (SS), (2) with 
8% HbF (SS+F), and (3) individuals homozygous for hemoglobin S treated with hydroxyurea (HU) therapy for 1 year (SS+HU). Retention of SSRBCs from the SS+HU group was significantly less than seen in both the SS and SS+F groups No difference was observed between the SS and SS+F groups. The percent of Hb F and F-cells did not differ between the SS+F and SS+HU groups. At baseline, the proportion of PS-exposed SSRBCs was not different between the SS and SS+HU groups. However, SSRBC treatment with activated neutrophil supernatant caused a 2-fold increase in PS-exposed SSRBCs in the SS control and no change in the SS+HU group. We conclude that 1) hydroxyurea attenuates SSRBC retention/adherence in the pulmonary circulation seen in response neutrophil activation, 2) hydroxyurea stabilizes SSRBC membrane PS and 3) hydroxyurea attenuation SSRBC retention/adherence in the pulmonary circulation occurs through a mechanism(s) independent of Hb F.
