Lipid Peroxidation in Sickle Cell Disease: The Contribution of Cell-Free Hemoglobin in Plasma.

摘要

Sickle cell disease (SCD) is an autosomal recessive disorder caused by a single point mutation in the gene that encodes for the beta subunit of hemoglobin (Hb). Upon deoxygenation, Hb monomers aggregate and polymerize, causing distortion of the red blood cell (RBC). Consequently, sickle RBCs are extremely fragile and prone to lysis, resulting in elevated levels of cell-free Hb in the plasma compartment.;Traditionally, the vascular complications seen in SCD have been attributed to RBC rigidity and poor blood flow through the microvasculature. Recently however, accumulating evidence suggests that vascular dysfunction may play an important role in the complex pathophysiology of SCD. Vascular dysfunction, due to NO scavenging, oxidative injury, and lipid oxidation products, is thought to be, in part, due to cell-free Hb.;Cell-free Hb, especially in combination with reactive oxygen species (ROS), has been shown to initiate lipid peroxidation in isolated lipoproteins. In addition, myoglobin, a Hb related protein, has been previously shown to initiate lipid peroxidation in rhabdomyolysis resulting in vascular complications.;In this study, we examined the role of cell-free Hb as a potential initiator of lipid peroxidation in SCD plasma by a) measuring tocopherol content in plasma, isolated LDL, and RBC membranes; b) examining the oxidative potential of SCD plasma; and c) examining Hb-mediated oxidation of LDL isolated from plasma. While cell-free Hb may represent a potential source of oxidative stress in SCD plasma, it appears unlikely that cell-free Hb can overcome the antioxidant capacity of SCD plasma to directly mediate lipid peroxidation.;In this study, we examined the role of cell-free Hb as a potential initiator of lipid peroxidation in SCD plasma by a) measuring tocopherol content in plasma, isolated LDL, and RBC membranes; b) examining the oxidative potential of SCD plasma; and c) examining Hb-mediated oxidation of LDL isolated from plasma. While cell-free Hb may represent a potential source of oxidative stress in SCD plasma, it appears unlikely that cell-free Hb can overcome the antioxidant capacity of SCD plasma to directly mediate lipid peroxidation.;In this study, we a) determined binding constants between B10 and Hb and; b) examined the potential of B10 to reduce cell-free Hb in vivo and in vitro. We conclude that B10 binds directly to Hb and is effective in reducing cell-free Hb both in vivo and in vitro..;By binding to Hb, haptoglobin also prevents the iron heme group from dissociating from the protein, inhibiting many of its pro-oxidative effects. The antioxidant activity of B10 was investigated by examining the peptide's ability to inhibit Hb-mediated oxidation in isolated LDL. These data indicate that B10 is an effective inhibitor of lipid peroxidation; however this antioxidant activity is independent of its ability to bind to Hb. The added antioxidant function, in which the available thiols in the peptide's sequence play a key role, suggest that B10 has potential as a peptide based therapeutic in SCD.;The conclusions presented in this study will lead to a better understanding of the relationship between cell-free Hb and vascular dysfunction in SCD. In addition, our study provides insight into the potential benefit of peptide based therapies in SCD.