Hemoglobin-haptoglobin complex (Hb-Hp complex)

The hemoglobin-haptoglobin complex is a high-affinity protein assembly formed in the plasma when haptoglobin binds to extracorpuscular hemoglobin released during intravascular hemolysis (UniProt P00738). This binding is essentially irreversible and serves a critical protective role by sequestering free hemoglobin, which otherwise promotes oxidative stress, scavenges nitric oxide, and causes tissue damage (PubMed: 23475935). Once formed, the complex is specifically recognized by the CD163 scavenger receptor expressed on the surface of monocytes and macrophages, leading to its rapid endocytosis and degradation (PubMed: 11159130). This process facilitates the safe recycling of iron and prevents renal damage caused by the filtration of free hemoglobin dimers through the kidneys. In clinical settings, haptoglobin is utilized as a therapeutic agent to manage conditions characterized by excessive hemolysis, such as during cardiac surgery or in hemolytic anemias, by promoting the formation of this complex and accelerating hemoglobin clearance (PubMed: 30111554).

Other names

Hb-HpHaptoglobin-hemoglobin complexHemoglobin-haptoglobin

Haptoglobin binds free hemoglobin with extremely high affinity to form the hemoglobin-haptoglobin complex, which is then specifically recognized and internalized by the CD163 scavenger receptor on macrophages for degradation and iron recycling (PubMed: 11159130, PubMed: 21940841).