Cholesterol bound to hemoglobin in normal human erythrocytes: a new form of cholesterol in circulation?

Objective: To study lipid fraction that is occasionally observed in red blood cell (RBC) hemolysate (supernatants from which membranes were separated). Study design: Plasma lipid profiles, cholesterol (Ch) and phospholipids (PL) in intact RBCs, RBC membranes and hemolysates were examined in young healthy male population in winter and summer. Results: The RBC Ch and PL content was significantly higher than in membranes, both in winter and summer. The “excess” of cholesterol (associated with phospholipid) was bound to hemoglobin yielding Hb–lipid adduct (Hb–Ch), the pools in the RBC membrane remaining virtually unaltered. Levels of hemoglobin–lipid complex (Hb–Ch), which were significantly higher in winter than in summer (30% and 19% of the total Hb, respectively), positively correlated with plasma HDL cholesterol levels. Conclusion: To our knowledge, this is the first demonstration of cholesterol binding to Hb. The results suggest influence of plasma lipoprotein metabolism on the formation of Hb–Ch.