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Hemoglobin induced oxidative stress is associated with both endogenous peroxidase activity and H2O2 generation from polyunsaturated fatty acids

Patients with increased hemolytic hemoglobin (Hb) have 10–20 times greater incidence of cardiovascular mortality than the general population. In the presence of an exogenous source of H2O2, Hb is essential and responsible for the oxidation of low‐density lipoproteins (LDL). However, the role of Hb peroxidase activity in LDL oxidation remains elusive. Our study indicated that Hb could induce the formation of H2O2 by reacting with LDL, linoleic acid, and cell membrane lipid extracts. In the presence of NaN3 (a peroxidase inhibitor), endogenous peroxidase activity and subsequent Hb‐induced LDL oxidation was significantly inhibited and H2O2 concentrations accumulated. Furthermore, Hb was shown to dramatically stimulate the expression of intercellular adhesion molecule‐1 (ICAM‐1) and vascular cell adhesion molecule‐1 (VCAM‐1) in both a concentration‐ and time‐ dependent manner. Nevertheless, this stimulation was completely inhibited by a potent antioxidant, probucol. We found that 2, 2′azo‐bis‐(2‐amindinopropane) hydrochloride (AAPH) could also induce LDL oxidation and stimulate the expression of ICAM‐1 and VCAM‐1, but was not inhibited by NaN3. In conclusion, the present study suggests that the oxidative effect of Hb to produce atherogenic oxidized LDL and to induce the production of ICAM‐1 and VCAM‐1 are due to H2O2 formation as well as its endogenous peroxidase activity toward polyunsaturated fatty acids. The biochemical and physiologic significance of this study are discussed.