Figure 4
From: Mechanisms of haptoglobin protection against hemoglobin peroxidation triggered endothelial damage
Intrinsic and extrinsic reaction pathways of Hb peroxidative endothelial damage. (a) The ‘intrinsic’ oxidation pathway (red) involves globin oxidation with the subsequent formation of Hb aggregates that induce direct endothelial damage. The proposed ‘extrinsic’ pathway (violet) involves oxidative transformation of bystander molecules (i.e., LDL) into toxic reaction products. (b) HUVECs and HPAECs were incubated with either LDL (0.5 mg/ml)+GOX 2.5 mU/ml, bvHb (2 mg/ml)+GOX, or LDL +bvHb+GOX to explore the extrinsic pathway of peroxidative toxicity. To compare the extrinsic pathway with the intrinsic pathway, some cells were treated with huHb (2 mg/ml)+GOX. Transendothelial resistance was measured with an ECIS instrument. (c) Hb-mediated LDL oxidation and protection by Hp. Left panel: O2 consumption was measured with an O2 sensitive micro-electrode in stirred reaction mixtures of LDL with huHb-Fe3+ (red), αXLHb-Fe3+ (dark violet), bvHb-Fe3+ (black), or huHb-Fe3+/Hp complex (blue). Right panel: the Hb/Hp complex (blue line) delayed the breakdown of endothelial electrical resistance compared with when αXLHb (dark violet) or bvHb (violet) were used in the reaction mixture with LDL+GOX. The control treatment (black line) was LDL+GOX in the absence of any Hb (LDL 0.5 mg/ml and Hbs 0.1 mg/ml). All ECIS traces represent mean±S.D. values of four replicate measurements
