Suitability of chemical in vitro models to investigate LDL oxidation: Study with different initiating conditions in native and α-tocopherol- supplemented LDL

Abstract

Isolated human LDL, used in the native form or supplemented with α- tocopherol (αT), were oxidized with Cu2+, 2,2'-azobis-(2-amidino propane) hydrochloride (AAPH), and H2O2 plus horseradish peroxidase (HRP). The oxidation kinetics were measured spectrophotometrically at 234 nm to follow the formation of conjugated dienes and evaluated as resistance to oxidation (lag phase, LP) and maximal oxidation rate (propagation rate, PR). The duration of LP in nonsupplemented LDL was different with the three prooxidant stimuli (LP, in min: 96 ± 19 for Cu2+, 28.7 ± 6.7 for HRP, and 67.1 ± 11.2 for AAPH). No correlation was found between the values obtained with Cu2+ and AAPH or HRP, but a significant correlation was found with AAPH and HRP (r = 0.798, P <0.002). In vitro αT supplementation prolonged the LP and decreased the PR with all the stimuli. The extent of increase in LP was highly correlated (r = 0.872, P <0.001 for Cu2+ and HRP; r = 0.603, P <0.03 for Cu2+ and AAPH; r = 0.749, P <0.005 for AAPH and HRP). Although the evaluation of ex vivo LDL oxidation is dependent on the prooxidant stimulus, the three prooxidant conditions used detect equally well the efficiency of αT supplementation in preventing LDL oxidation.