Alteration of lysophosphatidylcholine content in low density lipoprotein after oxidative modification: Relationship to endothelium dependent relaxation

Abstract

Objective: The aim was to examine the formation of lipid peroxidation products and the alteration in phospholipid content in low density lipoprotein (LDL) after oxidative modification by CuSO 4, and subsequently, to determine the ability of the modified LDL to impair endothelium dependent relaxation in rat aortic rings. Methods: Blood samples were obtained from normal human volunteers. LDL was prepared by sequential ultracentrifugation and it was oxidatively modified in the presence of 5 μM CuSO 4. Lipid peroxidation products (thiobarbituric acid reactive substances, TBARS), and alterations in electrophoretic mobility and phospholipid content were determined in normal (native) and oxidised LDL. Endothelium dependent relaxation was produced by acetylcholine (10 -8 - 10 -5 M) in phenylephrine precontracted rat aortic rings. Results: LDL incubated for 24 h with 5 μM CuSO 4 at 20°C and 37°C with constant agitation displayed higher amounts of TBARS than the respective native LDL. While the amounts of TBARS in LDL modified at 20°C and 37°C were similar, the former condition resulted in statistically smaller changes of phospholipid contents. LDL with higher lysophosphatidylcholine content showed greater impairment of endothelium dependent relaxation in rat aortic rings than LDL with lower lysophosphatidylcholine content. Conclusions: The raised lysophosphatidylcholine level in oxidatively modified LDL was related to the ability of the LDL to impair endothelium dependent relaxation. However, lipid peroxidation products assessed by TBARS did not relate to the phospholipid changes in LDL and therefore cannot be used to predict the vascular effects of LDL after oxidative modification.