L-4F, an Apolipoprotein A-1 Mimetic, Restores Nitric Oxide and Superoxide Anion Balance in Low-Density Lipoprotein-Treated Endothelial Cells

Abstract

Background— Low-density lipoprotein (LDL) impairs endothelial cell function by uncoupling endothelial nitric oxide synthase (eNOS) activity, which allows superoxide anion (O 2 ·− ) to be generated rather than nitric oxide (·NO). Recent reports indicate that apolipoprotein (apo) A-1 mimetics inhibit the development of atherosclerotic lesions in LDL receptor-null mice. Here we hypothesize that L-4F, an apoA-1 mimetic that inhibits atherosclerosis induced by hypercholesterolemia, protects endothelial cell function by preventing LDL from uncoupling eNOS activity. Methods and Results— Bovine aortic endothelial cells were incubated with LDL±L-4F, and changes in A23187-stimulated ·NO and O 2 ·− generation were determined by ozone chemiluminescence and superoxide dismutase-inhibitable ferricytochrome c reduction, respectively. Western analysis of eNOS immunoprecipitates was used to determine effects of LDL and L-4F on heat shock protein 90 (hsp90) interactions with eNOS. LDL decreased ·NO production and increased eNOS-dependent O 2 ·− generation. Pretreatment of LDL with L-4F increased ·NO and decreased O 2 ·− generation. By itself, L-4F had no effect on O 2 ·− but did increase ·NO generation. Stimulation of endothelial cells incubated with LDL decreased the association of hsp90 with eNOS. Pretreatment of LDL with L-4F prevented a decrease in hsp90 association with eNOS and often enhanced association on stimulation. Conclusions— These data demonstrate that L-4F protects endothelial cell function by preventing LDL from uncoupling eNOS activity. L-4F allows endothelial cell to maintain coupled eNOS activity to generate ·NO even in the face of atherogenic concentrations of LDL.