L-4F, an Apolipoprotein A-1 Mimetic, Dramatically Improves Vasodilation in Hypercholesterolemia and Sickle Cell Disease

Abstract

Background-Hypercholesterolemia and sickle cell disease (SCD) impair endothelium-dependent vasodilation by dissimilar mechanisms. Hypercholesterolemia impairs vasodilation by a low-density lipoprotein (LDL)-dependent mechanism. SCD has been characterized as a chronic state of inflammation in which xanthine oxidase (XO) from ischemic tissues increases vascular superoxide anion (O 2 ·Ϫ ) generation. Recent reports indicate that apolipoprotein (apo) A-1 mimetics inhibit atherosclerosis in LDL receptor-null (Ldlr Ϫ/Ϫ ) mice fed Western diets. Here we hypothesize that L-4F, an apoA-1 mimetic, preserves vasodilation in hypercholesterolemia and SCD by decreasing mechanisms that increase O 2 ·Ϫ generation. Methods and Results-Arterioles were isolated from hypercholesterolemic LdlrϪ/Ϫ mice and from SCD mice that were treated with either saline or L-4F (1 mg/kg per day). Vasodilation in response to acetylcholine was determined by videomicroscopy. Effects of L-4F on LDL-induced increases in endothelium-dependent O 2 ·Ϫ generation were determined on arterial segments via the hydroethidine assay and on stimulated endothelial cell cultures via superoxide dismutase-inhibitable ferricytochrome c reduction. Effects of L-4F on XO bound to pulmonary arterioles and content in livers of SCD mice were determined by immunofluorescence. Hypercholesterolemia impaired vasodilation in Ldlr Ϫ/Ϫ mice, which L-4F dramatically improved. L-4F inhibited LDL-induced increases in O 2 ·Ϫ in arterial segments and in stimulated cultures. SCD impaired vasodilation, increased XO bound to pulmonary endothelium, and decreased liver XO content. L-4F dramatically improved vasodilation, decreased XO bound to pulmonary endothelium, and increased liver XO content compared with levels in untreated SCD mice. Conclusions-These data show that L-4F protects endothelium-dependent vasodilation in hypercholesterolemia and SCD.Our findings suggest that L-4F restores vascular endothelial function in diverse models of disease and may be applicable to treating a variety of vascular diseases. Clinical studies clearly indicate that HDL plays an important role in protecting vascular function against atherosclerosis. 8 Transgenic expression of apoA-1, the major atheroprotective apolipoprotein of HDL, retards the progression of advanced lesions in transplanted aortas from apoE-null mice and remodels them to a more stable-appearing phenotype. 9 Intraperitoneal injection of an apoA-1 mimetic (5F) and parental administration of another apoA-1 mimetic (D-4F) enhances the ability of HDL to inhibit LDL oxidation and to protect mice from diet-induced atherosclerosis without changing plasma cholesterol levels. 6,10 Indeed, infusion of reconstituted HDL rapidly improves endothelium-and endothelial nitric oxide synthase (eNOS)-dependent forearm blood flow in hypercholesterolemic men, 11 confirming that HDL plays a critical role in protecting endothelial cell function.The mechanisms by which SCD have been shown to impair vasodilation at first glance appear distinctly different from tho...

Vasculoprotective Effects of Apolipoprotein Mimetic Peptides: An Evolving Paradigm in HDL Therapy

“…Endothelial dysfunction in LDLR -/-mice is associated with LDL-induced eNOS uncoupling with concomitant O 2 .-generation. Chronic treatment with 4F resulted in a significant improvement in the vasodilatory response of small arterioles from LDLR -/-mice compared to animals receiving vehicle [82]. As in the cell culture studies, the improvement in endothelium-dependent relaxation was associated with a decrease in vascular O 2 .-formation.…”

“…Similar to LDLR -/-mice, 4F treatment improved endothelial function in small arteries of SCD mice [82]. The authors proposed that the improved endothelial function in LDLR -/-mice was related to the ability of 4F to reduce the atherogenicity and pro-inflammatory properties of LDL.…”

“…These studies have been extended under in vivo conditions by examining effects of 4F on endothelial dysfunction in LDL receptor-null (LDLR -/-) and sickle cell disease (SCD) mice [82]. Endothelial dysfunction in LDLR -/-mice is associated with LDL-induced eNOS uncoupling with concomitant O 2 .-generation.…”

“…As in the cell culture studies, the improvement in endothelium-dependent relaxation was associated with a decrease in vascular O 2 .-formation. In contrast to LDLR -/-mice, endothelial dysfunction in SCD mice is associated with an increase in the circulating concentration of the pro-oxidant enzyme xanthine oxidase (XO) [82]. Circulating XO binds to the vascular endothelium and, in the presence of xanthine substrate, reduces NO bioactivity by generating O 2 .…”

“…In the case of SCD mice, it was suggested that 4F may reduce oxidative stress in the vessel wall and prevent the formation of inflammatory lipid mediators. A common mechanism, therefore, to explain vasoprotective effects of 4F in these 2 distinct models may lie in the ability of the peptide to prevent the action and/or formation of inhibitory lipid metabolites [82].…”