Expression of Apolipoprotein A-I in Rabbit Carotid Endothelium Protects Against Atherosclerosis

Abstract

Expression of atheroprotective genes in the blood vessel wall is potentially an effective means of preventing or reversing atherosclerosis. Development of this approach has been hampered by lack of a suitable gene-transfer vector. We used a helper-dependent adenoviral (HDAd) vector to test whether expression of apolipoprotein A-I (apoA-I) in the artery wall could retard the development of atherosclerosis in hyperlipidemic rabbits. Carotid arteries were infused with an HDAd expressing rabbit apoA-I or a "null" HDAd and harvested 2 and 4 weeks later. ApoA-I mRNA and protein were detected only in HDAdApoAI arteries. Lesion size, lipid and macrophage content, and adhesion molecule expression were similar in both groups at 2 weeks. Between 2 and 4 weeks, most of these measures of atherosclerosis increased in HDAdNull arteries, but were stable or decreased in HDAdApoAI arteries (P ≤ 0.04 for all end points in 4-week HDAdApoAI versus HDAdNull arteries). A longer-term study in chow-fed rabbits revealed persistence of HDAd vector DNA and apoA-I expression for ≥48 weeks, with stable vector DNA content and apoA-I expression from 4 to 48 weeks. Expression of apoA-I in arterial endothelium significantly retards atherosclerosis. HDAd provides prolonged, stable expression of a therapeutic transgene in the artery wall.

Improved Animal Models for Testing Gene Therapy for Atherosclerosis

“…Limited lesion development in HDAdNull-infused carotids may explain why we detected only a modest effect of HDAd-expressed apolipoprotein (apo) A-I gene therapy on lesion size at 4 weeks (Flynn et al, 2011) and failed to detect any effect of HDAd-expressed interleukin-10 gene therapy on lesion size at either 4 or 8 weeks . Another limitation of this model is that exposure to Ad during lesion initiation immunizes the rabbit to Ad capsid proteins (Schulick et al, 1997).…”

“…Accordingly, we began using HDAd to develop atheroprotective gene therapy in our rabbit carotid model. However, we found that lesions in fat-fed rabbit carotids infused with HDAdNull are much smaller than lesions in fat-fed rabbit carotids infused with FGAdNull, and that-unlike FGAdassociated lesions-HDAdNull-associated lesions regress spontaneously between 4 and 8 weeks after vector infusion Flynn et al, 2011). The small and transient character of atherosclerotic lesions in HDAdNull-infused carotids is likely because of the less inflammatory nature of HDAd (Wen et al, 2004).…”

“…Because these models were developed for the purpose of increasing lesion size above what we had obtained in HDAdNull-infused arteries harvested from rabbits enrolled in earlier studies Flynn et al, 2011), we include data from these ''historical control'' rabbits (n = 14 arteries from 7 rabbits) in one of the figures (Fig. 3).…”

“…They then underwent a ''mock'' Flynn et al, 2011). Triangles indicate the time of carotid surgery; the infusate for each group is indicated here.…”

“…More recently, we found that third-generation or helperdependent adenoviral vectors (HDAd) (Parks et al, 1996;Sandig et al, 2000) are superior agents for atheroprotective gene therapy because they stimulate vascular inflammation only minimally and can express a transgene in the artery wall for at least 48 weeks (Flynn et al, 2010(Flynn et al, , 2011. Accordingly, we began using HDAd to develop atheroprotective gene therapy in our rabbit carotid model.…”