Amit V. Khera, M.D., Marina Cuchel, M.D., Ph.D., Margarita de la Llera-Moya, Ph.D., Amrith Rodrigues, M.S., Megan F. Burke, B.A., Kashif Jafri, B.A., Benjamin C. French, Ph.D., Julie A. Phillips, Ph.D., Megan L. Mucksavage, M.Sc., Robert L. Wilensky, M.D., Emile R. Mohler, M.D., George H. Rothblat, Ph.D.,and Daniel J. Rader, M.D.

n engl j med 364;2 nejm.130 org january 13, 2011

Background

High-density lipoprotein (HDL) may provide cardiovascular protection by promoting reverse cholesterol transport from macrophages. We hypothesized that the capacity of HDL to accept cholesterol from macrophages would serve as a predictor of atherosclerotic burden.

Methods
We measured cholesterol efflux capacity in 203 healthy volunteers who underwent assessment of carotid artery intima–media thickness, 442 patients with angiographically confirmed coronary artery disease, and 351 patients without such angiographically
confirmed disease. We quantified efflux capacity by using a validated ex vivo system that involved incubation of macrophages with apolipoprotein B–depleted serum from the study participants.
Results
The levels of HDL cholesterol and apolipoprotein A-I were significant determinants of cholesterol efflux capacity but accounted for less than 40% of the observed variation. An inverse relationship was noted between efflux capacity and carotid
intima–media thickness both before and after adjustment for the HDL cholesterol level. Furthermore, efflux capacity was a strong inverse predictor of coronary disease status (adjusted odds ratio for coronary disease per 1-SD increase in efflux capacity, 0.70; 95% confidence interval [CI], 0.59 to 0.83; P<0.001). This relationship was attenuated, but remained significant, after additional adjustment for the HDL cholesterol level (odds ratio per 1-SD increase, 0.75; 95% CI, 0.63 to 0.90; P = 0.002) or apolipoprotein A-I level (odds ratio per 1-SD increase, 0.74; 95% CI, 0.61 to 0.89; P = 0.002). Additional studies showed enhanced efflux capacity in patients with the metabolic syndrome and low HDL cholesterol levels who were treated with pioglitazone, but not in patients with hypercholesterolemia who were treated with statins.

Conclusions
Cholesterol efflux capacity from macrophages, a metric of HDL function, has a strong inverse association with both carotid intima–media thickness and the likelihood of angiographic coronary artery disease, independently of the HDL cholesterol
level. (Funded by the National Heart, Lung, and Blood Institute and others.)

A robust inverse association between the level of high-density lipoprotein (HDL) cholesterol and the risk of cardiovascular
disease has fostered intensive research seeking to target HDL metabolism for therapeutic gain.1,2 However, some findings have called into question the hypothesis that pharmacologic increases in HDL cholesterol levels are necessarily beneficial.
Several therapies, including nicotinic acid and fibric acid derivatives, increase HDL cholesterol levels, but linking these increases to clinical risk reduction has proved challenging.3,4 Most strikingly, an inhibitor of cholesteryl ester transfer protein (CETP) was associated with an increase in the number of cardiovascular events, despite a 72% increase in HDL cholesterol levels.5 Finally,
neither rare nor common genetic variants associated with HDL cholesterol levels have been strongly linked to coronary disease.6-9 The static measurement of HDL cholesterol levels has inherent limitations as a metric of the functional effects of HDL in vivo. Reports of marked heterogeneity in the particle composition and biologic properties of HDL have reinforced
a need for validated assays of HDL function.10 HDL-mediated atheroprotection is most likely pleiotropic in nature, but the ability of HDL to promote reverse cholesterol transport by accepting cholesterol from lipid-laden macrophages (termed “cholesterol efflux capacity”) is thought to play a key role.11,12. We hypothesized that cholesterol efflux capacity is a determinant of atherosclerotic burden that is independent of the HDL cholesterol level.This study was designed to explore the pairwise
relationships of efflux capacity with the level of HDL cholesterol and two measures of atherosclerosis— carotid artery intima–media thickness and angiographically confirmed coronary artery disease.