Seeking Novel Targets for Improving In Vivo Macrophage-Specific Reverse Cholesterol Transport: Translating Basic Science into New Therapies for the Prevention and Treatment of Atherosclerosis

Epidemiologic studies have demonstrated that increased high-density lipoprotein cholesterol (HDL-C) is a protective factor against cardiovascular disease. However, the beneficial therapeutic effects of raising HDL-C are proving difficult to confirm in humans. Macrophage-specific reverse cholesterol transport (RCT) is thought to be one of the most important HDL-mediated cardioprotective mechanisms. A new approach was developed to measure in vivo RCT from labeled cholesterol macrophages to liver and feces in mice. Since its original publication, this method has been extensively used to assess the effects of genetic manipulation of pivotal genes involved in HDL metabolism on this major HDL antiatherogenic function in mice. These studies indicate that in vivo macrophage-specific RTC is a strong predictor of atherosclerosis susceptibility compared with steady-state plasma HDL-C levels or other global RCT measurements. This review aims to identify the best molecular targets for improving this HDL antiatherogenic function. Strong evidence supports a positive effect of interventions on macrophage adenosine triphosphate-binding cassette transporter (ABC) A1 and neutral cholesteryl ester hydrolase, apolipoprotein (apo) A-I, macrophage apoE, liver scavenger receptor class B type I and ABCG5/G8 on in vivo macrophage-specific RCT and atherosclerosis susceptibility. However, other genetic modifications have yielded conflicting results. Several preclinical studies tested the effects on macrophage-specific RCT in vivo of promising new HDL-based therapeutic agents, which include cholesteryl ester transfer protein inhibitors, apoA-I-directed therapies, liver X receptor and peroxisome proliferator-activated receptor agonists, intestinal cholesterol absorption inhibitors, fish oil and phenolic acid intake, inflammatory modulation and non-nucleoside reverse transcriptase inhibitors. This review also discusses recent findings on the potential effects of these therapeutic approaches on macrophage RCT in mice and cardiovascular risk in humans.