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Among the known mechanisms of reverse cholesterol transport (RCT), ATP binding cassette transporter G1 (ABCG1)-mediated free cholesterol (FC) transport is the most recent and least studied. Here, we have characterized the efficiencies of different acceptors using baby hamster kidney (BHK) cells transfected with human ABCG1 cDNA, which is inducible upon treatment with mifepristone. When normalized on particle number and particle surface area, the acceptor efficiency for FC efflux was as follows: small unilamellar vesicles (SUV).LDL.reconstituted HDL.HDL 2 5 HDL 3 . Based on phospholipid content, the order was reversed. ABCG1 also mediated phospholipid efflux to human serum and HDL 3 . ABCG1-mediated FC efflux correlated significantly with a number of HDL subfractions and components in serum collected from 25 normolipidemic individuals: apolipoprotein A-II (apoA-II) (r 2 5 0.7), apolipoprotein A-I (apoA-I) (r 2 5 0.5), HDL-C (r 2 5 0.4), HDL-PL (r 2 5 0.4), a-2 HDL (r 2 5 0.4), and preb HDL (r 2 5 0.2). ABCG1 did not enhance influx of FC or cholesteryl oleyl ether (COE) when cells were incubated with radiolabeled HDL 3 . ABCG1 expression did not increase the association of HDL 3 with cells. Compared with control cells, ABCG1 expression significantly increased the FC pool available for efflux and the rate constant for efflux. In conclusion, composition and particle size determine the acceptor efficiency for ABCG1-mediated efflux. ABCG1 increases cell membrane FC pools and changes its rate of desorption into the aqueous phase without enhancing the association with the

Walnut consumption improves cardiovascular disease risk; however, to our knowledge, the contribution of individual walnut components has not been assessed. This study evaluated the acute consumption of whole walnuts (85 g), separated nut skins (5.6 g), de-fatted nutmeat (34 g), and nut oil (51 g) on postprandial lipemia, endothelial function, and oxidative stress. Cholesterol efflux (ex vivo) was assessed in the whole walnut treatment only. A randomized, 4-period, crossover trial was conducted in healthy overweight and obese adults (n = 15) with moderate hypercholesterolemia. There was a treatment × time point interaction for triglycerides (P < 0.01) and increased postprandial concentrations were observed for the oil and whole walnut treatments (P < 0.01). Walnut skins decreased the reactive hyperemia index (RHI) compared with baseline (P = 0.02) such that a difference persisted between the skin and oil treatments (P = 0.01). The Framingham RHI was maintained with the oil treatment compared with the skins and whole nut (P < 0.05). There was a treatment effect for the ferric reducing antioxidant potential (FRAP) (P < 0.01), and mean FRAP was greater with the oil and skin treatments compared with the nutmeat (P < 0.01). Cholesterol efflux increased by 3.3% following whole walnut consumption in J774 cells cultured with postprandial serum compared with fasting baseline (P = 0.02). Walnut oil favorably affected endothelial function and whole walnuts increased cholesterol efflux. These 2 novel mechanisms may explain in part the cardiovascular benefits of walnuts.

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Objective-The goal of this study was to determine the influence of apolipoprotein A-I (apoA-I) tertiary structure domain properties on the antiatherogenic properties of the protein. Two chimeric hybrids with the N-terminal domains swapped (human-mouse apoA-I and mouse-human apoA-I) were expressed in apoA-I-null mice with adeno-associated virus (AAV) and used to study macrophage reverse cholesterol transport (RCT) in vivo. Methods and Results-The different apoA-I variants were expressed in apoA-I-null mice that were injected with [H 3 ]cholesterol-labeled J774 mouse macrophages to measure RCT. Significantly more cholesterol was removed from the macrophages and deposited in the feces via the RCT pathway in mice expressing mouse-H apoA-I compared with all other groups. Analysis of the individual components of the RCT pathway demonstrated that mouse-H apoA-I promoted ATP-binding cassette transporter A1-mediated cholesterol efflux more efficiently than all other variants, as well as increasing the rate of cholesterol uptake into liver cells. Conclusion-The structural domain properties of apoA-I affect the ability of the protein to mediate macrophage RCT.Replacement of the N-terminal helix bundle domain in the human apoA-I with the mouse apoA-I counterpart causes a gain of function with respect to macrophage RCT, suggesting that engineering some destabilization into the N-terminal helix bundle domain or increasing the hydrophobicity of the C-terminal domain of human apoA-I would enhance the antiatherogenic properties of the protein. Key Words: apolipoproteins Ⅲ cardiovascular disease prevention Ⅲ lipoproteins A polipoprotein A-I (apoA-I) is the major protein component of high-density lipoprotein (HDL), and its level in plasma is inversely associated with the risk of cardiovascular disease. [1][2][3] The antiatherogenic properties of apoA-I arise primarily through its role as a mediator of reverse cholesterol transport (RCT), a process by which excess cholesterol is removed from peripheral tissues and transported to the liver for catabolism. 4,5 ApoA-I has been shown to promote macrophage RCT in vivo. 6 Human apoA-I is a 243-residue protein made up of repeating amphipathic ␣-helices, 7 and it contains 2 domains, an N-terminal ␣-helix bundle spanning residues 1 to 189 and a separately folded C-terminal domain that spans the remainder of the molecule. 8 -10 The more hydrophobic C-terminal domain has high lipid affinity compared with the helix bundle domain. 11 Mouse apoA-I, which has 65% amino acid identity with human apoA-I, adopts a similar 2-domain structure. 12 However, compared with the human protein, the N-terminal domain of mouse apoA-I is relatively unstable and has high lipid affinity, whereas the C-terminal domain is more polar and has poor lipid affinity. 12 The differences in tertiary structure domain characteristics between human and mouse apoA-I present the opportunity to understand how the properties of these domains influence the functionality of apoA-I in the RCT pathway. To investigate this que...