Cholesterols efflux

Chen, W, Sun, Y, Welch, C, Gorelik, A, Leventhal, AR, Tabas, I, and Tall, AR, 2001. Preferential ATP-binding cassette transporter A1-mediated cholesterol efflux from late endosomes/lysosomes. J Biol Chem 276, 43564-43569. 

Faulkner, LE, Panagotopulos, SE, Johnson, JD, Woollett, LA, Hui, DY, Witting, SR, Maiorano, JN, and Davidson, WS, 2008. An analysis of the role of a retroendocytosis pathway in ATP-binding cassette transporter (ABCA1)—Mediated cholesterol efflux from macrophages. J Lipid Res, M800048-JLR800200. 

Ji, Y, Jian, B, Wang, N, Sun, Y, Moya, ML, Phillips, MC, Rothblat, GH, Swaney, JB, and Tall, AR, 1997. Scavenger receptor BI promotes high density lipoprotein-mediated cellular cholesterol efflux. J Biol Chem 272, 20982-20985. 

Koldamova, RP, Lefterov, IM, Ikonomovic, MD, Skoko, J, Lefterov, PI, Isanski, BA, DeKosky, ST, and Lazo, JS, 2003. 22R-hydroxycholesterol and 9-cw-retinoic acid induce ATP-binding cassette transporter A1 expression and cholesterol efflux in brain cells and decrease amyloid beta secretion. J Biol Chem 278, 13244-13256. 

Venkateswaran, A, Laffitte, BA, Joseph, SB, Mak, PA, Wilpitz, DC, Edwards, PA, and Tontonoz, P, 2000. Control of cellular cholesterol efflux by the nuclear oxysterol receptor LXR alpha. Proc Natl Acad Sci USA91, 12097-12102. 

Besides cholesterol efflux from arterial wall and its role in RCT, additional properties of HDL have been proposed for its protective anti-atherogenic activities. HDL protects vascular function by a number of potential alternative mechanisms, including inhibition of LDL oxidation [8,9], platelet aggregation and coagulation [10], and endothelial monocyte adhesion [11], as well as promotion of endothelial nitric oxide synthase (eNOS) [12], and prostacyclin synthesis [13-15]. The proposed alternate protective mechanisms for HDL are attractive but many of them lack validation under in vivo conditions. 

ApoA-1 is the major structural lipoprotein component of HDL particles. Transgenic over-expression of apoA-1 has been well documented to correlate very strongly with antiatherogenic effects seen in a number of animal models [89-91]. The genetic deficiency of apoA-1 in humans has also been linked to low levels of HDL and premature atherosclerosis [90-92]. It is believed that infusion of apoA-1 enhances the ABCAl-mediated cholesterol efflux from macrophages [93]. During the last decade, significant efforts have been spent to find small... 

Von Eckardstein, A., Nofer, J.R., and Assmann, G., 2001, High density hpoproteins and arteriosclerosis. Role of cholesterol efflux and reverse cholesterol transport, Arterioscler. Thromb. Vase. Biot. 21 13-27. 

Evidence from epidemiological, in vitro, and in vivo studies suggests that brain cholesterol may play a role in AD. The exact nature and magnitude of this role is unknown, but a number of possibilities have emerged, including modulation of APP cleavage pathways and ABP production and clearance, APOF-mediated cholesterol transport, and cholesterol efflux from the brain (556-558). 

Kim, W.S., Rahmant, A.S., Kamili, A., et al. (2006) Role of ABCGl and ABCAl in regulation of neuronal cholesterol efflux to apolipoprotein-E discs and suppression of amyloid-P peptide generation. J. Biol. Chem., 282, 2851-2861. 

The more widely accepted test is the cholesterol efflux assay on cultivated skin fibroblasts. After equilibration with radiolabeled cholesterol, fibroblasts are incubated with albumin in the presence or absence of lipid-free apoA-I. ApoA-I substantially increases cholesterol efflux from normal cells but not from Tangier cells [11, 30]. 

In the presence of lipid-free apoA-I, ABCA1 mediates cholesterol efflux from many cells including skin fibroblasts. This opens the possibility to test the activity of ABCA1 in cultivated skin fibroblasts of patients who are suspected to suffer from Tangier disease. 

Human skin fibroblasts are cultured from skin biopsy samples. The dermis is cut into small pieces (0.5 mm on each side) and placed into a dish in DMEM containing 10% (v/v) FCS and 1% (v/v) antibiotic-antimycotic solution. When these primary cultures are confluent they are split and cells between passage three and six are used for experiments. For the cholesterol efflux assay, cells are grown in 24-well plates to 60-80% confluence and are labeled with [1,2-3H]-cholesterol (1 pCi/well) for 24 h. Cells are then washed with DMEM and incubated for 4 h at 37°C with DMEM containing BSA (0.2%, v/v) and either 0 (negative control) or 5-30 pg/ml apoA-I. The efflux medium is collected and centrifuged to remove cell debris. Cells are solubilized in 0.1 mol/1 NaOH and the radioactivity in the efflux media and in the cell lysates is determined by scintillation counting [11, 30, 75]. 

Fractional cholesterol efflux is calculated as radioactivity in the medium/(radioactivity in the medium + cellular radioactivity). 

ApoA-I-mediated cholesterol efflux from fibroblasts of homozygous Tangier patients is reduced by more than 90% compared to normal control fibroblasts. Heterozygous carriers show significantly reduced cholesterol efflux from fibroblasts compared to unaffected family members. 

Zheng L, Settle M, Brubaker G, Schmitt D, Hazen SL, Smith JD, Kinter M (2005) Localization of Nitration and Chlorination Sites on Apolipoprotein A-I Catalyzed by Myeloperoxidase in Human Atheroma and Associated Oxidative Impairment in ABCA1-Dependent Cholesterol Efflux from Macrophages. J Biol Chem 280 38... 

Shao B, Oda MN, Bergt C, Fu X, Green PS, Biot N, Oram JF, Heinecke JW (2006) Myeloperoxidase Impairs ABCA1-Dependent Cholesterol Efflux through Methionine Oxidation and Site-Specific Tyrosine Chlorination of Apolipoprotein A-I. J Biol Chem 281 9001... 

Khovidhunkit W, Shigenaga JK, Moser AH, Feingold KR, Grunfeld C. Cholesterol efflux by acute-phase high density lipoprotein Role of lecithin Cholesterol acyltransfer-ase. J Lipid Res 2001 42 967-975. 

We conclude that pomegranate by-products contain potent polyphenols, which are able to reduce oxidative stress and attenuate macrophage cholesterol accumulation by inhibiting Ox-LDL uptake and stimulating HDL-mediated cholesterol efflux. 

Subsequently, serum lipid and lipoprotein profiles were obtained 70 mg/dL total cholesterol (normal is 130-200 mg/dL), 1 mg/dL HDL cholesterol (optimal is > 60 mg/dL), 180 mg/dL triglycerides (normal is 100-150 mg/dL), and less than 5 mg/dL apolipoprotein A-I (apoA-I normal is 140 mg/dL). Cholesterol efflux from patient skin fibroblasts to apoA-I, the main protein component of HDL, was reduced to 30% of normal. These results indicated Tangier disease, the definitive diagnosis of which was made when the sequencing of the ATP-binding cassette transporter A1 (ABCA /) gene revealed a nonsense mutation within exon 12. 

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