The identification of intestinal scavenger receptor class B, type I (SR-BI) by expression cloning and its role in cholesterol absorption

Altmann, Scott; Davis, Harry R.; Yao, Xiangdong; Laverty, Maureen; Compton, Douglas S; Zhu, Lian; Crona, James H.; Caplen, Mary Ann; Hoos, Lizbeth; Tetzloff, Glen; Priestley, Tony; Burnett, Duane A.; Strader, Catherine D.; Graziano, Michael P.

doi:10.1016/s1388-1981(01)00190-1

Cited by 144 publications

(115 citation statements)

References 40 publications

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“…However, these studies did not include a quantitative comparison of binding between recombinant proteins and BBMs, nor did they report deletion of the putative target in genetically modified mice. SR-BI (scavenger receptor type B1) was also identified as a potential target by using an expression cloning strategy employing ezetimibe binding to candidate proteins; this hypothesis was readily dismissed when neither cholesterol absorption nor ezetimibe activity were affected in SR-BI-deficient mice (16). Conversely, this article demonstrates that ezetimibe binds to native intestinal membranes and cells expressing recombinant NPC1L1 with comparable affinity and does not bind to membranes from NPC1L1-deficient mice, indicating a specific binding interaction between NPC1L1 and ezetimibe.…”

Section: Resultsmentioning

confidence: 99%

“…12). This phenomenon is believed to involve a variety of mediators, including the ATP-binding cassette (ABC) transporters ABCA1, ABCG5, and G8, and the scavenger receptor B1 (SRB1), but knockouts have ruled out each of these proteins as promoting net sterol uptake from the intestine (13)(14)(15)(16). Other multidrug-resistance transporters in the ABC and RND (resistance-nodulationdivision) superfamilies have also been proposed to be gatekeepers of intracellular sterol and lipid homeostasis in mammals, but their specific molecular functions remain uncertain (for a review, see ref.…”

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confidence: 99%

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The target of ezetimibe is Niemann-Pick C1-Like 1 (NPC1L1)

García‐Calvo

Lisnock

Bull

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

682

451

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Ezetimibe is a potent inhibitor of cholesterol absorption that has been approved for the treatment of hypercholesterolemia, but its molecular target has been elusive. Using a genetic approach, we recently identified Niemann-Pick C1-Like 1 (NPC1L1) as a critical mediator of cholesterol absorption and an essential component of the ezetimibe-sensitive pathway. To determine whether NPC1L1 is the direct molecular target of ezetimibe, we have developed a binding assay and shown that labeled ezetimibe glucuronide binds specifically to a single site in brush border membranes and to human embryonic kidney 293 cells expressing NPC1L1. Moreover, the binding affinities of ezetimibe and several key analogs to recombinant NPC1L1 are virtually identical to those observed for native enterocyte membranes. KD values of ezetimibe glucuronide for mouse, rat, rhesus monkey, and human NPC1L1 are 12,000, 540, 40, and 220 nM, respectively. Last, ezetimibe no longer binds to membranes from NPC1L1 knockout mice. These results unequivocally establish NPC1L1 as the direct target of ezetimibe and should facilitate efforts to identify the molecular mechanism of cholesterol transport.cholesterol ͉ intestinal brush border membranes

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

The target of ezetimibe is Niemann-Pick C1-Like 1 (NPC1L1)

García‐Calvo

Lisnock

Bull

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

682

451

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“…Decreased cholesterol uptake has been shown in brush-border membrane vesicles prepared from the proximal (but not distal) intestine of SR-BI-KO mice (184) and in brush-border membrane vesicles and Caco-2 cells preincubated with antibodies to SR-BI (71). However, targeted disruption of SR-BI in mice has little effect on in vivo intestinal cholesterol absorption (3,120,192), which suggests that SR-BI might not be essential for absorption of cholesterol from the intestine.…”

Section: Cholesterolmentioning

confidence: 99%

Intestinal lipid absorption

Iqbal¹,

Hussain²

2009

American Journal of Physiology-Endocrinology and Metabolism

628

461

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Our knowledge of the uptake and transport of dietary fat and fat-soluble vitamins has advanced considerably. Researchers have identified several new mechanisms by which lipids are taken up by enterocytes and packaged as chylomicrons for export into the lymphatic system or clarified the actions of mechanisms previously known to participate in these processes. Fatty acids are taken up by enterocytes involving protein-mediated as well as proteinindependent processes. Net cholesterol uptake depends on the competing activities of NPC1L1, ABCG5, and ABCG8 present in the apical membrane. We have considerably more detailed information about the uptake of products of lipid hydrolysis, the active transport systems by which they reach the endoplasmic reticulum, the mechanisms by which they are resynthesized into neutral lipids and utilized within the endoplasmic reticulum to form lipoproteins, and the mechanisms by which lipoproteins are secreted from the basolateral side of the enterocyte. apoB and MTP are known to be central to the efficient assembly and secretion of lipoproteins. In recent studies, investigators found that cholesterol, phospholipids, and vitamin E can also be secreted from enterocytes as components of high-density apoB-free/apoAI-containing lipoproteins. Several of these advances will probably be investigated further for their potential as targets for the development of drugs that can suppress cholesterol absorption, thereby reducing the risk of hypercholesterolemia and cardiovascular disease.intestine; dietary fat; triacylglycerol; cholesterol; phospholipids; fat-soluble vitamins; microsomal triglyceride transfer protein DIETARY FATS CONSIST OF A WIDE ARRAY of polar and nonpolar lipids (32, 33). Triacylglycerol (TAG) is the dominant fat in the diet, contributing 90 -95% of the total energy derived from dietary fat. Dietary fats also include phospholipids (PLs), sterols (e.g., cholesterol), and many other lipids (e.g., fatsoluble vitamins). The predominant PL in the intestinal lumen is phosphatidylcholine (PC), which is derived mostly from bile (10 -20 g/day in humans) but also from the diet (ϳ1-2 g/day). The predominant dietary sterols are cholesterol (mostly of animal origin) and ␤-sitosterol (the major plant sterol). Although ␤-sitosterol accounts for 25% of dietary sterols, it is not absorbed by humans under physiological conditions.Researchers have been investigating the various steps involved in lipid digestion, absorption, and metabolism to identify factors that could serve as targets for the development of drugs capable of reducing the risk of lipid-associated disorders, including dyslipidemias and cardiovascular disease. In so doing, they have explored key aspects of lipid digestion hydrolysis, emulsification, and micelle formation. They have also explored key issues of absorption, e.g., the uptake of the products of lipid hydrolysis by enterocytes (the epithelial cells lining the walls of the intestinal lumen) and their transport to intracellular compartments, where fatty acids and sterols are...

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“…Biochemical and molecular biological techniques were used for many years in an attempt to identify the intestinal transporter ezetimibe inhibited. These studies identified several candidate proteins, like scavenger receptor class B, type (SR-BI), but when these proteins were deleted in knockout mice they were not found to be involved, because cholesterol absorption was normal and ezetimibe was still active as a cholesterol absorption inhibitor 11) . Several years ago, a genomic/bioinformatics approach was used to identify genes involved in intestinal cholesterol uptake 12) .…”

Section: Discovery Of the Molecular Target Of Zetiamentioning

confidence: 99%

Zetia: Inhibition of Niemann-Pick C1 Like 1 (NPC1L1) to Reduce Intestinal Cholesterol Absorption and Treat Hyperlipidemia

Davis¹,

Veltri²

2007

JAT

Self Cite

140

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Zetia (ezetimibe) is a selective cholesterol absorption inhibitor, which potently inhibits the absorption of biliary and dietary cholesterol from the small intestine without affecting the absorption of fat-soluble vitamins, triglycerides or bile acids. Ezetimibe reduces the small intestinal enterocyte uptake and absorption of cholesterol by binding to Niemann-Pick C1 Like 1 (NPC1L1), which keeps cholesterol in the intestinal lumen for excretion. Ezetimibe undergoes glucuronidation to a single metabolite and localizes at the intestinal wall, where it binds with higher affinity for NPC1L1 than ezetimibe to prevent cholesterol absorption. Enterohepatic recirculation of ezetimibe and/or its glucuronide ensures repeated delivery to the intestinal site of action and limited peripheral exposure. Ezetimibe has no effect on the activity of major drug metabolizing enzymes (CYP450), which reduces any potential drug-drug interactions with other medications. Ezetimibe (10 mg/day) was found to inhibit cholesterol absorption by an average of 54% in hypercholesterolemic individuals and by 58% in vegetarians. Ezetimibe alone reduced plasma total and LDL-Cholesterol (18%) levels in patients with primary hypercholesterolemia. When ezetimibe was added to on-going statin treatment, an additional 25% reduction in LDL-C was found in patients with primary hypercholesterolemia and an additional 21% reduction in LDL-C in homozygous familial hypercholesterolemia. Ezetimibe in combination with statins produces additional reductions in plasma cholesterol levels and allows for more patients to achieve their LDL-C goals. . Zetia was identified through the characterization of the active biliary metabolites of its predecessor, SCH 48461, and extensive structure-activity relationship information obtained from a seven day cholesterol-fed hamster model 2) . Ezetimibe dose-dependently inhibited diet-induced hypercholesterolemia in hamsters with an ED50 of 0.04 mg/kg. In an acute model of intestinal absorption using radiolabeled cholesterol in rats, ezetimibe inhibited the appearance of radiolabeled cholesterol in plasma with an ED50 of 0.0015 mg/kg ninety minutes after dosing, indicating that the onset of activity was rapid 3) . Ezetimibe has proven to be most potent pre-clinically in cholesterol-fed rhesus monkeys with an ED50 0.0005 mg/kg/day. A single dose of the ezetimibe analog, SCH 48461, administered to cynomolgus monkeys fed a single cholesterol-containing meal caused a significant reduction of cholesterol in chylomicrons and chylomicron remnants during the postprandial phase without affecting triglyceride content 4) . Ezetimibe selectively inhibits the transport of cholesterol across the intestinal wall. Ezetimibe does not affect intestinal cholesteryl ester hydrolysis and the absorption of fatty acids thus generated. The free cholesterol from this hydrolysis, however, was not absorbed J Atheroscler

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The identification of intestinal scavenger receptor class B, type I (SR-BI) by expression cloning and its role in cholesterol absorption

Cited by 144 publications

References 40 publications

The target of ezetimibe is Niemann-Pick C1-Like 1 (NPC1L1)

The target of ezetimibe is Niemann-Pick C1-Like 1 (NPC1L1)

Intestinal lipid absorption

Zetia: Inhibition of Niemann-Pick C1 Like 1 (NPC1L1) to Reduce Intestinal Cholesterol Absorption and Treat Hyperlipidemia

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