Dietary cholesterol consumption and intestinal cholesterol absorption contribute to plasma cholesterol levels, a risk factor for coronary heart disease. The molecular mechanism of sterol uptake from the lumen of the small intestine is poorly defined. We show that Niemann-Pick C1 Like 1(NPC1L1) protein plays a critical role in the absorption of intestinal cholesterol. NPC1L1 expression is enriched in the small intestine and is in the brush border membrane of enterocytes. Although otherwise phenotypically normal, NPC1L1-deficient mice exhibit a substantial reduction in absorbed cholesterol, which is unaffected by dietary supplementation of bile acids. Ezetimibe, a drug that inhibits cholesterol absorption, had no effect in NPC1L1 knockout mice, suggesting that NPC1L1 resides in an ezetimibe-sensitive pathway responsible for intestinal cholesterol absorption.

Niemann-Pick C1 Like 1 (NPC1L1) is a protein localized in jejunal enterocytes that is critical for intestinal cholesterol absorption. The uptake of intestinal phytosterols and cholesterol into absorptive enterocytes in the intestine is not fully defined on a molecular level, and the role of NPC1L1 in maintaining whole body cholesterol homeostasis is not known. NPC1L1 null mice had substantially reduced intestinal uptake of cholesterol and sitosterol, with dramatically reduced plasma phytosterol levels. The NPC1L1 null mice were completely resistant to diet-induced hypercholesterolemia, with plasma lipoprotein and hepatic cholesterol profiles similar to those of wild type mice treated with the cholesterol absorption inhibitor ezetimibe. Cholesterol/cholate feeding resulted in down-regulation of intestinal NPC1L1 mRNA expression in wild type mice. NPC1L1 deficiency resulted in up-regulation of intestinal hydroxymethylglutaryl-CoA synthase mRNA and an increase in intestinal cholesterol synthesis, down-regulation of ABCA1 mRNA, and no change in ABCG5 and ABCG8 mRNA expression. NPC1L1 is required for intestinal uptake of both cholesterol and phytosterols and plays a major role in cholesterol homeostasis. Thus, NPC1L1 may be a useful drug target for the treatment of hypercholesterolemia and sitosterolemia.Cholesterol absorption of both dietary cholesterol and cholesterol cleared from the liver through biliary secretion contributes along with regulation of cholesterol biosynthesis to maintain a tight control of cholesterol homeostasis. The mechanism by which cholesterol moves from the intestinal lumen into the absorptive enterocytes lining the proximal small intestine is poorly understood. The identification of ezetimibe as a potent selective inhibitor of intestinal cholesterol uptake and absorption confirmed this mechanism as a key point of therapeutic intervention for lowering plasma cholesterol levels and indicated that this process is mediated by a specific transporter (1-4). Based on the properties of ezetimibe in animal models of cholesterol uptake, it was predicted that such a transporter would be expressed in jejunal enterocytes and localized to the brush border membrane, which forms the interface between the intestinal lumen and the intracellular compartments responsible for cholesterol esterification and packaging into chylomicrons.Through studies designed to understand the mechanism by which ezetimibe inhibits cholesterol absorption, we recently identified Niemann-Pick C1 Like 1 (NPC1L1) 1 as a critical protein for the intestinal absorption of dietary and biliary cholesterol (5). NPC1L1 was identified through a genomics-bioinformatics approach by sequencing an expression sequence tags library from rat jejunum, annotating the sequences, and searching databases for intestinal proteins with features of a cholesterol transporter (5). NPC1L1 was found to be highly expressed in the jejunum and localized on the surface of the absorptive enterocytes. Mice deficient in NPC1L1 exhibited a significant reduction in chol...

Leptin administration reduces obesity in leptin-deficient ob/ob mice; its effects in obese humans, who have high circulating leptin levels, remain to be determined. This longitudinal study was designed to determine whether diet-induced obesity in mice produces resistance to peripheral and/or central leptin treatment. Obesity was induced in two strains of mice by exposure to a 45% fat diet. Serum leptin increased in proportion to body weight ( P Ͻ 0.00001). Whereas C57BL/6 mice initially responded to peripherally administered leptin with a marked decrease in food intake, leptin resistance developed after 16 d on high fat diet; mice on 10% fat diet retained leptin sensitivity. In AKR mice, peripheral leptin significantly decreased food intake in both 10 and 45% fat-fed mice after 16 d of dietary treatment. However, after 56 d, both groups became resistant to peripherally administered leptin. Central administration of leptin to peripherally leptin-resistant AKR mice on 45% fat diet resulted in a robust response to leptin, with a dose-dependent decrease in food intake ( P Ͻ 0.00001) and body weight ( P Ͻ 0.0001) after a single intracerebroventricular infusion. These data demonstrate that, in a diet-induced obesity model, mice exhibit resistance to peripherally administered leptin, while retaining sensitivity to centrally administered leptin. ( J. Clin. Invest. 1997. 99:385-390.) Key words: leptin resistance • high fat diet • food intake • C57BL/6 • AKR

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

The family of G-protein-coupled receptors can be defined by their similar structural and functional characteristics. Although their primary sequences are quite diverse, these proteins share several common structural features that reflect their common mechanism of action. Mutagenesis and biophysical analysis of several of these receptors indicate that small molecule agonists and antagonists bind to a hydrophobic pocket buried in the transmembrane core of the receptor. In contrast, peptide ligands bind to both the extracellular and transmembrane domains. The mechanisms by which these peptide and small molecule agonists cause receptor activation are being explored by various approaches, but are not yet well defined. A deeper understanding of structural basis for the functional activity of this large family of receptors will have important implications for drug design in a variety of therapeutic areas.