| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Novel synthesis of cholesterol analogs: condensation of pregnenolone with dihydropyran or dihydrofuran Szendi, Z. and F. Sweet (1991), Steroids 56(9): 458-63. Abstract: Pregnenolone 3-(2'-tetrahydropyranyl) ether (1) was condensed with 3,4-2Hdihydropyran to mainly give (20R)-6'-(3',4'-2'Hdihydropyranyl)-pregn-5-ene-3 beta,20-diol 3-(2'-tetrahydropyranyl) ether (20R-3), according to nuclear magnetic resonance (NMR). Cold, dilute HCl in ethanol removed the tetrahydropyranyl group at C-3 and also opened the dihydropyranyl ring at the C-20 position of 20R-3 to give (20R)-27-norcholest-5-en-22-one-3 beta,20,26-triol (20R-5). Analogous results were obtained by condensing pregnenolone 3-acetate with 3,4-2Hdihydropyran to provide (20R)-6'-(3',4'-2'Hdihydropyranyl)-pregn-5-ene-3 beta,20-diol 3-acetate (20R-4). Acid-catalyzed opening of the dihydropyranyl ring at C-20 in 20R-4 yielded 20R-7, which, on acetylation followed by crystallization, provided (20R)-27-norcholest-5-en-22-one-3 beta,20,26-triol 3,26-diacetate (20R-8), identical to the diacetate made from 20R-5. Varying the reaction sequence beginning with 20(R,S)-4 gave an 84:16 ratio of 20R to 20S in a mixture of 20(R,S)-8, according to NMR analysis. Crystallization of the mixture from methanol provided pure 20R-8. Condensing 2,3-dihydrofuran and 1 for producing (20R)-5'-(2',3'-dihydrofuranyl)-pregn-5-ene-3 beta,20-diol 3-(2'-tetrahydropyranyl) ether (6) gave instead (20R)-26,27-bisnorcholest-5-en-22-one-3 beta,20,25-triol 3-(2'-tetrahydropyranyl) ether (20R-9) by partial hydrolysis during workup. Treating 20R-9 briefly with dilute HCl produced (20R)-26,27-bisnorcholest-5-en-22-one-3 beta,20,25-triol (20R-10).(ABSTRACT TRUNCATED AT 250 WORDS) |
| N-palmitoyl sphingomyelin bilayers: structure and interactions with cholesterol and dipalmitoylphosphatidylcholine Maulik, P. R. and G. G. Shipley (1996), Biochemistry 35(24): 8025-34. Abstract: The structure and thermotropic properties of N-palmitoyl sphingomyelin (C16:0-SM) and its interaction with cholesterol and dipalmitoylphosphatidylcholine (DPPC) have been studied by differential scanning calorimetry (DSC) and X-ray diffraction methods. DSC of hydrated multi-bilayers of C16:0-SM shows reversible chain-melting transitions. On heating, anhydrous C16:0-SM exhibits an endothermic transition at 75 degrees C (delta H = 4.0 kcal/mol). Increasing hydration progressively lowers the transition temperature (TM) and increases the transition enthalpy (delta H), until limiting values (TM = 41 degrees C, delta H = 7.5 kcal/mol) are observed for hydration values > 25 wt % H2O. X-ray diffraction at temperatures below (29 degrees C) TM show a bilayer gel structure (d = 73.5 A, sharp 4.2 A reflection) for C16:0-SM at full hydration; above TM, at 55 degrees C, a bilayer liquid-crystal phase is present (d = 66.6 A, diffuse 4.6 A reflection). Addition of cholesterol to C16:0-SM bilayers results in a progressive decrease in the enthalpy of the transition at 41 degrees C, and no cooperative transition is detected at > 50 mol % cholesterol. X-ray diffraction shows no difference in the bilayer periodicity, position/width of the wide-angle reflections, or electron density profiles at 29 and 55 degrees C when 50 mol % cholesterol is present. Thus, cholesterol inserts into C16:0-SM bilayers progressively removing the chain-melting transition and changing the structural characteristics of the bilayer. DSC and X-ray diffraction data show that DPPC is completely miscible with C16:0-SM bilayers in both the gel and liquid-crystalline phases; however, 30 mol % C16:0-SM removes the pre-transition exhibited by DPPC. |
| NPC1 and NPC2 regulate cellular cholesterol homeostasis through generation of low density lipoprotein cholesterol-derived oxysterols Frolov, A., S. E. Zielinski, et al. (2003), J Biol Chem 278(28): 25517-25. Abstract: Mutations in the Niemann-Pick disease genes cause lysosomal cholesterol accumulation and impaired low density lipoprotein (LDL) cholesterol esterification. These findings have been attributed to a block in cholesterol movement from lysosomes to the site of the sterol regulatory machinery. In this study we show that Niemann-Pick type C1 (NPC1) and Niemann-Pick type C2 (NPC2) mutants have increased cellular cholesterol, yet they are unable to suppress LDL receptor activity and cholesterol biosynthesis. Cholesterol overload in both NPC1 and NPC2 mutants results from the failure of LDL cholesterol tobothsuppresssterolregulatoryelement-bindingprotein-dependent gene expression and promote liver X receptor-mediated responses. However, the severity of the defect in regulation of sterol homeostasis does not correlate with endoplasmic reticulum cholesterol levels, but rather with the degree to which NPC mutant fibroblasts fail to appropriately generate 25-hydroxycholesterol and 27-hydroxycholesterol in response to LDL cholesterol. Moreover, we demonstrate that treatment with oxysterols reduces cholesterol in NPC mutants and is able to correct the NPC1I1061T phenotype, the most prevalent NPC1 disease genotype. Our findings support a role for NPC1 and NPC2 in the regulation of sterol homeostasis through generation of LDL cholesterol-derived oxysterols and have important implications for the treatment of NPC disease. |
| NPC1-containing compartment of human granulosa-lutein cells: a role in the intracellular trafficking of cholesterol supporting steroidogenesis Watari, H., E. J. Blanchette-Mackie, et al. (2000), Exp Cell Res 255(1): 56-66. Abstract: Steroidogenic cells represent unique systems for the exploration of intracellular cholesterol trafficking. We employed cytochemical and biochemical methods to explore the expression, regulation, and function of the Niemann-Pick C1 protein (NPC1) in human granulosa-lutein cells. NPC1 was localized in a subset of lysosome-associated membrane glycoprotein 2 (LAMP-2)-positive vesicles. By analyzing the sensitivity of NPC1 N-linked oligosaccharide chains to glycosidases and neuraminidase, evidence was obtained for movement of nascent NPC1 from the endoplasmic reticulum through the medial and trans compartments of the Golgi apparatus prior to its appearance in cytoplasmic vesicles. NPC1 protein content and the morphology and cellular distribution of NPC1-containing vesicles were not affected by treatment of the granulosa-lutein cells with 8-Br-cAMP, which stimulates cholesterol metabolism into progesterone. In contrast, steroidogenic acute regulatory (StAR) protein levels were increased by 8-Br-cAMP. Incubation of granulosa-lutein cells with low-density lipoprotein (LDL) in the presence of the hydrophobic amine, U18666A, caused accumulation of free cholesterol in granules, identified by filipin staining, that contained LAMP-2 and NPC1. These granules also stained for neutral lipid with Nile red, reflecting accumulation of LDL-derived cholesterol esters. LDL-stimulated progesterone synthesis was completely blocked by U18666A, leaving steroid output at levels similar to those of cells incubated in the absence of LDL. The hydrophobic amine also blocked the LDL augmentation of 8-Br-cAMP-stimulated progesterone synthesis, reducing steroid production to levels seen in cells stimulated with 8-Br-cAMP in the absence of LDL. Steroidogenesis recovered after U18666A was removed from the culture medium. U18666A treatment caused a 2-fold or more increase in NPC1 protein and mRNA levels, suggesting that disruption of NPC1's function activates a compensatory mechanism resulting in increased NPC1 synthesis. We conclude that the NPC1 compartment plays an important role in the trafficking of LDL-derived substrate in steroidogenic cells; that NPC1 expression is up-regulated when NPC1 action is blocked; and that the NPC1 compartment can be functionally separated from other intracellular pathways contributing substrate for steroidogenesis. |
| NSDHL, an enzyme involved in cholesterol biosynthesis, traffics through the Golgi and accumulates on ER membranes and on the surface of lipid droplets Caldas, H. and G. E. Herman (2003), Hum Mol Genet 12(22): 2981-91. Abstract: NSDHL, for NAD(P)H steroid dehydrogenase-like, encodes a sterol dehydrogenase or decarboxylase involved in the sequential removal of two C-4 methyl groups in post-squalene cholesterol biosynthesis. Mutations in this gene are associated with human CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects), an X-linked, male lethal disorder, as well as the mouse mutations bare patches and striated. In the present study, we have investigated the subcellular localization of tagged proteins encoded by wild-type and selected mutant murine Nsdhl alleles using confocal microscopy. In addition to an ER localization commonly found for enzymes of post-squalene cholesterol biosynthesis, we have identified a novel association of NSDHL with lipid droplets, which are endoplasmic reticulum (ER)-derived cytoplasmic structures that contain a neutral lipid core. We further demonstrate that trafficking through the Golgi is necessary for ER membrane localization of the protein and propose a model for the association of NSDHL with lipid droplets. The dual localization of NSDHL within ER membranes and on the surface of lipid droplets may provide another mechanism for regulation of the levels and sites of accumulation of intracellular cholesterol. |
| NTE-122, an acyl-coa:cholesterol acyltransferase inhibitor, prevents the progression of atherogenesis in cholesterol-fed rabbits Azuma, Y., K. Date, et al. (2001), Jpn J Pharmacol 86(1): 120-3. Abstract: The cholesterol-lowering and anti-atherosclerotic effects of NTE-122 (trans-1,4-bis1-cyclohexyl-3-(4-dimethylaminophenyl)ureidomethylcycloh exane), an acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, were evaluated in 1% cholesterol diet-fed rabbits. NTE-122 (1, 3 and 10 mg/kg per day) lowered the total cholesterol levels in both plasma and liver dose-dependently (by 99% and 94% at 10 mg/kg per day, respectively). In the aortic wall of the rabbits given NTE-122, the atherosclerotic lesion area in both aortic arch and thoracic aorta were dose-dependently reduced (by 100% at 10 mg/kg per day), and the total cholesterol content in aortic arch was also lowered significantly at more than 3 mg/kg per day. These results suggest that NTE-122 is capable of exhibiting anti-atherosclerotic effects. |
| N-terminal protein acylation confers localization to cholesterol, sphingolipid-enriched membranes but not to lipid rafts/caveolae McCabe, J. B. and L. G. Berthiaume (2001), Mol Biol Cell 12(11): 3601-17. Abstract: When variably fatty acylated N-terminal amino acid sequences were appended to a green fluorescent reporter protein (GFP), chimeric GFPs were localized to different membranes in a fatty acylation-dependent manner. To explore the mechanism of localization, the properties of acceptor membranes and their interaction with acylated chimeric GFPs were analyzed in COS-7 cells. Myristoylated GFPs containing a palmitoylated or polybasic region colocalized with cholesterol and ganglioside GM(1), but not with caveolin, at the plasma membrane and endosomes. A dipalmitoylated GFP chimera colocalized with cholesterol and GM(1) at the plasma membrane and with caveolin in the Golgi region. Acylated GFP chimeras did not cofractionate with low-density caveolin-rich lipid rafts prepared with Triton X-100 or detergent-free methods. All GFP chimeras, but not full-length p62(c-yes) and caveolin, were readily solubilized from membranes with various detergents. These data suggest that, although N-terminal acylation can bring GFP to cholesterol and sphingolipid-enriched membranes, protein-protein interactions are required to localize a given protein to detergent-resistant membranes or caveolin-rich membranes. In addition to restricting acceptor membrane localization, N-terminal fatty acylation could represent an efficient means to enrich the concentration of signaling proteins in the vicinity of detergent-resistant membranes and facilitate protein-protein interactions mediating transfer to a detergent-resistant lipid raft core. |
| Nuanced view on cholesterol. New guidelines on prevention of cardiovascular diseases Olsson, A. G. (1993), Lakartidningen 90(28-29): 2525-7. |
| Nuclear cholesterol content and nucleoside triphosphatase activity are altered in the JCR:LA-cp corpulent rat Czubryt, M. P., J. C. Russell, et al. (1996), J Cell Biochem 63(3): 349-57. Abstract: A nuclear pore complex-associated nucleoside triphosphatase (NTPase) activity is believed to provide energy for nuclear export of poly(A)+ mRNA. This study was initiated to determine if nuclear membrane lipid composition is altered during chronic hyperlipidemia, and what effect this has on NTPase activity. The JCR:LA-cp corpulent rat model is characterized by severe hypertriglyceridemia and moderate hypercholesterolemia, and thus represents an ideal animal model in which to study nuclear cholesterol and NTPase activity. NTPase activity was markedly increased in purified hepatic nuclei from corpulent female JCR:LA-cp rats in comparison to lean control rats as a function of assay time, GTP, ATP, and Mg2+. Nuclear membrane cholesterol and phospholipid content were significantly elevated in the corpulent animals. Nuclei of corpulent animals were less resistant to salt-induced lysis than nuclei of lean animals, suggesting a change in relative membrane integrity. Together, these results indicate that altered lipid metabolism in a genetic corpulent animal model can lead to changes in nuclear membrane lipid composition, which in turn may alter nuclear membrane NTPase activity and integrity. |
| Nuclear magnetic resonance characterization of 6 alpha-chloro-5 beta-cholestane-3 beta,5-diol formed from the reaction of hypochlorous acid with cholesterol Carr, A. C., C. C. Winterbourn, et al. (1997), Lipids 32(4): 363-7. Abstract: Hypochlorous acid generated by neutrophil myeloperoxidase has been shown to convert cholesterol into three different chlorohydrin isomers which previously had not been fully characterized. We have reacted hypochlorous acid with cholesterol/1,2-dipalmitoyl phosphatidylcholine liposomes to give these three major products and established that they are 6 beta-chloro-5 alpha-cholestane-3 beta,5-diol (chlorohydrin 1), 5 alpha-chloro-6 beta-cholestane-3,6-diol (chlorohydrin 2) and 6 alpha-chloro-5 beta-cholestane-3 beta,5-diol (chlorohydrin 3). These products were separated by thin-layer chromatography and fully characterized by 1H, 13C, attached proton test, doublequantum correlation spectroscopy, total correlation spectroscopy, heteronuclear multiple bond correlation and heteronuclear multiple quantum coherence nuclear magnetic resonance spectroscopy. |
| Nuclear magnetic resonance spectroscopy to determine the micellar cholesterol in human bile Ellul, J. P., G. M. Murphy, et al. (1992), FEBS Lett 300(1): 30-2. Abstract: The cholesterol of gallstones comes from the vesicular rather than the micellar phase of bile. Progress in this field has been limited because conventional analytical methods disturb the distribution of cholesterol between the two phases. The resonance of the cholesterol C6 proton occurs at a chemical shift of 5.4 ppm, to be shown by 2D NMR to be specific for biliary cholesterol, and arises only from the micellar mode. Thus integration of the C6 proton resonance peak area provides a direct non-invasive determination of the cholesterol distribution in human bile. |
| Nuclear membrane cholesterol can modulate nuclear nucleoside triphosphatase activity Ramjiawan, B., M. P. Czubryt, et al. (1996), J Cell Biochem 63(4): 442-52. Abstract: Previous work has suggested that changes in nuclear membrane cholesterol may induce a stimulation in nuclear nucleoside triphosphatase (NTPase) activity. The purpose of the present study was to directly investigate if nuclear membrane cholesterol can stimulate nuclear NTPase activity. The cholesterol content of nuclei was altered with a liposomal methodology. The cholesterol content of nuclei isolated from hepatic tissue was relatively low in comparison to that typically exhibited by other membrane fractions. Because of this, it was difficult to further deplete the nuclear membrane of cholesterol, but we could successfully increase the cholesterol content after exposure to cholesterol-enriched liposomes. Nuclear NTPase activity was potently stimulated (approximately 150-200% of control) by an increase in the nuclear membrane cholesterol content. The Vmax of the NTPase activity in the presence of ATP or GTP was significantly increased after cholesterol enrichment without altering the affinity of the enzyme for these moieties. Mg2+ dependency of NTPase activity was also altered by cholesterol incorporation into the nuclear membrane. Cholesterol enrichment of the nuclear membrane also left the nuclei more susceptible to damage by salt-induced lysis than control nuclei. Our results clearly demonstrate that the cholesterol content of the nuclear membrane will have significant, direct effects on nuclear integrity and NTPase activity. |
| Nuclear membrane sphingomyelin-cholesterol changes in rat liver after hepatectomy Albi, E., I. Peloso, et al. (1999), Biochem Biophys Res Commun 262(3): 692-5. Abstract: Sphingomyelin and cholesterol play an important role in stabilising the plasma membranes architecture and in many physiological process such as cell growth and differentiation. Degradation of sphingomyelin by exogenous sphingomyelinase induces a decrease of cholesterol due either to an increase of esterification or to a reduced biosynthesis. Variations of sphingomyelin due to the presence of a neutral-sphingomyelinase and of sphingomyelin-synthase have been recently shown in rat liver nuclear membranes. The aim of this research is to study the relation between sphingomyelin and cholesterol in the nuclear membranes following sphingomyelinase activation and during cell proliferation. The nuclear membranes, isolated from liver nuclei, were analysed for their content in protein, nucleic acids, and lipids (sphingomyelin and cholesterol) before and after sphingomyelinase activation and during hepatic regeneration. The activities of nuclear membrane SM-syntase and sphingomyelinase were also determined. The results confirmed that also in the nuclear membranes sphingomyelinase, especially exogenous, causes a strong decrease in cholesterol. The increase observed of sphingomyelin during the first 18 h after hepatectomy followed by a decrease at 24 h, due to the different activity of the enzymes, is accompanied by similar behaviour of cholesterol. This confirms the effect of neutral-sphingomyelinase on cholesterol, due to an increase of esterification process. Changes in cholesterol content modify the nuclear membranes fluidity and, as consequence, mRNA transport as previously shown. It can therefore be concluded that the neutral sphingomyelinase, present in the nuclei, may, across this mechanism, regulate the cell function. |
| Nuclear orphan receptors control cholesterol catabolism Russell, D. W. (1999), Cell 97(5): 539-42. |
| Nuclear receptor regulation of cholesterol and bile acid metabolism Repa, J. J. and D. J. Mangelsdorf (1999), Curr Opin Biotechnol 10(6): 557-63. Abstract: The metabolism of cholesterol and bile acids is transcriptionally regulated by classic feedforward and feedback signaling pathways. The mechanisms underlying this regulation have recently been elucidated by the characterization of three classes of orphan nuclear receptors. Furthermore, the study of these receptors suggests their potential as targets for new drug therapies. |
| Nuclear receptor regulation of cholesterol metabolism Nohara, A. and H. Mabuchi (2001), Nippon Rinsho 59 Suppl 2: 468-71. |
| Nuclear receptor signaling in the control of cholesterol homeostasis: have the orphans found a home? Ory, D. S. (2004), Circ Res 95(7): 660-70. Abstract: Cholesterol is essential for all mammalian cells. Cellular cholesterol requirements are met through de novo synthesis and uptake of plasma lipoproteins, homeostatic responses that are transcriptionally regulated by the sterol regulatory element-binding proteins (SREBPs). To prevent cytotoxicity attributable to accumulation of excess cholesterol, liver X receptors (LXRs) and the farnesoid X receptor (FXR), together with other members of the nuclear receptor superfamily, promote the storage, transport, and catabolism of sterols and their metabolites. Members of this metabolic nuclear receptor family include receptors for oxysterols (LXRs), bile acids (CAR, FXR, and PXR), and fatty acids (PPARs). Through coordinated regulation of transcriptional programs, these nuclear receptors regulate key aspects of cellular and whole-body sterol homeostasis, including cholesterol absorption, lipoprotein synthesis and remodeling, lipoprotein uptake by peripheral tissues, reverse cholesterol transport, and bile acid synthesis and absorption. This review focuses on the nuclear receptors that are central to the lipid metabolic signaling cascades, communication between lipid metabolites and their receptors, and the role of nuclear receptors in orchestrating the complex transcriptional programs that govern cholesterol and bile acid metabolism. |
| Nuclear receptors as potential targets for modulating reverse cholesterol transport Pelton, P. D., M. Patel, et al. (2005), Curr Top Med Chem 5(3): 265-82. Abstract: This review describes the role of nuclear receptors in the regulation of genes involved in cholesterol transport and synthetic modulators of these receptors. Increasing the efflux of cholesterol from peripheral cells, such as lipid-laden macrophages, through a process called reverse cholesterol transport (RCT) requires HDL. Increasing the circulating levels of HDL, as well as the efficiency of the RCT process, could result in a reduction in the development of coronary artery disease and atherosclerosis. Nuclear receptors of the RXR heterodimer family have recently been shown to regulate key genes involved in HDL metabolism and reverse cholesterol transport. These include the PPARs (peroxisome proliferator activated receptors), the LXR (liver X receptor) and the farnesoid X receptor (FXR). The synthesis of specific and potent ligands for these receptors has aided in ascertaining the physiological role of these receptors as lipid sensors and the potential therapeutic utility of modulators of these receptors in dyslipidemias and cardiovascular disease. |
| Nuclear receptors as targets for drug development: regulation of cholesterol and bile acid metabolism by nuclear receptors Makishima, M. (2005), J Pharmacol Sci 97(2): 177-83. Abstract: Nuclear receptors are ligand-dependent transcription factors that recently have been shown to play important roles in the metabolism of cholesterol and bile acids. Cholesterol homeostasis is maintained by de novo synthesis, absorption from diet, catabolism to bile acids and other steroids, and excretion into bile. Dysregulation of this mechanism leads to atherosclerosis and its life-threatening coronary and cerebrovascular sequelae. Conversion of cholesterol to bile acids in the liver is positively regulated by liver X receptor (LXR) alpha, a nuclear receptor for oxysterols. LXRalpha and LXRbeta, a second oxysterol receptor, regulate intestinal absorption and biliary excretion of cholesterol by inducing target gene expression. LXRs stimulate reverse cholesterol transport from peripheral tissues and exhibit antiatherogenic activity. Farnesoid X receptor (FXR), a bile acid receptor, represses bile acid synthesis and import in hepatocytes, stimulates bile acid export from cells, and protects hepatocytes from bile acid toxicity. Pregnane X receptor (PXR) and vitamin D receptor (VDR) respond to secondary bile acids and induce their catabolism. Thus, nuclear receptors play important roles in regulation of cholesterol and bile acid metabolism. |
| Nuclear receptors in cholesterol catabolism: molecular biology of the enterohepatic circulation of bile salts and its role in cholesterol homeostasis Redinger, R. N. (2003), J Lab Clin Med 142(1): 7-20. Abstract: Recent advances in bile-salt research have revolutionized thought pertaining to the regulation of cholesterol homeostasis by highlighting the molecular control of reverse cholesterol transport and cholesterol catabolism to bile acids. The latter involves both feed-forward and feedback regulation of bile-acid synthesis within the territory of the enterohepatic circulation of bile salts. Cholesterol is vital to advanced life forms because it has become essential for membrane structure and function and is a precursor to the synthesis of steroid hormones, vitamins A and D, and bile acids. The liver plays a major part in cholesterol metabolism in that it is capable of de novo cholesterol synthesis and uptake from high-density lipoprotein reverse cholesterol transport, low-density lipoprotein, and chylomicron remnant receptors, so that 50% of total body cholesterol is available to be catabolized to bile acids. Cholesterol catabolism to bile acids allows the eukaryote cell to maintain cholesterol homeostasis because it cannot degrade cholesterol's cyclopentanoperhydrophenanthrene ring. Bile-salt catabolic end products of cholesterol must also be regulated to maintain normal bile-acid pool size, secretion, and elimination to avoid bile-salt hepatocyte toxicity. Nuclear hormone receptors, after sensing inappropriate oxysterol and bile-salt levels, are transcription factors that initiate the genetic transactivation to modulate reverse cholesterol transport, cholesterol catabolism, and bile-acid metabolism contiguous to and within the enterohepatic circulation of bile salts so as to regulate cholesterol and bile-salt homeostasis, respectively. This new knowledge should spawn pharmacologic discoveries that modulate nuclear receptors for the treatment of disorders of cholesterol homeostasis. |