Showing papers on "Sterol published in 2000"
TL;DR: Data suggest that ABCG5 and ABCG8 normally cooperate to limit intestinal absorption and to promote biliary excretion of sterols, and that mutated forms of these transporters predispose to sterol accumulation and atherosclerosis.
Abstract: In healthy individuals, acute changes in cholesterol intake produce modest changes in plasma cholesterol levels. A striking exception occurs in sitosterolemia, an autosomal recessive disorder characterized by increased intestinal absorption and decreased biliary excretion of dietary sterols, hypercholesterolemia, and premature coronary atherosclerosis. We identified seven different mutations in two adjacent, oppositely oriented genes that encode new members of the adenosine triphosphate (ATP)-binding cassette (ABC) transporter family (six mutations in ABCG8 and one in ABCG5) in nine patients with sitosterolemia. The two genes are expressed at highest levels in liver and intestine and, in mice, cholesterol feeding up-regulates expressions of both genes. These data suggest that ABCG5 and ABCG8 normally cooperate to limit intestinal absorption and to promote biliary excretion of sterols, and that mutated forms of these transporters predispose to sterol accumulation and atherosclerosis.
1,575 citations
TL;DR: Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol-lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product.
Abstract: Plant sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane fluidity and permeability, although some plant sterols have a specific function in signal transduction. The phytosterols are products of the isoprenoid pathway. The dedicated pathway to sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3-hydroxymethyl-3-glutaryl coenzyme A (HGMR) is rate-limiting in the synthesis of cholesterol, this does not appear to be the case with the plant sterols. Up-regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the Δ5-sterols. A decline in sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon flow and end-product formation. The major post-squalene biosynthetic pathway is regulated by critical rate-limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end-point sterol esters or stanols. The commonly consumed plant sterols are sitosterol, stigmasterol and campesterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the sterols have a similar structure to cholesterol, and have the capacity to lower plasma cholesterol and LDL cholesterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol-lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C-5) occur in low amounts in the diet and are equally effective in lowering plasma cholesterol and do not cause an increase in plasma levels, unlike the sterols which can be detected in plasma.
© 2000 Society of Chemical Industry
917 citations
TL;DR: The study of orphan members of another family of transcription factors, the nuclear hormone receptors, found to regulate key pathways in bile acid metabolism, thereby controlling cholesterol elimination suggests their potential as targets for new drug therapies.
Abstract: Cholesterol balance is maintained by a series of regulatory pathways that control the acquisition of cholesterol from endogenous and exogenous sources and the elimination of cholesterol, facilitated by its conversion to bile acids. Over the past decade, investigators have discovered that a family of membrane-bound transcription factors, sterol regulatory element-binding proteins (SREBPs), mediate the end-product repression of key enzymes of cholesterol biosynthesis. Recently orphan members of another family of transcription factors, the nuclear hormone receptors, have been found to regulate key pathways in bile acid metabolism, thereby controlling cholesterol elimination. The study of these orphan nuclear receptors suggests their potential as targets for new drug therapies.
729 citations
TL;DR: The experiments indicate that the effect of sterol on the ability of saturated lipids to form a tightly packed and ordered state is the key to their effect on domain formation.
Abstract: Detergent-insoluble membrane domains, enriched in saturated lipids and cholesterol, have been implicated in numerous biological functions. To understand how cholesterol promotes domain formation, the effect of various sterols and sterol derivatives on domain formation in mixtures of the saturated lipid dipalmitoylphosphatidylcholine (DPPC) and a fluorescence quenching analogue of an unsaturated lipid was compared. Quenching measurements demonstrated that several sterols (cholesterol, dihydrocholesterol, epicholesterol, and 25-hydroxycholesterol) promote formation of DPPC-enriched domains. Other sterols and sterol derivatives had little effect on domain formation (cholestane and lanosterol) or, surprisingly, strongly inhibit it (coprostanol, androstenol, cholesterol sulfate, and 4-cholestenone). The effect of sterols on domain formation was closely correlated with their effects on DPPC insolubility. Those sterols that promoted domain formation increased DPPC insolubility, whereas those sterols that inhibit...
489 citations
TL;DR: The positive sterol response of the CETP gene is mediated by a nuclear receptor binding site that is activated by LXRs, and Cyp7a, the rate-limiting enzyme for conversion of cholesterol into bile acids in the liver, is also regulated by LXRalpha, suggesting that this class of nuclear receptor coordinates the regulation of HDL cholesterol ester catabolism and bile acid synthesis in the Liver.
Abstract: The cholesterol ester transfer protein (CETP) facilitates the transfer of HDL cholesterol esters from plasma to the liver. Transgenic mice expressing human CETP, controlled by its natural flanking region, increase expression of this gene in response to hypercholesterolemia. We established a CETP promoter-luciferase reporter assay in differentiated 3T3-L1 adipocytes to map the sterol upregulatory element. Promoter mutagenesis suggested that a direct repeat of a nuclear receptor binding sequence separated by 4 nucleotides (DR4 element, –384 to –399) was responsible for this activity. Using mice carrying normal or mutated promoter sequences, we confirmed the importance of this element for gene induction by dietary sterol. A gel retardation complex containing LXR/RXR was identified using the CETP DR4 element and adipocyte nuclear extracts. Both LXRα/RXRα and LXRβ/RXRα transactivated the CETP promoter via its DR4 element in a sterol-responsive fashion. Thus, the positive sterol response of the CETP gene is mediated by a nuclear receptor binding site that is activated by LXRs. That Cyp7a, the rate-limiting enzyme for conversion of cholesterol into bile acids in the liver, is also regulated by LXRα suggests that this class of nuclear receptor coordinates the regulation of HDL cholesterol ester catabolism and bile acid synthesis in the liver.
356 citations
TL;DR: The properties of cholesterol hydroxylase enzymes, which regulate the expression of genes that participate in both sterol and fat metabolism, and are intermediates in the transfer of sterols from the periphery to the liver are studied.
355 citations
TL;DR: Six novel feruloyl esters of triterpene alcohols and sterols, besides five known trans-ferulates, showed marked inhibitory activity against 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation in mice, and eight free sterols examined showed weaker activity than their corresponding ferulates.
Abstract: Six novel feruloyl esters of triterpene alcohols and sterols, viz., two trans-ferulates, cycloeucalenol and 24-methylenecholesterol trans-ferulates, and four cis-ferulates, cycloartenol, 24-methyelenecycloartanol, 24-methylcholesterol, and sitosterol cis-ferulates, besides five known trans-ferulates, cycloartenol (CAR), 24-methylenecycloartanol (24-MCA), 24-methylcholesterol, sitosterol, and stigmastanol trans-ferulates, and one known cis-ferulate, stigmastanol cis-ferulate, were isolated from the methanol extract of edible rice bran. These and eight other synthetic trans- and cis-ferulates of triterpene alcohols and sterols, along with the corresponding free alcohols, were evaluated with respect to their anti-inflammatory activity against 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation (1 microg per ear) in mice. All of the ferulates showed marked inhibitory activity, and their 50% inhibitory dose (ID(50)) was 0. 1-0.8 mg per ear. On the other hand, whereas two free triterpene alcohols, CAR and 24-MCA, showed strong inhibition (ID(50) 0.2-0.3 mg/ear), eight free sterols examined showed weaker activity (ID(50) 0.7-2.7 mg/ear) than their corresponding ferulates.
289 citations
TL;DR: The fact that smt1 null mutants still produce alkylated sterols and that SMT1 can catalyze both alkylation steps shows that there is considerable overlap in the substrate specificity of enzymes in sterol biosynthesis.
Abstract: The side chain in plant sterols can have either a methyl or ethyl addition at carbon 24 that is absent in cholesterol. The ethyl addition is the product of two sequential methyl additions. Arabidopsis contains three genes— sterol methyltransferase 1 ( SMT1) , SMT2, and SMT3— homologous to yeast ERG6 , which is known to encode an S -adenosylmethionine‐ dependent C-24 SMT that catalyzes a single methyl addition. The SMT1 polypeptide is the most similar of these Arabidopsis homologs to yeast Erg6p. Moreover, expression of Arabidopsis SMT1 in erg6 restores SMT activity to the yeast mutant. The smt1 plants have pleiotropic defects: poor growth and fertility, sensitivity of the root to calcium, and a loss of proper embryo morphogenesis. smt1 has an altered sterol content: it accumulates cholesterol and has less C-24 alkylated sterols content. Escherichia coli extracts, obtained from a strain expressing the Arabidopsis SMT1 protein, can perform both the methyl and ethyl additions to appropriate sterol substrates, although with different kinetics. The fact that smt1 null mutants still produce alkylated sterols and that SMT1 can catalyze both alkylation steps shows that there is considerable overlap in the substrate specificity of enzymes in sterol biosynthesis. The availability of the SMT1 gene and mutant should permit the manipulation of phytosterol composition, which will help elucidate the role of sterols in animal nutrition.
260 citations
TL;DR: STAEST and STEEST margarines reduced significantly and equally serum total and LDL cholesterol concentrations as part of a low-fat diet.
Abstract: Comparison of the effects of plant sterol ester and plant stanol ester-enriched margarines in lowering serum cholesterol concentrations in hypercholesterolaemic subjects on a low-fat diet
251 citations
TL;DR: It is proposed that synthesis of sterol signals in addition to BRs is important in mediating regulated cell growth and organization during embryonic development and indicates a novel role for sterols in the embryogenesis of plants.
Abstract: In flowering plants, the developing embryo consists of growing populations of cells whose fates are determined in a position-dependent manner to form the adult organism. Mutations in the FACKEL (FK) gene affect body organization of the Arabidopsis seedling. We report that FK is required for cell division and expansion and is involved in proper organization of the embryo. We isolated FK by positional cloning. Expression analysis in embryos revealed that FK mRNA becomes localized to meristematic zones. FK encodes a predicted integral membrane protein related to the vertebrate lamin B receptor and sterol reductases across species, including yeast sterol C-14 reductase ERG24. We provide functional evidence that FK encodes a sterol C-14 reductase by complementation of erg24. GC/MS analysis confirmed that fk mutations lead to accumulation of intermediates in the biosynthetic pathway preceding the C-14 reductase step. Although fk represents a sterol biosynthetic mutant, the phenotype was not rescued by feeding with brassinosteroids (BRs), the only plant sterol signaling molecules known so far. We propose that synthesis of sterol signals in addition to BRs is important in mediating regulated cell growth and organization during embryonic development. Our results indicate a novel role for sterols in the embryogenesis of plants.
242 citations
TL;DR: Tangier disease is an autosomal recessive genetic disorder characterized by a severe high-density lipoprotein (HDL) deficiency, sterol deposition in tissue macrophages, and prevalent atherosclerosis, which implies that an inability of newly synthesized apolipoproteins to acquire cellular lipids by the ABCA1 pathway leads to their rapid degradation and an over-accumulation of cholesterol in macrophage.
TL;DR: Esterified soy sterols and beta-sitostanol inhibited cholesterol absorption equally, despite the different structures of the plant sterols.
TL;DR: A clearer picture of the functions of ACAT enzymes in cellular cholesterol metabolism and physiologic processes is now emerging, and these insights may have relevance for the development of ACat inhibitors for treating hypercholesterolemia or atherosclerosis in humans.
TL;DR: A novel Arabidopsis dwarf mutant, fackel-J79, whose adult morphology resembles that of brassinosteroid-deficient mutants but also displays distorted embryos, supernumerary cotyledons, multiple shoot meristems, and stunted roots is reported.
Abstract: Here we report a novel Arabidopsis dwarf mutant, fackel-J79, whose adult morphology resembles that of brassinosteroid-deficient mutants but also displays distorted embryos, supernumerary cotyledons, multiple shoot meristems, and stunted roots. We cloned the FACKEL gene and found that it encodes a protein with sequence similarity to both the human sterol reductase family and yeast C-14 sterol reductase and is preferentially expressed in actively growing cells. Biochemical analysis indicates that the fk-J79 mutation results in deficient C-14 sterol reductase activity, abnormal sterol composition, and reduction of brassinosteroids (BRs). Unlike other BR-deficient mutants, the defect of hypocotyl elongation in fk-J79 cannot be corrected by exogenous BRs. The unique phenotypes and sterol composition in fk-J79 indicate crucial roles of sterol regulation and signaling in cell division and cell expansion in embryonic and post-embryonic development in plants.
TL;DR: These studies confirm the importance of CYP27 in bile acid synthesis and they reveal an unexpected function of the enzyme in triacylglycerol metabolism.
TL;DR: In a growth competition experiment are1are2 cells grow more slowly than wild-type after several rounds of cultivation, suggesting that Are1p and Are2p or steryl esters, the product formed by these two enzymes, are more important in the natural environment than under laboratory conditions.
Abstract: In the yeast Saccharomyces cerevisiae, two acyl-CoA:sterol acyltransferases (ASATs) that catalyze the synthesis of steryl esters have been identified, namely Are2p (Sat1p) and Are1p (Sat2p). Deletion of either ARE1 or ARE2 has no effect on cell viability, and are1are2 double mutants grow in a similar manner to wild-type despite the complete lack of cellular ASAT activity and steryl ester formation [Yang, H., Bard, M., Bruner, D. A., Gleeson, A., Deckelbaum, R. J., Aljinovic, G., Pohl, T. M., Rothstein, R. & Sturley, S. L. (1996) Science 272, 1353-1356; Yu, C., Kennedy, J., Chang, C. C. Y. & Rothblatt, J. A. (1996) J. Biol. Chem. 271, 24157-24163]. Here we show that both Are2p and Are1p reside in the endoplasmic reticulum as demonstrated by measuring ASAT activity in subcellular fractions of are1 and are2 deletion strains. This localization was confirmed by fluorescence microscopy using hybrid proteins of Are2p and Are1p fused to green fluorescent protein (GFP). Lipid analysis of are1 and are2 deletion strains revealed that Are2p and Are1p utilize sterol substrates in vivo with different efficiency; Are2p has a significant preference for ergosterol as a substrate, whereas Are1p esterifies sterol precursors, mainly lanosterol, as well as ergosterol. The specificity towards fatty acids is similar for both isoenzymes. The lack of steryl esters in are1are2 mutant cells is largely compensated by an increased level of free sterols. Nevertheless, terbinafine, an inhibitor of ergosterol biosynthesis, inhibits growth of are1are2 cells more efficiently than growth of wild-type. In a growth competition experiment are1are2 cells grow more slowly than wild-type after several rounds of cultivation, suggesting that Are1p and Are2p or steryl esters, the product formed by these two enzymes, are more important in the natural environment than under laboratory conditions.
TL;DR: It is shown that the Arabidopsis dwarf5 mutants are disrupted in a sterol Delta7 reduction step, indicating that it is required for the proper growth and development of these two organisms.
Abstract: Summary
The brassinosteroid (BR) biosynthetic pathway, and the sterol pathway which is prerequisite to the BR pathway, are rapidly being characterized because of the availability of a large number of characteristic dwarf mutants in Arabidopsis. Here we show that the Arabidopsis dwarf5 mutants are disrupted in a sterol Δ7 reduction step. dwf5 plants display the characteristic dwarf phenotype typical of other BR mutants. This phenotype includes small, round, dark-green leaves, and short stems, pedicels, and petioles. Metabolite tracing with 13C-labeled precursors in dwf5 verified a deficiency in a sterol Δ7 reductase activity. All six independent alleles contain loss-of-function mutations in the sterol Δ7 reductase gene. These include a putative mRNA instability mutation in dwf5-1, 3′ and 5′ splice-site mutations in dwf5-2 and dwf5-6, respectively, premature stop codons in dwf5-3 (R400Z) and dwf5-5 (R409Z), and a mis-sense mutation in dwf5-4 (D257N). The dwf5 plant could be restored to wild type by ectopic overexpression of the wild-type copy of the gene. Both the Arabidopsis dwf5 phenotype and the human Smith–Lemli–Opitz syndrome are caused by loss-of-function mutations in a sterol Δ7 reductase gene, indicating that it is required for the proper growth and development of these two organisms.
TL;DR: Women with elevated ratios of serum squalene, campesterol and sitosterol to cholesterol and low respective lathosterol values have enhanced risk for CAD, suggesting enhanced absorption and reduced synthesis of cholesterol may be related to coronary atherosclerosis.
TL;DR: Recent evidence has indicated that StAR can act as a sterol transfer protein and it is perhaps this characteristic which allows it to mobilize cholesterol to the inner mitochondrial membrane, while it appears that St AR is the acute regulator of steroid biosynthesis via its cholesterol transferring activity, its mechanism of action remains unknown.
TL;DR: It is demonstrated that SREBPs are involved in both sterol regulation and carbohydrate activation of the FAS promoter in primary hepatocytes, and that the previously implicated Sp1 site is largely dispensable for sterolregulation in established cultured cells, whereas a CCAAT-binding factor/nuclear factor Y is critically important.
Journal Article•
TL;DR: It is concluded that dietary phytosterols retard the growth and spread of breast cancer cells.
Abstract: The objective of the present study was to investigate the effect of dietary phytosterols on the growth and metastasis of the human breast cancer MDA-MB-231 cell line xenografted in SCID mice. Two groups of animals were fed AIN-93G diet supplemented with 0.2% cholic acid and 2% sterol (cholesterol or phytosterol mixture) for 15 days before inoculation of the tumor into the right inguinal mammary fat pad. Tumor growth and food consumption were recorded weekly throughout the 8 weeks of the experiment. At the end of the experiment, the animals fed phytosterol had a 40% lower serum cholesterol and 20 and 30 fold higher serum beta-sitosterol and campesterol, respectively as compared to those fed cholesterol. There was no difference between the two groups in body weight and food consumption. However, the tumor size in animals fed phytosterols was 33% smaller (P < 0.03) and had 20% fewer metastases to lymph nodes and lungs than the cholesterol group. At termination, the tumor weight of the animals fed the phytosterol diet was also less (P < 0.07) than that of the cholesterol group. It is concluded that dietary phytosterols retard the growth and spread of breast cancer cells.
TL;DR: The compartmentalization of cholesterol metabolism implies target-specific cholesterol trafficking between the endoplasmic reticulum, plasma membrane, lysosomes, mitochondria and peroxisomes and one hypothesis has been that sterol carrier protein-2 (SCP2, also known as the non-specific lipid transfer protein) acts in cholesterol transport through the cytoplasm.
TL;DR: Dilution of labeled dietary cholesterol by expanded intestinal cholesterol pool could have contributed to subnormal efficiency of cholesterol absorption, or transfer oflabel dietary cholesterol from intestinal oil phase to micellar phase may be competitively inhibited by expanded biliary secretion, resulting in reduced absorption of dietary cholesterol.
TL;DR: It is demonstrated that resistance observed clinically can result from the altered azole affinity of the fungal CYP51 enzyme, and inhibition of activity by fluconazole revealed a 7-fold-greater azole resistance of the recombinant protein than that of the wild type.
Abstract: The cytochrome P450 sterol 14α-demethylase (CYP51) of Candida albicans is involved in an essential step of ergosterol biosynthesis and is the target for azole antifungal compounds. We have undertaken site-directed mutation of C. albicans CYP51 to produce a recombinant mutant protein with the amino acid substitution R467K corresponding to a mutation observed clinically. This alteration perturbed the heme environment causing an altered reduced-carbon monoxide difference spectrum with a maximum at 452 nm and reduced the affinity of the enzyme for fluconazole, as shown by ligand binding studies. The specific activity of CYP51(R467K) for the release of formic acid from 3β-[32-3H]hydroxylanost-7-en-32-ol was 70 pmol/nmol of P450/min for microsomal protein compared to 240 pmol/nmol of P450/min for microsomal fractions expressing wild-type CYP51. Furthermore, inhibition of activity by fluconazole revealed a 7.5-fold-greater azole resistance of the recombinant protein than that of the wild type. This study demonstrates that resistance observed clinically can result from the altered azole affinity of the fungal CYP51 enzyme.
TL;DR: Evidence for regulation of sphingomyelin metabolism by cholesterol is less convincing and dependent on the model system under study, but a notable exception is the robust and specific regulation of both SM and cholesterol synthesis by 25-hydroxycholesterol.
TL;DR: Despite the seeming differences between fungal and plant SMT activities the recent data indicate that a distinct SMT or family of SMTs exist in these organisms which bind and transform sterols according to a similar mechanistic plan.
TL;DR: The use of dietary plant sterol regimens for lowering elevated serum cholesterol values has recently gained much interest, especially after the commercial introduction of margarines containing plant stanols esterified with fatty acids as mentioned in this paper.
Abstract: Intake of plant sterols (4-desmethyl sterols, phytosterols) reduces cholesterol absorption and lowers serum total and LDL cholesterol levels in humans. The use of dietary plant sterol regimens for lowering elevated serum cholesterol values has recently gained much interest, especially after the commercial introduction of margarines containing plant stanols esterified with fatty acids. The solubility of free, crystalline plant sterols and stanols in edible oils and fats is low, limiting their use especially in fat-containing food. By esterifying of, e.g., plant stanols with fatty acids derived from a vegetable oil fatty acid ester of plant stanols with fat-like properties are obtained. These fat-soluble forms of plant stanols provide a technically feasible way of introducing the adequate daily amount of plant sterol into foods for optimal reduction of the cholesterol absorption, without changing the taste of the finished product. The cholesterol-lowering effect of plant stanol esters has been extensively studied. Plant stanol esters effectively restrict the absorption of both dietary and biliary cholesterol causing plant stanol specific reductions in serum total and LDL cholesterol levels of up to 10% and 14%, respectively. Serum HDL cholesterol and triglyceride levels are not affected. The cholesterol-lowering effect of plant stanol esters complements the beneficial effects of a healthy diet and cholesterol medication.
TL;DR: This study shows that when rats are fed mixtures of SM and cholesterol the intestinal uptake of both lipids is decreased and the exposure of the colon to ceramide can be increased.
Abstract: Several studies have shown that there is a strong physical interaction between cholesterol and sphingomyelin (SM). The critical factor is thought to be the high degree of saturation in the very long acyl chains of SM. In this study we examined the effects of SM on cholesterol absorption in the rat and compared them with those of phosphatidylcholine (PC). Cholesterol absorption was studied by use of the dual-isotope plasma ratio method. We also studied the effect of sterols on the fecal excretion of undigested SM and its metabolites after a single oral meal of 3H-dihydrosphingosine-labeled SM. When cholesterol was given dissolved in soybean oil, without addition of SM or other phospholipids, absorption was 68 ± 12% in the rat intestine. As a general feature the absorption was less efficient from the cholesterol/phospholipid dispersions. In dispersions with cholesterol and SM, the lowest cholesterol absorption (9 ± 2%) was seen with a cholesterol:SM molar ratio of 1:1. With dispersions of cholesterol and different PC substrates the absorption of cholesterol was lower with saturated PC (16 ± 8%) than with soybean-PC (22 ± 4%) or dioleoyl PC (23 ± 8%). Uptake of SM in the rat intestine was reduced by sterols. For example, percentage recovery of 3H radioactivity in fecal lipids was 38 ± 8% when SM was given with cholesterol and 16 ± 3% without any sterol. One third of the radioactivity in feces was present as ceramide. Sitostanol had the same effect on uptake of SM as cholesterol. This study shows that when rats are fed mixtures of SM and cholesterol the intestinal uptake of both lipids is decreased. By feeding mixtures of SM and sterols the exposure of the colon to ceramide can be increased.
TL;DR: It is found that 2.1 g plant sterols/d from rice bran oil lowered serum total cholesterol by 5% and LDL cholesterol by 9% in normolipemic humans, whereas triterpene alcohols from sheanut oil did not significantly affect lipoprotein concentrations in all subjects combined.