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Showing papers on "Sterol published in 1997"


Journal ArticleDOI
TL;DR: It is concluded that S REBP-2 can replace SREBP-1 in regulating cholesterol synthesis in livers of mice and that the higher potency of SRE BP-2 relative to SREbp-1c leads to excessive hepatic cholesterol synthesisIn these animals.
Abstract: The synthesis of cholesterol and its uptake from plasma LDL are regulated by two membrane-bound transcription factors, designated sterol regulatory element binding protein-1 and -2 (SREBP-1 and SREBP-2). Here, we used the technique of homologous recombination to generate mice with disruptions in the gene encoding the two isoforms of SREBP-1, termed SREBP-1a and SREBP-1c. Heterozygous gene-disrupted mice were phenotypically normal, but 50- 85% of the homozygous (-/-) mice died in utero at embryonic day 11. The surviving -/- mice appeared normal at birth and throughout life. Their livers expressed no functional SREBP-1. There was a 1.5-fold upregulation of SREBP-2 at the level of mRNA and a two- to threefold increase in the amount of mature SREBP-2 in liver nuclei. Previous studies showed that SREBP-2 is much more potent than SREBP-1c, the predominant hepatic isoform of SREBP-1, in activating transcription of genes encoding enzymes of cholesterol synthesis. Consistent with this observation, the SREBP-1 -/- animals manifested elevated levels of mRNAs for 3-hydroxy-3-methylglutaryl coenzyme A synthase and reductase, farnesyl diphosphate synthase, and squalene synthase. Cholesterol synthesis, as measured by the incorporation of [3H]water, was elevated threefold in livers of the -/- mice, and hepatic cholesterol content was increased by 50%. Fatty acid synthesis was decreased in livers of the -/- mice. The amount of white adipose tissue was not significantly decreased, and the levels of mRNAs for lipogenic enzymes, adipocyte lipid binding protein, lipoprotein lipase, and leptin were normal in the -/- mice. We conclude from these studies that SREBP-2 can replace SREBP-1 in regulating cholesterol synthesis in livers of mice and that the higher potency of SREBP-2 relative to SREBP-1c leads to excessive hepatic cholesterol synthesis in these animals.

447 citations


Journal ArticleDOI
TL;DR: The results support the contention that the sterol 27-hydroxylase-mediated elimination of cholesterol is more important in macrophages than in endothelial cells.

233 citations


Journal ArticleDOI
TL;DR: Data indicate that voriconazole is more effective than fluconazole in blocking candidal sterol biosynthesis, consistent with the different antifungal potencies of these compounds.
Abstract: Voriconazole (UK-109,496) is a novel triazole derivative with potent broad-spectrum activity against various fungi, including some that are inherently resistant to fluconazole, such as Candida krusei. In this study we compared the effect of subinhibitory concentrations of voriconazole and fluconazole on sterol biosynthesis of fluconazole-resistant and -susceptible Candida albicans strains, as well as C. krusei, in an effort to delineate the precise mode of action of voriconazole. Voriconazole MICs ranged from 0.003 to 4 microg/ml, while fluconazole MICs ranged from 0.25 to >64 microg/ml. To investigate the effects of voriconazole and fluconazole on candidal sterols, yeast cells were grown in the absence and presence of antifungals. In untreated C. albicans controls, ergosterol was the major sterol (accounting for 53.6% +/- 2.2% to 71.7% +/- 7.8% of the total) in C. albicans and C. krusei strains. There was no significant difference between the sterol compositions of the fluconazole-susceptible and -resistant C. albicans isolates. Voriconazole treatment led to a decrease in the total sterol content of both C. albicans strains tested. In contrast, exposure to fluconazole did not result in a significant reduction in the total sterol content of the three candidal strains tested (P > 0.5). Gas-liquid chromatographic analysis revealed profound changes in the sterol profiles of both C. albicans strains and of C. krusei in response to voriconazole. This antifungal agent exerted a similar effect on the sterol compositions of both fluconazole-susceptible and -resistant C. albicans strains. Interestingly, a complete inhibition of ergosterol synthesis and accumulation of its biosynthetic precursors were observed in both strains treated with voriconazole. In contrast, fluconazole partially inhibited ergosterol synthesis. Analysis of sterols obtained from a fluconazole-resistant C. albicans strain grown in the presence of different concentrations of voriconazole showed that this agent inhibits ergosterol synthesis in a dose-dependent manner. In C. krusei, voriconazole significantly inhibited ergosterol synthesis (over 75% inhibition). C. krusei cells treated with voriconazole accumulated the following biosynthetic intermediates: squalene, 4,14-dimethylzymosterol, and 24-methylenedihydrolanosterol. Accumulation of these methylated sterols is consistent with the premise that this agent functions by inhibiting fungal P-450-dependent 14alpha-demethylase. As expected, treating C. krusei with fluconazole minimally inhibited ergosterol synthesis. Importantly, our data indicate that voriconazole is more effective than fluconazole in blocking candidal sterol biosynthesis, consistent with the different antifungal potencies of these compounds.

210 citations


Journal ArticleDOI
TL;DR: Results indicate the potential of lipid biosynthesis inhibitors as useful therapeutic agents in the treatment of leishmaniasis and Chagas' disease.
Abstract: Inhibitors of sterol and phospholipid biosynthesis in kinetoplastid parasites such as Trypanosoma cruzi, the causative agent of Chagas' disease, and different species of Leishmania have potent and selective activity as chemotherapeutic agents in vitro and in vivo. Recent work with the sterol C14α-demethylase inhibitor D0870, a bis triazole derivative, showed that this compound is capable of inducing radical parasitological cure in murine models of both acute and chronic Chagas' disease. Other inhibitors of this type, such as SCH 56592, have also shown curative, rather than suppressive, activity against T. cruzi in these models. Leishmania species have different susceptibilities to sterol biosynthesis inhibitors, both in vitro and in vivo. Leishmania braziliensis promastigotes, naturally resistant to C14α-demethylase inhibitors such as ketoconazole and D0870, were susceptible to these drugs when used in combination with the squalene epoxidase inhibitor terbinafine. Inhibitors of Δ 24(26) sterol methyl transferase have been shown to act as potent antiproliferative agents against Trypanosoma cruzi, both in vitro and in vivo. New inhibitors of this type which show enhanced activity and novel mechanisms of action have been synthesized. Recent work has also demonstrated that this type of enzyme inhibitors can block sterol biosynthesis and cell proliferation in Pneumocystis carinii, a fungal pathogen which had previously been found resistant to other sterol biosynthesis inhibitors. Ajoene, an antiplatelet compound derived from garlic, was shown to have potent antiproliferative activity against epimastigotes and amastigotes of Trypanosoma cruzi in vitro; this activity was associated with a significant alteration of the phospholipid composition of the cells with no significant effects on the sterol content. In addition, alkyllsophospholipids such as ilmofosine, miltefosine and edelfosine have been shown to block the proliferation of T. cruzi and Leishmania and alter both the phospholipid and sterol composition. These results indicate the potential of lipid biosynthesis inhibitors as useful therapeutic agents in the treatment of leishmaniasis and Chagas' disease.

185 citations


Journal ArticleDOI
TL;DR: The attractive, yet still unproven, hypothesis is that cholesterol translocation plays an important role in the overall platelet response and is intimately related to the sensitizing actions of cholesterol on these cells.
Abstract: Photoreceptor rod cells and blood platelets are remarkably different, yet both illustrate a similar phenomenon Both are strongly affected by membrane cholesterol, and the distribution of cholesterol in the membranes of both cell types is determined by the lipid composition within the membranes In rod cells, cholesterol strongly inhibits rhodopsin activity The relatively higher level of cholesterol in the plasma membrane serves to inhibit, and thereby conserve, the activity of rhodopsin, which becomes fully active in the low-cholesterol environment of the disk membranes of these same cells This physiologically important partitioning of cholesterol between disk membranes and plasma membranes occurs because the disk membranes are enriched with phosphatidylethanolamine, thus providing a thermodynamically unfavorable environment for the sterol Cholesterol enrichment of platelets renders these cells more responsive to stimuli of aggregation Stimuli for platelet aggregation cause a rapid transbilayer movement of cholesterol from the outer monolayer This stimulus-dependent redistribution of cholesterol appears to result from the concomitant movement of phosphatidylethanolamine into the outer monolayer The attractive, yet still unproven, hypothesis is that cholesterol translocation plays an important role in the overall platelet response and is intimately related to the sensitizing actions of cholesterol on these cells

160 citations


Journal ArticleDOI
TL;DR: This review summarizes the state of knowledge in these three areas: plant sterols, flavonoids, and plant sulfur compounds and explores possibilities for future work.
Abstract: Epidemiological studies have often shown relationships between vegetable/fruit intake and coronary heart disease that are not clearly attributable to major macronutrients or known vitamins and minerals. This suggests that other components of plants may be important in lowering risk of cardiovascular disease. Although the literature contains studies of a myriad of possible plant components, many of these studies are small or poorly controlled. Further, the supposition itself has led to claims of “miracle” ingredients with supposed mitigating effects on cardiovascular as well as other chronic diseases. A substantial body of evidence has accumulated in three areas: plant sterols, flavonoids, and plant sulfur compounds. This review summarizes the state of knowledge in these three areas and explores possibilities for future work. The plant kingdom contains a number of sterols that differ from cholesterol by having ethyl or methyl groups or unsaturation in the side chain. The predominant ones—sitosterol, stigmasterol, and campesterol—can be present in Western diets in amounts almost equal to dietary cholesterol.1 The most prominent is β-sitosterol, which differs from cholesterol in that it has an ethyl group at carbon 24 of the side chain. In the early 1950s it was noted that the addition of sitosterol to the diet of cholesterol-fed chickens or rabbits lowered cholesterol levels in both species and inhibited atherogenesis in the latter.2 Sitosterol or mixtures of soy sterols were studied extensively as cholesterol-lowering agents between 1950 and 1960.3 The preparations achieved cholesterol lowering of approximately 10%.4 The mode of action appears to involve inhibition of cholesterol absorption, although the plant sterols themselves are absorbed very poorly.5 The mechanism of inhibition of cholesterol absorption is believed to be through crystallization and co-precipitation. Ingestion of …

149 citations


Journal ArticleDOI
TL;DR: CYP61 was a cytochrome P-450 revealed during the yeast genome project when chromosome XIII was sequenced and revealed to have a similar affinity to azole drugs when compared with data available for CYP51, and the implications for antifungal treatment were considered.

139 citations


Journal ArticleDOI
TL;DR: The effects of in vivo Cd treatments on pea root plasma membrane (PM) lipid composition were studied and the physiological repercussions of changes in plasma membrane lipid composition, as a result of Cd exposure are discussed.
Abstract: The effects of in vivo Cd treatments on pea root plasma membrane (PM) lipid composition were studied. In the long-term experiment, plants were supplied with Cd: moderate stress (10 fitA) or strong stress (50 //M) for 10 d. Growth of root and shoot was severely affected in 50 fiM Cd-treated plants, as evidenced by the approximately 7-fold reduction in their Relative Growth Increment (RGI)- Treatment with Cd (10 ftM) resulted in changes to the lipid composition of the pea root PM, including increases in the degree of unsaturation of phospholipid-associated fatty acids and in the relative amount of stigmasterol (30-42%). This change was accompanied by a reduction in sitosterol content (26.8 to 17.4 //g mg 1 protein). However, the sterol composition was not altered in plants treated with 50 //M Cd for 10 d. The content of phosphatidylethanolamine and phosphatidylcholine (major phospholipids present in pea root PM) decreased as Cd level increased, but the ratio between them remained unaffected. In the short-term experiment, plants exposed to Cd (50 fiM) accumulated less sitosterol (from 27.7 to 14.0 fig gmg' 1 protein) over 72 h, but no significant effect on other measured lipids was observed. The physiological repercussions of changes in plasma membrane lipid composition, as a result of Cd exposure are discussed.

138 citations


Journal ArticleDOI
TL;DR: The cholesterol-lowering effect of GG appears to be mediated by an accelerated fecal excretion of steroids and a rise in the intestinal pool and biliary production of bile acids.
Abstract: The effect of dietary guar gum (GG, 7.5%) on lipid metabolism and on bile acid secretion and reabsorption was investigated in rats adapted to cholesterol-free or 0.3% cholesterol diets. Compared with controls (fiber-free/cholesterol-free), rats fed cholesterol had significantly elevated plasma and liver cholesterol and triglyceride. In these rats, GG had a potent plasma cholesterol-lowering effect and also counteracted the liver accumulation of triglyceride and cholesterol esters. Fecal excretion of sterols, the major route of cholesterol elimination, was markedly enhanced by GG, especially in rats fed the cholesterol-containing diet (P < 0.001). The biliary bile acid flux into the small intestine was enhanced by dietary cholesterol (+30%) or GG (+52%) or both (P < 0.001). The fecal excretion of bile acids was significantly elevated by GG alone (+74%) and by dietary cholesterol (+190%). Small intestine reabsorption of bile acids appears to be significantly enhanced by GG, which also enhanced the transfer of bile acids into the large intestine, hence a greater fecal loss of steroids, although bile acid reabsorption was very effective in the cecum. GG feeding induced liver hydroxymethyl-glutaryl coenzyme A (HMG CoA) reductase, even in cholesterol-fed rats, as well as cholesterol 7α-hydroxylase (P < 0.001). The cholesterol-lowering effect of GG thus appears to be mediated by an accelerated fecal excretion of steroids and a rise in the intestinal pool and biliary production of bile acids. Although liver HMG CoA reductase and cholesterol 7α-hydroxylase are induced in parallel, this is not sufficient to compensate for fecal steroid losses. J. Nutr. 127: 1068-1076, 1997.

137 citations


Journal ArticleDOI
TL;DR: There are two distinct sites for SREBP binding that control activation of the ACC PII promoter whereas previous work has shown there is only a single SRE BP site in the LDL receptor, and the two sites are equally important and dependent on one another for optimal function.

128 citations


Journal ArticleDOI
TL;DR: Biochemical improvement in sterol levels and in the ratio of cholesterol to total sterols was noted in all patients, and clinical improvement in growth and neurodevelopmental status was also observed.
Abstract: Patients with the RSH or Smith-Lemli-Optiz syndrome (SLOS) have an inborn error of cholesterol biosynthesis which results in a deficiency of cholesterol and an elevation of the cholesterol precursor, 7-dehydrocholesterol. A treatment protocol consisting of administration of cholesterol +/- bile acids was initiated in an attempt to correct the biochemical abnormalities seen. Fourteen patients (8 female, 6 male: ages 2 months to 15 years) have now been treated for 6-15 months. Three patients received cholesterol alone, while 11 patients received cholesterol and one or more bile acids. Biochemical improvement in sterol levels and in the ratio of cholesterol to total sterols was noted in all patients. The most marked improvement was noted in patients presenting with initial cholesterol levels < 40 mg/dl. No toxicity was observed. Clinical improvement in growth and neurodevelopmental status was also observed.

Journal ArticleDOI
TL;DR: In this small selected group of mildly hypercholesterolemic nonobese NIDDM subjects, the regulation of serum cholesterol levels was achieved by the homeostasis between cholesterol absorption, synthesis, and LDL fractional catabolism.
Abstract: OBJECTIVE Cholesterol and lipoprotein metabolism was studied in mildly hypercholesterolemic nonobese men with NIDDM to find out which metabolic parameters regulate serum cholesterol level in these NIDDM subjects. RESEARCH DESIGN AND METHODS Nonobese NIDDM subjects ( n = 13) and control subjects ( n = 18) with serum cholesterol ≥ 6.0 and triglycerides ≤ 2.5 mmol/l were studied on a similar monoene-enriched diet. Cholesterol absorption was studied with peroral double isotopes and by measuring serum plant sterols with gas-liquid chromatography; cholesterol synthesis was studied by measuring sterol balance and by measuring serum cholesterol precursor sterols; and LDL kinetics was measured with 131 I-labeled autologous apoprotein (apo) B. RESULTS Cholesterol absorption was significantly lower in NIDDM subjects than in the control subjects, as detected by low serum plant sterol levels and absorption percentage (23 vs. 29%, P −1 · day −1 , P −1 · day −1 , P P CONCLUSIONS In this small selected group of mildly hypercholesterolemic nonobese NIDDM subjects, the regulation of serum cholesterol levels was achieved by the homeostasis between cholesterol absorption, synthesis, and LDL fractional catabolism. Cholesterol turnover and removal of LDL apo B were high in NIDDM subjects, compared with the control subjects, whereas cholesterol absorption efficiency was abnormally low Because of the relatively small number of selected subjects, the present results are not directly applicable to the overall NIDDM population.

Journal ArticleDOI
TL;DR: Results indicate that cells regulate the balance between cholesterol and sphingomyelin content by regulating the proteolytic cleavage of SREBPs.
Abstract: The current studies explore the mechanism by which the sphingomyelin content of mammalian cells regulates transcription of genes encoding enzymes of cholesterol synthesis. Previous studies by others have shown that depletion of sphingomyelin by treatment with neutral sphingomyelinase causes a fraction of cellular cholesterol to translocate from the plasma membrane to the endoplasmic reticulum where it expands a regulatory pool that leads to down-regulation of cholesterol synthesis and up-regulation of cholesterol esterification. Here we show that sphingomyelinase treatment of cultured Chinese hamster ovary cells prevents the nuclear entry of sterol regulatory element binding protein-2 (SREBP-2), a membrane-bound transcription factor required for transcription of several genes involved in the biosynthesis and uptake of cholesterol. Nuclear entry is blocked because sphingomyelinase treatment inhibits the proteolytic cleavage of SREBP-2 at site 1, thereby preventing release of the active NH2-terminal fragments from cell membranes. Sphingomyelinase treatment thus mimics the inhibitory effect on SREBP processing that occurs when exogenous sterols are added to cells. Sphingomyelinase treatment did not block site 1 proteolysis of SREBP-2 in 25-RA cells, a line of Chinese hamster ovary cells that is resistant to the suppressive effects of sterols, owing to an activating point mutation in the gene encoding SREBP cleavage-activating protein. In 25-RA cells, sphingomyelinase treatment also failed to down-regulate the mRNA for 3-hydroxy-3-methylglutaryl CoA synthase, a cholesterol biosynthetic enzyme whose transcription depends on the cleavage of SREBPs. Considered together with previous data, the current results indicate that cells regulate the balance between cholesterol and sphingomyelin content by regulating the proteolytic cleavage of SREBPs.

Journal ArticleDOI
TL;DR: Evidence for a sterol modulation of the plant PM H+-ATPase activity is presented and H+ pumping was shown to be more sensitive to a sterols environment than was ATP hydrolysis.
Abstract: A partially purified H+-ATPase from the plasma membrane (PM) of corn (Zea mays L.) roots was inserted into vesicles prepared with soybean (Glycine max L.) phospholipids and various concentrations of individual sterols using either a freeze-thaw sonication or an octylglucoside dilution procedure. Both methods yielded a functional enzyme that retained its native characteristics. We have investigated the effects of typical plant sterols (i.e. sitosterol, stigmasterol, and 24-methylcholesterol) on both ATP hydrolysis and H+ pumping by the reconstituted corn root PM ATPase. We have also checked the influence of cholesterol and of two unusual sterols, 24-methylpollinastanol and 14[alpha],24-dimethylcholest-8-en-3[beta]-ol. Here we present evidence for a sterol modulation of the plant PM H+-ATPase activity. In particular, cholesterol and stigmasterol were found to stimulate the pump, especially when present at 5 mol%, whereas all of the other sterols tested behaved as inhibitors at any concentration in proteoliposomes. In all situations H+ pumping was shown to be more sensitive to a sterol environment than was ATP hydrolysis. Our results suggest the occurrence of binding sites for sterols on the plant PM H+-ATPase.

Journal ArticleDOI
TL;DR: Investigating if sterol C8–C7 isomerase inhibitors are high affinity ligands for the (+)‐[3H]‐pentazocine labelled sigma1‐binding site demonstrates that sigma 1‐binding protein and yeast isomerases are not only structurally but also pharmacologically related.
Abstract: 1. The sigma-drug binding site of guinea-pig liver is carried by a protein which shares significant amino acid sequence similarities with the yeast sterol C8-C7 isomerase (ERG2 protein). Pharmacologically-but not structurally-the sigma 1-site is also related to the emopamil binding protein, the mammalian sterol C8-C7 isomerase. We therefore investigated if sterol C8-C7 isomerase inhibitors are high affinity ligands for the (+)-[3H]-pentazocine labelled sigma 1-binding site. 2. Among the compounds which bound with high affinity to native hepatic and cerebral as well as to yeast expressed sigma 1-binding sites were the agricultural fungicide fenpropimorph (Ki 0.005 nM), the antihypocholesterinaemic drugs triparanol (Ki 7.0 nM), AY-9944 (Ki, 0.46 nM) and MDL28,815 (Ki 0.16 nM), the enantiomers of the ovulation inducer clomiphene (Ki 5.5 and 12 nM, respectively) and the antioestrogene tamoxifen (Ki 26 nM). 3. Except for tamoxifen these affinities are essentially identical with those for the [3H]-ifenprodil labelled sterol C8-C7 isomerase of S. cerevisiae. This demonstrates that sigma 1-binding protein and yeast isomerase are not only structurally but also pharmacologically related. Because of its affiliations with yeast and mammalian sterol isomerases we propose that the sigma 1-binding site is localized on a sterol isomerase related protein, involved in postsqualene sterol biosynthesis.

Journal ArticleDOI
TL;DR: In this paper, the sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oils were assessed for contents of sterol oxidation products.
Abstract: Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations. After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4 to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol are reported for the first time.

Journal ArticleDOI
TL;DR: The aim of the present work is to study the molecular basis of the interactions of AmB with these sterols contained in a DOPC film by using the monolayer technique and shows that these results provide a better understanding of the action of amphotericin B (activity/toxicity) at the membrane level.

Journal ArticleDOI
TL;DR: In this article, potato chips fried in palm oil, sunflower oil, and high-oleic sunflower oils were studied for the content of different phytosterol oxides during 0 to 25 weeks of storage in the dark.
Abstract: Potato chips fried in palm oil, sunflower oil, and high-oleic sunflower oil were studied for the content of different phytosterol oxides during 0 to 25 weeks of storage in the dark. Oxidation products of sitosterol (24α-ethyl-5-cholesten-3β-ol) and campesterol (24α-methyl-t-cholesten-3β-ol) were synthesized to help identify the phytosterol oxides. The oxides of phytosterols were analyzed by preparative thin-layer chromatography, solid-phase extraction, capillary column gas chromatography (GC), and GC-mass spectrometry. Epimers of 7-hydroxysitosterol and 7-hydroxycampesterol; 7-ketositosterol and 7-ketocampesterol; epimers of 5,6-epoxy-sitosterol and 5,6-epoxy-campesterol; 24α-ethylcholestane-3β,5,6β-triol (dihydroxysitosterol) and 24α-methylcholestane-3β,5,6β-triol (dihydroxycampesterol) were detected and quantitated in the samples of chips fried in different vegetable oils. Potato chips fried in palm oil had the lowest level of total sterol oxides, ranging from 5 to ca. 9 ppm in the lipids from time 0 to 25 wk of storage. The level of total sterol oxides in chip samples fried in sunflower oil ranged from 46 to 47 ppm, and the lipids in samples fried in high-oleic sunflower oil ranged from 35 to 58 ppm from 0 time to 25 wk of storage. During 25 wk of storage no considerable increase in sterol oxides was observed in the samples of chips fried in palm oil and sunflower oil. The chip samples fried in high-oleic sunflower oil had slightly higher levels of sterol oxides after 10 and 25 weeks of storage. In addition to the levels of individual sterol oxides, a new method for enrichment of phytosterol oxides from the unsaponifiables and full-scan mass spectra of various oxidation products of sitosterol and campesterol are reported in this paper.

Journal ArticleDOI
TL;DR: The results show that cryptogein has one binding site with strong affinity for dehydroergosterol, and this protein catalyzes the transfer of sterols between phospholipidic artificial membranes, the first evidence for the existence of an extracellular sterol carrier protein and for a molecular activity of Cryptogein.

Journal ArticleDOI
TL;DR: The data suggest that legume consumption lower LDL cholesterol by partially interrupting the enterohepatic circulation of bile acids and increases cholesterol saturation of biles by increasing hepatic secretion of cholesterol.

Journal ArticleDOI
TL;DR: The isolation of a cDNA clone encoding the plant sterol 14 alpha-demethylase, combined with the previously isolated cDNA clones for fungal and mammalian sterol 13 alpha-DEMethylases, provides an important tool in the rational design of specific inhibitors towards the individual sterol 12 alpha-methylases.
Abstract: Obtusifoliol 14 alpha-demethylase from Sorghum bicolor (L.) Moench has been cloned using a gene-specific probe generated using PCR primers designed from an internal 14 amino acid sequence. The sequence identifies sorghum obtusifoliol 14 alpha-demethylase as a cytochrome P450 and it is assigned to the CYP51 family together with the sterol 14 alpha-demethylases from fungi and mammals. The presence of highly conserved regions in the amino acid sequences, analogous substrates and the same metabolic role demonstrate that the sterol 14 alpha-demethylases are orthologous enzymes. The sterol 14 alpha-demethylases catalyse an essential step in sterol biosynthesis as evidenced by the absence of a 14 alpha-methyl group in all known functional sterols. A functional sorghum obtusifoliol 14 alpha-demethylase was expressed at high levels in Escherichia coli and purified using an efficient method based on temperature-induced Triton X-114 phase partitioning. The recombinant purified enzyme produced a type I spectrum with obtusifoliol as substrate. Reconstitution of purified recombinant enzyme with sorghum NADPH-cytochrome P450 reductase in dilaurylphosphatidylcholine micelles confirms that obtusifoliol 14 alpha-demethylase catalyses the 14 alpha-demethylation of obtusifoliol to 4 alpha-methyl-5 alpha-ergosta-8, 14,24(28)-trien-3 beta-ol as evidenced by GC-MS. The isolation of a cDNA clone encoding the plant sterol 14 alpha-demethylase, combined with the previously isolated cDNA clones for fungal and mammalian sterol 14 alpha-demethylases, provides an important tool in the rational design of specific inhibitors towards the individual sterol 14 alpha-demethylases.

Journal ArticleDOI
TL;DR: It is suggested that C-24 reduction of sterols takes place straight after sterol delta 8-->7 isomerization of zymosterol, which occurs several steps after C-32 demethylation of lanosterol in the 19-step pathway of cholesterol biosynthesis from Lanosterol.
Abstract: The membrane-bound sterol delta 24-reductase (24-reductase) catalyses anaerobic reduction of the 24(25)-enes of lanosterol and other obligatory intermediates of cholesterol biosynthesis from lanosterol. A novel assay method and properties of the 24-reductase are described. More than a 120-fold induction of the 24-reductase activity was achieved by feeding rats a diet containing 5% cholestyramine plus 0.1% lovastatin in chow and by modulating diurnal variation. With this enzyme induction condition, lanosterol was converted efficiently into dihydrolanosterol in both intact hepatic microsomes and freshly isolated hepatocytes only when either miconazole or CO was added to inhibit 14 alpha-demethylation of lanosterol. AR45 cells, which are deficient in 14 alpha-methyl demethylase (14 alpha-DM), exhibit lanosterol 24-reductase activity without addition of either CO or miconazole. Conversely, inhibition of the 24-reductase was not required for the expression of 14 alpha-DM activity. Studies on the substrate specificities for the 24-reductase using different 24(25)-enes showed that the most reactive substrate was 5 alpha-cholesta-7,24-dien-3 beta-ol, which exhibited a maximal 18-fold higher kcat than that of lanosterol without the aid of the 14 alpha-DM inhibitor. In addition, both the kinetic behaviour of lanosterol substrate in relation to the 24-reductase and a non-competitive inhibition mode of U18666A (Ki 0. 157 microM) as well as Triparanol (Ki 0.523 microM), two well-known 24-reductase inhibitors, were determined. On the basis of our new findings on the preferred substrate and on the negative effect of 14 alpha-DM on the 24-reductase, we suggest that C-24 reduction of sterols takes place straight after sterol delta 8-->7 isomerization of zymosterol, which occurs several steps after C-32 demethylation of lanosterol in the 19-step pathway of cholesterol biosynthesis from lanosterol.

Journal ArticleDOI
TL;DR: Screening of oat and Arabidopsis cDNA libraries with amplified labeled DNA fragments resulted in the isolation of sterol glucosyltransferase-specific cDNAs with insert lengths of ca.
Abstract: Steryl glucosides are characteristic lipids of plant membranes. The biosynthesis of these lipids is catalyzed by the membrane-bound UDP-glucose:sterol glucosyltransferase (EC 2.4.1.173). The purified enzyme (Warnecke and Heinz, Plant Physiol 105 (1994): 1067-1073) has been used for the cloning of a corresponding cDNA from oat (Avena sativa L.). Amino acid sequences derived from the amino terminus of the purified protein and from peptides of a trypsin digestion were used to construct oligonucleotide primers for polymerase chain reaction experiments. Screening of oat and Arabidopsis cDNA libraries with amplified labeled DNA fragments resulted in the isolation of sterol glucosyltransferase-specific cDNAs with insert lengths of ca. 2.3 kb for both plants. These cDNAs encode polypeptides of 608 (oat) and 637 (Arabidopsis) amino acid residues with molecular masses of 66 kDa and 69 kDa, respectively. The first amino acid of the purified oat protein corresponds to the amino acid 133 of the deduced polypeptide. The absence of these N-terminal amino acids reduces the molecular mass to 52 kDa, which is similar to the apparent molecular mass of 56 kDa determined for the purified protein. Different fragments of these cDNAs were expressed in Escherichia coli. Enzyme assays with homogenates of the transformed cells exhibited sterol glucosyltransferase activity.

Journal ArticleDOI
TL;DR: The results are consistent with the hypothesis that sterol 27-hydroxylase may be utilized by human macrophages as a defence towards a high cholesterol load, and may be less important in some other species.

Journal ArticleDOI
TL;DR: It is concluded that P450c27 is most likely not the 1alpha-hydroxylase of 25-hydroxyvitamin D3, contrary to a previous suggestion, and the development of this expression system and purification procedure creates the potential for structure/function analysis of P450 c27, including possible crystallization of this important enzyme.

Journal ArticleDOI
TL;DR: It is concluded that SCP-2 overexpression enhances the rate of cholesterol cycling, which reduces the availability of cholesterol for CE synthesis and alters the activity of a cellular cholesterol pool involved in regulating apoA-I-mediated high density lipoprotein cholesterol secretion.

Journal ArticleDOI
TL;DR: A thorough study of the sterolic composition of erg6 expressing the A. thaliana cDNA 411 (erg6-4118-pYeDP60) showed 24-methylene and 24-ethylidene derivatives of 4-desmethyl, 4alpha-methyl and 4,4-dimethyl sterols as well as 24- methyl and24-ethyl derivatives of 5alpha-stigmasta-8, Z-24(24(1))-dien-3beta
Abstract: Two methyl transfers are involved in the course of plant sterol biosynthesis and responsible for the formation of 24-alkyl sterols (mainly 24-ethyl sterols) which play major roles in plant growth and development. The first methyl transfer applies to cycloartenol, the second one to 24-methylene lophenol. Five cDNA clones encoding two Arabidopsis thaliana, two Nicotiana tabacum and one Ricinus communisS-adenosyl-L-methionine (AdoMet) sterol methyltransferases (SMT) were isolated. The deduced amino acid sequences of A. thaliana and N. tabacum SMT are about 80% identical in all possible combinations. In contrast they are about 40% identical with the deduced amino acid sequence of R. communis SMT and the published Glycine max sequence. Both A. thaliana and one N. tabacum SMT cDNAs were expressed in a yeast null mutant erg6, deficient in AdoMet zymosterol C24-methyltransferase and containing C24-non-alkylated sterols. In all cases, several 24-ethylidene sterols were synthesized. A thorough study of the sterolic composition of erg6 expressing the A. thaliana cDNA 411 (erg6-4118-pYeDP60) showed 24-methylene and 24-ethylidene derivatives of 4-desmethyl, 4α-methyl and 4,4-dimethyl sterols as well as 24-methyl and 24-ethyl derivatives of 4-desmethyl sterols. The structure of 5α-stigmasta-8, Z-24(241)-dien-3β-ol, the major sterol of transformed yeasts, was demonstrated by 400 MHz 1H NMR. Microsomes from erg6-4118-pYeDP60 were shown to possess AdoMet-dependent sterol-C-methyl-transferase activity. Delipidated preparations of these microsomes converted cycloartenol into 24-methylene cycloartanol and 24-methylene lophenol into 24-ethylidene lophenol, thus allowing the first identification of a plant sterol-C-methyltransferase cDNA. The catalytic efficiency of the expressed SMT was 17-times higher with 24-methylene lophenol than with cycloartenol. This result provides evidence that the A. thaliana cDNA 411 (and most probably the 3 plant SMT cDNAs presenting 80% identity with it) encodes a 24-methylene lophenol-C-241 methyltransferase catalyzing the second methylation step of plant sterol biosynthesis.

Journal ArticleDOI
TL;DR: All the methyl sterol constituents from the authors' algae show a saturated polynuclear system, and the pathways by which side‐chain modifications occur in dinoflagellate 4‐methyl sterols are considered, and a map of the fragmentation pattern of the trimethylsilyl‐4‐ methyl sterols under electronic impact is reported.
Abstract: The marine dinoflagellates Prorocentrum micans, Gonyaulax polyedra, Gymnodinium sp., and Alexandrium tamarense, collected from the Adriatic Sea during red-tide blooms, were cultured to investigate the 4-methyl sterol constituents. To ascertain a possible influence of cell age on the 4-methyl sterol content, for one strain (Gymnodinium sp.)we investigated the composition of these constituents at exponential and stationary growing phases. The lipid material extracted with acetone from the lyophilized algal samples was fractionated by thin-layer chromatography. The 4-methyl sterols recovered from the layer were converted into the corresponding OTMS derivatives. Nine of 11 constituents were identified by gas chromatography and gas chromatography-mass spectrometry; only two minor constituents were characterized by their gas chromatographic parameters. All free methyl sterols identified in the algal samples had been detected previously in various dinoflagellates. The 4-methyl sterol fractions generally contained very few constituents. Except for the Gymnodinium sp. sample, collected at the exponential growing phase (GyD2 exp), which contains 4,24-dimethylcholestan-3-ol as a unique constituent, dinosterol was the major component. Moreover, 4,24-ethylcholestan-3-ol was also an important constituent of both Prorocentrum and Gonyaulax strains, whereas considerable amounts of dinostanol characterized all the Gymnodinium sp. strains. In addition, the latter contained several minor constituents such as 4-methylcholestan-3-ol, 4,24-dimethylcholesta-22-en-3-ol, and 4-methyl-24-ethylcholestan-3-ol. 4-Methyl-24-methylene-cholestan-3-ol was a constituent of the Gymnodinium sp. sample, collected at the stationary growing phase (GyD2 stat)only, whereas 4-methylgorgostanol was identified only in the Alexandrium tamarense Gt4 strain. Except for 4-methyl-24-ethylcholesta-8(14)-en-3-ol, all the methyl sterol constituents from our algae show a saturated polynuclear system. The pathways by which side-chain modifications occur in dinoflagellate 4-methyl sterols are considered, and a map of the fragmentation pattern of the trimethylsilyl-4-methyl sterols under electronic impact is also reported.

Journal ArticleDOI
TL;DR: The results demonstrate that GC and GC-MS alone cannot generally be used for rigorous structure determinations of individual components in mixtures of unsaturated sterols, but all but a few of the 26 sterols could be distinguished by their combined chromatographic mobilities on the two GC columns coupled with critical examination of their mass spectra.

Journal ArticleDOI
Peter B. Jones1
TL;DR: It can be concluded that synthesis, as a contributor to circulating cholesterol concentrations, is sensitive to many dietary factors, and that mass isotopomer distribution analysis and deuterium incorporation approaches offer advantages over other methods.