Showing papers on "Sterol published in 1986"

Abnormal metabolism of shellfish sterols in a patient with sitosterolemia and xanthomatosis.

Abstract: Sitosterolemia and xanthomatosis together are a disease characterized by premature cardiovascular disease, and by elevated plasma concentrations of total sterols and of plant sterols, especially sitosterol which is hyperabsorbed. In order to determine whether this abnormal metabolism also involved other sterols, a patient with sitosterolemia was fed a diet high in shellfish that contain significant quantities of noncholesterol sterols, some of which are less well absorbed than cholesterol in humans. Compared with control subjects (n = 8), the sitosterolemic subject had an increased absorption of 22-dehydrocholesterol (71.5% vs. 43.8 +/- 11.4%, mean +/- SD), C-26 sterol (80.6% vs. 49.3 +/- 11.4%), brassicasterol (51.8% vs. 4.8 +/- 4.2%), and 24-methylene cholesterol (60.5% vs. 16.0 +/- 8.3%). This enhanced absorption was associated with an increased plasma total shellfish sterol level (13.1 mg/dl vs. 1.9 +/- 0.7 mg/dl in normals). In the sitosterolemic subject, as in normals, the shellfish sterols were not preferentially concentrated in any lipoprotein class, and 50-65% of these sterols were in the esterified form in plasma. Bile acids and neutral sterols were quantitated in bile obtained by duodenal aspiration. The bile acid composition did not differ significantly in the sitosterolemic subject compared with the normal controls. The sitosterolemic subject, though, was unable to concentrate normally the neutral shellfish sterols in bile. The normal controls concentrated the shellfish sterols in bile 6.3 +/- 1.7-fold relative to the plasma shellfish sterol concentration whereas the study subject was only able to concentrate them 2.1-fold. We propose that sitosterolemia and xanthomatosis occur from a generalized abnormality in the usual ability of the gut mucosa and other tissues of the body to discriminate among many different sterols. This has important implications for the understanding of the pathophysiology of this disease and for therapeutic recommendations.

Effect of selected oat sterols on the deterioration of heated soybean oil

Abstract: Two sterol fractions of different purity, each containing both Δ5-avenasterol and β-sitosterol, were separated from oat oil, and their antioxidant effects studied in soybean oil at 180 C. Oil samples with added pure β-sitosterol and control samples (no added sterol) also were studied.

Regulation of early enzymes of ergosterol biosynthesis in Saccharomyces cerevisiae

Abstract: In order to determine the regulation mechanisms of ergosterol biosynthesis in yeast, we developed growth conditions leading to high or limiting ergosterol levels in wild type and sterol-auxotrophic mutant strains. An excess of sterol is obtained in anaerobic sterol-supplemented cultures of mutant and wild type strains. A low sterol level is obtained in aerobic growth conditions in mutant strains cultured with optimal sterol supplementation and in wild type strain deprived of pantothenic acid, as well as in anaerobic cultures without sterol supplementation. Measurements of the specific activities of acetoacetyl-CoA thiolase, HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) synthase and HMG-CoA reductase (the first three enzymes of the pathway), show that in cells deprived of ergosterol, acetoacetyl-CoA thiolase and HMG-CoA synthase are generally increased. In an excess of ergosterol, in anaerobiosis, the same enzymes are strongly decreased. A 5-10-fold decrease is observed for acetoacetyl-CoA thiolase and HMG-CoA synthase. In contrast, HMG-CoA reductase is only slightly affected by these conditions. These results show that ergosterol could regulate its own synthesis, at least partially, by repression of the first two enzymes of the pathway. Our results also show that exogenous sterols, even if strongly incorporated by auxotrophic mutant cells, cannot suppress enzyme activities in aerobic growth conditions. Measurement of specific enzyme activities in mutant cells also revealed that farnesyl pyrophosphate thwarts the enhancement of the activities of the two first enzymes.

The lipid composition of azole-sensitive and azole-resistant strains of Candida albicans.

Abstract: SUMMARY: The lipid compositions of two azole-sensitive (A and B2630) and two azole-resistant (AD and KB) strains of the opportunistic fungal pathogen Candida albicans were studied by using several lipid extraction procedures: no differences were observed between the lipid content or total phospholipid/neutral lipid ratios of the four strains. All contained phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol and phosphatidylserine as major phospholipids, with smaller amounts of phosphatidylglycerol and diphosphatidylglycerol; the relative proportions of these lipids differed between all four strains. The fatty acid composition of each major phospholipid within each strain differed, and there were also interstrain differences. A marked effect of culture growth phase in batch culture on lipid composition was observed. The major neutral lipids in each strain were triacylglycerol, non-esterified sterol and non-esterified fatty acid. The fatty acid compositions of the three fatty-acid-containing neutral lipids were distinct from each other and the phospholipids, and there were also interstrain differences. All strains possessed (lyso)phospholipase activity, which was non-specific. The proportions of triacylglycerol and non-esterified fatty acid did not vary between strains, but the azole-resistant strains AD and KB contained more non-esterified sterol, giving them a phospholipid/sterol ratio approximately half that of azole-sensitive strains. There appeared to be a relationship between the phospholipid/sterol ratio of exponentially growing sensitive strains and their ability to take up azole; this did not extend to the resistant strains, which either did not take up azole (AD and KB) or took it up at a faster rate (Darlington) than sensitive strains.

Hydroxymethylglutaryl-CoA reductase, a key enzyme in phytosterol synthesis?

Abstract: Hydroxymethylglutaryl-CoA reductase (HMGR) regulates the synthesis of mevalonic acid (MVA), the precursor of the myriad of isoprenoid compounds functional in plant cells, with phytosterols representing one class of major importance. Recently, it has shown possible to solubilize and purify the membrane-bound enzyme from a heavy membrane fraction (P 16,000×g) isolated from a cell-free homogenate of etiolated radish seedlings. What is presently known about the molecular and kinetic properties of radish HMGR is reported. Mevinolin, a highly specific competitive inhibitor of HMGR, has been valuable as a research tool in studying the regulatory role of HMGR activity for the growth and development of intact seedlings and cell cultures. The results obtained indicate a primary effect of mevinolin on phytosterol accumulation, whereas other endproducts of the multibranched isoprenoid pathway, such as ubiquinone in the mitochondria or chlorophylls and carotenoids in the plastids, are less or not at all affected. This and other data can be interpreted to mean that the organelles are autonomous in their capacity to synthesize MVA. Since the mevinolin-induced drop in free sterol accumulation is paralleled by significant plant growth retardation, a rate-limiting role of HMGR activity for phytosterol synthesis and normal development of plants is suggested.

Receptor-mediated transport of cholesterol between cultured cells and high-density lipoproteins

Abstract: Publisher Summary This chapter focuses on the receptor-mediated transport of cholesterol between cultured cells and high-density lipoproteins (HDL). HDL appears to play a central role in the transport of cholesterol from peripheral cells to the liver, a pathway termed “reverse cholesterol transport.” The chapter describes experimental protocols that can be used to study cholesterol transport from cultured cells under conditions that may depend on the interaction of HDL with a cell surface receptor. These protocols are divided into three major areas of methodology: (1) modulation of HDL-binding activity, (2) assay of HDL-binding activity, and (3) assay of cholesterol transport. Several different types of cultured cells have been shown to undergo marked increases in HDL-binding activity in response to cholesterol loading of cells. These include human skin fibroblasts, arterial smooth muscle cells, bovine vascular endothelial cells, and mouse peritoneal macrophages. Cholesterol loading of cells can be achieved by designing incubation conditions that deliver sterol into cells by both receptor-independent and receptor-dependent processes.

Genetic analysis of plasma sitosterol, apoprotein B, and lipoproteins in a large Amish pedigree with sitosterolemia.

Abstract: We previously reported the finding of phytosterolemia, xanthomatosis, and hyperapobetalipoproteinemia (hyperapoB) in five siblings in a large Amish pedigree ascertained through a 13-year-old boy who died suddenly from advanced coronary atherosclerosis Here, we present further analyses of the plasma levels of the plant sterol, sitosterol, of low density (beta) lipoprotein (LDL) sterol, and of LDL B protein Of 254 relatives and spouses of the proband, 905% were examined A series of genetic models were explored using a pedigree analysis where parameters reflecting frequency, transmission, and penetrance of putative genotypes were examined simultaneously using a maximum likelihood approach Segregation analysis of the sitosterol levels showed that the phenotype of sitosterolemia was controlled by a rare autosomal recessive gene There was also significant familial correlation in plasma sitosterol levels that was attributed to a polygenic component under a mixed model but could also be due to shared environments such as diets The recessive model was supported by our finding that the plasma sitosterol levels in the parents and in six children born to three of the five sitosterolemics were less than 1 mg/dl, well within the normal range The phenotype of hyperapoB is based on an elevated level of LDL B protein in the presence of a normal LDL cholesterol level (low LDL sterol to LDL B ratio) For both LDL sterol and LDL B, a polygenic model showed a slightly greater improvement in ln likelihood than did the Mendelian single locus model when both were compared to a sporadic model Similar results were obtained for sterol levels of high density (alpha) lipoprotein (HDL) sterol When segregation analysis was performed using the ratio of LDL sterol to LDL B, the Mendelian single locus model gave a slightly better fit to the data than did the polygenic model While the analyses presented here provided unequivocal evidence for the recessive phenotype of phytosterolemia, we also identified a possible single gene factor that could account for the major portion of the strong familial aggregation in the ratio of LDL sterol to LDL B, and to a lesser extent LDL B However, there is clear evidence of familial aggregation for these traits in this pedigree beyond that due to Mendelian components

Design of high energy intermediate analogues to study sterol biosynthesis in higher plants.

Abstract: Several enzymes of plant sterol biosynthesis involve during their catalysis postulated or demonstrated carbocationic high energy intermediates (HEI). The aim of this study was to interfere with plant sterol biosynthesis by means of rationally designed species able to mimic these carbocationic HEI. It has been demonstrated previously that the design of transition state (TS) or HEI analogues could lead to powerful and specific inhibitors of enzymes. We applied this approach to the following target enzymes: 2,3-epoxy-2,3-dihydroqualene cyclase, AdoMet-cycloartenol-C-24-methyltransferase (AdoMet CMT), cycloeucalenol-obtusifoliol isomerase (COI) and Δ8-Δ7-sterol isomerase. Very potent inhibitors have been obtained in the four cases. As an example, analogues of cycloartenol substituted at C-25 by a charged heteroatom (N, As, S) have been synthesized and shown to be able to mimic the C-25 carbocationic HEI involved in the reaction catalyzed by the AdoMet CMT. These compounds were shown to be very potent and specific inhibitors of this enzyme both in vitro (Ki=2.10−8 M, Ki/Km=10−3) and in vivo. The potent inhibitors described are powerful tools to control in vivo the sterol profile of plant cells and therefore to study the structural and functional roles of sterols in cell membranes. Moreover, these compounds constitute leader molecules of a new class of rationally designed inhibitors which could be of value in plant protection.

Sterol composition and biosynthesis in sorghum: Importance to developmental regulation

Abstract: Sterol composition and biosynthesis have been examined in seeds, germinating seeds and blades from fally matured leaves ofSorghum bicolor in various stages of development'from seedlings (seven-day plants) to flowering (66-day) plants. The profile of the dominant free sterols of seeds was similar to that of leaf blades; both contained cholesterol, 24α-methylcholesterol (campesterol), 24β-methylcholesterol (dihydrobrassicasterol), 24α-ethylcholesterol (sitosterol) and 24α-ethylcholesta-5,22-dienol (stigmasterol). Sufficient sterol intermediates were identified in the plant to indicate separate post-cycloartenol pathways to sterolic end products. The total free sterol content of the seed (μg/seed) increased somewhat during the 20 hr germination period. However, as the plant developed (seven to 48 days), there was a logarithmic increase in the leaf blade sterol content (μg/leaf blade) which plateaued at the onset of floral differentiation (ca. day 41). Over the next 18 days (48 to 66 days-period of inflorescense development), the sterol content rapidly decreased. In the early stages of plant development, the leaf blade pentacyclic triterpenoid (PT) content was negligible. With the onset of floral differentiation, PT content increased logarithmically, reaching a plateau level that surpassed the sterol content as flowering progressed. These results imply that a critical mass of sterol is associated with sorghum for floral induction. Sterol loss from the leaves of the flowering plants presumably was compensated for by the diversion of 2,3-oxidosqualene (SO) from sterol synthesis to PT production. Additional feeding and trapping experiments with [2-(14)C]mevalonic acid, [2-(3)H]cycloartenol, [24-(3)H]lanosterol [4-(14)C]sitosterol and [4-(14)C]cholesterol fed to germinating seeds and leaves from flowering plants demonstrated that sorghum possessed a cycloartenolbased pathway; germinating seeds synthesized 24-alkylsterols but not cholesterol, although cholesterol was identified in both dry and germinating seeds by gas chromatography-mass spectroscopy (GC-MS); and mature leaves synthesized cholesterol and 24α-alkylsterols but not 24β-methylcholesterol.

Sterol carrier protein2: further evidence for its role in adrenal steroidogenesis.

Abstract: Homogeneous rat liver sterol carrier protein (SCP2) has been implicated in adrenal steroidogenesis by studies utilizing as a model system various sub-cellular fractions of rat adrenals. Levels of SCP2 were measured in rat adrenal subcellular fractions and various rat tissues using a highly sensitive radioimmunoassay. The levels of SCP2 in various tissues correlate well with the capacity of each tissue to either synthesize or metabolize cholesterol. The high level of SCP2 in adrenal mitochondria (46% of total tissue SCP2) is consistent with its proposed role of enhancing transfer of cholesterol from the outer to the inner mitochondrial membrane. Neither ACTH nor cycloheximide treatment of rats had a significant effect on SCP2 levels or distribution in the adrenal subcellular fractions. Western blot analysis of adrenal subcellular fractions indicates the presence of a protein of identical molecular weight and at least similar antigenicity as homogeneous rat liver SCP2. In the present studies, intact dispers...

Fatty acid composition of individual plasma steryl esters in phytosterolemia and xanthomatosis

Abstract: The bulk of the plasma plant sterol in phytosterolemia occurs in the esterified form and is carried mostly in the low and high density lipoproteins We have determined the fatty acid composition of the individual plasma steryl esters from a newly discovered subject with phytosterolemia and xanthomatosis For this purpose the intact steryl esters were subject to high temperature gas liquid chromatography (GLC) on a polar capillary column, which separated the major esters on the basis of molecular weight and degree of unsaturation of the fatty acids The saturated and unsaturated sterols esterified to saturated, monoenoic, dienoic and tetraenoic fatty acids were identified by GLC analysis of the sterol moieties of the corresponding AgNO3-TLC fractions of the steryl esters The GLC results were confirmed by reversed phase high performance liquid chromatography combined with mass spectrometry via direct liquid inlet interface It was found that, in general, each fatty acid was esterified to the same complement of sterols, and that the esterified sterols possessed a composition comparable to that of the free plasma sterols, which was comprised of about 75% cholesterol, 6% campesterol, 4% 22,23-dihydrobrassicasterol and 15% β-sitosterol The fatty acid composition of the steryl esters differed from that of the 2-position of the plasma phosphatidylcholines, which contained significantly less palmitic and oleic and more linoleic acid On the basis of these results and a review of the literature it is suggested that the plasma cholesteryl and plant steryl esters in phytosterolemia originate from both synthesis in plasma via the lecithin-cholesterol acyltransferase and synthesis in tissues via the acylCoA-cholesterol acyltransferase

Characteristics of sterol uptake in Saccharomyces cerevisiae.

Abstract: A Saccharomyces cerevisiae sterol auxotroph, FY3 (alpha hem1 erg7 ura), was used to probe the characteristics of sterol uptake in S. cerevisiae. The steady-state cellular concentration of free sterol at the late exponential phase of growth could be adjusted within a 10-fold range by varying the concentration of exogenously supplied sterol. When cultured on 1 microgram of sterol ml-1, the cells contained a minimal cellular free-cholesterol concentration of 0.85 nmol/mg (dry weight) and were termed sterol depleted. When cultured on 11 micrograms of sterol ml-1 or more, the cells contained a maximal cellular free-cholesterol concentration of 6.8 nmol/mg (dry weight) and were termed free sterol saturated. Cells with free-sterol concentrations below the maximal level were capable of accumulating free sterol from the medium. The capacity of the cells for cholesterol uptake was inversely proportional to the initial intracellular concentration. The uptake of sterol was shown to be a nonactive process that is independent of cellular energy sources or viability. The intracellular transport of sterol for esterification is not sensitive to anti-microtubule agents.

Sterol compositions of seeds and mature plants of family cucurbitaceae

Abstract: The sterol fractions of the unsaponifiable lipids obtained from 32 seed and mature plant (leaves and stems, pericarp of the fruit, and roots) materials from the 12 generaApodanthera, Benincasa, Citrullus, Coccinea, Cucumis, Cucurbita, Gynostemma, Lagenaria, Luffa, Momordica, Sechium andTrichosanthes, of the family Cucurbitaceae were investigated by gas liquid chromatography (GLC) on an OV-17 glass capillary column. Among the 23 sterols with Δ5-, Δ7- and Δ8-skeletons identified by GLC, the Δ7-sterols were found to be the major sterols of most of the Cucurbitaceae investigated. The seed materials contained 24-ethyl-Δ7-sterols possessing Δ25-bonds, i.e. 24-ethylcholesta-7,25-dienol and 24-ethylcholesta-7,22,25-trienol, whereas the mature plant materials contained 24-ethyl-Δ7sterols without a Δ25-bond, i.e. 24-ethylcholest-7-enol and 24-ethylcholesta-7,22-dienol, as the most predominant sterols, with a few exceptions. The isolation and identification of 24α-ethylcholesta-8(14),22-dienol from the aerial parts ofCucumis sativus also is described.

Effect of steroidal glycoalkaloids of the potato on the permeability of liposome membranes

Abstract: At pH 72, the potato glycoalkaloid α-chaconine caused release of entrapped peroxidase from phosphatidylcholine liposomes containing different free sterols but was ineffective against sterol-free liposomes The alkaloid was able to complex with all the tested sterols in vitro although there was no close correlation between the extent of sterol binding and liposome disruption α-Solanine also complexed with sterols in vitro but had no effects on sterol-containing liposomes under these conditions Both sterol concentration and alkaloid concentration were limiting factors in the action of chaconine but did not markedly affect that of solanine Solanine destabilized liposome membranes only at pH values of 8 and above but was less effective than chaconine The importance of the carbohydrate moiety of glycoalkaloids was further demonstrated by the inability of β2-chaconine to complex with sterols or disrupt liposomes

Methyl sterol and cyclopropane fatty acid composition of Methylococcus capsulatus grown at low oxygen tensions.

Abstract: Methylococcus capsulatus contained extensive intracytoplasmic membranes when grown in fed-batch cultures over a wide range of oxygen tensions (0.1 to 10.6%, vol/vol) and at a constant methane level. Although the biomass decreased as oxygen levels were lowered, consistently high amounts of phospholipid and methyl sterol were synthesized. The greatest amounts of sterol and phospholipid were found in cells grown between 0.5 and 1.1% oxygen (7.2 and 203 mumol/g [dry weight], respectively). While sterol was still synthesized in significant amounts in cells grown at 0.1% oxygen, the major sterol product was the dimethyl form. Analysis by capillary gas chromatography-mass spectrophotometry showed that the phospholipid esterified fatty acids were predominantly 16:0 and 16:1 and that the hexadecenoates consisted of cis delta 9, delta 10, and delta 11 isomers. At low oxygen tensions, the presence of large amounts (25%) of cyclopropane fatty acids (cy 17:0) with the methylene groups at the delta 9, delta 10, and delta 11 positions was detected. Although the delta 9 monoenoic isomer was predominant, growth at low oxygen levels enhanced the synthesis of the delta 10 isomers of 16:1 and cy 17:0. As the oxygen level was increased, the amount of cyclopropanes decreased, such that only a trace of cy 17:0 could be detected in cells grown at 10.6% oxygen. Although M. capsulatus grew at very low oxygen tensions, this growth was accompanied by changes in the membrane lipids.