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PubMed2002

Role of the sterol carrier protein-2 N-terminal membrane binding domain in sterol transfer.

Previous studies showed that the N-terminal 32 amino acids of sterol carrier protein-2 ((1-32)SCP(2)) comprise an amphipathic alpha-helix essential for SCP(2) binding to membranes [Huang et al. (1999) Biochemistry 38, 13231]. However, it is unclear whether membrane interaction of the (1-32)SCP(2) portion of SCP(2) is in itself sufficient to mediate intermembrane sterol transfer, possibly by altering membrane structure. In this study a fluorescent sterol exchange assay was used to resolve these issues and demonstrated that the SCP(2) N-terminal peptide (1-32)SCP(2) did not by itself enhance intermembrane sterol transfer but potentiated the ability of the SCP(2) protein to stimulate sterol transfer. Compared with SCP(2) acting alone, (1-32)SCP(2) potentiated the sterol transfer activity of SCP(2) by increasing the initial rate of sterol transfer by 2.9-fold and by decreasing the half-time of sterol transfer by 10-fold (from 11.6 to 1.2 min) without altering the size of the transferable fractions. The ability of a series of SCP(2) mutant N-terminal peptides to potentiate SCP(2)-mediated sterol transfer was directly correlated with membrane affinity of the respective peptide. N-Terminal peptide (1-32)SCP(2) did not potentiate intermembrane sterol transfer by binding sterol (dehydroergosterol), altering membrane fluidity (diphenylhexatriene) or membrane permeability (leakage assay). Instead, fluorescence lifetime measurements suggested that SCP(2) and (1-32)SCP(2) bound to membranes and thereby elicited a shift in membrane sterol microenvironment to become more polar. In summary, these data for the first time showed that while the N-terminal membrane binding domain of SCP(2) was itself inactive in mediating intermembrane sterol transfer, it nevertheless potentiated the ability of SCP(2) to enhance sterol transfer.

Binding Sites↗

PubMed2003

Changes in serum concentrations of noncholesterol sterols and lipoproteins in healthy subjects do not depend on the ratio of plant sterols to stanols in the diet.

Consumption of plant sterols or stanols increases their respective serum concentrations, whereas plant sterols might reduce serum concentrations of plant stanols and vice versa. This suggests that changes in serum plant sterol and stanol concentrations depend on the ratio of plant sterols to stanols in the diet. To examine this in more detail, healthy men (n = 15) and women (n = 29) consumed in random order for 3 wk 1.5 g/d of plant sterols plus 0.5 g of plant stanols (high sterol margarine), 1 g of each (low sterol margarine) or control margarine. Sterols and stanols were provided as fatty acid esters. Compared with the control period, serum cholesterol-standardized campesterol and sitosterol concentrations increased by 33 (P < 0.001) and 19% (P < 0.002), respectively, during the high sterol period, but by only 20 (P < 0.001) and 11% (P = 0.001), respectively, during the low sterol period. During the high sterol period, these values for campestanol and sitostanol were 18 (P = 0.063) and 1% (P = 0.630), and during the low sterol period 25 (P = 0.105) and 7% (P = 0.163), respectively. Effects on LDL cholesterol were similar. We therefore conclude that changes in serum plant sterol and stanol concentrations are not greatly affected by the simultaneous consumption of plant sterols and plant stanols, but are proportional to intakes. Furthermore, both mixtures were equally effective in lowering serum LDL cholesterol concentrations.

Adolescent↗

PubMed2005

Effect of statins on noncholesterol sterol levels: implications for use of plant stanols and sterols.

Normal serum contains small amounts of noncholesterol sterols, including those reflecting cholesterol absorption and those that are markers of cholesterol synthesis. Absorption marker sterols include serum plant sterols, whereas cholesterol precursor sterols correlate with whole-body synthesis of cholesterol. Thus, serum noncholesterol sterols, and especially their ratios to cholesterol, can be used to evaluate the major features of cholesterol metabolism (ie, synthesis and absorption). Statin treatment reduces serum cholesterol precursors but increases serum plant sterols severalfold, especially in subjects with high-absorption marker sterol levels indicative of efficient cholesterol and sterol absorption in general. Statin therapy is most effective in subjects with high serum cholesterol precursor levels. In subjects with high-absorption sterol markers, dietary cholesterol absorption inhibition (eg, with plant stanol and sterol ester margarine) needs to be combined with a statin to achieve effective serum cholesterol reduction. However, whereas dietary plant stanol esters reduce statin-induced elevations of serum plant sterol levels, serum plant sterol levels remain elevated during dietary plant sterol ester consumption. The clinical implication of high serum plant sterol levels is under active investigation.

Cholesterol, LDL↗

PubMed1986

Effect of host insect sterols on the development and sterol composition of Steinernema feltiae.

Steinernema feltiae (= Neoaplectana carpocapsae), 'All' strain, was propagated in larvae of the corn earworm, Heliothis zea, which contained various sterols, in order to determine how the sterol composition of the host affects the growth, development and sterol composition of this insect-parasitic nematode. S. feltiae completed its life cycle normally in insects containing primarily cholesterol, cholestanol or 7-dehydrocholesterol, although the sterol composition of the dauer stage was affected by the sterol composition of the host. When the nematode was reared in insects containing primarily cholesterol, 55% of the sterol in the dauers was cholesterol and the other 46% was lathosterol. In contrast, cholestanol (70%) and lathostetrol (31%) were the sterols present in nematodes reared in H. zea containing primarily cholestanol. Cholestanol (43%), lathosterol (34%), campestanol and/or another 24-methylsterol (23%) and cholesterol (1%) were the sterols present in nematodes reared in H. zea containing campestanol and cholestanol as its major sterols. Lathosterol was the major sterol present in nematodes reared in H. zea containing principally 7-dehydrochlesterol. Therefore, in each case, S. feltiae metabolized some host sterol to lathosterol but the relative percentage of lathosterol in the nematode increased as it was exposed to delta 0-, delta 5- and delta 5,7-sterols, respectively. The ability of S. feltiae to utilize different host sterols may, in part, explain its success in parasitizing a wide variety of insects.

Animals↗

PubMed1998

Characterization of the Saccharomyces cerevisiae ERG26 gene encoding the C-3 sterol dehydrogenase (C-4 decarboxylase) involved in sterol biosynthesis.

All but two genes involved in the ergosterol biosynthetic pathway in Saccharomyces cerevisiae have been cloned, and their corresponding mutants have been described. The remaining genes encode the C-3 sterol dehydrogenase (C-4 decarboxylase) and the 3-keto sterol reductase and in concert with the C-4 sterol methyloxidase (ERG25) catalyze the sequential removal of the two methyl groups at the sterol C-4 position. The protein sequence of the Nocardia sp NAD(P)-dependent cholesterol dehydrogenase responsible for the conversion of cholesterol to its 3-keto derivative shows 30% similarity to a 329-aa Saccharomyces ORF, YGL001c, suggesting a possible role of YGL001c in sterol decarboxylation. The disruption of the YGL001c ORF was made in a diploid strain, and the segregants were plated onto sterol supplemented media under anaerobic growth conditions. Segregants containing the YGL001c disruption were not viable after transfer to fresh, sterol-supplemented media. However, one segregant was able to grow, and genetic analysis indicated that it contained a hem3 mutation. The YGL001c (ERG26) disruption also was viable in a hem 1Delta strain grown in the presence of ergosterol. Introduction of the erg26 mutation into an erg1 (squalene epoxidase) strain also was viable in ergosterol-supplemented media. We demonstrated that erg26 mutants grown on various sterol and heme-supplemented media accumulate nonesterified carboxylic acid sterols such as 4beta, 14alpha-dimethyl-4alpha-carboxy-cholesta-8,24-dien-3be ta-ol and 4beta-methyl-4alpha-carboxy-cholesta-8,24-dien-3beta-o l, the predicted substrates for the C-3 sterol dehydrogenase. Accumulation of these sterol molecules in a heme-competent erg26 strain results in an accumulation of toxic-oxygenated sterol intermediates that prevent growth, even in the presence of exogenously added sterol.

Amino Acid Sequence↗

PubMed1997

Identification of cDNAs encoding sterol methyl-transferases involved in the second methylation step of plant sterol biosynthesis.

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 communis S-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, 4alpha-methyl and 4,4-dimethyl sterols as well as 24-methyl and 24-ethyl derivatives of 4-desmethyl sterols. The structure of 5alpha-stigmasta-8, Z-24(24(1))-dien-3beta-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-methyltransferase 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-24(1) methyltransferase catalyzing the second methylation step of plant sterol biosynthesis.

Amino Acid Sequence↗

PubMed1984

Sterol composition of normal human bile. Effects of feeding shellfish (marine) sterols.

To examine the sterol composition of normal human bile and the effects of dietary components from certain shellfish upon bile composition, we fed 7 subjects diets rich in shellfish for 2 wk following a typical American diet. The total cholesterol, bile acid, and phospholipid, and the individual sterols and bile acids of the bile samples during each dietary period were measured. In the bile of 7 subjects consuming the typical American diet, nine different neutral sterols, in addition to cholesterol, were identified. Similar patterns of these sterols have been found in human gallstones and in plasma after shellfish feeding. The five shellfish sterols (22-dehydrocholesterol, 24-methylene cholesterol, brassicasterol, isofucosterol, and a C-26 sterol) increased from 0.3% to a total of 5.2% (p less than 0.001) of total sterols. A comparison of the ratios of various shellfish sterols to cholesterol in plasma and in bile suggested selectively greater excretion of shellfish sterols relative to cholesterol. Our data demonstrated that human bile contains a mixture of sterols and that its sterol composition can be readily altered by dietary changes. The lithogenicity of the bile based on the ratio of cholesterol, bile acids, and phospholipids, and the bile acid composition was not affected by the presence of shellfish sterols. However, since some of these sterols occur in human gallstones, their lithogenic capacity cannot be ruled out.

Adult↗

PubMed1996

Plant sterol biosynthesis: identification and characterization of higher plant delta 7-sterol C5(6)-desaturase.

Microsomes obtained from maize seedlings catalyzed the introduction of the delta5-bond into delta7-sterols to yield the corresponding delta 5,7-sterols. Enzymatic bioassay conditions have been developed for the first time for delta 7-sterol C5(6)-desaturase in photosynthetic organisms. The properties of the microsomal system have been studied and the kinetics of the desaturation reaction has been established. The desaturation reaction requires molecular oxygen and NADH. Coenzyme efficiency studies indicate that NADH is more efficient that NADPH and that in the presence of NADH, NAD+ stimulates the desaturation process but cannot sustain the reaction by itself. The desaturation is strongly inhibited by cyanide, is sensitive to 1,10-phenanthroline and to salicylhydroxamic acid, but is insensitive to carbon monoxide, suggesting the involvement of a metal ion, presumably iron, in an enzyme-bound form in the desaturating system. From a series of incubations with delta 7-sterols and other sterol analogs, the substrate specificity for desaturation was determined. Our data indicate the substrate selectivity of the C5(6)-desaturation for 4-desmethyl-delta 7-sterols. Moreover, the results show that specificity of maize C5(6)-desaturase favored delta 7-sterols possessing a C24-methylene or ethylidene substituent compared to 24-ethyl-substituted delta 7-sterols. Finally, the results demonstrate directly that during plant sterol synthesis the delta 5-bond is introduced via the sequence delta 7-sterol-->delta 5,7-sterol-->delta 5-sterol.

Coenzymes↗

PubMed1979

Effects of various oxygenated sterols on cellular sterol biosynthesis in Chinese hamster lung cells resistant to 25-hydroxycholesterol.

The effects of a wide variety of oxygenated sterols upon sterol biosynthesis and hydroxymethylglutaryl-CoA reductase (mevalonate: NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34) activity in a wild-type clone and in a 25-hydroxycholesterol-resistant clone of Chinese hamster lung (Dede) cells are described. Derivatives of cholesterol which were oxygenated in the 6, 7 or 15 positions of the sterol nucleus or in the 20, 22, 24 or 25 positions of the sterol side chain were shown to be potent inhibitors of sterol synthesis and reductase activity in the wild-type cells but none of these substitutions had any effect on the 25-hydroxycholesterol-resistant A2 clone. A 32-hydroxylated derivative of lanosterol also suppressed sterol synthesis and reductase activity in wild-type cells but had no significant effect upon the A2 line. It was also appraent that a complete sterol side chain was necessary for inhibitory activity. Studies of a wide range of inhibitory sterols indicated that there was a close correlation between their effects upon sterol synthesis and reductase activity and that their inhibitory action was specific for sterol biosynthesis since little effect was observed upon fatty acid or CO2 synthesis. Previous studies had shown that the uptake of 25-hydroxycholesterol by the resistant A2 line was unimpaired and the present results indicate that metabolism of this oxygenated sterol is also unaltered. These results, in conjunction with previous studies, suggest that the resistant A2 line is defective in feedback regulation of cholesterol synthesis and that all of the oxygenated sterols tested suppress the biosynthetic pathway through at least one common step.

Acetates↗

PubMed1987

Relationship between intracellular sterol content and sterol esterification and hydrolysis in Saccharomyces cerevisiae.

The relationship between the supply of free sterol and the synthesis of steryl esters by an auxotroph of Saccharomyces cerevisiae has been examined in order to understand the role of cellular free sterol content in the regulatory interactions of sterol esterification. Our results show that the yeast cells must maintain an essential, low level of free sterol that is critical for growth. An additional, expandable pool of free sterol is maintained by the cells, provided there is adequate available sterol. As the quantity of sterol in the expandable pool increases, there is a progressively increasing rate of sterol esterification, which is consistent with the results from in vitro assays of acyl-Co A:ergosterol acyltransferase. Some increases in acyltransferase activity were insensitive to the protein synthetic inhibitor, cycloheximide. The data support the conclusion that sterol interconversion between the free and esterified forms is directed toward maintaining the essential amount of free sterol and that the activity of the relevant sterol enzymes in this organism are modulated in response to intracellular sterol content.

Acyltransferases↗

PubMed1985

Yeast sterols: yeast mutants as tools for the study of sterol metabolism.

Yeast mutants defective in ergosterol synthesis are valuable tools for investigating sterol metabolism. Both sterol mutants and sterol auxotrophs have been utilized in determining what sterol structural features are required for yeast cell viability. Both types of mutants can also be studied to ascertain how changes in sterol structure affect membrane properties. Other aspects of sterol metabolism, such as the specificity of sterol esterification, have been elucidated by the sterol auxotrophs. In broader applications, interrelationships between sterol metabolism and other cellular functions (e.g., heme metabolism) may also be examined with these mutants. By analyzing the lipid composition of the sterol mutants, on the other hand, much of the ergosterol biosynthetic pathway has been delineated. The unusual sterols of the mutants can also be obtained to develop assays for the enzymes involved in ergosterol synthesis. Thus, by utilizing mutants, the simple eukaryotic system of yeast may be extended to explore the entire field of sterol metabolism and its relationship to cellular physiology.

Chromatography, High Pressure Liquid↗

PubMed2003

Co-expression of N-terminal truncated 3-hydroxy-3-methylglutaryl CoA reductase and C24-sterol methyltransferase type 1 in transgenic tobacco enhances carbon flux towards end-product sterols.

The enzymes 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and C24-sterol methyltransferase type 1 (SMT1) have been proposed to be key steps regulating carbon flux through the sterol biosynthesis pathway. To further examine this hypothesis, we co-expressed the catalytic domain of Hevea brasiliensis HMGR (tHMGR) and Nicotiana tabacum SMT1 in tobacco, under control of both constitutive and seed-specific promoters, resulting in increased accumulation of total sterol in seed tissue by 2.5- and 2.1-fold, respectively. This enhancement is greater than when tHMGR and SMT1 were expressed singularly where, for example, seed-specific expression enhanced total sterols by 1.6-fold. Significantly, the relative level of 4-desmethyl sterols (end-product sterols) was higher in seed co-expressing tHMGR and SMT1 from seed-specific promoters (79% of total sterols) than when co-expressed from constitutive promoters (59% of total sterols) and similar to wild-type seed (80% of total sterols). These results demonstrate that HMGR and SMT1 work in concert to control carbon flux into end-product sterols and that the sterol composition can be controlled by the temporal activity of the promoters driving transgene expression. In addition, constitutive expression of the transgenes resulted in elevated accumulation of substrates for C4-demethylation reactions, which indicates that one or several enzymes catalysing such reactions limit carbon flow to end-product sterols, at least in a physiological situation when the carbon flow is upregulated.

Carbon↗

PubMed2003

Effects of microcrystalline plant sterol suspension and a powdered plant sterol supplement on hypercholesterolemia in genetically obese Zucker rats.

Because dietary fat appears to be an effective vehicle for dispensing plant sterols into the diet, a special plant-sterol-containing ingredient has recently been developed. This ingredient is a plant sterol suspension in oil in which the sterols are in microcrystalline form. The objective of the present study was to analyse the cholesterol-lowering effects and safety of two different plant sterol preparations, an orally administered microcrystalline plant sterol suspension (MPS) in rapeseed oil and a powdered plant sterol supplement, in obese Zucker rats. Dietary plant sterol supplements (0.5%, w/w) were given concurrently with a high cholesterol diet (HCD, 1% cholesterol and 18% fat, w/w). No significant changes in serum triglyceride, blood glucose, serum glutamate oxaloacetic transaminase and glutamic pyruvic transaminase values or body and liver weights were observed. The powdered plant sterol supplement lowered the serum cholesterol by 25% (P < 0.05) and the MPS diet by 35% (P < 0.001) compared with HCD by the end of the 12-week experiment. Interestingly, the plant sterol supplements also produced a marked reduction in serum ubiquinone levels, suggesting a possible effect on isoprene synthesis. Unlike the powdered plant sterol, both MPS and plain rapeseed oil decreased the serum baseline diene conjugation values, suggesting that they protect against oxidative stress-induced lipid peroxidation in rats. This lipid peroxidation diminishing effect is probably due to some antioxidative components in rapeseed oil. These findings indicate that an unesterified plant sterol, such as the microcrystalline suspension in oil, effectively prevents cholesterol absorption in obese Zucker rats.

Administration, Oral↗

PubMed2004

Adult sterol metabolism is not affected by a positive sterol balance in the neonatal Golden Syrian hamster.

Dietary components impact metabolism early in life. Some of the diet-induced effects are long lasting and can lead to various adult-based diseases. In the current studies, we examined the short-term effects of dietary cholesterol on neonatal hepatic sterol metabolism and the long-term effects that those early-life diets had on sterol metabolism in adulthood. Neonatal hamsters began consuming solid food as a supplement to milk by 5 days of age; diets contained 0 or 2% added cholesterol (wt/wt). By 10 days of age, plasma and liver cholesterol concentrations were 3.2- and 2.5-fold greater, respectively, in the neonates fed cholesterol. Hepatic sterol synthesis rates were suppressed 65% in cholesterol-fed neonates compared with control neonates. By 20 days of age, plasma and liver cholesterol concentrations were still greater and sterol synthesis rates were now suppressed maximally in neonates fed cholesterol compared with control neonates. The expression level of an apolipoprotein B-containing lipoprotein receptor (low-density lipoprotein receptor-related protein) was greater and the mature form of the sterol regulatory element-binding protein-2 was similar in livers of 20-day-old control neonates compared with control neonates at 10 days of age. To test whether the change in sterol balance in the neonatal period had a lasting effect on hepatic sterol metabolism, all animals were weaned on a low-cholesterol diet. At 70 days of age, hepatic sterol synthesis rates, plasma lipoprotein and liver cholesterol concentrations, and bile acid pool sizes and compositions were measured. Sterol balance in the adults was similar between animals fed either diet early in life, as demonstrated by a lack of difference in any parameter measured. Thus, even though dietary cholesterol suppressed hepatic sterol synthesis rates dramatically in the neonatal hamster, the change has little impact on sterol balance later in life.

Aging↗

PubMed1999

Enhanced sterol-acyl transferase activity promotes sterol accumulation in Saccharomyces cerevisiae.

The sterol-acyl transferase encoded by the gene ARE2 was transcriptionally deregulated in the yeast Saccharomyces cerevisiae to understand its role in sterol storage and sterol enrichment. Our results show that sterols can indeed be enriched in yeast by enhancing the capacity of the cells to esterify sterols. ARE2 overexpression had no impact on the accumulation of the early sterols such as lanosterol, but influenced the later intermediates and the end product ergosterol. Thus an enhanced conversion of free sterols to their esterified counterparts may provide a tool to increase the overall sterol content of the yeast cell. We have previously shown that the overexpression of a truncated version of the key enzyme of the early sterol pathway, HMG-CoA reductase (HMG1), leads to an increase in the early sterols such as lanosterol and zymosterol. The simultaneous deregulation of both genes in one strain produces a cumulative effect in that both early and late sterols are enhanced. Karmellae-like structures can be detected when Are2p is overexpressed. Are2p therefore constitutes a new member of the karmellae-inducing protein family.

Acyltransferases↗

PubMed1985

Modulation of yeast plasma membrane composition of a yeast sterol auxotroph as a function of exogenous sterol.

Plasma membranes isolated from a yeast sterol auxotroph (RD5-R) grown on 1, 5, and 15 micrograms ml-1 exogenous concentrations of sterol showed no discontinuity in plots of steady-state fluorescence anisotropy. Liposomes constructed from phospholipid and sterol extracted from RD5-R grown on different sterols indicated that exogenously supplied sterol modulated cellular phospholipids such that lipid-phase transitions were avoided. Liposomes derived from sterol and phospholipid extracted from the same culture exhibited no lipid-phase transitions. However, when phospholipid extracted from a culture grown on a specific sterol was mixed with sterol extracted from a heterologous culture grown on a different sterol to form liposomes, discontinuities were detected in the anisotropy measurements of the liposomes produced. Quantitative analyses revealed that the exogenously supplied sterol coordinately regulated specific phospholipid species, fatty acid composition, and sterol to phospholipid ratios in yeast auxotrophs.

Cell Membrane↗

PubMed1994

Mechanistic studies of sterol carrier protein-2 effects on L-cell fibroblast plasma membrane sterol domains.

The factors which regulate intermembrane sterol domains and exchange in biomembranes are not well understood. A new fluorescent sterol exchange assay allowed correlation of changes in polarization to sterol transfer. Analysis of spontaneous sterol exchange between L-cell plasma membranes indicated two exchangeable and one very slowly or nonexchangeable sterol domain. The exchangeable domains exhibited half-times of 23 and 140 min with fractional contributions of 5 and 30%, respectively. Sterol carrier protein-2 (SCP-2) enhanced sterol exchange between L-cell plasma membranes and altered sterol domain size in a concentration dependent manner. Previous model membrane studies indicate that SCP-2 alters sterol domains and exchange through interaction with anionic phospholipids. In contrast to these observations, the ionic shielding agents KCl, low pH, or neomycin were either totally or partially ineffective inhibitors of SCP-2 action in L-cell plasma membrane exchanges. Thus the mechanism of SCP-2 in sterol transfer appears to be less charge dependent in L-cell plasma membranes than in model membranes. The cholesterol lowering drug probucol was also capable of altering the sterol exchange kinetics.

Amino Acid Sequence↗

PubMed1986

Cholesterol precursor sterols, plant sterols, and cholestanol in human bile and gallstones.

Biliary and gallstone sterol compositions were analyzed in 20 consecutive cholecystectomized patients. The main intention was to identify and quantitate noncholesterol sterols and to compare the sterol patterns of the two sources. Cholesterol comprised approximately 97% of the stone and gallbladder bile sterols; the remainder were from plant sterols, cholestanol, and cholesterol precursors, mainly lathosterol and methylsterols (two methostenols, lanosterol, and two dimethylsterols). Desmosterol and delta 8-lathosterol were also identified in both the bile and the gallstones. The sterol patterns of the bile and gallstones differed markedly. Thus, the contents of the two lathosterols and the two methostenols were clearly higher in the gallstones, whereas lanosterol stayed almost totally, and other minor sterols were preferentially, in the bile. In fact, the gallstone methylsterols consisted mainly of the two methostenols, a pattern usually seen in esterified methylsterols in serum. The core and matrix of the stone, and large and small stones as well, had only a small variation in their sterol composition within each individual, suggesting that the pattern of the noncholesterol sterol precipitation remains the same during the growth of the stone. Centrifugation of the bile revealed sedimentation of methylsterols with the stonelike sterol pattern. It can be speculated that the soluble and poorly soluble bile sterols have different hepatic origins and that the similarity between (a) methylsterols in the stone and sediment and (b) esterified methylsterols in serum points to a common hepatic site of origin.

Bile↗