Showing papers on "Sterol published in 2006"

Multiple rare variants in NPC1L1 associated with reduced sterol absorption and plasma low-density lipoprotein levels.

Abstract: An approach to understand quantitative traits was recently proposed based on the finding that nonsynonymous (NS) sequence variants in certain genes are preferentially enriched at one extreme of the population distribution. The NS variants, although individually rare, are cumulatively frequent and influence quantitative traits, such as plasma lipoprotein levels. Here, we use the NS variant technique to demonstrate that genetic variation in NPC1L1 contributes to variability in cholesterol absorption and plasma levels of low-density lipoproteins (LDLs). The ratio of plasma campesterol (a plant sterol) to lathosterol (a cholesterol precursor) was used to estimate relative cholesterol absorption in a population-based study. Nonsynonymous sequence variations in NPC1L1 were five times more common in low absorbers (n = 26 of 256) than in high absorbers (n = 5 of 256) (P < 0.001). The rare variants identified in low absorbers were found in 6% of 1,832 African-Americans and were associated with lower plasma levels of LDL cholesterol (LDL-C) (96 ± 36 mg/dl vs. 105 ± 36 mg/dl; P = 0.005). These data, together with prior findings, reveal a genetic architecture for LDL-C levels that does not conform to current models for quantitative traits and indicate that a significant fraction of genetic variance in LDL-C is due to multiple alleles with modest effects that are present at low frequencies in the population. cholesterol absorption complex trait genetic architecture mutation plant sterol

Nonvesicular sterol movement from plasma membrane to ER requires oxysterol-binding protein–related proteins and phosphoinositides

Abstract: Sterols are moved between cellular membranes by nonvesicular pathways whose functions are poorly understood. In yeast, one such pathway transfers sterols from the plasma membrane (PM) to the endoplasmic reticulum (ER). We show that this transport requires oxysterol-binding protein (OSBP)–related proteins (ORPs), which are a large family of conserved lipid-binding proteins. We demonstrate that a representative member of this family, Osh4p/Kes1p, specifically facilitates the nonvesicular transfer of cholesterol and ergosterol between membranes in vitro. In addition, Osh4p transfers sterols more rapidly between membranes containing phosphoinositides (PIPs), suggesting that PIPs regulate sterol transport by ORPs. We confirmed this by showing that PM to ER sterol transport slows dramatically in mutants with conditional defects in PIP biosynthesis. Our findings argue that ORPs move sterols among cellular compartments and that sterol transport and intracellular distribution are regulated by PIPs.

Dietary acetic acid reduces serum cholesterol and triacylglycerols in rats fed a cholesterol-rich diet.

Abstract: To investigate the efficacy of the intake of vinegar for prevention of hyperlipidaemia, we examined the effect of dietary acetic acid, the main component of vinegar, on serum lipid values in rats fed a diet containing 1 % (w/w) cholesterol. Animals were allowed free access to a diet containing no cholesterol, a diet containing 1 % cholesterol without acetic acid, or a diet containing 1 % cholesterol with 0.3 % (w/w) acetic acid for 19 d. Then, they were killed after food deprivation for 7 h. Cholesterol feeding increased serum total cholesterol and triacylglycerol levels. Compared with the cholesterol-fed group, the cholesterol and acetic acid-fed group had significantly lower values for serum total cholesterol and triacylglycerols, liver ATP citrate lyase (ATP-CL) activity, and liver 3-hydroxy-3-methylglutaryl-CoA content as well as liver mRNA levels of sterol regulatory element binding protein-1, ATP-CL and fatty acid synthase (P<0.05). Further, the serum secretin level, liver acyl-CoA oxidase expression, and faecal bile acid content were significantly higher in the cholesterol and acetic acid-fed group than in the cholesterol-fed group (P<0.05). However, acetic acid feeding affected neither the mRNA level nor activity of cholesterol 7alpha-hydroxylase. In conclusion, dietary acetic acid reduced serum total cholesterol and triacylglycerol: first due to the inhibition of lipogenesis in liver; second due to the increment in faecal bile acid excretion in rats fed a diet containing cholesterol.

First Synthesis of Free Cholesterol−BODIPY Conjugates

Abstract: Analogues of cholesterol (compounds 1 and 2) and coprostanol (compound 3) containing the BODIPY fluorophore in the aliphatic tail of the free sterol have been synthesized starting with bisnorcholen...

SREBPs: sterol-regulated transcription factors.

Abstract: Studies of the feedback regulation of cholesterol synthesis in animals have led to the identification of a unique family of membrane-bound transcription factors, sterol regulatory element binding proteins (SREBPs) ([Brown and Goldstein, 1997][1]). In the presence of cholesterol, SREBPs are

Cytochrome P450 CYP710A Encodes the Sterol C-22 Desaturase in Arabidopsis and Tomato

Abstract: Δ22-Unsaturated sterols, containing a double bond at the C-22 position in the side chain, occur specifically in fungi and plants. Here, we describe the identification and characterization of cytochrome P450s belonging to the CYP710A family as the plant C-22 desaturase. Recombinant proteins of CYP710A1 and CYP710A2 from Arabidopsis thaliana and CYP710A11 from tomato (Lycopersicon esculentum) were expressed using a baculovirus/insect system. The Arabidopsis CYP710A1 and tomato CYP710A11 proteins exhibited C-22 desaturase activity with β-sitosterol to produce stigmasterol (CYP710A1, Km = 1.0 μM and kinetic constant [kcat] = 0.53 min−1; CYP710A11, Km = 3.7 μM and kcat = 10 min−1). In Arabidopsis transgenic lines with CYP710A1 and CYP710A11 overexpression, stigmasterol levels increased by 6- to 32-fold. Arabidopsis CYP710A2 was able to produce brassicasterol and stigmasterol from 24-epi-campesterol and β-sitosterol, respectively. Sterol profiling analyses for CYP710A2 overexpression and a T-DNA insertion event into CYP710A2 clearly demonstrated in planta that CYP710A2 was responsible for both brassicasterol and stigmasterol production. Semiquantitative PCR analyses and promoter:β-glucuronidase transgenic approaches indicated strict tissue/organ-specific regulation for each CYP710A gene, implicating differential tissue distributions of the Δ22-unsaturated sterols in Arabidopsis. Our results support the possibility that the CYP710 family may encode P450s of sterol C-22 desaturases in different organisms.

Arabidopsis CYP90B1 catalyses the early C-22 hydroxylation of C27, C28 and C29 sterols.

Abstract: Arabidopsis dwf4 is a brassinosteroid (BR)-deficient mutant, and the DWF4 gene encodes a cytochrome P450, CYP90B1. We report the catalytic activity and substrate specificity of CYP90B1. Recombinant CYP90B1 was produced in Escherichia coli, and CYP90B1 activity was measured in an in vitro assay reconstituted with NADPH-cytochrome P450 reductase. CYP90B1 converted campestanol (CN) to 6-deoxocathasterone, confirming that CYP90B1 is a steroid C-22 hydroxylase. The substrate specificity of CYP90B1 indicated that sterols with a double bond at positions C-5 and C-6 are preferred substrates compared with stanols, which have no double bond at the position. In particular, the catalytic efficiency (k[subscript cat]/K[subscript m]) of CYP90B1 for campesterol (CR) was 325 times greater than that for CN. As CR is more abundant than CN in planta, the results suggest that C-22 hydroxylation of CR before C-5[alpha] reduction is the main route of BR biosynthetic pathway, which contrasts with the generally accepted route via CN. In addition, CYP90B1 showed C-22 hydroxylation activity toward various C₂₇₋₂₉ sterols. Cholesterol (C₂₇ sterol) is the best substrate, followed by CR (C₂₈ sterol), whereas sitosterol (C₂₉ sterol) is a poor substrate, suggesting that the substrate preference of CYP90B1 may explain the discrepancy between the in planta abundance of C₂₇/C₂₈/C₂₉ sterols and C₂₇/C₂₈/C₂₉ BRs.

Cholesterol Hydroxyl Group Is Found To Reside in the Center of a Polyunsaturated Lipid Membrane

Abstract: Cholesterol and saturated lipid species preferentially partition into liquid ordered microdomains, such as lipid rafts, away from unsaturated lipid species for which the sterol has less affinity in the surrounding liquid-disordered membrane. To observe how cholesterol interacts with unsaturated phospholipids, we have determined, from one-dimensional neutron scattering length density profiles, the depth of cholesterol in phosphatidylcholine (PC) bilayers with varying amounts of acyl chain unsaturation. Through the use of [2,2,3,4,4,6-2H6]-labeled cholesterol, we show that in 1-palmitoyl-2-oleoylphosphatidylcholine (16:0−18:1 PC), 1,2-dioleoylphosphatidylcholine (18:1−18:1 PC), and 1-stearoyl-2-arachidonylphosphatidylcholine (18:0−20:4 PC) bilayers the center of mass of the deuterated sites is approximately 16 A from the bilayer center. This location places the hydroxyl group of the sterol moiety at the hydrophobic/hydrophilic bilayer interface, which is the generally accepted position. In dramatic contrast...

Stigmasterol reduces plasma cholesterol levels and inhibits hepatic synthesis and intestinal absorption in the rat.

Abstract: Plant sterols compete with cholesterol (cholest-5-en-3beta-ol) for intestinal absorption to limit absorption and lower plasma concentrations of cholesterol. Stigmasterol (24-ethyl-cholesta-5,22-dien-3beta-ol; Delta(22) derivative of sitosterol [24-ethyl-cholest-5-en-3beta-ol]), but not campesterol (24-methyl-cholest-5-en-3beta-ol) and sitosterol, is reported to inhibit cholesterol biosynthesis via inhibition of sterol Delta(24)-reductase in human Caco-2 and HL-60 cell lines. We studied the effect of feeding 0.5% stigmasterol on plasma and liver sterols and intestinal cholesterol and sitosterol absorption in 12 wild-type Kyoto (WKY) and 12 Wistar rats. After 3 weeks of feeding, cholesterol and sitosterol absorption was determined in 6 rats from each group by plasma dual-isotope ratio method. After 3 more weeks, plasma and hepatic sterols and hepatic enzyme activities were determined in all rats. After feeding stigmasterol, baseline plasma cholesterol was 1.3 times and plant sterols 3 times greater in WKY compared with Wistar rats. Stigmasterol feeding lowered plasma cholesterol by approximately 11%, whereas plasma campesterol and sitosterol levels were virtually unchanged in both rat strains, and stigmasterol constituted 3.2% of plasma sterols in WKY rats and 1% in Wistar rats. After 6 weeks of feeding, cholesterol and sitosterol absorption decreased 23% and 30%, respectively, in WKY, and 22% and 16%, respectively, in the Wistar rats as compared with untreated rats. The intestinal bacteria in both rat strains metabolized stigmasterol to mainly the 5beta-H stanol (>40%), with only small amounts of 5alpha-H derivative (approximately 1.5%), whereas the C-22 double bond was resistant to bacterial metabolism. Hepatic stigmasterol levels increased from 11 microg/g liver tissue to 104 mug/g in WKY rats and from 5 microg/g liver tissue to 21 microg/g in Wistar rats. 3-Hydroxy-3-methylglutaryl coenzyme A reductase activity was suppressed 4-fold in the WKY and almost 1.8-fold in Wistar rats, cholesterol 7alpha-hydroxylase activity was suppressed 1.6-fold in the WKY and 3.5-fold in Wistar rats, whereas cholesterol 27-hydroxylase activity was unchanged after feeding. In conclusion, stigmasterol, when fed, lowers plasma cholesterol levels, inhibits intestinal cholesterol and plant sterol absorption, and suppresses hepatic cholesterol and classic bile acid synthesis in Wistar as well as WKY rats. However, plasma and hepatic incorporation of stigmasterol is low.

Dual Effects of Plant Steroidal Alkaloids on Saccharomyces cerevisiae

Abstract: Many plant species accumulate sterols and triterpenes as antimicrobial glycosides. These secondary metabolites (saponins) provide built-in chemical protection against pest and pathogen attack and can also influence induced defense responses. In addition, they have a variety of important pharmacological properties, including anticancer activity. The biological mechanisms underpinning the varied and diverse effects of saponins on microbes, plants, and animals are only poorly understood despite the ecological and pharmaceutical importance of this major class of plant secondary metabolites. Here we have exploited budding yeast (Saccharomyces cerevisiae) to investigate the effects of saponins on eukaryotic cells. The tomato steroidal glycoalkaloid alpha-tomatine has antifungal activity towards yeast, and this activity is associated with membrane permeabilization. Removal of a single sugar from the tetrasaccharide chain of alpha-tomatine results in a substantial reduction in antimicrobial activity. Surprisingly, the complete loss of sugars leads to enhanced antifungal activity. Experiments with alpha-tomatine and its aglycone tomatidine indicate that the mode of action of tomatidine towards yeast is distinct from that of alpha-tomatine and does not involve membrane permeabilization. Investigation of the effects of tomatidine on yeast by gene expression and sterol analysis indicate that tomatidine inhibits ergosterol biosynthesis. Tomatidine-treated cells accumulate zymosterol rather than ergosterol, which is consistent with inhibition of the sterol C(24) methyltransferase Erg6p. However, erg6 and erg3 mutants (but not erg2 mutants) have enhanced resistance to tomatidine, suggesting a complex interaction of erg mutations, sterol content, and tomatidine resistance.

Antimicrobial activity of resin acid derivatives.

Abstract: The wide potential of resin acids as bioactive agents gave rise to a growing effort in the search for new applications of the natural forms and their derivatives. In some of these compounds, the antimicrobial activity is associated to the presence in the molecules of functional groups such as the hydroxyl, aldehyde, and ketone or to their cis or trans configurations. The resin acid family covers a spectrum of antimicrobial activities against several microorganisms, from bacteria to fungi, in which the mode of action was studied by electron microscopy. The morphological alterations are consistent with an unspecific mode of action causing inhibition of the fungal growth or damaging the fungal cells in parallel with a mechanism of resistance based on the retention of the compound by the lipid accumulation. The sterol composition of phytopathogenic fungi Botrytis cinerea and Lophodermium seditiosum treated with methyl cis-7-oxo-deisopropyldehydroabietate revealed the presence of ergosterol (M+ 396) and dihydroergosterol (M+ 398) in both cultures showing that this compound did not interfere with the ergosterol metabolic pathway of both fungi.

Characterization of several hazelnut (Corylus avellana L.) cultivars based in chemical, fatty acid and sterol composition

Abstract: Nineteen cultivars of hazelnuts (Corylus avellana L.) collected during the 2001 crop, from Vila Real, Portugal, were analysed for chemical composition, including moisture, total oil content, crude protein, ash, carbohydrates and nutritional value. Fat was the predominant component, ranging from 59.3 to 69.0%. Total oil was extracted and analysed for fatty acid and sterol compositions and oxidative stability. Fatty acid and sterol compositions were determined by Gas–Liquid Chromatography coupled to a Flame Ionisation Detector (GLC/FID). Monounsaturated fatty acids, particularly oleic acid, were predominant (78.7–84.6%). Total phytosterol content ranged from 133.8 to 263.0 mg/100 g of oil. Among the nine sterols identified and quantified, β-sitosterol was the major one with a mean percentage of 83.6%, while Δ5-avenasterol and campesterol were the second and the third components of the group with mean values of 6.1 and 5.8%, respectively. Since hazelnut oil can be used in olive oil adulteration, the values obtained were compared with published mean values of olive oils from different geographical origins.

Dietary fish protein alters blood lipid concentrations and hepatic genes involved in cholesterol homeostasis in the rat model.

Abstract: It is known that various dietary plant proteins are capable of influencing the lipid metabolism of human subjects and animals when compared with casein. Less, however, is known about the effects of fish protein on the cholesterol and triacylglycerol metabolism. Therefore, two experiments were conducted in which rats were fed diets containing 200 g of either fish protein, prepared from Alaska pollack fillets, or casein, which served as control, per kilogram, over 20 and 22 d, respectively. As parameters of lipid metabolism, the concentrations of cholesterol and triacylglycerols in the plasma and liver, the faecal excretion of bile acids and the hepatic expression of genes encoding proteins involved in lipid homeostasis were determined. In both experiments, rats fed fish protein had higher concentrations of cholesteryl esters in the liver, a lower concentration of cholesterol in the HDL fraction (rho > 1.063 kg/l) and lower plasma triacylglycerol concentrations than rats fed casein (P < 0.05). The gene expression analysis performed in experiment 2 showed that rats fed fish protein had higher relative mRNA concentrations of sterol regulatory element-binding protein (SREBP)-2, 3-hydroxy-3-methylglutaryl coenzyme A reductase, LDL receptor, apo AI, scavenger receptor B1 and lecithin-cholesterol-acyltransferase in their liver than did rats fed casein (P < 0.05). The faecal excretion of bile acids and the mRNA concentrations of cholesterol 7alpha-hydroxylase, SREBP-1c and corresponding target genes were not altered. These findings show that fish protein had multiple effects on plasma and liver lipids that were at least in part caused by an altered expression of the hepatic genes involved in lipid homeostasis.

Reduction of Cholesterol Absorption by Dietary Plant Sterols and Stanols in Mice Is Independent of the Abcg5/8 Transporter

Abstract: Dietary supplementation with plant sterols, stanols, and their esters reduces intestinal cholesterol absorption, thus lowering plasma LDL cholesterol concentration in humans. It was suggested that these beneficial effects are attributable in part to induction of genes involved in intestinal cholesterol transport, e.g., Abcg5 and Abcg8, via the liver X receptor (LXR), but direct proof is lacking. Male C57BL/6J mice were fed a purified diet (control), diets containing cholesterol (0.12 g/100 g) only, or in combination with either plant sterols or stanols (0.5 g/100 g) for 4 wk. Plant sterols and stanols dramatically increased neutral fecal sterol excretion (2.2 and 1.4-fold, respectively, compared with cholesterol-fed mice; P < 0.05). Cholesterol and cholesterol ester concentrations were higher in livers of mice fed cholesterol compared with controls (+135% and +925%; P < 0.05). Plant sterols and stanols completely prevented cholesterol accumulation as well as induction of LXR target genes in liver. Feeding plant sterols and stanols did not alter intestinal expression of Abcg5, Abcg8, or other LXR target genes nor of Npc1l1. Fractional cholesterol absorption in Abcg5-/- mice was reduced to the same extent by dietary plant sterols (49%) as in wild-type littermates (44%). Plant sterol and stanol-induced reduction of cholesterol absorption in mice is not associated with upregulation of intestinal LXR target genes nor is it influenced by Abcg5-deficiency. Our data indicate that dietary plant sterols and stanols inhibit cholesterol absorption within the intestinal lumen independently of LXR.