Critical role of ring structure in the differential uptake of cholesterol and plant sterols by membrane preparations in vitro

Bexarotene Binds to the Amyloid Precursor Protein Transmembrane Domain, Alters Its α-Helical Conformation, and Inhibits γ-Secretase Nonselectively in Liposomes

Bexarotene is a pleiotropic molecule that has been proposed as an amyloid-β (Aβ)-lowering drug for the treatment of Alzheimer's disease (AD). It acts by upregulation of an apolipoprotein E (apoE)-mediated Aβ clearance mechanism. However, whether bexarotene induces removal of Aβ plaques in mouse models of AD has been controversial. Here, we show by NMR and CD spectroscopy that bexarotene directly interacts with and stabilizes the transmembrane domain α-helix of the amyloid precursor protein (APP) in a region where cholesterol binds. This effect is not mediated by changes in membrane lipid packing, as bexarotene does not share with cholesterol the property of inducing phospholipid condensation. Bexarotene inhibited the intramembrane cleavage by γ-secretase of the APP C-terminal fragment C99 to release Aβ in cell-free assays of the reconstituted enzyme in liposomes, but not in cells, and only at very high micromolar concentrations. Surprisingly, in vitro, bexarotene also inhibited the cleavage of Notch1, another major γ-secretase substrate, demonstrating that its inhibition of γ-secretase is not substrate specific and not mediated by acting via the cholesterol binding site of C99. Our data suggest that bexarotene is a pleiotropic molecule that interfere with Aβ metabolism through multiple mechanisms.

Effects of Phytosterol Supplementation on Serum Levels of Lipid Profiles, Liver Enzymes, Inflammatory Markers, Adiponectin, and Leptin in Patients Affected by Nonalcoholic Fatty Liver Disease: A Double-Blind, Placebo-Controlled, Randomized Clinical Trial

OBJECTIVE

Considering the high prevalence of nonalcoholic fatty liver disease and based on the evidence about the role of dietary cholesterol in liver inflammation, and also with regard to the effect of phytosterols on the metabolism of cholesterol, we aimed at exploring the therapeutic potential of phytosterol supplementation against nonalcoholic fatty liver disease.

METHOD

Thirty-eight patients with nonalcoholic fatty liver disease were randomly divided into two groups: The phytosterol group (n = 19) received a 1.6-g phytosterol supplement daily and the control group (n = 19) received 1.6 g starch daily as placebo for an 8-week period. Blood samples of all patients were taken at baseline (week 0) and at the end of the study (week 8) for measurement of lipid profiles, liver enzymes, inflammatory markers, adiponectin, and leptin.

RESULTS

Phytosterol supplementation significantly improved the levels of low-density lipoprotein cholesterol, aspartate aminotransferase, alanine aminotransferase, and tumor necrosis factor alpha compared to the placebo group. On the other hand, there were no significant differences between the two groups in total cholesterol, triglycerides, high-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol, ratios of low-density lipoprotein cholesterol/high-density lipoprotein cholesterol and total cholesterol/high-density lipoprotein cholesterol, gamma-glutamyl transferase, interleukin 6, high-sensitivity C-reactive protein, adiponectin, and leptin.

CONCLUSIONS

The present study suggested that daily consumption of 1.6 g phytosterols efficiently lowers low-density lipoprotein cholesterol, aspartate aminotransferase, alanine aminotransferase, and tumor necrosis factor alpha in patients with nonalcoholic fatty liver disease.

Investigating the effectiveness of different tea types from various thyme kinds (Origanum onites, Thymbra spicata and Satureja cuneifolia) on anemia and anticholesterolemic activity

In a study on villagers settled on the outskirts of the Taurus Mountains and whose source of living is thyme, it was revealed that the villagers excessively consumed thyme by adding it to their tea and many of their foods; high incidences of anemia was found among these villagers. In this study, 42 male adult Wistar albino rats weighing 200–250 g were used. The rats were divided to six equal groups as follows: control, cholesterol (Chol), 80 mg/kg Origanum onites Labiatae (OOL), 80 mg/kg Thymbra spicata Labiatae (TSL), 80 mg/kg Satureja cuneifolia Labiatae (SCL), and 160 mg/kg TSL, and each group consisted of seven rats. The control group was fed with normal pellet feed. The Chol group and all the other groups, except for the control group, were fed with 2% cholesterol-containing pellet feed. Physiological serum of 4 ml was given to the control and Chol group, wheile 80 mg/kg of thymes tea was given to the OOL group, TSL group, and SCL group, and 160 mg/kg of thymes tea was given to the TSL group by means of a gavage for 30 days. In the blood samples, the hematologic parameters and the biochemical parameters of serum glucose, blood urea nitrogen, creatinine, total protein, albumin, iron (I), total iron-binding capacity, aminotransferase aspartate, alanine aminotransferase, alkaline phosphatase, lactate dehydrogenase, total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein cholesterol, triglyceride, and oxidized LDL levels were examined. The kidney and liver tissues were examined histopathologically. The results of the study showed that different types of thymes had an antihypercholesterolemic effect. In addition to the anemic effect detected in group TSL and the mild granular degeneration found in the liver of 80 mg/kg SCL group, distinct granular degeneration was observed in 160 mg/kg TSL group.

A high legume low glycemic index diet improves serum lipid profiles in men

Clinical studies have shown that fiber consumption facilitates weight loss and improves lipid profiles; however, the beneficial effects of high fermentable fiber low glycemic index (GI) diets under conditions of weight maintenance are unclear. In the Legume Inflammation Feeding Experiment, a randomized controlled cross-over feeding study, 64 middle-aged men who had undergone colonoscopies within the previous 2 years received both a healthy American (HA) diet (no legume consumption, fiber consumption = 9 g/1,000 kcal, and GI = 69) and a legume enriched (1.5 servings/1,000 kcal), high fiber (21 g/1,000 kcal), low GI (GI = 38) diet (LG) in random order. Diets were isocaloric and controlled for macronutrients including saturated fat; they were consumed each for 4 weeks with a 2-4 week break separating dietary treatments. Compared to the HA diet, the LG diet led to greater declines in both fasting serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) (P < 0.001 and P < 0.01, respectively). Insulin-resistant (IR) subjects had greater reductions in high density lipoprotein cholesterol (HDL-C; P < 0.01), and triglycerides (TAG)/HDL-C (P = 0.02) after the LG diet, compared to the HA diet. Insulin-sensitive (IS) subjects had greater reductions in TC (P < 0.001), LDL-C (P < 0.01), TC/HDL-C (P < 0.01), and LDL-C/HDL-C (P = 0.02) after the LG diet, compared to the HA diet. In conclusion, a high legume, high fiber, low GI diet improves serum lipid profiles in men, compared to a healthy American diet. However, IR individuals do not achieve the full benefits of the same diet on cardiovascular disease (CVD) lipid risk factors.

Investigating the membrane orientation and transversal distribution of 17beta-estradiol in lipid membranes by solid-state NMR

17beta-Estradiol (E(2)) is a potent estrogen, which modulates many important cellular functions by binding to specific estrogen receptors located in the cell nucleus and also on the plasma membrane. We have studied the membrane interaction of E(2) using a combination of solid-state NMR methods. (2)H NMR results indicate that E(2) does not cause a condensation effect of the surrounding phospholipids, which is contrary to the effects of cholesterol, and only very modest E(2) induced alterations of the membrane structure were detected. (1)H magic-angle spinning NMR showed well resolved signals from E(2) as well as of POPC in the membrane-lipid layer. Two-dimensional NOESY spectra revealed intense cross-peaks between E(2) and the membrane lipids indicating that E(2) is stably inserted into the membrane. The determination of intermolecular cross-relaxation rates revealed that E(2) is broadly distributed in the membrane with a maximum of the E(2) distribution function in the upper chain region of the membrane. We conclude that E(2) is highly dynamic in lipid membranes and may undergo rotations as it exhibits two polar hydroxyl groups on either side of the molecule.

Cholesterol-reducer, antioxidant and liver protective effects of Thymbra spicata L. var. spicata

ETHNOPHARMACOLOGICAL RELEVANCE

Thymbra spicata is a member of the Lamiaceae family; leaves of this plant have recently gained much popularity as a remedy to combat hypercholesterolaemia.

AIM OF THE STUDY

To evaluate the antihypercholesterolaemic, antioxidant and anti-steatohepatitic activities of the diethyl ether (DEE), ethyl acetate (EtOAc) and remaining aqueous (RA) extracts from Thymbra spicata var. spicata in mice.

MATERIALS AND METHODS

In this study, diethyl ether, ethyl acetate and remaining aqueous extracts of Thymbra spicata L. var. spicata P.H.Davis (Lamiaceae) were evaluated for the effects on the plasma total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglyceride (TG) and glucose; blood malondialdehyde (MDA) and reduced glutathione (GSH); erythrocyte superoxide dismutase (SOD) and catalase activity (CAT) in mice fed with high-fat diet (HFD).

RESULTS

The HFD induced an increase in plasma TC, TG, LDL, MDA concentrations compared to control group. However, administration of DEE with HFD reduced TC, LDL, TG and MDA concentrations, while increased HDL concentration, as well as GSH, SOD and CAT activities compared to HFD. The other extract from the plant was RA, which also showed a similar activity profile with DEE except CAT. On the other hand, administration of EtOAc extract with HFD decreased plasma TC, TG and MDA, while GSH concentration was increased. Histopathologically, best liver conditions were observed in DEE and lesser in RA extracts. Based on the results obtained in this investigation it is suggested that the DEE and partially RA extracts of Thymbra spicata var. spicata displayed significant antihypercholesterolaemic, antioxidant and anti-steatohepatitic activities. HPLC analysis of the DEE extract of Thymbra spicata var. spicata revealed the presence of carvacrol (44.13%).

CONCLUSION

The observed cholesterol-reducer, antioxidant and liver protective effects of the DEE and partially of RA extracts of Thymbra spicata which contain mainly carvacrol indicates that these extracts possess some potential medicinal value and explain their ethnomedical use.

A high-saturated fat diet enriched with phytosterol and pectin affects the fatty acid profile in guinea pigs

This paper presents the results of a study whose aim was to test the effects of several doses of pectin and phytosterols on the body weight gain and the FA content in female guinea pigs. The treatments resulted from supplementing with pectin and plant sterol a guinea pig diet (rich in saturated FA), following a 3 x 3 factorial design, with three levels of pectin (0, 3.67 and 6.93%) and three levels of phytosterols (0, 1.37, and 2.45%). Seventy-two female Dunkin Hartley guinea pigs were randomly assigned to the treatment groups (8 animals/group), the duration of the treatment being 4 wk. Pectin dietary intake led to a significant increase in body weight (P < 0.001), food consumption (P = 0.025), and feed efficiency (P < 0.001), but no influence of phytosterols on weight gain or food consumption was detected. We found a significant negative effect of the addition of phytosterols on lauric, myristic, and palmitic acid contents in feces, and a positive effect on their concentration in plasma and liver, but no significant effect on stearic acid content. Apparent FA absorption was assessed by calculating the ratio of FA in feces and diets that the absorption of the different FA could be compared, and the negative effect of phytosterol supplementation on these ratios, especially for lauric and myristic acids, was established.

Respective hydrolysis and esterification of esterified and free plant stanols occur rapidly in human intestine after their duodenal infusion in triacyl- or diacylglycerol

Esterification of dietary phytosterols and glycerols may affect intestinal absorption of cholesterol and non-cholesterol sterols. We infused plant stanol esters in triacylglycerol (TAG) (F1) and diacylglycerol (DG) (F2) oils, and free plant stanols in F1 and F2 (F3) to the duodenum of healthy human subjects and sampled the contents from the proximal jejunum (PJ). Free and ester sterols were analysed from the infusates, and intestinal contents before and after ultracentrifuge separation of oil, micelle and sediment phases. During the 60-cm intestinal passage, over 40% of plant stanol esters were hydrolysed (P < 0.05) but around 30% of the infused free plant stanols (P < 0.05) and up to 40% of cholesterol (P < 0.05) were esterified in PJ after infusions. TAG in F1 favoured accumulation of plant stanol esters in the oil phase of the PJ aspirates as compared with respective values of F2 and F3 (P < 0.05 for both). About one third of free plant stanols of F3 had been esterified (P < 0.05) and 17% precipitated mainly in free form in the PJ aspirates (P < 0.05 compared with F1 and F2). In conclusion, DG- and TAG-oils had no profound superiority over each other as intestinal carriers regarding hydrolysis/esterification of administered plant stanol esters and cholesterol and their partition in oil, micellar and sediment phases in the PJ. The unesterified plant stanols experienced partial esterification and sedimentation during their intestinal passage, which might influence their biochemical properties in that segment of the gut where cholesterol is absorbed.

Antihypercholesterolaemic and antioxidant activity assessment of some plants used as remedy in Turkish folk medicine

Ethanolic and aqueous extracts from five plant species used in Turkish traditional medicine were evaluated for in vivo hypercholesterolaemic and antioxidant activities: Agrostemma githago L., Potentilla reptans L., Thymbra spicata var. spicata L., Urtica dioica L. and Viscum album var. album L. We assayed the effects of the administration of plant extracts on serum total cholesterol, triglyceride, HDL-C, LDL-C, glucose, AST and ALT concentrations in mice fed with cholesterol-rich diet. In addition, plasma TAA, MDA and NO(x) levels in the same animals were assayed. All the aqueous plant extracts did not affect the serum cholesterol concentration. However, the ethanolic extracts of Agrostemma githago, Thymbra spicata and Viscum album decreased the serum cholesterol concentration in the mice fed with high-cholesterol diet without inducing any gastric damage. The ethanolic extracts of Thymbra spicata, Viscum album, Potentilla reptans and Urtica dioica and the aqueous extract of Agrostemma githago increased the serum HDL concentration, whereas the ethanolic extracts of Agrostemma githago, Thymbra spicata, Viscum album and Urtica dioica decreased the serum LDL-C concentration. Thymbra spicata and Viscum album were observed to decrease the serum triglyceride concentration. Among the plant extracts studied, the ethanolic extracts of Thymbra spicata significantly decreased the MDA level in mice. The ethanolic extract of Potentilla reptans increased in NO(x). None of these plants showed statistically prominent activity on plasma TAA. Results of the present study indicated that the ethanolic extracts of Agrostemma githago, Thymbra spicata and Viscum album showed potent hypocholesterolaemic activity in the mice fed with a diet containing high-cholesterol.

Dietary phytosterols reduce probucol-induced atherogenesis in apo E-KO mice

We have previously shown strong pro-atherogenic effects of probucol in apolipoprotein E-knockout (apo E-KO) mice. The aims of the present study were to investigate whether (a) dietary phytosterols reduce probucol-induced atherogenesis and (b) beneficial interactions exist between these agents. Male apo E-KO mice fed with an atherogenic diet supplemented with phytosterols or probucol or their combination for 14 weeks. Single therapy with either phytosterols or probucol resulted in a 25% reduction in plasma total cholesterol (TC) concentrations as compared to the control group. The effects of the combination therapy were more profound (60% reduction). While phytosterols reduced atherogenesis by 60%, probucol caused an increase of 150% in atherogenesis. Addition of phytosterols to probucol substantially reduced pro-atherogenic effects of probucol. This was associated with improved high density lipoprotein (HDL) concentrations. The ratio of TC to HDL cholesterol was markedly reduced in the combination therapy group as compared to the probucol-treated group. A strong positive association between the ratio of TC to HDL cholesterol and the extent of atherosclerotic lesions was observed. The coronary arteries of the probucol-treated group showed various stages of atherogenesis from infiltration of monocytes into intima to complete occlusion of the vessel by atheromatous lesions. Such pathological findings were not observed in the combination therapy group. Approximately 40% of the mice in the probucol-treated group and 10% of the animals in the combination therapy group developed skin lesions. Further studies warrant the investigation of the underlying mechanisms of the observed beneficial interactions between dietary phytosterols and probucol.

Diffusion of cholesterol and its precursors in lipid membranes studied by 1H pulsed field gradient magic angle spinning NMR

Cholesterol content is critical for membrane functional properties. We studied the influence of cholesterol and its precursors desmosterol and lanosterol on lateral diffusion of phospholipids and sterols by1H pulsed field gradients (PFG) magic angle spinning (MAS) NMR spectroscopy. The high resolution of resonances afforded by MAS NMR permitted simultaneous diffusion measurements on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and sterols. The cholesterol diffusion mirrored the DPPC behavior, but rates were slightly higher at all cholesterol concentrations. DPPC and cholesterol diffusion rates decreased and became cholesterol concentration dependent with the onset of liquid-ordered phase formation. The activation energies of diffusion in the coexistence region of liquid-ordered/liquid-disordered phases are higher by about a factor of 2 compared to pure DPPC and to the pure liquid-ordered state formed at higher cholesterol concentrations. We assume that the higher activation energies are a reflection of lipid diffusion across domain boundaries. In lanosterol- and desmosterol-containing membranes, the DPPC and sterol diffusion coefficients are somewhat higher. Whereas the desmosterol rates are only slightly higher than those of DPPC, the lanosterol diffusion rates significantly exceed DPPC rates, indicating a weaker interaction between DPPC and lanosterol.

Familial hypercholesterolemia in children

PURPOSE OF THIS REVIEW

This review provides an update on recent advances in the diagnosis and management of children with familial hypercholesterolemia.

RECENT FINDINGS

A large cross-sectional cohort study of paediatric familial hypercholesterolemia demonstrated that affected children had a 5-fold more rapid increase of carotid arterial wall intima-media thickness during childhood years than their affected siblings. This faster progression led to a significant deviation in terms of intima-media thickness from the age of 12 years and onwards. Low-density lipoprotein cholesterol was a strong and independent predictor of carotid artery intima-media thickness in these children, which confirms the pivotal role of low-density lipoprotein cholesterol for the development of atherosclerosis. In this condition lipid lowering by statin therapy is accompanied by carotid intima-media thickness regression in familial-hypercholesterolemic children, which suggests that initiation of low-density lipoprotein cholesterol-reducing medication in childhood already can inhibit or possibly reduce the faster progression of atherosclerosis. Furthermore, these trials demonstrated that statins are safe and do not impair growth or sexual development in these children. Conversely, products containing plant sterols reduced low-density lipoprotein cholesterol levels by 14%, but did not improve endothelial dysfunction as assessed by flow-mediated dilatation.

SUMMARY

Children with familial hypercholesterolemia clearly benefit from lipid-lowering strategies. Statins are safe agents and have been proven to reduce elevated low-density lipoprotein cholesterol levels significantly. In addition, statins improve surrogate markers for atherosclerosis. Therefore these agents should become the pivotal therapy in children with familial hypercholesterolemia.

Phytosterols in the prevention of human pathologies

Coronary heart disease is a major health problem in developed countries. Many studies have shown that elevated serum concentrations of total or low-density-lipoprotein cholesterol (LDL cholesterol) are high risk factors, whereas high concentrations of high-density-lipoprotein cholesterol (HDL cholesterol) or a low LDL to HDL cholesterol ratio may protect against coronary heart disease. Plant sterols and stanols derived from vegetable oils or wood pulp have been shown to lower total and LDL cholesterol levels in humans by inhibiting cholesterol absorption from the intestine. These findings may lead to new therapeutic options to treat hypercholesterolemia. In addition, phytosterols may influence cell growth and apoptosis of tumor cells. However, they can interfere with the absorption of fat soluble vitamins and carotenoids.

The potential of fluorescent and spin-labeled steroid analogs to mimic natural cholesterol

Cholesterol analogs are often used to investigate lipid trafficking and membrane organization of native cholesterol. Here, the potential of various spin (doxyl moiety) and fluorescent (7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group) labeled cholesterol analogs as well as of fluorescent cholestatrienol and the naturally occurring dehydroergosterol to mimic the unique properties of native cholesterol in lipid membranes was studied in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes by electron paramagnetic resonance, nuclear magnetic resonance, and fluorescence spectroscopy. As cholesterol, all analogs undergo fluctuating motions of large amplitude parallel to the bilayer normal. Native cholesterol keeps a strict orientation in the membrane with the long axis parallel to the bilayer normal. Depending on the chemical modification or the position of the label, cholesterol analogs may adopt an "up-side-down" orientation in the membrane or may even fluctuate between "upright" and up-side-down orientation by rotational motions about the short axis not typical for native cholesterol. Those analogs are not able to induce a comparable condensation of phospholipid membranes as known for native cholesterol revealed by 2H nuclear magnetic resonance. However, cholesterol-induced lipid condensation is one of the key properties of native cholesterol, and, therefore, a well suited parameter to assess the potential of steroid analogs to mimic cholesterol. The study points to extreme caution when studying cholesterol behavior by the respective analogs. Among seven analogs investigated, only a spin-labeled cholesterol with the doxyl group at the end of the acyl chain and the fluorophore cholestatrienol mimic cholesterol satisfactorily. Dehydroergosterol has a similar upright orientation as cholesterol and could be used at low concentration (about 1 mol %), at which its lower potential to enhance lipid packing density does not perturb membrane organization.

Metabolic effects of plant sterols and stanols (Review)

High serum LDL cholesterol concentration is a major risk factor for cardiovascular complications. This risk can be lowered by diet. In this respect foods containing plant sterol or stanol esters can be useful for mildly- and hypercholesteraemic subjects. Plant sterols and stanols, which are structurally related to cholesterol, decrease the incorporation of dietary and biliary cholesterol into micelles. This lowers cholesterol absorption. Furthermore, these components increase ABC-transporter expression, which may also contribute to the decreased cholesterol absorption. Consequently, cholesterol synthesis and LDL receptor activity increase, which ultimately leads to decreased serum LDL cholesterol concentrations. Animal studies have further shown that these dietary components may also lower atherosclerotic lesion development. Plant sterols and stanols also lower plasma lipid-standardized concentrations of the hydrocarbon carotenoids, but not those of the oxygenated cartenoids and tocopherols. Also, vitamin A and D concentrations are not affected. Although absorption of plant sterols and stanols (0.02-3.5%) is low compared to cholesterol (35-70%), small amounts are found in the circulation and may influence other physiological functions. However, there is no consistent evidence that plant sterols or stanols can change the risk of colon or prostate cancer, or immune status. In conclusion, plant sterols and stanols effectively reduce serum LDL cholesterol and atherosclerotic risk. In addition potential effects of plant sterols and stanols on other metabolic processes remain to be elucidated.

Differential effects of ergosterol and cholesterol on Cdk1 activation and SRE-driven transcription

Cholesterol is essential for cell growth and division, but whether this is just a consequence of its use in membrane formation or whether it also elicits regulatory actions in cell cycle machinery remains to be established. Here, we report on the specificity of this action of cholesterol in human cells by comparing its effects with those of ergosterol, a yeast sterol structurally similar to cholesterol. Inhibition of cholesterol synthesis by means of SKF 104976 in cells incubated in a cholesterol-free medium resulted in cell proliferation inhibition and cell cycle arrest at G2/M phase. These effects were abrogated by cholesterol added to the medium but not by ergosterol, despite that the latter was used by human cells and exerted similar homeostatic actions, as the regulation of the transcription of an SRE-driven gene construct. In contrast to cholesterol, ergosterol was unable to induce cyclin B1 expression, to activate Cdk1 and to resume cell cycle in cells previously arrested at G2. This lack of effect was not due to cytotoxicity, as cells exposed to ergosterol remained viable and, upon supplementing with UCN-01, an activator of Cdk1, they progressed through mitosis. However, in the presence of suboptimal concentrations of cholesterol, ergosterol exerted synergistic effects on cell proliferation. This is interpreted on the basis of the differential action of these sterols, ergosterol contributing to cell membrane formation and cholesterol being required for Cdk1 activation. In summary, the action of cholesterol on G2 traversal is highly specific and exerted through a mechanism different to that used for cholesterol homeostasis, reinforcing the concept that cholesterol is a specific regulator of cell cycle progression in human cells.

Solubilization of phytosterols in diacylglycerol versus triacylglycerol improves the serum cholesterol-lowering effect

OBJECTIVE

This study was performed to investigate the difference in the serum-cholesterol- and triglyceride-lowering activities between phytosterols dissolved in diacylglycerol (PS/DG) and dispersed in triacylglycerol (PS/TG). The effects of the solvent on the concentrations of serum beta-sitosterol and campesterol were examined.

DESIGN

The study had a randomised crossover design.

SUBJECTS

Twelve healthy normocholesterolemic or moderately hypercholesterolemic men aged 29-50 y participated in this study.

INTERVENTIONS

For 2 weeks before the test period (designated as the control period), all subjects consumed control mayonnaise (PS free) daily with supper and were randomly assigned to two groups for the 2 week test period; one group was given mayonnaise containing PS (500 mg/day) dissolved in DG (10 g/day), and the other mayonnaise containing PS (500 mg/day) dispersed in TG (10 g/day). After a wash out period consuming control PS-free mayonnaise for 4 weeks, the groups were reversed for 2 weeks.

RESULTS

PS/TG feeding had no effect on the serum cholesterol level. In contrast, PS/DG feeding significantly reduced the total and LDL cholesterol levels from the initial value of 5.57 to 5.31 mmol/l (4.7%; P<0.05) and from 3.69 to 3.39 mmol/l (7.6%; P<0.05), respectively. Moreover, the degree of total cholesterol reduction induced by PS/DG feeding in the test period was significantly greater than that induced by PS/TG feeding (P<0.05). In addition, the serum beta-sitosterol and campesterol concentrations did not change during the PS/TG or PS/DG feeding periods.

CONCLUSIONS

Dissolution of PS in DG had a better serum cholesterol lowering effect than dissolution in TG.

SPONSORSHIP

Kao Corporation.

Cyclodextrin-catalyzed extraction of fluorescent sterols from monolayer membranes and small unilamellar vesicles

This study examined the kinetics of sterol desorption from monolayer and small unilamellar vesicle membranes to 2-hydroxypropyl-beta-cyclodextrin. The sterols used include cholesterol, dehydroergosterol (ergosta-5,7,9,(11),22-tetraen-3beta-ol) and cholestatrienol (cholesta-5,7,9,(11)-trien-3beta-ol). Desorption rates of dehydroergosterol and cholestatrienol from pure sterol monolayers were faster (3.3-4.6-fold) than the rate measured for cholesterol. In mixed monolayers (sterol: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine 30:70 mol%), both dehydroergosterol and cholestatrienol desorbed faster than cholesterol. clearly indicating a difference in interfacial behavior of these sterols. In vesicle membranes desorption of dehydroergosterol was slower than desorption of cholestatrienol, and both rates were markedly affected by the phospholipid composition. Desorption of sterols was slower from sphingomyelin as compared to phosphatidylcholine vesicles. Desorption of fluorescent sterols was also faster from vesicles prepared by ethanol-injection as compared to extruded vesicles. The results of this study suggest that dehydroergosterol and cholestatrienol differ from cholesterol in their membrane behavior, therefore care should be exercised when experimental data derived with these probes are interpreted.

Effect of sterols and fatty acids on growth and triglyceride accumulation in 3T3-L1 cells

Epidemiologic studies suggest a role of dietary fat in the development of obesity. Populations that consume Western diets have a higher incidence of obesity than do those that consume a vegetarian type diet such as Asians. Because dietary fats are made up mostly of triglyceride with minor lipids such as sterols, the objective of this study was to examine the effect of different fatty acids, the main component of triglycerides, and sterols on cell growth and triglyceride accumulation in 3T3-L1 cells. These cells are being used as an in vitro model for studying obesity because upon differentiation in culture they accumulate triglycerides. Cells were seeded at 5,000 cells/cm(2) and supplemented with 0, 3, 10, or 30 microM of oleic acid, elaidic acid, or docosahexaenoic acid (DHA). Similarly, cells were supplemented with 0, 2, 8, or 16 microM of cholesterol, beta-sitosterol (SIT), or campesterol. Cell growth was measured by cell counting. Cellular triglycerides were measured by the Oil Red O method. In some experiments, fatty acids were combined with sterols and growth and triglyceride content were assessed as described. Both DHA and SIT had inhibitory effects on 3T3-L1 cell growth. However, SIT was more potent than DHA in this regard. The combination of SIT and oleic acid was the most potent in inhibiting cell growth and increasing cellular triglyceride content. It is concluded that cell growth and triglyceride accumulation in 3T3-L1 cells is influenced by fatty acid and sterols. When used alone, DHA and SIT inhibit cell growth. SIT was more effective in this process than was DHA. There was an interaction between fatty acids and sterols. The most effective combination inhibiting cell growth and triglyceride concentration was the combination of SIT and oleic acid. This combination reduced cell growth and increased triglyceride accumulation. These data suggest that diets rich in both monounsaturated fatty acids and phytosterols may play a role in controlling obesity.

Cholesterol-lowering efficacy of a sitostanol-containing phytosterol mixture with a prudent diet in hyperlipidemic men

BACKGROUND

Dietary plant sterols (phytosterols) have been shown to lower plasma lipid concentrations in animals and humans. However, the effect of phytosterol intake from tall oil on cholesterol and phytosterol metabolism has not been assessed in subjects fed precisely controlled diets.

OBJECTIVE

Our objective was to examine the effects of sitostanol-containing phytosterols on plasma lipid and phytosterol concentrations and de novo cholesterol synthesis rate in the context of a controlled diet.

DESIGN

Thirty-two hypercholesterolemic men were fed either a diet of prepared foods alone or a diet containing 1.7 g phytosterols/d for 30 d in a parallel study design.

RESULTS

No overall effects of diet on total cholesterol concentrations were observed, although concentrations were lower with the phytosterol-enriched than with the control diet on day 30 (P < 0.05). LDL-cholesterol concentrations on day 30 had decreased by 8.9% (P < 0.01) and 24.4% (P < 0.001) with the control and phytosterol-enriched diets, respectively. HDL-cholesterol and triacylglycerol concentrations did not change significantly. Moreover, changes in circulating campesterol and beta-sitosterol concentrations were not significantly different between phytosterol-fed and control subjects. In addition, there were no significant differences in fractional (0.091 +/- 0.028 and 0.091 +/- 0.026 pool/d, respectively) or absolute (0.61 +/- 0.24 and 0.65 +/- 0.23 g/d, respectively) synthesis rates of cholesterol observed between control and phytosterol-fed subjects.

CONCLUSION

Addition of blended phytosterols to a prudent North American diet improved plasma LDL-cholesterol concentrations by mechanisms that did not result in significant changes in endogenous cholesterol synthesis in hypercholesterolemic men.

Dietary sitostanol reciprocally influences cholesterol absorption and biosynthesis in hamsters and rabbits

The aim of this study was to examine the efficacy of variable dietary sitostanol (SI) concentrations on cholesterol absorption, synthesis and excretion rates in two animal models. Hamsters and rabbits were fed semi-purified diets supplemented with cholesterol and 1% (w/w) phytosterols containing either 0.007, 0.17, 0.8 or 1% (w/w) SI. The control (0% (w/w) SI) groups consumed the same diets but no phytosterols were added. The dual-isotope plasma ratio of [13C]- and [18O]cholesterol and deuterium incorporation methods were applied to measure simultaneously cholesterol absorption and fractional synthesis, respectively. Plasma total cholesterol levels were lower in rabbits and hamsters fed 0.8 and 1% (w/w) SI, respectively, as compared to their controls. Percent cholesterol absorption was lower (P = 0.03) in hamsters fed 1% (w/w) SI (42.5 +/- 13.3%) than control (65.1 +/- 13.4%). Moreover, cholesterol excretion in the feces was 77 and 57% higher (P = 0.017) in the 1% (w/w) SI- relative to control- and 0.17% (w/w) SI-fed groups, respectively. In rabbits, cholesterol excretion was 64% higher (P = 0.018) in 0.8% (w/w) SI- compared with control-fed groups. Fractional synthesis rate was higher (P = 0.033) in hamsters fed 1% (w/w) SI (0.116 +/- 0.054 pool day(-1)) as compared to control (0.053 +/- 0.034 pool day(-1)). However, cholesterol synthesis rates did not vary among groups fed variable concentrations of SI. In rabbits, percent cholesterol absorption and its fractional synthesis rate varied but did not reach significance. Fractional synthesis rate in hamsters was correlated (r = -0.32, P = 0.03) with percent cholesterol absorption. In conclusion, dietary SI exhibited a dose-dependent action in inhibiting cholesterol absorption while increasing cholesterol excretion and upregulating cholesterogenesis in hamsters resulting in lower circulating lipid levels.

Fluorescence properties of cholestatrienol in phosphatidylcholine bilayer vesicles

The fluorescent sterol delta 5,7,9,(11)-cholestatrien-3 beta-ol (cholestatrienol) was incoporated into 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) small unilamellar vesicles (SUV) with and without cholesterol in order to monitor sterol-sterol interactions in model membranes. Previously another fluorescent sterol, dehydroergosterol (F. Schroeder, Y. Barenholz, E. Gratton and T.E. Thompson. Biochemistry 26 (1987) 2441), was used for this purpose. However, there is some concern that dehydroergosterol may not be the best analogue for cholesterol. Fluorescence properties of cholestatrienol in POPC SUV were highly sensitive to cholestatrienol purity. The fluorescence decay of cholestatrienol in the POPC SUV was analyzed by assuming either that the decay is comprised of a discrete sum of exponential components or that the decay is made up of one or more component's distribution of lifetimes. The decay for cholestatrienol in POPC SUV analyzed using distributions had a lower chi 2 value and was described by a two-component Lorentzian function with centers near 0.86 and 3.24 ns, and fractional intensities of 0.96 and 0.04, respectively. Both distributions were quite narrow, i.e., 0.05 ns full-width at half-maximum peak height. It is proposed that the two lifetime distributions are generated by separate continua of environments for the cholestatrienol molecule described by different dielectric constants. In the range 0-6 mol% cholestatrienol, the cholestatrienol underwent a concentration-dependent relaxation. This process was characterized by red-shifted absorption and maxima and altered ratios of absorption and fluorescence excitation maxima. Fluorescence quantum yield, lifetime, steady-state anisotropy, limiting anisotropy and rotational rate remained constant. In contrast, in POPC vesicles containing between 6 and 33 mol% cholestatrienol, the fluorescent cholestatrienol partially segregated, resulting in quenching. Thus, below 6 mol% cholestatrienol, the cholestatrienol appeared to behave in part as monomers exposed to some degree to the aqueous solvent in a sterol-poor domain within POPC bilayers. Since the lifetime did not decrease above 6 mol% cholestatrienol, the fluorescence at high mol% values of cholestatrienol was due to cholestatrienol in the sterol-poor domain. The fluorescence intensity, quantum yield, steady-state anisotropy, and limiting anisotropy of cholestatrienol in the sterol-poor domain decreased to limiting, nonzero values while the rotational rate increased to a limiting value. Thus, the sterol-poor domain became more disordered when it coexisted with the sterol-rich domain.(ABSTRACT TRUNCATED AT 400 WORDS)