Dietary plant stanol esters reduce VLDL cholesterol secretion and bile saturation in apolipoprotein E*3-Leiden transgenic mice

Dietary plant sterols prevented cholesterol gallstone formation in mice

Cholesterol gallstone disease is a common global condition. This study investigated the role of plant sterols (PS) in the prevention of gallstone formation and the underlying mechanisms. Adult male mice were fed a lithogenic diet (LD) alone or supplemented with PS (LD-ps), phospholipids (LD-pl) or both PS and phospholipids (LD-ps/pl) for 8 weeks. Incidences of gallstone formation were compared among the groups. Lipids in the bile, liver and serum were analyzed. The expression of genes involved in cholesterol absorption, transport and metabolism in the liver and small intestine was determined. The incidences of gallstone formation were 100% (10/10), 20% (2/10), 100% (10/10) and 40% (4/10) in the LD, LD-ps, LD-pl and LD-ps/pl groups, respectively. Serum cholesterol and intestinal cholesterol absorption were decreased in PS-supplemented mice. The expression of genes related to cholesterol transport and metabolism in the liver was down-regulated by dietary PS. PS supplementation decreased Niemann-Pick C1-like 1 expression in the small intestine and reduced intestinal cholesterol absorption. Our results demonstrated that PS could inhibit intestinal cholesterol absorption and thus prevent cholesterol gallstone formation.

One-Step Preparative Separation of Phytosterols from Edible Brown Seaweed Sargassum horneri by High-Speed Countercurrent Chromatography

Sargassum horneri, a sargassaceae brown alga, is one of the main species in the subtidal seaweeds flora extensively distributed in the Yellow and East China Sea. It has been proven that the phytosterols are an important class of bioactive substances in S. horneri. In this work, a counter-current chromatography approach is proposed for preparative separation of phytol and two analogue sterols from a crude extract of S. horneri. A two-phase solvent system composed of n-hexane-acetonitrile-methanol (5:5:6, v/v) was selected and optimized. The effects of rotary speed and flow rate on the retention of the stationary phase were carefully studied. Under the optimum conditions, phytol and two analogue sterols, fucosterol and saringosterol, were baseline separated, producing 19.8 mg phytol, 23.7 mg fucosterol, and 3.1 mg saringosterol from 300 mg of crude S. horneri extract in one-step separation. The purities of three target compounds were all above 85%. The structures of phytol and two sterols were identified by nuclear magnetic resonance spectroscopy.

Triglyceride-Lowering Response to Plant Sterol and Stanol Consumption

Phytosterols (PS) have long been recognized for their cholesterol-lowering action, however, recent work has highlighted triglyceride (TG)-lowering responses to PS that may have been overlooked in previous human interventions and mechanistic animal model studies. This review assesses the current state of knowledge regarding the effect of dietary PS supplementation on blood TG concentrations by examining the average therapeutic response, potential mechanisms, and metabolic and genetic factors that may contribute to inter-individual variability. Data from human intervention trials demonstrates that, compared to baseline concentrations, PS supplementation results in a variable TG-lowering response ranging from 0.8 to 28%. It is evident that hypertriglyceridemic individuals (>1.7 mmol/L) have a greater TG-lowering response to PS (11-28%) than subjects with normal plasma TG concentrations (0.8-7%). Although a genetic basis for the variable TG-lowering effects of PS is probable, there are only limited studies to draw on. The available data suggest that polymorphisms in the apolipoprotein E (apoE) gene may affect responsiveness, with PS-induced reductions in TG more readily evident in apoE2 than apoE3 or E4 subjects. Although only a minimal number of animal model studies have been conducted to specifically examine the mechanisms whereby PS may reduce blood TG concentrations, it appears that there may be multiple mechanisms involved including interruption of intestinal fatty acid absorption and modulation of hepatic lipogenesis and very low density lipoprotein packaging and secretion. In summary, the available data suggest that PS may be an effective therapy to lower blood TG, particularly in hypertriglyceridemic individuals. However, before PS can be widely recommended as a TG-lowering therapy, studies that are specifically powered and designed to fully access therapeutic responses and the mechanisms involved are required.

Acute intake of plant stanol esters induces changes in lipid and lipoprotein metabolism-related gene expression in the liver and intestines of mice

The kinetics of plant stanol uptake and routing in 8-week-old C57BL/6J mice were determined after a plant stanol ester gavage. In addition, acute changes in intestinal and hepatic gene expression were investigated. Mice were fed a plant sterol/stanol poor diet from weaning. At the age of 8 weeks, they received an oral gavage consisting of 0.25 mg cholesterol + 50 mg plant stanol esters dissolved in olive oil. Animals were euthanized at different time points. In a second comparable set-up, mesenteric lymph-cannulated versus sham-operated mice received the same oral gavage, which was now deuterium labeled. Intestinal and hepatic sitostanol concentrations increased within 15 min post-gavage. This rapid hepatic appearance was absent in lymph-cannulated mice, suggesting a very fast lymph-mediated uptake. Hepatic mRNA expression of SREBP2 and its target genes rapidly decreased, whereas expression of LXR target genes increased. The intestinal SREBP2 pathway was increased, whereas the expression of LXR target genes hardly changed. The fivefold and sixfold increased expression of intestinal LDLr and PCSK9 is suggestive of TICE activation. We conclude that in C57BL/6J mice plant stanol kinetics are fast, and affect intestinal and hepatic gene expression within 15 min postprandial after lymph-mediated uptake.

Serum TG-lowering properties of plant sterols and stanols are associated with decreased hepatic VLDL secretion

Plant sterols and stanols are structurally similar to cholesterol and when added to the diet they are able to reduce serum total- and LDL-cholesterol concentrations. They also lower serum triglyceride concentrations in humans, particularly under conditions of hypertriglyceridemia. The aim of this study was to unravel the mechanism by which plant sterols and stanols reduce serum triglyceride concentrations in high-fat diet (HFD) fed mice. Male C57BL/6J mice were fed HFD for 4 weeks. Subsequently, they received HFD, HFD supplemented with 3.1% plant sterol ester (PSE) or HFD supplemented with 3.1% plant stanol ester (PSA) for another three weeks. Both PSE and PSA feeding resulted in decreased plasma triglyceride concentrations compared with HFD, while plasma cholesterol levels were unchanged. Interestingly, hepatic cholesterol levels were decreased in the PSE/PSA groups compared with HFD and no differences were found in hepatic triglyceride levels between groups. To investigate the mechanism underlying the hypotriglyceridemic effects from PSE/PSA feeding, we measured chylomicron and VLDL secretion. PSE and PSA feeding resulted in reduced VLDL secretion, while no differences were found between groups in chylomicron secretion. In conclusion, our data indicate that plasma triglyceride-lowering resulting from PSE and PSA feeding is associated with decreased hepatic VLDL secretion.

Consumption of plant sterols reduces plasma and hepatic triglycerides and modulates the expression of lipid regulatory genes and de novo lipogenesis in C57BL/6J mice

To investigate emerging clinical data suggesting a triglyceride (TAG)-lowering response to plant sterol (PS) therapy, we characterized changes in TAG metabolism in 16 C57BL/6J mice fed a basal control diet (CON) or the CON diet supplemented with 2% PS for 6 wk. PS consumption reduced (p<0.05) plasma (-28%) and hepatic (-30%) TAG concentrations compared with CON mice. PS consumption increased (p<0.05) hepatic lipogenic gene expression (sterol-regulatory-element-binding protein 1c, 2.4-fold of CON; fatty acid synthase, 6.5-fold of CON) and de novo lipogenesis (4.51+/-0.72 versus 2.82+/-0.61%/day) compared with CON. PS consumption increased (p<0.05) fecal palmitate and stearate excretion and reduced body weight gain compared with CON mice. Although no change in the transcription of intestinal fatty acid absorptive genes was observed, peroxisome proliferator-activated receptor alpha mRNA was reduced (p<0.05, 2.0-fold of CON) in the PS-fed mice. In conclusion, PS-fed C57BL/6J mice showed pronounced reductions in plasma and hepatic TAG concentrations despite increases in hepatic lipogenic gene expression and de novo lipogenesis. Interference with intestinal fatty acid/TAG metabolism as suggested by increased fecal fatty acid loss and reduced weight gain may be associated with the TAG-lowering response to PS consumption.

Plant stanol esters lower serum triacylglycerol concentrations via a reduced hepatic VLDL-1 production

Plant stanol esters not only lower low density lipoprotein cholesterol but also have previously been shown to lower serum triacylglycerol (TAG) concentrations, especially in subjects with elevated TAG concentrations. To find a possible explanation, we explored changes in serum lipoprotein profiles, as measured with nuclear magnetic resonance. For this, serum samples from two parallel-designed controlled studies were evaluated before and 8 weeks after the consumption of plant stanol esters. In the first study, dyslipidemic metabolic syndrome subjects participated and in the second study normolipidemic subjects. In metabolic syndrome subjects, plant stanol esters lowered concentrations of large (>60 nm) and medium (35–60 nm) VLDL particles as compared to controls. In normolipidemic subjects, the serum concentration of large VLDL-1 particles was also lowered, although less pronounced. Based on these findings, we hypothesize that the effect of plant stanol esters on serum TAG concentrations origins from a lowered hepatic production of large TAG-rich VLDL-1 particles.

Disodium ascorbyl phytostanol phosphate (FM-VP4), a modified phytostanol, is a highly active hypocholesterolaemic agent that affects the enterohepatic circulation of both cholesterol and bile acids in mice

Disodium ascorbyl phytostanol phosphate (FM-VP4) is a synthetic compound derived from sitostanol and campestanol that has proved to be efficient as a cholesterol-lowering therapy in mice and human subjects. However, the mechanism of action of FM-VP4 remains unknown. The present study tests the ability of FM-VP4 to alter intestinal and liver cholesterol homeostasis in mice. Female C57BL/6J mice were fed either a control chow or a 2 % FM-VP4-enriched diet for 4 weeks. FM-VP4 reduced the in vivo net intestinal cholesterol absorption and plasma and liver cholesterol concentrations by 2.2-, 1.5- and 1.6-fold, respectively, compared with control mice. Furthermore, FM-VP4 also showed an impact on bile acid homeostasis. In FM-VP4 mice, liver and intestinal bile acid content was increased by 1.3- and 2.3-fold, respectively, whereas faecal bile acid output was 3.3-fold lower. FM-VP4 also increased the intestinal absorption of orally administered [3H]taurocholic acid to small intestine in vivo. Inhibition of intestinal cholesterol absorption by FM-VP4 was not mediated via transcriptional increases in intestine liver X receptor (LXR)-alpha, adenosine triphosphate-binding cassette transporter (ABC)-A1, ABCG5/G8 nor to decreases in intestinal Niemann-Pick C1-like 1 (NPC1L1) expression. In contrast, FM-VP4 up-regulated liver LXRalpha, ABCA1, ABCG5, scavenger receptor class BI (SR-BI) and hydroxymethylglutaryl coenzyme A reductase (HMGCoA-R) gene expression, whereas it down-regulated several farnesoid X receptor (FXR)-target genes such as cytochrome P450 family 7 subfamily A polypeptide 1 (CYP7A1) and Na+/taurocholate co-transporter polypeptide (NTCP). In conclusion, FM-VP4 reduced intestinal cholesterol absorption, plasma and liver cholesterol and affected bile acid homeostasis by inducing bile acid intestinal reabsorption and changed the liver expression of genes that play an essential role in cholesterol homeostasis. This is the first phytosterol or stanol that affects bile acid metabolism and lowers plasma cholesterol levels in normocholesterolaemic mice.

Effect of rapeseed oil-derived plant sterol and stanol esters on atherosclerosis parameters in cholesterol-challenged heterozygous Watanabe Heritable Hyperlipidaemic rabbits

Rapeseed oil (RSO) is a novel source of plant sterols, containing the unique brassicasterol in concentrations higher than allowed for plant sterol blends in food products in the European Union. Effects of RSO sterols and stanols on aortic atherosclerosis were studied in cholesterol-fed heterozygous Watanabe heritable hyperlipidaemic (Hh-WHHL) rabbits. Four groups (n18 per group) received a cholesterol-added (2 g/kg) standard chow or this diet with added RSO stanol esters (17 g/kg), RSO stanol esters (34 g/kg) or RSO sterol esters (34 g/kg) for 18 weeks. Feeding RSO stanol esters increased plasma campestanol (P < 0·001) and sitostanol (P < 0·001) and aortic campestanol (P < 0·05) compared with controls. Feeding RSO sterol esters increased concentrations of plasma campesterol (P < 0·001), sitosterol (P < 0·001) and brassicasterol (P < 0·001) and aortic campesterol (P < 0·01). Significantly lower plasma cholesterol (P < 0·001) was recorded in the treated groups after 3 weeks and throughout the study. LDL-cholesterol was reduced 50 % in the high-dose RSO sterol ester (P < 0·01) and high-dose RSO stanol ester (P < 0·001) groups compared with controls. Atherosclerotic lesions were found in three rabbits in each of the RSO stanol ester groups and in one in the RSO sterol ester group. Aortic cholesterol was decreased in the treated groups (P < 0·001) in response to lowering of plasma cholesterol induced by RSO sterol and stanol esters. In conclusion, RSO stanol and sterol esters with a high concentration of brassicasterol were well tolerated. They were hypocholesterolaemic and inhibited experimental atherosclerosis in cholesterol-fed Hh-WHHL rabbits. A significant uptake of plant sterols into the blood and incorporation of campesterol and campestanol into aortic tissue was recorded.

Berberine and plant stanols synergistically inhibit cholesterol absorption in hamsters

The present study was conducted to determine the efficacy and underlying mechanism of berberine (BBR), plant stanols (PS) and their combination on plasma lipids. Male Golden Syrian hamsters were randomly divided into 4 groups (n=15/group) and fed a cornstarch-casein-sucrose-based diet containing 0.15% cholesterol and 5% fat. Three treatment groups were supplemented with 0.17% (equivalent to 100mgkg(-1)d(-1)) BBR, 1% PS, or a combination of both (BBRPS) for 4wk. At the end of the study, plasma lipids were analyzed with enzymatic methods, cholesterol absorption and synthesis using stable isotope tracer methodology, and gene and protein expressions in the liver and small intestine using real-time PCR and Western blot, respectively. BBR and PS significantly lowered plasma total- and nonHDL-cholesterol levels, and BBRPS markedly improved cholesterol-lowering efficacy compared to BBR or PS alone. Further examinations revealed that BBR and PS both inhibited cholesterol absorption and by contrast, increased cholesterol synthesis, and exerted a synergistic action when they were combined. Plasma total or nonHDL-cholesterol levels were significantly correlated with cholesterol absorption rates. BBR upregulated sterol 27-hydroxlase gene expression and BBRPS increased both cholesterol-7alpha-hydroxylase and sterol 27-hydroxlase gene expressions. BBR and PS also synergistically decreased plasma triacylglycerides. These findings suggest that the cholesterol-lowering action of BBR might involve a combination of inhibition of cholesterol absorption and stimulation of bile acid synthesis. The combination of BBR and PS improves cholesterol-lowering efficacy through a synergistic action on cholesterol absorption, in addition to synergistically reducing plasma triacylglycerols in hamsters.

Phytosterols do not change susceptibility to obesity, insulin resistance, and diabetes induced by a high-fat diet in mice

Most studies have focused on the cholesterol-lowering activity of phytosterols; however, other biological actions have also been attributed to these plant compounds. In this study, we investigated whether phytosterols could delay (progression phase) and/or reverse (regression phase) insulin resistance or type 2 diabetes mellitus in an experimental mouse model of diet-induced obesity, insulin resistance, and diabetes. Body mass, plasma lipid levels, insulin resistance, and hyperglycemia were determined. Phytosterol intake did not improve these metabolic parameters. Therefore, we were unable to substantiate any protective effect of phytosterol intake on diabetes development or regression in the mouse model used.

Inhibiting intestinal NPC1L1 activity prevents diet-induced increase in biliary cholesterol in Golden Syrian hamsters

Niemann-Pick C1-like 1 (NPC1L1) facilitates the uptake of sterols into the enterocyte and is the target of the novel cholesterol absorption inhibitor, ezetimibe. These studies used the Golden Syrian hamster as a model to delineate the changes in the relative mRNA expression of NPC1L1 and other proteins that regulate sterol homeostasis in the enterocyte during and following cessation of ezetimibe treatment and also to address the clinically important question of whether the marked inhibition of cholesterol absorption alters biliary lipid composition. In hamsters fed a low-cholesterol, low-fat basal diet, the abundance of mRNA for NPC1L1 in the small intestine far exceeded that in other regions of the gastrointestinal tract, liver, and gallbladder. In the first study, female hamsters were fed the basal diet containing ezetimibe at doses up to 2.0 mg.day(-1).kg body wt(-1). At this dose, cholesterol absorption fell by 82%, fecal neutral sterol excretion increased by 5.3-fold, and hepatic and intestinal cholesterol synthesis increased more than twofold, but there were no significant changes in either fecal bile acid excretion or biliary lipid composition. The ezetimibe-induced changes in intestinal cholesterol handling were reversed when treatment was withdrawn. In a second study, male hamsters were given a diet enriched in cholesterol and safflower oil without or with ezetimibe. The lipid-rich diet raised the absolute and relative cholesterol levels in bile more than fourfold. This increase was largely prevented by ezetimibe. These data are consistent with the recent finding that ezetimibe treatment significantly reduced biliary cholesterol saturation in patients with gallstones.

Preferential campesterol incorporation into various tissues in apolipoprotein E*3-Leiden mice consuming plant sterols or stanols

Intestinal absorption of plant sterols and stanols is much lower as compared with that of cholesterol; and therefore, serum concentrations are low. Circulating plant sterols and stanols are incorporated into tissues. However, hardly any data are available about tissue distributions of individual plant sterols and stanols, particularly in relation to their serum concentrations. We therefore fed female apolipoprotein E*3-Leiden mice a control diet, a plant sterol-enriched diet (1g/100 g diet), or a plant stanol-enriched diet (1g/100 g diet) for 8 weeks. In the sterol group, serum cholesterol-standardized campesterol and sitosterol concentrations were, respectively, 8 and 7 times higher as compared with those in the control group. Consequently, the serum campesterol-sitosterol ratio remained essentially unchanged. Cholesterol-standardized plant sterol concentrations increased significantly in all analyzed tissues, except brain. However, the campesterol-sitosterol ratio also increased in all tissues (except in liver and spleen), suggesting that campesterol is preferentially incorporated over sitosterol in those tissues. For the stanol group, serum plant stanol concentrations also increased; but the increase was but less pronounced. We conclude that, in apolipoprotein E*3-Leiden mice, campesterol is preferentially incorporated into most tissues over sitosterol, which cannot be deduced from changes in serum concentrations.

New insights into the molecular actions of plant sterols and stanols in cholesterol metabolism

Plant sterols and stanols (phytosterols/phytostanols) are known to reduce serum low-density lipoprotein (LDL)-cholesterol level, and food products containing these plant compounds are widely used as a therapeutic dietary option to reduce plasma cholesterol and atherosclerotic risk. The cholesterol-lowering action of phytosterols/phytostanols is thought to occur, at least in part, through competition with dietary and biliary cholesterol for intestinal absorption in mixed micelles. However, recent evidence suggests that phytosterols/phytostanols may regulate proteins implicated in cholesterol metabolism both in enterocytes and hepatocytes. Important advances in the understanding of intestinal sterol absorption have provided potential molecular targets of phytosterols. An increased activity of ATP-binding cassette transporter A1 (ABCA1) and ABCG5/G8 heterodimer has been proposed as a mechanism underlying the hypocholesterolaemic effect of phytosterols. Conclusive studies using ABCA1 and ABCG5/G8-deficient mice have demonstrated that the phytosterol-mediated inhibition of intestinal cholesterol absorption is independent of these ATP-binding cassette (ABC) transporters. Other reports have proposed a phytosterol/phytostanol action on cholesterol esterification and lipoprotein assembly, cholesterol synthesis and apolipoprotein (apo) B100-containing lipoprotein removal. The accumulation of phytosterols in ABCG5/G8-deficient mice, which develop features of human sitosterolaemia, disrupts cholesterol homeostasis by affecting sterol regulatory element-binding protein (SREBP)-2 processing and liver X receptor (LXR) regulatory pathways. This article reviews the progress to date in studying these effects of phytosterols/phytostanols and the molecular mechanisms involved.

Examination of encapsulated phytosterol ester supplementation on lipid indices associated with cardiovascular disease

OBJECTIVE

As opposed to traditional food based delivery we examined the efficacy of ingesting encapsulated phytosterol esters on indices of lipid health in hypercholesterolemic adults.

METHODS

We performed a randomized, double-blinded, parallel-group, placebo-controlled, clinical intervention examining 54 men and women (20-70 y of age) with a low-density lipoprotein cholesterol (LDL-C) level > or =3.33 mmol/L. Participants were not taking cholesterol-lowering medications. Treatment consisted of ingesting 2.6 g of encapsulated phytosterol esters (n = 25) or a matching placebo (n = 29) for 12 wk.

RESULTS

Total cholesterol (TC) levels at baseline (mean +/- SD) were 6.29 +/- 0.7 mmol/L in the phytosterol group and 6.00 +/- 0.7 mmol/L in the placebo group. Baseline LDL-C levels were 4.27 +/- 0.7 mmol/L in the treatment group and 4.00 +/- 0.8 mmol/L in the placebo group. Analysis of variance and Tukey's least significant difference post hoc analyses revealed a significant within-group reduction in TC (-0.23 +/- 0.4 mmol/L, P < 0.05) and LDL-C (-0.22 +/- 0.5 mmol/L, P < 0.05) for the phytosterol treatment group. Mean reductions in TC and LDL-C were greater than placebo (P < 0.05). Percentages of change from baseline for TC were -3.52% (95% confidence interval -6.44 to -0.40) for phytosterol treatment and 2.64% (95% confidence interval 0.30-5.60) for placebo. Those for LDL-C were -5.00% (95% confidence interval -9.92 to -0.08) for phytosterol and 4.89 (95% confidence interval 0.24-9.5) for placebo. No other significant effects were observed.

CONCLUSION

Encapsulated phytosterol ester ingestion appears to positively modulate LDL-C. Given that the reduction in LDL-C was not as extensive as in food-based trials, future investigations should examine potential timing and dose issues relative to encapsulated delivery.

Hepatic ABCG5/G8 overexpression reduces apoB-lipoproteins and atherosclerosis when cholesterol absorption is inhibited

We previously reported that liver-specific overexpression of ABCG5/G8 in mice is not atheroprotective, suggesting that increased biliary cholesterol secretion must be coupled with decreased intestinal cholesterol absorption to increase net sterol loss from the body and reduce atherosclerosis. To evaluate this hypothesis, we fed low density lipoprotein receptor-knockout (LDLr-KO) control and ABCG5/G8-transgenic (ABCG5/G8-Tg)xLDLr-KO mice, which overexpress ABCG5/G8 only in liver, a Western diet containing ezetimibe to reduce intestinal cholesterol absorption. On this dietary regimen, liver-specific ABCG5/G8 overexpression increased hepatobiliary cholesterol concentration and secretion rates (1.5-fold and 1.9-fold, respectively), resulting in 1.6-fold increased fecal cholesterol excretion, decreased hepatic cholesterol, and increased (4.4-fold) de novo hepatic cholesterol synthesis versus LDLr-KO mice. Plasma lipids decreased (total cholesterol, 32%; cholesteryl ester, 32%; free cholesterol, 30%), mostly as a result of reduced non-high density lipoprotein-cholesterol and apolipoprotein B (apoB; 36% and 25%, respectively). ApoB-containing lipoproteins were smaller and lipid-depleted in ABCG5/G8-TgxLDLr-KO mice. Kinetic studies revealed similar 125I-apoB intermediate density lipoprotein/LDL fractional catabolic rates, but apoB production rates were decreased 37% in ABCG5/G8-TgxLDLr-KO mice. Proximal aortic atherosclerosis decreased by 52% (male) and 59% (female) in ABCG5/G8-TgxLDLr-KO versus LDLr-KO mice fed the Western/ezetimibe diet. Thus, increased biliary secretion, resulting from hepatic ABCG5/G8 overexpression, reduces atherogenic risk in LDLr-KO mice fed a Western diet containing ezetimibe. These findings identify distinct roles for liver and intestinal ABCG5/G8 in modulating sterol metabolism and atherosclerosis.

Dietary sphingolipids lower plasma cholesterol and triacylglycerol and prevent liver steatosis in APOE*3Leiden mice

BACKGROUND

The prevalence of dyslipidemia and obesity resulting from excess energy intake and physical inactivity is increasing. The liver plays a pivotal role in systemic lipid homeostasis. Effective, natural dietary interventions that lower plasma lipids and promote liver health are needed.

OBJECTIVE

Our goal was to determine the effect of dietary sphingolipids on plasma lipids and liver steatosis.

DESIGN

APOE*3Leiden mice were fed a Western-type diet supplemented with different sphingolipids. Body cholesterol and triacylglycerol metabolism as well as hepatic lipid concentrations and lipid-related gene expression were determined.

RESULTS

Dietary sphingolipids dose-dependently lowered both plasma cholesterol and triacylglycerol in APOE*3Leiden mice; 1% phytosphingosine (PS) reduced plasma cholesterol and triacylglycerol by 57% and 58%, respectively. PS decreased the absorption of dietary cholesterol and free fatty acids by 50% and 40%, respectively, whereas intestinal triacylglycerol lipolysis was not affected. PS increased hepatic VLDL-triacylglycerol production by 20%, whereas plasma lipolysis was not affected. PS increased the hepatic uptake of VLDL remnants by 60%. Hepatic messenger RNA concentrations indicated enhanced hepatic lipid synthesis and VLDL and LDL uptake. The net result of these changes was a strong decrease in plasma cholesterol and triacylglycerol. The livers of 1% PS-fed mice were less pale, 22% lighter, and contained 61% less cholesteryl ester and 56% less triacylglycerol than livers of control mice. Furthermore, markers of liver inflammation (serum amyloid A) and liver damage (alanine aminotransferase) decreased by 74% and 79%, respectively, in PS-fed mice.

CONCLUSION

Sphingolipids lower plasma cholesterol and triacylglycerol and protect the liver from fat- and cholesterol-induced steatosis.

Anti-Atherosclerotic Effect of Amlodipine, Alone and in Combination With Atorvastatin, in APOE*3-Leiden/hCRP Transgenic Mice

We investigated the pleiotropic effects of a calcium antagonist (amlodipine) on early atherosclerosis development in the presence and absence of an HMG-CoA-reductase inhibitor (atorvastatin) in apolipoprotein E*3-Leiden/human C-reactive protein (E3L/CRP) transgenic mice. Male E3L/CRP transgenic mice were fed a cholesterol-containing diet either with or without amlodipine and/or atorvastatin. After 31 weeks, atherosclerosis in the aortic root area was quantified. Treatment with amlodipine did not significantly lower blood pressure, but resulted in a 43% reduction (P < 0.03) of lesion area as compared with the untreated group. Treatment with atorvastatin resulted in an 80% reduction of lesion area as compared with the untreated group (P < 0.001). Combined treatment with amlodipine and atorvastatin decreased the lesion area by 93%, significantly more than either treatment alone (P < 0.008). Plasma C-reactive protein levels were mildly elevated, on average 10 +/- 6 mg/L, and did not differ between groups, neither on baseline nor during treatment. Treatment with amlodipine, independently of blood pressure lowering, reduced atherosclerosis development in E3L/CRP mice. Atorvastatin had a strong anti-atherosclerotic effect, whereas co-treatment with amlodipine enhanced this effect significantly. Plasma C-reactive protein levels were not affected by any of the three treatments.

22,23-Epoxides of Sitosterol and Related 7-Oxygenated Δ5-Sterols

(22S,23S)-22,23-Epoxysitosterol, (22R,23R)-22,23-epoxysitosterol, (22S,23S)-22,23-epoxy-7-ketositosterol, (22R,23R)-22,23-epoxy-7-ketositosterol, (22S,23S)-22,23-epoxy-7alpha-hydroxysitosterol, (22R,23R)-22,23-epoxy-7alpha-hydroxysitosterol, (22S,23S)-22,23-epoxy-7beta-hydroxysitosterol, and (22R,23R)-22,23-epoxy-7beta-hydroxysitosterol were synthesized. Their 1H and 13C NMR and the mass spectra of their trimethylsilyl derivatives were studied.

Response of apolipoprotein E*3‐Leiden transgenic mice to dietary fatty acids: combining liver proteomics with physiological data

Dietary fatty acids have a profound impact on atherosclerosis, but mechanisms are not fully understood. We studied the effects of a saturated fat diet supplemented with fish oil, trans10,cis12 conjugated linoleic acid (CLA), or elaidic acid on lipid and glucose metabolism and liver protein levels of APOE*3 Leiden transgenic mice, a model for lipid metabolism and atherosclerosis. Fish oil lowered plasma and liver cholesterol and triglycerides, plasma free fatty acids, and glucose but increased plasma insulin. CLA lowered plasma cholesterol but increased plasma and liver triglycerides, plasma beta-hydroxybutyrate, and insulin. Elaidic acid lowered plasma and liver cholesterol. Proteomics identified significant regulation of 65 cytosolic and 8-membrane proteins. Many of these proteins were related to lipid and glucose metabolism, and to oxidative stress. Principal component analysis revealed that fish oil had a major impact on cytosolic proteins, and elaidic acid on membrane proteins. Correlation analysis between physiological and protein data revealed novel clusters of correlated variables, among which a metabolic syndrome cluster. The combination of proteomics and physiology gave new insights in mechanisms by which these dietary fatty acids regulate lipid metabolism and related pathways, for example, by altering protein levels of long-chain acyl-CoA thioester hydrolase and adipophilin in the liver.

Changes in intestinal and liver global gene expression in response to a phytosterol-enriched diet

BACKGROUND

Dietary phytosterols are a recommended therapeutic option for decreasing plasma cholesterol. The increased activity of ATP-binding cassette (ABC) transporters ABCA1, ABCG5 and ABCG8, or, alternatively, a decrease in Niemann-Pick C1 Like 1 (NPC1L1) could mediate the reduction in intestinal cholesterol absorption caused by phytosterols. Other biological properties such as a direct immune modulatory activity have recently been ascribed to these plant compounds.

METHODS

To gain insight into the molecular effects of phytosterols, global genome-wide gene profiling and real-time RT-PCR studies were conducted in small intestines and livers of phytosterol-treated apolipoprotein E-deficient (apoE(-/-)) mice. Re-testing of the main results was performed in C57BL/6J and LDL receptor-deficient (LDLR(-/-)) mice.

RESULTS

Intestinal cholesterol absorption was decreased in all mouse models but plasma cholesterol was only decreased in apoE(-/-) and LDLR(-/-) mice. ABCA1, ABCG5, ABCG8 and NPC1L1 mRNA levels were slightly reduced in the intestine of phytosterol-treated apoE(-/-) and LDLR(-/-) mice, but increased in C57BL/6J-treated mice. Phytosterols changed genes involved in immune regulation in apoE(-/-) mice. However, these changes were less extensive in LDLR(-/-) mice and were not found in C57BL/6J mice.

CONCLUSIONS

Inhibition of intestinal cholesterol absorption by phytosterols is not mediated via transcriptional changes in ABCA1, ABCG5, ABCG8 or NPC1L1. Changes suggestive of immunomodulation are associated with the hypocholesterolemic effect of phytosterols and with apoE deficiency.

Delineation of molecular changes in intrahepatic cholesterol metabolism resulting from diminished cholesterol absorption

The absorption of cholesterol by the small intestine is a major route for the net entry of cholesterol into the body and can therefore affect the plasma low density lipoprotein-cholesterol (LDL-C) concentration. These studies used ezetimibe, a potent inhibitor of cholesterol absorption, to delineate the biochemical and molecular changes in intrahepatic metabolism and biliary lipid secretion when there is a major reduction in chylomicron cholesterol delivery to the liver. In female LDL receptor (LDLR)-deficient (LDLR-/-) mice fed a basal diet containing ezetimibe (0-10 mg/day/kg body weight), cholesterol absorption was reduced up to 91%, fecal neutral sterol excretion was increased up to 4.7-fold, and plasma total cholesterol concentrations decreased by up to 18%. Blocking cholesterol absorption prevented the accumulation of very low density lipoproteins and LDL in the circulation of LDLR-/- mice fed a lipid-rich diet. In female LDLR+/+ mice fed the lipid-rich diet with ezetimibe, the relative mRNA level for the LDLR in the liver was 2-fold greater than in matching mice given the lipid-rich diet alone. We conclude that in the mouse the reduction in plasma LDL-C levels induced by blocking cholesterol absorption reflects both a diminished rate of LDL-C production and a modest increase in hepatic LDLR expression.

Rosuvastatin Reduces Plasma Lipids by Inhibiting VLDL Production and Enhancing Hepatobiliary Lipid Excretion in ApoE*3-Leiden Mice

The present study was designed to investigate the lipid-lowering properties and mechanisms of action of a new HMG-CoA reductase inhibitor, rosuvastatin, in female ApoE*3-Leiden transgenic mice. Mice received a high fat/cholesterol (HFC) diet containing either rosuvastatin (0 [control], 0.00125%, 0.0025%, or 0.005% [w/w]) or 0.05% (w/w) lovastatin. The highest dose of rosuvastatin reduced plasma cholesterol and triglyceride levels by 39% and 42%, respectively, compared with the HFC control. Lovastatin had no effect on plasma cholesterol and triglyceride levels. In ApoE*3-Leiden mice on a chow diet, rosuvastatin (0.005% [w/w]) decreased plasma cholesterol levels by 35% without having an effect on triglyceride levels. On a chow diet, expression of genes involved in cholesterol biosynthesis and uptake in the liver was increased by rosuvastatin. Further mechanistic studies in HFC-fed mice showed that rosuvastatin treatment resulted in decreased hepatic VLDL-triglyceride and VLDL-apolipoprotein B production. VLDL lipid composition remained unchanged, indicating a reduction in the number of VLDL particles secreted. Lipolytic activity and expression of genes involved in cholesterol and triglyceride synthesis and beta-oxidation of fatty acids in the liver were not affected by rosuvastatin treatment, and hepatic lipid content did not change. However, activity of hepatic diacylglycerol acyltransferase was significantly decreased by 25% after rosuvastatin treatment. Moreover, biliary excretion of cholesterol, phospholipids, and bile acids was increased during treatment. The results indicate that rosuvastatin treatment in ApoE*3-Leiden mice on a HFC diet leads to redistribution of cholesterol and triglycerides in the body, both by reduced hepatic VLDL production and triglyceride synthesis and by enhanced hepatobiliary removal of cholesterol, bile acids, and phospholipids, resulting in substantial reductions in plasma cholesterol and triglyceride levels.

Absence of an atheroprotective effect of the garlic powder printanor in APOE*3-Leiden transgenic mice

Numerous animal studies have reported that garlic can protect against atherosclerosis. However, a comparable number of studies do not support this observation. This contradiction may result from differences in study design, use of different animal models, and use of different garlic formulations and preparations. Here, we investigated the effect of the chemically well-characterized and production-controlled garlic powder printanor on atherosclerosis in the APOE*3-Leiden transgenic mouse, a mouse model well suited for evaluating anti-atherosclerotic properties of drugs and food components under human-like conditions. APOE*3-Leiden mice were fed a Western diet supplemented with either 5 or 50 g kg(-1) printanor. As a reference, the commercially available fermented garlic kyolic was included (1.6 g kg(-1) diet). Treatment with printanor demonstrated reduced body weight, coinciding with increased feces production and fecal fatty acids excretion. Printanor and kyolic treatment did not affect plasma lipids, markers of inflammation (serum amyloid A, serum-soluble intercellular adhesion molecule-1, and blood-leukocytes tumor necrosis factor-alpha (TNFalpha) production) and vascular activation (plasma von Willebrand factor (vWF)). As analyzed after 28 weeks of treatment, printanor and kyolic did not affect atherosclerotic lesion type, area or composition. Under conditions relevant to the human situation, the well-characterized and production-controlled garlic powder printanor does not display hypolipidemic, anti-inflammatory or anti-atherosclerotic properties.

Diet as a risk factor for cholesterol gallstone disease

Cholesterol gallstone disease is a common condition in western populations. The etiology is multifactorial with interaction of genetic and environmental factors. Obesity, aging, estrogen treatment, pregnancy and diabetes are consistently associated to a higher risk. A number of dietary factors have been involved in the pathogenesis of cholelithiasis. In this article we summarize several studies that have evaluated the role of diet as a potential risk factor for gallstone formation, including energy intake, cholesterol, fatty acids, fiber, carbohydrates, vitamins and minerals, and alcohol intake. Consumption of simple sugars and saturated fat has been mostly associated to a higher risk, while fiber intake and moderate consumption of alcohol, consistently reduce the risk. The association between cholesterol intake and gallstone disease has been variable in different studies. The effects of other dietary factors are less conclusive; additional studies are therefore necessary to clarify their relevance in the pathogenesis of gallstone disease. Recent discoveries of the role of orphan nuclear receptors in the regulation of fatty acid and hepatic cholesterol metabolism and excretion open new perspectives for a better understanding of the role of dietary constituents on cholesterol gallstone formation. KEY TEACHING POINTS: The etiology of cholesterol gallstone disease is multifactorial with interaction between genome and environment. It has been postulated that dietary constituents are important determinants for the formation of lithogenic bile. Intake of high energy, simple sugar and saturated fat favors gallstone formation. Fiber and moderate consumption of alcohol reduce the risk. The role of orphan nuclear receptors in the regulation of hepatic cholesterol metabolism and excretion open new leads for understanding the role of dietary constituents on cholesterol gallstone formation.

Well-characterized garlic-derived materials are not hypolipidemic in APOE*3-Leiden transgenic mice

Garlic is reported to have beneficial effects on risk factors associated with cardiovascular disease, including normalization of plasma lipid levels. However, numerous studies do not support this beneficial effect of garlic on plasma lipids. This contradiction may result from the use of different garlic-derived materials, experimental designs, and/or animal models. The present study investigated the hypolipidemic effect of garlic-derived materials in APOE*3-Leiden mice, a model well suited for drug and dietary intervention studies of hyperlipidemia. APOE*3-Leiden mice were fed a garlic-derived sulfur-rich compound, either allicin (0.29 g.L drinking water(-1)) or diallyldisulfide (0.27 g.kg diet(-1)), or powdered garlic, of either the kwai (42 g.kg diet(-1)) or morado (42 g.kg diet(-1)) variety. The amounts of garlic-derived materials supplied allowed free intake of allicin or allicin equivalents (diallyldisulfide, kwai, or morado) at 44 mg.kg body wt(-1).d(-1). Mice were fed a nonpurified diet for 4 wk, followed by a Western diet for 8 wk, both supplemented with the garlic-derived materials. These diets had no consistent effect on plasma lipids and did not affect lipoprotein profiles, which are markers for whole-body cholesterol synthesis and intestinal sterol absorption. The current data indicate that the postulated effects of garlic on cardiovascular disease are not caused via modulation of plasma lipid levels.

Differential effects of amlodipine and atorvastatin treatment and their combination on atherosclerosis in ApoE*3-Leiden transgenic mice

This study was designed to investigate the potential antiatherosclerotic effects of the calcium antagonist amlodipine as compared with the HMG-CoA reductase inhibitor atorvastatin and the combination of both in ApoE*3-Leiden transgenic mice. Four groups of 15 ApoE*3-Leiden mice were put on a high-cholesterol diet. One group received 0.002% (wt/wt) amlodipine in the diet, which had no effect on plasma cholesterol levels. Another group received 0.01% (wt/wt) atorvastatin, resulting in a decrease of plasma cholesterol by 50% by a reduction in very low density lipoprotein production. The combination group received both amlodipine and atorvastatin. After 28 weeks, atherosclerosis in the aortic root was quantified. Treatment with amlodipine had no significant effect on atherosclerotic lesion area, whereas atorvastatin markedly reduced atherosclerosis by 77% compared with the control group. Atorvastatin also reduced inflammation markers. The combination of amlodipine and atorvastatin tended to reduce lesion area by 61% compared with the atorvastatin-only group; however, this effect did not reach statistical significance. Amlodipine treatment significantly reduced calcification in the lesions, whereas atorvastatin alone had no effect. The combination of amlodipine and atorvastatin resulted in a near absence of calcium deposits in the lesions. This study demonstrates that amlodipine treatment alone does not significantly reduce atherosclerotic lesion development. Atorvastatin was shown to have strong antiatherosclerotic effects, and cotreatment with amlodipine may potentiate the antiatherosclerotic effect of atorvastatin.

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.

Sterol absorption by the small intestine

PURPOSE OF REVIEW

Cholesterol absorption is a selective process in that plant sterols and other non-cholesterol sterols are absorbed poorly or not at all. Recent research on the sterol efflux pumps adenosine triphosphate-binding cassette transporter G5 and adenosine triphosphate-binding cassette transporter G8 has not only provided an explanation for this selectivity, but also, together with the discovery of a new class of cholesterol absorption inhibitor, has yielded new insights into the mechanisms that potentially regulate the flux of cholesterol across the enterocyte. This review discusses these recent developments and their importance to the regulation of whole body cholesterol homeostasis.

RECENT FINDINGS

Adenosine triphosphate-binding cassette transporters G5/8 regulate plant sterol absorption and also the secretion into bile of cholesterol and non-cholesterol sterols. Loss of adenosine triphosphate-binding cassette transporter G5/8 function results in sitosterolemia. Ezetimibe, a novel, potent and selective inhibitor of cholesterol absorption which is effective in milligram doses, lowers plasma plant sterol concentrations in sitosterolemic subjects, thus suggesting that this drug might be inhibiting the activity of a putative sterol permease in the brush border membrane of the enterocyte that actively facilitates the uptake of cholesterol as well as other non-cholesterol sterols.

SUMMARY

Intestinal cholesterol absorption represents a major route for the entry of cholesterol into the body's miscible pools and therefore can potentially impact the plasma LDL-cholesterol concentration. The combined use of agents that inhibit the absorption and synthesis of cholesterol provides a powerful new approach to the prevention and treatment of atherosclerosis.

The human cholesteryl ester transfer protein I405V polymorphism is associated with plasma cholesterol concentration and its reduction by dietary phytosterol esters

We examined the relationships of I405V cholesteryl ester transfer protein (CETP), Taq1B CETP and apolipoprotein (apo)E polymorphisms with the pattern of response to dietary plant sterol ester (PSE) by plasma lipids and CETP concentrations as well as lecithin-cholesterol acyltransferase (LCAT) activity. Subjects with moderate primary hypercholesterolemia (20-60 y old; 50 women; 10 men) consumed margarine (20 g/d) without (placebo) or with PSE (2.8 g/d = 1.68 g/d phytosterols) for 4 wk each period, in a crossover, double-blind study. Plasma CETP concentration was measured by ELISA; endogenous LCAT activity was expressed as the percentage of esterification (30 min incubation) of the subjects' (14)C-unesterified cholesterol HDL. PSE reduced concentrations of plasma total cholesterol (TC) (10%) and LDL cholesterol (LDL-C) (12%). In relation to the I405V CETP polymorphism, the percentage reductions in TC with consumption of PSE for the II, IV and VV phenotypes were 7.2, 4.2 and not significant, respectively, whereas LDL-C significant reductions occurred only for II (9.5%). However, the CETP concentration diminished only in the II phenotype.

Free phytosterols effectively reduce plasma and liver cholesterol in gerbils fed cholesterol

The potential of free phytosterols (including 20% stanols) to lower plasma and liver lipids was assessed in three experiments with gerbils fed diets containing cholesterol. The first explored the ability of phytosterols (0.5%) to block absorption of 0.05, 0.10, and 0.5% cholesterol. The second assessed the importance of consuming phytosterols (0.75%) simultaneously with cholesterol (0.15%). The third compared free phytosterols (0.75%) with similar levels of esterified sterols or stanols using diets containing 0.15% cholesterol. A 5:1 ratio of phytosterols:cholesterol effectively blocked cholesterol absorption when the dietary cholesterol load was moderate. Consuming a 5:1 ratio with every meal was more effective than receiving equal phytosterols in a 10:1 ratio every other day. Finally, free phytosterols dissolved in fat were as effective as esterified sterols and stanols in lowering plasma and liver cholesterol, and all were equally effective at blocking cholesterol absorption as shown by increased fecal cholesterol output. Plant sterol accumulation in the liver was minimal for all test groups.

HOE 402 lowers serum cholesterol levels by reducing VLDL-lipid production, and not by induction of the LDL receptor, and reduces atherosclerosis in wild-type and LDL receptor-deficient mice

Previous rodent studies suggested that the potent hypolipidemic agent 4-amino-2-(4,4-dimethyl-2-oxo-1-imidazolidinyl)pyrimidine-5-N-(trifluoromethyl-phenyl) carboxamide monohydrochloride (HOE 402) is an inducer of the LDL receptor (LDLR). Using wild-type and heterozygous and homozygous LDLR-deficient (LDLR+/0 and LDLR0/0) mice, fed a low or high cholesterol diet, we investigated whether HOE 402 specifically induces the LDLR and whether other pathways are affected. Upon treatment with 0.05% (w/w) HOE 402, the serum cholesterol levels of wild-type, LDLR+/0 and LDLR0/0 mice, were maximally reduced by 53, 56, and 73%, respectively (P<0.05), by reducing levels in very low density-lipoprotein (VLDL), intermediate density-lipoprotein (IDL), and low density-lipoprotein (LDL) cholesterol, whereas high density-lipoprotein (HDL) cholesterol levels were increased. The observations that HOE 402 exhibited no effect on in vivo clearance of 125I-labeled LDL in wild-type mice, and clearly reduced serum cholesterol levels in LDLR0/0 mice, indicate that the LDLR is not the main target for the compound. In wild-type mice, production of VLDL-TG, and cholesterol were reduced by more than 50% by HOE 402 (P<0.05), whereas VLDL apolipoprotein B (ApoB) secretion was unaffected, indicating that HOE 402 treatment changes the size, rather than the number of the secreted VLDL particles. The reduced VLDL production was accompanied by a 22% decreased hepatic cholesterol ester concentration (P<0.05). Additionally, HOE 402 treatment strongly reduced the aortic content of atherosclerotic lesions by 90 and 72% in LDLR+/0 and LDLR0/0 mice, respectively (P<0.01). In conclusion, HOE 402 is a potent cholesterol-lowering compound, which inhibits VLDL production, and consequently attenuates atherosclerosis development.