Molecular Insights into the Mechanisms Underlying the Cholesterol- Lowering Effects of Phytosterols.

Dietary phytosterols, which comprise plant sterols and stanols, reduce plasma Low-Density Lipoprotein-Cholesterol (LDL-C) levels when given 2 g/day. Since this dose has not been reported to cause health-related side effects in long-term human studies, food products containing these plant compounds are used as potential therapeutic dietary options to reduce LDL-C and cardiovascular disease risk. Several mechanisms have been proposed to explain the cholesterol-lowering action of phytosterols. They may compete with dietary and biliary cholesterol for micellar solubilization in the intestinal lumen, impairing intestinal cholesterol absorption. Recent evidence indicates that phytosterols may also regulate other pathways. Impaired intestinal cholesterol absorption is usually associated with reduced cholesterol transport to the liver, which may reduce the incorporation of cholesterol into Very-Low- Density Lipoprotein (VLDL) particles, thereby lowering the rate of VLDL assembly and secretion. Impaired liver VLDL production may reduce the rate of LDL production. On the other hand, significant evidence supports a role for plant sterols in the Transintestinal Cholesterol Excretion (TICE) pathway, although the exact mechanisms by which they promote the flow of cholesterol from the blood to enterocytes and the intestinal lumen remains unknown. Dietary phytosterols may also alter the conversion of bile acids into secondary bile acids, and may lower the bile acid hydrophobic/hydrophilic ratio, thereby reducing intestinal cholesterol absorption. This article reviews the progress to date in research on the molecular mechanisms underlying the cholesterol-lowering effects of phytosterols.

A Functional Virgin Olive Oil Enriched with Olive Oil and Thyme Phenolic Compounds Improves the Expression of Cholesterol Efflux-Related Genes: A Randomized, Crossover, Controlled Trial.

The consumption of antioxidant-rich foods such as virgin olive oil (VOO) promotes high-density lipoprotein (HDL) anti-atherogenic capacities. Intake of functional VOOs (enriched with olive/thyme phenolic compounds (PCs)) also improves HDL functions, but the gene expression changes behind these benefits are not fully understood. Our aim was to determine whether these functional VOOs could enhance the expression of cholesterol efflux-related genes. In a randomized, double-blind, crossover, controlled trial, 22 hypercholesterolemic subjects ingested for three weeks 25 mL/day of: (1) a functional VOO enriched with olive oil PCs (500 mg/kg); (2) a functional VOO enriched with olive oil (250 mg/kg) and thyme PCs (250 mg/kg; FVOOT), and; (3) a natural VOO (olive oil PCs: 80 mg/kg, control intervention). We assessed whether these interventions improved the expression of cholesterol efflux-related genes in peripheral blood mononuclear cells by quantitative reverse-transcription polymerase chain reactions. The FVOOT intervention upregulated the expression of CYP27A1 (P = 0.041 and P = 0.053, versus baseline and the control intervention, respectively), CAV1 (P = 0.070, versus the control intervention), and LXRß, RXRα, and PPARß/δ (P = 0.005, P = 0.005, and P = 0.038, respectively, relative to the baseline). The consumption of a functional VOO enriched with olive oil and thyme PCs enhanced the expression of key cholesterol efflux regulators, such as CYP27A1 and nuclear receptor-related genes.

Phenol-enriched olive oils improve HDL antioxidant content in hypercholesterolemic subjects. A randomized, double-blind, cross-over, controlled trial.

At present, high-density lipoprotein (HDL) function is thought to be more relevant than HDL cholesterol quantity. Consumption of olive oil phenolic compounds (PCs) has beneficial effects on HDL-related markers. Enriched food with complementary antioxidants could be a suitable option to obtain additional protective effects. Our aim was to ascertain whether virgin olive oils (VOOs) enriched with (a) their own PC (FVOO) and (b) their own PC plus complementary ones from thyme (FVOOT) could improve HDL status and function. Thirty-three hypercholesterolemic individuals ingested (25 ml/day, 3 weeks) (a) VOO (80 ppm), (b) FVOO (500 ppm) and (c) FVOOT (500 ppm) in a randomized, double-blind, controlled, crossover trial. A rise in HDL antioxidant compounds was observed after both functional olive oil interventions. Nevertheless, α-tocopherol, the main HDL antioxidant, was only augmented after FVOOT versus its baseline. In conclusion, long-term consumption of phenol-enriched olive oils induced a better HDL antioxidant content, the complementary phenol-enriched olive oil being the one which increased the main HDL antioxidant, α-tocopherol. Complementary phenol-enriched olive oil could be a useful dietary tool for improving HDL richness in antioxidants.

Olive Oil Polyphenols Decrease LDL Concentrations and LDL Atherogenicity in Men in a Randomized Controlled Trial.

BACKGROUND: Olive oil polyphenols have shown protective effects on cardiovascular risk factors. Their consumption decreased oxidative stress biomarkers and improved some features of the lipid profile. However, their effects on LDL concentrations in plasma and LDL atherogenicity have not yet been elucidated. OBJECTIVE: Our objective was to assess whether the consumption of olive oil polyphenols could decrease LDL concentrations [measured as apolipoprotein B-100 (apo B-100) concentrations and the total number of LDL particles] and atherogenicity (the number of small LDL particles and LDL oxidizability) in humans. METHODS: The study was a randomized, cross-over controlled trial in 25 healthy European men, aged 20-59 y, in the context of the EUROLIVE (Effect of Olive Oil Consumption on Oxidative Damage in European Populations) study. Volunteers ingested 25 mL/d raw low-polyphenol-content olive oil (LPCOO; 366 mg/kg) or high-polyphenol-content olive oil (HPCOO; 2.7 mg/kg) for 3 wk. Interventions were preceded by 2-wk washout periods. Effects of olive oil polyphenols on plasma LDL concentrations and atherogenicity were determined in the sample of 25 men. Effects on lipoprotein lipase (LPL) gene expression were assessed in another sample of 18 men from the EUROLIVE study. RESULTS: Plasma apo B-100 concentrations and the number of total and small LDL particles decreased (mean ± SD: by 5.94% ± 16.6%, 11.9% ± 12.0%, and 15.3% ± 35.1%, respectively) from baseline after the HPCOO intervention. These changes differed significantly from those after the LPCOO intervention, which resulted in significant increases of 6.39% ± 16.6%, 4.73% ± 22.0%, and 13.6% ± 36.4% from baseline (P < 0.03). LDL oxidation lag time increased by 5.0% ± 10.3% from baseline after the HPCOO intervention, which was significantly different only relative to preintervention values (P = 0.038). LPL gene expression tended to increase by 26% from baseline after the HPCOO intervention (P = 0.08) and did not change after the LPCOO intervention. CONCLUSION: The consumption of olive oil polyphenols decreased plasma LDL concentrations and LDL atherogenicity in healthy young men. This trial was registered at www.controlled-trials.com as ISRCTN09220811.

Complementary phenol-enriched olive oil improves HDL characteristics in hypercholesterolemic subjects. A randomized, double-blind, crossover, controlled trial. The VOHF study.

SCOPE: Consumption of olive oil (OO) phenolic compounds (PCs) has beneficial effects on lipid profile. HDL functionality is currently considered to be a more important issue than its circulating quantity. Our aim was to assess whether functional virgin olive oils (FVOOs), one enriched with its own PC (500 ppm; FVOO) and another with OOPC (250 ppm) plus additional complementary PCs from thyme (250 ppm) (total: 500 ppm; FVOOT (functional virgin olive oil with thyme)), could improve HDL functionality related properties versus a virgin OO control (80 ppm; VOO). METHODS AND RESULTS: In a randomized, double-blind, crossover, controlled trial, 33 hypercholesterolemic volunteers received 25 mL/day of VOO, FVOO, and FVOOT during 3 wk. HDL cholesterol increased 5.74% (p < 0.05) versus its baseline after the FVOOT consumption in the participants without hypolipidemic medication. We detected, after FVOOT consumption, an increase in HDL2 -subclass (34.45, SD = 6.38) versus VOO intake (32.73, SD = 6.71). An increment in esterified cholesterol/free cholesterol and phospholipids/free cholesterol in HDL was observed after FVOOT consumption (1.73, SD = 0.56; 5.44, SD = 1.39) compared with VOO intervention (1.53, SD = 0.35; 4.97, SD = 0.81) and FVOO intervention (1.50, SD = 0.33; 4.97, SD = 0.81). Accordingly, lecithin-cholesterol acyltransferase mass increased after FVOOT consumption (1228 µg/mL, SD = 130), compared with VOO consumption (1160 µg/mL, SD = 144). An improvement in HDL oxidative-status was reflected after FVOOT consumption versus its baseline, given an increment in the paraoxonase activity (118 × 10(3) U/L, SD = 24). CONCLUSION: FVOOT improves HDL-subclass distribution and composition, and metabolism/antioxidant enzyme activities. FVOOT could be a useful dietary tool in the management of high cardiovascular risk patients.

Effects of functional olive oil enriched with its own phenolic compounds on endothelial function in hypertensive patients. A randomised controlled trial.

UNLABELLED: The additional health-promoting properties of functional virgin olive oil (FVOO) enriched with its own phenolic compounds (OOPC) versus the parental virgin olive oil (VOO) must be tested in appropriate human clinical trials. Our aim was to assess the effects of FVOO on endothelial function in hypertensive patients. Thirteen pre- and stage-1 hypertensive patients received a single dose of 30 mL of FVOO (OOPC=961 mg/kg) or VOO (OOPC=289 mg/kg) in a postprandial randomised, double blind, crossover trial. Endothelial function, measured as ischemic reactive hyperemia (IRH) and related biomarkers, were followed for 5h after consumption. Compared with VOO, FVOO increased IRH (P<0.05) and plasma Cmax of hydroxytyrosol sulphate, a metabolite of OOPC 2h postprandial (P=0.05). After FVOO ingestion, oxidised LDL decreased (P=0.010) in an inverse relationship with IRH AUC values (P=0.01). FVOO provided more benefits on endothelial function than a standard natural virgin olive oil in pre- and hypertensive patients. TRIAL REGISTRATION: isrctn.org. Identifier ISRCTN03450153.

Study of the catabolism of thyme phenols combining in vitro fermentation and human intervention.

The gut metabolism of four thyme phenolics (monoterpenes thymol and carvacrol, rosmarinic acid, and eriodictyol) was evaluated in vitro. After the in vitro transformations of the individual phenols had been studied, the presence of their microbial metabolites was investigated in human feces collected before and after a sustained intake (3 weeks) of 25 mL/day of a thyme phenol-enriched olive oil. Results of in vitro fermentation showed low degradation of thymol and carvacrol. By contrast, large catabolism was noted when rosmarinic acid and eriodictyol were fermented, yielding hydroxyphenylpropionic acid as the main metabolite. In accordance with these results, after the in vivo intervention with thyme phenol-enriched olive oil, an increase in the concentration of hydroxyphenylpropionic and phenylpropionic acids was observed in human feces, confirming the effective in vivo microbial degradation of rosmarinic acid and eriodictyol. Carvacrol was detected in fecal samples at trace levels, suggesting that monoterpenes are well absorbed in the upper part of the gastrointestinal tract.

Olive oil polyphenols enhance high-density lipoprotein function in humans: a randomized controlled trial.

OBJECTIVE: Olive oil polyphenols have shown beneficial properties against cardiovascular risk factors. Their consumption has been associated with higher cholesterol content in high-density lipoproteins (HDL). However, data on polyphenol effects on HDL quality are scarce. We, therefore, assessed whether polyphenol-rich olive oil consumption could enhance the HDL main function, its cholesterol efflux capacity, and some of its quality-related properties, such HDL polyphenol content, size, and composition. APPROACH AND RESULTS: A randomized, crossover, controlled trial with 47 healthy European male volunteers was performed. Participants ingested 25 mL/d of polyphenol-poor (2.7 mg/kg) or polyphenol-rich (366 mg/kg) raw olive oil in 3-week intervention periods, preceded by 2-week washout periods. HDL cholesterol efflux capacity significantly improved after polyphenol-rich intervention versus the polyphenol-poor one (+3.05% and -2.34%, respectively; P=0.042). Incorporation of olive oil polyphenol biological metabolites to HDL, as well as large HDL (HDL2) levels, was higher after the polyphenol-rich olive oil intervention, compared with the polyphenol-poor one. Small HDL (HDL3) levels decreased, the HDL core became triglyceride-poor, and HDL fluidity increased after the polyphenol-rich intervention. CONCLUSIONS: Olive oil polyphenols promote the main HDL antiatherogenic function, its cholesterol efflux capacity. These polyphenols increased HDL size, promoted a greater HDL stability reflected as a triglyceride-poor core, and enhanced the HDL oxidative status, through an increase in the olive oil polyphenol metabolites content in the lipoprotein. Our results provide for the first time a first-level evidence of an enhancement in HDL function by polyphenol-rich olive oil.

Faecal microbial metabolism of olive oil phenolic compounds: in vitro and in vivo approaches.

SCOPE: In the present study, the individual colonic metabolism of the main components of the virgin olive oil phenolic fraction was evaluated by an in vitro model using human faecal microbiota. To assess differences in metabolism related to the molecular structure, four phenolic standards were selected, tyrosol, hydroxytyrosol, hydroxytyrosol acetate and oleuropein. After studying the in vitro colonic metabolism pathways of the individual phenols, the presence of their colonic metabolites was investigated in human faecal samples obtained before and after the sustained intake (3 weeks) of a daily dose of 25 mL of a phenol-enriched olive oil. METHODS AND RESULTS: The in vitro colon fermentation of the four individual phenolic compounds revealed (i) an increase in phenolic acids, (ii) the stability of hydroxytyrosol and tyrosol and (iii) the high degradation of hydroxytyrosol acetate and oleuropein. Additionally, a moderate intake of a phenol-rich olive oil raised the concentration in human faeces of free hydroxytyrosol and phenylacetic and phenylpropionic acids. CONCLUSION: The products of colonic catabolism of olive oil phenolic compounds could be good candidates for novel preventive strategies and open a promising line of research into the preventive action of olive oil phenols in colon and other bowel diseases.

Olive oil polyphenols enhance the expression of cholesterol efflux related genes in vivo in humans. A randomized controlled trial.

Both oleic acid and polyphenols have been shown to increase high-density lipoprotein (HDL) cholesterol and to protect HDL from oxidation, a phenomenon associated with a low cholesterol efflux from cells. Our goal was to determine whether polyphenols from olive oil could exert an in vivo nutrigenomic effect on genes related to cholesterol efflux in humans. In a randomized, controlled, cross-over trial, 13 pre/hypertensive patients were assigned 30 ml of two similar olive oils with high (961 mg/kg) and moderate (289 mg/kg) polyphenol content. We found an increase in ATP binding cassette transporter-A1, scavenger receptor class B type 1, peroxisome proliferator-activated receptor (PPAR)BP, PPARα, PPARγ, PPARδ and CD36 gene expression in white blood cells at postprandial after high polyphenol olive oil when compared with moderate polyphenol olive oil intervention (P<.017), with COX-1 reaching borderline significance (P=.024). Linear regression analyses showed that changes in gene expression were related to a decrease in oxidized low-density lipoproteins and with an increase in oxygen radical absorbance capacity and olive oil polyphenols (P<.05). Our results indicate a significant role of olive oil polyphenols in the up-regulation of genes involved in the cholesterol efflux from cells to HDL in vivo in humans. These results are in agreement with previous ones concerning the fact that benefits associated with polyphenol-rich olive oil consumption on cardiovascular risk could be mediated through an in vivo nutrigenomic effect in humans.

HDL-related mechanisms of olive oil protection in cardiovascular disease.

The low incidence of cardiovascular disease in countries bordering the Mediterranean basin, where olive oil is the main source of dietary fat, and the negative association between this disease with high density lipoproteins has stimulated interest. This review summarizes the current knowledge gathered from human and animal studies regarding olive oil and high density lipoproteins. Cumulative evidence suggests that high density lipoprotein (HDL) cholesterol, and its main apolipoprotein A1, may be increased by consuming olive oil when compared with carbohydrate and low fat diets in humans. Conflicting results have been found in many studies when olive oil diets were compared with other sources of fat. The role of virgin olive oil minor components on its protective effect has been demonstrated by a growing number of studies although its exact mechanism remains to be elucidated. Dietary amount of olive oil, use of virgin olive oil, cholesterol intake, and physiopathological states such as genetic background, sex, age, obesity or fatty liver are variables that may offset those effects. Further studies in this field in humans and in animal models are warranted due to the complexity of HDL particles.