Sitosterol reduces micellar cholesterol solubility in model bile

β-Sitosterol mitigates the development of high-fructose diet-induced nonalcoholic fatty liver disease in growing male Sprague–Dawley rats

Fructose contributes to the development of nonalcoholic fatty liver disease (NAFLD). β-Sitosterol (Bst), a naturally occurring phytosterol, has antihyperlipidaemic and hepatoprotective properties. This study interrogated the potential protective effect of β-sitosterol against NAFLD in growing rats fed a high-fructose diet, modelling children fed obesogenic diets. Forty-four 21 day old male rat pups were randomly allocated to and administered the following treatments for 12 weeks: group I, standard rat chow (SRC) + plain drinking water (PW) + plain gelatine cube (PC); group II, SRC + 20% w/v fructose solution (FS) as drinking fluid + PC; group III, SRC + FS + 100 mg/kg fenofibrate in a gelatine cube; group IV, SRC + FS + 20 mg/kg β-sitosterol gelatine cube (Bst); group V, SRC + PW + Bst. Terminally, the livers were dissected out, weighed, total liver lipid content determined, and histological analyses done. Harvested plasma was used to determine the surrogate biomarkers of liver function. The high-fructose diet caused increased (p < 0.05) hepatic lipid (total) accretion (>10% liver mass), micro- and macrovesicular hepatic steatosis, and hepatic inflammation. β-Sitosterol and fenofibrate prevented the high-fructose diet-induced macrovesicular steatosis and prevented the progression of NAFLD to steatohepatitis. β-Sitosterol can prospectively be used to mitigate diet-induced NAFLD.

Lipid-lowering effects of Coffea arabica pulp aqueous extract in Caco-2 cells and hypercholesterolemic rats

BACKGROUND

Coffea arabica pulp (CP) is the first by-product obtained from coffee berries during coffee processing. The major constituents of CP, including chlorogenic acid, caffeine, and epicatechin exhibit anti-hyperlipidemic effects in in vitro and in vivo models. Whether Coffea arabica pulp aqueous extract (CPE) has a lipid-lowering effect remains unknown.

PURPOSE

This study examined the effect of CPE on cholesterol absorption, and identified the mechanisms involved in lowered cholesterol in in vitro and in vivo models.

METHODS

Uptake of [³H]-cholesterol micelles and the mode of CPE inhibition were determined using human intestinal Caco-2 cells, and subsequently, confirmed using isolated rat jejunal loops. In addition, the 12-week high-fat diet-induced hypercholesterolemic rats (HF) received either CPE (1000  mg/kg BW), a sole and high dose which was selected because it contained approximately 12  mg of CGA that was previously shown to have lipid-lowering effects, or ezetimibe (10  mg/kg BW), a cholesterol inhibitor. The rats were divided into HF, HF  ++ CPE, and HF  ++ ezetimibe groups for the next 12 weeks. Normal rats received a normal diet (ND) and CPE (ND  +  CPE). Body weights and lipid profiles were evaluated. Cholesterol transporter, Niemann-Pick C1-Like 1 (NPC1L1), protein expression and liver X receptor alpha (LXRα) mRNA expression were determined. In vitro micellar complex properties were also investigated.

RESULTS

CPE inhibited [³H]-cholesterol micelle transport in Caco-2 cells and rat jejunal loops in a dose-dependent, non-competitive manner partly by decreasing membrane NPC1L1 expression. Congruently, CPE and its major constituents activated LXRα which, in turn, down-regulated NPC1L1. Furthermore, CPE interfered with physicochemical characteristics of cholesterol mixed micelles. These data were consistent with decreased body weight and slowed body weight gain and improved lipid profiles by CPE in hypercholesterolemic rats while no change occurred in these parameters in normal rats. Down-regulated intestinal NPC1L1 expression mediated by increased LXRα mRNA were also observed in HF  ++ CPE and ND  +  CPE rats.

CONCLUSION

CPE has a cholesterol-lowering effect in in vitro and in vivo via inhibition of intestinal cholesterol absorption by down-regulating NPC1L1 mediated LXRα activation and interfering with micellar complex formation. Accordingly, CPE could be developed as nutraceutical product to prevent dyslipidemia-induced obesity and insulin resistance.

Inhibitory effects of Tiliacora triandra (Colebr.) Diels on cholesterol absorption

Background Natural supplements and herbal medicines have been attracted to use for managing elevated cholesterol levels. Tiliacora triandra (Colebr.) Diels (TT) or Yanang (in Thai) is commonly used as an ingredient in various types of Thai foods. In this study, we investigated the effect of methanolic TT leaf extract on cholesterol absorption by measuring the uptake and the efflux of cholesterol and cholesterol micellar solubility. In addition, we tested the effect of TT leaf extract on pancreatic lipase activity. Methods The uptake and efflux of cholesterol was determined by quantification of radioactivity in differentiated Caco-2 cells after treatment with radioactive cholesterol. Cholesterol mixed micelles were prepared for cholesterol uptake, efflux and solubility studies. The pancreatic lipase activity was determined using 4-methylumbelliferyl oleate as a substrate. Results Our finding showed that TT extract decreased the uptake of cholesterol by approximately 48% but did not affect the efflux of cholesterol. TT inhibited pancreatic lipase activity with the IC50 at 273.5 μg/mL and also decreased cholesterol micellar solubility. Conclusions These findings suggest that TT leaf extract seems to be a potential candidate as cholesterol-lowering agents.

The impact of galactooligosaccharides on the bioaccessibility of sterols in a plant sterol-enriched beverage: adaptation of the harmonized INFOGEST digestion method

The effect of the addition of galactooligosaccharides (GOS) on sterol bioaccessibility in three plant sterol (PS)-enriched milk-based fruit beverages (without GOS addition (MfB) and with 2.5 g (MfB-G2) and 5.0 g (MfB-G5) GOS per 250 mL) was evaluated after micellar gastrointestinal digestion. Cholesterol bioaccessibility was very similar among beverages, though a slight significant increase (from 80% to 85%) was observed by the addition of 5.0 g GOS. The addition of GOS did not affect total PS bioaccessibility (≈37%). Based on the results obtained after micellar digestion, it has been demonstrated that these beverages could be a suitable food matrix for simultaneous enrichment with PS and GOS. The harmonized in vitro digestion model INFOGEST was applied to the MfB beverage, but the cholesterol content could not be quantified due to its contribution of bile salts. Hence, it was proposed: (i) a change in porcine bile salt concentration from 10 mM to 1.4 mM (in order to compare with micellar digestion); or (ii) a change of bile salt origin (bovine instead of porcine), maintaining physiological concentration (10 mM, INFOGEST condition). Both options allowed cholesterol quantification, with bioaccessibilities of 62% (reduction of bile salts) and 38% (replacement of the bile salt source), whereas plant sterol bioaccessibilities were 22% and 14%, respectively. Therefore, the change of bile salt origin maintaining INFOGEST concentration is proposed as a method to evaluate sterol (cholesterol and PS) bioaccessibility in these beverages, demonstrating the need for the selection of appropriate conditions of the INFOGEST harmonized method according to the food matrix and compounds to be determined.

Sterols in Infant Formulas: A Bioaccessibility Study

The design of infant formulas (IFs) seeks to resemble human milk (HM) composition and functionality. The fat sources used usually comprise vegetable oil blends to mimic the fatty acid composition of HM and introduce changes in the animal/plant sterol ratio. In contrast, the use of milk fat globule membrane (MFGM)-rich ingredients could improve this aspect by increasing the ratio. The present study evaluates the bioaccessibility (BA) of sterols (cholesterol, desmosterol, brassicasterol, campesterol, stigmasterol, and β-sitosterol) in three IFs (with or without MFGM) using an in vitro digestion method simulating infant conditions. Analytical parameters confirmed the suitability of the method for all of these sterols. Results showed the presence of MFGM to increase cholesterol content (6-7 vs 2 mg/100 mL), this being the most bioaccessible sterol in the IFs. Although the BA of cholesterol was reduced in MFGM-enriched IF (65.6-80.4% vs 99.7%), the intake of bioaccessible cholesterol from these IFs was higher.

A positive impact on the serum lipid profile and cytokines after the consumption of a plant sterol-enriched beverage with a milk fat globule membrane: a clinical study

Positive impact on serum lipids and cytokines after functional beverage's intake by postmenopausal women.

Sorghum (Sorghum bicolor L.): Nutrients, bioactive compounds, and potential impact on human health

Sorghum is the fifth most produced cereal in the world and is a source of nutrients and bioactive compounds for the human diet. We summarize the recent findings concerning the nutrients and bioactive compounds of sorghum and its potential impact on human health, analyzing the limitations and positive points of the studies and proposing directions for future research. Sorghum is basically composed of starch, which is more slowly digested than that of other cereals, has low digestibility proteins and unsaturated lipids, and is a source of some minerals and vitamins. Furthermore, most sorghum varieties are rich in phenolic compounds, especially 3-deoxyanthocyanidins and tannins. The results obtained in vitro and in animals have shown that phenolics compounds and fat soluble compounds (polycosanols) isolated from sorghum benefit the gut microbiota and parameters related to obesity, oxidative stress, inflammation, diabetes, dyslipidemia, cancer, and hypertension. The effects of whole sorghum and its fractions on human health need to be evaluated. In conclusion, sorghum is a source of nutrients and bioactive compounds, especially 3-deoxyanthocyanidins, tannins, and polycosanols, which beneficially modulate, in vitro and in animals, parameters related to noncommunicable diseases. Studies should be conducted to evaluate the effects of different processing on protein and starch digestibility of sorghum as well as on the profile and bioavailability of its bioactive compounds, especially 3-deoxyanthocyanidins and tannins. Furthermore, the benefits resulting from the interaction of bioactive compounds in sorghum and human microbiota should be studied.

Critical Analysis on Characterization, Systemic Effect, and Therapeutic Potential of Beta-Sitosterol: A Plant-Derived Orphan Phytosterol

Beta-sitosterol (BS) is a phytosterol, widely distributed throughout the plant kingdom and known to be involved in the stabilization of cell membranes. To compile the sources, physical and chemical properties, spectral and chromatographic analytical methods, synthesis, systemic effects, pharmacokinetics, therapeutic potentials, toxicity, drug delivery and finally, to suggest future research with BS, classical as well as on-line literature were studied. Classical literature includes classical books on ethnomedicine and phytochemistry, and the electronic search included Pubmed, SciFinder, Scopus, the Web of Science, Google Scholar, and others. BS could be obtained from different plants, but the total biosynthetic pathway, as well as its exact physiological and structural function in plants, have not been fully understood. Different pharmacological effects have been studied, but most of the mechanisms of action have not been studied in detail. Clinical trials with BS have shown beneficial effects in different diseases, but long-term study results are not available. These have contributed to its current status as an "orphan phytosterol". Therefore, extensive research regarding its effect at cellular and molecular level in humans as well as addressing the claims made by commercial manufacturers such as the cholesterol lowering ability, immunological activity etc. are highly recommended.

Impact of Lipid Components and Emulsifiers on Plant Sterols Bioaccessibility from Milk-Based Fruit Beverages

Sterol bioaccessibility (BA) of three plant sterol (PS)-enriched milk-based fruit beverages (MFb) with different fat contents (1.1-2.4%), lipid sources (animal or vegetable), and without or with emulsifiers (whey proteins enriched with milk fat globule membrane (MFGM) or soy lecithin) was evaluated after simulated gastrointestinal digestion. The BA of total PS followed the order 31.4% (MFbM containing milk fat and whey proteins enriched with MFGM) = 28.2% (MFbO containing extra virgin olive oil and soy lecithin) > 8.7% (MFb without fat addition). Total and individual PS content in the bioaccessible fractions followed the order MFbM > MFbO > MFb. Consequently, formulation with MFGM is proposed in beverages of this kind to ensure optimum bioavailability of PS. Our results suggest that the BA of PS is influenced by the type and quantity of fat and the emulsifier type involved.

Quantification of Cholesterol Solubilized in Dietary Micelles: Dependence on Human Bile Salt Variability and the Presence of Dietary Food Ingredients

The solubility of cholesterol in bile salt (BS) micelles is important to understand the availability of cholesterol for absorption in the intestinal epithelium and to develop strategies to decrease cholesterol intake from the intestinal lumen. This has been the subject of intense investigation, due to the established relation between the development of diseases such as atherosclerosis and high levels of cholesterol in the blood. In this work we quantify the effect of BS variability on the amount of cholesterol solubilized. The effect of some known hypocholesterolemic agents usually found in the diet is also evaluated, as well as some insight regarding the mechanisms involved. The results show that, depending on the bile salt composition, the average value of sterol per micelle is equal to or lower than 1. The amount of cholesterol solubilized in the BS micelles is essentially equal to its total concentration until the solubility limit is reached. Altogether, this indicates that the maximum cholesterol solubility in the BS micellar solution is the result of saturation of the aqueous phase and depends on the partition coefficient of cholesterol between the aqueous phase and the micellar pseudophase. The effect on cholesterol maximum solubility for several food ingredients usually encountered in the diet was characterized using methodology developed recently by us. This method allows the simultaneous quantification of both cholesterol and food ingredient solubilized in the BS micelles even in the presence of larger aggregates, therefore avoiding their physical separation with possible impacts on the overall equilibrium. The phytosterols stigmasterol and stigmastanol significantly decreased cholesterol solubility with a concomitant reduction in the total amount of sterol solubilized, most pronounced for stigmasterol. Those results point toward coprecipitation being the major cause for the decrease in cholesterol solubilization by the BS micelles. The presence of tocopherol and oleic acid leads to a small decrease in the amount of cholesterol solubilized while palmitic acid slightly increases the solubility of cholesterol. Those dietary food ingredients are completely solubilized by the BS micelles, indicating that the effects on cholesterol solubility are due to changes in the properties of the mixed micelles.

Dietary Plant Sterol Esters Must Be Hydrolyzed to Reduce Intestinal Cholesterol Absorption in Hamsters

BACKGROUND

Elevated concentrations of LDL cholesterol are associated with the development of atherosclerosis and therefore are considered an important target for intervention to prevent cardiovascular diseases. The inhibition of cholesterol absorption in the small intestine is an attractive approach to lowering plasma cholesterol, one that is addressed by drug therapy as well as dietary supplementation with plant sterols and plant sterol esters (PSEs).

OBJECTIVE

This study was conducted to test the hypothesis that the cholesterol-lowering effects of PSE require hydrolysis to free sterols (FSs).

METHODS

Male Syrian hamsters were fed atherogenic diets (AIN-93M purified diet containing 0.12% cholesterol and 8% coconut oil) to which one of the following was added: no PSEs or ethers (control), 5% sterol stearate esters, 5% sterol palmitate esters (PEs), 5% sterol oleate esters (OEs), 5% sterol stearate ethers (STs; to mimic nonhydrolyzable PSE), or 3% FSs plus 2% sunflower oil. The treatments effectively created a spectrum of PSE hydrolysis across which cholesterol metabolism could be compared. Metabolic measurements included cholesterol absorption, plasma and liver lipid concentration, and fecal neutral sterol and bile acid excretion.

RESULTS

The STs and the PEs and SEs were poorly hydrolyzed (1.69-4.12%). In contrast, OEs were 88.3% hydrolyzed. The percent hydrolysis was negatively correlated with cholesterol absorption (r = -0.85; P < 0.0001) and positively correlated with fecal cholesterol excretion (r = 0.92; P < 0.0001), suggesting that PSE hydrolysis plays a central role in the cholesterol-lowering properties of PSE.

CONCLUSIONS

Our data on hamsters suggest that PSE hydrolysis and the presence of FSs is necessary to induce an optimum cholesterol-lowering effect and that poorly hydrolyzed PSEs may lower cholesterol through an alternative mechanism than that of competition with cholesterol for micelle incorporation.

Peptides from cowpea present antioxidant activity, inhibit cholesterol synthesis and its solubilisation into micelles

In previous studies, it was reported that the protein isolated from the cowpea interferes favourably in lipid metabolism, and reduces cholesterol synthesis. The present study investigated the role of cowpea peptide fractions in the micellar solubilisation of cholesterol, in the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) activity, and in the in vitro antioxidant capacity, considering the effects of thermal processing. The protein was isolated from the raw and cooked beans and digested to simulate human digestion. The peptides from the protein isolate of raw bean with molecular mass lower than 3kDa reduced 89% of the HMGCR enzymatic reaction velocity. The cooked cowpeas were more effective in inhibiting the micellar solubility of cholesterol than the raw ones but not the antioxidant activity. This is the first report that cowpea peptides inhibit cholesterol homeostasis in vitro in two distinct routes, and act as an antioxidant.

Black rice and anthocyanins induce inhibition of cholesterol absorption in vitro

Black rice (Oryza sativa L.) is often associated with blood lipid control. This study systematically assessed the inhibition of cholesterol absorption in vitro by black rice and explored cholesterol-lowering compounds present in this rice. Our results indicated that black rice extracts (BRE), which were aqueous, ethanol extracts and a fraction of macroporous resin caused the reduction of cholesterol absorption by inhibiting pancreatic lipase, decreasing the micellar cholesterol solubility and suppressing cholesterol uptake in Caco-2 cells. The inhibitory activity was positively associated with anthocyanin (cyanidin-3-glucoside (Cy-3-G) and peonidin-3-glucoside (Pn-3-G)) contents of the extracts. Therefore, the cholesterol absorption inhibiting properties of anthocyanins were further explored. The IC50 values of Cy-3-G and Pn-3-G against pancreatic lipase were 42.53 ± 4.45 and 18.13 ± 4.22 μg mL(-1), respectively. Kinetic analysis suggested that the enzymatic inhibitory mode of Cy-3-G and Pn-3-G belonged to the competitive type. In mixed micelles, Cy-3-G and Pn-3-G dose dependently reduced the solubility of cholesterol. Meanwhile, a potential mechanism of cholesterol reduction by anthocyanins was investigated. Results showed that anthocyanins led to precipitation of cholesterol from micellar solution, which may induce the reduction of cholesterol. In Caco-2 cells, Cy-3-G and Pn-3-G (40 μg mL(-1)) exhibited a significant reduction in cholesterol uptake, and the degree of this reduction was almost the same as that observed in the group treated with Ezetimibe at the same concentration. These findings provide important evidence that anthocyanins may partly contribute to the inhibitory effects of black rice on cholesterol absorption, and thus may be applied for the prevention and treatment of hypercholesterolaemia.

Conjugated and free sterols from black bean (Phaseolus vulgaris L.) seed coats as cholesterol micelle disruptors and their effect on lipid metabolism and cholesterol transport in rat primary hepatocytes

Phytosterols have been widely studied for their cholesterol-lowering effect. Conjugated phytosterol forms have been found more active than free moieties. There are no reports about the sterol profile of black bean seed coats neither its effects on cholesterol metabolism. The aim of this research was to identify and quantify phytosterols from black bean seed coats and to determine their effects on cholesterol micellar solubility and on mRNA and key protein levels involved in lipid/cholesterol metabolism and cholesterol transport in primary rat hepatocytes. Free phytosterols, acylated steryl glycosides, and steryl glycosides were extracted from black bean seed coats. They were identified through HPLC-MS-TOF and quantified through HPLC equipped with UV-visible and evaporative light-scattering detectors. Free and conjugated phytosterols from the coats significantly increased the inhibitory effect of cholesterol micelle formation compared with stigmasterol, which was used as control (P < 0.05). In addition, phytosterols of black bean seed coat decreased lipogenesis by the downregulation of lipogenic proteins such as sterol regulatory element-binding protein 1 and fatty acid synthesis (FAS) in primary rat hepatocytes. Regarding β-oxidation, phytosterols upregulated the expression of carnitine palmitoyltransferase I and promoted the β-oxidation of long-chain fatty acids. Phytosterols inhibited cholesterol micellar solubility and reduced the activation of the liver X receptor, decreasing hepatic FAS and promoting hepatic β-oxidation of long-chain fatty acids.

Study on the 3-hydroxy-3-methyl-glutaryl CoA reductase inhibitory properties of Agaricus bisporus and extraction of bioactive fractions using pressurised solvent technologies

BACKGROUND

Agaricus bisporus mushrooms were able to lower cholesterol levels in hypercholesterolaemic rats and it was suggested that dietary fibre might inhibit cholesterol absorption. However, A. bisporus extracts were also able to inhibit the 3-hydroxy-3-methyl-glutaryl CoA reductase (HMGCR, the key enzyme in the cholesterol biosynthetic pathway) and this might also contribute to the observed lowering of cholesterol levels in serum.

RESULTS

The methanol-water extracts obtained from A. bisporus were able to inhibit up to 60% the HMGCR activity using an in vitro assay. The HMGCR inhibitory capacities depended on cultivation conditions, strains, etc. The potential inhibitors were not statins, they might be β-glucans able to scavenge the substrate and impair the enzymatic reaction. They were present during all mushroom developmental stages and similarly distributed through all the tissues including the parts discarded as a by-product. Accelerated solvent extractions using 1:1 ethanol-water as pressurised solvent (10.7 MPa, 25°C, five cycles of 5 min) were more effective in the extraction of the HMGCiR inhibitor(s) than supercritical fluid extractions (9 MPa, 40°C) using CO2 with 10% ethanol.

CONCLUSION

A mushroom cultivation and two extraction procedures were optimised to obtain fractions from A. bisporus with high HMGCR inhibitory activities to design novel ingredients for hypocholesterolaemic functional foodstuffs.

Phytosterols esterified with conjugated linoleic acid. In vitro intestinal digestion and interaction on cholesterol bioaccessibility

Intestinal in vitro digestion of phytosterols esterified with conjugated linoleic acid (PS-CLA) was performed to study (1) the potential bioaccessibility of the released bioactive-lipid products and (2) the interference with cholesterol bioaccessibility. Commercial food-grade PS ester (PS-C) was assayed as reference. Hydrolysis of PS-CLA by digestive enzymes was similar to that of PS-C (51 and 47%, respectively), most lipids products being mainly included in the bioaccessible fraction, namely, the micellar phase (MP). Control assays in the absence of PS esters showed most cholesterol solubilized within the MP, whereas a displacement of total cholesterol was caused from MP after digestion of PS esters (14 and 36% displacement for PS-CLA and PS-C, respectively), cholesterol being partially precipitated. Precipitated cholesterol was linearly related to a parallel precipitation of saturated-chain PS, mainly determined by sitosterol (R² = 0.936). The higher composition in sitosteryl esters of PS-C with respect to PS-CLA might explain their different effects on cholesterol. Therefore, besides being a lipid delivery form of PS similar to other commercial esterified PS, the PS-CLA might have the additional advantage of being a lipid delivery form of CLA. Moreover, PS-CLA might hinder the bioaccessibility of cholesterol. Furthermore, the qualitative/quantitative profile in esterified PS forms might determine the magnitude of cholesterol interaction.

Phytosterol stearate esters elicit similar responses on plasma lipids and cholesterol absorption but different responses on fecal neutral sterol excretion and hepatic free cholesterol in male Syrian hamsters

The dietary impact of specific phytosterols incorporated into phytosterol fatty acid esters has not been elucidated. Therefore, we tested the hypothesis that phytosterol esters containing different sterol moieties (sitosterol, sitostanol, or stigmasterol) but the same fatty acid moiety (stearic acid) produce different effects on cholesterol metabolism. Male Syrian hamsters were fed sitosterol, sitostanol, and stigmasterol stearate esters (25 g/kg diet) in an atherogenic diet containing cholesterol (1.2 g/kg) and coconut oil (80 g/kg). The phytosterol stearates produced no decrease in cholesterol absorption or plasma non-high-density lipoprotein cholesterol despite a reduction in liver free cholesterol in hamsters fed both sitosterol and sitostanol stearate diets. In addition, sitosterol stearate significantly increased fecal esterified and total neutral sterol excretion. Stigmasterol stearate did not differ from control in neutral sterol excretion, plasma lipids, or hepatic lipid concentration. Sitosterol stearate demonstrated the highest level of net intestinal hydrolysis, whereas sitostanol and stigmasterol stearate equivalently demonstrated the lowest. The cholesterol-lowering effect in liver-but not plasma-and the limited presence of fecal free sterols indicate that intact (unhydrolyzed) phytosterol stearates may impact cholesterol metabolism by mechanisms unrelated to the role of free phytosterols. The consumption of phytosterol esters at 2.5% of the diet elicited only modest impacts on cholesterol metabolism, although sitosterol stearate had a slightly greater therapeutic impact by lowering liver free cholesterol and increasing esterified and total neutral sterol fecal excretion, possibly due to a greater level of intestinal hydrolysis.

Unrefined and refined black raspberry seed oils significantly lower triglycerides and moderately affect cholesterol metabolism in male Syrian hamsters

Unrefined and refined black raspberry seed oils (RSOs) were examined for their lipid-modulating effects in male Syrian hamsters fed high-cholesterol (0.12% g/g), high-fat (9% g/g) diets. Hamsters fed the refined and the unrefined RSO diets had equivalently lower plasma total cholesterol and high-density lipoprotein (HDL) cholesterol in comparison with the atherogenic coconut oil diet. The unrefined RSO treatment group did not differ in liver total and esterified cholesterol from the coconut oil-fed control animals, but the refined RSO resulted in significantly elevated liver total and esterified cholesterol concentrations. The unrefined RSO diets significantly lowered plasma triglycerides (46%; P=.0126) in comparison with the coconut oil diet, whereas the refined RSO only tended to lower plasma triglyceride (29%; P=.1630). Liver triglyceride concentrations were lower in the unrefined (46%; P=.0002) and refined (36%; P=.0005) RSO-fed animals than the coconut oil group, with the unrefined RSO diet eliciting a lower concentration than the soybean oil diet. Both RSOs demonstrated a null or moderate effect on cholesterol metabolism despite enrichment in linoleic acid, significantly lowering HDL cholesterol but not non-HDL cholesterol. Dramatically, both RSOs significantly reduced hypertriglyceridemia, most likely due to enrichment in α-linolenic acid. As a terrestrial source of α-linolenic acid, black RSOs, both refined and unrefined, provide a promising alternative to fish oil supplementation in management of hypertriglyceridemia, as demonstrated in hamsters fed high levels of dietary triglyceride and cholesterol.

Potential mechanisms of hypocholesterolaemic effect of Thai spices/dietary extracts

Several Thai spices/dietary ingredients were previously shown to have hypocholesterolaemic effects. These studies were mostly conducted in animal models in which the mechanisms of action were not yet well-established. Therefore, this study aimed to investigate the potential mechanism of hypocholesterolaemic action of 12 selected plants, namely Hibiscus sabdariffa L., Moringa oleifera Lam., Cucurbita moschata Duchesne, Ananas comosus (L.) Merr., Zingiber officinale, Morus alba L., Camellia sinensis (L.) Kuntze, Piper nigrum L., Alpinia galanga (L.) Willd., Curcuma zedoaria Rose, Bacopa monnieri (L.) Wettst. and Piper retrofractum Vahl., widely used as spices and ingredients in various types of Thai food. The extract of P. nigrum at 100 µg mL(-1) was found to be the most effective cholesterol uptake inhibitor whereas those of A. galanga and C. sinensis effectively inhibited pancreatic lipase activity with IC50 values of 8.99±3.41 and 12.36±1.23 µg mL(-1), respectively. The potency of extracts from H. sabdariffa, M. oleifera and C. moschata at 100 µg mL(-1) were found to be similar to 0.4 µg mL(-1) pravastatin in inhibiting HMG-CoA reductase and possibly reduced cholesterol biosynthesis. This study also demonstrated that several of the tested plants possessed multiple sites of action that were possibly responsible for their cholesterol-lowering effect in the in vivo model.

Phytosterols and phytosterolemia: gene-diet interactions

Phytosterol intake is recommended as an adjunctive therapy for hypercholesterolemia, and plant sterols/stanols can reduce cholesterol absorption at the intestinal lumen through the Niemann-Pick C1 Like 1 (NPC1L1) transporter pathway by competitive solubilization in mixed micelles. Phytosterol absorption is of less magnitude than cholesterol and is preferably secreted in the intestinal lumen by ABCG5/G8 transporters. Therefore, plasma levels of plant sterols/stanols are negligible compared with cholesterol, under an ordinary diet. The mechanisms of cholesterol and plant sterols absorption and the whole-body pool of sterols are discussed in this chapter. There is controversy about treatment with statins inducing further increase in plasma non-cholesterol sterols raising concerns about the safety of supplementation of plant sterols to such drugs. In addition, increase in plant sterols has also been reported upon consumption of plant sterol-enriched foods, regardless of other treatments. Rare mutations on ABCG5/G8 transporters affecting cholesterol/non-cholesterol extrusion, causing sitosterolemia with xanthomas and premature atheroslerotic disease are now known, and cholesterol/plant sterols absorption inhibitor, ezetimibe, emerges as the drug that reduces phytosterolemia and promotes xanthoma regression. On the other hand, common polymorphisms affecting the NPC1L1 transporter can interfere with the action of ezetimibe. Gene-diet interactions participate in this intricate network modulating the expression of genetic variants on specific phenotypes and can also affect the individual response to the hypolipidemic treatment. These very interesting aspects promoted a great deal of research in the field.

Phytosterol ester constituents affect micellar cholesterol solubility in model bile

Plant sterols and stanols (phytosterols) and their esters are nutraceuticals that lower LDL cholesterol, but the mechanisms of action are not fully understood. We hypothesized that intact esters and simulated hydrolysis products of esters (phytosterols and fatty acids in equal ratios) would differentially affect the solubility of cholesterol in model bile mixed micelles in vitro. Sodium salts of glycine- and taurine-conjugated bile acids were sonicated with phosphatidylcholine and either sterol esters or combinations of sterols and fatty acids to determine the amount of cholesterol solubilized into micelles. Intact sterol esters did not solubilize into micelles, nor did they alter cholesterol solubility. However, free sterols and fatty acids altered cholesterol solubility independently (no interaction effect). Equal contents of cholesterol and either campesterol, stigmasterol, sitosterol, or stigmastanol (sitostanol) decreased cholesterol solubility in micelles by approximately 50% compared to no phytosterol present, with stigmasterol performing slightly better than sitosterol. Phytosterols competed with cholesterol in a dose-dependent manner, demonstrating a 1:1 M substitution of phytosterol for cholesterol in micelle preparations. Unsaturated fatty acids increased the micelle solubility of sterols as compared with saturated or no fatty acids. No differences were detected in the size of the model micelles. Together, these data indicate that stigmasterol combined with saturated fatty acids may be more effective at lowering cholesterol micelle solubility in vivo.

Sitosterol reduces messenger RNA and protein expression levels of Niemann-Pick C1-like 1 in FHs 74 Int cells

Intake of plant sterols has long been shown to reduce cholesterol absorption and subsequently plasma cholesterol concentrations. Despite competition between plant sterols and cholesterol for incorporation into mixed micelles as a suggested major mechanism for the inhibition of cholesterol absorption by plant sterols, studies exist to support an alternative mechanism. For example, another mechanism may be the action of plant sterols to reduce cholesterol absorption at the cellular level. This study was undertaken to test the hypothesis that plant sterols can modulate the expression of transporters such as Niemann-Pick C1-like 1 (NPC1L1) and scavenger receptor class B, type I (SR-BI) to lower intestinal cholesterol absorption. FHs 74 Int cells, a human small intestine epithelial cell line, were used as a model of enterocytes. The cells were treated with 25alpha-hydroxycholesterol (25 micromol/L) or 250 micromol/L of sitosterol, stigmasterol, and cholesterol for 24 hours to measure genes involved in cholesterol absorption and metabolism by quantitative real-time polymerase chain reaction. 25Alpha-hydroxycholesterol, cholesterol, and sitosterol significantly reduced the messenger RNA (mRNA) expression of NPC1L1 and hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, whereas SR-BI mRNA was not altered by the sterols. Western blot analysis confirmed the reduction in NPC1L1 by sterols. Depletion of cellular cholesterol by mevinolin, a cholesterol synthesis inhibitor, increased NPC1L1 and HMG-CoA reductase mRNA; and repletion of cholesterol abolished the increase. Sitosterol, but not stigmasterol, reduced the mRNA levels of NPC1L1 and HMG-CoA reductase to a similar extent of cholesterol. In conclusion, sitosterol can inhibit the expression of NPC1L1 in the enterocytes, which could be an alternate mechanism for plant sterols to reduce intestinal cholesterol uptake.

Reduction in cholesterol absorption is enhanced by stearate-enriched plant sterol esters in hamsters

Consumption of plant sterol esters reduces plasma LDL cholesterol concentration by inhibiting intestinal cholesterol absorption. Commercially available plant sterol esters are prepared by esterifying free sterols to fatty acids from edible plant oils such as canola, soybean, and sunflower. To determine the influence of the fatty acid moiety on cholesterol metabolism, plant sterol esters were made with fatty acids from soybean oil (SO), beef tallow (BT), or purified stearic acid (SA) and fed to male hamsters for 4 wk. A control group fed no plant sterol esters was also included. Hamsters fed BT and SA had significantly lower cholesterol absorption and decreased concentrations of plasma non-HDL cholesterol and liver esterified cholesterol, and significantly greater fecal sterol excretion than SO and control hamsters. Cholesterol absorption was lowest in hamsters fed SA (7.5%), whereas it was 72.9% in control hamsters. Cholesterol absorption was correlated with fecal sterol excretion (r = -0.72, P < 0.001), liver cholesterol concentration (r = 0.88, P < 0.001), and plasma non-HDL cholesterol concentration (r = 0.85, P < 0.001). A multiple regression model that included each sterol ester type vs. cholesterol absorption indicated that intake of steryl stearate was the only dietary component that contributed significantly to the model (R2 = -0.75, P < 0.001). Therefore, our results demonstrate that BT and SA are more effective than SO in reducing cholesterol absorption, liver cholesterol, and plasma non-HDL cholesterol concentration, suggesting that cardioprotective benefits can be achieved by consuming stearate-enriched plant sterol esters.