Differential effects on inhibition of cholesterol absorption by plant stanol and plant sterol esters in apoE-/- mice

Phytosterols: Potential Metabolic Modulators in Neurodegenerative Diseases

Phytosterols constitute a class of natural products that are an important component of diet and have vast applications in foods, cosmetics, and herbal medicines. With many and diverse isolated structures in nature, they exhibit a broad range of biological and pharmacological activities. Among over 200 types of phytosterols, stigmasterol and β-sitosterol were ubiquitous in many plant species, exhibiting important aspects of activities related to neurodegenerative diseases. Hence, this mini-review presented an overview of the reported studies on selected phytosterols related to neurodegenerative diseases. It covered the major phytosterols based on biosynthetic considerations, including other phytosterols with significant in vitro and in vivo biological activities.

Sterols and Sterol Oxidation Products: Effect of Dietary Intake on Tissue Distribution in ApoE-Deficient Mice

Sterols and sterol oxidation products (SOPs) are well-known dietary factors influencing atherosclerosis; however, their distribution in vivo after dietary sterol/SOP intake is still unclear. Here, we investigated the tissue distribution of sterols and SOPs in ApoE^-/- mice after dietary exposure to diets supplemented with phytosterols (PS), phytosterol oxidation products (POPs), or cholesterol oxidation products (COPs). The results showed that PS intake reduced cholesterol in serum and the liver but increased cholesterol in the brain. PS intake increased the levels of PS in vivo and the levels of 7-keto- and triol-POPs in serum and the liver. COP intake elevated the level of all COPs in serum but did not change the 7-keto-cholesterol level in the liver and brain. All POPs in serum and parts of POPs in the liver and brain increased after dietary POP exposure. Our study indicated that dietary PS and SOPs accumulated in vivo with varying degrees and influenced cerebral cholesterol metabolism.

Combined Effects of Plant Sterols with Low Ratio of n-6/n-3 Polyunsaturated Fatty Acids against Atherosclerosis in ApoE-/- Mice

The effects of low ratio of n-6/n-3 polyunsaturated fatty acids (PUFA) have been clarified against atherosclerosis. Increasing evidence indicated that plant sterols (PS) have a significant cholesterol-lowering effect. This study explored the effects of PS combined with n-6/n-3 (2:1) PUFA on atherosclerosis and investigated the possible mechanism. In ApoE^-/- mice, the milk fat in high fat diets was replaced with n-6/n-3 (2:1) PUFA alone or supplemented with 6% PS for 16 weeks. Results demonstrated that PS combined with PUFA exerted commentary and synergistic effects on ameliorating atherosclerosis, improving lipid metabolism and lipid deposition in liver, and alleviating inflammatory response. These changes were accompanied with decreased serum TC, TG, LDL-C and increased fecal cholesterol efflux, as well as the lower inflammatory cytokine CRP, IL-6, TNF-α. It is suggested that the underlying mechanism of PS combined with n-6/n-3 (2:1) PUFA promoting the fecal cholesterol efflux may be mediated by liver X receptor α/ATP-binding cassette transporter A1 pathway.

Safety of the extension of use of plant sterol esters as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on the safety of an extension of use of the novel food 'plant sterol esters' when added to vegetable fat spreads and to liquid vegetable fat-based emulsions for cooking and baking purposes pursuant to Regulation (EU) 2015/2283. Member States expressed concerns in relation to plant sterol oxidation products (POP) and consumption by non-target population groups. The median (0.5%) and P90 (2.28%) value of the oxidation rates of plant sterols determined by a wide range of cooking experiments were used together with exposure estimates for plant sterol when added and cooked with vegetable fat spreads and liquids. The no-observed adverse effect level (NOAEL) of a subchronic rat study and an applied default uncertainty factor of 200 served to derive levels (i.e. 0.64 mg POP/kg body weight (bw) per day) considered safe for humans. This safe level of exposure would be exceeded at the P95 by all age groups when considering the P90 oxidation rate and using EFSA's comprehensive food consumption database for assessing the potential exposure. When considering the median oxidation rate, the safe level of 0.64 mg POP/kg bw per day would be exceeded at the highest P95 intake estimates in children below 9 years of age. When considering an intake of the maximum authorised use level of 3 g plant sterols/person per day and oxidation rates of 0.5% and 2.28%, the resulting daily POP intakes per kg bw by an adult weighing 70 kg would be 0.21 and 0.98 mg/kg bw per day, respectively, the latter value exceeding 0.64 mg/kg bw per day. The Panel concludes that the safety of the intended extension of use of plant sterol esters under the proposed conditions of use has not been established.

The Impact of Phytosterols on the Healthy and Diseased Brain

The central nervous system (CNS) is the most cholesterol-rich organ in mammals. Cholesterol homeostasis is essential for proper brain functioning and dysregulation of cholesterol metabolism can lead to neurological problems. Multiple sclerosis (MS) and Alzheimer's disease (AD) are examples of neurological diseases that are characterized by a disturbed cholesterol metabolism. Phytosterols (PS) are plant-derived components that structurally and functionally resemble cholesterol. PS are known for their cholesterol-lowering properties. Due to their ability to reach the brain, researchers have started to investigate the physiological role of PS in the CNS. In this review, the metabolism and function of PS in the diseased and healthy CNS are discussed.

Progress and perspectives in plant sterol and plant stanol research

Current evidence indicates that foods with added plant sterols or stanols can lower serum levels of low-density lipoprotein cholesterol. This review summarizes the recent findings and deliberations of 31 experts in the field who participated in a scientific meeting in Winnipeg, Canada, on the health effects of plant sterols and stanols. Participants discussed issues including, but not limited to, the health benefits of plant sterols and stanols beyond cholesterol lowering, the role of plant sterols and stanols as adjuncts to diet and drugs, and the challenges involved in measuring plant sterols and stanols in biological samples. Variations in interindividual responses to plant sterols and stanols, as well as the personalization of lipid-lowering therapies, were addressed. Finally, the clinical aspects and treatment of sitosterolemia were reviewed. Although plant sterols and stanols continue to offer an efficacious and convenient dietary approach to cholesterol management, long-term clinical trials investigating the endpoints of cardiovascular disease are still lacking.

The Lipid-lowering Effects and Associated Mechanisms of Dietary Phytosterol Supplementation

Phytosterols (PS) are plant-based structural analogous of mammalian cholesterol that have been shown to lower blood cholesterol concentrations by ~10%, although inter-individual response to PS supplementation due to subject-specific metabolic and genetic factors is evident. Recent work further suggests that PS may act as effective triglyceride (TG)-lowering agents with maximal TG reductions observed in hypertriglyceridemic subjects. Although PS have been demonstrated to interfere with cholesterol and perhaps TG absorption within the intestine, they also have the capacity to modulate the expression of lipid regulatory genes through liver X receptor (LXR) activation. Identification of single-nucleotide polymorphisms (SNP) in key cholesterol and TG regulating genes, in particular adenosine triphosphate binding cassette G8 (ABCG8) and apolipoprotein E (apoE) have provided insight into the potential of utilizing genomic identifiers as an indicator of PS responsiveness. While PS supplementation is deemed safe, expanding research into the atherogenic potential of oxidized phytosterols (oxyphytosterols) has emerged with their identification in arterial lesions. This review will highlight the lipid-lowering utility and associated mechanisms of PS and discuss novel applications and future research priorities for PS pertaining to in utero PS exposure for long-term cardiovascular disease risk protection and combination therapies with lipidlowering drugs.

Triptolide inhibits the progression of atherosclerosis in apolipoprotein E-/- mice

Atherosclerosis, the major cause of cardiovascular disease, is accompanied by a chronic inflammatory response during the disease. Triptolide (TPL) is an active natural compound that has been demonstrated to possess anti-inflammatory activities in various cell types. However, the effects of TPL on atherosclerosis have not yet been studied. The goal of the present study was to determine the effects of TPL on apolipoprotein E knock-out (ApoE^-/^-) mice fed with a high-fat diet and to analyze the changes in lipid metabolism and inflammatory cytokines to clarify the underlying molecular mechanisms. Firstly, the genotypes of ApoE^-/^- mice and corresponding wild-type mice were identified using polymerase chain reaction. The ApoE^-/^- mice were randomly divided into four groups: ApoE^-/^- model mice, and ApoE^-/^- mice treated with 25, 50 or 100 µg/kg TPL every twice day. Wild-type mice with the same genetic background constituted the fifth group. The mice in each group were given a high-fat diet from week 8 after birth until week 20. Total cholesterol and total triglyceride levels were determined at 16 and 20 weeks. The results demonstrated that the levels of total cholesterol and total triglyceride in the plasma were highly increased in ApoE^-/^- mice models, compared with those of wild-type mice, and the ApoE^-/^- mice treated with TPL had decreased levels of total cholesterol and total triglyceride in plasma, which exhibited a dose-dependent reduction as the dose of TPL increased. Moreover, the effects of TPL on the production of inflammatory cytokines in macrophages were determined by ELISA. The results demonstrated that the macrophages from ApoE^-/^- mice produced high levels of the inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-8. However, following treatment with TPL doses of 25, 50 and 100 µg/kg, the cytokine levels were significantly decreased in a dose-dependent manner. Additionally, proteins associated with lipid metabolism were tested by western blotting. The results showed that the expression of anti-ATP-binding cassette transporter A1 in the macrophages of ApoE^-/^- mice was increased following treatment with TPL. However, the expression levels of LXRα were not markedly changed following treatment of the mice with different doses of TPL. These results suggest that TPL inhibited the progression of atherosclerosis not only by inhibiting the chronic inflammatory response, but also by regulating lipid metabolism, which may provide new insights useful in the clinical therapy of atherosclerosis.

7β-Hydroxysitosterol crosses the blood-brain barrier more favored than its substrate sitosterol in ApoE-/- mice

In this study, we compare the distribution of intraperitoneally injected sitosterol, 7β-hydroxysitosterol or vehicle only (control) for 28days in male ApoE-/- mice. Furthermore we examine its impact on surrogate markers of cholesterol biosynthesis and sterol absorption rate in plasma, brain and liver tissues from these animals. Injection of sitosterol revealed a 32.1% (P=0.013) lower plasma total cholesterol compared with control. Cholesterol corrected plasma and absolute brain and liver levels of sitosterol are 4.1-, 1.7-, and 7.2-fold (P<0.001 for all) higher, respectively. This is in accordance with a reduced plasma campesterol to cholesterol ratio (-16.2%; P=0.018) together with a 24.1% (P=0.047) lower concentration of hepatic lathosterol. After injection of 7β-hydroxysitosterol the concentrations of 7β-hydroxysitosterol in plasma, brain and liver are 21.0-, 65.8- and 42.7-fold (P<0.001 for all) higher, respectively, compared with control. Injection of 7β-hydroxysitosterol revealed significantly lower plasma cholesterol corrected cholestanol and campesterol (-44.2%; P=0.001 and -24.5; P=0.004) as well as lower absolute liver cholestanol levels (-31.9%; P<0.001) compared with control. Intraperitoneally injected sitosterol and 7β-hydroxysitosterol differently influence cholesterol metabolism in plasma and liver. We conclude that the polar 7β-hydroxysitosterol compound can pass the blood brain barrier with higher efficacy than its substrate, sitosterol. Though present in higher amounts in the brain, both, sitosterol and 7β-hydroxysitosterol do not influence cholesterol metabolism in the brain as proven by our surrogate markers.

Potential risks associated with increased plasma plant-sterol levels

The consumption of plant sterols is associated with a decrease in LDL cholesterol. However, it is also associated with an increase in plasma plant-sterol (sitosterol, campesterol) levels that may be detrimental. Indeed, the genetic disease sitosterolaemia, which is characterized by elevated plasma levels of plant sterol, is associated with premature atherosclerosis. Yet, although plasma plant-sterol levels are recognized markers of cholesterol absorption, the relationship between such levels and atherosclerosis is not clear. Several studies have analysed the association between plasma plant-sterol levels and cardiovascular disease (CVD), but have found conflicting results. Although the largest prospective trials and genome-wide association studies suggest that high plasma levels of plant sterols are associated with increased CV risk, other studies have reported no such association and even an inverse relationship. Thus, the available data cannot confirm an increased CV risk with plant sterols, but cannot rule it out either. Only a prospective interventional trial to analyse the effects of plant-sterol-enriched food on the occurrence of CV events can exclude a potential CV risk linked with their consumption.

Cholesterol modulates LRP5 expression in the vessel wall

OBJECTIVE

Macrophages are key players in atherosclerotic lesion formation and progression. We have recently demonstrated that lipid-loaded macrophages show activation of the canonical Wnt signaling pathway.

METHODS

To test the in vivo role of the canonical Wnt pathway in atherosclerosis we used mice deficient in the Wnt signaling receptor LRP5 (LRP5(-/-)) fed a hypercholesterolemic diet (HC) to induce atherosclerosis. These dietary groups were further subdivided into two subgroups receiving their respective diets supplemented with 2% plant sterol esters (PSE). All mice remained on their assigned diets until age 18 weeks.

RESULTS

HC WT mice had mildly increased non-HDL cholesterol levels, developed aortic atherosclerotic lesions and showed upregulated expression levels of aortic Lrp5. HC LRP5(-/-) mice develop larger aortic atherosclerotic lesions than WT mice indicating that LRP5 has a protective function in atherosclerosis progression. The oral administration of PSE, a dietary cholesterol-lowering agent, had an effect in the expression levels of the Wnt signaling receptor and in atherosclerosis progression. We found that PSE reduced serum total cholesterol levels, abolished HC-induced LRP5 overexpression and reduced aortic atherosclerotic plaques.

CONCLUSION

The proatherogenic effects of the excess of plasma lipids are in part mediated by modulation of LRP5 in the aorta. LRP5 and canonical Wnt signaling exert a protective defense mechanism against hyperlipidemia and atherosclerosis lesion progression.

Non-cholesterol sterols and cholesterol metabolism in sitosterolemia

Sitosterolemia (STSL) is a rare autosomal recessive disease, manifested by extremely elevated plant sterols (PS) in plasma and tissue, leading to xanthoma and premature atherosclerotic disease. Therapeutic approaches include limiting PS intake, interrupting enterohepatic circulation of bile acid using bile acid binding resins such as cholestyramine, and/or ileal bypass, and inhibiting intestinal sterol absorption by ezetimibe (EZE). The objective of this review is to evaluate sterol metabolism in STSL and the impact of the currently available treatments on sterol trafficking in this disease. The role of PS in initiation of xanthomas and premature atherosclerosis is also discussed. Blocking sterols absorption with EZE has revolutionized STSL patient treatment as it reduces circulating levels of non-cholesterol sterols in STSL. However, none of the available treatments including EZE have normalized plasma PS concentrations. Future studies are needed to: (i) explore where cholesterol and non-cholesterol sterols accumulate, (ii) assess to what extent these sterols in tissues can be mobilized after blocking their absorption, and (iii) define the factors governing sterol flux.

Impaired hepatic and intestinal ATP-binding cassette transporter G5/8 was associated with high exposure of β-sitosterol and the potential risks to blood-brain barrier integrity in diabetic rats

OBJECTIVES

Plant sterols are thought to treat hypercholesterolemia via inhibiting intestinal cholesterol absorption. The aim of this study was to evaluate the contribution of impaired ATP-binding cassette transporter G5/8 (ABCG5/8) expression by diabetes to the increased β-sitosterol (BS) exposure and impact of increased BS on integrity of blood-brain barrier (BBB).

METHODS

Basal BS level in tissues of streptozotocin-inducted rats and ABCG5/8 protein levels in liver and intestine were investigated; pharmacokinetics of BS was studied following oral dose; and primarily cultured rat brain microvessel endothelial cells (rBMECs) were used to study BS transportation across BBB and effect of BS on BBB integrity.

KEY FINDINGS

Diabetic rats showed greatly upgraded basal levels of BS in plasma, intestine, cerebral and hippocampus, accompanied by impairment of ABCG5/8 protein expression in liver and intestine. Pharmacokinetics studies demonstrated higher AUC0-48 and Cmax , and lower faecal recoveries of BS after oral administration, indicating enhancement of absorption or efflux impairment. In-vitro data showed increased ratio of BS/cholesterol in high levels BS-treated rBMECs was associated with increased BBB permeability of some biomarkers including BS itself.

CONCLUSIONS

Impaired ABCG5/8 protein expression by diabetes led to increase in BS exposure, which may be harmful to BBB function.

Plant sterols and atherosclerosis

PURPOSE OF REVIEW

Plant sterols as ingredients to functional foods are recommended for lowering LDL cholesterol. However, there is an ongoing discussion whether the use of plant sterols is safe.

RECENT FINDINGS

Genetic analyses showed that common variants of the ATP binding cassette transporter G8 (ABCG8) and ABO genes are associated with elevated circulating plant sterols and higher risk for cardiovascular disease. However, these data do not prove a causal role for plant sterols in atherosclerosis because the risk alleles in ABCG8 and ABO are also related to elevated total and LDL cholesterol levels. The ABO locus exhibits still further pleiotropy. Moreover, analyses in the general population indicated that moderately elevated circulating plant sterols are not correlated with present or future vascular disease. In agreement, novel studies using food frequency questionnaires, studies in experimental animals, and dietary intervention studies support that ingestion of plant sterols may be beneficial to cardiovascular health.

SUMMARY

Taken together, current evidence supports the recommendations for the use of plant sterols as LDL cholesterol-lowering agents. Nevertheless, a prospective, randomized, controlled, double-blinded, intervention trial conclusively showing that plant sterol supplementation will prevent hard cardiovascular endpoints is not available to date.

Inhibition of cholesterol absorption: targeting the intestine

Atherosclerosis, the gradual formation of a lipid-rich plaque in the arterial wall is the primary cause of Coronary Artery Disease (CAD), the leading cause of mortality worldwide. Hypercholesterolemia, elevated circulating cholesterol, was identified as a key risk factor for CAD in epidemiological studies. Since the approval of Mevacor in 1987, the primary therapeutic intervention for hypercholesterolemia has been statins, drugs that inhibit the biosynthesis of cholesterol. With improved understanding of the risks associated with elevated cholesterol levels, health agencies are recommending reductions in cholesterol that are not achievable in every patient with statins alone, underlying the need for improved combination therapies. The whole body cholesterol pool is derived from two sources, biosynthesis and diet. Although statins are effective at reducing the biosynthesis of cholesterol, they do not inhibit the absorption of cholesterol, making this an attractive target for adjunct therapies. This report summarizes the efforts to target the gastrointestinal absorption of cholesterol, with emphasis on specifically targeting the gastrointestinal tract to avoid the off-target effects sometimes associated with systemic exposure.

Effect of unialgal diets on the composition of fatty acids and sterols in juvenile ark shell Tegillarca granosa Linnaeus

This study has investigated the effects of six different unialgal diets ( Chaetoceros calcitrans , Platymonas helgolandica , Chlorella sp., Isochrysis galbana , Nannochloropsis oculata , and Pavlova viridis ) on the composition of fatty acids and sterols in juvenile ark shell Tegillarca granosa Linnaeus. The best feeding effects on the growth of shellfish were found in C. calcitrans, followed by I. galbana and P. viridis, whereas Chlorella sp. and N. oculata exhibited relatively poor effects. The fatty acid and sterol compositions in the six microalgae and the juvenile ark shell after feeding were analyzed, and 39 fatty acids and 18 sterols were identified. Although the results demonstrate a close correlation between the sterol compositions in algal species and juvenile ark shell, a similar correlation was not observed between fatty acids. In the juvenile ark shell fed microalgae, the ratio of total saturated fatty acids (SFA) rapidly decreases, whereas the proportion of total polyunsaturated fatty acids (PUFAs) increases considerably. The abundances of AA, EPA, and DHA increase most significantly in shellfish with better growth (fed C. calcitrans, I. galbana, and P. viridis). The number of sterol species is reduced, but the total sterol content in groups fed corresponding microalgae increases, and abundant plant sterols, instead of cholesterol, are accumulated in juvenile ark shell fed appropriate microalgae I. galbana and P. viridis. Therefore, to be more conducive to human health, I. galbana and P. viridis, of the six experimental microalgae, are recommended for artificial ark shell culture.