Phytosterol oxidation products are absorbed in the intestinal lymphatics in rats but do not accelerate atherosclerosis in apolipoprotein E-deficient mice

Exogenous oxidized phytosterol may modulate linoleic acid metabolism through upregulation of fatty acid desaturase in rats

Previous in vitro studies have indicated that oxidized phytosterol (OPS) exhibits some toxicity; however, the harmful effects of OPS on fatty acid metabolism are not completely understood yet. Therefore, this study examined the effects of exogenous phytosterol (PS) and OPS on growth parameters and lipid metabolism in rats. Rats were provided with AIN-76 basal diet, basal diet +0.5% PS, or basal diet +0.5% OPS. We found that the level of cholesterol and triacylglycerols in the liver was significantly lower in OPS-fed rats than in basal diet-fed rats. The ratio of Δ6 desaturation index (20:3(n-6) + 20:4(n-6))/18:2(n-6) in the plasma was significantly higher in the OPS-fed rats than in the PS-fed rats. Additionally, the proportion of arachidonic acid (20:4) in the liver was significantly higher in the OPS-fed group compared with the control group. The mRNA expression levels of Δ6 and Δ5 desaturases were significantly higher in OPS-fed rats than in basal diet-fed rats, but remained unchanged in PS-fed rats. Moreover, the protein level of Δ6 desaturase was significantly higher in both PS- and OPS-fed rats compared with basal diet-fed rats, while the protein level of Δ5 desaturase tended to be higher only in OPS-fed rats than in basal diet-fed rats. Thus, exogenous OPS, but not PS, altered fatty acid composition through the upregulation of mRNA and protein levels of fatty acid desaturation enzymes in the liver. This indicates that exogenous OPS, unlike PS, may modulate the production of eicosanoids from arachidonic acid, potentially promoting allergic reactions, inflammation, and atherosclerosis.

Lipolysis and Sterol Stability and Bioaccessibility of Wholemeal Rye Bread Enriched with Plant Sterols Subjected to Adult and Elderly Digestion Conditions

This study evaluated the impact of different digestion conditions (adult and senior) on lipolysis and bioaccessibility of plant sterols (PS) and phytosterol oxidation products (POPs) in PS-enriched wholemeal rye bread. Under adult digestion conditions, the addition of gastric lipase (GL) reduced lipolysis products (by 6.1% for free fatty acids and 11.7% for monoacylglycerols) and the bioaccessibility of PS by 6.7%, compared to the control. In digestion with both GL and cholesterol esterase (CE), these reductions were 12.9, 20.1, and 11.3%, respectively. Both modifications (GL and GL + CE) increased the bioaccessibility of POPs by 4.5-4.0%. When simulating the elderly digestion, the modified gastric and intestinal phases did not alter PS bioaccessibility but decreased POPs bioaccessibility by 21.8% compared to control, along with reduced lipolysis. Incorporating GL and CE thus approached physiological conditions and influenced lipid digestion. Elderly simulated digestion conditions resulted in a positive outcome by maintaining PS bioaccessibility while reducing potentially harmful POPs.

Dietary Cholest-4-en-3-one, a Cholesterol Metabolite of Gut Microbiota, Alleviates Hyperlipidemia, Hepatic Cholesterol Accumulation, and Hyperinsulinemia in Obese, Diabetic db/db Mice

Previous studies have shown that dietary cholest-4-en-3-one (4-cholestenone, 4-STN) exerts anti-obesity and lipid-lowering effects in mice. However, its underlying mechanisms are not fully understood. In the present study, we evaluated whether 4-STN supplementation would protect obese diabetic db/db mice from obesity-related metabolic disorders. After four weeks of feeding of a 0.25% 4-STN-containing diet, dietary 4-STN was found to have significantly alleviated hyperlipidemia, hepatic cholesterol accumulation, and hyperinsulinemia; however, the effect was not sufficient to improve hepatic triglyceride accumulation or obesity. Further analysis demonstrated that dietary 4-STN significantly increased the content of free fatty acids and neutral steroids in the feces of db/db mice, indicating that the alleviation of hyperlipidemia by 4-STN was due to an increase in lipid excretion. In addition, dietary 4-STN significantly reduced the levels of desmosterol, a cholesterol precursor, in the plasma but not in the liver, suggesting that normalization of cholesterol metabolism by 4-STN is partly attributable to the suppression of cholesterol synthesis in extrahepatic tissues. In addition, dietary 4-STN increased the plasma and hepatic levels of 4-STN metabolites cholestanol (5α-cholestan-3β-ol) and coprostanol (5β-cholestan-3β-ol). Our results show that dietary 4-STN alleviates obesity-related metabolic disorders, such as hyperlipidemia, hepatic cholesterol accumulation, and hyperinsulinemia, in db/db mice.

Sterols in Inflammatory Diseases: Implications and Clinical Utility

The characteristic steroid skeleton, with its 4-ringed 17-carbon structure, is one of the most recognizable organic compounds in biochemistry. In the presence of a hydroxyl ion bound to the third carbon, this structure is defined as a "sterol" (chemical formula: C17H28O). The hydroxyl group provides a hydrophilic site for the otherwise hydrophobic molecule, yielding an amphipathic lipid, which is a vital property for cellular function. It is crucial to remark that the term "steroid" describes a larger group of compounds that often retain the hydroxyl group but are primarily characterized by methyl groups, double bonds in the rings, and an aliphatic side-chain extending from the 17th carbon. In addition to serving various structural roles in the cellular membrane, sterols and steroids contribute to cellular and systemic functions as messengers, hormones, and regulators of several critical metabolic pathways.Sterol nomenclature is often confusing, partly due to structural complexity and partly due to the sheer number of different compounds that fall under the definition. Fortunately, the foremost sterols of interest in biochemistry are much fewer, and therefore, these lipids have been defined and studied vigorously. With the renaissance of lipid research during the 1990s and 2000s, many different metabolites of sterols, and more specifically phytosterols, were found to be associated with various diseases and conditions, including cardiovascular disease, hypercholesterolemia, cancer, obesity, inflammation, diabetes, and inborn errors of metabolism; thus, it is evident that the ever-evolving research in this field has been, and will continue to be, exceedingly productive.With respect to inflammation and inflammatory diseases, plant-based sterols (i.e., phytosterols) have gained considerable fame due to their anti-inflammatory and cholesterol-lowering effects demonstrated by experimental and clinical research. Besides, the exceptional pharmacological benefits of these sterols, which operate as antioxidant, antidiabetic, and anti-atherosclerotic agents, have been the subject of various investigations. While the underlying mechanisms necessitate further research, the possible function of phytosterols in improving health outcomes is an important topic to explore.In this regard, the current review aims to offer comprehensive information on the therapeutic potential of plant-based sterols in the context of human health, with a focus on preclinical effects, bioavailability, and clinical use.

Heating and storage of structured acylglycerols with succinyl-linked stigmasterol residue does not cause negative chemical or biological changes

Four structured acylglycerols with stigmasterol bonded by a succinyl linker were investigated and their stability were analyzed. Samples were heated to 60 °C and kept at that temperature to simulate storage, and to 180 °C to simulate frying conditions. The degradation of the synthesized compounds and formed derivatives was determined, and their cytotoxicity and genotoxicity on normal human cells from the digestive system was determined. Holding at 180 °C resulted in greater degradation of the compounds than holding at 60 °C. The most stable compound in each sample proved to be one with oleic acid in its structure-1,3-dioleoyl-2-stigmasterylsuccinoyl-sn-glycerol (DO2SSt) at 60 °C and 1,2-dioleoyl-3-stigmasterylsuccinoyl-sn-glycerol (DO3SSt) at 180 °C. These results indicate that the type of fatty acid in the molecule is more important than its position in the glycerol structure. None of the diacylmonostigmasterylsuccinoyl-sn-glycerols (DASStGs) before or after heating exhibited cytotoxic or genotoxic potential to small intestine and colon mucosa cells.

The effects of dietary linoleic acid on reducing serum cholesterol and atherosclerosis development are nullified by a high-cholesterol diet in male and female apoE-deficient mice

Linoleic acid (LA) has a two-sided effect with regard to serum cholesterol-lowering and pro-inflammation, although whether this fatty acid reduces serum cholesterol and the development of atherosclerosis under high-cholesterol conditions has yet to be ascertained. In this study, we examine the effects of dietary LA on reducing serum cholesterol and atherosclerosis development under high-cholesterol conditions. Male and female apoE-deficient (ApoE-/-) mice were fed AIN-76-based diets containing 10% SFA and 0·04 % cholesterol, 10% LA and 0·04% low cholesterol (LALC), or 10% LA and 0·1% high cholesterol (LAHC) for 9 weeks. The results revealed significant reduction in serum cholesterol levels and aortic lesions with increasing levels of pro-inflammatory biomarkers (urinary isoprostane and aortic MCP-1 mRNA) in male and female LALC groups compared with those in the SFA groups (P < 0·05). Furthermore, whereas there were significant increases in the serum cholesterol levels and aortic lesions (P < 0·05), there was no difference in aortic MCP-1 mRNA levels in male and female LAHC groups compared with those in the LALC groups. A high-dietary intake of cholesterol eliminated the serum cholesterol-lowering activity of LA but had no significant effect on aortic inflammation in either male or female ApoE-/- mice. The inhibitory effect of LA on arteriosclerosis is cancelled by a high-cholesterol diet due to a direct increase in serum cholesterol levels. Accordingly, serum cholesterol levels might represent a more prominent pathogenic factor than aortic inflammation in promoting the development of atherosclerosis.

Plasma oxyphytosterols most likely originate from hepatic oxidation and subsequent spill-over in the circulation

We evaluated oxyphytosterol (OPS) concentrations in plasma and various tissues of two genetically modified mouse models with either increased cholesterol (apoE KO mice) or increased cholesterol and plant sterol (PS) concentrations (apoExABCG8 dKO mice). Sixteen female apoE KO and 16 dKO mice followed the same standard, low OPS-chow diet. Animals were euthanized at 36 weeks to measure PS and OPS concentrations in plasma, brain, liver and aortic tissue. Cholesterol and oxysterol (OS) concentrations were analyzed as reference for sterol oxidation in general. Plasma campesterol (24.1 ± 4.3 vs. 11.8 ± 3.0 mg/dL) and sitosterol (67.4 ± 12.7 vs. 4.9 ± 1.1 mg/dL) concentrations were severely elevated in the dKO compared to the apoE KO mice (p < 0.001). Also, in aortic and brain tissue, PS levels were significantly elevated in dKO. However, plasma, aortic and brain OPS concentrations were comparable or even lower in the dKO mice. In contrast, in liver tissue, both PS and OPS concentrations were severely elevated in the dKO compared to apoE KO mice (sum OPS: 7.4 ± 1.6 vs. 4.1 ± 0.8 ng/mg, p < 0.001). OS concentrations followed cholesterol concentrations in plasma and all tissues suggesting ubiquitous oxidation. Despite severely elevated PS concentrations, OPS concentrations were only elevated in liver tissue, suggesting that OPS are primarily formed in the liver and plasma concentrations originate from hepatic spill-over into the circulation.

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.

Dietary Sterols and Sterol Oxidation Products on Atherosclerosis: An Insight Provided by Liver Proteomic and Lipidomic

SCOPE

The development of atherosclerosis is closely associated with disorder of lipid metabolism. Dietary sterols and their oxidation products play a role in the pathogenesis of atherosclerosis. However, their effects on liver lipid metabolism during the atherosclerosis remain unknown.

METHODS AND RESULTS

Here, we apply lipidomic and proteomic analysis on liver of ApoE^-/- mice feed with phytosterols, cholesterol oxidation products (COPs), or phytosterol oxidation products (POPs) to profile lipid species and reveal the underlying mechanism. Dietary exposure of phytosterols, COPs, and POPs all reduce the accumulation of liver triglyceride (TG), but COPs and POPs accelerate the fibrosis of liver. Lipidomic analysis reveals that phytosterols mainly decrease the levels of phosphatidylinositol (PI), while COPs and POPs both increase the level of digalactosyldiacylglycerol (DGDG) and reduce TG with long-chain polyunsaturated fatty acids. Besides, COPs up-regulated levels of lipids associate with atherosclerosis risk, such as phosphatidylcholines (PC), phosphatidylethanolamine (PE) and ceramides (Cer). POPs down-regulate the level of acyl carnitine (AcCa). Furthermore, proteomic analysis shows that COPs promote oxidative phosphorylation and POPs inhibit the beta oxidation of fatty acids.

CONCLUSIONS

This study reveals that phytosterols, COPs, and POPs differently change the composition and metabolism of glycerophospholipids, sphingolipids, and glycerolipids in liver of ApoE^-/- mice.

Ablation of fatty acid desaturase 2 (FADS2) exacerbates hepatic triacylglycerol and cholesterol accumulation in polyunsaturated fatty acid-depleted mice

Deficiency of polyunsaturated fatty acids (PUFAs) is known to induce hepatic steatosis. However, it is not clearly understood which type of PUFA is responsible for the worsening of steatosis. This study observed a marked accumulation of hepatic triacylglycerol and cholesterol in fatty acid desaturase 2 knockout (FADS2^-/- ) mice lacking both C18 and ≥ C20 PUFAs that were fed a PUFA-depleted diet. Hepatic triacylglycerol accumulation was associated with enhanced sterol regulatory element-binding protein (SREBP)-1-dependent lipogenesis and decreased triacylglycerol secretion into the plasma via very-low-density lipoprotein (VLDL). Furthermore, upregulation of cholesterol synthesis contributed to increased hepatic cholesterol content in FADS2^-/- mice. These results suggest that ≥ C20 PUFAs synthesized by FADS2 are important in regulating hepatic triacylglycerol and cholesterol accumulation during PUFA deficiency.

Linking phytosterols and oxyphytosterols from food to brain health: origins, effects, and underlying mechanisms

Phytosterols and their oxidation products, namely oxyphytosterols, are natural compounds present in plant foods. With increased intake of phytosterol-enriched functional food products, the exposure of both phytosterols and oxyphytosterols is rising. Over the past ten years, researches have been focused on their absorption and metabolism in human body, as well as their biological effects. More importantly, recent studies showed that phytosterols and oxyphytosterols can traverse the blood-brain barrier and accumulate in the brain. As brain health problems resulting from ageing being more serious, attenuating central nervous system (CNS) disorders with active compounds in food are becoming a hot topic. Phytosterols and oxyphytosterols have been shown to implicated in cognition altering and the pathologies of several CNS disorders, including Alzheimer's disease and multiple sclerosis. We will overview these findings with a focus on the contents of phytosterols and oxyphytosterols in food and their dietary intake, as well as their origins in the brain, and illustrate molecular pathways through which they affect brain health, in terms of inflammation, cholesterol homeostasis, oxidative stress, and mitochondria function. The existing scientific gaps of phytosterols and oxyphytosterols to brain health in knowledge are also discussed, highlighting research directions in the future.

5α,6α-Epoxyphytosterols and 5α,6α-Epoxycholesterol Increase Nitrosative Stress and Inflammatory Cytokine Production in Rats on Low-Cholesterol Diet

Objective

Oxidized cholesterol derivatives are compounds with proven atherogenic and mutagenic effects. However, little is known about the effect of oxidized plant sterol derivatives (oxyphytosterols), whose structure is similar to the one of oxycholesterols. Our previous studies indicate that they have a similar profile of action, e.g., both exacerbate disorder of lipid metabolism and oxidative stress in experimental animals. The aim of the present study was to assess the effect of epoxycholesterol and epoxyphytosterols (mainly sitosterol) on the severity of nitrosative stress and the concentration of selected proinflammatory cytokines in blood and liver tissue of rats on a low-cholesterol diet. Material and Methods. Forty-five male Wistar rats were fed with feed containing 5α,6α-epoxyphytosterols (ES group, n: 15), 5α,6α-epoxycholesterol (ECh group, n: 15), and oxysterol-free feed (C group, n: 15) for 90 days (daily dose of oxysterols: 10 mg/kg). At the end of the experiment, nitrotyrosine, TNF-α, IL-1β, IL-6, and lipid metabolism parameters were determined in blood serum. Furthermore, nitrotyrosine, TNF-α, cholesterol, and triglyceride content were determined in liver homogenates.

Results

Serum nitrotyrosine, IL-1β, and TNF-α concentrations as well as TNF-α content in the liver were significantly higher in both groups exposed to oxysterols (ECh and ES groups) as compared to the C group. The serum IL-6 level and nitrotyrosine content in the liver were significantly higher in the ECh group, as compared to the C and ES groups. There was evidence to support the dyslipidemic effect of studied compounds.

Conclusions

The results indicate that oxidized plant sterols have a similar toxicity profile to that of oxycholesterols, including nitrosative stress induction, proinflammatory effect, and impaired lipid metabolism.

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.

Acyl moiety and temperature affects thermo-oxidative degradation of steryl esters. Cytotoxicity of the degradation products

Phytosterols and their esters are often used as functional ingredients in food products due to its lowering blood cholesterol properties. Products containing phytosterols and its esters are recommended for direct consumption, cooking, baking and frying, however during food preparation it is possible thermo-oxidative degradation is possible. Unsaturation of fatty acid present in steryl ester may further stimulates degradation. Free stigmasterol degraded faster than its esters, even with linoleic acid attached. The highest amount of degradation products was observed for free stigmasterol, followed by esters with linoleic and oleic acids. Polar dimers were fund in all heated samples, although for free stigmasterol heated at 60 °C were not detected. Whereas non-polar dimers were observed only in heated stigmasterol. Degradation of esterified stigmasterol generated degradation products with lower cytotoxicity.

5α,6α-Epoxyphytosterols and 5α,6α-Epoxycholesterol Increase Oxidative Stress in Rats on Low-Cholesterol Diet

Objective

Cholesterol oxidation products have an established proatherogenic and cytotoxic effect. An increased exposure to these substances may be associated with the development of atherosclerosis and cancers. Relatively little, though, is known about the effect of phytosterol oxidation products, although phytosterols are present in commonly available and industrial food products. Thus, the aim of the research was to assess the effect of 5α,6α-epoxyphytosterols, which are important phytosterol oxidation products, on redox state in rats.

Material and Methods

The animals were divided into 3 groups and exposed to nutritional sterols by receiving feed containing 5α,6α-epoxyphytosterols (ES group) and 5α,6α-epoxycholesterol (Ech group) or sterol-free feed (C group). The levels of malondialdehyde (MDA), conjugated dienes (CD), and ferric reducing antioxidant potential (FRAP) were assayed in the plasma; anti-7-ketocholesterol antibodies and activity of paraoxonase-1 (PON1) were determined in serum, whereas the activity of catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), S-glutathione transferase (GST), and superoxide dismutase (SOD) were assayed in RBCs.

Results

During the experiment, the levels of lipid peroxidation products increased, such as CD and anti-7-ketocholesterol antibodies. At the same time, the plasma levels of FRAP and serum activity of PON1 decreased alongside the reduced activity of GPx, GR, and SOD in RBCs. There was no effect of the studied compounds on the plasma MDA levels or on the activity of CAT and GST in RBCs.

Conclusions

Both 5α,6α-epoxyphytosterols and 5α,6α-epoxycholesterols similarly dysregulate the redox state in experimental animal model and may significantly impact atherogenesis.

Serum Concentration of Plant Sterol Oxidation Products (POP) Compared to Cholesterol Oxidation Products (COP) after Intake of Oxidized Plant Sterols: A Randomised, Placebo-Controlled, Double-Blind Dose‒Response Pilot Study

Plant sterols (PS) are oxidized to PS oxidation products (POP). This study quantified the change in serum POP compared to cholesterol oxidation products (COP) after the intake of increasing POP doses. This was a double-blind, randomized, placebo-controlled, dose‒response pilot study with healthy individuals in four groups (15 per group). The control group received products with no added PS or POP and treatment groups received daily 20–25 g margarine with added PS (mean 3 g/d) and two cookies (~28 g) for six weeks. Cookies delivered 8.7 (low-dose), 15.2 (medium-dose), or 37.2 (high-dose) mg/d POP. Fasting serum POP and COP were measured at the baseline, days 14, 28, and 42 in all participants and days 7, 21, and 35 in a subset. Sixty individuals completed the study; 52 were included in per protocol analysis. Serum POP increased with increasing POP intake and plateaued at dose >15 mg/d. Stabilized POP concentrations were (mean ± SD) 38.9 ± 6.9, 91.0 ± 27.9, 144.4 ± 37.9 and 203.0 ± 63.7 nmol/L, for control, low-, medium-, and high-dose POP groups, respectively. For all groups, the serum COP ranged from 213 to 262 nmol/L and the average POP/COP ratio was <1. Serum POP concentrations increased non-linearly, reaching stabilized concentrations in <7 days, and remained below COP concentrations after the intake of increasing POP doses.

Plasma oxyphytosterol concentrations are not associated with CVD status in Framingham Offspring Study participants

Dietary plant sterols, such as campesterol and sitosterol, reduce plasma cholesterol concentrations, but any relationship to plaque development and CVD remains unclear. Some epidemiologic studies have suggested that elevated plasma plant sterol concentrations are atherogenic, including the Framingham Offspring Study that identified a positive association between plant sterol concentrations and CVD status. We hypothesized that this suggested atherogenicity relates to the oxidation status of plant sterols (i.e., concentrations of plasma oxyphytosterols). Therefore, in the Framingham Offspring Study cohort, we measured plasma oxyphytosterol concentrations in 144 patients with documented CVD and/or more than 50% carotid stenosis and 383 matched controls. We analyzed plasma oxyphytosterol concentrations by GC/MS/MS and performed conditional logistic regression analysis to determine associations between plasma plant sterol or oxyphytosterol concentrations and CVD status. We found that higher total cholesterol (TC)-standardized campesterol concentrations [odds ratio (OR): 2.36; 95% CI: 1.60, 3.50] and higher sitosterol concentrations (OR: 1.47; 95% CI: 1.09, 1.97) were significantly associated with increased CVD risk, as in the earlier study. However, the sum of absolute oxyphytosterol concentrations (OR: 0.99; 95% CI: 0.81, 1.21) and the sum of TC-standardized oxyphytosterol concentrations (OR: 0.98; 95% CI: 0.80, 1.19) were not associated with an increased CVD risk. Results were comparable for individual absolute and TC-standardized oxycampesterol and oxysitosterol concentrations. Plasma nonoxidized TC-standardized sitosterol and campesterol concentrations showed weak or no correlations with oxyphytosterol concentrations, while all individual plasma concentrations of oxyphytosterol correlated with each other. In conclusion, circulating plasma oxyphytosterols are not associated with CVD risk in the Framingham Offspring Study.

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.

Plasma levels of the oxyphytosterol 7α-hydroxycampesterol are associated with cardiovascular events

BACKGROUND AND AIMS

There are safety issues regarding plant sterol ester-enriched functional food. Oxidized plant sterols, also called oxyphytosterols, are supposed to contribute to plant sterol atherogenicity. This study aimed to analyze associations of plasma oxyphytosterol levels with cardiovascular events.

METHODS

Plasma cholesterol was measured by gas chromatography-flame ionization detection. Plasma campesterol and sitosterol and their 7-oxygenated metabolites were analyzed by gas chromatography-mass selective detection.

RESULTS

In 376 patients admitted for elective coronary angiography, who were not on lipid-lowering drugs, 82 cardiovascular events occurred during a follow-up period of 4.2 ± 1.8 years. Patients with cardiovascular events had significantly higher 7α-hydroxycampesterol plasma levels (median, 0.46; [interquartile range (IQR) 0.22-0.81] nmol/L vs. median, 0.25 [IQR, 0.17-0.61] nmol/L; p = 0.003) and 7α-hydroxycampesterol-to-cholesterol ratios (median 0.08 [IQR, 0.04-0.14] nmol/mmol vs. median, 0.05 [IQR 0.03-0.11] nmol/mmol; p = 0.005) than controls without such events. Patients above the median were characterized by higher cumulative event rates in Kaplan-Meier-analysis (Logrank-test p = 0.084 and p = 0.025) for absolute and cholesterol corrected 7α-hydroxycampesterol, respectively. After adjustment for influencing factors and related lipids, the hazard ratios per one standard deviation of the log-transformed variables (HR) were 1.19 [95% confidence interval (CI), 0.95-1.48], p = 0.132 for 7α-hydroxycampesterol and HR, 1.18 [95% CI, 0.94-1.48], p = 0.154 for 7α-hydroxycampesterol-to-cholesterol ratio. None of the other investigated oxyphytosterols showed an association with cardiovascular events.

CONCLUSIONS

In patients not on lipid-lowering drugs, absolute plasma levels of 7α-hydroxycampesterol and their ratios to cholesterol are associated with cardiovascular events. Further research is required to elucidate the role of OPS in cardiovascular diseases.

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.

Effect of Fatty Acid Unsaturation on Phytosteryl Ester Degradation

This study examined the thermo-oxidative degradation of stigmasterol fatty acids esters. Stigmasterol stearate, oleate, linoleate and linolenate were synthesized by chemical esterification and their purity evaluated by ¹H-NMR and GC-MS. The degradation of stigmasterol esters was examined after heating them at 60 and 180 °C for 1, 2, 4, 8 and 12 h. It was established that stigmasterol esters were prone to thermo-oxidative degradation, with time and temperature affecting the degree of degradation. The unsaturation of fatty acids affected the rate of stigmasteryl ester degradation. The kinetics of StS and StO degradation were similar and the additional double bonds in StL and StLn resulted in their faster decomposition. The esters degraded faster at 180 than at 60 °C. The sterol and fatty acid molecules degraded at different rates, such that the fatty acid moiety deteriorated faster than the sterol at both temperatures, independent of the time of heating and the level of unsaturation.

TTC39B deficiency stabilizes LXR reducing both atherosclerosis and steatohepatitis

Cellular mechanisms that mediate steato-hepatitis, an increasingly prevalent condition in the Western world for which no therapies are available¹, are poorly understood. Despite the fact its synthetic agonists induce fatty liver, the Liver X receptor (LXR) transcription factor remains a target of interest because of its anti-atherogenic, cholesterol removal and anti-inflammatory activities. We discovered that tetratricopeptide repeat (TPR) domain protein 39B (Ttc39b, C9orf52) (T39), a high density lipoprotein (HDL) gene discovered in human genome wide association studies (GWAS)², promotes the ubiquitination and degradation of LXR. Chow-fed T39^-/- mice displayed increased HDL cholesterol levels associated with increased enterocyte ATP binding cassette transporter A1 (Abca1) expression and increased LXR protein without change in LXR mRNA. When challenged with a high fat/high cholesterol/bile salt (HF/HC/BS) diet, T39^-/- mice or mice with hepatocyte-specific T39 deficiency showed increased hepatic LXR protein and target gene expression, and unexpectedly protection from steato-hepatitis and death. Western Type Diet (WTD)-fed Low density lipoprotein receptor (Ldlr)^-/-T39^-/- mice showed decreased fatty liver, increased HDL, decreased LDL and reduced atherosclerosis. In addition to increasing hepatic Abcg5/8 expression and limiting dietary cholesterol absorption, T39 deficiency inhibited hepatic sterol regulatory element binding protein 1 (SREBP-1, ADD1) processing. This was explained by an increase in microsomal phospholipids containing polyunsaturated fatty acids (PUFA), linked to an LXRα-dependent increase in expression of enzymes mediating PC biosynthesis and incorporation of PUFA into phospholipids. The preservation of endogenous LXR protein activates a beneficial profile of gene expression that promotes cholesterol removal and inhibits lipogenesis. T39 inhibition could be an effective strategy for reducing both steato-hepatitis and atherosclerosis.

Phytosterol oxidation products (POP) in foods with added phytosterols and estimation of their daily intake: A literature review

To evaluate the content of phytosterol oxidation products (POP) of foods with added phytosterols, in total 14 studies measuring POP contents of foods with added phytosterols were systematically reviewed. In non‐heated or stored foods, POP contents were low, ranging from (medians) 0.03–3.6 mg/100 g with corresponding oxidation rates of phytosterols (ORP) of 0.03–0.06%. In fat‐based foods with 8% of added free plant sterols (FPS), plant sterol esters (PSE) or plant stanol esters (PAE) pan‐fried at 160–200°C for 5–10 min, median POP contents were 72.0, 38.1, and 4.9 mg/100 g, respectively, with a median ORP of 0.90, 0.48, and 0.06%. Hence resistance to thermal oxidation was in the order of PAE > PSE > FPS. POP formation was highest in enriched butter followed by margarine and rapeseed oil. In margarines with 7.5–10.5% added PSE oven‐heated at 140–200°C for 5–30 min, median POP content was 0.3 mg/100 g. Further heating under same temperature conditions but for 60–120 min markedly increased POP formation to 384.3 mg/100 g. Estimated daily upper POP intake was 47.7 mg/d (equivalent to 0.69 mg/kg BW/d) for foods with added PSE and 78.3 mg/d (equivalent to 1.12 mg/kg BW/d) for foods with added FPS as calculated by multiplying the advised upper daily phytosterol intake of 3 g/d with the 90% quantile values of ORP. In conclusion, heating temperature and time, chemical form of phytosterols added and the food matrix are determinants of POP formation in foods with added phytosterols, leading to an increase in POP contents.

Practical applications: Phytosterol oxidation products (POP) are formed in foods containing phytosterols especially when exposed to heat treatment. This review summarising POP contents in foods with added phytosterols in their free and esterified forms reveals that heating temperature and time, the chemical form of phytosterols added and the food matrix itself are determinants of POP formation with heating temperature and time having the biggest impact. The estimated upper daily intakes of POP is 78.3 mg/d for fat‐based products with added free plant sterols and 47.7 mg/d for fat‐based products with added plant sterol esters.

Phytosterols in foods are susceptible to oxidation to form phytosterol oxidation products (POP). This review summarizes literature data regarding POP contents of foods with added phytosterols that were exposed to storage and heat treatments.

Maternal Phytosterol Supplementation during Pregnancy and Lactation Modulates Lipid and Lipoprotein Response in Offspring of apoE-Deficient Mice

BACKGROUND

In utero exposure to excessive cholesterol has been shown to increase fetal plasma cholesterol concentration and predispose adult offspring to cardiovascular disease (CVD) risk. Because lipid-lowering drugs are contraindicated during pregnancy, natural cholesterol-lowering compounds may be a safe and effective alternative to reduce CVD risk in offspring born to hypercholesterolemic mothers.

OBJECTIVE

This study used the hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)) mouse model to test the hypothesis that mothers supplemented with phytosterols during gestation and lactation would produce offspring with a more favorable lipid profile than offspring from unsupplemented mothers, despite having a genetic predisposition toward hypercholesterolemia.

METHODS

Sixteen female apoE(-/-) mice were randomly assigned to 2 diets fed throughout the gestation and lactation periods: a cholesterol-enriched diet (CH) (0.15%) or the cholesterol-enriched diet supplemented with phytosterols (CH/PS) (2%). Serum lipids and lipoproteins were measured by enzyme assay and nuclear magnetic resonance spectroscopy, respectively, and liver cholesterol was analyzed by GC.

RESULTS

Compared with the CH-fed dams at the end of lactation, phytosterol-supplemented dams displayed lower (P < 0.05) serum total cholesterol (-55%), non-HDL cholesterol (-56%), and LDL cholesterol (-47%), but no change (P > 0.05) in HDL cholesterol and triacylglycerol (TG) concentrations. Pups from phytosterol-fed dams demonstrated lower (P < 0.05) total cholesterol (-25%), non-HDL cholesterol (-25%), LDL cholesterol (-47%), and TGs (-41%), without any change (P > 0.05) in HDL cholesterol compared with pups from CH-fed dams. Furthermore, compared with pups from CH-fed dams, pups from phytosterol-supplemented dams displayed a lower (P < 0.05) number of total LDL particles (-34%), VLDL particles (-31%), and HDL particles (-30%).

CONCLUSION

Our results in apoE(-/-) mice suggest that even under strong genetic predisposition to hypercholesterolemia, pups born to mothers supplemented with phytosterols during gestation and lactation exhibit favorable liver and serum lipid responses compared with pups from unsupplemented mothers.

Postprandial plasma oxyphytosterol concentrations after consumption of plant sterol or stanol enriched mixed meals in healthy subjects

Epidemiological studies have reported inconsistent results on the relationship between increased plant sterol concentrations with cardiovascular risk, which might be related to the formation of oxyphytosterols (plant sterol oxidation products) from plant sterols. However, determinants of oxyphytosterol formation and metabolism are largely unknown. It is known, however, that serum plant sterol concentrations increase after daily consumption of plant sterol enriched products, while concentrations decrease after plant stanol consumption. Still, we have earlier reported that fasting oxyphytosterol concentrations did not increase after consuming a plant sterol- or a plant stanol enriched margarine (3.0g/d of plant sterols or stanols) for 4weeks. Since humans are in a non-fasting state for most part of the day, we have now investigated effects on oxyphytosterol concentrations during the postprandial state. For this, subjects consumed a shake (50g of fat, 12g of protein, 67g of carbohydrates), containing no, or 3.0g of plant sterols or plant stanols. Blood samples were taken up to 8h and after 4h subjects received a second shake (without plant sterols or plant stanols). Serum oxyphytosterol concentrations were determined in BHT-enriched EDTA plasma via GC-MS/MS. 7β-OH-campesterol and 7β-OH-sitosterol concentrations were significantly higher after consumption of a mixed meal enriched with plant sterol esters compared to the control and plant stanol ester meal. These increases were seen only after consumption of the second shake, illustrative for a second meal effect. Non-oxidized campesterol and sitosterol concentrations also increased after plant sterol consumption, in parallel with 7β-OH concentrations and again only after the second meal. Apparently, plant sterols and oxyphytosterols follow the same second meal effect as described for dietary cholesterol. However, the question remains whether the increase in oxyphytosterols in the postprandial phase is due to absorption or endogenous formation.

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.

Oxyphytosterols as active ingredients in wheat bran suppress human colon cancer cell growth: identification, chemical synthesis, and biological evaluation

Consumption of whole grains has been reported to be associated with a lower risk of colorectal cancer. Recent studies illustrated that phytochemicals in wheat bran (WB) may protect against colorectal cancer. There is a growing interest in the phytosterol contents of foods as either intrinsic or added components due to their beneficial health effects. However, little is known whether phytosterols in WB contribute the observed chemopreventative activity of the grain. In the present study, we directly purified and identified four oxyphytosterols 1-4 from sterol-enriched fraction of WB, and also successfully synthesized five sterol oxides 5-8 and 13. Using these nine compounds as references, we outlined a comprehensive profile of steroids in WB using tandem liquid chromatography mass spectrometry with electrospray ionization (LC-ESI/MS(n), n = 2-3) techniques for the first time. Among them, three sterol oxides 13, 14, and 18 are novel compounds, and 14 compounds 3, 4, 6-11, 13, 14, 16, and 18-20 were reported in WB for the first time. Our results on the inhibitory effects of available sterol oxides 1-8 and 13 against the growth of human colon cancer cells HCT-116 and HT-29 showed that compounds 2-8 exerted significant antiproliferative effects, with oxysterol 8 being the most active one in both cells. We further demonstrated that four most active sterol oxides 5-8 could induce cell death through the apoptosis pathway. Our results showed that phytosterols, particularly oxyphytosterols, in WB possess significant antiproliferative properties, and thereby may greatly contribute the observed chemoprevention of the whole grain wheat.

Oxidation of β-sitosterol and campesterol in sunflower oil upon deep- and pan-frying of French fries

Fried foods, both deep-fried and pan-fried, are enjoyed by people worldwide. Frying is one of the main factors leading to formation of phytosterols (PS) oxidation products (POP) in vegetable oils. The aim of this study was to measure the oxidation of β-sitosterol (24α-ethyl-5-cholesten-3β-ol) and campesterol (24α-methyl-5-cholesten-3β-ol) in commercial sunflower oil (SFO) during deep- and pan-frying of French fries for different periods (30, 60, 120 and 240 min). The total amount of PS in SFO was 4732 μg/g, wherein the major PS were β-sitosterol and campesterol. The results of POP were confirmed by the GC-MS analysis that monitored the formation of oxides during frying. Upon frying, total PS content decreased whereas the highest decrease was measured after 240 min of frying. The oxidative stability (OS) of different sitosterol and campesterol during both frying methods was evaluated. In general, pan frying resulted in more PS oxidation than deep frying. β-Sitosterol oxides predominated while campesterol oxides were formed to a lesser extent. 7-Ketositosterol, followed by 7β-hydroxysitosterol, 5,6-epoxy derivatives and 7α-hydroxysitosterol were the main POP induced during frying. The proportion of 7-keto derivatives decreased during frying while the proportion of 7β-hydroxy derivatives increased. The formation of POP might be a limiting factor for frying in SFO for long periods.

Plant sterols from foods in inflammation and risk of cardiovascular disease: a real threat?

High dietary intakes of cholesterol together with sedentary habits have been identified as major contributors to atherosclerosis. The latter has long been considered a cholesterol storage disease; however, today atherosclerosis is considered a more complex disease in which both innate and adaptive immune-inflammatory mechanisms as well as bacteria play a major role, in addition to interactions between the arterial wall and blood components. This scenario has promoted nutritional recommendations to enrich different type of foods with plant sterols (PS) because of their cholesterol-lowering effects. In addition to cholesterol, PS can also be oxidized during food processing or storage, and the oxidized derivatives, known as phytosterol oxidation products (POPs), can make an important contribution to the negative effects of both cholesterol and cholesterol oxidation oxides (COPs) in relation to inflammatory disease onset and the development of atherosclerosis. Most current research efforts have focused on COPs, and evaluations of the particular role and physiopathological implications of specific POPs have been only inferential. Appreciation of the inflammatory role described for both COPs and POPs derived from foods also provides additional reasons for safety studies after long-term consumption of PS. The balance and relevance for health of all these effects deserves further studies in humans. This review summarizes current knowledge about the presence of sterol oxidation products (SOPs) in foods and their potential role in inflammatory process and cardiovascular disease.

Oxidised plant sterols as well as oxycholesterol increase the proportion of severe atherosclerotic lesions in female LDL receptor+/ − mice

Oxysterols (oxidised cholesterol) may play a role in the pathogenesis of CVD. Similar to cholesterol, plant sterols are susceptible to oxidation. However, less is known about the potential atherogenicity of oxidised plant sterols (oxyphytosterols). In the present study, the atherogenicity of a mixture of oxyphytosterols was examined by feeding female LDL receptor-deficient (LDLR+/ −) mice for 35 weeks a control diet (atherogenic high-fat diet; n 9), an oxysterol diet (control diet+0·025 % (w/w) oxysterols; n 12) or an oxyphytosterol diet (control diet+0·025 % (w/w) oxyphytosterols; n 12). In the LDLR+/ − mice, serum levels of cholesterol, lipoprotein profiles, cholesterol exposure and inflammatory markers at the end of the experiment were comparable between the three diet groups. Nevertheless, the proportion of severe atherosclerotic lesions was significantly higher after oxysterol (41 %; P= 0·004) and oxyphytosterol (34 %; P= 0·011) diet consumption than after control diet consumption (26 %). Oxyphytosterol levels in the lesions were the highest in the oxyphytosterol group. Here, we show that not only dietary oxysterols but also dietary oxyphytosterols increase the proportion of severe atherosclerotic lesions. This suggests that plant sterols when oxidised may increase atherosclerotic lesion severity instead of lowering the size and severity of lesions when fed in their non-oxidised form. Therefore, this finding might give an indication as to where to find the answer in the current hot debate about the potential atherogenicity of plant sterols. However, to what extent these results can be extrapolated to the human situation warrants further investigation.

Perilipin-mediated lipid droplet formation in adipocytes promotes sterol regulatory element-binding protein-1 processing and triacylglyceride accumulation

Sterol regulatory element-binding protein-1 (SREBP-1) has been thought to be a critical factor that assists adipogenesis. During adipogenesis SREBP-1 stimulates lipogenic gene expression, and peroxisome proliferator-activated receptor γ (PPARγ) enhances perilipin (plin) gene expression, resulting in generating lipid droplets (LDs) to store triacylglycerol (TAG) in adipocytes. Plin coats adipocyte LDs and protects them from lipolysis. Here we show in white adipose tissue (WAT) of plin-/- mice that nuclear active SREBP-1 and its target gene expression, but not nuclear SREBP-2, significantly decreased on attenuated LD formation. When plin-/- mouse embryonic fibroblasts (MEFs) differentiated into adipocytes, attenuated LDs were formed and nuclear SREBP-1 decreased, but enforced plin expression restored them to their original state. Since LDs are largely derived from the endoplasmic reticulum (ER), alterations in the ER cholesterol content were investigated during adipogenesis of 3T3-L1 cells. The ER cholesterol greatly reduced in differentiated adipocytes. The ER cholesterol level in plin-/- WAT was significantly higher than that of wild-type mice, suggesting that increased LD formation caused a change in ER environment along with a decrease in cholesterol. When GFP-SREBP-1 fusion proteins were exogenously expressed in 3T3-L1 cells, a mutant protein lacking the S1P cleavage site was poorly processed during adipogenesis, providing evidence of the increased canonical pathway for SREBP processing in which SREBP-1 is activated by two cleavage enzymes in the Golgi. Therefore, LD biogenesis may create the ER microenvironment favorable for SREBP-1 activation. We describe the novel interplay between LD formation and SREBP-1 activation through a positive feedback loop.

Design of foods with bioactive lipids for improved health

Numerous studies have found an association between the consumption of certain bioactive lipids and improved human health, e.g., the prevention, delay, or treatment of chronic and acute diseases, such as cancer, cardiovascular disease (CVD), osteoporosis, and immune disorders. In this review, we discuss food-based sources and potential beneficial attributes of major dietary bioactive lipids: polyunsaturated fatty acids; carotenoids; phytosterols and phytostanols; and fat-soluble vitamins. We summarize the various challenges associated with incorporating these bioactive lipids into foods and beverages, such as poor water solubility, high melting point, and low chemical stability. Finally, we propose several techniques that have been used to solve the challenges and integrate dietary bioactive lipids into foods for improved health.

Plant sterol oxidation products--analogs to cholesterol oxidation products from plant origin?

Cholesterol and plant sterols are lipids which are abundantly present in a western type diet of animal and plant origin, respectively. The daily intake averages 300 mg/day each. Over the past decades, a steadily increasing consumption of plant sterol enriched dairy products (2-3 g/day) took place to lower circulating LDL cholesterol concentrations. Like all unsaturated components, plant sterols can be attacked by reactive oxygen species resulting in plant sterol oxidation products (POPs). The most widespread methods for POP determination are high-performance liquid chromatography and gas-liquid chromatography. Yet, based on the low plasma POP concentrations in normophytosterolemic subjects (POPs: ∼0.3-4.5 ng/mL), a reliable quantification yielding an appropriate limit of detection remains a challenge. While the more abundantly present cholesterol oxidation products (COPs) have elaborately been studied, research on the metabolism and biological effects of POPs is only emerging. In relation to atherogenity, biological effects including modulation of cholesterol homeostasis, membrane functioning, and inflammation are attributed to POPs. Although mostly supra-physiological concentrations are applied in in vitro assays, anti-tumor activity, cytotoxicity and estrogen-competition have been attributed to specific POPs. However, it is not obvious, if and how POPs may exert in vivo adverse or beneficial health effects similar to those attributed to COPs. In the field of nutritional science, standardized methods for the determination of POPs are required to perform relevant biological studies and to assess their presence in complex foods or biological tissues and fluids. The aim of this review is to provide an overview and evaluation of the published methods and an update on the biological effects attributed to POPs.

Effect of phytosterols and their oxidation products on lipoprotein profiles and vascular function in hamster fed a high cholesterol diet

Human diets contain phytosterols and their oxidation products. We investigated effect of β-sitosterol (Si), stigmasterol (St), β-sitosterol oxidation products (SiOP) and stigmasterol oxidation products (StOP) on plasma total cholesterol and their interaction with the gene expression of enzymes, proteins and transporters involved in cholesterol absorption and metabolism. Sixty male hamsters were fed the control diet or one of four experimental diets containing 0.1% Si, 0.1% SiOP, 0.1% St and 0.1% StOP, respectively, for six weeks. SiOP and StOP groups had the relative liver weights greater than their corresponding non-oxidized forms, indicating they were possibly toxic. Results showed both Si and St groups reduced while SiOP and StOP hamsters lost the capacity of lowering plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL) and triacylglycerols (TG) compared with the control group. Si and St but not SiOP and StOP were anti-atherosclerotic. RT-PCR analysis demonstrated Si and St but not SiOP and StOP down-regulated mRNA levels of intestinal acyl CoA: cholesterol acyltransferase (ACAT2) and microsomal triglyceride protein (MTP). Aortas from Si and St hamsters relaxed better than those from the control and their corresponding SiOP and StOP-treated hamsters. It was concluded that Si and St not SiOP and StOP were beneficial in improving lipoprotein profile and aortic function.