A Comparison of the Potential Unfavorable Effects of Oxycholesterol and Oxyphytosterol in Mice: Different Effects, on Cerebral 24S-Hydroxychoelsterol and Serum Triacylglycerols Levels

Regulation of Th17/Treg Balance by 27-Hydroxycholesterol and 24S-Hydroxycholesterol Correlates with Learning and Memory Ability in Mice

Dysregulation of cholesterol metabolism and its oxidative products-oxysterols-in the brain is known to be associated with neurodegenerative diseases. It is well-known that 27-hydroxycholesterol (27-OHC) and 24S-hydroxycholesterol (24S-OHC) are the main oxysterols contributing to the pathogenesis of Alzheimer's disease (AD). However, the molecular mechanism of how 27-OHC and 24S-OHC cause cognitive decline remains unclear. To verify whether 27-OHC and 24S-OHC affect learning and memory by regulating immune responses, C57BL/6J mice were subcutaneously injected with saline, 27-OHC, 24S-OHC, 27-OHC+24S-OHC for 21 days. The oxysterols level and expression level of related metabolic enzymes, as well as the immunomodulatory factors were measured. Our results indicated that 27-OHC-treated mice showed worse learning and memory ability and higher immune responses, but lower expression level of interleukin-10 (IL-10) and interferon (IFN-λ2) compared with saline-treated mice, while 24S-OHC mice performed better in the Morris water maze test than control mice. No obvious morphological lesion was observed in these 24S-OHC-treated mice. Moreover, the expression level of interleukin-17A (IL-17A), granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage inflammatory protein 3α (MIP-3α) were significantly decreased after 24S-OHC treatment. Notably, compared with 27-OHC group, mice treated with 27-OHC+24S-OHC showed higher brain 24S-OHC level, accompanied by increased CYP46A1 expression level while decreased CYP7B1, retinoic acid-related orphan receptor gamma t (RORγt) and IL-17A expression level. In conclusion, our study indicated that 27-OHC is involved in regulating the expression of RORγt, disturbing Th17/Treg balance-related immune responses which may be associated with the learning and memory impairment in mice. In contrast, 24S-OHC is neuroprotective and attenuates the neurotoxicity of 27-OHC.

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.

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.

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.

Inhibition of Niemann-Pick C1-Like 1 by Ezetimibe Reduces Dietary 5β,6β-Epoxycholesterol Absorption in Rats

PURPOSE

Oxycholesterols (OCs) are produced from cholesterol by oxidation of the steroidal backbone and side-chain. OCs are present in blood and evidence suggests their involvement in disease development and progression. However, limited information is available regarding the absorption mechanisms and relative absorption rates of dietary OCs. Although ezetimibe is known to inhibit intestinal cholesterol absorption via Niemann-Pick C1-Like 1 (NPC1L1), whether it also inhibits dietary OC absorption is unclear.

METHODS

We investigated the effects of ezetimibe on OC absorption in rats fed an OC-rich diet containing 10 different OCs. We collected lymphatic fluid using permanent cannulation of the thoracic duct and quantified OC levels.

RESULTS

Ezetimibe treatment significantly reduced the apparent absorption of 5β,6β-epoxycholesterol (5,6β-epoxy) and its levels in the proximal intestinal mucosa in OC-fed rats. Using in silico analyses, the binding energy of NPC1L1 N-terminal domain (NPC1L1-NTD) and 5,6β-epoxy was found to be similar to that of NPC1L1-NTD and cholesterol, suggesting that polar uncharged amino acids located in the steroidal part of 5,6β-epoxy were involved.

CONCLUSION

Our results indicate that ezetimibe-mediated inhibition of dietary OC absorption varies depending on the specific OC, and only the absorption of 5,6β-epoxy is significantly reduced.

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.

Cholesterol and stigmasterol within a sunflower oil matrix: Thermal degradation and oxysterols formation

The characteristics of the lipid matrix surrounding sterols exert a great influence in their thermal oxidation process. The objective of this work was to assess the oxidation susceptibility of equal amounts of cholesterol and stigmasterol within a sunflower oil lipid matrix (ratio 1:1:200) during heating (180°C, 0-180min). Remaining percentage of sterols was determined and seven sterol oxidation products (SOPs) were analysed for each type of sterol along the heating treatment. Evolution of the fatty acid profile and vitamin E content of the oil was also studied. Overall oxidation status of the model system was assessed by means of Peroxides Value (PV) and TBARS. PV remained constant from 30min onwards and TBARS continued increasing along the whole heating treatment. Degradation of both cholesterol and stigmasterol fitted a first order curve (R(2)=0.937 and 0.883, respectively), with very similar degradation constants (0.004min(-1) and 0.005min(-1), respectively). However, higher concentrations of oxidation products were found from cholesterol (79μg/mg) than from stigmasterol (53μg/mg) at the end of the heating treatment. Profile of individual oxidation products was similar for both sterols, except for the fact that no 25-hydroxystigmasterol was detected. 7α-Hydroxy and 7-keto-derivatives were the most abundant SOPs at the end of the treatment. PUFA and vitamin E suffered a significant degradation along the process, which was correlated to sterols oxidation.

7keto-stigmasterol and 7keto-cholesterol induce differential proteome changes to intestinal epitelial (Caco-2) cells

Recent studies have expanded the appreciation of the roles of oxysterols triggering inflammatory, immune cytotoxic and apoptotic processes, but have not been considered for proteome analysis. A comparative proteomic study in intestinal epithelial cell cultures incubated (60 μM/24 h) with 7keto-cholesterol or 7keto-stigmasterol was performed. The influence of both compounds was studied following the nLC-TripleTOF analysis. Findings were compared to results for control cultures. In the principal component analysis (PCA) of proteome patterns, two components were extracted accounting for 99.8% of the variance in the protein expression. PCA analysis clearly discriminated between the perturbations in the proteome of cell cultures incubated with 7keto-cholesterol and 7keto-stigmasterol. These proteins participate in mitochondrial function, lipid homeostasis, inflammation and immunity and cell proliferation. Remarkable differences between proteome patterns in cell cultures exposed to 7keto-cholesterol and 7keto-stigmasterol affect macrophage migration inhibitory factor, apolipoprotein E, Bcl-2-associated transcription factor and cellular retinoic acid-binding protein. Besides, exposure to 7keto-stigmasterol increased the concentration of ubiquitin-conjugating enzyme E2 and the mitochondrial superoxide dismutase protein. Such findings raise new questions about safety studies and the regulatory potential of oxysterols in the differentiation and function of intestinal and associated immune cells, their response to environmental stimuli and impairment of absorption processes.

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.

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.

Current and new insights on phytosterol oxides in plant sterol-enriched food

Over the past 15 years, plant sterol-enriched foods have faced a great increase in the market, due to the asserted cholesterol-lowering effect of plant sterols. However, owing to their chemical structures, plant sterols can oxidize and produce a wide variety of oxidation products with controversial biological effects. Although oxyphytosterols can derive from dietary sources and endogenous formation, their single contribution should be better defined. The following review provides an overall and critical picture on the current knowledge and future perspectives of plant sterols-enriched food, particularly focused on occurrence of plant sterol oxidation products and their biological effects. The final objective of this overview is to evince the different aspects of plant sterols-enriched food that require further research, for a better understanding of the influence of plant sterols and their oxides on consumers' health.