Oxidized products of cholesterol: dietary and metabolic origin, and proatherosclerotic effects (review)

Blockade of mTORC1 via Rapamycin Suppresses 27-Hydroxycholestrol-Induced Inflammatory Responses

Atherosclerosis is characterized by the deposition and accumulation of extracellular cholesterol and inflammatory cells in the arterial blood vessel walls, and 27-hydroxycholesterol (27OHChol) is the most abundant cholesterol metabolite. 27OHChol is an oxysterol that induces immune responses, including immune cell activation and chemokine secretion, although the underlying mechanisms are not fully understood. In this study, we investigated the roles of the mechanistic target of rapamycin (mTOR) in 27HChol-induced inflammation using rapamycin. Treating monocytic cells with rapamycin effectively reduced the expression of CCL2 and CD14, which was involved with the increased immune response by 27OHChol. Rapamycin also suppressed the phosphorylation of S6 and 4EBP1, which are downstream of mTORC1. Additionally, it also alleviates the increase in differentiation markers into macrophage. These results suggest that 27OHChol induces inflammation by activating the mTORC1 signaling pathway, and rapamycin may be useful for the treatment of atherosclerosis-related inflammation involving 27OHchol.

Insight into the interaction of 5,6 epoxy-cholesterols with human serum albumin

5,6-Epoxy-cholesterols has been recently revealed to control metabolic pathway in breast cancer, which makes investigating their binding interaction with human serum albumin (HSA) an attractive field of research. The main aim of this article is to examine the binding interaction of 5,6 α-epoxy-cholesterol (5,6 α EC) and 5,6 β-epoxy-cholesterol (5,6 β- EC) with HSA using different spectroscopic methods and molecular modeling. These compounds interact with HSA via hydrophobic interactions and hydrogen bonds with binding constants 6.3 × 105 M-1 for 5,6 α-epoxy-cholesterol and 6.9 × 105 M-1 for 5,6 β-epoxy-cholesterol besides, the mechanism of the interaction can be attributed to static quenching. Circular dichroism data indicated that the α-helical content of HSA increased from 50.5 to 59.8 and 61.1 % after the addition of 5,6 α-ECs and 5,6 β-EC, respectively, with a ratio of 1:2. Thermodynamic analysis revealed that binding between 5,6-epoxy-cholesterols and HSA is spontaneous and entropy-driven. The molecular docking and esterase-like activity experiments were performed to envision a link between the experimental and theoretical results. The optimal binding site of 5,6-epoxy-cholesterols with HSA was located in subdomain IIA. Moreover, theoretical calculations were performed using the B3LYP function with the 6-311++G (d,p) basis set, indicating the HOMO-LUMO energy gap of 7.874 eV for 5,6 α-epoxy-cholesterol and 7.873 eV for 5,6 β-epoxy-cholesterol. The obtained findings are assumed to provide basic data for understanding the binding interactions of HSA with oxysterol compounds, which could help explore the pharmacokinetics and pharmacodynamics of oxysterol compounds.

Cytoprotective effects of α-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid, oleic acid and α-tocopherol on 7-ketocholesterol - Induced oxiapoptophagy: Major roles of PI3-K / PDK-1 / Akt signaling pathway and glutathione peroxidase activity in cell rescue

On murine N2a cells, 7-ketocholesterol induced an oxiapotophagic mode of cell death characterized by oxidative stress (reactive oxygen species overproduction on whole cells and at the mitochondrial level; lipid peroxidation), apoptosis induction (caspase-9, -3 and -7 cleavage, PARP degradation) and autophagy (increased ratio LC3-II / LC3-I). Oxidative stress was strongly attenuated by diphenyleneiodonium chloride which inhibits NAD(P)H oxidase. Mitochondrial and peroxisomal morphological and functional changes were also observed. Down regulation of PDK1 / Akt signaling pathways as well as of GSK3 / Mcl-1 and Nrf2 pathways were simultaneously observed in 7-ketocholesterol-induced oxiapoptophagy. These events were prevented by α-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid, oleic acid and α-tocopherol. The inhibition of the cytoprotection by LY-294002, a PI3-K inhibitor, demonstrated an essential role of PI3-K in cell rescue. The rupture of oxidative stress in 7-ketocholesterol-induced oxiapoptophagy was also associated with important modifications of glutathione peroxidase, superoxide dismutase and catalase activities as well as of glutathione peroxidase-1, superoxide dismutase-1 and catalase level and expression. These events were also counteracted by α-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid, oleic acid and α-tocopherol. The inhibition of the cytoprotection by mercaptosuccinic acid, a glutathione peroxidase inhibitor, showed an essential role of this enzyme in cell rescue. Altogether, our data support that the reactivation of PI3-K and glutathione peroxidase activities by α-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid, oleic acid and α-tocopherol are essential to prevent 7KC-induced oxiapoptophagy.

Cholesterol Oxidation Products: Potential Adverse Effect and Prevention of Their Production in Foods

Cholesterol oxidation products (COPs) are a group of substances formed during food processing. COPs in diet is a health concern because they may affect human health in association with the risk of various diseases including atherosclerosis, Alzheimer's disease, age-related macular degeneration, diabetes, and chronic gastrointestinal inflammatory colitis. Production of COPs in foods can be affected by many factors such as temperature, pH, light, oxygen, water, carbohydrates, fatty acids, proteins, and metal cations. The key issue is preventing its generation in foods. Some COPs can also be produced in vivo by both nonenzymatic and enzymatic-catalyzed oxidation reactions. Currently, a number of natural antioxidants such as catechins, flavonoids, and other polyphenols have been proven to inhibit the generation of COPs. In addition, measures taken during food processing can also minimize the production of COPs, such as the Maillard reaction and marinating food with plant polyphenol-rich seasonings. In conclusion, a comprehensive approach encompassing the suppression on COPs generation and implementation of processing measures is imperative to safeguard human health against the production of COPs in the food chain.

Effects of Supplementation with an Herbal Mixture on the Antioxidant Capacity of Milk

The aim of this study was to assess the effect of the addition of a standardized herbal mixture to the feed ration for Holstein-Friesian cows on the antioxidant capacity of milk. The study was carried out on a farm specialized in breeding dairy cattle. The exact study involved 30 cows in lactation III, which were in the first phase of lactation at the beginning of the experiment (15 cows-control group; 15 cows-experimental group). The nutrition supplied to the cows was based on the TMR (total mixed ration) system, with roughage and concentrate fodder used as the basis of the feed ration. The addition of a standardized blend of dried herbs, i.e., oregano (Origanum vulgare), thyme (Thymus vulgaris), purple coneflower (Echinacea purpurea), and cinnamon bark (Cinnamomum zeylanicum), was the experimental factor. Powdered herbs were administered as a component of the concentrate fodder at the dose of 3% DM ration/day/head. Milk samples were collected four times during the experiment (term 0 after the colostrum period and then after lactation weeks 2, 4, and 6). The following parameters were determined in the milk: the basic chemical composition, i.e., the content of total protein, fat, lactose, and casein; somatic cell count; content of selected whey proteins (α-lactalbumin, β-lactoglobulin, lactoferrin, BSA); and fat-soluble vitamins (A, D₃, E). Additionally, the milk antioxidant capacity (ABTS, FRAP, DPPH) was determined and the degree of antioxidant protection (DAP) was calculated. It was shown that the milk from cows receiving the herbal blend-supplemented fodder had a higher content of casein, compared to the control group. The herbal supplementation contributed to a significant increase in the content of bioactive compounds, i.e., selected whey proteins (β-lactoglobulin, lactoferrin) and lipophilic vitamins (A, E). The milk was also characterized by significantly higher antioxidant potential (regardless of the measurement method) and a higher degree of antioxidant protection (DAP).

25-Hydroxycholesterol Mediates Cholesterol Metabolism to Restrict Porcine Deltacoronavirus Infection via Suppression of Transforming Growth Factor β1

Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus in pigs, is one of the major pathogens for lethal watery diarrhea in piglets and poses a threat to public health because of its potential for interspecies transmission to humans. 25-Hydroxycholesterol (25HC), a derivative of cholesterol, exhibits multiple potential modulating host responses to pathogens, including viruses and bacteria, as well as pathogen-induced inflammation, while its antiviral effect on PDCoV and how it mediates the biological process of host cells to counter against infections remain poorly understood. Here, we thoroughly explored the antiviral effect of 25HC on PDCoV infection and tried to elucidate the underlying mechanisms. 25HC showed no toxic effect in LLC-PK1 cells and exerted antiviral ability against PDCoV infection in vitro. The viral cycle and time-of-addition analyses showed that 25HC mainly restricted the early and middle periods of the PDCoV postentry stage to inhibit infection. 25HC regulated disordered cholesterol metabolism induced by PDCoV infection and stimulated interferon-related lipid droplet accumulation. Transforming growth factor β1 (TGF-β1), screened by bioinformatic analyses, seemed to play an important role in PDCoV infection and was downregulated by 25HC. One interesting finding is that inhibition of TGF-β1 with the inhibitor asiaticoside exhibited a similar antiviral capacity to 25HC and demonstrated regulation of cholesterol metabolism. Taking all of the findings together, we verified the antiviral effect of 25HC on PDCoV through interference with cholesterol metabolism, which may be related to its suppression of TGFβ1. IMPORTANCE As an emerging enteropathogenic coronavirus in pigs, porcine deltacoronavirus (PDCoV) causes giant economic loss in the pig industry because of lethal diarrhea and possesses the potential for transmission from animals to humans. Several pieces of evidence have suggested the antiviral potential of cholesterol-25-hydroxylase and importance of cholesterol in viral infection. This study reports that 25-hydroxycholesterol (25HC) significantly restricted PDCoV infection through modulation of cholesterol metabolism, and we identified that lipid droplets play important roles in interferon response against virus infection. Moreover, this study identified the importance of TGF-β1 in CoV infection by bioinformatic analysis and verified that the inhibition of TGF-β1 showed anti-PDCoV capacity. Moreover, we uncovered the relationship between TGF-β and cholesterol metabolism initially. Given that the importance of cholesterol in viral infection, 25HC has a great potential to treat PDCoV infection and TGF-β1 can be a crucial antiviral target.

Cytoprotective activities of representative nutrients from the Mediterranean diet and of Mediterranean oils against 7-ketocholesterol- and 7β-hydroxycholesterol-induced cytotoxicity: Application to age-related diseases and civilization diseases

7-ketocholesterol and 7β-hydroxycholesterol are two oxysterols mainly formed by the autoxidation of cholesterol. These two molecules are interconvertible via specific enzymes. These two oxysterols are often observed at increased amounts in biological fluids as well as tissues and organs affected during age-related diseases and in diseases of civilization such as cardiovascular, neurodegenerative, and ocular diseases as well as type 2 diabetes and metabolic syndrome. Noteworthy, 7-ketocholesterol and 7β-hydroxycholesterol induce oxidative stress and inflammation, which are frequently observed in patients with age-related and civilization diseases. For this reason, the involvement of these two oxysterols in the pathophysiology of these diseases is widely suspected. In addition, the toxicity of these oxysterols can lead to death by oxiapoptophagy characterized by oxidative stress, apoptosis induction and autophagy criteria. To prevent, or even treat, certain age-related or civilization diseases associated with increased levels of 7-ketocholesterol and 7β-hydroxycholesterol, the identification of molecules or mixtures of molecules attenuating or inhibiting the toxic effects of these oxysterols allows to consider new treatments. In this context, many nutrients present in significant amounts in the Mediterranean diet, especially tocopherols, fatty acids, and polyphenols, have shown cytoprotective activities as well as several Mediterranean oils (argan and olive oils, milk thistle seed oil, and pistacia lentiscus seed oil). Consequently, a nutraceutical approach, rich in nutrients present in the Mediterranean diet, could thus make it possible to counteract certain age-related and civilization diseases associated with increased levels of 7-ketocholesterol and 7β-hydroxycholesterol.

New Function of Cholesterol Oxidation Products Involved in Osteoporosis Pathogenesis

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone strength, microarchitectural changes in bone tissues, and increased risk of fracture. Its occurrence is closely related to various factors such as aging, genetic factors, living habits, and nutritional deficiencies as well as the disturbance of bone homeostasis. The dysregulation of bone metabolism is regarded as one of the key influencing factors causing OP. Cholesterol oxidation products (COPs) are important compounds in the maintenance of bone metabolic homeostasis by participating in several important biological processes such as the differentiation of mesenchymal stem cells, bone formation in osteoblasts, and bone resorption in osteoclasts. The effects of specific COPs on mesenchymal stem cells are mainly manifested by promoting osteoblast genesis and inhibiting adipocyte genesis. This review aims to elucidate the biological roles of COPs in OP development, starting from the molecular mechanisms of OP, pointing out opportunities and challenges in current research, and providing new ideas and perspectives for further studies of OP pathogenesis.

[What is ultra-processed food and how is it related to diet-related diseases?]

Ultra-processed food is part of a modern lifestyle and accounts for about 46 % of daily energy intake in Germany. Cross-sectional and cohort studies indicate associations between consumption of ultra-processed food and a range of non-communicable diseases (obesity, diabetes, cancer, cardiovascular disease, and depression). As underlying mechanisms, a high energy density, altered food matrix, an unbalanced nutritional composition, high glycemic index, adverse additives, processing- and packaging contaminants are discussed. In order to understand the role of these potential mechanisms and to provide a scientifically based and risk-associated definition of ultra-processed food it is important to conduct appropriate intervention studies and to improve dietary assessment of processed food in prospective cohort studies.

Dietary cholesterol oxidation products: Perspectives linking food processing and storage with health implications

Dietary cholesterol oxidation products (COPs) are heterogeneous compounds formed during the processing and storage of cholesterol-rich foods, such as seafood, meat, eggs, and dairy products. With the increased intake of COPs-rich foods, the concern about health implications of dietary COPs is rising. Dietary COPs may exert deleterious effects on human health to induce several inflammatory diseases including atherosclerosis, neurodegenerative diseases, and inflammatory bowel diseases. Thus, knowledge regarding the effects of processing and storage conditions leading to formation of COPs is needed to reduce the levels of COPs in foods. Efficient methodologies to determine COPs in foods are also essential. More importantly, the biological roles of dietary COPs in human health and effects of phytochemicals on dietary COPs-induced diseases need to be established. This review summarizes the recent information on dietary COPs including their formation in foods during their processing and storage, analytical methods of determination of COPs, metabolic fate, implications for human health, and beneficial interventions by phytochemicals. The formation of COPs is largely dependent on the heating temperature, storage time, and food matrices. Alteration of food processing and storage conditions is one of the potent strategies to restrict hazardous dietary COPs from forming, including maintaining relatively low temperatures, shorter processing or storage time, and the appropriate addition of antioxidants. Once absorbed into the circulation, dietary COPs can contribute to the progression of several inflammatory diseases, where the absorbed dietary COPs may induce inflammation, apoptosis, and autophagy in cells in the target organs or tissues. Improved intake of phytochemicals may be an effective strategy to reduce the hazardous effects of dietary COPs.

A Comprehensive Review on Oxysterols and Related Diseases

The present review aims to provide a complete and comprehensive summary of current literature relevant to oxysterols and related diseases. Oxidation of cholesterol leads to the formation of a large number of oxidized products, generally known as oxysterols. They are intermediates in the biosynthesis of bile acids, steroid hormones, and 1,25- dihydroxyvitamin D3. Although oxysterols are considered as metabolic intermediates, there is a growing body of evidence that many of them are bioactive, and their absence or excess may be part of the cause of a disease phenotype. These compounds derive from either enzymatic or non-enzymatic oxidation of cholesterol. This study provides comprehensive information about the structures, formation, and types of oxysterols even when involved in certain disease states, focusing on their effects on metabolism and linkages with these diseases. The role of specific oxysterols as mediators in various disorders, such as degenerative (age-related) and cancer-related disorders, has now become clearer. Oxysterol levels may be employed as suitable markers for the diagnosis of specific diseases or in predicting the incidence rate of diseases, such as diabetes mellitus, Alzheimer's disease, multiple sclerosis, osteoporosis, lung cancer, breast cancer, and infertility. However, further investigations may be required to confirm these mentioned possibilities.

Up-regulation of PCSK6 by lipid oxidation products: A possible role in atherosclerosis

Atherosclerosis is a degenerative disease characterized by lesions that develop in the wall of large- and medium-sized arteries due to the accumulation of low-density lipoproteins (LDLs) in the intima. A growing bulk of evidence suggests that cholesterol oxidation products, known as oxysterols, and the aldehyde 4-hydroxy-2-nonenal (HNE), the major pro-atherogenic components of oxidized LDLs, significantly contribute to atherosclerotic plaque progression and destabilization, with eventual plaque rupture. The involvement of certain members of the protein convertase subtilisin/kexin proteases (PCSKs) in atherosclerosis has been recently hypothesized. Among them, PCSK6 has been associated with plaque instability, mainly thanks to its ability to stimulate the activity of matrix metalloproteinases (MMPs) involved in extracellular matrix remodeling and to enhance inflammation. In U937 promonocytic cells and in human umbilical vein endothelial cells, an oxysterol mixture and HNE were able to up-regulate the level and activity of PCSK6, resulting in MMP-9 activation as demonstrated by PCSK6 silencing. Inflammation, enhanced by these lipid oxidation products, plays a key role in the up-regulation of PCSK6 activity as demonstrated by cell pretreatment with NS-398, with epigallocatechin gallate or with acetylsalicylic acid, all with anti-inflammatory effects. For the first time, we demonstrated that both oxysterols and HNE, which substantially accumulate in the atherosclerotic plaque, up-regulate the activity of PCSK6. Of note, we also suggest a potential association between PCSK6 activity and MMP-9 activation, pointing out that PCSK6 could contribute to atherosclerotic plaque development.

Can Meat and Meat-Products Induce Oxidative Stress?

High meat and meat-products consumption has been related to degenerative diseases. In addition to their saturated fatty acids and cholesterol contents, oxidation products generated during their production, storage, digestion, and metabolization have been largely implicated. This review begins by summarizing the concept of meat and meat-products by the main international regulatory agencies while highlighting the nutritional importance of their consumption. The review also dials in the controversy of white/red meat classification and insists in the need of more accurate classification based on adequate scores. Since one of the negative arguments that meat receives comes from the association of its consumption with the increase in oxidative stress, main oxidation compounds (malondialdehyde, thermaloxidized compounds, 4-hydroxy-nonenal, oxysterols, or protein carbonyls) generated during its production, storage, and metabolization, are included as a central aspect of the work. The review includes future remarks addressed to study the effects meat consumption in the frame of diet-gene interactions, stressing the importance of knowing the genetic variables that make individuals more susceptible to a possible oxidative stress imbalance or antioxidant protection. The importance of consumed meat/meat-products in the frame of a personalized nutrition reach in plant-food is finally highlighted considering the importance of iron and plant biophenols on the microbiota abundance and plurality, which in turn affect several aspects of our physiology and metabolism.

Effects of n-3 and n-6 feeding sources on the quality and lipid oxidation of meat from feedlot-finished Bos indicus steers

This study was conducted to evaluate the fatty acid profile, sensory properties and lipid oxidation of meat on retail display (RD) from Nellore steers (n = 96) fed diets containing soybean (SOY), sunflower (SUN), or linseed (LIN) oil or a control diet (CON). After slaughtering, samples of the Longissimus muscle were collected for sensory properties (1 day), fatty acid composition (1 day) and oxidation stability (3 days under RDC) evaluations. No differences in total lipids, cholesterol, TBARS, and total SFAs, MUFAs, PUFAs, and PUFA/SFA were observed. However, meat from animals fed vegetable oil had more CLA than that of the CON samples. The flavour, juiciness and overall acceptability were affected by the treatments (P < 0.05), but no consistent effect of a specific oil source was observed. Meat colour was not affected by diets or days under RD, and 7-ketocholesterol was not detected in any sample. The oil sources used in this work were not effective in consistently changing meat properties.

Quality, functional and sensory evaluation of pasta fortified with extracts from Opuntia ficus-indica cladodes

BACKGROUND

The stems of Opuntia ficus-indica, known as cladodes, are a rich source of soluble fibers, which makes them an important candidate for the production of functional foods. Tagliatelle of durum wheat fortified with Opuntia cladode extract (OCE) at different levels of addition (10-30%, v/w) was prepared on a laboratory scale and quality characteristics and sensory acceptability were assessed.

RESULTS

The main quality parameters (optimal cooking time, swelling index, cooking loss, dry matter) and sensory analysis on a nine-point hedonic scale were comparable with those of the control pasta sample (no added OCE) when durum wheat was supplemented with OCE at up to 20% (v/w). An in vitro human simulated gastrointestinal digestion in the presence of cholesterol or its main dietary oxidized derivative, 7-ketocholesterol, showed that OCE-fortified pasta strongly reduced the bioaccessibility of both the sterols (the higher the incorporated OCE level, the higher the effect). Moreover the extent of starch digestion decreased with increasing levels of OCE.

CONCLUSION

The results of the present study indicate that OCE-fortified pasta comprises a food with healthy properties, such as blood cholesterol- and glucose-lowering capabilities. © 2019 Society of Chemical Industry.

Cholesterol Degradation and Production of Extracellular Cholesterol Oxidase from Bacillus pumilus W1 and Serratia marcescens W8

Cholesterol is a waxy substance present in all types of the body cells. The presence of higher concentration of low density lipoprotein (LDL) is characterized by abnormal cholesterol level and is associated with cardiovascular diseases which lead to the development of atheroma in arteries known as atherosclerosis. The transformation of cholesterol by bacterial cholesterol oxidase can provide a key solution for the treatment of diseases related to cholesterol and its oxidized derivatives. Previously isolated bacteria from oil-contaminated soil were screened for cholesterol degradation. Among fourteen, five isolates were able to utilize cholesterol. Two strains Serratia marcescens W1 and Bacillus pumilus W8 using cholesterol as only carbon and energy source were selected for degradation studies. Several parameters (incubation time, substrate concentration, pH, temperature, and different metal ions) for cholesterol decomposition by the selected bacterial strains were evaluated. Maximum cholesterol reduction was achieved on the 5th day of incubation, 1g/L of substrate concentration, pH 7, in the presence of Mg2+ and Ca2+ ions, and at 35°C. Cholesterol degradation was analyzed by enzymatic colorimetric method, thin layer chromatography (TLC), and high-performance liquid chromatography (HPLC). Under optimized conditions 50% and 84% cholesterol reduction were recorded with Serratia marcescens W1 and Bacillus pumilus W8, respectively. Cholesterol oxidase activity was assayed qualitatively and quantitatively. The results revealed that Serratia marcescens W1 and Bacillus pumilus W8 have great potential for cholesterol degradation and would be regarded as a source for cholesterol oxidase (CHO).

25-Hydroxycholesterol and 27-hydroxycholesterol inhibit human rotavirus infection by sequestering viral particles into late endosomes

A novel innate immune strategy, involving specific cholesterol oxidation products as effectors, has begun to reveal connections between cholesterol metabolism and immune response against viral infections. Indeed, 25-hydroxycholesterol (25HC) and 27-hydroxycholesterol (27HC), physiologically produced by enzymatic oxidation of cholesterol, act as inhibitors of a wide spectrum of enveloped and non-enveloped human viruses. However, the mechanisms underlying their protective effects against non-enveloped viruses are almost completely unexplored. To get insight into this field, we investigated the antiviral activity of 25HC and 27HC against a non-enveloped virus causing acute gastroenteritis in children, the human rotavirus (HRV). We found that 25HC and 27HC block the infectivity of several HRV strains at 50% inhibitory concentrations in the low micromolar range in the absence of cell toxicity. Both molecules affect the final step of virus penetration into cells by preventing the association of two cellular proteins: the oxysterol binding protein (OSBP) and the vesicle-associated membrane protein-associated protein-A (VAP-A). By altering the activity of these cellular mediators, 25HC and 27HC disturb the recycling of cholesterol between the endoplasmic reticulum and the late endosomes which are exploited by HRV to penetrate into the cell. The substantial accumulation of cholesterol in the late endosomal compartment results in sequestering viral particles inside these vesicles thereby preventing cytoplasmic virus replication. These findings suggest that cholesterol oxidation products of enzymatic origin might be primary effectors of host restriction strategies to counteract HRV infection and point to redox active lipids involvement in viral infections as a research area of focus to better focus in order to identify novel antiviral agents targets.

The role of autophagy in survival response induced by 27-hydroxycholesterol in human promonocytic cells

Autophagy has been shown to be stimulated in advanced atherosclerotic plaques by metabolic stress, inflammation and oxidized lipids. The lack of published studies addressing the potential stimulation of pro-survival autophagy by oxysterols, a family of cholesterol oxidation products, has prompted our study. Thus, the goal of the current study is to elucidate the molecular mechanism of the autophagy induced by 27-hydroxycholesterol (27-OH), that is one of the most abundant oxysterols in advanced atherosclerotic lesions, and to assess whether the pro-oxidant effect of the oxysterol is involved in the given response. Here we showed that 27-OH, in a low micromolar range, activates a pro-survival autophagic response in terms of increased LC3 II/LC3 I ratio and Beclin 1, that depends on the up-regulation of extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt pathways as a potential result of an intracellular reactive oxygen species increase provoked by the oxysterol in human promonocytic U937 cells. Moreover, 27-OH induced autophagy is dependent on the relation between nuclear factor erythroid 2 p45-related factor 2 (Nrf2)-dependent antioxidant response and p62. The data obtained highlight the involvement of cholesterol oxidation products in the pathogenesis of oxidative stress related chronic diseases like atherosclerosis. Therefore, deeply understanding the complex mechanism and generating synthetic or natural molecules targeting this survival mechanism might be very promising tools in the prevention of such diseases.

Oxidative stress as a possible mechanism of statin-induced myopathy

Statins, inhibitors of hydroxy methyl glutaryl coenzyme-A (HMG-CoA) reductase, are the most widely used drugs for treating hypercholesterolemia. However, statins can cause disabling myopathy as their main adverse effect. Several molecular mechanisms underlie the statin-induced myopathy including the decrease in the levels of essential mevalonate and cholesterol derivatives. This review discusses a further mechanism involving the loss of other anti-oxidant defenses besides ubiquinone (Co-Q) in skeletal muscles which produce a significant amount of reactive oxygen species (ROS). Therefore, to maintain their function, skeletal muscles need a high level of anti-oxidants.

Natural products as modulators of the nuclear receptors and metabolic sensors LXR, FXR and RXR

Nuclear receptors (NRs) represent attractive targets for the treatment of metabolic syndrome-related diseases. In addition, natural products are an interesting pool of potential ligands since they have been refined under evolutionary pressure to interact with proteins or other biological targets. This review aims to briefly summarize current basic knowledge regarding the liver X (LXR) and farnesoid X receptors (FXR) that form permissive heterodimers with retinoid X receptors (RXR). Natural product-based ligands for these receptors are summarized and the potential of LXR, FXR and RXR as targets in precision medicine is discussed.

Olive Oil Phenolics Prevent Oxysterol-Induced Proinflammatory Cytokine Secretion and Reactive Oxygen Species Production in Human Peripheral Blood Mononuclear Cells, Through Modulation of p38 and JNK Pathways

Scope

The aim of the present study was to investigate the ability of extra virgin olive oil (EVOO) polyphenols to counteract the proinflammatory effects induced by dietary and endogenous oxysterols in ex vivo immune cells.

Methods and results

Peripheral blood mononuclear cells (PBMCs), separated from the whole blood of healthy donors, were utilized and were stimulated with an oxysterols mixture, in the presence of physiologically relevant concentrations of the EVOO polyphenols, hydroxytyrosol, tyrosol, and homovanillic alcohol. Oxysterols significantly increased the production of proinflammatory cytokines, interleukin‐1β, regulated on activation, normal T‐cell expressed and secreted and macrophage migration inhibitory factor in ex vivo cultured PBMCs. Increased levels of reactive oxygen species (ROS) were also detected along with increased phosphorylation of the p38 and JNK. All phenolic compounds significantly reduced cytokine secretion induced by the oxysterols and inhibited ROS production and mitogen activated protein kinase phosphorylation.

Conclusions

These results suggest that extra virgin olive oil polyphenols modulate the immune response induced by dietary and endogenous cholesterol oxidation products in human immune cells and may hold benefit in controlling chronic immune and/or inflammatory processes.

Oxysterols and 4-hydroxy-2-nonenal contribute to atherosclerotic plaque destabilization

A growing bulk of evidence suggests that cholesterol oxidation products, known as oxysterols, and 4-hydroxy-2-nonenal (HNE), the major proatherogenic components of oxidized low density lipoproteins (oxLDLs), significantly contribute to atherosclerotic plaque progression and destabilization, with eventual plaque rupture. These oxidized lipids are involved in various key steps of this complex process, mainly thanks to their ability to induce inflammation, oxidative stress, and apoptosis. This review summarizes the current knowledge of the effects induced by these compounds on vascular cells, after their accumulation in the arterial wall and in the atherosclerotic plaque.

Influence of salt on lipid oxidation in meat and seafood products: A review

Sodium chloride, commonly known as salt, is a widely used additive in food industry due to its preservation and antimicrobial properties provided by its ability to reduce water activity. Moreover, the addition of salt to meat and seafood aims at improving water retention capacity and enhancing flavor due to its influence on the activity of some enzymes responsible for flavor development. On the other hand, salt added in meat and seafood can favor lipid oxidation, which is one of the main responsibles for quality losses in the food industry. In this review, the main mechanisms of fatty acids and cholesterol oxidation are described as well as the influence of salt on lipid oxidation in meat and seafood. Besides, the possible mechanisms of the pro-oxidant action of sodium chloride are presented and potential solutions to inhibit the salt action in lipid oxidation and decrease the salt content in food are discussed.

Degrees of Antioxidant Protection: A 2-Year Study of the Bioactive Properties of Organic Milk in Poland

The aim of this study was to determine the nutritional value of organic milk in Poland, investigate the influence of diet on antioxidant capacity and degree of antioxidant protection (DAP), and to examine the effect of season on the bioactive properties of milk from organic farms. From 2014 to 2015, 820 milk samples were collected from 6 organic farms during indoor feeding season (IDS) and pasture feeding season (PS). Pasture feeding season + corn grain (PSCG) cows' daily ration during pasture feeding season was enriched with 4 kg a day of corn to improve dietary energy balance. Milk obtained during PS was found to have a higher fat content, slight but significantly lower protein content compared with milk from IDS. The study showed that the content of monounsaturated fatty acids (MUFA) in milk fat was strongly linked to the concentration of polyunsaturated fatty acids (PUFA) and, to a lesser extent, on the supply of MUFA. The IDS data (concentration of vitamin E, A, and β-carotene) showed the lowest values compared with the PS and PSCG groups. Total antioxidant status (TAS) and DAP showed an increasing trend in organic milk. PSCG was associated with highest level of DAP (9% higher than PS and 79% higher than IDS) and TAS (37% higher than PS and 79% higher than IDS). The results obtained show that supplementation of the basic ration with corn grain improved both TAS and DAP. The higher DAP and TAS value is responsible for product stability, considering the risk factor related to levels of cholesterol-oxide intake in humans.

Contribution of cholesterol and oxysterols to the pathophysiology of Parkinson's disease

Neurodegenerative diseases are a major public health issue worldwide. Some countries, including France, have engaged in research into the causes of Parkinson's disease, Alzheimer's disease, and multiple sclerosis and the management of these patients. It should lead to a better understanding of the mechanisms leading to these diseases including the possible involvement of lipids in their pathogenesis. Parkinson's disease is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra and the accumulation of α-synuclein (Lewy bodies). Several in vivo studies have shown a relationship between the lipid profile [cholesterol, oxidized cholesterol products (oxysterols) formed either enzymatically or by auto-oxidation], the use of drugs regulating cholesterol levels, and the development of Parkinson's disease. Several oxysterols are present in the brain and could play a role in the development of this disease, particularly in the accumulation of α-synuclein, and through various side effects, such as oxidation, inflammation, and cell death. Consequently, in Parkinson's disease, some oxysterols could contribute to the pathophysiology of the disease and constitute potential biomarkers or therapeutic targets.

Involvement of Calcium in 7β-Hydroxycholesterol and Cholesterol-5β,6β-Epoxide-Induced Apoptosis

Oxidized low-density lipoprotein (oxLDL) is believed to play a central role in the development of atherosclerosis. The induction of apoptosis in cells of the arterial wall is a critical event in the development of atheroma. 7β-Hydroxycholesterol (7 β-OH) and cholesterol-5 β,6 β-epoxide ( β-epoxide) are components of oxLDL and have previously been shown to be potent inducers of apoptosis. The exact mechanism through which these oxysterols induce apoptosis remains to be fully elucidated. A perturbation of intra-cellular calcium homeostasis has been found to trigger apoptosis in many experimental systems. The aim of the present study was to determine the involvement of calcium signaling in 7 β-OH and β-epoxide–induced apoptosis. To this end, the authors employed the calcium channel blockers verapamil and nifedipine and inhibitors of calpain activation, ALLM and ALLN. Verapamil protected against the decrease in viability induced by 7 β-OH whereas nifedipine had a protective effect in both 7 β-OH and β-epoxide–treated cells, though these compounds did not restore viability to control levels. Verapamil, nifedipine, and ALLM prevented apoptosis induced by β-epoxide. None of the compounds employed in the current study protected against 7 β-OH–induced apoptosis. Our results implicate calcium signaling in the apoptotic pathway induced by β-epoxide and also highlight differences between apoptosis induced by 7 β-OH and β-epoxide.

Oxysterols: An emerging class of broad spectrum antiviral effectors

Oxysterols are a family of cholesterol oxidation derivatives that contain an additional hydroxyl, epoxide or ketone group in the sterol nucleus and/or a hydroxyl group in the side chain. The majority of oxysterols in the blood are of endogenous origin, derived from cholesterol via either enzymatic or non-enzymatic mechanisms. A large number of reports demonstrate multiple physiological roles of specific oxysterols. One such role is the inhibition of viral replication. This biochemical/biological property was first characterised against a number of viruses endowed with an external lipid membrane (enveloped viruses), although antiviral activity has since been observed in relation to several non-enveloped viruses. In the present paper, we review the recent findings about the broad antiviral activity of oxysterols against enveloped and non-enveloped human viral pathogens, and provide an overview of their putative antiviral mechnism(s).

Oxysterols and mechanisms of survival signaling

Oxysterols, a family of oxidation products of cholesterol, are increasingly drawing attention of scientists to their multifaceted biochemical properties, several of them of clear relevance to human pathophysiology. Taken up by cells through both vesicular and non-vesicular ways or often generated intracellularly, oxysterols contribute to modulate not only the inflammatory and immunological response but also cell viability, metabolism and function by modulating several signaling pathways. Moreover, they have been recognized as elective ligands for the most important nuclear receptors. The outcome of such a complex network of intracellular reactions promoted by these cholesterol oxidation products appears to be largely dependent not only on the type of cells, the dynamic conditions of the cellular and tissue environment but also on the concentration of the oxysterols. Here focus has been given to the cascade of molecular events exerted by relatively low concentrations of certain oxysterols that elicit survival and functional signals in the cells, with the aim to contribute to further expand the knowledge about the biological and physiological potential of the biochemical reactions triggered and modulated by oxysterols.

Nrf2 antioxidant defense is involved in survival signaling elicited by 27-hydroxycholesterol in human promonocytic cells

Cholesterol oxidation products such as oxysterols are considered critical factors in the atherosclerotic plaque formation since they induce oxidative stress, inflammation and apoptotic cell death. 27-hydroxycholesterol (27-OH) is one of the most represented oxysterols in atherosclerotic lesions. We recently showed that relatively low concentrations of 27-OH generated a strong survival signaling through an early and transient increase of cellular ROS level, that enhanced MEK-ERK/PI3K-Akt phosphorylation, in turn responsible of a sustained quenching of ROS production. It remains to identify the link between ERK/Akt up-regulation and the consequent quenching effect on ROS intracellular level that efficiently and markedly delay the pro-apoptotic effect of the oxysterol. Here we report on the potent activation of Nrf2 redox-sensitive transcription factor by low micromolar amount of 27-OH added to U937 promonocytic cells. The 27-OH-exerted induction of Nrf2 and subsequently of the target genes, HO-1 and NQO-1, was proved to be: (i) dependent upon the activation of ERK and Akt pathways, (ii) directly responsible for the quenching of intracellular oxidative stress and by this way (iii) ultimately responsible for the observed oxysterol-induced pro-survival response.

Obesity is associated with changes in oxysterol metabolism and levels in mice liver, hypothalamus, adipose tissue and plasma

Oxysterols are bioactive lipids derived from cholesterol that are linked to inflammatory processes. Because obesity and metabolic syndrome are characterized by inflammation and altered cholesterol metabolism, we sought to investigate the variations of oxysterol levels and their metabolic pathways induced by obesity in the liver, hypothalamus, adipose tissue and plasma. To this end, we used diet-induced and genetic (ob/ob and db/db) models of obesity. Among the oxysterols measured, we found that 4β-oxysterol levels were consistently decreased in the high-fat diet study, at different time-points, and in the ob/ob model. Overall, we did not find any correlation between cytochromes mRNA expression and variations of oxysterol levels. We also measured the levels of hepatic primary bile acids, in these three models and found similar profiles between HFD and ob/ob mice. However, although they are downstream metabolites of oxysterols, the variations in bile acid levels did not reflect the variations of their precursors. Our data show that, when considering oxysterol metabolism, the high-fat diet and ob/ob models are more closely related when compared to the db/db model. However, we were able to discriminate between lean and obese phenotypes based on liver oxysterol (4β-hydroxycholesterol, 27- hydroxycholesterol, 7-hydroxycholestenone) levels and enzyme (CYP3A11, CYP27A1, CYP7A1) expression.

Cholesterol Oxidation in Fish and Fish Products

Fish and fish products are important from a nutritional point of view due to the presence of high biological value proteins and the high content of polyunsaturated fatty acids, especially those of the n-3 series, and above all eicosapentaenoic acid and docosahexaenoic acid. However, these important food products also contain significant amounts of cholesterol. Although cholesterol participates in essential functions in the human body, it is unstable, especially in the presence of light, oxygen, radiation, and high temperatures that can cause the formation of cholesterol oxidation products or cholesterol oxides, which are prejudicial to human health. Fish processing involves high and low temperatures, as well as other methods for microbiological control, which increases shelf life and consequently added value; however, such processes favor the formation of cholesterol oxidation products. This review brings together data on the formation of cholesterol oxides during the preparation and processing of fish into food products which are recognized and recommended for their nutritional properties.

The effect of atorvastatin treatment on serum oxysterol concentrations and cytochrome P450 3A4 activity

AIMS

Atorvastatin is known to both inhibit and induce the cytochrome P450 3A4 (CYP3A4) enzyme in vitro. Some clinical studies indicate that atorvastatin inhibits CYP3A4 but there are no well-controlled longer term studies that could evaluate the inducing effect of atorvastatin. We aimed to determine if atorvastatin induces or inhibits CYP3A4 activity as measured by the 4β-hydroxycholesterol to cholesterol ratio (4βHC : C).

METHODS

In this randomized, double-blind, placebo-controlled 6 month study we evaluated the effects of atorvastatin 20 mg day(-1) (n = 15) and placebo (n = 14) on oxysterol concentrations and determined if atorvastatin induces or inhibits CYP3A4 activity as assessed by the 4βHC : C index. The respective 25-hydroxycholesterol and 5α,6α-epoxycholesterol ratios were used as negative controls.

RESULTS

Treatment with atorvastatin decreased 4βHC and 5α,6α-epoxycholesterol concentrations by 40% and 23%, respectively. The mean 4βHC : C ratio decreased by 13% (0.214 ± 0.04 to 0.182 ± 0.04, P = 0.024, 95% confidence interval (CI) of the difference -0.0595, -0.00483) in the atorvastatin group while no significant change occurred in the placebo group. The difference in change of 4βHC : C between study arms was statistically significant (atorvastatin -0.032, placebo 0.0055, P = 0.020, 95% CI of the difference -0.069, -0.0067). The ratios of 25-hydroxycholesterol and 5α,6α-epoxycholesterol to cholesterol did not change.

CONCLUSIONS

The results establish atorvastatin as an inhibitor of CYP3A4 activity. Furthermore, 4βHC : C is a useful index of CYP3A4 activity, including the conditions with altered cholesterol concentrations.

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.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Evaluation of cytotoxic and apoptotic effects of individual and mixed 7-ketophytosterol oxides on human intestinal carcinoma cells

Phytosterol oxidation products (POPs) are constituents of the human diet. Definitive information on the toxic or biological effects of POPs is limited and in some cases contradictory. This study evaluates the cytotoxicity of four individual 7-ketophytosterol oxides, including 7-ketositosterol (7K-SI), 7-ketocampesterol (7K-CA), 7-ketobrassicasterol (7K-BR), 7-ketostigmasterol (7K-ST), and a mixture of 7-ketophytosterols (7K-MIX) toward a human intestinal carcinoma (HIC) cell line. Results showed that all tested compounds reduced cell proliferation in a dose-dependent manner; especially 7K-SI and 7K-CA exhibited higher activities. Both compounds increased early apoptotic cells and caused cell cycle arrest in the G1 phase with cell accumulation in the S phase. No evidence of cell death was observed induced by 7K-ST and 7K-MIX. Furthermore, 7K-SI, 7K-CA, and 7K-BR induced apoptosis by enhancing caspase-3 activity and the modulatory effects of Bcl-2, while 7K-ST and 7K-MIX did not involve caspase-3 activation and Bcl-2 down-regulation.

Survival signaling elicited by 27-hydroxycholesterol through the combined modulation of cellular redox state and ERK/Akt phosphorylation

The oxysterol 27-hydroxycholesterol (27-OH) is increasingly considered to be involved in a variety of pathophysiological processes, having been shown to modulate cell proliferation and metabolism, and also to exert proinflammatory and proapoptotic effects. This study aimed to elucidate the molecular pathways whereby 27-OH may generate survival signals in cells of the macrophage lineage, and to clarify whether its known prooxidant effect is involved in that process. A net up-regulation of survival signaling, involving the extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt phosphorylation pathways, was observed in U937 promonocytic cells cultivated over time in the presence of a low micromolar concentration of the oxysterol. Interestingly, the up-regulation of both kinases was shown to be closely dependent on an early 27-OH-induced intracellular increase of reactive oxygen species (ROS). In turn, stimulation of ERK and PI3K/Akt both significantly quenched ROS steady state and markedly phosphorylated Bad, thereby determining a marked delay of the oxysterol׳s proapoptotic action. The 27-OH-induced survival pathways thus appear to be redox modulated and, if they occur within or nearby inflammatory cells during progression of chronic diseases such as cancer and atherosclerosis, they could significantly impact the growth and evolution of such diseases.

Carotenoids, inflammation, and oxidative stress--implications of cellular signaling pathways and relation to chronic disease prevention

Several epidemiologic studies have shown that diets rich in fruits and vegetables reduce the risk of developing several chronic diseases, such as type 2 diabetes, atherosclerosis, and cancer. These diseases are linked with systemic, low-grade chronic inflammation. Although controversy persists on the bioactive ingredients, several secondary plant metabolites have been associated with these beneficial health effects. Carotenoids represent the most abundant lipid-soluble phytochemicals, and in vitro and in vivo studies have suggested that they have antioxidant, antiapoptotic, and anti-inflammatory properties. Recently, many of these properties have been linked to the effect of carotenoids on intracellular signaling cascades, thereby influencing gene expression and protein translation. By blocking the translocation of nuclear factor κB to the nucleus, carotenoids are able to interact with the nuclear factor κB pathway and thus inhibit the downstream production of inflammatory cytokines, such as interleukin-8 or prostaglandin E2. Carotenoids can also block oxidative stress by interacting with the nuclear factor erythroid 2-related factor 2 pathway, enhancing its translocation into the nucleus, and activating phase II enzymes and antioxidants, such as glutathione-S-transferases. In this review, which is organized into in vitro, animal, and human investigations, we summarized current knowledge on carotenoids and metabolites with respect to their ability to modulate inflammatory and oxidative stress pathways and discuss potential dose-health relations. Although many pathways involved in the bioactivity of carotenoids have been revealed, future research should be directed toward dose-response relations of carotenoids, their metabolites, and their effect on transcription factors and metabolism.