Phospholipidosis and down-regulation of the PI3-K/PDK-1/Akt signalling pathway are vitamin E inhibitable events associated with 7-ketocholesterol-induced apoptosis

Oxysterols in Cell Viability, Phospholipidosis and Extracellular Vesicles Production in a Lung Cancer Model

The study carried out systematic research on the influence of selected oxysterols on cells viability, phospholipidosis and the level of secreted extracellular vesicles. Three oxidized cholesterol derivatives, namely 7α-hydroxycholesterol (7α-OH), 7- ketocholesterol (7-K) and 24(S)-hydroxycholesterol (24(S)-OH) were tested in three different concentrations: 50 μM, 100 μM and 200 μM for 24 h incubation with A549 lung cancer cell line. All the studied oxysterols were found to alter cells viability. The lowest survival rate of the cells was observed after 24 h of 7-K treatment, slightly better for 7α-OH while cells incubated with 24(S)-OH had the best survival rate among the oxysterols used. 7-K increased phospholipids accumulation in cells, however, most noticeable effect was noticed for 24(S)-OH. Changes in the level of extracellular vesicles secreted in cells culture after the treatment with oxysterols were also observed. It was found that all oxysterols used increased the level of secreted vesicles, both exosomes and ectosomes. The strongest effect was noticed for 24(S)-OH. Taken together, these results suggest that 7-K is the most potent inducer of cancer cell death, while 7α-OH is slightly less potent in this respect. The lower cytotoxic effect of 24(S)-OH correlates with greater phospholipids accumulation, extracellular vesicles production and better cells survival.

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.

Impact of Oxysterols in Age-Related Disorders and Strategies to Alleviate Adverse Effects

Oxysterols or cholesterol oxidation products are a class of molecules with the sterol moiety, derived from oxidative reaction of cholesterol through enzymatic and non-enzymatic processes. They are widely reported in animal-origin foods and prove significant involvement in the regulation of cholesterol homeostasis, lipid transport, cellular signaling, and other physiological processes. Reports of oxysterol-mediated cytotoxicity are in abundance and thus consequently implicated in several age-related and lifestyle disorders such as cardiovascular diseases, bone disorders, pancreatic disorders, age-related macular degeneration, cataract, neurodegenerative disorders such as Alzheimer's and Parkinson's disease, and some types of cancers. In this chapter, we attempt to review a selection of physiologically relevant oxysterols, with a focus on their formation, properties, and roles in health and disease, while also delving into the potential of natural and synthetic molecules along with bacterial enzymes for mitigating oxysterol-mediated cell damage.

Cholesterol-autoxidation metabolites in host defense against infectious diseases

Cholesterol plays essential roles in biological processes, including cell membrane stability and myelin formation. Cholesterol can be metabolized to oxysterols by enzymatic or nonenzymatic ways. Nonenzymatic cholesterol metabolites, also called cholesterol-autoxidation metabolites, are formed dependent on the oxidation of reactive oxygen species (ROS) such as OH• or reactive nitrogen species, such as ONOO- . Cholesterol-autoxidation metabolites are abundantly produced in diseases such as inflammatory bowel disease and atherosclerosis, which are associated with oxidative stress. Recent studies have shown that cholesterol-autoxidation metabolites can further regulate the immune system. Here, we review the literature and summarize how cholesterol-autoxidation metabolites, such as 25-hydroxycholesterol (25-OHC), 7α/β-OHC, and 7-ketocholesterol, deal with the occurrence and development of infectious diseases through pattern recognition receptors, inflammasomes, ROS production, nuclear receptors, G-protein-coupled receptor 183, and lipid availability. In addition, we include the research regarding the roles of these metabolites in COVID-19 infection and discuss our viewpoints on the future research directions.

MLLT11-TRIL complex promotes the progression of endometrial cancer through PI3K/AKT/mTOR signaling pathway

Endometrial cancer (EC) is a gynecological malignant tumor characterized by high incidence. EC occurrence and development are regulated by numerous molecules and signal pathways. There is a need to explore key regulatory molecules to identify potential therapeutic targets to reduce the incidence of EC. Treatment by targeting a single molecule is characterized by poor efficacy owing to the development of resistance and significant side effects. The current study explored potential candidates in EC by integrating bioinformatics analysis and in vivo and in vitro experimental validation to circumvent the limitation of low efficacy of currently used molecules. Molecular dynamics simulations provide details at the molecular level of intermolecular regulation. In the current study, MLLT11 and TRIL were identified as important regulatory molecules in EC. The two molecules formed a heteromultimer by binding to AKT protein, which induced its phosphorylation of threonine at position 308. Ultimately, the complex stimulates PI3K/AKT/mTOR signaling pathway, a pivotal pathway in tumors. The findings of the current study show a novel complex, MLLT11-TRIL, which can act as AKT protein agonist, thus inducing activity of PI3K/AKT/mTOR signaling pathway. Targeting MLLT11 and TRIL simultaneously, or blocking the formation of the MLLT11-TRIL complex, can abrogate progression of EC.

Macrophages, Low-Grade Inflammation, Insulin Resistance and Hyperinsulinemia: A Mutual Ambiguous Relationship in the Development of Metabolic Diseases

Metabolic derangement with poor glycemic control accompanying overweight and obesity is associated with chronic low-grade inflammation and hyperinsulinemia. Macrophages, which present a very heterogeneous population of cells, play a key role in the maintenance of normal tissue homeostasis, but functional alterations in the resident macrophage pool as well as newly recruited monocyte-derived macrophages are important drivers in the development of low-grade inflammation. While metabolic dysfunction, insulin resistance and tissue damage may trigger or advance pro-inflammatory responses in macrophages, the inflammation itself contributes to the development of insulin resistance and the resulting hyperinsulinemia. Macrophages express insulin receptors whose downstream signaling networks share a number of knots with the signaling pathways of pattern recognition and cytokine receptors, which shape macrophage polarity. The shared knots allow insulin to enhance or attenuate both pro-inflammatory and anti-inflammatory macrophage responses. This supposedly physiological function may be impaired by hyperinsulinemia or insulin resistance in macrophages. This review discusses the mutual ambiguous relationship of low-grade inflammation, insulin resistance, hyperinsulinemia and the insulin-dependent modulation of macrophage activity with a focus on adipose tissue and liver.

Role of non-coding RNAs on liver metabolism and NAFLD pathogenesis

Obesity and type 2 diabetes are major contributors to the growing prevalence of non-alcoholic fatty liver disease (NAFLD), a chronic liver condition characterized by accumulation of fat in individuals without a significant amount of alcohol intake. The NAFLD spectrum ranges from simple steatosis (early stages, known as NAFL), to non-alcoholic steatohepatitis (NASH), which can progress to fibrosis and cirrhosis or hepatocellular carcinoma. Obesity, type 2 diabetes, and NAFLD are strongly associated with insulin resistance. In the liver, insulin resistance increases hepatic glucose output, lipogenesis, and VLDL secretion, leading to a combination of hyperglycemia and hypertriglyceridemia. Aberrant gene expression is a hallmark of insulin resistance. Non-coding RNAs (ncRNAs) have emerged as prominent regulators of gene expression that operate at the transcriptional, post-transcriptional, and post-translational levels. In the last couple of decades a wealth of studies have provided evidence that most processes of liver metabolism are orchestrated by ncRNAs. This review focuses on the role of microRNAs, long non-coding RNAs and circular RNAs as coordinators of hepatic function, as well as the current understanding on how their dysregulation contributes to abnormal metabolism and pathophysiology in animal models of insulin resistance and NAFLD. Moreover, ncRNAs are emerging as useful biomarkers that may be able to discriminate between the different stages of NAFLD. The potential of ncRNAs as therapeutic drugs for NAFLD treatment and as biomarkers is discussed.

Different effects of oxysterols on a model lipid raft - Langmuir monolayer study complemented with theoretical calculations

Three oxysterols (7β-hydroxycholesterol; 7β-OH, 7-ketocholesterol; 7-K and 25-hydroxycholesterol, 25-OH) differing in the site of oxidation (ring system versus chain) and kind of polar group (hydroxyl versus carbonyl) were studied in lipid raft environment using the Langmuir monolayer technique complemented with theoretical calculations. Experiments were performed for the unmodified raft system, composed of sphingomyelin (SM) and cholesterol (Chol), and in the next step the raft was modified by the incorporation of oxysterol in different proportions. In the examined three-component system (Chol:SM:oxysterol), apart from interactions between the lipid raft components, the affinity of Chol to its oxidized derivatives also plays an important role. 25-OH was found to enhance interactions between SM and Chol and thus stabilize the raft, contrary to 7β-OH and 7-K, which exterted the fluidizing effect as well as the destabilization of the raft. Different action of oxysterols on model raft was observed. 7β-OH and 7-K, which are highly potent inducers of cell dath caused raft destabilization, while 25-OH, which is the least toxic of the investigated oxysterols, was found to stabilize the raft.

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.

An insight on 7- ketocholesterol mediated inflammation in atherosclerosis and potential therapeutics

7-ketocholesterol, a toxic oxidative product of oxysterol is a causative agent of several diseases and disabilities concomitant to aging including cardiovascular diseases like atherosclerosis. Auto-oxidation of cholesterol esters present in low-density lipoprotein (LDL) deposits lead to the formation of oxidized LDL (Ox-LDL) along with its byproducts, namely 7KCh. It is predominantly found in atherosclerotic plaque and also found to be more atherogenic than cholesterol by being cytotoxic, interfering with cellular homeostasis. This makes it a serious threat by being the foremost cause of morbidity and mortality worldwide and is likely to become more serious during forth coming years. It involves in mediating inflammatory mechanisms characterized by the advancement of fibroatheroma plaques. The atherosclerotic lesion is composed of Ox-LDL along with fibrotic mass consisting of immune cells and molecules. Macrophages being the specialized phagocytic cells, contribute to removal of detrimental contents of the lesion along with accumulated lipids leading to alteration of its biology and functionality due to its plasticity. Here, we have explored the known as well as proposed mechanisms involved with 7KCh associated atherogenesis along with potential therapeutic strategies for targeting 7KCh as a diagnostic and target in medicine.

Attenuation of 7-ketocholesterol- and 7β-hydroxycholesterol-induced oxiapoptophagy by nutrients, synthetic molecules and oils: Potential for the prevention of age-related diseases

Age-related diseases for which there are no effective treatments include cardiovascular diseases; neurodegenerative diseases such as Alzheimer's disease; eye disorders such as cataract and age-related macular degeneration; and, more recently, Severe Acute Respiratory Syndrome (SARS-CoV-2). These diseases are associated with plasma and/or tissue increases in cholesterol derivatives mainly formed by auto-oxidation: 7-ketocholesterol, also known as 7-oxo-cholesterol, and 7β-hydroxycholesterol. The formation of these oxysterols can be considered as a consequence of mitochondrial and peroxisomal dysfunction, leading to increased in oxidative stress, which is accentuated with age. 7-ketocholesterol and 7β-hydroxycholesterol cause a specific form of cytotoxic activity defined as oxiapoptophagy, including oxidative stress and induction of death by apoptosis associated with autophagic criteria. Oxiaptophagy is associated with organelle dysfunction and in particular with mitochondrial and peroxisomal alterations involved in the induction of cell death and in the rupture of redox balance. As the criteria characterizing 7-ketocholesterol- and 7β-hydroxycholesterol-induced cytotoxicity are often simultaneously observed in major age-related diseases (cardiovascular diseases, age-related macular degeneration, Alzheimer's disease) the involvement of these oxysterols in the pathophysiology of the latter seems increasingly likely. It is therefore important to better understand the signalling pathways associated with the toxicity of 7-ketocholesterol and 7β-hydroxycholesterol in order to identify pharmacological targets, nutrients and synthetic molecules attenuating or inhibiting the cytotoxic activities of these oxysterols. Numerous natural cytoprotective compounds have been identified: vitamins, fatty acids, polyphenols, terpenes, vegetal pigments, antioxidants, mixtures of compounds (oils, plant extracts) and bacterial enzymes. However, few synthetic molecules are able to prevent 7-ketocholesterol- and/or 7β-hydroxycholesterol-induced cytotoxicity: dimethyl fumarate, monomethyl fumarate, the tyrosine kinase inhibitor AG126, memantine, simvastatine, Trolox, dimethylsufoxide, mangafodipir and mitochondrial permeability transition pore (MPTP) inhibitors. The effectiveness of these compounds, several of which are already in use in humans, makes it possible to consider using them for the treatment of certain age-related diseases associated with increased plasma and/or tissue levels of 7-ketocholesterol and/or 7β-hydroxycholesterol.

Cyclodextrin dimers: A versatile approach to optimizing encapsulation and their application to therapeutic extraction of toxic oxysterols

We have developed a novel class of specifically engineered, dimerized cyclodextrin (CD) nanostructures for the encapsulation of toxic biomolecules such as 7-ketocholesterol (7KC). 7KC accumulates over time and causes dysfunction in many cell types, linking it to several age-related diseases including atherosclerosis and age-related macular degeneration (AMD). Presently, treatments for these diseases are invasive, expensive, and show limited benefits. CDs are cyclic glucose oligomers utilized to capture small, hydrophobic molecules. Here, a combination of in silico, in vitro, and ex vivo methods is used to implement a synergistic rational drug design strategy for developing CDs to remove atherogenic 7KC from cells and tissues. Mechanisms by which CDs encapsulate sterols are discussed, and we conclude that covalently linked head-to-head dimers of βCDs have substantially improved affinity for 7KC compared to monomers. We find that inclusion complexes can be stabilized or destabilized in ways that allow the design of CD dimers with increased 7KC selectivity while maintaining an excellent safety profile. These CD dimers are being developed as therapeutics to treat atherosclerosis and other debilitating diseases of aging.

Prevention by Dietary Polyphenols (Resveratrol, Quercetin, Apigenin) Against 7-Ketocholesterol-Induced Oxiapoptophagy in Neuronal N2a Cells: Potential Interest for the Treatment of Neurodegenerative and Age-Related Diseases

The Mediterranean diet is associated with health benefits due to bioactive compounds such as polyphenols. The biological activities of three polyphenols (quercetin (QCT), resveratrol (RSV), apigenin (API)) were evaluated in mouse neuronal N2a cells in the presence of 7-ketocholesterol (7KC), a major cholesterol oxidation product increased in patients with age-related diseases, including neurodegenerative disorders. In N2a cells, 7KC (50 µM; 48 h) induces cytotoxic effects characterized by an induction of cell death. When associated with RSV, QCT and API (3.125; 6.25 µM), 7KC-induced toxicity was reduced. The ability of QCT, RSV and API to prevent 7KC-induced oxidative stress was characterized by a decrease in reactive oxygen species (ROS) production in whole cells and at the mitochondrial level; by an attenuation of the increase in the level and activity of catalase; by attenuating the decrease in the expression, level and activity of glutathione peroxidase 1 (GPx1); by normalizing the expression, level and activity of superoxide dismutases 1 and 2 (SOD1, SOD2); and by reducing the decrease in the expression of nuclear erythroid 2-like factor 2 (Nrf2) which regulates antioxidant genes. QCT, RSV and API also prevented mitochondrial dysfunction in 7KC-treated cells by counteracting the loss of mitochondrial membrane potential (ΨΔm) and attenuating the decreased gene expression and/or protein level of AMP-activated protein kinase α (AMPKα), sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) implicated in mitochondrial biogenesis. At the peroxisomal level, QCT, RSV and API prevented the impact of 7KC by counteracting the decrease in ATP binding cassette subfamily D member (ABCD)3 (a peroxisomal mass marker) at the protein and mRNA levels, as well as the decreased expresssion of genes associated with peroxisomal biogenesis (Pex13, Pex14) and peroxisomal β-oxidation (Abcd1, Acox1, Mfp2, Thiolase A). The 7KC-induced decrease in ABCD1 and multifunctional enzyme type 2 (MFP2), two proteins involved in peroxisomal β-oxidation, was also attenuated by RSV, QCT and API. 7KC-induced cell death, which has characteristics of apoptosis (cells with fragmented and/or condensed nuclei; cleaved caspase-3; Poly(ADP-ribose) polymerase (PARP) fragmentation) and autophagy (cells with monodansyl cadaverine positive vacuoles; activation of microtubule associated protein 1 light chain 3–I (LC3-I) to LC3-II, was also strongly attenuated by RSV, QCT and API. Thus, in N2a cells, 7KC induces a mode of cell death by oxiapoptophagy, including criteria of OXIdative stress, APOPTOsis and autoPHAGY, associated with mitochondrial and peroxisomal dysfunction, which is counteracted by RSV, QCT, and API reinforcing the interest for these polyphenols in prevention of diseases associated with increased 7KC levels.

The Relationship between Serum Vitamin E Level and Risk Factors for Arteriosclerosis in Japanese Postmenopausal Women

Since vitamin E is one of the most potent antioxidant and anti-inflammatory agents, vitamin E can play a role against arteriosclerosis through various actions. Then, we have studied the relationship between serum vitamin E status and risk factors for arteriosclerosis in Japanese postmenopausal women. One hundred and seven subjects (70.0±7.7 y) were evaluated for vitamin E status by measuring serum α- and γ-tocopherol (αT and γT) levels. The number of arteriosclerosis risk factors was defined by the existence of high blood pressure, hyperglycemia, and dyslipidemia. Median serum αT and γT concentrations were 24.32 and 2.79 μmol/L, respectively. In none of the subjects, serum αT level was below the cutoff value (<12 μmol/L) for vitamin E deficiency which causes fragile erythrocyte and hemolysis. While no significant differences were found in serum levels of αT and γT between the groups categorized by the number of arteriosclerosis risks, serum levels of αT adjusted by serum total cholesterol (TC) and triglyceride (TG) decreased with an increasing number of arteriosclerotic risk factors (p=0.074). Serum αT level adjusted by serum TC and TG was also a negative significant predictor for the number of arteriosclerosis risk factors controlled by covariates associated with arteriosclerosis. The present study described that serum vitamin E level was positively associated with a lower number of arteriosclerotic risks, and its role for preventing noncommunicable diseases was suggested.

Prevention of 7-Ketocholesterol-Induced Overproduction of Reactive Oxygen Species, Mitochondrial Dysfunction and Cell Death with Major Nutrients (Polyphenols, ω3 and ω9 Unsaturated Fatty Acids) of the Mediterranean Diet on N2a Neuronal Cells

The brain, which is a cholesterol-rich organ, can be subject to oxidative stress in a variety of pathophysiological conditions, age-related diseases and some rare pathologies. This can lead to the formation of 7-ketocholesterol (7KC), a toxic derivative of cholesterol mainly produced by auto-oxidation. So, preventing the neuronal toxicity of 7KC is an important issue to avoid brain damage. As there are numerous data in favor of the prevention of neurodegeneration by the Mediterranean diet, this study aimed to evaluate the potential of a series of polyphenols (resveratrol, RSV; quercetin, QCT; and apigenin, API) as well as ω3 and ω9 unsaturated fatty acids (α-linolenic acid, ALA; eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA, and oleic acid, OA) widely present in this diet, to prevent 7KC (50 µM)-induced dysfunction of N2a neuronal cells. When polyphenols and fatty acids were used at non-toxic concentrations (polyphenols: ≤6.25 µM; fatty acids: ≤25 µM) as defined by the fluorescein diacetate assay, they greatly reduce 7KC-induced toxicity. The cytoprotective effects observed with polyphenols and fatty acids were comparable to those of α-tocopherol (400 µM) used as a reference. These polyphenols and fatty acids attenuate the overproduction of reactive oxygen species and the 7KC-induced drop in mitochondrial transmembrane potential (ΔΨm) measured by flow cytometry after dihydroethidium and DiOC₆(3) staining, respectively. Moreover, the studied polyphenols and fatty acids reduced plasma membrane permeability considered as a criterion for cell death measured by flow cytometry after propidium iodide staining. Our data show that polyphenols (RSV, QCT and API) as well as ω3 and ω9 unsaturated fatty acids (ALA, EPA, DHA and OA) are potent cytoprotective agents against 7KC-induced neurotoxicity in N2a cells. Their cytoprotective effects could partly explain the benefits of the Mediterranean diet on human health, particularly in the prevention of neurodegenerative diseases.

The bitterness of genitourinary infections: Properties, ligands of genitourinary bitter taste receptors and mechanisms linking taste sensing to inflammatory processes in the genitourinary tract

BACKGROUND

Though, first identified in the gastrointestinal tract, bitter taste receptors are now believed to be ubiquitously expressed in several regions of the body, including the respiratory tract, where they play a critical role in sensing and clearance of excess metabolic substrates, toxins, debris, and pathogens. More recently, bitter taste receptor expression has been reported in cells, tissues and organs of the genitourinary (GU) system, suggesting that these receptors may play an integral role in mediating inflammatory responses to microbial aggression in the GU tract. However, the mechanisms, linking bitter taste receptor sensing with inflammatory responses are not exactly clear. Here, I review recent data on the properties and ligands of bitter taste receptors and suggest mechanisms of bitter taste receptor signaling in the GU tract, and the molecular pathways that link taste sensing to inflammatory responses in GU tract.

METHOD

Computer-aided search was conducted in Scopus, PubMed, Web of Science and Google Scholar for relevant peer-reviewed articles published between 1990 and 2018, investigating the functional implication of bitter taste receptors in GU infections, using the following keywords: extra-oral bitter taste receptors, bitter taste receptors, GU bitter taste receptors, kidney OR renal OR ureteral OR urethral OR bladder OR detrusor smooth muscle OR testes OR spermatozoa OR prostate OR vaginal OR cervix OR ovarian OR endometrial OR myometrial OR placenta OR cutaneous bitter taste receptors. To identify research gaps on etiopathogenesis of GU infections/inflammation, additional search was conducted using the following keywords: GU inflammatory signaling, GU microbes, GU bacteria, GU virus, GU protozoa, GU microbial metabolites, and GU infection. The retrieved articles were filtered and further screened for relevance according to the aim of the study. A narrative review was performed for selected literatures.

RESULTS

Bitter taste receptors of the GU tract may constitute essential components of the pathogenetic mechanisms of GU infections/inflammation that are activated by microbial components, known as quorum sensing signal molecules. Based on accumulating evidences, indicating that taste receptors may signal downstream to activate inflammatory cascades, in addition to the nitric oxide-induced microbicidal effects produced upon taste receptor activation, it is suggested that the anti-inflammatory activities of bitter taste receptor stimulation are mediated via pathways involving the nuclear factor κB by downstream signaling of the metabolic and stress sensors, adenosine monophosphate-activated protein kinase and nicotinamide adenine dinucleotide-dependent silent mating type information regulation 2 homolog 1 (sirtuin 1), resulting to the synthesis of anti-inflammatory cytokines/chemokines, and antimicrobial factors, which ultimately, under normal conditions, leads to the elimination of microbial aggression.

CONCLUSIONS

GU bitter taste receptors may represent critical players in GU tract infections/inflammation. Bitter taste receptors may serve as important therapeutic target for treatment of a number of infectious diseases that affect the GU tract.

7-Ketocholesterol in disease and aging

7-Ketocholesterol (7KC) is a toxic oxysterol that is associated with many diseases and disabilities of aging, as well as several orphan diseases. 7KC is the most common product of a reaction between cholesterol and oxygen radicals and is the most concentrated oxysterol found in the blood and arterial plaques of coronary artery disease patients as well as various other disease tissues and cell types. Unlike cholesterol, 7KC consistently shows cytotoxicity to cells and its physiological function in humans or other complex organisms is unknown. Oxysterols, particularly 7KC, have also been shown to diffuse through membranes where they affect receptor and enzymatic function. Here, we will explore the known and proposed mechanisms of pathologies that are associated with 7KC, as well speculate about the future of 7KC as a diagnostic and therapeutic target in medicine.

Localisation of oxysterols at the sub-cellular level and in biological fluids

Oxysterols are oxidized derivatives of cholesterol that are formed enzymatically or via reactive oxygen species or both. Cholesterol or oxysterols ingested as food are absorbed and packed into lipoproteins that are taken up by hepatic cells. Within hepatic cells, excess cholesterol is metabolised to form bile acids. The endoplasmic reticulum acts as the main organelle in the bile acid synthesis pathway. Metabolised sterols originating from this pathway are distributed within other organelles and in the cell membrane. The alterations to membrane oxysterol:sterol ratio affects the integrity of the cell membrane. The presence of oxysterols changes membrane fluidity and receptor orientation. It is well documented that hydroxylase enzymes located in mitochondria facilitate oxysterol production via an acidic pathway. More recently, the presence of oxysterols was also reported in lysosomes. Peroxisomal deficiencies favour intracellular oxysterols accumulation. Despite the low abundance of oxysterols compared to cholesterol, the biological actions of oxysterols are numerous and important. Oxysterol levels are implicated in the pathogenesis of multiple diseases ranging from chronic inflammatory diseases (atherosclerosis, Alzheimer's disease and bowel disease), cancer and numerous neurodegenerative diseases. In this article, we review the distribution of oxysterols in sub-cellular organelles and in biological fluids.

α-Tocopherol preserves cardiac function by reducing oxidative stress and inflammation in ischemia/reperfusion injury

OBJECTIVE

Myocardial infarction (MI) is a leading cause of mortality and morbidity worldwide and new treatment strategies are highly sought-after. Paradoxically, reperfusion of the ischemic myocardium, as achieved with early percutaneous intervention, results in substantial damage to the heart (ischemia/reperfusion injury) caused by cell death due to aggravated inflammatory and oxidative stress responses. Chronic therapy with vitamin E is not effective in reducing the cardiovascular event rate, presumably through failing to reduce atherosclerotic plaque instability. Notably, acute treatment with vitamin E in patients suffering a MI has not been systematically investigated.

METHODS AND RESULTS

We applied alpha-tocopherol (α-TOH), the strongest anti-oxidant form of vitamin E, in murine cardiac ischemia/reperfusion injury induced by ligation of the left anterior descending coronary artery for 60 min. α-TOH significantly reduced infarct size, restored cardiac function as measured by ejection fraction, fractional shortening, cardiac output, and stroke volume, and prevented pathological changes as assessed by state-of-the-art strain and strain-rate analysis. Cardioprotective mechanisms identified, include a decreased infiltration of neutrophils into cardiac tissue and a systemic anti-inflammatory shift from Ly6Chigh to Ly6Clow monocytes. Furthermore, we found a reduction in myeloperoxidase expression and activity, as well as a decrease in reactive oxygen species and the lipid peroxidation markers phosphatidylcholine (PC) (16:0)-9-hydroxyoctadecadienoic acid (HODE) and PC(16:0)-13-HODE) within the infarcted tissue.

CONCLUSION

Overall, α-TOH inhibits ischemia/reperfusion injury-induced oxidative and inflammatory responses, and ultimately preserves cardiac function. Therefore, our study provides a strong incentive to test vitamin E as an acute therapy in patients suffering a MI.

Induction of a non-apoptotic mode of cell death associated with autophagic characteristics with steroidal maleic anhydrides and 7β-hydroxycholesterol on glioma cells

Steroidal maleic anhydrides were prepared in one step: lithocholic, chenodeoxicholic, deoxicholic, ursocholic, and hyodeoxicholic acid derivatives. Their capability to induce cell death was studied on C6 rat glioma cells, and 7β-hydroxycholesterol was used as positive cytotoxic control. The highest cytotoxicity was observed with lithocholic and chenodeoxicholic acid derivatives (23-(4-methylfuran-2,5-dione)-3α-hydroxy-24-nor-5β-cholane (compound 1a), and 23-(4-methylfuran-2,5-dione)-3α,7α-dihydroxy-24-nor-5β-cholane (compound 1b), respectively), which induce a non-apoptotic mode of cell death associated with mitochondrial membrane potential loss and reactive oxygen species overproduction. No cells with condensed and/or fragmented nuclei, no PARP degradation and no cleaved-caspase-3, which are apoptotic criteria, were observed. Similar effects were found with 7β-hydroxycholesterol. The cell clonogenic survival assay showed that compound 1b was more cytotoxic than compound 1a and 7β-hydroxycholesterol. Compound 1b and 7β-hydroxycholesterol also induce cell cycle modifications. In addition, compounds 1a and 1b, and 7β-hydroxycholesterol favour the formation of large acidic vacuoles revealed by staining with acridine orange and monodansylcadaverine evocating autophagic vacuoles; they also induce an increased ratio of [LC3-II / LC3-I], and modify the expression of mTOR, Beclin-1, Atg12, and Atg5-Atg12 which is are autophagic criteria. The ratio [LC3-II / LC3-I] is also strongly modified by bafilomycin acting on the autophagic flux. Rapamycin, an autophagic inducer, and 3-methyladenine, an autophagic inhibitor, reduce and increase 7β-hydroxycholesterol-induced cell death, respectively, supporting that 7β-hydroxycholesterol induces survival autophagy. Alpha-tocopherol also strongly attenuates 7β-hydroxycholesterol-induced cell death. However, rapamycin, 3-methyladenine, and α-tocopherol have no effect on compounds 1a and 1b-induced cell death. It is concluded that these compounds trigger a non apoptotic mode of cell death, involving the mitochondria and associated with several characteristics of autophagy.

Dietary cholesterol does not break your heart but kills your liver

It is increasingly accepted that dietary cholesterol has a much lower impact on the progression of cardiovascular disease than previously assumed. However, both animal experiments and human studies seem to support the view that dietary cholesterol may contribute to the transition from benign steatosis to the potentially fatal non-alcoholic steatohepatitis. Cholesterol esters and cholesterol accumulate in the hepatocyte and impair its function. This leads to oxidative stress and endoplasmic reticulum stress triggering the release of pro-inflammatory cytokines and rendering the hepatocyte more susceptible to apoptotic or necrotic cell death. Kupffer cells group around dying hepatocytes and phagocytose the hepatocyte debris and lipids. In addition, they are exposed to lipid peroxidation products released from hepatocytes. Kupffer cells, thus activated, release pro-inflammatory, chemotactic and profibrotic cytokines that promote inflammation and fibrosis. Therefore, dietary cholesterol may be harmful to the liver, in particular when administered in combination with polyunsaturated fatty acids that favor lipid peroxidation.

Vitamin E: Regulatory Role on Signal Transduction

Vitamin E modulates signal transduction pathways by several molecular mechanisms. As a hydrophobic molecule located mainly in membranes it contributes together with other lipids to the physical and structural characteristics such as membrane stability, curvature, fluidity, and the organization into microdomains (lipid rafts). By acting as the main lipid-soluble antioxidant, it protects other lipids such as mono- and poly-unsaturated fatty acids (MUFA and PUFA, respectively) against chemical reactions with reactive oxygen and nitrogen species (ROS and RNS, respectively) and prevents membrane destabilization and cellular dysfunction. In cells, vitamin E affects signaling in redox-dependent and redox-independent molecular mechanisms by influencing the activity of enzymes and receptors involved in modulating specific signal transduction and gene expression pathways. By protecting and preventing depletion of MUFA and PUFA it indirectly enables regulatory effects that are mediated by the numerous lipid mediators derived from these lipids. In recent years, some vitamin E metabolites have been observed to affect signal transduction and gene expression and their relevance for the regulatory function of vitamin E is beginning to be elucidated. In particular, the modulation of the CD36/FAT scavenger receptor/fatty acids transporter by vitamin E may influence many cellular signaling pathways relevant for lipid homeostasis, inflammation, survival/apoptosis, angiogenesis, tumorigenesis, neurodegeneration, and senescence. Thus, vitamin E has an important role in modulating signal transduction and gene expression pathways relevant for its uptake, distribution, metabolism, and molecular action that when impaired affect physiological and patho-physiological cellular functions relevant for the prevention of a number of diseases. © 2018 IUBMB Life, 71(4):456-478, 2019.

Soybean Oil-Derived Poly-Unsaturated Fatty Acids Enhance Liver Damage in NAFLD Induced by Dietary Cholesterol

While the impact of dietary cholesterol on the progression of atherosclerosis has probably been overestimated, increasing evidence suggests that dietary cholesterol might favor the transition from blunt steatosis to non-alcoholic steatohepatitis (NASH), especially in combination with high fat diets. It is poorly understood how cholesterol alone or in combination with other dietary lipid components contributes to the development of lipotoxicity. The current study demonstrated that liver damage caused by dietary cholesterol in mice was strongly enhanced by a high fat diet containing soybean oil-derived ω6-poly-unsaturated fatty acids (ω6-PUFA), but not by a lard-based high fat diet containing mainly saturated fatty acids. In contrast to the lard-based diet the soybean oil-based diet augmented cholesterol accumulation in hepatocytes, presumably by impairing cholesterol-eliminating pathways. The soybean oil-based diet enhanced cholesterol-induced mitochondrial damage and amplified the ensuing oxidative stress, probably by peroxidation of poly-unsaturated fatty acids. This resulted in hepatocyte death, recruitment of inflammatory cells, and fibrosis, and caused a transition from steatosis to NASH, doubling the NASH activity score. Thus, the recommendation to reduce cholesterol intake, in particular in diets rich in ω6-PUFA, although not necessary to reduce the risk of atherosclerosis, might be sensible for patients suffering from non-alcoholic fatty liver disease.

Induction of peroxisomal changes in oligodendrocytes treated with 7-ketocholesterol: Attenuation by α-tocopherol

The involvement of organelles in cell death is well established especially for endoplasmic reticulum, lysosomes and mitochondria. However, the role of the peroxisome is not well known, though peroxisomal dysfunction favors a rupture of redox equilibrium. To study the role of peroxisomes in cell death, 158 N murine oligodendrocytes were treated with 7-ketocholesterol (7 KC: 25-50 μM, 24 h). The highest concentration is known to induce oxiapoptophagy (OXIdative stress + APOPTOsis + autoPHAGY), whereas the lowest concentration does not induce cell death. In those conditions (with 7 KC: 50 μM) morphological, topographical and functional peroxisome alterations associated with modifications of the cytoplasmic distribution of mitochondria, with mitochondrial dysfunction (loss of transmembrane mitochondrial potential, decreased level of cardiolipins) and oxidative stress were observed: presence of peroxisomes with abnormal sizes and shapes similar to those observed in Zellweger fibroblasts, lower cellular level of ABCD3, used as a marker of peroxisomal mass, measured by flow cytometry, lower mRNA and protein levels (measured by RT-qPCR and western blotting) of ABCD1 and ABCD3 (two ATP-dependent peroxisomal transporters), and of ACOX1 and MFP2 enzymes, and lower mRNA level of DHAPAT, involved in peroxisomal β-oxidation and plasmalogen synthesis, respectively, and increased levels of very long chain fatty acids (VLCFA: C24:0, C24:1, C26:0 and C26:1, quantified by gas chromatography coupled with mass spectrometry) metabolized by peroxisomal β-oxidation. In the presence of 7 KC (25 μM), slight mitochondrial dysfunction and oxidative stress were found, and no induction of apoptosis was detected; however, modifications of the cytoplasmic distribution of mitochondria and clusters of mitochondria were detected. The peroxisomal alterations observed with 7 KC (25 μM) were similar to those with 7 KC (50 μM). In addition, data obtained by transmission electron microcopy and immunofluorescence microscopy by dual staining with antibodies raised against p62, involved in autophagy, and ABCD3, support that 7 KC (25-50 μM) induces pexophagy. 7 KC (25-50 μM)-induced side effects were attenuated by α-tocopherol but not by α-tocotrienol, whereas the anti-oxidant properties of these molecules determined with the FRAP assay were in the same range. These data provide evidences that 7 KC, at concentrations inducing or not cell death, triggers morphological, topographical and functional peroxisomal alterations associated with minor or major mitochondrial changes.

Cytoprotective Activities of Milk Thistle Seed Oil Used in Traditional Tunisian Medicine on 7-Ketocholesterol and 24S-Hydroxycholesterol-Induced Toxicity on 158N Murine Oligodendrocytes

The Asteraceae family is economically very important, because many of these plants are grown mainly for their food value, such as lettuce (Lactuca), chicory (Cichorium), and sunflower (Heliantus aminus). One of the typical properties of this family, which includes milk thistle (Sylibum marianum), is the richness of the oil in various compounds (flavonoids, alkaloids, tocopherols, and unsaturated fatty acids). Currently, and for the coming decades, age-related diseases, including neurodegenerative diseases, are a major public health problem. Preventing their appearance or opposing their evolution is a major objective. In this context, the cytoprotective activities of milk thistle seed oil produced in Tunisia were studied on the 158N model using 7-ketocholesterol (7KC) and 24S-hydroxycholesterol (24S) as cytotoxic agents. 7KC and 24S were used because they can be increased in the brain and body fluids of patients with major age-related neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases. In order to evaluate the cytoprotective properties of milk thistle seed oil, complementary techniques of microscopy, flow cytometry, and biochemistry were used. The chemical composition of milk thistle seed oil has also been determined by various chromatography techniques. Milk thistle seed oils from different area of Tunisia are rich in tocopherols and are strongly antioxidant according to various biochemical tests (KRL (Kit Radicaux Libres), FRAP (Ferric Reducing Antioxidant Power), and DPPH (2,2-diphenyl-1-picrylhydrazyl)). The main fatty acids are linoleic acid (C18:2 n-6) and oleic acid (C18:1 n-9). The main polyphenols identified are homovanillic acid, p-coumaric acid, quercetin, and apigenin, with a predominance of vanillic acid. On 158N cells, milk thistle seed oil attenuates the cytotoxicity of 7KC and 24S including: loss of cell adhesion, increased plasma membrane permeability, mitochondrial dysfunction, overproduction of reactive oxygen species, induction of apoptosis, and autophagy. The attenuation of the cytotoxicity of 7KC and 24S observed with the milk thistle seed oil is in the order of that observed with α-tocopherol used as a positive control. In the presence of nigella seed oil, considered potentially cytotoxic, no cytoprotective effects were observed. Given the chemical characteristics, antioxidant properties, and cytoprotective activities of milk thistle seed oil, our results highlight the potential benefit of this oil for human health.

Water-Soluble Vitamin E-Tocopheryl Phosphate

The hydrophobicity of vitamin E poses transport and metabolic challenges to regulate its bioavailability and to prevent its accumulation in lipid-rich tissues such as adipose tissue, brain, and liver. Water-soluble precursors of vitamin E (α-tocopherol, αT), such as its esters with acetate (αTA), succinate (αTS), or phosphate (αTP), have increased solubility in water and stability against reaction with free radicals, but they are rapidly converted during their uptake into the lipid-soluble vitamin E. Therefore, the bioavailability of these precursors as intact molecules is low; nevertheless, at least for αTS and αTP, the recent research has revealed unique regulatory effects on signal transduction and gene expression and the modulation of cellular events ranging from proliferation, survival/apoptosis, lipid uptake and metabolism, phagocytosis, long term potentiation, cell migration, telomere maintenance, and angiogenesis. Moreover, water-soluble derivatives of vitamin E including some based on αTP are increasingly used as components of nanocarriers for enhanced and targeted delivery of drugs and other molecules (vitamins, including αT and αTP itself, vitamin D3, carnosine, caffeine, docosahexaenoic acid (DHA), insulin) and cofactors such as coenzyme Q10. In this review, the chemical characteristics, transport, metabolic pathways, and molecular mechanisms of action of αTP in cells and tissues are summarized and put into perspective with its possible role in the prevention of a number of diseases.

Argan Oil-Mediated Attenuation of Organelle Dysfunction, Oxidative Stress and Cell Death Induced by 7-Ketocholesterol in Murine Oligodendrocytes 158N

Argan oil is widely used in Morocco in traditional medicine. Its ability to treat cardiovascular diseases is well-established. However, nothing is known about its effects on neurodegenerative diseases, which are often associated with increased oxidative stress leading to lipid peroxidation and the formation of 7-ketocholesterol (7KC) resulting from cholesterol auto-oxidation. As 7KC induces oxidative stress, inflammation and cell death, it is important to identify compounds able to impair its harmful effects. These compounds may be either natural or synthetic molecules or mixtures of molecules such as oils. In this context: (i) the lipid profiles of dietary argan oils from Berkane and Agadir (Morocco) in fatty acids, phytosterols, tocopherols and polyphenols were determined by different chromatographic techniques; and (ii) their anti-oxidant and cytoprotective effects in 158N murine oligodendrocytes cultured with 7KC (25-50 µM; 24 h) without and with argan oil (0.1% v/v) or α-tocopherol (400 µM, positive control) were evaluated with complementary techniques of cellular and molecular biology. Among the unsaturated fatty acids present in argan oils, oleate (C18:1 n-9) and linoleate (C18:1 n-6) were the most abundant; the highest quantities of saturated fatty acids were palmitate (C16:0) and stearate (C18:0). Several phytosterols were found, mainly schottenol and spinasterol (specific to argan oil), cycloartenol, β-amyrin and citrostadienol. α- and γ-tocopherols were also present. Tyrosol and protocatechic acid were the only polyphenols detected. Argan and extra virgin olive oils have many compounds in common, principally oleate and linoleate, and tocopherols. Kit Radicaux Libres (KRL) and ferric reducing antioxidant power (FRAP) tests showed that argan and extra virgin olive oils have anti-oxidant properties. Argan oils were able to attenuate the cytotoxic effects of 7KC on 158N cells: loss of cell adhesion, cell growth inhibition, increased plasma membrane permeability, mitochondrial, peroxisomal and lysosomal dysfunction, and the induction of oxiapoptophagy (OXIdation + APOPTOsis + autoPHAGY). Altogether, our data obtained in 158N oligodendrocytes provide evidence that argan oil is able to counteract the toxic effects of 7KC on nerve cells, thus suggesting that some of its compounds could prevent or mitigate neurodegenerative diseases to the extent that they are able to cross the blood-brain barrier.

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.

Alpha-Tocopherol prevents esophageal squamous cell carcinoma by modulating PPARγ-Akt signaling pathway at the early stage of carcinogenesis

The poor prognosis of esophageal squamous cell carcinoma (ESCC) emphasizes the urgent need to better understand the carcinogenesis and develop prevention strategies. Previous studies have highlighted the potential of using Vitamin E (tocopherols) for cancer chemoprevention, but the preventive activity of α-Tocopherol against ESCC remains to be elucidated. Our data showed that early-stage supplementation with α-Tocopherol significantly prevented esophageal carcinogenesis induced by N-nitrosomethylbenzylamine (NMBA) in ESCC rat model. In the Het-1A cell model, α-Tocopherol markedly suppressed cell proliferation, promoted cell cycle G2-phase arrest and increased apoptosis. Gene microarray and proteins array analysis indicated that Akt signaling was a potential target for α-Tocopherol. We further demonstrated that α-Tocopherol increased the expression of PPARγ and its downstream tumor suppressor PTEN. Knockdown of PPARγ activated Akt signaling transduction, whereas this process was attenuated by the presence of α-Tocopherol and PPARγ agonist Rosiglitazone. In contrast, the effect of α-Tocopherol on Akt inhibition was not observed in established tumors, neither in cancerous cell lines which constitutively expressed higher levels of PPARγ. These results were closely correlated with the ineffectiveness of α-Tocopherol in the late stage of ESCC carcinogenesis. Taken together, our study suggested that α-Tocopherol may serve as a PPARγ agonist for the chemoprevention of esophageal cancer.

Protective role of vitamin E preconditioning of human dermal fibroblasts against thermal stress in vitro

AIMS

Oxidative microenvironment of burnt skin restricts the outcome of cell based therapies of thermal skin injuries. The aim of this study was to precondition human dermal fibroblasts with an antioxidant such as vitamin E to improve their survival and therapeutic abilities in heat induced oxidative in vitro environment.

MAIN METHODS

Fibroblasts were treated with 100μM vitamin E for 24h at 37°C followed by heat shock for 10min at 51°C in fresh serum free medium.

KEY FINDINGS

Preconditioning with vitamin E reduced cell injury as demonstrated by decreased expression of annexin-V, cytochrome p450 (CYP450) mediated oxidative reactions, senescence and release of lactate dehydrogenase (LDH) accomplished by down-regulated expression of pro-apoptotic BAX gene. Vitamin E preconditioned cells exhibited remarkable improvement in cell viability, release of paracrine factors such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), stromal derived factor-1alpha (SDF-1α) and also showed significantly up-regulated levels of PCNA, VEGF, BCL-XL, FGF7, FGF23, FLNβ and Col7α genes presumably through activation of phosphatidylinositol 3-kinase (PI3-K)/Akt pathway.

SIGNIFICANCE

The results suggest that pretreatment of fibroblasts with vitamin E prior to transplantation in burnt skin speeds up the wound healing process by improving the antioxidant scavenging responses in oxidative environment of transplanted burn wounds.

Effect of vitamin E on 24(S)-hydroxycholesterol-induced necroptosis-like cell death and apoptosis

24(S)-Hydroxycholesterol (24S-OHC) has diverse physiological and pathological functions. In particular, cytotoxic effects of 24S-OHC in neuronal cells are important in development of neurodegenerative diseases. 24S-OHC induces necroptosis-like cell death in SH-SY5Y cells expressing little caspase-8. In the present study, 24S-OHC was found to induce apoptosis as determined by caspase-3 activation in all-trans-retinoic acid (atRA)-treated SH-SY5Y cells in which expression of caspase-8 was induced. 24S-OHC-induced cell death was inhibited by α-tocopherol (α-Toc) but not by α-tocotrienol (α-Toc3) in SH-SY5Y cells regardless of whether cells were treated with atRA. In contrast, cumene hydroperoxide (CumOOH)-induced cell death was significantly inhibited by α-Toc and α-Toc3. In atRA-treated SH-SY5Y cells, generation of reactive oxygen species (ROS) was induced by stimulation with CumOOH but was not induced by stimulation with 24S-OHC. These results suggest that inhibition of 24S-OHC-induced cell death by α-Toc cannot be explained by its radical scavenging antioxidant activity. Esterification of 24S-OHC followed by lipid droplet (LD) formation due to acyl-CoA:cholesterol acyltransferase 1 (ACAT1) are key events in 24S-OHC-induced cell death in atRA-treated SH-SY5Y cells as demonstrated by inhibition of cell death by ACAT1 inhibitor. LD number was not changed by treatment with either α-Toc or α-Toc3. The different physical properties of α-Toc and α-Toc3 may account for their different inhibitory effects on 24S-OHC-induced cell death.

Comparison of the effects of major fatty acids present in the Mediterranean diet (oleic acid, docosahexaenoic acid) and in hydrogenated oils (elaidic acid) on 7-ketocholesterol-induced oxiapoptophagy in microglial BV-2 cells

Increased levels of 7-ketocholesterol (7KC), which results mainly from cholesterol auto-oxidation, are often found in the plasma and/or cerebrospinal fluid of patients with neurodegenerative diseases and might contribute to activation of microglial cells involved in neurodegeneration. As major cellular dysfunctions are induced by 7KC, it is important to identify molecules able to impair its side effects. Since consumption of olive and argan oils, and fish is important in the Mediterranean diet, the aim of the study was to determine the ability of oleic acid (OA), a major compound of olive and argan oil, and docosahexaenoic acid (DHA) present in fatty fishes, such as sardines, to attenuate 7KC-induced cytotoxic effects. Since elaidic acid (EA), the trans isomer of OA, can be found in hydrogenated cooking oils and fried foods, its effects on 7KC-induced cytotoxicity were also determined. In murine microglial BV-2 cells, 7KC induces cell growth inhibition, mitochondrial dysfunctions, reactive oxygen species overproduction and lipid peroxidation, increased plasma membrane permeability and fluidity, nuclei condensation and/or fragmentation and caspase-3 activation, which are apoptotic characteristics, and an increased LC3-II/LC3-I ratio, which is a criterion of autophagy. 7KC is therefore a potent inducer of oxiapoptophagy (OXIdation+APOPTOsis+autoPHAGY) on BV-2 cells. OA and EA, but not DHA, also favor the accumulation of lipid droplets revealed with Masson's trichrome, Oil Red O, and Nile Red staining. The cytotoxicity of 7KC was strongly attenuated by OA and DHA. Protective effects were also observed with EA. However, 7KC-induced caspase-3 activation was less attenuated with EA. Different effects of OA and EA on autophagy were also observed. In addition, EA (but not OA) increased plasma membrane fluidity, and only OA (but not EA) was able to prevent the 7KC-induced increase in plasma membrane fluidity. Thus, in BV-2 microglial cells, the principal fatty acids of the Mediterranean diet (OA, DHA) were able to attenuate the major toxic effects of 7KC, thus reinforcing the interest of natural compounds present in the Mediterranean diet to prevent the development of neurodegenerative diseases.

Dietary phytochemicals in the protection against oxysterol-induced damage

The intake of fruits and vegetables is associated with reduced incidence of many chronic diseases. These foods contain phytochemicals that often possess antioxidant and free radical scavenging capacity and show anti-inflammatory action, which are also the basis of other bioactivities and health benefits, such as anticancer, anti-aging, and protective action for cardiovascular diseases, diabetes mellitus, obesity and neurodegenerative disorders. Many factors can be included in the etiopathogenesis of all of these multifactorial diseases that involve oxidative stress, inflammation and/or cell death processes, oxysterols, i.e. cholesterol oxidation products (COPs) as well as phytosterol oxidation products (POPs), among others. These oxidized lipids result from either spontaneous and/or enzymatic oxidation of cholesterol/phytosterols on the steroid nucleus or on the side chain and their critical roles in the pathophysiology of the abovementioned diseases has become increasingly evident. In this context, many studies investigated the potential of dietary phytochemicals (polyphenols, carotenoids and vitamins C and E, among others) to protect against oxysterol toxicity in various cell models mimicking pathophysiological conditions. This review, summarizing the mechanisms involved in the chemopreventive effect of phytochemicals against the injury by oxysterols may constitute a step forward to consider the importance of preventive strategies on a nutritional point of view to decrease the burden of many age-related chronic diseases.

Protective Effects of α-Tocopherol, γ-Tocopherol and Oleic Acid, Three Compounds of Olive Oils, and No Effect of Trolox, on 7-Ketocholesterol-Induced Mitochondrial and Peroxisomal Dysfunction in Microglial BV-2 Cells

Lipid peroxidation products, such as 7-ketocholesterol (7KC), may be increased in the body fluids and tissues of patients with neurodegenerative diseases and trigger microglial dysfunction involved in neurodegeneration. It is therefore important to identify synthetic and natural molecules able to impair the toxic effects of 7KC. We determined the impact of 7KC on murine microglial BV-2 cells, especially its ability to trigger mitochondrial and peroxisomal dysfunction, and evaluated the protective effects of α- and γ-tocopherol, Trolox, and oleic acid (OA). Multiple complementary chemical assays, flow cytometric and biochemical methods were used to evaluate the antioxidant and cytoprotective properties of these molecules. According to various complementary assays to estimate antioxidant activity, only α-, and γ-tocopherol, and Trolox had antioxidant properties. However, only α-tocopherol, γ-tocopherol and OA were able to impair 7KC-induced loss of mitochondrial transmembrane potential, which is associated with increased permeability to propidium iodide, an indicator of cell death. In addition, α-and γ-tocopherol, and OA were able to prevent the decrease in Abcd3 protein levels, which allows the measurement of peroxisomal mass, and in mRNA levels of Abcd1 and Abcd2, which encode for two transporters involved in peroxisomal β-oxidation. Thus, 7KC-induced side effects are associated with mitochondrial and peroxisomal dysfunction which can be inversed by natural compounds, thus supporting the hypothesis that the composition of the diet can act on the function of organelles involved in neurodegenerative diseases.

Structure activity relationship studies on cytotoxicity and the effects on steroid receptors of AB-functionalized cholestanes

Structure-activity relationship analysis and profiling of a library of AB-functionalized cholestane derivatives closely related to brassinosteroids (BRs) were performed to examine their antiproliferative activities and activities on steroid hormone receptors. Some of the compounds were found to have strong cytotoxic activity in several human normal and cancer cell lines. The presence of a 3-hydroxy or 3-oxo group and 2,3-vicinal diol or 3,4-vicinal diol moiety were found to be necessary for optimum biological activity, as well as a six-membered B ring. According to the profiling of all steroid receptors in both agonist and antagonist mode, the majority of the cholestanes were weakly active or inactive compared to the natural ligands. Estrogenic activity was detected for two compounds, two compounds possessed antagonistic properties on estrogen receptors and seven compounds showed agonistic activity. Two active cholestane derivatives were shown to strongly influence cell viability, proliferation, cell cycle distribution, apoptosis and molecular pathways responsible for these processes in hormone-sensitive/insensitive (MCF7/MDA-MB-468) breast cancer cell lines.

The role of oxysterols in vascular ageing

The ageing endothelium progressively loses its remarkable and crucial ability to maintain homeostasis of the vasculature, as it acquires a proinflammatory phenotype. Cellular and structural changes gradually accumulate in the blood vessels, and markedly in artery walls. Most changes in aged arteries are comparable to those occurring during the atherogenic process, the latter being more marked: pro-oxidant and proinflammatory molecules, mainly deriving from or triggered by oxidized low density lipoproteins (oxLDLs), are undoubtedly a major driving force of this process. Oxysterols, quantitatively relevant components of oxLDLs, are likely candidate molecules in the pathogenesis of vascular ageing, because of their marked pro-oxidant, proinflammatory and proapoptotic properties. An increasing bulk of experimental data point to the contribution of a variety of oxysterols of pathophysiological interest, also in the age-related genesis of endothelium dysfunction, intimal thickening due to lipid accumulation, and smooth muscle cell migration and arterial stiffness due to increasing collagen deposition and calcification. This review provides an updated analysis of the molecular mechanisms whereby oxysterols accumulating in the wall of ageing blood vessels may 'activate' endothelial and monocytic cells, through expression of an inflammatory phenotype, and 'convince' smooth muscle cells to proliferate, migrate and, above all, to act as fibroblast-like cells.

Helicobacter pylori modulates host cell survival regulation through the serine-threonine kinase, 3-phosphoinositide dependent kinase 1 (PDK-1)

BACKGROUND

Helicobacter pylori (H. pylori) infection affects cell survival signaling pathways including cell apoptosis and proliferation, which are considered risk factors for the development of gastric cancer when unregulated. In the present study, we investigated the effect of H. pylori infection on the phosphorylation state of 3-phosphoinositide-dependent kinase-1 (PDK-1), a master kinase that regulates phosphorylation of Akt (also known as protein kinase B, PKB) and cell survival.

METHODS

The activity of PDK-1 was examined in human gastric epithelial cells incubated in the presence or absence of different H. pylori strains. In addition, the role of H. pylori type IV secretion system and the mechanism of H. pylori effect on PDK-1 activity was examined.

RESULTS

In the presence of H. pylori, phosphorylation of the activation loop (serine 241) PDK-1 was rapidly lost suggesting that dephosphorylation of PDK-1 is a target for H. pylori to modulate cell survival. The extent of dephosphorylation was strain dependent with H. pylori 60190 being the most effective. H. pylori infection of gastric epithelial cells resulted in altered phosphorylation and degradation of Akt, suggesting that PDK-1 dephosphorylation affects cell survival pathways and thereby may contribute to disease pathogenesis.

CONCLUSION

We propose that dephosphorylation of PDK-1 and the resulting changes to Akt phosphorylation is one of the mechanisms by which infection with H. pylori alter the balance between apoptosis and cell proliferation and identify a host molecular mechanism regulated by H. pylori that ultimately contributes to carcinogenesis. Our studies therefore provide insights into one of the mechanisms by which H. pylori infection contributes to gastric cancer by regulating the activity of a cell survival signaling pathway.

7-Ketocholesterol and 5,6-secosterol induce human endothelial cell dysfunction by differential mechanisms

7-Ketocholesterol and 5,6-secosterol are cholesterol autoxidation products generated under oxidative stress by two distinct mechanisms. They are present in atherosclerotic plaques and are candidate players in the disease initiation and progression. While 7-ketocholesterol affects at cellular level, in particular apoptosis, are well known and reported on diverse cell lines, 5,6-secosterol is a recently discovered oxysterol with relatively few reports on the potential to affect endothelial cell functions. Endothelial cells have a central role in cardiovascular disease as they provide the barrier between blood and the vessel wall where atherosclerosis starts and progresses. Insults to endothelial cells provoke their dysfunction favoring pro-atherogenic and pro-thrombotic effects. In the present work, we tested 7-ketocholesterol and 5,6-secosterol on endothelial cells - focusing on apoptosis and the associated mitochondrial/lysosome alterations - and on endothelial function using the in vitro model of arterial relaxation of aortic rings. Our data provide evidence that 7-ketocholesterol and 5,6-secosterol are efficient instigators of apoptosis, which for 5,6-secosterol is associated to PKC and p53 up-regulation. In addition 5,6-secosterol is a potent inhibitor of endothelial-dependent arterial relaxation through PKC-dependent mechanisms. This may contribute to pro-atherogenic and pro-thrombotic mechanisms of 5,6-secosterol and highlights the role of cholesterol autoxidation in cardiovascular disease.

Involvement of oxysterols in age-related diseases and ageing processes

Ageing is accompanied by increasing vulnerability to major pathologies (atherosclerosis, Alzheimer's disease, age-related macular degeneration, cataract, and osteoporosis) which can have similar underlying pathoetiologies. All of these diseases involve oxidative stress, inflammation and/or cell death processes, which are triggered by cholesterol oxide derivatives, also named oxysterols. These oxidized lipids result either from spontaneous and/or enzymatic oxidation of cholesterol on the steroid nucleus or on the side chain. The ability of oxysterols to induce severe dysfunctions in organelles (especially mitochondria) plays key roles in RedOx homeostasis, inflammatory status, lipid metabolism, and in the control of cell death induction, which may at least in part contribute to explain the potential participation of these molecules in ageing processes and in age related diseases. As no efficient treatments are currently available for most of these diseases, which are predicted to become more prevalent due to the increasing life expectancy and average age, a better knowledge of the biological activities of the different oxysterols is of interest, and constitutes an important step toward identification of pharmacological targets for the development of new therapeutic strategies.

Regulatory metabolites of vitamin E and their putative relevance for atherogenesis

Vitamin E is likely the most important antioxidant in the human diet and α-tocopherol is the most active isomer. α-Tocopherol exhibits anti-oxidative capacity in vitro, and inhibits oxidation of LDL. Beside this, α-tocopherol shows anti-inflammatory activity and modulates expression of proteins involved in uptake, transport and degradation of tocopherols, as well as the uptake, storage and export of lipids such as cholesterol. Despite promising anti-atherogenic features in vitro, vitamin E failed to be atheroprotective in clinical trials in humans. Recent studies highlight the importance of long-chain metabolites of α-tocopherol, which are formed as catabolic intermediate products in the liver and occur in human plasma. These metabolites modulate inflammatory processes and macrophage foam cell formation via mechanisms different than that of their metabolic precursor α-tocopherol and at lower concentrations. Here we summarize the controversial role of vitamin E as a preventive agent against atherosclerosis and point the attention to recent findings that highlight a role of these long-chain metabolites of vitamin E as a proposed new class of regulatory metabolites. We speculate that the metabolites contribute to physiological as well as pathophysiological processes.

Cholesterol hydroperoxides and their degradation mechanism

Cholesterol is one of the oxidizable lipids constituting biomembranes and plasma lipoproteins. Cholesterol hydroperoxides (Chol-OOH) are the primary products if cholesterol is subjected to attack by reactive oxygen species. In particular, singlet molecular oxygen reacts with cholesterol to yield cholesterol 5α-hydroperoxide as the major hydroperoxide species. Chol-OOH may accumulate in biological systems because of its resistance to glutathione-dependent enzymatic detoxification reactions. Their degradation products (including hydroxycholesterol and 7-ketocholesterol) participate in the pathophysiological functions of oxysterols. Highly reactive cholesterol 5,6-secosterol present in atherosclerotic lesions can be derived from the degradation of cholesterol 5α-hydroperoxide. Chol-OOH themselves may affect the lipid rafts of biomembranes, thereby leading to the modification of signal transduction pathways.