Increased plasma levels of oxysterols, in vivo markers of oxidative stress, in patients with familial combined hyperlipidemia: reduction during atorvastatin and fenofibrate therapy

Oxysterols as Biomarkers of Aging and Disease

Oxysterols derive from either enzymatic or non-enzymatic oxidation of cholesterol. Even though they are produced as intermediates of bile acid synthesis pathway, they are recognised as bioactive compounds in cellular processes. Therefore, their absence or accumulation have been shown to be associated with disease phenotypes. This chapter discusses the contribution of oxysterol to ageing, age-related diseases such as neurodegeneration and various disorders such as cancer, cardiovascular disease, diabetes, metabolic and ocular disorders. It is clear that oxysterols play a significant role in development and progression of these diseases. As a result, oxysterols are being investigated as suitable markers for disease diagnosis purposes and some drug targets are in development targeting oxysterol pathways. However, further research will be needed to confirm the suitability of these potentials.

Molecular Mechanisms and Pathophysiological Significance of Eryptosis

Despite lacking the central apoptotic machinery, senescent or damaged RBCs can undergo an unusual apoptosis-like cell death, termed eryptosis. This premature death can be caused by, or a symptom of, a wide range of diseases. However, various adverse conditions, xenobiotics, and endogenous mediators have also been recognized as triggers and inhibitors of eryptosis. Eukaryotic RBCs are unique among their cell membrane distribution of phospholipids. The change in the RBC membrane composition of the outer leaflet occurs in a variety of diseases, including sickle cell disease, renal diseases, leukemia, Parkinson’s disease, and diabetes. Eryptotic erythrocytes exhibit various morphological alterations such as shrinkage, swelling, and increased granulation. Biochemical changes include cytosolic Ca2+ increase, oxidative stress, stimulation of caspases, metabolic exhaustion, and ceramide accumulation. Eryptosis is an effective mechanism for the elimination of dysfunctional erythrocytes due to senescence, infection, or injury to prevent hemolysis. Nevertheless, excessive eryptosis is associated with multiple pathologies, most notably anemia, abnormal microcirculation, and prothrombotic risk; all of which contribute to the pathogenesis of several diseases. In this review, we provide an overview of the molecular mechanisms, physiological and pathophysiological relevance of eryptosis, as well as the potential role of natural and synthetic compounds in modulating RBC survival and death.

Hibernating brown bears are protected against atherogenic dyslipidemia

To investigate mechanisms by which hibernators avoid atherogenic hyperlipidemia during hibernation, we assessed lipoprotein and cholesterol metabolisms of free-ranging Scandinavian brown bears (Ursus arctos). In winter- and summer-captured bears, we measured lipoprotein sizes and sub-classes, triglyceride-related plasma-enzyme activities, and muscle lipid composition along with plasma-levels of antioxidant capacities and inflammatory markers. Although hibernating bears increased nearly all lipid levels, a 36%-higher cholesteryl-ester transfer-protein activity allowed to stabilize lipid composition of high-density lipoproteins (HDL). Levels of inflammatory metabolites, i.e., 7-ketocholesterol and 11ß-prostaglandin F2α, declined in winter and correlated inversely with cardioprotective HDL2b-proportions and HDL-sizes that increased during hibernation. Lower muscle-cholesterol concentrations and lecithin-cholesterol acyltransferase activity in winter suggest that hibernating bears tightly controlled peripheral-cholesterol synthesis and/or release. Finally, greater plasma-antioxidant capacities prevented excessive lipid-specific oxidative damages in plasma and muscles of hibernating bears. Hence, the brown bear manages large lipid fluxes during hibernation, without developing adverse atherogenic effects that occur in humans and non-hibernators.

Oxysterol species generated by auto-oxidation in subclinical hypothyroidism

BACKGROUND

Auto-oxidized oxysterols are implicated in the pathogenesis of various chronic diseases. Their concentrations are indicators of oxidative stress in vivo and associated with atherosclerosis. Subclinical hypothyroidism is related with cardiac diseases and oxidative stress, but the exact mechanisms underlying these associations are not clear yet.

OBJECTIVE

To investigate the auto-oxidized oxysterols, 7-ketocholesterol (7-KC) and cholestane-3β,5α,6β-triol (chol-triol), in patients with subclinical hypothyroidism, as well as to evaluate the impact of restoring euthyroidism on oxysterol concentrations.

METHODS

In this prospective observational study, 64 patients with newly diagnosed autoimmune thyroiditis (41 with subclinical hypothyroidism and 23 euthyroidism), and 45 healthy controls were enrolled. Age, gender, and body mass index were matched among patient groups and healthy controls. Anthropometric measurements were obtained and fasting plasma 7-ketocholesterol and cholestane-3β,5α,6β-triol concentrations were measured by using liquid chromatography coupled with tandem mass spectrometry. Levothyroxine was then administered to all patients with subclinical-hypothyroidism. After three months, measurements of the oxysterols and serum cholesterols from the patients who have become euthyroid were repeated.

RESULTS

Concentrations of 7-ketocholesterol and cholestane-3β,5α,6β-triol were significantly higher in patients with subclinical-hypothyroidism when compared to both euthyroid patients and healthy controls (p < 0.001 for both oxysterols). After restoration of euthyroidism, concentrations of 7-ketocholesterol and cholestane-3β,5α,6β-triol decreased significantly and reached similar concentrations observed in healthy controls (p < 0.001 for both oxysterols).

CONCLUSIONS

Auto-oxidized oxysterol species are higher in patients with mild thyroid dysfunction, and supported the rationale for treating subclinical-hypothyroidism.

Identification of Anti-Severe Acute Respiratory Syndrome-Related Coronavirus 2 (SARS-CoV-2) Oxysterol Derivatives In Vitro

The development of effective antiviral drugs targeting the severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) is urgently needed to combat the coronavirus disease 2019 (COVID-19). We have previously studied the use of semi-synthetic derivatives of oxysterols, oxidized derivatives of cholesterol as drug candidates for the inhibition of cancer, fibrosis, and bone regeneration. In this study, we screened a panel of naturally occurring and semi-synthetic oxysterols for anti-SARS-CoV-2 activity using a cell culture infection assay. We show that the natural oxysterols, 7-ketocholesterol, 22(R)-hydroxycholesterol, 24(S)-hydroxycholesterol, and 27-hydroxycholesterol, substantially inhibited SARS-CoV-2 propagation in cultured cells. Among semi-synthetic oxysterols, Oxy210 and Oxy232 displayed more robust anti-SARS-CoV-2 activities, reducing viral replication more than 90% at 10 μM and 99% at 15 μM, respectively. When orally administered in mice, peak plasma concentrations of Oxy210 fell into a therapeutically relevant range (19 μM), based on the dose-dependent curve for antiviral activity in our cell-based assay. Mechanistic studies suggest that Oxy210 reduced replication of SARS-CoV-2 by disrupting the formation of double-membrane vesicles (DMVs); intracellular membrane compartments associated with viral replication. Our study warrants further evaluation of Oxy210 and Oxy232 as a safe and reliable oral medication, which could help protect vulnerable populations with increased risk of developing COVID-19.

The cholesterol metabolite 27-hydroxycholesterol inhibits SARS-CoV-2 and is markedly decreased in COVID-19 patients

There is an urgent need to identify antivirals against the coronavirus SARS-CoV-2 in the current COVID-19 pandemic and to contain future similar emergencies early on. Specific side-chain cholesterol oxidation products of the oxysterols family have been shown to inhibit a large variety of both enveloped and non-enveloped human viral pathogens. Here we report on the in vitro inhibitory activity of the redox active oxysterol 27-hydroxycholesterol against SARS-CoV-2 and against one of the common cold agents HCoV-OC43 human coronavirus without significant cytotoxicity. Interestingly, physiological serum levels of 27-hydroxycholesterol in SARS-CoV-2 positive subjects were significantly decreased compared to the matched control group, reaching a marked 50% reduction in severe COVID-19 cases. Moreover, no correlation at all was observed between 24-hydroxycholesterol and 25-hydroxycholesterol serum levels and the severity of the disease. Opposite to that of 27-hydroxycholesterol was the behaviour of two recognized markers of redox imbalance, i.e. 7-ketocholesterol and 7β-hydroxycholesterol, whose serum levels were significantly increased especially in severe COVID-19. The exogenous administration of 27-hydroxycholesterol may represent in the near future a valid antiviral strategy in the worsening of diseases caused by present and emerging coronaviruses.

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27-hydroxycholesterol (27OHC) inhibits the replication of SARS-CoV-2 by interfering with its entry into target cells.

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The broad antiviral effect of 27OHC is also exerted against another β-coronavirus, HCoV-OC43.

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Blood levels of 27OHC were decreased in SARS-CoV-2 infected individuals, especially in patients with severe COVID-19.

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COVID-19 patients showed increased serum levels of 7-ketocholesterol and 7β-hydroxycholesterol, markers of oxidative stress.

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.

Biotin attenuation of oxidative stress, mitochondrial dysfunction, lipid metabolism alteration and 7β-hydroxycholesterol-induced cell death in 158N murine oligodendrocytes

Mitochondrial dysfunction and oxidative stress are involved in neurodegenerative diseases associated with an enhancement of lipid peroxidation products such as 7β-hydroxycholesterol (7β-OHC). It is, therefore, important to study the ability of 7β-OHC to trigger mitochondrial defects, oxidative stress, metabolic dysfunctions and cell death, which are hallmarks of neurodegeneration, and to identify cytoprotective molecules. The effects of biotin were evaluated on 158N murine oligodendrocytes, which are myelin synthesizing cells, exposed to 7β-OHC (50 µM) with or without biotin (10 and 100 nM) or α-tocopherol (positive control of cytoprotection). The effects of biotin on 7β-OHC activities were determined using different criteria: cell adhesion; plasma membrane integrity; redox status. The impact on mitochondria was characterized by the measurement of transmembrane mitochondrial potential (ΔΨm), reactive oxygen species (ROS) overproduction, mitochondrial mass, quantification of cardiolipins and organic acids. Sterols and fatty acids were also quantified. Cell death (apoptosis, autophagy) was characterized by the enumeration of apoptotic cells, caspase-3 activation, identification of autophagic vesicles, and activation of LC3-I into LC3-II. Biotin attenuates 7β-OHC-induced cytotoxicity: loss of cell adhesion was reduced; antioxidant activities were normalized. ROS overproduction, protein and lipid oxidation products were decreased. Biotin partially restores mitochondrial functions: attenuation of the loss of ΔΨm; reduced levels of mitochondrial O₂^•- overproduction; normalization of cardiolipins and organic acid levels. Biotin also normalizes cholesterol and fatty acid synthesis, and prevents apoptosis and autophagy (oxiapoptophagy). Our data support that biotin, which prevents oligodendrocytes damages, could be useful in the treatment of neurodegeneration and demyelination.

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

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

Enhanced endoplasmic reticulum and mitochondrial stress in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a degenerative vascular disease with a complex aetiology that remains to be fully elucidated. Clinical management of AAA is limited to surgical repair, while an effective pharmacotherapy is still awaited. Endoplasmic reticulum (ER) stress and mitochondrial dysfunction have been involved in the pathogenesis of cardiovascular diseases (CVDs), although their contribution to AAA development is uncertain. Therefore, we aimed to determine their implication in AAA and investigated the profile of oxysterols in plasma, specifically 7-ketocholesterol (7-KC), as an ER stress inducer.In the present study, we determined aortic ER stress activation in a large cohort of AAA patients compared with healthy donors. Higher gene expression of activating transcription factor (ATF) 6 (ATF6), IRE-1, X-binding protein 1 (XBP-1), C/EBP-homologous protein (CHOP), CRELD2 and suppressor/enhancer of Lin-12-like (SEL1L) and greater protein levels of active ATF6, active XBP1 and of the pro-apoptotic protein CHOP were detected in human aneurysmatic samples. This was accompanied by an exacerbated apoptosis, higher reactive oxygen species (ROS) production and by a reduction in mitochondrial biogenesis in the vascular wall of AAA. The quantification of oxysterols, performed by liquid chromatography-(atmospheric pressure chemical ionization (APCI))-mass spectrometry, showed that levels of 7-KC were significantly higher while those of 7α-hydroxycholesterol (HC), 24-HC and 27-HC were lower in AAA patients compared with healthy donors. Interestingly, the levels of 7-KC correlate with the expression of ER stress markers.Our results evidence an induction of ER stress in the vascular wall of AAA patients associated with an increase in circulating 7-KC levels and a reduction in mitochondrial biogenesis suggesting their implication in the pathophysiology of this disease.

Secosterol-B affects endoplasmic reticulum structure in endothelial cells

Oxysterols, oxidized derivatives of cholesterol found in LDL and atherosclerotic plaques, trigger several biological responses involved in the initiation and progression of atherosclerosis. Endothelial dysfunction, which occurs when vascular homeostasis is altered, plays a key role in the pathogenesis of several metabolic diseases. The contribution of endoplasmic reticulum (ER) stress to endothelial disfunction is a relatively recent area of investigation. There is a well-established link between LDL oxidation and ER stress but the role played by specific products of lipid oxidation into this interaction is still to be defined. The present study shows that secosterol-B (SEC-B), 3β-hydroxy-5β-hydroxy-B-norcholestane-6βcarboxaldehyde, a cholesterol autoxidation product recently identified in the atherosclerotic plaque, is able to induce ER stress in HUVEC cells, as revealed by significant expansion and change of structure. At low doses, i.e. 1 and 5 μM, cells try to cope with this stress by activating autophagy and the ubiquitin proteasome system in the attempt to restore ER function. However, at higher doses, i.e. 20 μM, cell apoptosis occurs in a pathway that involves early phosphorylation of eIF2α and NF-kB activation, suggesting that the adaptive program fails and the cell activates the apoptotic program. These findings provide additional insight about the role of oxysterols in endothelial dysfunction and its potential involvement in atherosclerotic pathophysiology.

Oxysterol species: reliable markers of oxidative stress in diabetes mellitus

PURPOSE

To assess the plasma oxysterol species 7-ketocholesterol (7-Kchol) and cholestane-3β,5α,6β-triol (chol-triol) as biomarkers of oxidative stress in type 1 and type 2 diabetes mellitus (DM).

METHODS

In total, 26 type 1 and 80 type 2 diabetes patients, along with 205 age- and gender-matched healthy controls, were included in this study. Oxysterols were quantified by liquid chromatography coupled with tandem mass spectrometry and N,N-dimethylglycine derivatization. Correlations between oxysterols and clinical/biochemical characteristics of the diabetes patients, and factors affecting 7-Kchol and chol-triol, were also determined.

RESULTS

Plasma 7-Kchol and chol-triol levels were significantly higher in type 1 and type 2 diabetes patients compared to healthy controls (P < 0.001). Significant positive correlations were observed between oxysterol levels and levels of glycated hemoglobin (HbA1c), glucose, serum total cholesterol, low-density lipoprotein, very-low-density lipoprotein, and triglycerides, as well as the number of coronary risk factors. Statins, oral hypoglycemic agents, and antihypertensive agents reduced the levels of oxysterols in type 2 diabetes patients. Statin use, HbA1c levels, and the number of coronary risk factors accounted for 98.8% of the changes in 7-Kchol levels, and total cholesterol, smoking status, and the number of coronary risk factors accounted for 77.3% of the changes in chol-triol levels in type 2 diabetes patients.

CONCLUSIONS

Plasma oxysterol levels in DM, and particularly type 2 DM, may yield complementary information regarding oxidative stress for the clinical follow-up of diabetes patients, especially those with coronary risk factors.

The Oxysterol 7-Ketocholesterol Reduces Zika Virus Titers in Vero Cells and Human Neurons

Zika virus (ZIKV) is an emerging flavivirus responsible for a major epidemic in the Americas beginning in 2015. ZIKV associated with maternal infection can lead to neurological disorders in newborns, including microcephaly. Although there is an abundance of research examining the neurotropism of ZIKV, we still do not completely understand the mechanism by which ZIKV targets neural cells or how to limit neural cell infection. Recent research suggests that flaviviruses, including ZIKV, may hijack the cellular autophagy pathway to benefit their replication. Therefore, we hypothesized that ZIKV replication would be impacted when infected cells were treated with compounds that target the autophagy pathway. We screened a library of 94 compounds known to affect autophagy in both mammalian and insect cell lines. A subset of compounds that inhibited ZIKV replication without affecting cellular viability were tested for their ability to limit ZIKV replication in human neurons. From this second screen, we identified one compound, 7-ketocholesterol (7-KC), which inhibited ZIKV replication in neurons without significantly affecting neuron viability. Interestingly, 7-KC induces autophagy, which would be hypothesized to increase ZIKV replication, yet it decreased virus production. Time-of-addition experiments suggest 7-KC inhibits ZIKV replication late in the replication cycle. While 7-KC did not inhibit RNA replication, it decreased the number of particles in the supernatant and the relative infectivity of the released particles, suggesting it interferes with particle budding, release from the host cell, and particle integrity.

The effects of vitamin E or lipoic acid supplementation on oxyphytosterols in subjects with elevated oxidative stress: a randomized trial

Despite increased serum plant sterol concentrations after consumption of plant sterol enriched margarines, plasma oxyphytosterol concentrations were not increased in healthy subjects. Here, we assessed plasma oxyphytosterol concentrations and whether they are affected by antioxidants in subjects with elevated oxidative stress. Twenty subjects with impaired glucose tolerance (IGT) or type 2 diabetes (DM2) consumed for 4 weeks placebo, vitamin E (804 mg/d) or lipoic acid capsules (600 mg/d). Plasma and blood cell oxyphytosterol and oxycholesterol concentrations were determined in butylated hydroxytoluene-enriched EDTA plasma via GC-MS. Also, markers reflecting oxidative stress and antioxidant capacity were measured. Plasma oxycampesterol and oxysitosterol concentrations were 122% and 83% higher in IGT or DM2 subjects than in healthy subjects, as determined in an earlier study. Vitamin E or lipoic acid supplementation did not reduce plasma oxyphytosterol and oxycholesterol concentrations, or other markers reflecting oxidative stress or antioxidative capacity. Concentrations of different oxyphytosterols correlated within plasma, and within red blood cells and platelets. However, plasma and blood cell oxyphytosterol levels did not correlate. Although plasma oxyphytosterol concentrations are higher in IGT or DM2 subjects than in healthy subjects, 4-weeks vitamin E or lipoic acid supplementation does not lower plasma oxycholesterol or oxyphytosterol concentrations.

Therapeutic Effects of PPARα Agonist on Ocular Neovascularization in Models Recapitulating Neovascular Age-Related Macular Degeneration

Purpose

This study was designed to evaluate effects of fenofibric acid (Feno-FA), a peroxisome proliferator–activated receptor-alpha (PPARα) agonist, on ocular neovascularization (NV) in models recapitulating neovascular age-related macular degeneration (AMD), and to explore whether the effects are PPARα dependent.

Methods

Laser-induced choroidal NV (CNV) in rats and very low-density lipoprotein receptor knockout (Vldlr^−/−) mice received daily intraperitoneal injections of Feno-FA or vehicle. Vascular leakage was examined by fundus fluorescein angiography and permeability assay using Evans blue as tracer. In CNV rats, severity of CNV was evaluated by CNV areas and CNV volume. In Vldlr^−/− mice, subretinal NV (SRNV) and intraretinal NV (IRNV) were quantified in choroid flat mount and retina flat mount, respectively. Inflammatory factors were measured using Western blotting and retinal leukostasis assay. Further, Pparα^−/− mice and age-matched wild-type (WT) mice were used for laser-induced CNV and treated with Feno-FA to explore the underlying mechanism.

Results

Feno-FA significantly reduced vascular leakage in CNV rats and Vldlr^−/− mice, reduced CNV volume in laser-induced CNV rats, and suppressed SRNV and IRNV in Vldlr^−/− mice. In addition, Feno-FA downregulated the expression of inflammatory factors, including VEGF, TNF-α, and intercellular cell adhesion molecule-1 (ICAM-1), in the eyecups of CNV rats and decreased adherent retinal leukocytes in Vldlr^−/− mice. Furthermore, Pparα^−/− mice developed more severe CNV compared with WT mice, and PPARα knockout abolished the beneficial effects of Feno-FA on CNV.

Conclusions

Feno-FA has therapeutic effects on ocular NV in models recapitulating neovascular AMD through a PPARα-dependent mechanism.

Dietary docosahexaenoic acid supplementation prevents the formation of cholesterol oxidation products in arteries from orchidectomized rats

Testosterone deficiency has been correlated with increased cardiovascular diseases, which in turn has been associated with increased oxidative stress. Several studies have considered cholesterol oxidation products (COPs) as oxidative stress biomarkers, since some of them play pro-oxidant and pro-inflammatory roles. We have previously described the cardioprotective effects of a dosahexaenoic acid (DHA) supplemented diet on the aortic and mesenteric artery function of orchidectomized rats. The aim of this study was to investigate whether impaired gonadal function alters the formation of COPs, as well as the potential preventive role of a DHA-supplemented diet on that effect. For this purpose, aortic and mesenteric artery segments obtained from control and orchidectomized rats, fed with a standard or supplemented with DHA, were used. The content of the following COPs: 7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, cholestanetriol and 25-hydroxycholesterol, were analyzed by gas chromatography. The results showed that orchidectomy increased the formation of COPs in arteries from orchidectomized rats, which may participate in the orchidectomy-induced structural and functional vascular alterations already reported. The fact that the DHA-supplemented diet prevented the orchidectomy-induced COPs increase confirms the cardiovascular protective actions of DHA, which could be of special relevance in mesenteric arterial bed, since it importantly controls the systemic vascular resistance.

Low-density lipoprotein oxidation biomarkers in human health and disease and effects of bioactive compounds

Based on the significance of oxidized low-density lipoprotein (LDL) in health and disease, this review focuses on human studies addressing oxidation of LDL, including three lines of biomarkers, (i) ex vivo LDL resistance to oxidation, a "challenge test" model, (ii) circulating oxidized LDL, indicating the "current in vivo status", and (iii) autoantibodies against oxidized LDL as fingerprints of an immune response to oxidized LDL, along with circulating oxysterols and 4-hydroxynonenal as biomarkers of lipid peroxidation. Lipid peroxidation and oxidized LDL are hallmarks in the development of various metabolic, cardiovascular and other diseases. Changes further occur across life stages from infancy to older age as well as in athletes and smokers. Given their responsiveness to targeted nutritional interventions, markers of LDL oxidation have been employed in a rapidly growing number of human studies for more than 2 decades. There is growing interest in foods, which, besides providing energy and nutrients, exert beneficial effects on human health, such as protection of DNA, proteins and lipids from oxidative damage. Any health claim, however, needs to be substantiated by supportive evidence derived from human studies, using reliable biomarkers to demonstrate such beneficial effects. A large body of evidence has accumulated, demonstrating protection of LDL from oxidation by bioactive food compounds, including vitamins, other micronutrients and secondary plant ingredients, which will facilitate the selection of oxidation biomarkers for future human intervention studies and health claim support.

7-ketocholesterol and 27-hydroxycholesterol decreased doxorubicin sensitivity in breast cancer cells: estrogenic activity and mTOR pathway

Hypercholesterolemia is one of the risk factors for poor outcome in breast cancer therapy. To elucidate the influence of the main circulating oxysterols, cholesterol oxidation products, on the cell-killing effect of doxorubicin, cells were exposed to oxysterols at a subtoxic concentration. When cells were exposed to oxysterols in fetal bovine serum-supplemented medium, 7-ketocholesterol (7-KC), but not 27-hydroxycholesterol (27-HC), decreased the cytotoxicity of doxorubicin in MCF-7 (high estrogen receptor (ER)α/ERβ ratio) cells and the decreased cytotoxicity was restored by the P-glycoprotein inhibitor verapamil. 7-KC stimulated the efflux function of P-glycoprotein and reduced intracellular doxorubicin accumulation in MCF-7 but not in ERα(-) MDA-MB-231 and the resistant MCF-7/ADR cells. In MCF-7 cells, 7-KC increased the mRNA and protein levels of P-glycoprotein. The 7-KC-suppressed doxorubicin accumulation was restored by the fluvestrant and ERα knockdown. In a yeast reporter assay, the ERα activation by 7-KC was more potent than 27-HC. 7-KC, but not 27-HC, stimulated the expression of an ER target, Trefoil factor 1 in MCF-7 cells. When charcoal-stripped fetal bovine serum was used, both 7-KC and 27-HC induced Trefoil factor 1 expression and reduced doxorubicin accumulation in MCF-7 cells. 7-KC-reduced doxorubicin accumulation could be reversed by inhibitors of phosphatidylinositol 3-kinase, Akt, and mammalian target of rapamycin (mTOR). These findings demonstrate that 7-KC decreases the cytotoxicity of doxorubicin through the up-regulation of P-glycoprotein in an ERα- and mTOR-dependent pathway. The 7-KC- and 27-HC-elicited estrogenic effects are crucial in the P-glycoprotein induction in breast cancer cells.

Effect of anti-hyperlipidemia drugs on the alpha-tocopherol concentration and their potential for murine malaria infection

The current preventions of malaria are protection against mosquito bites and taking chemoprophylactic anti-malarial drugs. However, drug therapies are usually associated with adverse events and emergency of drug-resistant malaria parasites. Previous study showed that host plasma alpha-tocopherol deficiency enhanced resistance against malaria infection in mice. Here, we report a new prevention strategy against malaria by using anti-hyperlipidemia drugs, ezetimibe, berberine, cholestyramine, and probucol to modify the host plasma alpha-tocopherol concentration. The drugs were mixed with diet and fed to C57BL/6J mice for 2 weeks. Although all drugs reduced plasma alpha-tocopherol concentration after 2 weeks of feeding, probucol-treated mice showed 90 % reduction and it was the lowest alpha-tocopherol concentration among the four drugs. Ezetimibe, berberine, and combination of ezetimibe and berberine pretreatment for 2 weeks were not effective against infection of Plasmodium yoelii XL17, a lethal strain, for survival and parasitemia in mice. Two-week pretreatment and 1-week treatment after infection of cholestyramine had also no effect on malaria infection. Survival rates of cholestyramine, ezetimibe, and/or berberine treated mice were 0-22 %. However, probucol caused significant decrease in parasitemia and increased in mice survival following 2-week pretreatment and 1-week treatment after infection. All control mice died while all probucol treated mice survived during the course of infection. Thus, probucol which reduced plasma alpha-tocopherol concentration was effective in enhancing the host to resist malaria infection in mice. Our finding indicates that plasma alpha-tocopherol reducing drugs like probucol might be a candidate for beneficial prevention strategy for travelers from malaria-free area.

Cholesterol metabolites exported from human brain

The human brain contains approximately 25% of the body's cholesterol. The brain is separated from the circulation by the blood brain barrier. While cholesterol will not passes this barrier, oxygenated forms of cholesterol can cross the barrier. Here by measuring the difference in the oxysterol content of blood plasma in the jugular vein and in a forearm vein by mass spectrometry (MS) we were able to determine the flux of more than 20 cholesterol metabolites between brain and the circulation. We confirm that 24S-hydroxycholesterol is exported from brain at a rate of about 2-3mg/24h. Gas chromatography (GC)-MS data shows that the cholesterol metabolites 5α-hydroxy-6-oxocholesterol (3β,5α-dihydroxycholestan-6-one), 7β-hydroxycholesterol and 7-oxocholesterol, generally considered to be formed through reactive oxygen species, are similarly exported from brain at rates of about 0.1, 2 and 2mg/24h, respectively. Although not to statistical significance both GC-MS and liquid chromatography (LC)-MS methods indicate that (25R)26-hydroxycholesterol is imported to brain, while LC-MS indicates that 7α-hydroxy-3-oxocholest-4-enoic acid is exported from brain.

Gas chromatography-mass spectrometry microanalysis of alpha- and gamma-tocopherol in plasma and whole blood

BACKGROUND

Assessing vitamin E status in humans is critical for nutritional evaluation and verification of clinical and biological compliance of supplemented subjects. An accurate analytical method for measuring the two main vitamin E isoforms, i.e. α- and γ-tocopherol (α- and γ-TOH) in small volumes of plasma can facilitate the application of this analysis to clinical trials and in situations where a limited amount of sample is available.

METHODS

We have developed a micro method, which uses only 5 μL plasma, based on isotope dilution, trimethylsilation and GC-MS. The method was validated according to the guidelines of the International Conference on Harmonization of analytical procedures. The method was also applied to 5 μL of whole blood for the potential use in conditions were the availability of specimens is limited.

RESULTS

Accurate quantitation of α-TOH and γ-TOH was achieved at levels ≥ 0.417 μM and ≥ 0.007 μM, respectively. Within-day coefficient of variation was 1.31% and 4.70% for α-TOH and γ-TOH, respectively. Between-day coefficient of variation was 1.32% and 2.88% for α-TOH and γ-TOH, respectively. Recovery, assessed at three concentration levels, ranged 98-103% and 100-102% for α-TOH and γ-TOH, respectively. The method allowed the detection of α-TOH and γ-TOH in 5 μL whole blood and in membranes of red blood cells washed from 5 μL of blood as well. The analytical performance was assessed in plasma from a cohort of Italian healthy subjects (n = 205). The mean plasma concentrations were 28.01 ± 6.31 and 0.68 ± 0.48 μM (mean ± SD) for α-TOH and γ-TOH, respectively. Alpha-TOH correlated with total cholesterol (r = 0.617, p < 0.0001) and triglycerides (r = 0.420, p < 0.0001) while γ-TOH correlated modestly with total cholesterol (r = 0.213, p < 0.0001) but not with triglycerides. γ-TOH, but not α-TOH, was significantly lower in smokers than in non-smokers (0.72 ± 0.50 vs. 0.56 ± 0.37, μM, mean ± SD, p = 0.017). Given the high sensitivity, the method allowed to be applied to 5 μM whole blood without specific modification.

CONCLUSIONS

This micro-method represents an analytical advancement in α- and γ-TOH assay that is available to accurately verify the nutritional status and compliance after supplementation in large-scale settings, and to measure the two vitamers in conditions where sample availability is limited.

Lipid-lowering efficacy of atorvastatin

BACKGROUND

This represents the first update of this review, which was published in 2012. Atorvastatin is one of the most widely prescribed drugs and the most widely prescribed statin in the world. It is therefore important to know the dose-related magnitude of effect of atorvastatin on blood lipids.

OBJECTIVES

Primary objective To quantify the effects of various doses of atorvastatin on serum total cholesterol, low-density lipoprotein (LDL)-cholesterol, high-density lipoprotein (HDL)-cholesterol and triglycerides in individuals with and without evidence of cardiovascular disease. The primary focus of this review was determination of the mean per cent change from baseline of LDL-cholesterol. Secondary objectives • To quantify the variability of effects of various doses of atorvastatin.• To quantify withdrawals due to adverse effects (WDAEs) in placebo-controlled randomised controlled trials (RCTs).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 11, 2013), MEDLINE (1966 to December Week 2 2013), EMBASE (1980 to December Week 2 2013), Web of Science (1899 to December Week 2 2013) and BIOSIS Previews (1969 to December Week 2 2013). We applied no language restrictions.

SELECTION CRITERIA

Randomised controlled and uncontrolled before-and-after trials evaluating the dose response of different fixed doses of atorvastatin on blood lipids over a duration of three to 12 weeks.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility criteria for studies to be included and extracted data. We collected information on withdrawals due to adverse effects from placebo-controlled trials.

MAIN RESULTS

In this update, we found an additional 42 trials and added them to the original 254 studies. The update consists of 296 trials that evaluated dose-related efficacy of atorvastatin in 38,817 participants. Included are 242 before-and-after trials and 54 placebo-controlled RCTs. Log dose-response data from both trial designs revealed linear dose-related effects on blood total cholesterol, LDL-cholesterol, HDL-cholesterol and triglycerides. The Summary of findings table 1 documents the effect of atorvastatin on LDL-cholesterol over the dose range of 10 to 80 mg/d, which is the range for which this systematic review acquired the greatest quantity of data. Over this range, blood LDL-cholesterol is decreased by 37.1% to 51.7% (Summary of findings table 1). The slope of dose-related effects on cholesterol and LDL-cholesterol was similar for atorvastatin and rosuvastatin, but rosuvastatin is about three-fold more potent. Subgroup analyses suggested that the atorvastatin effect was greater in females than in males and was greater in non-familial than in familial hypercholesterolaemia. Risk of bias for the outcome of withdrawals due to adverse effects (WDAEs) was high, but the mostly unclear risk of bias was judged unlikely to affect lipid measurements. Withdrawals due to adverse effects were not statistically significantly different between atorvastatin and placebo groups in these short-term trials (risk ratio 0.98, 95% confidence interval 0.68 to 1.40).

AUTHORS' CONCLUSIONS

This update resulted in no change to the main conclusions of the review but significantly increases the strength of the evidence. Studies show that atorvastatin decreases blood total cholesterol and LDL-cholesterol in a linear dose-related manner over the commonly prescribed dose range. New findings include that atorvastatin is more than three-fold less potent than rosuvastatin, and that the cholesterol-lowering effects of atorvastatin are greater in females than in males and greater in non-familial than in familial hypercholesterolaemia. This review update does not provide a good estimate of the incidence of harms associated with atorvastatin because included trials were of short duration and adverse effects were not reported in 37% of placebo-controlled trials.

Oxidative stress and its significant roles in neurodegenerative diseases and cancer

Reactive oxygen and nitrogen species have been implicated in diverse pathophysiological conditions, including inflammation, neurodegenerative diseases and cancer. Accumulating evidence indicates that oxidative damage to biomolecules including lipids, proteins and DNA, contributes to these diseases. Previous studies suggest roles of lipid peroxidation and oxysterols in the development of neurodegenerative diseases and inflammation-related cancer. Our recent studies identifying and characterizing carbonylated proteins reveal oxidative damage to heat shock proteins in neurodegenerative disease models and inflammation-related cancer, suggesting dysfunction in their antioxidative properties. In neurodegenerative diseases, DNA damage may not only play a role in the induction of apoptosis, but also may inhibit cellular division via telomere shortening. Immunohistochemical analyses showed co-localization of oxidative/nitrative DNA lesions and stemness markers in the cells of inflammation-related cancers. Here, we review oxidative stress and its significant roles in neurodegenerative diseases and cancer.

Neural HO-1/sterol interactions in vivo: implications for Alzheimer's disease

BACKGROUND

Up-regulation of heme oxygenase-1 (HO-1) and altered cholesterol (CH) metabolism are characteristic of Alzheimer-diseased (AD) neural tissues. We previously provided evidence of significant HO-1/sterol interactions in vitro (cultured rat astroglia) and in post-mortem human AD brain (Religious Orders Study).

METHODS

The current experiments were designed to further delineate these interactions in vivo by comparing the behavior of HO-1/sterol interactions in two mouse models; (1) a novel HO-1 transgenic mouse (GFAP.HMOX1) engineered to selectively express human HO-1 in the astrocytic compartment and (2) the previously described triple transgenic AD mouse (3xTg-AD). In samples of frontal cortex, total CH, CH precursors and relevant oxysterols were quantified by gas chromatography-mass spectrometry (GC-MS) and HO-1 protein expression was assessed by ELISA. The relationships of HO-1 expression to total CH, CH precursors and total oxysterols were determined for both mouse models using linear regression analysis.

RESULTS

HO-1 expression is increased in GFAP.HMOX1 mice relative to wild type and in 11-12-month-old 3xTg-AD mice (with AD-like phenotype) relative to control mice and 5-6-month-old 3xTg-AD mice (no AD-like phenotype). Total oxysterols significantly decreased as HO-1 expression increased in GFAP.HMOX1 mice expressing high levels of HO-1, whereas total oxysterols increased as HO-1 expression increased in aged 3xTg-AD mice. Total CH and total CH precursors increased as HO-1 protein expression increased in 11-12-month-old 3xTg-AD mice relative to 5-6-month old 3xTg-AD mice.

CONCLUSIONS

Our findings indicate a differential impact of HO-1 on patterns of brain sterol and redox homeostasis that is contingent on the presence or absence of AD-like neuropathology. These data provide fresh insight concerning the regulation of sterol homeostasis within the aging and degenerating CNS which may inform the development of novel therapeutic and preventive strategies for the management of AD and related conditions.

Mechanism of action of anti-hypercholesterolemia drugs and their resistance

Coronary artery disease is one of the leading causes of death worldwide. One of the significant causes of this disease is hypercholesterolemia which is the result of various genetic alterations that are associated with the accumulation of specific classes of lipoprotein particles in plasma. A number of drugs are used to treat hypercholesterolemia like statin, fibrate, bile acid sequestrants, niacin, ezetimibe, omega-3 fatty acids and natural extracts. It has been observed that these drugs show diverse response in different individuals. The present review explains the mechanism of action of these drugs as well as mechanism of its lesser effectiveness or resistance in some individuals. There are various identified genetic variations that are associated with diversity in the drugs response. Therefore, present study helps to understand the ethiology of drug mechanism and resistance developed against drugs used to treat hypercholesterolemia.

Liver X receptor up-regulates α-tocopherol transfer protein expression and α-tocopherol status

Fat-soluble vitamin E (α-tocopherol) has antioxidant activity. α-Tocopherol transfer protein (α-TTP), a hepatic cytosolic protein, selectively binds α-tocopherol and has an important role regulating circulatory α-tocopherol levels. However, only a few studies have shown the transcriptional regulation of the α-TTP gene. Here, we demonstrate that liver X receptor (LXR) regulates α-TTP expression through direct interaction with the α-TTP gene promoter, and it modulates circulating α-tocopherol levels. LXR belongs to the nuclear receptor superfamily, acts as a ligand-dependent transcription factor for oxysterols and plays an important role in cholesterol metabolism and lipogenesis. We identified an LXR response element (LXRE; DR4, a direct repeat with four-nucleotides spacing) of the human α-TTP gene promoter by using luciferase and electrophoretic mobility shift assays. Mutations in this element abolished activation of this promoter. Moreover, treatment of vitamin E-deficient rats with T0901317, a synthetic LXR ligand, increased α-TTP expression in the liver and cerebrum and increased the plasma α-tocopherol levels. These results indicate that the LXR signaling pathway modulates α-TTP gene expression and plasma α-tocopherol levels. Our observations imply that the LXR signaling pathway might be a useful target for antioxidant properties by controlling the vitamin E status.

Statins more than cholesterol lowering agents in Alzheimer disease: their pleiotropic functions as potential therapeutic targets

Alzheimer disease (AD) is a progressive neurodegenerative disorder characterized by severe cognitive impairment, inability to perform activities of daily living and mood changes. Statins, long known to be beneficial in conditions where dyslipidemia occurs by lowering serum cholesterol levels, also have been proposed for use in neurodegenerative conditions, including AD. However, it is not clear that the purported effectiveness of statins in neurodegenerative disorders is directly related to cholesterol-lowering effects of these agents; rather, the pleiotropic functions of statins likely play critical roles. The aim of this review is to provide an overview on the new discoveries about the effects of statin therapy on the oxidative and nitrosative stress levels as well as on the modulation of the heme oxygenase/biliverdin reductase (HO/BVR) system in the brain. We propose a novel mechanism of action for atorvastatin which, through the activation of HO/BVR-A system, may contribute to the neuroprotective effects thus suggesting a potential therapeutic role in AD and potentially accounting for the observation of decreased AD incidence with persons on statin.

7-Ketocholesterol induces P-glycoprotein through PI3K/mTOR signaling in hepatoma cells

7-Ketocholesterol (7-KC) is found at an elevated level in patients with cancer and chronic liver disease. The up-regulation of an efflux pump, P-glycoprotein (P-gp) leads to drug resistance. To elucidate the effect of 7-KC on P-gp, P-gp function and expression were investigated in hepatoma cell lines Huh-7 and HepG2 and in primary hepatocyte-derived HuS-E/2 cells. At a subtoxic concentration, 48-h exposure to 7-KC reduced the intracellular accumulation and cytotoxicity of P-gp substrate doxorubicin in hepatoma cells, but not in HuS-E/2 cells. In Huh-7 cells, 7-KC elevated efflux function through the activation of phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway. 7-KC activated the downstream protein synthesis initiation factor 4E-BP1 and induced P-gp expression post-transcriptionally. The stimulation of efflux was reversible and could not be prevented by N-acetyl cysteine. Total cellular ATP content remained the same, whereas the lactate production was increased and fluorescence lifetime of protein-bound NADH was shortened. These changes suggested a metabolic shift to glycolysis, but glycolytic inhibitors did not eliminate 7-KC-mediated P-gp induction. These results demonstrate that 7-KC induces P-gp through PI3K/mTOR signaling and decreased the cell-killing efficacy of doxorubicin in hepatoma cells.

Lipid lowering efficacy of atorvastatin

BACKGROUND

Atorvastatin is one of the most widely prescribed drugs and the most widely prescribed statin in the world. It is therefore important to know the dose-related magnitude of effect of atorvastatin on blood lipids.

OBJECTIVES

To quantify the dose-related effects of atorvastatin on blood lipids and withdrawals due to adverse effects (WDAE).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library Issue 4, 2011, MEDLINE (1966 to November 2011), EMBASE (1980 to November 2011), ISI Web of Science (1899 to November 2011) and BIOSIS Previews (1969 to November 2011). No language restrictions were applied.

SELECTION CRITERIA

Randomised controlled and uncontrolled before-and-after trials evaluating the dose response of different fixed doses of atorvastatin on blood lipids over a duration of 3 to 12 weeks.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. WDAE information was collected from the placebo-controlled trials.

MAIN RESULTS

Two hundred fifty-four trials evaluated the dose-related efficacy of atorvastatin in 33,505 participants. Log dose-response data revealed linear dose-related effects on blood total cholesterol, low-density lipoprotein (LDL)-cholesterol and triglycerides. Combining all the trials using the generic inverse variance fixed-effect model for doses of 10 to 80 mg/day resulted in decreases of 36% to 53% for LDL-cholesterol. There was no significant dose-related effects of atorvastatin on blood high-density lipoprotein (HDL)-cholesterol. WDAE were not statistically different between atorvastatin and placebo for these short-term trials (risk ratio 0.99; 95% confidence interval 0.68 to 1.45).

AUTHORS' CONCLUSIONS

Blood total cholesterol, LDL-cholesterol and triglyceride lowering effect of atorvastatin was dependent on dose. Log dose-response data was linear over the commonly prescribed dose range. Manufacturer-recommended atorvastatin doses of 10 to 80 mg/day resulted in 36% to 53% decreases of LDL-cholesterol. The review did not provide a good estimate of the incidence of harms associated with atorvastatin because of the short duration of the trials and the lack of reporting of adverse effects in 37% of the placebo-controlled trials.

Potentiation of amyloid-β peptide neurotoxicity in human dental-pulp neuron-like cells by the membrane lipid peroxidation product 4-hydroxynonenal

Lipid peroxidation is generally considered as primarily implicated in the pathogenesis of Alzheimer's disease (AD); one of its more reactive end products, 4-hydroxynonenal (HNE), has been shown to cause neuron dysfunction and degeneration. HNE production in the brain is stimulated by the amyloid-β peptide (Aβ), whose excessive accumulation in specific brain areas is a hallmark of AD. Conversely, Aβ production is up-regulated by this multifunctional aldehyde. Findings reported here point to the ability of HNE and Aβ to interact, with consequent potentiation of Aβ's cytotoxicity as determined in vitro using neuron-like cells derived from human dental-pulp progenitor cells. Preincubation of cells with the aldehyde markedly up-regulated Aβ uptake and intracellular accumulation, by overexpressing two of the three components of the plasma membrane multireceptor complex CD36/CD47/β1-integrin: experimental and clinical data indicate that intraneuronal accumulation of Aβ is an early event possibly playing a primary role in AD pathogenesis. That HNE-mediated overexpression of CD36 and β1-integrin, which plays a key role in HNE's potentiating Aβ neurotoxicity, in terms of necrosis, was confirmed when this effect was prevented by specific antibodies against the two receptors.

The link between altered cholesterol metabolism and Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by the progressive loss of neurons and synapses, and by extracellular deposits of amyloid-β (Aβ) as senile plaques, Aβ deposits in the cerebral blood vessels, and intracellular inclusions of hyperphosphorylated tau in the form of neurofibrillary tangles. Several mechanisms contribute to AD development and progression, and increasing epidemiological and molecular evidence suggests a key role of cholesterol in its initiation and progression. Altered cholesterol metabolism and hypercholesterolemia appear to play fundamental roles in amyloid plaque formation and tau hyperphosphorylation. Over the last decade, growing evidence supports the idea that cholesterol oxidation products, known as oxysterols, may be the missing link between altered brain cholesterol metabolism and AD pathogenesis, as their involvement in neurotoxicity, mainly by interacting with Aβ peptides, is reported.

OSBP-related proteins (ORPs) in human adipose depots and cultured adipocytes: evidence for impacts on the adipocyte phenotype

Oxysterol-binding protein (OSBP) homologues, ORPs, are implicated in lipid homeostatic control, vesicle transport, and cell signaling. We analyzed here the quantity of ORP mRNAs in human subcutaneous (s.c.) and visceral adipose depots, as well as in the Simpson-Golabi-Behmel syndrome (SGBS) adipocyte cell model. All of the ORP mRNAs were present in the s.c and visceral adipose tissues, and the two depots shared an almost identical ORP mRNA expression pattern. SGBS adipocytes displayed a similar pattern, suggesting that the adipose tissue ORP expression pattern mainly derives from adipocytes. During SGBS cell adipogenic differentiation, ORP2, ORP3, ORP4, ORP7, and ORP8 mRNAs were down-regulated, while ORP11 was induced. To assess the impacts of ORPs on adipocyte differentiation, ORP3 and ORP8, proteins down-regulated during adipogenesis, were overexpressed in differentiating SGBS adipocytes, while ORP11, a protein induced during adipogenesis, was silenced. ORP8 overexpression resulted in reduced expression of the aP2 mRNA, while down-regulation of adiponectin and aP2 was observed in ORP11 silenced cells. Furthermore, ORP8 overexpression or silencing of ORP11 markedly decreased cellular triglyceride storage. These data identify the patterns of ORP expression in human adipose depots and SGBS adipocytes, and provide the first evidence for a functional impact of ORPs on the adipocyte phenotype.

PPAR-alpha Ligands as Potential Therapeutic Agents for Wet Age-Related Macular Degeneration

The peroxisome proliferator-activated receptors (PPAR's) are members of the steroid/thyroid nuclear receptor, superfamily of transcription factors. There are currently three known PPAR subtypes, α, β, and γ. The PPARs are now recognized participants in a number of biological pathways some of which are implicated in the pathogenesis of age-related macular degeneration (AMD). These include immune modulation, lipid regulation, and oxidant/antioxidant pathways important to the onset and progression of “dry” AMD, and vascular endothelial growth factor (VEGF) mediated pathways that stimulate choroidal neovascularization (CNV), characteristic of “wet” AMD. PPAR-α is found in retina and also on vascular cells important to formation of CNV. At this time, however, relatively little is known about potential contributions of PPAR-α to the pathogenesis of dry and wet AMD. This review examines current literature for potential roles of PPAR-α in the pathogenesis and potential treatment of AMD with emphasis on prevention and treatment of wet AMD.

Pathways of cholesterol oxidation via non-enzymatic mechanisms

Cholesterol has many functions, including those that affect biophysical properties of membranes, and is a precursor to hormone synthesis. These actions are governed by enzymatic pathways that modify the sterol nucleus or the isooctyl tail. The addition of oxygen to the cholesterol backbone produces its derivatives known as oxysterols. In addition to having an enzymatic origin, oxysterols can be formed in the absence of enzymatic catalysis in a pathway usually termed "autoxidation," which has been known for almost a century and observed under various experimental conditions. Autoxidation of cholesterol can occur through reactions initiated by free radical species, such as those arising from the superoxide/hydrogen peroxide/hydroxyl radical system and by non-radical highly reactive oxygen species such as singlet oxygen, HOCl, and ozone. The susceptibility of cholesterol to non-enzymatic oxidation has raised considerable interest in the function of oxysterols as biological effectors and potential biomarkers for the non-invasive study of oxidative stress in vivo.

α-Tocopherol impairs 7-ketocholesterol-induced caspase-3-dependent apoptosis involving GSK-3 activation and Mcl-1 degradation on 158N murine oligodendrocytes

In important and severe neurodegenerative pathologies, 7-ketocholesterol, mainly resulting from cholesterol autoxidation, may contribute to dys- or demyelination processes. On various cell types, 7-ketocholesterol has often been shown to induce a complex mode of cell death by apoptosis associated with phospholipidosis. On 158N murine oligodendrocytes treated with 7-ketocholesterol (20 μg/mL corresponding to 50 μM, 24-48 h), the induction of a mode of cell death by apoptosis characterised by the occurrence of cells with condensed and/or fragmented nuclei, caspase activation (including caspase-3) and internucleosomal DNA fragmentation was observed. It was associated with a loss of transmembrane mitochondrial potential (ΔΨm) measured with JC-1, with a dephosphorylation of Akt and GSK3 (especially GSK3β), and with degradation of Mcl-1. With α-tocopherol (400 μM), which was capable of counteracting 7-ketocholesterol-induced apoptosis, Akt and GSK3β dephosphorylation were inhibited as well as Mcl-1 degradation. These data underline that the potential protective effects of α-tocopherol against 7-ketocholesterol-induced apoptosis do not depend on the cell line considered, and that the cascade of events (Akt/GSK3β/Mcl-1) constitutes a link between 7-ketocholesterol-induced cytoplasmic membrane dysfunctions and mitochondrial depolarisation leading to apoptosis.

Cholesterol-independent neuroprotective and neurotoxic activities of statins: perspectives for statin use in Alzheimer disease and other age-related neurodegenerative disorders

Statins, long known to be beneficial in conditions where dyslipidemia occurs by lowering serum cholesterol levels, also have been proposed for use in neurodegenerative conditions, including Alzheimer disease. However, it is not clear that the purported effectiveness of statins in neurodegenerative disorders is directly related to cholesterol-lowering effects of these agents; rather, the pleiotropic functions of statins likely play critical roles. Moreover, it is becoming more apparent with additional studies that statins can have deleterious effects in preclinical studies and lack effectiveness in various recent clinical trials. This perspective paper outlines pros and cons of the use of statins in neurodegenerative disorders, with particular emphasis on Alzheimer disease.

Long-term high-dose atorvastatin decreases brain oxidative and nitrosative stress in a preclinical model of Alzheimer disease: a novel mechanism of action

Alzheimer disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory loss, inability to perform the activities of daily living and personality changes. Unfortunately, drugs effective for this disease are limited to acetylcholinesterase inhibitors that do not impact disease pathogenesis. Statins, which belong to the class of cholesterol-reducing drugs, were proposed as novel agents useful in AD therapy, but the mechanism underlying their neuroprotective effect is still unknown. In this study, we show that atorvastatin may have antioxidant effects, in aged beagles, that represent a natural higher mammalian model of AD. Atorvastatin (80 mg/day for 14.5 months) significantly reduced lipoperoxidation, protein oxidation and nitration, and increased GSH levels in parietal cortex of aged beagles. This effect was specific for brain because it was not paralleled by a concomitant reduction in all these parameters in serum. In addition, atorvastatin slightly reduced the formation of cholesterol oxidation products in cortex but increased the 7-ketocholesterol/total cholesterol ratio in serum. We also found that increased oxidative damage in the parietal cortex was associated with poorer learning (visual discrimination task). Thus, a novel pharmacological effect of atorvastatin mediated by reducing oxidative damage may be one mechanism underlying benefits of this drug in AD.

Advances in methods for the determination of biologically relevant lipid peroxidation products

Lipid peroxidation is recognized to be an important contributor to many chronic diseases, especially those of an inflammatory pathology. In addition to their value as markers of oxidative damage, lipid peroxidation products have also been shown to have a wide variety of biological and cell signalling effects. In view of this, accurate and sensitive methods for the measurement of lipid peroxidation products are essential. Although some assays have been described for many years, improvements in protocols are continually being reported and, with recent advances in instrumentation and technology, highly specialized and informative techniques are increasingly used. This article gives an overview of the most currently used methods and then addresses the recent advances in some specific approaches. The focus is on analysis of oxysterols, F(2)-isoprostanes and oxidized phospholipids by gas chromatography or liquid chromatography mass spectrometry techniques and immunoassays for the detection of 4-hydroxynonenal.

Oxysterols: A world to explore

Oxysterols (oxidized derivatives of cholesterol and phytosterols) can be generated in the human organism through different oxidation processes, some requiring enzymes. Furthermore, oxysterols are also present in food due to lipid oxidation reactions caused by heating treatments, contact with oxygen, exposure to sunlight, etc., and they could be absorbed from the diet, at different rates depending on their side chain length. In the organism, oxysterols can follow different routes: secreted into the intestinal lumen, esterified and distributed by lipoproteins to different tissues or degraded, mainly in the liver. Cholesterol oxidation products (COPs) have shown cytotoxicity, apoptotic and pro-inflammatory effects and they have also been linked with chronic diseases including atherosclerotic and neurodegenerative processess. In the case of phytosterol oxidation products (POPs), more research is needed on toxic effects. Nevertheless, current knowledge suggests they may also cause cytotoxic and pro-apoptotic effects, although at higher concentrations than COPs. Recently, new beneficial biological activities of oxysterols are being investigated. Whereas COPs are associated with cholesterol homeostasis mediated by different mechanisms, the implication of POPs is not clear yet. Available literature on sources of oxysterols in the organism, metabolism, toxicity and potential beneficial effects of these compounds are reviewed in this paper.

Ligand regulation of retinoic acid receptor-related orphan receptors: implications for development of novel therapeutics

PURPOSE OF REVIEW

In the late 1980s, the cloning of several nuclear receptors led to the intense search and isolation of new members of this superfamily. Despite their identification, many of these receptors were dubbed 'orphan' receptors, as their physiological ligands remained unknown. Recent reports have presented evidence for one family of orphan receptors, the retinoic acid receptor-related orphan receptors (RORs), in several pathologies, including osteoporosis, several autoimmune diseases, asthma, cancer, diabetes and obesity. The present review summarizes the studies identifying ligands for the RORs and evaluates their role as targets for potential therapeutics.

RECENT FINDINGS

Significant progress was made in the initial identification of ligands for the RORs when X-ray crystallographic studies identified several molecules within the ligand-binding pockets of RORalpha and RORbeta. Recently, we identified endogenous and synthetic ligands for RORalpha and RORgamma, thereby solidifying their function as ligand-dependent transcription factors.

SUMMARY

Recent studies have established roles for the RORs in physiological development and the advent of disease. Identification of ligands for the RORs, both endogenous and synthetic, has established these receptors as attractive new therapeutic targets for the treatment of ROR-related diseases.

Modulation of retinoic acid receptor-related orphan receptor alpha and gamma activity by 7-oxygenated sterol ligands

The retinoic acid receptor-related orphan receptors alpha and gamma (RORalpha (NR1F1) and RORgamma (NR1F3)) are orphan nuclear receptors and perform critical roles in regulation of development, metabolism, and immune function. Cholesterol and cholesterol sulfate have been suggested to be RORalpha ligands, but the physiological significance is unclear. To date, no endogenous RORgamma ligands have been described. Here, we demonstrate that 7-oxygenated sterols function as high affinity ligands for both RORalpha and RORgamma by directly binding to their ligand-binding domains (K(i) approximately 20 nM), modulating coactivator binding, and suppressing the transcriptional activity of the receptors. One of the 7-oxygenated sterols, 7alpha-hydroxycholesterol (7alpha-OHC), serves as a key intermediate in bile acid metabolism, and we show that 7alpha-OHC modulates the expression of ROR target genes, including Glc-6-Pase and phosphoenolpyruvate carboxykinase, in an ROR-dependent manner. Furthermore, glucose output from hepatocytes is suppressed by 7alpha-OHC functioning as an RORalpha/gamma ligand. Thus, RORalpha and RORgamma are ligand-regulated members of the NR superfamily and may serve as sensors for 7-oxygenated sterols.

7-ketocholesterol and 5,6-secosterol modulate differently the stress-activated mitogen-activated protein kinases (MAPKs) in liver cells

Enhanced oxidative stress is a common feature of liver diseases and contributes to chronic liver disease (CLD) progression by inducing fibrogenesis during liver regeneration. Peroxidation products of cholesterol metabolism, named oxysterols, are new and reliable markers of oxidative stress in vivo. Patients affected by CLDs present high plasma levels of oxysterols, raising the question of the origin and biological relevance of these compounds in the pathophysiology of chronic liver damage. The aim of this study was to examine the molecular basis of the biological effects of oxysterols on liver-derived cells, HepG2 and Huh7. Cells were treated with different concentrations (10(-9) to 10(-5) M) of 7-ketocholesterol used as a reference, and 5,6-secosterol, a recently discovered oxysterol. FACS investigations, caspase-3 activation, and Sytox Green immunofluorescent assay showed that pathological concentrations of oxysterols induced necrosis (30-50%) after 48 h of treatment. The two analyzed compounds displayed a similar, but not identical, behavior. In fact, 5,6-secosterol, but not 7-ketocholesterol, induced cell senescence. Notably, low concentrations of 5,6-secosterol caused a sustained activation of ERK1/2, inducing cell proliferation, this unexpected behavior should be better characterized by further studies. Since enhanced oxidative stress is known to worsen liver chronic hepatitis and frequently results in overall decreased cellular survival, our data suggest the important and different role oxysterols may have in interfering with physiological liver tissue regeneration in injured human liver. Antioxidant treatment may provide a highly specific and effective mean to counteract the common consequences of oxidative stress on chronic hepatitis, such as fibrosis/cirrhosis and liver failure.

Do statins cause myopathy by lowering vitamin E levels?

Statins and other lipid lowering drugs have been repeatedly described to decrease blood levels of minor fat soluble components such as vitamin E (as alpha-tocopherol). Clinical consequences of this secondary state of deficiency have not been described so far, but recent biochemical and molecular evidence on homeostatic and molecular responses to vitamin E deficiency in skeletal muscle cells may suggest the hypothesis presented in this paper of a role as risk factor in the development of statin-associated myopathy. This hypothesis that needs to be further investigated, could suggest the need for precautionary measures during lipid lowering therapy, which include timely diagnosis and active prevention of vitamin E deficiency.

Association of cholesterol oxidation and abnormalities in fatty acid metabolism in cystic fibrosis

BACKGROUND

Disarrangement in fatty acids and oxidative stress are features of cystic fibrosis. Cholesterol is very sensitive to oxidative stress.

OBJECTIVES

The objectives were to examine whether cholesterol oxidation products are altered in cystic fibrosis and whether they are associated with fatty acids and with characteristics of the disease state.

DESIGN

7-Ketocholesterol and 7beta-hydroxycholesterol (prototype molecules of free radical-mediated cholesterol oxidation) and the fatty acid profile were assessed by mass spectrometry in patients and in sex- and age-matched control subjects.

RESULTS

In a comparison with control subjects, mean (+/-SD) cholesterol oxidation was higher (7-ketocholesterol: 11.31 +/- 5.1 compared with 8.33 +/- 5.5 ng/mL, P = 0.03; 7beta-hydroxycholesterol: 14.5 +/- 6.8 compared with 9.7 +/- 4.1 ng/mL, P = 0.004), total saturated fatty acids were higher (31.90 +/- 1.93% compared with 30.31 +/- 0.98%, P < 0.001), monounsaturated fatty acids were higher (29.14 +/- 3.85% compared with 25.88 +/- 2.94%, P = 0.004), omega-6 (n-6) polyunsaturated fatty acids were lower (34.84 +/- 4.77 compared with 39.68 +/- 2.98%, P < 0.0001), and omega-3 (n-3) polyunsaturated fatty acids were comparable in patients with cystic fibrosis. Oxysterols were inversely associated with 24:0 and 18:2 omega-6 fatty acids but did not correlate with the increased oleic acid or with any of the omega-3 fatty acids.

CONCLUSIONS

Cystic fibrosis is characterized by relevant cholesterol oxidation that is associated with an abnormal fatty acid profile. The interplay between oxysterols and fatty acids potentially provides insight into the biological mechanisms that underlie this complex disease.