Cholesterol-3-beta, 5-alpha, 6-beta-triol induced genotoxicity through reactive oxygen species formation

Cholestane-3β,5α,6β-triol Induces Multiple Cell Death in A549 Cells via ER Stress and Autophagy Activation

Cholestane-3β,5α,6β-triol (CT) and its analogues are abundant in natural sources and are reported to demonstrate cytotoxicity toward different kinds of tumor cells without a deep probe into their mechanism of action. CT is also one of the major metabolic oxysterols of cholesterol in mammals and is found to accumulate in various diseases. An extensive exploration of the biological roles of CT over the past few decades has established its identity as an apoptosis inducer. In this study, the effects of CT on A549 cell death were investigated through cell viability assays. RNA-sequencing analysis and western blot of CT-treated A549 cells revealed the role of CT in inducing endoplasmic reticulum (ER) stress response and enhancing autophagy flux, suggesting a putative mechanism of CT-induced cell-death activation involving reactive oxygen species (ROS)-mediated ER stress and autophagy. It is reported for the first time that the upregulation of autophagy induced by CT can serve as a cellular cytotoxicity response in accelerating CT-induced cell death in A549 cells. This research provides evidence for the effect of CT as an oxysterol in cell response to oxidative damage and allows for a deep understanding of cholesterol in its response in an oxidative stress environment that commonly occurs in the progression of various diseases.

The Cholesterol-5,6-Epoxide Hydrolase: A Metabolic Checkpoint in Several Diseases

Cholesterol-5,6-epoxides (5,6-ECs) are oxysterols (OS) that have been linked to several pathologies including cancers and neurodegenerative diseases. 5,6-ECs can be produced from cholesterol by several mechanisms including reactive oxygen species, lipoperoxidation, and cytochrome P450 enzymes. 5,6-ECs exist as two different diastereoisomers: 5,6α-EC and 5,6β-EC with different metabolic fates. They can be produced as a mixture or as single products of epoxidation. The epoxide ring of 5,6α-EC and 5,6β-EC is very stable and 5,6-ECs are prone to hydration by the cholesterol-5,6-epoxide hydrolase (ChEH) to give cholestane-3β,5α,6β-triol, which can be further oxidized into oncosterone. 5,6α-EC is prone to chemical and enzymatic conjugation reactions leading to bioactive compounds such as dendrogenins, highlighting the existence of a new metabolic branch on the cholesterol pathway centered on 5,6α-EC. We will summarize in this chapter current knowledge on this pathway which is controlled by the ChEH.

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.

Chemical synthesis and biochemical properties of cholestane-5α,6β-diol-3-sulfonate: A non-hydrolysable analogue of cholestane-5α,6β-diol-3β-sulfate

Cholestane-3β,5α,6β-triol (CT) is a primary metabolite of 5,6-epoxycholesterols (5,6-EC) that is catalyzed by the cholesterol-5,6-epoxide hydrolase (ChEH). CT is a well-known biomarker for Niemann-Pick disease type C (NP-C), a progressive inherited neurodegenerative disease. On the other hand, CT is known to be metabolized by the 11β-hydroxysteroid-dehydrogenase of type 2 (11β-HSD2) into a tumor promoter named oncosterone that stimulates the growth of breast cancer tumors. Sulfation is a major metabolic transformation leading to the production of sulfated oxysterols. The production of cholestane-5α,6β-diol-3β-O-sulfate (CDS) has been reported in breast cancer cells. However, no data related to CDS biological properties have been reported so far. These studies have been hampered because sulfate esters of sterols and steroids are rapidly hydrolyzed by steroid sulfatase to give free steroids and sterols. In order to get insight into the biological properties of CDS, we report herein the synthesis and the characterization of cholestane-5α,6β-diol-3β-sulfonate (CDSN), a non-hydrolysable analogue of CDS. We show that CDSN is a potent inhibitor of 11β-HSD2 that blocks oncosterone production on cell lysate. The inhibition of oncosterone biosynthesis of a whole cell assay was observed but results from the blockage by CDSN of the uptake of CT in MCF-7 cells. While CDSN inhibits MCF-7 cell proliferation, we found that it potentiates the cytotoxic activity of post-lanosterol cholesterol biosynthesis inhibitors such as tamoxifen and PBPE. This effect was associated with an increase of free sterols accumulation and the appearance of giant multilamellar bodies, a structural feature reminiscent of Type C Niemann-Pick disease cells and consistent with a possible inhibition by CDSN of NPC1. Altogether, our data showed that CDSN is biologically active and that it is a valuable tool to study the biological properties of CDS and more specifically its impact on immunity and viral infection.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Impact of Oxysterols on Cell Death, Proliferation, and Differentiation Induction: Current Status

Oxysterols are oxidized derivatives of cholesterol produced by enzymatic activity or non-enzymatic pathways (auto-oxidation). The oxidation processes lead to the synthesis of about 60 different oxysterols. Several oxysterols have physiological, pathophysiological, and pharmacological activities. The effects of oxysterols on cell death processes, especially apoptosis, autophagy, necrosis, and oxiapoptophagy, as well as their action on cell proliferation, are reviewed here. These effects, also observed in several cancer cell lines, could potentially be useful in cancer treatment. The effects of oxysterols on cell differentiation are also described. Among them, the properties of stimulating the osteogenic differentiation of mesenchymal stem cells while inhibiting adipogenic differentiation may be useful in regenerative medicine.

Orthogonal targeting of osteoclasts and myeloma cells for radionuclide stimulated dynamic therapy induces multidimensional cell death pathways

Rationale: Multiple myeloma (MM) is a multifocal malignancy of bone marrow plasma cells, characterized by vicious cycles of remission and relapse that eventually culminate in death. The disease remains mostly incurable largely due to the complex interactions between the bone microenvironment (BME) and MM cells (MMC). In the “vicious cycle” of bone disease, abnormal activation of osteoclasts (OCs) by MMC causes severe osteolysis, promotes immune evasion, and stimulates the growth of MMC. Disrupting these cancer-stroma interactions would enhance treatment response.

Methods: To disrupt this cycle, we orthogonally targeted nanomicelles (NM) loaded with non-therapeutic doses of a photosensitizer, titanocene (TC), to VLA-4 (α4ß1, CD49d/CD29) expressing MMC (MM1.S) and αvß3 (CD51/CD61) expressing OC. Concurrently, a non-lethal dose of a radiopharmaceutical, ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG) administered systemically interacted with TC (radionuclide stimulated therapy, RaST) to generate cytotoxic reactive oxygen species (ROS). The in vitro and in vivo effects of RaST were characterized in MM1.S cell line, as well as in xenograft and isograft MM animal models.

Results: Our data revealed that RaST induced non-enzymatic hydroperoxidation of cellular lipids culminating in mitochondrial dysfunction, DNA fragmentation, and caspase-dependent apoptosis of MMC using VLA-4 avid TC-NMs. RaST upregulated the expression of BAX, Bcl-2, and p53, highlighting the induction of apoptosis via the BAK-independent pathway. The enhancement of multicopper oxidase enzyme F5 expression, which inhibits lipid hydroperoxidation and Fenton reaction, was not sufficient to overcome RaST-induced increase in the accumulation of irreversible function-perturbing α,ß-aldehydes that exerted significant and long-lasting damage to both DNA and proteins. In vivo, either VLA-4-TC-NM or αvß3-TC-NMs RaST induced a significant therapeutic effect on immunocompromised but not immunocompetent MM-bearing mouse models. Combined treatment with both VLA-4-TC-NM and αvß3-TC-NMs synergistically inhibited osteolysis, reduced tumor burden, and prevented rapid relapse in both in vivo models of MM.

Conclusions: By targeting MM and bone cells simultaneously, combination RaST suppressed MM disease progression through a multi-prong action on the vicious cycle of bone cancer. Instead of using the standard multidrug approach, our work reveals a unique photophysical treatment paradigm that uses nontoxic doses of a single light-sensitive drug directed orthogonally to cancer and bone cells, followed by radionuclide-stimulated generation of ROS to inhibit tumor progression and minimize osteolysis in both immunocompetent murine and immunocompromised human MM models.

Impact of cholesterol-pathways on breast cancer development, a metabolic landscape

ApoB-lipoproteins and their components modulate intracellular metabolism and have been associated with the development of neoplastic phenomena, such as proliferation, anchorage-independent growth, epithelial-mesenchymal transition, and cancer invasion. In cancer cells, the modulation of targets that regulate cholesterol metabolism, such as synthesis de novo, endocytosis, and oxidation, are contributing factors to cancer development. While mechanisms associated with sterol regulatory element-binding protein 2 (SREBP-2)/mevalonate, the low-density lipoprotein receptor (LDL-R) and liver X receptor (LXR) have been linked with tumor growth; metabolites derived from cholesterol-oxidation, such as oxysterols and epoxy-cholesterols, also have been described as tumor processes-inducers. From this notion, we perform an analysis of the role of lipoproteins, their association with intracellular cholesterol metabolism, and the impact of these conditions on breast cancer development, mechanisms that can be shared during atherogenesis promoted mainly by LDL. Pathways connecting plasma dyslipidemias in conjunction with the effect of cholesterol-derived metabolites on intracellular mechanisms and cellular plasticity phenomena could provide new approaches to elucidate the triggering factors of carcinogenesis, conditions that could be considered in the development of new therapeutic approaches.

Mutagenicity of 7-ketocholesterol in CHO cells: The role of lipid peroxidation

As an important cholesterol oxide, 7-ketocholesterol plays a deleterious role in the occurrence of cancer. Although the fact had been proved that 7-ketocholesterol could induce several biological phenomena, including apoptosis, DNA damage, et al., this issue whether 7-ketocholesterol led to mutagenesis in mammalian cells remains largely unexplored. Here, we investigated the major role of lipid peroxidation in the genotoxic response to 7-ketocholesterol in chinese hamster ovary (CHO) cells. The results showed that 7-ketocholesterol induced gene mutation and DNA double-strand breaks (DSBs) in concentration- and time-dependent manner. After CHO cells were treated with 25 μM 7-ketocholesterol for 48 h, the mutation frequency at hprt gene loci and the level of γ-H2AX protein were both significantly increased. Exposure to 7-ketocholesterol resulted in a concentration-dependent increase in the apoptotic rate and the protein expression of cleaved caspase-3 and -7 in CHO cells. Moreover, a significant increase of superoxide dismutase (SOD) activity and content of malondialdehyde (MDA) was also observed. Using a inhibitor of lipid peroxidation (butylated hydroxytoluene), it was found to remarkably inhibit the genotoxicity and MDA levels caused by 7-ketocholesterol. These findings indicated that lipid peroxidation was involved in the mutagenic process of 7-ketocholesterol in CHO cells.

The 5,6-epoxycholesterol metabolic pathway in breast cancer: Emergence of new pharmacological targets

Metabolic pathways have emerged as cornerstones in carcinogenic deregulation providing new therapeutic strategies for cancer management. Recently, a new branch of cholesterol metabolism has been discovered involving the biochemical transformation of 5,6-epoxycholesterols (5,6-ECs). The 5,6-ECs are metabolized in breast cancers to the tumour promoter oncosterone whereas, in normal breast tissue, they are metabolized to the tumour suppressor metabolite, dendrogenin A (DDA). Blocking the mitogenic and invasive potential of oncosterone will present new opportunities for breast cancer treatment. The reactivation of DDA biosynthesis, or its use as a drug, represents promising therapeutic approaches such as DDA-deficiency complementation, activation of breast cancer cell re-differentiation and breast cancer chemoprevention. This review presents current knowledge of the 5,6-EC metabolic pathway in breast cancer, focusing on the 5,6-EC metabolic enzymes ChEH and HSD11B2 and on 5,6-EC metabolite targets, the oxysterol receptor (LXRβ) and the glucocorticoid receptor. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Effects of Chitosan on Clostridium perfringens and Application in the Preservation of Pork Sausage

The effects of chitosan with 95% deacetylation degree (DD95) on the spore germination, cell proliferation, and heat resistance of Clostridium perfringens CCRC 10,648 and CCRC 13,019 were investigated, and its application on pork sausage with sodium nitrite reduction was also evaluated. DD95 chitosan can strongly reduce the heat resistance of both strains. The D₈₀ and D₁₀₀ values for strain CCRC 13,019 decreased from 40.98 and 4.64 min to 39.21 and 3.26 min, respectively, as a result of adding 250 ppm DD95; meanwhile, addition of chitosan decreased the D₈₀ and D₁₀₀ values for CCRC 10,648 from 41.15 and 6.46 min to 39.52 and 3.78 min, respectively. In pork sausage, addition of 3000 ppm DD95 chitosan considerably slowed down the bacterial proliferation and volatile basic nitrogen production. There were no significant differences in color (L* and b* values), shearing force, and hardness in the pork sausages with or without DD95 chitosan during storage at 4 and 25 °C. However, the addition of DD95 chitosan in pork sausage significantly retarded the decrease of the a* value. Therefore, DD95 chitosan could reduce the concentration of sodium nitrite required in pork sausages for color retention.

Role of oxysterol-binding protein-related proteins in malignant human tumours

The oxysterol-binding protein-related protein (ORP) family is a group of proteins that mediate oxysterol metabolism and bioactivity in cells. ORPs constitute a large family of lipid transfer proteins. Much of the current evidence indicates that certain members of the family of oxysterol-binding proteins (OSBPs) can lead to cancer. Many studies have revealed the putative roles of OSBPs in various cancer types. However, the exact effects and mechanisms of action of members of the OSBP/ORP family in cancer initiation and progression are currently unclear. This review focuses on ORP family members that can accelerate human tumour cell proliferation, migration, and invasion. The mechanisms and functions of various ORPs are introduced in detail. We also attempt to identify the roles of these proteins in malignant tumours with the ultimate aim of determining the exact role of the OSBP/ORP family in human tumour cells.

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.

Genotoxicity of lipid oxidation compounds

Lipid peroxidation, the oxidative degradation of membrane lipids by reactive oxygen species generates a large variety of breakdown products such as alkanes, aldehydes, ketones, alcohols, furans and others. Due to their reactivity aldehydes (alkanals, 2-alkenals, 2,4-alkadienals, 4-hydroxyalkenals) received a lot of attention, in particular because they can diffuse from the site of formation and interact with proteins and nucleic acids thus acting as second toxic messengers. The major aldehydic peroxidation product of membrane lipids is 4-hydroxynonenal (HNE). Since HNE and other 4-hydroxyalkenals are strong alkylating agents they have therefore been considered to be the biologically most important peroxidation products. Although initially research focused on the toxicological potential of these compounds it is now well known that they play also a crucial role in cell signaling under physiological and pathophysiological conditions. Thus, it is obvious that the biological effects will be determined by the intracellular concentrations which can trigger adaptation, DNA damage and cell death. This review will not cover all these aspects but will concentrate on the genotoxic properties of selected lipid oxidation products important in the context of pathophysiological developments together with a chapter on epigenetic modifications.

Metal ions accelerated phytosterol thermal degradation on Ring A & Ring B of steroid nucleus in oils

This study aimed to investigate the effect of metal ions on the degradation of phytosterols in oils. The oil was heated at 180°C for 1h with/without addition of Fe³⁺, Fe²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Na⁺, Al³⁺ and Mg²⁺. Variations of β-sitosterol, stigmasterol, campesterol, brassicasterol and their degradation products were confirmed by the GC-MS analysis. In general, the increase of the metal ion concentration resulted in more phytosterol degradation, and the ability of metal ions following decreasing order: Fe³⁺>Fe²⁺>Mn²⁺≥Cu²⁺≥Zn²⁺>Na⁺≥Mg²⁺>Al³⁺. Metal ions significantly induced phytosterol autoxidation on C5, C6 and C7 on Ring B of steroid nucleus at even a low concentration, and induced dehydration on the C3 hydroxyl to form dienes and trienes at high concentration. The metal ions in oils are accounted for increasing phytosterol degradation, which decreases food nutritional quality and gives rise to the formation of undesirable compounds.

The Role of Oxysterols in Human Cancer

Oxysterols are oxygenated derivatives of cholesterol formed in the human body or ingested in the diet. By modulating the activity of many proteins [e.g., liver X receptors (LXRs), oxysterol-binding proteins (OSBPs), some ATP-binding cassette (ABC) transporters], oxysterols can affect many cellular functions and influence various physiological processes (e.g., cholesterol metabolism, membrane fluidity regulation, intracellular signaling pathways). Therefore, the role of oxysterols is also important in pathological conditions (e.g., atherosclerosis, diabetes mellitus type 2, neurodegenerative disorders). Finally, current evidence suggests that oxysterols play a role in malignancies such as breast, prostate, colon, and bile duct cancer. This review summarizes the physiological importance of oxysterols in the human body with a special emphasis on their roles in various tumors.

Oxysterols in adipose tissue-derived mesenchymal stem cell proliferation and death

Mesenchymal stem cells (MSCs) are multipotent cells characterized by self-renewal and cellular differentiation capabilities. Oxysterols comprise a very heterogeneous group derived from cholesterol through enzymatic and non-enzymatic oxidation. Potent effects in cell death processes, including cytoxicity and apoptosis induction, were described in several cell lines. Very little is known about the effects of oxysterols in MSCs. 7-ketocholesterol (7-KC), one of the most important oxysterols, was shown to be cytotoxic to human adipose tissue-derived MSCs. Here, we describe the short-term (24h) cytotoxic effects of cholestan-3α-5β-6α-triol, 3,5 cholestan-7-one, (3α-5β-6α)- cholestane-3,6-diol, 7-oxocholest-5-en-3β-yl acetate, and 5β-6β epoxy-cholesterol, on MSCs derived from human adipose tissue. MSCs were isolated from adipose tissue obtained from three young, healthy women. Oxysterols, with the exception of 3,5 cholestan-7-one and 7-oxocholest-5-en-3β-yl acetate, led to a complex mode of cell death that include apoptosis, necrosis and autophagy, depending on the type of oxysterol and concentration, being cholestan-3α-5β-6α-triol the most effective. Inhibition of proliferation was also promoted by these oxysterols, but no changes in cell cycle were observed.

Effect of Transition Metal Ions on the B Ring Oxidation of Sterols and their Kinetics in Oil-in-Water Emulsions

This study investigated the effect of metal ions on the oxidation of sterols and their kinetics in oil-in-water emulsions. Sterol substrates were added with different metal ions (Cu(2+), Fe(2+), Mn(2+), Zn(2+), Na(+), and Mg(2+)) of five concentrations and investigated after 2 h of heating at 90 °C. The substrates added with Fe(2+) and Cu(2+) were heated continuously to evaluate the kinetics of four sterols and their corresponding sterol oxidation products (SOPs). Sterol oxidation increased as the metal ion concentration increased and the heating time was prolonged. The capability of the metal ions oxidizing sterols ranked as followed: Fe(2+) > Cu(2+) > Mn(2+) > Zn(2+) > Mg(2+) ≈ Na(+). 7-Ketosterol, 7β/7α-Hydroxysterol, 5β,6β/5α,6α-Epoxysterol, and Triols were the main oxides on the B ring, whereas 6β-Hydroxysterol was not or only slightly influenced. The acceleration of sterol degradation induced by Fe(2+) and Cu(2+), as well as the formation of oxidation products, followed first-order formation/elimination kinetics. The acceleration effect may be partly ascribed to the increase in elimination rate constant and formation rate constant. Transition metal ions can significantly induce sterol oxidation, which reduces food nutritional quality and triggers the formation of undesirable compounds, such as SOPs.

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.

Development and validation of a gas chromatography-mass spectrometry method for determination of sterol oxidation products in edible oils

An efficient GC-MS method for determination of sterol oxidation product profiles in edible oils was established by combination with optimized silylation, and validated using the standards of sitosterol oxidation products.

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.

One step synthesis of 6-oxo-cholestan-3β,5α-diol

Cholesterol metabolism has been recently linked to cancer, highlighting the importance of the characterization of new metabolic pathways in the sterol series. One of these pathways is centered on cholesterol-5,6-epoxides (5,6-ECs). 5,6-ECs can either generate dendrogenin A, a tumor suppressor present in healthy mammalian tissues, or the carcinogenic cholestane-3β,5α,6β-triol (CT) and its putative metabolite 6-oxo-cholestan-3β,5α-diol (OCDO) in tumor cells. We are currently investigating the identification of the enzyme involved in OCDO biosynthesis, which would be highly facilitated by the use of commercially unavailable [(14)C]-cholestane-3β,5α,6β-triol and [(14)C]-6-oxo-cholestan-3β,5α-diol. In the present study we report the one-step synthesis of [(14)C]-cholestane-3β,5α,6β-triol and [(14)C]-6-oxo-cholestan-3β,5α-diol by oxidation of [(14)C]-cholesterol with iodide metaperiodate (HIO4).

Short-term effects of 7-ketocholesterol on human adipose tissue mesenchymal stem cells in vitro

Oxysterols comprise a very heterogeneous group derived from cholesterol through enzymatic and non-enzymatic oxidation. Among them, 7-ketocholesterol (7-KC) is one of the most important. It has potent effects in cell death processes, including cytoxicity and apoptosis induction. Mesenchymal stem cells (MSCs) are multipotent cells characterized by self-renewal and cellular differentiation capabilities. Very little is known about the effects of oxysterols in MSCs. Here, we describe the short-term cytotoxic effect of 7-ketocholesterol on MSCs derived from human adipose tissue. MSCs were isolated from adipose tissue obtained from two young, healthy women. After 24 h incubation with 7-KC, mitochondrial hyperpolarization was observed, followed by a slight increase in the level of apoptosis and changes in actin organization. Finally, the IC50 of 7-KC was higher in these cells than has been observed or described in other normal or cancer cell lines.

Liver fluke-induced hepatic oxysterols stimulate DNA damage and apoptosis in cultured human cholangiocytes

Oxysterols are cholesterol oxidation products that are generated by enzymatic reactions through cytochrome P450 family enzymes or by non-enzymatic reactions involving reactive oxygen and nitrogen species. Oxysterols have been identified in bile in the setting of chronic inflammation, suggesting that biliary epithelial cells are chronically exposed to these compounds in certain clinical settings. We hypothesized that biliary oxysterols resulting from liver fluke infection participate in cholangiocarcinogenesis. Using gas chromatography/mass spectrometry, we identified oxysterols in livers from hamsters infected with Opisthorchis viverrini that develop cholangiocarcinoma. Five oxysterols were found: 7-keto-cholesta-3,5-diene (7KD), 3-keto-cholest-4-ene (3K4), 3-keto-cholest-7-ene (3K7), 3-keto-cholesta-4,6-diene (3KD), and cholestan-3β,5α,6β-triol (Triol). Triol and 3K4 were found at significantly higher levels in the livers of hamsters with O. viverrini-induced cholangiocarcinoma. We therefore investigated the effects of Triol and 3K4 on induction of cholangiocarcinogenesis using an in vitro human cholangiocyte culture model. Triol- and 3K4-treated cells underwent apoptosis. Western blot analysis showed significantly increased levels of Bax and decreased levels of Bcl-2 in these cells. Increased cytochrome c release from mitochondria was found following treatment with Triol and 3K4. Triol and 3K4 also induced formation of the DNA adducts 1,N(6)-etheno-2'-deoxyadenosine, 3,N(4)-etheno-2'-deoxycytidine and 8-oxo-7,8-dihydro-2'-deoxyguanosine in cholangiocytes. The data suggest that Triol and 3K4 cause DNA damage via oxidative stress. Chronic liver fluke infection increases production of the oxysterols Triol and 3K4 in the setting of chronic inflammation in the biliary system. These oxysterols induce apoptosis and DNA damage in cholangiocytes. Insufficient and impaired DNA repair of such mutated cells may enhance clonal expansion and further drive the change in cellular phenotype from normal to malignant.

Mechanisms of oxysterol-induced carcinogenesis

Oxysterols are oxidation products of cholesterol that are generated by enzymatic reactions mediated by cytochrome P450 family enzymes or by non-enzymatic reactions involving reactive oxygen and nitrogen species. Oxysterols play various regulatory roles in normal cellular processes such as cholesterol homeostasis by acting as intermediates in cholesterol catabolism. Pathological effects of oxysterols have also been described, and various reports have implicated oxysterols in several disease states, including atherosclerosis, neurological disease, and cancer. Numerous studies show that oxysterols are associated with various types of cancer, including cancers of the colon, lung, skin, breast and bile ducts. The molecular mechanisms whereby oxysterols contribute to the initiation and progression of cancer are an area of active investigation. This review focuses on the current state of knowledge regarding the role of oxysterols in carcinogenesis. Mutagenicity of oxysterols has been described in both nuclear and mitochondrial DNA. Certain oxysterols such as cholesterol-epoxide and cholestanetriol have been shown to be mutagenic and genotoxic. Oxysterols possess pro-oxidative and pro-inflammatory properties that can contribute to carcinogenesis. Oxysterols can induce the production of inflammatory cytokines such as interleukin-8 and interleukin-1β. Certain oxysterols are also involved in the induction of cyclo-oxygenase-2 expression. Inflammatory effects can also be mediated through the activation of liver-X-receptor, a nuclear receptor for oxysterols. Thus, several distinct molecular mechanisms have been described showing that oxysterols contribute to the initiation and progression of cancers arising in various organ systems.

Identification and pharmacological characterization of cholesterol-5,6-epoxide hydrolase as a target for tamoxifen and AEBS ligands

The microsomal antiestrogen binding site (AEBS) is a high-affinity target for the antitumor drug tamoxifen and its cognate ligands that mediate breast cancer cell differentiation and apoptosis. The AEBS, a hetero-oligomeric complex composed of 3beta-hydroxysterol-Delta8-Delta7-isomerase (D8D7I) and 3beta-hydroxysterol-Delta7-reductase (DHCR7), binds different structural classes of ligands, including ring B oxysterols. These oxysterols are inhibitors of cholesterol-5,6-epoxide hydrolase (ChEH), a microsomal epoxide hydrolase that has yet to be molecularly identified. We hypothesized that the AEBS and ChEH might be related entities. We show that the substrates of ChEH, cholestan-5alpha,6alpha-epoxy-3beta-ol (alpha-CE) and cholestan-5beta,6beta-epoxy-3beta-ol (beta-CE), and its product, cholestane-3beta,5alpha,6beta-triol (CT), are competitive ligands of tamoxifen binding to the AEBS. Conversely, we show that each AEBS ligand is an inhibitor of ChEH activity, and that there is a positive correlation between these ligands' affinity for the AEBS and their potency to inhibit ChEH (r2=0.95; n=39; P<0.0001). The single expression of D8D7I or DHCR7 in COS-7 cells slightly increased ChEH activity (1.8- and 2.6-fold), whereas their coexpression fully reconstituted ChEH, suggesting that the formation of a dimer is required for ChEH activity. Similarly, the single knockdown of D8D7I or DHCR7 using siRNA partially inhibited ChEH in MCF-7 cells, whereas the knockdown of both D8D7I and DHCR7 abolished ChEH activity by 92%. Taken together, our findings strongly suggest that the AEBS carries out ChEH activity and establish that ChEH is a new target for drugs of clinical interest, polyunsaturated fatty acids and ring B oxysterols.

Cholesterol oxidation in the retina: implications of 7KCh formation in chronic inflammation and age-related macular degeneration

This review will discuss the formation and potential implications of 7-ketocholesterol (7KCh) in the retina. 7KCh is a proinflammatory oxysterol known to be present in high amounts in oxidized LDL deposits associated with atheromatous plaques. 7KCh is generated in situ in these lipoprotein deposits where it can accumulate and reach very high concentrations. In normal primate retina, 7KCh has been found associated with lipoprotein deposits in the choriocapillaris, Bruch's membrane, and the retinal pigment epithelium (RPE). In photodamaged rats, 7KCh has been found in the neural retina in areas of high mitochondrial content, ganglion cells, photoreceptor inner segments and synapses, and the RPE. Intermediates found by LCMS indicate 7KCh is formed via a free radical-mediated mechanism catalyzed by iron. 7KCh seems to activate several kinase signaling pathways that work via nuclear factor κB and cause the induction of vascular endothelial growth factor, interleukin (IL)-6, and IL-8. There seems to be little evidence of 7KCh metabolism in the retina, although some form of efflux mechanism may be active. The chronic mode of formation and the potent inflammatory properties of 7KCh indicate it may be an "age-related" risk factor in aging diseases such as atherosclerosis, Alzheimer's, and age-related macular degeneration.

No evidence of genotoxic effect in vivo of the phytosterol oxidation products triols and epoxides

Phytosterols (PS) are naturally occurring compounds present in food products of plant origin. Due to reported positive health effects, some food products are also enriched with PS. In the same way as cholesterol is oxidised, PS also oxidise to a variety of oxidation products (POPs). The biological effects and safety aspects of POPs are still unclear. This study investigated whether POPs are genotoxic in vivo, using a flow cytometer-based micronucleus assay in mice. The highest dose of oxidation products administered was 67mg/kg b.w. for epoxides and 9.4mg/kg b.w. for triols. Synthesised and separated triols and epoxides from a mixture of sitosterol and campesterol were investigated. The frequency of micronucleated polychromatic erythrocytes (fMNPCE) in POP-exposed mice did not significantly differ from the control values in either of two experiments performed. The flow cytometer-based method also allows for restriction of the analysis to micronuclei with a high DNA content, indicating an aneugenic potency. Even with this approach, there was no significant increase in the frequency of micronucleated erythrocytes among POP-treated mice compared with control mice. Furthermore, no significant deviation in cell proliferation rate (%PCE) was observed.

Lipoproteins and protection of the arterial wall against infection: the "response to the threat of infection" hypothesis

The exact reason why lipoproteins are found in the arterial intima is not understood. On the basis of recent findings presented in the literature, we are proposing a hypothesis that the accumulation of lipoprotein in the arterial intima is originally a physiological process, part of our defences against infection designed to protect susceptible segments of the arterial wall from microbial invasion. In addition to the intrinsic antimicrobial activities of the deposited lipids, the formation of fibrin-based matrices within the intima is promoted, fibrinolysis is inhibited, the lipid content exerts a vasoconstrictive influence and smooth muscle cells are mobilised into the intima, all these phenomenons being instrumental in fighting off an infectious menace. Oxidized lipids (including oxysterols and lysophosphatidylcholine) resulting from the oxidation of lipoproteins close to sites of infection and inflammation are disseminated through the circulatory system and act as alarm signals at arterial walls, promoting the penetration and retention of lipoproteins in the intimal tissue of the most susceptible segments of the arterial network. Oxidized lipids in the intima constitute part of first-line antimicrobial defences and their presence acts as a signal to immune effector cells (notably macrophages and lymphocytes) which trigger the acquired immune response when foreign antigens are encountered.

Cellular toxicity of oxycholesterols

Oxycholesterols (OS) are formed from cholesterol or its immediate precursors by enzymatic or free radical action in vivo, or they may be derived from food. OS exhibit a wide spectrum of biological activities. In OS cytotoxicity, several mechanisms seem to be involved: e.g. inhibition of HMG-CoA reductase activity, antiproliferative action, apoptosis induction, replacement of cholesterol by OS in membranes followed by changes in cellular membrane structure and functionality, and immune system functions alteration. Furthermore, OS may be mutagenic and carcinogenic and may serve as intracellular signaling or regulatory molecules. Here we review OS cellular activities with special attention to the cytotoxic action in vivo and in vitro using experimental models.