Mutagenic cholesterol preparations

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.

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.

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.

10 Final Report on the Safety Assessment of Cholesterol

Cholesterol is used as an emulsifier in cosmetic skin and hair care products and eye and face makeup formulations at concentrations up to 5%.

The normal metabolism and excretion of Cholesterol is well documented in man and experimental animals. Cholesterol is not a significant dermal or ocular irritant. Cholesterol does not appear to have any genotoxic activity in bacterial or mammalian cell in vitro mutagenic and transformation assays. High doses of Cholesterol were teratogenic in rats. Cholesterol has not been established as a promoter, cocarcinogen, or total carcinogen.

Clinical studies to evaluate the safety of topically applied Cholesterol were restricted to products formulated with the ingredient. Most products were moisturizers containing 1.4% Cholesterol. The highest concentration of Cholesterol tested (6%) was evaluated in a modified prophetic test (110 subjects) and an RIPT (45 subjects); both assays had UVA and UVB exposure incorporated into the protocols. The Cholesterol-containing products were minimal to mild primary and cumulative skin irritants but not sensitizers or photosensitizers.

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.

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.

The effect of oxysterols, individually and as a representative mixture from food, on in vitro cultured bovine ovarian granulosa cells

The cytotoxicity of five oxysterols identified in cooked fish, 7-ketocholesterol, 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one, was investigated in primary cultures of bovine ovarian granulosa cells. Cells were exposed to the oxysterols individually and to a mixture of the same oxysterols for 24 h. Cell viability as determined by trypan blue exclusion and mitochondrial integrity (3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) reduction) was reduced by 0.5 and 2.5 microM 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one, but not by 0.5 or 2.5 microM 7-ketocholesterol under the same culture conditions. A mixture of 7-ketocholesterol, 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one 0.5 microM each; 2.5 microM oxysterol in total) did not change cell viability relative to controls. Lipid peroxidation, as determined by thiobarbituric acid reactive substances assay, was unaffected by a 24-hour exposure of granulosa cells to individual oxysterols but was increased slightly by the oxysterol mixture. The specific activities of antioxidant enzymes superoxide dismutase and catalase were increased to different extents (1.17- to 6.43-fold), relative to controls, by the administration of individual oxysterols and the oxysterol mixture. These results indicate that while some individual oxysterols can induce cytotoxic effects and defensive responses in bovine ovarian granulosa cells, administration of the same oxysterols as a mixture does not elicit the same responses. In addition, the oxysterols tested exerted a pro-apoptotic effect on granulosa cells when administered individually at concentrations of 0.5 and 2.5 microM, but not when administered as a 2.5 microM oxysterol mixture. The results suggest that major oxysterols are not universally cytotoxic, they may complete with other oxysterols for receptor sites, and that the simultaneous presence of several different oxysterol species may reduce the adverse effects of individual oxysterols.

Red Star Ruby (Sunrise) and blond qualities of Jaffa grapefruits and their influence on plasma lipid levels and plasma antioxidant activity in rats fed with cholesterol-containing and cholesterol-free diets

Bioactive compounds of peels and peeled red Star Ruby (Sunrise) and blond qualities of Jaffa grapefruits were analyzed and their antioxidant potential was assessed. The dietary fibers were determined according to Prosky et al., the total polyphenol content by Folin-Ciocalteu method and measured at 765 nm, minerals and trace elements by atomic absorption spectrometer, phenolic and ascorbic acids by HPLC and the antioxidant potential by two different antioxidant assays (DPPH and beta-carotene linoleate model system). It was found that the contents of most studied bioactive compounds in both qualities are comparable. Only the contents of total polyphenols and flavonoids were higher in red grapefruits, but not significant. The antioxidant potentials of red peeled grapefruits and their peels were significantly higher than of blond peeled grapefruits and their peels (P<0.05 in both cases). Diets supplemented with peeled red and blond qualities of Jaffa grapefruits and their peels have increased the plasma antioxidant capacity and improved plasma lipid levels, especially in rats fed with cholesterol added diet. In conclusion, both qualities of Jaffa grapefruits contain high quantities of bioactive compounds, but the antioxidant potential of red grapefruits is significantly higher. Diets supplemented with both qualities of Jaffa grapefruits improve the plasma lipid levels and increase the plasma antioxidant activity, especially in rats fed with cholesterol added diets. Jaffa grapefruits, especially their red Star Ruby quality, could be a valuable supplementation for diseases-preventing diets.

Oat (Avena sativa L.) and amaranth (Amaranthus hypochondriacus) meals positively affect plasma lipid profile in rats fed cholesterol-containing diets

Cereals are an important part of diets for hypercholesterolemic patients. However, some of these patients are allergic to these natural products. The purpose of the current study was to compare oatmeal with equal in nutritional values two allergy-free amaranth meals to determine whether this pseudocereal can be a substitute for allergic to cereals individuals. The total phenols of the samples were determined with the Folin-Chocalteu reagent, anthocyanins, and flavonoids spectrophotometrically. The antioxidant activities were estimated with nitric oxide scavenging radical (NO) and by beta-carotene bleaching (beta-carotene). It was found that the contents of different protein fractions, antioxidant compounds, and the antioxidant activities of oatmeal were significantly higher than those of the two amaranth samples. The results of kinetic reactions showed that samples differed in their capacities to quench these radicals, and oats have shown more antioxidant activity than amaranth. High correlation was observed between antioxidant activities and phenols (R(2) = 0.99). In the in vivo part of the investigation, 60 male Wistar rats were divided into five diet groups of 12 animals each; these groups were designated as Control, Chol, Chol/Oat, Chol/AmarI, and Chol/AmarII. The rats of the Control group were fed basal diet (BD) only. To the BD of the four other groups were added the following: 1% of cholesterol (Chol), 10% of oat meal and 1% of cholesterol (Chol/Oat), 10% of amaranth I meal, and 1% of cholesterol (Chol/AmarI) and 10% of amaranth II meal and 1% of cholesterol (Chol/AmarII). After 32 days of different feeding, diets supplemented with oat meal and, to lesser degree, with amaranth I and amaranth II hindered the rise in the plasma lipids: a) TC: 3.14 vs. 4.57 mmol/L, - 31.3%; 3.31 vs. 4.57 mmol/L - 27.6%; and 3.40 vs. 4.57, - 25.6%, respectively b) LDL-C: 1.69 vs. 3.31 mmol/L, - 49.9%; 2.05 vs. 3.31 mmol/L, - 38.1%; and 2.16 vs. 3.31 mmol/L, - 34.8%, respectively; c) TG: 0.73 vs. 0.88 mmol/L, - 17.1%; 0.75 vs. 0.88 mmol/L, - 14.8%; and 0.79 vs. 0.88 mmol/L, -10.2%, respectively. The HDL-PH was increased as follows: 0.79 vs. 0.63 mmol/L, -25.3%; 0.75 vs. 0.63 mmol/L, -23.0%; and 0.71 vs. 0.63 mmol/L, -12.7% for the Chol/Oat, Chol/AmarI and Chol/AmarII, respectively. No significant changes in the concentrations of HDL-C and TPH were found; however the HDL-C in the Chol/Oat group was slightly higher than in other groups. No changes in the Control group were registered. In conclusion, oat and amaranth meals positively affect plasma lipid profile in rats fed cholesterol-containing diets. The degree of this positive influence is directly connected to the contents of the bioactive components and the antioxidant activities of the studied samples. It is suggested that amaranth could be a valuable substitute for hypercholesterolemic patients allergic to cereals.

The influence of beer with different antioxidant potential on plasma lipids, plasma antioxidant capacity, and bile excretion of rats fed cholesterol-containing and cholesterol-free diets

The aim of this investigation was to assess the influence of beers with different antioxidant potentials on plasma lipid metabolism, plasma antioxidant capacity, and bile excretion of rats fed cholesterol-containing and cholesterol-free diets. Four types of beers were investigated in vitro. Two of them (designated as BeerHigh and BeerLow) with the highest and lowest antioxidant potentials (34.5% and 21.4% and 2.07 mmol/L and 1.65 mmol/L according to beta-carotene assay and Trolox equivalent antioxidant coefficient, respectively), were chosen for the experiment on rats. A total of 60 male Wistar rats were divided into 6 dietary groups of 10 rats each; the groups were designated as Control, BeerA, BeerB, Chol, Chol/BeerA, and Chol/BeerB. The rats in the Control group were fed a basal diet (BD) only, which included wheat starch, casein, soybean oil, vitamin, and mineral mixtures. To the BD of the other five groups were added the following: BeerHigh (BeerA), BeerLow (BeerB), 1% of cholesterol (Chol), 1% of cholesterol and BeerHigh (Chol/BeerA), and 1% of cholesterol and BeerLow (Chol/BeerB). After 4 weeks of feeding, diets supplemented with BeerHigh and, to a lesser degree, with BeerLow (Chol/BeerA and Chol/BeerB groups) hindered a rise in plasma lipids and a decrease in plasma antioxidant capacity, and increased the bile excretion indices. Supplementation with BeerHigh and, to a lesser degree, with BeerLow in rats fed cholesterol-free diets increased their plasma antioxidant capacity. No significant changes in the plasma lipid levels, antioxidant capacity, and bile excretion indices were observed in the Control group. In conclusion, beer was found to have a positively effect on plasma lipid profile and plasma antioxidant capacity, and to increase the bile excretion indices in rats fed cholesterol-containing diets. The degree of this positive influence is directly connected to the contents of the bioactive components and the related antioxidant potential of beer. It is suggested that to achieve the best results, beer with the highest antioxidant potential must be consumed.

Comparative content of some bioactive compounds in apples, peaches and pears and their influence on lipids and antioxidant capacity in rats

The aim of this study was to compare some bioactive compounds in apples, peaches and pears and their influence on lipids and antioxidant capacity in rats. The content of total polyphenols (g/100g) was 0.23 +/- 0.03; 0.22 +/- 0.03 and 0.68 +/- 0.1 in peeled fruits and 0.48 +/- 0.04, 0.47 +/- 0.04 and 1.2 +/- 0.12 in peels of peaches, pears and apples, respectively. Caffeic, p-coumaric and ferulic acids and the total radical-trapping antioxidative potential (TRAP) values in peeled apples and their peels were significantly higher than in peaches and pears, respectively. Contrarary, no significant differences in the content of dietary fiber among the studied fruits were found. The content of all studied indices in peels was significantly higher than peeled fruits (p < 0.05 ). A good correlation between the total polyphenols and the TRAP values was found in all fruits. Diets supplemented with apples and to a less extent with peaches and pears have improved lipid metabolism and increased the plasma antioxidant potential especially in rats fed with added cholesterol. The highest content of biologically active compounds and the best results in the experiment on rats makes apple preferable for dietary prevention of atherosclerosis and other diseases.

Heat acclimation in rats: modulation via lipid polyunsaturation

Heat acclimation of rats has been shown to enhance endurance of rat hearts to ischemic insult and acute heat stress. Common protective features have been shown to be operative during both these stress-inducing conditions. To explore the role of membrane lipid composition in the adaptive response, we analyzed two major parameters that impact membrane dynamics and order, the nonesterified cholesterol levels and the acyl chain composition of phospholipids, in rat heart and salivary glands, both major thermoregulatory organs, in short- and long-term heat-acclimated rats. Before exposure to heat, control salivary gland tissue has a higher cholesterol-to-phospholipid mole ratio (0.32 +/- 0.02) than heart (0.14 +/- 0.01), and the acyl chains of its phospholipids are 50% more saturated. The remodeling strategies of the tissues after exposure to heat differed. Heart cholesterol levels increased after short-term heat acclimation (approximately 50%), whereas salivary gland cholesterol levels decreased in acute heat stress and long-term heat acclimation (approximately 32%). Remodeling of phospholipid acyl chains, particularly an increase in docosahexaenoic acid, was a protective strategy in both tissues (57% in heart and >100% in salivary glands). Modifying membrane lipid composition by treating rats with liposomes composed of egg phosphatidylcholine (PC) before exposure to heat resulted in a 38% increase in endurance to thermal stress. The density and affinity of muscarinic receptors of submaxillary salivary glands, involved in the acclimation response, were measured in control and PC liposome-treated rats, and then both groups were subjected to short-term heat acclimation. After PC treatment the well-established compensatory upregulation of the muscarinic receptors and concomitant decrease in their affinity was blunted. The substantial increase in the thermal endurance of heat-challenged intact rats after treatment with PC liposomes (600 vs. 200 min) suggests that membrane lipid composition plays a role in the ability of these tissues to respond to heat stress.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Dietary persimmon improves lipid metabolism in rats fed diets containing cholesterol

The effect of dietary persimmon (Pers, 7.0%) on lipid metabolism and antioxidant activity was investigated in 40 male Wistar rats adapted to cholesterol-free or 1% cholesterol diets. The rats were divided in four groups of 10. The basal diet contained wheat starch, casein, soybean oil, and mineral and vitamin mixtures. The control group (C) consumed the basal diet. To the basal diet were added 7 g/100 g dry persimmon (Pers), 1 g/100 g cholesterol (Chol), or both (Chol/Pers). The experiment lasted 4 wk. Plasma total cholesterol (TC), LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), triglycerides (TG), total phospholipids (TPH), HDL phospholipids (HDL-PH), lipid peroxides (LP) and liver TC concentrations were measured. Groups did not differ before the experiment. In the Chol/Pers vs. Chol group, the persimmon-supplemented diet significantly (P < 0.05) lessened the rise in plasma lipids due to dietary cholesterol: TC (3.88 vs. 4. 88 mmol/L; -20%), LDL-C (2.24 vs. 3.27 mmol/L; -31%), TG (0.72 vs. 0. 89 mmol/L; -19%), LP (2.20 vs. 3.25 mmol/L; -32%) and TC in liver (32.8 vs. 49.9 micromol/g; -34%), (P < 0.001). The Chol/Pers diet significantly reduced the decrease in HDL-PH due to dietary cholesterol (0.73 vs. 0.58 mmol/L; -25.8%, P < 0.001) and decreased the level of TPH (1.32 vs. 1.73 mmol/L; -23%, P < 0.001). Persimmon in rats fed the basal diet without cholesterol did not significantly affect the variables measured. These results demonstrate that persimmon possesses hypolipidemic and antioxidant properties that are evident when persimmon is added to the diet of rats fed cholesterol. These properties are attributed to its water-soluble dietary fiber, carotenoids and polyphenols.

Biological effects of oxysterols: current status

A review of relevant literature on biological activities of oxysterols (OS) and cholesterol is presented. The data clearly demonstrate manifold biological activities, often detrimental, for OS compared with little or no such activity of a deleterious nature for cholesterol itself. Cholesterol is perhaps the single most important compound in animal tissue and, as such, it is difficult to imagine it as a toxin or hazard. In contrast, OS exhibit cytotoxicity to a wide variety of cells leading to angiotoxic and atherogenic effects; alter vascular permeability to albumin; alter prostaglandin synthesis and stimulate platelet aggregation, an important process facilitating atherosclerosis and thrombosis; alter the functionality of low density lipoprotein (LDL) receptors, possibly stimulating hypercholesterolaemia; modify cholesteryl ester accumulation in various cells, inducing foam cell formation; and enrich the LDL particle in cholesteryl esters, possibly increasing its atherogenicity. Furthermore, OS are mutagenic and carcinogenic, although some have been studied as antitumour agents based on their cytotoxic properties. Moreover, numerous studies have implicated OS in membrane and enzyme alterations that are interrelated with many of the foregoing effects. The authors find that OS deserve much more attention than cholesterol itself in terms of research activity but that unfortunately the reverse is true with regard to funding.

Cholesterol oxides and carcinogenesis

Experimental evidence indicates a relationship between cholesterol alpha-epoxide and skin cancer, and exposure of skin fibroblasts to ultraviolet radiation enduces formation of significant levels of this oxide. Colon cancer is also etiologically linked to cholesterol oxidation products. Higher than normal levels of cholestanetriol have been found in patients with colon cancer and also in those with precancerous disorders such as adenomatous polyps and ulcerative colitis. Higher than normal levels of cholesterol alpha-epoxide have been found in breast fluid aspirates of women with benign breast disease, with or without atypical hyperplasia of the epithelium, and this may be a factor in the increased incidence of breast cancer associated with hyperplasia. Similarly, the observed increased levels of cholesterol alpha and beta-epoxides in prostatic fluid of men with benign prostatic hypertrophy may be associated with subsequent development of prostate cancer. Cholesterol alpha-epoxide has been found to be mutagenic to fibroblasts in culture and to induce morphological transformation in hamster embryo cells and in mouse C3H cells. 25-Hydroxycholesterol and 20 alpha-hydroxycholesterol are potent suppressors of generation and proliferation of tumor-specific cytotoxic T lymphocytes. Although investigations into the role of cholesterol oxidation products in cancer are still in the early stages, evidence to date indicates a potentially significant role in the induction of some types of cancer.

Insulin-tumour interrelationship in EL4 lymphoma or thymoma-bearing mice. I. Alloxan-diabetic or non-diabetic mice

A study has been carried out in which a comparison was made between EL4 lymphoma (assumed to be an insulin-producing secreting tumour) and thymoma (an insulin-dependent tumour). Tumour development and incidence, 3H-thymidine incorporation and insulin content in tumours, the host's food intake, blood insulin, glucose and cholesterol were determined in non-diabetic and alloxan-diabetic mice. Whereas no significant differences were observed between the diabetic and non-diabetic EL4 tumour-bearing mice, the diabetic, thymoma tumour-bearing mice showed reduced tumour growth and lower tumour incidence as compared with their non-diabetic counterparts. Insulin administration to diabetic tumour bearing mice, enhanced 3H-thymidine incorporation in the thymoma tumour cells only, and the insulin content of the EL4 tumours was found to be higher than that of the thymoma tumours. Rapid diabetes remission was observed in the diabetic, EL4 tumour-bearing mice as compared with the thymoma tumour-bearing mice.

Mutagenic lipid peroxides from edible oils

Weak mutagenic activity was detected in several commercially available edible palm and corn oils using liquid incubation bioassays with Salmonella typhimurium TA1537. Chromatographic fractionation of unrefined palm oil established that mutagenic activity was present in three fractions that also contained fatty acyl hydroperoxides. Similar weak mutagenic activity was also demonstrated for linoleic and linolenic acid hydroperoxides. In all cases, the mutagenicity was abolished by exogenous catalase, implying that the observed activity was moderated by hydrogen peroxide.

Effect of cholesterol epoxides on the inhibition of intercellular communication and on mutation induction in Chinese hamster V79 cells

Cholesterol, cholesterol-5 alpha, 6 alpha-epoxide, cholesterol-5 beta, 6 beta-epoxide and cholestane-3 beta,5 alpha,6 beta-triol were tested for their ability to induce mutations at the Na+/K+-ATPase loci of the Chinese hamster V79 cells. None of these compounds induced ouabain-resistant mutations compared to the background mutation frequency in the control cells. These compounds were further tested for their ability to inhibit intercellular communication, using the Chinese hamster V79 cell metabolic cooperation assay. The diastereomeric epoxides and cholestane-triol, but not cholesterol, were found to be inhibitors of intercellular communication in a manner similar to other known tumor promoters.

Mutagenic characterization of cholesterol epoxides in Chinese hamster V79 cells

The uptake, metabolism and alkylating properties of the diastereomeric cholesterol epoxides were studied using Chinese hamster lung fibroblasts (V79 cells). Specific emphasis is given to the comparative cyto- and geno-toxic effects of cholesterol 5 beta,6 beta-epoxide (beta CE) and cholesterol 5 alpha,6 alpha-epoxide (alpha CE) and data are provided for the first time indicating that beta CE can induce more 6-thioguanine-resistant cells than alpha CE. Cholesterol 5 beta,6 beta-epoxide induced colonies of cells resistant to 6-thioguanine at 2-3-fold the frequencies observed with the alpha-isomer, but neither compound produced ouabain-resistant colonies. The cytotoxicity (LD50) of alpha CE was estimated to be 45-50 microM whereas beta CE displayed an LD50 of 25-29 microM. Inhibition of DNA synthesis (IC50) was observed over the same dose ranges as the LD50 for each epoxide isomer. The epoxides were assimilated by cells to an equal extent, however, beta CE was metabolized to cholestane 3 beta,5 alpha-6 beta-triol twice as rapidly as the alpha-isomer. Both epoxides reacted with 4-(4'-nitrobenzyl)-pyridine to a similar extent, and with identical nucleophilic selectivity at pH 7.4, but their alkylating activity was estimated on this basis to be two orders of magnitude less than methyl methanesulfonate. Binding experiments with the DNA or cultured V79 cells or with calf-thymus DNA indicated that interactions were noncovalent and DNA binding did not correlate with the potency of the epoxides to induce the 6-thioguanine-resistant phenotype. Our results could be interpreted as indicating that both cholesterol epoxide isomers are weak mutagens or that they might induce some epigenetic event repressing the hypoxanthine guanine-phosphoribosyltransferase gene. The similarity of the epoxides' alkylating activity and their DNA-binding properties are inconsistent with their different potencies in inducing the 6-thioguanine-resistant phenotype, suggesting that the mechanism leading to this phenotype is not necessarily the result of DNA alkylation.

Biological effects of oxysterols on platelet function

We have studied the in vitro exposure to various oxysterols on isolated rat platelets. The oxysterols (1-20 uM) were incubated either dissolved in methanol or as albumin-bound complexes. Aggregation (analyzed by turbidimetry) was measured after stimulation by thrombin or ADP. Serotonin secretion (analyzed by voltammetry) was measured after thombin stimulation. We found that platelet aggregation and serotonin secretion could be either not significantly affected (7B-hydroxy cholesterol) or potentiated (22S-hydroxy cholesterol, 3,5,6-hydroxy cholestan triol) or inhibited (25-hydroxy- and 7-oxo cholesterol), after in vitro incubation with different oxysterols. Our data indicate that a modulation of the platelet behavior occurs after in vitro incubation with different oxysterols, some derivatives acting as inhibitors and others as potentiators. These results provide new interesting information regarding the role of these sterols in cell membrane structure and function in relation to pathology.

Effect of cholesterol alpha and beta epoxides on cell killing and transformation

V-79 Chinese hamster lung fibroblasts and C3H-10T1/2 mouse embryo cells were used to study the toxicity and transformation effects of the 5 alpha,6 alpha, and 5 beta,6 beta-epoxy derivatives of cholesterol. Both epoxides were found to be carcinogenic, and the transformation frequency increased with epoxide concentration and exposure time. The 5 beta,6 beta-epoxide caused a higher level of transformation than the alpha-isomer, and this is consistent with its greater toxicity.

Intestinal absorption and fecal excretion of 5,6 alpha-epoxy-5 alpha-cholesta-3 beta-ol by the male Wistar rat

The intestinal absorption of 5,6 alpha-epoxy-5 alpha-cholesta-3 beta-ol, an oxysterol formed by cholesterol autoxidation, has been evaluated in the male Wistar rat. Measurement of the 14C/3H ratio in the serum (by the method of Zilversmit and Hugues) and in the feces showed that a large proportion of the epoxide was absorbed. Epoxide clearance from the blood was very rapid, but its excretion in the stool continued for several days, corresponding to the fraction of the epoxide stored in the animal.

Autoxidation of cholesterol in tallows heated under deep frying conditions: evaluation of oxysterols by GLC and TLC-FID

The products of cholesterol autoxidation (oxysterols) in heated animal food fat were determined qualitatively and quantitatively to evaluate their toxicity and those of the foods in which they occur. Samples of beef tallow were taken from deep-fat fryers while they were in use. The oxysterols were identified and assayed by gas liquid chromatography and thin layer chromatography on Chromarods with flame ionization detection (TLC-FID). The two methods were compared and the TLC-FID method was found more convenient for a rapid estimation of autoxidation. Of the original cholesterol, 25% was destroyed during cooking and partly transformed into 3 beta-5-6 beta-trihydroxy-5 alpha-cholestane, 7 alpha-hydroxy-, 7 beta-hydroxy-, 7-oxo-cholesterol, 7-oxo-cholesta-3-5-diene and cholesterol epoxides. Certain other oxysterols were present in smaller quantities.

Mutagenic sterol hydroperoxides

Sterol hydroperoxides 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide and 3 beta-hydroxycholest-5-ene-7 alpha-hydroperoxide show weak dose-response direct mutagenicity towards Salmonella typhimurium strain TA 1537 in a liquid medium incubation bioassay. Responses were compromised by metabolism of the sterol hydroperoxides and by phase separation during the incubation period. Mutagenicity responses were increased by added superoxide dismutase but diminished by added rat liver S9 enzymes and abolished by added catalase. Catalase also abolished the stimulatory effect of superoxide dismutase. These results indicate that superoxide and peroxide be implicated in the mutagenicity responses.

Capillary column gas-liquid chromatographic resolution of oxidized cholesterol derivatives

Fused-silica capillary columns were evaluated for the resolution of oxidized cholesterol derivatives. Thermal instability of diol derivatives, epimeric 7 alpha- and 7 beta-hydroxy, 4 beta-hydroxy, and 25-hydroxycholesterol, was observed during gas chromatography. After derivatization as trimethylsilyl ethers the foregoing diols, alpha-epoxide, cholestane-triol, 7-ketocholesterol, and cholesta-3,5-dien-7-one were completely resolved on a DB-1 column. Each oxidized sterol revealed excellent response linearity as the trimethylsilylated sterol, enabling reliable quantification. The identity of each derivatized sterol was confirmed by mass spectrometry.

Vitamin A and lung cancer: a perspective

Sixteen studies of the relationship between lung cancer and vitamin A in humans are critically reviewed: eight dietary studies and eight serum studies. Of the eight dietary studies, only five had case samples large enough to warrant meaningful statistical analysis. Three dietary studies reported a negative association between vitamin A intake and lung cancer after proper adjustment for cigarette smoking and socioeconomic effects; the results suggested that daily consumption of green-yellow vegetables reduces the risk of lung cancer in all categories of smokers. The reduction in risk was found to be greatest in persons in the higher socioeconomic strata. Four dietary studies suggested that high intake of dietary vitamin A has a protective effect against the development of squamous and small cell carcinoma of the lung in smokers. Three studies revealed a lower risk of lung cancer among persons who consume carrots and milk daily. None of the eight serum studies reviewed had large enough samples of lung cancer cases to allow for meaningful statistical analysis. However, four of the serum studies reported significantly lower serum vitamin A levels in lung cancer cases than in controls. Analysis of the above studies demonstrated shortcomings in each. Future studies should include all of the following factors: more complete vitamin A indices, examination of the histological type of lung cancer, a large enough pool of both male and female patients for statistical analysis, and proper adjustment for the effects of age, sex, smoking, and socioeconomic status.

A search for mutagens in human aortal lipid extracts

In view of hypotheses suggesting mutagenesis is implicated in atherosclerosis, a total of 18 lipid extracts of human aortal tissues was examined by the standard Ames mutagenicity bioassay using Salmonella typhimurium or by a liquid modification thereof. One lipid extract of intimal-medial tissue contained detectable mutagenic activity against test strain TA98 in the liquid medium bioassay and against TA1538 in the standard plate assay following metabolic activation. Six other samples appeared to have weak activity against strains TA98, TA1538, or TA100. The other aortal samples were nonmutagenic.

Cholesterol epoxide is a direct-acting mutagen

A 24-hr treatment of V79 Chinese hamster lung fibroblasts with 12.4 microM cholesterol 5 alpha, 6 alpha-epoxide induced 8-azaguanine-resistant mutants at frequencies 4.6- to 11.8-fold higher than the spontaneous mutation rate. We show that cholesterol epoxide, which is produced by in vivo cholesterol oxidation, is a weak direct-acting mutagen. Cholesterol epoxide was found to be accumulated by cells and transformed to cholestane-3 beta, 5 alpha, 6 beta-triol, which was more toxic and a more potent inhibitor of DNA synthesis than the epoxide but, at concentrations less than 17.8 microM, was not significantly mutagenic. Consideration of the rates of cholesterol epoxide conversion to cholestane triol shows that this conversion can result in abolition of the mutagenicity of the epoxide. Conditions under which conversion of the epoxide to the triol is low, as in the case of low epoxide hydrolase activity, favor mutagenicity whereas rapid conversion to triol favors cytotoxicity.

Metabolic epidemiology of prostatic cancer

A review of the epidemiological evidence indicates that dietary fat very likely has an etiologic role in the development of prostatic carcinoma. While this effect may be mediated by way of altered hormonal action on the prostate, there is little supporting evidence from assays of plasma or urinary hormones in case-control studies or the investigation of high-risk and low-risk groups. The application of metabolic epidemiology to this problem is most likely to succeed by direct studies of the prostate gland, and the performance of relevant assays on prostatic fluid. Estradiol and estrone levels were found to be higher in prostatic fluid than in serum, whereas for prolactin the reverse was true. Testosterone concentrations were very low in prostatic fluid, perhaps because of the high degree of plasma protein binding. Preliminary data indicated that prostatic fluid estradiol and prolactin levels are elevated in some prostate cancer patients; estrone levels appear to be normal.

Dietary cholesterol and lung cancer risk in a multiethnic population in Hawaii

We interviewed 364 subjects with lung cancer and 627 age- and sex-matched controls among the multiethnic population of Hawaii. Quantitative estimates of dietary cholesterol and vitamin A intakes were obtained, as well as smoking and occupational histories. Using multiple logistic regression analysis to control for potential confounding variables, we found a monotonic positive dose-response relationship between dietary cholesterol and lung cancer risk in all subjects, in smoking subjects, and in men. In each of these groups, subjects in the highest quartile of dietary cholesterol were at significantly increased risk of lung cancer (lower 95% confidence limit greater than 1.0). Among females, however, no clear association of dietary cholesterol with lung cancer risk was apparent.