The cytotoxic and mutagenic properties of cholesterol oxidation products

GPCR signaling regulates severe stress-induced organismic death in Caenorhabditis elegans

How an organism dies is a fundamental yet poorly understood question in biology. An organism can die of many causes, including stress-induced phenoptosis, also defined as organismic death that is regulated by its genome-encoded programs. The mechanism of stress-induced phenoptosis is still largely unknown. Here, we show that transient but severe freezing-thaw stress (FTS) in Caenorhabditis elegans induces rapid and robust phenoptosis that is regulated by G-protein coupled receptor (GPCR) signaling. RNAi screens identify the GPCR-encoding fshr-1 in mediating transcriptional responses to FTS. FSHR-1 increases ligand interaction upon FTS and activates a cyclic AMP-PKA cascade leading to a genetic program to promote organismic death under severe stress. FSHR-1/GPCR signaling up-regulates the bZIP-type transcription factor ZIP-10, linking FTS to expression of genes involved in lipid remodeling, proteostasis, and aging. A mathematical model suggests how genes may promote organismic death under severe stress conditions, potentially benefiting growth of the clonal population with individuals less stressed and more reproductively privileged. Our studies reveal the roles of FSHR-1/GPCR-mediated signaling in stress-induced gene expression and phenoptosis in C. elegans, providing empirical new insights into mechanisms of stress-induced phenoptosis with evolutionary implications.

Stress-Induced Phenoptosis: Mechanistic Insights and Evolutionary Implications

Evolution by natural selection results in biological traits that enable organismic adaptation and survival under various stressful environments. External stresses can be sometimes too severe to overcome, leading to organismic death either because of failure in adapting to such stress, or alternatively, through a regulated form of organismic death (phenoptosis). While regulated cell deaths, including apoptosis, have been extensively studied, little is known about the molecular and cellular mechanisms underlying phenoptosis and its evolutionary significance for multicellular organisms. In this article, we review documented phenomena and mechanistic evidence emerging from studies of stress-induced phenoptosis in the multicellular organism C. elegans and stress-induced deaths at cellular levels in organisms ranging from bacteria to mammals, focusing on abiotic and pathogen stresses. Genes and signaling pathways involved in phenoptosis appear to promote organismic death during severe stress and aging, while conferring fitness and immune defense during mild stress and early life, consistent with their antagonistic pleiotropy actions. As cell apoptosis during development can shape tissues and organs, stress-induced phenoptosis may also contribute to possible benefits at the population level, through mechanisms including kin selection, abortive infection, and soma-to-germline resource allocation. Current models can generate experimentally testable predictions and conceptual frameworks with implications for understanding both stress-induced phenoptosis and natural aging.

Analysis and formation of polycyclic aromatic hydrocarbons and cholesterol oxidation products in thin slices of dried pork during processing

This study aims to determine toxic compounds polycyclic aromatic hydrocarbons (PAHs) and cholesterol oxidation products (COPs) in thin slices of dried pork as affected by different flavorings and roasting temperature treatments through employing a QuEChERS method coupled with gas chromatograph-tandem mass spectrometer (GC-MS/MS) and gas chromatograph-mass spectrometer (GC-MS), respectively. By employing this method, high accuracy and precision was attained for freeze-dried pork hind leg sample. Following addition of 8 different flavorings with roasting temperature at 120, 160, and 200 °C, the levels of total COPs and PAHs in thin slices of dried pork followed a temperature-dependent increase during roasting, which was further confirmed by principle component analysis. High level of soy sauce or sugar inhibited COP formation, while the low-level minimized PAH formation in thin slices of dried pork during roasting. Sugar was more effective in inhibiting COP formation while soy sauce was more efficient in reducing PAH formation.

Biomolecules as Model Indicators of In Vitro and In Vivo Cold Plasma Safety

The potential applications for cold plasma in medicine are extensive, from microbial inactivation and induction of apoptosis in cancer cells to stimulating wound healing and enhancing the blood coagulation cascade. The safe bio-medical application of cold plasma and subsequent effect on complex biological pathways requires precision and a distinct understanding of how physiological redox chemistry is manipulated. Chemical modification of biomolecules such as carbohydrates, proteins, and lipids treated with cold plasma have been characterized, however, the context of how alterations of these molecules affect cell behavior or in vivo functionality has not been determined. Thus, this study examines the cytotoxic and mutagenic effects of plasma-treated molecules in vitro using CHO-K1 cells and in vivo in Galleria mellonella larvae. Specifically, albumin, glucose, cholesterol, and arachidonic acid were chosen as representative biomolecules, with established involvement in diverse bioprocesses including; cellular respiration, intracellular transport, cell signaling or membrane structure. Long- and short-term effects depended strongly on the molecule type and the treatment milieu indicating the impact of chemical and physical modifications on downstream biological pathways. Importantly, absence of short-term toxicity did not always correlate with absence of longer-term effects, indicating the need to comprehensively assess ongoing effects for diverse biological applications.

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 Cooking Cycle Times of Marinating Juice and Reheating on the Formation of Cholesterol Oxidation Products and Heterocyclic Amines in Marinated Pig Hock

In this work the effects of cooking cycle times of marinating juice and reheating on the formation of cholesterol oxidation products (COPs) and heterocyclic amines (HAs) in marinated pig hock were investigated. After the 12th cycle, the total content of COPs was 3.3, 2.0, and 2.0 times higher than that after the 1st cycle in the skin, subcutaneous fat, and lean meat, respectively. The total content of HAs was 5.8, 6.0, and 5.6 times higher than that after the 1st cycle in the skin, subcutaneous fat, and lean meat, respectively. Notably, more COPs were present in the lean meat than in the skin and subcutaneous fat, whereas the content of HAs in the skin was the highest. Compared with the unreheated samples, the total content of COPs and HAs in all tissues increased after reheating at 95 °C for 30 min or at 121 °C for 25 min, but no significant difference was found between different reheating conditions.

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.

Cholesterol-nitrone conjugates as protective agents against lipid oxidation: A model membrane study

Free radical scavengers such as α-phenyl-N-tert-butylnitrone (PBN) have been widely used as protective agents in several biological models. We recently designed two PBN derivatives by adding a cholesterol moiety to the parent nitrone to increase its lipophilicity. In addition to the cholesterol, a sugar group was also grafted to enhance the hydrophilic properties at the same time. In the present work we report on the synthesis of a third derivative bearing only a cholesterol moiety and the physical chemical and antioxidant characterization of these three derivatives. We demonstrated they were able to form stable monolayers at the air/water interface and with the two derivatives bearing a sugar group, repulsive interactions with 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) were observed. We next investigated the interaction with DLPC on a liposome model. Fluorescence spectroscopy experiments showed the addition of a cholesterol moiety causes an ordering effect whereas the presence of the sugar group led to a disordering effect. The protective effect against lipid oxidation was then investigated using dynamic light scattering and the formation of conjugated dienes was quantified spectrophotometrically. Two oxidizing systems were tested, i.e. the AAPH-thermolysis which generates peroxyl radicals and the Fenton reagent which is responsible of the formation of hydroxyl radicals. Due to their membrane localization, the three cholesteryl-PBN derivatives are able to prevent lipid oxidation with the two types of radical inducers but with a different mode of action.

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.

Health Risks of Food Oxidation

The impact of dietary habits on our health is indisputable. Consumer's concern on aging and age-related diseases challenges scientists to underline the potential role of food on the extension and guarantee of lifespan and healthspan. While some dietary components and habits are generally regarded as beneficial for our health, some others are being found to exert potential toxic effects and hence, contribute to the onset of particular health disorders. Among the latter, lipid and protein oxidation products formed during food production, storage, processing, and culinary preparation have been recently identified as potentially harmful to humans. Upon intake, food components are further degraded and oxidized during the subsequent digestion phases and the pool of compounds formed in the lumen is in close contact with the lamina propria of the intestines. Some of these oxidation products have been found to promote inflammatory conditions in the gut (i.e., bowel diseases) and are also reasonably linked to the onset of carcinogenic processes. Upon intestinal uptake, some species are distributed by the bloodstream causing an increase in oxidative stress markers and impairment of certain physiological processes through alteration of specific gene expression pathways. This chapter summarizes the most recent discoveries on this topic with particular stress on challenges that we face in the near future: understanding the molecular basis of disease, the suitability of using living animals vs in vitro model systems and the necessity of using massive genomic techniques and versatile mass spectrometric technology.

A new SPE/GC-fid method for the determination of cholesterol oxidation products. Application to subcutaneous fat from Iberian dry-cured ham

A new method for the isolation and analysis of cholesterol oxidation products (COPs) using solid phase extraction (SPE) and silica columns was developed using gas chromatography-flame ion detection (GC-FID). The method comprises of saponification and liquid-liquid extraction of the unsaponifiable fraction prior to the isolation and derivatization of the COPs to trimethylsilyl ethers. The COPs used in this study are cholestane-5α-6α-epoxide, cholestane-3β-5α-6β-triol, 25-hydroxycholesterol and 5-cholesten-3β-ol-7-one. In order to identify the COPs fraction a GC-ion-trap-mass spectrometry experiment were conducted using authentic standards to verify the presence of the COPs. The method was effective at rapidly separating the COPs (25 min run). Calibration curves were linear with the LODs and LOQs bellow 0.03 and 0.07 mgkg(-1) for all cases, respectively. This methodology gave a total recovery for every compound that was used in the study. Betulin was used as an internal standard to monitor the recovery. The method was validated with a standard mixture of COPs. The method has been applied to characterize the COP fraction of subcutaneous fat from Iberian dry-cured ham. Cholestane-5α-6α-epoxide, cholestane-3β-5α-6β-triol, 25-hydroxycholesterol and 5-cholesten-3β-ol-7-one have been identified for the first time in these samples.

Changes in the hepatic mitochondrial and membrane proteome in mice fed a non-alcoholic steatohepatitis inducing diet

Non-alcoholic steatohepatitis (NASH) accounts for a large proportion of cryptic cirrhosis in the Western societies. Nevertheless, we lack a deeper understanding of the underlying pathomolecular processes, particularly those preceding hepatic inflammation and fibrosis. In order to gain novel insights into early NASH-development from the first appearance of proteomic alterations to the onset of hepatic inflammation and fibrosis, we conducted a time-course analysis of proteomic changes in liver mitochondria and membrane-enriched fractions of female C57Bl/6N mice fed either a mere steatosis or NASH inducing diet. This data was complemented by quantitative measurements of hepatic glycerol-containing lipids, cholesterol and intermediates of the methionine cycle. Aside from energy metabolism and stress response proteins, enzymes of the urea cycle and methionine metabolism were found regulated. Alterations in the methionine cycle occur early in disease progression preceding molecular signs of inflammation. Proteins that hold particular promise in the early distinction between benign steatosis and NASH are methyl-transferase Mettl7b, the glycoprotein basigin and the microsomal glutathione-transferase.

Mass spectrometric detection of cholesterol oxidation in bovine sperm

We report on the presence and formation of cholesterol oxidation products (oxysterols) in bovine sperm. Although cholesterol is the most abundant molecule in the membrane of mammalian cells and is easily oxidized, this is the first report on cholesterol oxidation in sperm membranes as investigated by state-of-the-art liquid chromatographic and mass spectrometric methods. First, oxysterols are already present in fresh semen samples, showing that lipid peroxidation is part of normal sperm physiology. After chromatographic separation (by high-performance liquid chromatography), the detected oxysterol species were identified with atmospheric pressure chemical ionization mass spectrometry in multiple-reaction-monitoring mode that enabled detection in a broad and linear concentration range (0.05-100 pmol for each oxysterol species detected). Second, exposure of living sperm cells to oxidative stress does not result in the same level and composition of oxysterol species compared with oxidative stress imposed on reconstituted vesicles from protein-free sperm lipid extracts. This suggests that living sperm cells protect themselves against elevated oxysterol formation. Third, sperm capacitation induces the formation of oxysterols, and these formed oxysterols are almost completely depleted from the sperm surface by albumin. Fourth, and most importantly, capacitation after freezing/thawing of sperm fails to induce both the formation of oxysterols and the subsequent albumin-dependent depletion of oxysterols from the sperm surface. The possible physiological relevance of capacitation-dependent oxysterol formation and depletion at the sperm surface as well as the omission of this after freezing/thawing semen is discussed.

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.

Hepatic function and lipid metabolism are modulated by short-term feeding of cholesterol oxidation products in rats

Dietary cholesterol oxidation products (COPs) modulate various metabolic processes, particularly lipid metabolism. In this study, we observed that dietary COPs perturbed hepatic function, linoleic acid desaturation, and cholesterol catabolism in rats that were fed with diets containing 0.5% COPs for a short duration (7 days). The rats (age, 8 weeks) were fed American Institute of Nutrition (AIN)-purified diets containing 0.5% cholesterol or 0.5% COPs for 7 days. The glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and lactate dehydrogenase (LDH) levels were significantly high in rats fed with dietary COPs, but no such increase was observed in rats fed with dietary cholesterol, thereby indicating that dietary COPs may impair the hepatic function. The mRNA expression levels of Delta6 desaturase in the liver were significantly increased by dietary COPs, while these levels were significantly decreased by dietary cholesterol. However, the mRNA expression level of cholesterol 7alpha-hydroxylase (CYP7A1) in the liver was significantly decreased by dietary COPs and significantly increased by dietary cholesterol. Therefore, dietary COPs may modulate lipid metabolic processes such as linoleic acid desaturation and cholesterol catabolism even when they are consumed for a short duration. Hence, processed animal foods containing COPs should be consumed with caution.

Hormesis and a Chemical Raison D'être for Secondary Plant Metabolites

In plants, accumulation in specific compartments and huge structural diversity of secondary metabolites is one trait that is not understood yet. By exploring the diverse abiotic and biotic interactions of plants above- and belowground, we provide examples that are characterized by nonlinear effects of the secondary metabolites. We propose that redox chemistry, specifically the reduction of reactive oxygen species (ROS) and, in their absence, reduction of molecular oxygen by the identical secondary metabolite, is an important component of the hormetic effects caused by these compounds. This is illustrated for selected phenols, terpenoids, and alkaloids. The redox reactions are modulated by the variable availability of transition metals that serve as donors of electrons in a Fenton reaction mode. Low levels of ROS stimulate growth, cell differentiation, and stress resistance; high levels induce programmed cell death. We propose that provision of molecules that can participate in this redox chemistry is the raison d'être for secondary metabolites. In this context, the presence or absence of functional groups in the molecule is more essential than the whole structure. Accordingly, there exist no constraints that limit structural diversity. Redox chemistry is ubiquitous, from the atmosphere to the soil.

Influence of storage conditions on cholesterol oxidation in dried egg pasta

The oxidative characteristics of three different egg coproducts, namely, pasteurized eggs obtained from hens bred with organic methods (POE), pasteurized eggs from conventional breeding (PCE) and pasteurized spray-dried eggs (SPCE) obtained from conventional breeding, were analyzed. SPCE samples showed the highest content of peroxide (PV) and cholesterol oxides (COPs). In contrast, pasteurized eggs from organic breeding had the lowest index of oxidation. The three egg coproducts were used to produce dried egg pasta (spaghetti). The spaghetti was stored for 12 months at room temperature using typical pasta packaging (polypropylene foil) both under light, typical of retail conditions, and in the dark. Peroxide values and cholesterol oxidation were monitored at time 0 and then quarterly for 12 months. The oxidative parameters were significantly different in various egg coproducts, but the peroxide values of pasta were in the range of 3.0-3.5 mequiv of O(2)/kg of fat, with no differences in the types of pasta prepared with the various egg coproducts. Samples stored in the dark did not show any significant variations in peroxide values. However, PCE, SPCE and POE spaghetti stored in typical packaging increased the PV by 742.8, 846.7 and 625.7%, respectively. The pasta at time 0 showed COP values of about 50 microg of COPs/g of fat. During storage, COP values increased significantly. PCE, SPCE and POE spaghetti stored in the dark showed a content of total cholesterol oxides that was 2.0, 2.0, and 1.5 times lower than that of samples stored with typical pasta packaging.

Role of dietary mutagens in cancer and atherosclerosis

PURPOSE OF REVIEW

To provide an updated summary of dietary mutagens and their potential role in the etiology of cancer and atherosclerosis.

RECENT FINDINGS

Compelling evidence supports an accumulation of somatic mutations during carcinogenesis, leading to the activation of oncogenes or inactivation of tumor suppressor genes or both. There is also suggestive evidence that mutation provides an early event in atherosclerosis. Genome-wide association studies (GWAS) identify genes associated with familial cancers and atherosclerosis, but genes involved in sporadic events are less well characterized. Many dietary components are mutagenic, including natural dietary components, mutagens generated during cooking and processing of food or through contamination. Molecular epidemiology associates specific mutagens with specific types of cancer. Although chromosome mutations may provide a risk biomarker for atherosclerosis, they are not necessarily causal.

SUMMARY

Association studies, supported by molecular epidemiology, provide evidence that certain dietary mutagens, including aflatoxin B1, aristolochic acid and benzo[a]pyrene, are causal in some human cancers. Similar studies have correlated the level of oxidative DNA damage, DNA adducts and clastogenesis in arterial smooth muscle cells with atherogenic risk factors described through traditional epidemiology. However, establishing whether or not dietary mutagens lead to mutations that are causal in atherosclerosis remains a challenge for the newer genomic technologies.

Mammalian epoxide hydrolases in xenobiotic metabolism and signalling

Epoxide hydrolases catalyse the hydrolysis of electrophilic--and therefore potentially genotoxic--epoxides to the corresponding less reactive vicinal diols, which explains the classification of epoxide hydrolases as typical detoxifying enzymes. The best example is mammalian microsomal epoxide hydrolase (mEH)-an enzyme prone to detoxification-due to a high expression level in the liver, a broad substrate selectivity, as well as inducibility by foreign compounds. The mEH is capable of inactivating a large number of structurally different, highly reactive epoxides and hence is an important part of the enzymatic defence of our organism against adverse effects of foreign compounds. Furthermore, evidence is accumulating that mammalian epoxide hydrolases play physiological roles other than detoxification, particularly through involvement in signalling processes. This certainly holds true for soluble epoxide hydrolase (sEH) whose main function seems to be the turnover of lipid derived epoxides, which are signalling lipids with diverse functions in regulatory processes, such as control of blood pressure, inflammatory processes, cell proliferation and nociception. In recent years, the sEH has attracted attention as a promising target for pharmacological inhibition to treat hypertension and possibly other diseases. Recently, new hitherto uncharacterised epoxide hydrolases could be identified in mammals by genome analysis. The expression pattern and substrate selectivity of these new epoxide hydrolases suggests their participation in signalling processes rather than a role in detoxification. Taken together, epoxide hydrolases (1) play a central role in the detoxification of genotoxic epoxides and (2) have an important function in the regulation of physiological processes by the control of signalling molecules with an epoxide structure.

Mutagenesis and cardiovascular diseases Molecular mechanisms, risk factors, and protective factors

Although no generalization can be made, it is of interest that cancer, cardiovascular diseases, and other chronic conditions often share common risk factors and common protective factors as well as common pathogenetic determinants, such as DNA damage, oxidative stress, and chronic inflammation. Atherosclerosis is the most important cause of vascular forms representing the major cause of death in the population of many geographical areas. A great deal of studies support the "response-to-injury" theory. A variety of experimental and epidemiological findings are also in favor of the somatic mutation theory, which maintains that the earliest event in the atherogenic process is represented by mutations in arterial smooth muscle cells, akin to formation of a benign tumor. These two theories can be harmonized, also taking into account the highly diversified nature of atherosclerotic lesions. Molecular epidemiology studies performed in our laboratory and other laboratories have shown that DNA adducts are systematically present in arterial smooth muscle cells, and their levels are correlated with atherogenic risk factors known from traditional epidemiology. Oxidative DNA damage was also consistently detected in these cells. The role of glutathione S-transferase polymorphisms on the frequency of the above molecular alterations and of arterial diseases is rather controversial. Prevention of both cancer and atherosclerosis is based on avoidance of exposure to risk factors and on fortification of the host defense mechanisms by means of dietary principles and chemopreventive drugs.

Effect of storage on cholesterol oxide formation and fatty acid alterations in egg powder

The effect of the storage of egg powder on cholesterol oxide formation and alterations in the fatty acid composition was studied. Two commercial brands, A and B, were studied at 0 time and then monthly for up to 6 and 12 months, respectively. Five cholesterol oxides were identified and quantified (7-ketocholesterol, 7beta-hydroxycholesterol, 7alpha-hydroxycholesterol, 5,6alpha-epoxycholesterol, and 5,6beta-epoxycholesterol), the amounts of which increased during storage, although the cholesterol contents remained constant. The polyunsaturated fatty acid contents reduced during storage, whereas the levels of saturated and monounsaturated fatty acids and total lipids remained constant. High cholesterol oxide and trans fatty acid contents were found, a fact of concern because these compounds are hazardous to health, and egg powder is used in various food products widely consumed by the population, principally by infants.

Qualitative and quantitative comparison of the cytotoxic and apoptotic potential of phytosterol oxidation products with their corresponding cholesterol oxidation products

Phytosterols contain an unsaturated ring structure and therefore are susceptible to oxidation under certain conditions. Whilst the cytotoxicity of the analogous cholesterol oxidation products (COP) has been well documented, the biological effects of phytosterol oxidation products (POP)have not yet been fully ascertained. The objective of the present study was to examine the cytotoxicity of β-sitosterol oxides and their corresponding COP in a human monocytic cell line (U937), a colonic adenocarcinoma cell line (CaCo-2) and a hepatoma liver cell line (HepG2). 7β-Hydroxysitosterol, 7-ketositosterol, sitosterol-3β,5α,6β-triol and a sitosterol-5α,6α-epoxide–sitosterol-5β,6β-epoxide (6:1) mixture were found to be cytotoxic to all three cell lines employed; the mode of cell death was by apoptosis in the U937 cell line and necrosis in the CaCo-2 and HepG2 cells. 7β-Hydroxysitosterol was the only β-sitosterol oxide to cause depletion in glutathione, indicating that POP-induced apoptosis may not be dependent on the generation of an oxidative stress. A further objective of this study was to assess the ability of the antioxidants α-tocopherol, γ-tocopherol and β-carotene to modulate POP-induced cytotoxicity in U937 cells. Whilst α/γ-tocopherol protected against 7β-hydroxycholesterol-induced apoptosis, they did not confer protection against 7β-hydroxysitosterol-or 7-ketositosterol-induced toxicity, indicating that perhaps COP provoke different apoptotic pathways than POP. β-Carotene did not protect against COP- or POP-induced toxicity. In general, results indicate that POP have qualitatively similar toxic effects to COP. However, higher concentrations of POP are required to elicit comparable levels of toxicity.

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.

Increase in cholesterol and cholesterol oxidation products, and role of cholesterol oxidation products in kainate-induced neuronal injury

Little is known about changes in sterols, in particular cholesterol, and cholesterol oxidation products (COPs) in oxidative injury in neural tissues. We have therefore examined changes in cholesterol and COPs using a model of excitotoxic injury. Intracerebroventricular injections of kainate in rats resulted in an increase in immunoreactivity to cholesterol in the affected CA fields of the hippocampus. The increase was confirmed by increased filipin staining of cholesterol in adjacent sections from the same animals, and in hippocampal slice or neuronal cultures after kainate treatment. In neuronal cultures, addition of lovastatin, an inhibitor of cholesterol synthesis, attenuated the increased filipin staining after kainate treatment, indicating that the increase in cholesterol could involve increased cholesterol synthesis. Furthermore, gas chromatographic mass spectrometric (GC/MS) analysis of cholesterol and COPs in kainate-injected rat brain showed a marked increase in cholesterol and COPs including 7-ketocholesterol, 3 days after kainate treatment. The addition of some COPs, including 7-ketocholesterol and cholesterol epoxides to hippocampal slices resulted in neuronal injury as reflected by decreased staining of a neuronal marker in the affected CA fields. The ability of these COPs to produce neuronal injury was attenuated by glutathione, suggesting that oxidative mechanisms are involved in neuronal injury induced by these products. These results, together with GC/MS results that showed significant increase in 7-ketocholesterol at 3 days post-kainate injury suggest that 7-ketocholesterol may be a factor in aggravating oxidative damage to neurons, after the initial stages of kainate-induced neuronal injury.

Carbenoxolone induces oxidative stress in liver mitochondria, which is responsible for transition pore opening

Carbenoxolone (Cbx), a derivative of glycyrrhetinic acid, which has been found to affect mineralocorticoid and glucocorticoid receptors, induces swelling and membrane potential collapse when added to Ca(2+)-loaded liver mitochondria at 10 microM concentrations. These effects are strictly correlated with hydrogen peroxide generation, increase in oxygen uptake, and sulfhydryl and pyridine nucleotide oxidation. Cyclosporin A, bongkrekic acid, and N-ethylmaleimide completely abolish all the above-described effects, suggesting that Cbx can be considered an inducer of mitochondrial permeability transition by means of oxidative stress. Cbx can also trigger the apoptotic pathway because the above events are also correlated with the loss of cytochrome c. These effects are probably related to the conjugated carbonyl oxygen in C-11, which produces reactive oxygen species by interacting with the mitochondrial respiratory chain, mainly at the level of complex I but, most likely, also with complex III. The oxidative stress induced by Cbx, which is responsible for pore opening, excludes that this is related to a genomic effect of the compound.

A new LC/APCI-MS method for the determination of cholesterol oxidation products in food

Cholesterol oxidation products (COPs) can be formed in the body or in animal foods from cholesterol during food processing. A new method for the extraction and quantification of cholesterol, 7-ketocholesterol, cholestane-3beta-5alpha-6beta-triol, 25-hydroxycholesterol, 5,6alpha-epoxycholesterol, and 7beta-hydroxycholesterol by means of reversed-phase LC/atmospheric pressure chemical ionization mass spectrometry is presented. A baseline separation of all COPs was achieved, allowing a separate quantification also for isobaric compounds. The limits of detection were 15-30 ng/mL, quantification was performed from 100 ng/mL to 10 microg/mL with RSD < 2%. The method was applied successfully to the determination of cholesterol and COPs in processed foods such as pork, beef, chicken, and egg.

Influence of Lactation History on Breast Nipple Aspirate Fluid Yields and Fluid Composition

Analysis of nipple aspirate fluid (NAF) can be useful for understanding the impact that various lifestyle factors have on the biology of the breast. In this study, breast NAF was obtained at baseline from premenopausal women who volunteered for a dietary intervention trial. The influence of lactation history on both fluid yields and fluid composition was explored. We examined the levels of fat-soluble micronutrients (tocopherols, carotenoids, retinol), one lipid oxidation product (8-isoprostane), cholesterol, and protein in NAF. Roughly half of the women in the trial had never lactated, but this did not affect fluid yields appreciably. Carotenoid and tocopherol levels were significantly higher in NAF from women who lactated 6 months or more versus women who had lactated for shorter periods of time or never, but 8-isoprostane, protein, and cholesterol levels were not affected appreciably by lifetime lactation history. Longer times after weaning were associated with higher cholesterol levels, and there also was a suggestion the fat-soluble micronutrients declined with time after weaning. This is of interest since high cholesterol levels in breast fluid have been associated with an increased breast cancer risk, while carotenoids and tocopherols are thought to be protective. The results of this study provide further evidence of the potential benefits of prolonged lactation via its influence on NAF composition.

Dietary oxysterols induce in vivo toxicity of coronary endothelial and smooth muscle cells

Dietary cholesterol oxidation products (COPs) were reported to exhibit in vitro toxicity toward vascular cells. The aim of this study was to determine whether dietary COPs induce in vivo toxicity toward coronary arteries and to evaluate their effect on the coronary reactivity. Golden Syrian hamsters were fed either a normolipidic diet or a hyperlipidic diet with or without a mixture of COPs (1.4 mg/kg/day). At the end of the feeding periods, cardiac mitochondria and cytosol were prepared to determine the subcellular distribution of cytochrome c. Oxidative phosphorylation was evaluated with glutamate, pyruvate or palmitoylcarnitine as a substrate. The main coronary artery was examined all along its length by transmission electron microscopy (TEM). Plasma sterol concentrations were determined. Furthermore, at the end of the 3-month feeding period, the hearts were perfused at constant pressure by the Langendorff method. The endothelium-dependent reactivity to acetylcholine was evaluated. The myocardial sterol concentration was also estimated. After a 15-day diet with dietary COPs, a release of cytochrome c into the cytosolic fraction of the whole heart occurred, which indicated apoptosis of one or several types of cardiac cells probably induced by excess circulating cholestanetriol. The morphological data obtained by TEM after three months of diet suggested that mainly vascular cells (endothelial and smooth muscle cells) were damaged by dietary COPs, whereas cardiomyocytes appeared healthy. Furthermore, the mitochondrial oxidation of palmitoylcarnitine was reduced and that of pyruvate was increased, suggesting some maintenance of energy metabolism. This strengthens the hypothesis of apoptosis. Several changes in coronary reactivity suggesting an increased NO production were observed. In conclusion, dietary COPs triggered in vivo apoptosis of coronary cells through the release of cytochrome c in the cytosol. This toxicity was counterbalanced by an increased endothelium-dependent dilation.

Epoxide hydrolases: their roles and interactions with lipid metabolism

The epoxide hydrolases (EHs) are enzymes present in all living organisms, which transform epoxide containing lipids by the addition of water. In plants and animals, many of these lipid substrates have potent biologically activities, such as host defenses, control of development, regulation of inflammation and blood pressure. Thus the EHs have important and diverse biological roles with profound effects on the physiological state of the host organisms. Currently, seven distinct epoxide hydrolase sub-types are recognized in higher organisms. These include the plant soluble EHs, the mammalian soluble epoxide hydrolase, the hepoxilin hydrolase, leukotriene A4 hydrolase, the microsomal epoxide hydrolase, and the insect juvenile hormone epoxide hydrolase. While our understanding of these enzymes has progressed at different rates, here we discuss the current state of knowledge for each of these enzymes, along with a distillation of our current understanding of their endogenous roles. By reviewing the entire enzyme class together, both commonalities and discrepancies in our understanding are highlighted and important directions for future research pertaining to these enzymes are indicated.

New assays for detection and localization of endogenous lipid peroxidation products in living boar sperm after BTS dilution or after freeze–thawing

Reactive oxygen species have been implicated in sperm aberrations causing multiple pathologies including sub- and infertility. Freeze/thawing of sperm samples is routinely performed in the cattle breeding industries for semen storage prior to artificial insemination but unusual in porcine breeding industries as semen dilution and storage at 17 degrees C is sufficient for artificial insemination within 2-3 days. However, longer semen storage requires cryopreservation of boar semen. Freeze/thawing procedures induce sperm damage and induce reactive oxygen species in mammalian sperm and boar sperm seems to be more vulnerable for this than bull sperm. We developed a new method to detect reactive oxygen species induced damage at the level of the sperm plasma membrane in bull sperm. Lipid peroxidation in freshly stored and frozen/thawed sperm cells was assessed by mass spectrometric analysis of the main endogenous lipid classes, phosphatidylcholine and cholesterol and by fluorescence techniques using the lipid peroxidation reporter probe C11-BODIPY(581/591). Peroxidation as reported by the fluorescent probe, clearly corresponded with the presence of hydroxy- and hydroperoxyphosphatidylcholine in the sperm membranes, which are early stage products of lipid peroxidation. This allowed us, for the first time, to correlate endogenous lipid peroxidation with localization of this process in the living sperm cells. Cytoplasmatic droplets in incompletely matured sperm cells were intensely peroxidized. Furthermore, lipid peroxidation was particularly strong in the mid-piece and tail of frozen/thawed spermatozoa and significantly less intense in the sperm head. Induction of peroxidation in fresh sperm cells with the lipid soluble reactive oxygen species tert-butylhydroperoxide gave an even more pronounced effect, demonstrating antioxidant activity in the head of fresh sperm cells. Furthermore, we were able to show using the flow cytometer that spontaneous peroxidation was not a result of cell death, as only a pronounced subpopulation of living cells showed peroxidation after freeze-thawing. Although the method was established on bovine sperm, we discuss the importance of these assays for detecting lipid peroxidation in boar sperm cells.

Oxysterols from human bile induce apoptosis of canine gallbladder epithelial cells in monolayer culture

Oxysterols have been detected in various mammalian organs and blood. Biliary epithelium is exposed to high concentrations of cholesterol, and we have identified three keto-oxysterols (cholest-4-en-3-one, cholesta-4,6-dien-3-one, cholesta-3,5-dien-7-one) in human bile and gallstones. Because the effects of oxysterols on biliary physiology are not well defined, we investigated their biological effects on dog gallbladder epithelial cells. Enriched medium (culture medium containing taurocholate and lecithin and cholesterol +/- various oxysterols) was applied to confluent monolayers of dog gallbladder epithelial cells in culture. Cytotoxicity and apoptosis were studied by morphological analysis and flow cytometry. Oxysterols in the mitochondrial fraction were identified by gas chromatography/mass spectrometry, whereas release of cytochrome c from mitochondria was assayed by spectrophotometry and Western blot analysis. Compared with cells treated with culture medium or with enriched medium containing cholesterol, oxysterol-treated cells showed significantly increased apoptosis (P < 0.05). Exogenously applied oxysterols were recovered from the mitochondrial fraction. Cytochrome c release from mitochondria was increased significantly by cholest-4-en-3-one, cholesta-4,6-dien-3-one, and 5beta-cholestan-3-one (all P < 0.05). Thus oxysterols recovered from human bile and gallstones induce apoptosis of biliary epithelium via a mitochondrial-dependent pathway and may play a role in the pathogenesis of chronic inflammation and carcinogenesis in the gallbladder.

Combined effect of cooking (grilling and roasting) and chilling storage (with and without air) on lipid and cholesterol oxidation in chicken breast

The oxidation of the lipid fraction and cholesterol in raw and cooked chicken breast samples stored for 0 and 6 days at 4 degrees C under aerobic conditions and in vacuum packaging was studied. The multivariate statistical analysis showed significant effects of both culinary process and storage conditions on the lipid and cholesterol oxidation process, with a significant interaction between the two variables. Aerobic storage increased thiobarbituric acid reactive substances (TBA) from 0.04 to 0.06 ppm for raw samples, from 0.21 to 1.20 ppm for grilled samples, and from 0.24 to 1.62 ppm for roasted samples. During vacuum storage, only roasted samples showed significant increases in TBA. Levels of total cholesterol oxidation products (COP) remained low (2.88 to 4.35 microg/g of lipid) for all raw samples. Cooking increased COP levels to 12.85 and 11.54 microg/ g of lipid for grilled and roasted samples, respectively. Total COP and all individual COP except for cholestanetriol were significantly correlated with TBA and the peroxide index. However, the most extensive effect was attributable to the aerobic storage of cooked samples, which led to COP levels of 92.35 and 88.60 microg/g of lipid in grilled and roasted samples, respectively. Vacuum packaging did not increase COP levels for cooked samples.

Impairment of the cytotoxic and oxidative activities of 7 beta-hydroxycholesterol and 7-ketocholesterol by esterification with oleate

Atherosclerosis involves inflammatory processes, as well as cytotoxic and oxidative reactions. In atherosclerotic plaques, these phenomena are revealed by the presence of dead cells, oxidized lipids, and oxidative DNA damage, but the molecules triggering these events are still unknown. As 7 beta-hydroxycholesterol and 7-ketocholesterol, which are present at elevated concentrations in atherosclerotic lesions, are strongly cytotoxic and pro-oxidative, their effects were determined on cell death, superoxide anion and nitric oxide production, lipid peroxidation, and oxidative DNA damage. 7-Ketocholesterol- and 7 beta-hydroxycholesterol-induced cell death leads to a loss of mitochondrial potential, to increased permeability to propidium iodide, and to morphological nuclear changes (swelling, fragmentation, and/or condensation of nuclei). These effects are preceded by the formation of cytoplasmic monodansylcadaverine-positive structures and are associated with a rapid enhancement of cells overproducing superoxide anions, a decrease in cells producing nitric oxide, lipid peroxidation (formation of malondialdehyde and 4-hydroxynonenal adducts, low ratio of [unsaturated fatty acids]/[saturated fatty acids]) as well as oxidative DNA damage (8-oxoguanine formation). Noteworthy, none of the cytotoxic features previously observed with 7 beta-hydroxycholesterol and 7-ketocholesterol were noted with cholesterol, 7 beta-hydroxycholesteryl-3-oleate and 7-ketocholesteryl-3-oleate, with the exception of a slight increase in superoxide anion production with 7 beta-hydroxycholesteryl-3-oleate. This finding supports the theory that 7 beta-hydroxycholesterol and 7-ketocholesterol could induce cytotoxic and oxidative processes observed in atherosclerotic lesions and that esterification of these compounds may contribute to reducing atherosclerosis progression.

High dietary iron concentrations enhance the formation of cholesterol oxidation products in the liver of adult rats fed salmon oil with minimal effects on antioxidant status

The aim of this study was to investigate the effect of high dietary iron concentrations on the antioxidant status of rats fed two different types of fat. Four groups of male adult Sprague-Dawley rats were fed diets with adequate (50 mg iron supplemented per kg diet) or high (500 mg iron supplemented per kg diet) iron concentrations with either lard or salmon oil as dietary fat at 100 g/kg for 12 wk. The antioxidant status of the rats was profoundly influenced by the type of fat. Rats fed salmon oil diets had higher concentrations of thiobarbituric acid-reactive substances (TBARS) (P < 0.001), various cholesterol oxidation products (COP) (P < 0.001), total and oxidized glutathione (P < 0.05) and a lower concentration of alpha-tocopherol (P < 0.05) in liver and plasma than rats fed lard diets. The iron concentration of the diet did not influence the concentrations of TBARS, the activities of superoxide dismutase and glutathione peroxidase or the concentration of alpha-tocopherol in plasma or liver. The activity of catalase (P < 0.01) and the concentrations of total, oxidized and reduced glutathione (P < 0.05) in liver were slightly but significantly higher in rats fed high iron diets than in rats fed adequate iron diets, irrespective of the dietary fat. Rats fed the high iron diets with salmon oil, moreover, had higher concentrations of various COP in the liver (P < 0.001) than rats fed adequate iron diets with salmon oil. These results suggest that feeding a high iron diet does not generally affect the antioxidant status of rats but enhances the formation of COP, particularly if the diet is rich in polyunsaturated fatty acids.

Effects of riboflavin and fatty acid methyl esters on cholesterol oxidation during illumination

The effect of riboflavin or fatty acid methyl esters on cholesterol photooxidation was studied. Samples containing cholesterol, either alone or in combination with riboflavin or fatty acid methyl esters, were illuminated at 25 degrees C in an incubator for 28 days. The various cholesterol oxidation products (COPs) and cholesterol were analyzed by gas chromatography-mass spectrometry (GC-MS), and riboflavin was determined by HPLC. Results showed that the presence of riboflavin or fatty acid methyl esters facilitated production of COPs and degradation of cholesterol, and the degradation fits a first-order model. The COPs formed during light storage included 7 alpha-OH, 7 beta-OH, 7-keto, 3,5-cholestadien-7-one, 5,6alpha-EP, and 5,6beta-EP. The addition of riboflavin caused formation of 3,5-cholestadien-7-one through dehydration of 7-keto, whereas in the presence of docosahexaenoic acid methyl ester, the formation of 5,6alpha-EP or 5,6beta-EP was favored. Riboflavin was more effective for generation of COPs than fatty acid methyl esters.

Fatty acid modifications and cholesterol oxidation in pork loin during frying at different temperatures

The effect of frying with sunflower oil for 4 min at different temperatures (160, 170, and 180 degrees C) on fatty acids and cholesterol of pork loin meat was studied. Total fat content increased from 5.6% in fresh loin to 7.3, 7.8, and 12.1% at 160, 170, and 180 degrees C, respectively. Interactions with culinary fat gave rise to a significant increase in unsaturated acids/saturated acids and polyunsaturated acids/saturated acids ratios, which could be considered an advantage from a nutritional point of view. Less than 1 ppm (microg/g of sample) of cholesterol oxidation products was detected in fresh loin, whereas fried loin pork contained between 8.58 and 10.89 ppm. 7-Ketocholesterol (5.99 to 8.47 ppm in fried samples) and 7beta-hydroxycholesterol (1.43 to 2.55 ppm in fried samples) were the main cholesterol oxidation products. Cholestanetriol was not detected in any sample, and small quantities of 25-hydroxycholesterol and 5,6alpha-epoxycholesterol were found in the fried sample.