GC-MS characterization and quantification of sterols and cholesterol oxidation products

Improved production of Bacillus subtilis cholesterol oxidase by optimization of process parameters using response surface methodology

BACKGROUND

Cholesterol oxidase has numerous biomedical and industrial applications. In the current study, a new bacterial strain was isolated from sewage and was selected for its high potency for cholesterol degradation (%) and production of high cholesterol oxidase activity (U/OD600).

RESULTS

Based on the sequence of 16S rRNA gene, the bacterium was identified as Bacillus subtilis. The fermentation conditions affecting cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD600) of B. subtilis were optimized through fractional factorial design (FFD) and response surface methodology (RSM). According to this sequential optimization approach, 80.152% cholesterol degradation was achieved by setting the concentrations of cholesterol, inoculum size, and magnesium sulphate at 0.05 g/l, 6%, and 0.05 g/l, respectively. Moreover, 85.461 U of cholesterol oxidase/OD600 were attained by adjusting the fermentation conditions at initial pH, 6; volume of the fermentation medium, 15 ml/flask; and concentration of cholesterol, 0.05 g/l. The optimization process improved cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD600) by 139% and 154%, respectively. No cholesterol was detected in the spectroscopic analysis of the optimized fermented medium via gas chromatography-mass spectroscopy (GC-MS).

CONCLUSION

The current study provides principal information for the development of efficient production of cholesterol oxidase by B. subtilis that could be used in various applications.

A Comprehensive Update on Phytochemistry, Analytical Aspects, Medicinal Attributes, Specifications and Stability of Stigmasterol

Phytosterols are bioactive substances naturally found in plant cell membranes, and their chemical structure is comparable to cholesterol found in mammalian cells. They are widely distributed in plant foods like olive oil, nuts, seeds, and legumes. Amongst the variety of phytosterols, stigmasterol is the vital compound found abundantly in plants. Numerous hormones, including estrogen, progesterone, corticoids and androgen, are synthesized by stigmasterol. Multiple in-vitro and in-vivo investigations have shown that stigmasterol has various biological effects, including antioxidant, anticancer, antidiabetic, respiratory diseases, and lipid-lowering effects. Experimental research on stigmasterol provides indisputable proof that this phytosterol has the potential to be employed in supplements used to treat the illnesses mentioned above. This substance has a high potential, making it a noteworthy medication in the future. Although several researchers have investigated this phytosterol to assess its prospective qualities, it has not yet attained therapeutic levels, necessitating additional clinical studies. This review offers a comprehensive update on stigmasterol, including chemical framework, biosynthesis, synthetic derivatives, extraction and isolation, analytical aspects, pharmacological profile, patent status, clinical trials, stability and specifications as per regulatory bodies.

GC-MS analysis of oxysterols and their formation in cultivated liver cells (HepG2)

Oxysterols play a key role in many (patho)physiological processes and they are potential biomarkers for oxidative stress in several diseases. Here we developed a rapid gas chromatographic-mass spectrometry-based method for the separation and quantification of 11 biologically relevant oxysterols bearing hydroxy, epoxy, and dihydroxy groups. Efficient chromatographic separation (resolution ≥ 1.9) was achieved using a medium polarity 35%-diphenyl/65%-dimethyl polysiloxane stationary phase material (30 m × 0.25 mm inner diameter and 0.25 μm film thickness). Based on thorough analysis of the fragmentation during electron ionization we developed a strategy to deduce structural information of the oxysterols. Optimized sample preparation includes (i) extraction with a mixture of n-hexane/iso-propanol, (ii) removal of cholesterol by solid phase extraction with unmodified silica, and (iii) trimethylsilylation. The method was successfully applied on the analysis of brain samples, showing consistent results with previous studies and a good intra- and interday precision of ≤20%. Finally, we used the method for the investigation of oxysterol formation during oxidative stress in HepG2 cells. Incubation with tert-butyl hydroperoxide led to a massive increase in free radical formed oxysterols (7-keto-chol > 7β-OH-chol >> 7α-OH-chol), while 24 h incubation with the glutathione peroxidase 4 inhibitor RSL3 showed no increase in oxidative stress based on the oxysterol pattern. Overall, the new method described here enables the robust analysis of a biologically meaningful pattern of oxysterols with high sensitivity and precision allowing us to gain new insights in the biological formation and role of oxysterols.

Phytosterol Profiling of Apiaceae Family Seeds Spices Using GC-MS

Phytosterols are nutritionally vital phytoconstituent owing to their cholesterol (low-density plasma lipoprotein-cholesterol, LDL-C)-lowering, anti-inflammatory, and antioxidant properties. Among the widely used spices and herbs, the seeds spices of the Apiaceae family represented the healthiest fatty acid profile. Thus, to explore the other health-beneficial lipids, the present study was aimed to analyze the phytosterol profile of eight seed spices of the Apiaceae family, utilizing gas chromatography (GC)-mass spectrometry (MS). The sterols contents calculated on an oil (mg/100 g of oil) and spice weight (mg/100 g spices; dry weight) basis varied significantly among the seed spices (p < 0.05; Turkey HSD). The β-sitosterol and stigmasterol were the most dominating sterols among the studied spices, together accounted for 40.3 (Ajwain) to 69.8% (celery) of total sterols in the seed oil. Among the studied spices, the oil extracted from caraway seeds showed the highest total sterols (602.2 mg/100 g of oil). Interestingly, based on spice weight, fennel seeds also showed the similar highest number of total sterols (134.2 mg/100 g in fennel and 133.3 mg/100 g in caraway), owing to the high contents of oil (25.9%) in fennel seeds. Overall, celery, caraway, fennel, and anise seeds oil are rich sources of health-beneficial phytosterols.

Synthesis and search for 3β,3'β-disteryl ethers after high-temperature treatment of sterol-rich samples

It has been proven that at increased temperature, sterols can undergo various chemical reactions e.g., oxidation, dehydrogenation, dehydration and polymerisation. The objectives of this study are to prove the existence of dimers and to quantitatively analyse the dimers (3β,3'β-disteryl ethers). Sterol-rich samples were heated at 180 °C, 200 °C and 220 °C for 1 to 5 h. Quantitative analyses of the 3β,3'β-disteryl ethers were conducted using liquid extraction, solid-phase extraction and gas chromatography coupled with mass spectrometry. Additionally, for the analyses, suitable standards were synthetized from native sterols. To identify the mechanism of 3β,3'β-disteryl ether formation at high temperatures, an attempt was made to use the proposed synthesis method. Additionally, due to the association of sterols and sterol derivatives with atherosclerosis, preliminary studies with synthetized 3β,3'β-disteryl ethers on endothelial cells were conducted.

Metabolic fingerprinting unveils quinoa oil as a source of bioactive phytochemicals

Quinoa is a pseudo-cereal with high phytochemical contents with proven biological and nutritional significance. In recent decades several breeding programmes have introduced new and traditional quinoa varieties to North America and other non-traditional quinoa regions, raising questions regarding variability in their secondary metabolite profiles. In this work, we have fingerprinted 28 quinoa varieties cultivated in Washington State, focussing on the poorly investigated oil fraction. We found variability in both phenolics and carotenoid contents, which is reflected in different antioxidant capacities, as measured by FRAP and DPPH. Fatty acid profiles show significant differences in palmitic acid and long-chain fatty acids. Finally, conspicuous amounts of phytosterols and squalene were found. Through factor analysis, we classified the quinoa varieties into two groups: a first comprising varieties with higher phytochemical and PUFA contents and a second group, with higher linolenic and long-chain fatty acid contents. Both groups may be suitable for potential food applications.

Comprehensive chemical profiling of Pinellia species tuber and processed Pinellia tuber by gas chromatography-mass spectrometry and liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry

A comprehensive profiling method was established for the determination of various chemicals in Pinellia (P.) ternata and pedatisecta species. The profiling method comprises a fast ultrasonic extraction with various solvents, followed by GC-MS and LC-APCI-MS analysis. A total of 73 polar components as trimethylsilyl (TMS) derivatives were detected in methanol extract by GC-MS. The main components of the P. species were profiled as several kinds of fatty acids, amino acids, nucleic acids, carbohydrates, and phenolic compounds. The hexane extract was analyzed by LC-APCI-MS for the lipid profiling. A total of 35 lipid constituents [fatty acids and their esters, mono-, di-, and tri-acylglycerols] and four phytosterols were observed and tentatively characterized by LC-APCI-MS/MS. Among the phytochemicals detected in the hexane extract, triacylglycerols (TAGs) as the major component were identified by LC-APCI-MS and MS/MS. Based on the identified components, a significant difference in the chemical compositions of P. species tuber and processed P. ternata was found that the complete disappearance of TAGs and a considerable decrement of sucrose were observed in processed P. ternata. Furthermore, the degradation mechanism for TAGs in the presence of alum solution is suggested to occur during the processing P. ternata. Malic acid was found to be a characteristic compound for the classification of P. ternata and pedatisecta with different geographic origins. Based on the validated GC/MS method, twenty-four P. ternata, processed P. ternata and P. pedatisecta samples were profiled to measure the overall abundance of specific groups of compound and to identify diagnostic compounds. In addition, principal component analysis (PCA) on the GC/MS profiling data revealed a clear classification of P. species samples. In this study, the full chemical complement was for the first time reported for quality evaluation of P. species. The method can be usefully applied for phytochemical analysis of related herbal medicines.

Developmental changes in the sterol composition and the glycerol content of cuticular and internal lipids of three species of flies

The glycerol concentration and the composition of cuticular and internal sterols in three medically and forensically important fly species, viz., Musca domestica, Sarcophaga carnaria, and Calliphora vicina, were analyzed. The cuticular and internal lipid extracts were separated by HPLC-LLSD, after which the sterol fraction was characterized by GC/MS in total ion current (TIC) mode. The cuticular lipids of M. domestica larvae contained seven sterols, while in pupae and females, six sterols were identified. Five sterols were found in the cuticular lipids of M. domestica males. The internal lipids of M. domestica larvae and pupae contained six and seven sterols, respectively, while those of male and female flies contained only five sterols. Sitosterol, cholesterol, and campesterol were the dominant sterols in M. domestica, while campestanol, stigmasterol, sitostanol, and fucosterol were identified in low concentrations or in traces. In contrast, cuticular and internal lipids of S. carnaria and C. vicina contained only cholesterol. Glycerol was identified in all stages of M. domestica, S. carnaria, and C. vicina. For all the three examined fly species, the present study clearly showed species-specific developmental changes in the composition of cuticular and internal sterols as well as in the glycerol concentration.

Effect of Flaxseed Meals and Extracts on Lipid Stability in a Stored Meat Product

Flaxseeds have been recently in focus due to the antioxidant capacity of some of their compounds. However, there is a lack of easily accessible information concerning their activity against lipid oxidation in food systems. Therefore, the aim of the study was to determine the effect of defatted meals (DFM) and the aqueous extracts (AFE) obtained from brown and golden flaxseeds on lipid oxidation in pork meatballs. Fatty acid composition, peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and cholesterol content were monitored during 6 months of freezer storage. Cholesterol oxidation products were identified and quantified. Both DFM and AFE limited fatty acid and cholesterol oxidation during meatball storage. Their antioxidant effect depended on flax variety (brown or golden) and preparation type (DFM or AFE). Lower level of PV and TBARS, compared with the ones with AFE, were noted in meatballs with DFM. Both DFM and AFE, from the brown seed variety, protect the lipids against oxidation to a higher extent. During the storage, a cholesterol degradation was observed. AFE (particularly from the brown variety) limited changes in cholesterol content. Moreover, they stabilized fatty acid composition of stored meatballs. However, DFM efficiently inhibited cholesterol oxidation.

High-temperature GC-MS-based serum cholesterol signatures may reveal sex differences in vasospastic angina

Alterations of cholesterol metabolism are responsible for vasospastic angina and atherosclerosis. To comprehensively evaluate cholesterol metabolism, 18 sterols, including cholesterol, 6 cholesteryl esters (CEs), 3 cholesterol precursors, and 8 hydroxycholesterols (OHCs), were simultaneously analyzed using hybrid solid-phase extraction (SPE) purification coupled to high-temperature gas chromatography-mass spectrometry (HTGC-MS). Methanol-based hybrid SPE increased the selective extraction, and HTGC resulted in a good chromatographic resolution for the separation of lipophilic compounds. The limits of quantification of cholesterol and CEs ranged from 0.2 to 10.0 μg/ml, while OHCs and cholesterol precursors ranged from 0.01 to 0.10 μg/ml. Linearity as the correlation coefficient was higher than 0.99 with the exception of cholesteryl laurate, myristate, oleate, and linoleate (r² > 0.98). The precision (% coefficient of variation) and accuracy (% bias) ranged from 1.1 to 9.8% and from 75.9 to 125.1%, respectively. The overall recoveries of CEs ranged from 26.1 to 64.0%, and the recoveries of other sterols ranged from 83.8 to 129.3%. The cholesterol signatures showed sex differences in patients with vasospastic angina and may associate with 24-reductases. This technique can be useful for making clinical diagnoses and for an increased understanding of the pathophysiology of vasospastic angina.

High-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry determination of cholesterol uptake by Caco-2 cells

A simple, sensitive and selective liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometric method (LC/APCI-MS/MS) was developed and applied to quantitative determination of uptake of cholesterol by Caco-2 human intestine cells. Caco-2 cells were cultured in medium containing cholesterol-3,4-13C2 and phytosterols from nutritional supplements after in vitro digestion. Cellular cholesterol (cholesterol-3,4-13C2) and endogenous cholesterol were extracted using methanol/chloroform (1:2, v/v) and directly analyzed using LC/APCI-MS/MS with selected reaction monitoring (SRM), using cholesterol-2,2,3,4,4,6-d6 as an internal standard. Detection and quantification limits were 2.2 and 7.2 pmol, respectively. This method provides an effective tool for rapid determination of cholesterol uptake by cells with increased selectivity and sensitivity in comparison to previously reported LC/APCI-MS analysis using selected ion monitoring (SIM).

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.

Gas chromatographic separation and mass spectrometric identification of mixtures of oxyphytosterol and oxycholesterol derivatives

Pure individual phytosterols were prepared using reversed-phase HPLC in order to obtain the oxidized compounds of sitosterol, campesterol, stigmasterol and brassicasterol. 7-Hydroxy-, 7-keto-, 5,6-epoxy-, 4beta-hydroxy-, 4-ene-6-hydroxy-, 6-keto- and 5alpha,6beta-dihydroxyphytosterols were obtained as well as analogous compounds of cholesterol. The gas chromatographic properties as well as the electronic impact mass spectra of these compounds (as trimethylsilyl ether derivatives) were studied. These data were used to identify oxyphytosterols in a spread enriched in phytosterols: the oxyphytosterols represented no more than 68 microg/g of spread (about 0.08% of phytosterols were oxidised).

Safety evaluation of phytosterol esters. Part 8. Lack of genotoxicity and subchronic toxicity with phytosterol oxides

Vegetable oil spreads containing phytosterol-esters are marketed as a cholesterol-lowering functional food in more than 20 countries worldwide. An extensive package of safety data has shown phytosterol-esters to be safe for human use. However, even though phytosterols are very stable molecules, oxidation may occur at low levels under extreme heating conditions, resulting in phytosterol oxides. As there is some suggestion of adverse biological effects in the literature for the related cholesterol oxidation products, safety data have been generated for phytosterol oxides. A phytosterol oxide concentrate (POC) was generated by prolonged heating of phytosterol-esters in the presence of oxygen. The genotoxicity and subchronic toxicity of this mixture was assessed in a series of in vitro genotoxicity assays (bacterial mutation, chromosome aberration and micronucleus) and a subchronic feeding study in the rat. Results showed that a phytosterol oxide concentrate containing approximately 30% phytosterol oxides did not possess genotoxic potential and no obvious evidence of toxicity when administered in the diet of the rat for 90 consecutive days. In the latter study, a NOEL was established at an estimated dietary level of phytosterol oxides of 128 mg/kg/day for males and 144 mg/kg/day for females. In conclusion, these materials have been shown to raise no obvious concerns for human safety.

Preparation and mass spectrometry of 14 pure and 18O2-labeled oxidation products from the phytosterols β-sitosterol and stigmasterol

To lower cholesterol, phytosterols are currently introduced as food additives, where they may become oxidized. In addition, specific biological effects of oxyphytosterols are suggested by the recent molecular clarification of the phytosterol storage disease as a dysfunctional mutation of an active sterol reexporter potentially regulated by oxidized phytosterols. We therefore studied the hydroxybenzotriazole-mediated PbO(2)-driven oxidation of phytosterols and compared it to the oxidation of cholesterol. We prepared, identified, and purified standards of 14 oxidation products of two major phytosterols. The gas chromatographic mass spectrometric characteristics of the 7alpha- and 7beta-hydroxy-, 5alpha,6alpha-epoxy, 5beta,6beta-epoxy, 7keto-, 3beta,5alpha,6beta-trihydroxy-, 3keto-, and 7-dehydro-derivatives of beta-sitosterol and stigmasterol are presented. The method also provided a convenient access to prepare 18O-labeled oxyphytosterols of high chemical and isotopic purity and can easily be extended to further phytosterols and -stanols. This enables the gas chromatography-mass spectrometry analysis of oxyphytosterols and the study of their biological effects.

Identification of new steroidal hydrocarbons in refined oils and the role of hydroxy sterols as possible precursors

The dehydration of sterols during the refining process of vegetable oils results in the formation of steroidal hydrocarbons (sterenes or steradienes) with two double bonds in the ring system. Other steroidal hydrocarbons whose structures were in agreement with the presence of three double bonds in the ring system were detected in the sterene fractions of refined vegetable oils. The 5alpha-, 7alpha-, and 7beta-hydroxy derivatives of cholesterol and phytosterols have been dehydrated in n-butanol/H(3)PO(4) to form steroidal hydrocarbons with three double bonds at the 2, 4, and 6 positions in the ring system. These hydrocarbons had the same relative retention time and mass spectra as those present in the sterene fractions of refined oils. The dehydration of the hydroxy sterols dissolved in extra virgin olive oil and in the presence of 1% bleaching earths at 80 degrees C for 1 h results in the formation of the same steroidal hydrocarbons found in the refined oils.

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.

Mass spectrometry characterization of the 5alpha-, 7alpha-, and 7beta-hydroxy derivatives of beta-sitosterol, campesterol, stigmasterol, and brassicasterol

The 5alpha-hydroperoxides of beta-sitosterol, campesterol, stigmasterol, and brassicasterol were obtained by photooxidation of the respective sterols in pyridine in the presence of hematoporphyrine as sensitizer. The reduction of the hydroperoxides gives the corresponding 5alpha-hydroxy derivatives. The 7alpha- and 7beta-hydroperoxides of the sterols were obtained by allowing an aliquot of the 5alpha-hydroperoxides to isomerize to 7alpha-hydroperoxides, which in turn epimerize to 7beta-hydroperoxides. The reduction gave the corresponding 7alpha- and 7beta-hydroxy derivatives. The 5alpha-, 7alpha-, and 7beta-hydroxy derivatives of beta-sitosterol, campesterol, stigmasterol, and brassicasterol were identified by comparing thin-layer chromatography mobilities, specific color reactions, and mass spectral data with those of the corresponding hydroxy derivatives of cholesterol, which were synthesized in the same manner. The phytosterols had the same behavior to photooxidation as cholesterol and, moreover, the different phytosterols photooxidized at about the same rate. The mass spectra of the trimethylsilyl ethers of the hydroxy derivatives of the phytosterols investigated and of the corresponding hydroxy derivatives of cholesterol have the same fragmentation patterns and similar relative ion abundances.

Purification and characterization of deep sea shark Centrophorus squamosus liver oil 1-O-alkylglycerol ether lipids

The 1-O-alkylglycerol composition of the liver oil of the deep sea shark Centrophorus squamosus, a species which provides edible flesh, has been determined. After various fractionations of the oil, the unsaponifiable fraction was characterized by means of gas chromatography/mass spectrometry, electron impact, and positive-ion chemical ionization. The oil is composed of 60% unsaponifiable matter, containing 45% squalene, 4.5% cholesterol, and 10% of linear saturated and monounsaturated glycerol ethers with 14-18 carbon atoms. After a first separation by chromatography on silicic acid, monounsaturated glycerol ethers have been separated from the saturated homologues, in particular from 1-O-octadecylglycerol (batyl alcohol) and 1-O-hexadecylglycerol (chimyl alcohol), via urea complexation. This newer application of the urea method, already used in the past to extract saturated from polyunsaturated fatty acids, allowed the purification of the main components of the complex unsaturated glycerol ether fraction, namely, 1-O-octadecen-9'ylglycerol (selachyl alcohol) and 1-O-hexadecen-9'ylglycerol.

Cholesterol interaction with free radicals produced from carbon tetrachloride or bromotrichloromethane by either catalytic decomposition or via liver microsomal activation

The reaction between cholesterol (Ch) and trichloromethyl or trichloromethyl peroxyl radicals was studied. The latter were generated from CCl4 either by benzoyl peroxide (BP) catalysis or via thermal activation or by liver microsomal NADPH-dependent biotransformation of CBrCl3. The structure of the products formed was elucidated by gas chromatography-mass spectrometry (GC/MS). Under aerobic conditions and using thermal activation of CCl4, the formation of 6 products was observed. Two (I and II) were dehydrated Ch derivatives (one also having a third double bond) (I). Another product was a delta(5)-3 ketone derivative of Ch (III). Two additional reaction products were determined as ketocholesterols (IV and V). One chloro Ch was also formed (VI). At low concentrations of BP, reaction was more extensive than under thermal activation, and the formation of peaks I to IV was also observed. When the reaction was conducted anaerobically and using thermal activation of CCl4 to generate radicals, only products I and II were formed in low yield. Under anaerobic conditions, but using catalyst, compounds I and III were produced plus two new isomeric ketocholesterol derivatives (VIII and IX) and also a compound having an extra hydroxyl group on the Ch structure (X). In order to check whether similar reactions are observable under biological experimental conditions, we used activation of CBrCl3 by liver microsomes. The incubation using only microsomes (without CBrCl3 or NADPH) showed two ketocholesterol peaks (A and B). In the presence of CBrCl3 we could detect peak B and hydroxycholesterol (C) and two others, ketocholesterols (D and E). D was the only peak showing close similarity (spectrum and retention time) to one of those observed in the chemical reaction system (V). The reaction of CBrCl3 in the presence of NADPH showed peaks B, C, D and E, in low abundance and a 7-ketocholesterol (F). If some of the reaction products reported here were formed during the intoxication with these haloalkanes, significant biological consequences might be expected.

Isolation and quantification of cholesterol oxides in dairy products by selected ion monitoring mass spectrometry

A method for isolation, detection and quantification of cholesterol oxidation products based on solid phase extraction in combination with preparative HPLC and gas chromatography-mass spectrometry selected ion monitoring has been developed for dairy products. The isolation procedure had a high recovery and artifact formation was minimal, as shown by isotope labelling. The limits of detection ranged from 0.3 to 35 pg/microliters of the isomeric forms of 7-hydroxycholesterol, 20 alpha-hydroxycholesterol, the isomeric forms of cholesterol-5,6-epoxides, cholestanetriol, 25-hydroxycholesterol and 7-ketocholesterol corresponding to a limit of quantification of 2-6 ng oxysterol/g lipid in the dairy product, depending on the nature of the cholesterol oxidation product.