Identification of cholesta-3,5-dien-7-one by gas chromatography-mass spectrometry in the erythrocyte membrane of alcoholic patients

p-TsOH-Catalyzed one-pot transformation of di- and trihydroxy steroids towards diverse A/B-ring oxo-functionalization

A milder, facile, and greener transformative protocol, specifically on solid supports, to yield A-ring and/or B-ring oxo-functionalized steroids has been accomplished.

In vivo interconversion of 7beta-hydroxycholesterol and 7-ketocholesterol, potential surrogate markers for oxidative stress

The oxysterols 7beta-hydroxycholesterol and 7-ketocholesterol are cholesterol autoxidation products. These two oxysterols are formed as a result of low density lipoprotein oxidation and in a study on biomarkers for oxidative stress in patients with atherosclerosis, 7beta-hydroxycholesterol was found to be the strongest predictor of progression of carotid atherosclerosis. Interconversion of 7beta-hydroxycholesterol and 7-ketocholesterol in vitro has been reported recently, using recombinant 11beta-hydroxysteroid dehydrogenase or rodent liver microsomes. In this study deuterium-labeled 7beta-hydroxycholesterol or 7-ketocholesterol was administered intravenously to two healthy volunteers and blood samples were collected at different time points. The mean half-life for elimination of 7beta-hydroxycholesterol from the circulation was estimated to be 1.9 h. The corresponding half-life for 7-ketocholesterol was estimated to be 1.5 h. Infusion of deuterium-labeled 7-ketocholesterol resulted in labeling of 7beta-hydroxycholesterol and vice versa. In addition, the biological within-day and between-day variations of the two oxysterols were determined. In summary, the present investigation clearly shows an interconversion of 7beta-hydroxycholesterol and 7-ketocholesterol in humans.

Determination of phosphatidylcholine monohydroperoxides using quadrupole time-of-flight mass spectrometry

An improved technique for the analysis of phosphatidylcholine (PC) monohydroperoxides was developed using quadrupole time-of-flight (Q-TOF) mass spectrometry with electrospray ionization. Separation was obtained using an HPLC C8 column with a gradient of methanol and 10 mM aqueous ammonium acetate. Monohydroperoxides of palmitoyl-linoleoyl (C16:0/C18:2) PC, stearoyl-linoleoyl (C18:0/C18:2) PC, and oleoyl-linoleoyl (C18:1/C18:2) PC were detected mainly as MH(+) and [M+Na](+) ions in the heart of the intact rat. Using standard synthetic PCOOH (C16:0/C18:2-OOH), the lipid extract component was identified as (C16:0/C18:2-OOH) PC based on the product ions of ESI-MS-MS and, the PCOOH concentration was quantitated using HPLC with chemiluminescence detection. Two epoxyhydroxy derivatives of the three PCs mentioned above were also detected. This is the first report to show the presence of monohydroperoxides and epoxyhydroxy-derivatives of (C16:0/C18:2)PC, (C18:0/C18:2)PC, and (C18:1/C18:2) PC in the rat heart.

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.

Cholesterol-derived hydroperoxides in alcoholic liver disease

Human liver samples from 33 patients were collected at autopsy (controls, n = 9; fatty liver, n = 12; liver cirrhosis, n = 12), and samples homogenized. Lipids extracted with chloroform and methanol were injected into the octyl column of a high-performance liquid chromatograph with post-column chemiluminescence. Liquid chromatography-mass spectrometry was developed to identify 7-hydroperoxycholest-5-en-3 beta-ol (7-OOH). We found that two cholesterol-derived hydroperoxides, 7 alpha-hydroperoxycholest-5-en-3 beta-ol (7 alpha-OOH) and 7 beta-hydroperoxycholest-5-en-3 beta-ol (7 beta-OOH), are present in significantly elevated amounts (12.4 and 25.0 nmol/g tissue, respectively) in lipid extracts from alcoholic fatty liver, but not in extracts from alcoholic cirrhotic liver. 7 alpha-OOH and 7 beta-OOH are early intermediates produced during free radical-mediated cholesterol oxidation and can serve as molecular indicators of chain peroxidative damage in cell membranes. This is the first demonstration of 7 alpha-OOH and 7 beta-OOH accumulations in human liver, and it is presumed to reflect greater oxidative stress pathology in alcoholic fatty liver.

Cholesterol hydroperoxides in erythrocyte membranes of alcoholic patients

Evidence for the presence of 5alpha-hydroperoxycholest-6-en-3beta-ol (cholesterol 5alpha-hydroperoxide, Ch 5alpha-OOH) and 7alpha- and 7beta-hydroperoxycholest-5-en-3beta-ols (cholesterol 7-hydroperoxides: Ch 7alpha-OOH and Ch 7beta-OOH, respectively) in human erythrocyte membrane was found. Blood samples were collected from alcoholic patients and healthy volunteers (controls), and their cholesterol hydroperoxides were analyzed by high-performance liquid chromatography postcolumn chemiluminescence and roughly identified by liquid chromatography-mass spectrometry. Ch 7alpha-OOH and Ch 7beta-OOH were present in each sample, being significantly higher in alcoholic samples than in control samples. Ch 5alpha-OOH was present in some alcoholic samples, but not in the control ones. The accumulation of cholesterol hydroperoxides suggests enhanced lipid peroxidation by active oxygen species and/or a reduced elimination system for lipid peroxide in alcoholic patients.

Abnormality of very long-chain fatty acids of erythrocyte membrane in alcoholic patients

Profiles of very long-chain fatty acids were studied in the erythrocyte membrane of five alcoholic patients. We identified three fatty acids as cis-16-pentacosenoic acid (C25:1), cis-17-hexacosenoic acid (C26:1), and hexacosenoic acid (C26:1), and hexacosanoic acid (C26:0) by gas chromatography-mass spectrometry. The ratios of C26:1/C22:0, C26:0/C22:0, C24:1/C22:0, and C24:0/C22:0 were increased. These findings suggest that active oxygen species or free radicals generated by chronic alcohol consumption in alcohol patients interrupt the peroxisomal beta-oxidation of fatty acids, because very long-chain fatty acids are mainly metabolized by the peroxisomal beta-oxidation system. This is the first study showing accumulation of very long-chain fatty acids in the erythrocyte membrane of alcoholic patients.

Oxysterols found in opacified cornea of fish

We describe a new concept implicating oxidized cholesterol derivatives and very long-chain fatty acids as possible factors in the development of corneal opacification after death. Corneal tissues, removed from both fresh and stale fish eyes, were examined for cholesterol derivatives and fatty acids after methanolysis of lipids. Cholesta-3,5-dien-7-one, cholest-4-en-3-one, hexacosenoic acid, and hexacosenoic acid were identified via gas chromatography/mass spectrometry in opacified corneas, but not in significant amounts in fresh ones. The present study confirmed the presence of lipid hydrolysis and a peroxidation process in the opacified cornea.