| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Fluorescence lifetime distributions of parinaroyl phospholipids in choline plasmalogen and phosphatidylcholine bilayers containing different amounts of cholesterol Loidl, J., F. Paltauf, et al. (1990), Chem Phys Lipids 56(1): 27-36. Abstract: The fluorescence decay of alkenylparinaroyl- and palmitoylparinaroyl glycerophosphocholines in vesicles of the unlabeled alkenyloleoyl and palmitoyloleoyl analogs was determined by multifrequency phase and modulation fluorometry. The measured phase angles and demodulations could be equally well fitted to a biexponential decay, as well as unimodal or bimodal continuous lifetime distributions. The latter model was applied to study the influence of cholesterol on parinaroyl phospholipid fluorescence in vesicles. The long-living component of a bimodal lifetime distribution was sensitive toward the presence of the sterol. Upon increasing cholesterol concentrations, its lifetime center increased and its distribution widths decreased. Lifetime distribution widths in vesicles of alkenyloleoyl- or palmitoyloleoyl-glycerophosphocholine (choline plasmalogen and phosphatidylcholine, respectively) were reduced by the sterol to the same extent. We interprete the sterol-induced lifetime distribution narrowing as an effect due to an increase of membrane homogeneity in cholesterol-phospholipid membranes. |
| Fluorocholesterols, in contrast to hydroxycholesterols, exhibit interfacial properties similar to cholesterol Kauffman, J. M., P. W. Westerman, et al. (2000), J Lipid Res 41(6): 991-1003. Abstract: We used an automated Langmuir-Pockels surface balance to characterize the air-water interfacial properties of cholesterol (CH) and its derivatives with hydrophilic OH and F substitutions at isologous sites on the sterol body or side chain. We studied 6-fluorocholesterol, 25-fluorocholesterol, 25,26,26,26,27,27,27-heptafluorocholesterol, 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol, alone and in mixtures with 1-palmitoyl-2-oleoyl-sn-3-glycero-phosphocholine (POPC). Pressure;-area isotherms of the fluorocholesterols were essentially indistinguishable from CH and all condensed POPC monomolecular layers (monolayers) to variable degrees. Both nucleus-substituted hydroxycholesterols formed expanded monolayers, with lift-offs from baseline 22-26 A(2)/molecule larger than CH, suggesting interfacial tilting; furthermore, in binary mixtures, they condensed POPC monolayers less than CH. In contrast, the side chain hydroxylated CHs were oriented horizontally in the interface at large molecular areas, and became vertical below 140 A(2)/molecule with the side chain-OH rather than 3-OH group anchored in the subphase, as evidenced by low collapse pressures and smaller molecular areas than CH. Both side chain hydroxycholesterols expanded POPC monolayers at molar ratios <30%, but induced condensation with higher ratios, suggesting that OH-acyl chain (POPC) repulsion is superceded at higher mole fractions by lateral phase separation and intersteroidal H-bonding.These studies predict that fluorocholesterols should exhibit intramembrane spatial occupancy nearly identical to CH, whereas nucleus and especially side chain hydroxycholesterols will perturb membrane lipid packing notably. |
| Fluorometric method for the enzymatic determination of cholesterol Amundson, D. M. and M. Zhou (1999), J Biochem Biophys Methods 38(1): 43-52. Abstract: A fluorometric method for the enzymatic determination of cholesterol content has been developed using a novel fluorogenic H2O2 probe, Amplex Red. This assay is performed in a 96-well microplate, and it is a one-step method amenable to automated procedures. Using commercially available cholesterol, our assay allows detection of 5 pmol (2 ng) cholesterol per well, which is 100-fold more sensitive than published fluorometric and colorimetric methods. When applied to the measurement of cholesterol levels in serum and food samples, the Amplex Red-based method has been found more attractive since the oxidation product of the Amplex Red method has superior long wavelength spectra which are less susceptible to interference from the biological compounds. |
| Fluvastatin reduces tissue factor expression and macrophage accumulation in carotid lesions of cholesterol-fed rabbits in the absence of lipid lowering Baetta, R., M. Camera, et al. (2002), Arterioscler Thromb Vasc Biol 22(4): 692-8. Abstract: The expression of tissue factor (TF), mainly by infiltrated inflammatory cells, has been shown to be responsible for the thrombogenicity associated with atheroma. The contribution of the nonlipid-related effects of statins to the clinical benefits of statin therapy is currently under intense investigation. In this study, we evaluated the ability of fluvastatin to modulate TF expression and macrophage accumulation in rabbit carotid intimal lesions independently of cholesterol lowering. Male rabbits were fed for 30 days a 1% cholesterol-rich diet with or without fluvastatin at 5 mg/kg per day. Two weeks from the start of treatment, a silastic collar was placed around the carotid artery. Fifteen days later, the animals were killed, and carotid segments were excised and processed. The atherogenic diet caused a consistent increase in plasma cholesterol levels (610+/-231 mg/dL versus 50+/-9 mg/dL at baseline), which were not affected by fluvastatin (603+/-248 mg/dL). In the rabbits fed a high cholesterol diet without fluvastatin, an intimal lesion with macrophage accumulation and TF expression was detected. Fluvastatin significantly reduced TF and macrophage content of the lesion (-50% for both). Results indicate that fluvastatin may attenuate the inflammatory and thrombogenic potential of atherosclerotic lesions through a mechanism(s) other than cholesterol reduction, providing new insight regarding the complex mode of action of statins. |
| Fluvastatin: effects beyond cholesterol lowering Corsini, A. (2000), J Cardiovasc Pharmacol Ther 5(3): 161-75. Abstract: Coronary heart disease (CHD) remains a major therapeutic challenge in the Western world, and strategies aimed at cholesterol lowering form the mainstay of treatment. Fluvastatin is an established 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor ("statin") for the treatment of hypercholesterolemia. Its efficacy and safety have been established in numerous clinical trials. Emerging evidence now indicates that treatment with fluvastatin slows the progression of atherosclerotic CHD and reduces the incidence of cardiovascular morbimortality in the secondary prevention setting. This effect of fluvastatin cannot be explained by cholesterol lowering alone; nonlipid-related mechanisms (so-called "pleiotropic effects") undoubtedly contribute to a certain extent, and are probably linked to modulation of the mevalonate pathway. This review discusses the experimental evidence regarding the antiatherosclerotic and antithrombotic effects of fluvastatin that may contribute to its beneficial action on disease progression and clinical events. Such effects include decreased expression of adhesion molecules in monocytes and leucocyte-endothelium adherence responses, immunomodulation, prevention of low-density lipoprotein oxidation, inhibition of cholesterol esterification and accumulation, along with effects on smooth muscle cell proliferation and migration. Pleiotropic actions aimed at plaque stabilization (eg, decreased secretion of matrix metalloproteinases by macrophages), together with effects on platelet activity, tissue factor expression, and endothelial function, may contribute to an antithrombotic effect of fluvastatin. Taken together, the results of these studies indicate that the effects of fluvastatin, at therapeutic doses, may extend beyond cholesterol lowering. |
| Foam cell formation containing lipid droplets enriched with free cholesterol by hyperlipidemic serum Mori, M., H. Itabe, et al. (2001), J Lipid Res 42(11): 1771-81. Abstract: A monoclonal antibody, ASH1a/256C (256C), which binds to atherosclerotic lesions in Watanabe heritable hyperlipidemic rabbit (WHHL) aorta in vivo, recognizes complex structures of phosphatidylcholine mixed with neutral lipids. In the present study, a cell culture system is described in which foam cells express 256C-positive lipid droplets. J774.1 macrophages were incubated in the presence of a small volume of WHHL serum for 24 h to produce foam cells, which were then incubated without the WHHL serum for 3 days. Oil red O-positive lipid droplets appeared on day 1, and were present in the cells during the whole incubation period. The lipid droplets in the cells were positively immunostained with antibody 256C on day 4, although they were negative on day 1. Expression of the antigenic lipid droplets was also induced by the addition of acetylated LDL or sera from patients with hyperlipidemia. When foam cells were induced by the addition of WHHL serum, cellular content of cholesteryl ester was greatly increased but then decreased to near basal levels by day 4. Concomitantly, cellular free cholesterol increased during the culture period, indicating that the cholesteryl ester changes to free cholesterol by day 4. The lipid droplets in the foam cells on day 4 were positively stained with filipin, a fluorescent probe for free cholesterol, as well as with 256C antibody, indicating that free cholesterol is enriched in antigenic lipid droplets. These observations suggest that hydrolysis and rearrangement of cellular cholesterol take place in foam cells to form complex structures of phosphatidylcholine and free cholesterol in lipid droplets. |
| Focal increases in vascular cell adhesion molecule-1 and intimal macrophages at atherosclerosis-susceptible sites in the rabbit aorta after short-term cholesterol feeding Truskey, G. A., R. A. Herrmann, et al. (1999), Arterioscler Thromb Vasc Biol 19(2): 393-401. Abstract: We tested the hypotheses that vascular cell adhesion molecule-1 (VCAM-1) expression on endothelium at lesion-prone sites in the rabbit aorta correlates with exposure to plasma cholesterol and that macrophage accumulation is associated with endothelial cells expressing VCAM-1. After rabbits were fed 0.25% cholesterol for 2 weeks, VCAM-1 expression was selectively increased at the distal and lateral portions of the major abdominal branches. In the arch and the celiac, superior mesenteric, and renal artery branches, VCAM-1 expression was positively correlated with the plasma cholesterol integrated over the duration of the experiments. After 2 weeks of cholesterol feeding, more macrophages were present around distal and lateral portions of the intercostal arteries and major abdominal branches relative to nonbranch regions. In the arch and around the intercostals and major abdominal branches, macrophage densities were positively correlated with the integrated plasma cholesterol. VCAM-1 and macrophage levels were correlated in lesion-prone regions. In normocholesterolemic rabbits, 23+/-4% (mean+/-SEM) of the macrophages were directly associated with VCAM-1-positive endothelium. After 2 weeks of 0.25% cholesterol feeding, the association increased to 37+/-4% (P<0.015). Associations were highest around the lateral and distal regions of the major abdominal branches. These results suggest that (1) VCAM-1 expression and intimal macrophage densities are influenced by plasma cholesterol and regional factors such as arterial fluid dynamics and (2) VCAM-1 plays a significant role in the localization of macrophages. |
| Food products containing free tall oil-based phytosterols and oat beta-glucan lower serum total and LDL cholesterol in hypercholesterolemic adults Maki, K. C., F. Shinnick, et al. (2003), J Nutr 133(3): 808-13. Abstract: This randomized, double-blind, controlled trial evaluated the influence of low fat, low saturated fat food products that contained free tall oil-based phytosterols (TOP) and oat beta-glucan (from whole oats and bran concentrate) on serum lipid concentrations in adults with mild-to-moderate hypercholesterolemia. After a 5-wk National Cholesterol Education Program Step I diet lead-in period, 112 subjects incorporated one of two treatments into their diets for 6 wk: food products (cereal, snack bar and beverage) that provided 1.8 g TOP and 2.8 g beta-glucan/d and contained < or =3.0 g total fat and < or =1.0 g saturated fat (TOP/beta-glucan treatment) or similar control foods. The serum LDL cholesterol response from baseline to the end of study was significantly larger in the TOP/beta-glucan treated group than in the control group, in which there was no change (-3.7 vs. 0.4%; P = 0.013). Likewise, total cholesterol decreased in the TOP/beta-glucan treatment group and did not change significantly in the controls (-2.3 vs. 0.8%; P = 0.043). Serum HDL cholesterol and triglyceride responses did not differ between the groups. The results of this trial suggest that consumption of a group of low fat, TOP and beta-glucan- containing foods is a useful adjunct in the dietary management of hypercholesterolemia. |
| Food sources of energy, macronutrients, cholesterol, and fiber in diets of women Krebs-Smith, S. M., F. J. Cronin, et al. (1992), J Am Diet Assoc 92(2): 168-74. Abstract: Data from the 1985 Continuing Survey of Food Intakes by individuals were used to calculate the contributions of individual foods to women's intakes of energy, protein, carbohydrate, fat, saturated fatty acids, cholesterol, and fiber. We separated nearly all food mixtures into their constituent ingredients, grouped the ingredients together with similar foods, and examined the contributions of those foods. Yeast breads that were neither whole grain nor higher fiber contributed about 7% of the energy to the diets, which made them the leading source of energy of the foods we examined. The leading sources of protein were animal products: poultry contributed approximately 12%, beef contributed about 19%, cheese contributed about 8%, and pork contributed about 6%. The various fats and oils were the greatest contributors to fat, and cheese was the chief source of saturated fatty acids. Eggs were the major source of cholesterol; they provided around 36% of the total. Two of the top three sources of carbohydrate--regular soft drinks and sugar--are composed entirely of simple sugars. Potatoes provided around 11% of the fiber, which made them the leading source of fiber. This article shows that the relative ranking of foods and the contribution of each food depend on the way food codes are combined. Therefore, citing one food as the major source of a particular food component without including documentation of how foods are combined can be misleading. |
| Foods contributing to absolute intake and variance in intake of fat, fatty acids and cholesterol in middle-aged Japanese Tokudome, Y., N. Imaeda, et al. (1999), J Epidemiol 9(2): 78-90. Abstract: On the basis of 351 one-day weighed diet records, we selected foods/recipes contributing to nutrients of interest for a data-based food frequency questionnaire by contribution analysis and multiple regression analysis. Total fat was largely of animal and vegetable origin, irrespective of analytic methods. Saturated fatty acid was mostly from animal and vegetable sources according to contribution analysis, and that of animal origin was the main contributor by multiple regression analysis. Mono-unsaturated fatty acid was substantially supplied by animal and vegetable products by either analytic method. Poly-unsaturated fatty acid, n-6 poly-unsaturated fatty acid and linoleic acid were found to be of vegetable origin and chicken egg according to contribution analysis; while vegetable oil and mayonnaise were the major contributors to variance in intake. Arachidonic acid was, however, mostly provided by animal sources including chicken egg and fish, irrespective of analytic methods. N-3 poly-unsaturated fatty acids and alpha-linolenic acid were of vegetable and marine origin. Eicosapentaenoic and docosahexaenoic acids were particularly from marine products, irrespective of analytic methods, except for chicken egg in docosahexaenoic acid by contribution analysis. Cholesterol was of animal and marine origin by either analytic method. Thus, foods contributing to absolute intake and variance in intake of fat, fatty acids and cholesterol differed considerably. |
| Formation and functioning of fused cholesterol side-chain cleavage enzymes Nazarov, P. A., V. L. Drutsa, et al. (2003), DNA Cell Biol 22(4): 243-52. Abstract: We studied the properties of various fused combinations of the components of the mitochondrial cholesterol side-chain cleavage system including cytochrome P450scc, adrenodoxin (Adx), and adrenodoxin reductase (AdR). When recombinant DNAs encoding these constructs were expressed in Escherichia coli, both cholesterol side-chain cleavage activity and sensitivity to intracellular proteolysis of the three-component fusions depended on the species of origin and the arrangement of the constituents. To understand the assembly of the catalytic domains in the fused molecules, we analyzed the catalytic properties of three two-component fusions: P450scc-Adx, Adx-P450scc, and AdR-Adx. We examined the ability of each fusion to carry out the side-chain cleavage reaction in the presence of the corresponding missing component of the whole system and examined the dependence of this reaction on the presence of exogenously added individual components of the double fusions. This analysis indicated that the active centers in the double fusions are either unable to interact or are misfolded; in some cases they were inaccessible to exogenous partners. Our data suggest that when fusion proteins containing P450scc, Adx, and AdR undergo protein folding, the corresponding catalytic domains are not formed independently of each other. Thus, the correct folding and catalytic activity of each domain is determined interactively and not independently. |
| Formation of biologically active oxysterols during ozonolysis of cholesterol present in lung surfactant Pulfer, M. K. and R. C. Murphy (2004), J Biol Chem 279(25): 26331-8. Abstract: Exposure of the lung to concentrations of ozone found in ambient air is known to cause toxicity to the epithelial cells of the lung. Because of the chemical reactivity of ozone, it likely reacts with target molecules in pulmonary surfactant, a lipid-rich material that lines the epithelial cells in the airways. Phospholipids containing unsaturated fatty acyl groups and cholesterol would be susceptible to attack by ozone, which may lead to the formation of cytotoxic products. Whereas free radicalderived oxidized cholesterol products have been frequently studied for their cytotoxic effects, ozonized cholesterol products have not been studied, although they could reasonably play a role in the toxicity of ozone. The reaction of ozone with cholesterol yielded a complex series of products including 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al, 5-hydroperoxy-B-homo-6-oxa-cholestan-3beta,7a-diol, and 5beta,6beta-epoxycholesterol. Mass spectrometry and radioactive monitoring were used to identify the major cholesterol-derived product during the reaction of 2 ppm ozone in surfactant as 5beta,6beta-epoxycholesterol, which is only a minor product during ozonolysis of cholesterol in solution. A dose-dependent formation of 5beta,6beta-epoxycholesterol was also seen during direct exposure of intact cultured human bronchial epithelial cells (16-HBE) to ozone. Studies of the metabolism of this epoxide in lung epithelial cells yielded small amounts of the expected metabolite, cholestan-3beta,5alpha,6beta-triol, and more abundant levels of an unexpected metabolite, cholestan-6-oxo-3beta,5alpha-diol. Both 5beta,6beta-epoxycholesterol and cholestan-6-oxo-3beta,5alpha-diol were shown to be cytotoxic to cultured 16-HBE cells. A possible mechanism for cytotoxicity is the ability of these oxysterols to inhibit isoprenoid-based cholesterol biosynthesis in these cells. |
| Formation of biologically active substances during cholesterol oxidation on the surface of fluorocarbon emulsions Berezov, A. T., A. S. Ivanov, et al. (1990), Biull Eksp Biol Med 110(9): 285-6. Abstract: Oxidative modification of cholesterol on the surface of fluorocarbon emulsions was studied. The oxidation yielded one primary product--7-peroxycholesterol. It was shown that the obtained cholesterol C7 derivatives possess a high biological activity. It was concluded that the possibility of oxidative modification of plasma substances on the surface of fluorocarbon emulsion particles with the formation of highly active compounds must be taken into account when using the fluorocarbon particles in medicine. |
| Formation of cholesterol monohydrate crystals in macrophage-derived foam cells Tangirala, R. K., W. G. Jerome, et al. (1994), J Lipid Res 35(1): 93-104. Abstract: In a previous study using the J774 macrophage foam cells, we quantitated the accumulation of unesterified (free) cholesterol derived from cholesteryl ester hydrolysis in lysosomes, after phagocytic uptake of cholesteryl ester droplets. In the present study, we examined whether the accumulation of free cholesterol in lysosomes leads to the formation of cholesterol monohydrate crystals by analyzing the lipid composition of low density lysosome fractions isolated from cholesteryl ester-loaded macrophages after a 24-h incubation. Phase diagrams of the constituent lipids in the lipid-filled lysosomes predicted the formation of cholesterol monohydrate crystals. The formation of cholesterol monohydrate crystals was observed in cholesteryl ester-loaded macrophages after a 48-h incubation by polarizing light microscopy. The crystals had a density of 1.04 g/ml and the morphology of cholesterol monohydrate crystals with an acute edge angle of about 80 degrees. The crystals appeared as needles as well as plates and melted only when heated to greater than 85 degrees C. The physical properties of these crystals are characteristic of cholesterol monohydrate. In our studies, crystal formation was observed even when cells had active acyl-CoA:cholesterol acyltransferase or when cholesterol efflux was stimulated. Electron microscopy and acid phosphatase cytochemistry of lysosomes in cholesteryl ester-loaded cells confirmed that cholesterol crystal formation occurred within lipid-loaded lysosomes. Time-lapse video microscopic studies revealed that most of the cells containing cholesterol monohydrate crystals not only remain viable but also have the capacity to translocate single crystals within cells. The data demonstrate that lysosomal accumulation of free cholesterol in macrophages after phagocytic uptake and hydrolysis of cholesteryl ester droplets leads to the formation of cholesterol monohydrate crystals within lipid-filled lysosomes. Such a process may lead to deposition of free cholesterol and cholesterol monohydrate crystals in macrophage foam cells during the progression of atherosclerosis. |
| Formation of cholesterol oxides in irradiated raw and cooked chicken meat during storage Lee, J. I., S. Kang, et al. (2001), Poult Sci 80(1): 105-8. Abstract: The objective of this study was to determine the effect of electron-beam irradiation on the oxidation of cholesterol in raw and cooked chicken meats with different packaging and storage times. Patties were prepared with skinless chicken breasts and legs. Half of the patties were used for raw meat study and the other half for cooked meat work. For cooked samples, patties were cooked in an electric oven to an internal temperature of 70 C. Raw and cooked meat patties were either aerobically or vacuum-packaged before irradiation. Irradiated patties were stored at 4 C up to 2 wk, and the amounts of cholesterol oxides in the patties were analyzed at 0, 7, and 14 d of storage. In raw chicken meat with vacuum packaging, 7beta-hydroxycholesterol and beta-epoxide were the only two cholesterol oxides present in significant amounts. In raw chicken meat with aerobic packaging, 7alpha-hydroxycholesterol and 7-keiocholesterol, which were not detected in vacuum-packaged raw chicken meat, were found. 7beta-Hydroxycholesterol in raw chicken meat was increased by irradiation and storage time, regardless of packaging. The kinds of cholesterol oxides found in cooked meat were basically the same as those found in raw chicken, but the levels in cooked meats at all storage time were higher than those of the raw meats. With vacuum packaging, irradiation had no consistent effect on the amount of beta-epoxide, 7alpha-hydroxycholesterol, or 7-ketocholesterol, but storage significantly influenced the amount of 7-ketocholesterol, 7beta-hydroxycholesterol, and total cholesterol oxides in cooked chicken meat. With aerobic packaging, irradiation significantly increased the formation of 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, and 7-ketocholesterol in cooked meat stored for 0 and 7 d. After 14 d of storage, however, irradiation had minor effects on the formation of cholesterol oxides in aerobically packaged cooked chicken. |
| Formation of ecdysteroids by Y-organs of the crab, Menippe mercenaria. II. Incorporation of cholesterol into 7-dehydrocholesterol and secretion products in vitro Rudolph, P. H. and E. Spaziani (1992), Gen Comp Endocrinol 88(2): 235-42. Abstract: The conversion in vitro of cholesterol (Ch) to nonpolar metabolites and ecdysteroids was studied in Y-organs of the xanthid crab, Menippe mercenaria. In one set of experiments, Y-organs were prelabeled in vivo by injecting crabs with 100 microCi of 3HCh, and halved glands were then incubated for 24 and 48 hr in the presence of unlabeled Ch. In another set, unlabeled Y-organs were incubated in standard medium containing 10 microCi/ml of 3HCh. Both polar and nonpolar metabolites were surveyed by HPLC. The early metabolite, 7-dehydrocholesterol (7-dhCh), was the only labeled derivative of Ch detectable in Y-organ tissue after incubation; preincubation amounts of 7-dhCh were higher in glands from de-eyestalked crabs vs glands from intact crabs, and labeling was an order of magnitude higher in glands incubated with labeled Ch vs those prelabeled in vivo. Specific activity calculations indicate highly efficient conversion of 7-dhCh to ecdysteroid secretions. Analyses of the incubation media revealed two polar secretory products, synthesized from Ch in vitro. These coeluted with the authentic standards, 3-dehydroecdysone and 25-deoxyecdysone. Secretion of 3-dehydroecdysone always exceeded that of 25-deoxyecdysone (ratio range, 1.9 to 14.4), in both de-eyestalked and intact crabs. |
| Formation of novel C21-bile acids from cholesterol in the rat. Structure identification of the major Di- and trihydroxylated species Lund, E., K. M. Boberg, et al. (1991), J Biol Chem 266(8): 4929-37. Abstract: We recently showed that previously unknown di- and trihydroxylated C21-bile acids are major degradation products of sitosterol and campesterol in bile-fistulated female Wistar rats. Using a mixture of 4-14C- and 22-3H-labeled cholesterol it was shown that such C21-bile acids are formed also from cholesterol in amounts up to about 25% of the total formation of bile acids. The C21-bile acids were formed from labeled cholesterol also in perfused rat liver, demonstrating that the liver is the site of synthesis. The major trihydroxylated C21-bile acids in bile were identified, by means of mass spectrometry, NMR, stereospecific dehydrogenases, and reagents, as 5 beta-pregnan-3 alpha, 11 beta, 15 beta-triol-21-oic acid and 5 beta-pregnan-3 alpha, 11 beta, 15 alpha-triol-21-oic acid. The corresponding 11-oxo-isomers were also present. A minor trihydroxylated C21-bile acid was identified as 5 beta-pregnan-3 alpha, 11 beta, 16-triol-21-oic acid. The major dihydroxylated C21-bile acid was identified by the same means as 5 alpha-pregnan-3 alpha, 12 alpha-diol-21-oic acid. Male rats converted 4-14C-cholesterol into C21-bile acids less efficiently than did female rats. None of the C21-bile acids from male rats contained a 15-hydroxyl group. It is speculated that the novel C21-bile acids are formed both from cholesterol and from plant sterols by an initial hydroxylation at C21 followed by peroxisomal or mitochondrial beta-oxidation. The presence of a hydroxyl group at C15 may facilitate this reaction. The above formation of C21-bile acids shows that mammalian liver is able to degrade the side chain of cholesterol beyond the C24 stage, even in the absence of a blocking group at C24. C21-bile acids, or one of their precursors, are hydroxylated in the liver by a hitherto unknown 11 beta-hydroxylase. The possible physiological importance of the C21-bile acids is discussed. |
| Formation of oxysterols from different pools of cholesterol as studied by stable isotope technique: cerebral origin of most circulating 24S-hydroxycholesterol in rats, but not in mice Meaney, S., D. Lutjohann, et al. (2000), Biochim Biophys Acta 1486(2-3): 293-8. Abstract: In order to study the origin of different oxysterols in the circulation, in particular 24S-hydroxycholesterol, different pools of cholesterol in rat and mouse were labelled by feeding the animals with a diet supplemented with 0.3 or 0.5% hexadeuterium-labelled cholesterol, respectively, for 10 days. The incorporation of deuterium label in cholesterol and different oxysterols was measured by combined gas chromatography-mass spectrometry in selected tissues and in the circulation. In both rat and mouse, a high incorporation of label was found in cholesterol present in serum and liver (up to 77%). Incorporation of label was similar in 7 alpha- and 7 beta-hydroxycholesterol of the same origin. There was no significant incorporation of deuterium in brain cholesterol, and little or no incorporation in the brain oxysterols investigated, in both animals. In the testis, the incorporation of the deuterium label in cholesterol was less than half of that in the liver, with similarly reduced labelling of the testicular oxysterols. 24S-Hydroxycholesterol in the circulation contained a deuterium content that was about 50% of that of serum and liver cholesterol in the mouse experiment and about 30% in the rat experiment. Thus, about 50% of circulating 24S-hydroxycholesterol in the mouse and about 70% of this fraction in the rat must originate from pools of cholesterol that are not in equilibrium with plasma and liver cholesterol. The liver is probably responsible for a considerable part of the extracerebral formation of 24S-hydroxycholesterol, since this organ contained detectable amounts of 24S-hydroxycholesterol with a relatively high incorporation of deuterium in both animal species. The results are consistent with a cerebral origin of more than half of the 24S-hydroxycholesterol in the circulation of rats, but not in mice. |
| Formation of pregnenolone- and dehydroepiandrosterone-fatty acid esters by lecithin-cholesterol acyltransferase in human plasma high density lipoproteins Lavallee, B., P. R. Provost, et al. (1996), Biochim Biophys Acta 1299(3): 306-12. Abstract: Pregnenolone- (PREG-), and dehydroepiandrosterone- (DHEA-) fatty acid esters (FA) are present in human plasma, where they are associated with lipoproteins. Because plasma has the ability to form PREG-FA and DHEA-FA in vitro from their unconjugated steroid counterparts, we postulated that the LCAT enzyme might be responsible for their formation. Here we show that lecithin-cholesterol acyltransferase (LCAT) has PREG and DHEA esterifying activities. First, VLDL, IDL, LDL, and HDL were isolated by the sequential ultracentrifugation micromethod from the plasma of fasting men and women and tested for their ability to form PREG-FA, DHEA-FA, and cholesteryl esters in vitro from their respective unconjugated counterparts. The results showed that the three steroids were esterified only in HDL subfractions. The rate of tritiated PREG esterification was clearly higher than that of tritiated cholesterol and DHEA, both in total plasma and isolated HDL, and no gender difference was observed. Second, human and guinea pig LCAT were purified and used in phosphatidylcholine-reconstituted vesicles containing human apoAI to show their ability to esterify tritiated cholesterol, PREG, and DHEA in the absence of unlabeled steroid. The amount of cholesteryl ester, PREG-FA, and DHEA-FA increased after incubation as a function of time and amount of purified LCAT, showing that PREG is preferentially acylated by LCAT compared to cholesterol and DHEA. The PREG and DHEA esterifying activities of LCAT were cofactor-dependent, as shown by the absence of acylation without apoAI. Finally, we determined by HPLC the fatty acid moiety of PREG-FA and DHEA-FA formed in human plasma and guinea pig and rat sera in vitro after incubation with unconjugated tritiated PREG and DHEA. We showed that the fatty acid moieties of newly formed tritiated PREG-FA and DHEA-FA were similar to that reported for cholesteryl esters in the plasma of the three species. We conclude that LCAT has a lecithin-steroid acyltransferase activity and that PREG is probably the preferential substrate of this enzyme. In addition, the fact that the differences in the fatty acid moieties of cholesteryl esters of human, guinea pig, and rat plasmas are also observed for PREG-FA and DHEA-FA suggests that the LCAT is the sole circulating enzyme that has PREG and DHEA esterifying activities. |
| Formation of progesterone and 1-dehydroprogesterone from cholesterol in fermentation cultures of Mycobacterium aurum Horhold, C. and K. H. Bohme (1990), J Steroid Biochem 36(1-2): 181-3. Abstract: The formation of progesterone and 1-dehydroprogesterone from cholesterol in fermentation cultures of Mycobacterium aurum ATCC 25790 was studied with the aim of clarifying the microbial pathway. The C22-intermediate (20S)-20-carboxy-1,4-pregnadien-3-one was microbiologically converted via the undetectable corresponding aldehyde into the C22-alcohol. However in the fermentation broth without microorganisms, but containing 2,2'-bipyridyl and copper ions, synthetically prepared C22-aldehyde was oxidized to the corresponding C21-compound 1-dehydroprogesterone, suggesting that the enzymatically originated C22-aldehydes may be immediately chemically oxidized to the corresponding C21-ketones. |