26-Hydroxycholesterol: synthesis, metabolism, and biologic activities

Effects of replacing fishmeal with different proportions of mixed protein source in the diet of largemouth bass (Micropterus salmoides)

Fishmeal is an important protein source for largemouth bass (Micropterus salmoides). However, the production of fishmeal is decreasing each year and the price of fishmeal is rising. Therefore, it is necessary to find new high-quality and suitable protein sources. This study used a mixed animal protein source (chicken meal:blood meal:shrimp meal:brewer's yeast = 50:12.5:25:12.5) to replace fishmeal. Using a 48 % fishmeal group as the control, five diets with different fishmeal levels (FM48, FM44, FM40, FM36, FM32) were established to determine the effects on largemouth bass growth performance, liver health and intestinal health. There were no significant differences in the percentage weight gain, specific growth rate, feed conversion rate, and condition factor of largemouth bass, but the hepatosomatic and viscerosomatic indexes were significantly decreased when the dietary fishmeal level was reduced to 40 %. The content of taurine, glycine, and histidine was significantly reduced in the muscle of largemouth bass fed the FM32 diet compared with those fed the FM48 and FM44 diets. Mixed protein feed reduced the total bile acid content and increased the low-density lipoprotein cholesterol content in the plasma of largemouth bass. The replacement of fishmeal with the mixed protein source inhibited the expression of tnf-α and caspase 3 and enhanced the expression of apoa1 in the liver, as well as enhancing the protein expression of FXR and SREBP and inhibiting the protein expression of P-PPARA in the liver. The intestinal pparα expression was suppressed when dietary fishmeal was replaced. When dietary fishmeal decreased, the mucosal folds height and muscle layer thickness also decreased. In conclusion, partial replacement of fishmeal with the mixed protein source did not affect the growth performance, while lipid metabolism and intestinal health were negatively affected when dietary fishmeal levels were below 36 %.

A mixed animal and plant protein source replacing fishmeal affects bile acid metabolism and apoptosis in largemouth bass (Micropterus salmoides)

Chicken meal, shrimp meal, blood meal, and soybean protein concentrate are common alternatives to fishmeal. This study used them to prepare three diets with different levels of fishmeal (FM48, FM40, and FM32) for largemouth bass (Micropterus salmoides). The results found no significant difference in the growth performance of largemouth bass fed different diets. Mixed protein increased the total cholesterol (T-CHO) content in plasma, and reduced the total superoxide dismutase (T-SOD) activity in plasma and liver. Targeted metabolomics analysis found that the low fishmeal diets affected the cholesterol and bile acid metabolism of largemouth bass. Mixed protein inhibited cyp7a1 and enhanced hmgcr and pparγ mRNA levels, as well as enhanced the expression levels of FXR in the liver. The fish-fed FM32 diet showed inhibited fxr, rxrα, and cyp7a1 mRNA levels in the intestine. The results of TUNEL fluorescence staining showed that mixed protein induced apoptosis in largemouth bass. The caspase 3 and caspase 9 mRNA levels in the fish-fed FM40 and FM32 diet significantly increased, as well as the expression levels of CASPASE 3. The experiment also found that it could induce oxidative stress and endoplasmic reticulum stress. In conclusion, the replacement of fishmeal with mixed animal and plant protein diets did not affect the growth performance, but the health and bile acid metabolism of largemouth bass was affected when the fishmeal level was reduced to 32%.

Analysis of bioactive compounds present in different crude extracts of Benincasa hispida and Cucurbita moschata seeds by gas chromatography-mass spectrometry

Plant seeds are the resources of many different bioactive components. The chemical composition of the different crude extracts from Benincasa hispida (White pumpkin) and Cucurbita moschata (Pumpkin) seeds with three different polarity-based solvents (n-hexane, n-hexane-chloroform (2:1), and methanol) was analyzed to identify the biologically active compounds. Each of the extracts was analyzed by gas chromatography-mass spectrometry. Different extracts of targeted seeds showed different biologically active compounds that have different pharmacological potentialities. 9, 12-Octadecadienoic acid (ZZ) was the most potent bioactive compound present in three different extracts of both B. hispida and C. moschata. Another bioactive compound comparatively low percentage present in both plants was n-hexadecanoic acid. Other major pharmacologically active compounds present in both plants were 9- Octadecenoic acid (Z)-, methyl ester, and 9, 12-Octadecadienoic acid methyl ester (E, E). Besides these compounds, a few more biologically active compounds were present in the two plants separately. The findings of this study support the use of these seeds in modern functional foods, nutraceuticals, and medicinal purposes, and the whole seeds would give better health benefits rather than use any extract. Although further pharmacological examinations should be carried out to conclude the medicinal application of the seeds of these two plants as well as to understand the mechanism of the potential health benefits.

Impact of Oxysterols on Cell Death, Proliferation, and Differentiation Induction: Current Status

Oxysterols are oxidized derivatives of cholesterol produced by enzymatic activity or non-enzymatic pathways (auto-oxidation). The oxidation processes lead to the synthesis of about 60 different oxysterols. Several oxysterols have physiological, pathophysiological, and pharmacological activities. The effects of oxysterols on cell death processes, especially apoptosis, autophagy, necrosis, and oxiapoptophagy, as well as their action on cell proliferation, are reviewed here. These effects, also observed in several cancer cell lines, could potentially be useful in cancer treatment. The effects of oxysterols on cell differentiation are also described. Among them, the properties of stimulating the osteogenic differentiation of mesenchymal stem cells while inhibiting adipogenic differentiation may be useful in regenerative medicine.

Estimation of drug-likeness properties of GC-MS separated bioactive compounds in rare medicinal Pleione maculata using molecular docking technique and SwissADME in silico tools

The main aim of the paper was to determine bioactive compounds in Pleione maculata extracts using gas chromatographic technique and to investigate their drug-likeness potential using molecular docking algorithm and ADME studies on the recent intractable disease, for example, SARS-CoV-2. Pleione maculata sample was prepared for GC–MS analysis. The peak components were identified based on the NIST Library. Molecular docking was performed using PatchDock, and energy refinement was carried out using the FireDock algorithm followed by drug-likeness analysis using the SwissADME tool. The mass spectrum revealed various pharmacologically important compounds and novel compounds 8-oxatetracyclo{5.2.1.1(2,6). 1(4,10)}dodecane, 7-tert-butyl-1,9,9-trimeth, docosane, 2,4-dimethyl, kryptogenin 2,4-dinitrophenyl hydrazine, and N-decyl-alpha,D-2-deoxyglycoside which are reported for the first time. Molecular docking using PatchDock illustrates GC–MS compounds Nor-diazepam,3-{N-hydroxymethyl}aminocarbonyloxy a good docking and high binding affinity with atomic contact energy -10.95 kcal/mol against SARS-CoV-2 spike protein S2 subunit. ADME analysis predicts Nor-diazepam,3-{N-hydroxymethyl}aminocarbonyloxy and andrographolide showed very high drug-likeness parameters with no metabolism disturbances. The random control antiviral drug arabidiol revealed a lower binding affinity and lower solubility compared to bioactive compounds of P. maculata. The study depicts the first and novel report on various pharmaceutical important GC–MS bioactive compounds and molecular docking study on Pleione maculata having potential against various intractable diseases.

The Liver under the Spotlight: Bile Acids and Oxysterols as Pivotal Actors Controlling Metabolism

Among the myriad of molecules produced by the liver, both bile acids and their precursors, the oxysterols are becoming pivotal bioactive lipids which have been underestimated for a long time. Their actions are ranging from regulation of energy homeostasis (i.e., glucose and lipid metabolism) to inflammation and immunity, thereby opening the avenue to new treatments to tackle metabolic disorders associated with obesity (e.g., type 2 diabetes and hepatic steatosis) and inflammatory diseases. Here, we review the biosynthesis of these endocrine factors including their interconnection with the gut microbiota and their impact on host homeostasis as well as their attractive potential for the development of therapeutic strategies for metabolic disorders.

Mitochondrial oxysterol biosynthetic pathway gives evidence for CYP7B1 as controller of regulatory oxysterols

The aim of this paper was to more completely study the mitochondrial CYP27A1 initiated acidic pathway of cholesterol metabolism. The mitochondrial CYP27A1 initiated pathway of cholesterol metabolism (acidic pathway) is known to synthesize two well-described vital regulators of cholesterol/lipid homeostasis, (25R)-26-hydroxycholesterol (26HC) and 25-hydroxycholesterol (25HC). Both 26HC and 25HC have been shown to be subsequently 7α-hydroxylated by Cyp7b1; reducing their regulatory abilities and furthering their metabolism to chenodeoxycholic acid (CDCA). Cholesterol delivery into the inner mitochondria membrane, where CYP27A1 is located, is considered the pathway's only rate-limiting step. To further explore the pathway, we increased cholesterol transport into mitochondrial CYP27A1 by selectively increased expression of the gene encoding the steroidogenic acute transport protein (StarD1). StarD1 overexpression led to an unanticipated marked down-regulation of oxysterol 7α-hydroxylase (Cyp7b1), a marked increase in 26HC, and the formation of a third vital regulatory oxysterol, 24(S)-hydroxycholesterol (24HC), in B6/129 mice livers. To explore the further metabolism of 24HC, as well as, 25HC and 26HC, characterizations of oxysterols and bile acids using three murine models (StarD1 overexpression, Cyp7b1^-/-, Cyp27a1^-/-) and human Hep G2 cells were conducted. This report describes the discovery of a new mitochondrial-initiated pathway of oxysterol/bile acid biosynthesis. Just as importantly, it provides evidence for CYP7B1 as a key regulator of three vital intracellular regulatory oxysterol levels.

Formation of the steroidal C-25 chiral center via the asymmetric alkylation methodology

A novel approach for the preparation of steroids containing a chiral center at C-25 is reported. The key stereochemistry inducing step was asymmetric alkylation of pseudoephenamine amides of steroidal C-26 acids. The reaction proceeded with high diastereoselectivity (dr > 99 : 1). The developed methodology was successfully applied to the synthesis of (25R)- and (25S)-cholestenoic acids as well as (25R)- and (25S)-26-hydroxy brassinolides.

Expression and roles of steroidogenic acute regulatory (StAR) protein in 'non-classical', extra-adrenal and extra-gonadal cells and tissues

The activity of the steroidogenic acute regulatory (StAR) protein is indispensable and rate limiting for high output synthesis of steroid hormones in the adrenal cortex and the gonads, known as the 'classical' steroidogenic organs (StAR is not expressed in the human placenta). In addition, studies of recent years have shown that StAR is also expressed in many tissues that produce steroid hormones for local use, potentially conferring some functional advantage by acting via intracrine, autocrine or paracrine fashion. Others hypothesized that StAR might also function in non-steroidogenic roles in specific tissues. This review highlights the evidence for the presence of StAR in 17 extra-adrenal and extra-gonadal organs, cell types and malignancies. Provided is the physiological context and the rationale for searching for the presence of StAR in such cells. Since in many of the tissues the overall level of StAR is relatively low, we also reviewed the methods used for StAR detection. The gathered information suggests that a comprehensive understanding of StAR activity in 'non-classical' tissues will require the use of experimental approaches that are able to analyze StAR presence at single-cell resolution.

C-26 vs. C-27 hydroxylation of insect steroid hormones: regioselectivity of a microsomal cytochrome P450 from a hormone-resistant cell line

Hydroxylation of steroids at one of the side chain terminal methyl groups, commonly linked to C-26, represents an important regulatory step established in many phyla. Discrimination between the two sites, C-26 and C-27, requires knowing the stereochemistry of the products. 26-Hydroxylation of the insect steroid hormone 20-hydroxyecdysone by a microsomal cytochrome P450 was previously found to be responsible for hormonal resistance in a Chironomus cell line mainly producing the (25S)-epimer of 20,26-dihydroxyecdysone. Here, we studied the 25-desoxy analog of 20-hydroxyecdysone, ponasterone A, to elucidate the stereochemistry of the expected 26-hydroxy product, inokosterone, which occurs as C-25 epimers in nature. We identified the predominant metabolite as the C-25 R epimer of inokosterone on comparison by RP-HPLC with the (25R)- and (25S)-epimers the stereochemistry of which was confirmed by X-ray crystallography. (25R)-inokosterone was further oxidized to the 26-aldehyde identified by mass spectroscopy, borohydride reduction and metabolic transformation to 26-carboxylic acid. The (25S)-epimers of inokosterone and its aldehyde were minor products. With 20-hydroxyecdysone as substrate, we newly identified the (25R)-epimer of 20,26-dihydroxyecdysone as a minor product. In conclusion, the present stereochemical studies revealed high regioselectivity of the Chironomus enzyme to hydroxylate both steroids at the same methyl group, denoted C-27.

Effectors of rapid homeostatic responses of endoplasmic reticulum cholesterol and 3-hydroxy-3-methylglutaryl-CoA reductase

The cholesterol content of the endoplasmic reticulum (ER) and the activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) imbedded therein respond homeostatically within minutes to changes in the level of plasma membrane cholesterol. We have now examined the roles of sterol regulatory element-binding protein (SREBP)-dependent gene expression, side chain oxysterol biosynthesis, and cholesterol precursors in the short term regulation of ER cholesterol levels and HMGR activity. We found that SREBP-dependent gene expression is not required for the response to changes in cell cholesterol of either the pool of ER cholesterol or the rate of cholesterol esterification. It was also found that the acute proteolytic inactivation of HMGR triggered by cholesterol loading required the conversion of cholesterol to 27-hydroxycholesterol. High levels of exogenous 24,25-dihydrolanosterol drove the inactivation of HMGR; lanosterol did not. However, purging endogenous 24,25-dihydrolanosterol, lanosterol, and other biosynthetic sterol intermediates by treating cells with NB-598 did not greatly affect either the setting of their ER cholesterol pool or the inactivation of their HMGR. In summary, neither SREBP-regulated genes nor 27-hydroxycholesterol is involved in setting the ER cholesterol pool. On the other hand, 27-hydroxycholesterol, rather than cholesterol itself or biosynthetic precursors of cholesterol, stimulates the rapid inactivation of HMGR in response to high levels of cholesterol.

Atherosclerosis: immune and inflammatory aspects

This review article discusses the historical origin of our continuously evolving model of the etiology of atherosclerotic cardiovascular disease. The basic molecular biologic concepts underlying the development of coronary artery disease and the dynamic connection between the immune system and arterial integrity are explored. Emphasis is placed on the role of inflammation as a driving force in the process of atherosclerosis and vascular endothelium as a modulating factor in the pathogenesis of coronary artery disease.

Cholesterol oxides: their occurrence and methods to prevent their generation in foods

Eight cholesterol oxides are commonly found in foods with high cholesterol content, such as meat, egg yolk and full fat dairy products. Factors known to increase the production of cholesterol oxides in foods are heat, light, radiation, oxygen, moisture, low pH, certain pro-oxidising agents and the storage of food at room temperature. Processes, such as pre-cooking, freeze-drying, dehydration and irradiation, have all been reported to result in increased production of cholesterol oxides in meats. As prepared consumer foods are becoming increasingly popular, the consumption of higher levels of cholesterol oxides in foods is inevitable. An understanding of the mechanisms involved in the generation of cholesterol oxides may assist in their reduction in foods and possibly reduce the impact of these compounds on human health.

Human sterol 27-hydroxylase (CYP27) overexpressor transgenic mouse model. Evidence against 27-hydroxycholesterol as a critical regulator of cholesterol homeostasis

CYP27-overexpressed transgenic mice were generated with the use of a human full-length CYP27 coding region cloned into a ubiquitous expression vector. Positive transgenic mice were identified by tail DNA genotyping and high fecal 27-hydroxycholesterol content. The levels of 27-hydroxycholesterol were found to be 3-5 times higher in the circulation and the tissues of the overexpressed mice when compared with littermate controls. There were no gross morphological differences between the overexpressed mice and their controls. Total cholesterol and triglyceride levels were not affected by overexpression of CYP27. Serum lathosterol was also normal, suggesting a normal rate of cholesterol synthesis. Serum levels of 7alpha-hydroxycholesterol were unaffected, suggesting a normal rate of bile acid formation in the pathway involving cholesterol 7alpha-hydroxylase. Biliary bile acid composition was slightly affected by CYP27 overexpression in female but not in male mice. Fecal levels of neutral steroids were slightly but significantly increased in overexpressor female mice but not in male mice. Levels of 24-hydroxycholesterol in the circulation were significantly reduced in the overexpressed mice, probably as a consequence of a recently described catabolic pathway involving CYP27. Combined with the results of our previous work on mice with a disruption of the CYP27 gene, the present results suggest that the levels of 27-hydroxycholesterol are not of critical importance for cholesterol homeostasis in mice.

Oxysterol profiles of normal human arteries, fatty streaks and advanced lesions

OBJECTIVE

Human atherosclerotic lesions of different stages have quantitative differences in cholesterol and oxysterol content, but information on the oxysterol profile in fatty streaks is limited. This study aims to provide more detailed oxysterol quantification in human fatty streaks, as well as normal aorta and advanced lesions.

METHODS

A newly adapted method was used, including oxysterol purification by means of a silica cartridge; and it was ensured that artifactual oxysterol formation was kept to a minimum. Cholesterol and oxysterols were estimated by GC and identification confirmed by GC-MS in samples of normal human arterial intima, intima with near-confluent fatty streaks and advanced lesions, in necropsy samples.

RESULTS

The oxysterols 7 alpha-hydroxycholesterol, cholesterol-5 beta, 6 beta-epoxide, cholesterol-5 alpha, 6 alpha-epoxide, 7 beta-hydroxycholesterol, 7-ketocholesterol and 27-hydroxycholesterol (formerly known as 26-hydroxycholesterol) were found in all the lesions, but were at most very low in the normal aorta, both when related to wet weight and when related to cholesterol. Most components of the normal artery showed some cross-correlation on linear regression analysis, but cross-correlations were weaker in the fatty streaks and advanced lesions. However, in fatty streak there was a marked positive correlation between 27-hydroxycholesterol and cholesterol.

CONCLUSION

The findings confirm that oxysterols are present in fatty streaks and advanced lesions and may arise from different cholesterol oxidation mechanisms, including free radical-mediated oxidation and enzymatic oxidation.

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.

Down-regulation of mammalian 3-hydroxy-3-methylglutaryl coenzyme A reductase activity with highly purified liposomal cholesterol

Chinese hamster ovary-215 cells (CHO-215) cannot synthesize C27 and C28 sterols because of a defect in the reaction that decarboxylates 4-carboxysterols [Plemenitas, A., Havel, C.M. & Watson, J.A. (1990) J. Biol. Chem. 265, 17012-17017]. Thus, CHO-215 cell growth is dependent on an exogenous metabolically functional source of cholesterol. We used CHO-215 cells to (a) determine whether highly purified (> 99.5%) cholesterol, in egg lecithin liposomes, could down-regulate derepressed 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and if so (b) determine whether the loss in reductase catalytic activity correlated kinetically with the synthesis and accumulation of detectable oxycholesterol derivatives. Liposomal cholesterol (26-39 microM) supported maximum CHO-215 growth and initiated suppression of HMG-CoA reductase activity at concentrations greater than 50 microM. Maximum suppression (50-60%) of reductase activity was achieved with 181.3 microM liposomal cholesterol in 6 h. Also, regulatory concentrations of highly purified liposomal [3H]cholesterol were not converted (biologically or chemically) to detectable levels of oxy[3H]cholesterol derivatives during 3-6 h incubations. Lastly, a broad-spectrum cytochrome P450 inhibitor (miconazole) had no effect on liposomal cholesterol-mediated suppression of HMG-CoA reductase activity. These observations established that (a) highly purified cholesterol, incorporated into egg lecithin liposomes, can signal the down-regulation of derepressed mammalian cell HMG-CoA reductase activity and (b) if oxycholesterol synthesis was required for liposomal cholesterol-mediated down-regulation, the products had to be more potent than 24-, 25-, or 26-/27-hydroxycholesterol.

Biochemical characterization of a truncated form of CYP27A purified from rabbit liver mitochondria

During purification of CYP27A from rabbit liver mitochondria, a cytochrome P450 of different molecular size was co-isolated. The latter enzyme has an apparent M(r) 51,000 which is slightly lower than that of CYP27A. The 51,000-M(r) protein was found to be present in mitochondria from liver, small intestine, kidney, and spleen but not in lung, testis, heart, or brain mitochondria. Determination of the N-terminal sequence revealed that the 51,000-M(r) protein is a truncated form of CYP27A lacking the first 12 residues. The truncated enzyme was less efficient than the full-length CYP27A in the 27-hydroxylation of C(27)-sterols and much less efficient in the 25-hydroxylation of 1alpha-hydroxyvitamin D(3). The K(m) values for cholesterol and 5beta-cholestane-3alpha,7alpha,12alpha-triol were about the same with both enzymes whereas the K(m) for 1alpha-hydroxyvitamin D(3) was much higher with the truncated CYP27A. The results strongly indicate that the 51,000-M(r) protein is formed via proteolytic processing of CYP27A by endogenous protease(s) in some of the tissues examined. The truncation at the N terminus markedly impairs the ability of CYP27A to use 1alpha-hydroxyvitamin D(3) as substrate and to catalyze 25-hydroxylation in the bioactivation of vitamin D(3).

Oxysterols in cap and core of human advanced atherosclerotic lesions

OBJECTIVE

Different parts of the advanced atherosclerotic lesion have characteristic differences in lipid content, but the distribution of lipid oxidation products has not been reported. This study provides novel data on oxysterol and hydroxyoctadecadienoic acids quantification in core versus cap. It compares the lipid composition of core and cap to assess the topographical distribution of evidence of lipid oxidation.

METHODS

Lipids and oxidised lipids were analysed by gas chromatography (GC) and GC-mass spectrometry (GC-MS) in samples of human atheromatous lipid core and fibrous cap of individual advanced atherosclerotic plaques (Stary, Type V) in necropsy samples.

RESULTS

The total lipid was of course massively greater in the core than in the cap. The oxidation products, cholest-5-en-3beta,26-diol (26-OH-CHOL) and cholest-5-en-3beta,7beta-diol (7beta-OH-CHOL) were detected in all the samples. 26-OH-CHOL was more abundant in the core than in the cap when related both to wet weight and to cholesterol. 7Beta-OH-CHOL levels were significantly higher in the core than in the cap when related to wet weight but not when related to cholesterol. Because the processing included a sodium borohydride reduction step, the 7beta-OH-CHOL detected could partly originate from 7-ketocholesterol or 7-hydroperoxycholesterol. Several isomeric hydroxyoctadecadienoic acids were detected in both core and cap, more in the cap when related to cholesterol content. Most of the components of the cap showed a high degree of cross-correlation on linear regression analysis, but cross-correlations were weaker for the core. The core samples contained a larger proportion of linoleate relative to oleate than the fibrous cap.

CONCLUSION

The findings suggest that the different lipid and oxidised lipid contents of cap and core may be due to variations in oxidative activity in different parts of the lesion.

Regulation of bile acid biosynthesis

This article provides a review of the pathways through which cholesterol is degraded to bile acids. Regulation of key enzymes in the bile acid biosynthestic pathways is discussed. The important role of these pathways in the maintenance of cholesterol homeostasis and the possible therapeutic implications for the treatment of hypercholesterolemia are emphasized.

Bile duct cells: a novel in vitro model for the study of lipid metabolism and bile acid production

Immortalized bile duct cells (BDC), derived from transgenic mice harboring the SV40 thermosensitive immortalizing mutant gene ts458, were utilized to investigate the role of the biliary epithelium in lipid and sterol metabolism. This cell model closely resembles the in vivo situation because it expresses the specific phenotypic marker cytokeratin 19 (CK-19), exhibits the formation of bile duct-like structures, and displays well-formed microvilli projected from the apical side to central lumen. The BDC were found to incorporate [14C]oleic acid (in nmol/mg protein) into triglycerides (121 +/- 6), phospholipids (PL; 59 +/- 3), and cholesteryl ester (16 +/- 1). The medium lipid content represented 5.90 +/- 0.16% (P < 0. 005) of the total intracellular production, indicating a limited lipid export capacity. Analysis of PL composition demonstrated the synthesis of all classes of polar lipids, with phosphatidylcholine and phosphatidylethanolamine accounting for 60 +/- 1 and 24 +/- 1%, respectively, of the total. Differences in PL distribution were apparent between cells and media. Substantial cholesterol synthesis was observed in BDC, as determined by the incorporation of [14C]acetate suggesting the presence of hydroxymethylglutaryl-CoA (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. With the use of [14C]acetate and [14C]cholesterol as precursors, both tauro- and glycoconjugates of bile acids were synthesized, indicating the presence of cholesterol 7alpha- and 26R-hydroxylases, the key enzymes involved in bile acid formation. The transport of bile acids was not limited, as shown by their marked accumulation in the medium (>6-fold of cell content). HMG-CoA reductase (53.0 +/- 6.7), cholesterol 7alpha-hydroxylase (15. 5 +/- 0.5), and acyl-CoA:cholesterol acyltransferase (ACAT; 201.7 +/- 10.2) activities (in pmol. min-1. mg protein-1) were present in the microsomal fractions. Our data show that biliary epithelial cells actively synthesize lipids and may directly contribute bile acids to the biliary fluid in vivo. This BDC line thus represents an efficient experimental tool to evaluate biliary epithelium sterol metabolism and to study biliary physiology.

Oxysterol regulation of steroidogenic acute regulatory protein gene expression. Structural specificity and transcriptional and posttranscriptional actions

Oxysterols exert a major influence over cellular cholesterol homeostasis. We examined the effects of oxysterols on the expression of steroidogenic acute regulatory protein (StAR), which increases the delivery of cholesterol to sterol-metabolizing P450s in the mitochondria. 22(R)-hydroxycholesterol (22(R)-OHC), 25-OHC, and 27-OHC each increased steroidogenic factor-1 (SF-1)-mediated StAR gene transactivation by approximately 2-fold in CV-1 cells. In contrast, cholesterol, progesterone, and the 27-OHC metabolites, 27-OHC-5beta-3-one and 7alpha,27-OHC, had no effect. Unlike our findings in CV-1 cells, SF-1-dependent StAR promoter activity was not augmented by 27-OHC in COS-1 cells, Y-1 cells, BeWo choriocarcinoma cells, Chinese hamster ovary (CHO) cells, and human granulosa cells. Studies examining the metabolism of 27-OHC indicated that CV-1 cells formed a single polar metabolite, 3beta-OH-5-cholestenoic acid from radiolabeled 27-OHC. However, this metabolite inhibited StAR promoter activity in CV-1, COS-1 and CHO cells. Because 7alpha,27-OHC was unable to increase SF-1-dependent StAR promoter activity, we examined 27-OHC 7alpha-hydroxylase in COS-1 and CHO cells. COS-1 cells contained high 7alpha-hydroxylase activity, whereas the enzyme was undetectable in CHO cells. The hypothesis that oxysterols act in CV-1 cells to increase StAR promoter activity by reducing nuclear levels of sterol regulatory element binding protein was tested. This notion was refuted when it was discovered that sterol regulatory element binding protein-1a is a potent activator of the StAR promoter in CV-1, COS-1, and human granulosa cells. Human granulosa and theca cells, which express endogenous SF-1, contained more than 5-fold more StAR protein following addition of 27-OHC, whereas StAR mRNA levels remained unchanged. We conclude that 1) there are cell-specific effects of oxysterols on SF-1-dependent transactivation; 2) the ability to increase transactivation is limited to certain oxysterols; 3) there are cell-specific pathways of oxysterol metabolism; and 4) oxysterols elevate StAR protein levels through posttranscriptional actions.

Cell-mediated oxidation of LDL: comparison of different cell types of the atherosclerotic lesion

The three major cell types of the human atherosclerotic lesion--macrophages (Mø), smooth muscle cells (SMC) and endothelial cells (EC)--were compared for their ability to oxidise low density lipoprotein (LDL) in vitro under identical conditions. Near-confluent cultures were incubated for up to 48 h with 50 microg protein/ml LDL in Ham's F10 medium supplemented with 7 microM Fe2+. All three cell types oxidised LDL readily using our culture conditions. After 24 and 48 h, the degree of LDL oxidation was in the order: Mø > SMC > EC when based on cell growth area and EC > SMC > Mo when based on cellular DNA content. However, LDL oxidation in vitro progressed more slowly between 24 and 48 h, probably due to increasing toxicity to the cells and/or depletion of polyunsaturated fatty acids. We therefore compared the time of onset of LDL oxidation. The earliest increase in LDL oxidation was always apparent with SMC. Gas chromatography revealed that LDL oxidation by all three cell types followed a similar pattern. The polyunsaturated fatty acids linoleic acid (18:2) and arachidonic acid (20:4) were depleted (to 10.3-18.1% and 4.5-24.7% respectively, compared to native LDL), whereas the content of stearic acid (18:0) and oleic acid (18:1) remained unchanged. Cholesterol was depleted (to 54.1-75.6% of native LDL) with a concomitant rise in 7 -hydroxycholesterol (to 60.6-128.1 microg/mg LDL). This corresponds to a conversion of 4.9, 9.5 and 10.4% of LDL cholesterol in EC-, SMC- and Mo-modified LDL respectively. All three cell types showed significant toxicity in the oxidising culture after 24h. The possible relevance to LDL oxidation in atherosclerosis is discussed.

Activities of recombinant human cytochrome P450c27 (CYP27) which produce intermediates of alternative bile acid biosynthetic pathways

The primary physiological significance of cytochrome P450c27 (CYP27) has been associated with its role in the degradation of the side chain of C27 steroids in the hepatic bile acid biosynthesis pathway, which begins with 7alpha-hydroxylation of cholesterol in liver. However, recognition that in humans P450c27 is a widely or ubiquitously expressed mitochondrial P450, and that there are alternative pathways of bile acid synthesis which begin with 27-hydroxylation of cholesterol catalyzed by P450c27, suggests the need to reevaluate the role of this enzyme and its catalytic properties. 27-Hydroxycholesterol was thought to be the only product formed upon reaction of P450c27 with cholesterol. However, the present study demonstrates that recombinant human P450c27 is also able to further oxidize 27-hydroxycholesterol giving first an aldehyde and then 3beta-hydroxy-5-cholestenoic acid. Kinetic data indicate that in a reconstituted system, after 27-hydroxycholesterol is formed from cholesterol, it is released from the P450 and then competes with cholesterol for reentry the enzyme active site for further oxidation. Under subsaturating substrate concentrations, the efficiencies of oxidation of 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenal to the acid by human P450c27 are greater than the efficiency of hydroxylation of cholesterol to 27-hydroxycholesterol indicating that the first hydroxylation step in the overall conversion of cholesterol into 3beta-hydroxy-5-cholestenoic acid is rate-limiting. Interestingly, 3beta-hydroxy-5-cholestenoic acid was found to be further metabolized by the recombinant human P450c27, giving two monohydroxylated products with the hydroxyl group introduced at different positions on the steroid nucleus.

Markedly reduced bile acid synthesis but maintained levels of cholesterol and vitamin D metabolites in mice with disrupted sterol 27-hydroxylase gene

Sterol 27-hydroxylase is important for the degradation of the steroid side chain in conversion of cholesterol into bile acids and has been ascribed a regulatory role in cholesterol homeostasis. Its deficiency causes the autosomal recessive disease cerebrotendinous xanthomatosis (CTX), characterized by progressive dementia, xanthomatosis, and accelerated atherosclerosis. Mice with a disrupted cyp27 (cyp27(-/-)) had normal plasma levels of cholesterol, retinol, tocopherol, and 1,25-dihydroxyvitamin D. Excretion of fecal bile acids was decreased (<20% of normal), and formation of bile acids from tritium-labeled 7alpha-hydroxycholesterol was less than 15% of normal. Compensatory up-regulation of hepatic cholesterol 7alpha-hydroxylase and hydroxymethylglutaryl-CoA reductase (9- and 2-3-fold increases in mRNA levels, respectively) was found. No CTX-related pathological abnormalities were observed. In CTX, there is an increased formation of 25-hydroxylated bile alcohols and cholestanol. In bile and feces of the cyp27(-/-) mice only traces of bile alcohols were found, and there was no cholestanol accumulation. It is evident that sterol 27-hydroxylase is more important for bile acid synthesis in mice than in humans. The results do not support the contention that 27-hydroxylated steroids are critical for maintenance of cholesterol homeostasis or levels of vitamin D metabolites in the circulation.

Genetic analysis of a Japanese cerebrotendinous xanthomatosis family: identification of a novel mutation in the adrenodoxin binding region of the CYP 27 gene

Cerebrotendinous xanthomatosis (CTX), an autosomal recessive lipid-storage hereditary disorder, is caused by mutations in the sterol 27-hydroxylase gene (CYP 27). A 24-year-old female Japanese CTX patient and her parents were studied for a CYP 27 mutation. Multiple xanthomas were the main complaint of the patient and plasma cholestanol level was markedly elevated. Sterol analysis of a xanthoma biopsy confirmed cholesterol and cholestanol deposition, and the cholestanol accounted for 8.1% of the total sterols. Sterol 27-hydroxylase activity in fibroblasts derived from the patient was undetectable, while the activities in fibroblasts from her mother and father were 54% and 41% of the normal level, respectively. Direct sequence analysis showed a missense mutation of A for G substitution in the CYP 27 gene at codon 362 (CGT 362Arg to CAT 362His) with a homozygous pattern in the patient, and a heterozygous pattern in the parents. The mutation, which eliminates a normal HgaI endonuclease site at position 1195 of the cDNA and is located at the adrenodoxin binding region of the gene, is most probably responsible for the decreased sterol 27-hydroxylase activity in this Japanese CTX family. The combined data strongly support that the primary enzymatic defect in CTX is the disruption of sterol 27-hydroxylase and that the disease is inherited in an autosomal recessive trait.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Peripheral benzodiazepine receptor ligands in rat liver mitochondria: effect on 27-hydroxylation of cholesterol

The effect of peripheral benzodiazepine receptor ligands: PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)isoquinoline-3-carboxamid e), Ro 5-4864 (4-chlorodiazepam), hemin, N-methyl protoporphyrin IX and protoporphyrin IX on liver mitochondrial 27-hydroxylation of cholesterol was studied by adding them together with [4-14C]cholesterol. N-Methyl protoporphyrin IX, PK11195 and protoporphyrin IX stimulated mitochondrial 27-hydroxylation of [4-14C] cholesterol in vitro, the first two being the most potent (2-3-fold increase). Ro 5-4864 and hemin were not active. 27-Hydroxylation of [4-14C]cholesterol was reduced to below control levels (respectively 40 and 56% decrease compared to control, P < 0.01) when PK11195, N-methyl protoporphyrin IX or protoporphyrin IX were allowed to equilibrate in vitro with mitochondria for 20 min at 37 degrees C. Hepatic protoporphyria was induced using 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) (100 mg/kg, i.p.) to study the effect of in vivo accumulation of large amounts of dicarboxylic porphyrins, i.e. endogenous peripheral benzodiazepine receptor ligands, on cholesterol 27-hydroxylation. DDC treatment caused an increase in total porphyrin content in liver homogenate (10-fold) and mitochondria (2-fold). Mitochondrial 27-hydroxylation of [4-14C]cholesterol was depressed after treatment (60% decrease, P < 0.01). We suggest that peripheral benzodiazepine receptor ligands act on liver mitochondrial 27-hydroxylation of cholesterol by a mechanism coupled to these receptors and that the time of exposure of peripheral benzodiazepine receptors to ligands is a major factor. The modulation of 27-hydroxycholesterol production may have a physiological role in liver and possibly in other tissues.

Bile acids in the assessment of hepatocellular function

Bile acids, which are synthesized in the liver from cholesterol, are important in the production of bile flow, excretion of cholesterol, and intestinal digestion and absorption of fats and fat-soluble vitamins. Increases and/or alterations in concentrations of bile acids in serum are specific and sensitive indicators of hepatobiliary disorders. Synthesis of bile acids in hepatocytes involves steps in endoplasmic reticulum, cytosol, mitochondria, and peroxisomes. Other important hepatocellular processes involving bile acids include active uptake by the basolateral membrane, intracellular transport, P-450-mediated conjugations and hydroxylations, and canalicular secretion. Hydrophobic bile acids produce hepatotoxicity in vivo and in vitro. In experimental and epidemiologic studies, some of these forms have been identified as causative agents in the development of colon and liver (experimental only) cancer. Conversely, several hydrophilic forms, primarily ursodeoxycholic acid, have demonstrated cytoprotective properties in a variety of clinical and experimental hepatobiliary diseases and disorders. Because bile acids can have dramatically different properties and effects, determination of mechanisms of action of these compounds has become an active area of research. Primary isolated hepatocytes provide an opportunity to investigate bile acid-related functions and effects in well-designed, carefully controlled studies. Short-term cultures have been used to study a variety of issues related to bile acids, including cytotoxicity, synthesis, and hepatocellular processing. With these systems, however, many functions of mature hepatocytes, including those pertaining to bile acids, can be lost when cultures are maintained for more than several days. Recent developments in culture techniques permit long-term maintenance of functionally stable, differentiated cells. Pertaining to bile acid research, these systems remain to be fully characterized but, in appropriate situations, they should provide important alternatives to in vivo studies and short-term in vitro assays.

Depletion of alpha-tocopherol in human atherosclerotic lesions

Estimations of alpha-tocopherol content were made on a series of human necropsy samples of normal arterial wall and of atherosclerotic lesions. The results were compared with stage of lesion, shown by histology, and with the amounts of cholesterol and hydroxycholesterols in the same lesions. The ratio of alpha-tocopherol to cholesterol levels varied widely in normal arterial wall but was consistently low in lesions, especially in lesions rich in macrophage foam cells. The results suggested that significant accumulation of hydroxycholesterols, found almost exclusively in lesions, only occurred when alpha-tocopherol levels were low in relation to the cholesterol content. This suggests that oxidative activity in the lesion may lead to significant oxidation of constituents of low-density lipoprotein only after alpha-tocopherol has been depleted.

A novel nonhepatic hydroxycholesterol 7 alpha-hydroxylase that is markedly stimulated by interleukin-1 beta. Characterization in the immature rat ovary

During studies on the regulation of rat ovarian steroidogenic enzymes by interleukin-1 beta (IL-1 beta), we observed substantial metabolism of 25-hydroxycholesterol to two unusual polar products. This unexpected effect was observed both in isolated granulosa cells and in whole ovarian dispersates and was also induced by tumor necrosis factor alpha, but not by insulin-like growth factor I or follicle-stimulating hormone. The effect was dependent on time and the dose of IL-1 beta and was blocked by and IL-1 receptor antagonist. The formation of the polar metabolites was inhibited by ketoconazole and trilostane, but not by aminoglutethimide. Subsequent purification of these novel metabolites and analysis by gas chromatography/ mass spectrometry, NMR, and high performance liquid chromatography revealed them to be related 7 alpha-hydroxylated hydroxycholesterols (cholest-4-ene-7 alpha,25-diol-3-one and cholest-5-ene-3 beta,7 alpha,25-triol). IL-1 beta-stimulated ovarian 7 alpha-hydroxylase activity (3-10 pmol/min/mg of cellular protein) was nearly 4-fold that of control levels using 25-hydroxycholesterol as substrate. Activities at or below control levels were observed when IL-1 beta-treated cell sonicates were boiled or assayed in the presence of NADH (rather than NADPH), indicating that involvement of a nonenzymatic process was unlikely. IL-1 beta-stimulated 7 alpha-hydroxylase activity was inhibited to basal levels by a 10-fold excess of unlabeled 25- or 27-hydroxycholesterol, but not by cholesterol, pregnenolone, progesterone, testosterone, or dehydroepiandrosterone, suggesting that ovarian 7 alpha-hydroxylase is specific for hydroxycholesterols. Furthermore, when IL-1 beta-treated ovarian cultures were incubated with radiolabeled cholesterol or testosterone, no 7 alpha-hydroxylated products were observed. We were also unable to detect any mRNA transcripts for liver cholesterol 7 alpha-hydroxylase in IL-1 beta-stimulated ovarian cultures. This study describes an ovarian hydroxycholesterol 7 alpha-hydroxylase that differs from liver cholesterol 7 alpha-hydroxylase and from other nonhepatic progestin/ androgen 7 alpha-hydroxylases. The novel finding of the regulation of a 7 alpha-hydroxylase by IL-1 beta (and tumor necrosis factor alpha) suggests a unique role for cytokines in the regulation of cholesterol metabolism in the ovary and possibly other tissues.

7 alpha-Hydroxylation of 25-hydroxycholesterol and 27-hydroxycholesterol in human fibroblasts

The metabolism of 27-hydroxycholesterol and 25-hydroxycholesterol was studied in cultures of human diploid fibroblasts. Both steroids underwent 7 alpha-hydroxylation with subsequent oxidation to 7 alpha-hydroxy-3-oxo-delta 4 steroids. A minor fraction of the 27-hydroxysteroids was oxidized to acids. Competition experiments indicated that both hydroxycholesterols were hydroxylated by the same enzyme, different from cholesterol 7 alpha-hydroxylase. 7 alpha,25-Dihydroxycholesterol suppressed the activity of HMG-CoA reductase at least as effectively as 25-hydroxycholesterol whereas 7 alpha,25-dihydroxy-4-cholesten-3-one was a less effective suppressor. The results suggest that cholesterol might be converted to 7 alpha-hydroxylated bile acid precursors in extrahepatic tissues in vivo and that the regulation of the activity of HMG-CoA reductase by oxysterols might be modulated by 7 alpha-hydroxylation and subsequent oxidation by 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase.

Lipids and oxidised lipids in human atherosclerotic lesions at different stages of development

Lipids and oxidised lipids were analysed by GC and GC-MS in human necropsy samples of normal artery and individual atherosclerotic lesions, from aorta and common carotid artery, including fatty streaks, intermediate lesions and advanced lesions. Age-related increases were seen for linoleate, oleate and cholesterol in normal artery, but not in lesions. Each category of lesion was much richer than normal artery in all the lipids measured and in oxidised lipids (oxysterols and hydroxyoctadecadienoic acids), although a degree of overlap existed between the compositions of the various categories of lesion. 26-Hydroxycholesterol and 7 beta-hydroxycholesterol levels were extremely low or undetectable in normal artery, but significantly higher in each of the categories of lesions. The generally wide variation in lipid composition of individual lesions within each category, and the fact that a few individual lesions showed no detectable 26-hydroxycholesterol or 7 beta-hydroxycholesterol, suggested that the lipid oxidation in lesions and therefore perhaps the progression of lesions may be intermittent. Fatty streaks showed the highest concentration of 7 beta-hydroxycholesterol relative to cholesterol, and the lowest ratio of linoleate to oleate, suggesting that this type of lesion experiences the greatest concentration of free radical activity. Levels of the enzymatic product 26-hydroxycholesterol were approximately proportional to cholesterol in all the categories of lesions. 26-Hydroxycholesterol was significantly more abundant in advanced lesions than in intermediate lesions or fatty streaks. 26-Hydroxycholesterol levels were higher in macrophage-rich intermediate and advanced lesions than in their fibrous counterparts. This distinction between macrophage-rich and fibrous lesions was also true for most of the other lipid components, consistent with the involvement of macrophages in lipid accumulation, lipid oxidation and lesion development.

Failure of vitamin E to protect cultured human arterial smooth muscle cells against oxysterol-induced cytotoxicity

OBJECTIVE

The cytotoxicity of oxysterols including 7 alpha-hydroxycholesterol (7 alpha OHC), 7 beta-hydroxycholesterol (7 beta OHC), cholesterol 5 alpha,6 alpha-epoxide (alpha epoxyC), cholesterol 5 beta,6 beta-epoxide (beta epoxyC), 7-ketocholesterol (7ketoC), 26-hydroxycholesterol (26OHC), cholesterol-3 beta,5 alpha,6 beta-triol (TriolC) and the possible protecting effect of vitamin E on 26OHC-induced cytotoxicity were investigated in smooth muscle cells isolated from the arteries of human umbilical cords.

METHODS

To study the cytotoxicity of oxysterols, the cells were incubated with each oxysterol at a level of 10 micrograms/ml from 24 to 120 hours, then 45Ca++ uptake, cytosolic free Ca++ level, [3H]thymidine incorporation, total DNA content and viable cell number were measured. Cholesterol was used as a control. For tracing the possible origin of cytotoxicity of 26OHC, cholesterol, phospholipid and 26OHC content in the membrane were investigated from 24 to 72 hours. For determining whether antioxidants had a protective effect against the cytotoxicity of 26OHC, vitamin E and butylated hydroxytoluene (BHT) were used.

RESULTS

The results indicated that the oxysterols elevated 45Ca++ uptake and cytosolic free Ca++ level, but diminished [3H]thymidine incorporation, total DNA content and viable cell number. 26OHC lowered the cholesterol content of the membrane and incorporated into the membrane after 24 hours of the incubation, but did not alter the total phospholipid content of the membrane until 72 hours. Neither vitamin E or BHT significantly protected the cells from the 26OHC-induced alterations.

CONCLUSION

We suggest that the cytotoxicity of oxysterols, which might result in an alteration in Ca++ ion flow into the cell by decreasing cholesterol content and incorporating oxysterol itself into the membranes, could not be protected by vitamin E.

Effects of 26-aminocholesterol, 27-hydroxycholesterol, and 25-hydroxycholesterol on proliferation and cholesterol homeostasis in arterial myocytes

The major relation existing between cell growth and cholesterol homeostasis prompted us to investigate the effect of 26-aminocholesterol (26-NH2), 27-hydroxycholesterol (27-OH), and 25-hydroxycholesterol (25-OH) on these cellular events. To test this relation, we incubated human and rat arterial myocytes with the sterols for 72 hours. All the tested compounds (0.5 to 7.5 mumol/L) inhibited rat and human myocyte proliferation and cholesterol biosynthesis in a dose-dependent manner. 26-NH2 was more potent than oxysterols in inhibiting human myocyte proliferation but equieffective in rat cells; 27-OH and 25-OH displayed similar activity in both cell lines. Inhibition of nuclear incorporation of thymidine in rat myocytes is consistent with decreased cell count. The antiproliferative effect of the tested sterols was reversible. The high inhibition (80%) of cholesterol biosynthesis necessary to induce a decrease in myocyte proliferation suggests a causal relation between the cholesterol synthetic pathway and these cellular processes. In addition, all the tested sterols were able to inhibit hydroxymethyl glutaryl-coenzyme A reductase activity in intact myocytes but not in cell-free extracts. The finding that 26-NH2 but not 27-OH or 25-OH does not suppress LDL receptor activity in either human or rat myocytes supports the achievement of selectivity over the coordinately regulated LDL receptor gene. The ability of 26-NH2 to interfere with myocyte proliferation and cholesterol synthesis without affecting the LDL receptor pathway confers at least in vitro a pharmacological interest on the compound in the process of atherogenesis.

Lipids and oxidised lipids in human atheroma and normal aorta

Lipids and oxidised lipids were analysed by GC and GC-MS in samples of human atheroma (necrotic gruel from the interior of advanced atherosclerotic plaques in the aorta) and human normal aorta (lesion-free intima plus inner media) from necropsy subjects. Cholest-5-en-3 beta,26-diol and cholest-5-en-3 beta,7 beta-diol were detected in all the atheroma samples examined but not in significant amounts in normal aorta. In atheroma, cholest-5-en-3 beta,26-diol was approximately proportional to cholesterol. Several isomeric hydroxy-octadecadienoic acids were detected in atheroma, and, in smaller amounts, in normal aorta. Many of the components of atheroma showed a high degree of cross-correlation on linear regression analysis, whilst cross-correlations were somewhat weaker for normal aorta. Atheroma showed a vast accumulation of lipid, especially cholesterol, in comparison to normal aorta. The atheroma samples contained a larger proportion of linoleate relative to oleate than the normal aorta. Levels of fatty acids relative to cholesterol were lower for atheroma than for normal aorta. The chemical composition of atheroma appeared unrelated to the age of the subject, whereas age-related increases in linoleate, oleate and cholesterol content were seen in the samples of normal aorta.

24-, 25- and 27-hydroxylation of cholesterol by a purified preparation of 27-hydroxylase from pig liver

Pig liver mitochondria were found to catalyze 27-, 25- and 24-hydroxylation of cholesterol at relative rates of about 1:0.2:0.04. An apparently homogeneous preparation of pig liver mitochondrial cytochrome P-450-27 was found to catalyze the same three hydroxylations at about the same relative rates when reconstituted with adrenodoxin and adrenodoxin reductase. The 24-hydroxycholesterol formed was shown to consist of one of the two possible stereoisomers. When using specifically deuterium-labeled substrates a significant isotope effect was observed in the case of 24-hydroxylation (KH/KD > 10), but not 25-hydroxylation (KH/KD = 1.1), or 27-hydroxylation (KH/KD = 1.1). The difference between the 24-hydroxylation and the other two hydroxylations may be due to different interactions between cholesterol and the same enzyme, with a resulting difference with respect to the rate-limiting step in the reaction. The physiological significance of the mitochondrial 24-hydroxylation is discussed.