An Interferon Regulated MicroRNA Provides Broad Cell-Intrinsic Antiviral Immunity through Multihit Host-Directed Targeting of the Sterol Pathway.

In invertebrates, small interfering RNAs are at the vanguard of cell-autonomous antiviral immunity. In contrast, antiviral mechanisms initiated by interferon (IFN) signaling predominate in mammals. Whilst mammalian IFN-induced miRNA are known to inhibit specific viruses, it is not known whether host-directed microRNAs, downstream of IFN-signaling, have a role in mediating broad antiviral resistance. By performing an integrative, systematic, global analysis of RNA turnover utilizing 4-thiouridine labeling of newly transcribed RNA and pri/pre-miRNA in IFN-activated macrophages, we identify a new post-transcriptional viral defense mechanism mediated by miR-342-5p. On the basis of ChIP and site-directed promoter mutagenesis experiments, we find the synthesis of miR-342-5p is coupled to the antiviral IFN response via the IFN-induced transcription factor, IRF1. Strikingly, we find miR-342-5p targets mevalonate-sterol biosynthesis using a multihit mechanism suppressing the pathway at different functional levels: transcriptionally via SREBF2, post-transcriptionally via miR-33, and enzymatically via IDI1 and SC4MOL. Mass spectrometry-based lipidomics and enzymatic assays demonstrate the targeting mechanisms reduce intermediate sterol pathway metabolites and total cholesterol in macrophages. These results reveal a previously unrecognized mechanism by which IFN regulates the sterol pathway. The sterol pathway is known to be an integral part of the macrophage IFN antiviral response, and we show that miR-342-5p exerts broad antiviral effects against multiple, unrelated pathogenic viruses such Cytomegalovirus and Influenza A (H1N1). Metabolic rescue experiments confirm the specificity of these effects and demonstrate that unrelated viruses have differential mevalonate and sterol pathway requirements for their replication. This study, therefore, advances the general concept of broad antiviral defense through multihit targeting of a single host pathway.

Developing an Enzyme-Assisted Derivatization Method for Analysis of C27 Bile Alcohols and Acids by Electrospray Ionization-Mass Spectrometry.

Enzyme-assisted derivatization for sterol analysis (EADSA) is a technology designed to enhance sensitivity and specificity for sterol analysis using electrospray ionization⁻mass spectrometry. To date it has only been exploited on sterols with a 3ß-hydroxy-5-ene or 3ß-hydroxy-5α-hydrogen structure, using bacterial cholesterol oxidase enzyme to convert the 3ß-hydroxy group to a 3-oxo group for subsequent derivatization with the positively charged Girard hydrazine reagents, or on substrates with a native oxo group. Here we describe an extension of the technology by substituting 3α-hydroxysteroid dehydrogenase (3α-HSD) for cholesterol oxidase, making the method applicable to sterols with a 3α-hydroxy-5ß-hydrogen structure. The 3α-HSD enzyme works efficiently on bile alcohols and bile acids with this stereochemistry. However, as found by others, derivatization of the resultant 3-oxo group with a hydrazine reagent does not go to completion in the absence of a conjugating double bond in the sterol structure. Nevertheless, Girard P derivatives of bile alcohols and C27 acids give an intense molecular ion ([M]⁺) upon electrospray ionization and informative fragmentation spectra. The method shows promise for analysis of bile alcohols and 3α-hydroxy-5ß-C27-acids, enhancing the range of sterols that can be analyzed at high sensitivity in sterolomic studies.

Identification of unusual oxysterols and bile acids with 7-oxo or 3ß,5α,6ß-trihydroxy functions in human plasma by charge-tagging mass spectrometry with multistage fragmentation.

7-Oxocholesterol (7-OC), 5,6-epoxycholesterol (5,6-EC), and its hydrolysis product cholestane-3ß,5α,6ß-triol (3ß,5α,6ß-triol) are normally minor oxysterols in human samples; however, in disease, their levels may be greatly elevated. This is the case in plasma from patients suffering from some lysosomal storage disorders, e.g., Niemann-Pick disease type C, or the inborn errors of sterol metabolism, e.g., Smith-Lemli-Opitz syndrome and cerebrotendinous xanthomatosis. A complication in the analysis of 7-OC and 5,6-EC is that they can also be formed ex vivo from cholesterol during sample handling in air, causing confusion with molecules formed in vivo. When formed endogenously, 7-OC, 5,6-EC, and 3ß,5α,6ß-triol can be converted to bile acids. Here, we describe methodology based on chemical derivatization and LC/MS with multistage fragmentation (MSn) to identify the necessary intermediates in the conversion of 7-OC to 3ß-hydroxy-7-oxochol-5-enoic acid and 5,6-EC and 3ß,5α,6ß-triol to 3ß,5α,6ß-trihydroxycholanoic acid. Identification of intermediate metabolites is facilitated by their unusual MSn fragmentation patterns. Semiquantitative measurements are possible, but absolute values await the synthesis of isotope-labeled standards.

The role of microRNA-155/liver X receptor pathway in experimental and idiopathic pulmonary fibrosis.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is progressive and rapidly fatal. Improved understanding of pathogenesis is required to prosper novel therapeutics. Epigenetic changes contribute to IPF; therefore, microRNAs may reveal novel pathogenic pathways. OBJECTIVES: We sought to determine the regulatory role of microRNA (miR)-155 in the profibrotic function of murine lung macrophages and fibroblasts, IPF lung fibroblasts, and its contribution to experimental pulmonary fibrosis. METHODS: Bleomycin-induced lung fibrosis in wild-type and miR-155-/- mice was analyzed by histology, collagen, and profibrotic gene expression. Mechanisms were identified by in silico and molecular approaches and validated in mouse lung fibroblasts and macrophages, and in IPF lung fibroblasts, using loss-and-gain of function assays, and in vivo using specific inhibitors. RESULTS: miR-155-/- mice developed exacerbated lung fibrosis, increased collagen deposition, collagen 1 and 3 mRNA expression, TGF-ß production, and activation of alternatively activated macrophages, contributed by deregulation of the miR-155 target gene the liver X receptor (LXR)α in lung fibroblasts and macrophages. Inhibition of LXRα in experimental lung fibrosis and in IPF lung fibroblasts reduced the exacerbated fibrotic response. Similarly, enforced expression of miR-155 reduced the profibrotic phenotype of IPF and miR-155-/- fibroblasts. CONCLUSIONS: We describe herein a molecular pathway comprising miR-155 and its epigenetic LXRα target that when deregulated enables pathogenic pulmonary fibrosis. Manipulation of the miR-155/LXR pathway may have therapeutic potential for IPF.

Defective cholesterol metabolism in amyotrophic lateral sclerosis.

As neurons die, cholesterol is released in the central nervous system (CNS); hence, this sterol and its metabolites may represent a biomarker of neurodegeneration, including in amyotrophic lateral sclerosis (ALS), in which altered cholesterol levels have been linked to prognosis. More than 40 different sterols were quantified in serum and cerebrospinal fluid (CSF) from ALS patients and healthy controls. In CSF, the concentration of cholesterol was found to be elevated in ALS samples. When CSF metabolite levels were normalized to cholesterol, the cholesterol metabolite 3ß,7α-dihydroxycholest-5-en-26-oic acid, along with its precursor 3ß-hydroxycholest-5-en-26-oic acid and product 7α-hydroxy-3-oxocholest-4-en-26-oic acid, were reduced in concentration, whereas metabolites known to be imported from the circulation into the CNS were not found to differ in concentration between groups. Analysis of serum revealed that (25R)26-hydroxycholesterol, the immediate precursor of 3ß-hydroxycholest-5-en-26-oic acid, was reduced in concentration in ALS patients compared with controls. We conclude that the acidic branch of bile acid biosynthesis, known to be operative in-part in the brain, is defective in ALS, leading to a failure of the CNS to remove excess cholesterol, which may be toxic to neuronal cells, compounded by a reduction in neuroprotective 3ß,7α-dihydroxycholest-5-en-26-oic acid.

Lipid metabolism in mycobacteria--Insights using mass spectrometry-based lipidomics.

Diseases including tuberculosis and leprosy are caused by species of the Mycobacterium genus and are a huge burden on global health, aggravated by the emergence of drug resistant strains. Mycobacteria have a high lipid content and complex lipid profile including several unique classes of lipid. Recent years have seen a growth in research focused on lipid structures, metabolism and biological functions driven by advances in mass spectrometry techniques and instrumentation, particularly the use of electrospray ionization. Here we review the contributions of lipidomics towards the advancement of our knowledge of lipid metabolism in mycobacterial species.

Quantitative charge-tags for sterol and oxysterol analysis.

BACKGROUND: Global sterol analysis is challenging owing to the extreme diversity of sterol natural products, the tendency of cholesterol to dominate in abundance over all other sterols, and the structural lack of a strong chromophore or readily ionized functional group. We developed a method to overcome these challenges by using different isotope-labeled versions of the Girard P reagent (GP) as quantitative charge-tags for the LC-MS analysis of sterols including oxysterols. METHODS: Sterols/oxysterols in plasma were extracted in ethanol containing deuterated internal standards, separated by C18 solid-phase extraction, and derivatized with GP, with or without prior oxidation of 3ß-hydroxy to 3-oxo groups. RESULTS: By use of different isotope-labeled GPs, it was possible to analyze in a single LC-MS analysis both sterols/oxysterols that naturally possess a 3-oxo group and those with a 3ß-hydroxy group. Intra- and interassay CVs were <15%, and recoveries for representative oxysterols and cholestenoic acids were 85%-108%. By adopting a multiplex approach to isotope labeling, we analyzed up to 4 different samples in a single run. Using plasma samples, we could demonstrate the diagnosis of inborn errors of metabolism and also the export of oxysterols from brain via the jugular vein. CONCLUSIONS: This method allows the profiling of the widest range of sterols/oxysterols in a single analytical run and can be used to identify inborn errors of cholesterol synthesis and metabolism.

Revised sample preparation for the analysis of oxysterols by enzyme-assisted derivatisation for sterol analysis (EADSA).

Sterols, and specifically oxysterols, play important roles in the biosynthesis of bile acids and steroid hormones as well as possessing biological activities in their own right. Analysis of oxysterols is complicated due to their low abundance in biological systems and poor ionisation characteristics in mass spectrometry. Over the past decade, we have developed a liquid chromatography-mass spectrometry method termed enzyme-assisted derivatisation for sterol analysis (EADSA). Our derivatisation procedure relies on two solid-phase extraction steps to (i) separate cholesterol from oxysterols and (ii) remove excess derivatisation reagents. Recent inter-batch variation in C18 reversed-phase cartridges has led us to experiment with alternative columns. Here, we present our findings and report an improved sample preparation procedure using polymeric hydrophilic-lipophilic balanced reversed-phase cartridges.

Role of AMACR (α-methylacyl-CoA racemase) and MFE-1 (peroxisomal multifunctional enzyme-1) in bile acid synthesis in mice.

Cholesterol is catabolized to bile acids by peroxisomal ß-oxidation in which the side chain of C27-bile acid intermediates is shortened by three carbon atoms to form mature C24-bile acids. Knockout mouse models deficient in AMACR (α-methylacyl-CoA racemase) or MFE-2 (peroxisomal multifunctional enzyme type 2), in which this ß-oxidation pathway is prevented, display a residual C24-bile acid pool which, although greatly reduced, implies the existence of alternative pathways of bile acid synthesis. One alternative pathway could involve Mfe-1 (peroxisomal multifunctional enzyme type 1) either with or without Amacr. To test this hypothesis, we generated a double knockout mouse model lacking both Amacr and Mfe-1 activities and studied the bile acid profiles in wild-type, Mfe-1 and Amacr single knockout mouse line and Mfe-1 and Amacr double knockout mouse lines. The total bile acid pool was decreased in Mfe-1-/- mice compared with wild-type and the levels of mature C24-bile acids were reduced in the double knockout mice when compared with Amacr-deficient mice. These results indicate that Mfe-1 can contribute to the synthesis of mature bile acids in both Amacr-dependent and Amacr-independent pathways.

On the formation of 7-ketocholesterol from 7-dehydrocholesterol in patients with CTX and SLO.

A new mechanism for formation of 7-ketocholesterol was recently described involving cytochrome P-450 (CYP)7A1-catalyzed conversion of 7-dehydrocholesterol into 7-ketocholesterol with cholesterol-7,8-epoxide as a side product. Some patients with cerebrotendinous xanthomatosis (CTX) and all patients with Smith-Lemli-Opitz syndrome (SLO) have markedly increased levels of 7-dehydrocholesterol in plasma and tissues. In addition, the former patients have markedly upregulated CYP7A1. We hypothesized that these patients may produce 7-ketocholesterol from 7-dehydrocholesterol with formation of cholesterol-7,8-epoxide as a side product. In accord with this hypothesis, two patients with CTX were found to have increased levels of 7-ketocholesterol and 7-dehydrocholesterol, as well as a significant level of cholesterol-7,8-epoxide. The latter steroid was not detectable in plasma from healthy volunteers. Downregulation of CYP7A1 activity by treatment with chenodeoxycholic acid reduced the levels of 7-ketocholesterol in parallel with decreased levels of 7-dehydrocholesterol and cholesterol-7,8-epoxide. Three patients with SLO were found to have markedly elevated levels of 7-ketocholesterol as well as high levels of cholesterol-7,8-epoxide. The results support the hypothesis that 7-dehydrocholesterol is a precursor to 7-ketocholesterol in SLO and some patients with CTX.

Evaluation of novel derivatisation reagents for the analysis of oxysterols.

Oxysterols are oxidised forms of cholesterol that are intermediates in the synthesis of bile acids and steroid hormones. They are also ligands to nuclear and G protein-coupled receptors. Analysis of oxysterols in biological systems is challenging due to their low abundance coupled with their lack of a strong chromophore and poor ionisation characteristics in mass spectrometry (MS). We have previously used enzyme-assisted derivatisation for sterol analysis (EADSA) to identify and quantitate oxysterols in biological samples. This technique relies on tagging sterols with the Girard P reagent to introduce a charged quaternary ammonium group. Here, we have compared several modified Girard-like reagents and show that the permanent charge is vital for efficient MS(n) fragmentation. However, we find that the reagent can be extended to include sites for potential stable isotope labels without a loss of performance.

Studies on the analysis of 25-hydroxyvitamin D(3) by isotope-dilution liquid chromatography-tandem mass spectrometry using enzyme-assisted derivatisation.

The total serum concentration of 25-hydroxyvitamins D (25-hydroxyvitamin D3 and 25-hydroxyvitamin D2) is currently used as an indicator of vitamins D status. Vitamins D insufficiency is claimed to be associated with multiple diseases, thus accurate and precise reference methods for the quantification of 25-hydroxyvitamins D are needed. Here we present a novel enzyme-assisted derivatisation method for the analysis of vitamins D metabolites in adult serum utilising 25-[26,26,26,27,27,27-(2)H6]hydroxyvitamin D3 as the internal standard. Extraction of 25-hydroxyvitamins D from serum is performed with acetonitrile, which is shown to be more efficient than ethanol. Cholesterol oxidase is used to oxidize the 3ß-hydroxy group in the vitamins D metabolites followed by derivatisation of the newly formed 3-oxo group with Girard P reagent. 17ß-Hydroxysteroid dehydrogenase type 10 is shown to oxidize selectively the 3α-hydroxy group in the 3α-hydroxy epimer of 25-hydroxyvitamin D3. Quantification is achieved by isotope-dilution liquid chromatography-tandem mass spectrometry. Recovery experiments for 25-hydroxyvitamin D3 performed on adult human serum give recovery of 102-106%. Furthermore in addition to 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3 and other uncharacterised dihydroxy metabolites, were detected in adult human serum.

Liver disease in infancy caused by oxysterol 7 α-hydroxylase deficiency: successful treatment with chenodeoxycholic acid.

A child of consanguineous parents of Pakistani origin developed jaundice at 5 weeks and then, at 3 months, irritability, a prolonged prothrombin time, a low albumin, and episodes of hypoglycaemia. Investigation showed an elevated alanine aminotransferase with a normal γ-glutamyl-transpeptidase. Analysis of urine by electrospray ionisation tandem mass spectrometry (ESI-MS/MS) showed that the major peaks were m/z 480 (taurine-conjugated 3ß-hydroxy-5-cholenoic acid) and m/z 453 (sulphated 3ß-hydroxy-5-cholenoic acid). Analysis of plasma by gas chromatography-mass spectrometry (GC-MS) showed increased concentrations of 3ß-hydroxy-5-cholenoic acid, 3ß-hydroxy-5-cholestenoic acid and 27-hydroxycholesterol, indicating oxysterol 7 α-hydroxylase deficiency. The patient was homozygous for a mutation (c.1249C>T) in CYP7B1 that alters a highly conserved residue in oxysterol 7 α-hydroxylase (p.R417C) - previously reported in a family with hereditary spastic paraplegia type 5. On treatment with ursodeoxycholic acid (UDCA), his condition was worsening, but on chenodeoxycholic acid (CDCA), 15 mg/kg/d, he improved rapidly. A biopsy (after 2 weeks on CDCA), showed a giant cell hepatitis, an evolving micronodular cirrhosis, and steatosis. The improvement in liver function on CDCA was associated with a drop in the plasma concentrations and urinary excretions of the 3ß-hydroxy-Δ5 bile acids which are considered hepatotoxic. At age 5 years (on CDCA, 6 mg/kg/d), he was thriving with normal liver function. Neurological development was normal apart from a tendency to trip. Examination revealed pes cavus but no upper motor neuron signs. The findings in this case suggest that CDCA can reduce the activity of cholesterol 27-hydroxylase - the first step in the acidic pathway for bile acid synthesis.

The Cerebrospinal Fluid Profile of Cholesterol Metabolites in Parkinson's Disease and Their Association With Disease State and Clinical Features.

Disordered cholesterol metabolism is linked to neurodegeneration. In this study we investigated the profile of cholesterol metabolites found in the cerebrospinal fluid (CSF) of Parkinson's disease (PD) patients. When adjustments were made for confounding variables of age and sex, 7α,(25R)26-dihydroxycholesterol and a second oxysterol 7α,x,y-trihydroxycholest-4-en-3-one (7α,x,y-triHCO), whose exact structure is unknown, were found to be significantly elevated in PD CSF. The likely location of the additional hydroxy groups on the second oxysterol are on the sterol side-chain. We found that CSF 7α-hydroxycholesterol levels correlated positively with depression in PD patients, while two presumptively identified cholestenoic acids correlated negatively with depression.

Bile acid biosynthesis in Smith-Lemli-Opitz syndrome bypassing cholesterol: Potential importance of pathway intermediates.

Bile acids are the end products of cholesterol metabolism secreted into bile. They are essential for the absorption of lipids and lipid soluble compounds from the intestine. Here we have identified a series of unusual Δ5-unsaturated bile acids in plasma and urine of patients with Smith-Lemli-Opitz syndrome (SLOS), a defect in cholesterol biosynthesis resulting in elevated levels of 7-dehydrocholesterol (7-DHC), an immediate precursor of cholesterol. Using liquid chromatography - mass spectrometry (LC-MS) we have uncovered a pathway of bile acid biosynthesis in SLOS avoiding cholesterol starting with 7-DHC and proceeding through 7-oxo and 7ß-hydroxy intermediates. This pathway also occurs to a minor extent in healthy humans, but elevated levels of pathway intermediates could be responsible for some of the features SLOS. The pathway is also active in SLOS affected pregnancies as revealed by analysis of amniotic fluid. Importantly, intermediates in the pathway, 25-hydroxy-7-oxocholesterol, (25R)26-hydroxy-7-oxocholesterol, 3ß-hydroxy-7-oxocholest-5-en-(25R)26-oic acid and the analogous 7ß-hydroxysterols are modulators of the activity of Smoothened (Smo), an oncoprotein that mediates Hedgehog (Hh) signalling across membranes during embryogenesis and in the regeneration of postembryonic tissue. Computational docking of the 7-oxo and 7ß-hydroxy compounds to the extracellular cysteine rich domain of Smo reveals that they bind in the same groove as both 20S-hydroxycholesterol and cholesterol, known activators of the Hh pathway.

Formation and metabolism of oxysterols and cholestenoic acids found in the mouse circulation: Lessons learnt from deuterium-enrichment experiments and the CYP46A1 transgenic mouse.

While the presence and abundance of the major oxysterols and cholestenoic acids in the circulation is well established, minor cholesterol metabolites may also have biological importance and be of value to investigate. In this study by observing the metabolism of deuterium-labelled cholesterol in the pdgfbret/ret mouse, a mouse model with increased vascular permeability in brain, and by studying the sterol content of plasma from the CYP46A1 transgenic mouse overexpressing the human cholesterol 24S-hydroxylase enzyme we have been able to identify a number of minor cholesterol metabolites found in the circulation, make approximate-quantitative measurements and postulate pathways for their formation. These "proof of principle" data may have relevance when using mouse models to mimic human disease and in respect of the increasing possibility of treating human neurodegenerative diseases with pharmaceuticals designed to enhance the activity of CYP46A1 or by adeno-associated virus delivery of CYP46A1.

Mining for Oxysterols in Cyp7b1-/- Mouse Brain and Plasma: Relevance to Spastic Paraplegia Type 5.

Deficiency in cytochrome P450 (CYP) 7B1, also known as oxysterol 7α-hydroxylase, in humans leads to hereditary spastic paraplegia type 5 (SPG5) and in some cases in infants to liver disease. SPG5 is medically characterized by loss of motor neurons in the corticospinal tract. In an effort to gain a better understanding of the fundamental biochemistry of this disorder, we have extended our previous profiling of the oxysterol content of brain and plasma of Cyp7b1 knockout (-/-) mice to include, amongst other sterols, 25-hydroxylated cholesterol metabolites. Although brain cholesterol levels do not differ between wild-type (wt) and knockout mice, we find, using a charge-tagging methodology in combination with liquid chromatography-mass spectrometry (LC-MS) and multistage fragmentation (MSn), that there is a build-up of the CYP7B1 substrate 25-hydroxycholesterol (25-HC) in Cyp7b1-/- mouse brain and plasma. As reported earlier, levels of (25R)26-hydroxycholesterol (26-HC), 3ß-hydroxycholest-5-en-(25R)26-oic acid and 24S,25-epoxycholesterol (24S,25-EC) are similarly elevated in brain and plasma. Side-chain oxysterols including 25-HC, 26-HC and 24S,25-EC are known to bind to INSIG (insulin-induced gene) and inhibit the processing of SREBP-2 (sterol regulatory element-binding protein-2) to its active form as a master regulator of cholesterol biosynthesis. We suggest the concentration of cholesterol in brain of the Cyp7b1-/- mouse is maintained by balancing reduced metabolism, as a consequence of a loss in CYP7B1, with reduced biosynthesis. The Cyp7b1-/- mouse does not show a motor defect; whether the defect in humans is a consequence of less efficient homeostasis of cholesterol in brain has yet to be uncovered.

Additional pathways of sterol metabolism: Evidence from analysis of Cyp27a1-/- mouse brain and plasma.

Cytochrome P450 (CYP) 27A1 is a key enzyme in both the acidic and neutral pathways of bile acid biosynthesis accepting cholesterol and ring-hydroxylated sterols as substrates introducing a (25R)26-hydroxy and ultimately a (25R)26-acid group to the sterol side-chain. In human, mutations in the CYP27A1 gene are the cause of the autosomal recessive disease cerebrotendinous xanthomatosis (CTX). Surprisingly, Cyp27a1 knockout mice (Cyp27a1-/-) do not present a CTX phenotype despite generating a similar global pattern of sterols. Using liquid chromatography - mass spectrometry and exploiting a charge-tagging approach for oxysterol analysis we identified over 50 cholesterol metabolites and precursors in the brain and circulation of Cyp27a1-/- mice. Notably, we identified (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids, indicating the presence of an additional sterol 26-hydroxylase in mouse. Importantly, our analysis also revealed elevated levels of 7α-hydroxycholest-4-en-3-one, which we found increased the number of oculomotor neurons in primary mouse brain cultures. 7α-Hydroxycholest-4-en-3-one is a ligand for the pregnane X receptor (PXR), activation of which is known to up-regulate the expression of CYP3A11, which we confirm has sterol 26-hydroxylase activity. This can explain the formation of (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids; the acid with the former stereochemistry is a liver X receptor (LXR) ligand that increases the number of oculomotor neurons in primary brain cultures. We hereby suggest that a lack of a motor neuron phenotype in some CTX patients and Cyp27a1-/- mice may involve increased levels of 7α-hydroxycholest-4-en-3-one and activation PXR, as well as increased levels of sterol 26-hydroxylase and the production of neuroprotective sterols capable of activating LXR.

Metabolism of Non-Enzymatically Derived Oxysterols: Clues from sterol metabolic disorders.

Cholestane-3ß,5α,6ß-triol (3ß,5α,6ß-triol) is formed from cholestan-5,6-epoxide (5,6-EC) in a reaction catalysed by cholesterol epoxide hydrolase, following formation of 5,6-EC through free radical oxidation of cholesterol. 7-Oxocholesterol (7-OC) and 7ß-hydroxycholesterol (7ß-HC) can also be formed by free radical oxidation of cholesterol. Here we investigate how 3ß,5α,6ß-triol, 7-OC and 7ß-HC are metabolised to bile acids. We show, by monitoring oxysterol metabolites in plasma samples rich in 3ß,5α,6ß-triol, 7-OC and 7ß-HC, that these three oxysterols fall into novel branches of the acidic pathway of bile acid biosynthesis becoming (25R)26-hydroxylated then carboxylated, 24-hydroxylated and side-chain shortened to give the final products 3ß,5α,6ß-trihydroxycholanoic, 3ß-hydroxy-7-oxochol-5-enoic and 3ß,7ß-dihydroxychol-5-enoic acids, respectively. The intermediates in these pathways may be causative of some phenotypical features of, and/or have diagnostic value for, the lysosomal storage diseases, Niemann Pick types C and B and lysosomal acid lipase deficiency. Free radical derived oxysterols are metabolised in human to unusual bile acids via novel branches of the acidic pathway, intermediates in these pathways are observed in plasma.

First international descriptive and interventional survey for cholesterol and non-cholesterol sterol determination by gas- and liquid-chromatography-Urgent need for harmonisation of analytical methods.

Serum concentrations of lathosterol, the plant sterols campesterol and sitosterol and the cholesterol metabolite 5α-cholestanol are widely used as surrogate markers of cholesterol synthesis and absorption, respectively. Increasing numbers of laboratories utilize a broad spectrum of well-established and recently developed methods for the determination of cholesterol and non-cholesterol sterols (NCS). In order to evaluate the quality of these measurements and to identify possible sources of analytical errors our group initiated the first international survey for cholesterol and NCS. The cholesterol and NCS survey was structured as a two-part survey which took place in the years 2013 and 2014. The first survey part was designed as descriptive, providing information about the variation of reported results from different laboratories. A set of two lyophilized pooled sera (A and B) was sent to twenty laboratories specialized in chromatographic lipid analysis. The different sterols were quantified either by gas chromatography-flame ionization detection, gas chromatography- or liquid chromatography-mass selective detection. The participants were requested to determine cholesterol and NCS concentrations in the provided samples as part of their normal laboratory routine. The second part was designed as interventional survey. Twenty-two laboratories agreed to participate and received again two different lyophilized pooled sera (C and D). In contrast to the first international survey, each participant received standard stock solutions with defined concentrations of cholesterol and NCS. The participants were requested to use diluted calibration solutions from the provided standard stock solutions for quantification of cholesterol and NCS. In both surveys, each laboratory used its own internal standard (5α-cholestane, epicoprostanol or deuterium labelled sterols). Main outcome of the survey was, that unacceptably high interlaboratory variations for cholesterol and NCS concentrations are reported, even when the individual laboratories used the same calibration material. We discuss different sources of errors and recommend all laboratories analysing cholesterol and NCS to participate in regular quality control programs.