the cellular fate of cholesterol by fl uorescence microscopy, various fl uorescent analogs ( 13-16 ), sterol binding toxins ( 17 ), and anti-cholesterol antibodies ( 18 ) have been used. Isotope-labeled cholesterol ( 1 ) and isotope-labeled toxins ( 19 ) have been employed to follow metabolism or organization of cholesterol in membranes, respectively. A probe suitable for conveniently tracing both cholesterol metabolism and localization would be of great value.With the advent of bioorthogonal chemistry ( 20 ), including click chemistry ( 21 ), the sensitive and specifi c detection of compounds containing azido groups or terminal alkynes has become possible. Lipids containing an alkyne moiety have been used to trace their metabolism and distribution ( 22-26 ) and to monitor protein lipidation ( 27-30 ) or protein-lipid interaction ( 31 ). Thus far, no alkyne-bearing analog of cholesterol has been used to trace cholesterol in mammalian cells.Here we report on the synthesis and use of alkyne cholesterol to study cholesterol metabolism by in vitro assays, and in vivo by using various cells. These data are supplemented by cellular localization studies of the probe. MATERIALS AND METHODSFilipin and azide-PEG3-biotin conjugate were obtained from Sigma. Borondifl uorodipyrromethene (Bodipy)-cholesterol [23-(dipyrrometheneboron-difl uoride)-24-norcholesterol] was from 26,26,27,27, H 6 , and 4-cholesten-3-one were from C/D/N Isotopes and Steraloids, respectively. LD540 was described before ( 32 ). Antibodies against calnexin (Stressgen, SPA-860), EGFR (Epitomics, 2235-1), GM130 (Epitomics, 1837-1), and HSP60 (Stressgen, SPA-806) were used.Abstract Cholesterol is an important lipid of mammalian cells and plays a fundamental role in many biological processes. Its concentration in the various cellular membranes differs and is tightly regulated. Here, we present a novel alkyne cholesterol analog suitable for tracing both cholesterol metabolism and localization. This probe can be detected by click chemistry employing various reporter azides. Alkyne cholesterol is accepted by cellular enzymes from different biological species (Brevibacterium, yeast, rat, human) and these enzymes include cholesterol oxidases, hydroxylases, and acyl transferases that generate the expected metabolites in in vitro and in vivo assays. Using fl uorescence microscopy, we studied the distribution of cholesterol at subcellular resolution, detecting the lipid in the Golgi and at the plasma membrane, but also in the endoplasmic reticulum and mitochondria. In summary, alkyne cholesterol represents a versatile, sensitive, and easy-to-use tool for tracking cellular cholesterol metabolism and localization as it allows for manifold detection methods including mass spectrometry, thin-layer chromatography/fl uorography, and fl uorescence microscopy. Cholesterol is the major sterol of mammalian cell membranes ( 1 ). Beyond its role for discrete membrane structures such as caveolae ( 2 ) or microdomains ( 3 ), cholesterol also specifi cally interacts with numerous...

Long-term consumption of dietary fiber is generally considered beneficial for weight management and metabolic health, but the results of interventions vary greatly depending on the type of dietary fibers involved. This study provides a comprehensive evaluation of the effects of a specific dietary fiber consisting of a wheat-bran extract enriched in arabinoxylan-oligosaccharides (AXOS) in a human intervention trial. An integrated multi-omics analysis has been carried out to evaluate the effects of an intervention trial with an AXOS-enriched diet in overweight individuals with indices of metabolic syndrome. Microbiome analyses were performed by shotgun DNA sequencing in feces; in-depth metabolomics using nuclear magnetic resonance in fecal, urine, and plasma samples; and massive lipid profiling using mass spectrometry in fecal and serum/plasma samples. In addition to their bifidogenic effect, we observed that AXOS boost the proportion of Prevotella species. Metagenome analysis showed increases in the presence of bacterial genes involved in vitamin/cofactor production, glycan metabolism, and neurotransmitter biosynthesis as a result of AXOS intake. Furthermore, lipidomics analysis revealed reductions in plasma ceramide levels. Finally, we observed associations between Prevotella abundance and short-chain fatty acids (SCFAs) and succinate concentration in feces and identified a potential protective role of Eubacterium rectale against metabolic disease given that its abundance was positively associated with plasma phosphatidylcholine levels, thus hypothetically reducing bioavailability of choline for methylamine biosynthesis. The metagenomics, lipidomics, and metabolomics data integration indicates that sustained consumption of AXOS orchestrates a wide variety of changes in the gut microbiome and the host metabolism that collectively would impact on glucose homeostasis. (This study has been registered at ClinicalTrials.gov under identifier NCT02215343.) IMPORTANCE The use of dietary fiber food supplementation as a strategy to reduce the burden of diet-related diseases is a matter of study given its cost-effectiveness and the positive results demonstrated in clinical trials. This multi-omics assessment, on different biological samples of overweight subjects with signs of metabolic syndrome, sheds light on the early and less evident effects of short-term AXOS intake on intestinal microbiota and host metabolism. We observed a deep influence of AXOS on gut microbiota beyond their recognized bifidogenic effect by boosting concomitantly a wide diversity of butyrate producers and Prevotella copri, a microbial species abundant in non-Westernized populations with traditional lifestyle and diets enriched in fresh unprocessed foods. A comprehensive evaluation of hundreds of metabolites unveiled new benefits of the AXOS intake, such as reducing the plasma ceramide levels. Globally, we observed that multiple effects of AXOS consumption seem to converge in reversing the glucose homeostasis impairment.

Short chain fatty acids (SCFAs) are generated by the degradation and fermentation of complex carbohydrates, (i.e., dietary fiber) by the gut microbiota relevant for microbe–host communication. Here, we present a method for the quantification of SCFAs in fecal samples by liquid chromatography tandem mass spectrometry (LC-MS/MS) upon derivatization to 3-nitrophenylhydrazones (3NPH). The method includes acetate, propionate, butyrate, and isobutyrate with a run time of 4 min. The reproducible (coefficients of variation (CV) below 10%) quantification of SCFAs in human fecal samples was achieved by the application of stable isotope labelled internal standards. The specificity was demonstrated by the introduction of a quantifier and qualifier ions. The method was applied to investigate the pre-analytic stability of SCFAs in human feces. Concentrations of SCFA may change substantially within hours; the degree and kinetics of these changes revealed huge differences between the donors. The fecal SCFA level could be preserved by the addition of organic solvents like isopropanol. An analysis of the colon content of mice either treated with antibiotics or fed with a diet containing a non-degradable and -fermentable fiber source showed decreased SCFA concentrations. In summary, this fast and reproducible method for the quantification of SCFA in fecal samples provides a valuable tool for both basic research and large-scale studies.

There has been an increasing interest during recent years in the role of the gut microbiome on health and disease. Therefore, metabolites in human feces related to microbial activity are attractive surrogate marker to track changes of microbiota induced by diet or disease. Such markers include 5α/β-stanols as microbiome-derived metabolites of sterols. Currently, reliable, robust, and fast methods to quantify fecal sterols and their related metabolites are missing. We developed a liquid chromatography-high-resolution mass spectrometry (LC-MS/HRMS) method for the quantification of sterols and their 5α/β-stanols in human fecal samples. Fecal sterols were extracted and derivatized to N, N-dimethylglycine esters. The method includes cholesterol, coprostanol, cholestanol and sitosterol, 5α/β-sitostanol, campesterol and 5α/β-campestanol. Application of a biphenyl column permits separation of isomeric 5α- and 5β-stanols. Sterols are detected in parallel reaction monitoring (PRM) mode and stanols in full scan mode. HRMS allows differentiation of isobaric β-stanols and the [M + 2] isotope peak of the coeluting sterol. Performance characteristics meet the criteria recommended by Food and Drug Administration (FDA) and European Medicines Agency (EMA) guidelines. Analysis of fecal samples from healthy volunteers revealed high interindividual variability of sterol and stanol fractions. Interestingly, cholesterol and sitosterol showed similar fractions of mainly 5β-stanols. In contrast, campesterol is substantially converted to 5α-campestanol and might be a poorer substrate for bacterial metabolism. Robust and fast quantification of fecal sterols and their related stanols by LC-MS/HRMS offers great potential to find novel microbiome-related biomarker in large-scale studies.