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Metabolomics has found numerous applications in the study of liver metabolism in health and disease. Metabolomics studies can be conducted in a variety of biological matrices ranging from easily accessible biofluids such as urine, blood or feces, to organs, tissues or even cells. Sample collection and storage are critical steps for which standard operating procedures must be followed. Inappropriate sample collection or storage can indeed result in high variability, interferences with instrumentation or degradation of metabolites. In this review, we will first highlight important general factors that should be considered when planning sample collection in the study design of metabolomic studies, such as nutritional status and circadian rhythm. Then, we will discuss in more detail the specific procedures that have been described for optimal pre-analytical handling of the most commonly used matrices (urine, blood, feces, tissues and cells).

ObjectiveWe evaluated the influence of sex on the pathophysiology of non-alcoholic fatty liver disease (NAFLD). We investigated diet-induced phenotypic responses to define sex-specific regulation between healthy liver and NAFLD to identify influential pathways in different preclinical murine models and their relevance in humans.DesignDifferent models of diet-induced NAFLD (high-fat diet, choline-deficient high-fat diet, Western diet or Western diet supplemented with fructose and glucose in drinking water) were compared with a control diet in male and female mice. We performed metabolic phenotyping, including plasma biochemistry and liver histology, untargeted large-scale approaches (liver metabolome, lipidome and transcriptome), gene expression profiling and network analysis to identify sex-specific pathways in the mouse liver.ResultsThe different diets induced sex-specific responses that illustrated an increased susceptibility to NAFLD in male mice. The most severe lipid accumulation and inflammation/fibrosis occurred in males receiving the high-fat diet and Western diet, respectively. Sex-biased hepatic gene signatures were identified for these different dietary challenges. The peroxisome proliferator-activated receptor α (PPARα) co-expression network was identified as sexually dimorphic, and in vivo experiments in mice demonstrated that hepatocyte PPARα determines a sex-specific response to fasting and treatment with pemafibrate, a selective PPARα agonist. Liver molecular signatures in humans also provided evidence of sexually dimorphic gene expression profiles and the sex-specific co-expression network for PPARα.ConclusionsThese findings underscore the sex specificity of NAFLD pathophysiology in preclinical studies and identify PPARα as a pivotal, sexually dimorphic, pharmacological target.Trial registration numberNCT02390232.

Current fructose consumption levels often overwhelm the intestinal capacity to absorb fructose. We investigated the impact of fructose malabsorption on intestinal endocrine function and addressed the role of the microbiota in this process. To answer this question, a mouse model of moderate fructose malabsorption [ketohexokinase mutant (KHK)−/−] and wild‐type (WT) littermate mice were used and received a 20%‐fructose (KHK‐F and WT‐F) or 20%‐glucose diet. Cholecystokinin (Cck) mRNA and protein expression in the ileum and cecum, as well as preproglucagon (Gcg) and neurotensin (Nts) mRNA expression in the cecum, increased in KHK‐F mice. In KHK‐F mice, triple‐label immunohistochemistry showed major up‐regulation of CCK in enteroendocrine cells (EECs) that were glucagon‐like peptide‐1 (GLP‐1)+/Peptide YY (PYY−) in the ileum and colon and GLP‐1−/PYY− in the cecum. The cecal microbiota composition was drastically modified in the KHK‐F in association with an increase in glucose, propionate, succinate, and lactate concentrations. Antibiotic treatment abolished fructose malabsorption‐dependent induction of cecal Cck mRNA expression and, in mouse GLUTag and human NCI‐H716 cells, Cck mRNA expression levels increased in response to propionate, both suggesting a microbiota‐dependent process. Fructose reaching the lower intestine can modify the composition and metabolism of the microbiota, thereby stimulating the production of CCK from the EECs possibly in response to propionate.—Zhang, X., Grosfeld, A., Williams, E., Vasiliauskas, D., Barretto, S., Smith, L., Mariadassou, M., Philippe, C., Devime, F., Melchior, C., Gourcerol, G., Dourmap, N., Lapaque, N., Larraufie, P., Blottière, H. M., Herberden, C., Gerard, P., Rehfeld, J. F., Ferraris, R. P., Fritton, J. C., Ellero‐Simatos, S., Douard, V. Fructose malabsorption induces cholecystokinin expression in the ileum and cecum by changing microbiota composition and metabolism. FASEB J. 33, 7126–7142 (2019). http://www.fasebj.org

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SUMMARY1. Magnesium uptake can be measured in ferret red cells incubated in media containing more than 1 mM-magnesium. Uptake is substantially increased if the sodium concentration in the medium is reduced.2. Magnesium uptake is half-maximally activated by 0-37 mM-external magnesium when the external sodium concentration is 5 mm. Increasing the external sodium concentration increases the magnesium concentration needed to activate the system.3. Magnesium uptake is increased by reducing the external sodium concentration. Uptake is half-maximum at sodium concentrations of 17, 22 and 62 mm when the external magnesium concentrations are 2, 5 and 10 mm respectively.4. Replacement of external sodium with cholihe does not affect the membrane potential of ferret red cells over a 45 min period.5. Magnesium uptake from media containing 5 mm-sodium is inhibited by amiloride, quinidine and imipramine. It is not affected by ouabain or bumetanide. Vanadate stimulates magnesium uptake but has no effect on magnesium efflux. 6. When cell ATP content is reduced to 19 jtmol (1 cell)-' by incubating cells for 3 h with 2-deoxyglucose, magnesium uptake falls by 50 % in the presence of 5 mMsodium and is completely abolished in the presence of 145 mM-sodium. Some of the inhibition may be due to the increase in intracellular ionized magnesium concentration ([Mg2+]i) from 0 7 to 1-0 mm which occurs under these conditions. 7. Magnesium uptake can be driven against a substantial electrochemical gradient if the external sodium concentration is reduced sufficiently.8. These findings are discussed in terms of several possible models for magnesium transport. It is concluded that the majority of magnesium uptake observed in lowsodium media is via sodium-magnesium antiport. A small portion of uptake is through a parallel leak pathway. It is believed that the antiport is responsible for maintaining [Mg2+]i below electrochemical equilibrium in these cells at physiological external sodium concentration. Thus in ferret red cells the direction of magnesium transport can be reversed by reversing the sodium gradient.

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] i and pH i and the re-estimate changes in these parameters upon Na ϩ removal. pH-dependency of K D "MgATP" described by Zhang et al. and Bock et al.In Zhang et al. [7], the apparent dissociation con-(pH)) (in M) at 25 and 37°C were expressed as quadratic functions of pH.Since our previous 31 P-NMR experiments were carried out at 32°C, we calculated K D. "MgZhang ATP"(pH) at 32°C from Eqs. 1A and 1B by using the van't Hoff iso- Japanese Journal of Physiology, 52, 323-326, 2002 Key words: magnesium, pH, smooth muscle. Abstract:In the present technical note for