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BACKGROUND: Although imatinib is a well-established first-line drug for treating a vast majority of gastrointestinal stromal tumours (GIST), GISTs acquire secondary resistance during therapy. Multi-omics approaches provide an integrated perspective to empower the development of personalised therapies through a better understanding of functional biology underlying the disease and molecular-driven selection of the best-targeted individualised therapy. In this study, we applied integrative metabolomic and transcriptomic analyses to elucidate tumour biochemical processes affected by imatinib treatment. MATERIALS AND METHODS: A GIST xenograft mouse model was used in the study, including 10 mice treated with imatinib and 10 non-treated controls. Metabolites in tumour extracts were analysed using gas chromatography coupled with mass spectrometry (GC-MS). RNA sequencing was also performed on the samples subset (n=6). RESULTS: Metabolomic analysis revealed 21 differentiating metabolites, whereas next-generation RNA sequencing data analysis resulted in 531 differentially expressed genes. Imatinib significantly changed the profile of metabolites associated mainly with purine and pyrimidine metabolism, butanoate metabolism, as well as alanine, aspartate, and glutamate metabolism. The related changes in transcriptomic profiles included genes involved in kinase activity and immune responses, as well as supported its impact on the purine biosynthesis pathway. CONCLUSIONS: Our multi-omics study confirmed previously known pathways involved in imatinib anticancer activity as well as correlated imatinib-relevant downregulation of expression of purine biosynthesis pathway genes with the reduction of respectful metabolites. Furthermore, considering the importance of the purine biosynthesis pathway for cancer proliferation, we identified a potentially novel mechanism for the anti-tumour activity of imatinib. Based on the results, we hypothesise metabolic modulations aiming at the reduction in purine and pyrimidine pool may ensure higher imatinib efficacy or re-sensitise imatinib-resistant tumours. ispartof: Transl Oncol vol:30 pages:101632- ispartof: location:United States status: published

Background The effects of fermented food consumption on the small intestine microbiome and its role on host homeostasis are largely uncharacterised as our knowledge on intestinal microbiota relies mainly on faecal samples analysis. We investigated changes in small intestinal microbial composition and functionality, short chain fatty acid (SCFA) profiles, and on gastro-intestinal (GI) permeability in ileostomy subjects upon the consumption of fermented milk products. Results We report the results from a randomised, cross-over, explorative study where 16 ileostomy subjects underwent 3, 2-week intervention periods. In each period, they consumed either milk fermented by Lacticaseibacillus rhamnosus CNCM I-3690, or milk fermented by Streptococcus thermophilus CNCM I-1630 and Lactobacillus delbrueckii subsp. bulgaricus CNCM I-1519, or a chemically acidified milk (placebo) daily. We performed metataxonomic, metatranscriptomic analysis, and SCFA profiling of ileostomy effluents as well as a sugar permeability test to investigate the microbiome impact of these interventions and their potential effect on mucosal barrier function. Consumption of the intervention products impacted the overall small intestinal microbiome composition and functionality, mainly due to the introduction of the product-derived bacteria that reach in several samples 50% of the total microbial community. The interventions did not affect the SCFA levels in ileostoma effluent, or gastro-intestinal permeability and the effects on the endogenous microbial community were negligible. The impact on microbiome composition was highly personalised, and we identified the poorly characterised bacterial family, Peptostreptococcaceae, to be positively associated with a low abundance of the ingested bacteria. Activity profiling of the microbiota revealed that carbon- versus amino acid-derived energy metabolism of the endogenous microbiome could be responsible for the individual-specific intervention effects on the small intestine microbiome composition and function, reflected also on urine microbial metabolites generated through proteolytic fermentation. Conclusions The ingested bacteria are the main drivers of the intervention effect on the small intestinal microbiota composition. Their transient abundance level is highly personalised and influenced by the energy metabolism of the ecosystem that is reflected by its microbial composition (http://www.clinicaltrials.gov, ID NCT NCT02920294).

Reduction of A. muciniphila relative abundance in the gut microbiota is a widely accepted signature associated with obesity-related metabolic disorders. Using untargeted metabolomics profiling of fasting plasma, our study aimed at identifying metabolic signatures associated with beneficial properties of alive and pasteurized A. muciniphila when administrated to a cohort of insulin-resistant individuals with metabolic syndrome. Our data highlighted either shared or specific alterations in the metabolome according to the form of A. muciniphila administered with respect to a control group. Common responses encompassed modulation of amino acid metabolism, characterized by reduced levels of arginine and alanine, alongside several intermediates of tyrosine, phenylalanine, tryptophan, and glutathione metabolism. The global increase in levels of acylcarnitines together with specific modulation of acetoacetate also suggested induction of ketogenesis through enhanced beta-oxidation. Moreover, our data pinpointed some metabolites of interest considering their emergence as substantial compounds pertaining to health and diseases in the more recent literature.

Phosphatidylethanolamine N-methyltransferase (PEMT) is a hepatic integral membrane protein localized to the endoplasmic reticulum (ER). PEMT catalyzes approximately 30% of hepatic phosphatidylcholine (PC) biosynthesis. Pemt(-/-) mice fed a high-fat diet (HFD) develop steatohepatitis. Interestingly, portions of the ER located close to the canaliculus are enriched in PEMT. Phospholipid balance and asymmetrical distribution by adenosine triphosphatase phospholipid transporting 8B1 (ATP8B1) on the canalicular membrane is required for membrane integrity and biliary processes. We hypothesized that PEMT is an important supplier of PC to the canaliculus and that PEMT activity is critical for the maintenance of canalicular membrane integrity and bile formation following HFD feeding when there is an increase in overall hepatic PC demand. Pemt(+/+) and Pemt(-/-) mice were fed a chow diet, an HFD, or a choline-supplemented HFD. Plasma and hepatic indices of liver function and parameters of bile formation were determined. Pemt(-/-) mice developed cholestasis, i.e, elevated plasma bile acid (BA) concentrations and decreased biliary secretion rates of BAs and PC, during HFD feeding. The maximal BA secretory rate was reduced more than 70% in HFD-fed Pemt(-/-) mice. Hepatic ABCB11/bile salt export protein, responsible for BA secretion, was decreased in Pemt(-/-) mice and appeared to be retained intracellularly. Canalicular membranes of HFD-fed mice contained fewer invaginations and displayed a smaller surface area than Pemt(+/+). mice. Choline supplementation (CS) prevented and reversed the development of HFD-induced cholestasis. Conclusion: We propose that hepatic PC availability is critical for bile formation. Dietary CS might be a potential noninvasive therapy for a specific subset of patients with cholestasis.

Background: Macrophages play an important role in regulating adipose tissue function, while their frequencies in adipose tissue vary between individuals. Adipose tissue infiltration by high frequencies of macrophages has been linked to changes in adipokine levels and low-grade inflammation, frequently associated with the progression of obesity. The objective of this project was to assess the contribution of relative macrophage frequencies to the overall subcutaneous adipose tissue gene expression using publicly available datasets.Methods: Seven publicly available microarray gene expression datasets from human subcutaneous adipose tissue biopsies (n = 519) were used together with TissueDecoder to determine the adipose tissue cell-type composition of each sample. We divided the subjects in four groups based on their relative macrophage frequencies. Differential gene expression analysis between the high and low relative macrophage frequencies groups was performed, adjusting for sex and study. Finally, biological processes were identified using pathway enrichment and network analysis.Results: We observed lower frequencies of adipocytes and higher frequencies of adipose stem cells in individuals characterized by high macrophage frequencies. We additionally studied whether, within subcutaneous adipose tissue, interindividual differences in the relative frequencies of macrophages were reflected in transcriptional differences in metabolic and inflammatory pathways. Adipose tissue of individuals with high macrophage frequencies had a higher expression of genes involved in complement activation, chemotaxis, focal adhesion, and oxidative stress. Similarly, we observed a lower expression of genes involved in lipid metabolism, fatty acid synthesis, and oxidation and mitochondrial respiration.Conclusion: We present an approach that combines publicly available subcutaneous adipose tissue gene expression datasets with a deconvolution algorithm to calculate subcutaneous adipose tissue cell-type composition. The results showed the expected increased inflammation gene expression profile accompanied by decreased gene expression in pathways related to lipid metabolism and mitochondrial respiration in subcutaneous adipose tissue in individuals characterized by high macrophage frequencies. This approach demonstrates the hidden strength of reusing publicly available data to gain cell-type-specific insights into adipose tissue function.

BackgroundA vegetarian diet (VD) may reduce future cardiovascular risk in patients with ischemic heart disease.Methods and ResultsA randomized crossover study was conducted in subjects with ischemic heart disease, assigned to 4‐week intervention periods of isocaloric VD and meat diet (MD) with individually designed diet plans, separated by a 4‐week washout period. The primary outcome was difference in oxidized low‐density lipoprotein cholesterol (LDL‐C) between diets. Secondary outcomes were differences in cardiometabolic risk factors, quality of life, gut microbiota, fecal short‐chain and branched‐chain fatty acids, and plasma metabolome. Of 150 eligible patients, 31 (21%) agreed to participate, and 27 (87%) participants completed the study. Mean oxidized LDL‐C (−2.73 U/L), total cholesterol (−5.03 mg/dL), LDL‐C (−3.87 mg/dL), and body weight (−0.67 kg) were significantly lower with the VD than with the MD. Differences between VD and MD were observed in the relative abundance of several microbe genera within the families Ruminococcaceae, Lachnospiraceae, and Akkermansiaceae. Plasma metabolites, includingl‐carnitine, acylcarnitine metabolites, and phospholipids, differed in subjects consuming VD and MD. The effect on oxidized LDL‐C in response to the VD was associated with a baseline gut microbiota composition dominated by several genera of Ruminococcaceae.ConclusionsThe VD in conjunction with optimal medical therapy reduced levels of oxidized LDL‐C, improved cardiometabolic risk factors, and altered the relative abundance of gut microbes and plasma metabolites in patients with ischemic heart disease. Our results suggest that composition of the gut microbiota at baseline may be related to the reduction of oxidized LDL‐C observed with the VD.RegistrationURL:https://www.clini​caltr​ials.gov; Unique identifier: NCT02942628.

Objective: To investigate the impact of gut microbiota manipulation on fasting and postprandial skeletal muscle metabolism in humans. Methods: 40 obese, insulin-resistant males were randomized to amoxicillin (broad-spectrum antibiotic), vancomycin (narrow-spectrum antibiotic), or placebo (7 days, 1,500 mg/day). Before and after treatment, forearm blood flow and metabolite fluxes across forearm muscle were measured under fasting and postprandial (high-fat mixed-meal) conditions. Results: Vancomycin decreased bacterial diversity, reduced the abundance of Gram-positive Firmicutes, and increased the abundance of Gram-negative Proteobacteria, whereas amoxicillin did not affect microbial composition. Neither vancomycin nor amoxicillin treatment affected fasting and postprandial plasma glucose, free fatty acid (FFA), triacylglycerol (TAG), glycerol, lactate, and insulin concentrations or forearm blood flow. Fasting and postprandial net forearm muscle glucose uptake and the release of lactate were not significantly altered by antibiotic treatment as compared to placebo. Finally, antibiotic treatment did not change fasting and postprandial glycerol, FFA, and TAG fluxes across forearm muscle. Conclusion: The present study demonstrates that short-term antibiotic treatment has no effects on fasting and postprandial forearm substrate metabolism and blood flow in obese men with impaired glucose metabolism. These data suggest that short-term strategies targeting the gut microbiota to improve metabolic health may not be effective in obese humans.

Mice homozygous for the human GRACILE syndrome mutation (Bcs1l (c.A232G)) display decreased respiratory chain complex III activity, liver dysfunction, hypoglycemia, rapid loss of white adipose tissue and early death. To assess the underlying mechanism of the lipodystrophy in homozygous mice (Bcs1l(p.S)(78G)), these and wild-type control mice were subjected to a short 4-hour fast. The homozygotes had low baseline blood glucose values, but a similar decrease in response to fasting as in wild-type mice, resulting in hypoglycemia in the majority. Despite the already depleted glycogen and increased triacylglycerol content in the mutant livers, the mice responded to fasting by further depletion and increase, respectively. Increased plasma free fatty acids (FAs) upon fasting suggested normal capacity for mobilization of lipids from white adipose tissue into circulation. Strikingly, however, serum glycerol concentration was not increased concomitantly with free FM, suggesting its rapid uptake into the liver and utilization for fuel or gluconeogenesis in the mutants. The mutant hepatocyte mitochondria were capable of responding to fasting by appropriate morphological changes, as analyzed by electron microscopy, and by increasing respiration. Mutants showed increased hepatic gene expression of major metabolic controllers typically associated with fasting response (Ppargc1a, Fgf21, Cd36) already in the fed state, suggesting a chronic starvation-like metabolic condition. Despite this, the mutant mice responded largely normally to fasting by increasing hepatic respiration and switching to FA utilization, indicating that the mechanisms driving these adaptations are not compromised by the CIII dysfunction. Summary statement: Bcs1l mutant mice with severe CIII deficiency, energy deprivation and post-weaning lipolysis respond to fasting similarly to wild-type mice, suggesting largely normal systemic lipid mobilization and utilization mechanisms.

Purpose of reviewThe view on bile salts has evolved over the years from being regarded as simple detergents that aid intestinal absorption of fat-soluble nutrients to being important hormone-like integrators of metabolism. This review provides an update on the rapidly developing field of interactions between bile salts and lipid metabolism, with a particular emphasis on the underlying mechanisms.Recent findingsThe nuclear receptor farnesoid X receptor (FXR) plays major roles in bile salt-mediated signaling pathways. The recent identification of novel FXR targets and factors involved in FXR signaling highlights the interactions of bile acids with lipid metabolism. Exciting data have been reported on the use of intestine-specific FXR agonists as well as antagonists. In addition, encouraging results for treatment of hepatic steatosis obtained with obeticholic acid in the FLINT trial underline the therapeutic potential of bile salt signaling and metabolism for the treatment of lipid disorders.SummaryModulation of FXR activity appears to be a potent target, not only for improving bile salt homeostasis, but also to improve lipid metabolism. Depending on the metabolic context both, FXR agonists as well as antagonists, could prove to be of therapeutic benefit.

Purpose of review The view on bile salts has evolved over the years from being regarded as simple detergents that aid intestinal absorption of fat-soluble nutrients to being important hormone-like integrators of metabolism. This review provides an update on the rapidly developing field of interactions between bile salts and lipid metabolism, with a particular emphasis on the underlying mechanisms. Recent findings The nuclear receptor farnesoid X receptor (FXR) plays major roles in bile salt-mediated signaling pathways. The recent identification of novel FXR targets and factors involved in FXR signaling highlights the interactions of bile acids with lipid metabolism. Exciting data have been reported on the use of intestine-specific FXR agonists as well as antagonists. In addition, encouraging results for treatment of hepatic steatosis obtained with obeticholic acid in the FLINT trial underline the therapeutic potential of bile salt signaling and metabolism for the treatment of lipid disorders. Summary Modulation of FXR activity appears to be a potent target, not only for improving bile salt homeostasis, but also to improve lipid metabolism. Depending on the metabolic context both, FXR agonists as well as antagonists, could prove to be of therapeutic benefit.

WOS:000394558200001; International audience; Evidence, mostly from experimental models, has accumulated, indicating that modifications of bacterial metabolite concentrations in the large intestine Luminal content, notably after changes in the dietary composition, may have important beneficial or deleterious consequences for the colonic epithelial cell metabolism and physiology in terms of mitochondrial energy metabolism, reactive oxygen species production, gene expression, DNA integrity, proliferation, and viability. Recent data suggest that for some bacterial metabolites, like hydrogen sulfide and butyrate, the extent of their oxidation in colonocytes affects their capacity to modulate gene expression in these cells. Modifications of the luminal bacterial metabolite concentrations may, in addition, affect the colonic pH and osmolarity, which are known to affect colonocyte biology per se. Although the colonic epithelium appears able to face, up to some extent, changes in its Luminal environment, notably by developing a metabolic adaptive response, some of these modifications may likely affect the homeostatic process of colonic epithelium renewal and the epithelial barrier function. The contribution of major changes in the colonocyte luminal environment in pathological processes, like mucosaL inflammation, preneoplasia, and neoplasia, although suggested by several studies, remains to be precisely evaluated, particularly in a long-term perspective.

A targeted reversed-phase gradient UPLC-MS/MS assay has been developed for the quantification/monitoring of amino acids and amino-containing compounds in human plasma and serum using pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AccQTag UltraTM). Derivatization of the target amino-containing compounds reagent required minimal sample preparation and resulted in analytes with excellent chromatographic and mass spectrometric properties. The resulting method, which requires only 10 µl of sample, provides the reproducible and robust separation of 66 analytes in 7.5 minutes, including baseline resolution of isomers such as e.g. leucine and isoleucine. The assay has been validated for the quantification of 33 amino compounds (predominantly amino acids) over a concentration range from 2-20 and 800µM. Intra- and inter-day accuracy of between 0.05-15.6 and 0.78 -13.7 % and precision between 0.91-16.9 % and 2.12-15.9 % were obtained. A further 33 biogenic amines can be monitored in samples for relative changes in concentration rather than quantification. Application of the assay to samples derived from healthy controls and patients suffering from acetaminophen (APAP, paracetamol) induced acute liver failure (ALF) showed significant differences in the amounts of aromatic and branched chain amino acids between the groups as well as a number of other analytes, including the novel observation of increased concentrations of sarcosine in ALF patients. The properties of the developed assay, including short analysis time, make it suitable for high throughput targeted UPLC-ESI-MS/MS metabonomic analysis in clinical and epidemiological environments.

To investigate the potential of therapies which reduce glucocorticoid action in patients with Type 2 diabetes we performed a randomized, double-blinded, placebo-controlled crossover study of acute glucocorticoid blockade, using the glucocorticoid receptor antagonist RU38486 (mifepristone) and cortisol biosynthesis inhibitor (metyrapone), in 14 men with Type 2 diabetes. Stable isotope dilution methodologies were used to measure the rates of appearance of glucose, glycerol, and free fatty acids (FFAs), including during a low-dose (10 mU·m −2·min−1) hyperinsulinemic clamp, and subgroup analysis was conducted in patients with high or low liver fat content measured by magnetic resonance spectroscopy ( n = 7/group). Glucocorticoid blockade lowered fasting glucose and insulin levels and improved insulin sensitivity of FFA and glycerol turnover and hepatic glucose production. Among this population with Type 2 diabetes high liver fat was associated with hyperinsulinemia, higher fasting glucose levels, peripheral and hepatic insulin resistance, and impaired suppression of FFA oxidation and FFA and glycerol turnover during hyperinsulinemia. Glucocorticoid blockade had similar effects in those with and without high liver fat. Longer term treatments targeting glucocorticoid action may be useful in Type 2 diabetes with and without fatty liver.

Within boreal and temperate forest ecosystems, the majority of trees and shrubs form beneficial relationships with mutualistic ectomycorrhizal (ECM) fungi that support plant health through increased access to nutrients as well as aiding in stress and pest tolerance. The intimate interaction between fungal hyphae and plant roots results in a new symbiotic “organ” called the ECM root tip. Little is understood concerning the metabolic reprogramming that favors the formation of this hybrid tissue in compatible interactions and what prevents the formation of ECM root tips in incompatible interactions. We show here that the metabolic changes during favorable colonization between the ECM fungus Laccaria bicolor and its compatible host, Populus trichocarpa, are characterized by shifts in aromatic acid, organic acid, and fatty acid metabolism. We demonstrate that this extensive metabolic reprogramming is repressed in incompatible interactions and that more defensive compounds are produced or retained. We also demonstrate that L. bicolor can metabolize a number of secreted defensive compounds and that the degradation of some of these compounds produces immune response metabolites (e.g., salicylic acid from salicin). Therefore, our results suggest that the metabolic responsiveness of plant roots to L. bicolor is a determinant factor in fungus–host interactions.

Rationale: High-fat diet with obesity-associated co-morbidities triggers cardiac remodeling and renders the heart more vulnerable to ischemia/reperfusion injury. However, the effect of high-fat diet without obesity and associated co-morbidities is presently unknown.Objectives: To characterize a non-obese mouse model of high-fat diet, assess the vulnerability of hearts to reperfusion injury and to investigate cardiac cellular remodeling in relation to the mechanism(s) underlying reperfusion injury.Methods and Results: Feeding C57BL/6J male mice high-fat diet for 20 weeks did not induce obesity, diabetes, cardiac hypertrophy, cardiac dysfunction, atherosclerosis or cardiac apoptosis. However, isolated perfused hearts from mice fed high-fat diet were more vulnerable to reperfusion injury than those from mice fed normal diet. In isolated cardiomyocytes, high-fat diet was associated with higher diastolic intracellular Ca2+ concentration and greater damage to isolated cardiomyocytes following simulated ischemia/reperfusion. High-fat diet was also associated with changes in mitochondrial morphology and expression of some related proteins but not mitochondrial respiration or reactive oxygen species turnover rates. Proteomics, western blot and high-performance liquid chromatography techniques revealed that high-fat diet led to less cardiac oxidative stress, higher catalase expression and significant changes in expression of putative components of the mitochondrial permeability transition pore (mPTP). Inhibition of the mPTP conferred relatively more cardio-protection in the high-fat fed mice compared to normal diet.Conclusions: This study shows for the first time that high-fat diet, independent of obesity-induced co-morbidities, triggers changes in cardiac oxidative state, calcium handling and mitochondria which are likely to be responsible for increased vulnerability to cardiac insults.

Iron (Fe) deficiency is an important agricultural concern that leads to lower yields and crop quality. A better understanding of the condition at the metabolome level could contribute to the design of strategies to ameliorate Fe-deficiency problems. Fe-sufficient and Fe-deficient soybean leaf extracts and whole leaves were analyzed by liquid (1)H nuclear magnetic resonance (NMR) and high-resolution magic-angle spinning NMR spectroscopy, respectively. Overall, 30 compounds were measurable and identifiable (comprising amino and organic acids, fatty acids, carbohydrates, alcohols, polyphenols, and others), along with 22 additional spin systems (still unassigned). Thus, metabolite differences between treatment conditions could be evaluated for different compound families simultaneously. Statistically relevant metabolite changes upon Fe deficiency included higher levels of alanine, asparagine/aspartate, threonine, valine, GABA, acetate, choline, ethanolamine, hypoxanthine, trigonelline, and polyphenols and lower levels of citrate, malate, ethanol, methanol, chlorogenate, and 3-methyl-2-oxovalerate. The data indicate that the main metabolic impacts of Fe deficiency in soybean include enhanced tricarboxylic acid cycle activity, enhanced activation of oxidative stress protection mechanisms and enhanced amino acid accumulation. Metabolites showing accumulation differences in Fe-starved but visually asymptomatic leaves could serve as biomarkers for early detection of Fe-deficiency stress.

The worldwide prevalence of obesity-associated pathologies, including type 2 diabetes, requires thorough investigation of mechanisms and interventions. Recent studies have highlighted thyroid hormone analogs and derivatives as potential agents able to counteract such pathologies. In this study, in rats receiving a high-fat diet (HFD), we analyzed the effects of a 4-wk daily administration of a naturally occurring iodothyronine, 3,5-diiodo-L-thyronine (T2), on the gastrocnemius muscle metabolic/structural phenotype and insulin signaling. The HFD-induced increases in muscle levels of fatty acid translocase (3-fold; P

Seeds ofMedicago truncatula, a genomic model species for legumes, exhibit physiological and physical dormancy. Here, the factors influencing the germination behaviour of freshly harvested and stored seeds were investigated using several genotypes. Hardseededness is promoted when mature seeds are equilibrated at relative humidities (RH) below 75%. The release of physical dormancy during imbibition was dependent on the initial water content/RH that the seeds were dried to: the drier the seeds, the longer the imbibition time needed to break physical dormancy. The kinetics of physical dormancy release was slower than that of physiological dormancy, making it possible to uncouple both phenomena. Freshly harvested embryos without seed coverings germinated at the same speed as afterripened seeds. The depth of dormancy varied between differentM. truncatulagenotypes, from more to less dormant: DZA315.16>A17 (Jemalong)>R108>DZA45.5. This difference was eliminated by removing the endosperm. Collectively, these observations indicate that the endosperm is likely the main factor in the reduced germination of freshly harvested seeds. White light decreased germination speed of dormant seeds whereas it had no effect on non-dormant seeds. Recently harvested seeds were most dormant at temperatures above 17°C, whereas afterripened seeds germinated over a wider range of temperature. Fluridone could efficiently break dormancy, reinforcing the role of abscisic acid (ABA) synthesis. However, dormancy was not affected by gibberellic acid (100 μM GA3) or nitrate. The particular dormancy features unravelled here forM. truncatula, combined with the available genomic resources, make it a new, useful model for genetic and molecular studies which can complement those developed for Arabidopsis.

The oxysterol-activated nuclear receptor liver X receptor alpha (LXR alpha) has been implicated in the control of both cholesterol and fatty acid metabolism. In this study, we have evaluated the effects of excess dietary cholesterol on hepatic cholesterol metabolism, lipogenesis, and VLDL production in homozygous (Lxr alpha(-/-)), heterozygous (Lxr alpha(+/-)), and wild-type mice. Mice were fed either chow or a cholesterol-enriched diet (1%, w/w) for 2 weeks. On the high-cholesterol diet, fractional cholesterol absorption was higher in Lxr alpha(-/-) mice than in controls, leading to delivery of more dietary cholesterol to the liver. Lxr alpha(-/-) mice were not able to induce expression of hepatic Abcg5/Abcg8, and massive accumulation of free cholesterol and cholesteryl esters (CEs) occurred. Interestingly, despite the inability to upregulate Abcg5/Abcg8, the highly increased hepatic free cholesterol content did stimulate biliary cholesterol output in Lxr alpha(-/-) mice. Hepatic cholesterol accumulation was accompanied by decreased hepatic expression of lipogenic genes, probably caused by impaired sterol-regulatory element binding protein 1c processing, lower hepatic triglyceride (TG) contents, strongly reduced plasma TG concentrations (290%), and reduced VLDL-TG production rates (-60%) in Lxr alpha(-/-) mice. VLDL particles were smaller and CE-enriched under these conditions. Lxr alpha deficiency did not affect VLDL formation under chow-fed conditions. Hepatic stearyl coenzyme A desaturase 1 expression was decreased dramatically in Lxr alpha(-/-) mice and did not respond to cholesterol feeding, but fatty acid profiles of liver and VLDL were only slightly different between Lxr alpha(-/-) and wild-type mice. Our data indicate that displacement of TGs by CEs during the VLDL assembly process underlies hypotriglyceridemia in cholesterol-fed Lxr alpha(-/-) mice. - van der Veen, J. N., R. Havinga, V. W. Bloks, A. K. Groen, and F. Kuipers. Cholesterol feeding strongly reduces hepatic VLDL-triglyceride production in mice lacking the liver X receptor a.

BACKGROUND: Obesity may be associated with a lowered use of fat as a fuel, which may contribute to the enlarged adipose tissue stores. AIM: The aim of the present study was to study fatty acid use in the fasting state and in response to a high fat load in a large cohort of obese subjects (n = 701) and a lean reference group (n = 113). METHODS: Subjects from eight European centers underwent a test meal challenge containing 95 en% fat [energy content 50% of estimated resting energy expenditure (EE)]. Fasting and postprandial fat oxidation and circulating metabolites and hormones were determined over a 3-h period. RESULTS: Postprandial fat oxidation (as percent of postprandial EE, adjusted for fat mass, age, gender, center, and energy content of the meal) decreased with increasing body mass index (BMI) category (P < 0.01), an effect present only in those obese subjects with a relatively low fasting fat oxidation (below median, interaction BMI category x fasting fat oxidation, P < 0.001). Fasting fat oxidation increased with increasing BMI category (P < 0.001), which was normalized after adjustment for fat-free mass and fat mass. Furthermore, insulin resistance was positively associated with postprandial fat oxidation (P < 0.05) and negatively associated with fasting fat oxidation (expressed as percent of EE), independent of body composition. CONCLUSIONS: The present data indicate an impaired capacity to regulate fat oxidation in the obese insulin-resistant state, which is hypothesized to play a role in the etiology of both obesity and insulin resistance.