Implication of fermentable carbohydrates targeting the gut microbiota on conjugated linoleic acid production in high-fat-fed mice.

In vitro experiments have shown that isolated human gut bacteria are able to metabolise PUFA into conjugated PUFA like conjugated linoleic acids (CLA). The hypothesis of the present paper was that high-fat (HF) diet feeding and supplementation with fermentable carbohydrates that have prebiotic properties modulate the in vivo production of CLA by the mouse gut microbiota. Mice were treated for 4 weeks as follows: control (CT) groups were fed a standard diet; HF groups were fed a HF diet rich in linoleic acid (18 : 2n-6); the third groups were fed with the HF diet supplemented with either inulin-type fructans (HF-ITF) or arabinoxylans (HF-Ax). HF diet feeding increased rumenic acid (cis-9,trans-11-18 : 2 CLA) content both in the caecal and liver tissues compared with the CT groups. ITF supplementation had no major effect compared with the HF diet whereas Ax supplementation increased further rumenic acid (cis-9,trans-11-18 : 2 CLA) in the caecal tissue. These differences between both prebiotics may be linked to the high fat-binding capacity of Ax that provides more substrates for bacterial metabolism and to differential modulation of the gut microbiota (specific increase in Roseburia spp. in HF-Ax v. HF). In conclusion, these experiments supply the proof of concept that the mouse gut microbiota produces CLA in vivo, with consequences on the level of CLA in the caecal and liver tissues. We postulate that the CLA-producing bacteria could be a mediator to consider in the metabolic effects of both HF diet feeding and prebiotic supplementation.

Prebiotic approach alleviates hepatic steatosis: implication of fatty acid oxidative and cholesterol synthesis pathways.

SCOPE: Recent data suggest that gut microbiota contributes to the regulation of host lipid metabolism. We report how fermentable dietary fructo-oligosaccharides (FOS) control hepatic steatosis induced by n-3 PUFA depletion, which leads to hepatic alterations similar to those observed in non-alcoholic fatty liver disease patients. METHODS AND RESULTS: C57Bl/6J mice fed an n-3 PUFA-depleted diet for 3 months were supplemented with FOS during the last 10 days of treatment. FOS-treated mice exhibited higher caecal Bifidobacterium spp. and lower Roseburia spp. content. Microarray analysis of hepatic mRNA revealed that FOS supplementation reduced hepatic triglyceride accumulation through a proliferator-activated receptor α-stimulation of fatty acid oxidation and lessened cholesterol accumulation by inhibiting sterol regulatory element binding protein 2-dependent cholesterol synthesis. Cultured precision-cut liver slices confirmed the inhibition of fatty acid oxidation. FOS effects were related to a decreased hepatic micro-RNA33 expression and to an increased colonic glucagon-like peptide 1 production. CONCLUSIONS: The changes in gut microbiota composition by n-3 PUFA-depletion and prebiotics modulate hepatic steatosis by changing gene expression in the liver, a phenomenon that could implicate micro-RNA and gut-derived hormones. Our data underline the advantage of targeting the gut microbiota by colonic nutrients in the management of liver disease.

Restoring specific lactobacilli levels decreases inflammation and muscle atrophy markers in an acute leukemia mouse model.

The gut microbiota has recently been proposed as a novel component in the regulation of host homeostasis and immunity. We have assessed for the first time the role of the gut microbiota in a mouse model of leukemia (transplantation of BaF3 cells containing ectopic expression of Bcr-Abl), characterized at the final stage by a loss of fat mass, muscle atrophy, anorexia and inflammation. The gut microbial 16S rDNA analysis, using PCR-Denaturating Gradient Gel Electrophoresis and quantitative PCR, reveals a dysbiosis and a selective modulation of Lactobacillus spp. (decrease of L. reuteri and L. johnsonii/gasseri in favor of L. murinus/animalis) in the BaF3 mice compared to the controls. The restoration of Lactobacillus species by oral supplementation with L. reuteri 100-23 and L. gasseri 311476 reduced the expression of atrophy markers (Atrogin-1, MuRF1, LC3, Cathepsin L) in the gastrocnemius and in the tibialis, a phenomenon correlated with a decrease of inflammatory cytokines (interleukin-6, monocyte chemoattractant protein-1, interleukin-4, granulocyte colony-stimulating factor, quantified by multiplex immuno-assay). These positive effects are strain- and/or species-specific since L. acidophilus NCFM supplementation does not impact on muscle atrophy markers and systemic inflammation. Altogether, these results suggest that the gut microbiota could constitute a novel therapeutic target in the management of leukemia-associated inflammation and related disorders in the muscle.

Hepatic n-3 polyunsaturated fatty acid depletion promotes steatosis and insulin resistance in mice: genomic analysis of cellular targets.

Patients with non-alcoholic fatty liver disease are characterised by a decreased n-3/n-6 polyunsaturated fatty acid (PUFA) ratio in hepatic phospholipids. The metabolic consequences of n-3 PUFA depletion in the liver are poorly understood. We have reproduced a drastic drop in n-3 PUFA among hepatic phospholipids by feeding C57Bl/6J mice for 3 months with an n-3 PUFA depleted diet (DEF) versus a control diet (CT), which only differed in the PUFA content. DEF mice exhibited hepatic insulin resistance (assessed by euglycemic-hyperinsulinemic clamp) and steatosis that was associated with a decrease in fatty acid oxidation and occurred despite a higher capacity for triglyceride secretion. Microarray and qPCR analysis of the liver tissue revealed higher expression of all the enzymes involved in lipogenesis in DEF mice compared to CT mice, as well as increased expression and activation of sterol regulatory element binding protein-1c (SREBP-1c). Our data suggest that the activation of the liver X receptor pathway is involved in the overexpression of SREBP-1c, and this phenomenon cannot be attributed to insulin or to endoplasmic reticulum stress responses. In conclusion, n-3 PUFA depletion in liver phospholipids leads to activation of SREBP-1c and lipogenesis, which contributes to hepatic steatosis.

Gut microbiota fermentation of prebiotics increases satietogenic and incretin gut peptide production with consequences for appetite sensation and glucose response after a meal.

BACKGROUND: We have previously shown that gut microbial fermentation of prebiotics promotes satiety and lowers hunger and energy intake in humans. In rodents, these effects are associated with an increase in plasma gut peptide concentrations, which are involved in appetite regulation and glucose homeostasis. OBJECTIVE: Our aim was to examine the effects of prebiotic supplementation on satiety and related hormones during a test meal for human volunteers by using a noninvasive micromethod for blood sampling to measure plasma gut peptide concentrations. DESIGN: This study was a randomized, double-blind, parallel, placebo-controlled trial. A total of 10 healthy adults (5 men and 5 women) were randomly assigned to groups that received either 16 g prebiotics/d or 16 g dextrin maltose/d for 2 wk. Meal tolerance tests were performed in the morning to measure the following: hydrogen breath test, satiety, glucose homeostasis, and related hormone response. RESULTS: We show that the prebiotic treatment increased breath-hydrogen excretion (a marker of gut microbiota fermentation) by approximately 3-fold and lowered hunger rates. Prebiotics increased plasma glucagon-like peptide 1 and peptide YY concentrations, whereas postprandial plasma glucose responses decreased after the standardized meal. The areas under the curve for plasma glucagon-like peptide 1 and breath-hydrogen excretion measured after the meal (0-60 min) were significantly correlated (r = 0.85, P = 0.007). The glucose response was inversely correlated with the breath-hydrogen excretion areas under the curve (0-180 min; r = -0.73, P = 0.02). CONCLUSION: Prebiotic supplementation was associated with an increase in plasma gut peptide concentrations (glucagon-like peptide 1 and peptide YY), which may contribute in part to changes in appetite sensation and glucose excursion responses after a meal in healthy subjects.

Lipid peroxidation is not a prerequisite for the development of obesity and diabetes in high-fat-fed mice.

The mechanism, by which a high-fat (HF) diet could impair glucose metabolism, is not completely understood but could be related to inflammation, lipotoxicity and oxidative stress. Lipid peroxides have been proposed as key mediators of intracellular metabolic response. The purpose of the present study was to analyse, in mice fed with a HF diet, the possible association between obesity and glucose tolerance on the one hand, and between oxidative stress and lipid peroxidation on the other hand. The present results show that a HF diet (70 % energy as fat), v. a high-carbohydrate chow diet (control), increases body weight and fat mass development, and impairs glycaemia and insulinaemia within 4 weeks. It also promotes the expression of NADPH oxidase in the liver--signing both oxidative and inflammatory stress--but decreases thiobarbituric acid-reactive substances content in the liver as well as in epididymal, subcutaneous and visceral adipose tissues. HF diet, with elevated vitamin E content, induces high concentration of alpha-tocopherol in liver and adipose tissues, which contributes to the protection against lipid peroxidation. Thus, lipid peroxidation in key organs is not necessarily related to the development of metabolic disorders associated with diabetes and obesity.