Defective NOD2 peptidoglycan sensing promotes diet-induced inflammation, dysbiosis, and insulin resistance.

Pattern recognition receptors link metabolite and bacteria-derived inflammation to insulin resistance during obesity. We demonstrate that NOD2 detection of bacterial cell wall peptidoglycan (PGN) regulates metabolic inflammation and insulin sensitivity. An obesity-promoting high-fat diet (HFD) increased NOD2 in hepatocytes and adipocytes, and NOD2(-/-) mice have increased adipose tissue and liver inflammation and exacerbated insulin resistance during a HFD. This effect is independent of altered adiposity or NOD2 in hematopoietic-derived immune cells. Instead, increased metabolic inflammation and insulin resistance in NOD2(-/-) mice is associated with increased commensal bacterial translocation from the gut into adipose tissue and liver. An intact PGN-NOD2 sensing system regulated gut mucosal bacterial colonization and a metabolic tissue dysbiosis that is a potential trigger for increased metabolic inflammation and insulin resistance. Gut dysbiosis in HFD-fed NOD2(-/-) mice is an independent and transmissible factor that contributes to metabolic inflammation and insulin resistance when transferred to WT, germ-free mice. These findings warrant scrutiny of bacterial component detection, dysbiosis, and protective immune responses in the links between inflammatory gut and metabolic diseases, including diabetes.

[Intestinal microbiota and novel therapeutic perspectives for the treatment of metabolic diseases]. / Le microbiote intestinal à l'origine de nouvelles perspectives thérapeutiques pour les maladies métaboliques ?

A new organ has emerged over the course of the last century: the intestinal microbiota. It is characterized by numerous functions provided by several billions of bacteria inhabiting and living in harmony in the lumen and in the mucosal layer of the intestinal epithelium. More than 4 million genes composed by more than 1 500 species interact with each other, with the host and the environment to set up a mutualistic ecological group. A nutritional stress will modify the terms of the symbiosis between the host and the microbiota for the control of energy homeostasis. It is now thought that the pandemic of diabetes and obesity, not being due to the sole variations of our genome, would be due to changes in our metagenome: our intestinal bacteria. This organ which genomic varies on an everyday basis is inherited from our mother and the closed environment at birth. The corresponding diversity, the rapid evolution of gene expression, its influence on metabolism, as well as the very recent discovery of the existence of an tissue microbiota within the host, open new therapeutic pharmacological and nutritional opportunities as well as the identification of very accurate biomarkers constituting a personalized metagenomic identity card. Hence, individualized medicine foresees its origin within the metagenome.

Metagenome and metabolism: the tissue microbiota hypothesis.

Over the last decade, the research community has revealed the role of a new organ: the intestinal microbiota. It is considered as a symbiont that is part of our organism since, at birth, it educates the immune system and contributes to the development of the intestinal vasculature and most probably the nervous system. With the advent of new generation sequencing techniques, a catalogue of genes that belong to this microbiome has been established that lists more than 5 million non-redundant genes called the metagenome. Using germ free mice colonized with the microbiota from different origins, it has been formally demonstrated that the intestinal microbiota causes the onset of metabolic diseases. Further to the role of point mutations in our genome, the microbiota can explain the on-going worldwide pandemic of obesity and diabetes, its dissemination and family inheritance, as well as the diversity of the associated metabolic phenotypes. More recently, the discovery of bacterial DNA within host tissues, such as the liver, the adipose tissue and the blood, which establishes a tissue microbiota, introduces new opportunities to identify targets and predictive biomarkers based on the host to microbiota interaction, as well as to define new strategies for pharmacological, immunomodulatory vaccines and nutritional applications.

Blood microbiota dysbiosis is associated with the onset of cardiovascular events in a large general population: the D.E.S.I.R. study.

AIM: We recently described a human blood microbiome and a connection between this microbiome and the onset of diabetes. The aim of the current study was to assess the association between blood microbiota and incident cardiovascular disease. METHODS AND RESULTS: D.E.S.I.R. is a longitudinal study with the primary aim of describing the natural history of the metabolic syndrome and its complications. Participants were evaluated at inclusion and at 3-, 6-, and 9-yearly follow-up visits. The 16S ribosomal DNA bacterial gene sequence, that is common to the vast majority of bacteria (Eubac) and a sequence that mostly represents Proteobacteria (Pbac), were measured in blood collected at baseline from 3936 participants. 73 incident cases of acute cardiovascular events, including 30 myocardial infarctions were recorded. Eubac was positively correlated with Pbac (r = 0.59; P<0.0001). In those destined to have cardiovascular complications, Eubac was lower (0.14±0.26 vs 0.12±0.29 ng/µl; P = 0.02) whereas a non significant increase in Pbac was observed. In multivariate Cox analysis, Eubac was inversely correlated with the onset of cardiovascular complications, (hazards ratio 0.50 95% CI 0.35-0.70) whereas Pbac (1.56, 95%CI 1.12-2.15) was directly correlated. CONCLUSION: Pbac and Eubac were shown to be independent markers of the risk of cardiovascular disease. This finding is evidence for the new concept of the role played by blood microbiota dysbiosis on atherothrombotic disease. This concept may help to elucidate the relation between bacteria and cardiovascular disease.

Intestinal MicrobiOMICS to define health and disease in human and mice.

Over the last five years an increasing effort has been made to understand the role of intestinal microbiota in health and disease, resulting in regarding to it as a new organ actively involved in the control of host metabolism, both in humans and mice. Amongst hundreds (up to thousand) germ species inhabiting the intestine, few of them are cultivable. Nevertheless, next-generation sequencing-based molecular technologies have been developed, allowing to overcome this problem and shed light on the way the gut microbiota undergoes dramatic changes during (patho)-physiological modifications of the host. Hence, the study of the overall gut germ genome (metagenome) and transcriptome (microbiome) has been launched. Thus, Genomics and Transcriptomics have begun to be increasingly used, opening the so called "Omics" era, including Proteomics and Metabolomics techniques as well. Taken together, the "Omics" allow the study of gut microbiota impact on whole host metabolism, resulting in the definition of new metabolic profiles (i.e. the presence of metabolites within the blood defines a metabolomic profile), others than those based on nucleic acid analyses only. Once demonstrated the involvement of gut microbiota within metabolic diseases, "Omics" analyses has allowed the identification of the obesity-induced gut microbiota imbalance, characterized by increased Firmicutes to Bacteroidetes ratio (metagenomics) and of the so called "core microbiome", focusing on the gut microbiota at a gene- rather than, solely, at a taxonomic-level. In addition, metabolomics studies revealed, for instance, the implication of gut microbiota to nonalcoholic fatty liver disease in insulin-resistant mice. Additionally, the use of germ-free (axenic) mice has made possible the microflora transfer to investigate the mechanisms through which gut microbes modulate host metabolism, albeit the molecular actors of the host� � � gut-microbiota interplay remain to be fully determined. Here, we report the role of "Omics" in the multiple analyses of gut microbiota-driven metabolic modifications of the host, proposing also to focus on lipopolysaccharides (LPS), the Gram negative proinflammatory molecules we already showed to be the initiators of metabolic diseases.

Gut microbiota and diabetes: from pathogenesis to therapeutic perspective.

More than several hundreds of millions of people will be diabetic and obese over the next decades in front of which the actual therapeutic approaches aim at treating the consequences rather than causes of the impaired metabolism. This strategy is not efficient and new paradigms should be found. The wide analysis of the genome cannot predict or explain more than 10-20% of the disease, whereas changes in feeding and social behavior have certainly a major impact. However, the molecular mechanisms linking environmental factors and genetic susceptibility were so far not envisioned until the recent discovery of a hidden source of genomic diversity, i.e., the metagenome. More than 3 million genes from several hundreds of species constitute our intestinal microbiome. First key experiments have demonstrated that this biome can by itself transfer metabolic disease. The mechanisms are unknown but could be involved in the modulation of energy harvesting capacity by the host as well as the low-grade inflammation and the corresponding immune response on adipose tissue plasticity, hepatic steatosis, insulin resistance and even the secondary cardiovascular events. Secreted bacterial factors reach the circulating blood, and even full bacteria from intestinal microbiota can reach tissues where inflammation is triggered. The last 5 years have demonstrated that intestinal microbiota, at its molecular level, is a causal factor early in the development of the diseases. Nonetheless, much more need to be uncovered in order to identify first, new predictive biomarkers so that preventive strategies based on pre- and probiotics, and second, new therapeutic strategies against the cause rather than the consequence of hyperglycemia and body weight gain.

Intestinal mucosal adherence and translocation of commensal bacteria at the early onset of type 2 diabetes: molecular mechanisms and probiotic treatment.

A fat-enriched diet modifies intestinal microbiota and initiates a low-grade inflammation, insulin resistance and type-2 diabetes. Here, we demonstrate that before the onset of diabetes, after only one week of a high-fat diet (HFD), live commensal intestinal bacteria are present in large numbers in the adipose tissue and the blood where they can induce inflammation. This translocation is prevented in mice lacking the microbial pattern recognition receptors Nod1 or CD14, but overtly increased in Myd88 knockout and ob/ob mouse. This 'metabolic bacteremia' is characterized by an increased co-localization with dendritic cells from the intestinal lamina propria and by an augmented intestinal mucosal adherence of non-pathogenic Escherichia coli. The bacterial translocation process from intestine towards tissue can be reversed by six weeks of treatment with the probiotic strain Bifidobacterium animalis subsp. lactis 420, which improves the animals' overall inflammatory and metabolic status. Altogether, these data demonstrate that the early onset of HFD-induced hyperglycemia is characterized by an increased bacterial translocation from intestine towards tissues, fuelling a continuous metabolic bacteremia, which could represent new therapeutic targets.

Role of central nervous system glucagon-like Peptide-1 receptors in enteric glucose sensing.

OBJECTIVE: Ingested glucose is detected by specialized sensors in the enteric/hepatoportal vein, which send neural signals to the brain, which in turn regulates key peripheral tissues. Hence, impairment in the control of enteric-neural glucose sensing could contribute to disordered glucose homeostasis. The aim of this study was to determine the cells in the brain targeted by the activation of the enteric glucose-sensing system. RESEARCH DESIGN AND METHODS: We selectively activated the axis in mice using a low-rate intragastric glucose infusion in wild-type and glucagon-like peptide-1 (GLP-1) receptor knockout mice, neuropeptide Y-and proopiomelanocortin-green fluorescent protein-expressing mice, and high-fat diet diabetic mice. We quantified the whole-body glucose utilization rate and the pattern of c-Fos positive in the brain. RESULTS: Enteric glucose increased muscle glycogen synthesis by 30% and regulates c-Fos expression in the brainstem and the hypothalamus. Moreover, the synthesis of muscle glycogen was diminished after central infusion of the GLP-1 receptor (GLP-1Rc) antagonist Exendin 9-39 and abolished in GLP-1Rc knockout mice. Gut-glucose-sensitive c-Fos-positive cells of the arcuate nucleus colocalized with neuropeptide Y-positive neurons but not with proopiomelanocortin-positive neurons. Furthermore, high-fat feeding prevented the enteric activation of c-Fos expression. CONCLUSIONS: We conclude that the gut-glucose sensor modulates peripheral glucose metabolism through a nutrient-sensitive mechanism, which requires brain GLP-1Rc signaling and is impaired during diabetes.

Synergy between Lactobacillus paracasei and its bacterial products to counteract stress-induced gut permeability and sensitivity increase in rats.

Stressful events result in the alteration of gut permeability and sensitivity. Lactobacillus paracasei NCC2461 (Lpa) therapy prevents antibiotic-induced visceral hyperalgesia in mice. This study aimed at evaluating the influence of 3 probiotic strains: Bifidobacterium lactis NCC362, Lactobacillus johnsonii NCC533, and Lpa on stress-mediated alterations of colorectal hyperalgesia, on gut paracellular permeability and whether bacteria and/or bacterial products present in the spent culture medium (SCM) were involved in the antinociceptive properties of the effective strain. Rat pups were separated from their mothers 3 h/d during postnatal d 2-14. At wk 13, gut paracellular permeability was determined as a percentage of urinary excreted (51)Cr-EDTA and visceral sensitivity to colorectal distension (CRD), assessed by abdominal muscle electromyography. Visceral sensitivity was also analyzed in adults rats subjected to partial restraint stress (PRS, 2 h restriction of body movements). Rats received either the probiotics resuspended in SCM or fresh growth medium as control for 2 wk. Maternal deprivation significantly increased colonic sensitivity in response to CRD and enhanced gut paracellular permeability compared with control rats. Only Lpa treatment significantly improved stress-induced visceral pain and restored normal gut permeability. Similarly, among the 3 probiotics tested, only Lpa prevented PRS-mediated visceral hyperalgesia. Both bacteria and bacterial products present in Lpa SCM were required for the antinociceptive properties against PRS. This study illustrates strain-specific effects and suggests a synergistic interplay between L. paracasei bacteria and bacterial products generated during fermentation and growth that confers the ability to suppress PRS-induced hypersensitivity in rats.

Metabolic endotoxemia initiates obesity and insulin resistance.

Diabetes and obesity are two metabolic diseases characterized by insulin resistance and a low-grade inflammation. Seeking an inflammatory factor causative of the onset of insulin resistance, obesity, and diabetes, we have identified bacterial lipopolysaccharide (LPS) as a triggering factor. We found that normal endotoxemia increased or decreased during the fed or fasted state, respectively, on a nutritional basis and that a 4-week high-fat diet chronically increased plasma LPS concentration two to three times, a threshold that we have defined as metabolic endotoxemia. Importantly, a high-fat diet increased the proportion of an LPS-containing microbiota in the gut. When metabolic endotoxemia was induced for 4 weeks in mice through continuous subcutaneous infusion of LPS, fasted glycemia and insulinemia and whole-body, liver, and adipose tissue weight gain were increased to a similar extent as in high-fat-fed mice. In addition, adipose tissue F4/80-positive cells and markers of inflammation, and liver triglyceride content, were increased. Furthermore, liver, but not whole-body, insulin resistance was detected in LPS-infused mice. CD14 mutant mice resisted most of the LPS and high-fat diet-induced features of metabolic diseases. This new finding demonstrates that metabolic endotoxemia dysregulates the inflammatory tone and triggers body weight gain and diabetes. We conclude that the LPS/CD14 system sets the tone of insulin sensitivity and the onset of diabetes and obesity. Lowering plasma LPS concentration could be a potent strategy for the control of metabolic diseases.

Impairment of the intestinal barrier by ethanol involves enteric microflora and mast cell activation in rodents.

Alcohol hepatic toxicity in heavy drinkers is associated with high endotoxin blood levels and increased intestinal permeability. Because endotoxins can cross damaged mucosa, we investigated the mechanisms through which ethanol impairs the colonic epithelium of rats submitted to acute alcohol intake. Colonic permeability to (51)Cr-ethylenediamintetraacetic acid was increased 24 hours after 3.0 g/kg ethanol intake (3.2 +/- 0.2% versus 2.2 +/- 0.2%) and was associated with significant endotoxemia. Antibiotics and doxantrazole (a mast cell membrane stabilizer) significantly inhibited the effect of ethanol. Two hours after intake, plasma concentrations of ethanol were twofold higher in antibiotic-treated rats than in controls (155.8 +/- 9.3 mg/dl versus 75.7 +/- 7.6 mg/dl, P < 0.001). Lumenal concentrations of acetaldehyde were markedly increased after ethanol intake (132.6 +/- 31.6 micromol/L versus 20.8 +/- 1.4 micromol/L, P < 0.05) and antibiotics diminished this increase (86.2 +/- 10.9 micromol/L). In colonic samples mounted in Ussing chambers, acetaldehyde but not ethanol increased dextran flux across the mucosa by 54%. Doxantrazole inhibited the effect of acetaldehyde. This study demonstrates that an acute and moderate ethanol intake alters the epithelial barrier through ethanol oxidation into acetaldehyde by the colonic microflora and downstream mast cell activation. Such alterations that remain for longer periods could result in excessive endotoxin passage, which could explain the subsequent endotoxemia frequently observed in patients with alcoholic liver disease.