Metformin is widely used in the treatment of type 2 diabetes (T2D), but its mechanism of action is poorly defined. Recent evidence implicates the gut microbiota as a site of metformin action. In a double-blind study, we randomized individuals with treatment-naive T2D to placebo or metformin for 4 months and showed that metformin had strong effects on the gut microbiome. These results were verified in a subset of the placebo group that switched to metformin 6 months after the start of the trial. Transfer of fecal samples (obtained before and 4 months after treatment) from metformin-treated donors to germ-free mice showed that glucose tolerance was improved in mice that received metformin-altered microbiota. By directly investigating metformin-microbiota interactions in a gut simulator, we showed that metformin affected pathways with common biological functions in species from two different phyla, and many of the metformin-regulated genes in these species encoded metalloproteins or metal transporters. Our findings provide support for the notion that altered gut microbiota mediates some of metformin's antidiabetic effects.

Hepatic steatosis is a multifactorial condition that is often observed in obese patients and is a prelude to non-alcoholic fatty liver disease. Here, we combine shotgun sequencing of fecal metagenomes with molecular phenomics (hepatic transcriptome and plasma and urine metabolomes) in two well-characterized cohorts of morbidly obese women recruited to the FLORINASH study. We reveal molecular networks linking the gut microbiome and the host phenome to hepatic steatosis. Patients with steatosis have low microbial gene richness and increased genetic potential for the processing of dietary lipids and endotoxin biosynthesis (notably from Proteobacteria), hepatic inflammation and dysregulation of aromatic and branched-chain amino acid metabolism. We demonstrated that fecal microbiota transplants and chronic treatment with phenylacetic acid, a microbial product of aromatic amino acid metabolism, successfully trigger steatosis and branched-chain amino acid metabolism. Molecular phenomic signatures were predictive (area under the curve = 87%) and consistent with the gut microbiome having an effect on the steatosis phenome (>75% shared variation) and, therefore, actionable via microbiome-based therapies.

OBJECTIVEThis study sought to identify the profile of circulating microRNAs (miRNAs) in type 2 diabetes (T2D) and its response to changes in insulin sensitivity. RESEARCH DESIGN AND METHODSThe circulating miRNA profile was assessed in a pilot study of 12 men: 6 with normal glucose tolerance (NGT) and 6 T2D patients. The association of 10 circulating miRNAs with T2D was cross-sectionally validated in an extended sample of 45 NGT vs. 48 T2D subjects (65 nonobese and 28 obese men) and longitudinally in 35 T2D patients who were recruited in a randomized, double-blinded, and placebo-controlled 3-month trial of metformin treatment. Circulating miRNAs were also measured in seven healthy volunteers before and after a 6-h hyperinsulinemiceuglycemic clamp and insulin plus intralipid/heparin infusion. RESULTSCross-sectional studies disclosed a marked increase of miR-140-5p, miR-142-3p, and miR-222 and decreased miR- 423-5p, miR-125b, miR-192, miR-195, miR-130b, miR-532-5p, and miR-126 in T2D patients. Multiple linear regression analyses revealed that miR-140-5p and miR-423-5p contributed independently to explain 49.5% (P < 0.0001) of fasting glucose variance after controlling for confounders. A discriminant function of four miRNAs (miR-140-5p, miR-423-5p, miR-195, and miR-126) was specific for T2D with an accuracy of 89.2% (P < 0.0001). Metformin (but not placebo) led to significant changes in circulating miR-192 (49.5%; P = 0.022), miR-140-5p (215.8%; P = 0.004), and miR-222 (247.2%; P = 0.03), in parallel to decreased fasting glucose and HbA 1c . Furthermore, while insulin infusion during clamp decreased miR-222 (262%; P = 0.002), the intralipid/heparin mixture increased circulating miR-222 (163%; P = 0.015) and miR-140-5p (67.5%; P = 0.05). CONCLUSIONSThis study depicts the close association between variations in circulating miRNAs and T2D and their potential relevance in insulin sensitivity.

The human intestine is home to a diverse range of bacterial and fungal species, forming an ecological community that contributes to normal physiology and disease susceptibility. Here, the fungal microbiota (mycobiome) in obese and non-obese subjects was characterized using Internal Transcribed Spacer (ITS)-based sequencing. The results demonstrate that obese patients could be discriminated by their specific fungal composition, which also distinguished metabolically “healthy” from “unhealthy” obesity. Clusters according to genus abundance co-segregated with body fatness, fasting triglycerides and HDL-cholesterol. A preliminary link to metabolites such as hexadecanedioic acid, caproic acid and N-acetyl-L-glutamic acid was also found. Mucor racemosus and M. fuscus were the species more represented in non-obese subjects compared to obese counterparts. Interestingly, the decreased relative abundance of the Mucor genus in obese subjects was reversible upon weight loss. Collectively, these findings suggest that manipulation of gut mycobiome communities might be a novel target in the treatment of obesity.

Aims/hypothesis Circulating lipopolysaccharide-binding protein (LBP) is an acute-phase reactant known to be increased in obesity. We hypothesised that LBP is produced by adipose tissue (AT) in association with obesity. Methods LBP mRNA and LBP protein levels were analysed in AT from three cross-sectional (n=210, n=144 and n=28) and three longitudinal (n=8, n=25, n=20) human cohorts; in AT from genetically manipulated mice; in isolated adipocytes; and in human and murine cell lines. The effects of a high-fat diet and exposure to lipopolysaccharide (LPS) and peroxisome proliferator-activated receptor (PPAR)γ agonist were explored. Functional in vitro and ex vivo experiments were also performed. Results LBP synthesis and release was demonstrated to increase with adipocyte differentiation in human and mouse AT, Electronic supplementary material The online version of this article

OBJECTIVECirculating markers of iron overload are associated with insulin resistance. Less is known about the impact of iron overload on adipose tissue (AT). We hypothesized that gene expression markers of iron metabolism in AT could be associated with insulin action. RESEARCH DESIGN AND METHODSThe AT expression of ferroportin (SLC40A1), transferrin (TF), TF receptor (TFRC), ferritin (FT) heavy polypeptide 1 (FTH1), and FT light polypeptide (FTL) was analyzed cross-sectionally in three independent cohorts and also after weight lossinduced changes in insulin sensitivity (clamp M value) in an independent fourth cohort. RESULTSIn human AT, TF mRNA and protein levels were decreased with obesity and insulin resistance in the three cohorts and were positively associated with adipogenic mRNAs and insulin action. Otherwise, FTL mRNA and protein and SLC40A1 transcripts were positively associated with BMI and negatively linked to adipogenic genes and insulin action. Bariatric surgery-induced weight loss led to increased TF and decreased TFRC, FTH1, FTL, and SLC40A1 in subcutaneous AT in parallel to improved insulin action. CONCLUSIONSThese results suggest that iron overload impacts on AT in association with insulin resistance.

Current findings suggest impaired miRNA target gene expression in obese AT in close association with inflammation, both improving after weight loss.

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