Microbiota analysis and transient elastography reveal new extra-hepatic components of liver steatosis and fibrosis in obese patients.

Obesity could lead to metabolic dysfunction-associated fatty liver disease (MAFLD), which severity could be linked to muscle and gut microbiota disturbances. Our prospective study enrolled 52 obese patients whose MAFLD severity was estimated by transient elastography. Patients with severe steatosis (n = 36) had higher ALAT values, fasting blood glucose levels as well as higher visceral adipose tissue area and skeletal muscle index evaluated by computed tomography. Patients with fibrosis (n = 13) had higher ASAT values, increased whole muscle area and lower skeletal muscle density index. In a multivariate logistic regression analysis, myosteatosis was the strongest factor associated with fibrosis. Illumina sequencing of 16S rRNA gene amplicon was performed on fecal samples. The relative abundance of fecal Clostridium sensu stricto was significantly decreased with the presence of liver fibrosis and was negatively associated with liver stiffness measurement and myosteatosis. In addition, 19 amplicon sequence variants were regulated according to the severity of the disease. Linear discriminant analysis effect size (LEfSe) also highlighted discriminant microbes in patients with fibrosis, such as an enrichment of Enterobacteriaceae and Escherichia/Shigella compared to patients with severe steatosis without fibrosis. All those data suggest a gut-liver-muscle axis in the pathogenesis of MAFLD complications.

Effect of Abdominal Visceral Fat Change on the Regression of Erosive Esophagitis: A Prospective Cohort Study.

Background/Aims: Although abdominal visceral fat has been associated with erosive esophagitis in cross-sectional studies, there are few data on the longitudinal effect. We evaluated the effects of abdominal visceral fat change on the regression of erosive esophagitis in a prospective cohort study. Methods: A total of 163 participants with erosive esophagitis at baseline were followed up at 34 months and underwent esophagogastroduodenoscopy and computed tomography at both baseline and follow-up. The longitudinal effects of abdominal visceral fat on the regression of erosive esophagitis were evaluated using relative risk (RR) and 95% confidence intervals (CIs). Results: Regression was observed in approximately 49% of participants (n=80). The 3rd (RR, 0.13; 95% CI, 0.02 to 0.71) and 4th quartiles (RR, 0.07; 95% CI, 0.01 to 0.38) of visceral fat at follow-up were associated with decreased regression of erosive esophagitis. The highest quartile of visceral fat change reduced the probability of the regression of erosive esophagitis compared to the lowest quartile (RR, 0.10; 95% CI, 0.03 to 0.28). Each trend showed a dose-dependent pattern (p for trend <0.001). The presence of baseline Helicobacter pylori increased the regression of erosive esophagitis (RR, 2.40; 95% CI, 1.05 to 5.48). Conclusions: Higher visceral fat at follow-up and a greater increase in visceral fat reduced the regression of erosive esophagitis in a dose-dependent manner.

Intestinal Ralstonia pickettii augments glucose intolerance in obesity.

An altered intestinal microbiota composition has been implicated in the pathogenesis of metabolic disease including obesity and type 2 diabetes mellitus (T2DM). Low grade inflammation, potentially initiated by the intestinal microbiota, has been suggested to be a driving force in the development of insulin resistance in obesity. Here, we report that bacterial DNA is present in mesenteric adipose tissue of obese but otherwise healthy human subjects. Pyrosequencing of bacterial 16S rRNA genes revealed that DNA from the Gram-negative species Ralstonia was most prevalent. Interestingly, fecal abundance of Ralstonia pickettii was increased in obese subjects with pre-diabetes and T2DM. To assess if R. pickettii was causally involved in development of obesity and T2DM, we performed a proof-of-concept study in diet-induced obese (DIO) mice. Compared to vehicle-treated control mice, R. pickettii-treated DIO mice had reduced glucose tolerance. In addition, circulating levels of endotoxin were increased in R. pickettii-treated mice. In conclusion, this study suggests that intestinal Ralstonia is increased in obese human subjects with T2DM and reciprocally worsens glucose tolerance in DIO mice.

Adipose tissue microbiota in humans: an open issue.

BACKGROUND: A specific 'adipose tissue' microbiota has been recently identified in mice and hypothesized in humans. The purpose of this study was to verify the presence of microbiota of human whole adipose tissue and isolated adipocytes by combining culture-dependent and independent methods. METHODS: Standard microbiological cultural techniques and 16S ribosomal RNA (16S rRNA) gene sequencing (Illumina technology) on DNA and RNA were employed to study (a) whole abdominal subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from 14 obese and five normal-weight subjects and (b) mature adipocytes isolated from SAT and VAT after collagenase digestion or mechanical separation. To optimize the 16S rRNA gene detection, we used different DNA extraction methods (lysis with proteinase K, proteinase K+lysozyme and microbeads) and amplification procedures (semi-quantitative standard PCR and real-time quantitative PCR). RESULTS: Microbiological cultures were negative in all analyzed samples. In enzymatically isolated adipocytes, 90% of the sequenced bacterial DNA belonged to Clostridium histolyticum, the bacterium from which the collagenase enzyme was isolated. Bacterial 16S rRNA gene was not detected from DNA and RNA of whole SAT and VAT, as well as of mechanically isolated mature adipocytes, even after blocking with a specific primer the nonspecific amplification of human mitochondrial 12S rRNA. CONCLUSIONS: Our results do not support the presence of a human adipose tissue microbiota. In addition, they emphasized the technical problems encountered when applying metagenomic studies to human tissues with very low or absent bacterial load.

Plasma lipopolysaccharide is closely associated with glycemic control and abdominal obesity: evidence from bariatric surgery.

OBJECTIVE: It is of vital importance to elucidate the triggering factors of obesity and type 2 diabetes to improve patient care. Bariatric surgery has been shown to prevent and even cure diabetes, but the mechanism is unknown. Elevated levels of lipopolysaccharide (LPS) predict incident diabetes, but the sources of LPS are not clarified. The objective of the current study was to evaluate the potential impact of plasma LPS on abdominal obesity and glycemic control in subjects undergoing bariatric surgery. RESEARCH DESIGN AND METHODS: This was a prospective observational study involving a consecutive sample of 49 obese subjects undergoing bariatric surgery and 17 controls. Main assessments were plasma LPS, HbA1c, adipose tissue volumes (computed tomography), and quantified bacterial DNA in adipose tissue compartments. RESULTS: Plasma levels of LPS were elevated in obese individuals compared with controls (P < 0.001) and were reduced after bariatric surgery (P = 0.010). LPS levels were closely correlated with HbA1c (r = 0.56; P = 0.001) and intra-abdominal fat volumes (r = 0.61; P < 0.001), but only moderately correlated with subcutaneous fat volumes (r = 0.33; P = 0.038). Moreover, there was a decreasing gradient (twofold) in bacterial DNA levels going from mesenteric via omental to subcutaneous adipose tissue compartments (P = 0.041). Finally, reduced LPS levels after bariatric surgery were directly correlated with a reduction in HbA1c (r = 0.85; P < 0.001). CONCLUSIONS: Our findings support a hypothesis of translocated gut bacteria as a potential trigger of obesity and diabetes, and suggest that the antidiabetic effects of bariatric surgery might be mechanistically linked to, and even the result of, a reduction in plasma levels of LPS.