Gut Microbiota and Modulation of Liver Damage in NAFLD
Condition: Simple Steatosis (SS); Non-alcoholic Steatohepatitis (NASH); Obesity
MeSH terms: Fatty Liver; Non-alcoholic Fatty Liver Disease
Study type: Observational

Summary: 
      Several experimental data suggest that gut-derived endotoxin and GM composition can act as a
      "second hit" or insult to convert hepatic SS to NASH and cause both local hepatic and
      systemic inflammation.This study's aim is to analyze microbiota diversity, providing
      information both on intestinal microbial composition and on the metabolic processes linked to
      them. In addition, we will correlate, for the first time, GM composition to hepatic and white
      adipose tissue gene expression patterns of interest and serum and fecal markers possibly
      related to impaired fat storage and inflammation. We aim to provide preliminary data to
      design future intervention studies with pre- or probiotics or bile acid derivatives to
      prevent/treat inflammation and fibrosis in NAFLD patients.
    

Detailed description: 
      Non-alcoholic fatty liver disease (NAFLD) includes benign hepatic simple steatosis (SS) and
      the more severe steatohepatitis (NASH), which is characterized by inflammation and fibrosis
      potentially leading to cirrhosis and hepatocellular carcinoma. Current research is focused on
      what are the risk factors and determinants of NASH. NAFLD is associated with the metabolic
      syndrome, and the prevalence has been described to be up to 98% in morbidly obese individuals
      undergoing bariatric surgery. NAFLD in non-obese subjects have a different clinical profile
      than in obese individuals, being associated with insulin resistance (IR), differential
      distribution of visceral adipose tissue, recent increase in body weight and/or presence of
      overweight, intake of high cholesterol diet and genetic background.

      Gut microbiota (GM) regulates fat metabolism in mice. In humans its alterations have been
      linked to diabetes, obesity, IR, atherosclerosis and inflammation, SS and NAFLD.

      Several experimental data suggest that gut-derived endotoxin and GM composition can act as a
      "second hit" or insult to convert hepatic SS to NASH and cause both local hepatic and
      systemic inflammation. With regard to human studies, Muozaki et al. have recently showed, by
      using a polymerase chain reaction (PCR) TaqMan system approach, that obese patients with
      NASH, have a lower percentage of fecal Bacteroidetes (Bacteroidetes to total bacteria counts)
      compared to both SS and healthy controls and a higher percentage of C. coccoides compared to
      those with SS . In addition, Zhu et al. showed in pediatric subjects, by using a 16S
      ribosomal RNA detection method, an unique pattern of enterotypes in patients with NASH, in
      obese individuals with no sign of liver damage and in lean healthy controls. Finally, Wai-Sun
      Wong et al. showed, also using a 16S ribosomal RNA detection method, that a small group of
      Chinese NASH patients demonstrated fecal dysbiosis but not significant changes in
      biodiversity compared to healthy subjects. Finally, inflammation in patients with symptomatic
      atherosclerosis has been shown to be associated with lower levels of butyrate producing gut
      bacteria such as Roseburia.

      Among the possible factors involved in determining NAFLD severity, serum bile acid (BA)
      concentration and its post-prandial variations have been recently linked to the regulation of
      body weight, liver fat and inflammation and glucose and lipid metabolism. These BA regulatory
      functions are mediated by their interaction with the farnesoid X receptor (FXR)and the G
      Protein-Coupled BA Receptor 1 (GPBAR1 or TGR5) at both hepatic and subcutaneous adipose
      tissue levels. No human study has been directed to investigating the mechanisms through which
      GM composition influences inflammation and fibrosis in both obese and non-obese patients with
      NAFLD.

      Liver biopsy is clinically advisable during bariatric surgery, due to the high prevalence of
      NAFLD and NASH in morbidly obese patients. It has been previously suggested that the high
      prevalence of histologically proven NAFLD in patients with gallstones may also justify
      routine liver biopsy during cholecystectomy, even in non-obese subjects, to establish the
      diagnosis, stage, and possible therapy. The latter suggestion has been very recently
      reinforced by the evidence that, in humans, cholecystectomy may represent an independent risk
      factor for NAFLD detected at ultrasounds and by the experimental demonstration that
      cholecystectomy increases hepatic triglycerides content.

      In the present research project we will study patients with histologically proven SS or with
      NASH. Liver biopsy will be performed during bariatric surgery (sleeve gastrectomy) or
      cholecystectomy in patients with preoperative evidence of NAFLD at ultrasounds. We will
      compare GM composition using, for the first time, the most accurate method available, that is
      metagenomic shotgun. This method allows to analyze microbiota diversity, providing
      information both on intestinal microbial composition and on the metabolic processes linked to
      them. In addition, we will correlate, for the first time, GM composition to hepatic and, only
      in the obese patients, also to white adipose tissue gene expression patterns of interest and
      serum and fecal markers possibly related to impaired fat storage and inflammation. We aim to
      provide preliminary data to design future intervention studies with pre- or probiotics or
      bile acid derivatives to prevent/treat inflammation and fibrosis in NAFLD patients.
    

Intervention name(s): liver and white adipose tissue biopsies
Intervention type(s): Procedure
Observational model: Case-Control
Time perspective: Cross-Sectional
Sampling method: Probability Sample
Study population: 
        two groups of patients with morbid obesity undergoing sleeve gastrectomy will be enrolled.
        Grouping in patients with simple steatosis (SS) or non-alcoholic steatohepatitis (NASH)
        will be performed based on the histological diagnosis of the type of NAFLD obtained at
        operation. Two groups of non-obese patients undergoing cholecystectomy for gallstone
        disease will be enrolled. Grouping in patients with simple steatosis (SS) or non-alcoholic
        steatohepatitis (NASH) will be performed based on the histological diagnosis of the type of
        NAFLD obtained at operation.
      
Biospecimen description: 
      Stool samples, serum, plasma, liver and (only in the obese patients) adipose tissue
    
Keywords: Simple steatosis (SS); Non-alcoholic steatohepatitis (NASH); Gut microbiota (GM); Non alcoholic fatty liver disease (NAFLD)