Histologic Disease Persists beyond Mucosal Healing and Could Predict Reactivation in Ulcerative Colitis.

Mucosal healing (MH) is the main target in ulcerative colitis (UC) treatment. Even if MH lowers the risk of disease reactivation, some patients still relapse. Histologic activity (HA) beyond MH could explain these cases. This study aims to assess how many patients with MH have HA and which lesions are associated with relapse. We retrospectively enrolled UC patients showing MH, expressed as a Mayo Endoscopic Subscore (MES) of 0 and 1 upon colonoscopy. We reviewed the histological reports of biopsies evaluating the presence of typical lesions of UC and assessed the number of clinical relapses after 12 months. Among 100 enrolled patients, 2 showed no histological lesions. According to univariate analysis, patients with a higher number of histological lesions at the baseline had a higher risk of relapse (OR 1.25, p = 0.012), as well as patients with basal plasmacytosis (OR 4.33, p = 0.005), lamina propria eosinophils (OR 2.99, p = 0.047), and surface irregularity (OR 4.70, p = 0.010). However, in the multivariate analysis, only basal plasmacytosis (OR 2.98, p = 0.050) and surface irregularity (OR 4.50, p = 0.024) were confirmed as risk factors for disease reactivation. HA persists in a significant percentage of patients with MH. Despite the presence of MH, patients with basal plasmacytosis and surface irregularity have a higher risk of relapse.

Inflammatory Bowel Diseases and Non-Alcoholic Fatty Liver Disease: Piecing a Complex Puzzle Together.

Inflammatory bowel diseases (IBD), comprising Crohn's disease and ulcerative colitis, are systemic and multifaceted disorders which affect other organs in addition to the gastrointestinal tract in up to 50% of cases. Extraintestinal manifestations may present before or after IBD diagnosis and negatively impact the intestinal disease course and patients' quality of life, often requiring additional diagnostic evaluations or specific treatments. Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. Current evidence shows an increased prevalence of NAFLD (and its more advanced stages, such as liver fibrosis and steatohepatitis) in IBD patients compared to the general population. Many different IBD-specific etiopathogenetic mechanisms have been hypothesized, including chronic inflammation, malabsorption, previous surgical interventions, changes in fecal microbiota, and drugs. However, the pathophysiological link between these two diseases is still poorly understood. In this review, we aim to provide a comprehensive overview of the potential mechanisms which have been investigated so far and highlight open issues still to be addressed for future studies.

Cellular and Molecular Determinants of Biologic Drugs Resistance and Therapeutic Failure in Inflammatory Bowel Disease.

The advent of biologic drugs has revolutionized the treatment of Inflammatory Bowel Disease, increasing rates of response and mucosal healing in comparison to conventional therapies by allowing the treatment of corticosteroid-refractory cases and reducing corticosteroid-related side effects. However, biologic therapies (anti-TNFα inhibitors, anti-α4ß7 integrin and anti-IL12/23) are still burdened by rates of response that hover around 40% (in biologic-naïve patients) or lower (for biologic-experienced patients). Moreover, knowledge of the mechanisms underlying drug resistance or loss of response is still scarce. Several cellular and molecular determinants are implied in therapeutic failure; genetic predispositions, in the form of single nucleotide polymorphisms in the sequence of cytokines or Human Leukocyte Antigen, or an altered expression of cytokines and other molecules involved in the inflammation cascade, play the most important role. Accessory mechanisms include gut microbiota dysregulation. In this narrative review of the current and most recent literature, we shed light on the mentioned determinants of therapeutic failure in order to pave the way for a more personalized approach that could help avoid unnecessary treatments and toxicities.

Popular diets and nutritional assessment in the management of irritable bowel syndrome in inflammatory bowel disease: an overview of current evidence.

There is an increasing interest in using popular diets to manage inflammatory bowel diseases (IBDs), such as ulcerative colitis and Crohn disease. These conditions are often associated with nutritional deficiencies, protein­energy malnutrition, micronutrient malnutrition, altered body composition, and sarcopenia. While dietary interventions can be supportive in treating intestinal symptoms of adult IBD patients, it is important to note that current guidelines from major scientific societies do not recommend any specific dietary interventions in this field. This review aims to provide a summary of the current evidence on dietary­nutritional management for patients with IBD, specifically when the disease appears to be in remission, but the patient continues to experience irritable bowel syndrome (IBS) symptoms or functional gastrointestinal symptoms. We focus on vital aspects, such as malnutrition and sarcopenia definitions, screening, and nutritional assessment. We then discuss in detail the most popular diets used for IBD management over the years, characterizing each one in terms of effects on gut inflammation, IBS­like symptoms, and potential risk of malnutrition. These diets include a low­fermentable oligosaccharides, disaccharides, monosaccharides, and polyols diet, a gluten­free diet, a Mediterranean diet, and a plant­based diet. To date, current evidence does not conclusively establish the optimal diet for patients with IBS, suggesting that personalized dietary approaches may be the best strategy.

Transition from intravenous to subcutaneous biological therapies in inflammatory bowel disease: An online survey of patients.

BACKGROUND: The transition from in-hospital intravenous administration to subcutaneous therapies to treat inflammatory bowel disease (IBD) can raise some concerns among patients due to the self-administration concerns, the management of potential side effects and the overall worries related to a change of treatment. This study aimed at evaluating patients' opinion about the switch from intravenous to subcutaneous formulations and their knowledge on new available therapeutic options. METHODS: We conducted a survey using a questionnaire prepared by a team of gastroenterologists and nurses working at the IBD unit. It consists of 31 items and has been divided into four sections: descriptive, commitment, knowledge and passage mode opinion. The questions were formulated in Italian and conceived according to daily consultations with patients in everyday practice, without any previous piloting or specific medical literature reference. The survey was administered to consecutive IBD patients in intravenous biological treatment; patients currently or previously treated with subcutaneous therapy were excluded. RESULTS: Four hundred questionnaires were distributed to participants. As many as 311 patients (77.7%) completed the survey, while the remaining were excluded from the analysis; 155 (49.8%) patients were favorable to switch from intravenous to subcutaneous therapy, while only 78 (25.1%) disagreed. In univariate and multi-variate analysis, the approval rate for home therapy was significantly associated with the distance from the IBD center and work/family/personal commitments. Surprisingly, only a quarter of the IBD patients knew that almost all available therapeutic agents have a subcutaneous administration route. Regarding patients' opinion on the efficacy of subcutaneous administration of biological agents compared to intravenous drugs, 194 (63%) had no definite idea, while 44 (14%) believed that the effectiveness could be reduced. CONCLUSION: The transition from in-hospital to subcutaneous therapeutic management of biological therapy at home was generally viewed favorably by patients, especially if they have commitments or were residents far from the IBD center.

Effectiveness and Safety of Switching from Intravenous to Subcutaneous Vedolizumab Formulation in Inflammatory Bowel Disease Patients in Clinical Remission.

BACKGROUND AND AIMS: Subcutaneous vedolizumab formulation has been shown to be as effective and safe as the intravenous one in randomized control trials. Real-life data are limited especially for patients receiving long-term intravenous therapy. This study aimed to evaluate the safety and effectiveness of switching from intravenous to subcutaneous vedolizumab in a large cohort of patients with stable clinical remission. METHODS: In this prospective cohort study, we enrolled consecutive patients attending our center between September 2021 and April 2022. The baseline demographic characteristics, 12- and 24-weeks follow-up clinical activity, C-reactive protein levels, and adverse events were recorded. The primary endpoint was to assess combined steroid-free clinical remission plus biochemical remission 24-week after the switch. RESULTS: 93 patients (43 Crohn's disease, 50 ulcerative colitis), switched to subcutaneous vedolizumab after a median duration of intravenous treatment of 36 months [IQR 16-52]. At baseline, 80 patients (86%) had a combined remission. At 24-week, 89.2% (n=74) maintained combined steroid-free clinical remission plus biochemical remission. 25 adverse events were reported, mostly SARS-CoV-2 infections and injection site reactions, with a further four recurrence episodes. Twelve patients (12.9%) discontinued subcutaneous administration and restarted intravenous vedolizumab. CONCLUSIONS: Switching from intravenous to subcutaneous vedolizumab can be considered effective and safe for maintaining remission in patients with inflammatory bowel disease. In addition, this might reduce healthcare costs. However, large-scale real-life studies with long-term follow-up are necessary.

Serial Fecal Microbiota Infusions via Colonoscopy for Active Ulcerative Colitis: A Feasibility, Safety, and Translational Monocentric Italian Study.

The effectiveness of fecal microbiota transplantation (FMT) in ulcerative colitis (UC) remains unclear. This study aimed to investigate the feasibility and effectiveness of serial fecal infusions via colonoscopy in patients with active UC. Subjects with mild-to-moderate UC received three consecutive fecal infusions via colonoscopy. A control population with the same baseline features receiving Infliximab treatment was enrolled. Adverse events and clinical, endoscopic, and microbial outcomes were investigated. Nineteen patients with mildly-to-moderately active UC were enrolled. Clinical response was obtained in six patients at week 2, in eight at week 6, and in nine at week 12. Clinical response was maintained in eight patients at week 24. Endoscopic remission at week 12 was reached in six patients. In the control population, 13/19 patients achieved clinical response at week 6, and 10/19 patients maintained clinical response after 6 months. Microbiota richness was higher in responders compared with the non-responders. Peptostreptococcus, Lactobacillus, and Veillonella were higher in non-responders, while Parabacteroides, Bacteroides, Faecalibacterium, and Akkermansia were higher in responders at all timepoints. Serial FMT infusions appear to be feasible, safe, and effective in UC patients, with a potential role in inducing and maintaining clinical response. Specific bacteria predict the response to FMT.

Ecology and Machine Learning-Based Classification Models of Gut Microbiota and Inflammatory Markers May Evaluate the Effects of Probiotic Supplementation in Patients Recently Recovered from COVID-19.

Gut microbiota (GM) modulation can be investigated as possible solution to enhance recovery after COVID-19. An open-label, single-center, single-arm, pilot, interventional study was performed by enrolling twenty patients recently recovered from COVID-19 to investigate the role of a mixed probiotic, containing Lactobacilli, Bifidobacteria and Streptococcus thermophilus, on gastrointestinal symptoms, local and systemic inflammation, intestinal barrier integrity and GM profile. Gastrointestinal Symptom Rating Scale, cytokines, inflammatory, gut permeability, and integrity markers were evaluated before (T0) and after 8 weeks (T1) of probiotic supplementation. GM profiling was based on 16S-rRNA targeted-metagenomics and QIIME 2.0, LEfSe and PICRUSt computational algorithms. Multiple machine learning (ML) models were trained to classify GM at T0 and T1. A statistically significant reduction of IL-6 (p < 0.001), TNF-α (p < 0.001) and IL-12RA (p < 0.02), citrulline (p value < 0.001) was reported at T1. GM global distribution and microbial biomarkers strictly reflected probiotic composition, with a general increase in Bifidobacteria at T1. Twelve unique KEGG orthologs were associated only to T0, including tetracycline resistance cassettes. ML classified the GM at T1 with 100% score at phylum level. Bifidobacteriaceae and Bifidobacterium spp. inversely correlated to reduction of citrulline and inflammatory cytokines. Probiotic supplementation during post-COVID-19 may trigger anti-inflammatory effects though Bifidobacteria and related-metabolism enhancement.

The Microbiota-Gut-Brain Axis: Psychoneuroimmunological Insights.

There is growing interest in the role that the intestinal microbiota and the related autoimmune processes may have in the genesis and presentation of some psychiatric diseases. An alteration in the communication of the microbiota-gut-brain axis, which constitutes a communicative model between the central nervous system (CNS) and the gastro-enteric tract, has been identified as one of the possible causes of some psychiatric diseases. The purpose of this narrative review is to describe evidence supporting a role of the gut microbiota in psychiatric diseases and the impact of diet on microbiota and mental health. Change in the composition of the gut microbiota could determine an increase in the permeability of the intestinal barrier, leading to a cytokine storm. This could trigger a systemic inflammatory activation and immune response: this series of events could have repercussions on the release of some neurotransmitters, altering the activity of the hypothalamic-pituitary-adrenal axis, and reducing the presence of trophic brain factors. Although gut microbiota and psychiatric disorders seem to be connected, more effort is needed to understand the potential causative mechanisms underlying the interactions between these systems.

Evaluation of tolerability and major factors affecting the adherence to probiotic therapy in patients with irritable bowel syndrome: a prospective, observational, real-life study.

BACKGROUND: Probiotics have been evaluated in multiple clinical trials on irritable bowel syndrome (IBS). However, in real-life long-term compliance could be low. Our study is single-center, observational and prospective, aiming both to evaluate the adherence to prescription of probiotic therapy in real-life and to identify factors able to influence adherence to therapy. METHODS: Fifty patients diagnosed with IBS according to Rome IV and receiving a clinical prescription of a multistrain probiotic preparation (VSL#3® manufactured by Nutrilinea Srl and marketed in Italy by Ferring S.p.A., Milan, Italy) have been enrolled and 49 completed the follow-up. Two months after baseline a second visit was made to assess adherence and eventual reasons for discontinuation. RESULTS: Sixty percent of patients took all the prescribed probiotic therapy in real-life setting, with perceived benefits in more than 60% of cases. Among the 20 patients with reduced adherence, 5 took less than 50%, 12 took 50% and 2 took more than 50% but less than 80% of the prescribed doses. Principal reasons of not complete adherence among the 20 patients were: price of the product (8/20), mild adverse events (AEs) (6/20) and poor appreciation of flavour (3/20). CONCLUSIONS: This study suggested that the adherence to probiotic therapy is affected by different factors in patients with IBS in a real-life setting. The main reason for lack of adherence was the price of the product. Other reasons are mild AEs (mainly bloating) and low palatability.

Radiomics could predict surgery at 10 years in Crohn's disease.

BACKGROUND: Predicting clinical outcomes represents a major challenge in Crohn's disease (CD). Radiomics provides a method to extract quantitative features from medical images and may successfully predict clinical course. AIMS: The aim of this pilot study is to evaluate the use of radiomics to predict 10-year surgery for CD patients. METHODS: We selected a cohort of CD patients with CT scan enterographies and a 10-year follow up. The R library Moddicom was used to extract radiomic features from each lesion of CD, segmented in the CT scans. A logistic regression model based on selected radiomic features was developed to predict 10-year surgery. The model was evaluated by computing the area under the curve (AUC) of the receiver operating characteristic curve, sensitivity, specificity, positive and negative predictive values (PPV, NPV). RESULTS: We enroled 30 patients, with 44 CT scans and 93 lesions. We extracted 217 radiomic features from each lesion. The developed model was based on two radiomic features and presented an AUC (95% CI) of 0.83 (0.73-0.91) in predicting 10-year surgery. Sensitivity, specificity, PPV, NPV of the radiomic model were equal to 0.72, 0.90, 0.79, 0.86, respectively. CONCLUSION: Radiomics could be a helpful tool to identify patients with high risk for surgery and needing a stricter monitoring.

Effect of a Multistrain Probiotic on Leaky Gut in Patients with Diarrhea-Predominant Irritable Bowel Syndrome: A Pilot Study.

BACKGROUND: A probiotic mixture prevented epithelial barrier impairment in various experimental models. The objective was to evaluate its effects in patients suffering from IBS with diarrhea (IBS-D) with confirmed leaky gut. METHODS: IBS-D patients with increased intestinal permeability measured by radionuclide tracers were enrolled in this pilot, open-label, prospective, interventional, single-center, Phase IV study. Patients received two capsules of a multistrain probiotic a day for 30 days and were evaluated by repeated intestinal permeability tests, the Bristol Stool Scale, and patient-perceived quality of life and satisfaction. RESULTS: Of the 30 enrolled patients (mean age: 42.1 [SD: 13.1] years; female: 60%), 27 completed the study (full analysis set [FAS]), and 18 had no major protocol violation (per protocol set [PPS]). On D30, an improvement of intestinal permeability was observed in 81.5% of patients in FAS, normalization being observed in 37% of the participants (44% in PPS). The mean intestinal permeability was significantly decreased: baseline minus D30, 3.4 (95% CI: 1.7, 5.2); the IBS-QOL total score was significantly increased: D30 minus baseline, 8.0 (95% CI: 3.0, 12.9); and stool consistency was significantly improved. On D15 and D30, 96.3% of patients claimed that their IBS symptoms had been satisfactory alleviated, and a significant improvement was reported for the following VAS-IBS items: abdominal pain, diarrhea, and impact of gastrointestinal problems in daily life. Compliance and tolerance were satisfactory. CONCLUSION: The multistrain probiotic tested may reduce intestinal permeability in a considerable proportion of patients and may improve abdominal pain, stool consistency, and quality of life. These results pave the way for larger, placebo-controlled clinical studies.

Cytomegalovirus Infection: An Underrated Target in Inflammatory Bowel Disease Treatment.

CMV infection is still a matter of concern in IBD patients, especially regarding the disease's relapse management. Why IBD patients, particularly those affected by ulcerative colitis, are more susceptible to CMV reactivation is not totally explained, although a weakened immune system could be the reason. Various techniques, ranging from serology to histology, can be employed to detect intestinal CMV infection; however, there is currently disagreement in the literature regarding the most effective diagnostic test. Furthermore, CMV involvement in steroid resistance has been broadly discussed, but whether CMV infection is a cause or consequence of the disease severity and, consequently, steroid refractoriness is still debated. Its potential contribution to the lack of response to advanced therapy and small molecules must be more valued and wholly explored. In this review, we look at the actual literature on CMV in IBD patients, and we suggest a pragmatic algorithm for clinical practice management of CMV infection.

Extracellular Vesicles: Novel Potential Therapeutic Agents in Inflammatory Bowel Diseases.

Patients affected by inflammatory bowel diseases (IBD) can nowadays benefit from a growing number of pharmacological options. However, in moderate-to-severe cases, the therapeutic response is still far from optimal, and treatment changes and optimizations are often required. Thus, researchers in this field are strongly engaged in studies aiming to identify new potential therapeutic targets. Extracellular vesicles (EVs) are tiny subcellular bodies with a phospholipid bilayer envelope containing bioactive molecules, which are released from different cells and are involved in intercellular communication. Recent pre-clinical data show their emerging role in the pathogenesis and treatment of IBD. In our review, we summarize current evidence about the function of EVs as active therapeutic agents in ulcerative colitis and Crohn's disease, analyzing the properties of EVs derived from different cellular sources and the mechanisms through which they may improve intestinal inflammation.

The Microbiome Revolution: New Insights for Personalized Medicine.

The availability of new culture-independent techniques to study microbes led to the explosion of the gut microbiota revolution in recent decades [...].

Effectiveness and safety of vedolizumab in a matched cohort of elderly and nonelderly patients with inflammatory bowel disease: the IG-IBD LIVE study.

BACKGROUND: Vedolizumab registration trials were the first to include elderly patients with moderate-to-severe ulcerative colitis (UC) or Crohn's disease (CD), but few real-life data have been reported in this population. AIMS: We investigated the effectiveness and safety of vedolizumab in matched cohorts of elderly and nonelderly UC and CD patients. METHODS: The Long-term Italian Vedolizumab Effectiveness (LIVE) study is a retrospective-prospective study including UC and CD patients who started vedolizumab from April 2016 to June 2017. Elderly patients (≥65 years) were matched clinically 1:2 to nonelderly patients (18-64 years); the 2 groups were followed until drug discontinuation or June 2019. RESULTS: The study included 198 elderly (108 UC, 90 CD) and 396 matched nonelderly patients (205 UC, 191 CD). Nonelderly UC patients had a significantly higher persistence on vedolizumab compared to elderly patients (67.6% vs. 51.4%, p = 0.02). No significant difference in effectiveness was observed between elderly and nonelderly CD patients (59.4% vs. 52.4%, p = 0.32). Age ≥65 years was associated with lower persistence in UC; for CD, previous exposure to anti-TNF-α agents, Charlson comorbidity index >2 and moderate-to-severe clinical activity at baseline were associated with lower persistence. There were recorded 130 adverse events, with comparable rates between the two groups. A Charlson comorbidity index >2 was associated with an increased risk of adverse events. CONCLUSION: Vedolizumab can be considered a safe option in elderly IBD patients. Its effectiveness in elderly UC patients may be reduced, while no age-dependent effect on effectiveness was observed in CD.

Intestinal Permeability and Dysbiosis in Female Patients with Recurrent Cystitis: A Pilot Study.

Recurrent cystitis (RC) is a common disease, especially in females. Anatomical, behavioral and genetic predisposing factors are associated with the ascending retrograde route, which often causes bladder infections. RC seems to be mainly caused by agents derived from the intestinal microbiota, and most frequently by Escherichia coli. Intestinal contiguity contributes to the etiopathogenesis of RC and an alteration in intestinal permeability could have a major role in RC. The aim of this pilot study is to assess gut microbiome dysbiosis and intestinal permeability in female patients with RC. Patients with RC (n = 16) were enrolled and compared with healthy female subjects (n = 15) and patients with chronic gastrointestinal (GI) disorders (n = 238). We calculated the Acute Cystitis Symptom Score/Urinary Tract Infection Symptom Assessment (ACSS/UTISA) and Gastrointestinal Symptom Rating Scale (GSRS) scores and evaluated intestinal permeability and the fecal microbiome in the first two cohorts. Patients with RC showed an increased prevalence of gastrointestinal symptoms compared with healthy controls. Of the patients with RC, 88% showed an increased intestinal permeability with reduced biodiversity of gut microbiota compared to healthy controls, and 68% of the RC patients had a final diagnosis of gastrointestinal disease. Similarly, GI patients reported a higher incidence of urinary symptoms with a diagnosis of RC in 20%. Gut barrier impairment seems to play a major role in the pathogenesis of RC. Further studies are necessary to elucidate the role of microbiota and intestinal permeability in urinary tract infections.

Impact of SARS-CoV-2 Infection on the Course of Inflammatory Bowel Disease in Patients Treated with Biological Therapeutic Agents: A Case-Control Study.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has raised concerns in patients with inflammatory bowel disease (IBD), not only due to consequences of coronavirus disease 2019 itself but also as a possible cause of IBD relapse. The main objective of this study was to assess the role of SARS-CoV-2 in IBD clinical recurrence in a cohort of patients undergoing biological therapy. Second, we evaluated the difference in C-reactive protein (CRP) levels between the start and end of the follow-up period (ΔCRP) and the rate of biological therapy discontinuation. Patients with IBD positive for SARS-CoV-2 infection were compared with non-infected patients. IBD recurrence was defined as the need for intensification of current therapy. We enrolled 95 IBD patients with SARS-CoV-2 infection and 190 non-infected patients. During follow-up, 11 of 95 (11.6%) SARS-CoV-2-infected patients experienced disease recurrence compared to 21 of 190 (11.3%) in the control group (p = 0.894). Forty-six (48.4%) SARS-CoV-2-infected patients discontinued biological therapy versus seven (3.7%) in the control group (p < 0.01). In the multivariate analysis, biological agent discontinuation (p = 0.033) and ΔCRP (p = 0.017), but not SARS-CoV-2 infection (p = 0.298), were associated with IBD recurrence. SARS-CoV-2 infection was not associated with increased IBD recurrence rates in this cohort of patients treated with biological agents.

Comparison of performances of infliximab biosimilars CT-P13 versus SB2 in the treatment of inflammatory bowel diseases: a real-life multicenter, observational study in Italy.

BACKGROUND: To compare the performances of Infliximab (IFX) biosimilar CT-P13 and SB2 in the treatment of Inflammatory Bowel Diseases (IBD) outpatients in Italy. RESEARCH DESIGN AND METHODS: Three hundred and eighty IBD outpatients were retrospectively evaluated. The primary endpoint was to compare the two IFX biosimilars in terms of reaching and maintenance of remission at any timepoint. RESULTS: 197 patients with Ulcerative Colitis (UC) and 183 patients with Crohn's Disease (CD) treated with CT-P13 or SB2 and having a median (IQR) follow-up of 12 (6-36) months were compared: 230 (60.5%) were naïve to anti-TNFα, 20 (5.26%) were switched from IFX originator or from IFX CT-P13 to IFX SB2. Clinical remission was achieved in 133 (67.5%) UC patients and in 164 (89.6%) CD patients (p < 0.000), with no differences between CT-P13 and SB2 in the rate of remission in UC (p = 0.667) and CD (p = 0.286). Clinical response, steroid-free remission, rate of surgery, mucosal healing (MH) in UC, switching from IFX originator or from other biosimilar, and safety were similar. Higher MH rate was obtained in CD patients treated with CT-P13 (p = 0.004). CONCLUSION: This first comparative study found that both IFX biosimilars CT-P13 and SB2 are effective and safe in managing IBD outpatients.

Bariatric procedures and microbiota: patient selection and outcome prediction.

Obesity is a major health issue throughout the world and bariatric surgery plays a key role in its management and treatment. The role of microbiota in determining the pathogenesis of obesity has been widely studied, while its role in determining the outcome of bariatric surgery is an emerging issue that will be an outcome in near future studies. Studies on mice first showed the key role of microbiota in determining obesity, highlighting the fat mass increase in mice transplanted with microbiota from fat individuals, as well as the different microbiota composition between mice undergone to low-fat or high-fat diets. This led to characterize the asset of microbiota composition in obesity: increased abundance of Firmicutes, reduced abundance of Bacteroidetes and other taxonomical features. Variations on the composition of gut microbiome have been detected in patients undergone to diet and/or bariatric surgery procedures. Patients undergone to restricting diets showed lower level of trimethylamine N-oxide and other metabolites strictly associated to microbiome, as well as patients treated with bariatric surgery showed, after the procedure, changes in the relative abundance of Bacteroidetes, Firmicutes and other phyla with a role in the pathogenesis of obesity. Eventually, studies have been led about the effects that the modification of microbiota could have on obesity itself, mainly focusing on elements like fecal microbiota transplantation and probiotics such as inulin. This series of studies and considerations represent the first step in order to select patients eligible to bariatric surgery and to predict their outcome.