Kevin P. Rioux

Fecal Microbiome and Volatile Organic Compound Metabolome in Obese Humans With Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS The histopathology of nonalcoholic fatty liver disease (NAFLD) is similar to that of alcoholic liver disease. Colonic bacteria are a source of many metabolic products, including ethanol and other volatile organic compounds (VOC) that may have toxic effects on the human host after intestinal absorption and delivery to the liver via the portal vein. Recent data suggest that the composition of the gut microbiota in obese human beings is different from that of healthy-weight individuals. The aim of this study was to compare the colonic microbiome and VOC metabolome of obese NAFLD patients (n = 30) with healthy controls (n = 30). METHODS Multitag pyrosequencing was used to characterize the fecal microbiota. Fecal VOC profiles were measured by gas chromatography-mass spectrometry. RESULTS There were statistically significant differences in liver biochemistry and metabolic parameters in NAFLD. Deep sequencing of the fecal microbiome revealed over-representation of Lactobacillus species and selected members of phylum Firmicutes (Lachnospiraceae; genera, Dorea, Robinsoniella, and Roseburia) in NAFLD patients, which was statistically significant. One member of phylum Firmicutes was under-represented significantly in the fecal microbiome of NAFLD patients (Ruminococcaceae; genus, Oscillibacter). Fecal VOC profiles of the 2 patient groups were different, with a significant increase in fecal ester compounds observed in NAFLD patients. CONCLUSIONS A significant increase in fecal ester VOC is associated with compositional shifts in the microbiome of obese NAFLD patients. These novel bacterial metabolomic and metagenomic factors are implicated in the etiology and complications of obesity.

NLRP3 inflammasome plays a key role in the regulation of intestinal homeostasis

Background: Attenuated innate immune responses to the intestinal microbiota have been linked to the pathogenesis of Crohns disease (CD). Recent genetic studies have revealed that hypofunctional mutations of NLRP3, a member of the NOD‐like receptor (NLR) superfamily, are associated with an increased risk of developing CD. NLRP3 is a key component of the inflammasome, an intracellular danger sensor of the innate immune system. When activated, the inflammasome triggers caspase‐1‐dependent processing of inflammatory mediators, such as IL‐1&bgr; and IL‐18. Methods: In the current study we sought to assess the role of the NLRP3 inflammasome in the maintenance of intestinal homeostasis through its regulation of innate protective processes. To investigate this role, Nlrp3−/− and wildtype mice were assessed in the dextran sulfate sodium and 2,4,6‐trinitrobenzenesulfonic acid models of experimental colitis. Results: Nlrp3−/− mice were found to be more susceptible to experimental colitis, an observation that was associated with reduced IL‐1&bgr;, reduced antiinflammatory cytokine IL‐10, and reduced protective growth factor TGF‐&bgr;. Macrophages isolated from Nlrp3−/− mice failed to respond to bacterial muramyl dipeptide. Furthermore, Nlrp3‐deficient neutrophils exhibited reduced chemotaxis and enhanced spontaneous apoptosis, but no change in oxidative burst. Lastly, Nlrp3−/− mice displayed altered colonic &bgr;‐defensin expression, reduced colonic antimicrobial secretions, and a unique intestinal microbiota. Conclusions: Our data confirm an essential role for the NLRP3 inflammasome in the regulation of intestinal homeostasis and provide biological insight into disease mechanisms associated with increased risk of CD in individuals with NLRP3 mutations. (Inflamm Bowel Dis 2011)

Invasive potential of gut mucosa-derived Fusobacterium nucleatum positively correlates with IBD status of the host.

Background: Fusobacterium nucleatum is a heterogeneous oral pathogen that is also a common resident of the human gut mucosa. Given that some strains of F. nucleatum are known to be invasive and proinflammatory in the oral mucosa, we compared strains isolated from patients with inflammatory bowel disease (IBD) with strains isolated from healthy controls to determine 1) whether this species was more commonly associated with IBD patients; and 2) whether gut‐derived F. nucleatum strains from IBD patients showed an increased capacity for invasion. Methods: Biopsy material was obtained from 56 adult patients undergoing colonoscopy for colon cancer screening purposes or assessment of irritable bowel syndrome status (34 patients), or to assess for presence of gastrointestinal disease (i.e., IBD or indeterminate colitis, 22 patients). We enumerated Fusobacterium spp. strains isolated from human gut biopsy material in a blinded fashion, and then compared the virulence potential of a subset of F. nucleatum strains using an invasion assay in a Caco‐2 model system. Results: Fusobacterium spp. were isolated from 63.6% of patients with gastrointestinal disease compared to 26.5% of healthy controls (P = 0.01). In total, 69% of all Fusobacterium spp. recovered from patients were identified as F. nucleatum. F. nucleatum strains originating from inflamed biopsy tissue from IBD patients were significantly more invasive in a Caco‐2 cell invasion assay than strains that were isolated from healthy tissue from either IBD patients or control patients (P < 0.05 to 0.001). Conclusions: This study indicates that colonization of the intestinal mucosa by highly invasive strains of F. nucleatum may be a useful biomarker for gastrointestinal disease. (Inflamm Bowel Dis 2011;)

The potential role of prebiotic fibre for treatment and management of non-alcoholic fatty liver disease and associated obesity and insulin resistance.

Non‐alcoholic fatty liver disease (NAFLD) and the more severe non‐alcoholic steatohepatitis (NASH) represent a spectrum of diseases involving hepatic fat accumulation and histological features essentially identical to alcoholic liver disease; however, they occur in the absence of excessive alcohol intake. They typically arise in conjunction with one or more features of the metabolic syndrome. Lifestyle mediated weight loss remains the primary mode of therapy for NAFLD and NASH, but this is often ineffective and adjunctive medical and surgical treatments are presently lacking. Prebiotic fibres are a group of non‐digestible carbohydrates that modulate the human microbiota in a manner that is advantageous to host health. Rodent studies suggest that dietary supplementation with prebiotic fibres positively impacts NAFLD by modifying the gut microbiota, reducing body fat, and improving glucoregulation. Future research should focus on placebo‐controlled, human, clinical trials using histological endpoints to address the effects of prebiotics on NAFLD and NASH. The aim of this review is to summarize current knowledge about prebiotics as an emerging therapeutic target for NAFLD.

Environmental particulate matter induces murine intestinal inflammatory responses and alters the gut microbiome.

Background Particulate matter (PM) is a key pollutant in ambient air that has been associated with negative health conditions in urban environments. The aim of this study was to examine the effects of orally administered PM on the gut microbiome and immune function under normal and inflammatory conditions. Methods Wild-type 129/SvEv mice were gavaged with Ottawa urban PM10 (EHC-93) for 7–14 days and mucosal gene expression analyzed using Ingenuity Pathways software. Intestinal permeability was measured by lactulose/mannitol excretion in urine. At sacrifice, segments of small and large intestine were cultured and cytokine secretion measured. Splenocytes were isolated and incubated with PM10 for measurement of proliferation. Long-term effects of exposure (35 days) on intestinal cytokine expression were measured in wild-type and IL-10 deficient (IL-10−/−) mice. Microbial composition of stool samples was assessed using terminal restriction fragment length polymorphism. Short chain fatty acids were measured in caecum. Results Short-term treatment of wild-type mice with PM10 altered immune gene expression, enhanced pro-inflammatory cytokine secretion in the small intestine, increased gut permeability, and induced hyporesponsiveness in splenocytes. Long-term treatment of wild-type and IL-10−/− mice increased pro-inflammatory cytokine expression in the colon and altered short chain fatty acid concentrations and microbial composition. IL-10−/− mice had increased disease as evidenced by enhanced histological damage. Conclusions Ingestion of airborne particulate matter alters the gut microbiome and induces acute and chronic inflammatory responses in the intestine.

Mesalazine (5-aminosalicylic acid) alters faecal bacterial profiles, but not mucosal proteolytic activity in diarrhoea-predominant irritable bowel syndrome

Aliment Pharmacol Ther 2011; 34: 374–383

Optimizing clinical use of mesalazine (5-aminosalicylic acid) in inflammatory bowel disease.

Mesalazine [5-aminosalicylic acid (5-ASA)] has been used for over 30 years in the treatment of inflammatory bowel disease (IBD). It is a highly effective, safe, and well-tolerated drug for treatment of mild to moderate ulcerative colitis, which represents most patients with this disease. Recent studies of patient adherence to 5-ASA therapies in ulcerative colitis have highlighted the need for regimens that enable long-term compliance to significantly reduce the risk of troublesome and debilitating flares in the short term, and possibly colon cancer in the long term. Indeed, much of the recent innovation in clinical use of 5-ASA in colitis has come from studies of novel delivery mechanisms and simplified oral dosing schedules. These studies have provided much needed clarity on essential matters such as starting dose, dose escalation, and efficacy in terms of the ideal clinical endpoint - mucosal healing. Various manufacturers are re-evaluating their products to determine the safety and efficacy of such dosing regimens. Although once widely employed in the treatment of Crohn’s disease (CD), the accumulated body of evidence now suggests that there is a much more limited role for 5-ASA in this particular form of inflammatory bowel disease. Recent 5-ASA randomized-controlled trials, comparative studies, and outcomes research have led to refined treatment strategies and awareness for practitioners to better inform, engage and facilitate patients in optimal use of 5-ASA in inflammatory bowel disease.

Influences of intestinal bacteria in human inflammatory bowel disease.

Microbes that reside in the human intestinal tract and interact with immune and epithelial cells are strongly implicated as causative or predisposing agents of inflammatory bowel disease (IBD). Recent studies using metagenomic approaches have revealed differences in the fecal and mucosa-associated microbiota of patients with IBD, but it remains unclear whether this is a cause or consequence of chronic intestinal inflammation. A few microbes have been singled out as candidate pathogens in IBD and remain the subject of ongoing study. Complex imbalances in gut bacterial community structure and/or deficiencies in their functional capabilities may be a greater issue in IBD development. A more complete understanding of host-microbiota interactions in IBD is hampered by several remaining but surmountable methodological and technical challenges.

Sequence Polymorphisms in a Surface PPE Protein Distinguish Types I, II, and III of Mycobacterium avium subsp. paratuberculosis

ABSTRACT In the last 2 decades, a variety of different molecular typing methods have been developed to differentiate strains of Mycobacterium avium subsp. paratuberculosis. The most successful techniques are based on insertion sequences, repetitive loci, comparative genomics, or single nucleotide polymorphisms. In the present study, we chose to examine whether a single M. avium subsp. paratuberculosis gene could serve as a means of differentiation of a variety of isolates. The MAP1506 gene locus encodes a member of the polymorphic PPE protein family that has putative roles relevant to M. avium subsp. paratuberculosis pathogenicity. The MAP1506 locus was sequenced from a collection of 58 M. avium subsp. paratuberculosis isolates from different sources, hosts, and typing profiles. Following sequence alignment and analysis, it was found that bovine (type II) strains of M. avium subsp. paratuberculosis consistently differed from ovine (type I) and intermediate (type III) strains in seven and eight nucleotides, respectively. Polymorphic regions of the MAP1506 locus were selected for analysis by denaturing gradient gel electrophoresis, allowing visual discrimination of the three subtypes of M. avium subsp. paratuberculosis isolates. This is the first report describing the use of PCR and denaturing gradient gel electrophoresis on a single gene as a method to distinguish types I, II, and III of M. avium subsp. paratuberculosis.

VSL#3® probiotic therapy does not reduce portal pressures in patients with decompensated cirrhosis

In patients with decompensated cirrhosis, bacterial translocation can contribute to splanchnic vasodilatation, decreased effective circulating volume, and portal hypertension. The primary objective of this randomized, double blind placebo controlled trial was to evaluate the effect of the probiotic VSL#3® on the hepatic venous pressure gradient (HVPG).