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Abstract
The gut microbiota has a significant role in human health and disease. Dysbiosis of
the intestinal ecosystem contributes to the development of certain illnesses that
can be reversed by favorable alterations by probiotics. The published literature was
reviewed to identify scientific data showing a relationship between imbalance of gut
bacteria and development of diseases that can be improved by biologic products. The
medical conditions vary from infectious and antibiotic-associated diarrhea to obesity
to chronic neurologic disorders. A number of controlled clinical trials have been
performed to show important biologic effects in a number of these conditions through
administration of prebiotics, probiotics, and synbiotics. Controlled clinical trials
have identified a limited number of prebiotics, probiotic strains, and synbiotics
that favorably prevent or improve the symptoms of various disorders including inflammatory
bowel disease, irritable bowel syndrome, infectious and antibiotic-associated diarrhea,
diabetes, nonalcoholic fatty liver disease, necrotizing enterocolitis in very low
birth weight infants, and hepatic encephalopathy. Studies have shown that probiotics
alter gut flora and lead to elaboration of flora metabolites that influence health
through 1 of 3 general mechanisms: direct antimicrobial effects, enhancement of mucosal
barrier integrity, and immune modulation. Restoring the balance of intestinal flora
by introducing probiotics for disease prevention and treatment could be beneficial
to human health. It is also clear that significant differences exist between different
probiotic species. Metagenomics and metatranscriptomics together with bioinformatics
have allowed us to study the cross-talk between the gut microbiota and the host, furthering
insight into the next generation of biologic products.
Toll-like receptors (TLRs) play a crucial role in host defense against microbial infection. The microbial ligands recognized by TLRs are not unique to pathogens, however, and are produced by both pathogenic and commensal microorganisms. It is thought that an inflammatory response to commensal bacteria is avoided due to sequestration of microflora by surface epithelia. Here, we show that commensal bacteria are recognized by TLRs under normal steady-state conditions, and this interaction plays a crucial role in the maintenance of intestinal epithelial homeostasis. Furthermore, we find that activation of TLRs by commensal microflora is critical for the protection against gut injury and associated mortality. These findings reveal a novel function of TLRs-control of intestinal epithelial homeostasis and protection from injury-and provide a new perspective on the evolution of host-microbial interactions.
In spite of the much evidence for the beneficial effects of probiotics, their anti-obesity effects have not been well examined. We evaluated the effects of the probiotic Lactobacillus gasseri SBT2055 (LG2055) on abdominal adiposity, body weight and other body measures in adults with obese tendencies. We conducted a multicenter, double-blind, randomized, placebo-controlled intervention trial. Subjects (n=87) with higher body mass index (BMI) (24.2-30.7 kg/m(2)) and abdominal visceral fat area (81.2-178.5 cm(2)) were randomly assigned to receive either fermented milk (FM) containing LG2055 (active FM; n=43) or FM without LG2055 (control FM; n=44), and were asked to consume 200 g/day of FM for 12 weeks. Abdominal fat area was determined by computed tomography. In the active FM group, abdominal visceral and subcutaneous fat areas significantly (P<0.01) decreased from baseline by an average of 4.6% (mean (confidence interval): -5.8 (-10.0, -1.7) cm(2)) and 3.3% (-7.4 (-11.6, -3.1) cm(2)), respectively. Body weight and other measures also decreased significantly (P<0.001) as follows: body weight, 1.4% (-1.1 (-1.5, -0.7) kg); BMI, 1.5% (-0.4 (-0.5, -0.2) kg/m(2)); waist, 1.8% (-1.7 (-2.1, -1.4) cm); hip, 1.5% (-1.5 (-1.8, -1.1) cm). In the control group, by contrast, none of these parameters decreased significantly. High-molecular weight adiponectin in serum increased significantly (P<0.01) in the active and control groups by 12.7% (0.17 (0.07, 0.26) microg/ml) and 13.6% (0.23 (0.07, 0.38) microg/ml), respectively. The probiotic LG2055 showed lowering effects on abdominal adiposity, body weight and other measures, suggesting its beneficial influence on metabolic disorders.
SCFAs (short-chain fatty acids), fermentation products of bacteria, influence epithelial-specific gene expression. We hypothesize that SCFAs affect goblet-cell-specific mucin MUC2 expression and thereby alter epithelial protection. In the present study, our aim was to investigate the mechanisms that regulate butyrate-mediated effects on MUC2 synthesis. Human goblet cell-like LS174T cells were treated with SCFAs, after which MUC2 mRNA levels and stability, and MUC2 protein expression were analysed. SCFA-responsive regions and cis-elements within the MUC2 promoter were identified by transfection and gel-shift assays. The effects of butyrate on histone H3/H4 status at the MUC2 promoter were established by chromatin immunoprecipitation. Butyrate (at 1 mM), as well as propionate, induced an increase in MUC2 mRNA levels. MUC2 mRNA levels returned to basal levels after incubation with 5-15 mM butyrate. Interestingly, this decrease was not due to loss of RNA stability. In contrast, at concentrations of 5-15 mM propionate, MUC2 mRNA levels remained increased. Promoter-regulation studies revealed an active butyrate-responsive region at -947/-371 within the MUC2 promoter. In this region we identified an active AP1 (c-Fos/c-Jun) cis-element at -818/-808 that mediates butyrate-induced activation of the promoter. Finally, MUC2 regulation by butyrate at 10-15 mM was associated with increased acetylation of histone H3 and H4 and methylation of H3 at the MUC2 promoter. In conclusion, 1 mM butyrate and 1-15 mM propionate increase MUC2 expression. The effects of butyrate on MUC2 mRNA are mediated via AP-1 and acetylation/methylation of histones at the MUC2 promoter.
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