Microbial influences in inflammatory bowel diseases

Importance of nutrition in inflammatory bowel disease

Inflammatory bowel disease (IBD) results from the interaction between an individual’s immune response and precipitant environmental factors, which generate an anomalous chronic inflammatory response in those who are genetically predisposed. Various feeding practices have been implicated in the origin of IBD based on epidemiological observations in developed countries, but we do not have solid evidence for the etiological role played by specific food types. IBD is associated with frequent nutritional deficiencies, the pattern and severity of which depends on the extent, duration and activity of the inflammation. Nutritional support allows these deficiencies in calories, macro- and micro-nutrients to be rectified. Enteral nutrition is also a primary therapy for IBD, especially for Crohn’s disease, as it allows the inflammatory activity to be controlled, kept in remission, and prevents or delays the need for surgery. Nutritional support is especially important in childhood IBD as an alternative to pharmacological treatment. This report discusses the complex relationship between diet and IBD.

Fecal coliform testing to identify effective antibiotic therapies for patients with antibiotic-resistant pouchitis

BACKGROUND & AIMS

Empiric antibiotic therapy (eg, a combination of ciprofloxacin and metronidazole) is effective in treating the majority of patients with inflammation of the ileal reservoir (pouchitis). Unfortunately, up to 20% of patients develop refractory or rapidly relapsing disease. We developed a fecal sensitivity analysis to determine which antibiotics are most likely to be effective in patients who do not respond to empiric antibiotic therapy or have relapsed after long-term therapy.

METHODS

Fecal samples from 15 patients with active pouchitis (pouch disease activity index [PDAI], > or =7) who failed standard antibiotic treatment were inoculated onto Iso-sensitest agar. Antibiotic testing discs were added, incubated, and sensitivity patterns were recorded. Patients then were treated with antibiotics based on predicted sensitivity; PDAI scores were assessed 4 weeks later. Thirteen patients enrolled in the study had failed to enter remission after treatment with ciprofloxacin and metronidazole and 2 patients had relapsed after maintenance treatment with ciprofloxacin.

RESULTS

Antibiotic coliform sensitivity testing showed ciprofloxacin resistance in all samples, co-amoxiclav resistance in 4 samples, trimethoprim resistance in 11 samples, and cefixime resistance in 8 samples. All 15 patients were treated with an antibiotic to which their fecal coliforms were sensitive; 12 (80%) achieved clinical remission (PDAI score, 0).

CONCLUSIONS

Fecal coliform sensitivity analysis can identify effective antibiotic therapies for patients with antibiotic-resistant pouchitis. This targeted antibiotic approach is recommended in all patients who fail to respond to empiric antibiotic treatment or relapse after long-term antibiotic therapy.

Patterns and scales in gastrointestinal microbial ecology

The body surfaces of humans and other animals are colonized at birth by microorganisms. The majority of microbial residents on the human body exist within gastrointestinal (GI) tract communities, where they contribute to many aspects of host biology and pathobiology. Recent technological advances have expanded our ability to perceive the membership and physiologic traits of microbial communities along the GI tract. To translate this information into a mechanistic and practical understanding of host-microbe and microbe-microbe relationships, it is necessary to recast our conceptualization of the GI tract and its resident microbial communities in ecological terms. This review depicts GI microbial ecology in the context of 2 fundamental ecological concepts: (1) the patterns of biodiversity within the GI tract and (2) the scales of time, space, and environment within which we perceive those patterns. We show how this conceptual framework can be used to integrate our existing knowledge and identify important open questions in GI microbial ecology.

Twin studies reveal specific imbalances in the mucosa-associated microbiota of patients with ileal Crohn's disease

BACKGROUND

Large interindividual variation in the composition of the intestinal microbiota between unrelated individuals has made it challenging to identify specific aspects of dysbiosis that lead to Crohn's disease (CD).

METHODS

To reduce variations in exposure during establishment of the gut flora and the influence of genotype, we studied the mucosa-associated microbiota of monozygotic twin pairs that were discordant (n = 6) or concordant (n = 4) for CD. DNA was extracted from biopsies collected from 5 locations between the ileum and rectum. Bacterial 16S ribosomal RNA genes were amplified and community composition assessed by terminal-restriction fragment length polymorphism, cloning and sequencing, and quantitative real-time polymerase chain reaction (PCR).

RESULTS

The microbial compositions at all biopsy locations for each individual were similar, regardless of disease state, but there were differences between individuals. In particular, individuals with predominantly ileal CD had a dramatically lower abundance (P < 0.001) of Faecalibacterium prausnitzii and increased abundance (P < 0.03) of Escherichia coli compared to healthy co-twins and those with CD localized in the colon. This dysbiosis was significantly correlated to the disease phenotype rather than genotype.

CONCLUSIONS

The reduced abundance of F. prausnitzii and increased abundance of E. coli are indicative of an ileal CD phenotype, distinct from colonic CD, and the relative abundances of these specific bacterial populations are promising biomarker candidates for differential diagnosis of CD and eventually customized treatment.

Do NSAIDs, antibiotics, infections, or stress trigger flares in IBD?

Non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics, enteric or other systemic infections, and stress have all been reported to be potential triggers of inflammatory bowel disease (IBD). Although a mechanism of triggering a flare of IBD can be hypothesized for each factor, the associations of these factors with flares of IBD remains confusing. In this review, we analyze the literature that explores these associations. There is some evidence to support an association between NSAID use and flares but little data to associate antibiotic use directly with flares. An important connection between antibiotic use and an exacerbation of symptoms is through the development of Clostridium difficile infections. However, for all enteric infections, including C. difficile, it is unclear whether these infections simply trigger symptoms in patients with IBD that resolve on resolution of the infection, or whether they truly trigger a flare of intestinal inflammation that outlasts the infection. There is a paucity of evidence that other systemic infections trigger flares of IBD. Although there is strong evidence for an association between perceived stress levels and flares, there is a weaker association between a simple accounting of stressful life events and flares. Much of the literature is limited by a lack of adequate control groups and failure to report on base rates in the population under study (i.e., NSAIDs and antibiotic use, occurrence of infections, and stress levels). More large population-based matched cohort or case crossover studies and a continued emphasis on prospective designs are needed to better explore these potential associations. Clinical implications given the current state of knowledge are discussed.

Targeting the human microbiome with antibiotics, probiotics, and prebiotics: gastroenterology enters the metagenomics era

Studies of metagenomics and the human microbiome will tremendously expand our knowledge of the composition of microbial communities in the human body. As our understanding of microbial variation and corresponding genetic parameters is refined, this information can be applied to rational remodeling or "tailoring" of human-associated microbial communities and their associated functions. Physiologic features such as the development of innate and adaptive immunity, relative susceptibilities to infections, immune tolerance, bioavailability of nutrients, and intestinal barrier function may be modified by changing the composition and functions of the microbial communities. The specialty of gastroenterology will be affected profoundly by the ability to modify the gastrointestinal microbiota through the rational deployment of antibiotics, probiotics, and prebiotics. Antibiotics might be used to remove or suppress undesirable components of the human microbiome. Probiotics can introduce missing microbial components with known beneficial functions for the human host. Prebiotics can enhance the proliferation of beneficial microbes or probiotics, to maximize sustainable changes in the human microbiome. Combinations of these approaches might provide synergistic and effective therapies for specific disorders. The human microbiome could be manipulated by such "smart" strategies to prevent and treat acute gastroenteritis, antibiotic-associated diarrhea and colitis, inflammatory bowel disease, irritable bowel syndrome, necrotizing enterocolitis, and a variety of other disorders.

[A case of actinomycosis of gallbladder presenting as acute cholecystitis]

Actinomycosis is a chronic suppurative and granulomatous disease, characterized by the formation of abscess, draining sinuses, abundant granulation, and dense fibrous tissue. Actinomycosis of the gallbladder is extremely rare. We report a case of an 56-years old man who abruptly presented with right upper quadrant abdominal pain. Abdominal CT showed that the gallbladder had 2 cm sized stone and an edematous thick wall. Our preoperative diagnosis was acute calculous cholecystitis. After the management of acute cholecystitis, laparoscopic cholecystectomy was performed but converted to open surgery due to severe adhesion to liver and greater omentum. Partial cholecystectomy was performed. Histologic section of the gallbladder showed sulfur granule with gram-positive branching bacilli compatible with actinomyces. After cholecystectomy, the patient received intravenous penicillin G for 2 weeks, followed by oral penicillin for 3 months.

High-throughput quantitative analysis of the human intestinal microbiota with a phylogenetic microarray

Gut microbiota carry out key functions in health and participate in the pathogenesis of a growing number of diseases. The aim of this study was to develop a custom microarray that is able to identify hundreds of intestinal bacterial species. We used the Entrez nucleotide database to compile a data set of bacterial 16S rRNA gene sequences isolated from human intestinal and fecal samples. Identified sequences were clustered into separate phylospecies groups. Representative sequences from each phylospecies were used to develop a microbiota microarray based on the Affymetrix GeneChip platform. The designed microbiota array contains probes to 775 different bacterial phylospecies. In our validation experiments, the array correctly identified genomic DNA from all 15 bacterial species used. Microbiota array has a detection sensitivity of at least 1 pg of genomic DNA and can detect bacteria present at a 0.00025% level of overall sample. Using the developed microarray, fecal samples from two healthy children and two healthy adults were analyzed for bacterial presence. Between 227 and 232 species were detected in fecal samples from children, whereas 191 to 208 species were found in adult stools. The majority of identified phylospecies belonged to the classes Clostridia and Bacteroidetes. The microarray revealed putative differences between the gut microbiota of healthy children and adults: fecal samples from adults had more Clostridia and less Bacteroidetes and Proteobacteria than those from children. A number of other putative differences were found at the genus level.

Intestinal fibrosis in IBD--a dynamic, multifactorial process

Intestinal fibrosis is a common and potentially serious complication of IBD that results from the reaction of intestinal tissue to the damage inflicted by chronic inflammation. The traditional view that fibrosis is inevitable or irreversible in patients with IBD is progressively changing in light of improved understanding of the cellular and molecular mechanisms that underlie the pathogenesis of fibrosis in general, and, in particular, intestinal fibrosis. These mechanisms are complex and dynamic, and involve multiple cell types, interconnected cellular events and a large number of soluble factors. In addition, owing to a breakdown of the epithelial barrier during inflammation of the gut, luminal bacterial products induce an innate immune response, which is triggered by activation of immune and nonimmune cells alike. Comprehension of the mechanisms of intestinal fibrosis will create a conceptual and practical framework that could achieve the specific blockade of fibrogenic pathways, allow for the estimation of risk of fibrotic complications, permit the detection of early fibrotic changes and, eventually, enable the development of treatments customized to the type and stage of each patient's IBD.

Influence of fecal sample storage on bacterial community diversity

Previous studies have identified a correlation, either positive or negative, between specific stool bacteria strains and certain autoimmune diseases. These conflicting data may relate to sample collection. The aim of this work was to evaluate the influence of the collection parameters of time and temperature on bacterial community composition. Samples were taken from healthy children and immediately divided in 5 sub-samples. One sample was frozen immediately at -80°C, while the other aliquots were frozen 12, 24, 48, and 72h later DNA extracted from each sample was used to amplify the 16S rRNA with barcoded primers. The amplified products were pooled and partial 16S rRNA sequences were obtained by pyrosequencing. Person-to-person variability in community diversity was high. A list of those taxa that comprise at least 1% of the community was made for each individual. None of these were present in high numbers in all individuals. The Bacteroides were present in the highest abundance in three of four subjects. A total of 23,701 16S rRNA sequences were obtained with an average of 1,185 reads per sample with an average length of 200 bases. Although pyrosequencing of amplified 16S rRNA identified changes in community composition over time (~10%), little diversity change was observed at 12 hours (3.06%) with gradual changes occurring after 24 (8.61%), 48 (9.72%), and 72 h (10.14%), post collection.

Reproducible community dynamics of the gastrointestinal microbiota following antibiotic perturbation

Shifts in microbial communities are implicated in the pathogenesis of a number of gastrointestinal diseases, but we have limited understanding of the mechanisms that lead to altered community structures. One difficulty with studying these mechanisms in human subjects is the inherent baseline variability of the microbiota in different individuals. In an effort to overcome this baseline variability, we employed a mouse model to control the host genotype, diet, and other possible influences on the microbiota. This allowed us to determine whether the indigenous microbiota in such mice had a stable baseline community structure and whether this community exhibited a consistent response following antibiotic administration. We employed a tag-sequencing strategy targeting the V6 hypervariable region of the bacterial small-subunit (16S) rRNA combined with massively parallel sequencing to determine the community structure of the gut microbiota. Inbred mice in a controlled environment harbored a reproducible baseline community that was significantly impacted by antibiotic administration. The ability of the gut microbial community to recover to baseline following the cessation of antibiotic administration differed according to the antibiotic regimen administered. Severe antibiotic pressure resulted in reproducible, long-lasting alterations in the gut microbial community, including a decrease in overall diversity. The finding of stereotypic responses of the indigenous microbiota to ecologic stress suggests that a better understanding of the factors that govern community structure could lead to strategies for the intentional manipulation of this ecosystem so as to preserve or restore a healthy microbiota.

Serious events with infliximab in patients with inflammatory bowel disease: a 9-year cohort study in the Netherlands

BACKGROUND

The tumour necrosis factor-alpha inhibitor infliximab is incorporated in the treatment guidelines for patients with inflammatory bowel disease (IBD). However, concerns about serious adverse events such as infections, malignancies and death do exist.

OBJECTIVE

To evaluate the occurrence of serious events of infliximab during 9 years in a single-centre cohort of patients with IBD.

METHODS

Consecutive patients (>18 years) with a proven diagnosis of IBD who started treatment for IBD with infliximab at our referral centre in the Netherlands, from June 1999 to October 2007, were included. Infusion data were collected prospectively and medical records were reviewed retrospectively. All serious events were recorded and scored in the following categories: events leading to hospitalization, infections, malignancies and death. Severity and relationship to the use of infliximab were assessed for every serious event.

RESULTS

147 patients (33% male, mean age at first infusion 38 years, standard deviation = 12) received a total number of 1924 infusions (median per patient = 10, range 1-70). A total of 89 patients (61%) were hospitalized during follow-up, involving a total of 300 hospitalizations. Of these, 60 hospitalizations (20%) were considered at least possibly related to the use of infliximab. In 21 hospitalizations, the occurrence of a serious infection was considered at least possibly related to infliximab. Of all hospitalized patients, 70 patients (79%) underwent 139 surgical procedures, of which 70 surgeries (50%) were gastrointestinal related. Nine patients (6%) developed malignancies during follow-up: four colorectal carcinomas, one carcinoid tumour with another primary signet-ring cell carcinoma of the small bowel, one breast cancer, two skin cancers and one superficial melanoma. During follow-up, eight patients (5%) died: six as a result of malignancies, one patient as a result of a complication of short bowel syndrome and one patient due to unknown reasons. Patients who developed malignancies tended to have a longer disease duration than those who did not.

CONCLUSION

Clinicians prescribing biological therapies should be aware of the development of serious events in their patients. Thorough follow-up of all patients during treatment with infliximab is warranted. If infliximab is considered in patients with IBD not responding to conventional treatment, efforts to exclude other possible underlying causes for worsening of symptoms should be made. Careful prescribing and monitoring during follow-up remains necessary.

Endogenous antigen presenting cell-derived IL-10 inhibits T lymphocyte responses to commensal enteric bacteria

Interleukin-10 deficient (IL-10-/-) mice develop chronic T cell-mediated colitis when colonized with normal commensal bacteria, but germ-free (GF) IL-10-/- mice remain disease-free. Antigen presenting cells (APC) secrete regulatory cytokines that help determine T lymphocyte activation or tolerance. CD4(+) T cells from the mesenteric lymph nodes of inflamed IL-10-/- mice secrete more IFN-gamma and IL-17 when cultured with cecal bacterial lysate-pulsed splenic APC from IL-10-/- mice than when cultured with normal control APC. GF IL-10-/- APC induce similar IFN-gamma and IL-17 responses; therefore, the functional difference between normal and IL-10 deficient APC is inherent to the lack of IL-10 and not secondary to inflammation. Bacterial lysate-pulsed normal APC cultured with CD4(+) cells from colitic IL-10-/- mice or with exogenous IFN-gamma secrete higher amounts of IL-10 compared to the same APC cultured with naïve T cells. APC enriched for CD11c(+) cells are potent activators of IFN-gamma and IL-17 production by CD4(+) cells from IL-10-/- mice. These APC also produce IL-12/IL-23 p40 and IL-10. Recombinant IL-10 suppressed and anti-IL-10 receptor antibody increased IFN-gamma, IL-17 and IL-12/IL-23 p40 production in bacterial lysate-pulsed APC and plus CD4(+) T cell co-cultures. Taken together, our results show that endogenous IL-10 produced by APC inhibits responses to commensal bacteria and influences the ability of APC to stimulate IFN-gamma-producing effector lymphocytes, which reciprocally, induce IL-10 production by APC. Cytokines produced by APC are an important determinant of pathogenic versus protective mucosal immune responses to colonic bacterial stimulation.

Lactobacillus reuteri prevents colitis by reducing P-selectin-associated leukocyte- and platelet-endothelial cell interactions

Recent findings indicate that dextran sodium sulfate (DSS)-induced colitis is associated with a prothrombogenic phenotype, with P-selectin playing a major role in platelet recruitment. It has been suggested that probiotics may ameliorate colonic inflammation. We therefore investigated how treatment with Lactobacillus reuteri influenced P-selectin expression, leukocyte and platelet endothelial cell interactions, and colitis severity in DSS-treated rats. Rats were divided into the following four groups: nontreated, DSS treated (5% in drinking water for 9 days), L. reuteri, and L. reuteri and DSS treated. The rats were anesthetized with Inactin (120 mg/kg ip), and the dual radiolabeled monoclonal antibody technique was used to quantify P-selectin expression. Leukocyte-endothelial and platelet-endothelial cell interactions were studied in colonic venules with intravital microscopy. Colitis severity was assessed using a disease activity index. Disease activity index increased, as did the expression of P-selectin in the entire colon after DSS treatment, but both were reduced to control levels with L. reuteri pretreatment. The increased platelet- and leukocyte-endothelial cell interactions after DSS treatment were abolished by pretreatment with L. reuteri. L. reuteri protects against DSS-induced colitis in rats. The protection is associated with reduced P-selectin expression and a decrease in leukocyte- and platelet-endothelial cell interactions.

Intestinal dendritic cells and epithelial barrier dysfunction in Crohn's disease

Crohn's disease (CD) is a chronic gastrointestinal inflammatory disorder considered to be the result of an inappropriate and exaggerated mucosal immune reaction to yet undefined triggers from the gut flora in genetically predisposed individuals. This inflammatory phenomenon has been characterized by an adaptive T-cell response in addition to an abnormal function of the innate immune system. Dendritic cells (DCs) are constituents of this innate system, inducing T-cell activation via antigen presentation. In the gut, mucosal DCs are separated from the luminal milieu by a monolayer of cylindrical epithelial cells that forms an anatomical and physiological barrier that controls the normal traffic of antigens between both compartments. An imbalance of colonic and ileal DC distribution in tissues from CD patients as well as functional differences between DCs isolated from normal and diseased intestinal samples have been demonstrated. Moreover, a gut barrier defect in the para- and transepithelial routes in addition to a significant reduction in the intestinal secretion of epithelial products involved in barrier function has been well documented in CD. Therefore, this may expose the diseased mucosa to overwhelming amounts of antigens, resulting in abnormal DC activation and a subsequent imbalance in their distribution. In conclusion, this review provides a summary of relevant progress in CD, intestinal epithelial permeability, and DCs highlighting a potential relationship between increased epithelial permeability and abnormal DC distribution during the pathogenesis of intestinal inflammation.

Increased transmucosal uptake of E. coli K12 in collagenous colitis persists after budesonide treatment

OBJECTIVES

Collagenous colitis is increasingly recognized as a common diarrheal disorder of inflammatory origin. Intestinal inflammation is generally associated with increased mucosal permeability, but little is known about barrier function in microscopic colitis. Our aim was to investigate the mucosal barrier to nonpathogenic bacteria in collagenous colitis.

METHODS

The study included 33 individuals, 25 with collagenous colitis (14 in clinical remission, 11 with active disease, and 8 of these again after 6 weeks budesonide treatment) and 8 control patients. Bowel movements were registered for 1 week. Endoscopic biopsies from the sigmoid colon were mounted in modified Ussing chambers and assessed for short-circuit current (I(sc)), transepithelial resistance (TER), and transmucosal passage of chemically killed Escherichia coli K12.

RESULTS

Bacterial uptake was increased in patients in remission, 1.6 U (1.1-3.0) and in those with active disease, 4.6 U (2.5-5.8; median (IQR)), compared to controls, 0.7 U (0.1-1.1; P=0.004 and P-0.001, respectively). Active disease also had significant decrease in transepithelial resistance (TER) after 120 min, -9.7 Omega cm(2) ((-13)-(-4.3)), compared to controls, -5.2 Omega cm(2) ((-7.2)-(-3.1)), P-0.03; or patients in remission, -4.8 Omega cm(2) ((-8.0)-(-1.2)), P=0.04. Budesonide decreased median stool frequency to 1.9 (1.3-2.2) compared to 3.8 (3.7-4.2) before treatment (P=0.01), but bacterial uptake was still increased after budesonide 2.9 U (1.5-3.8), (P=0.006 compared to controls), and there were no significant changes in histology.

CONCLUSIONS

Collagenous colitis presents with significantly increased uptake and altered mucosal reactivity to nonpathogenic bacteria. Budesonide induces clinical remission and restores mucosal reactivity but does not abolish the increased bacterial uptake. An underlying barrier dysfunction may explain the frequent and rapid relapses in CC.

Lipopolysaccharide activates innate immune responses in murine intestinal myofibroblasts through multiple signaling pathways

Myofibroblasts (MF) play an important role in intestinal wound healing. A compromised epithelial barrier exposes intestinal subepithelial MF to luminal bacterial products. However, responses of murine intestinal MF to bacterial adjuvants and potential roles of intestinal MF in innate immune responses are not well defined. Our aims in this study were to determine innate immune responses and intracellular signaling pathways of intestinal MF exposed to LPS, a prototypic Toll-like receptor (TLR) ligand. Expression of TLR4 in primary murine intestinal MF cultures was confirmed by RT-PCR and Western blotting. LPS-induced secretion of prostaglandin E2 (PGE2), interleukin (IL)-6, and keratinocyte-derived chemokines (KC) was measured by ELISA. Intracellular responses to LPS were assessed by Western blotting for NF-kappaB p65, Ikappa-Balpha, Akt, p38 MAP kinase, and cyclooxygenase-2 (COX-2). LPS induced rapid phosphorylation of NF-kappaB p65, Akt, and p38 MAPK and degradation of Ikappa-Balpha. LPS induced expression of COX-2 and secretion of PGE2 (2.0+/-0.8-fold induction vs. unstimulated cells), IL-6 (6.6+/-0.4-fold induction), and KC (12.5+/-0.4-fold induction). Inhibition of phosphoinositide-3 (PI3)-kinase, p38 MAPK, or NF-kappaB pathways reduced LPS-induced PGE2, IL-6, and KC secretion. These studies show that primary murine intestinal MF respond to LPS, evidenced by activation of NF-kappaB, PI3-kinase, and MAPK signaling pathways and secretion of proinflammatory molecules. Inhibition of these pathways attenuated LPS-dependent PGE2, IL-6, and KC production, indicating that LPS activates MF by multiple signaling pathways. These data support the hypothesis that MF are a component of the innate immune system and may exert paracrine effects on adjacent epithelial and immune cells by responding to luminal bacterial adjuvants.

The epidemiology and pathogenesis of neoplasia in the small intestine

PURPOSE

The mucosa of the small intestine encompasses about 90% of the luminal surface area of the digestive system, but only 2% of the total annual gastrointestinal cancer incidence in the United States.

METHODS

The remarkable contrast in age-standardized cancer incidence between the small and large intestine has been reviewed with respect to the cell type patterns, demographic features, and molecular characteristics of neoplasms.

RESULTS

Particularly noteworthy is the predominance of adenocarcinoma in the colon, which exceeds 98% of the total incidence by cell type, in contrast to that of 30% to 40% in the small intestine, resulting in an age-standardized ratio of rates exceeding 50-fold. The prevalence of adenomas and carcinomas is most prominent in the duodenum and proximal jejunum. The positive correlation in global incidence rates of small and large intestinal neoplasms and the reciprocal increases in risk of second primary adenocarcinomas suggest that there are common environmental risk factors. The pathophysiology of Crohn inflammatory bowel disease and the elevated risk of adenocarcinoma demonstrate the significance of the impaired integrity of the mucosal barrier and of aberrant immune responses to luminal indigenous and potentially pathogenic microorganisms.

CONCLUSION

In advancing a putative mechanism for the contrasting mucosal susceptibilities of the small and large intestine, substantial differences are underscored in the diverse taxonomy, concentration and metabolic activity of anaerobic organisms, rate of intestinal transit, changing pH, and the enterohepatic recycling and metabolism of bile acids. Experimental and epidemiologic studies are cited that suggest that the changing microecology, particularly in the colon, is associated with enhanced metabolic activation of ingested and endogenously formed procarcinogenic substrates.

Tomato lycopene extract prevents lipopolysaccharide-induced NF-kappaB signaling but worsens dextran sulfate sodium-induced colitis in NF-kappaBEGFP mice

Background

The impact of tomato lycopene extract (TLE) on intestinal inflammation is currently unknown. We investigated the effect of TLE on lipopolysaccharide (LPS)-induced innate signaling and experimental colitis.

Methodology/Principal Findings

Mice were fed a diet containing 0.5 and 2% TLE or isoflavone free control (AIN-76). The therapeutic efficacy of TLE diet was assessed using dextran sulfate sodium (DSS) exposed mice and IL-10^−/−;NF-κB^EGFP mice, representing an acute and spontaneous chronic colitis model respectively. A mini-endoscope was used to determine the extent of macroscopic mucosal lesions. Murine splenocytes and intestinal epithelial cells were used to determine the in vitro impact of TLE on LPS-induced NF-κB signaling. In vitro, TLE blocked LPS-induced IκBα degradation, RelA translocation, NF-κB transcriptional activity and MIP-2 mRNA accumulation in IEC-18 cells. Moreover, LPS-induced IL-12p40 gene expression was dose-dependently inhibited in TLE-treated splenocytes. Interestingly, DSS-induced acute colitis worsened in TLE-fed NF-κB^EGFP mice compared to control diet as measured by weight loss, colonoscopic analysis and histological scores. In contrast, TLE-fed IL-10^−/−;NF-κB^EGFP mice displayed decreased colonic EGFP expression compared to control diet. IL-6, TNFα, and MCP-1 mRNA expression were increased in the colon of TLE-fed, DSS-exposed NF-κB^EGFP mice compared to the control diet. Additionally, caspase-3 activation and TUNEL positive cells were enhanced in TLE diet-fed, DSS-exposed mice as compared to DSS control mice.

Conclusions/ Significance

These results indicate that TLE prevents LPS-induced proinflammatory gene expression by blocking of NF-κB signaling, but aggravates DSS-induced colitis by enhancing epithelial cell apoptosis.

Post-translational inhibition of IP-10 secretion in IEC by probiotic bacteria: impact on chronic inflammation

Background

Clinical and experimental studies suggest that the probiotic mixture VSL#3 has protective activities in the context of inflammatory bowel disease (IBD). The aim of the study was to reveal bacterial strain-specific molecular mechanisms underlying the anti-inflammatory potential of VSL#3 in intestinal epithelial cells (IEC).

Methodology/Principal Findings

VSL#3 inhibited TNF-induced secretion of the T-cell chemokine interferon-inducible protein (IP-10) in Mode-K cells. Lactobacillus casei (L. casei) cell surface proteins were identified as active anti-inflammatory components of VSL#3. Interestingly, L. casei failed to block TNF-induced IP-10 promoter activity or IP-10 gene transcription at the mRNA expression level but completely inhibited IP-10 protein secretion as well as IP-10-mediated T-cell transmigration. Kinetic studies, pulse-chase experiments and the use of a pharmacological inhibitor for the export machinery (brefeldin A) showed that L. casei did not impair initial IP-10 production but decreased intracellular IP-10 protein stability as a result of blocked IP-10 secretion. Although L. casei induced IP-10 ubiquitination, the inhibition of proteasomal or lysosomal degradation did not prevent the loss of intracellular IP-10. Most important for the mechanistic understanding, the inhibition of vesicular trafficking by 3-methyladenine (3-MA) inhibited IP-10 but not IL-6 expression, mimicking the inhibitory effects of L. casei. These findings suggest that L. casei impairs vesicular pathways important for the secretion of IP-10, followed by subsequent degradation of the proinflammatory chemokine. Feeding studies in TNF^ΔARE and IL-10^−/− mice revealed a compartimentalized protection of VSL#3 on the development of cecal but not on ileal or colonic inflammation. Consistent with reduced tissue pathology in IL-10^−/− mice, IP-10 protein expression was reduced in primary epithelial cells.

Conclusions/Significance

We demonstrate segment specific effects of probiotic intervention that correlate with reduced IP-10 protein expression in the native epithelium. Furthermore, we revealed post-translational degradation of IP-10 protein in IEC to be the molecular mechanism underlying the anti-inflammatory effect.

Defensins and inflammation: the role of defensins in inflammatory bowel disease

Defensins are antimicrobial peptides produced at a variety of epithelial surfaces. In the intestinal tract, they contribute to host immunity and assist in maintaining the balance between protection from pathogens and tolerance to normal flora. However, attenuated expression of defensins compromises host immunity and hence may alter the balance toward inflammation. Altered defensin production is suggested to be an integral element in the pathogenesis of inflammatory bowel disease (IBD). Evidence for this is shown in Crohn's disease where reduced alpha-defensin levels are seen in patients with ileal disease and reduced beta-defensin levels in those with colonic involvement. Further evidence is provided by research linking nucleotide oligomerization domain 2 (NOD2) mutations and deficient defensin expression. However, alternate studies suggest that NOD2 status and defensin expression are independent, and that defensin deficiency is due to mucosal surface destruction as a result of inflammatory changes, indicating that reduced defensin expression is a symptom of the disease and not the cause. Although it is clear that defensin expression is altered in IBD, it is less clear whether defensin deficiency is implicated in the pathogenesis of IBD or is a consequence of the disease process. The aim of this article is to review the current knowledge of defensins in IBD and discuss their potential role in IBD pathogenesis.

Targeted epithelial tight junction dysfunction causes immune activation and contributes to development of experimental colitis

BACKGROUND & AIMS

Inflammatory bowel disease (IBD) is a multifactorial disease thought to be caused by alterations in epithelial function, innate and adaptive immunity, and luminal microbiota. The specific role of epithelial barrier function remains undefined, although increased activity of intestinal epithelial myosin light chain kinase (MLCK), which is the primary mechanism of tumor necrosis factor-induced barrier dysfunction, occurs in human IBD. Our aim was to determine whether, in an intact epithelium, primary dysregulation of the intestinal epithelial barrier by pathophysiologically relevant mechanisms can contribute to development of colitis.

METHODS

We developed transgenic (Tg) mice that express constitutively active MLCK (CA-MLCK) specifically within intestinal epithelia. Their physiology, immune status, and susceptibility to disease were assessed and compared with non-Tg littermate controls.

RESULTS

CA-MLCK Tg mice demonstrated significant barrier loss but grew and gained weight normally and did not develop spontaneous disease. CA-MLCK Tg mice did, however, develop mucosal immune activation demonstrated by increased numbers of lamina propria CD4(+)lymphocytes, redistribution of CD11c+cells, increased production of interferon-gamma and tumor necrosis factor, as well as increased expression of epithelial major histocompatibility complex class I. When challenged with CD4+CD45+Rb(hi) lymphocytes, Tg mice developed an accelerated and more severe form of colitis and had shorter survival times than non-Tg littermates.

CONCLUSIONS

Primary pathophysiologically relevant intestinal epithelial barrier dysfunction is insufficient to cause experimental intestinal disease but can broadly activate mucosal immune responses and accelerate the onset and severity of immune-mediated colitis.

Effect of a probiotic preparation (VSL#3) on induction and maintenance of remission in children with ulcerative colitis

OBJECTIVES

Several probiotic compounds have shown promise in the therapy of ulcerative colitis (UC). However, a strong sustained benefit remains to be seen. Uncontrolled pilot studies suggest that a probiotic preparation (VSL#3) maintains remission in mild to moderate UC and reduces active inflammation in adult patients. Aims of our prospective, 1-year, placebo-controlled, double-blind study were to assess the efficacy of VSL#3 on induction and maintenance of remission and to evaluate the safety and tolerability of the probiotic preparation therapy in children with active UC.

METHODS

A total of 29 consecutive patients (mean age: 9.8 years; range: 1.7-16.1 years; female/male: 13/16) with newly diagnosed UC were randomized to receive either VSL#3 (weight-based dose, range: 450-1,800 billion bacteria/day; n=14) or an identical placebo (n=15) in conjunction with concomitant steroid induction and mesalamine maintenance treatment. Children were prospectively evaluated at four time points: within 1 month, 2 months, 6 months, and 1 year after diagnosis or at the time of relapse. Lichtiger colitis activity index and a physician's global assessment were used to measure disease activity. At baseline, within 6 months and 12 months or at the time of relapse, all patients were assessed endoscopically and histologically.

RESULTS

All 29 patients responded to the inflammatory bowel disease (IBD) induction therapy. Remission was achieved in 13 patients (92.8%) treated with VSL#3 and IBD therapy and in 4 patients (36.4%) treated with placebo and IBD therapy (P<0.001). Overall, 3 of 14 (21.4%) patients treated with VSL#3 and IBD therapy and 11 of 15 (73.3%) patients treated with placebo and IBD therapy relapsed within 1 year of follow-up (P=0.014; RR=0.32; CI=0.025-0.773; NNT=2). All 3 patients treated with VSL#3 and 6 of 11 (54.5%) patients treated with placebo relapsed within 6 months of diagnosis. At 6 months, 12 months, or at time of relapse, endoscopic and histological scores were significantly lower in the VSL#3 group than in the placebo group (P<0.05). There were no biochemical or clinical adverse events related to VSL#3.

CONCLUSIONS

This is the first pediatric, randomized, placebo-controlled trial that suggests the efficacy and safety of a highly concentrated mixture of probiotic bacterial strains (VSL#3) in active UC and demonstrates its role in maintenance of remission.

Mycobacterium avium subspecies paratuberculosis and its relationship with Crohn’s disease

The hypothesis postulating that Mycobacterium avium paratuberculosis (MAP) is the cause of Crohn’s disease (CD) has been circulating for many years. Advances in molecular techniques, such as polymerase chain reaction and culture methods, have enabled researchers to demonstrate that there is an association between MAP and CD. Recently, genome-wide association studies have identified novel susceptibility genes for CD, which are critical for generation of an adaptive immune response that is protective against intracellular pathogens, including M. tuberculosis infection. However, the role of MAP as a cause of CD suffered a setback with the report that administration of antimycobacterial therapy failed to lead to a sustained response in CD patients. Accordingly, this review sought neither to confirm nor refute this, but instead to survey recent literature on the role of MAP in CD.

Methods for generating and colonizing gnotobiotic zebrafish

Vertebrates are colonized at birth by complex and dynamic communities of microorganisms that can contribute significantly to host health and disease. The ability to raise animals in the absence of microorganisms has been a powerful tool for elucidating the relationships between animal hosts and their microbial residents. The optical transparency of the developing zebrafish and relative ease of generating germ-free (GF) zebrafish make it an attractive model organism for gnotobiotic research. Here we provide a protocol for generating zebrafish embryos; deriving and rearing GF zebrafish; and colonizing zebrafish with microorganisms. Using these methods, we typically obtain 80-90% sterility rates in our GF derivations with 90% survival in GF animals and 50-90% survival in colonized animals through larval stages. Obtaining embryos for derivation requires approximately 1-2 h, with a 3- to 8-h incubation period before derivation. Derivation of GF animals takes 1-1.5 h, and daily maintenance requires 1-2 h.

Faecal microbiota profile of Crohn's disease determined by terminal restriction fragment length polymorphism analysis

BACKGROUND

Terminal restriction fragment length polymorphism (T-RFLP) analyses are powerful tools to assess the diversity of complex microbiota. T-RFLPs permit rapid comparisons of microbiota from many samples.

AIM

To perform T-RFLP analyses of faecal microbiota in Crohn's disease (CD) patients to investigate potential alterations in faecal microbial communities and furthermore to analyse the effects of elemental diet on faecal microbiota profiles.

METHODS

Thirty-four patients with CD and 30 healthy individuals were enrolled in the study. DNA was extracted from stool samples and 16S rRNA genes were amplified by PCR. PCR products were digested with BslI restriction enzymes and T-RF lengths were determined.

RESULTS

Faecal microbial communities were classified into seven clusters. Almost all healthy individuals (28/30) were included in cluster I, II and III, but the majority of CD patients (25/34) could be divided into another four clusters (cluster IV-VII). Prediction of bacteria based on the BslI-digested T-RFLP database showed a significant decrease in Clostridium cluster IV, Clostridium cluster XI and subcluster XIVa in CD patients. In contrast, Bacteroides significantly increased in CD patients. Significant increases in Enterobacteriales were also observed in CD patients. Furthermore, elemental diets modulated faecal bacterial communities in CD patients.

CONCLUSIONS

Terminal restriction fragment length polymorphism analyses showed that the diversity of faecal microbiota in patients with CD differed from that of healthy individuals. Furthermore, elemental diets modulated faecal microbiota composition, and this effect may be involved in mechanisms of clinical effects of elemental diet.

Melatonin and ulcerative colitis: evidence, biological mechanisms, and future research

Ulcerative colitis (UC) is an inflammatory bowel disease that afflicts up to 1 million people in the US. Current treatments for UC are mostly nonspecific, not always effective, and often accompanied by serious side effects. Therefore, there is considerable interest in finding alternative and more tolerable treatments for this disease. Physiologic data suggest that melatonin is an important regulator of both inflammation and motility in the gastrointestinal tract, and data from in vitro studies, animal experiments, and limited studies in humans suggest that supplemental melatonin may have an ameliorative effect on colitis. In this review we summarize the evidence regarding melatonin as a possible therapeutic agent in UC and discuss possible biological mechanisms and directions for future research.

Microbes in gastrointestinal health and disease

Most, if not all, animals coexist with a complement of prokaryotic symbionts that confer a variety of physiologic benefits. In humans, the interaction between animal and bacterial cells is especially important in the gastrointestinal tract. Technical and conceptual advances have enabled rapid progress in characterizing the taxonomic composition, metabolic capacity, and immunomodulatory activity of the human gut microbiota, allowing us to establish its role in human health and disease. The human host coevolved with a normal microbiota over millennia and developed, deployed, and optimized complex immune mechanisms that monitor and control this microbial ecosystem. These cellular mechanisms have homeostatic roles beyond the traditional concept of defense against potential pathogens, suggesting these pathways contribute directly to the well-being of the gut. During their coevolution, the bacterial microbiota has established multiple mechanisms to influence the eukaryotic host, generally in a beneficial fashion, and maintain their stable niche. The prokaryotic genomes of the human microbiota encode a spectrum of metabolic capabilities beyond that of the host genome, making the microbiota an integral component of human physiology. Gaining a fuller understanding of both partners in the normal gut-microbiota interaction may shed light on how the relationship can go awry and contribute to a spectrum of immune, inflammatory, and metabolic disorders and may reveal mechanisms by which this relationship could be manipulated toward therapeutic ends.

Campylobacter jejuni mediated disruption of polarized epithelial monolayers is cell-type specific, time dependent, and correlates with bacterial invasion

The precise mechanism by which the most common cause of bacterial enterocolitis in humans, Campylobacter jejuni, perturbs the intestinal mucosa remains elusive. To define effects of C. jejuni infection on mucosal permeability, Madin-Darby canine kidney (MDCK)-I and T84 cell monolayers were infected with C. jejuni for up to 48 h. All three tested C. jejuni strains caused a 73-78% reduction in transepithelial electrical resistance (TER) in intestinal (T84) cell monolayers, whereas only one strain slightly reduced TER of MDCK-I cells by 25% after 48 h infection. Infection with C. jejuni strains also caused a 2.3-4.5-fold increase in dextran permeability, but only in T84 cells. C. jejuni infection of monolayers also caused morphologic changes in desmosomes, observed by transmission electron microscopy. The cell-type specificity, demonstrated by increased T84 monolayer permeability, correlated with higher bacterial invasion into these cells, relative to MDCK-I cells. In T84 cells, invasion and bacterial translocation preceded barrier disruption and inhibition of C. jejuni invasion using a pharmacological inhibitor of phosphoinositide 3-kinase, reduced the drop in TER. These findings suggest that C. jejuni disruption of monolayers is mediated by invasion, provide new insights into C. jejuni-host epithelial barrier interactions, and offer potential mechanisms of intestinal injury and chronic immune stimulation.

Bacterial-mucosal interactions in inflammatory bowel disease: an alliance gone bad

The complex interaction of genetic, microbial, and environmental factors may result in continuous activation of the mucosal immune system leading to inflammatory bowel disease (IBD). Most present treatments for IBD involve altering or suppressing the aberrant immune response; however, the role of the intestinal microbiota in the pathophysiology of IBD is becoming more evident. The epithelial layer is essential for the proper functioning of the gastrointestinal tract, and its increased permeability to the luminal antigens may lead to the inflammatory processes and mucosal damage observed in IBD. Factors affecting the efficacy of the epithelial barrier include presence of pathogenic bacteria (e.g., Helicobacter spp.), presence of probiotic bacteria, availability of selected nutrients, and others. Defective function of the mucosal barrier might facilitate the contact of bacterial antigens and adjuvants with innate and adaptive immune cells to generate prolonged inflammatory responses. This review will briefly describe the complex structure of the epithelial barrier in the context of bacterial-mucosal interactions observed in human IBD and mouse models of colitis.

Probiotic administration alters the gut flora and attenuates colitis in mice administered dextran sodium sulfate

BACKGROUND

Probiotics are used in the therapy of inflammatory bowel disease. This study aimed to determine whether prior administration of probiotic lactobacilli and bifidobacteria would prevent disease and change gut flora in an animal model of colitis.

METHODS

Swiss albino mice received a probiotic mixture (four Lactobacillus and four Bifidobacterium species) or medium (control) for a week prior to induction of colitis by oral 4% dextran sodium sulfate (DSS) for seven days. Appropriate non-colitis controls were used. Histological damage was assessed (n = 5 per group), as was expression of mRNA for tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, transforming growth factor (TGF)-beta1 and SOCS-1 in the colonic mucosa (n = 6 per group). Secretion of TNF-alpha was measured in distal colon organ culture (n = 5-6 per group). Levels of Bacteroides, Bifidobacterium, and Lactobacillus acidophilus in feces were quantified by real time polymerase chain reaction (PCR) targeting 16S rDNA.

RESULTS

Compared to untreated DSS colitis, probiotic treatment significantly reduced weight loss (P < 0.05), shifted histological damage to lesser grades of severity (P < 0.001), reduced mRNA expression of TNF-alpha and TGF-beta1 (P < 0.05), and down-regulated production of TNF-alpha from distal colon explants (P < 0.05). Colitis induced a significant reduction in the relative proportions of Bifidobacterium, Bacteroides and Lactobacillus acidophilus group bacteria in feces, and these levels were significantly increased in probiotic-treated mice compared to DSS mice (P < 0.001).

CONCLUSION

Prior administration of probiotic bacteria reduced mucosal inflammation and damage in DSS-induced colitis. DSS colitis was associated with significant changes in the fecal anaerobic bacterial flora and these changes were modulated by administration of probiotic bacteria.

Specific microbiota direct the differentiation of IL-17-producing T-helper cells in the mucosa of the small intestine

The requirements for in vivo steady state differentiation of IL-17-producing T-helper (Th17) cells, which are potent inflammation effectors, remain obscure. We report that Th17 cell differentiation in the lamina propria (LP) of the small intestine requires specific commensal microbiota and is inhibited by treating mice with selective antibiotics. Mice from different sources had marked differences in their Th17 cell numbers and animals lacking Th17 cells acquired them after introduction of bacteria from Th17 cell-sufficient mice. Differentiation of Th17 cells correlated with the presence of cytophaga-flavobacter-bacteroidetes (CFB) bacteria in the intestine and was independent of toll-like receptor, IL-21 or IL-23 signaling, but required appropriate TGF-beta activation. Absence of Th17 cell-inducing bacteria was accompanied by increase in Foxp3+ regulatory T cells (Treg) in the LP. Our results suggest that composition of intestinal microbiota regulates the Th17:Treg balance in the LP and may thus influence intestinal immunity, tolerance, and susceptibility to inflammatory bowel diseases.

Innate immune signalling at intestinal mucosal surfaces: a fine line between host protection and destruction

PURPOSE OF REVIEW

Emerging evidence underscores that inappropriate innate immune responses driven by commensals contribute to the pathogenesis of chronic inflammatory bowel diseases in genetically susceptible hosts. The present review focuses on defining the recently described mechanistic functions through which the innate immune signalling apparatus shapes mucosal homeostasis of the intestine in health and disease.

RECENT FINDINGS

Commensal-induced innate immune signalling actively drives at least six major interdependent functions to control homeostasis in the healthy intestinal mucosa: 1) barrier preservation, 2) inhibition of apoptosis and inflammation, 3) acceleration of wound repair and tissue regeneration, 4) exclusion of harmful pathogens through autophagy and other antimicrobial defenses, while 5) maintaining immune tolerance towards harmless commensals, and 6) linkage to adaptive immunity. Any disturbance of this peaceful and mutually beneficial host-commensal relationship may imbalance innate immune signalling, which predisposes to chronic intestinal inflammation and associated tumourigenesis in inflammatory bowel diseases.

SUMMARY

Recent advances have highlighted the complex mechanistics and functional diversity of innate immunity that paradoxically mediate both protective and destructive responses in the intestinal mucosa. Related signalling targets may offer novel therapeutic approaches in the treatment of inflammatory bowel diseases and inflammation-related cancer.

Limited effects of dietary curcumin on Th-1 driven colitis in IL-10 deficient mice suggest an IL-10-dependent mechanism of protection

Curcumin (diferulolylmethane) demonstrates profound anti-inflammatory effects in intestinal epithelial cells (IEC) and in immune cells in vitro and exhibits a protective role in rodent models of chemically induced colitis, with its presumed primary mechanism of action via inhibition of NF-kappaB. Although it has been demonstrated effective in reducing relapse rate in ulcerative colitis patients, curcumin's effectiveness in Crohn's disease (CD) or in Th-1/Th-17 mediated immune models of CD has not been evaluated. Therefore, we investigated the effects of dietary curcumin (0.1-1%) on the development of colitis, immune activation, and in vivo NF-kappaB activity in germ-free IL-10(-/-) or IL-10(-/-);NF-kappaB(EGFP) mice colonized with specific pathogen-free microflora. Proximal and distal colon morphology showed a mild protective effect of curcumin only at 0.1%. Colonic IFN-gamma and IL-12/23p40 mRNA expression followed similar pattern ( approximately 50% inhibition at 0.1%). Secretion of IL-12/23p40 and IFN-gamma by colonic explants and mesenteric lymph node cells was elevated in IL-10(-/-) mice and was not decreased by dietary curcumin. Surprisingly, activation of NF-kappaB in IL-10(-/-) mice (phospho-NF-kappaBp65) or in IL-10(-/-);NF-kappaB(EGFP) mice (whole organ or confocal imaging) was not noticeably inhibited by curcumin. Furthermore, we demonstrate that IL-10 and curcumin act synergistically to downregulate NF-kappaB activity in IEC and IL-12/23p40 production by splenocytes and dendritic cells. In conclusion, curcumin demonstrates limited effectiveness on Th-1 mediated colitis in IL-10(-/-) mice, with moderately improved colonic morphology, but with no significant effect on pathogenic T cell responses and in situ NF-kappaB activity. In vitro studies suggest that the protective effects of curcumin are IL-10 dependent.

Interactions of the intestinal epithelium with the pathogen and the indigenous microbiota: a three-way crosstalk

The mucosal surfaces of the gastrointestinal tract harbor a vast number of commensal microbiota that have coevolved with the host, and in addition display one of the most complex relationships with the host. This relationship affects several important aspects of the biology of the host including the synthesis of nutrients, protection against infection, and the development of the immune system. On the other hand, despite the existence of several lines of mucosal defense mechanisms, pathogenic organisms such as Shigella and Salmonella have evolved sophisticated virulence strategies for breaching these barriers. The constant challenge from these pathogens and the attempts by the host to counter them set up a dynamic equilibrium of cellular and molecular crosstalk. Even slight perturbations in this equilibrium may be detrimental to the host leading to severe bacterial infection or even autoimmune diseases like inflammatory bowel disease. Several experimental model systems, including germ-free mice and antibiotic-treated mice, have been used by various researchers to study this complex relationship. Although it is only the beginning, it promises to be an exciting era in the study of these host-microbe relationships.

Stevioside and related compounds: therapeutic benefits beyond sweetness

Stevioside, an abundant component of Stevia rebaudiana leaf, has become well-known for its intense sweetness (250-300 times sweeter than sucrose) and is used as a non-caloric sweetener in several countries. A number of studies have suggested that, beside sweetness, stevioside along with related compounds, which include rebaudioside A (second most abundant component of S. rebaudiana leaf), steviol and isosteviol (metabolic components of stevioside) may also offer therapeutic benefits, as they have anti-hyperglycemic, anti-hypertensive, anti-inflammatory, anti-tumor, anti-diarrheal, diuretic, and immunomodulatory actions. It is of interest to note that their effects on plasma glucose level and blood pressure are only observed when these parameters are higher than normal. As steviol can interact with drug transporters, its role as a drug modulator is proposed. This review summarizes the current knowledge of the pharmacological actions, therapeutic applications, pharmacokinetics and safety of stevioside and related compounds. Although much progress has been made concerning their biological and pharmacological effects, questions regarding chemical purity and safety remain unsolved. These issues are discussed to help guide future research directions.

Impaired autophagy of an intracellular pathogen induced by a Crohn's disease associated ATG16L1 variant

The genetic risk factors predisposing individuals to the development of inflammatory bowel disease are beginning to be deciphered by genome-wide association studies. Surprisingly, these new data point towards a critical role of autophagy in the pathogenesis of Crohn's disease. A single common coding variant in the autophagy protein ATG16L1 predisposes individuals to the development of Crohn's disease: while ATG16L1 encoding threonine at amino acid position 300 (ATG16L1*300T) confers protection, ATG16L1 encoding for alanine instead of threonine (ATG16L1*300A, also known as T300A) mediates risk towards the development of Crohn's disease. Here we report that, in human epithelial cells, the Crohn's disease-associated ATG16L1 coding variant shows impairment in the capture of internalized Salmonella within autophagosomes. Thus, we propose that the association of ATG16L1*300A with increased risk of Crohn's disease is due to impaired bacterial handling and lowered rates of bacterial capture by autophagy.

NK cell activation and immune response in inflammatory bowel disease

Inflammatory bowel disease (IBD) is closely associated with the abnormal immune response of intestinal immune system to enterobacteria and dietary antigens. Large amounts of mononuclear lymphocyte infiltrates and high expression levels of proinflammatory cytokines and costimulatory molecules are present in inflamed mucosa. NK cells, involved in innate and acquired immune response, have cytolitic activities through secretion of lytic proteins, and produce proinflammatory mediators. Increased infiltration of NK cells present in inflamed mucosa of IBD expresses high levels of activated molecules and proinflammatory cytokines, and plays a role in intestinal mucosal damage.

Aberrant innate immune responses in TLR-ligand activated HLA-B27 transgenic rat cells

BACKGROUND

Commensal enteric microbiota initiate and perpetuate immune-mediated colitis in HLA-B27 transgenic (TG) rats but not wildtype (non-TG) littermates. However, the role of the innate immune response to bacterial components has not been established.

METHODS

We examined responses induced by bacterial adjuvants through Toll-like receptor (TLR) and NOD2 signaling in T-cell-depleted splenocytes from HLA-B27 TG rats versus non-TG controls.

RESULTS

We found that various bacterial adjuvants induced TNF production by cells obtained from specific pathogen-free (SPF) and germ-free (GF, sterile) TG and non-TG rats. Peptidoglycan-polysaccharide (PG-PS), lipopolysaccharide (LPS), and CpG DNA motifs stimulated higher levels of TNF production by SPF TG rat spleen cells compared to non-TG cells. CD11b/c cell depletion eliminated PG-PS and LPS-induced TNF and dramatically reduced CpG-stimulated TNF production. Both SPF and GF TG rat spleens contain more cells that express high levels of CD11b/c and show enhanced mRNA expression of TLR-2 and TLR-4 compared to non-TG rat spleens. In contrast, constitutive and bacterial-induced IL-10 production was markedly lower in TG cells compared to non-TG cells of rats from the same SPF or GF housing conditions. Notably, the ratio of TNF to IL-10 produced after TLR ligand activation was significantly higher in TG than non-TG cells.

CONCLUSIONS

HLA-B27 TG rats have an aberrant cell composition, altered functional TLR expression, and an intrinsic defect in IL-10 production in response to TLR ligands, which may result in exaggerated proinflammatory responses to commensal enteric bacteria and uncontrolled inflammation in this colitis model.

Microecology, obesity, and probiotics

PURPOSE OF REVIEW

Description of the role that the microbiota may play in human health, energy harvest, and obesity.

RECENT FINDINGS

The adult human gut may contain up to 100 trillion microbial organisms, known as the microbiota. Major advances in defining the quality, quantity, and physiologic activity of the intestinal microbiota were precipitated by the conversion from culture-based techniques to metagenomics. The microbiota may serve various functions including promoting development of the human immune system, modulating inflammation, and affecting calorie extraction.

SUMMARY

Recent evidence, in humans and animal models, supports a role for the microbiota in obesity. Not only is the presence of bacteria important, but also the relative proportions of microbial communities, specifically Firmicutes and Bacteriodetes, appear to be important in energy homeostasis. The microbiota may also affect the immune and inflammatory response in human organisms. Although there is limited data supporting the manipulation of the gut microbiota, using probiotics, antibiotics, and/or prebiotics to treat obesity, novel therapeutic agents may be developed.