Dual infection with Helicobacter bilis and Helicobacter hepaticus in p-glycoprotein-deficient mdr1a-/- mice results in colitis that progresses to dysplasia

Helicobacter bilis colonization of the biliary system in patients with pancreaticobiliary maljunction

BACKGROUND

Helicobacter bilis is considered to be a causative factor in the pathogenesis of biliary cancer. This study investigated the prevalence of H. bilis colonization of the biliary system of patients with pancreaticobiliary maljunction (PBM).

METHODS

Bile juice and biliary tissue samples were collected from 17 patients with PBM and 27 controls who had benign biliary disease without PBM. DNA extracted from each biliary sample was subjected to polymerase chain reaction (PCR) analysis for H. bilis and Helicobacter pylori.

RESULTS

PCR assays revealed that 12 of the 17 patients with PBM were positive for H. bilis DNA, compared with eight of 27 patients without PBM (P = 0.009). Among patients with PBM, H. bilis DNA was identified in six of eight children, including a 2-month-old infant, and in six of nine adults. The high prevalence of H. bilis DNA in the biliary system of patients with PBM was independent of age, sex, common bile duct dilatation, configuration of the pancreatic and bile ducts, and amylase activity in bile.

CONCLUSION

H. bilis colonization of the biliary system is extremely common in patients with PBM. This may point to a role in the pathogenesis of biliary cancer.

CD4+ lymphocytes modulate prostate cancer progression in mice

Chronic inflammation contributes to the development of prostate cancer in humans. Here, we show that male Apc(Min/+) mice also develop prostate carcinoma with increasing age, mimicking that seen in humans in their 5th or 6th decade of life. Proinflammatory cytokines were significantly linked with cancer and increasing age in our mouse model; however, prostate and bowel tissues lacked evidence of inflammatory cell infiltrates other than mast cells. Lymphocytes protected against cancer, and protection from prostate cancer resided in antiinflammatory CD4(+)CD25(+) regulatory (T(REG)) cells that downregulated inflammatory cytokines. Supplementation with syngeneic T(REG) cells collected from wild-type mice reduced the levels of interleukin (IL)-6 (p < 0.05) and IL-9 (p < 0.001) and lowered prostate cancer risk (p < 0.05). Depletion of CD25(+) cells in 2-month-old animals increased the expression of IL-6 (p < 0.005) within prostate and increased the frequency of high-grade prostatic intraepithelial neoplasia (p < 0.05) and microinvasive prostatic carcinoma (p < 0.05) in dorsolateral prostate. Depletion of CD25(+) cells in young animals also increased the frequency of intestinal cancer in Min mice. Taken together, chronically elevated proinflammatory cytokines promoted carcinoma in Apc(Min/+) mice. T(REG) lymphocytes downregulated inflammation-associated carcinogenic processes and contributed to immune and epithelial homeostasis.

Intestinal mucosal inflammation leads to systemic genotoxicity in mice

Inflammatory bowel disease, including ulcerative colitis and Crohn's disease, substantially increases the risk of colorectal cancer. However, mechanisms linking mucosal inflammation to the sequence of dysplasia are incompletely understood. Whereas studies have shown oxidative damage to the colon, this study tests whether genotoxicity is elicited systemically by acute and chronic intestinal inflammation. In this study, genotoxic endpoints were assessed in peripheral leukocytes (DNA single- and double-stranded breaks and oxidative DNA damage) and normochromatic erythrocytes (micronuclei) during chemical or immune-mediated colitis. During three consecutive cycles of intestinal inflammation induced by dextran sulfate sodium administration, genotoxicity to peripheral leukocytes and erythroblasts was detected in both acute and chronic phases of dextran sulfate sodium-induced inflammation. Reactive oxygen species-mediated oxidative stress and DNA damage was confirmed with positive 8-oxoguanine and nitrotyrosine staining in peripheral leukocytes. Levels of DNA damage generally decreased during remission and increased during treatment, correlating with clinical symptoms and systemic inflammatory cytokine levels. In Galphai2(-/-) and interleukin-10(-/-) transgenic mice susceptible to immune-mediated colitis and inflammation-associated adenocarcinoma, similar levels of peripheral leukocyte and erythroblast genotoxicity were also observed. Moreover, this systemic genotoxicity was observed in mice with subclinical inflammation, which was further elevated in those with severe mucosal inflammation. We propose that mucosal inflammation, by eliciting substantial and ongoing systemic DNA damage, contributes early on to genetic instability necessary for progression to inflammatory bowel disease-associated dysplasia and the development of cancer.

Helicobacter-based mouse models of digestive system carcinogenesis

Animal models are necessary to reproduce the complex host, microbial and environmental influences associated with infectious carcinogenesis of the digestive system. Today, mouse models are preferred by most researchers because of cost efficiencies, rapid reproduction, choice of laboratory reagents, and availability of genetically engineered mutants to study specific gene functions in vivo. Mouse models have validated the once-provocative hypothesis that Helicobacter pylori infection is a major risk factor for gastric carcinoma, dispelling early skepticism over the pathogenic nature of this organism in the human stomach. Enterohepatic Helicobacter spp. induce inflammatory bowel disease and colorectal carcinoma in susceptible mouse strains, permitting study of host immunity and microbial factors at the cellular and molecular level. H. hepaticus is the only proven infectious hepatocarcinogen of mice and has been used to explore mechanisms of inflammation-associated liver cancer as seen in human chronic viral hepatitis. For example, this model was used to identify for the first time a potential mechanism for male-predominant liver cancer risk independent of circulating sex hormones. Helicobacter-based mouse models of digestive system carcino-genesis are used to investigate the basic biology of inflammation-associated human cancers and to evaluate therapeutic interventions at the discovery level. Because of exciting advances in genetic engineering of mice, in vivo imaging, and system-wide genomics and proteomics, these models will provide even more information in the future. This chapter introduces the mouse as a model species; summarizes important models of inflammation-associated cancer incited by murine Helicobacter infection; and describes methods for the collection, sampling, and histologic grading of mouse digestive system tissues.

Bacterial infection of Smad3/Rag2 double-null mice with transforming growth factor-beta dysregulation as a model for studying inflammation-associated colon cancer

Alterations in genes encoding transforming growth factor-beta-signaling components contribute to colon cancer in humans. Similarly, mice deficient in the transforming growth factor-beta signaling molecule, Smad3, develop colon cancer, but only after a bacterial trigger occurs, resulting in chronic inflammation. To determine whether Smad3-null lymphocytes contribute to increased cancer susceptibility, we crossed Smad3-null mice with mice deficient in both B and T lymphocytes (Rag2(-/-) mice). Helicobacter-infected Smad3/Rag2-double knockout (DKO) mice had more diffuse inflammation and increased incidence of adenocarcinoma compared with Helicobacter-infected Smad3(-/-) or Rag2(-/-) mice alone. Adoptive transfer of WT CD4(+)CD25(+) T-regulatory cells provided significant protection of Smad3/Rag2-DKO from bacterial-induced typhlocolitis, dysplasia, and tumor development, whereas Smad3(-/-) T-regulatory cells provided no protection. Immunohistochemistry, real-time reverse transcriptase-polymerase chain reaction, and Western blot analyses of colonic tissues from Smad3/Rag2-DKO mice 1 week after Helicobacter infection revealed an influx of macrophages, enhanced nuclear factor-kappaB activation, increased Bcl(XL)/Bcl-2 expression, increased c-Myc expression, accentuated epithelial cell proliferation, and up-regulated IFN-gamma, IL-1alpha, TNF-alpha, IL-1beta, and IL-6 transcription levels. These results suggest that the loss of Smad3 increases susceptibility to colon cancer by at least two mechanisms: deficient T-regulatory cell function, which leads to excessive inflammation after a bacterial trigger; and increased expression of proinflammatory cytokines, enhanced nuclear factor-kappaB activation, and increased expression of both pro-oncogenic and anti-apoptotic proteins that result in increased cell proliferation/survival of epithelial cells in colonic tissues.

Effects of Helicobacter infection on research: the case for eradication of Helicobacter from rodent research colonies

Infection of mouse colonies with Helicobacter spp. has become an increasing concern for the research community. Although Helicobacter infection may cause clinical disease, investigators may be unaware that their laboratory mice are infected because the pathology of Helicobacter species is host-dependent and may not be recognized clinically. The effects of Helicobacter infections are not limited to the gastrointestinal system and can affect reproduction, the development of cancers in gastrointestinal organs and remote organs such as the breast, responses to vaccines, and other areas of research. The data we present in this review show clearly that unintentional Helicobacter infection has the potential to significantly interfere with the reliability of research studies based on murine models. Therefore, frequent screening of rodent research colonies for Helicobacter spp. and the eradication of these pathogens should be key goals of the research community.

Murine norovirus: an intercurrent variable in a mouse model of bacteria-induced inflammatory bowel disease

Murine norovirus (MNV) has recently been recognized as a widely prevalent viral pathogen in mouse colonies and causes disease and mortality in mice with impaired innate immunity. We tested the hypothesis that MNV infection would alter disease course and immune responses in mice with inflammatory bowel disease (IBD). FVB.129P2-Abcb1a(tm1Bor) N7 (Mdr1a-/-) mice develop spontaneous IBD that is accelerated by infection with Helicobacter bilis. As compared with controls, Mdr1a-/- mice coinfected with MNV4 and H. bilis showed greater weight loss and IBD scores indicative of severe colitis, demonstrating that MNV4 can modulate the progression of IBD. Compared with controls, mice inoculated with MNV4 alone had altered levels of serum biomarkers, and flow cytometric analysis of immune cells from MNV4-infected mice showed changes in both dendritic cell (CD11c+) and other nonT cell (CD4- CD8-) populations. Dendritic cells isolated from MNV4-infected mice induced higher IFNgamma production by polyclonal T cells in vitro at 2 d after infection but not at later time points, indicating that MNV4 infection enhances antigen presentation by dendritic cells early after acute infection. These findings indicate that acute infection with MNV4 is immunomodulatory and alters disease progression in a mouse model of IBD.

Helicobacter typhlonius and Helicobacter rodentium differentially affect the severity of colon inflammation and inflammation-associated neoplasia in IL10-deficient mice

Infection with Helicobacter species is endemic in many animal facilities and may alter the penetrance of inflammatory bowel disease (IBD) phenotypes. However, little is known about the relative pathogenicity of H. typhlonius, H. rodentium, and combined infection in IBD models. We infected adult and neonatal IL10-/- mice with H. typhlonius, H. rodentium, or both bacteria. The severity of IBD and incidence of inflammation-associated colonic neoplasia were assessed in the presence and absence of antiHelicobacter therapy. Infected IL10-/- mice developed IBD with severity of noninfected (minimal to no inflammation) < H. rodentium < H. typhlonius <mixed H. rodentium + H. typhlonius (severe inflammation). Inflammation-associated colonic neoplasia was common in infected mice and its incidence correlated with IBD severity. Combined treatment with amoxicillin, clarithromycin, metronidazole, and omeprazole eradicated Helicobacter in infected mice and ameliorated established IBD in both infected and noninfected mice. Infection of IL10-/- mice with H. rodentium, H. typhlonius, or both organisms can trigger development of severe IBD that eventually leads to colonic neoplasia. The high incidence and multiplicity of neoplastic lesions in infected mice make this model well-suited for future research related to the development and chemoprevention of inflammation-associated colon cancer. The similar antiinflammatory effect of antibiotic therapy in Helicobacter-infected and -noninfected IL10-/- mice with colitis indicates that unidentified microbiota in addition to Helicobacter drive the inflammatory process in this model. This finding suggests a complex role for both Helicobacter and other intestinal microbiota in the onset and perpetuation of IBD in these susceptible hosts.

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.

Helicobacter infection decreases reproductive performance of IL10-deficient mice

Infections with a variety of Helicobacter species have been documented in rodent research facilities, with variable effects on rodent health. Helicobacter typhlonius has been reported to cause enteric disease in immunodeficient and IL10(-/-) mice, whereas H. rodentium has only been reported to cause disease in immunodeficient mice coinfected with other Helicobacter species. The effect of Helicobacter infections on murine reproduction has not been well studied. The reproductive performance of C57BL/6 IL10(-/-) female mice intentionally infected with H. typhlonius, H. rodentium, or both was compared with that of age-matched uninfected controls or similarly infected mice that received antihelicobacter therapy. The presence of Helicobacter organisms in stool and relevant tissues was detected by PCR assays. Helicobacter infection of IL10(-/-) female mice markedly decreased pregnancy rates and pup survival. The number of pups surviving to weaning was greatest in noninfected mice and decreased for H. rodentium > H. typhlonius >> H. rodentium and H. typhlonius coinfected mice. Helicobacter organisms were detected by semiquantitative real-time PCR in the reproductive organs of a subset of infected mice. Treatment of infected mice with a 4-drug regimen consisting of amoxicillin, clarithromycin, metronidazole, and omeprazole increased pregnancy rates, and pup survival and dam fecundity improved. We conclude that infection with H. typhlonius, H. rodentium, or both decreased the reproductive performance of IL10(-/-) mice. In addition, antihelicobacter therapy improved fecundity and enhanced pup survival.

Innate immunity in Crohn's disease: the reverse side of the medal

The etiology of Crohn's disease (CD) remains poorly understood. Both mice and human studies suspected a perverse link between the microbiota and the lining of the gut mucosa. There is now emerging evidence that suggests that such a pathologic condition might result from an overly aggressive immune response to microbial antigens in genetically predisposed individuals. However, the multiple pathophysiologic processing steps linking environmental exposure to the clinical expression of CD are, for the most part, unknown. Herein, we review evidences reflecting a general causing defect of the innate immune function of the intestinal mucosa of CD patients, which might lead to a sustained microbial-induced inflammatory response. Changing the paradigms of CD pathophysiology might lead to entirely new therapeutic approaches aiming to boost the innate immune response.

Scanning single fiber endoscopy: a new platform technology for integrated laser imaging, diagnosis, and future therapies

Remote optical imaging of human tissue in vivo has been the foundation for the growth of minimally invasive medicine. This article describes a new type of endoscopic imaging that has been developed and applied to the human esophagus, pig bile duct, and mouse colon. The technology is based on a single optical fiber that is scanned at the distal tip of an ultrathin and flexible shaft that projects red, green, and blue laser light onto tissue in a spiral pattern. The resulting images are high-quality color video that is expected to produce future endoscopes that are thinner, longer, more flexible, and able to directly integrate the many recent advances of laser diagnostics and therapies.

Serum biomarkers in a mouse model of bacterial-induced inflammatory bowel disease

BACKGROUND

The diagnosis and classification of inflammatory bowel disease (IBD) require both clinical and histopathologic data. Serum biomarkers would be of considerable benefit to noninvasively monitor the progression of disease, assess effectiveness of therapies, and assist in understanding disease pathogenesis. Currently, there are limited noninvasive biomarkers for monitoring disease progression in animal IBD models, which are used extensively to develop new therapies and to understand IBD pathogenesis.

METHODS

Serum biomarkers of early and late IBD were identified using multianalyte profiling in mdr1a(-/-) mice with IBD triggered by infection with Helicobacter bilis. The correlation of changes in these biomarkers with histopathology scores and clinical signs in the presence and in the absence of antibiotic treatment was determined.

RESULTS

Serum levels of interleukin (IL)-11, IL-17, 10-kDa interferon-gamma-inducible protein (IP-10), lymphotactin, monocyte chemoattractant protein (MCP)-1, and vascular cell adhesion molecule (VCAM)-1 were elevated early in IBD. In late, more severe IBD, serum levels of IL-11, IP-10, haptoglobin, matrix metalloproteinase-9, macrophage inflammatory protein (MIP)-1gamma, fibrinogen, immunoglobulin A, MIP-3 beta (beta), VCAM-1, apolipoprotein (Apo) A1, and IL-18 were elevated. All late serum biomarkers except Apo A1 correlated with histopathology scores. Antibiotic treatment improved clinical signs of IBD and decreased mean serum values of many of the biomarkers. For all biomarkers, the individual pathology scores correlated significantly with individual serum analyte levels after treatment.

CONCLUSIONS

Serum analyte measurement is a useful, noninvasive method for monitoring disease in a mouse model of bacterial-induced IBD.

ABC multidrug transporters: structure, function and role in chemoresistance

Three ATP-binding cassette (ABC)-superfamily multidrug efflux pumps are known to be responsible for chemoresistance; P-glycoprotein (ABCB1), MRP1 (ABCC1) and ABCG2 (BCRP). These transporters play an important role in normal physiology by protecting tissues from toxic xenobiotics and endogenous metabolites. Hydrophobic amphipathic compounds, including many clinically used drugs, interact with the substrate-binding pocket of these proteins via flexible hydrophobic and H-bonding interactions. These efflux pumps are expressed in many human tumors, where they likely contribute to resistance to chemotherapy treatment. However, the use of efflux-pump modulators in clinical cancer treatment has proved disappointing. Single nucleotide polymorphisms in ABC drug-efflux pumps may play a role in responses to drug therapy and disease susceptibility. The effect of various genotypes and haplotypes on the expression and function of these proteins is not yet clear, and their true impact remains controversial.

TLR4 signalling in the intestine in health and disease

The colonic epithelium is lined along its apical membrane with approximately 10(14) bacteria/g of tissue. Commensal bacteria outnumber mammalian cells in the gut severalfold. The reason for this degree of commensalism probably resides in the recent recognition of the microbiome as an important source of metabolic energy in the setting of poorly digestible nutrients. As in many themes in biology, the host may have sacrificed short-term benefit, i.e. nutritional advantages, for long-term consequences, such as chronic inflammation or colon cancer. In the present review, we examine the role of TLR (Toll-like receptor) signalling in the healthy host and the diseased host. We pay particular attention to the role of TLR signalling in idiopathic IBD (inflammatory bowel disease) and colitis-associated carcinogenesis. In general, TLR signalling in health contributes to homoeostatic functions. These include induction of antimicrobial peptides, proliferation and wound healing in the intestine. The pathogenesis of IBD, ulcerative colitis and Crohn's disease may be due to increased TLR or decreased TLR signalling respectively. Finally, we discuss the possible role of TLR signalling in colitis-associated neoplasia.

Evidence for the involvement of infectious agents in the pathogenesis of Crohn's disease

Many advances have been made in the understanding of Crohn's disease (CD) pathogenesis during the last decade. CD is currently seen as a predominantly T-lymphocyte-driven disease characterized by the presence of a complex cocktail of interacting cytokines, chemokines and other mediators produced by a variety of cell types. Prevailing theories of CD pathogenesis suggest that patients' T-lymphocytes are inappropriately activated in the setting of an immune imbalance, which is itself caused by an unfortunate confluence of genetic and environmental factors. The T-cell response then leads to the chronic inflammation characteristic for the disease. Various environmental factors may play a role in the development of CD, but microbes are most consistently implied. This theory is based on epidemiological, clinicopathological, genetic and experimental evidence. Despite the abundance of arguments for the implication of bacteria in the aetiopathogenesis of CD, the precise role of bacteria in this disease still remains elusive. Three not necessarily mutually exclusive theories have been proposed: (1) an unidentified persistent pathogen; (2) an abnormally permeable mucosal barrier leading to excessive bacterial translocation; and (3) a breakdown in the balance between putative "protective" versus "harmful" intestinal bacteria ("dysbiosis"). At present, one cannot exclude with certainty any of these three proposed hypotheses; they may all apply to CD to a certain extent.

Role of Toll-like receptors in gastrointestinal malignancies

Mounting evidence supports the tenet that innate immune responses to luminal microbes participate in the development of gastrointestinal malignancies. The gastrointestinal tract is relatively unique in that it has evolved in the presence of diverse enteric microflora. Intestinal flora is required to develop a normal adaptive immune response in the periphery. With the characterization of the innate immune system, we have begun to understand the adaptations the intestine has made to the microbiota. The interaction between the microbiota and the intestinal mucosa through Toll-like receptors (TLRs) is required to maintain intestinal homeostasis. In particular, intestinal epithelial cells and lamina propria mononuclear cells such as antigen-presenting cells and T cells must respond to breaches in the mucosal barrier by activating TLR-dependent pathways that result in increased epithelial proliferation, wound healing and recruitment of acute inflammatory cells. In the setting of chronic inflammation such as Helicobacter pylori (H. pylori) infection in the stomach or idiopathic inflammatory bowel disease, the process of repair may eventually result in carcinogenesis. The following review highlights human and animal data that support a role for innate immune responses and TLRs specifically in promoting gastrointestinal malignancies. Candidate pathways linking TLRs to gastrointestinal malignancies include activation of nuclear factor-kappaB and cyclooxygenase-2. Studying the link between innate immune signaling and gastrointestinal malignancies offers the possibility to identify novel ways to both prevent and treat gastrointestinal cancer.

Neonatal co-infection with helicobacter species markedly accelerates the development of inflammation-associated colonic neoplasia in IL-10(-/-) mice

BACKGROUND

Inflammatory bowel disease (IBD) is hypothesized to represent an aberrant immune response against enteric bacteria that occurs in a genetically susceptible host. Humans and mice with IBD are at markedly increased risk for colonic neoplasia. However, the long lead time required before development of inflammation-associated colon neoplasia in commonly used murine models of IBD slows the development of effective chemopreventative therapies.

MATERIALS AND METHODS

Neonatal coinfection with Helicobacter typhlonius and Helicobacter rodentium was used to trigger the onset of IBD in mice deficient in the immunoregulatory cytokine interleukin (IL)-10. The severity of colon inflammation and incidence of neoplasia was determined histologically.

RESULTS

IL-10(-/-) mice demonstrated early onset, severe colon inflammation following neonatal infection with H. typhlonius and H. rodentium. The incidence of inflammation-associated colon neoplasia was approximately 95% at a mean age of 21 +/- 2 weeks. Mutation of endoglin, an accessory receptor for TGF-beta, did not affect the severity of IBD or the incidence of neoplasia in this model.

CONCLUSIONS

The rapid onset of severe colon inflammation and multiple neoplastic lesions in the colons of IL-10(-/-) mice neonatally coinfected with H. typhlonius and H. rodentium makes this model well-suited for investigating the mechanisms involved in inflammation-associated colon cancer as well as its chemoprevention.

The NADPH quinone reductase MdaB confers oxidative stress resistance to Helicobacter hepaticus

An mdaB mutant strain in a quinone reductase (MdaB) of Helicobacter hepaticus type strain ATCC51449 was constructed by insertional mutagenesis, and the MdaB protein was purified and compared to the Helicobacter pylori enzyme. While wild type H. hepaticus cells could tolerate 6% O(2) for growth, the mdaB strain was clearly inhibited at this oxygen level. Disruption of the gene downstream of mdaB (HH1473) did not affect the oxidative stress phenotype of the strain. The mdaB mutant was also more sensitive to oxidative stress reagents such as H(2)O(2), cumene hydroperoxide, t-butyl hydroperoxide, and paraquat. All H. hepaticus mdaB strains isolated constitutively up-expressed another oxidative stress-combating enzyme, superoxide dismutase; this is in contrast to H. pylori mdaB strains. H. hepaticus MdaB is a flavoprotein catalyzing quinone reduction using a two-electron transfer mechanism from NAD(P)H to quinone. The H. hepaticus enzyme specific activity was far less than for the H. pylori enzyme purified in the same manner.

Mutation at the polymerase active site of mouse DNA polymerase delta increases genomic instability and accelerates tumorigenesis

Mammalian DNA polymerase delta (Pol delta) is believed to replicate a large portion of the genome and to synthesize DNA in DNA repair and genetic recombination pathways. The effects of mutation in the polymerase domain of this essential enzyme are unknown. Here, we generated mice harboring an L604G or L604K substitution in highly conserved motif A in the polymerase active site of Pol delta. Homozygous Pold1(L604G/L604G) and Pold1(L604K/L604K) mice died in utero. However, heterozygous animals were viable and displayed no overall increase in disease incidence, indicative of efficient compensation for the defective mutant polymerase. The life spans of wild-type and heterozygous Pold1(+/L604G) mice did not differ, while that of Pold1(+/L604K) mice was reduced by 18%. Cultured embryonic fibroblasts from the heterozygous strains exhibited comparable increases in both spontaneous mutation rate and chromosome aberrations. We observed no significant increase in cancer incidence; however, Pold1(+/L604K) mice bearing histologically diagnosed tumors died at a younger median age than wild-type mice. Our results indicate that heterozygous mutation at L604 in the polymerase active site of DNA polymerase delta reduces life span, increases genomic instability, and accelerates tumorigenesis in an allele-specific manner, novel findings that have implications for human cancer.

Rapid reversal of interleukin-6-dependent epithelial invasion in a mouse model of microbially induced colon carcinoma

Chronic inflammation of mucosal surfaces renders them increasingly susceptible to epithelial cancers both in humans and mice. We have previously shown that anti-inflammatory CD4(+)CD45RB(lo)CD25(+) regulatory (Treg or T(R)) lymphocytes down-regulate inflammation and block development of bacteria-triggered colitis and colorectal cancer (CRC) in 129/SvEv Rag2-/- mice. Interestingly, T(R) cells collected from Interleukin (IL)-10-deficient cell donors not only failed to suppress carcinogenesis but instead promoted invasive mucinous colonic carcinoma with a strong gender bias expressing in male mice. We found we show that peritoneal invasion in this model is dependent on pleiotropic cytokine IL-6. Mucinous carcinoma arose rapidly and consistently after treatment with IL10-/- T(R) cells, which were found to express Foxp3+ and localize throughout tumor tissue. Carcinogenesis was rapidly reversible with transfer of wild type IL10-competent T(R) cells. Likewise, treatment with IL10-Ig fusion protein was sufficient to revert the lesions histologically, and restore inflammatory cytokine and oncogene expression to base line levels. These studies indicate an essential role for IL 6 in this CRC phenotype. Furthermore, immune-competent T(R) cells were important not only for preventing pathology but also for constructive remodeling of bowel following tumorigenic microbial insults. These data provide insights into etiopathogenesis of inflammation-associated epithelial invasion and maintenance of epithelial homeostasis.

Increased susceptibility to colitis and colorectal tumors in mice lacking core 3-derived O-glycans

Altered intestinal O-glycan expression has been observed in patients with ulcerative colitis and colorectal cancer, but the role of this alteration in the etiology of these diseases is unknown. O-glycans in mucin core proteins are the predominant components of the intestinal mucus, which comprises part of the intestinal mucosal barrier. Core 3–derived O-glycans, which are one of the major types of O-glycans, are primarily expressed in the colon. To investigate the biological function of core 3–derived O-glycans, we engineered mice lacking core 3 β1,3-N-acetylglucosaminyltransferase (C3GnT), an enzyme predicted to be important in the synthesis of core 3–derived O-glycans. Disruption of the C3GnT gene eliminated core 3–derived O-glycans. C3GnT-deficient mice displayed a discrete, colon-specific reduction in Muc2 protein and increased permeability of the intestinal barrier. Moreover, these mice were highly susceptible to experimental triggers of colitis and colorectal adenocarcinoma. These data reveal a requirement for core 3–derived O-glycans in resistance to colonic disease.

Bacteria in the pathogenesis of inflammatory bowel disease

PURPOSE OF REVIEW

Inflammatory bowel disease is thought to result from an abnormal response to the gut microbiota. This review discusses advances in knowledge of the changes in gut microbiota and host response in inflammatory bowel disease.

RECENT FINDINGS

Approximately 15% of Crohn's disease cases in western populations result from mutations in NOD2/CARD15. This disease leads to defective intestinal defensin production and defective monocyte interleukin-8 response to bacterial peptidoglycan. A similar defective interleukin-8 response and consequent delayed neutrophil recruitment have also been shown in patients with Crohn's disease who do not have the NOD2 mutation. A consequence seems to be the accumulation in tissue of macrophages containing various bacteria, perhaps particularly Escherichia coli. In keeping with this patients with Crohn's disease have circulating antibodies against bacterial flagellar proteins of enterobacteria and clostridia. In ulcerative colitis, there is less evidence for invasion by or immune response to bacteria but changes in gut microbiota include a relative deficiency of bifidobacteria. There is considerable interest in probiotic or prebiotic therapies although so far little evidence for their efficacy.

SUMMARY

Molecular techniques are giving us better insight into the gut microbiota in inflammatory bowel disease that should translate into improved therapies.

Extragastric manifestations of Helicobacter pylori infection--other Helicobacter species

Recent studies have indicated a strong link between Helicobacter pylori and idiopathic thrombocytopenic purpura and iron deficiency anemia. Interesting results have also been obtained for ischemic heart disease, though most putative associations between H. pylori infection and extragastric disease remain speculative. With regard to other Helicobacter species, Helicobacter felis has been shown to play a role in gastric carcinogenesis in mouse models. An increased susceptibility to cholesterol gallstone formation has been described in animals fed a lithogenic diet and infected with Helicobacter bilis, or co-infected with Helicobacter hepaticus and Helicobacter rodentium. Finally, enterohepatic Helicobacter species have also been exploited to better understand inflammatory bowel disease.

Rapid onset of ulcerative typhlocolitis in B6.129P2-IL10tm1Cgn (IL-10-/-) mice infected with Helicobacter trogontum is associated with decreased colonization by altered Schaedler's flora

Infection with Helicobacter trogontum, a urease-positive helicobacter isolated from subclinically infected rats, was evaluated in B6.129P2-IL10(tm1Cgn) (interleukin-10(-/-) [IL-10(-/-)]) and C57BL/6 (B6) mice. In a first experiment, IL-10(-/-) mice naturally infected with Helicobacter rodentium had subclinical typhlocolitis but developed severe diarrhea and loss of body condition with erosive to ulcerative typhlocolitis within 1 to 3 weeks of experimental infection with H. trogontum. A second experiment demonstrated that helicobacter-free IL-10(-/-) mice dosed with H. trogontum also developed severe clinical signs and typhlocolitis within 2 to 4 weeks, whereas B6 mice colonized with H. trogontum were resistant to disease. In a third experiment, using helicobacter-free IL-10(-/-) mice, dosing with H. trogontum resulted in acute morbidity and typhlocolitis within 8 days. Acute typhlocolitis was accompanied by signs of sepsis supported by degenerative hemograms and recovery of Escherichia coli and Proteus spp. from the livers of infected mice. Quantitative PCR data revealed that H. rodentium and H. trogontum may compete for colonization of the lower bowel, as H. trogontum established higher colonization levels in the absence of H. rodentium (P < 0.003). H. trogontum-induced typhlocolitis was also associated with a significant decrease in the levels of colonization by five of eight anaerobes that comprise altered Schaedler's flora (P < 0.002). These results demonstrate for the first time that H. rodentium infection in IL-10(-/-) mice causes subclinical typhlocolitis and that infection with H. trogontum (with or without H. rodentium) induces a rapid-onset, erosive to ulcerative typhlocolitis which impacts the normal anaerobic flora of the colon and increases the risk of sepsis.

Modulation of host immune responses by the cytolethal distending toxin of Helicobacter hepaticus

Persistent murine infection with Helicobacter hepaticus leads to chronic gastrointestinal inflammation and neoplasia in susceptible strains. To determine the role of the virulence factor cytolethal distending toxin (CDT) in the pathogenesis of this organism, interleukin-10-deficient (IL-10-/-) mice were experimentally infected with wild-type H. hepaticus and a CDT-deficient isogenic mutant. Both wild-type H. hepaticus and the CDT-deficient mutant successfully colonized IL-10-/- mice, and they reached similar tissue levels by 6 weeks after infection. Only animals infected with wild-type type H. hepaticus developed significant typhlocolitis. However, by 4 months after infection, the CDT-deficient mutant was no longer detectable in IL-10-/- mice, whereas wild-type H. hepaticus persisted for the 8-month duration of the experiment. Animals infected with wild-type H. hepaticus exhibited severe typhlocolitis at 8 months after infection, while animals originally challenged with the CDT-deficient mutant had minimal cecal inflammation at this time point. In follow-up experiments, animals that cleared infection with the CDT-deficient mutant were protected from rechallenge with either mutant or wild-type H. hepaticus. Animals infected with wild-type H. hepaticus developed serum immunoglobulin G1 (IgG1) and IgG2c responses against H. hepaticus, while animals challenged with the CDT-deficient mutant developed significantly lower IgG2c responses and failed to mount IgG1 responses against H. hepaticus. These results suggest that CDT plays a key immunomodulatory role that allows persistence of H. hepaticus and that in IL-10-/- mice this alteration of the host immune response results in the development of colitis.

Helicobacter hepaticus Dps protein plays an important role in protecting DNA from oxidative damage

The ferritin-like DNA-binding protein from starved cells (Dps) family proteins are present in a number of pathogenic bacteria. Dps in the enterohepatic pathogen, Helicobacter hepaticus is characterized and a H. hepaticus dps mutant was generated by insertional mutagenesis. While the wild type H. hepaticus cells were able to survive in an atmosphere containing up to 6.0% O2, the dps mutant failed to grow in 3.0% O2, and it was also more sensitive to oxidative reagents like H2O2, cumene hydroperoxide and t-butyl hydroperoxide. Upon air exposure, the dps- cells had more damaged DNA than the wild type; they became coccoid or lysed and they contained approximately 6-fold higher amount of 8-oxoguanine (8-oxoG) DNA lesions than wild type cells. Purified H. hepaticus Dps was shown to be able to bind both iron and DNA. The iron-loaded form of Dps protein had much greater DNA binding ability than the native Dps or the iron-free Dps.

MDR1 C3435T polymorphism is predictive of later onset of ulcerative colitis in Japanese

Recently, a silent polymorphism of C3435T of the MDR1 gene, encoding the multidrug resistant transporter MDR1/P-glycoprotein, has been found to be associated with susceptibility to ulcerative colitis (UC), but this remains controversial. This study was conducted to find a possible reason for the discrepancies, and it was suggested that the age of onset was important for the association, namely, C3435T was predictive of susceptibility to later onset UC, but not for early onset UC. Linkage disequilibrium of C3435T with T-129C, C1236T and G2677A, T was suggested to be altered in UC, but the analysis of their haplotype provided no advantage in terms of prediction over that with only C3435T. The effect of C3435T on susceptibility could not be explained by that on mRNA expression in rectal mucosa, but it was greater in the C(3435)-noncarriers in the early onset group, allowing the individualization of steroid-based pharmacotherapy.

Helicobacter infection is required for inflammation and colon cancer in SMAD3-deficient mice

Accumulating evidence suggests that intestinal microbial organisms may play an important role in triggering and sustaining inflammation in individuals afflicted with inflammatory bowel disease (IBD). Moreover, individuals with IBD are at increased risk for developing colorectal cancer, suggesting that chronic inflammation may initiate genetic or epigenetic changes associated with cancer development. We tested the hypothesis that bacteria may contribute to the development of colon cancer by synergizing with defective transforming growth factor-beta (TGF-beta) signaling, a pathway commonly mutated in human colon cancer. Although others have reported that mice deficient in the TGF-beta signaling molecule SMAD3 develop colon cancer, we found that SMAD3-deficient mice maintained free of the Gram-negative enterohepatic bacteria Helicobacter spp. for up to 9 months do not develop colon cancer. Furthermore, infection of SMAD3(-/-) mice with Helicobacter triggers colon cancer in 50% to 66% of the animals. Using real-time PCR, we found that Helicobacter organisms concentrate in the cecum, the preferred site of tumor development. Mucinous adenocarcinomas develop 5 to 30 weeks after infection and are preceded by an early inflammatory phase, consisting of increased proliferation of epithelial cells; increased numbers of cyclooxygenase-2-positive cells, CD4(+) T cells, macrophages; and increased MHC class II expression. Colonic tissue revealed increased transcripts for the oncogene c-myc and the proinflammatory cytokines interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, IFN-gamma, and tumor necrosis factor-alpha, some of which have been implicated in colon cancer. These results suggest that bacteria may be important in triggering colorectal cancer, notably in the context of gene mutations in the TGF-beta signaling pathway, one of the most commonly affected cellular pathways in colorectal cancer in humans.

Bacteria and mucosal inflammation of the gut: lessons from Helicobacter pylori

The human gastrointestinal tract is colonized by an abundance of bacteria, which are in constant interaction with the epithelial lining usually leading to an intricate balance between tolerance and immunological response. There is ample evidence that the abundant presence of bacteria thus plays a role in the maintenance of human health, as well as in the induction of chronic inflammatory diseases of the gastrointestinal tract. Research in this field is, however, considerably hampered by the abundance of bacterial species, many of which have not even been characterized, and are difficult to culture specifically. These important limitations may to some extent be overcome by recent molecular biologic methods. Furthermore however, the adherent mucosal flora may differ largely from the luminal flora and that in excreta. These characteristics do not pertain to Helicobacter pylori, which generally colonizes the human stomach as a single strain with stable characteristics. Such colonization is stable throughout life, but can be treated. Furthermore, the association with chronic gastritis is very strong. For these reasons, H. pylori serves as an excellent model for the understanding of the processes involved in bacterial colonization and host response including mediation of immunoregulation, and the mechanisms by which this response can lead to disease.