The "Swiss roll": a simple technique for histological studies of the rodent intestine

Cdx function is required for maintenance of intestinal identity in the adult

The homeodomain transcription factors Cdx1 and Cdx2 are expressed in the intestinal epithelium from early development, with expression persisting throughout the life of the animal. While our understanding of the function of Cdx members in intestinal development has advanced significantly, their roles in the adult intestine is relatively poorly understood. In the present study, we found that ablation of Cdx2 in the adult small intestine severely impacted villus morphology, proliferation and intestinal gene expression patterns, resulting in the demise of the animal. Long-term loss of Cdx2 in a chimeric model resulted in loss of all differentiated intestinal cell types and partial conversion of the mucosa to a gastric-like epithelium. Concomitant loss of Cdx1 did not exacerbate any of these phenotypes. Loss of Cdx2 in the colon was associated with a shift to a cecum-like epithelial morphology and gain of cecum-associated genes which was more pronounced with subsequent loss of Cdx1. These findings suggest that Cdx2 is essential for differentiation of the small intestinal epithelium, and that both Cdx1 and Cdx2 contribute to homeostasis of the colon.

In vivo structure/function and expression analysis of the CX3C chemokine fractalkine

The CX3C chemokine family is composed of only one member, CX3CL1, also known as fractalkine, which in mice is the sole ligand of the G protein-coupled, 7-transmembrane receptor CX3CR1. Unlike classic small peptide chemokines, CX3CL1 is synthesized as a membrane-anchored protein that can promote integrin-independent adhesion. Subsequent cleavage by metalloproteases, either constitutive or induced, can generate shed CX3CL1 entities that potentially have chemoattractive activity. To study the CX3C interface in tissues of live animals, we generated transgenic mice (CX3CL1cherry:CX3CR1gfp), which express red and green fluorescent reporter genes under the respective control of the CX3CL1 and CX3CR1 promoters. Furthermore, we performed a structure/function analysis to differentiate the in vivo functions of membrane-tethered versus shed CX3CL1 moieties by comparing their respective ability to correct established defects in macrophage function and leukocyte survival in CX3CL1-deficient mice. Specifically, expression of CX3CL1(105Δ), an obligatory soluble CX3CL1 isoform, reconstituted the formation of transepithelial dendrites by intestinal macrophages but did not rescue circulating Ly6Clo CX3CR1hi blood monocytes in CX3CR1gfp/gfp mice. Instead, monocyte survival required the full-length membrane-anchored CX3CL1, suggesting differential activities of tethered and shed CX3CL1 entities.

A multiparametric approach to monitor the effects of γ-secretase inhibition along the whole intestinal tract

γ-secretase inhibitors (GSIs) have been recently proposed as chemopreventive agents in gastrointestinal neoplasia, because they lead, through inhibition of the Notch signaling pathway, to goblet cell conversion in some intestinal adenomas of the Apc^Min mice, and halt epithelial cell proliferation. In this study, we examine in depth, in normal mice, the effects of a GSI, dibenzazepine (DBZ), intraperitoneally administered for 8 days at a non toxic dose, on the gene expression pattern of secretory mucin (MUC), goblet cell conversion, organization of the crypt structural-proliferative units, stem cell niche and apoptotic compartments, along the entire length of the small intestine and colon. We demonstrate that DBZ elicits a homogeneous goblet cell conversion all along the mouse intestinal tract, associated with an overexpression of the gene Muc2 without ectopic expression of the gastric genes Muc5ac and Muc6, and with the emergence of lysozyme-positive ‘intermediate cells’ in the colon. Furthermore, DBZ treatment induces a heterogeneous reorganization of the crypt structural-proliferative units along the intestinal tract and of the stem cell niche in the colon, without disturbing the apoptotic compartment. These findings point to uncoupled effects of a GSI on goblet cell conversion and reorganization of the intestinal crypt structural-proliferative units and stem cell niche, and suggest caution in the use of GSIs as chemopreventive agents for intestinal neoplasia.

High dietary niacin may increase prostaglandin formation but does not increase tumor formation in ApcMin/+ mice

High doses of niacin (nicotinic acid) used to treat dyslipidemias cause flushing, due to high levels of prostaglandin D(2) (PGD(2)). GPR109A, a G-protein coupled receptor, triggers the flushing in the skin. In addition to boosting PGD(2), niacin binding to GPR109A activates the entire prostanoid cascade. We found that GPR109A occurs throughout the gastrointestinal tract. Mice that alternated between a 1% niacin diet and a control diet had higher urinary prostaglandin E(2) (PGE(2)) metabolite levels when on niacin (2.8-fold increase; 95% confidence interval, 1.8-3.9). PGE(2) promotes tumors in the intestines, whereas PGD(2) may have an opposite effect, on the basis of our report showing that transgenic hematopoietic prostaglandin D synthase suppresses intestinal adenomas in Apc(Min/+) mice. To determine if either tumor growth or tumor suppression prevails, we fed Apc(Min/+) mice a 1% niacin diet and assessed tumor development. A 1% niacin diet did not affect the number of tumors scored histologically in Apc(Min/+) mice at 14 wk (33 mice on niacin, 33 controls). Although niacin stimulates production of various prostaglandins, our results support an interpretation that very high intakes of niacin are safe in relation to intestinal tumors in this model.

Effect of endostatin on 1,2-dimethylhydrazine-induced colon tumor in mice

Endostatin, one of the most potent negative regulators of angiogenesis, is naturally occurring as an inhibitor of angiogenesis capable of inhibiting tumor growth and their metastases. We aimed to investigate the in vivo activities of low dose of recombinant human endostatin on 1,2-dimethylhydrazine (DMH)-induced mice colon cancer. Thirty male Balb-c mice were injected with DMH (20 mg/kg/week) subcutaneously once a week for 12 weeks to induce colon cancer. Twelve weeks after the last DMH injection, 7 µg rh-endostatin was injected every day for 6 weeks. The animals were killed after 30 weeks for histopathological examination. The weight of the animals, tumor inhibition rates, death rates and the distribution of the lesions in colon were evaluated after the mice were killed. The mean colonic lesions incidence in single tumor bearing mice was 11 ± 4.0 in those treated with DMH and 8.1 ± 3.7 in those treated with endostatin. When we look at the distribution of lesions in the colon, they occurred in the distal colon. At the end of our study, we noticed that the number of lesions decreased by 25% in the group of endostatin, considering the number of the lesions in the group of DMH. But there was no statistical difference between the mice treated with endostatin and those treated with DMH. It will be very significant to identify endostatin therapeutic effects as long as proper dose of endostatin is administrated at the proper time, duration and proper tumor model.

Postnatal intestinal engraftment of prospectively selected enteric neural crest stem cells in a rat model of Hirschsprung disease

BACKGROUND

Identification of neuronal progenitor/stem cells in the postnatal gut suggests the development of transplantation approaches to enteric nervous system (ENS) diseases. Many clinical applications would require engrafting large segments of postnatal gut in vivo. We investigated the ability of unselected gut cells vs selected enteric neural crest stem cells (eNCSCs) to engraft and differentiate in the postnatal gut in the Hirschsprung disease (HD, ednrb(sl/sl)) rat.

METHODS

Total intestinal cells or eNCSCs (α(4) integrin(+), p75(++)) from embryonic day (E)14.5 rats carrying a marker transgene (human placental alkaline phosphatase, hPAP) were injected intraperitoneally (i.p.) into neonatal HD rats and their healthy littermates. The entire gut was systematically analyzed 3 weeks later for hPAP(+) cells between the serosal surface and the muscularis mucosae. Engrafted cells were examined for HuC/D, S-100B, neuropeptide Y (NPY), neuronal nitric oxide synthase (nNOS), and vasoactive intestinal peptide (VIP) expression.

KEY RESULTS

No rats (0/33) injected with unselected cells had hPAP(+) cells in the ENS that expressed neuronal or glial markers. 5/11 healthy and 4/5 HD rats injected with eNCSCs showed widespread but low density engraftment in the ENS with cells expressing neuronal or glial markers. Neurons expressed nNOS and VIP. There was no engraftment in the colon of either HD or wildtype rats.

CONCLUSIONS & INFERENCES

Enteric neural crest stem cells will engraft diffusely throughout the postnatal gut of HD rats and differentiate into neurons and glia. Engraftment is not uniform, likely related to age-dependent changes in the gut mesenchyme. Intraperitoneal injection is easily performed in sick neonates and may be developed as a technique to supply exogenous ENS cells to the diseased postnatal gut.

Linear ubiquitination prevents inflammation and regulates immune signalling

Members of the tumour necrosis factor (TNF) receptor superfamily have important functions in immunity and inflammation. Recently linear ubiquitin chains assembled by a complex containing HOIL-1 and HOIP (also known as RBCK1 and RNF31, respectively) were implicated in TNF signalling, yet their relevance in vivo remained uncertain. Here we identify SHARPIN as a third component of the linear ubiquitin chain assembly complex, recruited to the CD40 and TNF receptor signalling complexes together with its other constituents, HOIL-1 and HOIP. Mass spectrometry of TNF signalling complexes revealed RIP1 (also known as RIPK1) and NEMO (also known as IKKγ or IKBKG) to be linearly ubiquitinated. Mutation of the Sharpin gene (Sharpin(cpdm/cpdm)) causes chronic proliferative dermatitis (cpdm) characterized by inflammatory skin lesions and defective lymphoid organogenesis. Gene induction by TNF, CD40 ligand and interleukin-1β was attenuated in cpdm-derived cells which were rendered sensitive to TNF-induced death. Importantly, Tnf gene deficiency prevented skin lesions in cpdm mice. We conclude that by enabling linear ubiquitination in the TNF receptor signalling complex, SHARPIN interferes with TNF-induced cell death and, thereby, prevents inflammation. Our results provide evidence for the relevance of linear ubiquitination in vivo in preventing inflammation and regulating immune signalling.

Standardized Post-Mortem Examination and Fixation Procedures for Mutant and Treated Mice

A procedure for post-mortem examination (or necropsy) of mice is provided. The aim is to obtain a "holistic" picture of organs and systems at the anatomical and histological levels. The major issue is tissue preservation, which is achieved by rapid transfer into a fixative solution, usually neutral buffered formalin. Fixation is the first of the four basic steps in histopathological analyses of tissues, which also include embedding, sectioning, and staining. The protocols provided here describe routine methods for tissue fixation, as these methods are integral parts of any necropsy procedure. There is also a Strategic Planning section that addresses the overall approach to histopathological evaluation, as well as specifics such as age and gender of the mice, cohort size, and controls. Curr. Protoc. Mouse Biol. 1:17-53. © 2011 by John Wiley & Sons, Inc.

Necropsy and sampling procedures in rodents

Necropsy is a major step of most studies using laboratory animals. During necropsy, tissue and organ changes noticeable grossly can be recorded, and important tissue samples can be stored for subsequent evaluation. It is therefore important that the personnel in charge of this key experimentation step be adequately trained and aware of the study endpoints.

Histopathology procedures: from tissue sampling to histopathological evaluation

Histological procedures aim to provide good quality sections that can be used for a light microscopic evaluation of human or animal tissue changes in either spontaneous or induced diseases. Routinely, tissues are fixed with neutral formalin 10%, embedded in paraffin, and then manually sectioned with a microtome to obtain 4-5 μm-thick paraffin sections. Dewaxed sections are then stained with hematoxylin and eosin (H&E) or can be used for other purposes (special stains, immunohistochemistry, in situ hybridization, etc.). During this process, many steps and procedures are critical to ensure standard and interpretable sections. Key recomendations are given here to achieve this objective.

A key role for E-cadherin in intestinal homeostasis and Paneth cell maturation

Background

E-cadherin is a major component of adherens junctions. Impaired expression of E-cadherin in the small intestine and colon has been linked to a disturbed intestinal homeostasis and barrier function. Down-regulation of E-cadherin is associated with the pathogenesis of infections with enteropathogenic bacteria and Crohn's disease.

Methods and Findings

To genetically clarify the function of E-cadherin in intestinal homeostasis and maintenance of the epithelial defense line, the Cdh1 gene was conditionally inactivated in the mouse intestinal epithelium. Inactivation of the Cdh1 gene in the small intestine and colon resulted in bloody diarrhea associated with enhanced apoptosis and cell shedding, causing life-threatening disease within 6 days. Loss of E-cadherin led cells migrate faster along the crypt-villus axis and perturbed cellular differentiation. Maturation and positioning of goblet cells and Paneth cells, the main cell lineage of the intestinal innate immune system, was severely disturbed. The expression of anti-bacterial cryptidins was reduced and mice showed a deficiency in clearing enteropathogenic bacteria from the intestinal lumen.

Conclusion

These results highlight the central function of E-cadherin in the maintenance of two components of the intestinal epithelial defense: E-cadherin is required for the proper function of the intestinal epithelial lining by providing mechanical integrity and is a prerequisite for the proper maturation of Paneth and goblet cells.

Store-operated Ca2+ entry through ORAI1 is critical for T cell-mediated autoimmunity and allograft rejection

ORAI1 is the pore-forming subunit of the Ca(2+) release-activated Ca(2+) (CRAC) channel, which is responsible for store-operated Ca(2+) entry in lymphocytes. A role for ORAI1 in T cell function in vivo has been inferred from in vitro studies of T cells from human immunodeficient patients with mutations in ORAI1 and Orai1(-/-) mice, but a detailed analysis of T cell-mediated immune responses in vivo in mice lacking functional ORAI1 has been missing. We therefore generated Orai1 knock-in mice (Orai1(KI/KI)) expressing a nonfunctional ORAI1-R93W protein. Homozygosity for the equivalent ORAI1-R91W mutation abolishes CRAC channel function in human T cells resulting in severe immunodeficiency. Homozygous Orai1(KI/KI) mice die neonatally, but Orai1(KI/KI) fetal liver chimeric mice are viable and show normal lymphocyte development. T and B cells from Orai1(KI/KI) mice display severely impaired store-operated Ca(2+) entry and CRAC channel function resulting in a strongly reduced expression of several key cytokines including IL-2, IL-4, IL-17, IFN-γ, and TNF-α in CD4(+) and CD8(+) T cells. Cell-mediated immune responses in vivo that depend on Th1, Th2, and Th17 cell function were severely attenuated in ORAI1-deficient mice. Orai1(KI/KI) mice lacked detectable contact hypersensitivity responses and tolerated skin allografts significantly longer than wild-type mice. In addition, T cells from Orai1(KI/KI) mice failed to induce colitis in an adoptive transfer model of inflammatory bowel disease. These findings reaffirm the critical role of ORAI1 for T cell function and provide important insights into the in vivo functions of CRAC channels for T cell-mediated immunity.

PARK2 deletions occur frequently in sporadic colorectal cancer and accelerate adenoma development in Apc mutant mice

In 100 primary colorectal carcinomas, we demonstrate by array comparative genomic hybridization (aCGH) that 33% show DNA copy number (DCN) loss involving PARK2, the gene encoding PARKIN, the E3 ubiquitin ligase whose deficiency is responsible for a form of autosomal recessive juvenile parkinsonism. PARK2 is located on chromosome 6 (at 6q25-27), a chromosome with one of the lowest overall frequencies of DNA copy number alterations recorded in colorectal cancers. The PARK2 deletions are mostly focal (31% approximately 0.5 Mb on average), heterozygous, and show maximum incidence in exons 3 and 4. As PARK2 lies within FRA6E, a large common fragile site, it has been argued that the observed DCN losses in PARK2 in cancer may represent merely the result of enforced replication of locally vulnerable DNA. However, we show that deficiency in expression of PARK2 is significantly associated with adenomatous polyposis coli (APC) deficiency in human colorectal cancer. Evidence of some PARK2 mutations and promoter hypermethylation is described. PARK2 overexpression inhibits cell proliferation in vitro. Moreover, interbreeding of Park2 heterozygous knockout mice with Apc(Min) mice resulted in a dramatic acceleration of intestinal adenoma development and increased polyp multiplicity. We conclude that PARK2 is a tumor suppressor gene whose haploinsufficiency cooperates with mutant APC in colorectal carcinogenesis.

The role of prostaglandin E2 (PGE 2) in toll-like receptor 4 (TLR4)-mediated colitis-associated neoplasia

Background

We have previously found that TLR4-deficient (TLR4-/-) mice demonstrate decreased expression of mucosal PGE ₂ and are protected against colitis-associated neoplasia. However, it is still unclear whether PGE ₂ is the central factor downstream of TLR4 signaling that promotes intestinal tumorigenesis. To further elucidate critical downstream pathways involving TLR4-mediated intestinal tumorigenesis, we examined the effects of exogenously administered PGE ₂ in TLR4-/- mice to see if PGE ₂ bypasses the protection from colitis-associated tumorigenesis.

Method

Mouse colitis-associated neoplasia was induced by azoxymethane (AOM) injection followed by two cycles of dextran sodium sulfate (DSS) treatment. Two different doses of PGE ₂ (high dose group, 200 μg, n = 8; and low dose group, 100 μg, n = 6) were administered daily during recovery period of colitis by gavage feeding. Another group was given PGE ₂ during DSS treatment (200 μg, n = 5). Inflammation and dysplasia were assessed histologically. Mucosal Cox-2 and amphiregulin (AR) expression, prostanoid synthesis, and EGFR activation were analyzed.

Results

In control mice treated with PBS, the average number of tumors was greater in WT mice (n = 13) than in TLR4-/- mice (n = 7). High dose but not low dose PGE ₂ treatment caused an increase in epithelial proliferation. 28.6% of PBS-treated TLR4-/- mice developed dysplasia (tumors/animal: 0.4 ± 0.2). By contrast, 75.0% (tumors/animal: 1.5 ± 1.2, P < 0.05) of the high dose group and 33.3% (tumors/animal: 0.3 ± 0.5) of the low dose group developed dysplasia in TLR4-/- mice. Tumor size was also increased by high dose PGE ₂ treatment. Endogenous prostanoid synthesis was differentially affected by PGE ₂ treatment during acute and recovery phases of colitis. Exogenous administration of PGE ₂ increased colitis-associated tumorigenesis but this only occurred during the recovery phase. Lastly, PGE ₂ treatment increased mucosal expression of AR and Cox-2, thus inducing EGFR activation and forming a positive feedback mechanism to amplify mucosal Cox-2.

Conclusions

These results highlight the importance of PGE ₂ as a central downstream molecule involving TLR4-mediated intestinal tumorigenesis.

The Mongolian gerbil as a model for inflammatory bowel disease

Mongolian gerbils are used as biomedical research models for a variety of diseases and are in some cases suited better than other rodents for basic research and therapeutic studies. The aim of this study was to establish and characterize a dextran sulphate sodium (DSS)-induced model in gerbils for the human inflammatory bowel disease (IBD) and to utilize them for a therapeutic study in vivo. Four concentrations (0.5%, 1%, 2% and 4%) of DSS were administered via drinking water for 7 days; based on these results, a concentration of 3% DSS was given for 9 days in a second approach. Fluid uptake and general clinical condition were assessed daily using a clinical score. Caecum and colon were scored histologically. Fluid uptake was affected by addition of DSS to the drinking water. First clinical symptoms were observed at day 4 of DSS treatment with a considerable increase in clinical score parameters only in gerbils receiving 2% or 4% DSS. Histologically, ulceration and inflammation were observed predominantly in the caecum of gerbils treated with at least 1% DSS; reproducible inflammation in the colon required at least 2% DSS. Using 3% DSS for 9 days, considerably more inflammation was induced in the colon, comparable with lesions usually observed in the mouse model. Using an optimized protocol, DSS treatment induces reproducibly typhlocolitis in Mongolian gerbils, rendering them as a useful model for IBD.

Murine Colitis modeling using Dextran Sulfate Sodium (DSS)

Colitis can occur from viral or bacterial infections, ischemic insult, or autoimmune disorders; most notably Ulcerative Colitis and the colonic variant of Crohn’s Disease - Crohn’s Colitis. Acute colitis may present with abdominal pain and distention, malabsorption, diarrhea, hematochezia and mucus in the stool. We are beginning to understand the complex interactions between the environment, genetics, and epithelial barrier dysfunction in Inflammatory Bowel Disease and animal models of colitis have been essential in advancing our understanding of this disease. One popular model involves supplementing the drinking water of mice with low-molecular weight Dextran Sodium Sulfate (DSS), resulting in epithelial damage and a robust inflammatory response in the colon lasting several days ¹.Variations of this approach can be used to model acute injury, acute injury followed by repair, and repeated cycles of DSS interspersed with recovery modeling chronic inflammatory diseases ². After a single four-day treatment of 3% DSS in drinking water, mice show signs of acute colitis including weight loss, bloody stools, and diarrhea. Mice are euthanized at the conclusion of the treatment course and at necropsy dissected colons are processed and can be 'Swiss rolled" ³ to allow microscopic analysis of the entire colon or infused with formalin as "sausages" to allow macroscopic analysis. Tissue is then embedded in paraffin, sectioned, and stained for histologic review.

Hirschsprung's disease: the "Swiss roll" technique revisited

PURPOSE

During pull-through for Hirschsprung's disease (HSCR), the assessment of innervation is mainly based on the presence of ganglion cells when conventional Hematoxylin and Eosin (HE) staining is used. In hypoganglionosis, the evaluation is difficult. We adapted a standardized methodology for the examination of resected bowel after HSCR surgery, using the technique described by Moolenbeek on rodent intestine and later by Meier-Ruge in children. We have analysed the entire innervation of surgically resected bowels and compared the results with the follow up of patients.

METHODS

Three longitudinal strips of colon were harvested from the mesenteric, anti-mesenteric and intermediate part in the whole length of resected colon of six patients with HSCR. Each strip was divided into two parts. One of the contiguous strips was assessed with HE and Hematoxylin-Phloxin-Safran, and the other one with acetylcholinesterase (AChE) histochemistry. We analyzed the distribution of ganglion cells and nerve arrangement along the strips with both techniques and compared the results obtained in the three different regions of the bowel.

RESULTS

There was no significant difference in the pattern of innervation circumferentially. There was a correlation between a progressive increase of AChE activity and nerve hypertrophy and a decrease of ganglion cells from the proximal to the distal part of the resected colon in the submucosa and the myenteric plexus. Nerve hypertrophy and AChE-positive reaction in the mucosa were found at the resection border in patients who presented postoperative complications.

CONCLUSIONS

Simultaneous assessment of nerve cells, nerve fibers and AChE activity is important in the evaluation of the innervation of the bowel segment proximal to the aganglionic zone. The method described is feasible and can be adapted to older children and adults with larger bowels. These results point out the importance of assessing nerve fibers in intraoperative biopsies during pull-through procedures to prevent uncomplete surgical bowel resection.

Effects of the endothelin-converting enzyme inhibitor SM-19712 in a mouse model of dextran sodium sulfate-induced colitis

BACKGROUND

Ingestion by mice of dextran sodium sulfate (DSS) induces colonic vasoconstriction and inflammation, with some of the effects potentially mediated by the vasoconstrictor endothelin-1 (ET-1).

METHODS

In this study, mice given 5% 40 kD DSS for 5-6 days had elevated colonic immunostaining for ET-1 and platelet endothelial cell adhesion molecule-1 (PECAM-1). Increased ET-1 can induce microvascular constriction; however, the increase in PECAM-1 is consistent with angiogenesis that could decrease flow resistance.

RESULTS

Our measurements of intestinal blood flow, via infused microspheres, suggests that these 2 factors may offset each other, with only a nonsignificant tendency for a DSS-induced decrease in flow. Daily administration of the endothelin converting enzyme inhibitor SM-19712 (15 mg/kg) attenuated DSS-induced increases in colonic immunostaining of ET-1 and PECAM-1.

CONCLUSIONS

SM-19712 attenuated histologic signs of tissue injury and inflammation induced by DSS, and decreased the extent of loose stools and fecal blood. However, the inhibitor did not significantly decrease DSS-induced colon shortening or tissue levels of myeloperoxidase (an indicator of neutrophil infiltration).

CpG motifs of bacterial DNA exert protective effects in mouse models of IBD by antigen-independent tolerance induction

BACKGROUND & AIMS

Prophylactic treatment of mice with CpG motifs of bacterial DNA protects from experimental inflammatory bowel disease, at least partly via induction of inhibitory T-cells. The aim of this study was to elucidate whether these CpG-dependent protective effects require presence of bacterial flora suggesting antigen-specific regulatory activity.

METHODS

Germ-free BALB/c and IL-10(-/-) mice were treated with CpG-oligodeoxynucleotides (ODN), control-ODN, or PBS. CD4(+)CD62L(+) cells of these mice were transferred into SCID recipients. CpG-ODN-treated germ-free IL-10(-/-) mice were transferred into colitogenic environment. Monoclonal antibodies were used to neutralize TGF-beta and IFN-alpha/beta during CpG-ODN treatment. CD4(+)CD62L(+) cells of donors were evaluated for cytokine secretion and FOXP3, PD-1, and CD25 expression.

RESULTS

Compared to PBS or control-ODN treatment, CpG-ODN application to germ-free donors led to decreased intestinal inflammation as indicated by histology, decreased proinflammatory cytokines, and increased IL-10 secretion. Protection was also observed after cotransfer of cells from PBS and CpG-ODN treated donors. Anti-TGF-beta and anti-INF-alpha/beta partly reversed the protective CpG-ODN effect. CpG-ODN-treated germ-free IL-10(-/-) mice transferred into colitogenic environment developed significantly less colitis than controls but not recipients of IL-10(-/-)CD4(+)CD62L(+)cells. CD4(+)CD62L(+)cells of CpG-treated germ-free animals displayed increased expression of regulatory markers.

CONCLUSIONS

Even without pre-existence of bacterial flora CpG-ODN exposition induces tolerance, indicating that CpG-ODN-induced regulatory T-cells are not bacterial antigen specific. TGF-beta and IFN-alpha/beta play major roles in induction of regulatory cells, and although IL10-independent mechanisms play a role in CpG-ODN protection, this cytokine likely is important for the effector mechanism of CpG-ODN-induced regulatory T-cells.

Lack of genotoxic effect of food dyes amaranth, sunset yellow and tartrazine and their metabolites in the gut micronucleus assay in mice

The food dyes amaranth, sunset yellow and tartrazine were administered twice, at 24h intervals, by oral gavage to mice and assessed in the in vivo gut micronucleus test for genotoxic effects (frequency of micronucleated cells) and toxicity (apoptotic and mitotic cells). The concentrations of each compound and their main metabolites (sulfanilic acid and naphthionic acid) were measured in faeces during a 24-h period after single oral administrations of the food dyes to mice. Parent dye compounds and their main aromatic amine metabolites were detected in significant amounts in the environment of colonic cells. Acute oral exposure to food dye additives amaranth, sunset yellow and tartrazine did not induce genotoxic effect in the micronucleus gut assay in mice at doses up to 2000 mg/kg b.w. Food dyes administration increased the mitotic cells at all dose levels when compared to controls. These results suggest that the transient DNA damages previously observed in the colon of mice treated by amaranth and tartrazine by the in vivo comet assay [Sasaki, Y.F., Kawaguchi, S., Kamaya, A., Ohshita, M., Kabasawa, K., Iwama, K., Taniguchi, K., Tsuda, S., 2002. The comet assay with 8 mouse organs: results with 39 currently used food additives. Mutat. Res. 519, 103-119] are unable to be fixed in stable genotoxic lesions and might be partly explained by local cytotoxicity of the dyes.

Betacellulin stimulates growth of the mouse intestinal epithelium and increases adenoma multiplicity in Apc+/Min mice

We employed transgenic mice overexpressing betacellulin (BTC) to study its effects in the gut. BTC stimulated crypt cell proliferation and markedly increased intestinal size, while the crypt-villus architecture was preserved. Introduction of a dominant negative epidermal growth factor receptor (EGFR) completely abolished the intestinal hyperplasia. BTC increased polyp multiplicity but did not change the mean size or the histological quality of intestinal polyps in Apc(+/Min) mice. Analysis of intact and cleaved caspase-3 levels indicated that BTC has anti-apoptotic effects in the intestinal epithelium. We conclude that increased BTC levels support the survival of nascent adenomas in Apc(+/Min) mice, resulting in a larger total polyp number at later stages.

Supplementation with galactooligosaccharides and inulin increases bacterial translocation in artificially reared newborn rats

Supplementation of formulas with prebiotics enhances the growth of lactate producing bacteria, and fecal lactate, and acetate levels in infants. High concentrations of organic acids in intestinal lumen have, however, been shown to impair the intestinal barrier function. To determine whether stimulating the colonic microbiotal metabolism with prebiotics would impair the neonatal intestinal barrier function, artificially reared rats were fed milk formula with or without a mixture of galactooligosaccharides/inulin (GOS/Inulin, 88/12; 5.6 g/L) from the 7th d of life (d7) until weaning (d20). At d18, GOS/inulin supplementation had increased the concentrations of acetate and lactate in colonic lumen. Although neither ileum-associated microbiota nor colonic permeability (assessed in Ussing chambers), nor the expression of tight junction claudin-2 and claudin-3 mRNA were altered, GOS/inulin supplementation was associated with increased bacterial translocation (BT) toward spleen. None of these effects persisted at d40. We conclude that GOS/inulin supplementation may increase BT in an immature gut. The balance between the potential infectious risk of BT vs. its putative beneficial effect on the maturation of neonatal immune system clearly warrants further study.

Matrix metalloproteinase-7 (matrilysin) controls neutrophil egress by generating chemokine gradients

Matrilysin [matrix metalloproteinase 7 (MMP7)] is induced by mucosal injury of many tissues. To assess function of this proteinase, we subjected wild-type and Mmp7(-/-) mice to acute colon injury. When matrilysin expression was increasing, 73% of wild-type mice died, whereas only 32% of Mmp7(-/-) mice succumbed. Although re-epithelialization was delayed in Mmp7(-/-) mice, overall injury did not differ markedly between genotypes. We hypothesized that differences in acute inflammation caused increased mortality in wild-type mice. Indeed, whereas overall neutrophil influx into tissue was similar in wild-type and Mmp7(-/-) mice, their location and extent of migration differed between genotypes. Neutrophils were dispersed throughout the mucosa and within the lumen of wild-type mice, but these leukocytes were largely confined to the submucosa in Mmp7(-/-) mice. The levels of neutrophil chemokines, keratinocyte-derived chemokine and MIP-2, increased in the colon tissue of both genotypes, but these factors were detected only in lumenal lavages of wild-type mice. Our findings indicate that matrilysin mediates beneficial and deleterious effects in response to injury. On one hand, it promotes re-epithelialization, but it also controls the transepithelial influx of neutrophils, which if excessive, can lead to tissue damage.

Concurrent repletion of iron and zinc reduces intestinal oxidative damage in iron- and zinc-deficient rats

AIM: To understand the interactions between iron and zinc during absorption in iron- and zinc-deficient rats, and their consequences on intestinal oxidant-antioxidant balance.

METHODS: Twenty-four weanling Wistar-Kyoto rats fed an iron- and zinc-deficient diet (< 6.5 mg Fe and 4.0 mg Zn/kg diet) for 4 wk were randomly divided into three groups (n = 8, each) and orally gavaged with 4 mg iron, 3.3 mg zinc, or 4 mg iron + 3.3 mg zinc for 2 wk. On the last day of repletion, 3 h before the animals were sacrificed, they received either 37 mBq of ⁵⁵Fe or ⁶⁵Zn, to study their localization in the intestine, using microautoradiography. Hemoglobin, iron and zinc content in plasma and liver were measured as indicators of iron and zinc status. Duodenal sections were used for immunochemical staining of ferritin and metallothionein. Duodenal homogenates (mitochondrial and cytosolic fractions), were used to assess aconitase activity, oxidative stress, functional integrity and the response of antioxidant enzymes.

RESULTS: Concurrent repletion of iron- and zinc-deficient rats showed reduced localization of these minerals compared to rats that were teated with iron or zinc alone; these data provide evidence for antagonistic interactions. This resulted in reduced formation of lipid and protein oxidation products and better functional integrity of the intestinal mucosa. Further, combined repletion lowered iron-associated aconitase activity and ferritin expression, but significantly elevated metallothionein and glutathione levels in the intestinal mucosa. The mechanism of interactions during combined supplementation and its subsequent effects appeared to be due to modulation of cytosolic aconitase, which in turn influenced the labile iron pool and metallothionein levels, and hence reduced intestinal oxidative damage.

CONCLUSION: Concurrent administration of iron and zinc corrects iron and zinc deficiency, and also reduces the intestinal oxidative damage associated with iron supplementation.

Genome-wide analysis of PPARalpha activation in murine small intestine

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a fatty acid-activated transcription factor that governs a variety of biological processes. Little is known about the role of PPARalpha in the small intestine. Since this organ is frequently exposed to high levels of PPARalpha ligands via the diet, we set out to characterize the function of PPARalpha in small intestine using functional genomics experiments and bioinformatics tools. PPARalpha was expressed at high levels in both human and murine small intestine. Detailed analyses showed that PPARalpha was expressed most highly in villus cells of proximal jejunum. Microarray analyses of total tissue samples revealed, that in addition to genes involved in fatty acid and triacylglycerol metabolism, transcription factors and enzymes connected to sterol and bile acid metabolism, including FXR and SREBP1, were specifically induced. In contrast, genes involved in cell cycle and differentiation, apoptosis, and host defense were repressed by PPARalpha activation. Additional analyses showed that intestinal PPARalpha-dependent gene regulation occurred in villus cells. Functional implications of array results were corroborated by morphometric data. The repression of genes involved in proliferation and apoptosis was accompanied by a 22% increase in villus height and a 34% increase in villus area of wild-type animals treated with WY14643. This is the first report providing a comprehensive overview of processes under control of PPARalpha in the small intestine. We show that PPARalpha is an important transcriptional regulator in small intestine, which may be of importance for the development of novel foods and therapies for obesity and inflammatory bowel diseases.

Epidermal growth factor receptor signaling is required for microadenoma formation in the mouse azoxymethane model of colonic carcinogenesis

Colonic carcinogenesis involves the progressive dysregulation of homeostatic mechanisms that control growth. The epidermal growth factor (EGF) receptor (EGFR) regulates colonocyte growth and differentiation and is overexpressed in many human colon cancers. A requirement for EGFR in colonic premalignancy, however, has not been shown. In the current study, we used a specific EGFR antagonist, gefitinib, to investigate this role of the receptor in azoxymethane colonic premalignancy. The azoxymethane model shares many clinical, histologic, and molecular features of human colon cancer. Mice received azoxymethane i.p. (5 mg/kg/wk) or saline for 6 weeks. Animals were also gavaged with gefitinib (10 mg/kg body weight) or vehicle (DMSO) thrice weekly for 18 weeks, a dose schedule that inhibited normal receptor activation by exogenous EGF. Compared with control colonocytes [bromodeoxyuridine (BrdUrd), 2.2+/-1.2%], azoxymethane significantly increased proliferation (BrdUrd, 12.6+/-2.8%), whereas gefitinib inhibited this hyperproliferation (BrdUrd, 6.2+/-4.0%; <0.005). Azoxymethane significantly induced pro-transforming growth factor-alpha (6.4+/-1.3-fold) and increased phospho-(active) EGFR (5.9+/-1.1-fold), phospho-(active) ErbB2 (2.3+/-0.2-fold), and phospho-(active) extracellular signal-regulated kinase (3.3+/-0.4-fold) in premalignant colonocytes. Gefitinib inhibited activations of these kinases by >75% (P<0.05). Gefitinib also significantly reduced the number of large aberrant crypt foci and decreased the incidence of colonic microadenomas from 75% to 33% (P<0.05). Gefitinib concomitantly decreased cell cycle-regulating cyclin D1 and prostanoid biosynthetic enzyme cyclooxygenase-2 in microadenomas, suggesting that these regulators are key targets of EGFR in colonic carcinogenesis. These results show for the first time that EGFR signaling is required for early stages of colonic carcinogenesis. Our findings suggest, moreover, that inhibitors of EGFR might be useful in chemopreventive strategies in individuals at increased risk for colonic malignancies.

A 90-day dietary study on kappa carrageenan with emphasis on the gastrointestinal tract

Groups of Fischer 344 rats (20/sex/group) received control or treated diets at levels of 0, 25,000 or 50,000 ppm kappa carrageenan with a molecular weight range (Mw) of 196,000-257,000 Da for 90 days. The Low Molecular Weight Tail (LMT) ranged between 1.9% and 12.0%<50 kDa (mean 7%) based on the results of a program initiated to develop a validated analytical method to measure the LMT. This is the first GLP dietary study in which carrageenan is characterized by percentage LMT. Clinical examinations were performed daily. Individual food consumption/body weight measurements were made weekly. Ophthalmic exam was conducted prior to and at the end of treatment. Hematology/serum chemistry and urinalysis evaluations were done at necropsy, as were organ weight determinations for adrenals, brain, heart, kidneys, liver, ovaries, spleen, testes and thyroid with parathyroids. Full histopathological evaluation of organs was conducted on the control and 50,000 ppm groups, including hematoxylin-eosin-stained cross sections of paraffin-embedded rolled colon. Clinical signs were limited to soft feces in high dose rats and to a lesser extent in low dose rats. There were no treatment-related effects on body weights, urinalysis, hematology or clinical chemistry parameters, or on organ weights or ophthalmic, macroscopic or microscopic findings. The gastrointestinal tract appeared normal in detailed histopathological evaluation using the Swiss roll technique. The NOAEL is 50,000 ppm in the diet (mean calculated test material consumption of 3394+/-706 mg/kg/day in males, 3867+/-647 mg/kg/day in females). The results of the study provide evidence that it is not necessary to characterize carrageenan by a specification for LMT (less than 5% below 50 kDa) as has been done in Commission Directive 2004/45/EC of 16 April 2004 (Commission Directive, 2004/45/EC of 16 April 2004 amending Directive 96/77/EC laying down specific purity criteria on food additives other than colors and sweeteners. Official Journal of European Union 20 April, 2004, L113/19-L113/21).

Cd14,Gbp1, andPla2g2a: three major candidate genes for experimental IBD identified by combining QTL and microarray analyses

Induction of inflammatory bowel (IBD)-like disease in mice by a targeted mutation in the Il10 gene ( Il10−/−) is inbred strain dependent. C3H/HeJBir (C3) mice are colitis susceptible, whereas C57BL/6J (B6) mice are resistant. Genetic dissection of this susceptibility revealed 10 colitogenic quantitative trait loci (QTL). The aim of this study was to identify valuable candidate genes by a combination of QTL mapping and microarray analyses. Sixteen genes were differentially expressed between B6- and C3- Il10−/−mice and were located within the QTL intervals. Three major candidate genes ( Cd14, Gbp1, Pla2g2a) showed prominent expression differences between B6- and C3- Il10−/−as well as between B6 and C3 wild-type mice, which was confirmed by semiquantitative or real-time RT-PCR. Because strain differences are known for Gbp1 and Pla2g2a, further analyses focused on Cd14. Western blot analysis revealed strain differences also on the protein level. Cd14 expression in animals with defective and intact Toll-like receptor (TLR)4 signaling (C3, C3H/HeN, B6, B6- Tlr4tm1Aki) make the TLR4 defect of C3 mice unlikely to be the reason for higher Cd14 expression. Less Cd14 expression in germ-free mice indicates a contribution of the microflora on Cd14 expression. Stimulation of naive peritoneal macrophages with bacterial antigens showed lower CD14 surface expression in B6 than in C3 mice. In conclusion, the large number of candidate genes was reduced to three major candidates that play an important role in inflammatory processes and immune response. Strain differences for them are already known or are shown in this study.

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.

Cause and Effect Considerations in Diagnostic Pathology and Pathology Phenotyping of Genetically Engineered Mice (GEM)

Over the next several decades, biology is embarking on its most ambitious project yet: to annotate the human genome functionally, prioritizing and focusing on those genes relevant to development and disease. Model systems are fundamental prerequisites for this task, and genetically engineered mice (GEM) are by far the most accessible mammalian system because of their anatomical, physiological, and genetic similarity to humans. The scientific utility of GEM has become commonplace since the technology to produce them was established in the early 1980s. Conceptually, however, an efficiently coordinated high-throughput approach that permits correlation between newly discovered genes, functional properties of their protein products, and biological relevance of these products as drug targets has yet to be established. The discipline of veterinary anatomical pathology (hereafter referred to as pathology) is not immune to this requirement for evolution and adaptation, and to address relationships and tissue consequences between tens of thousands of genes and their cognate proteins, novel interdisciplinary technologies and approaches must emerge. Although many of the techniques of pathology are well established, in the context of pathology's contribution to functional annotation of the genome, several conceptually important and unresolved issues remain to be addressed. While an ever-increasing arsenal of genetic and molecular tool-sets are available to evaluate and understand the function of genes and their pathophysiological mechanisms, pathology will continue to play an essential role in confirming cause and effect relationships of gene function in development and disease. This role will continue to be dependent on keen observation, a systematic but disciplined approach, expert knowledge of strain-dependent anatomical differences and incidental lesions, and relevant tissue-based evidence. Miniaturization and high-throughput adaptation of these methods must also continue so that they can complement parallel phenotyping efforts, provide pathology-based data in pace with concurrent phenotyping efforts, and continue to find new utility in the collective effort of functional annotation.

Enhanced histopathology of mucosa-associated lymphoid tissue

The secretory epithelial surfaces of the body are a major route of entry for potentially pathogenic substances. The organized mucosal lymphoid tissues that are found within the gastrointestinal and respiratory tracts are therefore particularly important as a first line of defense against harmful compounds. The major function of these mucosa-associated lymphoid tissues (MALT) is to initiate local IgA immune responses, which are then passed on to draining lymph nodes. For enhanced histopathology, the separate compartments of each lymphoid tissue should be evaluated separately for changes in size and lymphocyte cellularity and descriptive rather than interpretive terminology should be used to characterize any changes. The organization of MALT is similar to that of lymph nodes with B-cell-rich follicles and T-cell-rich interfollicular areas. Therefore, these two compartments should be evaluated separately for changes in size and lymphocyte cellularity and the germinal center development within lymphoid follicles should be evaluated as well.

Probiotic effects of Lactobacillus casei on DSS-induced ulcerative colitis in mice

We tested the effect of Lactobacillus casei strain Shirota (LcS) on the murine model of ulcerative colitis induced by dextran sodium sulphate. The effect of LcS was tested either as a prophylactic 10 days before the onset of the disease, simultaneously with ulcerative colitis induction or continued 10 days after the disease was induced. LcS was not able to prevent the disease induction in any of the experiments. However, important clinical parameters including blood anemia indicators, body weight, and organ weight were improved in the animals receiving LcS as compared with the ulcerative colitis-induced controls. Increased colonic epithelial regeneration in the LcS treated animals was observed in the chronic stage. The results seemed better for the simultaneous short LcS treatment where some parameters remained similar to the PBS controls, including disease activity scores measured in the acute stage. We can conclude that although LcS alone cannot prevent the induction of ulcerative colitis by dextran sodium sulphate, it can improve the clinical condition of the mice. This could imply important biological consequences for the human situation. Further studies including LcS or other probiotic bacteria together with the available treatment are encouraged.

Macroscopic, microscopic and biochemical characterisation of spontaneous colitis in a transgenic mouse, deficient in the multiple drug resistance 1a gene

1 A novel animal model of spontaneous colonic inflammation, the multiple drug-resistant (mdr1) a(-/-) mouse, was identified by Panwala and colleagues in 1998. The aim of our study was to further characterise this model, specifically by measuring cytokines that have been implicated in inflammatory bowel disease (IBD) (IL-8 and IFN-gamma) in the colon/rectum of mdr1a(-/-) mice, and by determining the sensitivity of these, together with the macroscopic, microscopic and disease signs of colitis, to dexamethasone (0.05, 0.3 and 2 mg kg(-1) subcutaneously (s.c.) daily for 7 days). 2 All mdr1a(-/-) mice had microscopic evidence of inflammation in the caecum and colon/rectum, while control mice with the same genetic background did not. Significant increases in colon/rectum and caecal weights and also in cytokine levels (both IFN-gamma and IL-8) in homogenised colon/rectum were observed in mdr1a(-/-) mice compared to mdr1a(+/+) mice. 3 Dexamethasone reduced the increases in tissue weights and also microscopic grading of colitis severity, but had no effect on IFN-gamma or IL-8. 4 This study supports the similarity of the gastrointestinal inflammation present in mdr1a(-/-) mice to that of human IBD, in particular Crohn's disease. This has been demonstrated at the macroscopic and microscopic levels, and was supported further by elevations in colonic levels of IFN-gamma and IL-8 and the disease signs observed. The incidence of colitis was much higher than previously reported, with all mice having microscopic evidence of colitis. The limited variance between animals in the parameters measured suggests that this model is reproducible.

Refined histopathologic scoring system improves power todetect colitis QTL in mice

Induction of colitis in mice by a targeted mutation in the I110 gene is inbred strain dependent. C3H/ HeJBir (C3H) mice are colitis susceptible while C57BL/6J (B6) mice are resistant. Identification of quantitative trait loci (QTL) determining the differential strain responsiveness requires histopathologic scoring of multiple lesion subphenotypes in both cecum and colon. Here we show that ability to detect a major C3H-derived QTL on Chr 3 (cytokine deficiency-induced colitis susceptibility 1, Cdcs1) was critically dependent upon the degree of refinement of the histopathologic scoring system. QTL mapping was performed using a first-back-cross population of interleukin-10-deficient mice and applying two different grading systems to assess lesion subphenotypes. The same histological specimens were scored by two independent pathologists using either a very detailed scoring system for four subphenotypes developed at The Jackson Laboratory (TJL) or a simpler scoring system developed at the Hannover Medical School (MHH). The more detailed TJL subphenotyping protocol increased power to identify Cdcs1 (a maximum LOD score of 4.28 versus a LOD score of 1.77 when using the abbreviated MHH subphenotyping scoring system). This study shows that for QTL mapping in a mouse model of colitis, in which histology represents the gold standard for phenotyping, ability to detect linkage is critically dependent upon the degree of refinement adopted for separately scoring the multiple histopathologic lesions comprising this complex phenotype.

Intraspecies variability in the dose-response relationship for Salmonella Enteritidis associated with genetic differences in cellular immune response

To evaluate the effects of differences in host cellular immunity, we studied the dose-response relationship for infection with Salmonella enterica serovar Enteritidis (SE) in two different rat strains, skewed towards T helper 1 (Th1, Lewis rats) or T helper 2 (Th2, Brown Norway rats) immunoregulation. Rats were exposed orally to different doses of SE after overnight starvation and neutralization of gastric acid. Animals were observed for clinical signs of disease, fecal excretion and SE load in spleen and cecum, histopathology of the cecum, hematology, and cellular and humoral immune responses. Exponential dose-response models were used for binary or continuous outcomes to analyze the experimental data. Cytokine patterns, antibody isotypes, and contact hypersensitivity tests confirmed that Lewis rats are Th1 prone, whereas Brown Norway rats are Th2 prone. The probability of infection per single SE cell was approximately 100 times higher in Brown Norway rats than in Lewis rats. Cellular immune responses were more pronounced in Lewis rats but antibody responses were higher in Brown Norway rats. When infected, colonization levels and inflammation are highest in the intestinal tract of Th2 skewed rats, but systemic infection is more intense in Th1 skewed rats. Successful colonization by only one or two SE clones resulted in a marked increase of neutrophil counts by a factor of two to three in both rat strains.

Bacteria-induced intestinal cancer in mice with disrupted Gpx1 and Gpx2 genes

Two glutathione peroxidase (GPX) isozymes, GPX-1 and GPX-2 (GPX-GI), are the major enzymes that reduce hydroperoxides in intestinal epithelium. We have previously demonstrated that targeted disruption of both the Gpx1 and Gpx2 genes (GPX-DKO) results in a high incidence of ileocolitis in mice raised under conventional conditions, which include the harboring of Helicobacter species [non-specific-pathogen-free (non-SPF) conditions]. In this study, we have characterized GPX-DKO mice that have microflora-associated intestinal cancers, which are correlated with increased intestinal pathology/inflammation. We found that GPX-DKO mice raised under germ-free conditions have virtually no pathology or tumors. After colonizing germ-free mice with commensal microflora without any known pathogens (SPF), <9% of GPX-DKO mice develop tumors in the ileum or the colon. However, about one-fourth of GPX-DKO mice raised under non-SPF conditions from birth or transferred from SPF conditions at weaning have predominantly ileal tumors. Nearly 30% of tumors are cancerous; most are invasive adenocarcinomas and a few signet-ring cell carcinomas. On the basis of these results, we conclude that GPX-DKO mice are highly susceptible to bacteria-associated inflammation and cancer. The sensitivity exhibited in these mice suggests that peroxidative stress plays an important role in ileal and colonic pathology and inflammation, which can lead to tumorigenesis.

Oral (gavage), in utero and post-natal exposure of Sprague–Dawley rats to low doses of tributyltin chloride

The immunotoxic effects of tributyltin chloride (TBTC) were examined in the offspring of Sprague-Dawley rats exposed in utero from day 8 of gestation, through lactation and post-weaning until pups reached the age of 30 days (male and female), 60 days (female) and 90 days (male). Daily oral (gavage) doses of 0.025, 0.25 and 2.5 mg/kg body weight/day were administered in olive oil 7 days/week. Immunologic endpoints were investigated at the termination of each study. Statistically significant results (P<0.05) included the following: At 30 days, the mean percent and absolute natural killer (NK) cell numbers were increased in male and female rats treated with the high TBTC dose. At 60 days, female rats had increased mean serum IgM levels at the low and high TBTC doses, increased mean percentage CD4(+)8(+) (immature) T lymphocytes at the middle and high doses, a non-linear dose-response increase in NK cell activity at the 50:1 and 100:1 effector:target cell ratios (pairwise comparisons significant at the low dose compared with control), and increased mean numbers of L. monocytogenes colony-forming bacteria on Day 2 post-infection (significant for trend) and Day 3 post infection (pairwise comparisons significant only in the middle dose). The 90-day male rats had decreased mean serum IgA levels at the middle dose group; increased IgM levels at the high dose group, increased IgG levels at the middle and high doses; decreased IgG2(a) in the high dose compared to the control; a dose-related increase in the mean percentage NK cell numbers (pairwise comparisons significant at the high dose compared with the control) and increased mean NK cell activity (pairwise comparisons significant at all dose groups compared with the control). The delayed-type hypersensitivity response to oxazolone was increased in the low and middle doses and decreased in the high dose. Thymus atrophy was observed in the high TBTC dose across all ages. Thus, in utero and post-natal treatment of F1 rats with low levels of TBTC affected some aspects of humoral and cell mediated immunity as well as the number and function of cells which are involved in the host's immunosurveillance mechanisms against tumours and viral infections.

Revised guides for organ sampling and trimming in rats and mice--part 1

This is the first part of a series of three articles on trimming instructions of rat and mouse protocol organs and tissues in regulatory type toxicity studies. It is based on the experience made in the European RITA and American NACAD working groups and is an extended revision of trimming guides published in 1995 (Bahnemann et al.). The optimum localization for tissue preparation, the sample size, the direction of sectioning and the number of sections to be prepared is described organ by organ. These descriptions are illustrated for each organ by a schematic drawing and a macro-photograph showing the plane of section as well as a low power view of the H&E stained slide demonstrating the optimum "end-product". This revision will improve the quality and efficiency of routine procedures and facilitate daily work in the histotechnical lab. It will promote intra- and inter-study reproducibility and comparability and thus lead to a further coherence within each study and improvement of the validity of historical control data.

In vivo production of hydroxyl radical by Enterococcus faecalis colonizing the intestinal tract using aromatic hydroxylation

Enterococcus faecalis is an intestinal commensal that produces extracellular superoxide (O(2)(*-)) through autoxidation of membrane-associated demethylmenaquinone. To assess free radical production by E. faecalis in vivo, intestinal tracts of rats were colonized using wild-type E. faecalis or a mutant strain with attenuated O(2)(*-) production. Ex vivo electron paramagnetic resonance spin trapping study of colonic contents (mean +/- SD) showed 1.4 +/- 1.5 and 0.094 +/- 0.24 microM 5,5-dimethyl-1-pyrroline-N-oxide-hydroxyl radical adduct/gm stool for rats colonized with wild-type and mutant strains, respectively (p = .002). In vivo hydroxyl radical production was further assayed by aromatic hydroxylation using phenyl N-tert-butylnitrone (PBN) and D-phenylalanine. Hydroxylated PBN and D-phenylalanine products were recovered from stool (microM/gm colonic contents/10(9) colony forming units) and urine (microM/h/ml), respectively, and quantified using electrochemical detection. Hydroxylated (OH) PBNs and isomeric tyrosines (hydroxylated phenylalanine) were significantly increased (mean +/- SD) for rats colonized with wild-type E. faecalis (2-OH PBN, 63 +/- 58; 3-OH PBN, 63 +/- 84; ortho-tyrosine, 31 +/- 27; meta-tyrosine, 17 +/- 14) compared to the mutant strain (2-OH PBN, 2.5 +/- 7.3 (p < .001); 3-OH PBN, 3.9 +/- 12.3 (p = .01); ortho-tyrosine, 1.9 +/- 6.0 (p < .001); meta-tyrosine, 1.5 +/- 3.4 (p = .03)). Similar differences were observed following in vitro incubations of these bacteria with aromatic targets. These results confirm in vivo production of hydroxyl radical by E. faecalis colonizing the intestine, and indicate this bacterium may be a potent source of oxidative stress on the intestinal epithelium.

Helicobacter bilis infection accelerates and H. hepaticus infection delays the development of colitis in multiple drug resistance-deficient (mdr1a-/-) mice

mdr1a-deficient mice lack P-glycoprotein and spontaneously develop colitis with age. Helicobacter spp. are gram-negative organisms that have been associated with colitis in certain mouse strains, but Helicobacter spp. have been excluded as contributing to the spontaneous colitis that develops in mdr1a-/- mice. We wished to determine whether infection with either H. bilis or H. hepaticus would accelerate the development of inflammatory bowel disease (IBD) in mdr1a-/- mice. We found that H. bilis infection induced diarrhea, weight loss, and IBD in mdr1a-/- mice within 6 to 17 weeks post-inoculation and before the expected onset of spontaneous IBD. Histopathology of H. bilis-induced IBD included crypt hyperplasia, inflammatory cell infiltrates, crypt abscesses, and obliteration of normal gut architecture. Reverse transcription-polymerase chain reaction and Taqman analysis from colonic tissue showed increased transcripts for interferon-gamma and interleukin-10 from H. bilis-infected colitic mdr1a-/- mice. Additionally, mesenteric lymph nodes had increased cellularity with expansion of CD4+ and CD8+ T cells and B cells and increased proliferation to soluble H. bilis antigens with elaboration of interferon-gamma, tumor necrosis factor-alpha and interleukin-10. In contrast, H. hepaticus infection of mdr1a-/- mice did not accelerate disease but rather delayed the onset of spontaneous colitis which was milder in severity. mdr1a-/- mice infected with Helicobacter spp. may provide a useful tool to explore the pathogenesis of microbial-induced IBD in a model with a presumed epithelial cell "barrier" defect.

Helicobacter-induced inflammatory bowel disease in IL-10- and T cell-deficient mice

Inflammatory bowel disease (IBD) is thought to result from a dysregulated mucosal immune response to luminal microbial antigens, with T lymphocytes mediating the colonic pathology. Infection with Helicobacter spp has been reported to cause IBD in immunodeficient mice, some of which lack T lymphocytes. To further understand the role of T cells and microbial antigens in triggering IBD, we infected interleukin (IL)-10(-/-), recombinase-activating gene (Rag)1(-/-), T-cell receptor (TCR)-alpha(-/-), TCR-beta(-/-), and wild-type mice with Helicobacter hepaticus or Helicobacter bilis and compared the histopathological IBD phenotype. IL-10(-/-) mice developed severe diffuse IBD with either H. bilis or H. hepaticus, whereas Rag1(-/-), TCR-alpha(-/-), TCR-beta(-/-), and wild-type mice showed different susceptibilities to Helicobacter spp infection. Proinflammatory cytokine mRNA expression was increased in the colons of Helicobacter-infected IL-10(-/-) and TCR-alpha(-/-) mice with IBD. These results confirm and extend the role of Helicobacter as a useful tool for investigating microbial-induced IBD and show the importance, but not strict dependence, of T cells in the development of bacterial-induced IBD.

A rat model for dose-response relationships of Salmonella Enteritidis infection

AIMS

To develop an animal model to study dose-response relationships of enteropathogenic bacteria.

METHODS AND RESULTS

Adult, male Wistar Unilever rats were exposed orally to different doses of Salmonella enterica serovar Enteritidis after overnight starvation and neutralization of gastric acid by sodium bicarbonate. The spleen was the most sensitive and reproducible organ for detection of dose-dependent systemic infection. Illness was only observed in animals exposed to doses of 10(8) cfu or more. At lower doses, histopathological changes in the gastro-intestinal tract were observed, but these were not accompanied by illness. Marked changes in numbers and types of white blood cells, as well as delayed-type hyperresponsiveness, indicated a strong, dose-dependent cellular immune response to Salm. Enteritidis.

CONCLUSION

The rat model is a sensitive and reproducible tool for studying the effects of oral exposure to Salm. Enteritidis over a wide dose range.

SIGNIFICANCE AND IMPACT OF THE STUDY

The rat model allows controlled quantification of different factors related to the host, pathogen and food matrix on initial stages of infection by food-borne bacterial pathogens.

Enhanced antigen-specific delayed-type hypersensitivity and immunoglobulin G2b responses after oral administration of viable Lactobacillus casei YIT9029 in Wistar and Brown Norway rats

In this study, the effects of orally administered viable Lactobacillus casei Shirota strain YIT9029 on the immunity parameters of Wistar and Brown Norway rats were examined. For this purpose, we used the Trichinella spiralis host resistance model. Two weeks before and during T. spiralis infection, rats were fed 10(9) viable L. casei bacteria 5 days per week. The T. spiralis-specific delayed-type hypersensitivity (DTH) response was significantly enhanced in both Wistar and Brown Norway rats given L. casei. In both rat strains fed L. casei, serum T. spiralis-specific immunoglobulin G2b (IgG2b) concentrations were also significantly increased. In the model, no significant effects of L. casei on larval counts or inflammatory reactions in the tongue musculature, body weights, or lymphoid organ weights were observed. Serum specific antibody responses, other than IgG2b, were not changed by feeding of L. casei. In contrast to L. casei, it was shown that orally administered Bifidobacterium breve or Bifidobacterium bifidum had no influence on the measured infection and immunity indices in the rat infection model. Since the rat DTH response is considered to be a manifestation of Th1 cell-mediated immunity and the IgG2b isotype has been associated with Th1 activity, it was concluded that Th1 cells could play an active role in the immunomodulatory effects of orally administered L. casei. Furthermore, our data do not indicate that the effect of oral supplementation with L. casei is dependent on the genetic background of the host.

Increased gut permeability and bacterial translocation in Pseudomonas pneumonia-induced sepsis

OBJECTIVE

Gut injury and barrier dysfunction may contribute to the pathogenesis of sepsis and multiple organ dysfunction syndrome. The objective of this study was to determine whether gut injury could be demonstrated in hyperdynamic, normotensive sepsis induced by Pseudomonas pneumonia.

DESIGN

Randomized animal study.

SETTING

University laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Sepsis was induced by intratracheal instillation of Pseudomonas aeruginosa.

MEASUREMENTS AND MAIN RESULTS

We measured gut mucosal and microvascular injury. In the first experiment, gut mucosal permeability was measured by 51Cr-EDTA uptake in control (n = 6), pneumonia 20-hr (n = 4), and pneumonia 40-hr (n = 4) groups. In the second experiment, microvascular permeability was measured by albumin extravasation, and morphologic abnormalities were scored in control (n = 6), pneumonia 20-hr (n = 9), and pneumonia 40-hr (n = 11) groups. Bacterial translocation to mesenteric lymph nodes was determined in both experiments. Cardiac index increased significantly in the pneumonia compared with control rats (64+/-2.1, 68+/-1.3, vs. 46+/-2 mL/min/100 g, p < .05; all results are listed in the order of pneumonia 20-hr, pneumonia 40-hr, and control groups as mean +/- SEM). Mean blood pressure was normal and was not different between groups (112+/-3, 111+/-2, vs. 118+/-2 mm Hg). 51Cr-EDTA recovery in urine 6 hrs after gavage increased significantly in both pneumonia groups vs. controls (17.5+/-2.2%, 17.9+/-7%, vs. 4+/-0.7%; p < .05). Albumin leak (tissue/plasma ratio) increased significantly in the middle and distal small intestine in the pneumonia 40-hr group vs. controls (0.68+/-0.05, 0.76+/-0.07, vs. 0.45+/-0.04, p < .05 in the middle small gut; 0.75+/-0.09, 0.85+/-0.07, vs. 0.51+/-0.05, p < .05 in the distal small gut). Bacterial translocation to mesenteric lymph nodes increased significantly in pneumonia 40-hr rats vs. controls (positive culture 67% vs. 8%; p < .05).

CONCLUSIONS

This study demonstrates gut mucosal and microvascular injury and gut barrier dysfunction in normotensive sepsis secondary to bacterial pneumonia. The mechanism and significance of the injury need to be determined.

Digestive System 1

This chapter deals with the digestive system. The major and minor salivary glands and their secretions also represent and integral part of the protective mechanism of the oral cavity, and derangement of saliva production may lead to loss of integrity of the oral mucosa. Drug-induced abnormalities of taste sensation are also well-described phenomena occurring in man although human studies are necessary for the detection of these effects. Inflammation of the oral cavity may involve the buccal mucosa, the gingiva (gingivitis), the tongue (glossitis), and the peridontal tissues (peridontitis). Therapeutic agents can induce inflammatory lesions in the tongue. Moreover, a protective layer of mucus, a visco-elastic material containing high molecular weight glycoproteins produced by the major and minor salivary glands, covers the stratified squamous mucosa of the oral cavity. Salivary secretions also possess digestive enzyme activity although in herbivores and carnivores, it is usually low in contrast to high digestive enzyme activity in omnivorous species.

Cyclooxygenase-2-dependent arachidonic acid metabolites are essential modulators of the intestinal immune response to dietary antigen

Intestinal inflammatory diseases are mediated by dysregulated immune responses to undefined luminal antigens. Feeding hen egg-white lysozyme to mice expressing a transgenic T-cell receptor that recognizes hen egg-white lysozyme peptide 46-61 resulted in no intestinal pathology; however, simultaneous administration of cyclooxygenase-2 inhibitors and dietary hen egg-white lysozyme resulted in increased proliferation of lamina propria mononuclear cells and crypt epithelial cells, crypt expansion and villus blunting. Lamina propria mononuclear cells produce high levels of cyclooxygenase-2-dependent arachidonic acid metabolites, which act as immunomodulators in the immune response to dietary antigen. These findings establish that cyclooxygenase-2-dependent arachidonic acid metabolites are essential in the development and maintenance of intestinal immune homeostasis.

Intestinal T lymphocytes of different rat strains in immunotoxicity

In order to study the intestinal mucosal immune cells, with emphasis on single T lymphocytes, an inventory was made of single and organized lymphocytes in the epithelium and lamina propria of the small intestines of untreated Wistar, Fischer 344, and Lewis rats. The single and organized lymphocytes were examined microscopically. In addition, the single lymphocytes in the epithelium (IEL) and lamina propria (LPL) were analyzed by flow cytometry. Next, the use of flow cytometry analysis was explored to detect changes in the IEL T-lymphocyte population in subacute oral studies with the immunomodulating agents azathioprine and hexachlorobenzene. Untreated random-bred Wistar rats exhibited a large interindividual variability in IEL composition, while the variability was small in inbred Fischer 344 and Lewis rats. The explorative study with the 2 model immunomodulating compounds demonstrated that hexachlorobenzene increased the number of intraepithelial T lymphocytes with CD8+ phenotype at the cost of T cells with CD4+ phenotype in Lewis rats. Azathioprine did not induce distinct effects on the percentages of IEL. The data indicate that the intraepithelial lymphocytes in the intestines are a potential target for orally administered immunomodulating compounds and should therefore receive more attention in toxicologic pathology studies.