Systemic uptake and intestinal inflammatory effects of luminal bacterial cell wall polymers in rats with acute colonic injury

Macrophages-microenvironment crosstalk in fibrostenotic inflammatory bowel disease: from basic mechanisms to clinical applications

INTRODUCTION

Intestinal fibrosis is a common complication of Inflammatory Bowel Disease (IBD) with no available drugs. The current therapeutic principle is surgical intervention as the core. Intestinal macrophages contribute to both the progression of inflammation and fibrosis. Understanding the role of macrophages in the intestinal microenvironment could bring new hope for fibrosis prevention or even reversal.

AREAS COVERED

This article reviewed the most relevant reports on macrophage in the field of intestinal fibrosis. The authors discussed current opinions about how intestinal macrophages function and interact with surrounding mediators during inflammation resolution and fibrostenotic IBD. Based on biological mechanisms findings, authors summarized related clinical trial outcomes.

EXPERT OPINION

The plasticity of intestinal macrophages allows them to undergo dramatic alterations in their phenotypes or functions when exposed to gastrointestinal environmental stimuli. They exhibit distinct metabolic characteristics, secrete various cytokines, express unique surface markers, and transmit different signals. Nevertheless, the specific mechanism through which the intestinal macrophages contribute to intestinal fibrosis remains unclear. It should further elucidate a novel therapeutic approach by targeting macrophages, especially distinct mechanisms in specific subgroups of macrophages involved in the progression of fibrogenesis in IBD.

Contribution of the Gut Microbiota to Intestinal Fibrosis in Crohn's Disease

In Crohn's disease (CD), intestinal fibrosis is a critical determinant of a patient's prognosis. Although inflammation may be a prerequisite for the initiation of intestinal fibrosis, research shows that the progression or continuation of intestinal fibrosis can occur independently of inflammation. Thus, once initiated, intestinal fibrosis may persist even if medical treatment controls inflammation. Clearly, an understanding of the pathophysiological mechanisms of intestinal fibrosis is required to diminish its occurrence. Accumulating evidence suggests that the gut microbiota contributes to the pathogenesis of intestinal fibrosis. For example, the presence of antibodies against gut microbes can predict which CD patients will have intestinal complications. In addition, microbial ligands can activate intestinal fibroblasts, thereby inducing the production of extracellular matrix. Moreover, in various animal models, bacterial infection can lead to the development of intestinal fibrosis. In this review, we summarize the current knowledge of the link between intestinal fibrosis in CD and the gut microbiota. We highlight basic science and clinical evidence that the gut microbiota can be causative for intestinal fibrosis in CD and provide valuable information about the animal models used to investigate intestinal fibrosis.

Characterization and Analysis of the Temporal and Spatial Dynamic of Several Enteritis Modeling Methodologies

Inflammatory bowel disease (IBD), such as Crohn’s disease and ulcerative colitis, is a complex disease involving genetic, immune, and microbiological factors. A variety of animal models of IBD have been developed to study the pathogenesis of human IBD, but there is no model that can fully represent the complexity of IBD. In this study, we established two acute enteritis models by oral 3% DSS or intraperitoneal injection of anti-CD3 antibody, and two chronic enteritis models by feeding 3 cycles of 1.5% DSS or 3 months of the high-fat diet, respectively, and then examined the clinical parameters, histological changes, and cytokine expression profiles after the successful establishment of the models. Our results indicated that in 3% DSS-induced acute enteritis, the colorectal injury was significantly higher than that of the small intestine, while in anti-CD3 antibody-induced acute enteritis, the small intestine injury was significantly higher than that of colorectal damage. Besides, in the 1.5% DSS-induced chronic enteritis, the damage was mainly concentrated in the colorectal, while the damage caused by long-term HFD-induced chronic enteritis was more focused on the small intestine. Therefore, our work provides a reference for selecting appropriate models when conducting research on factors related to the pathogenesis of IBD or evaluating the potential diagnosis and treatment possibilities of pharmaceuticals.

Innate lymphoid cells in organ fibrosis

Innate lymphoid cells (ILCs) are a recently identified family of lymphoid effector cells. ILCs are mainly clustered into 3 groups based on their unique cytokine profiles and transcription factors typically attributed to the subsets of T helper cells. ILCs have a critical role in the mucosal immune response through promptly responding to pathogens and producing large amount of effector cytokines of type 1, 2, or 3 responses. In addition to the role of early immune responses against infections, ILCs, particularly group 2 ILCs (ILC2), have recently gained attention for modulating remodeling and fibrosis especially in the mucosal tissues. Herein, we overview the current knowledge in this area, highlighting roles of ILCs on fibrosis in the mucosal tissues, especially focusing on the gut and lung. We also discuss some new directions for future research by extrapolating from knowledge derived from studies on Th cells.

The hepatocyte as a microbial product-responsive cell

Much research has focused on the responses to microbial products of immune cells such as monocytes, macrophages, and neutrophils. Although the liver is a primary response organ in various infections, relatively little is known about the antimicrobial responses of its major cell type, the hepatocyte. It is now known that the recognition of bacteria occurs via cell-surface proteins that are members of the Toll-like receptor (TLR) family. In addition, lipopolysaccharide (LPS) is bound by circulating LPS-binding protein (LBP) and presented to cell-surface CD14, which in turn interacts with TLR and transduces an intracellular signal. We investigated the CD14 and TLR2 responses of whole liver and isolated hepatocytes, and demonstrated that these cells can be induced to express the molecules necessary for responses to both Gram-positive and Gram-negative bacteria. Our findings may have clinical implications for pathological states such as sepsis.

Alterations of colonic contractility in an interleukin-10 knockout mouse model of inflammatory bowel disease

Background/Aims

Inflammatory bowel disease is commonly accompanied by colonic dysmotility and causes changes in intestinal smooth muscle contractility. In this study, colonic smooth muscle contractility in a chronic inflammatory condition was investigated using smooth muscle tissues prepared from interleukin-10 knockout (IL-10^−/−) mice.

Methods

Prepared smooth muscle sections were placed in an organ bath system. Cholinergic and nitrergic neuronal responses were observed using carbachol and electrical field stimulation with L-NG-nitroarginine methyl ester (L-NAME). The expression of interstitial cells of Cajal (ICC) networks, muscarinic receptors, neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) was observed via immunofluorescent staining.

Results

The spontaneous contractility and expression of ICC networks in the proximal and distal colon was significantly decreased in IL-10^−/− mice compared to IL-10^+/+ mice. The contractility in response to carbachol was significantly decreased in the proximal colon of IL-10^−/− mice compared to IL-10^+/+ mice, but no significant difference was found in the distal colon. In addition, the expression of muscarinic receptor type 2 was reduced in the proximal colon of IL-10^−/− mice. The nictric oxide-mediated relaxation after electrical field stimulation was significantly decreased in the proximal and distal colon of IL-10^−/− mice. In inflamed colon, the expression of nNOS decreased, whereas the expression of iNOS increased.

Conclusions

These results suggest that damage to the ICC network and NOS system in the proximal and distal colon, as well as damage to the smooth muscle cholinergic receptor in the proximal colon may play an important role in the dysmotility of the inflamed colon.

Microbiota signalling through MyD88 is necessary for a systemic neutrophilic inflammatory response

In the present study, we have found that intestinal flora strongly influence peritoneal neutrophilic inflammatory responses to diverse stimuli, including pathogen-derived particles like zymosan and sterile irritant particles like crystals. When germ-free and flora-deficient (antibiotic-treated) mice are challenged with zymosan intraperitoneally, neutrophils are markedly impaired in their ability to extravasate from blood into the peritoneum. In contrast, in these animals, neutrophils can extravasate in response to an intraperitoneal injection of the chemokine, macrophage inflammatory protein 2. Neutrophil recruitment upon inflammatory challenge requires stimulation by microbiota through a myeloid differentiation primary response gene (88) (MyD88) -dependent pathway. MyD88 signalling is crucial during the development of the immune system but depending upon the ligand it may be dispensable at the time of the actual inflammatory challenge. Furthermore, pre-treatment of flora-deficient mice with a purified MyD88-pathway agonist is sufficient to restore neutrophil migration. In summary, this study provides insight into the role of gut microbiota in influencing acute inflammation at sites outside the gastrointestinal tract.

Protective effects of N-acetylcysteine on acetic acid-induced colitis in a porcine model

Background

Ulcerative colitis is a chronic inflammatory disease and involves multiple etiological factors. Acetic acid (AA)-induced colitis is a reproducible and simple model, sharing many characteristics with human colitis. N-acetylcysteine (NAC) has been widely used as an antioxidant in vivo and in vitro. NAC can affect several signaling pathways involving in apoptosis, angiogenesis, cell growth and arrest, redox-regulated gene expression, and inflammatory response. Therefore, NAC may not only protect against the direct injurious effects of oxidants, but also beneficially alter inflammatory events in colitis. This study was conducted to investigate whether NAC could alleviate the AA-induced colitis in a porcine model.

Methods

Weaned piglets were used to investigate the effects of NAC on AA-induced colitis. Severity of colitis was evaluated by colon histomorphology measurements, histopathology scores, tissue myeloperoxidase activity, as well as concentrations of malondialdehyde and pro-inflammatory mediators in the plasma and colon. The protective role of NAC was assessed by measurements of antioxidant status, growth modulator, cell apoptosis, and tight junction proteins. Abundances of caspase-3 and claudin-1 proteins in colonic mucosae were determined by the Western blot method. Epidermal growth factor receptor, amphiregulin, tumor necrosis factor-alpha (TNF-α), and toll-like receptor 4 (TLR4) mRNA levels in colonic mucosae were quantified using the real-time fluorescent quantitative PCR.

Results

Compared with the control group, AA treatment increased (P < 0.05) the histopathology scores, intraepithelial lymphocyte (IEL) numbers and density in the colon, myeloperoxidase activity, the concentrations of malondialdehyde and pro-inflammatory mediators in the plasma and colon, while reducing (P < 0.05) goblet cell numbers and the protein/DNA ratio in the colonic mucosa. These adverse effects of AA were partially ameliorated (P < 0.05) by dietary supplementation with NAC. In addition, NAC prevented the AA-induced increase in caspase-3 protein, while stimulating claudin-1 protein expression in the colonic mucosa. Moreover, NAC enhanced mRNA levels for epidermal growth factor and amphiregulin in the colonic mucosa.

Conclusion

Dietary supplementation with NAC can alleviate AA-induced colitis in a porcine model through regulating anti-oxidative responses, cell apoptosis, and EGF gene expression.

Development of a peptidoglycan-polysaccharide murine model of Crohn's disease: effect of genetic background

The peptidoglycan-polysaccharide (PGPS) model using inbred rats closely mimics Crohn's disease. Our aim was to identify mouse strains that develop ileocolitis in response to bowel wall injection with PGPS. Mouse strains studied included NOD2 knockout animals, RICK/RIP2 knockout animals, and genetically inbred strains that are susceptible to inflammation. Mice underwent laparotomy with intramural injection of PGPS or human serum albumin in the terminal ileum, ileal Peyer's patches, and cecum. Gross abdominal score, cecal histologic score, and levels of pro-fibrotic factor mRNAs were determined 20 to 32 days after laparotomy. PGPS-injected wild-type and knockout mice with mutations in the NOD2 pathway had higher abdominal scores than human serum albumin-injected mice. The RICK knockout animals tended to have higher mean abdominal scores than the NOD2 knockout animals, but the differences were not significant. CBA/J mice were shown to have the most robust response to PGPS, demonstrating consistently higher abdominal scores than other strains. Animals killed on day 26 had an average gross abdominal score of 6.1 ± 1.5, compared with those on day 20 (3.0 ± 0.0) or day 32 (2.8 ± 0.9). PGPS-injected CBA/J mice studied 26 days after laparotomy developed the most robust inflammation and most closely mimicked the PGPS rat model and human Crohn's disease.

Animal models of intestinal fibrosis: new tools for the understanding of pathogenesis and therapy of human disease

Fibrosis is a serious condition complicating chronic inflammatory processes affecting the intestinal tract. Advances in this field that rely on human studies have been slow and seriously restricted by practical and logistic reasons. As a consequence, well-characterized animal models of intestinal fibrosis have emerged as logical and essential systems to better define and understand the pathophysiology of fibrosis. In point of fact, animal models allow the execution of mechanistic studies as well as the implementation of clinical trials with novel, pathophysiology-based therapeutic approaches. This review provides an overview of the currently available animal models of intestinal fibrosis, taking into consideration the methods of induction, key characteristics of each model, and underlying mechanisms. Currently available models will be classified into seven categories: spontaneous, gene-targeted, chemical-, immune-, bacteria-, and radiation-induced as well as postoperative fibrosis. Each model will be discussed in regard to its potential to create research opportunities to gain insights into the mechanisms of intestinal fibrosis and stricture formation and assist in the development of effective and specific antifibrotic therapies.

Effects of Bifidobacterium infantis 35624 on post-inflammatory visceral hypersensitivity in the rat

BACKGROUND

Irritable bowel syndrome patients have abnormal visceral perception. Probiotic organisms may produce beneficial effects in these patients by reducing visceral hypersensitivity.

AIM

To investigate the effects of the probiotic organism, Bifidobacterium infantis 35624, on post-inflammatory visceral hypersensitivity in rats.

METHODS

Colitis was induced using intracolonic administration of trinitrobenzenesulfonic acid; control rats received saline (day 0). Myeloperoxidase (MPO) levels and colonic damage scores were determined. From days 15-29, rats (n = 10/group) rats were orally dosed with 2 ml of B. infantis ≥ 10(8) colony-forming units/ml or vehicle (MRS broth). A second series of rats (n = 10/group) was dosed in the same manner from days 15-59. The level of colonic stimulation during colorectal distension (CRD) was determined by recording a visceromotor response (VMR) to CRD at 30 mmHg pre- and post-treatment. Post-treatment samples of colonic tissue were weighed, graded for morphologic damage, and assayed for MPO levels.

RESULTS

All rats were hypersensitive at day 15. On day 30, hypersensitivity to colorectal distension remained in the vehicle group, but was significantly reduced in the B. infantis group (mean VMR/10 min: vehicle = 15.4 ± 1.0 vs. B. infantis = 7.6 ± 1.0, p < 0.001). A similar, significant effect was observed at day 60. On both day 30 and day 60, tissue weight, colonic damage scores, and MPO levels resembled those of control animals.

CONCLUSIONS

Oral administration of Bifidobacterium infantis 35624 normalized sensitivity to colorectal distension in a rat model of post-inflammatory colonic hypersensitivity.

Impact of experimental colitis on hepatobiliary transporter expression and bile duct injury in mice

BACKGROUND AND AIMS

The pathogenetic link between ulcerative colitis and sclerosing cholangitis (SC) is unclear. We hypothesized that colitis induces changes in bile composition via inflammation-induced reduction of hepatobiliary transporter gene expression, ultimately resulting in cholestasis and bile duct injury.

METHODS

Alterations in transporter expression and bile secretion in acute dextran sulphate sodium (DSS)-induced colitis were compared with lipopolysaccharide (LPS)-treated mice serving as positive control. Whether chronic DSS-colitis elicits cholangitis in genetically predisposed animals was studied in heterozygous multidrug resistance gene 2 knockout mice (Mdr2(+/-)).

RESULTS

LPS but not DSS-colitis changed major hepatobiliary transporters (Ntcp, Bsep, Mrp2-4, Ostalpha/beta, Abcg5/8, Oatp1-4, Mdr1b and Mdr2), enzymes (Cyp3a11 and Cyp7a1), nuclear receptors (RXRalpha, FXR, CAR and PXR) and proinflammatory mediators (tumour necrosis factor alpha and inducible nitric oxide synthase). Formation of toxic bile reflected by an increased bile acid/phospholipid ratio was observed neither in acute nor in chronic colitis, although heterozygous Mdr2(+/-) mice developed mild portal inflammation after chronic colitis.

CONCLUSIONS

In contrast to LPS, DSS-colitis has a minor impact on hepatobiliary gene expression and bile secretion. Therefore, intestinal inflammation-associated changes of hepatobiliary transporter expression do not play a pathogenetic role in SC.

Temporal and spatial analysis of clinical and molecular parameters in dextran sodium sulfate induced colitis

Background

Inflammatory bowel diseases (IBD), including mainly ulcerative colitis (UC) and Crohn's disease (CD), are inflammatory disorders of the gastrointestinal tract caused by an interplay of genetic and environmental factors. Murine colitis model induced by Dextran Sulfate Sodium (DSS) is an animal model of IBD that is commonly used to address the pathogenesis of IBD as well as to test efficacy of therapies. In this study we systematically analyzed clinical parameters, histological changes, intestinal barrier properties and cytokine profile during the colitic and recovery phase.

Methods

C57BL/6 mice were administered with 3.5% of DSS in drinking water for various times. Clinical and histological features were determined using standard criteria. Myeloperoxidase (MPO) activity, transepithelial permeability and proinflammatory mediators were determined in whole colon or proximal and distal parts of colon.

Results

As expected after administration of DSS, mice manifest loss of body weight, shortening of colon length and bloody feces. Histological manifestations included shortening and loss of crypts, infiltration of lymphocytes and neutrophil, symptoms attenuated after DSS withdrawal. The MPO value, as inflammation indicator, also increases significantly at all periods of DSS treatment, and even after DSS withdrawal, it still held at very high levels. Trans-mucosal permeability increased during DSS treatment, but recovered to almost control level after DSS withdrawal. The production of proinflammatory mediators by colonic mucosa were enhanced during DSS treatment, and then recovered to pre-treated level after DSS withdrawal. Finally, enhanced expression of proinflammatory mediators also revealed a different profile feature in proximal and distal parts of the colon.

Conclusion

Experimental colitis induced by DSS is a good animal model to study the mechanisms underlying the pathogenesis and intervention against IBD, especially UC.

Bacterial peptidoglycan triggers Candida albicans hyphal growth by directly activating the adenylyl cyclase Cyr1p

Human serum potently induces hyphal development of the polymorphic fungal pathogen Candida albicans, a phenotype that contributes critically to infections. The fungal adenylyl cyclase Cyr1p is a key component of the cAMP/PKA-signaling pathway that controls diverse infection-related traits, including hyphal morphogenesis. However, identity of the serum hyphal inducer(s) and its fungal sensor remain unknown. Our initial analyses of active serum fractions revealed signs of bacterial peptidoglycan (PGN)-like molecules. Here, we show that several purified and synthetic muramyl dipeptides (MDPs), subunits of PGN, can strongly promote C. albicans hyphal growth. Analogous to PGN recognition by the mammalian sensors Nod1 and Nod2 through their leucine-rich-repeat (LRR) domain, we show that MDPs activate Cyr1p by directly binding to its LRR domain. Given the abundance of PGN in the intestine, a natural habitat and invasion site for C. albicans, our findings have important implications for the mechanisms of infection by this pathogen.

Microbial influences in inflammatory bowel diseases

The predominantly anaerobic microbiota of the distal ileum and colon contain an extraordinarily complex variety of metabolically active bacteria and fungi that intimately interact with the host's epithelial cells and mucosal immune system. Crohn's disease, ulcerative colitis, and pouchitis are the result of continuous microbial antigenic stimulation of pathogenic immune responses as a consequence of host genetic defects in mucosal barrier function, innate bacterial killing, or immunoregulation. Altered microbial composition and function in inflammatory bowel diseases result in increased immune stimulation, epithelial dysfunction, or enhanced mucosal permeability. Although traditional pathogens probably are not responsible for these disorders, increased virulence of commensal bacterial species, particularly Escherichia coli, enhance their mucosal attachment, invasion, and intracellular persistence, thereby stimulating pathogenic immune responses. Host genetic polymorphisms most likely interact with functional bacterial changes to stimulate aggressive immune responses that lead to chronic tissue injury. Identification of these host and microbial alterations in individual patients should lead to selective targeted interventions that correct underlying abnormalities and induce sustained and predictable therapeutic responses.

NOD2 transgenic mice exhibit enhanced MDP-mediated down-regulation of TLR2 responses and resistance to colitis induction

BACKGROUND & AIMS

Mutations in the CARD15 gene encoding NOD2 are susceptibility factors in Crohn's disease. We explored the mechanism of this susceptibility using mice that over express NOD2.

METHODS

Cellular and molecular responses of mice bearing an NOD2 transgene or administered plasmids that express wild-type and mutated NOD2 constructs were examined.

RESULTS

In initial studies, we showed that splenocytes from NOD2 transgenic mice as compared with littermate controls exhibit decreased interleukin (IL)-12p70 responses to peptidoglycan (PGN), a TLR2 ligand that contains muramyl dipeptide, but not other TLR ligands; in contrast, IL-12 responses to PAM(3)CSK(4), a TLR2 ligand that does not contain muramyl dipeptide, were normal. Similarly, transgenic mice as compared with controls exhibited greatly decreased IL-12p40 responses to intraperitoneal administration of PGN but not to lipopolysaccharide. In further studies, we showed using electrophoretic mobility shift assay that PGN-stimulated cells from transgenic mice exhibited decreased activation of nuclear factor kappaB. Finally, in a series of studies on the effect of the NOD2 on susceptibility to induced colitis, we found that (1) transgenic mice were highly resistant to induction of PGN colitis and partially resistant to induction of trinitrobenzene sulfonic acid (TNBS) colitis and (2) mice administered a plasmid expressing a wild-type NOD2 gene were completely resistant to TNBS colitis whereas mice administered a plasmid expressing an NOD2 gene with the Crohn's disease frameshift mutation were only slightly resistant to TNBS colitis.

CONCLUSIONS

These data offer new evidence that NOD2 mutations contribute to inflammatory bowel disease by causing excessive TLR2 cytokine responses.

Animal models of inflammatory bowel disease

In inflammatory bowel disease (IBD), experimental models have proven to be important tools for detecting potential therapeutic agents and for investigating the mechanisms of pathogenesis. This review is intended to cover recent advances in basic IBD model applications. The use of more than 20 animal models has allowed the detection of numerous protective pharmacological agents, including a number of immunomodulatory agents that have entered the therapeutic armamentarium. The models have been classified into five main categories based on the methods of induction: gene knockout (KO), transgenic, chemical, adoptive transfer, and spontaneous (each with subcategories).

Basic aspects and pharmacology of probiotics: an overview of pharmacokinetics, mechanisms of action and side-effects

Probiotics have been defined as non-pathogenic micro-organisms that, when ingested, exert a positive influence on host health or physiology. Their pharmacology is more complex than that of inert drugs but is now being studied in detail. Some strains have a high survival capacity until they reach the faeces, whereas others are rapidly killed by acid and bile (a characteristic that can be used for the delivery of active intracellular components). Potential translocation and permanent colonization are rare but possible events; and should come under closer scrutiny. Mechanisms of action can be direct or indirect through modifications of the endogenous flora or through immunomodulation. The active components are poorly known but include bacterial formylated peptides, peptidoglycan cell wall constituents and nucleotides. Although the safety of commercial probiotics is excellent, this aspect should be studied in more detail, especially in immunocompromised hosts.

Dietary glycine prevents peptidoglycan polysaccharide-induced reactive arthritis in the rat: role for glycine-gated chloride channel

Peptidoglycan polysaccharide (PG-PS) is a primary structural component of bacterial cell walls and causes rheumatoid-like arthritis in rats. Recently, glycine has been shown to be a potential immunomodulator; therefore, the purpose of this study was to determine if glycine would be protective in a PG-PS model of arthritis in vivo. In rats injected with PG-PS intra-articularly, ankle swelling increased 21% in 24 to 48 h and recovered in about 2 weeks. Three days prior to reactivation with PG-PS given intravenously (i.v.), rats were divided into two groups and fed a glycine-containing or nitrogen-balanced control diet. After i.v. PG-PS treatment joint swelling increased 2.1 +/- 0.3 mm in controls but only 1.0 +/- 0.2 mm in rats fed glycine. Infiltration of inflammatory cells, edema, and synovial hyperplasia in the joint were significantly attenuated by dietary glycine. Tumor necrosis factor alpha (TNF-alpha) mRNA was detected in ankle homogenates from rats fed the control diet but not in ankles from rats fed glycine. Moreover, intracellular calcium was increased significantly in splenic macrophages treated with PG-PS; however, glycine blunted the increase about 50%. The inhibitory effect of glycine was reversed by low concentrations of strychnine or chloride-free buffer, and it increased radiolabeled chloride influx nearly fourfold, an effect also inhibited by strychnine. In isolated splenic macrophages, glycine blunted translocation of the p65 subunit of NF-kappaB into the nucleus, superoxide generation, and TNF-alpha production caused by PG-PS. Further, mRNA for the beta subunit of the glycine receptor was detected in splenic macrophages. This work supports the hypothesis that glycine prevents reactive arthritis by blunting cytokine release from macrophages by increasing chloride influx via a glycine-gated chloride channel.

IL-2-deficient mice raised under germfree conditions develop delayed mild focal intestinal inflammation

Interleukin-2 (IL-2) amplifies immune stimuli and influences B cell differentiation. IL-2-deficient mice spontaneously develop intestinal inflammation if raised under specific pathogen-free (SPF) conditions. We quantitatively determined the aggressiveness and kinetics of gastrointestinal and hepatic inflammation in the presence or absence of viable bacteria in IL-2-deficient mice. Breeding colonies were maintained under SPF and germfree (GF) conditions. Intestinal tissues, serum, and mesenteric lymph nodes were obtained from mice at different ages for blind histological scoring, immunoglobulin measurements, mucosal T cell infiltration, and cytokine secretion. GF IL-2 -/- mice developed mild, focal, and nonlethal intestinal inflammation with delayed onset, whereas the more aggressive inflammation in SPF IL-2 -/- mice led to their death between 28 and 32 wk. Periportal hepatic inflammation was equal in the presence or absence of bacterial colonization. Intestinal immunoglobulin secretion decreased significantly by 13 wk of age in IL-2 -/- mice in both GF and SPF environments. In contrast to other genetically engineered rodents, IL-2 -/- mice develop mild focal gastrointestinal and active portal tract inflammation in the absence of viable bacteria.

Review article: Role of the enteric microflora in the pathogenesis of intestinal inflammation and arthritis

Strong associations exist between intestinal inflammation and arthritis, ranging from infections with enteric pathogens to idiopathic inflammatory bowel disease. Increased exposure of the lamina propia and systemic circulation to enteric microflora and their products are a result of increased proliferation of the luminal bacteria, pathogenic invasion or enhanced mucosal permeability. Data suggest that anaerobic bacteria and other constituents of the normal luminal microbial flora induce and sustain chronic intestinal inflammation and arthritis. However, the normal host develops a tolerance to such bacteria and maintains homeostasis through a controlled inflammatory response and an almost impermeable mucosal barrier.

Effect of cyclo-oxygenase inhibition on in vitro B-cell function after burn injury

The role of PGE2 in suppression of B-cell function after burn injury was investigated. Splenocytes from burned or sham-burned mice were isolated 8 days after burn injury and cultured with lipopolysaccharide with or without the addition of prostaglandin E2 (PGE2) or indomethacin (Indo). Anti-peptidoglycan polysaccharide immunoglobulin (Ig)M (specific antibody to a bacterial antigen), total IgM, and total IgG levels in culture supernatant and lymphocyte proliferation were measured. All B-cell functions were significantly suppressed by burn injury. PGE2 suppressed all B-cell functions except for IgG synthesis. Indo restored anti-peptidoglycan polysaccharide IgM to normal levels, but did not have a significant effect on suppressed proliferation and total IgM synthesis. IgG synthesis was increased by PGE2 and inhibited by Indo. Although not all B-cell suppression was accounted for by PGE2, this prostaglandin appeared to be a mechanism responsible for impaired antigen specific antibody response and isotype switching. Successful restoration of specific antibody synthesis to bacterial antigen suggests a potential therapeutic role for a cyclo-oxygenase blocking agent after burn injury.

Normal luminal bacteria, especially Bacteroides species, mediate chronic colitis, gastritis, and arthritis in HLA-B27/human beta2 microglobulin transgenic rats

Genetic and environmental factors are important in the pathogenesis of clinical and experimental chronic intestinal inflammation. We investigated the influence of normal luminal bacteria and several groups of selected bacterial strains on spontaneous gastrointestinal and systemic inflammation in HLA-B27 transgenic rats. Rats maintained germfree for 3-9 mo were compared with littermates conventionalized with specific pathogen-free bacteria. Subsequently, germfree transgenic rats were colonized with groups of five to eight bacteria that were either facultative or strictly anaerobic. Transgenic germfree rats had no gastroduodenitis, colitis, or arthritis, but developed epididymitis and dermatitis to the same degree as conventionalized rats. Colonic proinflammatory cytokine expression was increased in transgenic conventionalized rats but was undetectable in germfree and nontransgenic rats. Colitis progressively increased over the first 4 wk of bacterial exposure, then plateaued. Only transgenic rats colonized with defined bacterial cocktails which contained Bacteroides spp. had colitis and gastritis. Normal luminal bacteria predictably and uniformly induce chronic colonic, gastric and systemic inflammation in B27 transgenic F344 rats, but all bacterial species do not have equal activities.

Animal models of intestinal and joint inflammation

Recent rodent models have been exploited to explore mechanisms of intestinal and joint inflammation. HLA-B27 transgenic rats develop colitis, gastritis, and arthritis when raised in a conventional environment, but have no evidence of inflammation under germfree (sterile) conditions. Metronidazole treatment attenuates gastrointestinal inflammation, suggesting that anaerobic bacteria are important. Experimental bacterial over-growth of predominantly anaerobic bacteria reactivates arthritis in Lewis rats which have been previously injected intra-articularly with bacterial cell wall polymers. Reactivation arthritis is mediated by interleukin-1, tumour necrosis factor-alpha, and can be blocked by metronidazole. Intramural injection of the bacterial cell wall polymer, peptidoglycan-polysaccharide, leads to biphasic, chronic granulomatous enterocolitis and peripheral arthritis in Lewis rats, but only transient intestinal inflammation and no arthritis in Buffalo or MHC-matched Fischer rats. Chronic granulomatous inflammation is mediated by T lymphocytes and interleukin-1 and is dependent on persistent antigenic stimulation by poorly biodegradable bacterial polymers. Results in these models firmly incriminate resident normal enteric flora (especially anaerobes), bacterial products, and host genetic susceptibility in the pathogenesis of spondyloarthropathies. We suggest that increased uptake of luminal bacterial components across the inflamed mucosa leads to systemic distribution of these arthropathic products. The genetically susceptible host develops reactive arthritis due to defective downregulation of inflammation in response to immunologically active bacterial components.

Increased permeability occurs in rat ileum following induction of pan-colitis

Acetic acid-induced pan colitis in rats leads not only to colonic injury but also to a bystander ileal injury, characterized by decreased fluid and electrolyte absorption without associated histological injury or infiltration of inflammatory cells. To examine the nature of this decreased ileal fluid and electrolyte absorption, we measured effect of acetic acid-induced pancolitis on ileal transmural sodium and chloride transport, as well as on ileal permeability to mannitol and inulin on mucosal sheets mounted in Ussing chambers. In addition, ileal tight junctional morphology was assessed by electron microscopy. In colitic animals, ileal serosal-to-mucosal sodium and chloride transmural fluxes were increased (P<0.05); compatible with the observed decrease in net fluid absorption. Mannitol and inulin ileal serosal-to-mucosal and mucosal-to-serosal ileal fluxes were similarly increased (P<0.05), suggesting that an increase in ileal permeability occurred during acetic acid-induced pancolitis. This increase in ileal permeability was not accompanied by changes in tight junctional ultrastructure. These results suggest that: (1) the decrease in ileal fluid and electrolyte absorption seen during acetic acid-induced rat pancolitis occurred in parallel with a rise in both transcellular and paracellular permeability, and (2) the ileal permeability changes were not accompanied by structural changes.

Endotoxaemia and cytokine production in experimental colitis

Systemic endotoxaemia is a well recognized feature of inflammatory bowel disease but its pathogenic role remains uncertain. This study examined plasma endotoxin and cytokine concentrations and the acute-phase protein response in a hapten-induced model of experimental colitis. On days 2, 8 and 14 after induction of colitis with trinitrobenzenesulphonic acid in ethanol (TNBS-E), plasma endotoxin, immunoglobulin (Ig) G and IgM endotoxin-core antibody (EndoCAb), tumour necrosis factor (TNF), interleukin (IL) 6 and alpha 2-macroglobulin (alpha 2M) concentrations and colon macroscopic inflammation score were determined. At all time points there was significant colonic inflammation when compared with control values (P < 0.0001). Animals treated with TNBS-E had raised concentrations of endotoxin at all time points (P < 0.04). In TNBS-E-treated animals EndoCAb concentrations were reduced on day 2 (P < 0.0001) and later increased. There were increases in IL-6 and alpha 2M concentrations in TNBS-E-treated animals but no significant change in TNF concentrations. Endotoxin concentrations correlated with macroscopic inflammation score, IL-6 and alpha 2M concentrations. There was a less consistent correlation between EndoCAb concentrations and these parameters. These results suggest that endotoxin is a mediator of the systemic response in this model of experimental colitis.

Burn injury induces a biphasic immunoglobulin M response to bacterial antigen

We studied 75 BALB/c mice to examine the role of impaired immunoglobulin M (IgM) synthesis in the increased risk of bacterial infection after burn injury by investigating the kinetics of IgM synthesis to peptidoglycan polysaccharide (PGPS), a ubiquitous bacterial antigen. Splenocytes were isolated 1, 5, and 8 days postburn (PBD) and cultured with lipopolysaccharide for 5 days. Culture supernatant was collected and anti-PGPS IgM and total IgM levels were measured by ELISA. Total IgM-secreting cells were measured by ELISPOT assay. Total IgM and anti-PGPS IgM per IgM-secreting cell were calculated. On PBD 1, anti-PGPS IgM synthesis but not total IgM synthesis is increased in burned animals. By PBD 5, total IgM and anti-PGPS IgM synthesis in the burn group start to fall and by PBD 8, both are significantly decreased. The early increase in anti-PGPS IgM synthesis represents a positive response to bacterial challenge. However, the late nonspecific decrease in total IgM and anti-PGPS IgM synthesis suggests a potential mechanism for increased susceptibility to bacterial infection 5 to 10 days after burn injury.

Significance of systemic endotoxaemia in inflammatory bowel disease

Quantitative and qualitative disturbances in faecal flora suggest a role for enteric bacteria and their products in the pathogenesis of inflammatory bowel disease (IBD). This study investigated the hypothesis that systemically circulating endotoxins are of pathogenic significance in IBD by measuring antibody, cytokine, and acute phase protein responses. Systemic endotoxaemia was found in 88% patients with ulcerative colitis (n = 25) and 94% with Crohn's disease (n = 31) during clinical relapse. Systemic endotoxaemia correlated positively with anatomic extent and clinical activity of ulcerative colitis. Circulating tumour necrosis factor (TNF) was detected in 40% of patients with ulcerative colitis and 45% with Crohn's disease. Plasma TNF concentrations correlated with clinical and laboratory measures of disease activity and were associated with a surgical outcome to the disease episode. Plasma soluble TNF receptor p55 concentration correlated positively with disease activity and endotoxin core antibody concentrations. Plasma IgG endotoxin core antibody concentrations were significantly increased in patients with Crohn's disease and correlated with systemic endotoxaemia. The presence of systemic endotoxaemia, its correlation with disease activity, disease extent, and endotoxin core antibody concentration and the detection of circulating TNF and soluble TNF receptors all support a pathogenic role for endotoxins in IBD.

Phlogistic properties of peptidoglycan-polysaccharide polymers from cell walls of pathogenic and normal-flora bacteria which colonize humans

PG-PS polymers which can induce experimental chronic inflammation in joints and other tissues can be isolated from the cell walls of human pathogens, such as group A streptococci, as well as from certain indigenous bacterial species which colonize the human intestinal tract. The structural and biological properties that are required for cell wall fragments to express this remarkable activity are still not well defined, but polymer size, resistance to tissue enzymes, and capacity to sustain activation of complement, macrophages, neutrophils, and T cells are properties associated with the most active preparations. There is increasing evidence that PG-PS structures with arthropathogenic activity occur in the human intestinal lumen and that these polymers can be translocated systemically. These observations support the concept that PG-PS, derived from a variety of bacterial species, can be part of the etiology of rheumatoid arthritis and other chronic inflammatory diseases. Since the PG component provides a common element to which all individuals are exposed, it follows that susceptibility is related to efficiency of disposal of bacterial cell wall debris, as well as to cytokine networks and immune cell function (51).

Bacterial cell wall polymers (peptidoglycan-polysaccharide) cause reactivation of arthritis

Intraperitoneal (i.p.) injection of peptidoglycan-polysaccharide derived from group A streptococci (PG-APS) causes chronic arthritis with spontaneous remissions and exacerbations. We hypothesized that, following i.p. injection, PG-APS released from hepatic stores mediated spontaneous recurrences of arthritis. We tested whether transplanted livers with large amounts of PG-APS were able to reactivate quiescent arthritis. Saline-loaded (group 1) or PG-APS-loaded (group 2) livers were transplanted into rats which had been injected intra-articularly 10 days earlier with PG-APS in one joint and saline in the other. A comparison was made with the arthritis that occurred in rats injected i.p. with PG-APS which did not receive transplants (group 3). Arthritis was monitored by serial measurement of joint diameters. Transplantation of saline-loaded livers (group 1) caused no reactivation of arthritis. However, transplantation of PG-APS-loaded livers (group 2) reactivated arthritis (P < 0.0001). Injection of PG-APS i.p. (group 3) induced the most-severe arthritis. PG-APS levels in plasma decreased with time, and PG-APS accumulated in the spleen in groups 2 and 3. Plasma and hepatic levels of PG-APS in rats injected i.p. with PG-APS were greater than levels in rats transplanted with PG-APS-loaded livers, which in turn were greater than levels in rats with saline-loaded livers. Plasma tumor necrosis factor did not correlate with recurrence of arthritis. Transplantation with PG-APS-loaded livers induced reactivation of arthritis in preinjured joints. The extent of arthritis was proportional to hepatic PG-APS content. Reactivation of arthritis may be mediated by slow release of liver-sequestered PG-APS or cytokines (not tumor necrosis factor) released by the liver.

Effect of putative phospholipase A2 inhibitors on acetic acid-induced acute colitis in the rat

Phospholipase activation may play an important role in ulcerative colitis. This hypothesis was tested by evaluating the effect of two non-selective phospholipase (PL) A2 inhibitors, quinacrine and p-bromophenacyl-bromide (pBPB), on acetic acid-induced colitis in the rat. The calcium antagonist verapamil, which may also act as a PLA2 inhibitor, was also tested. Acute colitis was induced in an isolated colonic segment by instillation of 4 per cent acetic acid for 15 s; this induces a uniform colitis after 4 days. The severity of colitis was evaluated histologically, by measuring myeloperoxidase (MPO) activity and by determining plasma exudation into the lumen of the colon (permeability) with 125I-labelled albumin given intravenously. All three putative PLA2 inhibitors tested were found to prevent the development of colitis. Intravenous administration of quinacrine 10 mg kg-1 at 30 min before instillation of acetic acid resulted in a normal mucosal appearance, normal MPO activity and a significantly reduced increase in plasma exudation into the colon. A similar effect was achieved using verapamil. Intracolonic administration of either quinacrine or pBPB also prevented acetic acid-induced colitis. However, three doses, starting immediately after acetic acid administration and repeated on the first and second days, were needed to achieve this, whereas one dose produced only a partial effect. PLA2 may play an important role in acetic acid-induced colitis and inhibition of its activity may offer an alternative mode of treatment in ulcerative colitis.

Crohn's disease monocytes are primed for accentuated release of toxic oxygen metabolites

BACKGROUND

Inflammatory bowel disease occurs in regions of the intestine characterized by a bowel content high in bacteria. Intestinal bacteria synthesize cell wall products such as lipopolysaccharide; when normal monocytes or macrophages come in contact with these products, they can be primed to release a number of inflammatory mediators. Mediators such as toxic oxygen metabolites released as part of the respiratory burst may contribute to inflammatory tissue damage. The aim of this study was to determine if monocytes from patients with Crohn's disease are primed by lipopolysaccharide for a greater respiratory burst.

METHODS

The generation of superoxide anion was measured by superoxide dismutase inhibitable reduction of ferricytochrome c.

RESULTS

Freshly isolated monocytes from active untreated Crohn's disease patients (n = 8) showed enhanced stimulated release of superoxide anion when compared with normal monocytes (n = 15; 3.80 +/- 0.12 vs. 1.02 +/- 0.06 nmol/5 min; P < 0.001). We tested the hypothesis that the monocyte priming factor in Crohn's disease serum may be lipopolysaccharide by showing that Crohn's disease serum lost its ability to prime normal monocytes after lipopolysaccharide was removed (0.25 +/- 0.25 nmol/5 min, P < 0.001).

CONCLUSIONS

These studies indicate that bacterial cell wall products may be important proinflammatory molecules involved in the initiation and/or perpetuation of Crohn's disease.

The effect of exogenous administration of Lactobacillus reuteri R2LC and oat fiber on acetic acid-induced colitis in the rat

The potential beneficial effect of exogenous administration of Lactobacillus on acetic acid-induced colitis was evaluated in the rat. Colitis was induced by instillation of 4% acetic acid for 15 sec in an exteriorized colonic segment. This produced uniform colitis with a threefold increase in myeloperoxidase (MPO) activity of the colonic tissue (an index of neutrophil infiltration) and a sixfold increase in plasma exudation into the lumen of the colon (mucosal permeability) as evaluated 4 days after acetic acid administration. Intracolonic administration of L. reuteri R2LC immediately after acetic acid administration, at a dose of 5 ml of 7 x 10(7) colony-forming units (CFU)/ml in two forms: either as pure bacterial suspension or as fermented oatmeal soup, prevented the development of colitis. Thus, the morphologic score, MPO activity, and mucosal permeability were almost normalized by Lactobacillus treatment. Initiating the treatment 24 h after acetic acid administration or using lower doses of 1 ml for 3 consecutive days resulted in a smaller protective effect. We conclude that exogenous administration of L. reuteri R2LC prevents the development of acetic acid-induced colitis in the rat.

Acetic acid-induced colitis results in bystander ileal injury

The extent of the small intestinal injury following experimental acetic acid induction of colitis in rats was examined. Following intraluminal colonic administration of radiolabelled acetic acid, high levels of radioactivity were identified in the colon and in the liver, while low background levels were found in jejunum, ileum, caecum, and heart. The increased level of radioactivity in the liver relative to that of the heart suggests that a significant portion of the colonic intraluminal acetic acid was absorbed directly into the portal circulation. The colon, which was the only segment of intestine in direct contact with the acetic acid, had the highest levels of radiolabelled acetic acid, demonstrated a marked macroscopic mucosal ulceration, an enhanced myeloperoxidase activity, and a fall in in vivo fluid absorption. The jejunum, which demonstrated low levels of radiolabelled acetic acid was normal without evidence of injury. In contrast, the ileum, which displayed the same levels of radiolabelled acetic acid as did the jejunum, also demonstrated a significant fall in in vivo fluid absorption but showed no mucosal ulceration or increased myeloperoxidase activity. These studies have shown that acetic acid induction of colitis produces evidence of ileal injury but that this injury is not the result of inadvertent delivery of acetic acid or recruitment of neutrophils to the ileal mucosa.

The effect of dexamethasone and endotoxin administration on biliary IgA and bacterial adherence

Adherence of bacteria to the intestinal epithelial cell may be the crucial initiating event for invasion and translocation and is normally prevented by both immune (IgA) and nonimmune (mucus, peristalsis, desquamation) mucosal defense mechanisms. The purpose of the present study was to examine the effect of endotoxin administration on mucosal immunity and to define the role of glucocorticoids, commonly released during endotoxicosis, in this process. Thirty female Fisher rats were randomly assigned to three groups of 10 animals each. Group I (CONT), was fed rat chow and H2O ad lib., Group II (DEX) was administered 0.8 mg/kg subcutaneously of dexamethasone, and Group III (ETX) was given 1 mg/kg of endotoxin. Twenty-four hours later animals were sacrificed and mesenteric lymph nodes and vigorously washed stool-free ceca were collected and cultured. Bile was collected and assayed for IgA from 5 animals in each group. A significant decrease (P < 0.05) in secretory IgA was noted in animals treated with either dexamethasone or endotoxin (CONT = 332 +/- 42, DEX = 78 +/- 24, ETX = 68 +/- 16 micrograms/mg protein +/- SEM). No difference in S-IgA between animals in the dexamethasone-treated group and the endotoxin-treated group was noted (P = NS). A statistically significant increase (P < 0.001) in bacteria adherent to the cecal wall in both the dexamethasone-treated rats and the endotoxin-treated rats over that in = 7.5 +/- 0.8, CONT = 6.4 +/- 0.6 cfu/g(log10) +/- SD). Our results suggest that endotoxin or glucocorticoid administration results in significant bacterial adherence to the cecal mucosa and a decrease in IgA.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation of endogenous bacterial cell wall polymers by the muralytic enzyme mutanolysin prevents hepatobiliary injury in genetically susceptible rats with experimental intestinal bacterial overgrowth

Jejunal self-filling blind loops with subsequent small bowel bacterial overgrowth (SBBO) induce hepatobiliary injury in genetically susceptible Lewis rats. Lesions consist of portal tract inflammation, bile duct proliferation, and destruction. To determine the pathogenesis of SBBO-induced hepatobiliary injury, we treated Lewis rats with SBBO by using several agents with different mechanisms of activity. Buffer treatment, ursodeoxycholic acid, prednisone, methotrexate, and cyclosporin A failed to prevent SBBO-induced injury as demonstrated by increased plasma aspartate aminotransferase (AST) and elevated histology scores. However, hepatic injury was prevented by mutanolysin, a muralytic enzyme whose only known activity is to split the beta 1-4 N-acetylmuramyl-N-acetylglucosamine linkage of peptidoglycan-polysaccharide (PG-PS), a bacterial cell wall polymer with potent inflammatory and immunoregulatory properties. Mutanolysin therapy started on the day blind loops were surgically created and continued for 8 wk significantly diminished AST (101 +/- 37 U/liter) and liver histology scores (2.2 +/- 2.7) compared to buffer-treated rats (228 +/- 146 U/liter, P < 0.05, 8.2 +/- 1.9, P < 0.001 respectively). Mutanolysin treatment started during the early phase of hepatic injury, 16-21 d after surgery, decreased AST in 7 of 11 rats from 142 +/- 80 to 103 +/- 24 U/liter contrasted to increased AST in 9 of 11 buffer-treated rats from 108 +/- 52 to 247 +/- 142 U/liter, P < 0.05. Mutanolysin did not change total bacterial numbers within the loop, eliminate Bacteroides sp., have in vitro antibiotic effects, or diminish mucosal PG-PS transport. However, mutanolysin treatment prevented elevation of plasma anti-PG antibodies and tumor necrosis factor-alpha (TNF alpha) levels which occurred in buffer treated rats with SBBO and decreased TNF alpha production in isolated Kupffer cells stimulated in vitro with PG-PS. Based on the preventive and therapeutic activity of this highly specific muralytic enzyme, we conclude that systemic uptake of PG-PS derived from endogenous enteric bacteria contributes to hepatobiliary injury induced by SBBO in susceptible rat strains.

Are intestinal bacteria involved in the etiology of rheumatoid arthritis? Review article

Observations in bowel-related joint diseases give support to this hypothesis. In Crohn's disease and ulcerative colitis, the bowel wall inflammation is complicated in about 20% of the patients by joint inflammation. Bowel infection by Salmonella, Shigella and Yersinia can provoke joint inflammation and supports an etiological link between bowel bacteria and arthritis. The arthropathic properties of the most abundant group of intestinal bacteria, i.e. the obligate anaerobic bacteria, were studied in an animal model. Cell wall fragments (CWF), with peptidoglycan as the major component, from some Eubacterium and Bifidobacterium species induced a severe chronic polyarthritis in Lewis rats after a single intraperitoneal injection. Eubacterium was found in numbers of 10(8)-10(9) per gram in stools of healthy subjects and rheumatoid arthritis (RA) patients. CWF of isolated strains of E. aerofaciens were arthropathic. Soluble peptidoglycan polysaccharide complexes (PG-PS) originating from the obligate anaerobic flora were purified from human intestinal contents. PG-PS from ileostomy fluid that proved to be less processed by intestinal enzymes induced chronic arthritis in rats after a single administration in oil in the base of the tail. It was concluded that the human intestinal bowel contains soluble bacterial cell wall products that are arthropathic in an animal model. Peptidoglycan (PG) or its subunits was reported to be present in mammalian tissues. Immunohistochemical studies from our group showed the presence of intestinal PG-PS in sections of normal rat spleen. Bacterial cell wall or PG-induced joint inflammation in rats is proven to be absolutely dependent on functional T cells. T-cell lines were isolated from the lymph nodes of rats with an E. aerofaciens CWF arthritis. A helper T-cell line B13 was in vivo arthritogenic in knee or ankle joints upon intravenous injection in rats and proliferated in vitro on syngeneic spleen cells alone, but was additionally stimulated by intestinal PG-PS and E. aerofaciens CWF. It was postulated that the arthritogenic T cells that seem to be autoreactive are, in fact, recognizing bacterial PG-PS on antigen-presenting cells (APC). It is generally accepted that RA is a T-cell-dependent process and that therefore the reaction is directed at small peptides bound by the major histocompatibility complex of APC. The only peptides present in arthritis inducing intestinal PG-PS and in CWF are PG peptides interlinking the sugar chains. We feel that the immunoreaction against PG peptides plays a pivotal role in experimental and human arthritis of an unknown etiology.

Evidence for peptidoglycan absorption in rats with experimental small bowel bacterial overgrowth

Surgical creation of jejunal self-filling blind loops (SFBL) causes small bowel bacterial overgrowth which is associated with hepatobiliary inflammation in the susceptible Lewis and Wistar rat strains. Since hepatic injury occurs when small bowel anaerobic bacterial concentrations are increased 4 to 6 log10 units per ml and hepatic bacterial cultures are negative, we postulate that the inflammation is caused by absorption of phlogistic cell wall polymers originating from bacteria within the loop. To demonstrate absorption of bacterial cell wall polymers, we measured plasma and hepatic levels of immunoreactive peptidoglycan-polysaccharide (PG-PS) following intraluminal injection as well as anti-PG antibodies as an indirect measure of absorption and/or accumulation of endogenous PG. PG-PS purified from group A streptococci was detected in plasma by enzyme-linked immunosorbent assay after intraluminal injection; rats with SFBL showed significantly more uptake into plasma and the liver than sham-operated rats or SFBL rats which were treated with metronidazole (P less than 0.025). Total plasma immunoglobulin A (IgA), IgG, and IgM levels did not differ among sham-operated rats and those with self-emptying blind loops or SFBL, but plasma anti-PG IgA (P less than 0.05), IgG, and IgM (P less than 0.01) levels were increased in rats with SFBL. Metronidazole and tetracycline prevented the elevation of anti-PG antibody, but gentamicin and polymyxin B did not. Anti-lipid A, anti-soy protein, and anti-chow antibodies in plasma were not consistently increased in rats with SFBL indicating the lack of a generalized antibody response to luminal antigens. These data suggest that PG from normal flora bacteria is absorbed from the intestinal lumen and that mucosal injury and/or increased luminal concentrations of PG, such as those induced by small bowel bacterial overgrowth, lead to enhanced absorption of potentially inflammatory bacterial polymers.

Antiinflammatory effects of various drugs on acetic acid induced colitis in the rat

The efficacy of various drugs used to treat ulcerative colitis, (sulfasalazine, 5-aminosalicylate, hydrocortisone) was investigated in a model of acetic acid-induced colitis in the rat. Subsequently, we tested the ability of antioxidant/5-lipoxygenase inhibitors (gossypol and nordihydroguiaretic acid [NDGA]) and a cyclooxygenase inhibitor (indomethacin) to attenuate the macroscopic colonic damage and/or neutrophil influx (myeloperoxidase activity [MPO]) associated with this model of colitis. Oral pretreatment with either sulfasalazine, gossypol, or NDGA significantly decreased colonic MPO activity induced by acetic acid. Intrarectal administration of such drugs resulted in an even larger reduction of the colonic inflammation, with gossypol being the most potent compound. Oral or intrarectal administration of corticosteroids (dexamethasone, hydrocortisone) also attenuated the parameters of acetic acid induced colitis. In contrast, pretreatment with indomethacin was ineffective, or when administered daily after colitis induction, indomethacin actually increased colonic neutrophil influx significantly. Our data suggest that both the route of drug administration and dosing regimen employed affect the antiinflammatory potency and/or efficacy of compounds on colitis induced by acetic acid in the rat. Drugs which were effective against this colitis may act by scavenging of oxygen derived free radicals.

Hepatic inflammation in rats with experimental small intestinal bacterial overgrowth

Hepatobiliary inflammation and other extraintestinal manifestations accompany certain intestinal disorders, perhaps because of proliferation or enhanced transport of luminal bacteria or their phlogistic cell-wall components. Using jejunal self-filling blind loops to create small bowel bacterial overgrowth, we compared biochemical and histological evidence of hepatic inflammation in 3 rat strains chosen for their variable inflammatory responses to bacterial cell wall polymers. Lewis and Wistar rats developed weight loss, hepatomegaly, and hepatic inflammation 4 and 12 wk, respectively, after creation of SFBL. Plasma aspartate aminotransferase levels in Lewis rats 4 wk (578 +/- 77 U/L) and Wistar rats 12 wk (220 +/- 35 U/L) after self-filling blind loops were significantly greater than in rats with self-emptying blind loops (112 +/- 24 U/L, p less than 0.001; 104 +/- 22, p less than 0.05) or sham-operated Lewis (84 +/- 24, p less than 0.001) or Wistar (78 +/- 10, p less than 0.001) rats. Randomized comparison using a histology grading score showed abnormalities that paralleled aminotransferase values. Lewis and Wistar rats with self-filling blind loops had hepatic injury with bile duct proliferation, fibrosis and acute and chronic periportal and focal parenchymal inflammation. Lewis and Wistar rats with self-emptying blind loops developed occasional mild histologic lesions. 50% of Lewis rats with self-filling blind loops for 4 wk died compared with only 15% in other groups. However, Buffalo rats with self-filling blind loops developed no weight loss, hepatomegaly, or hepatic injury. Anaerobic cultures of blood, peritoneum and liver were negative in all strains. Diet-restricted, sham-operated Wistar rats with weights similar to the Wistar rats with self-filling blind loops did not develop histologic abnormalities or elevated aminotransferase levels (76 +/- 31 U/L). These results show that experimental small bowel bacterial overgrowth causes significant hepatic inflammation leading to fibrosis in susceptible rat strains. Caloric deprivation and hepatic bacterial invasion are not etiologically responsible. We suggest that bacterial cell wall polymers or other bacterial toxins from the blind loop cause hepatic lesions in genetically susceptible hosts.

Hapten-induced model of chronic inflammation and ulceration in the rat colon

We have developed a simple and reproducible rat model of chronic colonic inflammation by the intraluminal instillation of a solution containing a "barrier breaker" and a hapten. Administration of the hapten 2,4,6-trinitrobenzenesulfonic acid (5-30 mg) in 0.25 ml of 50% ethanol as the "barrier breaker" produced dose-dependent colonic ulceration and inflammation. At a dose of 30 mg, trinitrobenzenesulfonic acid/ethanol-induced ulceration and marked thickening of the bowel wall persisted for at least 8 wk. Histologically, the inflammatory response included mucosal and submucosal infiltration by polymorphonuclear leukocytes, macrophages, lymphocytes, connective tissue mast cells, and fibroblasts. Granulomas were observed in 57% of the rats killed 3 wk after induction of inflammation. Langhan's-type giant cells were also observed. Segmental ulceration and inflammation were common. The characteristics and relatively long duration of inflammation and ulceration induced in this model afford an opportunity to study the pathophysiology of colonic inflammatory disease in a specifically controlled fashion, and to evaluate new treatments potentially applicable to inflammatory bowel disease in humans.

Eicosanoid regulation of acute intestinal vascular permeability induced by intravenous peptidoglycan-polysaccharide polymers

A model of rapidly developing, self-limited acute vascular permeability changes localized to the gut-associated lymphoid tissue (GALT) of the rat was used to study the role of prostaglandins (PGs), thromboxanes (Txs), and leukotrienes (LTs) in the in vivo regulation of early intestinal inflammatory events. Sprague-Dawley rats were pretreated with metabolites, enzyme inhibitors, or receptor antagonists of the arachidonic acid pathway before intravenous injection of sonicated peptidoglycan-polysaccharide polymers derived from group A streptococci (PG-APS, 5 micrograms rhamnose/g body weight). Rats were killed five minutes after PG-APS injection and were evaluated grossly for petechiae of the intestinal parenchyma and lymphoid aggregates. Indomethacin or dexamethasone increased intestinal injury by PG-APS by inducing mid-small bowel and cecal parenchymal hemorrhage. Indomethacin significantly diminished colonic lymphoid aggregate hemorrhage. PGE1, PGE2, and prostacyclin dramatically inhibited GALT hemorrhage; prostacyclin was the most potent with an effective dose of 0.1 microgram/kg. Dazmegrel, a specific Tx synthetase antagonist, significantly inhibited PG-APS-induced vascular permeability. Dazmegrel continued to diminish colonic lymphoid aggregated hemorrhage during concurrent treatment with indomethacin, which removed potential endogenous prostaglandin protection. Diethylcarbamazine, a lipoxygenase inhibitor, and FPL-55712, a LT receptor antagonist, inhibited the PG-APS-induced lesions, with FPL-55712 being more potent. LT blockade had a predominant effect on the intestinal parenchymal hemorrhage. We postulate that the normal homeostatic suppression of inflammation induced by phlogistic bacterial cell wall polymers is PG mediated, and that pathological responses are Tx and LT dependent.

Hapten-induced model of chronic inflammation and ulceration in the rat colon

We have developed a simple and reproducible rat model of chronic colonic inflammation by the intraluminal instillation of a solution containing a "barrier breaker" and a hapten. Administration of the hapten 2,4,6-trinitrobenzenesulfonic acid (5-30 mg) in 0.25 ml of 50% ethanol as the "barrier breaker" produced dose-dependent colonic ulceration and inflammation. At a dose of 30 mg, trinitrobenzenesulfonic acid/ethanol-induced ulceration and marked thickening of the bowel wall persisted for at least 8 wk. Histologically, the inflammatory response included mucosal and submucosal infiltration by polymorphonuclear leukocytes, macrophages, lymphocytes, connective tissue mast cells, and fibroblasts. Granulomas were observed in 57% of the rats killed 3 wk after induction of inflammation. Langhan's-type giant cells were also observed. Segmental ulceration and inflammation were common. The characteristics and relatively long duration of inflammation and ulceration induced in this model afford an opportunity to study the pathophysiology of colonic inflammatory disease in a specifically controlled fashion, and to evaluate new treatments potentially applicable to inflammatory bowel disease in humans.

Effect of a soluble bacterial carbohydrate fraction on the viscosity of intestinal contents in healthy subjects and patients with Crohn's disease

Supernatants of faecal suspensions from patients with Crohn's disease (CD) showed much lower viscosity than those from healthy subjects. Material responsible for the viscosity could be precipitated with ethanol. Gel filtration indicated that the viscosity was not due to the glycoprotein fraction but to a fraction with higher molecular weight and relatively high contents of muramic acid suggesting a bacterial origin. The concentration and viscosity of this fraction are less in faeces from patients with CD than in that of healthy subjects.