Low endogenous prostaglandin E2 predisposes to relapsing inflammation in experimental rat enterocolitis

Intramural injection of peptidoglycan-polysaccharide (PG-PS) induces acute enterocolitis that spontaneously relapses in Lewis but not Fischer rats. Interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-alpha) induce prostaglandin E2 (PGE2) secretion, which inhibits secretion of these cytokines by macrophages, suggesting an inhibitory feedback mechanism. We postulate that Lewis rat susceptibility to relapse is due to an imbalance between protective prostaglandins and cytokines. Female Fischer and Lewis rats were injected with PG-PS (37.5 microg/g) or human serum albumin intramurally. Tissue IL-1alpha and PGE2 immunoreactivities and myeloperoxidase (MPO) activity were determined. Relapsing rats had lower PGE2 and PGE2:IL-1alpha ratios than nonrelapsing rats (P < 0.05). In Fischer rats, 2 mg/kg/day indomethacin potentiated cecal MPO and IL-1alpha concentrations above PG-PS alone (P < 0.05). Misoprostol treatment blocked PG-PS-induced IL-1alpha and MPO and inhibited the potentiating effect of indomethacin on MPO and IL-1alpha (P < 0.05). In conclusion, increased endogenous PG may be protective against relapsing inflammation in PG-PS induced enterocolitis, at least partially via inhibition of proinflammatory cytokines. An imbalance between protective prostaglandins and proinflammatory cytokines may be involved in the pathogenesis of chronic relapsing inflammation in genetically susceptible hosts.

Curcumin blocks cytokine-mediated NF-kappa B activation and proinflammatory gene expression by inhibiting inhibitory factor I-kappa B kinase activity

NF-kappa B plays a critical role in the transcriptional regulation of proinflammatory gene expression in various cells. Cytokine-mediated activation of NF-kappa B requires activation of various kinases, which ultimately leads to the phosphorylation and degradation of I kappa B, the NF-kappa B cytoplasmic inhibitor. The food derivative curcumin has been shown to inhibit NF-kappa B activity in some cell types. In this report we investigate the mechanism of action of curcumin on cytokine-induced proinflammatory gene expression using intestinal epithelial cells (IEC). Curcumin inhibited IL-1 beta-mediated ICAM-1 and IL-8 gene expression in IEC-6, HT-29, and Caco-2 cells. Cytokine-induced NF-kappa B DNA binding activity, RelA nuclear translocation, I kappa B alpha degradation, I kappa B serine 32 phosphorylation, and I kappa B kinase (IKK) activity were blocked by curcumin treatment. Wound-induced p38 phosphorylation was not inhibited by curcumin treatment. In addition, mitogen-activated protein kinase/ERK kinase kinase-1-induced IL-8 gene expression and 12-O-tetraphorbol 12-myristate 13-acetate-responsive element-driven luciferase expression were inhibited by curcumin. However, I kappa B alpha degradation induced by ectopically expressed NF-kappa B-inducing kinase or IKK was not inhibited by curcumin treatment. Therefore, curcumin blocks a signal upstream of NF-kappa B-inducing kinase and IKK. We conclude that curcumin potently inhibits cytokine-mediated NF-kappa B activation by blocking a signal leading to IKK activity.

Curcumin Blocks Cytokine-Mediated NF-κB Activation and Proinflammatory Gene Expression by Inhibiting Inhibitory Factor I-κB Kinase Activity

NF-κB plays a critical role in the transcriptional regulation of proinflammatory gene expression in various cells. Cytokine-mediated activation of NF-κB requires activation of various kinases, which ultimately leads to the phosphorylation and degradation of IκB, the NF-κB cytoplasmic inhibitor. The food derivative curcumin has been shown to inhibit NF-κB activity in some cell types. In this report we investigate the mechanism of action of curcumin on cytokine-induced proinflammatory gene expression using intestinal epithelial cells (IEC). Curcumin inhibited IL-1β-mediated ICAM-1 and IL-8 gene expression in IEC-6, HT-29, and Caco-2 cells. Cytokine-induced NF-κB DNA binding activity, RelA nuclear translocation, IκBα degradation, IκB serine 32 phosphorylation, and IκB kinase (IKK) activity were blocked by curcumin treatment. Wound-induced p38 phosphorylation was not inhibited by curcumin treatment. In addition, mitogen-activated protein kinase/ERK kinase kinase-1-induced IL-8 gene expression and 12-O-tetraphorbol 12-myristate 13-acetate-responsive element-driven luciferase expression were inhibited by curcumin. However, IκBα degradation induced by ectopically expressed NF-κB-inducing kinase or IKK was not inhibited by curcumin treatment. Therefore, curcumin blocks a signal upstream of NF-κB-inducing kinase and IKK. We conclude that curcumin potently inhibits cytokine-mediated NF-κB activation by blocking a signal leading to IKK activity.

Kininogens are antithrombotic proteins In vivo

Kininogens have recently been shown to possess antiadhesive, anticoagulant, and profibrinolytic properties and can inhibit platelet activation at low thrombin concentrations. To test whether kininogens have antithrombotic properties in vivo, we devised a model of limited arterial injury confined to removal of the endothelium. Brown-Norway Katholiek strain rats with an absence of low- and high-molecular-weight kininogen due to a single point mutation, A163T, were compared in the thrombosis model to the wild-type animals, which were otherwise genetically identical. Despite an equivalent vascular injury, the mean time (+/-SEM) for a 90% decrease in flow measured by laser Doppler was 38.4+/-17 minutes in the kininogen-deficient rats compared with 194+/-29 minutes in the wild-type animals (P<0.002). The degree of vascular injury was the same. No evidence for disseminated intravascular coagulation (decrease in factor V, antithrombin, or fibrinogen) or excessive fibrinolysis (elevation of fibrinogen degradation products) was found in either group of animals. The results suggest that kininogens have antithrombotic properties at low concentrations of thrombin and that inhibitory peptides derived from kininogen may constitute a new antithrombotic strategy.

Bacterial cell wall polymers promote intestinal fibrosis by direct stimulation of myofibroblasts

Normal luminal bacteria and bacterial cell wall polymers are implicated in the pathogenesis of chronic intestinal inflammation. To determine the direct involvement of bacteria and their products on intestinal fibrogenesis, the effects of purified bacterial cell wall polymers on collagen and cytokine synthesis were evaluated in intestinal myofibroblast cultures established from normal fetal and chronically inflamed cecal tissues. In this study, the intestines of Lewis rats were intramurally injected with peptidoglycan-polysaccharide polymers. Collagen and transforming growth factor (TGF)-beta1 mRNA levels were measured and correlated with mesenchymal cell accumulation by immunohistochemistry. The direct effects of cell wall polymers on fibrogenic cytokine and collagen alpha1 (type I) expression were evaluated in intestinal myofibroblast cultures. We found that intramural injections of bacterial cell wall polymers induced chronic granulomatous enterocolitis with markedly increased collagen synthesis and concomitant increased TGF-beta1 and interleukin (IL)-6 expression. Intestinal myofibroblast cultures were established, which both phenotypically and functionally resemble the mesenchymal cells that are involved in fibrosis in vivo. Bacterial cell wall polymers directly stimulated collagen alpha1 (I), TGF-beta1, IL-1beta, and IL-6 mRNA expression in the intestinal myofibroblasts derived from both normal and inflamed cecum. Neutralization of endogenous TGF-beta1 inhibited in vitro collagen gene expression. From our results, we conclude that increased exposure to luminal bacterial products can directly activate intestinal mesenchymal cells, which accumulate in areas of chronic intestinal inflammation, thus stimulating intestinal fibrosis in genetically susceptible hosts.

Differential induction of colitis and gastritis in HLA-B27 transgenic rats selectively colonized with Bacteroides vulgatus or Escherichia coli

Resident bacteria play an important role in initiating and perpetuating gastrointestinal inflammation. We previously demonstrated that six commensal bacteria including Bacteroides vulgatus caused more aggressive colitis and gastritis in HLA-B27 transgenic rats than did the other five bacteria without B. vulgatus. This study compared the degree of gastrointestinal inflammation in gnotobiotic HLA-B27 transgenic rats monoassociated with either B. vulgatus or Escherichia coli. Gnotobiotic transgenic rats raised in Trexler isolators were selectively colonized with either B. vulgatus or E. coli. Control rats were either germfree or colonized with six common commensal bacteria (Streptococcus faecium, E. coli, Streptococcus avium, Eubacterium contortum, Peptostreptococcus productus, and B. vulgatus [DESEP-B]). After 1 month, all the rats were killed and tissues were prepared for histologic and biochemical evaluation. Colitis induced by B. vulgatus monoassociation was almost equal to that in DESEP-B-colonized rats and was significantly more severe than E. coli-induced colitis, which was absent by histological testing and mild by colonic myeloperoxidase and interleukin-1beta concentration determinations. However, gastritis was detectable only in DESEP-B-associated rats. These studies suggest that not all resident bacteria have equal proinflammatory capabilities, since B. vulgatus alone is more active than E. coli alone in inducing colitis, and that colitis and gastritis result from different luminal bacterial stimuli.

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.

TNF receptor-associated factor-2 is involved in both IL-1 beta and TNF-alpha signaling cascades leading to NF-kappa B activation and IL-8 expression in human intestinal epithelial cells

Cytokine signaling involves the participation of many adaptor proteins, including the docking protein TNF receptor-associated factor-2 (TRAF-2), which is believed to transmit the TNF-alpha signal through both the I kappa B/NF-kappa B and c-Jun N-terminal kinase (JNK)/stress-related protein kinase (SAPK) pathways. The physiological role of TRAF proteins in cytokine signaling in intestinal epithelial cells (IEC) is unknown. We characterized the effect of a dominant-negative TRAF-2 delivered by an adenoviral vector (Ad5dnTRAF-2) on the cytokine signaling cascade in several IEC and also investigated whether inhibiting the TRAF-2-transmitting signal blocked TNF-alpha-induced NF-kappa B and IL-8 gene expression. A high efficacy and level of Ad5dnTRAF-2 gene transfer were obtained in IEC using a multiplicity of infection of 50. Ad5dnTRAF-2 expression prevented TNF-alpha-induced, but not IL-1 beta-induced, I kappa B alpha degradation and NF-kappa B activation in NIH-3T3 and IEC-6 cells. TNF-alpha-induced JNK activation was also inhibited in Ad5dnTRAF-2-infected HT-29 cells. Induction of IL-8 gene expression by TNF-alpha was partially inhibited in Ad5dnTRAF-2-transfected HT-29, but not in control Ad5LacZ-infected, cells. Surprisingly, IL-1 beta-mediated IL-8 gene expression was also inhibited in HT-29 cells as measured by Northern blot and ELISA. We concluded that TRAF-2 is partially involved in TNF-alpha-mediated signaling through I kappa B/NF-kappa B in IEC. In addition, our data suggest that TRAF-2 is involved in IL-1 beta signaling in HT-29 cells. Manipulation of cytokine signaling pathways represents a new approach for inhibiting proinflammatory gene expression in IEC.

TNF Receptor-Associated Factor-2 Is Involved in Both IL-1β and TNF-α Signaling Cascades Leading to NF-κB Activation and IL-8 Expression in Human Intestinal Epithelial Cells

Cytokine signaling involves the participation of many adaptor proteins, including the docking protein TNF receptor-associated factor-2 (TRAF-2), which is believed to transmit the TNF-α signal through both the IκB/NF-κB and c-Jun N-terminal kinase (JNK)/stress-related protein kinase (SAPK) pathways. The physiological role of TRAF proteins in cytokine signaling in intestinal epithelial cells (IEC) is unknown. We characterized the effect of a dominant-negative TRAF-2 delivered by an adenoviral vector (Ad5dnTRAF-2) on the cytokine signaling cascade in several IEC and also investigated whether inhibiting the TRAF-2-transmitting signal blocked TNF-α-induced NF-κB and IL-8 gene expression. A high efficacy and level of Ad5dnTRAF-2 gene transfer were obtained in IEC using a multiplicity of infection of 50. Ad5dnTRAF-2 expression prevented TNF-α-induced, but not IL-1β-induced, IκBα degradation and NF-κB activation in NIH-3T3 and IEC-6 cells. TNF-α-induced JNK activation was also inhibited in Ad5dnTRAF-2-infected HT-29 cells. Induction of IL-8 gene expression by TNF-α was partially inhibited in Ad5dnTRAF-2-transfected HT-29, but not in control Ad5LacZ-infected, cells. Surprisingly, IL-1β-mediated IL-8 gene expression was also inhibited in HT-29 cells as measured by Northern blot and ELISA. We concluded that TRAF-2 is partially involved in TNF-α-mediated signaling through IκB/NF-κB in IEC. In addition, our data suggest that TRAF-2 is involved in IL-1β signaling in HT-29 cells. Manipulation of cytokine signaling pathways represents a new approach for inhibiting proinflammatory gene expression in IEC.

Varying cecal bacterial loads influences colitis and gastritis in HLA-B27 transgenic rats

BACKGROUND & AIMS

Recent data support an important role of resident luminal bacteria in experimental colitis. We determined how altered cecal bacterial loads influence colitis and gastritis.

METHODS

A cecal self-filling blind loop (SFBL) was created or the cecum was excluded from the fecal stream in specific pathogen-free HLA-B27 transgenic (TG) rats with early colitis and in nontransgenic (nonTG) littermates; controls underwent sham operation (SHAM). Luminal bacterial concentrations were determined by culture and counting chamber.

RESULTS

TG rats with SFBL had more severe cecal inflammation and leukocytosis than TG SHAM controls. TG excluded rats with low cecal bacterial loads had no cecal inflammation and less colitis and gastritis than SHAM controls, despite having normal distal colonic and gastric bacterial concentrations. Metronidazole attenuated cecal inflammation and eliminated Bacteroides in SFBL TG rats. NonTG SFBL rats had mild cecal inflammation and no gastritis and colitis. The ratio of total anaerobic to aerobic bacteria was 1000-fold greater in SFBL than in SHAM rats, with a 10,000-fold increased ratio of Bacteroides spp. to aerobes.

CONCLUSIONS

The luminal bacterial load and composition determines the activity of cecal inflammation in genetically susceptible hosts. Lowering cecal bacterial concentrations can diminish inflammation in remote organs.

Differential expression of interleukin 1 receptor antagonist isoforms in human intestinal epithelial cells

BACKGROUND & AIMS

Regulatory cytokines mediate intestinal epithelial cell (IEC) participation in mucosal immune responses. The aim of this study was to investigate the expression of secretory and intracellular isoforms of interleukin 1 receptor antagonist (IL-1Ra) in human primary IECs and carcinoma-derived cell lines.

METHODS

Primary IECs were isolated from patients with Crohn's disease or ulcerative colitis and from normal controls. Isoform-specific IL-1Ra messenger RNA (mRNA) and protein were assessed by reverse-transcription polymerase chain reaction and Western blot analysis. Expression during cellular differentiation was determined by in situ immunohistochemistry on sequentially released, native IECs and in vitro differentiated cell lines. Intracellular IL-1Ra I function was analyzed by permanent transfection of Caco-2 cells.

RESULTS

Intracellular IL-1Ra I protein accumulated in surface IECs with extension to the crypts during inflammation. Secretory IL-1Ra and intracellular IL-1Ra II mRNA, but not the corresponding protein, was detected. Transcription of intracellular IL-1Ra I mRNA was significantly up-regulated with inflammation and in vitro by phorbol myristate acetate and interleukin 1beta. In vitro differentiated cells had higher constitutive intracellular IL-1Ra I protein content. Intracellular IL-1Ra I expression in Caco-2 cells decreased IL-1beta-stimulated interleukin 8 secretion.

CONCLUSIONS

Native human IECs and certain cell lines constitutively express intracellular IL-1Ra type I, which is up-regulated by inflammation, inflammatory stimuli, and cellular differentiation. Constitutive expression of this anti-inflammatory cytokine may contribute to mucosal protection.

Specific NF-kappaB blockade selectively inhibits tumour necrosis factor-alpha-induced COX-2 but not constitutive COX-1 gene expression in HT-29 cells

Cyclo-oxygenase (COX) is the key regulatory enzyme of the prostaglandin/eicosanoid pathway. While COX-1 is mostly constitutively expressed, the COX-2 isoform is inducible by proinflammatory cytokines. We used an adenoviral vector containing an NF-kappaB super-repressor (Ad5IkappaB) to investigate the role of NF-kappaB in tumour necrosis factor-alpha (TNF-alpha)-mediated COX-2 gene expression in a colonic epithelial cell line. COX-1 mRNA and protein were constitutively expressed in uninfected, control Ad5LacZ- or Ad5IkappaB-infected HT-29 cells with no apparent change following TNF-alpha exposure. COX-2 mRNA and protein expression was undetectable in unstimulated cells but was strongly up-regulated after TNF-alpha stimulation in uninfected and Ad5LacZ-infected HT-29 cells. This induction was prevented in Ad5IkappaB cells. TNF-alpha increased prostaglandin E2 production by 20-fold in Ad5LacZ-infected HT-29 cells compared with uninfected cells and was significantly inhibited in Ad5IkappaB-infected cells in agreement with the COX-2 mRNA findings. We conclude that NF-kappaB activation is critical in mediating COX-2, but not COX-1 gene expression in HT-29 cells. Selective inhibition of COX-2 expression with the NF-kappaB super-repressor may be useful in distinguishing the role of inducible versus constitutive prostaglandins in intestinal function and provides greater specificity than pharmacological inhibitors.

Resident enteric bacteria are necessary for development of spontaneous colitis and immune system activation in interleukin-10-deficient mice

Mice with targeted deletion of the gene for interleukin-10 (IL-10) spontaneously develop enterocolitis when maintained in conventional conditions but develop only colitis when kept in specific-pathogen-free (SPF) environments. This study tested the hypothesis that enteric bacteria are necessary for the development of spontaneous colitis and immune system activation in IL-10-deficient mice. IL-10-deficient mice were maintained in either SPF conditions or germfree conditions or were populated with bacteria known to cause colitis in other rodent models. IL-10-deficient mice kept in SPF conditions developed colitis in all segments of the colon (cecum and proximal and distal colon). These mice exhibited immune system activation as evidenced by increased expression of CD44 on CD4(+) T cells; increased mesenteric lymph node cell numbers; and increased production of immunoglobulin A (IgA), IgG1, and IL-12 p40 from colon fragment cultures. Mice populated with bacterial strains, including Bacteroides vulgatus, known to induce colitis in other rodent models had minimal colitis. Germfree IL-10-deficient mice had no evidence of colitis or immune system activation. We conclude therefore that resident enteric bacteria are necessary for the development of spontaneous colitis and immune system activation in IL-10-deficient mice.

Localization and secretion of tissue kallikrein in peptidoglycan-induced enterocolitis in Lewis rats

The plasma kallikrein-kinin system is a mediator of intestinal inflammation induced by peptidoglycan-polysaccharide from group A streptococci (PG-APS) in rats. In this study we investigated the participation of intestinal tissue kallikrein (ITK). Lewis rats were injected intramurally with PG-APS. ITK was visualized by immunohistochemical staining. Cecal ITK concentration was measured by radioimmunoassay, and gene expression was evaluated by RNase protection assay. Kallikrein-binding protein (KBP) was evaluated in plasma by ELISA. Tissue kallikrein was identified in cecal goblet cells in both control and PG-APS-injected rats and in macrophages forming granulomas in inflamed tissues. Cecal ITK was significantly lower in acute and chronic phases of inflammation and in supernatant from in vitro cultures of inflamed cecum. ITK mRNA levels were not significantly different. Plasma KBP levels were significantly reduced in inflamed rats. The presence of tissue kallikrein in macrophages suggests participation in experimental colitis. The decrease of ITK in the inflamed intestine associated with unchanged mRNA levels suggests ITK release during intestinal inflammation.

Subtherapeutic corticosteroids potentiate the ability of interleukin 10 to prevent chronic inflammation in rats

BACKGROUND & AIMS

Interleukin (IL)-10, which inhibits macrophages and T-helper lymphocyte type 1 (TH1) lymphocytes, attenuates chronic granulomatous inflammation induced by bacterial cell wall polymers. This study determines whether corticosteroids enhance the protective effects of IL-10 in cultured peripheral blood mononuclear cells (PBMNCs) and in vivo when started before or after the onset of experimental chronic granulomatous inflammation.

METHODS

Intestines of Lewis rats were injected intramurally with streptococcal peptidoglycan-polysaccharide (PG-APS) polymers. Daily murine recombinant IL-10 and/or dexamethasone (DEX) therapy was started 12 hours before or at several intervals after PG-APS injection.

RESULTS

IL-10 plus corticosteroids additively inhibited IL-1beta secretion in human PBMNCs but preserved the beneficial IL-1RA/IL-1beta ratio induced by IL-10. IL-10 started before PG-APS injection significantly attenuated intestinal and extraintestinal inflammation, with even more pronounced effects in combination with subtherapeutic doses of DEX. The combination of DEX decreased the effective dose of IL-10 by at least one half. After onset of systemic inflammation using doses effective for prevention, IL-10 monotherapy had nearly no benefit and DEX plus IL-10 was similar to the mild therapeutic effect of DEX alone.

CONCLUSIONS

The combination of IL-10 and corticosteroids allows lower doses of both agents in preventing chronic intestinal and systemic inflammation. However, timing of IL-10 administration is a critical variable in regulating inflammation.

The specificity of peptides bound to human histocompatibility leukocyte antigen (HLA)-B27 influences the prevalence of arthritis in HLA-B27 transgenic rats

Human histocompatibility leukocyte antigen B27 is highly associated with the rheumatic diseases termed spondyloarthropathies, but the mechanism is not known. B27 transgenic rats develop a spontaneous disease resembling the human spondyloarthropathies that includes arthritis and colitis. To investigate whether this disease requires the binding of specific peptides to B27, we made a minigene construct in which a peptide from influenza nucleoprotein, NP383-391 (SRYWAIRTR), which binds B27 with high affinity, is targeted directly to the ER by the signal peptide of the adenovirus E3/gp19 protein. Rats transgenic for this minigene, NP1, were made and bred with B27 rats. The production of the NP383-391 peptide in B27(+)NP1(+) rats was confirmed immunologically and by mass spectrometry. The NP1 product displaced approximately 90% of the 3H-Arg-labeled endogenous peptide fraction in B27(+)NP1(+) spleen cells. Male B27(+)NP1(+) rats had a significantly reduced prevalence of arthritis, compared with B27(+)NP- males or B27(+) males with a control construct, NP2, whereas colitis was not significantly affected by the NP1 transgene. These findings support the hypothesis that B27-related arthritis requires binding of a specific peptide or set of peptides to B27, and they demonstrate a method for efficient transgenic targeting of peptides to the ER.

Kallikrein-kininogen system activation and bradykinin (B2) receptors in indomethacin induced enterocolitis in genetically susceptible Lewis rats

BACKGROUND

The plasma kallikrein-kinin (K-K) system is activated in acute and chronic relapsing intestinal inflammation induced in Lewis rats by intramural injection of exogenous bacterial components.

AIMS

To determine whether this effect is model specific, K-K system activation was investigated in a modified indomethacin induced enterocolitis model, as well as bradykinin 2 (B2) receptor distribution in the normal and acutely inflamed intestine.

METHODS

Lewis rats injected with daily sublethal doses of indomethacin for two days developed acute (two days) and chronic (14 days) intestinal inflammation. Plasma prekallikrein (amidolytic), high molecular weight kininogen (HK, coagulant) and cleavage of HK (western blot) were assayed to detect K-K activation.

RESULTS

Liver and spleen weights were significantly higher, and body weights and haematocrit values were significantly lower in the indomethacin group than in the control group. During both acute and chronic phases, rats displayed K-K system activation manifested by a significant decrease in plasma prekallikrein and HK functional levels, and by HK cleavage. Plasma T kininogen (a major acute phase protein) was significantly elevated. B2 receptors were identified in both normal and inflammatory intestine with more prominent specific immunohistochemical staining in the acutely inflamed tissue.

CONCLUSIONS

K-K system activation occurs in association with both acute and chronic phases of intestinal injury, regardless of the triggering agent, suggesting that activation of this system is integrally involved in intestinal inflammation in genetically susceptible hosts. Localisation of B2 receptors across intestinal layers provides a structural basis for the kinin function in the intestine.

A rat model of ileal pouch-rectal anastomosis

After colectomy and ileal pouch-rectal anastomosis, pouchitis may occur. Pouchitis is a poorly defined condition with unknown etiology. The aim of this study was to develop an animal model of pouchitis. Ileal pouch-rectal anastomosis was created in Lewis and Sprague-Dawley rats. Rats were studied 4 and 8 weeks after surgery, and pouchitis was assessed by stool output, histology, and tissue myeloperoxidase (MPO) levels. Some rats were treated with allopurinol or metronidazole beginning the day of surgery. Rats with pouches demonstrated inflammation with a monocytic infiltration, luminal exudate, mucosal ulcerations, and serosal inflammation. Rats with pouches had increased anaerobic bacterial flora compared with normal ileum. After creation of pouches, Lewis rats (histology score = 8.4 +/- 1.6; MPO = 17.3 +/- 3.6, mean +/- SD) developed more severe inflammation than Sprague-Dawley rats did (histology score = 4.3 +/- 1.8; MPO = 5.5 +/- 3.6) within 4 weeks, p < 0.001 and 8 weeks after surgery, p < 0.05. Stool output was also greater in Lewis (55 +/- 7 g/kg/day) compared with Sprague-Dawley rats with pouches (43 +/- 5 g/kg/day), p < 0.05. Metronidazole treatment reduced histology score (6.0 +/- 0.5) p < 0.05 and MPO (5.9 +/- 1.6) p < 0.001 in rats with pouches compared with rats with pouches that had no treatment. Allopurinol treatment in rats with pouches reduced histology score (4.0 +/- 1.7) and MPO (3.9 +/- 1.6), p < 0.001, compared with rats with pouches that had no treatment. Ileal pouch-rectal anastomosis in rats induced inflammation within 4 weeks, demonstrated differential host genetic susceptibility, and was associated with increased number of pouch bacteria. Anaerobes, especially bacteroides sp. and free radical, may mediate inflammation. Ileal pouch-rectal anastomosis surgery in rats may be a useful animal model for the study pouchitis.

Cytokines induce NF-kappaB in activated but not in quiescent rat hepatic stellate cells

The hepatic stellate cell (HSC), after a fibrogenic stimulus, is transformed from a quiescent to an activated phenotype, including the induction of responsiveness to a variety of agonists. We investigated the activation of nuclear factor-kappaB (NF-kappaB) and the expression of the NF-kappaB-responsive genes intercellular adhesion molecule 1 (ICAM-1) and macrophage inflammatory protein-2 (MIP-2) in freshly isolated and culture-activated HSC by tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta. Inhibitor-kappaB was rapidly (<15 min) degraded, and NF-kappaB activity was induced in culture-activated but not in freshly isolated HSC after cytokine stimulation. After 30 min of stimulation, immunofluorescence revealed that the NF-kappaB p65 subunit was predominantly found in the nuclei of activated HSC compared with the cytoplasmic localization in unstimulated cells. No nuclear translocation appeared in freshly isolated HSC after stimulation, despite the presence of functional TNF-alpha receptors. NF-kappaB nuclear translocation appeared first partially after 4-5 days and completely after 9 days in culture. Consistent with this time course TNF-alpha induced the mRNA of the NF-kappaB-dependent genes ICAM-1 and MIP-2 in activated but not in quiescent HSC. Therefore, cytokines induce NF-kappaB activity and ICAM-1 and MIP-2 mRNAs in activated but not in quiescent HSC, through a postreceptor mechanism of regulation.

Mediation by NF-kappa B of cytokine induced expression of intercellular adhesion molecule 1 (ICAM-1) in an intestinal epithelial cell line, a process blocked by proteasome inhibitors

BACKGROUND/AIMS

The gene promoter for the intercellular adhesion molecule ICAM-1 possesses binding sites for several transcriptional factors, including nuclear factor kappa B (NF-kappa B). The role of NF-kappa B in ICAM-1 gene regulation was therefore examined by using different proteasome inhibitors in tumour necrosis factor alpha (TNF-alpha) stimulated IEC-6 rat intestinal epithelial cells.

METHODS

ICAM-1 expression was analysed by enzyme linked immunosorbent assay (ELISA), reverse transcriptase polymerase chain reaction, and immunohistochemistry. Steady state levels of cytoplasmic I kappa B protein were evaluated by western blot, and nuclear translocation of NF-kappa B was determined by electrophoretic mobility shift assay and immunofluorescence staining. Cell adhesion was assayed by measuring the binding of fluorescence labelled MOLT-4 cells.

RESULTS

TNF-alpha induced ICAM-1 mRNA and protein expression in IEC-6 cells, which was followed by increased adhesion of MOLT-4 lymphocytes. Blocking TNF-alpha induced I kappa B alpha degradation with proteasome inhibitors reduced TNF-alpha induced NF-kappa B activation and ICAM-1 gene induction and notably decreased MOLT-4 cell adhesion without affecting Jun N-terminal kinase (JNK/SAPK) activity or de novo protein synthesis.

CONCLUSION

TNF-alpha induction of ICAM-1 expression is mediated by the transcription factor NF-kappa B and can be inhibited by blocking I kappa B alpha degradation. Thus the I kappa B/NF-kappa B system is a promising target for pharmacological modulation of the expression of adhesion molecules and other inflammatory genes in the intestine.

Inhibition of NFkappaB in activated rat hepatic stellate cells by proteasome inhibitors and an IkappaB super-repressor

The hepatic stellate cell (HSC), following a fibrogenic stimulus, is transformed from a quiescent to an activated cell. Cytokines induce NFkappaB activity in activated but not in quiescent HSCs with subsequent expression of NFkappaB-responsive genes, such as intercellular adhesion molecule (ICAM)-1 and interleukin (IL)-6. We investigated the effect of proteasome inhibitors and an IkappaB super-repressor on the cytokine mediated activation of NFkappaB, ICAM-1, and IL-6 in activated HSCs. Culture-activated HSCs were stimulated with IL-1beta or tumor necrosis factor alpha (TNFalpha) in the presence or absence of proteasome inhibitors, ALLN or MG-132, or after infection with an adenovirus expressing the IkappaB super-repressor (Ad5IkappaB) or beta-galactosidase (Ad5LacZ) as a control. NFkappaB activity was evaluated by immunofluorescence and by electrophoretic mobility shift assay. The steady state level of cytoplasmic IkappaB protein was measured by Western Blot. ICAM-1 and IL-6 expression was measured by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbant assay. Proteasome inhibitors, which block the degradation of IkappaB, and the Ad5IkappaB, which provides an exogenous nondegradable IkappaB, block the stimulation of NFkappaB activity by TNFalpha and IL-1beta in activated HSCs. These reagents block the subsequent nuclear translocation of p65 NFkappaB and induction of ICAM-1 and IL-6 by cytokines. The specificities of the proteasome inhibitors and the IkappaB super-repressor are demonstrated by their failure to block c-Jun N-terminal kinase induction by cytokines. Cytokine-induced stimulation of NFkappaB, ICAM-1, and IL-6 is blocked by proteasome inhibitors and Ad5IkappaB in activated HSCs. Inhibition of IkappaBalpha degradation is a potential target for anti-inflammatory therapy in the liver and might influence the activation process of HSCs following fibrotic stimuli.

Specific inhibition of plasma kallikrein modulates chronic granulomatous intestinal and systemic inflammation in genetically susceptible rats

The kallikrein-kinin (K-K) (contact) system is activated during acute and chronic relapsing phases of enterocolitis induced in genetically susceptible Lewis rats by intramural injection of peptidoglycan-polysaccharide (PG-APS). Using the selective plasma kallikrein inhibitor P8720, we investigate whether activation of the K-K system plays a primary role in chronic granulomatous intestinal and systemic inflammation in this model. Group I (negative control) received human serum albumin intramurally. Group II (treatment) received PG-APS intramurally and P8720 orally. Group III (positive control) received PG-APS intramurally and albumin orally. P8720 attenuated the consumption of the contact proteins, high molecular weight kininogen (P<0.03), and factor XI (P<0.04) in group II vs. group III. P8720 decreased chronic intestinal inflammation measured by blinded gross (P<0.01) and histologic (P<0.0005) scores as well as systemic complications (arthritis, splenomegaly, hepatomegaly, leukocytosis, and acute-phase reaction) (P<0.01) in group II as compared with group III. We conclude that relapsing chronic enterocolitis and systemic complications are in part due to plasma K-K system activation, and that inhibition of this pathway is a potential therapeutic approach to human inflammatory bowel disease and associated extraintestinal manifestations.

Inhibition of Proinflammatory Molecule Production by Adenovirus-Mediated Expression of a Nuclear Factor κB Super-Repressor in Human Intestinal Epithelial Cells

NF-κB plays a major role in the transcriptional regulation of many proinflammatory genes in multiple cell lineages, including intestinal epithelial cells (IEC). Activation of NF-κB requires both phosphorylation and degradation of its natural cytoplasmic inhibitor, IκB. We tested whether a super-repressor of NF-κB activity, which is a mutated nondegradable IκBα resistant to phosphorylation and degradation, could be delivered into IEC using an adenoviral vector (Ad5IκB) and determined the anti-inflammatory potential of this inhibitor following different stimuli. We showed for the first time that recombinant adenovirus efficiently infected (&gt;80%) transformed as well as primary IEC. Cytoplasmic levels of the NF-κB super-repressor protein were more than 50-fold higher than those of endogenous IκB, and this mutated IκB was resistant to IL-1β-induced degradation. Immunofluorescent RelA nuclear staining was strongly inhibited in Ad5IκB-infected IEC compared with control Ad5LacZ, and NF-κB, but not AP-1 binding activity, was reduced by more than 70% as measured by electrophoretic mobility shift assay (EMSA). Induction of inducible nitric-oxide synthase (iNOS), IL-1β, and IL-8 genes by IL-1β, TNF-α, or PMA was blocked in Ad5IκB-infected cells but not in Ad5LacZ controls as assayed by RT-PCR and ELISA. In addition, IL-1β-induced IL-8 secretion was totally inhibited by Ad5IκB in primary colonic IEC. We conclude that an adenoviral vector efficiently transfers a nondegradable IκB in both transformed and native IEC. The strong inhibition of NF-κB activity and the resulting down-regulation of multiple proinflammatory molecules by Ad5IκB suggests an exciting approach for in vivo intestinal gene therapy and illustrates the key role of NF-κB in transcriptional regulation of the inflammatory phenotype of IEC.

Inhibition of proinflammatory molecule production by adenovirus-mediated expression of a nuclear factor kappaB super-repressor in human intestinal epithelial cells

NF-kappaB plays a major role in the transcriptional regulation of many proinflammatory genes in multiple cell lineages, including intestinal epithelial cells (IEC). Activation of NF-kappaB requires both phosphorylation and degradation of its natural cytoplasmic inhibitor, IkappaB. We tested whether a super-repressor of NF-kappaB activity, which is a mutated nondegradable IkappaB alpha resistant to phosphorylation and degradation, could be delivered into IEC using an adenoviral vector (Ad5 IkappaB) and determined the antiinflammatory potential of this inhibitor following different stimuli. We showed for the first time that recombinant adenovirus efficiently infected (>80%) transformed as well as primary IEC. Cytoplasmic levels of the NF-kappaB super-repressor protein were more than 50-fold higher than those of endogenous IkappaB, and this mutated IkappaB was resistant to IL-1beta-induced degradation. Immunofluorescent RelA nuclear staining was strongly inhibited in Ad5 IkappaB-infected IEC compared with control Ad5LacZ and NF-kappaB, but not AP-1 binding activity, was reduced by more than 70% as measured by electrophoretic mobility shift assay (EMSA). Induction of inducible nitric-oxide synthase (iNOS), IL-1beta, and IL-8 genes by IL-1beta, TNF-alpha, or PMA was blocked in Ad5 IkappaB-infected cells but not in Ad5 LacZ controls as assayed by RT-PCR and ELISA. In addition, IL-1beta-induced IL-8 secretion was totally inhibited by Ad5 IkappaB in primary colonic IEC. We conclude that an adenoviral vector efficiently transfers a nondegradable IkappaB in both transformed and native IEC. The strong inhibition of NF-kappaB activity and the resulting down-regulation of multiple proinflammatory molecules by Ad5 IkappaB suggests an exciting approach for in vivo intestinal gene therapy and illustrates the key role of NF-kappaB in transcriptional regulation of the inflammatory phenotype of IEC.

Pathogenesis and immune mechanisms of chronic inflammatory bowel diseases

The inflammatory bowel diseases (IBDs) are characterized by intestinal inflammation of unknown etiology. Two distinct disorders, Crohn's disease and ulcerative colitis, have been identified. Three theories of IBD etiology are currently under consideration: 1) reaction to a persistent intestinal infection, 2) existence of a defective mucosal barrier to luminal antigens, and 3) a dysregulated host immune response to ubiquitous antigens. In each of these theories, either pathogenic or resident luminal bacteria constantly stimulate the mucosal and systemic immune systems to perpetuate the inflammatory cascade. Chronicity of inflammation results from an interaction of the persistent stimulus of microbial antigens with genetically determined host susceptibility factors that determine the individual's immune response or mucosal barrier function. The pathogenesis of IBD involves a series of steps, beginning with the breach of the intestinal mucosal barrier by infectious agents or toxins. The defective barrier exposes lamina propria immune cells to the continual presence of resident luminal bacteria, bacterial products, or dietary antigens, which perpetuates the inflammatory cascade. Many immunoregulatory abnormalities are noted in IBD, including the ratio of proinflammatory to immunosuppressive cytokines, selective activation of T(H) lymphocyte subsets, and abnormalities in epithelial antigen presentation. When activated during the initial inflammatory process, macrophages and T lymphocytes secrete a host of cytokines, which recruit other inflammatory cell types, thereby continuing the process. Tissue injury is the net result of the soluble products of the activated inflammatory cells. Knowledge of the pathogenesis in IBD suggests that the ultimate goals of therapy should be to block the proinflammatory mediators toward the proximal, rather than the distal, end of the cascade, to decrease the constant antigenic drive of luminal bacteria, and to correct the dysregulated immune response.

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.

Review article: How relevant to human inflammatory bowel disease are current animal models of intestinal inflammation?

New rodent models of chronic intestinal inflammation are mediated by a TH1-cell and macrophage dominated immune response to luminal bacterial constituents. The pathology of these spontaneous and induced models differ widely and caution is needed when assessing the comparative aspects of such animal models and human inflammatory bowel diseases (IBD). Considerable immunological and therapeutic evidence suggests that chronic and immune-mediated models are relevant in human IBD and that pathogenic principles are similar. However, animal models have not been able to duplicate exactly the pathological characteristics of ulcerative colitis or Crohn's disease, indicating a need for caution in extrapolating data from experimental models to human IBD.

Evidence for altered regulation of I kappa B alpha degradation in human colonic epithelial cells

The nuclear factor kappaB (NF-kappaB) regulates the transcription of genes bearing the kappaB consensus motif. Transmigration of NF-kappaB from the cytoplasm to the nucleus is regulated by the IkappaB family of inhibitory NF-kappaB-binding proteins. Dissociation of the NF-kappaB-IkappaB complex requires both phosphorylation and degradation of IkappaBs. We demonstrate that IL-1beta induces complete IkappaB alpha degradation in Caco-2 cell lines but not in HT-29, T84, SW-480 transformed cell lines, or native colonic epithelial cells. A similar lack of IkappaB alpha degradation in HT-29 cells followed TNF-alpha and bacterial polymer stimulation. IL-1beta stimulated NF-kappaB nuclear translocation and NF-kappaB-dependent IL-1beta and IL-8 expression in both Caco-2 and HT-29 cells as assayed by electrophoretic mobility shift assay, immunofluorescence, kappaB-luciferase transfection, reverse transcriptase-PCR analysis and ELISA. In HT-29 cells stimulated with IL-1beta, IkappaB alpha was phosphorylated and when cycloheximide blocked new protein synthesis, IkappaB alpha was partially degraded. NF-kappaB cytoplasmic to nuclear transmigration was incomplete and preceded IkappaB alpha degradation in 9T-29 cells, in contrast to complete coordinated NF-kappaB nuclear translocation and IkappaB alpha degradation in Caco-2 cells. Greater sensitivity of HT-29 cells to a calpain inhibitor, as measured by IL-8 secretion, suggested enhanced resistance to IkappaB alpha proteolysis. These data show that IL-1beta induces NF-kappaB activity and expression of NF-kappaB-dependent genes in colonic epithelial cells and suggest altered regulation of IkappaB alpha degradation compared with other cell lineages, which may result in their increased responsiveness to therapeutic blockade.

Enteric Microflora in IBD: Pathogens or Commensals?

: Both pathogenic and normal enteric microflora can induce and perpetuate chronic intestinal inflammation with systemic manifestations in genetically susceptible hosts. At the present time, there is no convincing indication that the majority of cases of ulcerative colitis or Crohn's disease is caused by persistent infection by Mycobacterium paratuberculosis, measles, Listeria monocytogenes, or Helicobacter species, but this possibility remains a valid hypothesis. Transient infection with any of a number of pathogens including upper respiratory tract infections and common enteric pathogens could provide one of the environmental triggers that initiate or reactivate IBD, which is then perpetuated in susceptible hosts by resident (not pathogenic) commensal luminal bacteria. Recent results in animal models demonstrate the absence of colitis, gastritis, and arthritis in a sterile (germ-free) environment, showing the importance of resident bacteria as persistent antigenic stimuli in the genetically susceptible hosts. Furthermore, there is an indication that not all normal luminal bacteria have equal capacities to induce mucosal injury, since some species can induce inflammation (Bacteroides), some are neutral (E. coli) and others may be protective (Lactobacilli). These observations have important therapeutic implications, such that altering luminal bacterial components and thereby decreasing the persistent antigenic drive offer alternative or adjuvant approaches to ongoing efforts to block mucosal immune responses to these stimuli.

Activation of the kallikrein-kinin system in arthritis and enterocolitis in genetically susceptible rats: modulation by a selective plasma kallikrein inhibitor

We have developed models of acute and chronic inflammatory arthritis and enterocolitis using peptidoglycan-polysaccharide injected intraperitoneally or subserosally (intramurally) into the distal ileum and cecum. Acute inflammation occurs in both Buffalo and Lewis rats, characterized by inflammation of the injected areas of the intestine. However, only the genetically susceptible Lewis rat develops chronic synovitis and joint erosion or adhesions and granulomatous enterocolitis. In the Lewis rat but not the Buffalo rat, these changes are accompanied by a decrease in plasma prekallikrein and high-molecular-weight kininogen, reflecting activation of the kallikrein-kinin system. Pretreatment with a specific plasma kallikrein inhibitor modulates the acute and chronic arthritis. The same inhibitor partially abrogates the acute changes characteristic of enterocolitis, and preliminary data suggest similar results in the chronic model. The results of these studies indicate that the kallikrein-kinin system plays an important role in arthritis and enterocolitis induced by bacterial products and that kallikrein inhibitors are potential therapeutic agents for inflammatory arthritis and inflammatory bowel disease.

Evidence for altered regulation of I kappa B alpha degradation in human colonic epithelial cells

The nuclear factor kappaB (NF-kappaB) regulates the transcription of genes bearing the kappaB consensus motif. Transmigration of NF-kappaB from the cytoplasm to the nucleus is regulated by the IkappaB family of inhibitory NF-kappaB-binding proteins. Dissociation of the NF-kappaB-IkappaB complex requires both phosphorylation and degradation of IkappaBs. We demonstrate that IL-1beta induces complete IkappaB alpha degradation in Caco-2 cell lines but not in HT-29, T84, SW-480 transformed cell lines, or native colonic epithelial cells. A similar lack of IkappaB alpha degradation in HT-29 cells followed TNF-alpha and bacterial polymer stimulation. IL-1beta stimulated NF-kappaB nuclear translocation and NF-kappaB-dependent IL-1beta and IL-8 expression in both Caco-2 and HT-29 cells as assayed by electrophoretic mobility shift assay, immunofluorescence, kappaB-luciferase transfection, reverse transcriptase-PCR analysis and ELISA. In HT-29 cells stimulated with IL-1beta, IkappaB alpha was phosphorylated and when cycloheximide blocked new protein synthesis, IkappaB alpha was partially degraded. NF-kappaB cytoplasmic to nuclear transmigration was incomplete and preceded IkappaB alpha degradation in 9T-29 cells, in contrast to complete coordinated NF-kappaB nuclear translocation and IkappaB alpha degradation in Caco-2 cells. Greater sensitivity of HT-29 cells to a calpain inhibitor, as measured by IL-8 secretion, suggested enhanced resistance to IkappaB alpha proteolysis. These data show that IL-1beta induces NF-kappaB activity and expression of NF-kappaB-dependent genes in colonic epithelial cells and suggest altered regulation of IkappaB alpha degradation compared with other cell lineages, which may result in their increased responsiveness to therapeutic blockade.

Interleukin 10 suppresses experimental chronic, granulomatous inflammation induced by bacterial cell wall polymers

BACKGROUND AND AIMS

Interleukin 10 (IL10) inhibits monocyte/macrophage and T lymphocyte effector functions. This study examined the effect of systemically administered IL10 on acute and chronic granulomatous enterocolitis, hepatitis, and arthritis in a rat model.

METHODS

Lewis rats were injected intramurally with streptococcal peptidoglycan-polysaccharide (PG-APS) polymers. Beginning 12 hours before PG-APS injection, rats were treated daily with subcutaneous murine recombinant IL10 or vehicle for three or 17 days.

RESULTS

IL10 attenuated acute enterocolitis in a dose dependent fashion (p < 0.01). Protective effects were more profound in the chronic granulomatous phase with decreased enterocolitis and markedly inhibited leucocytosis, hepatic granulomas, and chronic erosive arthritis (p < 0.001). IL10 downregulated tissue IL1, IL6, tumour necrosis factor alpha, and interferon gamma gene expression, consistent with the in vitro effects of IL10 on PG-APS-stimulated splenocytes. Caecal IL1 protein concentrations and IL2 and interferon gamma secretion by in vitro stimulated mesenteric lymph nodes were downregulated in IL10 treated animals.

CONCLUSIONS

These results indicate that exogenous IL10 can inhibit experimental granulomatous inflammatory responses and suggest that IL10 treatment could be an effective new therapeutic approach in human disorders such as Crohn's disease, rheumatoid arthritis, and sarcoidosis.

Local production of corticotropin releasing hormone is increased in experimental intestinal inflammation in rats

BACKGROUND/AIMS

Corticotropin releasing hormone (CRH) suppresses immunological functions via stimulation of the pituitary-adrenal axis, but is also found in peripheral tissues. Peripheral proinflammatory activity of CRH is suggested by increased tissue concentrations in arthritis and in vitro immunostimulatory effects. This study evaluated intestinal CRH concentrations, immunolocalisation, and synthesis in chronic enterocolitis and investigated in vitro responsiveness of lamina propria mononuclear cells to CRH.

METHODS

Chronic granulomatous enterocolitis was induced by intramural injection of peptidoglycan-polysaccharide polymers in the ileocaecal region of Lewis rats. CRH protein was measured in caecal specimens by immunohistochemistry and radioimmunoassay and caecal CRH mRNA expression was analysed by reverse transcriptase polymerase chain reaction.

RESULTS

In the chronically inflamed caecum abundant immunoreactive CRH was found in inflammatory cells, mesenchymal cells, as well as in myenteric plexi. In contrast, only a few CRH containing cells were detected in normal and HSA injected control caecums. Moreover, caecal CRH protein levels were increased during chronic enterocolitis. Local CRH synthesis as indicated by mRNA expression was considerably increased in chronic enterocolitis whereas it was undetectable or low in uninflamed caecum. In addition, CRH stimulated in vitro proliferation of lamina propria mononuclear cells and inhibited mitogen induced proliferation.

CONCLUSION

Increased CRH protein and mRNA expression in chronic enterocolitis and responsiveness of intestinal mononuclear cells to CRH indicate an immunomodulatory role for locally produced CRH in intestinal inflammation.

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.

Selective plasma kallikrein inhibitor attenuates acute intestinal inflammation in Lewis rat

A specific plasma kallikrein inhibitor, Bz-Pro-Phe-boroArg (P8720), was used to define the relationship between the kallikrein-kinin (K-K) system and acute intestinal inflammation induced by bacterial peptidoglycan-polysaccharide (PG-APS) in Lewis rats. Group I received human serum albumin (HSA) intramurally in the intestine and was treated with HSA. Group II received PG-APS and was treated with P8720. Group III received PG-APS and was treated with HSA. P8720 attenuated the decrease of high-molecular-weight kininogen and factor XI activity (group II vs group III, P < 0.01). P8720 therapy significantly but modestly decreased acute intestinal inflammation measured by gross gut score (P < 0.01) and more dramatically reduced the tissue myeloperoxidase activity (P < 0.05), a measure of granulocyte recruitment, in group II compared with group III. We conclude that the K-K system is directly involved in the pathogenesis of the acute phase of experimental acute inflammation. A specific inhibitor may modulate inflammatory bowel disease.

Selective kallikrein-kinin system activation in inbred rats differentially susceptible to granulomatous enterocolitis

BACKGROUND & AIMS

Crohn's disease is characterized by unrestrained inflammation with a genetic component. Genetic susceptibility and activation of the kalli-krein-kinin (contact) system were investigated in experimental enterocolitis and extraintestinal inflammation induced by bacterial polymers.

METHODS

Kinetics of inflammation in inbred Lewis and Buffalo rats injected subserosally with peptidoglycan-polysaccharide polymers were correlated with in vivo and in vitro activation of the contact system.

RESULTS

Lewis rats had a biphasic course of enterocolitis. Acute inflammation peaked 1 day after injection, gradually decreasing until day 14 when intestinal inflammation spontaneously reactivated and persisted for 16 weeks, accompanied by arthritis, granulomatous hepatitis, anemia, and leukocytosis. Self-limited acute enterocolitis in Buffalo rats resolved by 24 days without extraintestinal involvement. Consumption of the precursor proteins prekalli-krein and high-molecular-weight kininogen indicated activation of the plasma contact system in Lewis rats and closely correlated with chronic intestinal inflammation. Contact system activation did not occur in Buffalo rats, even during acute inflammation. In vitro studies showed a decreased rate of kininogen cleavage in Buffalo plasma.

CONCLUSIONS

Selective in vivo and in vitro activation of the contact system in susceptible Lewis rats suggests that this pathway is one determinant of genetic susceptibility to granulomatous enterocolitis and systemic complications.

Bacterial Cell Wall Polymer-Induced Granulomatous Inflammation

Local or systemic injection of peptidoglycan-polysaccharide polymers, which are the primary structural components of cell walls of nearly all bacteria, leads to acute inflammation, which can develop into chronic, spontaneously relapsing, granulomatous inflammation in a number of organs. Evolution into chronic granulomatous inflammation is dependent upon persistence of poorly biodegradable cell wall polymers within tissues, genetically determined host susceptibility, and generation of a T-lymphocyte-mediated immune response. Intraperitoneal injection of peptidoglycan-polysaccharide fragments from group A streptococci or selected intestinal bacteria into susceptible Lewis rats leads to chronic, spontaneously reactivating erosive arthritis and hepatic granulomas. Subserosal (intramural) injection of poorly biodegradable cell wall fragments into the distal intestine of Lewis rats induces chronic, spontaneously relapsing granulomatous enterocolitis with associated arthritis, hepatic granulomas, anemia, and leukocytosis. Chronic inflammation does not occur in T-lymphocyte-deficient rats and is prevented by cyclosporin-A therapy and degradation of peptidoglycan by the muralytic enzyme, mutanolysin. Moreover, resistant Buffalo and Fischer F344 rats, the latter sharing identical MHC antigens with Lewis rats, develop only acute inflammation with no chronic granulomatous response. Peptidoglycan-polysaccharide polymers activate almost every limb of the inflammatory response. Blockade of specific pathways suggests that interleukin-1, transforming growth factor-beta, plasma kallikrein, and T lymphocytes are dominant mediators of peptidoglycan-polysaccharide-induced arthritis, hepatic granulomas, and enterocolitis. Because of the similarity of immune mechanisms of these rat models to human disease, bacterial cell wall-induced inflammation provides unique opportunities to study pathogenic mechanisms of granuloma formation in response to ubiquitous microbial agents and to test novel therapeutic agents.

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.

Cytokine regulation of experimental intestinal inflammation in genetically engineered and T-lymphocyte reconstituted rodents

Phenotypically similar intestinal inflammation and systemic wasting develops following overexpression or targeted deletion of several key immunoregulatory molecules and transfer of lymphocyte subsets into immunodeficient recipients. Although many of these recently described models of intestinal inflammation have not been thoroughly investigated, several consistent features are present which provide important insights into the role of cytokines in the pathogenesis of intestinal inflammation: (i) entirely distinct genetic alterations of cytokine expression and T-lymphocyte activity can lead to phenotypically similar intestinal inflammation, suggesting that human inflammatory bowel disease could have marked genetic heterogeneity; (ii) dysregulation of any of a number to immunoregulatory molecules can result in intestinal inflammation, illustrating the complexity of the mucosal immune response; (iii) active immunosuppression is critical to maintaining mucosal homeostasis; (iv) interferon-gamma and CD4+ lymphocytes, probably of the TH1 phenotype, are required for progression of chronic intestinal inflammation; (v) monokines are consistently upregulated, but tumour necrosis factor blockade is only partially protective. These models represent powerful new tools to understand better the basic mechanisms of mucosal immunoregulation and to develop novel therapeutic approaches of enhancing endogenous immunosuppressive pathways and blocking key regulatory cytokines and cells.

Current concepts of the etiology and pathogenesis of ulcerative colitis and Crohn's disease

Although the causes, events initiating and triggering inflammation, and the precise immunoregulatory defects of IBD are still not known, investigations have provided a better understanding of the mechanisms of perpetuation of inflammation, genetic susceptibility, tissue injury, and symptoms. Ulcerative colitis and Crohn's disease are related disorders that probably share susceptibility genes and have similar nonspecific inflammatory mediator profiles. These diseases, however, almost certainly have different causes and respond to different antigenic stimuli. It is probable that both ulcerative colitis and Crohn's disease represent heterogenic groups of diseases that share similar mechanisms of tissue damage but have different initiating events and immunoregulatory abnormalities. Rodent models demonstrate that a wide variety of initial injuries or perturbations of immunoregulatory pathways can lead to similar phenotypes of intestinal injury, and human studies show evidence of genetic heterogeneity. It is equally apparent from these models that initiating and perpetuating mechanisms are entirely distinct and that the intestine has a remarkable ability to heal. Chronicity of disease depends on continued exposure to toxic luminal components, most commonly of bacterial origin, and genetically determined host susceptibility. Precise mechanisms of differential genetic susceptibility remain unclear, but defective down-regulation of inflammation is consistent with clinical and experimental observations. The author proposes the following sequence of events (Fig. 9). Nonspecific intestinal inflammation can be induced by a wide variety of enteric infections or ingested toxins. Resultant increased mucosal permeability leads to enhanced uptake of toxic luminal bacterial products, which potentiate local injury. The vast majority of hosts respond to these injurious events by promptly down-regulating the inflammatory response and rapidly healing the mucosal damage without residual scarring. The genetically susceptible host, however, who lacks the ability to suppress the inflammatory response efficiently, has inappropriate amplification of the immune cascade. In response to constant exposure to phlogistic luminal constituents, these patients develop an unrestrained inflammatory response, leading to tissue destruction, chronic inflammation, and fibrosis. Thus, IBD is caused by a genetically determined defective down-regulation of inflammation driven by ubiquitous antigens. Luminal anaerobic bacterial antigens are the stimuli in Crohn's disease, but ulcerative colitis may be caused by functionally abnormal aerobic bacteria or primary defects in epithelial cell physiology. Spontaneous or therapy-induced remissions can be achieved, but the risk of reactivation of inflammation is high because of the frequent exposure to triggering episodes that can reignite the inflammatory cascade. [formula: see text] This theory suggests that the intestine is in a constant state of controlled inflammation, mediated by a balance between aggressive luminal forces and host protective mechanisms (Fig. 10). This delicate balance can be deranged by any number of environmental triggering events and is in dysequilibrium in IBD. Amplification of the inflammatory response activates effector cells and cascades of soluble inflammatory molecules, which mediate tissue injury and physiologic responses leading to symptoms of IBD. These relatively nonspecific events are the target of most current therapeutic agents, which can inhibit but not completely block intestinal inflammation because of the overwhelming number of parallel pathways involved. Specific inhibition of selected effector molecules is intellectually intriguing but is less likely to paralyze the inflammatory response during clinically apparent inflammation than is blockade of key immunoregulatory cells and molecules. Better understanding of initiating, perpetuating, and immunoregulatory mechanisms should provide more

Reactivation of arthritis induced by small bowel bacterial overgrowth in rats: role of cytokines, bacteria, and bacterial polymers

Arthritis is often associated with intestinal diseases, but the etiology is not known. We developed a rat model whereby arthritis was reactivated by experimental small bowel bacterial overgrowth (SBBO). Self-limited monoarticular arthritis was induced by intra-articular injection of 2 micrograms of rhamnose peptidoglycan-polysaccharide derived from group A streptococci into the ankle joints in female Lewis rats. Eleven days after intra-articular injection, when swelling was resolving, experimental SBBO induced by surgical creation of jejunal self-filling blind loops reactivated arthritis, but SBBO induced by creation of self-emptying blind loops, which minimally increases luminal bacteria, and sham operation did not (P < 0.001). Increased joint diameters in rats with self-filling blind loops persisted for at least 56 days after surgery. Reactivation of arthritis due to SBBO was prevented by anti-tumor necrosis factor alpha antiserum and interleukin 1 receptor antagonist (P < 0.001), indicating that these cytokines mediate joint swelling secondary to intestinal injury. Recombinant bactericidal/permeability-increasing protein, an agent which neutralizes endotoxin, and metronidazole, which is active against anaerobic bacteria, prevented arthritis (P < 0.001), but polymyxin B (which also neutralizes endotoxin) and gentamicin had no effect. Mutanolysin, an enzyme which degrades peptidoglycan-polysaccharide from group A streptococci, exacerbated arthritis for the first 6 days but then diminished joint swelling from 12 to 21 days after surgery (P < 0.001). These studies introduce a reproducible animal model of reactivation of arthritis secondary to intestinal injury and demonstrate a role for bacterial products from endogenous enteric organisms.

Inhibition of plasma kallikrein prevents peptidoglycan-induced arthritis in the Lewis rat

We investigate whether the previously shown contact system activation plays a pathogenetic role in a rat model of acute inflammation induced by peptidoglycan-polysaccharide (PG-APS) using a new specific plasma kallikrein inhibitor, Bz-Pro-Phe-boroArg-OH (P8720). Group I (control) received neither PG-APS nor inhibitor. Group II (disease-treated) received PG-APS intraperitoneally (IP) and P8720 orally. Group III (disease-untreated) received PG-APS IP. Anemia was evident at 49 h in group III but was not present (P < 0.01) in groups I and II. Spleen weight was significantly decreased in group II compared to group III. Acute arthritis progressively developed in group III from 27 to 49 h, but P8720 decreased the joint swelling in group II by 61% (P < 0.0005). We observed a significant fall in prekallikrein and factor XI (P < 0.01) in groups II and III but not in group I. The decrease in the functional levels of high molecular weight kininogen (P < 0.05) observed in group III were prevented by P8720 in group II. The changes in T-kininogen and alpha 1-inhibitor 3 acute-phase proteins were partially prevented by P8720. We conclude that the inflammatory reactions leading to arthritis and anemia, as well as the acute-phase reaction, are due in part to contact activation, and that specific kallikrein inhibitors may have therapeutic potential.

Tissue interleukin 1 and interleukin-1 receptor antagonist expression in enterocolitis in resistant and susceptible rats

BACKGROUND/AIMS

Subserosal injection of purified group A streptococcal peptidoglycan-polysaccharide (PG-APS) induces chronic relapsing granulomatous enterocolitis and systemic inflammation in susceptible inbred Lewis rats but only transient intestinal injury in Buffalo and Fischer rats. Cecal interleukin 1 (IL-1) and IL-1 receptor antagonist (IL-1ra) expression was measured in inbred rats displaying differential susceptibility to experimental enterocolitis.

METHODS

The ileum and cecum of Lewis, Buffalo, and Fischer rats were subserosally injected with purified PG-APS or albumin. IL-1 and IL-1ra messenger RNA (mRNA) and protein (IL-1 only) were measured 1 or 27 days later. PG-APS-injected Lewis rats were treated with recombinant human IL-1ra. Kinetics of IL-1 and IL-1ra mRNA expression were studied in peritoneal cells.

RESULTS

All rats strains developed acute inflammation with increased cecal concentrations of IL-1 beta and IL-1ra mRNA. Lewis rats developed chronic enterocolitis and had higher IL-1 and IL-1ra mRNA tissue levels than Buffalo or Fischer rats, which displayed no chronic inflammation. IL-1 beta and IL-1ra were produced by submucosal granulomas and correlated with inflammation. IL-1 alpha protein levels paralleled IL-1 beta mRNA expression. IL-1ra treatment attenuated acute and chronic enterocolitis, adhesions, and arthritis. PG-APS induced IL-1 and IL-1ra expression in peritoneal cells from Lewis and Fischer rats.

CONCLUSIONS

Bacterial cell wall polymers stimulate IL-1 and IL-1ra expression in vivo and in vitro. These counterbalancing cytokines are increased in experimental enterocolitis and have important immunoregulatory roles in intestinal inflammation.