Nonhemopoietic cell TLR4 signaling is critical in causing early lipopolysaccharide-induced ileus

Radiographic and histopathological study of gastrointestinal dysmotility in lipopolysaccharide-induced sepsis in the rat

BACKGROUND

Sepsis is a highly incident condition in which a cascade of proinflammatory cytokines is involved. One of its most frequent consequences is ileus, which can increase mortality. Animal models such as that induced by systemic administration of lipopolysaccharide (LPS) are useful to deeply evaluate this condition. The effects of sepsis on the gastrointestinal (GI) tract have been explored but, to our knowledge, in vivo studies showing the motor and histopathological consequences of endotoxemia in an integrated way are lacking. Our aim was to study in rats the effects of sepsis on GI motility, using radiographic methods, and to assess histological damage in several organs.

METHODS

Male rats were intraperitoneally injected with saline or E. coli LPS at 0.1, 1, or 5 mg kg-1 . Barium sulfate was intragastrically administered, and X-rays were performed 0-24 h afterwards. Several organs were collected for organography, histopathology, and immunohistochemistry studies.

KEY RESULTS

All LPS doses caused gastroparesia, whereas changes in intestinal motility were dose-and time-dependent, with an initial phase of hypermotility followed by paralytic ileus. Lung, liver, stomach, ileum, and colon (but not spleen or kidneys) were damaged, and density of neutrophils and activated M2 macrophages and expression of cyclooxygenase 2 were increased in the colon 24 h after LPS 5 mg kg-1 .

CONCLUSIONS AND INFERENCES

Using radiographic, noninvasive methods for the first time, we show that systemic LPS causes dose-, time-, and organ-dependent GI motor effects. Sepsis-induced GI dysmotility is a complex condition whose management needs to take its time-dependent changes into account.

Interleukin-17 as a spatiotemporal bridge from acute to chronic inflammation: Novel insights from computational modeling

A systematic review of several acute inflammatory diseases ranging from sepsis and trauma/hemorrhagic shock to the relevant pathology of the decade, COVID-19, points to the cytokine interleukin (IL)-17A as being centrally involved in the propagation of inflammation. We summarize the role of IL-17A in acute inflammation, leveraging insights made possible by biological network analysis and novel computational methodologies aimed at defining the spatiotemporal spread of inflammation in both experimental animal models and humans. These studies implicate IL-17A in the cross-tissue spread of inflammation, a process that appears to be in part regulated through neural mechanisms. Although acute inflammatory diseases are currently considered distinct from chronic inflammatory pathologies, we suggest that chronic inflammation may represent repeated, cyclical episodes of acute inflammation driven by mechanisms involving IL-17A. Thus, insights from computational modeling of acute inflammatory diseases may improve diagnosis and treatment of chronic inflammation; in turn, therapeutics developed for chronic/autoimmune disease may be of benefit in acute inflammation. This article is categorized under: Immune System Diseases > Computational Models.

TLR2 and TLR4 Modulate Mouse Ileal Motility by the Interaction with Muscarinic and Nicotinic Receptors

Irritable bowel syndrome (IBS) is a chronic functional bowel disorder characterized by intestinal dysmotility. Changes in intestinal microbiota (dysbiosis) can lead to alterations in neuro-muscular functions in the gut. Toll-like receptors (TLRs) 2 and 4 recognize intestinal bacteria and are involved in the motor response induced by gastrointestinal (GI) neurotransmitters. Acetylcholine (ACh) is a well-known neurotransmitter involved in the regulation of GI motility. This study aimed to evaluate the role of TLR2 and TLR4 in the intestinal motor-response induced by ACh in the mouse ileum, as well as the expression and function of the muscarinic and nicotinic ACh receptors. Muscle contractility studies showed that the contractions induced by ACh were significantly lower in TLR2^−/− and TLR4^−/− with respect to WT mice. In WT mice, the contractions induced by ACh were reduced in the presence of AF-DX AF-DX 116 (a muscarinic ACh receptor (mAChR) M2 antagonist), 4-DAMP (a mAChR M3 antagonist), mecamylamine (a nicotinic AChR receptor (nAChR) α3β4 antagonist) and α-bungarotoxin (a nAChR α7 antagonist). In TLR2^−/− mice, the contractions induced by ACh were increased by AF-DX 116 and mecamylamine. In TLR4^−/− mice, the contractions induced by ACh were reduced by α-bungarotoxin and 4-DAMP. The mRNA and protein expressions of M3 and α3 receptors were diminished in the ileum from TLR2^−/− and TLR4^−/− with respect to WT mice. However, the levels of mRNA and protein of β4 were diminished only in TLR4^−/− but not in TLR2^−/− mice. In conclusion, our results show that TLR2 and TLR4 modulates the motor responses to ACh in the mouse ileum. TLR2 acts on muscarinic M2 and M3 and nicotinic α3β4 ACh receptors, while TLR4 acts on muscarinic M3 and nicotinic α3β4 and α7 ACh receptors.

Briarane-Related Diterpenoids from Octocoral Briareum stechei

A known polyoxygenated briarane, briaexcavatolide P (1), was isolated from a Formosan octocoral Briareum stechei. Moreover, the same species B. stechei, collected from Okinawan waters, yielded three chlorine-containing briaranes, including two new compounds, briastecholides B (2) and C (3) as well as a known analogue, briarenol R (4). The structures of 1-4 were established using spectroscopic methods. In addition, briarane 1 demonstrated anti-inflammatory activity in lipo-polysaccharide-induced RAW 264.7 mouse macrophage cells by suppressing the expression of inducible nitric oxide synthase (iNOS) protein.

Briarenols W-Z: Chlorine-Containing Polyoxygenated Briaranes from Octocoral Briareum stechei (Kükenthal, 1908)

Briareum stechei is proven to be a rich source of 3,8-cyclized cembranoids (briarane) with a bicyclo[8.4.0] carbon core. In the present study, four previously unreported briaranes, briarenols W-Z (1-4), along with solenolide A (5), briarenolide M (6), briaexcavatolide F (7), and brianolide (8), were isolated and characterized through spectroscopic analysis, and the absolute configuration of 8 was corroborated by a single-crystal x-ray diffraction analysis. Briaranes 2 and 5 were found to induce significant inflammatory activity in lipopolysaccharide (LPS)-induced RAW 264.7 mouse macrophage cells by enhancing the expression of the inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins.

GLP-2 Acutely Prevents Endotoxin-Related Increased Intestinal Paracellular Permeability in Rats

BACKGROUND

Circulating endotoxin (lipopolysaccharide, LPS) increases the gut paracellular permeability. We hypothesized that glucagon-like peptide-2 (GLP-2) acutely reduces LPS-related increased intestinal paracellular permeability by a mechanism unrelated to its intestinotrophic effect.

METHODS

We assessed small intestinal paracellular permeability in vivo by measuring the appearance of intraduodenally perfused FITC-dextran 4000 (FD4) into the portal vein (PV) in rats 1-24 h after LPS treatment (5 mg/kg, ip). We also examined the effect of a stable GLP-2 analog teduglutide (TDG) on FD4 permeability.

RESULTS

FD4 movement into the PV was increased 6 h, but not 1 or 3 h after LPS treatment, with increased PV GLP-2 levels and increased mRNA expressions of proinflammatory cytokines and proglucagon in the ileal mucosa. Co-treatment with a GLP-2 receptor antagonist enhanced PV FD4 concentrations. PV FD4 concentrations 24 h after LPS were higher than FD4 concentrations 6 h after LPS, reduced by exogenous GLP-2 treatment given 6 or 12 h after LPS treatment. FD4 uptake measured 6 h after LPS was reduced by TDG 3 or 6 h after LPS treatment. TDG-associated reduced FD4 uptake was reversed by the VPAC1 antagonist PG97-269 or L-NAME, not by EGF or IGF1 receptor inhibitors.

CONCLUSIONS

Systemic LPS releases endogenous GLP-2, reducing LPS-related increased permeability. The therapeutic window of exogenous GLP-2 administration is at minimum within 6-12 h after LPS treatment. Exogenous GLP-2 treatment is of value in the prevention of increased paracellular permeability associated with endotoxemia.

TLR2 and TLR4 interact with sulfide system in the modulation of mouse colonic motility

BACKGROUND

H₂ S is a neuromodulator that may inhibit intestinal motility. H₂ S production in colon is yielded by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) enzymes and sulfate-reducing bacteria (SRB). Toll-like receptors (TLRs) recognize intestinal microbiota. The aim of this work was to evaluate the influence of TLR2 and TLR4 on the endogenous and SRB-mediated synthesis of H₂ S and its consequences on the colonic motility of mouse.

METHODS

Muscle contractility studies were performed in colon from WT, Tlr2^-/- , and Tlr4^-/- mice. The mRNA levels of TLR2, TLR4, CBS, CSE, and SRB were measured by real-time PCR. Free sulfide levels in colon and feces were determined by colorimetric assays.

RESULTS

NaHS and GYY4137, donors of H₂ S, reduced the contractility of colon. Aminooxyacetic acid (AOAA), inhibitor of CBS, and D-L propargylglycine (PAG), inhibitor of CSE, increased the contractility of colon. In vivo treatment with NaHS or GYY4137 inhibited the spontaneous contractions and upregulated TLR2 expression. The in vivo activation of TLR4 with lipopolysaccharide increased the contractile response to PAG, mRNA levels of CSE, and the free sulfide levels of H₂ S in colon. In Tlr2^-/- and Tlr4^-/-  mice, the contractions induced by AOAA and PAG and mRNA levels of CBS and CSE were lower with respect to WT mice. Deficiency of TLR2 or TLR4 provokes alterations in free sulfide levels and SRB of colon.

CONCLUSIONS AND INFERENCES

Our study demonstrates interaction between TLR2 and TLR4 and the sulfide system in the regulation of colonic motility and contributes to the pathophysiology knowledge of intestinal motility disorders.

The pathogenesis of proventricular dilatation disease

Bornaviruses cause neurologic diseases in several species of birds, especially parrots, waterfowl and finches. The characteristic lesions observed in these birds include encephalitis and gross dilatation of the anterior stomach — the proventriculus. The disease is thus known as proventricular dilatation disease (PDD). PDD is characterized by extreme proventricular dilatation, blockage of the passage of digesta and consequent death by starvation. There are few clinical resemblances between this and the bornaviral encephalitides observed in mammals. Nevertheless, there are common virus-induced pathogenic pathways shared across this disease spectrum that are explored in this review. Additionally, a review of the literature relating to gastroparesis in humans and the control of gastric mobility in mammals and birds points to several plausible mechanisms by which bornaviral infection may result in extreme proventricular dilatation.

Development of A Novel Murine Model of Combined Radiation and Peripheral Tissue Trauma Injuries

Detonation of a 10-kiloton nuclear bomb in an urban setting would result in >1 million casualties, the majority of which would present with combined injuries. Combined injuries, such as peripheral tissue trauma and radiation exposure, trigger inflammatory events that lead to multiple organ dysfunction (MOD) and death, with gastrointestinal (GI) and pulmonary involvement playing crucial roles. The objective of this study was to develop an animal model of combined injuries, peripheral tissue trauma (TBX animal model) combined with total body irradiation with 5% bone marrow shielding (TBI/BM5) to investigate if peripheral tissue trauma contributes to reduced survival. Male C57BL/6J mice were exposed to TBX10%, irradiation (TBI/BM5), or combined injuries (TBX10% + TBI/BM5). Experiments were conducted to evaluate mortality at day 7 after TBI/BM5. Serial euthanasia was performed at day 1, 3 and 6 or 7 after TBI/BM5 to evaluate the time course of pathophysiologic processes in combined injuries. Functional tests were performed to assess pulmonary function and GI motility. Postmortem samples of lungs and jejunum were collected to assess tissue damage. Results indicated higher lethality and shorter survival in the TBX10% +T BI/BM5 group than in the TBX10% or TBI/BM5 groups (day 1 vs. day 7 and 6, respectively). TBI/BM5 alone had no effects on the lungs but significantly impaired GI function at day 6. As expected, in the animals that received severe trauma (TBX10%), we observed impairment in lung function and delay in GI transit in the first 3 days, effects that decreased at later time points. Trauma combined with radiation (TBX10% + TBI/BM5) significantly augmented impairment of the lung and GI function in comparison to TBX10% and TBI/BM5 groups at 24 h. Histologic evaluation indicated that combined injuries caused greater tissue damage in the intestines in TBX10% + TBI/BM5 group when compared to other groups. We describe here the first combined tissue trauma/radiation injury model that will allow conduction of mechanistic studies to identify new therapeutic targets and serve as a platform for testing novel therapeutic interventions.

Role of nitric oxide in the pathogenesis of Barrett’s-associated carcinogenesis

Barrett’s esophagus (BE), a premalignant condition to Barrett’s adenocarcinoma (BAC), is closely associated with chronic inflammation due to gastro-esophageal reflux. Caudal type homeobox 2 (CDX2), a representative marker of BE, is increased during the metaplastic and neoplastic transformation of BE. Nitric oxide (NO) has been proposed to be a crucial mediator of Barrett’s carcinogenesis. We previously demonstrated that CDX2 might be induced directly under stimulation of large amounts of NO generated around the gastro-esophageal junction (GEJ) by activating epithelial growth factor receptor in a ligand-independent manner. Thus, we reviewed recent developments on the role of NO in Barrett’s carcinogenesis. Notably, recent studies have reported that microbial communities in the distal esophagus are significantly different among groups with a normal esophagus, reflux esophagitis, BE or BAC, despite there being no difference in the bacterial quantity. Considering that microorganism components can be one of the major sources of large amounts of NO, these studies suggest that the bacterial composition in the distal esophagus might play an important role in regulating NO production during the carcinogenic process. Controlling an inflammatory reaction due to gastro-esophageal reflux or bacterial composition around the GEJ might help prevent the progression of Barrett’s carcinogenesis by inhibiting NO production.

Lipopolysaccharide Regulation of Intestinal Tight Junction Permeability Is Mediated by TLR4 Signal Transduction Pathway Activation of FAK and MyD88

Gut-derived bacterial LPS plays an essential role in inducing intestinal and systemic inflammatory responses and have been implicated as a pathogenic factor in necrotizing enterocolitis and inflammatory bowel disease. The defective intestinal tight junction barrier was shown to be an important factor contributing to the development of intestinal inflammation. LPS, at physiological concentrations, causes an increase in intestinal tight junction permeability (TJP) via a TLR4-dependent process; however, the intracellular mechanisms that mediate LPS regulation of intestinal TJP remain unclear. The aim of this study was to investigate the adaptor proteins and the signaling interactions that mediate LPS modulation of intestinal tight junction barrier using in vitro and in vivo model systems. LPS caused a TLR4-dependent activation of membrane-associated adaptor protein focal adhesion kinase (FAK) in Caco-2 monolayers. LPS caused an activation of both MyD88-dependent and -independent pathways. Small interfering RNA silencing of MyD88 prevented an LPS-induced increase in TJP. LPS caused MyD88-dependent activation of IL-1R-associated kinase 4. TLR4, FAK, and MyD88 were colocalized. Small interfering silencing of TLR4 inhibited TLR4-associated FAK activation, and FAK knockdown prevented MyD88 activation. In vivo studies also confirmed that the LPS-induced increase in mouse intestinal permeability was associated with FAK and MyD88 activation; knockdown of intestinal epithelial FAK prevented an LPS-induced increase in intestinal permeability. Additionally, high-dose LPS-induced intestinal inflammation was dependent on the TLR4/FAK/MyD88 signal transduction axis. To our knowledge, our data show for the first time that the LPS-induced increases in intestinal TJP and intestinal inflammation were regulated by TLR4-dependent activation of the FAK/MyD88/IL-1R-associated kinase 4 signaling pathway.

Toll-like receptors 2 and 4 modulate the contractile response induced by serotonin in mouse ileum: analysis of the serotonin receptors involved

BACKGROUND

Microbiota through toll-like receptors (TLR) may regulate gastrointestinal motility by activating neuroendocrine mechanisms. We evaluated the influence of TLR2 and TLR4 in the spontaneous contractions and serotonin (5-HT)-induced motor response in mouse ileum, and the 5-HT receptors involved.

METHODS

Muscle contractility studies to evaluate the spontaneous intestinal motility and the response to 5-HT were performed in the ileum from wild type (WT), TLR2(-/-), TLR4(-/-), and TLR2/4 double knockout (DKO) mice. 5-HT receptor expression was determined by real-time PCR.

KEY RESULTS

The amplitude of spontaneous contractions in ileum was higher in TLR2(-/-), TLR4(-/-), and TLR2/4 DKO mice with respect to WT. 5-HT evoked concentration-dependent contractile responses in the ileum from TLR2(-/-) and TLR4(-/-) mice similar to WT. However, in ileum from TLR2/4 DKO, 5-HT did not induce any contractile response. Expression of 5-HT2A, 5-HT2B, 5-HT2C, and 5-HT3 receptors resulted increased in ileum from TLR4(-/-) and TLR2/4 DKO. Expression of the 5-HT4 receptor was diminished in TLR2(-/-) and TLR2/4 DKO. High levels of 5-HT7 receptor expression were found in TLR2/4 DKO but not in TLR2(-/-) or TLR4(-/-). In WT and TLR4(-/-), 5-HT2, 5-HT3, 5-HT4, and 5-HT7 receptor antagonists reduced the contractile response evoked by 5-HT. In TLR2(-/-) mice, 5-HT4 antagonist did not reduce the 5-HT response. In TLR2/4 DKO mice, only 5-HT4 and 5-HT7 receptor antagonists reduced the relaxing response induced by 5-HT.

CONCLUSIONS & INFERENCES

TLR2 and TLR4 signaling may modulate the spontaneous contractions and the serotonin contractile response by acting on 5-HT2, 5-HT3, 5-HT4, and 5-HT7 receptors.

Myocyte TLR4 enhances enteric and systemic inflammation driving late murine endotoxic ileus

Myocytes are nonhemopoietic in origin and functionally essential in generating gastrointestinal motility. In endotoxemia, a rapid-onset nonhemopoietic mechanism potently triggers early ileus in a Toll-like receptor 4 (TLR4)/myeloid differentiation primary response gene 88 (MyD88)-dependent manner. Moreover, synergistically with hemopoietic cells, nonhemopoietic cells escalate late ileus via an IL-6 receptor-dependent inflammation-driven pathway. We therefore specifically investigated the role of myocytes in TLR4-triggered inflammation and ileus. TLR4(+/+), TLR4(-/-), bmTLR4(+/+)/TLR4(-/-) chimera, SM22-Cre(-/-)TLR4(flox/flox), and selective myocyte TLR4-deficient (SM22-Cre(+/-)TLR4(flox/flox)) mice were injected intraperitoneally with purified lipopolysaccharide. SM22-driven Cre recombinase activity was selectively detected in cardiac, gastrointestinal, skeletal, and vascular myocytes, of small-sized vessels in a two-color fluorescent Cre reporter mouse. In contrast to nonhemopoietic TLR4 deficiency, deletion of myocyte TLR4 signaling prevented neither endotoxin-induced suppression of spontaneous jejunal contractility in vitro nor early ileus in vivo at 6 h. Circulating plasma colony-stimulating factor 3 was greatly elevated during endotoxemia, independent of myocyte TLR4 signaling or time. TLR4 activation of myocytes contributed significantly to an early enteric IL-6 mRNA induction and systemic IL-6 release, as well as to a late increase in circulating chemokine (C-X-C motif) ligand 1 (CXCL1) and IL-17. Consequently, inhibition of myocyte TLR4 signaling allowed functional recovery of motility by preventing inflammation-driven late ileus at 24 h. Direct TLR4 activation of myocytes is not responsible for nonhemopoietic-mediated early ileus. However, myocytes are proinflammatory cells that potently drive enteric and systemic inflammation, subsequently fueling late mediator-triggered ileus. Specifically, the myocyte TLR4-dependent inflammatory signature of elevated plasma IL-6, CXCL1, and IL-17 is strongly associated with late rodent ileus.

Toll-like receptor 4 contributes to the inhibitory effect of morphine on colonic motility in vitro and in vivo

Opioids rank among the most potent analgesic drugs but gastrointestinal side effects, especially constipation, limit their therapeutic utility. The adverse effects of opioids have been attributed to stimulation of opioid receptors, but emerging evidence suggests that opioids interact with the innate immune receptor Toll-like receptor 4 (TLR4) and its signalling pathway. As TLR4 signalling affects gastrointestinal motility, we examined the involvement of TLR4 in morphine-induced depression of peristaltic motility in the guinea-pig intestine in vitro and male C57BL/6N mice in vivo. While the TLR4 antagonist TAK-242 (0.1 μM and 1 μM) did not alter the morphine-induced inhibition of peristalsis in the isolated guinea-pig small intestine, the morphine-induced decrease in pellet propulsion velocity in colonic segments was attenuated by TAK-242 (0.1 μM). The ability of TAK-242 (4 mg/kg) to mitigate the morphine-induced suppression of colonic motility was replicated in mice in vivo by measuring the expulsion time of beads inserted in the distal colon. The inhibition of upper gastrointestinal transit of mice by morphine was not affected by pre-treatment with TAK-242 (4 mg/kg) in vivo. This is the first report that morphine-induced inhibition of colonic peristalsis is alleviated by TLR4 antagonism. We therefore conclude that TLR4 may contribute to opioid-induced constipation.

Human colonic myogenic dysfunction induced by mucosal lipopolysaccharide translocation and oxidative stress

BACKGROUND

Impairment of gastrointestinal motility is frequently observed in patients with severe infection.

AIM

To assess whether exposure of human colonic mucosa to pathogenic lipopolysaccharide affects smooth muscle contractility.

METHODS

Human colonic mucosa and submucosa were sealed between two chambers, with the luminal side facing upwards and covered with Krebs solution, with or without lipopolysaccharide from a pathogenic strain of Escherichia coli (O111:B4; 1,000 ng/mL), and with the submucosal side facing downwards into Krebs. The solution on the submucosal side was collected following 30-min mucosal exposure to Krebs without (N-undernatant) or with lipopolysaccharide (lipopolysaccharide undernatant). Undernatants were tested for lipopolysaccharide and hydrogen peroxide levels and for their effects on smooth muscle cells in the presence of catalase, indomethacin or MG132.

RESULTS

Smooth muscle cells incubated with N-undernatant had a maximal contraction of 32 ± 5% that was reduced by 62.9 ± 12% when exposed to lipopolysaccharide undernatant. Inhibition of contraction was reversed by catalase, indomethacin and MG132. Lipopolysaccharide levels were higher in the lipopolysaccharide undernatant (2.7 ± 0.7 ng/mL) than in N-undernatant (0.45 ± 0.06 ng/mL) as well as hydrogen peroxide levels (133.75 ± 15.9 vs 82 ± 7.5 nM respectively).

CONCLUSIONS

Acute exposure of colonic mucosa to pathogenic lipopolysaccharide impairs muscle cell contractility owing to both lipopolysaccharide mucosal translocation and production of free radicals.

Systemic inflammation with enhanced brain activation contributes to more severe delay in postoperative ileus

BACKGROUND

The severity of postoperative ileus (POI) has been reported to result from decreased contractility of the muscularis inversely related to the number of infiltrating leukocytes. However, we previously observed that the severity of POI is independent of the number of infiltrating leukocytes, indicating that different mechanisms must be involved. Here, we hypothesize that the degree of tissue damage in response to intestinal handling determines the upregulation of local cytokine production and correlates with the severity of POI.

METHODS

Intestinal transit, the inflammatory response, I-FABP (marker for tissue damage) levels and brain activation were determined after different intensities of intestinal handling.

KEY RESULTS

Intense handling induced a more pronounced ileus compared with gentle intestinal manipulation (IM). No difference in leukocytic infiltrates in the handled and non-handled parts of the gut was observed between the two intensities of intestinal handling. However, intense handling resulted in significantly more tissue damage and was accompanied by a systemic inflammation with increased plasma levels of pro-inflammatory cytokines. In addition, intense but not gentle handling triggered enhanced c-Fos expression in the nucleus of the solitary tract (NTS) and area postrema (AP). In patients, plasma levels of I-FABP and inflammatory cytokines were significantly higher after open compared with laparoscopic surgery, and were associated with more severe POI.

CONCLUSIONS & INFERENCES

Not the influx of leukocytes, rather the manipulation-induced damage and subsequent inflammatory response determine the severity of POI. The release of tissue damage mediators and pro-inflammatory cytokines into the systemic circulation most likely contribute to the impaired motility of non-manipulated intestine.

Antioxidants counteract lipopolysaccharide-triggered alterations of human colonic smooth muscle cells

Gut dysmotility develops in individuals during and after recovering from infective acute gastroenteritis and it is apparently due to a direct effect of circulating lipopolysaccharides (LPS). This is an endotoxin with a prooxidant activity derived from gram-negative bacteria. Due to the lack of human models available so far, the mechanisms underlying LPS-induced gut dysmotility are, however, poorly investigated. In the present work long-term effects of LPS and their reversibility have been assessed by means of different analytical cytology methods on pure primary cultures of human colonic smooth muscle cells. We found that LPS triggered the following alterations: (i) a redox imbalance with profound changes of contractile microfilament network, and (ii) the induction of cell cycle progression with dedifferentiation from a contractile to a synthetic phenotype. These alterations persisted also after LPS removal. Importantly, two unrelated antioxidants, alpha-tocopherol and N-acetylcysteine, were able to reverse the cytopathic effects of LPS and to restore normal muscle cell function. The present data indicate that LPS is capable of triggering a persistent and long-term response that could contribute to muscle dysfunction occurring after an infective and related inflammatory burst and suggest a reappraisal of antioxidants in the management of postinfective motor disorders of the gut.

Microbiota, innate immune system, and gastrointestinal muscle: ongoing studies

AIM

To test the activities of culture-extracted or commercially available toll-like receptors (TLRs) ligands to establish their direct impact on target gastrointestinal motor cells.

METHODS

Short-term and long-term effects of Shigella flexneri M90T and Escherichia coli K-2 strains-extracted lipopolysaccharides (LPS), commercially highly purified LPS (E. coli O111:B4 and EH100), and Pam2CSK4 and Pam3CSK4, which bind TLR2/6 and TLR1/2 heterodimers, respectively, have been assessed on pure primary cultures of colonic human smooth muscle cells (HSMC).

RESULTS

Pathogenic Shigella-LPS and nonpathogenic E. coli K-2-LPS induced a time-dependent decrease of resting cell length and acetylcholine-induced contraction, with both alterations occurring rapidly and being more pronounced in response to the former. However, their effects differed, prolonging HSMC exposure with Shigella-LPS effects maintained throughout the 4 hours of observation compared with E. coli K-2-LPS, which disappeared after 60 minutes of incubation. Similar differences in magnitude and time dependency of myogenic effects were observed between pure TLR4 and TLR2/1 or TLR2/6 ligands. The specific activation of TLR4 with LPS from pathogen or nonpathogen E. coli, O111:B4 and EH100, respectively, induced smooth muscle alterations that progressively increased, prolonging incubation, whereas TLR2 ligands induced short-term alterations, of a lesser magnitude, which decreased over time. The real-time polymerase chain reaction analysis showed that HSMC express mRNA for TLR1, 2, 4, and 6, substantiating a direct effect of TLR ligands on human colonic smooth muscle.

CONCLUSIONS

This study highlights that bacterial products can directly affect gastrointestinal motility and that TLRs subtypes may differ in their cellular activity.

Role of interleukin-6 in hemopoietic and non-hemopoietic synergy mediating TLR4-triggered late murine ileus and endotoxic shock

BACKGROUND

Early murine endotoxin-induced ileus at 6 h is exclusively mediated by non-hemopoietic TLR4/MyD88 signaling despite molecular activation of hemopoietic cells which included a significant IL-6 mRNA induction. Our objective was to define the role of hemopoietic cells in LPS/TLR4-triggered ileus and inflammation over time, and identify mechanisms of ileus.

METHODS

CSF-1(-/-) , TLR4 non-chimera and TLR4 chimera mice were single-shot intraperitoneal injected with ultrapure lipopolysaccharide (UP-LPS) and studied up to 4 days. Subgroups of TLR4(WT) mice were additionally intravenously injected with exogenous recombinant IL-6 (rmIL-6) or murine soluble IL-6 receptor blocking antibody (anti-sIL-6R mAB).

KEY RESULTS

Hemopoietic TLR4 signaling independently mediated UP-LPS-induced ileus at 24 h, but chemotactic muscularis neutrophil extravasation was not causatively involved and mice lacking CSF-1-dependent macrophages died prematurely. Synergy of hemopoietic and non-hemopoietic cells determined ileus severity and mortality which correlated with synergistic cell lineage specific transcription of inflammatory mediators like IL-6 within the intestinal muscularis. Circulating IL-6 levels were LPS dose dependent, but exogenous rmIL-6 did not spark off a self-perpetuating inflammatory response triggering ileus. Sustained therapeutic inhibition of functional IL-6 signaling efficiently ameliorated late ileus while preemptive antibody-mediated IL-6R blockade was marginally effective in mitigating ileus. However, IL-6R blockade did not prevent endotoxin-associated mortality nor did it alter circulating IL-6 levels.

CONCLUSIONS & INFERENCES

A time-delayed bone marrow-driven mechanism of murine endotoxin-induced ileus exists, and hemopoietic cells synergize with non-hemopoietic cells thereby prolonging ileus and fueling intestinal inflammation. Importantly, IL-6 signaling via IL-6R/gp130 drives late ileus, yet it did not regulate mortality in endotoxic shock.

Iatrogenic extracellular matrix disruption as a local trigger for postoperative ileus

BACKGROUND

Active matrix metallopeptidase 9 (MMP-9) disruption of the extracellular matrix (ECM) plays an important role in inflammatory disorders. In this study, we investigated the inflammatory role of MMP-9 and the ECM breakdown product hyaluronan as a trigger for the postoperative intestinal inflammatory response of postoperative ileus.

METHODS

We performed a standardized intestinal surgical manipulation on rats to produce ileus assessed by the oral non-digestible fluorescein isothiocyanate-dextran transit assay. We studied isolated intestinal muscularis extracts for mRNA expressions of interleukin 6 (IL-6), MMP-9 and CD44. We quantified peritoneal MMP-9 activity using zymography, and quantified peritoneal fluid and serum for hyaluronan and tissue inhibitor of metalloproteinase 1 levels by enzyme-linked immunosorbent assay (ELISA). We cultured peritoneal macrophages and exposed them to peritoneal fluid or synthetic hyaluronan for ELISA analysis of IL-6 and macrophage inflammatory protein-1α.

RESULTS

Transit was significantly delayed after surgical manipulation, and extracts of the isolated jejunal and colonic muscularis demonstrated a significant induction of IL-6, MMP-9, and CD44 mRNAs compared with controls. Zymography confirmed significant MMP-9 activity in peritoneal fluid compared with controls. Enzyme-linked immunosorbent assay measurements showed a significant up-regulation in hyaluronan and tissue inhibitor of metalloproteinase 1 in the peritoneal fluid and serum. In addition, ELISA and reverse transcriptase-polymerase chain reaction measurements of peritoneal macrophages stimulated with postsurgical peritoneal fluid and synthetic hyaluronan resulted in higher expressions of IL-6 and macrophage inflammatory protein-1α in the macrophage supernatant.

CONCLUSIONS

Our results confirm that MMP-9 disruption in the ECM with hyaluronan release and muscularis CD44 receptor induction has the potential to trigger muscularis proinflammatory cascades that cause postoperative ileus. Matrix metallopeptidase 9 inhibition may be a novel therapeutic approach to limit postoperative ileus.

Differential molecular and cellular immune mechanisms of postoperative and LPS-induced ileus in mice and rats

Ileus is caused by the initiation of a complex cascade of molecular and cellular inflammatory responses within the intestinal muscularis, which might be species specific. Our objective was to investigate a possible immunological divergence in the mechanisms of postoperative- and endotoxin-induced ileus in C57BL/6 mice and Sprague-Dawley rats. Gastrointestinal transit (GIT) was measured at 24 h after the injurious stimulus. MPO-staining and F4/80 immunohistochemistry were used to quantify polymorphonuclear and monocyte infiltration of jejunal muscularis whole-mounts, and intestinal muscularis MCP-1, ICAM-1 and iNOS gene expression was assessed by RT-PCR. Intestinal muscularis subjected to in vivo surgical manipulation (SM) or LPS treatment was cultured for 24 h, and the liberation of nitric oxide and chemokines/cytokines into the culture medium was analyzed by Griess reaction and Luminex multiplex assay. Intestinal SM and lipopolysaccharide (LPS) (15 mg/kg) caused a significant delay in gastrointestinal transit, which was more severe in mice compared to rats in both injury models. Both SM- and LPS-triggered neutrophil and monocytic extravasation into the rat jejunal muscularis exceeded the cellular infiltration seen in mice. These results correlated with significantly greater increases in rat muscularis MCP-1 (syn. CCL2), ICAM-1 and iNOS message with more subsequent NO production after SM or LPS compared to mouse. The cultured muscularis obtained from SM mice released significantly more inflammatory proteins such as TNF-α, IL-1-α, IL-4 and GM-CSF compared to the manipulated rat muscularis. In contrast, LPS initiated the secretion of significantly more IL-1β by the inflamed rat muscularis compared to the mouse, but GM-CSF (syn. CSF2) liberation from mouse muscularis was markedly higher compared to LPS-treated rat muscularis. The data indicate that mechanistically the development of ileus in rat is mediated predominately through a leukocytic pathway consisting of chemotaxis, cellular extravasation and NO liberation. Whereas, the more intense mouse ileus evolves via a potent but injury-specific local cytokine response.

Hydrogen-enriched preservation protects the isogeneic intestinal graft and amends recipient gastric function during transplantation

BACKGROUND

Inhaled hydrogen gas exerts antioxidant and anti-inflammatory effects in rat intestinal transplantation. Here, we investigated whether ex vivo donor organ treatment with dissolved hydrogen would prevent intestinal graft injury.

METHODS

Isogeneic intestinal transplantation was performed in Lewis rats with vascular flush, luminal preservation, and cold graft storage in nitrogen-bubbled (SITxN2) or hydrogen-bubbled (SITxH2) preservation solution. Lactated Ringer's solution and 3-hr cold ischemia time were used for mechanistic investigations, whereas survival experiments were performed with University of Wisconsin solution and 6-hr cold ischemia time.

RESULTS

During the early phase of ischemia-reperfusion injury, hydrogen-enriched solution significantly preserved mucosal graft morphology, diminished graft malondialdehyde levels demonstrating substantial reduction potential and blunted proinflammatory molecular responses (early growth response gene [EGR-1], interleukin [IL]-6, IL-1ß, and inducible nitric oxide synthase) within the reperfused intestinal graft muscularis. During the late phase of ischemia-reperfusion injury, circulating IL-6 protein and lactate dehydrogenase levels were significantly ameliorated in SITxH2 animals, which were associated with a favorable functional outcome in in vivo liquid gastrointestinal transit and recipient solid gastric emptying of chrome steel balls, and marked prevention of the posttransplant associated suppression of in vitro muscarinic jejunal contractility. Reflecting improved graft preservation, hydrogen preloading of grafts increased recipient survival rates from 41% to 80%. Anti-inflammatory and antiapoptotic heme oxygenase-1 was significantly upregulated in the hydrogen-treated graft muscularis but not mucosa before reperfusion.

CONCLUSIONS

Graft preloading with hydrogen demonstrated superior morphologic and functional graft protection in rodent intestinal transplantation, ultimately facilitating recipient survival. Antioxidant capacity and muscularis heme oxygenase-1 upregulation are possible protective mechanisms.

Interplay between inflammation, immune system and neuronal pathways: Effect on gastrointestinal motility

Sepsis is a systemic inflammatory response representing the leading cause of death in critically ill patients, mostly due to multiple organ failure. The gastrointestinal tract plays a pivotal role in the pathogenesis of sepsis-induced multiple organ failure through intestinal barrier dysfunction, bacterial translocation and ileus. In this review we address the role of the gastrointestinal tract, the mediators, cell types and transduction pathways involved, based on experimental data obtained from models of inflammation-induced ileus and (preliminary) clinical data. The complex interplay within the gastrointestinal wall between mast cells, residential macrophages and glial cells on the one hand, and neurons and smooth muscle cells on the other hand, involves intracellular signaling pathways, Toll-like receptors and a plethora of neuroactive substances such as nitric oxide, prostaglandins, cytokines, chemokines, growth factors, tryptases and hormones. Multidirectional signaling between the different components in the gastrointestinal wall, the spinal cord and central nervous system impacts inflammation and its consequences. We propose that novel therapeutic strategies should target inflammation on the one hand and gastrointestinal motility, gastrointestinal sensitivity and even pain signaling on the other hand, for instance by impeding afferent neuronal signaling, by activation of the vagal anti-inflammatory pathway or by the use of pharmacological agents such as ghrelin and ghrelin agonists or drugs interfering with the endocannabinoid system.

Mechanical strain and TLR4 synergistically induce cell-specific inflammatory gene expression in intestinal smooth muscle cells and peritoneal macrophages

Mechanical trauma of the gut is an unavoidable event in abdominal surgery. Former studies demonstrated that intestinal manipulation induces a strong inflammation within the tunica muscularis. We hypothesized that mechanical strain initiates or aggravates proinflammatory responses in intestinal smooth muscle cells (iSMC) or macrophages. First, an appropriate isolation and culture method for neonatal rat iSMC was established. Purified iSMC and primary peritoneal macrophages (pMacs) were subjected to static or cyclic strain, and gene expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), IL-6, and IL-1β was analyzed by quantitative PCR. Supernatants from stretched iSMC were transferred to untreated pMacs or contrariwise, and medium transfer-triggered inflammatory gene expression was measured in unstretched cells. Finally, we investigated the synergistic effect of static strain on LPS-induced proinflammatory gene expression. Although cyclic strain failed, static strain significantly induced iNOS, COX-2, and IL-1β mRNA in iSMC. pMacs showed an increase in all inflammatory genes investigated as well as macrophage inflammatory protein (MIP)-1α and MIP-2 mRNA after static strain. Both cell entities liberated unknown mediators in response to stretch that mutually stimulated iNOS gene expression. Finally, mechanostimulation amplified LPS-induced iNOS and IL-1β gene expression in iSMC as well as COX-2 and IL-6 mRNA in pMacs. In conclusion, static strain initiates proinflammatory gene expression in iSMC and pMacs and triggers a bidirectional paracrine communication between both cultured cell entities via the liberation of unknown mediators. Furthermore, static strain synergistically operates with Toll-like receptor 4 ligation in a cell-specific manner. Hence, this study demonstrates that mechanical strain functions as an immunomodulatory stimulus in abdominal cells.

The enteric nervous system as a regulator of intestinal epithelial barrier function in health and disease

The intestinal epithelia proliferate and differentiate along the crypt villus axis to constitute a barrier cell layer separating some 10¹³ potentially harmful bacteria from a sterile mucosal compartment. Strict regulatory mechanisms are required to maintain a balance between the appropriate uptake of luminal food components and proteins, while constraining the exposure of the mucosal compartment to luminal antigens and microbes. The enteric nervous system is increasingly recognized as such a regulatory housekeeper of the epithelial barrier integrity, in addition to its ascribed immunomodulatory potential. Inflammation affects both epithelial integrity and barrier function and, in turn, loss of barrier function perpetuates inflammatory conditions. The observation that inflammatory conditions affect enteric neurons may add to the dysregulated barrier function in chronic disease. Here, we review the current understanding of the regulatory role of the nervous system in the maintenance of barrier function in healthy state, or during pathological conditions of, for instance, stress-induced colitis, surgical trauma or inflammation. We will discuss the clinical potential for advances in understanding the role of the enteric nervous system in this important phenomenon.

Dominant role of the MyD88-dependent signaling pathway in mediating early endotoxin-induced murine ileus

TLR4 ligation by pathogen-associated molecular patterns, such as Gram-negative bacteria-derived LPS, triggers a nonhematopoietic cell-mediated ileus during early endotoxemia. Our objective was to investigate the quantitative contributions of the two downstream signaling pathways of TLR4, namely the adapter proteins myeloid differentiation primary response gene 88 (MyD88) and Toll-IL-1-resistance (TIR) domain-containing adaptor-inducing IFN-beta (TRIF). Six hours after intraperitoneal injection of highly purified LPS (UP-LPS, 5 mg/kg), in vivo gastrointestinal transit and intestinal muscularis gene transcripts of inflammatory mediators chemokine (C-X-C motif) ligand 10, synonymous IP-10 (CXCL10), granulomonocyte colony stimulating factor (GM-CSF, synonymous CSF-2), IL-1beta, IL-6, IL-10, and inducible NO synthase (iNOS) were assessed in mice with transgenic loss-of-function for MyD88 or TRIF. LPS-induced MyD88 and TRIF mRNA upregulation was quantified within the intestinal muscularis of TLR4-competent and TLR4-mutant mice, and MyD88 mRNA levels were additionally measured in TLR4 bone marrow chimeras. MyD88 deficiency completely protected mice from early endotoxin-induced ileus, while TRIF deficiency partially ameliorated ileus severity. LPS induction of the primary downstream signaling element MyD88 was TLR4 dependent and was derived in equal amounts from both the hematopoietic and the nonhematopoietic cells. Conversely, no induction of TRIF mRNA was detectable. Significant gene induction of all inflammatory mediators was dependent on intracellular signal transduction by MyD88, while the TRIF MyD88-independent pathway predominantly regulated the molecular levels of CXCL10. In summary, MyD88 and TRIF are nonredundant signaling pathways in early endotoxin-induced rodent ileus, but MyD88 is the essential adaptor molecule for transduction of early TLR4-induced ileus and inflammatory signaling. The dependency of ileus on individual adaptor protein pathways is also reflected in the manifestation of specific molecular inflammatory events within the intestinal muscularis externa.

Membrane TLR signaling mechanisms in the gastrointestinal tract during sepsis

Our bacterial residents are deadly Janus-faced indwellers that can lead to a sepsis-induced systemic inflammatory response syndrome and multiple organ failure. Over half of ICU patients suffer from infections and sepsis remains one of the top 10 causes of death worldwide. Severe ileus frequently accompanies sepsis setting up an insidious cycle of gut-derived microbial translocation and the copious intestinal production of potent systemic inflammatory mediators. Few therapeutic advances have occurred to prevent/treat the sequelae of sepsis. Here, we selectively review studies on cellular membrane-bound Toll-like receptor (TLR) mechanisms of ileus. Virtually, no data exist on Gram-positive/TLR2 signaling mechanisms of ileus; however, TLR2 is highly inducible by numerous inflammatory mediators and studies using clinically relevant scenarios of Gram-positive sepsis are needed. Specific Gram-negative/TLR4 signaling pathways are being elucidated using a 'reverse engineering' approach, which has revealed that endotoxin-induced ileus is dually mediated by classical leukocyte signaling and by a MyD88-dependent non-bone marrow-derived mechanism, but the specific roles of individual cell populations are still unknown. Like TLR2, little is also know of the role of flagellin/TLR5 signaling in ileus. But, much can be learned by understanding TLR signaling in other systems. Clearly, the use of polymicrobial models provides important clinical relevancy, but the simultaneous activation of virtually all pattern recognition receptors makes it impossible to discretely study specific pathways. We believe that the dissection of individual TLR pathways within the gastrointestinal tract, which can then be intelligently reassembled in a meaningful manner, will provide insight into treatments for sepsis.