The dual effect of cannabinoid receptor-1 deficiency on the murine postoperative ileus

Role of Macrophages and Mast Cells as Key Players in the Maintenance of Gastrointestinal Smooth Muscle Homeostasis and Disease

The gut contains the largest macrophage pool in the body, with populations of macrophages residing in the mucosa and muscularis propria of the gastrointestinal (GI) tract. Muscularis macrophages (MMs), which are located within the muscularis propria, interact with cells essential for GI function, such as interstitial cells of Cajal, enteric neurons, smooth muscle cells, enteric glia, and fibroblast-like cells, suggesting that these immune cells contribute to several aspects of GI function. This review focuses on the latest insights on the factors contributing to MM heterogeneity and the functional interaction of MMs with other cell types essential for GI function. This review integrates the latest findings on macrophages in other organs with increasing knowledge of MMs to better understand their role in a healthy and diseased gut. We describe the factors that contribute to (muscularis macrophage) MM heterogeneity, and the nature of MM interactions with cells regulating GI function. Finally, we also describe the increasing evidence suggesting a critical role of another immune cell type, the mast cell, in normal and diseased GI physiology.

Improved motility in the gastrointestinal tract of a postoperative ileus rat model with ilaprazole

Postoperative ileus (POI), a symptom that occurs after abdominal surgery, reduces gastrointestinal motility. Although its mechanism is unclear, POI symptoms are known to be caused by inflammation 6 to 72 h after surgery. As proton pump inhibitors exhibit protective effect against acute inflammation, the purpose of this study was to determine the effect of ilaprazole on a POI rat model. POI was induced in rats by abdominal surgery. Rats were divided into six groups: control: normal rat + 0.5% CMC-Na, vehicle: POI rat + 0.5% CMC-Na, mosapride: POI rat + mosapride 2 mg/kg, ilaprazole 1 mg/kg: POI rat + ilaprazole 1 mg/kg, ilaprazole 3 mg/kg: POI rat + ilaprazole 3 mg/kg, and ilaprazole 10 mg/kg: POI rat + ilaprazole 10 mg/kg. Gastrointestinal motility was confirmed by measuring gastric emptying (GE) and gastrointestinal transit (GIT). In the small intestine, inflammation was confirmed by measuring TNF-α and IL-1β; oxidative stress was confirmed by SOD, GSH, and MDA levels; and histological changes were observed by H&E staining. Based on the findings, GE and GIT were decreased in the vehicle group and improved in the ilaprazole 10 mg/kg group. In the ilaprazole 10 mg/kg group, TNF-α and IL-1β levels were decreased, SOD and GSH levels were increased, and MDA levels were decreased. Histological damage was also reduced in the ilaprazole-treated groups. These findings suggest that ilaprazole prevents the decrease in gastrointestinal motility, a major symptom of postoperative ileus, and reduces inflammation and oxidative stress.

Experimental postoperative ileus: is Th2 immune response involved?

Rationale: Postoperative ileus (POI) is a frequent complication arising after gastrointestinal surgery but pathogenesis of POI is still not fully understood. While Th1 immune cells are implicated in POI, the involvement of Th2 cells has not yet been clarified. Given the impact of reactive oxygen species (ROS) in the regulation of Th1 and Th2 balance, we hypothesized that not only Th1 but also Th2 immune response can be involved in the development of experimental POI. Methods: The intestinal transit test was performed using carbon gum arabic. Electron microscopy was employed to assess tissue morphology and the presence of immune cells. Cytokines, IgE and ROS were measured. Immune cells from Peyer's patches were analyzed by Flow Cytometry and toluidine blue staining was used for detection of mast cells. Transcriptional factors were analyzed by Western blot. Results: POI is associated with an increase in both Th2 cytokines and Th2 cells. We have further demonstrated that POI induces a Th2-dependent activation of memory and non-memory B cells. This was accompanied by an increase in a number of mast cells in the colon of POI mice as well by an increased IgE and histamine plasma levels. We found that POI-induced accumulation of ROS was associated with an increased expression of the transcriptional factors HMBGI, NF-κB, and p38. This increased expression seemed to be associated with a Th2 response. Conclusion: Th2 immune response can be involved in the activation of mast cells in POI, which was associated with ROS mediated activation of NF-κB and p38 MAPK signaling pathway.

The role of CA1 CB1 receptors on lithium-induced spatial memory impairment in rats

Lithium, a glycogen synthase kinase-3β (GSK-3β) inhibitor, prevents cannabinoid withdrawal syndrome, but there is limited data exploring the interaction between lithium and cannabinoid system on memory processes. The present study aimed to test the interaction between dorsal hippocampal (CA1 region) cannabinoid system and lithium on spatial memory in rats. Spatial memory was assessed in Morris Water Maze (MWM) apparatus by a single training session of eight trials. The results showed that pre-training intra-CA1 microinjection of ACPA, the cannabinoid type 1 receptor (CB1r) agonist, at doses of 0.001, 0.01 or 1 µg/rat, or AM251, the cannabinoid type 1 receptor (CB1r) antagonist, at doses of 1, 10 or 100 ng/rat, increased escape latency and traveled distance to the platform, suggesting a spatial learning impairment, whereas intraperitoneal administration of lithium (0.5, 1 or 5 mg/kg) had no effect on spatial learning. Also, rats that received lithium plus a lower dose of ACPA (0.001 µg/rat) or AM251 (1 ng/rat) had successful performance in the MWM. In the probe test, the results showed that pre-training administration of lithium (5 mg/kg) and ACPA (0.01 or 1 µg/rat) but not AM251 (at all doses used) impaired spatial memory retrieval. Also, lower dose of ACPA (0.001 µg/rat) or AM251 (1 ng/rat) potentiated the effect of ineffective doses of lithium (0.5 and 1 mg/kg) on spatial memory retrieval, while restored the effect of effective dose of lithium (5 mg/kg). In conclusion, cannabinoids may have a dual effect on lithium-induced spatial memory impairment in rats.

Role of transient receptor potential melastatin 2 in surgical inflammation and dysmotility in a mouse model of postoperative ileus

In this study, we investigated the role of transient receptor potential melastatin 2 (TRPM2), a nonselective cation channel abundantly expressed in inflammatory cells such as macrophages, in the development of postoperative ileus, a complication of abdominal surgery characterized by gastrointestinal dysmotility. In wild-type mice, we found that intestinal manipulation, a maneuver that elicits symptoms typical of postoperative ileus, delays the transit of fluorescein-labeled dextran, promotes the infiltration of CD68⁺ macrophages, Ly6B.2⁺ neutrophils, and MPO⁺ cells into intestinal muscles, boosts expression of IL-1β, IL-6, TNF-α, iNOS, and CXCL2 in intestinal muscles and peritoneal macrophages, enhances phosphorylation of ERK and p38 MAPK in intestinal muscles, and amplifies IL-1β, IL-6, TNF-α, iNOS, and CXCL2 expression in resident and thioglycolate-elicited peritoneal macrophages following exposure to lipopolysaccharide. Remarkably, TRPM2 deficiency completely blocks or diminishes these effects. Indeed, intestinal manipulation appears to activate TRPM2 in resident muscularis macrophages and elicits release of inflammatory cytokines and chemokines, which, in turn, promote infiltration of macrophages and neutrophils into the muscle, ultimately resulting in dysmotility. NEW & NOTEWORTHY Activation of transient receptor potential melastatin 2 (TRPM2) releases inflammatory cytokines and chemokines, which, in turn, promote the infiltration of inflammatory cells and macrophages into intestinal muscles, ultimately resulting in dysmotility. Thus TRPM2 is a promising target in treating dysmotility due to postoperative ileus, a complication of abdominal surgery.

Alterations in the gut barrier and involvement of Toll-like receptor 4 in murine postoperative ileus

BACKGROUND

The changes in the gut barrier (GB) and associated mechanisms in postoperative ileus (POI) are still unclear. Toll-like receptor 4 (TLR4) is involved in inflammation, which may cause GB dysfunction and POI. Here, the roles of the GB in POI in relation to TLR4-dependent signaling pathways were explored.

METHODS

POI was induced by small bowel manipulation in wild-type (WT) and TLR4-knockout (TLR4-/-) mice. Twenty-four hours after manipulation, indices of gastrointestinal (GI) transit, GB structure and function, inflammation, and related signaling pathways were analyzed.

KEY RESULTS

Normal GI motility and GB function were not affected by TLR4 knockout. Compared with WT POI mice, TLR4-/-POI mice showed milder GI transit retardation, GB dysfunction, and inflammatory responses. In WT mice, GB disorder was characterized by colonic goblet cells depletion, increased gut claudin-2 expression, and decreased CD4+/CD8+ ratios in intestinal Peyer's patches. Green fluorescent protein-tagged Escherichia coli in the gut was detected in plasma and extraintestinal organs, followed with increased plasma lipopolysaccharide. These changes displayed in WT POI mice were less severe in TLR4-/-POI mice. Furthermore, the mRNA and protein expression of interleukin-6, monocyte chemotactic protein-1, pp38 and pJNK in the intestine, and TNF-α level in plasma were significantly increased in WT, but not TLR4-/-POI mice.

CONCLUSIONS & INFERENCES

These results indicate that GB is impaired in the experimental POI, with inflammation being involved in this pathological process. TLR4 deficiency alleviated GB dysfunction and suppressed inflammation by disrupting the activation of mitogen-activated protein kinase signaling pathways, thereby ameliorating POI.

Critical Evaluation of Animal Models of Gastrointestinal Disorders

Preclinical research remains an important tool for discovery and validation of novel therapeutics for gastrointestinal disorders. While in vitro assays can be used to verify receptor-ligand interactions and test for structural activity of new compounds, only whole-animal studies can demonstrate drug efficacy within the gastrointestinal system. Most major gastrointestinal disorders have been modeled in animals; however the translational relevance of each model is not equal. The purpose of this chapter is to provide a critical evaluation of common animal models that are being used to develop pharmaceuticals for gastrointestinal disorders. For brevity, the models are presented for upper gastrointestinal disorders involving the esophagus, stomach, and small intestine and lower gastrointestinal disorders that focus on the colon. Particular emphasis is used to explain the face and construct validity of each model, and the limitations of each model, including data interpretation, are highlighted. This chapter does not evaluate models that rely on surgical or other non-pharmacological interventions for treatment.

Involvement of Cannabinoid Signaling in Vincristine-Induced Gastrointestinal Dysmotility in the Rat

Background: In different models of paralytic ileus, cannabinoid receptors are overexpressed and endogenous cannabinoids are massively released, contributing to gastrointestinal dysmotility. The antitumoral drug vincristine depresses gastrointestinal motility and a similar mechanism could participate in this effect. Therefore, our aim was to determine, using CB₁ and CB₂ antagonists, whether an increased endocannabinoid tone is involved in vincristine-induced gastrointestinal ileus.

Methods: First, we confirmed the effects of vincristine on the gut mucosa, by conventional histological techniques, and characterized its effects on motility, by radiographic means. Conscious male Wistar rats received an intraperitoneal injection of vincristine (0.1–0.5 mg/kg), and barium sulfate (2.5 ml; 2 g/ml) was intragastrically administered 0, 24, or 48 h later. Serial X-rays were obtained at different time-points (0–8 h) after contrast. X-rays were used to build motility curves for each gastrointestinal region and determine the size of stomach and caecum. Tissue samples were taken for histology 48 h after saline or vincristine (0.5 mg/kg). Second, AM251 (a CB₁ receptor antagonist) and AM630 (a CB₂ receptor antagonist) were used to determine if CB₁ and/or CB₂ receptors are involved in vincristine-induced gastrointestinal dysmotility.

Key results: Vincristine induced damage to the mucosa of ileum and colon and reduced gastrointestinal motor function at 0.5 mg/kg. The effect on motor function was particularly evident when the study started 24 h after administration. AM251, but not AM630, significantly prevented vincristine effect, particularly in the small intestine, when administered thrice. AM251 alone did not significantly alter gastrointestinal motility.

Conclusions: The fact that AM251, but not AM630, is capable of reducing the effect of vincristine suggests that, like in other experimental models of paralytic ileus, an increased cannabinoid tone develops and is at least partially responsible for the alterations induced by the antitumoral drug on gastrointestinal motor function. Thus, CB₁ antagonists might be useful to prevent/treat ileus induced by vincristine.

Cannabinoids regulate intestinal motor function and electrophysiological activity of myocytes in rodents

BACKGROUND AND AIMS

This study aims to investigate the effects of cannabinoid (CB)1 and CB2 receptor ligands on intestinal motor function and muscular electrophysiological activity in rodent gastrointestinal (GI) tract.

METHODS

Lipopolysaccharide (LPS) was used to induce intestinal hypomotility. The effect of selective CB1 and CB2 agonists and antagonists on contractility of the muscle strips from rat jejunum was measured using organ bath, and the membrane potential of the jejunal smooth muscle cells was recorded with intracellular microelectrodes. The single cell patch clamp technique was applied to record delayed rectifying potassium currents (IKV) and spontaneous transient outward currents (STOC).

RESULTS

LPS significantly reduced contractility of the smooth muscle strips (p <0.010) and caused hyperpolarization of membrane potential of the smooth muscle cells (p <0.010). This LPS-induced effect was reversed by AM251 and AM630, selective CB1 and CB2 antagonists, respectively, which promoted contractions of smooth muscle strips and triggered cell depolarization (p <0.010). LPS-induced changes were further enhanced in the presence of CB agonists, HU210 and WIN55 (p <0.050 or p <0.010). No effect of HU210 or AM251 on IKV and STOC has been observed. This ex vivo study suggests that CB1 and CB2 receptors are involved in intestinal motor function in normal and LPS-induced pathological states and the regulation of the membrane potential of smooth muscle cells is very likely one of the effective mechanisms.

CONCLUSIONS

This is one of the first reports on neuronal regulation of intestinal motility through CB-dependent pathways with potential application in the treatment of inflammatory and functional GI disorders.

Mangiferin ameliorates the intestinal inflammatory response and the impaired gastrointestinal motility in mouse model of postoperative ileus

Our previous study has shown that mangiferin (MGF), a glucosylxanthone from Mangifera indica, exerts gastrointestinal prokinetic action involving a cholinergic mechanism. Postoperative ileus (POI) is a temporary disturbance in gastrointestinal motility following surgery, and intestinal inflammatory response plays a critical role in the pathogenesis of POI. The present study investigated to know whether MGF having anti-inflammatory and prokinetic actions can ameliorate the intestinal inflammation and impaired gastrointestinal transit seen in the mouse model of POI. Experimental POI was induced in adult male Swiss mice by standardized small intestinal manipulation (IM). Twenty-four hours later, gastrointestinal transit was assessed by charcoal transport. MGF was administered orally 1 h before the measurement of GIT. To evaluate the inflammatory response, plasma levels of proinflammatory cytokines TNF-α, IL-1β, IL-6, and chemokine MCP-1, and the myeloperoxidase activity, nitrate/nitrite level, and histological changes of ileum were determined in mice treated or not with MGF. Experimental POI in mice was characterized by decreased gastrointestinal transit and marked intestinal and systemic inflammatory response. MGF treatment led to recovery of the delayed intestinal transit induced by IM. MGF in ileum significantly inhibited the myeloperoxidase activity, a marker of neutrophil infiltration, and nitrate/nitrite level and reduced the plasma levels of TNF-α, IL-1β, IL-6, and MCP-1 as well. MGF treatment ameliorates the intestinal inflammatory response and the impaired gastrointestinal motility in the mouse model of POI.

Eudragit nanoparticles loaded with silybin: a detailed study of preparation, freeze-drying condition and in vitro/in vivo evaluation

The objective of this work was use of silybin nanoparticles in treatment of ulcerative colitis (UC). Eudragit RL PO nanoparticles loaded with silybin were produced using solvent-evaporation emulsification technique. Then, they were coated by Eudragit FS30D. Drug release was studied in different physiological environments. Colitis was induced by 4% of acetic acid in rats which received freeze-dried nanoparticles of silybin (75 mg/kg/day), dexamethasone (1 mg/kg/day), blank nanoparticles and normal saline orally for 5 days. Then macroscopic, histopathological evaluation and biochemical analysis, including myeloperoxidase (MPO) activity, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels in colon tissues were determined using enzyme-linked immunosorbent assay (ELISA) kits. Macroscopic and histopathological scores were improved by the optimised nanoparticles. The optimised nanoparticles had a particle size of 109 ± 6 nm, zeta potential of 15.4 ± 2 mV, loading efficiency of 98.3 ± 12% and release efficiency of 40.8 ± 5.5% at 24 h. TNF-α, IL-6 and MPO activity were reduced significantly by nanoparticles compared to control group (p < 0.05).

Genetic Manipulation of the Endocannabinoid System

The physiological and pathophysiological functions of the endocannabinoid system have been studied extensively using transgenic and targeted knockout mouse models. The first gene deletions of the cannabinoid CB(1) receptor were described in the late 1990s, soon followed by CB(2) and FAAH mutations in early 2000. These mouse models helped to elucidate the fundamental role of endocannabinoids as retrograde transmitters in the CNS and in the discovery of many unexpected endocannabinoid functions, for example, in the skin, bone and liver. We now have knockout mouse models for almost every receptor and enzyme of the endocannabinoid system. Conditional mutant mice were mostly developed for the CB(1) receptor, which is widely expressed on many different neurons, astrocytes and microglia, as well as on many cells outside the CNS. These mouse strains include "floxed" CB(1) alleles and mice with a conditional re-expression of CB(1). The availability of these mice made it possible to decipher the function of CB(1) in specific neuronal circuits and cell populations or to discriminate between central and peripheral effects. Many of the genetic mouse models were also used in combination with viral expression systems. The purpose of this review is to provide a comprehensive overview of the existing genetic models and to summarize some of the most important discoveries that were made with these animals.

Irritable bowel syndrome: Emerging paradigm in pathophysiology

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, characterized by abdominal pain, bloating, and changes in bowel habits. These symptoms cannot be explained by structural abnormalities and there is no specific laboratory test or biomarker for IBS. Therefore, IBS is classified as a functional disorder with diagnosis dependent on the history taking about manifested symptoms and careful physical examination. Although a great deal of research has been carried out in this area, the pathophysiology of IBS is complex and not completely understood. Multiple factors are thought to contribute to the symptoms in IBS patients; altered gastrointestinal motility, visceral hypersensitivity, and the brain-gut interaction are important classical concepts in IBS pathophysiology. New areas of research in this arena include inflammation, postinfectious low-grade inflammation, genetic and immunologic factors, an altered microbiota, dietary factors, and enteroendocrine cells. These emerging studies have not shown consistent results, provoking controversy in the IBS field. However, certain lines of evidence suggest that these mechanisms are important at least a subset of IBS patients, confirming that IBS symptoms cannot be explained by a single etiological mechanism. Therefore, it is important to keep in mind that IBS requires a more holistic approach to determining effective treatment and understanding the underlying mechanisms.

Peritoneal air exposure elicits an intestinal inflammation resulting in postoperative ileus

BACKGROUND

The pathogenesis of postoperative ileus (POI) is complex. The present study was designed to investigate the effects of peritoneal air exposure on the POI intestinal inflammation and the underlying mechanism.

METHODS

Sprague-Dawley rats were randomized into five groups (6/group): the control group, the sham group, and three exposure groups with peritoneal air exposure for 1, 2, or 3 h. At 24 h after surgery, we analyzed the gastrointestinal transit, the serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-10, the myeloperoxidase activity, and the levels of TNF-α, IL-1β, IL-6, and IL-10 in the ileum and colon. The oxidant and antioxidant levels in the ileum and colon were analyzed by measuring malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and total antioxidant capacity (T-AOC).

RESULTS

Peritoneal air exposure caused an air-exposure-time-dependent decrease in the gastrointestinal transit. The length of peritoneal air exposure is correlated with the severity of both systemic and intestinal inflammations and the increases in the levels of MDA, SOD, GSH-Px, and T-AOC.

CONCLUSIONS

The length of peritoneal air exposure is proportional to the degree of intestinal paralysis and the severity of intestinal inflammation, which is linked to the oxidative stress response.