Protective effect of exogenous nitrite in postoperative ileus

Targeting cell death pathways in intestinal ischemia-reperfusion injury: a comprehensive review

Intestinal ischemia-reperfusion (I/R) is a multifaceted pathological process, and there is a lack of clear treatment for intestinal I/R injury. During intestinal I/R, oxidative stress and inflammation triggered by cells can trigger a variety of cell death mechanisms, including apoptosis, autophagy, pyroptosis, ferroptosis, and necrosis. These cell death processes can send a danger signal for the body to be damaged and prevent intestinal I/R injury. Therefore, identifying key regulatory molecules or markers of these cell death mechanisms when intestinal I/R injury occurs may provide valuable information for the treatment of intestinal I/R injury. This paper reviews the regulatory molecules and potential markers that may be involved in regulating cell death during intestinal I/R and elaborates on the cell death mechanism of intestinal I/R injury at the molecular level to provide a theoretical basis for discovering new molecules or markers regulating cell death during intestinal I/R injury and provides ideas for drug development for the treatment of intestinal I/R injury.

Postoperative ileus-An ongoing conundrum

BACKGROUND

Postoperative ileus is common and is a major clinical problem. It has been widely studied in patients and in experimental models in laboratory animals. A wide variety of treatments have been tested to prevent or modify the course of this disorder.

PURPOSE

This review draws together information on animal studies of ileus with studies on human patients. It summarizes some of the conceptual advances made in understanding the mechanisms that underlie paralytic ileus. The treatments that have been tested in human subjects (both pharmacological and non-pharmacological) and their efficacy are summarized and graded consistent with current clinical guidelines. The review is not intended to provide a comprehensive overview of ileus, but rather a general understanding of the major clinical problems associated with it, how animal models have been useful to elucidate key mechanisms and, finally, some perspectives from both scientists and clinicians as to how we may move forward with this debilitating yet common condition.

Cholinergic System and Its Therapeutic Importance in Inflammation and Autoimmunity

Neurological and immunological signals constitute an extensive regulatory network in our body that maintains physiology and homeostasis. The cholinergic system plays a significant role in neuroimmune communication, transmitting information regarding the peripheral immune status to the central nervous system (CNS) and vice versa. The cholinergic system includes the neurotransmitter\ molecule, acetylcholine (ACh), cholinergic receptors (AChRs), choline acetyltransferase (ChAT) enzyme, and acetylcholinesterase (AChE) enzyme. These molecules are involved in regulating immune response and playing a crucial role in maintaining homeostasis. Most innate and adaptive immune cells respond to neuronal inputs by releasing or expressing these molecules on their surfaces. Dysregulation of this neuroimmune communication may lead to several inflammatory and autoimmune diseases. Several agonists, antagonists, and inhibitors have been developed to target the cholinergic system to control inflammation in different tissues. This review discusses how various molecules of the neuronal and non-neuronal cholinergic system (NNCS) interact with the immune cells. What are the agonists and antagonists that alter the cholinergic system, and how are these molecules modulate inflammation and immunity. Understanding the various functions of pharmacological molecules could help in designing better strategies to control inflammation and autoimmunity.

Hemin reduces postoperative ileus in a heme oxygenase 1-dependent manner while dimethyl fumarate does without heme oxygenase 1-induction

BACKGROUND

Postoperative ileus (POI), the impairment of gastrointestinal motility after abdominal surgery, is mainly due to intestinal muscular inflammation. Carbon monoxide (CO)-releasing compounds were shown to exert an anti-inflammatory effect in murine POI partially through induction of heme oxygenase-1 (HO-1). The influence of hemin and dimethyl fumarate (DMF), currently used for multiple sclerosis (MS), was therefore tested in murine POI.

METHODS

C57BL/6J mice were anesthetized and after laparotomy, POI was induced via intestinal manipulation (IM). Animals were treated with either 30 mg kg^-1 hemin intraperitoneally (ip), 30 mg kg^-1 DMF ip, or 100 mg kg^-1 intragastrically (ig) 24 hours before IM. Intestinal transit was assessed 24 hours postoperatively and mucosa-free muscularis or whole segments of the small intestine were stored for later analysis. Intestinal HO-1 protein expression was studied at 6, 12, and 24 hours after administration of hemin or DMF in non-manipulated mice.

KEY RESULTS

Pretreatment with hemin and DMF, both ig and ip, prevented the delayed transit seen after IM. Concomitantly, both hemin and DMF significantly reduced the increased interleukin-6 levels and the elevated leukocyte infiltration in the muscularis. Hemin but not DMF caused a significant increase in intestinal HO-1 protein expression and co-administration of the HO-1 inhibitor chromium mesoporphyrin abolished the protective effects of hemin on POI; DMF reduced the IM-induced activation of NF-κB and ERK 1/2.

CONCLUSIONS AND INFERENCES

Both hemin and DMF improve the delayed transit and inflammation seen in murine POI, but only hemin does so in a HO-1-dependent manner.

The H2S-Releasing Naproxen Derivative ATB-346 and the Slow-Release H2S Donor GYY4137 Reduce Intestinal Inflammation and Restore Transit in Postoperative Ileus

Objective: Intestinal inflammation triggers postoperative ileus (POI), commonly seen after abdominal surgery and characterized by impaired gastrointestinal transit; when prolonged, this leads to increased morbidity. Hydrogen sulfide (H2S) is recognized as an important mediator of many (patho)physiological processes, including inflammation, and is now investigated for anti-inflammatory application. Therefore, the aim of this study was to investigate the effect of the H2S-releasing naproxen derivative ATB-346, developed to reduce gastrointestinal injury by naproxen, and the slow-release H2S donor GYY4137 on intestinal inflammation and delayed gastrointestinal transit in murine POI. Methods: C57Bl6J mice were fasted for 6 h, anesthetized and after laparotomy, POI was induced by compressing the small intestine with two cotton applicators for 5 min (intestinal manipulation; IM). GYY4137 (50 mg/kg, intraperitoneally), ATB-346 (16 mg/kg, intragastrically) or naproxen (10 mg/kg, intragastrically) were administered 1 h before IM. At 24 h postoperatively, gastrointestinal transit was assessed via fluorescent imaging, and mucosa-free muscularis segments were prepared for later analysis. Inflammatory parameters and activity of inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 were measured. Histological examination of whole tissue sections was done on hematoxylin-eosin stained slides. Results: Pre-treatment with GYY4137 (geometric center; GC: 7.6 ± 0.5) and ATB-346 (GC: 8.4 ± 0.3) prevented the delayed transit induced by IM (GC: 3.6 ± 0.5 vs. 9.0 ± 0.4 in non-operated controls) while naproxen only partially did (GC: 5.9 ± 0.5; n = 8 for all groups). GYY4137 and ATB-346 significantly reduced the IM-induced increase in muscular myeloperoxidase (MPO) activity and protein levels of interleukin (IL)-6, IL-1β and monocyte chemotactic protein 1; the reduction by naproxen was less pronounced and only reached significance for MPO activity and IL-6 levels. All treatments significantly reduced the increase in COX-2 activity caused by IM, whereas only GYY4137 significantly reduced the increase in iNOS activity. Naproxen treatment caused significant histological damage of intestinal villi. Conclusion: The study shows that naproxen partially prevents POI, probably through its inhibitory effect on COX-2 activity. Both ATB-346 and GYY4137 were more effective, the result with GYY4137 showing that H2S per se can prevent POI.

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.

Disruption of the pacemaker activity of interstitial cells of Cajal via nitric oxide contributes to postoperative ileus

BACKGROUND

Interstitial cells of Cajal (ICC) serve as intestinal pacemakers. Postoperative ileus (POI) is a gastrointestinal motility disorder that occurs following abdominal surgery, which is caused by inflammation-induced dysfunction of smooth muscles and enteric neurons. However, the participation of ICC in POI is not well understood. In this study, we investigated the functional changes of ICC in a mouse model of POI.

METHODS

Intestinal manipulation (IM) was performed to induce POI. At 24 h or 48 h after IM, the field potential of the intestinal tunica muscularis was investigated. Tissues were also examined by immunohistochemistry and electron microscopic analysis.

KEY RESULTS

Gastrointestinal transit was significantly decreased with intestinal tunica muscularis inflammation at 24 h after IM, which was ameliorated at 48 h after IM. The generation and propagation of pacemaker potentials were disrupted at 24 h after IM and recovered to the control level at 48 h after IM. ICC networks, detected by c-Kit immunoreactivity, were remarkably disrupted at 24 h after IM. Electron microscopic analysis revealed abnormal vacuoles in the ICC cytoplasm. Interestingly, the ICC networks recovered at 48 h after IM. Administration of aminoguanidine, an inducible nitric oxide synthase inhibitor, suppressed the disruption of ICC networks. Ileal smooth muscle tissue cultured in the presence of nitric oxide donor, showed disrupted ICC networks.

CONCLUSIONS AND INFERENCES

The generation and propagation of pacemaker potentials by ICC are disrupted via nitric oxide after IM, and this disruption may contribute to POI. When inflammation is ameliorated, ICC can recover their pacemaker function.

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.

Protective effect of exogenous nitrite in postoperative ileus

BACKGROUND AND PURPOSE

As the pathogenesis of postoperative ileus (POI) involves inflammation and oxidative stress, comparable to ischaemia/reperfusion injury which can be ameliorated with nitrite, we investigated whether nitrite can protect against POI and explored the mechanisms involved.

EXPERIMENTAL APPROACH

We used intestinal manipulation (IM) of the small intestine to induce POI in C57BL/6J mice. Sodium nitrite (48 nmol) was administered intravenously just before IM. Intestinal transit was assessed using fluorescent imaging. Bethanechol-stimulated jejunal circular muscle contractions were measured in organ baths. Inflammatory parameters, neutrophil infiltration, inducible NOS (iNOS) activity, reactive oxygen species (ROS) levels, mitochondrial complex I activity and cGMP were measured in the intestinal muscularis.

KEY RESULTS

Pre-treatment with nitrite markedly improved the delay in intestinal transit and restored the reduced intestinal contractility observed 24 h following IM. This was accompanied by reduced protein levels of TNF-α, IL-6 and the chemokine CCL2, along with reduced iNOS activity and ROS levels. The associated neutrophil influx at 24 h was not influenced by nitrite. IM reduced mitochondrial complex I activity and cGMP levels; treatment with nitrite increased cGMP levels. Pre-treatment with the NO scavenger carboxy-PTIO or the soluble guanylyl cyclase inhibitor ODQ abolished nitrite-induced protective effects.

CONCLUSIONS AND IMPLICATIONS

Exogenous nitrite deserves further investigation as a possible treatment for POI. Nitrite-induced protection of POI in mice was dependent on NO and this effect was not related to inhibition of mitochondrial complex I, but did involve activation of soluble guanylyl cyclase.