Role of mast cells in mucosal diseases: current concepts and strategies for treatment

Role of CD34 in inflammatory bowel disease

Inflammatory bowel disease (IBD) is caused by a variety of pathogenic factors, including chronic recurrent inflammation of the ileum, rectum, and colon. Immune cells and adhesion molecules play an important role in the course of the disease, which is actually an autoimmune disease. During IBD, CD34 is involved in mediating the migration of a variety of immune cells (neutrophils, eosinophils, and mast cells) to the inflammatory site, and its interaction with various adhesion molecules is involved in the occurrence and development of IBD. Although the function of CD34 as a partial cell marker is well known, little is known on its role in IBD. Therefore, this article describes the structure and biological function of CD34, as well as on its potential mechanism in the development of IBD.

Mechanisms of Regulation of Transporters of Amino Acid Absorption in Inflammatory Bowel Diseases

Intestinal absorption of dietary amino acids/peptides is essential for protein homeostasis, which in turn is crucial for maintaining health as well as restoration of health from significant diseases. Dietary amino acids/peptides are absorbed by unique transporter processes present in the brush border membrane of absorptive villus cells, which line the entire length of the intestine. To date, the only nutrient absorptive system described in the secretory crypt cells in the mammalian intestine is the one that absorbs the amino acid glutamine. Majority of the amino acid transporters are sodium dependent and therefore require basolateral membrane Na-K-ATPase to maintain an efficient transcellular Na gradient for their activity. These transport processes are tightly regulated by various cellular and molecular mechanisms that facilitate their optimal activity during normal physiological processes. Malabsorption of amino acids, recently described in pathophysiological states such as in inflammatory bowel disease (IBD), is undoubtedly responsible for the debilitating symptoms of IBD such as malnutrition, weight loss and ultimately a failure to thrive. Also recently, in vivo models of IBD and in vitro studies have demonstrated that specific immune-inflammatory mediators/pathways regulate specific amino acid transporters. This provides possibilities to derive novel nutrition and immune-based treatment options for conditions such as IBD. © 2020 American Physiological Society. Compr Physiol 10:673-686, 2020.

Airway pathological heterogeneity in asthma: Visualization of disease microclusters using topological data analysis

BACKGROUND

Asthma is a complex chronic disease underpinned by pathological changes within the airway wall. How variations in structural airway pathology and cellular inflammation contribute to the expression and severity of asthma are poorly understood.

OBJECTIVES

Therefore we evaluated pathological heterogeneity using topological data analysis (TDA) with the aim of visualizing disease clusters and microclusters.

METHODS

A discovery population of 202 adult patients (142 asthmatic patients and 60 healthy subjects) and an external replication population (59 patients with severe asthma) were evaluated. Pathology and gene expression were examined in bronchial biopsy samples. TDA was applied by using pathological variables alone to create pathology-driven visual networks.

RESULTS

In the discovery cohort TDA identified 4 groups/networks with multiple microclusters/regions of interest that were masked by group-level statistics. Specifically, TDA group 1 consisted of a high proportion of healthy subjects, with a microcluster representing a topological continuum connecting healthy subjects to patients with mild-to-moderate asthma. Three additional TDA groups with moderate-to-severe asthma (Airway Smooth Muscle^High, Reticular Basement Membrane^High, and Remodeling^Low groups) were identified and contained numerous microclusters with varying pathological and clinical features. Mutually exclusive T_H2 and T_H17 tissue gene expression signatures were identified in all pathological groups. Discovery and external replication applied to the severe asthma subgroup identified only highly similar "pathological data shapes" through analyses of persistent homology.

CONCLUSIONS

We have identified and replicated novel pathological phenotypes of asthma using TDA. Our methodology is applicable to other complex chronic diseases.

Urinary bladder hypersensitivity and dysfunction in female mice following early life and adult stress

Early adverse events have been shown to increase the incidence of interstitial cystitis/painful bladder syndrome in adulthood. Despite high clinical relevance and reports of stress-related symptom exacerbation, animal models investigating the contribution of early life stress to female urological pain are lacking. We examined the impact of neonatal maternal separation (NMS) on bladder sensitivity and visceral neuroimmune status both prior-to, and following, water avoidance stress (WAS) in adult female mice. The visceromotor response to urinary bladder distension was increased at baseline and 8d post-WAS in NMS mice, while colorectal sensitivity was transiently increased 1d post-WAS only in naïve mice. Bladder micturition rate and output, but not fecal output, were also significantly increased following WAS in NMS mice. Changes in gene expression involved in regulating the stress response system were observed at baseline and following WAS in NMS mice, and WAS reduced serum corticosterone levels. Cytokine and growth factor mRNA levels in the bladder, and to a lesser extent in the colon, were significantly impacted by NMS and WAS. Peripheral mRNA levels of stress-responsive receptors were differentially influenced by early life and adult stress in bladder, but not colon, of naïve and NMS mice. Histological evidence of mast cell degranulation was increased in NMS bladder, while protein levels of protease activated receptor 2 (PAR2) and transient receptor potential ankyrin 1 (TRPA1) were increased by WAS. Together, this study provides new insight into mechanisms contributing to stress associated symptom onset or exacerbation in patients exposed to early life stress.

[New molecules in the treatment of inflammatory bowel disease]

Inflammatory bowel disease (IBD) is a disorder of unknown aetiology that provokes chronic inflammation of the gastrointestinal tract. Anti-tumor necrosis factor drugs have represented a major advance in the treatment of IBD patients in the last few years and also have a good safety profile. Nevertheless, these treatments are not effective in all patients and, in initial responders, there can be a loss of response in the long-term. Consequently, new treatments are needed for IBD, aimed at distinct therapeutic targets. In the last few years, new molecules have been incorporated into the therapeutic armamentarium of IBD patients. Golimumab is an anti-tumor necrosis factor monoclonal antibody with demonstrated effectiveness in the treatment of ulcerative colitis. The use of CT-P13 (biosimilar infliximab) has been approved in Europe for the same indications as the original infliximab. More recently, vedolizumab, an anti-α4β7 integrin monoclonal antibody, has been approved for the treatment of Crohn's disease and ulcerative colitis. A large number of molecules are currently under development, some of which will, in the future, broaden the therapeutic options available in the treatment of IBD patients. Finally, in the next few years, studies should aim to identify factors predictive of response to the distinct biological agents for IBD in order to allow personalized selection of the best therapeutic alternative for each patient.

Current stage in inflammatory bowel disease: What is next?

In recent years, the incidence of inflammatory bowel disease (IBD) has been on the rise, extending to countries where it was infrequent in the past. As a result, the gap between high and low incidence countries is decreasing. The disease, therefore, has an important economic impact on the healthcare system. Advances in recent years in pharmacogenetics and clinical pharmacology have allowed for the development of treatment strategies adjusted to the patient profile. Concurrently, new drugs aimed at inflammatory targets have been developed that may expand future treatment options. This review examines advances in the optimization of existing drug treatments and the development of novel treatment options for IBD.

Mast cell regulation of Na-glutamine co-transporters B0AT1 in villus and SN2 in crypt cells during chronic intestinal inflammation

Background

In the chronically inflamed rabbit small intestine, brush border membrane (BBM) Na-glutamine co-transport is inhibited in villus cells (mediated by B0AT1), while it is stimulated in crypt cells (mediated by SN2/SNAT5). How mast cells, known to be enhanced in the chronically inflamed intestine, may regulate B0AT1 in villus and SN2/SNAT5 in crypt cell is unknown. Thus, the aim of the present study is to determine the regulation of B0AT1 and SN2/SNAT5 by mast cells during chronic enteritis.

Methods

Chronic intestinal inflammation was induced in male rabbits with intra-gastric inoculation of Eimeria magna oocytes. Rabbits with chronic inflammation were treated with ketotifen (10 mg/day) or saline (Placebo) for 2 days. Villus and crypts cells were isolated from the rabbit intestine using the Ca++ chelation technique. Na/K-ATPase activity was measured as Pi from cellular homogenate. BBM vesicles (BBMV) were prepared from villus and crypt cells and uptake studies were performed using rapid filtration technique with ³H-Glutamine. Western blot analyses were done using B0AT1 and SN2 specific antibodies.

Results

In villus cells, Na-glutamine co-transport inhibition observed during inflammation was completely reversed by ketotifen, a mast cell stabilizer. In contrast, in crypt cells, Na-glutamine co-transport stimulation was reversed to normal levels by ketotifen. Kinetic studies demonstrated that ketotifen reversed the inhibition of B0AT1 in villus cells by restoring co-transporter numbers in the BBM, whereas the stimulation of SN2/SNAT5 in crypts cells was reversed secondary to restoration of affinity of the co-transporter. Western blot analysis showed that ketotifen restored immune-reactive levels of B0AT1 in villus cells, while SN2/SNAT5 levels from crypts cell remained unchanged.

Conclusion

In the present study we demonstrate that mast cells likely function as a common upstream immune pathway regulator of the Na-dependent glutamine co-transporters, B0AT1 in villus cells and SN2 in crypts cells that are uniquely altered in the chronically inflamed small intestine.

Current, new and future biological agents on the horizon for the treatment of inflammatory bowel diseases

Biological agents for inflammatory bowel diseases (IBD) targeting tumor necrosis factor (TNF) have changed the way to treat IBD refractory to standard medications and allowed us to reach new therapeutic goals such as mucosal healing and deep remission. A better understanding of the components of the pathological processes that are a hallmark of IBD has led to the development of a new family of biological agents in Crohn's disease and ulcerative colitis. Biosimilars, which are copy versions of currently licensed biological agents, will be soon available. The biosimilar of infliximab is as effective and as safe as its originator in rheumatologic conditions, while a new anti-TNF agent, namely golimumab, has been recently approved for refractory ulcerative colitis. Beyond TNF blockers, anti-adhesion molecules appear to be a potent drug class for IBD. Vedolizumab was recently approved for both Crohn's disease and ulcerative colitis. Numerous other compounds are in the pipeline. Ustekinumab looks very promising for Crohn's disease. Smad7 antisense oligonucleotide might enrich our armamentarium if preliminary data are confirmed in upcoming clinical trials. Herein, we review the efficacy and safety of new and emerging biological agents that are currently investigated in IBD clinical trials.

Splanchnic-aortic inflammatory axis in experimental portal hypertension

Splanchnic and systemic low-grade inflammation has been proposed to be a consequence of long-term prehepatic portal hypertension. This experimental model causes minimal alternations in the liver, thus making a more selective study possible for the pathological changes characteristic of prehepatic portal hypertension. Low-grade splanchnic inflammation after long-term triple partial portal vein ligation could be associated with liver steatosis and portal hypertensive intestinal vasculopathy. In fact, we have previously shown that prehepatic portal hypertension in the rat induces liver steatosis and changes in lipid and carbohydrate metabolism similar to those produced in chronic inflammatory conditions described in metabolic syndrome in humans. Dysbiosis and bacterial translocation in this experimental model suggest the existence of a portal hypertensive intestinal microbiome implicated in both the splanchnic and systemic alterations related to prehepatic portal hypertension. Among the systemic impairments, aortopathy characterized by oxidative stress, increased levels of proinflammatory cytokines and profibrogenic mediators stand out. In this experimental model of long-term triple portal vein ligated-rats, the abdominal aortic proinflammatory response could be attributed to oxidative stress. Thus, the increased aortic reduced-nicotinamide-adenine dinucleotide phosphate [NAD(P)H] oxidase activity could be associated with reactive oxygen species production and promote aortic inflammation. Also, oxidative stress mediated by NAD(P)H oxidase has been associated with risk factors for inflammation and atherosclerosis. The splanchnic and systemic pathology that is produced in the long term after triple partial portal vein ligation in the rat reinforces the validity of this experimental model to study the chronic low-grade inflammatory response induced by prehepatic portal hypertension.

Jejunoileal bypass as the main procedure in the onset of immune-related conditions: the model of BADAS

Bariatric surgery represents a common approach for the control of severe morbid obesity, reducing caloric intake by modifying the anatomy of the gastrointestinal tract. Following jejunoileal bypass, a large spectrum of complications has been described, with rheumatic manifestation present in up to 20% of cases. Although bowel bypass syndrome, also called blind loop syndrome, is a well-recognized complication of jejunoileal bypass, the same syndrome was recognized in patients who had not had intestinal bypass surgery, and the term the 'bowel-associated dermatosis-arthritis syndrome' (BADAS) was coined. The pathogenesis of BADAS is as yet poorly understood and only few data concerning this issue have been published in the literature. The aim of the present paper is to review the literature and to discuss putative pathogenic mechanisms of BADAS, focusing on the immune system.

Alteration of pancreatic cancer cell functions by tumor-stromal cell interaction

Pancreatic cancer shows a characteristic tissue structure called desmoplasia, which consists of dense fibrotic stroma surrounding cancer cells. Interactions between pancreatic cancer cells and stromal cells promote invasive growth of cancer cells and establish a specific microenvironment such as hypoxia which further aggravates the malignant behavior of cancer cells. Pancreatic stellate cells (PSCs) play a pivotal role in the development of fibrosis within the pancreatic cancer tissue, and also affect cancer cell function. PSCs induce epithelial-mesenchymal transition and cancer stem cell (CSC)-related phenotypes in pancreatic cancer cells by activating multiple signaling pathways. In addition, pancreatic cancer cells and PSCs recruit myeloid-derived suppressor cells which attenuate the immune reaction against pancreatic cancer cells. As a result, pancreatic cancer cells become refractory against conventional therapies. The formation of the CSC-niche by stromal cells facilitates postoperative recurrence, re-growth of therapy-resistant tumors and distant metastasis. Conventional therapies targeting cancer cells alone have failed to conquer pancreatic cancer, but targeting the stromal cells and immune cells in animal experiments has provided evidence of improved therapeutic responses. A combination of novel strategies altering stromal cell functions could contribute to improving the pancreatic cancer prognosis.

A Phenotypic Screening Approach in Cord Blood–Derived Mast Cells to Identify Anti-Inflammatory Compounds

Mast cells are unique hematopoietic cells that are richly distributed in the skin and mucosal surfaces of the respiratory and gastrointestinal tract. They play a key role in allergic inflammation by releasing a cocktail of granular constituents, including histamine, serine proteases, and various eicosanoids and cytokines. As such, a number of drugs target either inhibition of mast cell degranulation or the products of degranulation. To identify potential novel drugs and mechanisms in mast cell biology, assays were developed to identify inhibitors of mast cell degranulation and activation in a phenotypic screen. Due to the challenges associated with obtaining primary mast cells, cord blood–derived mononuclear cells were reproducibly differentiated to mast cells and assays developed to monitor tryptase release and prostaglandin D2 generation. The tryptase assay was particularly sensitive, requiring only 500 cells per data point, which permitted a set of approximately 12,000 compounds to be screened robustly and cost-effectively. Active compounds were tested for concomitant inhibition of prostaglandin D2 generation. This study demonstrates the robustness and effectiveness of this approach in the identification of potential novel compounds and mechanisms targeting mast cell–driven inflammation, to enable innovative drug discovery efforts to be prosecuted.