Modulation of visceral pain and inflammation by protease-activated receptors

Thrombin stories in the gut

Many studies have demonstrated the involvement of proteases in gut physiology and pathophysiology over the recent years. Among them, thrombin has appeared for a long time as an old player only involved in blood clotting upon tissue injury. The fact that thrombin receptors (Protease-Activated Receptors-1 and -4) are expressed and functional in almost all cell types of the gut, contributing to barrier, immune or motility functions, suggested that thrombin could actually be at the crossroad of intestinal physiology. Recent work has unraveled the constitutive release of active thrombin by intestinal epithelial cells, opening new research avenues on the role of thrombin in the gut. These roles are considered in the present review, as well as the regulation of thrombin in the gut. The potential of thrombin as a target for treatments of intestinal pathologies is also discussed here.

Elafin and its precursor trappin-2: What is their therapeutic potential for intestinal diseases?

Elafin and its precursor trappin-2 are known for their contribution to the physiological mucosal shield against luminal microbes. Such a contribution seems to be particularly relevant in the gut, where the exposure of host tissues to heavy loads of microbes is constant and contributes to mucosa-associated pathologies. The expression of trappin-2/elafin has been shown to be differentially regulated in diseases associated with gut inflammation. Accumulating evidence has demonstrated the protective effects of trappin-2/elafin in gut intestinal disorders associated with acute or chronic inflammation, or with gluten sensitization disorders. The protective effects of trappin-2/elafin in the gut are discussed in terms of their pleiotropic modes of action: acting as protease inhibitors, transglutaminase substrates, antimicrobial peptides or as a regulator of pro-inflammatory transcription factors. Further, the question of the therapeutic potential of trappin-2/elafin delivery at the intestinal mucosa surface is raised. Whether trappin-2/elafin mucosal delivery should be considered to ensure intestinal tissue repair is also discussed.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Thrombin Induced Apoptosis through Calcium-Mediated Activation of Cytosolic Phospholipase A2 in Intestinal Myofibroblasts

Thrombin is a serine protease that participates in a variety of biological signaling through protease-activated receptors. Intestinal myofibroblasts play central roles in maintaining intestinal homeostasis. In this study, we found that thrombin-induced apoptosis is mediated by the calcium-mediated activation of cytosolic phospholipase A₂ in the CCD-18Co cell. Thrombin reduced cell viability by inducing apoptosis and proteinase-activated receptor-1 antagonist attenuated thrombin-induced cell death. Endogenous ceramide did not affect the cell viability itself, but a ceramide-mediated pathway was involved in thrombin-induced cell death. Thrombin increased intracellular calcium levels and cytosolic phospholipase A₂ activity. The ceramide synthase inhibitor Fumonisin B₁, intracellular calcium chelator BAPTA-AM, and cytosolic phospholipase A₂ inhibitor AACOCF₃ inhibited thrombin-induced cell death. Thrombin stimulated arachidonic acid release and reactive oxygen species generation, which was blocked by AACOCF₃, BAPTA-AM, and the antioxidant reagent Trolox. Taken together, thrombin triggered apoptosis through calcium-mediated activation of cytosolic phospholipase A₂ in intestinal myofibroblasts.

Long-term personalized low FODMAP diet in IBS

Irritable bowel syndrome (IBS) patients often resort to dietary interventions to manage their symptoms, as these are frequently exacerbated by various food items. A diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) is now considered by many a first-line treatment option for IBS, as it has been found to be superior to alternative dietary interventions. However, concerns have been raised as restricting fermentable carbohydrates might result in nutritional deficits or alter composition and function of the gut microbiome in the long term. The study by Staudacher et al., published in this issue of the journal, is the first prospective study to follow IBS patients after completing all three phases of the low FODMAPs diet (restriction, reintroduction, and personalization), demonstrating that this is safe and effective in long-term, when patients are supervised by a dietician. This mini-review provides an up-to-date overview of the use of fermentable carbohydrate's restrictions for symptom management in IBS patients, while summarizing the current knowledge on the possible mechanisms of action behind low fermentable carbohydrate diet efficacy.

PAR-1 Antagonism to Promote Gut Mucosa Healing in Crohn's Disease Patients: A New Avenue for CVT120165

A new paradigm has been added for the treatment of inflammatory bowel diseases such as Crohn's disease and ulcerative colitis. In addition to resolving symptoms and inflammatory cell activation, the objective of tissue repair and mucosal healing is also now considered a primary goal. In the search of mediators that would be responsible for delayed mucosal healing, protease-activated receptor-1 (PAR-1) has emerged as a most interesting target. Indeed, in Crohn's disease, the endogenous PAR-1 agonist thrombin is drastically activated. Activation of PAR-1 is known to be associated with epithelial dysfunctions that hamper mucosal homeostasis. This review gathers the scientific evidences of a potential role for PAR-1 in mucosal damage and mucosal dysfunctions associated with chronic intestinal inflammation. The potential clinical benefits of PAR-1 antagonism to promote mucosal repair in CD patients are discussed. Targeted local delivery of a PAR-1 antagonist molecule such as CVT120165, a formulated version of the FDA-approved PAR-1 antagonist vorapaxar, at the mucosa of Crohn's disease patients could be proposed as a new indication for IBD that could be rapidly tested in clinical trials.

Colitis Linked to Endoplasmic Reticulum Stress Induces Trypsin Activity Affecting Epithelial Functions

BACKGROUND AND AIMS

Intestinal epithelial cells [IECs] from inflammatory bowel disease [IBD] patients exhibit an excessive induction of endoplasmic reticulum stress [ER stress] linked to altered intestinal barrier function and inflammation. Colonic tissues and the luminal content of IBD patients are also characterized by increased serine protease activity. The possible link between ER stress and serine protease activity in colitis-associated epithelial dysfunctions is unknown. We aimed to study the association between ER stress and serine protease activity in enterocytes and its impact on intestinal functions.

METHODS

The impact of ER stress induced by Thapsigargin on serine protease secretion was studied using either human intestinal cell lines or organoids. Moreover, treating human intestinal cells with protease-activated receptor antagonists allowed us to investigate ER stress-resulting molecular mechanisms that induce proteolytic activity and alter intestinal epithelial cell biology.

RESULTS

Colonic biopsies from IBD patients exhibited increased epithelial trypsin-like activity associated with elevated ER stress. Induction of ER stress in human intestinal epithelial cells displayed enhanced apical trypsin-like activity. ER stress-induced increased trypsin activity destabilized intestinal barrier function by increasing permeability and by controlling inflammatory mediators such as C-X-C chemokine ligand 8 [CXCL8]. The deleterious impact of ER stress-associated trypsin activity was specifically dependent on the activation of protease-activated receptors 2 and 4.

CONCLUSIONS

Excessive ER stress in IECs caused an increased release of trypsin activity that, in turn, altered intestinal barrier function, promoting the development of inflammatory process.

Pruritogenic mechanisms and gut sensation: putting the "irritant" into irritable bowel syndrome

Chronic abdominal pain is a common clinical condition experienced by patients with irritable bowel syndrome (IBS). A general lack of suitable treatment options for the management of visceral pain is the major contributing factor to the debilitating nature of the disease. Understanding the underlying causes of chronic visceral pain is pivotal to identifying new effective therapies for IBS. This review provides the current evidence, demonstrating that mediators and receptors that induce itch in the skin also act as "gut irritants" in the gastrointestinal tract. Activation of these receptors triggers specific changes in the neuronal excitability of sensory pathways responsible for the transmission of nociceptive information from the periphery to the central nervous system leading to visceral hypersensitivity and visceral pain. Accumulating evidence points to significant roles of irritant mediators and their receptors in visceral hypersensitivity and thus constitutes potential targets for the development of more effective therapeutic options for IBS.

The relationship between gut microbiota and proteolytic activity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease that affects 3.8-9.2% of the world population. It affects the physiology and psychology of patients and increases the burden on families, the healthcare system, society, and economic development. Presently, a large number of studies have shown that compared to healthy individuals, the composition and diversity of gut microbiota in IBS patients have changed, and the proteolytic activity (PA) in fecal supernatant and colonic mucosa of IBS patients has also increased. These findings indicate that the imbalance of intestinal microecology and intestinal protein hydrolysis is closely related to IBS. Furthermore, the intestinal flora is a key substance that regulates the PA and is associated with IBS. The current review described the intestinal microecology and intestinal proteolytic activity of patients with IBS and also discussed the effect of intestinal flora on PA. In summary, this study proposed a pivotal role of gut microbiota and PA in IBS, respectively, and provided an in-depth insight into the diagnosis and treatment targets of IBS as well as the formulation of new treatment strategies for other digestive diseases and protease-related diseases.

Computational Functional Genomics-Based AmpliSeq™ Panel for Next-Generation Sequencing of Key Genes of Pain

The genetic background of pain is becoming increasingly well understood, which opens up possibilities for predicting the individual risk of persistent pain and the use of tailored therapies adapted to the variant pattern of the patient's pain-relevant genes. The individual variant pattern of pain-relevant genes is accessible via next-generation sequencing, although the analysis of all "pain genes" would be expensive. Here, we report on the development of a cost-effective next generation sequencing-based pain-genotyping assay comprising the development of a customized AmpliSeq™ panel and bioinformatics approaches that condensate the genetic information of pain by identifying the most representative genes. The panel includes 29 key genes that have been shown to cover 70% of the biological functions exerted by a list of 540 so-called "pain genes" derived from transgenic mice experiments. These were supplemented by 43 additional genes that had been independently proposed as relevant for persistent pain. The functional genomics covered by the resulting 72 genes is particularly represented by mitogen-activated protein kinase of extracellular signal-regulated kinase and cytokine production and secretion. The present genotyping assay was established in 61 subjects of Caucasian ethnicity and investigates the functional role of the selected genes in the context of the known genetic architecture of pain without seeking functional associations for pain. The assay identified a total of 691 genetic variants, of which many have reports for a clinical relevance for pain or in another context. The assay is applicable for small to large-scale experimental setups at contemporary genotyping costs.

Antiapoptotic Effect by PAR-1 Antagonist Protects Mouse Liver Against Ischemia-Reperfusion Injury

BACKGROUND

Coagulation disturbances in several liver diseases lead to thrombin generation, which triggers intracellular injury via activation of protease-activated receptor-1 (PAR-1). Little is known about the thrombin/PAR-1 pathway in hepatic ischemia-reperfusion injury (IRI). The present study aimed to clarify whether a newly selective PAR-1 antagonist, vorapaxar, can attenuate liver damage caused by hepatic IRI, with a focus on apoptosis and the survival-signaling pathway.

METHODS

A 60-min hepatic partial-warm IRI model was used to evaluate PAR-1 expression in vivo. Subsequently, IRI mice were treated with or without vorapaxar (with vehicle). In addition, hepatic sinusoidal endothelial cells (SECs) pretreated with or without vorapaxar (with vehicle) were incubated during hypoxia-reoxygenation in vitro.

RESULTS

In naïve livers, PAR-1 was confirmed by immunohistochemistry and immunofluorescence analysis to be located on hepatic SECs, and IRI strongly enhanced PAR-1 expression. In IRI mice models, vorapaxar treatment significantly decreased serum transaminase levels, improved liver histological damage, reduced the number of apoptotic cells as evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling staining (median: 135 versus 25, P = 0.004), and induced extracellular signal-regulated kinase 1/2 (ERK 1/2) cell survival signaling (phospho-ERK/total ERK 1/2: 0.96 versus 5.34, P = 0.004). Pretreatment of SECs with vorapaxar significantly attenuated apoptosis and induced phosphorylation of ERK 1/2 in vitro (phospho-ERK/total ERK 1/2: 0.66 versus 3.04, P = 0.009). These changes were abolished by the addition of PD98059, the ERK 1/2 pathway inhibitor, before treatment with vorapaxar.

CONCLUSIONS

The results of the present study revealed that hepatic IRI induces significant enhancement of PAR-1 expression on SECs, which may be associated with suppression of survival signaling pathways such as ERK 1/2, resulting in severe apoptosis-induced hepatic damage. Thus, the selective PAR-1 antagonist attenuates hepatic IRI through an antiapoptotic effect by the activation of survival-signaling pathways.

Painful interactions: Microbial compounds and visceral pain

Visceral pain, characterized by abdominal discomfort, originates from organs in the abdominal cavity and is a characteristic symptom in patients suffering from irritable bowel syndrome, vulvodynia or interstitial cystitis. Most organs in which visceral pain originates are in contact with the external milieu and continuously exposed to microbes. In order to maintain homeostasis and prevent infections, the immune- and nervous system in these organs cooperate to sense and eliminate (harmful) microbes. Recognition of microbial components or products by receptors expressed on cells from the immune and nervous system can activate immune responses but may also cause pain. We review the microbial compounds and their receptors that could be involved in visceral pain development.

Protease-activated receptor 1 is implicated in irritable bowel syndrome mediators-induced signaling to thoracic human sensory neurons

Proteases and protease-activated receptors (PARs) are major mediators involved in irritable bowel syndrome (IBS). Our objectives were to decipher the expression and functionality (calcium signaling) of PARs in human dorsal root ganglia (DRG) neurons and to define mechanisms involved in human sensory neuron signaling by IBS patient mediators. Human thoracic DRG were obtained from the national disease resource interchange. Expression of PAR1, PAR2, and PAR4 was assessed by immunohistochemistry and quantitative reverse transcription PCR (RT-qPCR) in whole DRG or in primary cultures of isolated neurons. Calcium signaling in response to PAR agonist peptides (PAR-AP), their inactive peptides (PAR-IP), thrombin (10 U/mL), supernatants from colonic biopsies of patients with IBS, or healthy controls, with or without PAR1 or PAR4 antagonist were studied in cultured human DRG neurons. PAR1, PAR2, and PAR4 were all expressed in human DRG, respectively, in 20%, 40%, and 40% of the sensory neurons. PAR1-AP increased intracellular calcium concentration in a dose-dependent manner. This increase was inhibited by PAR1 antagonism. By contrast, PAR2-AP, PAR4-AP, and PAR-IP did not cause calcium mobilization. PAR1-AP-induced calcium flux was significantly reduced by preincubation with PAR4-AP, but not with PAR2-AP. Thrombin increased calcium flux, which was inhibited by a PAR1 antagonist and increased by a PAR4 antagonist. Supernatants from colonic biopsies of patients with IBS induced calcium flux in human sensory neurons compared with healthy controls, and this induction was reversed by a PAR1 antagonist. Taken together, our results highlight that PAR1 antagonism should be investigated as a new therapeutic target for IBS symptoms.

The functional role of protease-activated receptors on contractile responses by activation of Ca2+ sensitization pathways in simian colonic muscles

It has been known that activation of protease-activated receptors (PARs) affects gastrointestinal motility. In this study, we tested the effects of PAR agonists on electrical and contractile responses and Ca²⁺ sensitization pathways in simian colonic muscles. The Simian colonic muscle was initially hyperpolarized by PAR agonists. After the transient hyperpolarization, simian colonic muscle repolarized to the control resting membrane potential (RMP) without a delayed depolarization. Apamin significantly reduced the initial hyperpolarization, suggesting that activation of small conductance Ca²⁺-activated K⁺ (SK) channels is involved in the initial hyperpolarization. In contractile experiments, PAR agonists caused an initial relaxation followed by an increase in contractions. These delayed contractile responses were not matched with the electrical responses that showed no after depolarization of the RMP. To investigate the possible involvement of Rho-associated protein kinase 2 (ROCK) pathways in the PAR effects, muscle strips were treated with ROCK inhibitors, which significantly reduced the PAR agonist-induced contractions. Furthermore, PAR agonists increased MYPT1 phosphorylation, and ROCK inhibitors completely blocked MYPT1 phosphorylation. PAR agonists alone had no effect on CPI-17 phosphorylation. In the presence of apamin, PAR agonists significantly increased CPI-17 phosphorylation, which was blocked by protein kinase C (PKC) inhibitors suggesting that Ca²⁺ influx is increased by apamin and is activating PKC. In conclusion, these studies show that PAR activators induce biphasic responses in simian colonic muscles. The initial inhibitory responses by PAR agonists are mainly mediated by activation of SK channels and delayed contractile responses are mainly mediated by the CPI-17 and ROCK Ca²⁺ sensitization pathways in simian colonic muscles. NEW & NOTEWORTHY In the present study, we found that the contractile responses of simian colonic muscles to protease-activated receptor (PAR) agonists are different from the previously reported contractile responses of murine colonic muscles. Ca²⁺ sensitization pathways mediate the contractile responses of simian colonic muscles to PAR agonists without affecting the membrane potential. These findings emphasize novel mechanisms of PAR agonist-induced contractions possibly related to colonic dysmotility in inflammatory bowel disease.

Thrombin modifies growth, proliferation and apoptosis of human colon organoids: a protease-activated receptor 1- and protease-activated receptor 4-dependent mechanism

BACKGROUND AND PURPOSE

Thrombin is massively released upon tissue damage associated with bleeding or chronic inflammation. The effects of this thrombin on tissue regrowth and repair has been scarcely addressed and only in cancer cell lines. Hence, the purpose of the present study was to determine thrombin's pharmacological effects on human intestinal epithelium growth, proliferation and apoptosis, using three-dimensional cultures of human colon organoids.

EXPERIMENTAL APPROACH

Crypts were isolated from human colonic resections and cultured for 6 days, forming human colon organoids. Cultured organoids were exposed to 10 and 50 mU·mL^-1 of thrombin, in the presence or not of protease-activated receptor (PAR) antagonists. Organoid morphology, metabolism, proliferation and apoptosis were followed.

KEY RESULTS

Thrombin favoured organoid maturation leading to a decreased number of immature cystic structures and a concomitant increased number of larger structures releasing cell debris and apoptotic cells. The size of budding structures, metabolic activity and proliferation were significantly reduced in organoid cultures exposed to thrombin, while apoptosis was dramatically increased. Both PAR1 and PAR4 antagonists inhibited apoptosis regardless of thrombin doses. Thrombin-induced inhibition of proliferation and metabolic activity were reversed by PAR4 antagonist for thrombin's lowest dose and by PAR1 antagonist for thrombin's highest dose.

CONCLUSIONS AND IMPLICATIONS

Overall, our data suggest that the presence of thrombin in the vicinity of human colon epithelial cells favours their maturation at the expense of their regenerative capacities. Our data point to thrombin and its two receptors PAR1 and PAR4 as potential molecular targets for epithelial repair therapies.

Visceral hypersensitivity in inflammatory bowel diseases and irritable bowel syndrome: The role of proteases

Proteases, enzymes catalyzing the hydrolysis of peptide bonds, are present at high concentrations in the gastrointestinal tract. Besides their well-known role in the digestive process, they also function as signaling molecules through the activation of protease-activated receptors (PARs). Based on their chemical mechanism for catalysis, proteases can be classified into several classes: serine, cysteine, aspartic, metallo- and threonine proteases represent the mammalian protease families. In particular, the class of serine proteases will play a significant role in this review. In the last decades, proteases have been suggested to play a key role in the pathogenesis of visceral hypersensitivity, which is a major factor contributing to abdominal pain in patients with inflammatory bowel diseases and/or irritable bowel syndrome. So far, only a few preclinical animal studies have investigated the effect of protease inhibitors specifically on visceral sensitivity while their effect on inflammation is described in more detail. In our accompanying review we describe their effect on gastrointestinal permeability. On account of their promising results in the field of visceral hypersensitivity, further research is warranted. The aim of this review is to give an overview on the concept of visceral hypersensitivity as well as on the physiological and pathophysiological functions of proteases herein.

Functional Genomic Analysis of the Impact of Camelina (Camelina sativa) Meal on Atlantic Salmon (Salmo salar) Distal Intestine Gene Expression and Physiology

The inclusion of plant meals in diets of farmed Atlantic salmon can elicit inflammatory responses in the distal intestine (DI). For the present work, fish were fed a standard fish meal (FM) diet or a diet with partial replacement of FM with solvent-extracted camelina meal (CM) (8, 16, or 24 % CM inclusion) during a 16-week feeding trial. A significant decrease in growth performance was seen in fish fed all CM inclusion diets (Hixson et al. in Aquacult Nutr 22:615-630, 2016). A 4x44K oligonucleotide microarray experiment was carried out and significance analysis of microarrays (SAM) and rank products (RP) methods were used to identify differentially expressed genes between the DIs of fish fed the 24 % CM diet and those fed the FM diet. Twelve features representing six known transcripts and two unknowns were identified as CM responsive by both SAM and RP. The six known transcripts (including thioredoxin and ependymin), in addition to tgfb, mmp13, and GILT, were studied using qPCR with RNA templates from all four experimental diet groups. All six microarray-identified genes were confirmed to be CM responsive, as was tgfb and mmp13. Histopathological analyses identified signs of inflammation in the DI of salmon fed CM-containing diets, including lamina propria and sub-epithelial mucosa thickening, infiltration of eosinophilic granule cells, increased goblet cells and decreased enterocyte vacuolization. All of these were significantly altered in 24 % CM compared to all other diets, with the latter two also altered in 16 % CM compared with 8 % CM and control diet groups. Significant correlation was seen between histological parameters as well as between five of the qPCR analyzed genes and histological parameters. These molecular biomarkers of inflammation arising from long-term dietary CM exposure will be useful in the development of CM-containing diets that do not have deleterious effects on salmon growth or physiology.

Gut pain & visceral hypersensitivity

Visceral pain is a highly complex entity whose experience is variable in health and disease. It can occur in patients with organic disease and also in those without any readily identifiable structural or biochemical abnormality such as in the functional gastrointestinal disorders (FGID). Despite considerable progress in our understanding of the culpable underlying mechanisms significant knowledge gaps remain, representing a significant unmet need in gastroenterology. A key, but not universal, pathological feature is that patients with FGID often display heightened sensitivity to experimental gut stimulation, termed visceral hypersensitivity. A plethora of factors have been proposed to account for this epiphenomenon including peripheral sensitization, central sensitization, aberrant central processing, genetic, psychological and abnormalities within the stress responsive systems. Further research is needed, bringing together complementary research themes from a diverse array of academic disciplines ranging from gastroenterology to nociceptive physiology to functional neuro-imaging, to address this unmet need.

Mechanisms of visceral pain in health and functional gastrointestinal disorders

Background and aims Chronic visceral pain is common both in patients with identifiable organic disease and also in those without any structural, biochemical or immunological abnormality such as in the functional gastrointestinal disorders (FGIDs). We aim to provide a contemporaneous summary of pathways involved in visceral nociception and how a variety of mechanisms may influence an individual's experience of visceral pain. Methods In this narrative review, we have brought together evidence through a detailed search of Medline in addition to using our experience and exposure to recent research developments from ourselves and other research groups. Results FGIDs are a heterogeneous group of disorders whose aetiology largely remains an enigma. The germane hypothesis for the genesis and maintenance of chronic visceral pain in FGIDs is the concept of visceral hypersensitivity. A number of peripheral and central mechanisms have been proposed to account for this epiphenomenon. In the periphery, inflammatory mediators activate and sensitize nociceptive afferent nerves by reducing their transduction thresholds and by inducing the expression and recruitment of hitherto silent nociceptors culminating in an increase in pain sensitivity at the site of injury known as primary hyperalgesia. Centrally, secondary hyperalgesia, defined as an increase in pain sensitivity in anatomically distinct sites, occurs at the level of the spinal dorsal horn. Moreover, the stress responsive physiological systems, genetic and psychological factors may modulate the experience of visceral pain. We also address some novel aetiological concepts in FGIDs, namely the gastrointestinal microbiota, connective tissue abnormalities and the gastrointestinal neuromuscular disorders. Firstly, the gastrointestinal microbiota is a diverse and dynamic ecosystem, that safeguards the host from external pathogens, aids in the metabolism of polysaccharides and lipids, modulates intestinal motility, in addition to modulating visceral perception. Secondly, connective tissue disorders, which traditionally have been considered to be confined largely to the musculoskeletal system, have an increasing evidence base demonstrating the presence of visceral manifestations. Since the sensorimotor apparatus of the GI tract is embedded within connective tissue it should not be surprising that such disorder may result in visceral pain and abnormal gut motility. Thirdly, gastrointestinal neuromuscular diseases refer to a heterogeneous group of disorders in which symptoms arise from impaired GI motor activity often manifesting as abnormal transit with or without radiological evidence of transient or persistent dilation of the viscera. Although a number of these are readily recognizable, such as achalasia or Hirschsprung's disease, the cause in a number of patients is not. An international working group has recently addressed this "gap", providing a comprehensive morphologically based diagnostic criteria. Conclusions/implications Although marked advances have been made in understanding the mechanisms that contribute to the development and maintenance of visceral pain, many interventions have failed to produce tangible improvement in patient outcomes. In the last part of this review we highlight an emerging approach that has allowed the definition and delineation of temporally stable visceral pain clusters, which may improve participant homogeneity in future studies, potentially facilitate stratification of treatment in FGID and lead to improvements in diagnostic criteria and outcomes.

Sensitization of peripheral sensory nerves by mediators from colonic biopsies of diarrhea-predominant irritable bowel syndrome patients: a role for PAR2

OBJECTIVES

This study examined whether mediators from biopsies of human irritable bowel syndrome (IBS) colons alter intrinsic excitability of colonic nociceptive dorsal root ganglion (DRG) neurons by a protease activated receptor 2 (PAR2)-mediated mechanism.

METHODS

Colonic mucosal biopsies from IBS patients with constipation (IBS-C) or diarrhea (IBS-D) and from healthy controls were incubated in medium, and supernatants were collected. Small-diameter mouse colonic DRG neurons were incubated in supernatants overnight and perforated patch current-clamp recordings obtained. Measurements of rheobase and action potential discharge at twice rheobase were compared between IBS and controls to assess differences in intrinsic excitability.

RESULTS

Supernatants from IBS-D patients elicited a marked increase in neuronal excitability compared with controls. These changes were consistent among individual patients but the relative contribution of rheobase and action potential discharge varied. In contrast, no differences in neuronal excitability were seen with IBS-C patient supernatants. The increased excitability seen with IBS-D supernatant was not observed in PAR2 knockout mice. A cysteine protease inhibitor, which had no effect on the pronociceptive actions of a serine protease, inhibited the proexcitatory actions of IBS-D supernatant.

CONCLUSIONS

Soluble mediators from colonic biopsies from IBS-D but not IBS-C patients sensitized colonic nociceptive DRG neurons, suggesting differences between these two groups. PAR2 signaling plays a role in this action and this protease signaling pathway could provide novel biomarkers and therapeutic targets for treatment.

Trypsin potentiates human fibrocyte differentiation

Trypsin-containing topical treatments can be used to speed wound healing, although the mechanism of action is unknown. To help form granulation tissue and heal wounds, monocytes leave the circulation, enter the wound tissue, and differentiate into fibroblast-like cells called fibrocytes. We find that 20 to 200 ng/ml trypsin (concentrations similar to those used in wound dressings) potentiates the differentiation of human monocytes to fibrocytes in cell culture. Adding trypsin inhibitors increases the amount of trypsin needed to potentiate fibrocyte differentiation, suggesting that the potentiating effect is dependent on trypsin proteolytic activity. Proteases with other site specificities such as pepsin, endoprotease GluC, and chymotrypsin do not potentiate fibrocyte differentiation. This potentiation requires the presence of albumin in the culture medium, and tryptic fragments of human or bovine albumin also potentiate fibrocyte differentiation. These results suggest that topical trypsin speeds wound healing by generating tryptic fragments of albumin, which in turn potentiate fibrocyte differentiation.

Sensitization of sodium channels by cystathionine β-synthetase activation in colon sensory neurons in adult rats with neonatal maternal deprivation

BACKGROUND

The pathogenesis of pain in irritable bowel syndrome (IBS) is poorly understood and treatment remains difficult. We have previously reported that TTX-resistant (TTX-R) sodium channels in colon-specific dorsal root ganglion (DRG) neurons were sensitized and the expression of the endogenous hydrogen sulfide producing enzyme cystathionine β-synthetase (CBS) was upregulated in a rat model of visceral hypersensitivity induced by neonatal maternal deprivation (NMD). However, the detailed molecular mechanism for activation of sodium channels remains unknown. This study was designed to examine roles for CBS-H₂S signaling in sensitization of sodium channels in a previously validated rat model of IBS.

METHODS

Neonatal male rats (postnatal days 2-15) were exposed to a 3 hour period of daily maternal separation with temperature maintained at ~33 °C. Colon-specific dorsal root ganglion (DRG) neurons were labeled with DiI and acutely dissociated for measuring excitability and sodium channel current under whole-cell patch clamp configurations. The expression of Na(V)1.8 was analyzed by Western blot and Immunofluorescence study. The endogenous H₂S producing enzyme CBS antagonist was injected intraperitoneally.

RESULTS

We showed that CBS was colocalized with Na(V)1.8 in colon-specific DRG neurons pre-labeled with DiI. Pretreatment of O-(Carboxymethyl) hydroxylamine hemihydrochloride (AOAA), an inhibitor of CBS, significantly reduced expression of Na(V)1.8 in NMD rats. AOAA treatment also inhibited the TTX-R sodium current density, right-shifted the V₁/₂ of activation curve, and reversed hyperexcitability of colon-specific DRG neurons in NMD rats. Conversely, addition of NaHS, a donor of H₂S, greatly enhanced TTX-R sodium current density, left shifted the activation curve and enhanced excitability of colon DRG neurons in age-matched healthy rats. Furthermore, application of H-89, an inhibitor of protein kinase A, markedly attenuated the potentiation of TTX-R sodium current density by NaHS.

CONCLUSION

These data suggest that sensitization of sodium channels of colon DRG neurons in NMD rats is most likely mediated by CBS-H₂S signaling, thus identifying a potential target for treatment for chronic visceral pain in patients with IBS.

Trypsin impaired epithelial barrier function and induced IL-8 secretion through basolateral PAR-2: a lesson from a stratified squamous epithelial model

Immune-mediated injury by the protease-activated receptor-2-interleukin-8 (PAR-2-IL8) pathway may underlie the development of gastroesophageal reflux disease (GERD). However, the localization of PAR-2 and the mechanism of PAR-2 activation remain unclear. This study aimed to address these questions on an esophageal stratified squamous epithelial model and in the human esophageal mucosa of GERD patients. Normal human esophageal epithelial cells were cultured with the air-liquid interface system to establish the model. SLIGKV-NH2 (PAR-2 synthetic agonist), trypsin (PAR-2 natural activator), and weak acid (pH 4, 5, and 6) were added to either the apical or basolateral compartment to evaluate their effects on transepithelial electrical resistance (TEER) and IL-8 production. PAR-2 localization was examined both in the cell model and biopsies from GERD patients by immunohistochemistry. Apical trypsin stimulation induced IL-8 accompanied by decreased TEER in vitro, whereas the effective concentration from the basolateral side was 10 times lower. SLIGKV-NH2 from basolateral but not apical stimulation induced IL-8 production. Apical weak acid stimulation did not influence TEER or IL-8 production. Immunohistochemistry showed intense reactivity of PAR-2 in the basal and suprabasal layers after stimulation with trypsin. A similar PAR-2 reactivity that was mainly located at the basal and suprabasal layers was detected in GERD patients. In conclusion, the activation of the PAR-2-IL-8 pathway probably occurred at the basal and suprabasal layers, while the esophageal epithelial barrier may influence the activation of PAR-2. Under proton pump inhibitor therapy, refluxed trypsin may remain active and be a potential agent in the pathogenesis of refractory GERD.

Food patch testing for irritable bowel syndrome

BACKGROUND

The traditional classification of irritable bowel syndrome (IBS) as a functional disorder has been challenged in recent years by evidence of ongoing low-grade gastrointestinal tract inflammation. Inflammation may alter gastrointestinal motility and thus be central to the pathogenesis of IBS. Many foods and food additives are known to cause allergic contact dermatitis. We hypothesize that allergenic foods and food additives may elicit a similar allergic reaction in the gastrointestinal tract, giving rise to symptoms suggestive of IBS.

OBJECTIVE

We sought to determine whether skin patch testing to a panel of foods and food additives may identify food allergens that may be responsible for symptoms of IBS.

METHODS

We performed skin patch testing to common allergenic foods and food additives on individuals with a history of or symptoms suggestive of IBS. We used patch test-guided avoidance diets to determine whether avoidance alleviates IBS symptoms.

RESULTS

Thirty of the 51 study participants showed at least 1 doubtful or positive patch test result. Fourteen of the participants reported symptomatic improvement, ranging from slight to great, upon avoidance of the foods/food additives to which they reacted.

LIMITATIONS

Double-blind study design, inclusion of only patients with active IBS, larger sample size, more balanced gender distribution, testing of more foods/food additives, and longer duration of and more precise quantification of response to dietary avoidance are suggested for future studies.

CONCLUSION

Allergic contact enteritis to ingested foods, food additives, or both may contribute to IBS symptoms. Patch testing may be useful in identifying the causative foods.

The expression of protease-activated receptor 2 and 4 in the colon of irritable bowel syndrome patients

BACKGROUND

Irritable bowel syndrome (IBS) pathophysiology has not been fully understood. Abnormalities of serine proteases have been identified in IBS patients. In addition, protease-activated receptors (PAR) activation interferes with several components of the pathogenesis of IBS, so, evaluating the PAR expression in IBS patients may contribute to understanding the pathogenesis of the disease.

AIMS

This study aimed to investigate whether the expression of PAR4 and PAR2 in the colon was changed in IBS patients and was associated with IBS.

METHODS

Colon mucosal biopsies of 34 IBS patients (16 constipation- and 18 diarrhea-predominant) and 18 control subjects were collected. Gene transcripts of PAR2, PAR4, tryptase, and trypsin were quantified using real-time polymerase chain reaction (PCR) and the expression of PAR2 and PAR4 receptors was also measured by immunohistology and image analysis.

RESULTS

In IBS patients, the mRNA expression of tryptase and trypsin normalized against β-actin gene was higher compared to control subjects (P < 0.001). No difference was observed in the PAR2 mRNA level or protein level between control subjects on the one hand and IBS patients or subgroups on the other. In IBS or IBS subgroups patients, the expression of PAR4 in the mRNA level or protein level was lower than the control subjects.

CONCLUSIONS

This study, for the first time, indicated the PAR4 expression in IBS patients. Decreased PAR4 expression may help us to understand the pathogenesis of IBS.

Proteinase-activated receptors 1 and 2 mediate contraction of human oesophageal muscularis mucosae

Proteinase-activated receptors 1 and 2 mediate contraction of the human gallbladder. In the present study, we investigated effects mediated by proteinase-activated receptors (PARs) in the human oesophagus by measuring contraction of muscularis mucosae strips isolated from the human oesophagus. Both PAR(1) agonists (thrombin, SFLLRN-NH(2) and TFLLR-NH(2)) and PAR(2) agonists (trypsin, 2-furoyl-LIGRLO-NH(2) and SLIGKV-NH(2)) caused concentration-dependent contraction. In contrast, PAR(1) and PAR(2) control peptides did not cause contraction. The existence of PAR(1) and PAR(2) in the human oesophageal muscularis mucosae was confirmed by immunohistochemistry and reverse transcription-polymerase chain reaction. On the other hand, PAR(4) agonists, GYPGKF-NH(2), GYPGQV-NH(2) and AYPGKF-NH(2), did not cause contraction or relaxation in resting or carbachol-contracted muscularis mucosae strips, suggesting that PAR(4) is not involved in human oesophageal motility. The contractile responses to SFLLRN-NH(2) and trypsin in the human oesophagus were insensitive to atropine and tetrodotoxin, indicating that the contractile response was not neurally mediated. Taken together, these results demonstrate that PAR(1) and PAR(2) but not PAR(4) mediate contraction in human oesophageal muscularis mucosae. PAR(1) and PAR(2) may influence human oesophageal motility.

PAR4: a new role in the modulation of visceral nociception

Protease-activated receptors (PARs) are a family of G-protein-coupled receptors with a widespread distribution that are involved in various physiological functions including inflammation and nociception. In a recent study in Neurogastroenterology and Motility, Augé et al. describe for the first time the presence of PAR4 on visceral primary afferent neurons and its role in modulating colonic nociceptive responses, colonic hypersensitivity and primary afferent responses to PAR2 and Transient Receptor Potential Vanilloid-4 (TRPV4). Using the model of visceromotor response (VMR) to colorectal distension (CRD), they show that a PAR4 agonist delivered into the colon lumen decreases basal visceral response to CRD and reduces the exacerbated VMR to CRD induced by treatment with PAR2 or TRPV4 agonists. In isolated sensory neurons, they show that a PAR4 agonist inhibits calcium mobilization induced by PAR2 or TRPV4 agonists. Finally, they describe increased pain behaviour evoked by luminal application of mustard oil in PAR4 deficient mice compared to wild type controls. The newly discovered role of PAR4 in modulating visceral pain adds to our growing understanding of the contribution of colonic proteases and PARs to the mechanisms involved in colonic hypersensitivity and their potential role as therapeutic targets for irritable bowel syndrome.

Protease-activated receptor-4 (PAR 4): a role as inhibitor of visceral pain and hypersensitivity

Protease-activated receptor-4 (PAR(4)) belongs to the family of receptors activated by the proteolytic cleavage of their extracellular N-terminal domain and the subsequent binding of the newly released N-terminus. While largely expressed in the colon, the role of PAR(4) in gut functions has not been defined. We have investigated the effects of PAR(4) agonist on colonic sensations and sensory neuron signalling, and its role in visceral pain. We observed that a single administration of the PAR(4) agonist peptide (AYPGKF-NH(2)), but not the control peptide (YAPGKF-NH(2)) into the colon lumen of mice significantly reduced the visceromotor response to colorectal distension at different pressures of distension. Further, intracolonic administration of the PAR(4) agonist, but not the control peptide, was able to significantly inhibit PAR(2) agonist- and transcient receptor potential vanilloid-4 (TRPV4) agonist-induced allodynia and hyperalgesia in response to colorectal distension. Protease-activated receptor-4 was detected in sensory neurons projecting from the colon, and isolated from the dorsal root ganglia, where it co-expressed with PAR(2) and TRPV4. In total sensory neurons, PAR(4) agonist exposure inhibited free intracellular calcium mobilization induced by the pro-nociceptive agonists of PAR(2) and TRPV4. Finally, PAR(4)-deficient mice experienced increased pain behaviour in response to intracolonic administration of mustard oil, compared with wild-type littermates. These results show that PAR(4) agonists modulate colonic nociceptive response, inhibit colonic hypersensitivity and primary afferent responses to pro-nociceptive mediators. Endogenous activation of PAR(4) also plays a major role in controlling visceral pain. These results identify PAR(4) as a previously unknown modulator of visceral nociception.

Unbalanced expression of protease-activated receptors-1 and -2 in the colon of diarrhea-predominant irritable bowel syndrome patients

OBJECTIVE

The aim of this study is to determine whether a changed expression ratio of PAR-1 and PAR-2 in the colon is associated with diarrhea-predominant IBS patients.

METHODS

PAR-1, -2, thrombin, mast cell tryptase, tryptophan hydroxylase (TPH), and chromgranin A (ChrA) in colonic biopsy samples from 10 diarrhea-predominant IBS patients and 13 healthy control subjects were semiquantified with immunofluorescence and image analysis. Serotonin concentrations in biopsy samples were evaluated by capillary electrophoresis.

RESULTS

Significantly lower expression of PAR-1 and higher expression of mast cell tryptase was detected in the colons of patients, with statistically unchanged expression of PAR-2. Thrombin-, TPH-, and ChrA-positive cells were markedly increased in IBS patients, but no significant difference in serotonin concentration existed in the colons between two groups. The ratio of PAR-1/PAR-2 expression was significantly decreased in patients (0.33+/-0.19 versus 0.66+/-0.22, P=0.001) and negatively correlated to ChrA-positive cells.

CONCLUSIONS

Changed expression ratio of PAR-1 to PAR-2 in the colon is connected with diarrhea-predominant IBS patients. Methods to restore an appropriate balance of PAR-1 and PAR-2 activation in the colon may offer a promising future therapeutic strategy for IBS patients.

Thrombin receptor: An endogenous inhibitor of inflammatory pain, activating opioid pathways

Serine proteases such as thrombin, trypsin and mast cell tryptase can act on different cell types through protease-activated receptors (PARs). These receptors have been shown to be implicated in several phenomena such as inflammation, platelet activation, immune response and atherosclerosis. Several studies recently reported PARs expression on neurons and some of them demonstrated that these receptors could interfere with nociception. The contribution of PAR(1) to inflammatory pain and the mechanism involved in this phenomenon were investigated. Intraplantar injection of PAR(1) agonist increased withdrawal latency and reduced response frequency to von Frey filaments, thus inhibiting nociceptive response to both mechanical and thermal stimuli in mice. PAR(1) agonist also reduced carrageenan-induced inflammatory hyperalgesia. The anti-nociceptive effects of PAR(1) agonist were mediated by endogenous opioids, as this effect was inhibited by local injection of naloxone methiodide, and because intraplantar injection of PAR(1) agonist increased mRNA expression of the endogenous opioid precursor proenkephalin. However, PAR(1) agonist was not able to inhibit calcium signals in isolated sensory neurons exposed to pro-nociceptive agents. Finally, despite similar inflammatory parameters, PAR(1)-deficient mice showed a strong potentiation of inflammatory hyperalgesia induced by the intraplantar injection of either formalin or carrageenan, or in the chronic model of collagen-induced arthritis, compared to wild-type mice. This study highlights a previously unknown endogenous mechanism of analgesia, showing a central role for the thrombin receptor PAR(1) in the regulation of inflammatory pain and as an activator of opioid pathways.

Serine proteases decrease intestinal epithelial ion permeability by activation of protein kinase Czeta

Epithelial permeability to ions and larger molecules in the gut is essential for fluid balance, and its dysregulation contributes to intestinal pathology. We investigated the effect of digestive serine proteases on epithelial paracellular permeability. Trypsin, chymotrypsin, and elastase elicited sustained increases in transepithelial resistance (R(TE)) in polarized monolayers of three intestinal epithelial cell lines. This effect was reflected by decreases in paracellular conductances of Na+ and Cl- and a concomitant decrease in permeability to 3,000 molecular weight dextran. The enzyme activities of the proteases were required, yet activators of known protease-activated receptors (PARs) did not reproduce the effect of these proteases on R(TE). PKCzeta isoform-specific inhibitor significantly reduced the trypsin-induced increase in R(TE) whereas PKCzeta activity was increased in cells treated with trypsin and chymotrypsin compared with control cells; this activity was reduced to control levels in the presence of PKCzeta-specific inhibitor. Ca2+ chelators and pharmacological inhibitors of cell signaling support the role for PKCzeta in the protease-induced effect. Finally, we showed that treatment with the serine proteases increased occludin immunostaining and zonula occludin-1 coimmunoprecipitation with occludin in the detergent-insoluble fraction of cell lysates, and these increases were ablated by pretreatment with PKCzeta-specific inhibitor. This finding indicates increased insertion of occludin into the cell junctional complex. These data demonstrate a role for serine proteases in the facilitation of epithelial barrier function through a mechanism that is independent of PARs and is mediated by activation of PKCzeta.

Acute stress increases colonic paracellular permeability in mice through a mast cell-independent mechanism: involvement of pancreatic trypsin

AIMS

Increased colonic paracellular permeability (CPP) is a key feature of gastro-intestinal disorders as irritable bowel syndrome and inflammatory bowel diseases. Stress stimulates exocrine pancreatic secretion through cholinergic pathways, and trypsin is known to increase CPP. Consequently we have investigated in this work whether trypsin released into the gut lumen following an acute stress may participate to the short-term increase in CPP.

MAIN METHODS

Mice were treated with atropine or a non-selective CRF (corticotropin-releasing factor) receptor antagonist (alpha-helical CRF (9-41)), before being submitted to a 2-h stress session. Then, CPP and protease activity in colonic contents (total proteolytic, trypsin activity, and mouse mast cell protease (MMCP)-1 levels) were determined. The effects of colonic contents from sham-stressed or stressed animals on CPP were evaluated in mice colonic tissues mounted in Ussing chambers, in presence or not of soybean trypsin inhibitor (SBTI) or FSLLRY, a protease-activated receptor-2 (PAR2) antagonist.

KEY FINDINGS

Acute stress significantly increased CPP, proteolytic and trypsin activities, and MMCP-1 levels. Atropine inhibited stress-induced impairment of CPP and strongly diminished total proteolytic and trypsin activities in stressed animals, but not MMCP-1 levels. Colonic contents from stressed animals increased CPP in mice tissues, this effect being inhibited by SBTI and PAR2 antagonist.

SIGNIFICANCE

Acute stress activates cholinergic pathways, to trigger exocrine pancreatic secretion. Trypsin, released in these conditions, may be responsible for colonic barrier alterations through the activation of PAR2.

Expression of protease-activated receptor-2 (PAR-2) in patients with nasopharyngeal carcinoma: correlation with clinicopathological features and prognosis

We aimed at determining whether the expression of protease-activated receptor 2 (PAR-2) is involved in the progression of nasopharyngeal carcinoma (NPC) and correlated with latent membrane protein 1 (LMP-1), matrix metalloproteinases-9 (MMP9), and angiogenesis of tumor. PAR-2, LMP-1, and MMP9 expressions were detected in 57 biopsies of primary NPC by immunohistochemistry. The presence of Epstein-Barr virus (EBV) was determined using EBER in situ hybridization, and intratumoral microvessels were highlighted by staining endothelial cells for anti-CD34. The correlations with immunostainings and clinicopathological factors, as well as the follow-up data of patients, were analyzed statistically. Strong expression of PAR-2 in 61.4% (35/57) of the biopsies was correlated with extensive lymph node metastasis and advanced stage of NPC. The patients with PAR-2/LMP-1 or PAR-2/MMP9 dual high-expression tumors had a significant worse prognosis than those with single protein high expression and dual low or negative expression tumors (P=0.013 and 0.004, respectively). Angiogenesis in the tumor is related to overall survival of NPC patients (P=0.001), and exhibits strong PAR-2 expression or LMP-1 expression in tumors associated with increased intratumoral microvessel density (P=0.026 and 0.006, respectively). PAR-2 is a possible mediator cooperating with LMP-1 and MMP9 to influence the progression of NPC by inducing angiogenesis and promoting lymph node metastasis.

Kallikreins and proteinase-mediated signaling: proteinase-activated receptors (PARs) and the pathophysiology of inflammatory diseases and cancer

Proteinases such as thrombin and trypsin can affect tissues by activating a novel family of G protein-coupled proteinase-activated receptors (PARs 1-4) by exposing a 'tethered' receptor-triggering ligand (TL). Work with synthetic TL-derived PAR peptide sequences (PAR-APs) that stimulate PARs 1, 2 and 4 has shown that PAR activation can play a role in many tissues, including the gastrointestinal tract, kidney, muscle, nerve, lung and the central and peripheral nervous systems, and can promote tumor growth and invasion. PARs may play roles in many settings, including cancer, arthritis, asthma, inflammatory bowel disease, neurodegeneration and cardiovascular disease, as well as in pathogen-induced inflammation. In addition to activating or disarming PARs, proteinases can also cause hormone-like effects via PAR-independent mechanisms, such as activation of the insulin receptor. In addition to proteinases of the coagulation cascade, recent data suggest that members of the family of kallikrein-related peptidases (KLKs) represent endogenous PAR regulators. In summary: (1) proteinases are like hormones, signaling in a paracrine and endocrine manner via PARs or other mechanisms; (2) KLKs must now be seen as potential hormone-like PAR regulators in vivo; and (3) PAR-regulating proteinases, their target PARs, and their associated signaling pathways appear to be novel therapeutic targets.

Derivatized 2-furoyl-LIGRLO-amide, a versatile and selective probe for proteinase-activated receptor 2: binding and visualization

The proteinase-activated receptor-2 (PAR2)-activating peptide with an N-terminal furoyl group modification, 2-furoyl-LIGRLO-NH2 (2fLI), was derivatized via its free ornithine amino group to yield [3H]propionyl-2fLI and Alexa Fluor 594-2fLI that were used as receptor probes for ligand binding assays and receptor visualization both for cultured cells in vitro and for colonic epithelial cells in vivo. The binding of the radiolabeled and fluorescent PAR2 probes was shown to be present in PAR2-transfected Kirsten normal rat kidney cells, but not in vector-alone-transfected cells, and was abolished by pretreatment of cells with saturating concentrations of receptor-selective PAR2 peptide agonists such as SLIGRL-NH2 and the parent agonist 2fLI but not by reverse-sequence peptides such as 2-furoyl-OLRGIL-NH2 that cannot activate PAR2. The relative orders of potencies for a series of PAR2 peptide agonists to compete for the binding of [3H]propionyl-2fLI (2fLI >> SLIGRL-NH2 approximately= trans-cinnamoyl-LIGRLO-NH2 > SLIGKV-NH2 > SLIGKT-NH2) mirrored qualitatively their relative potencies for PAR2-mediated calcium signaling in the same cells or for vasorelaxation in a rat aorta vascular assay. In the vascular assay, the potency of Alexa Fluor 594-2fLI was the same as 2fLI. We conclude that ornithine-derivatized 2fLI peptides are conveniently synthesized PAR2 probes that will be of value for future studies of receptor binding and visualization.

Proteinase-activated receptor-1 (PAR(1)) and PAR(2) but not PAR(4) mediate contraction in human and guinea-pig gallbladders

Proteinase-activated receptor-1 (PAR(1)) and PAR(2) mediate contraction in the guinea-pig gallbladder. To investigate and compare the effects mediated by PARs in the human gallbladder with those in the guinea-pig gallbladder, we measured contractions of isolated human and guinea-pig gallbladder strips caused by PAR agonists. Results in human were similar to those in guinea-pig gallbladder. The PAR(1) agonists, thrombin, TFLLR-NH2 and SFLLRN-NH2, as well as the PAR(2) agonists, trypsin, SLIGKV-NH2 and SLIGRL-NH2, caused contraction in both human and guinea-pig gallbladders. These indicate the existence of PAR(1) and PAR(2) mediating gallbladder contraction. Furthermore, the existence of PAR(1) and PAR(2) in the human gallbladder was confirmed by reverse transcription-polymerase chain reaction. In contrast, FSLLR-NH2, a PAR(1) control peptide, and VKGILS-NH2, a PAR(2) control peptide, as well as three PAR(4) agonists, GYPGKF-NH2, GYPGQV-NH2 and AYPGKF-NH2, did not cause any contraction or relaxation. The contractile responses to TFLLR-NH2, SFLLRN-NH2 and trypsin in both human and guinea-pig gallbladders were insensitive to atropine and tetrodotoxin, suggesting direct effects. These results demonstrate that, similar to the guinea-pig gallbladder, both PAR(1) and PAR(2) but not PAR(4) mediate muscle contraction in the human gallbladder. PAR(1) and PAR(2) may play important roles in the control of both human and guinea-pig gallbladder motility.

Hepta and octapeptide agonists of protease-activated receptor 2

Protease-activated receptor 2 (PAR(2)) is a G protein-coupled cell surface receptor for trypsin-like enzymes. Proteolytic cleavage at a specific site in the extracellular N-terminus exposes a receptor-activating sequence, the 'tethered ligand', which binds intramolecularly to initiate receptor signalling. Peptide or small molecule agonists for PAR(2), devoid of the non-specific and proteolytic effects of enzyme activators, may be promising therapeutic agents for proliferative and inflammatory diseases reportedly mediated by PAR(2). Synthetic hexapeptides that correspond to the native tethered ligand of human or rodent PAR(2) (SLIGKV and SLIGRL, respectively) can activate the receptor independently of proteolytic cleavage; however, known peptide agonists have much lower potency compared to protease-mediated activation. Here, we investigated the agonist activity of 94 hepta and octapeptide derivatives of the human and rodent PAR(2)-tethered ligand sequences in human airway epithelial (A549) cells which endogenously express PAR(2). Thirty synthetic peptides were found to be as potent as or more potent than SLIGRL on the basis of intracellular Ca(2+) responses. The more active peptide agonists were also examined for agonist cross-reactivity at PAR(1) in Chinese Hamster Ovary (CHO) cells that endogenously express functional PAR(1) but not PAR(2). Two potent and PAR(2)-selective agonists were further examined for their capacity to relax phenylephrine-contracted rat aortic rings. Our findings reveal an important role for carboxyl extensions to native PAR(2) activating peptides in potentiating agonist activity.

Expression of a functional metabotropic glutamate receptor 5 on enteric glia is altered in states of inflammation

The metabotropic glutamate receptor 5 (mGluR5) is expressed by astrocytes and its expression is modulated by inflammation. Enteric glia have many similarities to astrocytes and are the most numerous cell in the enteric nervous system (ENS). We investigated whether enteric glia express a functional mGluR5 and whether expression of this receptor was altered in colitis. In both enteric plexuses of the ileum and colon of guinea pigs and mice, we observed widespread glial mGluR5 expression. Incubation of isolated segments of the guinea pig ileum with the mGluR5 specific agonist RS-2-chloro-5-hydroxyphenylglycine (CHPG) caused a dose-dependent increase in the glial expression of c-Fos and the phosphorylated form of the extracellular signal-regulated kinase 1/2. Preincubation of tissues with the group I metabotropic glutamate receptor antagonist, S-4-carboxyphenylglycine, abolished the effects of CHPG. We examined mGluR5 expression in the guinea pig trinitrobenzene sulfonic acid and the IL-10 gene-deficient (IL-10(-/-)) mouse models of colitis. In guinea pigs, mGluR5 immunoreactivity became diffusely localized over the colonic myenteric ganglia, suggesting a change in receptor distribution. In contrast, glial mGluR5 expression was significantly reduced in the colonic myenteric plexus of IL-10(-/-) mice, as assessed with both real-time quantitative RT-PCR as well as immunohistochemistry and image analysis. These changes occurred without concomitant changes to enteric ganglia or glial fibrillary acidic protein expression in the IL-10(-/-) mouse. Our data suggest that enteric glia are a functional target of the glutamatergic neurotransmitter system in the ENS and that changes in mGluR5 expression may be of physiological significance during colitis.

[Stress-mast cell axis and regulation of gut mucosal inflammation: from intestinal health to an irritable bowel]

The functional gastrointestinal disorders and the irritable bowel syndrome, in particular, represent one of the commonest causes of medical consultation and the most frequent diagnosis raised by the gastroenterologists. Despite their high prevalence, the aetiology and pathophysiology of these functional digestive disorders remains unclear and specific diagnostic markers and clearly effective therapeutic options are lacking as well. These factors generate an important impairment in the quality of life in these patients and a growing sanitary burden. Recent studies showing the presence of low grade intestinal mucosal inflammation along with mast cell hyperplasia may contribute to the development and perpetuation of visceral hypersensitivity and dismotility patterns and epithelial barrier abnormalities, characteristic of the irritable bowel syndrome. In this article we will review the role of the stress-mast cell axis in the modulation of the gut mucosal inflammation and in the pathophysiology of the irritable bowel syndrome.

Protease-activated receptor 2, dipeptidyl peptidase I, and proteases mediate Clostridium difficile toxin A enteritis

BACKGROUND & AIMS

We studied the role of protease-activated receptor 2 (PAR(2)) and its activating enzymes, trypsins and tryptase, in Clostridium difficile toxin A (TxA)-induced enteritis.

METHODS

We injected TxA into ileal loops in PAR(2) or dipeptidyl peptidase I (DPPI) knockout mice or in wild-type mice pretreated with tryptase inhibitors (FUT-175 or MPI-0442352) or soybean trypsin inhibitor. We examined the effect of TxA on expression and activity of PAR(2) and trypsin IV messenger RNA in the ileum and cultured colonocytes. We injected activating peptide (AP), trypsins, tryptase, and p23 in wild-type mice, some pretreated with the neurokinin 1 receptor antagonist SR140333.

RESULTS

TxA increased fluid secretion, myeloperoxidase activity in fluid and tissue, and histologic damage. PAR(2) deletion decreased TxA-induced ileitis, reduced luminal fluid secretion by 20%, decreased tissue and fluid myeloperoxidase by 50%, and diminished epithelial damage, edema, and neutrophil infiltration. DPPI deletion reduced secretion by 20% and fluid myeloperoxidase by 55%. In wild-type mice, FUT-175 or MPI-0442352 inhibited secretion by 24%-28% and tissue and fluid myeloperoxidase by 31%-71%. Soybean trypsin inhibitor reduced secretion to background levels and tissue myeloperoxidase by up to 50%. TxA increased expression of PAR(2) and trypsin IV in enterocytes and colonocytes and caused a 2-fold increase in Ca(2+) responses to PAR(2) AP. AP, tryptase, and trypsin isozymes (trypsin I/II, trypsin IV, p23) caused ileitis. SR140333 prevented AP-induced ileitis.

CONCLUSIONS

PAR(2) and its activators are proinflammatory in TxA-induced enteritis. TxA stimulates existing PAR(2) and up-regulates PAR(2) and activating proteases, and PAR(2) causes inflammation by neurogenic mechanisms.

A pilot study of fecal serine-protease activity: a pathophysiologic factor in diarrhea-predominant irritable bowel syndrome

BACKGROUND & AIMS

The pathogenesis of irritable bowel syndrome (IBS) remains only partially understood, and no specific or universally effective patient management procedure has been developed to date. Our study was designed to evaluate if colonic luminal serine-proteases may be a relevant pathophysiologic marker of IBS.

METHODS

Fecal samples of 38 IBS patients, 15 patients with ulcerative colitis (UC), and 15 healthy controls were studied. Fecal serine-protease activity was determined photometrically by using azocasein as a proteolytic substrate; fecal pancreatic elastase-1 and mast cell tryptase content were measured by enzyme-linked immunosorbent assay. Fecal secretory leukocyte protease inhibitor concentration was determined by enzyme-linked immunosorbent assay in control subjects and in patients with diarrhea-predominant IBS.

RESULTS

Fecal serine-protease activity was 3-fold higher in patients with diarrhea-predominant IBS than in both controls and IBS patients with either constipation or alternating bowel habits. Fecal serine-protease activity was not correlated with the frequency of bowel movements in all groups. Increased serine-protease activity also was detected in stools of UC patients. No significant difference was observed in the fecal mast cell tryptase and pancreatic elastase concentrations between all groups, or in the fecal secretory leukocyte protease inhibitor concentration between controls and diarrhea-predominant IBS patients.

CONCLUSIONS

Fecal serine-protease activity is increased markedly in patients with diarrhea-predominant IBS. This increase, however, is not coupled with changes in either mast cell tryptase or pancreatic elastase concentrations. Thus, serine-protease activity in the colon may be a pathophysiologic factor in the development of diarrhea-predominant IBS.

Neural Upregulation in Interstitial Cystitis

Interstitial cystitis (IC) is a syndrome of bladder hypersensitivity with symptoms of urgency, frequency, and chronic pelvic pain. Although no consensus has been reached on the underlying cause of IC, several pathophysiologic mechanisms, including epithelial dysfunction, mast cell activation, and neurogenic inflammation, have been proposed. Despite multiple different causes of urinary cystitis, the bladder's response to cystitis is limited and typical. Animal experiments have shown upregulation of proteinase-activated receptors, tryptase, beta-nerve growth factor, inducible nitric oxide synthase, nuclear transcription factor-kappaB, c-Fos, phosphodiesterase 1C, cyclic adenosine monophosphate (cAMP)-dependent protein kinase, and proenkephalin B. After the noxious stimulus has abated, downregulation of genes appears to follow. Distention of the bladder results in the release of adenosine triphosphate (ATP) from urothelial cells, which activates purinergic P2X3 receptors. Activation by ATP of P2X3-expressing afferents is a fundamental signaling factor in bladder sensation and appears to play a role in bladder reflexes. Fos proteins present in spinal cord neurons have been shown to be upregulated in animals that have undergone cyclophosphamide-induced chemical cystitis. These and other findings suggest that neural upregulation occurs both peripherally and centrally in subjects with chronic cystitis. It is unclear whether neural mechanisms and inflammation are the cause of IC or the result of other initiating events. Neural upregulation is known to play a role in the chronicity of pain, urgency, and frequency and represents an exciting area of research that may lead to additional treatments and a better understanding of IC.

The emergence of proteinase-activated receptor-2 as a novel target for the treatment of inflammation-related CNS disorders

The signalling molecules that are involved in inflammatory pathways are now thought to play a part in many disorders of the central nervous system (CNS). In common with peripheral chronic inflammatory diseases such a rheumatoid arthritis and ulcerative colitis, evidence now exists for the involvement of inflammatory cytokines, for example tumour necrosis factor (TNF) and interleukins (IL), in neurological disorders. A common factor observed with the up-regulation of these cytokines in peripheral inflammatory diseases, is the increased expression of the proteinase-activated receptor (PAR) subtype PAR-2. Indeed, recent evidence suggests that targeting PAR-2 helps reduce joint swelling observed in animal models of arthritis. So could targeting this receptor prove to be useful in treating those CNS disorders where inflammatory processes are thought to play an intrinsic role? The aim of this review is to summarize the emerging data regarding the role of PAR-2 in neuroinflammation and ischaemic injury and discuss its potential as an exciting new target for the prevention and/or treatment of CNS disorders.

Proteinase-activated receptors in the lower urinary tract

Proteinase-activated receptors (PARs) are G-protein-coupled receptors that convert specific extracellular proteolytic activity into intracellular signals, and have been suggested to play diverse roles in the body. In this review, evidence for the roles of PARs in bladder contractility and inflammation are presented. The role of PARs in prostate cancer is also reviewed. The existing literature in this area can be difficult to interpret due to the many nonspecific actions of the pharmacological tools employed. Although there are reports that PAR activators can cause contraction of bladder smooth muscle, further pharmacological and molecular studies are required to define roles for these receptors in bladder contractility. While structural studies suggest that roles for PARs in bladder inflammation are likely, few functional investigations have been performed. The significance of the expression of PARs on sensory nerves innervating the bladder and changes in receptor expression in inflammatory disease models are fascinating areas for future research. Finally, it seems probable that PARs, particularly PAR1, may play important roles in the growth and metastasis of prostate cancers.

Protease-activated receptor-1 (PAR1) and PAR2 but not PAR4 mediate relaxations in lower esophageal sphincter

Protease-activated receptor-1 (PAR1), PAR2 and PAR4 activation can alter the gastrointestinal motility. To investigate effects mediated by PARs in the lower esophageal sphincter, we measured contraction or relaxation of transverse strips from the guinea-pig lower esophageal sphincter caused by PAR1 (TFLLR-NH2 and SFLLRN-NH2), PAR2 (SLIGKV-NH2 and SLIGRL-NH2) and PAR4 peptide agonists (GYPGKF-NH2, GYPGQV-NH2 and AYPGKF-NH2) as well as PAR protease activators (thrombin and trypsin). In resting lower esophageal sphincter strips, TFLLR-NH2 and SFLLRN-NH2 caused moderate concentration-dependent relaxation whereas thrombin did not cause any relaxation or contraction. Furthermore, in carbachol-contracted strips, TFLLR-NH2 and SFLLRN-NH2 caused marked whereas thrombin caused mild concentration-dependent relaxation. These indicate the existence of PAR1 mediating relaxation. Similarly, in resting lower esophageal sphincter strips, trypsin caused moderate concentration-dependent relaxation whereas SLIGRL-NH2 and SLIGKV-NH2 did not cause any relaxation or contraction. In addition, in carbachol-contracted strips, trypsin caused marked whereas SLIGRL-NH2 and SLIGKV-NH2 caused mild concentration-dependent relaxation. These indicate the existence of PAR2 mediating relaxation. The relaxant response of thrombin, TFLLR-NH2, trypsin and SLIGKV-NH2 was insensitive to atropine or tetrodotoxin, suggesting a direct effect. The relaxant response of trypsin was not affected by apamin, charybdotoxin, indomethacin and capsaicin but was attenuated by NG-nitro-L-arginine methyl ester, indicating involvement of NO. FSLLR-NH2, a PAR1 control peptide, and VKGILS-NH2, a PAR2 control peptide, as well as all three PAR4 peptide agonists, GYPGKF-NH2, GYPGQV-NH2 and AYPGKF-NH2, did not cause any relaxation or contraction. Taken together, these results demonstrate that PAR1 and PAR2 but not PAR4 mediate relaxations in the guinea-pig lower esophageal sphincter.