Effects of luminal thymol on epithelial transport in human and rat colon

Allyl isothiocyanate, an activator of TRPA1, increases gastric mucosal blood flow through calcitonin gene-related peptide and adrenomedullin in anesthetized rats

Allyl isothiocyanate (AITC) activates transient receptor potential ankyrin 1 (TRPA1) channel, which is involved in the control of intestinal mucosal blood flow. However, the mechanism underlying the increased gastric mucosal blood flow (GMBF) in response to AITC remains unknown. We examined the effect of AITC on GMBF in the ex vivo stomachs of normal and sensory deafferented rats using a laser Doppler flowmeter. Mucosal application of AITC increased GMBF in a concentration-dependent manner. Repeated AITC exposure resulted in a marked desensitization. The increased GMBF response induced by AITC was entirely blocked by co-application of TRPA1 channel blockers HC-030031 or AP-18. Increased GMBF in response to AITC was significantly attenuated by chemical deafferentation following systemic capsaicin injections (total dose: 100 mg/kg). In contrast, increased GMBF responses to capsaicin, a transient receptor potential vanilloid 1 (TRPV1) activator, were completely abolished by chemical deafferentation. The increased GMBF response to AITC was markedly inhibited by BIBN 4096, a calcitonin gene-related peptide receptor (CGRP) antagonist, or AGP-8412, an adrenomedullin receptor antagonist. These results suggest that AITC-stimulated TRPA1 activation results in the increased GMBF through the release of CGRP and adrenomedullin.

The gut odorant receptor and taste receptor make sense of dietary components: A focus on gut hormone secretion

Odorant receptors (ORs) and taste receptors (TRs) are expressed primarily in the nose and tongue in which they transduce electrical signals to the brain. Advances in deciphering the dietary component-sensing mechanisms in the nose and tongue prompted research on the role of gut chemosensory cells. Acting as the pivotal interface between the body and dietary cues, gut cells "smell" and "taste" dietary components and metabolites by taking advantage of chemoreceptors-ORs and TRs, to maintain physiological homeostasis. Here, we reviewed this novel field, highlighting the latest discoveries pertinent to gut ORs and TRs responding to dietary components, their impacts on gut hormone secretion, and the mechanisms involved. Recent studies indicate that gut cells sense dietary components including fatty acid, carbohydrate, and phytochemical by activating relevant ORs, thereby modulating GLP-1, PYY, CCK, and 5-HT secretion. Similarly, gut sweet, umami, and bitter receptors can regulate the gut hormone secretion and maintain homeostasis in response to dietary components. A deeper understanding of the favorable influence of dietary components on gut hormone secretion via gut ORs and TRs, coupled with the facts that gut hormones are involved in diverse physiological or pathophysiological phenomena, may ultimately lead to a promising treatment for various human diseases.

A Technique of Measurement of Gastrointestinal Luminal Nutrient Sensing and These Absorptions: Ussing Chamber (Short-Circuit Current) Technique

The gastrointestinal (GI) tract is a series of hollow organs that play roles in food digestion and nutrient absorption. To perform these functions, they should recognize the luminal environment and elicit adequate physiological responses, including digestive juice secretion, peristaltic movements, etc. The Ussing chamber technique is an electrophysiological method for measuring transepithelial ion transport and permeability as short-circuit current (I_sc) and transepithelial electrical tissue conductance (G_t) or resistance (TEER), respectively, in vitro. This technique can be applied for the measurement of luminal nutrient sensing and absorption. This article introduces practical methods for measuring luminal nutrient sensing and absorption using intestinal mucosa specimens isolated from humans and experimental animals.

EFFECTS OF 2-METHYL-2-THIAZOLINE ON CIRCULATORY DYNAMICS AND INTESTINAL VASCULAR SYSTEM IN RABBITS WITH ENDOTOXIC SHOCK

ABSTRACT

We hypothesized that circulatory and jejunal mucosal blood flow would improve after 2-methyl-2thiazoline (2MT) administration in endotoxic shock. This study aimed to evaluate changes in systemic circulation and in superior mesenteric venous (SMV) blood flow and jejunal mucosal tissue blood flow of the intestinal vascular system over time after administration of 2MT in rabbits with endotoxic shock. We created four groups (n = 6 each): control group, LPS (1 mg/kg) group, 2MT (80 mg/kg) group, and LPS-2MT group. As indicators of circulation, we measured MAP, heart rate, cardiac index, lactic acid level, SMV blood flow, and jejunal mucosal tissue blood flow every 30 min from 0 to 240 min. The drop in MAP observed in the LPS group was suppressed by 2MT administration. Superior mesenteric venous blood flow dropped temporarily with LPS administration but then rose thereafter. After administration of 2MT to the LPS group, SMV blood flow began to rise earlier than that in the LPS group and did not decline below that of the control group thereafter. In the LPS group, jejunal mucosal tissue blood flow transiently decreased and then increased but at a lower level than that in the control group. However, in the LPS-2MT group, although a transient decrease in jejunal mucosal tissue blood flow was observed, its flow then improved to the level of the control group. An interaction between 2MT and LPS was observed for jejunal mucosal tissue blood flow from 90 to 180 min and at 240 min (P < 0.05). We showed that 2MT maintained MAP and improved SMV blood flow and jejunal mucosal tissue blood flow. In a rabbit model of endotoxic shock, 2MT had a positive effect on MAP and jejunal mucosal tissue blood flow.

Treatment of Gastrointestinal Disorders-Plants and Potential Mechanisms of Action of Their Constituents

The worldwide prevalence of gastrointestinal diseases is about 40%, with standard pharmacotherapy being long-lasting and economically challenging. Of the dozens of diseases listed by the Rome IV Foundation criteria, for five of them (heartburn, dyspepsia, nausea and vomiting disorder, constipation, and diarrhoea), treatment with herbals is an official alternative, legislatively supported by the European Medicines Agency (EMA). However, for most plants, the Directive does not require a description of the mechanisms of action, which should be related to the therapeutic effect of the European plant in question. This review article, therefore, summarizes the basic pharmacological knowledge of synthetic drugs used in selected functional gastrointestinal disorders (FGIDs) and correlates them with the constituents of medicinal plants. Therefore, the information presented here is intended as a starting point to support the claim that both empirical folk medicine and current and decades-old treatments with official herbal remedies have a rational basis in modern pharmacology.

Not Only COVID-19: Involvement of Multiple Chemosensory Systems in Human Diseases

Chemosensory systems are deemed marginal in human pathology. In appraising their role, we aim at suggesting a paradigm shift based on the available clinical and experimental data that will be discussed. Taste and olfaction are polymodal sensory systems, providing inputs to many brain structures that regulate crucial visceral functions, including metabolism but also endocrine, cardiovascular, respiratory, and immune systems. Moreover, other visceral chemosensory systems monitor different essential chemical parameters of “milieu intérieur,” transmitting their data to the brain areas receiving taste and olfactory inputs; hence, they participate in regulating the same vital functions. These chemosensory cells share many molecular features with olfactory or taste receptor cells, thus they may be affected by the same pathological events. In most COVID-19 patients, taste and olfaction are disturbed. This may represent only a small portion of a broadly diffuse chemosensory incapacitation. Indeed, many COVID-19 peculiar symptoms may be explained by the impairment of visceral chemosensory systems, for example, silent hypoxia, diarrhea, and the “cytokine storm”. Dysregulation of chemosensory systems may underlie the much higher mortality rate of COVID-19 Acute Respiratory Distress Syndrome (ARDS) compared to ARDSs of different origins. In chronic non-infectious diseases like hypertension, diabetes, or cancer, the impairment of taste and/or olfaction has been consistently reported. This may signal diffuse chemosensory failure, possibly worsening the prognosis of these patients. Incapacitation of one or few chemosensory systems has negligible effects on survival under ordinary life conditions but, under stress, like metabolic imbalance or COVID-19 pneumonia, the impairment of multiple chemosensory systems may lead to dire consequences during the course of the disease.

TRPA1: Pharmacology, natural activators and role in obesity prevention

Transient receptor potential ankyrin 1 (TRPA1) channel is a calcium permeable, non-selective cation channel, expressed in the sensory neurons and non-neuronal cells of different tissues. Initially studied for its role in pain and inflammation, TRPA1 has now functionally involved in multiple other physiological functions. TRPA1 channel has been extensively studied for modulation by pungent compounds present in the spices and herbs. In the last decade, the role of TRPA1 agonism in body weight reduction, secretion of hunger and satiety hormones, insulin secretion and thermogenesis, has unveiled the potential of the TRPA1 channel to be used as a preventive target to tackle obesity and associated comorbidities including insulin resistance in type 2 diabetes. In this review, we summarized the recent findings of TRPA1 based dietary/non-dietary modulation for its role in obesity prevention and therapeutics.

The TRPA1 Agonist Cinnamaldehyde Induces the Secretion of HCO3- by the Porcine Colon

A therapeutic potential of the TRPA1 channel agonist cinnamaldehyde for use in inflammatory bowel disease is emerging, but the mechanisms are unclear. Semi-quantitative qPCR of various parts of the porcine gastrointestinal tract showed that mRNA for TRPA1 was highest in the colonic mucosa. In Ussing chambers, 1 mmol·L^-1 cinnamaldehyde induced increases in short circuit current (ΔI_sc) and conductance (ΔG_t) across the colon that were higher than those across the jejunum or after 1 mmol·L^-1 thymol. Lidocaine, amiloride or bumetanide did not change the response. The application of 1 mmol·L^-1 quinidine or the bilateral replacement of 120 Na⁺, 120 Cl^- or 25 HCO₃^- reduced ΔG_t, while the removal of Ca²⁺ enhanced ΔG_t with ΔI_sc numerically higher. ΔI_sc decreased after 0.5 NPPB, 0.01 indometacin and the bilateral replacement of 120 Na⁺ or 25 HCO₃^-. The removal of 120 Cl^- had no effect. Cinnamaldehyde also activates TRPV3, but comparative measurements involving patch clamp experiments on overexpressing cells demonstrated that much higher concentrations are required. We suggest that cinnamaldehyde stimulates the secretion of HCO₃^- via apical CFTR and basolateral Na⁺-HCO₃^- cotransport, preventing acidosis and damage to the epithelium and the colonic microbiome. Signaling may involve the opening of TRPA1, depolarization of the epithelium and a rise in PGE2 following a lower uptake of prostaglandins via OATP2A1.

Human ectopic olfactory receptors and their food originated ligands: a review

Ectopic olfactory receptors (EORs) are expressed in non-nasal tissues of human body. They belong to the G-protein coupled receptor (GPCR) superfamily. EORs may not be capable of differentiating odorants as nasal olfactory receptors (ORs), but still can be triggered by odorants and are involved in different biological processes such as anti-inflammation, energy metabolism, apoptosis etc. Consumption of strong flavored foods like celery, oranges, onions, and spices, is a good aid to attenuate inflammation and boost our immune system. During the digestion of these foods in human digestive system and the metabolization by gut microbiota, the odorants closely interacting with EORs, may play important roles in various bio-functions like serotonin release, appetite regulation etc., and ultimately impact health and diseases. Thus, EORs could be a potential target linking the ligands from food and their bioactivities. There have been related studies in different research fields of medicine and physiology, but still no systematic food oriented review. Our review portrays that EORs could be a potential target for functional food development. In this review, we summarized the EORs found in human tissues, their impacts on health and disease, ligands interacting with EORs exerting specific biological effects, and the mechanisms involved.

Lysophosphatidic Acid Increases Maturation of Brush Borders and SGLT1 Activity in MYO5B-deficient Mice, a Model of Microvillus Inclusion Disease

BACKGROUND & AIM

Myosin VB (MYO5B) is an essential trafficking protein for membrane recycling in gastrointestinal epithelial cells. The inactivating mutations of MYO5B cause the congenital diarrheal disease, microvillus inclusion disease (MVID). MYO5B deficiency in mice causes mislocalization of SGLT1 and NHE3, but retained apical function of CFTR, resulting in malabsorption and secretory diarrhea. Activation of lysophosphatidic acid (LPA) receptors can improve diarrhea, but the effect of LPA on MVID symptoms is unclear. We investigated whether LPA administration can reduce the epithelial deficits in MYO5B-knockout mice.

METHODS

Studies were conducted with tamoxifen-induced, intestine-specific knockout of MYO5B (VilCre^ERT2;Myo5b^flox/flox) and littermate controls. Mice were given LPA, an LPAR2 agonist (GRI977143), or vehicle for 4 days after a single injection of tamoxifen. Apical SGLT1 and CFTR activities were measured in Üssing chambers. Intestinal tissues were collected, and localization of membrane transporters was evaluated by immunofluorescence analysis in tissue sections and enteroids. RNA sequencing and enrichment analysis were performed with isolated jejunal epithelial cells.

RESULTS

Daily administration of LPA reduced villus blunting, frequency of multivesicular bodies, and levels of cathepsins in intestinal tissues of MYO5B-knockout mice compared with vehicle administration. LPA partially restored the brush border height and the localization of SGLT1 and NHE3 in small intestine of MYO5B-knockout mice and enteroids. The SGLT1-dependent short-circuit current was increased and abnormal CFTR activities were decreased in jejunum from MYO5B-knockout mice given LPA compared with vehicle.

CONCLUSIONS

LPA may regulate a MYO5B-independent trafficking mechanism and brush border maturation, and therefore be developed for treatment of MVID.

Therapeutic potential of ectopic olfactory and taste receptors

Olfactory and taste receptors are expressed primarily in the nasal olfactory epithelium and gustatory taste bud cells, where they transmit real-time sensory signals to the brain. However, they are also expressed in multiple extra-nasal and extra-oral tissues, being implicated in diverse biological processes including sperm chemotaxis, muscle regeneration, bronchoconstriction and bronchodilatation, inflammation, appetite regulation and energy metabolism. Elucidation of the physiological roles of these ectopic receptors is revealing potential therapeutic and diagnostic applications in conditions including wounds, hair loss, asthma, obesity and cancers. This Review outlines current understanding of the diverse functions of ectopic olfactory and taste receptors and assesses their potential to be therapeutically exploited.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Dietary supplementation of essential oils in dairy cows: evidence for stimulatory effects on nutrient absorption

Results of recent in vitro experiments suggest that essential oils (EO) may not only influence ruminal fermentation but also modulate the absorption of cations like Na+, Ca2+ and NH4 + across ruminal epithelia of cattle and sheep through direct interaction with epithelial transport proteins, such as those of the transient receptor potential family. The aim of the current study was to examine this hypothesis by testing the effect of a blend of essential oils (BEO) on cation status and feed efficiency in lactating dairy cows. In the experiment, 72 dairy cows in mid-to-end lactation were divided into two groups of 36 animals each and fed the same mixed ration with or without addition of BEO in a 2×2 cross-over design. Feed intake, milk yield and composition, plasma and urine samples were monitored. Feeding BEO elevated milk yield, milk fat and protein yield as well as feed efficiency, whereas urea levels in plasma and milk decreased. In addition, plasma calcium levels increased significantly upon BEO supplementation, supporting the hypothesis that enhanced cation absorption might contribute to the beneficial effects of these EO.

Thymol Improves Barrier Function and Attenuates Inflammatory Responses in Porcine Intestinal Epithelial Cells during Lipopolysaccharide (LPS)-Induced Inflammation

It is well-known that essential oil thymol exhibits antibacterial activity. The protective effects of thymol on pig intestine during inflammation is yet to be investigated. In this study, an in vitro lipopolysaccharide (LPS)-induced inflammation model using IPEC-J2 cells was established. Cells were pretreated with thymol for 1 h and then exposed to LPS for various assays. Interleukin 8 (IL-8) secretion, the mRNA abundance of cytokines, reactive oxygen species (ROS), nutrient transporters, and tight junction proteins was measured. The results showed that LPS stimulation increased IL-8 secretion, ROS production, and tumor necrosis factor alpha (TNF-α) mRNA abundance ( P < 0.05), but the mRNA abundance of sodium-dependent glucose transporter 1 (SGLT1), excitatory amino acid transporter 1 (EAAC1), and H⁺/peptide cotransporter 1 (PepT1) were decreased ( P < 0.05). Thymol blocked ROS production ( P < 0.05) and tended to decrease the production of LPS-induced IL-8 secretion ( P = 0.0766). The mRNA abundance of IL-8 and TNF-α was reduced by thymol pretreatment ( P < 0.05), but thymol did not improve the gene expression of nutrient transporters ( P > 0.05). The transepithelial electrical resistance (TEER) was reduced and cell permeability increased by LPS treatment ( P < 0.05), but these effects were attenuated by thymol ( P < 0.05). Moreover, thymol increased zonula occludens-1 (ZO-1) and actin staining in the cells. However, the mRNA abundance of ZO-1 and occludin-3 was not affected by either LPS or thymol treatments. These results indicated that thymol enhances barrier function and reduce ROS production and pro-inflammatory cytokine gene expression in the epithelial cells during inflammation. The regulation of barrier function by thymol and LPS may be at post-transcriptional or post-translational levels.

TRPA1: a molecular view

The transient receptor potential ankyrin 1 (TRPA1) ion channel is expressed in pain-sensing neurons and other tissues and has become a major target in the development of novel pharmaceuticals. A remarkable feature of the channel is its long list of activators, many of which we are exposed to in daily life. Many of these agonists induce pain and inflammation, making TRPA1 a major target for anti-inflammatory and analgesic therapies. Studies in human patients and in experimental animals have confirmed an important role for TRPA1 in a number of pain conditions. Over the recent years, much progress has been made in elucidating the molecular structure of TRPA1 and in discovering binding sites and modulatory sites of the channel. Because the list of published mutations and important molecular sites is steadily growing and because it has become difficult to see the forest for the trees, this review aims at summarizing the current knowledge about TRPA1, with a special focus on the molecular structure and the known binding or gating sites of the channel.

Involvement of butyrate in electrogenic K+ secretion in rat rectal colon

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are synthesized from dietary carbohydrates by colonic bacterial fermentation. These SCFAs supply energy, suppress cancer, and affect ion transport. However, their roles in ion transport and regulation in the intracellular environment remain unknown. In order to elucidate the roles of SCFAs, we measured short-circuit currents (I_SC) and performed RT-PCR and immunohistochemical analyses of ion transporters in rat rectal colon. The application of 30 mM butyrate shifted I_SC in a negative direction, but did not attenuate the activity of epithelial Na⁺ channels (ENaC). The application of bumetanide, a Na⁺-K⁺-2Cl⁻ cotransporter inhibitor, to the basolateral side reduced the negative I_SC shift induced by butyrate. The application of XE991, a KCNQ-type K⁺ channel inhibitor, to the apical side decreased the I_SC shift induced by butyrate in a dose-dependent manner. The I_SC shift was independent of HCO₃⁻ and insensitive to ibuprofen, an SMCT1 inhibitor. The mucosa from rat rectal colon expressed mRNAs of H⁺-coupled monocarboxylate transporters (MCT1, MCT4, and MCT5, also referred to as SLC16A1, SLC16A3, and SLC16A4, respectively). RT-PCR and immunofluorescence analyses demonstrated that KCNQ2 and KCNQ4 localized to the apical membrane of surface cells in rat rectal colon. These results indicate that butyrate, which may be transported by H⁺-coupled monocarboxylate transporters, activates K⁺ secretion through KCNQ-type K⁺ channels on the apical membrane in rat rectal colon. KCNQ-type K⁺ channels may play a role in intestinal secretion and defense mechanisms in the gastrointestinal tract.

Odorant Receptors Containing Conserved Amino Acid Sequences in Transmembrane Domain 7 Display Distinct Expression Patterns in Mammalian Tissues

Mammalian genomes are well established, and highly conserved regions within odorant receptors that are unique from other G-protein coupled receptors have been identified. Numerous functional studies have focused on specific conserved amino acids motifs; however, not all conserved motifs have been sufficiently characterized. Here, we identified a highly conserved 18 amino acid sequence motif within transmembrane domain seven (CAS-TM7) which was identified by aligning odorant receptor sequences. Next, we investigated the expression pattern and distribution of this conserved amino acid motif among a broad range of odorant receptors. To examine the localization of odorant receptor proteins, we used a sequence-specific peptide antibody against CAS-TM7 which is specific to odorant receptors across species. The specificity of this peptide antibody in recognizing odorant receptors has been confirmed in a heterologous in vitro system and a rat-based in vivo system. The CAS-TM7 odorant receptors localized with distinct patterns at each region of the olfactory epithelium; septum, endoturbinate and ectoturbinate. To our great interests, we found that the CAS-TM7 odorant receptors are primarily localized to the dorsal region of the olfactory bulb, coinciding with olfactory epithelium-based patterns. Also, these odorant receptors were ectopically expressed in the various non-olfactory tissues in an evolutionary constrained manner between human and rats. This study has characterized the expression patterns of odorant receptors containing particular amino acid motif in transmembrane domain 7, and which led to an intriguing possibility that the conserved motif of odorant receptors can play critical roles in other physiological functions as well as olfaction.

Analgesic-Like Activity of Essential Oil Constituents: An Update

The constituents of essential oils are widely found in foods and aromatic plants giving characteristic odor and flavor. However, pharmacological studies evidence its therapeutic potential for the treatment of several diseases and promising use as compounds with analgesic-like action. Considering that pain affects a significant part of the world population and the need for the development of new analgesics, this review reports on the current studies of essential oils’ chemical constituents with analgesic-like activity, including a description of their mechanisms of action and chemical aspects.

Correlation between genotype and phenotype in three families with Peutz-Jeghers Syndrome

Peutz-Jeghers syndrome (PJS) is a hereditary disorder characterized by mucocutaneous pigmentations, gastrointestinal (GI) polyposis and an increased risk of certain malignancies. Little is known about the causative genes of PJS, or their association with the clinical phenotypes of PJS. The present study reports the results of clinical and genetic analysis of three Chinese families with PJS. In addition, the medical histories and clinical manifestations of these families were compared. DNA was collected from the blood samples of patients with PJS and controls. Serine/threonine kinase 11 (STK11), olfactory receptor family 4 subfamily C member 45 (OR4C45) and zonadhesin (ZAN) were amplified by polymerase chain reaction, and analyzed by sequencing and cloning. Two PJS-affected members of one family had a de novo single base deletion (NM_000455.4:c.842delC) in the STK11 gene, and their clinical presentations reflected the quantity of mutant STK11 copies in a dose-dependent manner. No pathogenic variants of OR4C45 or ZAN were found in the patients with PJS, although a new single nucleotide polymorphism (NM_003386.2:c.5768delG) of ZAN was identified. The results of the current study identified that a STK11 mutation dose-dependent genotype-phenotype relationship exists in patients with PJS. In addition, an early onset and high severity of oral pigmentations in PJS was indicative of serious GI phenotypes. These findings may aid the diagnosis and treatment of PJS.

Desacetyl bisacodyl-induced epithelial Cl(-) secretion in rat colon and rectum

The purpose of this study was to clarify the mode of desacetyl bisacodyl (DAB)-induced secretory action in intestinal tissues using an Ussing chamber assay. DAB is the active metabolite of the laxative bisacodyl. In mucosal-submucosal preparations, mucosal application of DAB induced a transient decrease followed by subsequent increases in short-circuit current and tissue conductance in a concentration-dependent manner. DAB-induced responses occurred from the middle colon to the rectal segment but not in the proximal colon. Moreover, these responses were not observed under chloride (Cl(-))-free conditions or in the presence of DAB on the serosal side of the mucosalsubmucosal specimens. Treatment with tetrodotoxin had no effect on the DAB-induced responses; however, mucosal treatment with a COX inhibitor piroxicam resulted in the elimination of responses. These results suggest that DAB may contribute to the laxative action by inducing Cl(-) secretion which is associated with the COX signaling pathway. This study also demonstrated that the DAB target molecule is present on the mucosal side from the middle colon to the rectal segment.

Transient receptor potential ankyrin 1 agonists improve intestinal transit in a murine model of postoperative ileus

BACKGROUND

Stimulation of transient receptor potential ankyrin 1 (TRPA1), which abundantly expressed in enterochromaffin cells (ECC), has been reported to exert apparently contradictory results in in vitro contractility and in vivo gastrointestinal (GI) transit evaluations. The pharmaceutical-grade Japanese traditional medicine daikenchuto (TU-100) has been reported to be beneficial for postoperative ileus (POI) and accelerate GI transit in animals and humans. TU-100 was recently shown to increase intestinal blood flow via stimulation of TRPA1 in the epithelial cells of the small intestine (SI).

METHODS

The effects of various TRPA1 agonists on motility were examined in a manipulation-induced murine POI model, in vitro culture of SI segments and an ECC model cell line, RIN-14B.

KEY RESULTS

Orally administered TRPA1 agonists, aryl isothiocyanate (AITC) and cinnamaldehyde (CA), TU-100 ingredients, [6]-shogaol (6S) and γ-sanshool (GS), improved SI transit in a POI model. The effects of AITC, 6S and GS but not CA were abrogated in TRPA1-deficient mice. SI segments show periodic peristaltic motor activity whose periodicity disappeared in TRPA1-deficient mice. TU-100 augmented the motility. AITC, CA and 6S increased 5-HT release from isolated SI segments and the effects of all these compounds except for CA were lost in TRPA1-deficient mice. 6S and GS induced a release of 5-HT from RIN-14B cells in a dose- and TRPA1-dependent manner.

CONCLUSIONS & INFERENCES

Intraluminal TRPA1 stimulation is a potential therapeutic strategy for GI motility disorders. Further investigation is required to determine whether 5-HT and/or ECC are involved in the effect of TRPA1 on motility.

Effects of ε-viniferin, a dehydrodimer of resveratrol, on transepithelial active ion transport and ion permeability in the rat small and large intestinal mucosa

ε-Viniferin is a dehydrodimer of resveratrol, a polyphenol synthesized in many plants, including grapevine. The present study investigated the effects of ε-viniferin and resveratrol on epithelial secretory and barrier functions in isolated rat small and large intestinal mucosa. Mucosa-submucosa tissue preparations of various segments of the rat large and small intestines were mounted on Ussing chambers, and short-circuit current (Isc) and tissue conductance (Gt) were continuously measured. The mucosal addition of ε-viniferin (>10(-5) mol/L) and resveratrol (>10(-4) mol/L) to the cecal mucosa, which was the most sensitive region, induced an increase in Isc and a rapid phase decrease (P-1) followed by rapid (P-2) and broad (P-3) peak increases in Gt in concentration-dependent manners. Mucosal ε-viniferin (10(-4) mol/L), but not resveratrol (10(-4) mol/L), increased the permeability of FITC-conjugated dextran (4 kDa). The mucosal ε-viniferin-evoked changes in Isc (Cl(-) secretion), but not in Gt, were attenuated by a selective cyclooxygenase (COX)-1 inhibitor and a selective EP4 prostaglandin receptor. The mucosal ε-viniferin-evoked increase in Isc was partially attenuated, and P-2, but not P-1 or P-3, change in Gt was abolished by a transient receptor potential cation channel, subfamily A, member 1 (TRPA1) inhibitor. Moreover, the mucosal ε-viniferin concentration-dependently attenuated the mucosal propionate (1 mmol/L)-evoked increases in Isc and Gt Immunohistochemical studies revealed COX-1-immunoreactive epithelial cells in the cecal crypt. The present study showed that mucosal ε-viniferin modulated transepithelial ion transport and permeability, possibly by activating sensory epithelial cells expressing COX-1 and TRPA1. Moreover, mucosal ε-viniferin decreased mucosal sensitivity to other luminal molecules such as short-chain fatty acids. In conclusion, these results suggest that ε-viniferin modifies intestinal mucosal transport and barrier functions.

Action of thymol on spontaneous excitatory transmission in adult rat spinal substantia gelatinosa neurons

Thymol, which is contained in thyme essential oil, has various actions including antinociception and nerve conduction inhibition. Although thymol activates transient receptor potential (TRP) channels expressed in heterologous cells, it remains to be examined whether this is so in native neurons. It has not yet been examined how thymol affects synaptic transmission. In order to know how thymol modulates excitatory transmission with a focus on TRP activation, we investigated its effect on glutamatergic spontaneous excitatory transmission in lamina II (substantia gelatinosa; SG) neurons with which nerve terminals expressing TRP channels make synaptic contacts. The experiment was performed by using the blind whole-cell patch-clamp technique in adult rat spinal cord slices. Superfusing thymol (1 mM) for 3 min reversibly increased the frequency of spontaneous excitatory postsynaptic current (sEPSC) with a minimal increase in its amplitude in all neurons examined. Seventy-seven% of the neurons produced an outward current at a holding potential of -70 mV. The sEPSC frequency increase and outward current produced by thymol were concentration-dependent with almost the same half-maximal effective concentration (EC50) values of 0.18 and 0.14 mM, respectively. These activities were repeated at a time interval of 30 min, although the sEPSC frequency increase but not outward current recovered with a slow time course. Voltage-gated Na(+)-channel blocker tetrodotoxin did not affect the thymol activities. The sEPSC frequency increase was inhibited by TRPA1 antagonist HC-030031 but not TRPV1 and TRPM8 antagonist (capsazepine and BCTC, respectively), while these antagonists had no effect on the outward current. This was so, albeit the two thymol activities had similar EC50 values. It is concluded that thymol increases the spontaneous release of L-glutamate onto SG neurons by activating TRPA1 channels while producing an outward current without TRP activation. Considering that the SG plays a pivotal role in modulating nociceptive transmission from the periphery, these actions of thymol could contribute to at least a part of its antinociceptive effect.

Involvement of the gut chemosensory system in the regulation of colonic anion secretion

The primary function of the gastrointestinal (GI) tract is the extraction of nutrients from the diet. Therefore, the GI tract must possess an efficient surveillance system that continuously monitors the luminal content for beneficial or harmful compounds. Recent studies have shown that specialized cells in the intestinal lining can sense changes in this content. These changes directly influence fundamental GI processes such as secretion, motility, and local blood flow via hormonal and/or neuronal pathways. Until recently, most studies examining the control of ion transport in the colon have focused on neural and hormonal regulation. However, study of the regulation of gut function by the gut chemosensory system has become increasingly important, as failure of this system causes dysfunctions in host homeostasis, as well as functional GI disorders. Furthermore, regulation of ion transport in the colon is critical for host defense and for electrolytes balance. This review discusses the role of the gut chemosensory system in epithelial transport, with a particular emphasis on the colon.

Effect of free thymol on differential gene expression in gastric mucosa of the young pig

Thymol is the most common molecule in thyme and has been proposed as an oral alternative to antibiotics in the feed of pigs and broilers. The knowledge of the in vivo physiological effects of thymol on tissues is limited, particularly its impact on the gastric mucosa, where it is primarily absorbed when it is orally supplied. In this study, thymol (TH, 50 mg/ kg BW) or a placebo (CO) was introduced directly into the stomach of 8 weaned pigs that were slaughtered 12 h later and sampled for gastric oxyntic and pyloric mucosa. The analysis of whole transcript expression was performed using Affymetrix© Porcine Gene 1.1 ST array strips. Affymetrix Transcripts IDs were associated with 13 406 human gene names based on Sus scrofa Ensemble. Gene Set Enrichment Analysis was performed, comparing TH and CO pigs. For each gene set, the normalized enrichment score (NES) was defined as significant when the false discovery rate % was <25 and the P-value of NES was <0.05. In response to TH, 72 and 19 gene sets were significantly enriched in the oxyntic and pyloric mucosa, respectively. Several gene sets involved in mitosis and its regulation ranked near the top, primarily in the oxyntic mucosa; the gene set DIGESTION ranked first and ninth in the pyloric and oxyntic mucosa, respectively. Within this group, somatostatin (SST), SST receptors, peptide transporter 1 (SLC15A1) and calpain 9 (gastrointestinal tract-specific calpain) were the most strongly upregulated genes. Thymol reduced the enrichment of 120 and 59 gene sets in the oxyntic and pyloric mucosa, respectively. Several gene sets related to ion transport and channeling and aqueous pores across membranes, including short transient receptor potential (TRP) channel 4, potassium voltage-gated channel members 1 and 2, and ryanodine receptors 2 and 3, were less enriched. The downregulation of these genes sensitive to thymol in vitro could depend on the thymol dose and contact with the gastric tissues that causes an adaptive response with their reduced activation. Conversely, the activation of the TRPA1 gene (ranked 1072 and 128 among all the genes in the oxyntic and pyloric mucosa, respectively) indicates the involvement of another TRP-regulating cellular calcium storage. In conclusion, the stimulation of gastric proliferative activity and the control of digestive activity by thymol can influence positively gastric maturation and function in the weaned pigs. These properties should be considered in addition to thymol's antimicrobial properties when supplementation of this molecule in feed is evaluated.

Exome sequencing revealed novel germline mutations in Chinese Peutz-Jeghers syndrome patients

BACKGROUND AND AIMS

Peutz-Jeghers Syndrome (PJS) is an autosomal dominant disorder which predisposes to the development of various cancers. Germline mutation in the serine/threonine kinase 11 gene (STK11) is known as one of the major causes of PJS. However, a notable proportion of PJS samples do not carry any mutation in STK11, suggesting possible genetic heterogeneity in the disease and the existence of other causative variants.

METHODS AND RESULTS

In order to identify other germline variants in the coding regions of the genome that are associated with PJS, we performed exome sequencing in three Chinese individuals with PJS and identified 16 common germline variants (12 protein-coding including STK11, 4 in pre-microRNAs). We further validated protein-coding variants in six PJS individuals (three with wild-type STK11) and predicted the functional impact. As result, we found that 7 coding variants are likely to have functional impacts. Especially, we identified 2 new germline variants which are represented in all six PJS samples and are independent of STK11 mutation.

CONCLUSIONS

Our study provided an exomic view of PJS. The germline variants identified in our analysis may help to resolve the complex genetic background of the disease and thus lead to the discovery of novel causative variants of PJS.

Epithelial transient receptor potential ankyrin 1 (TRPA1)-dependent adrenomedullin upregulates blood flow in rat small intestine

The functional roles of transient receptor potential (TRP) channels in the gastrointestinal tract have garnered considerable attention in recent years. We previously reported that daikenchuto (TU-100), a traditional Japanese herbal medicine, increased intestinal blood flow (IBF) via adrenomedullin (ADM) release from intestinal epithelial (IE) cells (Kono T et al. J Crohns Colitis 4: 161-170, 2010). TU-100 contains multiple TRP activators. In the present study, therefore, we examined the involvement of TRP channels in the ADM-mediated vasodilatatory effect of TU-100. Rats were treated intraduodenally with the TRP vanilloid type 1 (TRPV1) agonist capsaicin (CAP), the TRP ankyrin 1 (TRPA1) agonist allyl-isothiocyanate (AITC), or TU-100, and jejunum IBF was evaluated using laser-Doppler blood flowmetry. All three compounds resulted in vasodilatation, and the vasodilatory effect of TU-100 was abolished by a TRPA1 antagonist but not by a TRPV1 antagonist. Vasodilatation induced by AITC and TU-100 was abrogated by anti-ADM antibody treatment. RT-PCR and flow cytometry revealed that an IEC-6 cell line originated from the small intestine and purified IE cells expressed ADM and TRPA1 but not TRPV1. AITC increased ADM release in IEC cells remarkably, while CAP had no effect. TU-100 and its ingredient 6-shogaol (6SG) increased ADM release dose-dependently, and the effects were abrogated by a TRPA1 antagonist. 6SG showed similar TRPA1-dependent vasodilatation in vivo. These results indicate that TRPA1 in IE cells may play an important role in controlling bowel microcirculation via ADM release. Epithelial TRPA1 appears to be a promising target for the development of novel strategies for the treatment of various gastrointestinal disorders.

Activation of TRPA1 by luminal stimuli induces EP4-mediated anion secretion in human and rat colon

In gastrointestinal (GI) physiology, anion and fluid secretion is an important function for host defense and is induced by changes in the luminal environment. The transient receptor potential A1 (TRPA1) channel is considered to be a chemosensor in several sensory tissues. Although the function of TRPA1 has been studied in GI motility, its contribution to the transepithelial ion transport system has rarely been discussed. In the present study, we investigated the secretory effect of the potential TRPA1 agonist allyl isothiocyanate (AITC) in rat and human colon using an Ussing chamber. The mucosal application of AITC (10(-6)-10(-3) M) induced Cl(-) and HCO(3)(-) secretion in a concentration-dependent manner, whereas the serosal application induced a significantly weaker effect. AITC-evoked anion secretion was attenuated by tissue pretreatment with piroxicam and prostaglandin (PG) E(2); however, this secretion was not affected by TTX, atropine, or extracellular Ca(2+) depletion. These experiments indicate that TRPA1 activation induces anion secretion through PG synthesis, independent of neural pathways in the colon. Further analysis also indicates that AITC-evoked anion secretion is mediated mainly by the EP(4) receptor subtype. The magnitude of the secretory response exhibited segmental heterogeneity in rat colon. Real-time PCR analysis showed the segmental difference was corresponding to the differential expression of EP(4) receptor and cyclooxygenase-1 and -2. In addition, RT-PCR, in situ hybridization, and immunohistochemical studies showed TRPA1 expression in the colonic epithelia. Therefore, we conclude that the activation of TRPA1 in colonic epithelial cells is likely involved in the host defense mechanism through rapid anion secretion.