The inhibitory effects of hydrogen sulfide on pacemaker activity of interstitial cells of cajal from mouse small intestine

Effects of natural products on functional constipation: analysis of active ingredient and mechanism

Constipation is a prevalent clinical ailment of the gastrointestinal system, yet its pathogenesis remains ambiguous. Despite the availability of numerous treatment modalities, they are insufficient in resolving the issue for patients. This work conducted a comprehensive review of the existing literature pertaining to the utilization of natural products for the treatment of constipation, with a focus on the efficacy of natural products in treating constipation, and to provide a comprehensive summary of their underlying mechanisms of action. Upon conducting a thorough review of the extant literature, we found that natural products can effectively treat constipation as modern synthetic drugs and compounded drugs with acetylcholinesterase (AChE) effects, rich in fiber and mucus, and the effects of increasing the tension of the ileum and gastrointestinal tract muscle, mediating signaling pathways, cytokine, excitability of the smooth muscle of the gastrointestinal tract, and regulating the homeostasis of intestinal flora. However, there is a wide variety of natural products, and there are still relatively few studies; the composition of natural products is complex, and the mechanism of action of natural products cannot be clarified. In the future, we need to further improve the detailed mechanism of natural products for the treatment of constipation.

The Role of Small Intestinal Bacterial Overgrowth in Obesity and Its Related Diseases

Obesity has become a major public health problem worldwide and its occurrence is increasing globally. Obesity has also been shown to be involved in the occurrence and development of many diseases and pathological conditions, such as nonalcoholic fatty liver disease (NAFLD), type 2 diabetes mellitus (T2DM), insulin resistance (IR). In recent years, gut microbiota has received extensive attention as an important regulatory part involved in host diseases and health status. A growing body of evidence suggests that gut microbiota dysbiosis has a significant adverse effect on the host. Small intestinal bacterial overgrowth (SIBO), a type of intestinal microbial dysbiosis, has been gradually revealed to be associated with obesity and its related diseases. The presence of SIBO may lead to the destruction of intestinal barrier integrity, increased intestinal permeability, increased endotoxin levels, activation of inflammatory responses, and translocation of bacteria from the colon to the small intestine. However, the causal relationship between SIBO and obesity and the specific mechanisms have not been well elucidated. This review discusses the cross-talk between SIBO and obesity and its related diseases, and expounds its potential mechanisms and interventions, which may help to discover new therapeutic targets for obesity and its related diseases and develop treatment options.

The Role of H2S in the Gastrointestinal Tract and Microbiota

The pathways and mechanisms of the production of H₂S in the gastrointestinal tract are briefly described, including endogenous H₂S produced by the organism and H₂S from microorganisms in the gastrointestinal tract. In addition, the physiological regulatory functions of H₂S on gastrointestinal motility, sensation, secretion and absorption, endocrine system, proliferation and differentiation of stem cells, and the possible mechanisms involved are introduced. In view of the complexity of biosynthesis, physiological roles, and the mechanism of H₂S, this chapter focuses on the interactions and dynamic balance among H₂S, gastrointestinal microorganisms, and the host. Finally, we focus on some clinical gastrointestinal diseases, such as inflammatory bowel disease, colorectal cancer, functional gastrointestinal disease, which might occur or develop when the above balance is broken. Pharmacological regulation of H₂S or the intestinal microorganisms related to H₂S might provide new therapeutic approaches for some gastrointestinal diseases.

Action Mode of Gut Motility, Fluid and Electrolyte Transport in Chronic Constipation

Chronic constipation is a common gastrointestinal disorder, with a worldwide incidence of 14–30%. It negatively affects quality of life and is associated with a considerable economic burden. As a disease with multiple etiologies and risk factors, it is important to understand the pathophysiology of chronic constipation. The purpose of this review is to discuss latest findings on the roles of gut motility, fluid, and electrolyte transport that contribute to chronic constipation, and the main drugs available for treating patients. We conducted searches on PubMed and Google Scholar up to 9 February 2021. MeSH keywords “constipation”, “gastrointestinal motility”, “peristalsis”, “electrolytes”, “fluid”, “aquaporins”, and “medicine” were included. The reference lists of searched articles were reviewed to identify further eligible articles. Studies focusing on opioid-induced constipation, evaluation, and clinic management of constipation were excluded. The occurrence of constipation is inherently connected to disorders of gut motility as well as fluid and electrolyte transport, which involve the nervous system, endocrine signaling, the gastrointestinal microbiota, ion channels, and aquaporins. The mechanisms of action and application of the main drugs are summarized; a better understanding of ion channels and aquaporins may be helpful for new drug development. This review aims to provide a scientific basis that can guide future research on the etiology and treatment of constipation.

The transient receptor potential A1 ion channel (TRPA1) modifies in vivo autonomous ureter peristalsis in rats

AIMS

The current study aimed to explore the expression of transient receptor potential A1 ion channels (TRPA1) in the rat ureter and to assess if TRPA1-active compounds modulate ureter function.

METHODS

The expression of TRPA1 in rat ureter tissue was studied by immunofluorescence. The TRPA1 distribution was compared to calcitonin gene-related peptide (CGRP), α-actin (SMA1), anoctamin-1 (ANO1), and c-kit. For in vivo analyses, a catheter was implanted in the right ureter of 50 rats. Ureter peristalsis and pressures were continuously recorded by a data acquisition set-up during intraluminal infusion of saline (baseline), saline plus protamine sulfate (PS; to disrupt the urothelium), saline plus PS with hydrogen sulfide (NaHS) or cinnamaldehyde (CA). Comparisons were made between rats treated systemically with vehicle or a TRPA1-antagonist (HC030031).

RESULTS

TRPA1-immunoreactive nerves co-expressed CGRP and were mainly located in the suburothelial region of the ureter. Immunoreactivity for TRPA1 was also encountered in c-kit-positive but ANO1-negative cells of the ureter suburothelium and wall. In vivo, HC030031-treated rats had elevated baseline peristaltic frequency (p < 0.05) and higher intraluminal pressures (p < 0.01). PS increased the frequency of ureter peristalsis versus baseline in vehicle-treated rats (p < 0.001) but not in HC030031-treated rats. CA (p < 0.001) and NaHS (p < 0.001) decreased ureter peristalsis. This was counteracted by HC030031 (p < 0.05 and p < 0.01).

CONCLUSIONS

In rats, TRPA1 is expressed on cellular structures considered of importance for peristaltic and mechanoafferent functions of the ureter. Functional data indicate that TRPA1-mediated signals regulate ureter peristalsis. This effect was pronounced after mucosal disruption and suggests a role for TRPA1 in ureter pathologies involving urothelial damage.

The role of hydrogen sulfide in gastrointestinal tract functioning (review)

Despite a fairly large amount of literature data about the involvement of hydrogen sulfide in physiological and pathophysiological processes, its role in gastrointestinal tract functioning has not been studied sufficiently. This review systematizes and generalizes the mechanisms of H2S-associated regulation of gastrointestinal secretion and motility on the basis of literature sources processing and own research results. We analysed world professional literature and sources in Google Scholar, PubMed, MedLine, Embase, Cochrane, and data from more than 50 articles and books on the problem were processed in the article. This review gives a synopsis of the H2S function in the regulation of the secretory and motor-evacuation function, and in stimulating the reparative properties of the digestive tract, and indicates the main mechanisms.

H2S-producing enzymes in anoxia-tolerant vertebrates: Effects of cold acclimation, anoxia exposure and reoxygenation on gene and protein expression

To lend insight into the potential role of the gasotransmitter hydrogen sulfide (H₂S) in facilitating anoxia survival of anoxia-tolerant vertebrates, we quantified the gene expression of the primary H₂S-synthesizing enzymes, 3-mercaptopyruvate sulfurtransferase (3MST), cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), in ventricle and brain of normoxic, anoxic and reoxygenated 21 °C- and 5 °C-acclimated freshwater turtles (Trachemys scripta) and 10 °C-acclimated crucian carp (Carassius carassius). Semi-quantitative Western blotting analysis was also conducted to assess 3MST and CBS protein abundance in ventricle and brain of 5 °C turtles and 10 °C crucian carp subjected to normoxia, anoxia and reoxygenation. We hypothesized that if H₂S was advantageous for anoxia survival, expression levels would remain unchanged or be upregulated with anoxia and/or reoxygenation. Indeed, for both species, gene and protein expression were largely maintained with anoxia exposure (24 h, 21 °C; 5 d, 10 °C; 14 d, 5 °C). With reoxygenation, 3MST expression was increased in turtle and crucian carp brain at the protein and gene level, respectively. Additionally, the effect of cold acclimation on gene expression was assessed in several tissues of the turtle. Expression levels were maintained in most tissues, but decreased in others. The maintenance of gene and protein expression of the H₂S-producing enzymes with anoxia exposure and the up-regulation of 3MST with reoxygenation suggests that H₂S may facilitate anoxic survival of the two champions of vertebrate anoxia survival. The differential effects of cold acclimation on H₂S enzyme expression may influence blood flow to different tissues during winter anoxia.

Quercetin promotes gastrointestinal motility and mucin secretion in loperamide-induced constipation of SD rats through regulation of the mAChRs downstream signal

CONTEXT

Quercetin (QCT) has been known as a potential therapeutic strategy for gastrointestinal diseases because it contributes to the stabilization of mast cells, the prevention of histamine release and modulation of CaCC chloride channel.

OBJECTIVE

We investigated the laxative effect and action mechanism of QCT in Lop-induced constipation model.

MATERIALS AND METHODS

Constipation of SD rats was induced by subcutaneous injection of loperamide (Lop) (4 mg/kg weight) in 0.5% Tween 20 twice a day for three days. After 24 h, the constipation group was further treated with 1× PBS (Lop + Vehicle treated group), 10 mg/kg of QCT (Lop + LQCT treated group), 20 mg/kg of QCT (Lop + MQCT treated group) or 40 mg/kg QCT (Lop + HQCT treated group) at once. At 24 h after QCT treatment, the constipation phenotypes were measured and the transverse colon was collected from SD rats.

RESULTS

The gastrointestinal motility, the number of stools and histological structures were significantly recovered in Lop + QCT treated group compared with the Lop + Vehicle treated group. Also, above activity of epithelial cells and smooth muscle cells were regulated by the mRNA expression of the muscarinic acetylcholine receptors M2 and M3 (mAChR M2 and M3) and some mediators of their downstream signalling pathway. Finally, laxative effects of QCT on mAChR signalling pathway were significantly inhibited by the treatment of mAChR antagonist in primary smooth muscle of rat intestine cells (pRISMCs).

CONCLUSIONS

This study provides the first strong evidence that QCT can be considered an important candidate for improving chronic constipation induced by Lop treatment in animal models.

Augmentation of cGMP/PKG pathway and colonic motility by hydrogen sulfide

Hydrogen sulfide (H2S), like nitric oxide (NO), causes smooth muscle relaxation, but unlike NO, does not stimulate soluble guanylyl cyclase (sGC) activity and generate cyclic guanosine 5'-monophosphate (cGMP). The aim of this study was to investigate the interplay between NO and H2S in colonic smooth muscle. In colonic smooth muscle from rabbit, mouse, and human, l-cysteine, substrate of cystathionine-γ-lyase (CSE), or NaHS, an H2S donor, inhibited phosphodiesterase 5 (PDE5) activity and augmented the increase in cGMP levels, IP3 receptor phosphorylation at Ser1756 (measured as a proxy for PKG activation), and muscle relaxation in response to NO donor S-nitrosoglutathione (GSNO), suggesting augmentation of cGMP/PKG pathway by H2S. The inhibitory effect of l-cysteine, but not NaHS, on PDE5 activity was blocked in cells transfected with CSE siRNA or treated with CSE inhibitor d,l-propargylglycine (dl-PPG), suggesting activation of CSE and generation of H2S in response to l-cysteine. H2S levels were increased in response to l-cysteine, and the effect of l-cysteine was augmented by GSNO in a cGMP-dependent protein kinase-sensitive manner, suggesting augmentation of CSE/H2S by cGMP/PKG pathway. As a result, GSNO-induced relaxation was inhibited by dl-PPG. In flat-sheet preparation of colon, l-cysteine augmented calcitonin gene-related peptide release in response to mucosal stimulation, and in intact segments, l-cysteine increased the velocity of pellet propulsion. These results demonstrate that in colonic smooth muscle, there is a novel interplay between NO and H2S. NO generates H2S via cGMP/PKG pathway, and H2S, in turn, inhibits PDE5 activity and augments NO-induced cGMP levels. In the intact colon, H2S promotes colonic transit.NEW & NOTEWORTHY Hydrogen sulfide (H2S) and nitric oxide (NO) are important regulators of gastrointestinal motility. The studies herein provide the cross talk between NO and H2S signaling to mediate smooth muscle relaxation and colonic transit. H2S inhibits phosphodiesterase 5 activity to augment cGMP levels in response to NO, which, in turn, via cGMP/PKG pathway, generates H2S. These studies suggest that interventions targeted at restoring NO and H2S homeostasis within the smooth muscle may provide novel therapeutic approaches to mitigate motility disorders.

Hydrogen sulphide as a signalling molecule regulating physiopathological processes in gastrointestinal motility

The biology of H₂ S is a still developing area of research and several biological functions have been recently attributed to this gaseous molecule in many physiological systems, including the cardiovascular, urogenital, respiratory, digestive and central nervous system (CNS). H₂ S exerts anti-inflammatory effects and can be considered an endogenous mediator with potential effects on gastrointestinal motility. During the last few years, we have investigated the role of H₂ S as a regulator of gastrointestinal motility using both animal and human tissues. The aim of the present work is to review published data regarding the potential role of H₂ S as a signalling molecule regulating physiopathological processes in gastrointestinal motor function. H₂ S is endogenously produced by defined enzymic pathways in different cell types of the intestinal wall including neurons and smooth muscle. Inhibition of H₂ S biosynthesis increases motility and H₂ S donors cause smooth muscle relaxation and inhibition of propulsive motor patterns. Impaired H₂ S production has been described in animal models with gastrointestinal motor dysfunction. The mechanism(s) of action underlying these effects may include several ion channels, although no specific receptor has been identified. At this time, even though there is much experimental evidence for H₂ S as a modulator of gastrointestinal motility, we still do not have conclusive experimental evidence to definitively propose H₂ S as an inhibitory neurotransmitter in the gastrointestinal tract, causing nerve-mediated relaxation.

Uridine stimulate laxative effect in the loperamide-induced constipation of SD rats through regulation of the mAChRs signaling pathway and mucin secretion

Background

Uridine (Urd), which has been reported as a major component of RNA, plays an important role in various biological process including neuroprotection, biochemical modulation and glycolysis, although its role in constipation has yet to be established. Therefore, in this study, we investigated the laxative effects of Urd on chronic constipation.

Methods

The constipation phenotypes and their related mechanisms were investigated in the transverse colons of SD rats with loperamide (Lop)-induced constipation after treatment with 100 mg/kg of Urd.

Results

The number, weight and water contents of stools were significantly higher in the Lop + Urd treated group than the Lop + Vehicle treated group, while food intake and water consumption of the same group were maintained at a constant level. The thickness of the mucosa layer, muscle and flat luminal surface, as well as the number of goblet cells, paneth cells and lipid droplets were enhanced in the Lop + Urd treated group. Furthermore, the expression of the muscarinic acetylcholine receptors M2 and M3 (mAChR M2 and M3) at the transcriptional and translational level was recovered in the Lop + Urd treated group, while some markers such as Gα and inositol triphosphate (IP3) in their downstream signaling pathway were completely recovered by Urd treatment. Moreover, the ability for mucin secretion and the expression of membrane water channel (aquaporine 8, AQP8) were increased significantly in the Lop + Urd treated group compared with Lop + Vehicle treated group. Finally, the activity of Urd was confirmed in primary smooth muscle of rat intestine cells (pRISMC) based on Gα expression and IP3 concentration.

Conclusions

The results of the present study provide the first strong evidence that Urd can be considered an important candidate for improving chronic constipation induced by Lop treatment in animal models.

Sulfate-reducing bacteria slow intestinal transit in a bismuth-reversible fashion in mice

BACKGROUND

Hydrogen sulfide (H₂ S) serves as a mammalian cell-derived gaseous neurotransmitter. The intestines are exposed to a second source of this gas by sulfate-reducing bacteria (SRB). Bismuth subsalicylate binds H₂ S rendering it insoluble. The aim of this study was to test the hypothesis that SRB may slow intestinal transit in a bismuth-reversible fashion.

METHODS

Eighty mice were randomized to five groups consisting of Live SRB, Killed SRB, SRB+Bismuth, Bismuth, and Saline. Desulfovibrio vulgaris, a common strain of SRB, was administered by gavage at the dose of 1.0 × 10⁹ cells along with rhodamine, a fluorescent dye. Intestinal transit was measured 50 minutes after gavage by euthanizing the animals, removing the small intestine between the pyloric sphincter and the ileocecal valve and visualizing the distribution of rhodamine across the intestine using an imaging system (IVIS, Perkin-Elmer). Intestinal transit (n=50) was compared using geometric center (1=minimal movement, 100=maximal movement). H₂ S concentration (n=30) was also measured when small intestinal luminal content was allowed to generate this gas.

KEY RESULTS

The Live SRB group had slower intestinal transit as represented by a geometric center score of 40.2 ± 5.7 when compared to Saline: 73.6 ± 5.7, Killed SRB: 77.9 ± 6.9, SRB+Bismuth: 81.0 ± 2.0, and Bismuth: 73.3 ± 4.2 (P<.0001). Correspondingly, the Live SRB group had the highest luminal H₂ S concentration of 4181.0 ± 968.0 ppb compared to 0 ± 0 ppb for the SRB+Bismuth group (P<.0001).

CONCLUSIONS & INFERENCES

Live SRB slow intestinal transit in a bismuth-reversible fashion in mice. Our results demonstrate that intestinal transit is slowed by SRB and this effect could be abolished by H₂ S-binding bismuth.

Effects of five candidate laxatives derived from Liriope platyphylla on the 5-HT receptor signaling pathway in three cell types present in the transverse colon

The laxative effects of aqueous extract of Liriope platyphylla (AEtLP) on loperamide (Lop)‑induced constipation have been reported; however, the key compounds and the mechanism underlying these effects remain unclear. Therefore, the laxative effects of five candidates derived from L. platyphylla: Diosgenin (DG), 5-hydroxymethylfurfural (5-HMF), adenosine (AD), hydroxypropyl cellulose (HPC) and uridine (UD) were investigated by examining the alteration of G protein α (Gα) expression, protein kinase C (PKC) phosphorylation and inositol triphosphate (IP3) concentration levels in the 5-hydroxytryptamine (5‑HT; serotonin) receptor signaling pathway. Primary rat intestine smooth muscle cells (pRISMCs), intestinal epithelial cells (IEC)‑18 and B35 cells were cotreated with Lop and the five compounds in order to screen the candidates. AEtLP, prucalopride (PCP) and bisacodyl (BS) served as positive controls. In pRISMCs, Gα expression levels were recovered in the majority of candidate‑treated groups, whereas PKC phosphorylation recovery was observed only in the DG, 5‑HMF and AD treatment groups. In IEC‑18 cells, the AD treatment group mimicked the effects of PCP on PKC phosphorylation levels, whereas the DG, 5‑HMF, HPC and UD treatment groups mimicked the effects of AEtLP and BS. In B35 cells, a greater upregulation of PKC phosphorylation levels were observed in the UD treatment group compared with the PCP and BS treatment groups, whereas DG, 5‑HMF and AD treatment reduced the PKC phosphorylation levels to a greater extent than AEtLP treatment. However, effects similar to AEtLP, PCP and BS on Gα expression levels were not detected in any treatment groups in IEC‑18 and B35 cells. Furthermore, the level of IP3 was enhanced only in pRISMCs, in which all five candidates were effective, while the greatest concentration was observed in the UD treatment group. In conclusion, the results of the present study suggest that UD may be considered the compound with the greatest laxative activity, which may regulate the 5‑HT receptor signaling pathway.

H2S, a novel gasotransmitter, involves in gastric accommodation

H₂S is produced mainly by two enzymes:cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE), using L-cysteine (L-Cys) as the substrate. In this study, we investigated the role of H₂S in gastric accommodation using CBS^+/− mice, immunohistochemistry, immunoblot, methylene blue assay, intragastric pressure (IGP) recording and electrical field stimulation (EFS). Mouse gastric fundus expressed H₂S-generating enzymes (CBS and CSE) and generated detectable amounts of H₂S. The H₂S donor, NaHS or L-Cys, caused a relaxation in either gastric fundus or body. The gastric compliance was significantly increased in the presence of L-Cys (1 mM). On the contrary, AOAA, an inhibitor for CBS, largely inhibited gastric compliance. Consistently, CBS^+/− mice shows a lower gastric compliance. However, PAG, a CSE inhibitor, had no effect on gastric compliances. L-Cys enhances the non-adrenergic, non-cholinergic (NANC) relaxation of fundus strips, but AOAA reduces the magnitude of relaxations to EFS. Notably, the expression level of CBS but not CSE protein was elevated after feeding. Consistently, the production of H₂S was also increased after feeding in mice gastric fundus. In addition, AOAA largely reduced food intake and body weight in mice. Furthermore, a metabolic aberration of H₂S was found in patients with functional dyspepsia (FD). In conclusion, endogenous H₂S, a novel gasotransmitter, involves in gastric accommodation.

Effects of hydrogen sulphide on motility patterns in the rat colon

BACKGROUND AND PURPOSE

Hydrogen sulphide (H2 S) is an endogenous gaseous signalling molecule with putative functions in gastrointestinal motility regulation. Characterization of H2 S effects on colonic motility is crucial to establish its potential use as therapeutic agent in the treatment of colonic disorders.

EXPERIMENTAL APPROACH

H2 S effects on colonic motility were characterized using video recordings and construction of spatio-temporal maps. Microelectrode and muscle bath studies were performed to investigate the mechanisms underlying H2 S effects. NaHS was used as the source of H2 S.

KEY RESULTS

Rhythmic propulsive motor complexes (RPMCs) and ripples were observed in colonic spatio-temporal maps. Serosal addition of NaHS concentration-dependently inhibited RPMCs. In contrast, NaHS increased amplitude of the ripples without changing their frequency. Therefore, ripples became the predominant motor pattern. Neuronal blockade with lidocaine inhibited RPMCs, which were restored after administration of carbachol. Subsequent addition of NaHS inhibited RPMCs. Luminal addition of NaHS did not modify motility patterns. NaHS inhibited cholinergic excitatory junction potentials, carbachol-induced contractions and hyperpolarized smooth muscle cells, but did not modify slow wave activity.

CONCLUSIONS AND IMPLICATIONS

H2 S modulated colonic motility inhibiting propulsive contractile activity and enhancing the amplitude of ripples, promoting mixing. Muscle hyperpolarization and inhibition of neurally mediated cholinergic responses contributed to the inhibitory effect on propulsive activity. H2 S effects were not related to changes in the frequency of slow wave activity originating in the network of interstitial cells of Cajal located near the submuscular plexus. Luminal H2 S did not modify colonic motility probably because of epithelial detoxification.

Carbon monoxide, hydrogen sulfide, and nitric oxide as signaling molecules in the gastrointestinal tract

Carbon monoxide (CO) and hydrogen sulfide (H2S) used to be thought of simply as lethal and (for H2S) smelly gaseous molecules; now they are known to have important signaling functions in the gastrointestinal tract. CO and H2S, which are produced in the gastrointestinal tract by different enzymes, regulate smooth muscle membrane potential and tone, transmit signals from enteric nerves, and can regulate the immune system. The pathways that produce nitric oxide, H2S, and CO interact; each can inhibit and potentiate the level and activity of the other. However, there are significant differences between these molecules, such as in half-lives; CO is more stable and therefore able to have effects distal to the site of production, whereas nitric oxide and H2S are short lived and act only close to sites of production. We review their signaling functions in the luminal gastrointestinal tract and discuss how their pathways interact. We also describe other physiological functions of CO and H2S and how they might be used as therapeutic agents.

Hydrogen sulfide signaling in the gastrointestinal tract

SIGNIFICANCE

The current literature regarding the effects of the gaseous signal molecule hydrogen sulfide (H2S) in the gastrointestinal system is reviewed. Bacterial, host and pharmaceutical-derived H2S are all considered and presented according to the physiological or pathophysiological effects of the gaseous signal molecule. These subjects include the toxicology of intestinal H2S with emphasis on bacterial-derived H2S, especially from sulfate-reducing bacteria, the role of endogenous and exogenous H2S in intestinal inflammation, and the roles of H2S in gastrointestinal motility, secretion and nociception.

RECENT ADVANCES

While its pro- and anti-inflammatory, smooth muscle relaxant, prosecretory, and pro- and antinociceptive actions continue to remain the major effects of H2S in this system; recent findings have expanded the potential molecular targets for H2S in the gastrointestinal tract.

CRITICAL ISSUES

Numerous discrepancies remain in the literature, and definitive molecular targets in this system have not been supported by the use of competitive antagonism.

FUTURE DIRECTIONS

Future work will hopefully resolve discrepancies in the literature and identify molecular targets and mechanisms of action for H2S. It is clear from the current literature that the long-appreciated relationship between H2S and the gastrointestinal tract continues to be strong as we endeavor to unravel its mysteries.

Hydrogen sulfide (H₂S) and hypoxia inhibit salmonid gastrointestinal motility: evidence for H₂S as an oxygen sensor

Hydrogen sulfide (H(2)S) has been shown to affect gastrointestinal (GI) motility and signaling in mammals and O(2)-dependent H(2)S metabolism has been proposed to serve as an O(2) 'sensor' that couples hypoxic stimuli to effector responses in a variety of other O(2)-sensing tissues. The low P(O2) values and high H(2)S concentrations routinely encountered in the GI tract suggest that H(2)S might also be involved in hypoxic responses in these tissues. In the present study we examined the effect of H(2)S on stomach, esophagus, gallbladder and intestinal motility in the rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) and we evaluated the potential for H(2)S in oxygen sensing by examining GI responses to hypoxia in the presence of known inhibitors of H(2)S biosynthesis and by adding the sulfide donor cysteine (Cys). We also measured H(2)S production by intestinal tissue in real time and in the presence and absence of oxygen. In tissues exhibiting spontaneous contractions, H(2)S inhibited contraction magnitude (area under the curve and amplitude) and frequency, and in all tissues it reduced baseline tension in a concentration-dependent relationship. Longitudinal intestinal smooth muscle was significantly more sensitive to H(2)S than other tissues, exhibiting significant inhibitory responses at 1-10 μmol l(-1) H(2)S. The effects of hypoxia were essentially identical to those of H(2)S in longitudinal and circular intestinal smooth muscle; of special note was a unique transient stimulatory effect upon application of both hypoxia and H(2)S. Inhibitors of enzymes implicated in H(2)S biosynthesis (cystathionine β-synthase and cystathionine γ-lyase) partially inhibited the effects of hypoxia whereas the hypoxic effects were augmented by the sulfide donor Cys. Furthermore, tissue production of H(2)S was inversely related to O(2); addition of Cys to intestinal tissue homogenate stimulated H(2)S production when the tissue was gassed with 100% nitrogen (~0% O(2)), whereas addition of oxygen (~10% O(2)) reversed this to net H(2)S consumption. This study shows that the inhibitory effects of H(2)S on the GI tract of a non-mammalian vertebrate are identical to those reported in mammals and they provide further evidence that H(2)S is a key mediator of the hypoxic response in a variety of O(2)-sensitive tissues.

Evidence that endogenous hydrogen sulfide exerts an excitatory effect on gastric motility in mice

The present study was designed to investigate the effect of endogenous hydrogen sulfide (H₂S) on gastric motility in mice. Western blotting and immunocytochemistry were used to determine expression levels of the H₂S-producing enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) in gastric tissues and cultured smooth muscle cells. Physiological and intracellular recordings and the whole-cell patch clamp technique were used to evaluate the effect of H₂S on the mechanical and electrical activities in muscle strips and in isolated smooth muscle cells, respectively. The results showed that CBS and CSE were expressed in mouse gastric smooth muscle. NaHS, a H₂S donor, inhibited the amplitude and frequency of spontaneous contraction at high concentrations (>200 μM). However, NaHS at low concentrations (<100 μM) enhanced the basal tension and increased the contractile amplitude of muscle strips. This excitatory effect was not altered by the blockade of the enteric nerve with TTX, but was abolished by tetraethylammonium (TEA) or 4-aminopyridine (4-AP). Aminooxyacetic acid (AOA), but not propargylglycine (PAG), caused a concentration-dependent inhibition of spontaneous contraction. This effect was restored by L-cysteine and NaHS. In addition, NaHS at low concentrations (<100 μM) produced a depolarization of the membrane potential, whereas AOA hyperpolarized the membrane potential and decreased the amplitude of slow waves. Furthermore, AOA increased whole-cell delayed rectifier K⁺ current (I(K(V))). These findings suggest that endogenous H₂S appears to be an excitatory gaseous mediator during physiological regulation of gastric motility and this excitable effect is mediated by depolarization of the membrane potential via inhibition of I(K(V)).

Interplay of hydrogen sulfide and nitric oxide on the pacemaker activity of interstitial cells of cajal from mouse small intestine

We studied whether nitric oxide (NO) and hydrogen sulfide (H(2)S) have an interaction on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of NO and H(2)S on pacemaker activities were investigated by using the whole-cell patch-clamp technique and intracellular Ca(2+) analysis at 30℃ in cultured mouse ICC. Exogenously applied (±)-S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, or sodium hydrogen sulfide (NaHS), a donor of H(2)S, showed no influence on pacemaker activity (potentials and currents) in ICC at low concentrations (10 µM SNAP and 100 µM NaHS), but SNAP or NaHS completely inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction at high concentrations (SNAP 100 µM and NaHS 1 mM). Co-treatment with 10 µM SNAP plus 100 µM NaHS also inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction. ODQ, a guanylate cyclase inhibitor, or glibenclamide, an ATP-sensitive K(+) channel inhibitor, blocked the SNAP+NaHS-induced inhibition of pacemaker currents in ICC. Also, we found that SNAP+NaHS inhibited the spontaneous intracellular Ca(2+) ([Ca(2+)](i)) oscillations in cultured ICC. In conclusion, this study describes the enhanced inhibitory effects of NO plus H(2)S on ICC in the mouse small intestine. NO+H(2)S inhibited the pacemaker activity of ICC by modulating intracellular Ca(2+). These results may be evidence of a physiological interaction of NO and H(2)S in ICC for modulating gastrointestinal motility.

Hydrogen sulfide is a partially redox-independent activator of the human jejunum Na+ channel, Nav1.5

Hydrogen sulfide (H(2)S) is produced endogenously by L-cysteine metabolism. H(2)S modulates several ion channels with an unclear mechanism of action. A possible mechanism is through reduction-oxidation reactions attributable to the redox potential of the sulfur moiety. The aims of this study were to determine the effects of the H(2)S donor NaHS on Na(V)1.5, a voltage-dependent sodium channel expressed in the gastrointestinal tract in human jejunum smooth muscle cells and interstitial cells of Cajal, and to elucidate whether H(2)S acts on Na(V)1.5 by redox reactions. Whole cell Na(+) currents were recorded in freshly dissociated human jejunum circular myocytes and Na(V)1.5-transfected human embryonic kidney-293 cells. RT-PCR amplified mRNA for H(2)S enzymes cystathionine β-synthase and cystathionine γ-lyase from the human jejunum. NaHS increased native Na(+) peak currents and shifted the half-point (V(1/2)) of steady-state activation and inactivation by +21 ± 2 mV and +15 ± 3 mV, respectively. Similar effects were seen on the heterologously expressed Na(V)1.5 α subunit with EC(50)s in the 10(-4) to 10(-3) M range. The reducing agent dithiothreitol (DTT) mimicked in part the effects of NaHS by increasing peak current and positively shifting steady-state activation. DTT together with NaHS had an additive effect on steady-state activation but not on peak current, suggesting that the latter may be altered via reduction. Pretreatment with the Hg(2+)-conjugated oxidizer thimerosal or the alkylating agent N-ethylmaleimide inhibited or decreased NaHS induction of Na(V)1.5 peak current. These studies show that H(2)S activates the gastrointestinal Na(+) channel, and the mechanism of action of H(2)S is partially redox independent.

The therapeutic potential of hydrogen sulfide: separating hype from hope

Hydrogen sulfide (H(2)S) has become the hot new signaling molecule that seemingly affects all organ systems and biological processes in which it has been investigated. It has also been shown to have both proinflammatory and anti-inflammatory actions and proapoptotic and anti-apoptotic effects and has even been reported to induce a hypometabolic state (suspended animation) in a few vertebrates. The exuberance over potential clinical applications of natural and synthetic H(2)S-"donating" compounds is understandable and a number of these function-targeted drugs have been developed and show clinical promise. However, the concentration of H(2)S in tissues and blood, as well as the intrinsic factors that affect these levels, has not been resolved, and it is imperative to address these points to distinguish between the physiological, pharmacological, and toxicological effects of this molecule. This review will provide an overview of H(2)S metabolism, a summary of many of its reported "physiological" actions, and it will discuss the recent development of a number of H(2)S-donating drugs that show clinical potential. It will also examine some of the misconceptions of H(2)S chemistry that have appeared in the literature and attempt to realign the definition of "physiological" H(2)S concentrations upon which much of this exuberance has been established.

Hydrogen sulfide as a signaling molecule in the enteric nervous system

Hydrogen sulfide (H₂S) is produced by sulfate-reducing bacteria present in the colon. Recently, it has been demonstrated that mammals have enzymatic pathways to produce H₂S. As H₂S was added to the list of gaseous signaling molecules, the number of papers related to H₂S biology has increased exponentially. However, the physiological role of H₂S in the gastrointestinal tract is still unknown. Endogenous production in different cell types indicates that H₂S might participate in various functions such as pain, motility and secretion. Nevertheless, experimental protocols to demonstrate a physiological role for H₂S are not easy to perform due to the lack of specific antagonists. Genetically modified animals lacking a specific route of H₂S synthesis are useful biological tools although whether they alter gastrointestinal function are still unknown. In this issue of Neurogastroenterology and Motility, Krueger et al. examine the role of H₂S in secretion and in afferent neuronal activation using sodium hydrosulfide as a source of H2S. Interestingly, sodium hydrosulfide causes secretion and increased spike activity in afferent neurons. The mechanism partly involves transient receptor potential vanilloid type I located on afferent neurons, causing local release of substance P, which in turn activates cholinergic secretomotor neurons. These novel observations extend our understanding of the function of H₂S in the gastrointestinal tract.