Potential role of the gaseous mediator hydrogen sulphide (H2S) in inhibition of human colonic contractility

Effects of hydrogen sulfide on relaxation responses in the lower esophageal sphincter in rabbits: the potential role of potassium channels

Hydrogen sulfide (H2S) is a significant physiologic inhibitory neurotransmitter. The main goal of this research was to examine the contribution of diverse potassium (K+) channels and nitric oxide (NO) in mediating the H2S effect on electrical field stimulation (EFS)-induced neurogenic contractile responses in the lower esophageal sphincter (LES). EFS-induced contractile responses of rabbit isolated LES strips were recorded using force transducers in organ baths that contain Krebs-Henseleit solutions (20 ml). Cumulative doses of NaHS, L-cysteine, PAG, and AOAA were evaluated in NO-dependent and NO-independent groups. The experiments were conducted again in the presence of K+ channel blockers. In both NO-dependent and NO-independent groups, NaHS, L-cysteine, PAG, and AOAA significantly reduced EFS-induced contractile responses. In the NO-dependent group, the effect of NaHS and L-cysteine decreased in the presence of 4-AP, and also the effect of NaHS decreased in the NO-dependent and independent group in the presence of TEA. In the NO-independent group, K+ channel blockers didn't change L-cysteine-induced relaxations. K+ channel blockers had no impact on the effects of PAG and AOAA. In addition, NaHS significantly relaxed 80-mM KCl-induced contractions, whereas L-cysteine, PAG, and AOAA did not. In the present study, H2S decreased the amplitudes of EFS-induced contraction responses. These results suggest that Kv channels and NO significantly contribute to exogenous H2S and endogenous H2S precursor L-cysteine inhibitory effect on lower esophageal sphincter smooth muscle.

Relationship among Parkinson's disease, constipation, microbes, and microbiological therapy

This comprehensive review elucidates the complex interplay between gut microbiota and constipation in Parkinson's disease (PD), a prevalent non-motor symptom contributing significantly to patients' morbidity. A marked alteration in the gut microbiota, predominantly an increase in the abundance of Proteobacteria and Bacteroidetes, is observed in PD-related constipation. Conventional treatments, although safe, have failed to effectively alleviate symptoms, thereby necessitating the development of novel therapeutic strategies. Microbiological interventions such as prebiotics, probiotics, and fecal microbiota transplantation (FMT) hold therapeutic potential. While prebiotics improve bowel movements, probiotics are effective in enhancing stool consistency and alleviating abdominal discomfort. FMT shows potential for significantly alleviating constipation symptoms by restoring gut microbiota balance in patients with PD. Despite promising developments, the causal relationship between changes in gut microbiota and PD-related constipation remains elusive, highlighting the need for further research in this expanding field.

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.

Dysregulated cystathionine-β-synthase/hydrogen sulfide signaling promotes chronic stress-induced colonic hypermotility in rats

BACKGROUND

Hydrogen sulfide (H₂ S), an important endogenous gasotransmitter, is involved in the modulation of gastrointestinal motility, but whether it mediates the intestinal dysmotility in irritable bowel syndrome (IBS) is not known. This study explored the significance of cystathionine-β-synthase (CBS)/H₂ S signaling in stress-induced colonic dysmotility.

METHODS

A rat model of IBS was established using chronic water avoidance stress (WAS). Colonic pathological alterations were detected histologically. Intestinal motility was determined by intestinal transit time (ITT) and fecal water content (FWC). Visceral sensitivity was assessed using the visceromotor response (VMR) to colorectal distension (CRD). Real-time PCR, Western blotting, and immunostaining were performed to identify the expression of CBS in the colon. The contractions of distal colon were studied in an organ bath system and H₂ S content was measured by ELISA. The effects of SAM, a selective CBS activator, on colonic dysmotility were examined. MEK1 was tested as a potential upstream effector of CBS/H₂ S loss.

KEY RESULTS

After 10 days of WAS, the ITT was decreased and FWC was increased, and the VMR magnitude in response to CRD was enhanced. The colonic CBS expression and H₂ S levels were significantly declined in WAS-exposed rats, and the density of CBS-positive enteric neurons in the myenteric plexus in WAS-treated rats was lower than that in controls. SAM treatment relieved WAS-induced colonic hypermotility via increased H₂ S production. AZD6244, a selective inhibitor of MEK1, partially reversed CBS downregulation and colonic hypermotility in WAS-treated rats.

CONCLUSIONS & INFERENCES

Decreased CBS/H₂ S signaling through increased MEK1 signaling might be important in the pathogenesis of chronic stress-induced colonic hypermotility. SAM could be administered for disorders associated with intestinal hypermotility.

Role of Hydrogen Sulfide in the Development of Colonic Hypomotility in a Diabetic Mouse Model Induced by Streptozocin

Hydrogen sulfide (H₂S), a novel gasotransmitter, is involved in the regulation of gut motility. Alterations in the balance of H₂S play an important role in the pathogenesis of diabetes. This study was conducted to investigate the role of H₂S in the colonic hypomotility of mice with streptozotocin (STZ)-induced diabetes. A single intraperitoneal injection of STZ was used to induce the type 1 diabetes model. Male C57BL/6 mice were randomized into a control group and an STZ-treated group. Immunohistochemistry, Western blotting, H₂S generation, organ bath studies and whole-cell patch clamp techniques were carried out in single smooth muscle cells (SMCs) of the colon. We found that STZ-induced diabetic mice showed decreased stool output, impaired colonic contractility, and increased endogenous generation of H₂S (p < 0.05). H₂S-producing enzymes were upregulated in the colon tissues of diabetic mice (p < 0.05). The exogenous H₂S donor sodium hydrosulfide (NaHS) elicited a biphasic action on colonic muscle contraction with excitation at lower concentrations and inhibition at higher concentrations. NaHS (0.1 mM) increased the currents of voltage-dependent calcium channels (VDCCs), while NaHS at 0.5 mM and 1.5 mM induced inhibition. Furthermore, NaHS reduced the currents of both voltage-dependent potassium (K_V) channels and large conductance calcium-activated potassium (BK) channels in a dose-dependent manner. These results show that spontaneous contraction of colonic muscle strips from diabetic mice induced by STZ was significantly decreased, which may underlie the constipation associated with diabetes mellitus (DM). H₂S overproduction with subsequent suppression of muscle contraction via VDCCs on SMCs may contribute in part to the pathogenesis of colonic hypomotility in DM. SIGNIFICANCE STATEMENT: Hydrogen sulfide may exhibit a biphasic effect on colonic motility in mice by regulating the activities of voltage-dependent calcium channels and voltage-dependent and large conductance calcium activated potassium channels. H₂S overproduction with subsequent suppression of muscle contraction via VDCCs may contribute to the pathogenesis of colonic hypomotility in diabetes mellitus.

Cystathionine γ-lyase mediates cell proliferation, migration, and invasion of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an epithelia-derived malignancy with a distinctive geographic distribution. Cystathionine γ-lyase (CSE) is involved in cancer development and progression. Nevertheless, the role of CSE in the growth of NPC is unknown. In this study, we found that CSE levels in human NPC cells were higher than those in normal nasopharyngeal cells. CSE overexpression enhanced the proliferative, migrative, and invasive abilities of NPC cells and CSE downregulation exerted reverse effects. Overexpression of CSE decreased the expressions of cytochrome C, cleaved caspase (cas)-3, cleaved cas-9, and cleaved poly-ADP-ribose polymerase, whereas CSE knockdown exhibited reverse effects. CSE overexpression decreased reactive oxygen species (ROS) levels and the expressions of phospho (p)-extracellular signal-regulated protein kinase 1/2, p-c-Jun N-terminal kinase, and p-p38, but promoted the expressions of p-phosphatidylinositol 3-kinase (PI3K), p-AKT, and p-mammalian target of rapamycin (mTOR), whereas CSE knockdown showed oppose effects. In addition, CSE overexpression promoted NPC xenograft tumor growth and CSE knockdown decreased tumor growth by modulating proliferation, angiogenesis, cell cycle, and apoptosis. Furthermore, DL-propargylglycine (an inhibitor of CSE) dose-dependently inhibited NPC cell growth via ROS-mediated mitogen-activated protein kinase (MAPK) and PI3K/AKT/mTOR pathways without significant toxicity. In conclusion, CSE could regulate the growth of NPC cells through ROS-mediated MAPK and PI3K/AKT/mTOR cascades. CSE might be a novel tumor marker for the diagnosis and prognosis of NPC. Novel donors/drugs that inhibit the expression/activity of CSE can be developed in the treatment of NPC.

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.

Endogenous H2S-Activable Liposomal Nanoplatform for Synergistic Colorectal Tumor Ablation at Mild Apparent Temperature

Photoinduced hyperthermia possesses great potential in photothermal therapy and thermal-responsive chemotherapy of tumors. However, traditional thermal-triggered drug release requires high temperature, which results in unpleasant activation of thermal-induced cellular self-protection. In this work, a Cu-complex modified and drug-loaded liposomal nanoplatform was constructed for endogenous H₂S-activated synergistic ablation of colorectal tumors. In response to H₂S, the incorporated Cu-complex contributed to the formation of semiconductor CuS on the surface of the as-designed liposomal nanoplatform, which led to local heating under near-infrared (NIR) laser irradiation to achieve simultaneous photothermal therapy and drug release. It is noteworthy that although the drug release occurred at a mild apparent temperature, it was actually triggered by the high eigen temperature on the surface of the liposomal nanoplatform. Therefore, efficient and synergistic photothermal and chemotherapy was achieved under mild apparent temperatures. This work provides insights into achieving selective and bioactivated photothermal therapy and therefore thermal-controlled drug release without using excessive hyperthermia.

The role of gasotransmitters in neonatal physiology

The gasotransmitters, nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO), are endogenously-produced volatile molecules that perform signaling functions throughout the body. In biological tissues, these small, lipid-permeable molecules exist in free gaseous form for only seconds or less, and thus they are ideal for paracrine signaling that can be controlled rapidly by changes in their rates of production or consumption. In addition, tissue concentrations of the gasotransmitters are influenced by fluctuations in the level of O₂ and reactive oxygen species (ROS). The normal transition from fetus to newborn involves a several-fold increase in tissue O₂ tensions and ROS, and requires rapid morphological and functional adaptations to the extrauterine environment. This review summarizes the role of gasotransmitters as it pertains to newborn physiology. Particular focus is given to the vasculature, ventilatory, and gastrointestinal systems, each of which uniquely illustrate the function of gasotransmitters in the birth transition and newborn periods. Moreover, given the relative lack of studies on the role that gasotransmitters play in the newborn, particularly that of H₂S and CO, important gaps in knowledge are highlighted throughout the review.

TLR2 and TLR4 interact with sulfide system in the modulation of mouse colonic motility

BACKGROUND

H₂ S is a neuromodulator that may inhibit intestinal motility. H₂ S production in colon is yielded by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) enzymes and sulfate-reducing bacteria (SRB). Toll-like receptors (TLRs) recognize intestinal microbiota. The aim of this work was to evaluate the influence of TLR2 and TLR4 on the endogenous and SRB-mediated synthesis of H₂ S and its consequences on the colonic motility of mouse.

METHODS

Muscle contractility studies were performed in colon from WT, Tlr2^-/- , and Tlr4^-/- mice. The mRNA levels of TLR2, TLR4, CBS, CSE, and SRB were measured by real-time PCR. Free sulfide levels in colon and feces were determined by colorimetric assays.

RESULTS

NaHS and GYY4137, donors of H₂ S, reduced the contractility of colon. Aminooxyacetic acid (AOAA), inhibitor of CBS, and D-L propargylglycine (PAG), inhibitor of CSE, increased the contractility of colon. In vivo treatment with NaHS or GYY4137 inhibited the spontaneous contractions and upregulated TLR2 expression. The in vivo activation of TLR4 with lipopolysaccharide increased the contractile response to PAG, mRNA levels of CSE, and the free sulfide levels of H₂ S in colon. In Tlr2^-/- and Tlr4^-/-  mice, the contractions induced by AOAA and PAG and mRNA levels of CBS and CSE were lower with respect to WT mice. Deficiency of TLR2 or TLR4 provokes alterations in free sulfide levels and SRB of colon.

CONCLUSIONS AND INFERENCES

Our study demonstrates interaction between TLR2 and TLR4 and the sulfide system in the regulation of colonic motility and contributes to the pathophysiology knowledge of intestinal motility disorders.

Spasmolytic activity of Aquilariae Lignum Resinatum extract on gastrointestinal motility involves muscarinic receptors, calcium channels and NO release

CONTEXT

Aquilariae Lignum Resinatum (ALR), the dry rhizome of Aquilaria agallocha R. (Thymelaeaeeae), has been widely used to treat emesis, stomachache and gastrointestinal dysfunction.

OBJECTIVE

This study evaluates the effects of ALR methanol extract on gastrointestinal motility (GIM) and possible mechanisms of the action involved.

MATERIALS AND METHODS

In vivo, the study evaluated the effects of ALR (200-800 mg/kg) on gastric emptying and small intestinal motility in normal and neostigmine-induced adult KM mice. The in vitro effects of ALR (0.2-1.6 mg/mL) on GIM were performed on isolated jejunum of Wistar rats, pretreated with acetylcholine (ACh), KCl, CaCl₂, and pre-incubation with l-NAME (a selective inhibitor of the nitric oxide synthase).

RESULTS

In vivo, ALR (800 mg/kg) decreased gastric emptying (70.82 ± 9.81%, p < 0.01, compared with neostigmine group 91.40 ± 7.81%), small intestinal transit (42.82 ± 3.82%, p < 0.01, compared with neostigmine group 85.53 ± 5.57%). In vitro, ALR concentration dependently decreased the contractions induced by ACh (10^-5 M) and KCl (60 mM) with respective EC₅₀ values of 0.35 and 0.32 mg/mL. The Ca²⁺ concentration-response curves were shifted by ALR to the right, similar to that caused by verapamil (the positive). The spasmolytic activity of ALR was inhibited by pre-incubation with l-NAME.

DISCUSSION AND CONCLUSIONS

ALR played a spasmolytic role in GIM, which is probably mediated through inhibition of muscarinic receptors, blockade of Ca²⁺ influx and NO release. This is the first study presenting a comprehensive description of the effects of ALR on GIM.

Inhibition of RhoA/Rho kinase pathway and smooth muscle contraction by hydrogen sulfide

Hydrogen sulfide (H₂ S) plays an important role in smooth muscle relaxation. Here, we investigated the expression of enzymes in H₂ S synthesis and the mechanism regulating colonic smooth muscle function by H₂ S. Expression of cystathionine-γ-lyase (CSE), but not cystathionine-β-synthase (CBS), was identified in the colonic smooth muscle of rabbit, mouse, and human. Carbachol (CCh)-induced contraction in rabbit muscle strips and isolated muscle cells was inhibited by l-cysteine (substrate of CSE) and NaHS (an exogenous H₂ S donor) in a concentration-dependent fashion. H₂ S induced S-sulfhydration of RhoA that was associated with inhibition of RhoA activity. CCh-induced Rho kinase activity also was inhibited by l-cysteine and NaHS in a concentration-dependent fashion. Inhibition of CCh-induced contraction by l-cysteine was blocked by the CSE inhibitor, dl-propargylglycine (DL-PPG) in dispersed muscle cells. Inhibition of CCh-induced Rho kinase activity by l-cysteine was blocked by CSE siRNA in cultured cells and DL-PPG in dispersed muscle cells. Stimulation of Rho kinase activity and muscle contraction in response to CCh was also inhibited by l-cysteine or NaHS in colonic muscle cells from mouse and human. Collectively, our studies identified the expression of CSE in colonic smooth muscle and determined that sulfhydration of RhoA by H₂ S leads to inhibition of RhoA and Rho kinase activities and muscle contraction. The mechanism identified may provide novel therapeutic approaches to mitigate gastrointestinal motility disorders.

Reduction of hydrogen sulfide synthesis enzymes cystathionine-β-synthase and cystathionine-γ-lyase in the colon of patients with Hirschsprungs disease

PURPOSE

Hirschsprung associated enterocolitis (HAEC) is the most common cause of morbidity and mortality in Hirschsprung Disease (HSCR). The pathogenesis of HAEC is poorly understood. In recent years, there is increasing evidence that a compromised intestinal barrier function plays a major role in the pathogenesis of HAEC. Hydrogen sulfide, synthesized from L-cysteine by two key enzymes, cystathionine-β-synthase (CBS) and cystathionine-γ-lysase (CSE) is reported to play a key role in regulating gastrointestinal motility and promoting resolution of inflammation. We designed this study to test the hypothesis that CBS and CSE expression is altered in the colon of patients with HSCR.

METHODS

We investigated CBS and CSE protein expression in both the aganglionic and ganglionic regions of HSCR patients (n=10) versus healthy control colon (n=10). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expression was quantified using quantitative real-time polymerase chain reaction (qPCR), Western blot analysis, and densitometry.

MAIN RESULTS

qPCR and Western blot analysis revealed that CBS and CSE are expressed in the normal human colon. CBS and CSE expression was significantly decreased (p<0.003) in the ganglionic and aganglionic bowel in HSCR compared to controls. Confocal microscopy revealed that CBS and CSE expression in smooth muscles, interstitial cells of Cajal, platelet-derived growth factor-alpha receptor-positive cells, enteric neurons and colonic epithelium was markedly decreased in HSCR specimens compared to controls.

CONCLUSION

We demonstrate for the first time the expression and distribution of CBS/CSE in patients with HSCR. The observed decreased expression of CBS and CSE may affect mucosal integrity and colonic contractility and thus render HSCR patients more susceptible to develop HAEC.

International Union of Basic and Clinical Pharmacology. CII: Pharmacological Modulation of H2S Levels: H2S Donors and H2S Biosynthesis Inhibitors

Over the last decade, hydrogen sulfide (H₂S) has emerged as an important endogenous gasotransmitter in mammalian cells and tissues. Similar to the previously characterized gasotransmitters nitric oxide and carbon monoxide, H₂S is produced by various enzymatic reactions and regulates a host of physiologic and pathophysiological processes in various cells and tissues. H₂S levels are decreased in a number of conditions (e.g., diabetes mellitus, ischemia, and aging) and are increased in other states (e.g., inflammation, critical illness, and cancer). Over the last decades, multiple approaches have been identified for the therapeutic exploitation of H₂S, either based on H₂S donation or inhibition of H₂S biosynthesis. H₂S donation can be achieved through the inhalation of H₂S gas and/or the parenteral or enteral administration of so-called fast-releasing H₂S donors (salts of H₂S such as NaHS and Na₂S) or slow-releasing H₂S donors (GYY4137 being the prototypical compound used in hundreds of studies in vitro and in vivo). Recent work also identifies various donors with regulated H₂S release profiles, including oxidant-triggered donors, pH-dependent donors, esterase-activated donors, and organelle-targeted (e.g., mitochondrial) compounds. There are also approaches where existing, clinically approved drugs of various classes (e.g., nonsteroidal anti-inflammatories) are coupled with H₂S-donating groups (the most advanced compound in clinical trials is ATB-346, an H₂S-donating derivative of the non-steroidal anti-inflammatory compound naproxen). For pharmacological inhibition of H₂S synthesis, there are now several small molecule compounds targeting each of the three H₂S-producing enzymes cystathionine-β-synthase (CBS), cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Although many of these compounds have their limitations (potency, selectivity), these molecules, especially in combination with genetic approaches, can be instrumental for the delineation of the biologic processes involving endogenous H₂S production. Moreover, some of these compounds (e.g., cell-permeable prodrugs of the CBS inhibitor aminooxyacetate, or benserazide, a potentially repurposable CBS inhibitor) may serve as starting points for future clinical translation. The present article overviews the currently known H₂S donors and H₂S biosynthesis inhibitors, delineates their mode of action, and offers examples for their biologic effects and potential therapeutic utility.

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.

Sensitivity of salivary hydrogen sulfide to psychological stress and its association with exhaled nitric oxide and affect

BACKGROUND

Hydrogen sulfide (H₂S) is the third gasotransmitter recently discovered after nitric oxide (NO) and carbon monoxide. Both NO and H₂S are involved in multiple physiological functions. Whereas NO has been shown to vary with psychological stress, the influence of stress on H₂S and the relationship between H₂S and NO are unknown. We therefore examined levels of salivary H₂S and NO in response to a stressful final academic exam period.

METHODS

Measurements of stress, negative affect, and fraction of exhaled NO (FE_NO), were obtained from students (N=16) and saliva was collected at three time points: low-stress period in the semester, early exam period, and late exam period. Saliva was immediately analyzed for H₂S with the fluorescent probe Sulfidefluor-4.

RESULTS

H₂S increased significantly during the early exam period and FE_NO decreased gradually towards the late exam period. H₂S, FE_NO, negative affect, and stress ratings were positively associated with each other: as stress level and negative affect increased, values of H₂S increased; in addition, as FE_NO levels decreased, H₂S also decreased. Asthma status did not modify these associations.

CONCLUSION

Sustained academic stress increases H₂S and these changes are correlated with NO and the experience of stress and negative affect. These findings motivate research with larger samples to further explore the interaction and function of H₂S and FE_NO during psychological stress.

A hydrogen sulfide probe activates Nrf2, inhibits cancer cell growth and induces cell apoptosis

Application of a probe for hydrogen sulfide, HF-NBD.

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.

A new ratiometric fluorescent probe for rapid, sensitive and selective detection of endogenous hydrogen sulfide in mitochondria

We have developed a new ratiometric fluorescent probe composed of a coumarin-merocyanine dyad based on the FRET mechanism. The probe showed clear dual-emission signal changes in blue and red spectral windows upon addition of H2S in a dose dependent manner under a single wavelength excitation. The probe targeted mitochondria with high selectivity and sensitivity toward H2S.

P2Y(1) receptors mediate purinergic relaxation in the equine pelvic flexure

In the equine large intestine, the knowledge of the basic mechanisms underlying motility function is crucial to properly treat motility disorders. P2Y1 receptors are responsible for mediating purinergic colonic relaxation in several species. In vitro experimental studies of the circular muscle from the equine pelvic flexure (n = 6) were performed to characterize inhibitory and excitatory neuromuscular transmission. Electrophysiological studies showed that electrical field stimulation (EFS) evoked biphasic inhibitory junction potentials (IJPs) in smooth muscle cells: a fast IJP (IJPf) followed by a sustained IJP (IJPs). IJPs was sensitive to L-NNA 1 mM (a nitric oxide synthase inhibitor) (P <0.01), while IJPf was abolished by MRS2500 1 µM (a P2Y1 receptor antagonist) (P <0.001). EFS (5 Hz for 2 min) in the organ bath inhibited rhythmic contractions to 3.0 ± 2.5% of basal area under the curve (P <0.0001). EFS under MRS2500 1 µM or L-NNA 1 mM incubation inhibited contractions to 6.0 ± 2.8% (P <0.05) and 24.4 ± 11.3% respectively (P <0.05). Combination of MRS2500 1 µM and L-NNA 1 mM completely reversed the EFS-induced inhibition of colonic motility. Non-nitrergic, non-purinergic conditions were used to reveal voltage-dependent EFS-induced contractions sensitive to atropine 1 µM (P <0.001) and, therefore, cholinergic. In conclusion, nerve-mediated relaxation and contraction in the equine pelvic flexure involve the same mechanisms as those observed in the human colon. P2Y1 receptors mediate purinergic relaxations and are potential targets for the treatment of equine colonic motor disorders.

Hydrogen Sulfide in Physiology and Diseases of the Digestive Tract

Hydrogen sulfide (H₂S) is a Janus-faced molecule. On one hand, several toxic functions have been attributed to H₂S and exposure to high levels of this gas is extremely hazardous to health. On the other hand, H₂S delivery based clinical therapies are being developed to combat inflammation, visceral pain, oxidative stress related tissue injury, thrombosis and cancer. Since its discovery, H₂S has been found to have pleiotropic effects on physiology and health. H₂S is a gasotransmitter that exerts its effect on different systems, such as gastrointestinal, neuronal, cardiovascular, respiratory, renal, and hepatic systems. In the gastrointestinal tract, in addition to H₂S production by mammalian cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), H₂S is also generated by the metabolic activity of resident gut microbes, mainly by colonic Sulfate-Reducing Bacteria (SRB) via a dissimilatory sulfate reduction (DSR) pathway. In the gut, H₂S regulates functions such as inflammation, ischemia/ reperfusion injury and motility. H₂S derived from gut microbes has been found to be associated with gastrointestinal disorders such as ulcerative colitis, Crohn’s disease and irritable bowel syndrome. This underscores the importance of gut microbes and their production of H₂S on host physiology and pathophysiology.

Reduction of hydrogen sulfide synthesis enzymes in the esophagus of patients with achalasia: effect of hydrogen sulfide in achalasia

BACKGROUND

The aim of the present study was to investigate whether the synthesis of endogenous hydrogen sulfide (H2 S) was altered in achalasia patients and to determine the effects of H2 S on esophageal motility.

METHODS

(1) Tissue samples in lower esophageal sphincter (LES) were obtained from 22 achalasia patients during peroral endoscopic myotomy. LES muscle from eight esophageal carcinoma patients was obtained as control. The expression of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) was detected by immunohistochemical staining. (2) Rabbit esophageal smooth muscle strips were used to measure isometric contractions. The effects of sodium hydrosulfide (NaHS) and L-cysteine on contractile activity and bethanechol-stimulated contractile activity were evaluated. The contraction of esophageal muscle strips was also measured after the inhibition of CBS and CSE by aminooxyacetic acid (AOA) and propargylglycine (PAG).

KEY RESULTS

Both CBS and CSE could be detected in biopsies from achalasia patients and controls. Compared with controls, the expression of CBS and CSE in the LES of achalasia patients was significantly reduced (p < 0.001). Both NaHS and L-cysteine concentration-dependently inhibited esophageal contractile activity (both p < 0.05). After inhibition of CBS and CSE by PAG and AOA, esophageal contractile activity increased significantly, and this effect could be restored by NaHS but not L-cysteine (p < 0.05).

CONCLUSIONS & INFERENCES

H2 S synthesis enzymes are significantly reduced in patients with achalasia compared with the controls. H2 S inhibits esophageal contractile activity concentration-dependently, and the inhibition of H2 S synthesis enzymes increases esophageal contractile activity. H2 S might be involved in the development of achalasia.