Hydrogen sulfide up-regulates substance P in polymicrobial sepsis-associated lung injury

Substance P Promotes Leukocyte Infiltration in the Liver and Lungs of Mice with Sepsis: A Key Role for Adhesion Molecules on Vascular Endothelial Cells

Substance P (SP), encoded by the Tac1 gene, has been shown to promote leukocyte infiltration and organ impairment in mice with sepsis. Neurokinin-1 receptor (NK1R) is the major receptor that mediates the detrimental impact of SP on sepsis. This investigation studied whether SP affects the expression of adhesion molecules, including intercellular cell adhesion molecule-1 (ICAM1) and vascular cell adhesion molecule-1 (VCAM1) on vascular endothelial cells in the liver and lungs, contributing to leukocyte infiltration in these tissues of mice with sepsis. Sepsis was induced by caecal ligation and puncture (CLP) surgery in mice. The actions of SP were inhibited by deleting the Tac1 gene, blocking NK1R, or combining these two methods. The activity of myeloperoxidase and the concentrations of ICAM1 and VCAM1 in the liver and lungs, as well as the expression of ICAM1 and VCAM1 on vascular endothelial cells in these tissues, were measured. The activity of myeloperoxidase and the concentration of ICAM1 and VCAM1 in the liver and lungs, as well as the expression of ICAM1 and VCAM1 on vascular endothelial cells in these tissues, increased in mice with CLP surgery-induced sepsis. Suppressing the biosynthesis of SP and its interactions with NK1R attenuated CLP surgery-induced alterations in the liver and lungs of mice. Our findings indicate that SP upregulates the expression of ICAM1 and VCAM1 on vascular endothelial cells in the liver and lungs, thereby increasing leukocyte infiltration in these tissues of mice with CLP surgery-induced sepsis by activating NK1R.

Searching for Novel Sources of Hydrogen Sulfide Donors: Chemical Profiling of Polycarpa aurata Extract and Evaluation of the Anti-Inflammatory Effects

Hydrogen sulfide (H2S) is a signaling molecule endogenously produced within mammals' cells that plays an important role in inflammation, exerting anti-inflammatory effects. In this view, the research has shown a growing interest in identifying natural H2S donors. Herein, for the first time, the potential of marine extract as a source of H2S-releasing agents has been explored. Different fractions obtained by the Indonesian ascidian Polycarpa aurata were evaluated for their ability to release H2S in solution. The main components of the most active fraction were then characterized by liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and NMR spectroscopy. The ability of this fraction to release H2S was evaluated in a cell-free assay and J774 macrophages by a fluorimetric method, and its anti-inflammatory activity was evaluated in vitro and in vivo by using carrageenan-induced mouse paw edema. The anti-inflammatory effects were assessed by inhibiting the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and interleukin-6 (IL-6), coupled with a reduction in nitric oxide (NO) and IL-6 levels. Thus, this study defines the first example of a marine source able to inhibit inflammatory responses in vivo through the release of H2S.

Pharmacological Inhibition and Genetic Deletion of Cystathionine Gamma-Lyase in Mice Protects against Organ Injury in Sepsis: A Key Role of Adhesion Molecules on Endothelial Cells

Hydrogen sulfide (H2S), synthesized by cystathionine gamma-lyase (Cth), contributes to the inflammatory response observed in sepsis. This study examines the effect of Cth-derived H2S in adhesion molecules on endothelial cells of vital organs in mice in a cecal ligation puncture (CLP)-induced model of sepsis, using two different and complementary approaches: Cth gene deletion and pharmacological inhibition. Our findings revealed a decreased level of H2S-synthesizing activity (via Cth) in both Cth-/- mice and PAG-treated wild-type (WT) mice following CLP-induced sepsis. Both treatment groups had reduced MPO activity and expression of chemokines (MCP-1 and MIP-2α), adhesion molecules (ICAM-1 and VCAM-1), ERK1/2 phosphorylation, and NF-κB in the liver and lung compared with in CLP-WT mice. Additionally, we found that PAG treatment in Cth-/- mice had no additional effect on the expression of ERK1/2 phosphorylation, NF-κB, or the production of chemokines and adhesion molecules in the liver and lung compared to Cth-/- mice following CLP-induced sepsis. The WT group with sepsis had an increased immunoreactivity of adhesion molecules on endothelial cells in the liver and lung than the WT sham-operated control. The Cth-/-, PAG-treated WT, and Cth-/- groups of mice showed decreased immunoreactivity of adhesion molecules on endothelial cells in the liver and lung following sepsis. Inhibition of H2S production via both approaches reduced adhesion molecule expression on endothelial cells and reduced liver and lung injury in mice with sepsis. In conclusion, this study demonstrates that H2S has an important role in the pathogenesis of sepsis and validates PAG use as a suited tool for investigating the Cth/H2S-signalling axis in sepsis.

A dual mode 'turn-on' fluorescence-Raman (SERS) response probe based on a 1H-pyrrol-3(2H)-one scaffold for monitoring H2S levels in biological samples

Discovery of the biological signaling roles of H2S has spurred great interest in developing reliable methods for its accurate detection and quantification. As considerable variation in its levels is seen during pathological conditions such as sepsis, real-time quantification methods have relevance in diagnosis as well. Of various approaches, reaction-based probes which respond through 'off-on' fluorescence emission remain the most studied. Since the intensity of emission is related to the analyte concentration in these measurements, the presence of built-in features which provide an opportunity for internal referencing will be advantageous. In view of this, a dual mode response system that senses H2S through characteristic fluorescence and Raman (SERS) signals based on a 1H-pyrrol-3(2H)-one scaffold was developed and is the main highlight of this report. This probe offers several advantages such as fast response (<1 min), and high selectivity and sensitivity with a detection limit of ∼7 nM. Imaging of H2S in HepG2 cells, making use of the SERS signal from the thiolysis product is also demonstrated.

Hydrogen Sulfide: A Gaseous Mediator and Its Key Role in Programmed Cell Death, Oxidative Stress, Inflammation and Pulmonary Disease

Hydrogen sulfide (H₂S) has been acknowledged as a novel gaseous mediator. The metabolism of H₂S in mammals is tightly controlled and is mainly achieved by many physiological reactions catalyzed by a suite of enzymes. Although the precise actions of H₂S in regulating programmed cell death, oxidative stress and inflammation are yet to be fully understood, it is becoming increasingly clear that H₂S is extensively involved in these crucial processes. Since programmed cell death, oxidative stress and inflammation have been demonstrated as three important mechanisms participating in the pathogenesis of various pulmonary diseases, it can be inferred that aberrant H₂S metabolism also functions as a critical contributor to pulmonary diseases, which has also been extensively investigated. In the meantime, substantial attention has been paid to developing therapeutic approaches targeting H₂S for pulmonary diseases. In this review, we summarize the cutting-edge knowledge on the metabolism of H₂S and the relevance of H₂S to programmed cell death, oxidative stress and inflammation. We also provide an update on the crucial roles played by H₂S in the pathogenesis of several pulmonary diseases. Finally, we discuss the perspective on targeting H₂S metabolism in the treatment of pulmonary diseases.

Hydrogen Sulfide and Substance P Levels in Patients with Escherichia coli and Klebsiella pneumoniae Bacteraemia

Hydrogen sulfide (H2S) and substance P (SP) are known from animal models and in vitro studies as proinflammatory mediators. In this study, peripheral blood concentrations of H2S and SP were measured in patients with Escherichia coli or Klebsiella pneumoniae bacteraemia. Fifty patients were recruited from general wards at Christchurch Hospital, during 2020–2021. Samples from age- and sex-matched healthy subjects previously recruited as controls for studies of cardiovascular disease were used as controls. The concentrations of H2S were higher than controls on day 0, day 1, and day 2, and SP was higher than controls on all 4 days. The concentrations of H2S were highest on day 0, whereas SP concentrations were higher on day 2 than other days. Interleukin-6 and C-reactive protein were significantly higher on day 0 and day 1, respectively. The concentrations of H2S and SP did not differ between 15 non-septic (SIRS 0-1) and the 35 septic subjects (SIRS ≥ 2). Substance P concentrations were higher in subjects with abdominal infection than urinary tract infections on day 0 (p = 0.0002) and day 1 (p = 0.0091). In conclusion, the peak H2S concentrations precede the SP peak in patients with Gram-negative bacteraemia, but this response varies with the site of infection.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

Sepsis, a potentially lethal condition resulting from failure to control the initial infection, is associated with a dysregulated host defense response to pathogens and their toxins. Sepsis remains a leading cause of morbidity, mortality and disability worldwide. The pathophysiology of sepsis is very complicated and is not yet fully understood. Worse still, the development of effective therapeutic agents is still an unmet need and a great challenge. Gases, including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S), are small-molecule biological mediators that are endogenously produced, mainly by enzyme-catalyzed reactions. Accumulating evidence suggests that these gaseous mediators are widely involved in the pathophysiology of sepsis. Many sepsis-associated alterations, such as the elimination of invasive pathogens, the resolution of disorganized inflammation and the preservation of the function of multiple organs and systems, are shaped by them. Increasing attention has been paid to developing therapeutic approaches targeting these molecules for sepsis/septic shock, taking advantage of the multiple actions played by NO, CO and H₂S. Several preliminary studies have identified promising therapeutic strategies for gaseous-mediator-based treatments for sepsis. In this review article, we summarize the state-of-the-art knowledge on the pathophysiology of sepsis; the metabolism and physiological function of NO, CO and H₂S; the crosstalk among these gaseous mediators; and their crucial effects on the development and progression of sepsis. In addition, we also briefly discuss the prospect of developing therapeutic interventions targeting these gaseous mediators for sepsis.

Genetic analysis of potential biomarkers and therapeutic targets in ferroptosis from coronary artery disease

Ferroptosis plays a key role in the death of cells including cardiomyocytes, and it is related to a variety of cardiac diseases. However, the role of ferroptosis‐related genes (FRGs) in coronary artery disease (CAD) is not well characterized. We downloaded CAD‐related information and FRGs from the gene expression omnibus (GEO) database and Ferroptosis Database (FerrDb) respectively. A total of 10 CAD‐related DE‐FRGs were obtained, which were closely linked to autophagy regulation and immune response. Subsequently, CA9, CBS, CEBPG, HSPB1, SLC1A4, STMN1 and TRIB3 among the 10 DE‐FRGs were identified as marker genes by LASSO and SVM‐RFE algorithms, which had tolerable diagnostic capabilities. Subsequent functional enrichment analysis showed that these marker genes may play a corresponding role in CAD by participating in the regulation of immune response, amino acid metabolism, cell cycle and multiple pathways related to the pathogenesis of CAD. Furthermore, a total of 58 drugs targeting 7 marker genes had been obtained. On the contrary, the ceRNA network revealed a complex regulatory relationship based on the marker genes. Also, CIBERSORT analysis showed that the changes in the immune microenvironment of CAD patients may be related to CBS, HSPB1 and CEBPG. We developed a diagnostic potency and provided an insight for exploring the mechanism for CAD. Before clinical application, further research is needed to test its diagnostic value for CAD.

Hydrogen Sulfide in Inflammation: A Novel Mediator and Therapeutic Target

Significance: Inflammation is a normal response to injury, but uncontrolled inflammation can lead to several diseases. In recent years, research has shown endogenously synthesized hydrogen sulfide (H₂S) to be a novel mediator of inflammation. This review summarizes the current understanding and recent advances of H₂S role with respect to inflammation in different diseases. Recent Advances: Promising early results from clinical studies suggest an important role of H₂S in human inflammatory disease. Critical Issues: Defining the precise mechanism by which H₂S contributes to inflammation is a complex challenge, and there is active ongoing research that is focused on addressing this question. Most of this work has been conducted on animal models of human disease and isolated/cultured cells, and its translation to the clinic is another challenge in the area of H₂S research. Future Directions: Defining the mechanism by which H₂S acts as an inflammatory mediator will help us better understand different inflammatory diseases and help develop novel therapeutic approaches for these diseases.

The Role of Hydrogen Sulfide in Respiratory Diseases

Respiratory diseases are leading causes of death and disability around the globe, with a diverse range of health problems. Treatment of respiratory diseases and infections has been verified to be thought-provoking because of the increasing incidence and mortality rate. Hydrogen sulfide (H₂S) is one of the recognized gaseous transmitters involved in an extensive range of cellular functions, and physiological and pathological processes in a variety of diseases, including respiratory diseases. Recently, the therapeutic potential of H₂S for respiratory diseases has been widely investigated. H₂S plays a vital therapeutic role in obstructive respiratory disease, pulmonary fibrosis, emphysema, pancreatic inflammatory/respiratory lung injury, pulmonary inflammation, bronchial asthma and bronchiectasis. Although the therapeutic role of H₂S has been extensively studied in various respiratory diseases, a concrete literature review will have an extraordinary impact on future therapeutics. This review provides a comprehensive overview of the effective role of H₂S in respiratory diseases. Besides, we also summarized H₂S production in the lung and its metabolism processes in respiratory diseases.

Hydrogen Sulfide and its Interaction with Other Players in Inflammation

Hydrogen sulfide (H₂S) plays a vital role in human physiology and in the pathophysiology of several diseases. In addition, a substantial role of H₂S in inflammation has emerged. This chapter will discuss the involvement of H₂S in various inflammatory diseases. Furthermore, the contribution of reactive oxygen species (ROS), adhesion molecules, and leukocyte recruitment in H₂S-mediated inflammation will be discussed. The interrelationship of H₂S with other gasotransmitters in inflammation will also be examined. There is mixed literature on the contribution of H₂S to inflammation due to studies reporting both pro- and anti-inflammatory actions. These apparent discrepancies in the literature could be resolved with further studies.

H2S in acute lung injury: a therapeutic dead end(?)

This review addresses the plausibility of hydrogen sulfide (H₂S) therapy for acute lung injury (ALI) and circulatory shock, by contrasting the promising preclinical results to the present clinical reality. The review discusses how the narrow therapeutic window and width, and potentially toxic effects, the route, dosing, and timing of administration all have to be balanced out very carefully. The development of standardized methods to determine in vitro and in vivo H₂S concentrations, and the pharmacokinetics and pharmacodynamics of H₂S-releasing compounds is a necessity to facilitate the safety of H₂S-based therapies. We suggest the potential of exploiting already clinically approved compounds, which are known or unknown H₂S donors, as a surrogate strategy.

The Role of Host-Generated H2S in Microbial Pathogenesis: New Perspectives on Tuberculosis

For centuries, hydrogen sulfide (H₂S) was considered primarily as a poisonous gas and environmental hazard. However, with the discovery of prokaryotic and eukaryotic enzymes for H₂S production, breakdown, and utilization, H₂S has emerged as an important signaling molecule in a wide range of physiological and pathological processes. Hence, H₂S is considered a gasotransmitter along with nitric oxide (•NO) and carbon monoxide (CO). Surprisingly, despite having overlapping functions with •NO and CO, the role of host H₂S in microbial pathogenesis is understudied and represents a gap in our knowledge. Given the numerous reports that followed the discovery of •NO and CO and their respective roles in microbial pathogenesis, we anticipate a rapid increase in studies that further define the importance of H₂S in microbial pathogenesis, which may lead to new virulence paradigms. Therefore, this review provides an overview of sulfide chemistry, enzymatic production of H₂S, and the importance of H₂S in metabolism and immunity in response to microbial pathogens. We then describe our current understanding of the role of host-derived H₂S in tuberculosis (TB) disease, including its influences on host immunity and bioenergetics, and on Mycobacterium tuberculosis (Mtb) growth and survival. Finally, this review discusses the utility of H₂S-donor compounds, inhibitors of H₂S-producing enzymes, and their potential clinical significance.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.

Protective effect of diallyl disulfide against cerulein-induced acute pancreatitis and associated lung injury in mice

Garlic (Allium sativum) - derived organosulfur compound diallyl disulfide (DADS) possesses antioxidant, anti-inflammatory and anti-cancer effects. This study was aimed to investigate the anti-inflammatory role and the underlying molecular mechanisms of DADS in cerulein-induced acute pancreatitis (AP) and associated lung injury. Administration of DADS significantly attenuated the severity of pancreatic and pulmonary inflammation by inhibiting cerulein induced serum amylase, myeloperoxidase activity (MPO) and histological changes in pancreas and lung. Furthermore, the anti-inflammatory effect of DADS was associated with the decrease in tumor necrosis factor (TNF)-α,cystathionine-γ-lyase (CSE), preprotachykinin A (PPTA), neurokinin-1-receptor (NK1R) expression and hydrogen sulfide (H₂S) production in both pancreas and lung. In addition, DADS reduced caerulein-induced I-κB degradation and subsequent translocation of NF-κB in the pancreas and lung. These results show for the first time that in AP, DADS exhibits an anti-inflammatory effect by inhibiting CSE/H₂S and SP/NK1R signaling and NF-кB pathway.

Cystathionine-Gamma-Lyase-Derived Hydrogen Sulfide-Regulated Substance P Modulates Liver Sieve Fenestrations in Caecal Ligation and Puncture-Induced Sepsis

Cystathionine-γ-lyase (CSE) isa hydrogen sulfide (H₂S)-synthesizing enzyme that promotesinflammation by upregulating H₂S in sepsis. Liver sinusoidal endothelial cells (LSECs) are fenestrated endothelial cells (liver sieve) that undergo alteration during sepsis and H₂S plays a role in this process. Substance P (SP) is encoded by the preprotachykinin A (PPTA) gene, and promotes inflammation in sepsis; however, its regulation by H₂S is poorly understood. Furthermore, the interaction between H₂S and SP in modulating LSEC fenestrations following sepsis remains unclear. This study aimed to investigate whether CSE/H₂S regulates SP and the neurokinin-1 receptor (NK-1R) andmodulates fenestrations in LSECs following caecalligation and puncture (CLP)-induced sepsis. Here we report thatthe absence of either CSE or H₂S protects against liver sieve defenestration and gaps formation in LSECsin sepsis by decreased SP-NK-1R signaling. Following sepsis, there is an increased expression of liver CSE and H₂S synthesis, and plasma H₂S levels, which were aligned with higher SP levels in the liver, lungs and plasma and NK-1R in the liver and lungs. The genetic deletion of CSE led to decreased sepsis-induced SP and NK-1R in the liver, lungs and plasma SP suggesting H₂S synthesized through CSE regulates the SP-NK-1R pathway in sepsis. Further, mice deficient in the SP-encoding gene (PPTA) preservedsepsis-induced LSEC defenestrationand gaps formation, as seen by maintenance of patent fenestrations and fewer gaps. In conclusion, CSE/H₂S regulates SP-NK-1R and modulates LSEC fenestrations in sepsis.

Dexamethasone ameliorates H2S-induced acute lung injury by increasing claudin-5 expression via the PI3K pathway

Acute lung injury (ALI) is a major outcome of exposure to high levels of hydrogen sulfide (H₂S). Dexamethasone (DXM) has been used to treat ALI. However, the mechanisms involved in H₂S-induced ALI and the protective mechanisms of DXM in treating ALI are still nebulous. To explore the mechanisms involved, we evaluated the role of claudin-5 in the protective effect of DXM against H₂S-induced ALI. Sprague-Dawley rats were exposed to H₂S to establish the ALI model. In parallel with the animal model, a cell model was also established by incubating human umbilical vein endothelial cells (HUVECs) with NaHS. Lung hematoxylin-eosin staining, electron microscope assay, and wet/dry ratio were used to identify whether the ALI was successfully induced by H₂S, and changes in claudin-5 expression were detected in both rats and HUVECs. Our results revealed that claudin-5 was markedly decreased after H₂S exposure and that DXM significantly attenuated the H₂S-induced downregulation of claudin-5 in both rats and HUVECs. In the animal experiment, p-Akt and p-FoxO₁ presented a similar tendency as claudin-5, but their levels decreased 6 h prior to the levels of claudin-5. In a further investigation, the DXM-induced protective effect on ALI and rescue effect on downregulation of claudin-5 were both blocked by LY294002. The current study demonstrated that claudin-5 was involved in the development of H₂S-induced ALI and that DXM exerted protective effects through increasing claudin-5 expression by activating the phosphatidylinositol 3-kinase pathway. Therefore, claudin-5 might represent a novel pharmacological target for treating ALI induced by H₂S and other hazardous gases.

Cystathionine-Gamma-Lyase Gene Deletion Protects Mice against Inflammation and Liver Sieve Injury following Polymicrobial Sepsis

Background

Hydrogen sulfide (H₂S), produced by the activity of cystathionine-gamma-lyase (CSE), is a key mediator of inflammation in sepsis. The liver sinusoidal endothelial cells (LSECs) are important target and mediator of sepsis. The aim of this study was to investigate the role of CSE-derived H₂S on inflammation and LSECs fenestrae in caecal-ligation and puncture (CLP)-induced sepsis using CSE KO mice.

Methods

Sepsis was induced by CLP, and mice (C57BL/6J, male) were sacrificed after 8 hours. Liver, lung, and blood were collected and processed to measure CSE expression, H₂S synthesis, MPO activity, NF-κB p65, ERK1/2, and cytokines/chemokines levels. Diameter, frequency, porosity and gap area of the liver sieve were calculated from scanning electron micrographs of the LSECs.

Results

An increased CSE expression and H₂S synthesizing activity in the liver and lung of wild-type mice following CLP-induced sepsis. This was associated with an increased liver and lung MPO activity, and increased liver and lung and plasma levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β, and the chemokines MCP-1 and MIP-2α. Conversely, CSE KO mice had less liver and lung injury and reduced inflammation following CLP-induced sepsis as evidenced by decreased levels of H₂S synthesizing activity, MPO activity, and pro-inflammatory cytokines/chemokines production. Extracellular-regulated kinase (ERK1/2) and nuclear factor-κB p65 (NF-κB) became significantly activated after the CLP in WT mice but not in CSE KO mice. In addition, CLP-induced damage to the LSECs, as indicated by increased defenestration and gaps formation in the LSECs compared to WT sham control. CSE KO mice showed decreased defenestration and gaps formation following sepsis.

Conclusions

Mice with CSE (an H₂S synthesising enzyme) gene deletion are less susceptible to CLP-induced sepsis and associated inflammatory response through ERK1/2-NF-κB p65 pathway as evidenced by reduced inflammation, tissue damage, and LSECs defenestration and gaps formation.

H2S and Inflammation: An Overview

Inflammation is a response to traumatic, infectious, post-ischemic, toxic, or autoimmune injury. However, uncontrolled inflammation can lead to disease, and inflammation is now believed to be responsible for several disease conditions. Research in our laboratory has shown that hydrogen sulfide (H2S) acts as a novel mediator of inflammation. At present, work in several research groups worldwide is focused on determining the role of H2S in inflammation. H2S has been implicated in different inflammatory conditions. Most of this research involved working with animal models of disease and in vitro systems. Recent research, however, points to a role of H2S in clinical inflammatory disease as well. This chapter describes our current understanding of the role of H2S in inflammation.

Hydrogen sulfide prodrugs-a review

Hydrogen sulfide (H₂S) is recognized as one of three gasotransmitters together with nitric oxide (NO) and carbon monoxide (CO). As a signaling molecule, H₂S plays an important role in physiology and shows great potential in pharmaceutical applications. Along this line, there is a need for the development of H₂S prodrugs for various reasons. In this review, we summarize different H₂S prodrugs, their chemical properties, and some of their potential therapeutic applications.

Role of hydrogen sulphide in airways

The toxicity of hydrogen sulfide (H₂S) has been known for a long time, as it is prevalent in the atmosphere. However accumulative data suggest that H₂S is also endogenously produced in mammals, including man, and is the third important gas signaling molecule, besides nitric oxide and carbon monoxide. H₂S can be produced via non enzymatic pathways, but is mainly synthesized from L-cysteine by the enzymes cystathionine-γ-lyase, cystathionine-β-synthetase, cysteine amino transferase and 3-mercaptopyruvate sulfurtransferase (3MTS). The formation of H₂S from D-cysteine via the enzyme D-amino acid oxidase and 3MTS has also been described. Endogenous H₂S not only participates in the regulation of physiological functions of the respiratory system, but also seems to contribute to the pathophysiology of airway diseases such as chronic obstructive pulmonary disease, asthma and pulmonary fibrosis, as well as in inflammation, suggesting its possible use as a biomarker for these diseases. This review summarizes the different implications of hydrogen sulfide in the physiology of airways and the pathophysiology of airway diseases.

In vivo study of the effects of exogenous hydrogen sulfide on lung mitochondria in acute lung injury in rats

Background

Acute lung injury (ALI) is a serious disease with high incidence in ICU, and impaired mitochondria function plays a significant role in ALI. In this study, we examined the possible roles of exogenous hydrogen sulfide (H₂S) in lung mitochondria regulation in ALI rats.

Methods

The rat ALI model was induced by an intra-tongue vein Lipopolysaccharide (LPS) injection. We used sodium hydrosulphide (NaHS) as the H₂S donor. We randomly divided 40 Sprague–Dawley rats into five groups: control, LPS injury, LPS + low-dose NaHS (0.78 mg•kg^-1), LPS + middle-dose NaHS (1.56 mg•kg^-1), and LPS + high-dose NaHS (3.12 mg•kg^-1). Rats were killed 3 h after NaHS administration. We calculated a semi-quantitative histological index of lung injury assessments and measured the lung wet-to-dry weight ratio. We further analyzed serum for interleukin-1β levels using enzyme-linked immunosorbent assays. We observed lung mitochondria ultrastructures with an electron microscope. We examined oxidative stress markers in lung mitochondria and the mitochondrial swelling and activity. We analyzed lung mitochondria and cytosol Cyt-c protein expression using Western blotting.

Results

Compared to the control group, the quantitative assessment score index, wet-to-dry weight ratios, and interleukin-1β content in the LPS injury group were significantly increased and the mitochondrial ultrastructure damaged. Furthermore, mitochondrial activity, adenosine triphosphatease, superoxide dismutase, glutathione peroxidase, and mitochondrial Cyt-c protein expression were significantly decreased, and malondialdehyde content, mitochondrial swelling, and cytosol Cyt-c protein expression were significantly increased in the LPS injury group compared to the control group. These effects were lessened by NaHS.

Conclusion

Exogenous H₂S provided a protective effect against ALI by decreasing the mitochondrial lipid peroxidation level and protecting the cell structure in the LPS-induced rat models. Its regulatory effect on lung mitochondria is positively correlated with the dosage.

H2S during circulatory shock: some unresolved questions

Numerous papers have been published on the role of H2S during circulatory shock. Consequently, knowledge about vascular sulfide concentrations may assume major importance, in particular in the context of "acute on chronic disease", i.e., during circulatory shock in animals with pre-existing chronic disease. This review addresses the questions (i) of the "real" sulfide levels during circulatory shock, and (ii) to which extent injury and pre-existing co-morbidity may affect the expression of H2S producing enzymes under these conditions. In the literature there is a huge range on sulfide blood levels during circulatory shock, in part as a result of the different analytical methods used, but also due to the variable of the models and species studied. Clearly, some of the very high levels reported should be questioned in the context of the well-known H2S toxicity. As long as "real" sulfide levels during circulatory shock are unknown and/or undetectable "on line" due to the lack of appropriate techniques, it appears to be premature to correlate the measured blood levels of hydrogen sulfide with the severity of shock or the H2S therapy-related biological outcomes. The available data on the tissue expression of the H2S-releasing enzymes during circulatory shock suggest that a "constitutive" CSE expression may play a crucial role of for the maintenance of organ function, at least in the kidney. The data also indicate that increased CBS and CSE expression, in particular in the lung and the liver, represents an adaptive response to stress states.

Hydrogen sulfide acts as a pro-inflammatory mediator in rheumatic disease

OBJECTIVE

Hydrogen sulfide (H₂ S) is a gaseous mediator produced in the body. In experimental models, endogenously produced H₂ S has been shown to have pro-inflammatory effects. The aim of this study was to investigate whether H₂ S is present in three common rheumatic diseases, rheumatoid arthritis (RA), gout and osteoarthritis (OA) and to determine if H₂ S levels correlate with disease activity.

METHODS

Patients with RA, gout, OA, and healthy controls (n = 30 each) were recruited. Plasma and where possible, synovial fluid (SF), were obtained. Levels of H₂ S and interleukin-6 (IL-6) (a known inflammatory marker as a positive control) were determined and assessed for their relationship with disease activity.

RESULTS

SF-H₂ S levels were significantly elevated in both RA and gout when compared to respective plasma levels. Plasma levels of H₂ S were not different from those in healthy controls in patients with either RA or gout. In OA, plasma levels of H₂ S were significantly elevated compared to healthy controls. In RA, SF-H₂ S levels correlated with Disease Activity Score (DAS)-28 and tender joint count.

CONCLUSION

H₂ S is present in the joint and acts as a pro-inflammatory mediator in rheumatic diseases. H₂ S may be a novel therapeutic target for these conditions.

Hydrogen sulfide regulates Ca(2+) homeostasis mediated by concomitantly produced nitric oxide via a novel synergistic pathway in exocrine pancreas

AIM

The present study was designed to explore the effects of hydrogen sulfide (H2S) on Ca(2+) homeostasis in rat pancreatic acini.

RESULTS

Sodium hydrosulfide (NaHS; an H2S donor) induced a biphasic increase in the intracellular Ca(2+) concentration ([Ca(2+)]i) in a dose-dependent manner. The NaHS-induced [Ca(2+)]i elevation persisted with an EC50 of 73.3 μM in the absence of extracellular Ca(2+) but was abolished by thapsigargin, indicating that both Ca(2+) entry and Ca(2+) release contributed to the increase. The [Ca(2+)]i increase was markedly inhibited in the presence of NG-monomethyl L-arginine or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), and diaminofluorescein-2/diaminofluorescein-2 triazole (DAF-2/DAF-2T) fluorometry demonstrated that nitric oxide (NO) was also produced by H2S in a dose-dependent manner with an EC50 of 64.8 μM, indicating that NO was involved in the H2S effect. The H2S-induced [Ca(2+)]i increase was inhibited by pretreatment with U73122, xestospongin C, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, KT5823, and GP2A, indicating that phospholipase C (PLC), the inositol 1,4,5-trisphosphate (IP3) receptor, soluble guanylate cyclase (sGC), protein kinase G (PKG), and Gq-protein play roles as intermediate components in the H2S-triggered intracellular signaling.

INNOVATION

To our knowledge, our study is the first one highlighting the effect of H2S on intracellular Ca(2+) dynamics in pancreatic acinar cells. Moreover, a novel cascade was presumed to function via the synergistic interaction between H2S and NO.

CONCLUSION

We conclude that H2S affects [Ca(2+)]i homeostasis that is mediated by H2S-evoked NO production via an endothelial nitric oxide synthase (eNOS)-NO-sGC-cyclic guanosine monophosphate-PKG-Gq-protein-PLC-IP3 pathway to induce Ca(2+) release, and this pathway is identical to the one we recently proposed for a sole effect of NO and the two gaseous molecules synergistically function to regulate Ca(2+) homeostasis.

Hydrogen sulfide donors in research and drug development

This review summarized most of the H₂S donors such as inorganic compounds, natural products, anethole trithione derivatives and synthetic compounds used in research and drug development. These special bioactivities provided us some effective strategies for antiphlogosis, cancer therapy, cardiovascular protection and so on.

Enhanced expression of cystathionine β-synthase and cystathionine γ-lyase during acute cholecystitis-induced gallbladder inflammation

Background

Hydrogen sulfide (H₂S) has recently been shown to play an important role in the digestive system, but the role of endogenous H₂S produced locally in the gallbladder is unknown. The aim of this study was to investigate whether gallbladder possesses the enzymatic machinery to synthesize H₂S, and whether H₂S synthesis is changed in gallbladder inflammation during acute acalculous cholecystitis (AC).

Methods

Adult male guinea pigs underwent either a sham operation or common bile duct ligation (CBDL). One, two, or three days after CBDL, the animals were sacrificed separately. Hematoxylin and eosin-stained slides of gallbladder samples were scored for inflammation. H₂S production rate in gallbladder tissue from each group was determined; immunohistochemistry and western blotting were used to determine expression levels of the H₂S-producing enzymes cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) in gallbladder.

Results

There was a progressive inflammatory response after CBDL. Immunohistochemistry analysis showed that CBS and CSE were expressed in the gallbladder epithelium, muscular layer, and blood vessels and that the expression increased progressively with increasing inflammation following CBDL. The expression of CBS protein as well as the H₂S-production rate was significantly increased in the animals that underwent CBDL, compared to those that underwent the sham operation.

Conclusions

Both CBS and CSE are expressed in gallbladder tissues. The expression of these enzymes, as well as H₂S synthesis, was up-regulated in the context of inflammation during AC.

TRPV1 and SP: key elements for sepsis outcome?

Sensory neurons play important roles in many disorders, including inflammatory diseases, such as sepsis. Sepsis is a potentially lethal systemic inflammatory reaction to a local bacterial infection, affecting thousands of patients annually. Although associated with a high mortality rate, sepsis outcome depends on the severity of systemic inflammation, which can be directly influenced by several factors, including the immune response of the patient. Currently, there is a lack of effective drugs to treat sepsis, and thus there is a need to develop new drugs to improve sepsis outcome. Several mediators involved in the formation of sepsis have now been identified, but the mechanisms underlying the pathology remain poorly understood. The transient receptor potential vanilloid 1 (TRPV1) receptor and the neuropeptide substance P (SP) have recently been demonstrated as important targets for sepsis and are located on sensory neurones and non-neuronal cells. Herein, we highlight and review the importance of sensory neurones for the modulation of sepsis, with specific focus on recent findings relating to TRPV1 and SP, with their distinct abilities to alter the transition from local to systemic inflammation and also modify the overall sepsis outcome. We also emphasize the protective role of TRPV1 in this context.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Sodium hydrogen sulfide inhibits nicotine and lipopolysaccharide-induced osteoclastic differentiation and reversed osteoblastic differentiation in human periodontal ligament cells

Although previous studies have demonstrated that hydrogen sulfide (H(2)S) stimulated or inhibited osteoclastic differentiation, little is known about the effects of H(2)S on the differentiation of osteoblasts and osteoclasts. To determine the possible bioactivities of H(2)S on bone metabolism, we investigated the in vitro effects of H(2)S on cytotoxicity, osteoblastic, and osteoclastic differentiation as well as the underlying mechanism in lipopolysaccharide (LPS) and nicotine-stimulated human periodontal ligament cells (hPDLCs). The H(2)S donor, NaHS, protected hPDLCs from nicotine and LPS-induced cytotoxicity and recovered nicotine- and LPS-downregulated osteoblastic differentiation, such as alkaline phosphatase (ALP) activity, mRNA expression of osteoblasts, including ALP, osteopontin (OPN), and osteocalcin (OCN), and mineralized nodule formation. Concomitantly, NaHS inhibited the differentiation of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in mouse bone marrow cells and blocked nicotine- and LPS-induced osteoclastogenesis regulatory molecules, such as RANKL, OPG, M-CSF, MMP-9, TRAP, and cathepsin K mRNA. NaHS blocked nicotine and LPS-induced activation of p38, ERK, MKP-1, PI3K, PKC, and PKC isoenzymes, and NF-κB. The effects of H(2)S on nicotine- and LPS-induced osteoblastic and osteoclastic differentiation were remarkably reversed by MKP-1 enzyme inhibitor (vanadate) and expression inhibitor (triptolide). Taken together, we report for the first time that H(2)S inhibited cytotoxicity and osteoclastic differentiation and recovered osteoblastic differentiation in a nicotine- and periodontopathogen-stimulated hPDLCs model, which has potential therapeutic value for treatment of periodontal and inflammatory bone diseases.

Neuropeptides in sepsis: from brain pathology to systemic inflammation

Septic encephalopathy is frequently diagnosed in critically ill patients and in up to 70% of patients with severe systemic infection [19]. The syndrome is defined by diffuse cerebral dysfunction or structural abnormalities attributed to the effects of systemic infection, rather than a direct central nervous system cause. The clinical characteristics can range from mild delirium to deep coma, but patients are often medically sedated making the diagnosis difficult. Any manifestation, however, is specific and markers of disease are lacking [43]. Sepsis survivors present long term cognitive impairment, including alterations of memory, attention and concentration [10,54]. Here, we propose that neuropeptides may play a key role in septic encephalopathy, leading to a vicious circle characterized by brain disease and systemic inflammation.

Ursolic acid attenuates lipopolysaccharide-induced acute lung injury in a mouse model

AIM

To assess whether ursolic acid (UA) can attenuate lipopolysachharide (LPS)-induced acute lung injury and improve the survival time in a mouse model.

MATERIALS & METHODS

The mice were challenged with LPS and survival time was monitored from 0-96 h after LPS treatment. TNF-α, IL-6, IL-1β, HMGB1, nitric oxide (NO) and IL-10 concentration in serum were measured by ELISA. Myeloperoxidase activity, malondialdehyde, lung wet:dry weight ratio and lung permeability in lung tissues were detected. NF-κB, HMGB1 and inducible NO synthase in the lungs were detected by western blot.

RESULTS

UA markedly rescued lethality, improved survival time and lung pathological changes, inhibited TNF-α, IL-6, IL-1β, HMGB1 and NO, and increased IL-10 expression. In addition, UA can also decrease myeloperoxidase, malondialdehyde, lung wet:dry weight ratio and lung permeability. UA attenuated NF-κB, HMGB1 and inducible NO synthase protein expression in the lungs.

CONCLUSION

The results suggest that UA is capable of improving survival time and LPS-induced acute lung injury. UA has a potentially therapeutic role in septic shock.

Role of hydrogen sulfide in the pathology of inflammation

Hydrogen sulfide (H2S) is a well-known toxic gas that is synthesized in the human body from the amino acids cystathionine, homocysteine, and cysteine by the action of at least two distinct enzymes: cystathionine-γ-lyase and cystathionine-β-synthase. In the past few years, H2S has emerged as a novel and increasingly important biological mediator. Imbalances in H2S have also been shown to be associated with various disease conditions. However, defining the precise pathophysiology of H2S is proving to be a complex challenge. Recent research in our laboratory has shown H2S as a novel mediator of inflammation and work in several groups worldwide is currently focused on determining the role of H2S in inflammation. H2S has been implicated in different inflammatory conditions, such as acute pancreatitis, sepsis, joint inflammation, and chronic obstructive pulmonary disease (COPD). Active research on the role of H2S in inflammation will unravel the pathophysiology of its actions in inflammatory conditions and may help develop novel therapeutic approaches for several, as yet incurable, disease conditions.

Inhaled hydrogen sulfide protects against lipopolysaccharide-induced acute lung injury in mice

BACKGROUND

Local pulmonary and systemic infections can lead to acute lung injury (ALI). The resulting lung damage can evoke lung failure and multiple organ dysfunction associated with increased mortality. Hydrogen sulfide (H2S) appears to represent a new therapeutic approach to ALI. The gas has been shown to mediate potent anti-inflammatory and organ protective effects in vivo. This study was designed to define its potentially protective role in sepsis-induced lung injury.

METHODS

C57BL/6 N mice received lipopolysaccharide (LPS) intranasally in the absence or presence of 80 parts per million H2S. After 6 h, acute lung injury was determined by comparative histology. Bronchoalveolar lavage (BAL) fluid was analyzed for total protein content and differential cell counting. BAL and serum were further analyzed for interleukin-1β, macrophage inflammatory protein-2, and/or myeloperoxidase glycoprotein levels by enzyme-linked immunosorbent assays. Differences between groups were analyzed by one way analysis of variance.

RESULTS

Histological analysis revealed that LPS instillation led to increased alveolar wall thickening, cellular infiltration, and to an elevated ALI score. In the presence of H2S these changes were not observed despite LPS treatment. Moreover, neutrophil influx, and pro-inflammatory cytokine release were enhanced in BAL fluid of LPS-treated mice, but comparable to control levels in H2S treated mice. In addition, myeloperoxidase levels were increased in serum after LPS challenge and this was prevented by H2S inhalation.

CONCLUSION

Inhalation of hydrogen sulfide protects against LPS-induced acute lung injury by attenuating pro-inflammatory responses.

Hydrogen sulfide and inflammation: the good, the bad, the ugly and the promising

Hydrogen sulfide is rapidly gaining ground as a physiological mediator of inflammation, but there is no clear consensus as to its precise role in inflammatory signaling. This article discusses the disparate anti-inflammatory ('the good') and proinflammatory ('the bad') effects of endogenous and pharmacological H(2)S in disparate animal model and cell culture systems. We also discuss 'the ugly', such as problems of using wholly specific inhibitors of enzymatic H(2)S synthesis, and the use of pharmacological donor compounds, which release H(2)S too quickly to be physiologically representative of endogenous H(2)S synthesis. Furthermore, recently developed slow-release H(2)S donors, which offer a more physiological approach to understanding the complex role of H(2)S in acute and chronic inflammation ('the promising') are discussed.

Hydrogen sulfide in cell survival: a double-edged sword

Hydrogen sulfide (H(2)S) has been found to play an important role as a signal molecule in regulating cell survival. It appears paradoxical that, on one side, H(2)S acts as a physiological intercellular messenger to stimulate cell growth, and on the other side, it may display cytotoxic activity. This article summarizes the current body of evidence demonstrating the cytoprotective versus cytotoxic effects of H(2)S in mammalian cells and describes the janus-faced properties of this important gasotransmitter. This article will also provide a brief description of the current signaling mechanisms that have been demonstrated to be responsible for these different actions. The pharmacologic regulation of H(2)S production and the potential clinical significance of H(2)S are highlighted.

Contributions of TRPV1, endovanilloids, and endoplasmic reticulum stress in lung cell death in vitro and lung injury

Endogenous agonists of transient receptor potential vanilloid-1 (TRPV1) (endovanilloids) are implicated as mediators of lung injury during inflammation. This study tested the hypothesis that endovanilloids produced following lipopolysaccharide (LPS) treatment activate TRPV1 and cause endoplasmic reticulum stress/GADD153 expression in lung cells, representing a mechanistic component of lung injury. The TRPV1 agonist nonivamide induced GADD153 expression and caused cytotoxicity in immortalized and primary human bronchial, bronchiolar/alveolar, and microvascular endothelial cells, proportional to TRPV1 mRNA expression. In CF-1 mice, Trpv1 mRNA was most abundant in the alveoli, and intratracheal nonivamide treatment promoted Gadd153 expression in the alveolar region. Treatment of CF-1 mice with LPS increased Gadd153 in the lung, lactate dehydrogenase (LDH) in bronchoalveolar lavage (BAL) fluid, and lung wet-to-dry weight ratio. Cotreating mice with LPS and the TRPV1 antagonist LJO-328 reduced Gadd153 induction and LDH in BAL but did not inhibit increases in lung wet-to-dry ratio. In Trpv1(-/-) mice treated with LPS, Gadd153 induction and LDH in BAL were reduced relative to wild-type mice, and the wet-to-dry weight ratios of lungs from both wild-type and Trpv1(-/-) mice decreased. Organic extracts of blood collected from LPS-treated mice were more cytotoxic to TRPV1-overexpressing cells compared with BEAS-2B cells and extracts from control mice, however, most pure endovanilloids did not produce cytotoxicity in a characteristic TRPV1-dependent manner. Collectively, these data indicate a role for TRPV1, and endogenous TRPV1 agonists, in ER stress and cytotoxicity in lung cells but demonstrate that ER stress and cytotoxicity are not essential for pulmonary edema.

Hydrogen sulfide upregulates cyclooxygenase-2 and prostaglandin E metabolite in sepsis-evoked acute lung injury via transient receptor potential vanilloid type 1 channel activation

Hydrogen sulfide (H(2)S) has been shown to promote transient receptor potential vanilloid type 1 (TRPV1)-mediated neurogenic inflammation in sepsis and its associated multiple organ failure, including acute lung injury (ALI). Accumulating evidence suggests that the cyclooxygenase-2 (COX-2)/PGE(2) pathway plays an important role in augmenting inflammatory immune response in sepsis and respiratory diseases. However, the interactions among H(2)S, COX-2, and PGE(2) in inciting sepsis-evoked ALI remain unknown. Therefore, the aim of this study was to investigate whether H(2)S would upregulate COX-2 and work in conjunction with it to instigate ALI in a murine model of polymicrobial sepsis. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in male Swiss mice. dl-propargylglycine, an inhibitor of H(2)S formation, was administrated 1 h before or 1 h after CLP, whereas sodium hydrosulfide, an H(2)S donor, was given during CLP. Mice were treated with TRPV1 antagonist capsazepine 30 min before CLP, followed by assessment of lung COX-2 and PGE(2) metabolite (PGEM) levels. Additionally, septic mice were administrated with parecoxib, a selective COX-2 inhibitor, 20 min post-CLP and subjected to ALI and survival analysis. H(2)S augmented COX-2 and PGEM production in sepsis-evoked ALI by a TRPV1 channel-dependent mechanism. COX-2 inhibition with parecoxib attenuated H(2)S-augmented lung PGEM production, neutrophil infiltration, edema, proinflammatory cytokines, chemokines, and adhesion molecules levels, restored lung histoarchitecture, and protected against CLP-induced lethality. The strong anti-inflammatory and antiseptic actions of selective COX-2 inhibitor may provide a potential therapeutic approach for the management of sepsis and sepsis-associated ALI.

Hydrogen sulfide and neurogenic inflammation in polymicrobial sepsis: involvement of substance P and ERK-NF-κB signaling

Hydrogen sulfide (H₂S) has been shown to induce transient receptor potential vanilloid 1 (TRPV1)-mediated neurogenic inflammation in polymicrobial sepsis. However, endogenous neural factors that modulate this event and the molecular mechanism by which this occurs remain unclear. Therefore, this study tested the hypothesis that whether substance P (SP) is one important neural element that implicates in H₂S-induced neurogenic inflammation in sepsis in a TRPV1-dependent manner, and if so, whether H₂S regulates this response through activation of the extracellular signal-regulated kinase-nuclear factor-κB (ERK-NF-κB) pathway. Male Swiss mice were subjected to cecal ligation and puncture (CLP)-induced sepsis and treated with TRPV1 antagonist capsazepine 30 minutes before CLP. DL-propargylglycine (PAG), an inhibitor of H₂S formation, was administrated 1 hour before or 1 hour after sepsis, whereas sodium hydrosulfide (NaHS), an H₂S donor, was given at the same time as CLP. Capsazepine significantly attenuated H₂S-induced SP production, inflammatory cytokines, chemokines, and adhesion molecules levels, and protected against lung and liver dysfunction in sepsis. In the absence of H₂S, capsazepine caused no significant changes to the PAG-mediated attenuation of lung and plasma SP levels, sepsis-associated systemic inflammatory response and multiple organ dysfunction. In addition, capsazepine greatly inhibited phosphorylation of ERK_1/2 and inhibitory κBα, concurrent with suppression of NF-κB activation even in the presence of NaHS. Furthermore, capsazepine had no effect on PAG-mediated abrogation of these levels in sepsis. Taken together, the present findings show that H₂S regulates TRPV1-mediated neurogenic inflammation in polymicrobial sepsis through enhancement of SP production and activation of the ERK-NF-κB pathway.

Preprotachykinin-A gene deletion regulates hydrogen sulfide-induced toll-like receptor 4 signaling pathway in cerulein-treated pancreatic acinar cells

OBJECTIVE

This study aimed to determine the effect of hydrogen sulfide (H2S) on Toll-like receptor 4 (TLR4)-mediated innate immune signaling in acute pancreatitis (AP) via substance P.

METHODS

Male Swiss mice were treated with hourly intraperitoneal injections of cerulein (50 μg/kg) for 10 hours. dl-propargylglycine ([PAG] 100 mg/kg, intraperitoneally), an inhibitor of H2S formation, was administered 1 hour after the induction of AP. Pancreatic acinar cells from male preprotachykinin-A gene-knockout mice (PPTA) and their wild-type counterparts were incubated with or without cerulein (10 M for 60 minutes). To better understand the effect of H2S in inflammation, acinar cells were stimulated with cerulein after addition of H2S donor, sodium hydrosulfide. In addition, cerulein-treated pancreatic acinar cells were pretreated with PAG (30 μM) for 1 hour.

RESULTS

The H2S inhibitor PAG eliminated TLR4, interleukin 1 receptor-associated kinase 4, tumor necrosis factor receptor-associated factor 6, and nuclear factor-κB (NF-κB) levels in in vitro and in vivo models of cerulein-induced AP. PPTA gene deletion reduced TLR4, myeloid differentiation factor 88, interleukin 1 receptor-associated kinase 4, tumor necrosis factor receptor-associated factor 6, and NF-κB in cerulein-treated pancreatic acinar cells, whereas administration of sodium hydrosulfide resulted in a further rise in TLR4 and NF-κB levels in cerulein-treated pancreatic acinar cells.

CONCLUSION

The present findings show for the first time that in AP, H2S may up-regulate the TLR4 pathway and NF-κB via substance P.

Altered host response to murine gammaherpesvirus 68 infection in mice lacking the tachykinin 1 gene and the receptor for substance P

The tachykinins are implicated in neurogenic inflammation and the neuropeptide substance P in particular has been shown to be a proinflammatory mediator. A role for the tachykinins in host response to viral infection has been previously demonstrated using either TAC1- or NK1 receptor-deficient transgenic mice. However, due to redundancy in the peptide-receptor complexes we wished determine whether a deficiency in TAC1 and NK1(R) in combination exhibited an enhanced phenotype. TAC1 and NK1(R)-deficient mice were therefore crossed to generate transgenic mice in both (NK1(-/-)×TAC1(-/-)). As expected, after infection with the respiratory pathogen murine gammaherpesvirus (MHV-68), TAC1 and NK1(R)-deficient mice were more susceptible to infection than wild-type C57BL/6 controls. However, unexpectedly, NK1(-/-)×TAC1(-/-) mice were more resistant to infection arguing for a lack of feedback inhibition through alternative receptors in these mice. Histopathological examination did not show any great differences in the inflammatory responses between groups of infected animals, except for the presence of focal perivascular B cell accumulations in lungs of all the knockout mice. These were most pronounced in the NK1(-/-)×TAC1(-/-) mice. These results confirm an important role for TAC1 and NK1(R) in the control of viral infection but reinforce the complex nature of the peptide-receptor interactions.

Hydrogen sulfide and substance P in inflammation

Hydrogen sulfide (H(2)S) plays an important role in cardiovascular, central nervous, and gastrointestinal systems. Being the third gaseous mediator, H(2)S has been shown to act as a vasodilator. In recent times, more and more attention has been paid to the biological functions of H(2)S in inflammation. Substance P is an 11 amino acid neuropeptide that is released from nerve endings in many tissues. Subsequent to its release, substance P binds to neurokinin-1 (NK-1) receptors on the surface of effector cells and, in addition to being a mediator of pain, it plays an important role in many inflammatory states including asthma, immune-complex-mediated lung injury, experimental arthritis, and inflammatory bowel disease. Substance P has been shown to increase microvascular permeability and promote plasma extravasation. Using animal models of inflammation of different etiologies such as acute pancreatitis, sepsis, and burns, studies in our laboratory have recently shown an important role of the pro-inflammatory action of H(2)S and substance P.

Role of hydrogen sulfide in severe burn injury-induced inflammation in mice

Endogenous hydrogen sulfide (H(2)S) is naturally synthesized in many types of mammalian cells from L-cysteine in the reactions catalyzed by cystathionine-β-synthase and cystathionine-γ-lyase (CSE). H(2)S has been demonstrated to play a proinflammatory role in various animal models of hindpaw edema, acute pancreatitis, lipopolysaccharide-induced endotoxemia and cecal ligation, and puncture-induced sepsis. Full-thickness burns that exceed 25% of the total body surface area (TBSA) produce a profound systemic inflammatory reaction characterized by leukocyte activation and plasma leakage in the microvasculature of tissues and organs remote from the wound. The aim of this study was to investigate the effect of local burn injury on induced distant organ endogenous H(2)S release and expression of CSE. Male BALB/c mice were subjected to 30% TBSA full-thickness burn and treated with saline (administered intraperitoneally [i.p.]); DL-propargylglycine (PAG, 50 mg/kg i.p.), which is a CSE inhibitor; or sodium hydrosulfide (NaHS, 10 mg/kg i.p.), which is an H(2)S donor. PAG was administered either 1 h before or 1 h after the burn injury, whereas NaHS was given at the same time as the burn injury. Measurements of liver myeloperoxidase (MPO) activities, liver H(2)S-synthesizing activity, plasma H(2)S level and liver and lung CSE mRNA expression and histological examination of tissues were performed after burn injury. Burn injury significantly increased the plasma H(2)S level and liver H(2)S synthesis 8 h after burn compared with the sham group. Burn injury also resulted in a significant upregulation of CSE mRNA in liver and lung. Prophylactic as well as therapeutic administration of PAG significantly reduced burn-associated systemic inflammation, as evidenced by MPO activity and histological changes in liver and lung. Injection of NaHS significantly aggravated burn-associated systemic inflammation. Therefore, our findings show for the first time the role of H(2)S in contributing to inflammatory damage after burn injury.