Exogenous hydrogen sulfide induces functional inhibition and cell death of cytotoxic lymphocytes subsets

Cystathionine γ-lyase contributes to exacerbation of periodontal destruction in experimental periodontitis under hyperglycemia

BACKGROUND

Diabetes is one of the major inflammatory comorbidities of periodontitis via 2-way interactions. Cystathionine γ-lyase (CTH) is a pivotal endogenous enzyme synthesizing hydrogen sulfide (H2S), and CTH/H2S is crucially implicated in modulating inflammation in various diseases. This study aimed to explore the potential role of CTH in experimental periodontitis under a hyperglycemic condition.

METHODS

CTH-silenced and normal human periodontal ligament cells (hPDLCs) were cultured in a high glucose and Porphyromonas gingivalis lipopolysaccharide (P.g-LPS) condition. The effects of CTH on hPDLCs were assessed by Cell Counting Kit 8 (CCK8), real-time quantitative polymerase chain reaction (RT-qPCR), and enzyme-linked immunosorbent assay (ELISA). The model of experimental periodontitis under hyperglycemia was established on both Cth-/- and wild-type (WT) mice, and the extent of periodontal destruction was assessed by micro-CT, histology, RNA-Seq, Western blot, tartrate-resistant acid phosphatase (TRAP) staining and immunostaining.

RESULTS

CTH mRNA expression increased in hPDLCs in response to increasing concentration of P.g-LPS stimulation in a high glucose medium. With reference to WT mice, Cth-/- mice with experimental periodontitis under hyperglycemia exhibited reduced bone loss, decreased leukocyte infiltration and hindered osteoclast formation, along with reduced expression of proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) in periodontal tissue. RNA-seq-enriched altered NF-κB pathway signaling in healthy murine gingiva with experimental periodontitis mice under hyperglycemia. Accordingly, phosphorylation of p65 (P-p65) was alleviated in CTH-silenced hPDLCs, leading to decreased expression of IL6 and TNF. CTH knockdown inhibited activation of nuclear factor kappa-B (NF-κB) pathway and decreased production of proinflammatory cytokines under high glucose and P.g-LPS treatment.

CONCLUSION

The present findings suggest the potential of CTH as a therapeutic target for tackling periodontitis in diabetic patients.

One-carbon metabolism shapes T cell immunity in cancer

One-carbon metabolism (1CM), comprising folate metabolism and methionine metabolism, serves as an important mechanism for cellular energy provision and the production of vital signaling molecules, including single-carbon moieties. Its regulation is instrumental in sustaining the proliferation of cancer cells and facilitating metastasis; in addition, recent research has shed light on its impact on the efficacy of T cell-mediated immunotherapy. In this review, we consolidate current insights into how 1CM affects T cell activation, differentiation, and functionality. Furthermore, we delve into the strategies for modulating 1CM in both T cells and tumor cells to enhance the efficacy of adoptively transferred T cells, overcome metabolic challenges in the tumor microenvironment (TME), and maximize the benefits of T cell-mediated immunotherapy.

The Influence of Balneotherapy Using Salty Sulfide-Hydrogen Sulfide Water on Selected Markers of the Cardiovascular System: A Prospective Study

Background: The sulfide-hydrogen sulfide brine balneotherapy (HSBB), including a combination of dissolved hydrogen sulfide (H2S) gas, inorganic sulfur ions (S2-), and hydrosulfide ions (HS-), is one of the most important and most effective forms of spa treatment in patients with osteoarticular disorders (OADs). Some cardiovascular diseases (CVDs) are often considered to be contraindications to HSBB since the presence of thiol groups may lead to an increased quantity of reactive oxygen species (ROS), which damage the vascular endothelium, and endothelial dysfunction is considered to be the main cause of atherosclerosis. However, there are a number of literature reports suggesting this theory to be false. H2S is a member of the endogenous gaseous transmitter family and, since it is a relatively recent addition, it has the least well-known biological properties. H2S-NO interactions play an important role in oxidative stress in CVDs. The general objective of this study was to assess the cardiovascular safety of HSBB and analyze the effect of HSBB on selected cardiovascular risk markers. Methods: A total of 100 patients at the age of 76.3 (±7.5) years from the Włókniarz Sanatorium in Busko-Zdrój were initially included in the study. The following parameters were assessed: age, sex, height, body weight, body surface area (BSA), body mass index (BMI), systolic (SBP) and diastolic blood pressure (DBP), heart rate, the diagnosis of OAD that was the indication for balneotherapy, creatinine (CREAT), glomerular filtration rate (GFR), lipid panel, C-reactive protein (CRP), uric acid (UA), and fibrinogen (FIBR) and cardiovascular markers: (cardiac troponin T (cTnT), N-terminal pro-B-type natriuretic peptide (NT-proBNP). Results: A significant decrease in DBP and a trend towards SBP reduction were observed over the course of the study. A significant decrease was observed in CRP levels decreasing from 2.7 (±3.6) mg/L to 2.06 (±1.91) mg/L, whereas FIBR rose significantly from 2.95 (±0.59) g/L to 3.23 (±1.23) g/L. LDL-C levels decreased slightly, statistically significant, from 129.36 (±40.67) mg/dL to 123.74 (±36.14) mg/dL. HSBB did not affect the levels of evaluated cardiovascular biomarkers, namely NT-proBNP (137.41 (±176.52) pg/mL vs. 142.89 (±182.82) pg/mL; p = 0.477) and cTnT (9.64 (±4.13) vs. 9.65 (±3.91) ng/L; p = 0.948). A multiple regression analysis of pre-balneotherapy and post-balneotherapy values showed cTnT levels to be independently correlated only with CREAT levels and GFR values. None of the assessed parameters independently correlated with the NT-proBNP level. Conclusions: HSBB resulted in a statistically significant improvement in a subclinical pro-inflammatory state. HSBB has a beneficial effect in modifying key cardiovascular risk factors by reducing LDL-C levels and DBP values. HSBB has a neutral effect on cardiovascular ischemia/injury. Despite slightly elevated baseline levels of the biochemical marker of HF (NT-proBNP), HSBB causes no further increase in this marker. The use of HSBB in patients with OAD has either a neutral effect or a potentially beneficial effect on the cardiovascular system, which may constitute grounds for further studies to verify the current cardiovascular contraindications for this form of therapy.

Hydrogen Sulfide Signaling in the Tumor Microenvironment: Implications in Cancer Progression and Therapy

Significance: Cancer is a complex and heterotypic structure with a spatial organization that contributes to challenges in therapeutics. Enzymes associated with producing the gasotransmitter hydrogen sulfide (H2S) are differentially expressed in tumors. Indeed, critical and paradoxical roles have been attributed to H2S in cancer-promoting characteristics by targeting both cancer cells and their milieu. This review focuses on the evidence and knowledge gaps of H2S on the tumor redox microenvironment and the pharmacological effects of H2S donors on cancer biology. Recent Advances: Endogenous and pharmacological concentrations of H2S evoke different effects on the same cell type: physiological H2S concentrations have been associated with tumor development and progression. In contrast, pharmacological concentrations have been associated with anticancer effects. Critical Issues: The exact threshold between the promotion and inhibition of tumorigenesis by H2S is largely unknown. The main issues covered in this review include H2S-modulated signaling pathways that are critical for cancer cells, the potential effects of H2S on cellular components of the tumor microenvironment, temporal modulation of H2S in promoting or inhibiting tumor progression (similar to observed for inflammation), and pharmacological agents that modulate H2S and which could play a role in antineoplastic therapy. Future Directions: Given the complexity and heterogeneity of tumor composition, mechanistic studies on context-dependent pharmacological effects of H2S donors for cancer therapy are necessary. These studies must determine the critical signaling pathways and the cellular components involved to allow advances in the rational use of H2S donors as antineoplastic agents. Antioxid. Redox Signal. 40, 250-271.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Microbial metabolites in the pathogenesis of periodontal diseases: a narrative review

The purpose of this narrative review is to highlight the importance of microbial metabolites in the pathogenesis of periodontal diseases. These diseases, involving gingivitis and periodontitis are inflammatory conditions initiated and maintained by the polymicrobial dental plaque/biofilm. Gingivitis is a reversible inflammatory condition while periodontitis involves also irreversible destruction of the periodontal tissues including the alveolar bone. The inflammatory response of the host is a natural reaction to the formation of plaque and the continuous release of metabolic waste products. The microorganisms grow in a nutritious and shielded niche in the periodontal pocket, protected from natural cleaning forces such as saliva. It is a paradox that the consequences of the enhanced inflammatory reaction also enable more slow-growing, fastidious, anaerobic bacteria, with often complex metabolic pathways, to colonize and thrive. Based on complex food chains, nutrient networks and bacterial interactions, a diverse microbial community is formed and established in the gingival pocket. This microbiota is dominated by anaerobic, often motile, Gram-negatives with proteolytic metabolism. Although this alternation in bacterial composition often is considered pathologic, it is a natural development that is promoted by ecological factors and not necessarily a true "dysbiosis". Normal commensals are adapting to the gingival crevice when tooth cleaning procedures are absent. The proteolytic metabolism is highly complex and involves a number of metabolic pathways with production of a cascade of metabolites in an unspecific manner. The metabolites involve short chain fatty acids (SCFAs; formic, acetic, propionic, butyric, and valeric acid), amines (indole, scatole, cadaverine, putrescine, spermine, spermidine) and gases (NH₃, CO, NO, H₂S, H₂). A homeostatic condition is often present between the colonizers and the host response, where continuous metabolic fluctuations are balanced by the inflammatory response. While it is well established that the effect of the dental biofilm on the host response and tissue repair is mediated by microbial metabolites, the mechanisms behind the tissue destruction (loss of clinical attachment and bone) are still poorly understood. Studies addressing the functions of the microbiota, the metabolites, and how they interplay with host tissues and cells, are therefore warranted.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Sp1 S-Sulfhydration Induced by Hydrogen Sulfide Inhibits Inflammation via HDAC6/MyD88/NF-κB Signaling Pathway in Adjuvant-Induced Arthritis

Histone deacetylase 6 (HDAC6) acts as a regulator of the nuclear factor kappa-B (NF-κB) signaling pathway by deacetylating the non-histone protein myeloid differentiation primary response 88 (MyD88) at lysine residues, which is an adapter protein for the Toll-like receptor (TLR) and interleukin (IL)-1β receptor. Over-activated immune responses, induced by infiltrated immune cells, excessively trigger the NF-κB signaling pathway in other effector cells and contribute to the development of rheumatoid arthritis (RA). It has also been reported that HDAC6 can promote the activation of the NF-κB signaling pathway. In the present study, we showed that HDAC6 protein level was increased in the synovium tissues of adjuvant-induced arthritis rats. In addition, hydrogen sulfide (H₂S) donor S-propargyl-cysteine (SPRC) can inhibit HDAC6 expression and alleviate inflammatory response in vivo. In vitro study revealed that HDAC6 overexpression activated the NF-κB signaling pathway by deacetylating MyD88. Meanwhile, sodium hydrosulfide (NaHS) or HDAC6 inhibitor tubastatin A (tubA) suppressed the pro-inflammatory function of HDAC6. Furthermore, the reduced expression of HDAC6 appeared to result from transcriptional inhibition by S-sulfhydrating specificity protein 1 (Sp1), which is a transcription factor of HDAC6. Our results demonstrate that Sp1 can regulate HDAC6 expression, and S-sulfhydration of Sp1 by antioxidant molecular H₂S ameliorates RA progression via the HDAC6/MyD88/NF-κB signaling pathway.

Hydrogen Sulfide Produced by Gut Bacteria May Induce Parkinson's Disease

Several bacterial species can generate hydrogen sulfide (H2S). Study evidence favors the view that the microbiome of the colon harbors increased amounts of H2S producing bacteria in Parkinson's disease. Additionally, H2S can easily penetrate cell membranes and enter the cell interior. In the cells, excessive amounts of H2S can potentially release cytochrome c protein from the mitochondria, increase the iron content of the cytosolic iron pool, and increase the amount of reactive oxygen species. These events can lead to the formation of alpha-synuclein oligomers and fibrils in cells containing the alpha-synuclein protein. In addition, bacterially produced H2S can interfere with the body urate metabolism and affect the blood erythrocytes and lymphocytes. Gut bacteria responsible for increased H2S production, especially the mucus-associated species of the bacterial genera belonging to the Desulfovibrionaceae and Enterobacteriaceae families, are likely play a role in the pathogenesis of Parkinson's disease. Special attention should be devoted to changes not only in the colonic but also in the duodenal microbiome composition with regard to the pathogenesis of Parkinson's disease. Influenza infections may increase the risk of Parkinson's disease by causing the overgrowth of H2S-producing bacteria both in the colon and duodenum.

Buffering Adaptive Immunity by Hydrogen Sulfide

T cell-mediated adaptive immunity is designed to respond to non-self antigens and pathogens through the activation and proliferation of various T cell populations. T helper 1 (Th1), Th2, Th17 and Treg cells finely orchestrate cellular responses through a plethora of paracrine and autocrine stimuli that include cytokines, autacoids, and hormones. Hydrogen sulfide (H₂S) is one of these mediators able to induce/inhibit immunological responses, playing a role in inflammatory and autoimmune diseases, neurological disorders, asthma, acute pancreatitis, and sepsis. Both endogenous and exogenous H₂S modulate numerous important cell signaling pathways. In monocytes, polymorphonuclear, and T cells H₂S impacts on activation, survival, proliferation, polarization, adhesion pathways, and modulates cytokine production and sensitivity to chemokines. Here, we offer a comprehensive review on the role of H₂S as a natural buffer able to maintain over time a functional balance between Th1, Th2, Th17 and Treg immunological responses.

Clinical efficacy of medical hydrology: an umbrella review

The aim of this research was to summarize available scientific evidence on the efficacy of medical hydrology for the management of any health condition. The search was conducted on 26th March 2021, in the following databases: Medline (via PubMed), EMBASE, Web of Science, Cochrane Library, and Google Scholar. All relevant literature reviews investigating the clinical efficacy of interventions characterized by the use of natural mineral waters and muds were included. The quality of studies was assessed with the "AMSTAR 2" tool. After article screening, 49 reviews were included in this work. Overall, retrieved scientific evidence suggests that spa therapy is beneficial for patients affected by some specific musculoskeletal conditions, with improvements potentially lasting up to 9 months. Moreover, balneotherapy can be an integrative support for the management of chronic venous insufficiency and some inflammatory skin diseases like psoriasis. The role of spa therapy in rehabilitation appears relevant as well. More limited, although interesting evidence exists for inhalation and hydropinic therapies. Globally, retrieved evidence suggests that, besides individual wellbeing, medical hydrology can be useful for public health. In particular, higher-quality studies seem to support the integrative use of spa-related interventions for conditions like osteoarthritis, fibromyalgia, low back pain of rheumatic origin, and chronic venous insufficiency. However, the body of evidence has some limitations and further clinical trials should be designed for each relevant application to consolidate and expand acquired knowledge.

Hydrogen Sulfide Inhibits TMPRSS2 in Human Airway Epithelial Cells: Implications for SARS-CoV-2 Infection

The COVID-19 pandemic has now affected around 190 million people worldwide, accounting for more than 4 million confirmed deaths. Besides ongoing global vaccination, finding protective and therapeutic strategies is an urgent clinical need. SARS-CoV-2 mostly infects the host organism via the respiratory system, requiring angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) to enter target cells. Therefore, these surface proteins are considered potential druggable targets. Hydrogen sulfide (H2S) is a gasotransmitter produced by several cell types and is also part of natural compounds, such as sulfurous waters that are often inhaled as low-intensity therapy and prevention in different respiratory conditions. H2S is a potent biological mediator, with anti-oxidant, anti-inflammatory, and, as more recently shown, also anti-viral activities. Considering that respiratory epithelial cells can be directly exposed to H2S by inhalation, here we tested the in vitro effects of H2S-donors on TMPRSS2 and ACE2 expression in human upper and lower airway epithelial cells. We showed that H2S significantly reduces the expression of TMPRSS2 without modifying ACE2 expression both in respiratory cell lines and primary human upper and lower airway epithelial cells. Results suggest that inhalational exposure of respiratory epithelial cells to natural H2S sources may hinder SARS-CoV-2 entry into airway epithelial cells and, consequently, potentially prevent the virus from spreading into the lower respiratory tract and the lung.

New Therapeutic Approaches Using Hydrogen Sulfide Donors in Inflammation and Immune Response

Significance: Inflammation and immune response are associated with many pathological disorders, including rheumatoid arthritis, lupus, heart failure, and cancer(s). In recent times, important roles of hydrogen sulfide (H₂S) have been evidenced by researchers in inflammatory responses, as well as immunomodulatory effects in several disease models. Recent Advances: Numerous biological targets, including cytochrome c oxidase, various kinases, enzymes involved in epigenetic changes, transcription factors, namely nuclear factor kappa B and nuclear factor erythroid 2-related factor 2, and several membrane ion channels, are shown to be sensitive to H₂S and have been widely investigated in various preclinical models. Critical Issues: A complete understanding of the effects of H₂S in inflammatory and immune response is vital in the development of novel H₂S generating therapeutics. In this review, the biological effects and pharmacological properties of H₂S in inflammation and immune response are addressed. The review also covers some of the novel H₂S releasing prodrugs developed in recent years as tools to study this fascinating molecule. Future Directions: H₂S plays important roles in inflammation and immunity-related processes. Future researches are needed to further assess the immunomodulatory effects of H₂S and to assist in the design of more efficient H₂S carrier systems, or drug formulations, for the management of immune-related conditions in humans. Antioxid. Redox Signal. 35, 341-356.

Status of mannose-binding lectin (MBL) and complement system in COVID-19 patients and therapeutic applications of antiviral plant MBLs

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by a virus called "Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)." In the majority of patients, infection with COVID-19 may be asymptomatic or may cause only mild symptoms. However, in some patients, there can also be immunological problems, such as macrophage activation syndrome (CSS) that results in cytokine storm syndrome (CSS) and acute respiratory distress syndrome (ARDS). Comprehension of host-microbe communications is the critical aspect in the advancement of new therapeutics against infectious illnesses. Endogenous animal lectins, a class of proteins, may perceive non-self glycans found on microorganisms. Serum mannose-binding lectin (sMBL), as a part of the innate immune framework, recognizes a wide range of microbial microorganisms and activates complement cascade via an antibody-independent pathway. Although the molecular basis for the intensity of SARS-CoV-2 infection is not generally understood, scientific literature indicates that COVID-19 is correlated with unregulated activation of the complement in terms of disease severity. Disseminated intravascular coagulation (DIC), inflammation, and immune paralysis contribute to unregulated complement activation. Pre-existing genetic defects in MBL and their association with complement play a major role in immune response dysregulation caused by SARS-CoV-2. In order to generate anti-complement-based therapies in Covid-19, an understanding of sMBL in immune response to SARS-CoV-2 and complement is therefore essential. This review highlights the role of endogenous sMBL and complement activation during SARS-CoV-2 infection and their therapeutic management by various agents, mainly plant lectins, since antiviral mannose-binding plant lectins (pMBLs) offer potential applications in the prevention and control of viral infections.

Morphological and Immunohistochemical Features of the Heart under the Effect of Hydrogen Sulfide Balneotherapy

The effects of hydrogen sulfide baths and sulfide-silt mud applications on the abdominal wall were studied in outbred white rats. Heart preparations stained with hematoxylin and eosin were analyzed and the mean numbers of cells expressing Ki-67, Nkx-2.5, and mesenchymal stem cell markers were determined. Hydrogen sulfide balneotherapy promoted the development of blood capillaries in rat hearts and an increased the expression of CD34. A decrease in the regenerative potential of the myocardium was found due to a decrease in the content of proliferating cells and cells expressing CD73, CD90, and CD105, and also due to the absence of cells stained for cardiomyogenic differentiation marker Nkx-2.5.

From in vitro research to real life studies: an extensive narrative review of the effects of balneotherapy on human immune response

Purpose

The biologic mechanisms by which balneotherapy (BT) alleviates symptoms of different diseases are still poorly understood. Recently, preclinical models and clinical trials have been developed to study the effects of BT on the immune system. This review summarizes the currently available evidence regarding the effects of spa therapy on the immune response, to confirm the role of BT in the enhancement of immune system and open interesting research fields.

Methods

PubMed and Google Scholar were searched from 1997 up to June 2020, with search criteria including terms related to BT and immune system. We selected only in vitro research, randomized controlled trials (RCTs) or clinical trials.

Results

In vitro studies on human and animal samples have demonstrated that thermal waters exert anti-inflammatory and immunomodulatory effects. In particular, H₂S donors seem to counteract the inflammatory processes in psoriatic lesions, arthritic fibroblast-like synoviocytes and chondrocytes, and regulate important factors implicated in osteoarthritis pathogenesis and progression. RCTs and clinical trials revealed, after BT, a reduction in circulating levels of pro-inflammatory molecules, such as TNF-α, IL-1β, and C-reactive protein, and an increase in anti-inflammatory molecules such as the IGF-1 growth factor especially in musculoskeletal diseases.

Conclusion

Further preclinical studies and RCTs could help to exploit BT in real life for preventive and therapeutic treatments.

The Scientific Basis for Occupational Exposure Limits for Hydrogen Sulphide-A Critical Commentary

OBJECTIVES

Occupational exposure limits for hydrogen sulphide (H₂S) vary considerably; three expert group reports, published from 2006 to 2010, each recommend different limits. Some jurisdictions are considering substantial reductions.

METHODS

This review assesses the scientific evidence used in these recommendations and presents a new systematic review of human studies from 2006-20, identifying 33 studies.

RESULTS

The three major reports all give most weight to two sets of studies: of physiological effects in human volunteers, and of effects in the nasal passages of rats and mice. The human studies were done in one laboratory over 20 years ago and give inconsistent results. The breathing style and nasal anatomy of rats and mice would make them more sensitive than humans to inhaled agents. Each expert group applied different uncertainly factors. From these reports and the further literature review, no clear evidence of detrimental health effects from chronic occupational exposures specific to H₂S was found. Detailed studies of individuals in communities with natural sources in New Zealand have shown no detrimental effects. Studies in Iceland and Italy show some associations; these and various other small studies need verification.

CONCLUSIONS

The scientific justification for lowering occupational exposure limits is very limited. There is no clear evidence, based on currently available studies, that lower limits will protect the health of workers further than will the current exposure limits used in most countries. Further review and assessment of relevant evidence is justified before exposure limits are set.

Effects of gut microbiota on atherosclerosis through hydrogen sulfide

Cardiovascular diseases are the leading cause of death and morbidity worldwide. Atherosclerotic cardiovascular disease (ASCVD) is affected by both environmental and genetic factors. Microenvironmental disorders of the human gut flora are associated with a variety of health problems, not only gastrointestinal diseases, such as inflammatory bowel disease, but also extralintestinal organs. Hydrogen sulfide (H₂S) is the third gas signaling molecule other than nitric oxide and carbon monoxide. In the cardiovascular system, H₂S plays important roles in the regulation of blood pressure, angiogenesis, smooth muscle cell proliferation and apoptosis, anti-oxidative stress, cardiac functions. This review is aiming to explore the potential role of gut microbiota in the development of atherosclerosis through hydrogen sulfide production as a novel therapeutic direction for atherosclerosis.

Hydrogen Sulfide: a Novel Immunoinflammatory Regulator in Rheumatoid Arthritis

Hydrogen sulfide (H₂S), an endogenous, gaseous, signaling transmitter, has been shown to have vasodilative, anti-oxidative, anti-inflammatory, and cytoprotective activities. Increasing evidence also indicates that H₂S can suppress the production of inflammatory mediators by immune cells, for example, T cells and macrophages. Inflammation is closely related to an immune response in several diseases such as rheumatoid arthritis (RA), multiple sclerosis (MS), systemic lupus erythematosus (SLE), and cancer. Considering these biological effects of H₂S, a potential role in the treatment of immune-related RA is being exploited. In the present review, we will provide an overview of the therapeutic potential of H₂S in RA treatment.

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.

Protocols and self-checking plans for the safety of post-COVID-19 balneotherapy

During the COVID-19 pandemics, balneotherapic establishments were closed in Italy like in the rest of Europe. The Italian Foundation for Research in balneotherapy (FoRST) was asked to prepare a safety protocol to be proposed to the National Health Authorities to allow the establishments to restart their activity when possible, under safe conditions (the so-called Phase-2). The group of experts proposed the following hygienic and sanitary protocols of risk management for the initial reopening of the balneology settings in Italy. The plan aims to define the operating procedures to be implemented at the balneology establishments for the beginning of Phase-2 and to keep them constantly updated in the different periods that will characterize Phase-2 in relation to the trends of the disease. To this end the procedures, defined on the basis of the scientific state-of-the-art available today, will be updated and revised from time to time whenever further scientific evidence and directives from the Health Authorities make it necessary and/or useful.

A comprehensive analysis to understand the mechanism of action of balneotherapy: why, how, and where they can be used? Evidence from in vitro studies performed on human and animal samples

Balneotherapy (BT) is one of the most commonly used complementary therapies for many pathological conditions. Its beneficial effects are related to physical and chemical factors, but the exact mechanism of action is not fully understood. Recently, there has been an increased interest in the use of preclinical models to investigate the influence of BT on inflammation, immunity, and cartilage and bone metabolism. The objective of this comprehensive analysis was to summarize the current knowledge about the in vitro studies in BT and to revise the obtained results on the biological effects of mineral waters. Special attention has been paid to the main rheumatological and dermatological conditions, and to the regulation of the immune response. The objective of this review was to summarize the in vitro studies, on human and animal samples, investigating the biological effects of BT. In particular, we analyzed the properties of a thermal water, as a whole, of an inorganic molecule, such as hydrogen sulfide in different cell cultures (keratinocytes, synoviocytes, chondrocytes, and peripheral blood cells), or of the organic component. The results corroborated the scientific value of in vitro studies in demonstrating the anti-inflammatory, antioxidant, chondroprotective, and immunosuppressive role of BT at the cellular level. However, the validity of the cell culture model is limited by several sources of bias, as the differences in experimental procedures, the high heterogeneity among the available researches, and the difficulties in considering all the chemical and physical factors of BT. We would like to stimulate the scientific community to standardize the experimental procedures and enhance in vitro research in the field of BT.

NK cells: A double edge sword against SARS-CoV-2

Natural killer (NK) cells are pivotal effectors of the innate immunity protecting an individual from microbes. They are the first line of defense against invading viruses, given their substantial ability to directly target infected cells without the need for specific antigen presentation. By establishing cellular networks with a variety of cell types such as dendritic cells, NK cells can also amplify and modulate antiviral adaptive immune responses. In this review, we will examine the role of NK cells in SARS-COV2 infections causing the ongoing COVID19 pandemic, keeping in mind the controversial role of NK cells specifically in viral respiratory infections and in inflammatory-driven lung damage. We discuss lessons learnt from previous coronavirus outbreaks in humans (caused by SARS-CoV-1 and MERS-COV).

Hydrogen sulfide biosynthesis is impaired in the osteoarthritic joint

Osteoarthritis (OA) is the most common form of arthritis and it is a leading cause of disability in the elderly. Its complete etiology is not known although there are several metabolic, genetic, epigenetic, and local contributing factors involved. At the moment, there is no cure for this pathology and treatment alternatives to retard or stop its progression are intensively being sought. Hydrogen sulfide (H₂S) is a small gaseous molecule and is present in sulfurous mineral waters as its active component. Data from recent clinical trials shows that balneotherapy (immersion in mineral and/or thermal waters from natural springs) in sulfurous waters can improve OA symptoms, in particular, pain and function. Yet, the underlying mechanisms are poorly known. Hydrogen sulfide is also considered, with NO and CO, an endogenous signaling gasotransmitter. It is synthesized endogenously with the help of three enzymes, cystathionine gamma-lyase (CTH), cystathionine beta-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MPST). Here, the expression of these three enzymes was demonstrated by quantitative real-time polymerase chain reaction (qRT-PCR) and their protein abundance [by immunohistochemistry and Western blot (WB)] in human articular cartilage. No significant differences were found in CBS or CTH expression or abundance, but mRNA and protein levels of 3-MPST were significantly reduced in cartilage form OA donors. Also, the biosynthesis of H₂S from OA cartilage, measured with a specific microelectrode, was significantly lower than in OA-free tissue. Yet, no differences were found in H₂S concentration in serum from OA patients and OA-free donors. The current results suggest that reduced levels of the mitochondrial enzyme 3-MPST in OA cartilage might be, at least in part, responsible for a reduction in H₂S biosynthesis in this tissue and that impaired H₂S biosynthesis in the joint might be a contributing factor to OA. This could contribute to explain why exogenous supplementation of H₂S, for instance with sulfurous thermal water, has positive effects in OA patients.

Hydrogen sulfide upregulates miR-16-5p targeting PiK3R1 and RAF1 to inhibit neutrophil extracellular trap formation in chickens

Hydrogen sulfide (H₂S) is a toxic air pollutant that causes immune damage. Recent studies have found that neutrophil extracellular trap (NET) formation is one way in which neutrophils exert immune functions. In addition, the formation of NETs is also related to thrombosis and autoimmune diseases. Recent studies have shown that miRNAs are involved in the regulation of a variety of pathophysiological processes. Here, we investigated the role of H₂S in regulating the formation of NETs by affecting miR-16-5p. Our study established an in vitro H₂S exposure model for neutrophils using phorbol-myristate-acetate (PMA) to induce NET formation. We observed the morphological changes of cells with scanning electron microscopy and fluorescence microscopy. Then, the content of extracellular DNA and the expression of MPO and NE in each group were detected. The results showed that H₂S inhibited the formation of NETs. The expression of miR-16-5p and its target genes PiK3R1 and RAF1 was then measured by qRT-PCR. H₂S upregulated miR-16-5p and inhibited expression of the target genes PiK3R1 and RAF1, and it subsequently inhibited the Pi3K/AKT and ERK pathways and decreased respiratory burst levels. Furthermore, H₂S attenuated inositol 1,4,5-trisphosphate receptor (IP3R)-mediated endoplasmic reticulum calcium outflow as well as autophagy caused by PMA. This study enriches H₂S immunotoxicity research and provides a possible solution for the treatment of NET-related diseases.

Hydrogen sulfide exposure induces apoptosis and necroptosis through lncRNA3037/miR-15a/BCL2-A20 signaling in broiler trachea

Hydrogen sulfide (H₂S) is an air pollutant, has toxic effects on respiratory tract. However, the underlying mechanisms of H₂S induced respiratory toxicity and the roles of long non-coding RNAs (lncRNA) and microRNA (miRNA) in this process remain poorly understood. To clear this, we investigated the change of tracheal tissue ultrastructure and the expression profiles of lncRNAs and miRNAs of chicken trachea exposed to H₂S for 42 days. Results showed that H₂S exposure triggered apoptosis, necroptosis, and differential expression of 16 lncRNAs and 18 miRNAs in broiler tracheas. The results of LMH cells stimulated by NaHS in vitro also showed the occurrence of apoptosis and necroptosis. LncRNA3037 is down-regulated and miR-15a is up-regulated in tracheal tissue and LMH cells under H₂S exposure. Bioinformatics analysis and dual luciferase reporter system showed lncRNA3037 bound directly to miR-15a and negatively regulates each other. A20 and BCL2 are the target genes of miR-15a and negatively regulated by it. Overexpression of miR-15a caused apoptosis and necroptosis and its inhibition partially reversed apoptosis and necroptosis of LMH cells caused by NaHS stimulation and lncRNA3037 knockdown. Taken together, we concluded that H₂S exposure mediates apoptosis and necroptosis through lncRNA3037/miR-15/A20-BCL2. These results provide new insights for unveiling the biological effects of H₂S in vivo and in vitro.

Sulphurous thermal water inhalation impacts respiratory metabolic parameters in heavy smokers

Sulphurous thermal water inhalations have been traditionally used in the treatment of airway diseases. In vivo and in vitro studies reported that they ameliorate mucus rheology, mucociliary clearance and reduce inflammation. Cigarette smoking induces an inflammatory damage, with consequent remodeling of respiratory airways, which in turn affect pulmonary functions. Despite the anti-inflammatory effects of H₂S are clinically documented in several airway inflammatory diseases, data on the effects of sulphurous thermal water treatment on pulmonary function and biomarkers of airways inflammation in smokers are still scant. Therefore, we investigated whether a conventional cycle of sulphurous thermal water inhalation produced changes in markers of respiratory inflammation and function. A cohort of 504 heavy current and former smokers underwent 10-day cycles of sulphurous thermal water inhalation. Pulmonary function and metabolic analyses on exhaled breath condensate were then performed at day 0 and after the 10-day treatment. Spirometric data did not change after spa therapy, while exhaled breath condensate analysis revealed that a single 10-day cycle of sulphurous water inhalation was sufficient to induce a statistically significant increase of citrulline levels along with a decrease in ornithine levels, thus shifting arginine metabolism towards a reduced nitric oxide production, i.e. an anti-inflammatory profile. Overall, sulphurous thermal water inhalation impacts on arginine catatabolic intermediates of airways cells, shifting their metabolic balance towards a reduction of the inflammatory activity, with potential benefits for smokers.

Biological Effects of Thermal Water-Associated Hydrogen Sulfide on Human Airways and Associated Immune Cells: Implications for Respiratory Diseases

Natural mineral (thermal) waters have been used for centuries as treatment for various diseases. However, the scientific background of such therapeutic action is mostly empiric and based on knowledge acquired over time. Among the various types of natural mineral waters, sulfurous thermal waters (STWs) are the most common type in the center of Portugal. STWs are characterized by high pH, poor mineralization, and the presence of several ions and salts, such as bicarbonate, sodium, fluoride, silica, and carbonate. Furthermore, these waters are indicated as a good option for the treatment of various illnesses, namely respiratory diseases (e.g., allergic rhinitis, asthma, and chronic obstructive pulmonary disease). From the sulfide species present in these waters, hydrogen sulfide (H₂S) stands out due to its abundance. In healthy conditions, H₂S-related enzymes (e.g., cystathionine β-synthase and cystathionine γ-lyase) are expressed in human lungs, where they have mucolytic, antioxidant, anti-inflammatory, and antibacterial roles, thus contributing to airway epithelium homeostasis. These roles occur mainly through S-sulfhydration, a post-translational modification through which H₂S is able to change the activity of several targets, such as ion channels, second messengers, proteins, among others. However, in respiratory diseases the metabolism of H₂S is altered, which seems to contribute somehow to the respiratory deterioration. Moreover, H₂S has been regarded as a good biomarker of airway dysfunction and severity, and can be measured in serum, sputum, and exhaled air. Hence, in this review we will recapitulate the effects of STWs on lung epithelial-immune crosstalk through the action of its main component, H₂S.

Inhibition of endogenous hydrogen sulfide production improves viral elimination in CVB3-infected myocardium in mice

BACKGROUND

To find whether administration of hydrogen sulfide has interaction with coxsackie virus B3 (CVB3) replication and spread.

METHODS

Six-week-old inbred male Balb/c mice were injected intraperitoneally with CVB3. Mice were randomized to four groups (n = 10 for each group): group N (sham infection + vehicle), group C (virus + vehicle), group P (virus + DL-proparglygylcine (PAG)), and group S (virus + sodium hydrogen sulfide (NaHS)). PAG and NaHS were administered intraperitoneally daily and mice were killed on day 4 after viral inoculation. Serum specimens were obtained to assay tumor necrosis factor-α (TNFα) level, and heart specimens were harvested for histological examination, 50% tissue culture infection dose (TCID50) assay, reverse transcription-polymerase chain reaction and Western blot analysis.

RESULTS

The ratio of heart-weight to body-weight and inflammatory scores showed no significant difference between infected groups. The circulatory and local concentrations of TNFα, nitric oxide synthase 2 messenger RNA, and protein were higher in group P, and were lower in group S compared to those in group C. Mice treated with PAG and NaHS had significantly lower and higher viral stocks than those inoculated with CVB3 only, respectively.

CONCLUSION

Inhibition of endogenous hydrogen sulfide production contributed to viral clearance in acute viremia of CVB3-induced myocarditis.

A case of vitiligo cured with cucumber and sulfur

This study investigates a 42-year-old man who used sulfur powder adhered to cucumber slices to successfully self-treat a vitiligo condition. The treatment has resulted in no recurrence of the disease for 21 years. We analyzed the mechanism of this folk prescription for vitiligo, concluding that the success of the self-treatment may be mainly associated with hydrogen sulfide (H₂ S). The antibacterial activity of pentathionic acid (H₂ S₅ O₆ ) and the antioxidant activity of cucumber might also play a role in the treatment.

Contribution of sulfate-reducing bacteria to homeostasis disruption during intestinal inflammation

Alteration in microbial populations and metabolism are key events associated with disruption of intestinal homeostasis and immune tolerance during intestinal inflammation. A substantial imbalance in bacterial populations in the intestine and their relationships with the host have been observed in patients with inflammatory bowel disease (IBD), believed to be part of an intricate mechanism of triggering and progression of intestinal inflammation. Because elevated numbers of sulfate-reducing bacteria (SRB) have been found in the intestines of patients with IBD, the study of their interaction with intestinal cells and their potential involvement in IBD has been the focus of investigation to better understand the intestinal pathology during IBD, as well as to find new ways to treat the disease. SRB not only directly interact with intestinal epithelial cells during intestinal inflammation but may also promote intestinal damage through generation of hydrogen sulfide at high levels. Herein we review the literature to discuss the various aspects of SRB interaction with host intestinal tissue, focusing on their interaction with intestinal epithelial and immune cells during intestinal inflammation.

Gasotransmitters and the immune system: Mode of action and novel therapeutic targets

Gasotransmitters are a group of gaseous molecules, with pleiotropic biological functions. These molecules include nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). Abnormal production and metabolism of these molecules have been observed in several pathological conditions. The understanding of the role of gasotransmitters in the immune system has grown significantly in the past years, and independent studies have shed light on the effect of exogenous and endogenous gasotransmitters on immune responses. Moreover, encouraging results come from the efficacy of NO-, CO- and H₂S -donors in preclinical animal models of autoimmune, acute and chronic inflammatory diseases. To date, data on the influence of gasotransmitters in immunity and immunopathology are often scattered and partial, and the scarcity of clinical trials using NO-, CO- and H₂S -donors, reveals that more effort is warranted. This review focuses on the role of gasotransmitters in the immune system and covers the evidences on the possible use of gasotransmitters for the treatment of inflammatory conditions.

Hydrogen Sulfide Attenuates Hypertensive Inflammation via Regulating Connexin Expression in Spontaneously Hypertensive Rats

BACKGROUND Hydrogen sulfide (H2S) has anti-inflammatory and anti-hypertensive effects, and connexins (Cxs) are involved in regulation of immune homeostasis. In this study, we explored whether exogenous H2S prevents hypertensive inflammation by regulating Cxs expression of T lymphocytes in spontaneously hypertensive rats (SHR). MATERIAL AND METHODS We treated SHR with sodium hydrosulfide (NaHS) for 9 weeks. Vehicle-treated Wistar-Kyoto rats (WKYs) were used as a control. The arterial pressure was monitored by the tail-cuff method, and vascular function in basilar arteries was examined by pressure myography. Hematoxylin and eosin staining was used to show vascular remodeling and renal injury. The percentage of T cell subtypes in peripheral blood, surface expressions of Cx40/Cx43 on T cell subtypes, and serum cytokines level were determined by flow cytometry or ELISA. Expression of Cx40/Cx43 proteins in peripheral blood lymphocytes was analyzed by Western blot. RESULTS Chronic NaHS treatment significantly attenuated blood pressure elevation, and inhibited inflammation of target organs, vascular remodeling, and renal injury in SHR. Exogenous NaHS also improved vascular function by attenuating KCl-stimulated vasoconstrictor response in basilar arteries of SHR. In addition, chronic NaHS administration significantly suppressed inflammation of peripheral blood in SHR, as evidenced by the decreased serum levels of IL-2, IL-6, and CD4/CD8 ratio and the increased IL-10 level and percentage of regulatory T cells. NaHS treatment decreased hypertension-induced Cx40/Cx43 expressions in T lymphocytes from SHR. CONCLUSIONS Our data demonstrate that H2S reduces hypertensive inflammation, at least partly due to regulation of T cell subsets balance by Cx40/Cx43 expressions inhibition.

Hydrogen sulfide exposure induces NLRP3 inflammasome-dependent IL-1β and IL-18 secretion in human mononuclear leukocytes in vitro

The aim was to investigate if hydrogen sulfide (H₂S) induces the formation of the NLRP3 inflammasome and subsequent IL‐1β and IL‐18 secretion in human peripheral blood mononuclear cells (PBMCs) and in the human monocyte cell line THP1. Bacterial production of H₂S has been suggested to participate in the inflammatory host response in periodontitis pathogenesis. H₂S is a toxic gas with pro‐inflammatory properties. It is produced by bacterial degradation of sulfur‐containing amino acids, for example, cysteine. We hypothesize that H₂S affects the inflammatory host response by inducing formation of the NLRP3 inflammasome and thereby causes the secretion of IL‐1ß and IL‐18. PBMCs from eight healthy blood donors, the human monocyte cell line THP1 Null, and two variants of the THP1 cell line unable to form the NLRP3 inflammasome were cultured in the presence or absence of 1 mM sodium hydrosulfide (NaHS) in 24‐well plates at 37°C for 24 hr. Supernatants were collected and the IL‐1β and IL‐18 concentrations were measured with DuoSet ELISA Development kit. PBMCs exposed to NaHS produced more IL‐1ß and IL‐18 than unexposed control cells (p = .023 and p = .008, respectively). An increase of extracellular potassium ions (K⁺) inhibited the secretion of IL‐1ß and IL‐18 (p = .008). Further, NaHS triggered the secretion of IL‐1ß and IL‐18 in human THP1‐Null monocytes (p = .0006 and p = .002, respectively), while the NaHS‐dependent secretion was reduced in the monocyte cell lines unable to form the NLRP3 inflammasome. Hence, the results suggest that NaHS induces the formation of the NLRP3 inflammasome and thus the secretion of IL‐1ß and IL‐18. Enhanced NLRP3 inflammasome‐dependent secretion of IL‐1β and IL‐18 in human mononuclear leukocytes exposed to NaHS in vitro is reported. This may be a mode for H₂S to contribute to the inflammatory host response and pathogenesis of periodontal disease.

Anti-inflammatory effects of H2S during acute bacterial infection: a review

Hydrogen sulfide (H₂S), previously only considered a toxic environmental air pollutant, is now increasingly recognized as an important signaling molecule able to modulate several cellular pathways in many human tissues. As demonstrated in recent studies, H₂S is produced endogenously in response to different cellular stimuli and plays different roles in controlling a number of physiological responses. The precise role of H₂S in inflammation is still largely unknown. In particular, the role of H₂S in the regulation of the inflammatory response in acute and chronic infections is being actively investigated because of its potential therapeutic use. To study the effect of H₂S as an anti-inflammatory mediator during bacterial infections, we developed an ex vivo model of primary cells and cell lines infected with Mycoplasma. Our data demonstrate a dichotomic effect of H₂S on the NF-kB and Nrf-2 molecular pathways, which were inhibited and stimulated, respectively.

Sulphurous Mineral Waters: New Applications for Health

Sulphurous mineral waters have been traditionally used in medical hydrology as treatment for skin, respiratory, and musculoskeletal disorders. However, driven by recent intense research efforts, topical treatments are starting to show benefits for pulmonary hypertension, arterial hypertension, atherosclerosis, ischemia-reperfusion injury, heart failure, peptic ulcer, and acute and chronic inflammatory diseases. The beneficial effects of sulphurous mineral waters, sulphurous mud, or peloids made from sulphurous mineral water have been attributed to the presence of sulphur mainly in the form of hydrogen sulphide. This form is largely available in conditions of low pH when oxygen concentrations are also low. In the organism, small amounts of hydrogen sulphide are produced by some cells where they have numerous biological signalling functions. While high levels of hydrogen sulphide are extremely toxic, enzymes in the body are capable of detoxifying it by oxidation to harmless sulphate. Hence, low levels of hydrogen sulphide may be tolerated indefinitely. In this paper, we review the chemistry and actions of hydrogen sulphide in sulphurous mineral waters and its natural role in body physiology. This is followed by an update of available data on the impacts of exogenous hydrogen sulphide on the skin and internal cells and organs including new therapeutic possibilities of sulphurous mineral waters and their peloids.

Hydrogen Sulfide Regulates Homeostasis of Mesenchymal Stem Cells and Regulatory T Cells

Hydrogen sulfide (H₂S) has long been known as a toxic gas. However, recently accumulated evidence suggests that H₂S contributes to a variety of physiologic and pathologic processes. Endogenous H₂S production is regulated by multiple enzymes that are differentially expressed in the cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems. Alteration of H₂S metabolism may affect multiple signaling pathways and tissue homeostasis. The growing number of diverse targets for which H₂S serves as a gasotransmitter has been extensively reviewed elsewhere. In this review, the authors discuss current emerging evidence that H₂S regulates mesenchymal stem cell and T-cell functions.

Hydrogen Sulfide Is a Novel Regulator of Bone Formation Implicated in the Bone Loss Induced by Estrogen Deficiency

Hydrogen sulfide (H2 S) is a gasotransmitter known to regulate bone formation and bone mass in unperturbed mice. However, it is presently unknown whether H2 S plays a role in pathologic bone loss. Here we show that ovariectomy (ovx), a model of postmenopausal bone loss, decreases serum H2 S levels and the bone marrow (BM) levels of two key H2 S-generating enzymes, cystathione β-synthase (CBS) and cystathione γ-lyase (CSE). Treatment with the H2 S-donor GYY4137 (GYY) normalizes serum H2 S in ovx mice, increases bone formation, and completely prevents the loss of trabecular bone induced by ovx. Mechanistic studies revealed that GYY increases murine osteoblastogenesis by activating Wnt signaling through increased production of the Wnt ligands Wnt16, Wnt2b, Wnt6, and Wnt10b in the BM. Moreover, in vitro treatment with 17β-estradiol upregulates the expression of CBS and CSE in human BM stromal cells (hSCs), whereas an H2 S-releasing drug induces osteogenic differentiation of hSCs. In summary, regulation of H2 S levels is a novel mechanism by which estrogen stimulates osteoblastogenesis and bone formation in mice and human cells. Blunted production of H2 S contributes to ovx-induced bone loss in mice by limiting the compensatory increase in bone formation elicited by ovx. Restoration of H2 S levels is a potential novel therapeutic approach for postmenopausal osteoporosis. © 2015 American Society for Bone and Mineral Research.

CD47-dependent regulation of H₂S biosynthesis and signaling in T cells

Pharmacological concentrations of H2S donors inhibit some T cell functions by inhibiting mitochondrial function, but evidence is also emerging that H2S at physiological concentrations produced via chemical sources and endogenously is a positive physiological mediator of T cell function. Expression of the H2S biosynthetic enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) is induced in response to T cell receptor signaling. Inhibiting the induction of these enzymes limits T cell activation and proliferation, which can be overcome by exposure to exogenous H2S at submicromolar concentrations. Exogenous H2S at physiological concentrations increases the ability of T cells to form an immunological synapse by altering cytoskeletal actin dynamics and increasing the reorientation of the microtubule-organizing center. Downstream, H2S enhances T cell receptor-dependent induction of CD69, CD25, and Interleukin-2 (IL-2) gene expression. The T cell stimulatory activity of H2S is enhanced under hypoxic conditions that limit its oxidative metabolism by mitochondrial and nonenzymatic processes. Studies of the receptor CD47 have revealed the first endogenous inhibitory signaling pathway that regulates H2S signaling in T cells. Binding of the secreted protein thrombospondin-1 to CD47 elicits signals that block the stimulatory activity of exogenous H2S on T cell activation and limit the induction of CSE and CBS gene expression. CD47 signaling thereby inhibits T cell receptor-mediated T cell activation.

Hydrogen sulfide treatment ameliorates long-term renal dysfunction resulting from prolonged warm renal ischemia-reperfusion injury

INTRODUCTION

The incidence of renal cell carcinoma (RCC) continues to rise concurrently with the increased prevalence of end-stage renal disease worldwide. Treatment for small renal masses continues to be partial nephrectomy mostly involving the clamping of renal blood vessels. Although necessary, this technique results in warm renal ischemia and reperfusion injury (IRI) to the afflicted kidney. We have recently demonstrated that hydrogen sulfide (H2S), a novel endogenous gaseous molecule, protects against prolonged cold and short-term warm renal IRI. In the current study, we examined whether exogenous H2S has long-term protective effects against warm renal IRI associated with renal surgical procedures.

METHODS

Uni-nephrectomized Lewis rats underwent 1 hour of warm ischemia induced by clamping of the renal pelvis. Animals underwent either intraperitoneal treatment with phosphate buffered saline (PBS; IRI group) or PBS supplemented with 150 μM NaHS (H2S group), and were compared against Sham-operated rats.

RESULTS

H2S treatment improved long-term renal function as serum creatinine at day 7 was significantly decreased in the H2S group compared to IRI animals (p < 0.05). H2S treatment decreased the expression of pro-inflammatory markers TLR-4, TNF-α, IFNγ, IL-2 and ICAM-1, increased the expression of pro-survival molecule Bcl-2 and decreased the expression of pro-apoptotic marker BID at postoperative day 1. H2S-treated kidneys also showed a significant decrease (p < 0.05) in infiltration of macrophages at day 7 post-IRI compared to no treatment.

CONCLUSION

H2S treatment improved long-term renal function and decreased long-term inflammation associated with warm IRI, and may offer a novel therapeutic approach to preventing warm IRI-induced renal injury associated with renal surgical procedures.

Sulfur compounds block MCP-1 production by Mycoplasma fermentans-infected macrophages through NF-κB inhibition

Background and aims

Hydrogen sulfide (H₂S), together with nitric oxide (NO) and carbon monoxide (CO), belongs to a family of endogenous signaling mediators termed “gasotransmitters”. Recent studies suggest that H₂S modulates many cellular processes and it has been recognized to play a central role in inflammation, in the cardiovascular and nervous systems. By infecting monocytes/macrophages with Mycoplasma fermentans (M.F.), a well-known pro-inflammatory agent, we evaluated the effects of H₂S.

Methods

M.F.-infected cells were analyzed by ELISA and real time RT-PCR to detect the M.F. effects on MCP-1 and on MMP-12 expression. The role of two different H₂S donors (NaHS and GYY4137) on MF-infected cells was determined by treating infected cells with H₂S and then testing the culture supernatants for MCP-1 and on MMP-12 production by ELISA assay. In order to identify the pathway/s mediating H₂S- anti-inflammatory activity, cells were also treated with specific pharmaceutical inhibitors. Cytoplasmic and nuclear accumulation of NF-κB heterodimers was analyzed.

Results

We show that H₂S was able to reduce the production of pro-inflammatory cytokine MCP-1, that was induced in monocytes/macrophages during M.F. infection. Moreover, MCP-1 was induced by M.F. through Toll-like receptor (TLR)-mediated nuclear factor-κB (NF-κB) activation, as demonstrated by the fact that TLR inhibitors TIRAP and MyD88 and NF-κB inhibitor IKK were able to block the cytokine production. In contrast H₂S treatment of M.F. infected macrophages reduced nuclear accumulation of NF-κB heterodimer p65/p52.

Conclusions

Our data demonstrate that under the present conditions H₂S is effective in reducing Mycoplasma-induced inflammation by targeting the NF-κB pathway. This supports further studies for possible clinical applications.

Sulphurous thermal water increases the release of the anti-inflammatory cytokine IL-10 and modulates antioxidant enzyme activity

The beneficial effects of hot springs have been known for centuries and treatments with sulphurous thermal waters are recommended in a number of chronic pathologies as well as acute recurrent infections. However, the positive effects of the therapy are often evaluated in terms of subjective sense of wellbeing and symptomatic clinical improvements. Here, the effects of an S-based compound (NaSH) and of a specific sulphurous thermal water characterized by additional ions such as sodium chloride, bromine and iodine (STW) were investigated in terms of cytokine release and anti-oxidant enzyme activity in primary human monocytes and in saliva from 50 airway disease patients subjected to thermal treatments. In vitro, NaSH efficiently blocked the induction of pro-inflammatory cytokines and counterbalanced the formation of ROS. Despite STW not recapitulating these results, possibly due to the low concentration of S-based compounds reached at the minimum non-toxic dilution, we found that it enhanced the release of IL-10, a potent anti-inflammatory cytokine. Notably, higher levels of IL-10 were also observed in patients' saliva following STW treatment and this increase correlated positively with salivary catalase activity (r2 = 0.19, *p less than 0.01). To our knowledge, these results represent the first evidence suggesting that S-based compounds and STW may prove useful in facing chronic inflammatory and age-related illness due to combined anti-inflammatory and anti-oxidant properties.

Cardioprotection of H2S by downregulating iNOS and upregulating HO-1 expression in mice with CVB3-induced myocarditis

AIMS

To explore the effects and potential mechanisms of hydrogen sulfide (H2S) in CVB3-induced mice with myocarditis.

MAIN METHODS

A total of 75 six-week-old inbred male Balb/c mice were divided randomly into four groups (N, C, P and S). Group N was the negative control. The others were inoculated intraperitoneally (i.p.) with CVB3. Subsequently, groups P and S were injected i.p. once a day with DL-Proparglygylcine (PAG) and NaHS respectively. Group C was the positive control. Inducible nitric oxide synthase (iNOS) and heme oxygenase-1(HO-1) expression on cardiac tissues were evaluated by histopathological examination, immunohistochemistry, RT-PCR and Western blot.

KEY FINDINGS

The heart-weight to body-weight (HW/BW) ratio, the histologic scores and the iNOS mRNA and protein expression levels were higher, and the HO-1 mRNA and protein expression levels were lower in mice treated with PAG than those mice solely inoculated with CVB3. Mice in group S had a significant decreased in the HW/BW ratio, the histologic scores and the iNOS mRNA and protein expression levels, and had a significant increased in the HO-1 mRNA and protein expression levels compared to the mice in group C. H2S can attenuate inflammatory cell infiltration, alleviate cardiac edema, and limit myocardial lesions.

SIGNIFICANCE

Our data support that H2S can inhibit iNOS overexpression and induce HO-1 expression, both of which contribute to the cardioprotection of H2S in CVB3-induced mice myocarditis.

Skin, Inflammation and Sulfurous Waters: What is Known, What is Believed

One could argue that balneotherapy and mud therapy would have not lasted 2,000 years or so If they were not effective. No doubt a long history cannot be taken per se as scientific proof of efficacy. Some empiricism is still present in the field: the concept of spa itself is quite confounding, whereas spring waters are used for leisure purposes but also for non-acute patient therapy and late phases of clinical recovery. These confounding elements ultimately feed the opinion of those who aprioristically reject any potential beneficial effect of balneotherapy: instead, it should at least generate questions that deserve scientific answers. Clinical practices sequentially integrating pharmacological therapy with those natural principles for which a sufficient scientific demonstration is available, would probably cut the costs of public health, generating widespread advantages for the community. Recently, it has become evident that mineral waters may have intrinsic pharmacological properties. Of the numerous salts dissolved in thermal waters that might show pharmacological properties, for certain hydrogen sulfide (H2S) contained in sulfurous waters is the one that has obtained greater scientific attention, to which should be added the extensive scientific effort recently dedicated to H2S as a cellular gasotransmitter, independently from its natural sources. Dermatology and cosmetics are among the most studied applications of sulfurous waters, around which, however, some empiricism still confounds opinions: we therefore considered that a state-of-the-art focus on this topic might be timely and useful for future studies.

Sulfide induces apoptosis and Rho kinase-dependent cell blebbing in Jurkat cells

Hydrogen sulfide (H₂S) is a toxic gaseous substance, and accidental exposure to high concentrations of H₂S has been reported to be lethal to humans. Inhaled and absorbed H₂S is partially dissolved within the circulation and causes toxic effects on lymphocytes. However, the mechanisms involved in H₂S toxicity have not been well documented. In this study, we examined the cellular uptake and injury of sulfide-exposed human T lymphocytes (Jurkat). Cells were exposed to a H₂S donor, sodium hydroxysulfide (NaHS), at pH 6.0, 7.0, or 8.0 for 1 h at 37 °C in a sealed conical tube to avoid the loss of dissolved H₂S gas. Cytotoxicity and cellular sulfide concentrations increased dramatically as the pH of the NaHS solution decreased. Sulfide enhanced the cleavage of caspase-3 and poly (ADP-ribose) polymerase and induced early cellular apoptosis. A pan-caspase inhibitor reduced sulfide-induced apoptosis. These results indicate that sulfide induces pH-dependent and caspase-dependent apoptosis. We also found that blebbing of the plasma membrane occurred in sulfide-exposed cells. Both ROCK-1 and ROCK-2 (Rho kinases) were activated by sulfide, and sulfide-induced cell blebbing was suppressed by a ROCK inhibitor, suggesting that a Rho pathway is involved in sulfide-induced blebbing in lymphocytes.

Impact of sulphurous water politzer inhalation on audiometric parameters in children with otitis media with effusion

OBJECTIVES

The positive effects of spa therapy on ear, nose, and throat pathology are known but robust literature in this field, is still lacking. The aim of this study was to assess through a retrospective analysis, the effects on otitis media with effusion of Politzer endotympanic inhalation of sulphurous waters in children aged 5-9 years.

METHODS

A cohort of 95 patients was treated with Politzer insufflations of sulphurous water: 58 patients did a cycle consisting of a treatment of 12 days per year for three consecutive years; 37 patients followed the same procedure for 5 years consecutively. The control population was represented by untreated, age-matched children. A standard audiometric test was used before and after each cycle of treatment.

RESULTS

One cycle of Politzer inhalation of sulphur-rich water improved the symptoms. Three cycles definitively stabilized the improvement of hearing function.

CONCLUSION

Our results show that otitis media with effusion in children can be resolved by an appropriate non-pharmacological treatment of middle ear with sulphur-rich water.

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.