Hydrogen sulfide attenuates particulate matter-induced human lung endothelial barrier disruption via combined reactive oxygen species scavenging and Akt activation

Particulate matter increases connexin 43 expression and exacerbates endothelial barrier disruption

OBJECTIVES

Particulate Matter (PM) air pollution is known to exacerbate cardiopulmonary diseases. We previously demonstrated that PM mediates endothelial injury and barrier disruption by modulating the endothelial cytoskeleton and cell-cell junctions, but the effects of PM exposure on cell-cell communication and gap junction activity are still unknown.

METHODS

This study focused on the characterization of PM-regulated endothelial dysfunction through connexin 43 (Cx43), the most abundant gap junction protein expressed in lung endothelial cells (ECs), using cultured human lung endothelial cells and a well-characterized PM sample.

RESULTS

PM exposure induced a time-dependent increase of Cx43 in human lung ECs at both the mRNA and protein levels. N-acetylcysteine (NAC), a reactive oxygen species (ROS) scavenger, significantly suppressed PM-induced Cx43 expression. Cx43 proteins on the plasma membrane and ER/Golgi apparatus were elevated in response to a PM challenge. In addition, PM induced gap junction activity, which was indicated by green fluorescence dye transfer between two adjacent ECs. Moreover, GAP27, a selective Cx43 channel inhibitor, attenuated PM-induced human lung EC barrier disruption, which was reflected by rescued trans-endothelial electrical resistance (TER) with an electric cell-substrate impedance sensing system. Moreover, knocking down Cx43 alleviated PM-induced myosin light chain (MLC) phosphorylation.

CONCLUSIONS

These results strongly suggest that Cx43 plays a key role in PM-mediated endothelial barrier disruption and signal transduction. Cx43 may be a therapeutic target in PM-mediated cardiopulmonary disorders.

Hydrogen Sulfide Ameliorates SARS-CoV-2-Associated Lung Endothelial Barrier Disruption

Recent studies have confirmed that lung microvascular endothelial injury plays a critical role in the pathophysiology of COVID-19. Our group and others have demonstrated the beneficial effects of H2S in several pathological processes and provided a rationale for considering the therapeutic implications of H2S in COVID-19 therapy. Here, we evaluated the effect of the slow-releasing H2S donor, GYY4137, on the barrier function of a lung endothelial cell monolayer in vitro, after challenging the cells with plasma samples from COVID-19 patients or inactivated SARS-CoV-2 virus. We also assessed how the cytokine/chemokine profile of patients' plasma, endothelial barrier permeability, and disease severity correlated with each other. Alterations in barrier permeability after treatments with patient plasma, inactivated virus, and GYY4137 were monitored and assessed by electrical impedance measurements in real time. We present evidence that GYY4137 treatment reduced endothelial barrier permeability after plasma challenge and completely reversed the endothelial barrier disruption caused by inactivated SARS-CoV-2 virus. We also showed that disease severity correlated with the cytokine/chemokine profile of the plasma but not with barrier permeability changes in our assay. Overall, these data demonstrate that treatment with H2S-releasing compounds has the potential to ameliorate SARS-CoV-2-associated lung endothelial barrier disruption.

Sulfide regulation of cardiovascular function in health and disease

Hydrogen sulfide (H2S) has emerged as a gaseous signalling molecule with crucial implications for cardiovascular health. H2S is involved in many biological functions, including interactions with nitric oxide, activation of molecular signalling cascades, post-translational modifications and redox regulation. Various preclinical and clinical studies have shown that H2S and its synthesizing enzymes - cystathionine γ-lyase, cystathionine β-synthase and 3-mercaptosulfotransferase - can protect against cardiovascular pathologies, including arrhythmias, atherosclerosis, heart failure, myocardial infarction and ischaemia-reperfusion injury. The bioavailability of H2S and its metabolites, such as hydropersulfides and polysulfides, is substantially reduced in cardiovascular disease and has been associated with single-nucleotide polymorphisms in H2S synthesis enzymes. In this Review, we highlight the role of H2S, its synthesizing enzymes and metabolites, their roles in the cardiovascular system, and their involvement in cardiovascular disease and associated pathologies. We also discuss the latest clinical findings from the field and outline areas for future study.

Impact of Particles on Pulmonary Endothelial Cells

According to the WHO, air quality affects around 40 million people, contributing to around 21,000 premature deaths per year. Severe respiratory diseases, such as asthma and chronic obstructive pulmonary disorder, can be promoted by air pollution, which has already been documented; this is one of the reasons why air quality is a very relevant factor for human health and well-being. Aerosols are an aggregation of solid or liquid particles dispersed in the air and can be found in the form of dust or fumes. Aerosols can be easily inhaled or absorbed by the skin, which can lead to adverse health effects according to their sizes that range from the nanometre to the millimetre scale. Based on the PRISMA methodology and using the Rayyan QCRI platform, it was possible to assess more than four hundred research articles. This systematic review study aimed to understand the impact of particles on pulmonary endothelial cells, namely particulate matter in different sizes, cigarette smoke, diesel exhaust particles and carbon black. The main conclusions were that particles induce multiple health effects on endothelial cells, namely endothelial dysfunction, which can lead to apoptosis and necrosis, and it may also cause necroptosis in lung structure.

Precipitation of aqueous transition metals in particulate matter during the dithiothreitol (DTT) oxidative potential assay

Transition metals in particulate matter (PM) are hypothesized to have enhanced toxicity based on their oxidative potential (OP). The acellular dithiothreitol (DTT) assay is widely used to measure the OP of PM and its chemical components. In our prior study, we showed that the DTT assay (pH 7.4, 0.1 M phosphate buffer, 37 °C) provides favorable thermodynamic conditions for precipitation of multiple metals present in PM. This study utilizes multiple techniques to characterize the precipitation of aqueous metals present at low concentrations in the DTT assay. Metal precipitation was identified using laser particle light scattering analysis, direct chemical measurement of aqueous metal removal, and microscopic imaging. Experiments were run with aqueous metals from individual metal salts and a well-characterized urban PM standard (NIST SRM-1648a, Urban Particulate Matter). Our results demonstrated rapid precipitation of metals in the DTT assay. Metal precipitation was independent of DTT but dependent on metal concentration. Metal removal in the chemically complex urban PM samples exceeded the thermodynamic predictions and removal seen in single metal salt experiments, suggesting co-precipitation and/or adsorption may have occurred. These results have broad implications for other acellular assays that study PM metals using phosphate buffer, and subsequently, the PM toxicity inferred from these assays.

Air pollution-regulated E-cadherin mediates contact inhibition of proliferation via the hippo signaling pathways in emphysema

Air pollution has been linked to emphysema in chronic obstruction pulmonary disease (COPD). However, the underlying mechanisms in the development of emphysema due to air pollution remain unclear. The objective of this study was to investigate the role of components of the Hippo signaling pathway for E-cadherin-mediated contact inhibition of proliferation in the lungs after air pollution exposure. E-Cadherin-mediated contact inhibition of proliferation via the Hippo signaling pathway was investigated in Sprague-Dawley (SD) rats whole-body exposed to air pollution, and in alveolar epithelial A549 cells exposed to diesel exhaust particles (DEPs), E-cadherin-knockdown, and high-mobility group box 1 (HMGB1) treatment. Underlying epithelial differentiation, apoptosis, and senescence were also examined, and the interaction network among these proteins was examined. COPD lung sections were used to confirm the observations in rats. Expressions of HMGB1 and E-cadherin were negatively regulated in the lungs and A549 cells by air pollution, and this was confirmed by knockdown of E-cadherin and by treating A549 cells with HMGB1. Depletion of phosphorylated (p)-Yap occurred after exposure to air pollution and E-cadherin-knockdown, which resulted in decreases of SPC and T1α. Exposure to air pollution and E-cadherin-knockdown respectively downregulated p-Sirt1 and increased p53 levels in the lungs and in A549 cells. Moreover, the protein interaction network suggested that E-cadherin is a key activator in regulating Sirt1 and p53, as well as alveolar epithelial cell differentiation by SPC and T1α. Consistently, downregulation of E-cadherin, p-Yap, SPC, and T1α was observed in COPD alveolar regions with particulate matter (PM) deposition. In conclusion, our results indicated that E-cadherin-mediated cell-cell contact directly regulates the Hippo signaling pathway to control differentiation, cell proliferation, and senescence due to air pollution. Exposure to air pollution may initiate emphysema in COPD patients.

Aesculetin Inhibits Airway Thickening and Mucus Overproduction Induced by Urban Particulate Matter through Blocking Inflammation and Oxidative Stress Involving TLR4 and EGFR

Particulate matter (PM) is a mixture of solid and liquid air pollutant particles suspended in the air, varying in composition, size, and physical features. PM is the most harmful form of air pollution due to its ability to penetrate deep into the lungs and blood streams, causing diverse respiratory diseases. Aesculetin, a coumarin derivative present in the Sancho tree and chicory, is known to have antioxidant and anti-inflammatory effects in the vascular and immune system. However, its effect on PM-induced airway thickening and mucus hypersecretion is poorly understood. The current study examined whether naturally-occurring aesculetin inhibited airway thickening and mucus hypersecretion caused by urban PM₁₀ (uPM₁₀, particles less than 10 μm). Mice were orally administrated with 10 mg/kg aesculetin and exposed to 6 μg/mL uPM₁₀ for 8 weeks. To further explore the mechanism(s) involved in inhibition of uPM₁₀-induced mucus hypersecretion by aesculetin, bronchial epithelial BEAS-2B cells were treated with 1–20 µM aesculetin in the presence of 2 μg/mL uPM₁₀. Oral administration of aesculetin attenuated collagen accumulation and mucus hypersecretion in the small airways inflamed by uPM₁₀. In addition, aesculetin inhibited uPM₁₀-evoked inflammation and oxidant production in lung tissues. Further, aesculetin accompanied the inhibition of induction of bronchial epithelial toll-like receptor 4 (TLR4) and epidermal growth factor receptor (EFGR) elevated by uPM₁₀. The inhibition of TLR4 and EGFR accompanied bronchial mucus hypersecretion in the presence of uPM₁₀. Oxidative stress was responsible for the epithelial induction of TLR4 and EGFR, which was disrupted by aesculetin. These results demonstrated that aesculetin ameliorated airway thickening and mucus hypersecretion by uPM₁₀ inhalation by inhibiting pulmonary inflammation via oxidative stress-stimulated TLR4 and EGFR. Therefore, aesculetin may be a promising agent for treating airway mucosa-associated disorders elicited by urban coarse particulates.

Endothelium as a Source and Target of H2S to Improve Its Trophism and Function

The vascular endothelium consists of a single layer of squamous endothelial cells (ECs) lining the inner surface of blood vessels. Nowadays, it is no longer considered as a simple barrier between the blood and vessel wall, but a central hub to control blood flow homeostasis and fulfill tissue metabolic demands by furnishing oxygen and nutrients. The endothelium regulates the proper functioning of vessels and microcirculation, in terms of tone control, blood fluidity, and fine tuning of inflammatory and redox reactions within the vessel wall and in surrounding tissues. This multiplicity of effects is due to the ability of ECs to produce, process, and release key modulators. Among these, gasotransmitters such as nitric oxide (NO) and hydrogen sulfide (H₂S) are very active molecules constitutively produced by endotheliocytes for the maintenance and control of vascular physiological functions, while their impairment is responsible for endothelial dysfunction and cardiovascular disorders such as hypertension, atherosclerosis, and impaired wound healing and vascularization due to diabetes, infections, and ischemia. Upregulation of H₂S producing enzymes and administration of H₂S donors can be considered as innovative therapeutic approaches to improve EC biology and function, to revert endothelial dysfunction or to prevent cardiovascular disease progression. This review will focus on the beneficial autocrine/paracrine properties of H₂S on ECs and the state of the art on H₂S potentiating drugs and tools.

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.

Inhibitory functions of cardamonin against particulate matter-induced lung injury through TLR2,4-mTOR-autophagy pathways

Particulate matter with an aerodynamic diameter equal to or less than 2.5 μm (PM_2.5) is a form of air pollutant that causes significant lung damage when inhaled. Cardamonin, a flavone found in Alpinia katsumadai Heyata seeds, has been reported to have anti-inflammatory and anticoagulative activity. The aim of this study was to determine the protective effects of cardamonin on PM_2.5-induced lung injury. Mice were treated with cardamonin via tail-vein injection 30 min after the intratracheal instillation of PM_2.5. The results showed that cardamonin markedly reduced the pathological lung injury, lung wet/dry weight ratio, and hyperpermeability caused by PM_2.5. Cardamonin also significantly inhibited PM_2.5-induced myeloperoxidase (MPO) activity in lung tissue, decreased the levels of PM_2.5-induced inflammatory cytokines and effectively attenuated PM_2.5-induced increases in the number of lymphocytes in the bronchoalveolar lavage fluid (BALF). And, cardamonin increased the phosphorylation of mammalian target of rapamycin (mTOR) and dramatically suppressed the PM_2.5-stimulated expression of toll-like receptor 2 and 4 (TLR 2,4), MyD88, and the autophagy-related proteins LC3 II and Beclin 1. In conclusion, these findings indicate that cardamonin has a critical anti-inflammatory effect due to its ability to regulate both the TLR2,4-MyD88 and mTOR-autophagy pathways and may thus be a potential therapeutic agent against PM_2.5-induced lung injury.

Effect of Air Pollution on Glutathione S-Transferase Activity and Total Antioxidant Capacity: Cross Sectional Study in Kuwait

BACKGROUND

Air pollution poses a significant threat to human health worldwide. Investigating potential health impacts is essential to the development of regulations and legislation to minimize health risks.

OBJECTIVES

The aim of the present study was to investigate the potentially hazardous effect of air pollution on the Ali Sabah Al Salem residential area in Kuwait by comparing the pollution level to a control area (Al-Qirawan) by assessing two biomarkers: erythrocyte glutathione S-transferases (e-GST) and total blood antioxidant, and then correlating the activity to pollution-related oxidative stress.

METHODS

The average concentrations of several airborne gases were measured at Ali Sabah Al Salem and Al-Qirawan, including ozone, carbon monoxide, nitrogen dioxide, nitrogen oxides, particulate matter less than 10 μm (PM₁₀), sulfur dioxide, ammonia, carbon dioxide, hydrogen sulfide, methane, and non-methane hydrocarbon. A total of fifty-eight participants were sampled from two different areas and divided into two groups. The study group was composed of 40 residents exposed to polluted ambient air in the Ali Sabah Al Salem residential area. A reference group composed of 18 residents in the Al-Qairawan area living far from major pollution sources was also tested.

RESULTS

All measured gases were higher in concentration at Ali Sabah Al Salem compared to the Al-Qirawan area. Furthermore, PM₁₀ and sulfur dioxide were higher than World Health Organization (WHO) guidelines. The e-GST activity was lower among participants of the Ali Sabah Al Salem residential area compared to participants living in the Al-Qairawan area. The total antioxidant capacity in whole blood of Ali Sabah Al Salem residents was significantly (p<0.0001) higher than in control subjects.

CONCLUSIONS

Residents in Ali Sabah Al Salem are exposed to a high level of air pollution that has a serious impact on glutathione S-transferases levels. Subsequently, regulations on pollution sources are needed to lower current health risks. Furthermore, the present study provides evidence that finger-prick blood sampling is a quick, non-invasive method suitable for screening e-GST activity and total antioxidants which may be applied for surveillance purposes.

PARTICIPANT CONSENT

Obtained.

ETHICS APPROVAL

The study was approved by the Scientific Research Committee of the Public Authority for Applied Education and Training, Kuwait.

COMPETING INTERESTS

The authors declare no competing financial interests.

Neuroprotective effects of ammonium tetrathiomolybdate, a slow-release sulfide donor, in a rodent model of regional stroke

BACKGROUND

Several therapeutic strategies to rescue the brain from ischemic injury have improved outcomes after stroke; however, there is no treatment as yet for reperfusion injury, the secondary damage caused by necessary revascularization. Recently we characterized ammonium tetrathiomolybdate (ATTM), a drug used as a copper chelator over many decades in humans, as a new class of sulfide donor that shows efficacy in preclinical injury models. We hypothesized that ATTM could confer neuroprotection in a relevant rodent model of regional stroke.

METHODS AND RESULTS

Brain ischemia was induced by transient (90-min) middle cerebral artery occlusion (tMCAO) in anesthetized Wistar rats. To mimic a clinical scenario, ATTM (or saline) was administered intravenously just prior to reperfusion. At 24 h or 7 days post-reperfusion, rats were assessed using functional (rotarod test, spontaneous locomotor activity), histological (infarct size), and molecular (anti-oxidant enzyme capacity, oxidative damage, and inflammation) outcome measurements. ATTM-treated animals showed improved functional activity at both 24 h and 7-days post-reperfusion, in parallel with a significant reduction in infarct size. These effects were additionally associated with increased brain antioxidant enzyme capacity, decreased oxidative damage, and a late (7-day) effect on pro-inflammatory cytokine levels and nitric oxide products.

CONCLUSION

ATTM confers significant neuroprotection that, along with its known safety profile in humans, provides encouragement for its development as a novel adjunct therapy for revascularization following stroke.

Inhibitory functions of maslinic acid on particulate matter-induced lung injury through TLR4-mTOR-autophagy pathways

Particulate matter (PM), the collection of all liquid and solid particles suspended in air, includes both organic and inorganic particles, many of which are health-hazards. PM particles with a diameter equal to or less than 2.5 μm (PM_2.5) is a form of air pollutant that causes significant lung damage when inhaled. Maslinic acid (MA) prevents oxidative stress and pro-inflammatory cytokine generation, but there is little information available regarding its role in PM-induced lung injury. Therefore, the purpose of this study was to determine the protective activity of MA against PM_2.5-induced lung injury. The mice were divided into seven groups (n = 10 each): a mock control group, an MA control (0.8 mg/kg mouse body weight) group, an opted PM_2.5 produced from diesel (10 mg/kg mouse body weight) group, a diesel PM_2.5+MA (0.2, 0.4, 0.6, and 0.8 mg/kg mouse body weight) groups. Mice were treated with MA via tail-vein injection 30 min after the intratracheal instillation of a diesel PM_2.5. Changes in the wet/dry weight ratio of the lung tissue, total protein/total cell and lymphocyte counts, inflammatory cytokines in the bronchoalveolar lavage fluid (BALF), vascular permeability, and histology were monitored in diesel PM_2.5-treated mice. The results showed that MA reduced pathological lung injury, the wet/dry weight ratio of the lung tissue, and hyperpermeability caused by diesel PM_2.5. MA also inhibited diesel PM_2.5-induced myeloperoxidase (MPO) activity in the lung tissue, decreased the levels of diesel PM_2.5-induced inflammatory cytokines, including tumor necrosis factor (TNF)-α and interleukin (IL)-1β, reduced nitric oxide (NO) and total protein in the BALF, and effectively attenuated diesel PM_2.5-induced increases in the number of lymphocytes in the BALF. In addition, MA increased the protein phosphorylation of the mammalian target of rapamycin (mTOR) and dramatically suppressed diesel PM_2.5-stimulated expression of toll-like receptor 4 (TLR4), MyD88, and the autophagy-related proteins LC3 II and Beclin 1. In conclusion, these findings indicate that MA has a critical anti-inflammatory effect due to its ability to regulate both the TLR4-MyD88 and mTOR-autophagy pathways and may thus be a potential therapeutic agent against diesel PM_2.5-induced lung injury.

Hydrogen Sulfide Attenuates Particulate Matter-Induced Emphysema and Airway Inflammation Through Nrf2-Dependent Manner

Purpose

To investigate whether hydrogen sulfide provide protective effects on atmosphere particulate matter (PM)-induced emphysema and airway inflammation and its mechanism.

Methods

Wild type C57BL/6 and Nrf2 knockout mice were exposed to PM (200 µg per mouse). Hydrogen sulfide or propargylglycine were administered by intraperitoneal injection respectively 30 min before PM exposure, mice were anesthetized 29th day after administration. Mice emphysema, airway inflammation, and oxidative stress were evaluated, the expression of NLRP3, active caspase-1, and active caspase-3 were detected. Alveolar epithelial A549 cells line were transfected with control small interfering RNA (siRNA) or Nrf2 siRNA and then incubated with or without hydrogen sulfide for 30 min before exposed to fine particulate matter for 24 h, cell viability, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling (TUNEL) assay, the secretion of interleukin (IL)-1β, ASC speck formation, the expression level of NLRP3, active caspase-1, and active caspase-3 were measured.

Results

PM significantly increased mice emphysema and airway inflammation measured by mean linear intercept, alveolar destroy index and total cell, neutrophil counts, cytokines IL-6, tumor necrosis factor (TNF)-α, CXCL1, IL-1β in bronchoalveolar lavage fluid. PM-induced mice emphysema and airway inflammation was greatly attenuated by hydrogen sulfide, while propargylglycine aggravated that. PM-induced oxidative stress was reduced by hydrogen sulfide as evaluated by 8-OHdG concentrations in lung tissues. The expression of NLRP3, active caspase-1, and active caspase-3 enhanced by PM were also downregulated by hydrogen sulfide in mice lung. The protective effect of hydrogen sulfide on emphysema, airway inflammation, inhibiting oxidative stress, NLRP3 inflammasome formation, and anti-apoptosis was inhibited by Nrf2 knockout in mice. Similarly, hydrogen sulfide attenuated the secretion of IL-1β, NLRP3 expression, caspase-1 activation, ASC speck formation, and apoptosis caused by fine particulate matter exposure in A549 cells but not in Nrf2 silenced cells.

Conclusion

Hydrogen sulfide played a protect role in PM-induced mice emphysema and airway inflammation by inhibiting NLRP3 inflammasome formation and apoptosis via Nrf2-dependent pathway.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Growth and Remodeling

Ischemic vascular remodeling occurs in response to stenosis or arterial occlusion leading to a change in blood flow and tissue perfusion. Altered blood flow elicits a cascade of molecular and cellular physiological responses leading to vascular remodeling of the macro- and micro-circulation. Although cellular mechanisms of vascular remodeling such as arteriogenesis and angiogenesis have been studied, therapeutic approaches in these areas have had limited success due to the complexity and heterogeneous constellation of molecular signaling events regulating these processes. Understanding central molecular players of vascular remodeling should lead to a deeper understanding of this response and aid in the development of novel therapeutic strategies. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are gaseous signaling molecules that are critically involved in regulating fundamental biochemical and molecular responses necessary for vascular growth and remodeling. This review examines how NO and H₂ S regulate pathophysiological mechanisms of angiogenesis and arteriogenesis, along with important chemical and experimental considerations revealed thus far. The importance of NO and H₂ S bioavailability, their synthesis enzymes and cofactors, and genetic variations associated with cardiovascular risk factors suggest that they serve as pivotal regulators of vascular remodeling responses. © 2019 American Physiological Society. Compr Physiol 9:1213-1247, 2019.

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.

Association of Kidney Tissue Barrier Disrupture and Renal Dysfunction in Resuscitated Murine Septic Shock

Septic shock-related kidney failure is characterized by almost normal morphological appearance upon pathological examination. Endothelial barrier disrupture has been suggested to be of crucial importance for septic shock-induced organ dysfunction. Therefore, in murine resuscitated cecal ligation and puncture (CLP)-induced septic shock, we tested the hypothesis whether there is a direct relationship between the kidney endothelial barrier injury and renal dysfunction. Anesthetized mice underwent CLP, and 15 h later, were anesthetized again and surgically instrumented for a 5-h period of intensive care comprising lung-protective mechanical ventilation, fluid resuscitation, continuous i.v. norepinephrine to maintain target hemodynamics, and measurement of creatinine clearance (CrCl). Animals were stratified according to low or high CrCl. Nitrotyrosine formation, expression of the inducible isoform of the nitric oxide synthase, and blood cytokine (tumor necrosis factor, interleukin-6, interleukin-10) and chemokine (monocyte chemoattractant protein-1, keratinocyte-derived chemokine) levels were significantly higher in animals with low CrCl. When plotted against CrCl and neutrophil gelatinase-associated lipocalin levels, extravascular albumin accumulation, and tissue expression of the vascular endothelial growth factor and angiopoietin-1 showed significant mathematical relationships related to kidney (dys)function. Preservation of the constitutive expression of the hydrogen sulfide producing enzyme cystathione-γ-lyase was associated with maintenance of organ function. The direct quantitative relation between microvascular leakage and kidney (dys)function may provide a missing link between near-normal tissue morphology and septic shock-related renal failure, thus further highlighting the important role of vascular integrity in septic shock-related renal failure.

Beyond a Gasotransmitter: Hydrogen Sulfide and Polysulfide in Cardiovascular Health and Immune Response

SIGNIFICANCE

Hydrogen sulfide (H₂S) metabolism leads to the formation of oxidized sulfide species, including polysulfide, persulfide, and others. Evidence is emerging that many biological effects of H₂S may indeed be due to polysulfide and persulfide activation of signaling pathways and reactivity with discrete small molecules. Recent Advances: Exogenous oxidized sulfide species, including polysulfides, are more reactive than H₂S with a wide range of molecules. Importantly, endogenous polysulfide and persulfide formation has been reported to occur via transsulfuration enzymes, cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS).

CRITICAL ISSUES

In light of the recent understanding of oxidized sulfide metabolite formation and reactivity, comparatively few studies have been reported comparing cellular biological and in vivo effects of H₂S donors versus polysulfide and persulfide donors. Likewise, it is equally unclear when, how, and to what extent persulfide and polysulfide formation occurs in vivo under pathophysiological conditions.

FUTURE DIRECTIONS

Additional studies regarding persulfide and polysulfide formation and molecular reactions are needed in nearly all aspects of biology to better understand how sulfide metabolites contribute to key chemical biology reactions involved in cardiovascular health and immune responses. Antioxid. Redox Signal. 27, 634-653.

Hydrogen Sulfide Prevents and Partially Reverses Ozone-Induced Features of Lung Inflammation and Emphysema in Mice

Hydrogen sulfide (H2S), a novel signaling gasotransmitter in the respiratory system, may have antiinflammatory properties in the lung. We examined the preventive and therapeutic effects of H2S on ozone-induced features of lung inflammation and emphysema. C57/BL6 mice were exposed to ozone or filtered air over 6 weeks. Sodium hydrogen sulfide (NaHS), an H2S donor, was administered to the mice either before ozone exposure (preventive effect) or after completion of 6 weeks of ozone exposure (therapeutic effect). The ozone-exposed mice developed emphysema, measured by micro-computed tomography and histology, airflow limitation, measured by the forced maneuver system, and increased lung inflammation with augmented IL-1β, IL-18, and matrix metalloproteinase-9 (MMP-9) gene expression. Ozone-induced changes were associated with increased Nod-like receptor pyrin domain containing 3 (NLRP3)-caspase-1 activation and p38 mitogen-activated protein kinase phosphorylation and decreased Akt phosphorylation. NaHS both prevented and reversed lung inflammation and emphysematous changes in alveolar space. In contrast, NaHS prevented, but did not reverse, ozone-induced airflow limitation and bronchial structural remodeling. In conclusion, NaHS administration prevented and partially reversed ozone-induced features of lung inflammation and emphysema via regulation of the NLRP3-caspase-1, p38 mitogen-activated protein kinase, and Akt pathways.

Particulate matter disrupts human lung endothelial cell barrier integrity via Rho-dependent pathways

Increased exposure to ambient particulate matter (PM) is associated with elevated morbidity and mortality in patients with cardiopulmonary diseases and cancer. We and others have shown that PM induces lung microvascular barrier dysfunction which potentially enhances the systemic toxicity of PM. However, the mechanisms by which PM disrupts vascular endothelial integrity remain incompletely explored. We hypothesize that PM induces endothelial cell (EC) cytoskeleton rearrangement via Rho GTPase-dependent pathways to facilitate vascular hyperpermeability. Fine PM induced time-dependent activation of cytoskeletal machinery with increases in myosin light chain (MLC) phosphorylation and EC barrier disruption measured by transendothelial electrical resistance (TER), events attenuated by the Rho-dependent kinase (ROCK) inhibitor Y-27632 or the reactive oxygen species (ROS) scavenger, N-acetylcysteine (NAC). Both Y-27632 and NAC prevented PM-induced stress fiber formation and phospho-MLC accumulation in human lung ECs. PM promotes rapid accumulation of Rho-GTP. This event is attenuated by NAC or knockdown of RhoA (siRNA). Consistent with ROCK activation, PM induced phosphorylation of myosin light chain phosphatase (MYPT) at Thr850, a post-translational modification known to inhibit phosphatase activity. Furthermore, PM activates the guanine nucleotide exchange factor (GEF) for Rho, p115, with p115 translocation to the cell periphery, in a ROS-dependent manner. Together these results demonstrate that fine PM induces EC cytoskeleton rearrangement via Rho-dependent pathways that are dependent upon the generation of oxidative stress. As the disruption of vascular integrity further contributes to cardiopulmonary physiologic derangements, these findings provide pharmacologic targets for prevention of PM-induced cardiopulmonary toxicity.

Vascular biology of hydrogen sulfide

Hydrogen sulfide (H₂S) is a ubiquitous signaling molecule with important functions in many mammalian organs and systems. Observations in the 1990s ascribed physiological actions to H₂S in the nervous system, proposing that this gasotransmitter acts as a neuromodulator. Soon after that, the vasodilating properties of H₂S were demonstrated. In the past decade, H₂S was shown to exert a multitude of physiological effects in the vessel wall. H₂S is produced by vascular cells and exhibits antioxidant, antiapoptotic, anti-inflammatory, and vasoactive properties. In this concise review, we have focused on the impact of H₂S on vascular structure and function with an emphasis on angiogenesis, vascular tone, vascular permeability and atherosclerosis. H₂S reduces arterial blood pressure, limits atheromatous plaque formation, and promotes vascularization of ischemic tissues. Although the beneficial properties of H₂S are well established, mechanistic insights into the molecular pathways implicated in disease prevention and treatment remain largely unexplored. Unraveling the targets and downstream effectors of H₂S in the vessel wall in the context of disease will aid in translation of preclinical observations. In addition, acute regulation of H₂S production is still poorly understood and additional work delineating the pathways regulating the enzymes that produce H₂S will allow pharmacological manipulation of this pathway. As the field continues to grow, we expect that H₂S-related compounds will find their way into clinical trials for diseases affecting the blood vessels.

Hydrogen Sulfide Prevents Formation of Reactive Oxygen Species through PI3K/Akt Signaling and Limits Ventilator-Induced Lung Injury

The development of ventilator-induced lung injury (VILI) is still a major problem in mechanically ventilated patients. Low dose inhalation of hydrogen sulfide (H₂S) during mechanical ventilation has been proven to prevent lung damage by limiting inflammatory responses in rodent models. However, the capacity of H₂S to affect oxidative processes in VILI and its underlying molecular signaling pathways remains elusive. In the present study we show that ventilation with moderate tidal volumes of 12 ml/kg for 6 h led to an excessive formation of reactive oxygen species (ROS) in mice lungs which was prevented by supplemental inhalation of 80 parts per million of H₂S. In addition, phosphorylation of the signaling protein Akt was induced by H₂S. In contrast, inhibition of Akt by LY294002 during ventilation reestablished lung damage, neutrophil influx, and proinflammatory cytokine release despite the presence of H₂S. Moreover, the ability of H₂S to induce the antioxidant glutathione and to prevent ROS production was reversed in the presence of the Akt inhibitor. Here, we provide the first evidence that H₂S-mediated Akt activation is a key step in protection against VILI, suggesting that Akt signaling limits not only inflammatory but also detrimental oxidative processes that promote the development of lung injury.

Hydrogen sulfide metabolism regulates endothelial solute barrier function

Hydrogen sulfide (H₂S) is an important gaseous signaling molecule in the cardiovascular system. In addition to free H₂S, H₂S can be oxidized to polysulfide which can be biologically active. Since the impact of H₂S on endothelial solute barrier function is not known, we sought to determine whether H₂S and its various metabolites affect endothelial permeability. In vitro permeability was evaluated using albumin flux and transendothelial electrical resistance. Different H₂S donors were used to examine the effects of exogenous H₂S. To evaluate the role of endogenous H₂S, mouse aortic endothelial cells (MAECs) were isolated from wild type mice and mice lacking cystathionine γ-lyase (CSE), a predominant source of H₂S in endothelial cells. In vivo permeability was evaluated using the Miles assay. We observed that polysulfide donors induced rapid albumin flux across endothelium. Comparatively, free sulfide donors increased permeability only with higher concentrations and at later time points. Increased solute permeability was associated with disruption of endothelial junction proteins claudin 5 and VE-cadherin, along with enhanced actin stress fiber formation. Importantly, sulfide donors that increase permeability elicited a preferential increase in polysulfide levels within endothelium. Similarly, CSE deficient MAECs showed enhanced solute barrier function along with reduced endogenous bound sulfane sulfur. CSE siRNA knockdown also enhanced endothelial junction structures with increased claudin 5 protein expression. In vivo, CSE genetic deficiency significantly blunted VEGF induced hyperpermeability revealing an important role of the enzyme for barrier function. In summary, endothelial solute permeability is critically regulated via exogenous and endogenous sulfide bioavailability with a prominent role of polysulfides.

•

Polysulfide from cystathionine γ-lyase (CSE) and exogenous polysulfide donors increases endothelial permeability.

•

The ability of polysulfide to increase permeability is associated with junction disruption and stress fiber formation.

•

CSE expression in vivo regulates VEGF induced hyper-permeability.

SIRT3 Mediates the Antioxidant Effect of Hydrogen Sulfide in Endothelial Cells

AIM

Oxidative stress is a key contributor to endothelial dysfunction and associated cardiovascular pathogenesis. Hydrogen sulfide (H2S) is an antioxidant gasotransmitter that protects endothelial cells against oxidative stress. Sirtuin3 (SIRT3), which belongs to the silent information regulator 2 (SIR2) family, is an important deacetylase under oxidative stress. H2S is able to regulate the activity of several sirtuins. The present study aims to investigate the role of SIRT3 in the antioxidant effect of H2S in endothelial cells.

RESULTS

Cultured EA.hy926 endothelial cells were exposed to hydrogen peroxide (H2O2) as a model of oxidative stress-induced cell injury. GYY4137, a slow-releasing H2S donor, improved cell viability, reduced oxidative stress and apoptosis, and improved mitochondrial function following H2O2 treatment. H2S reversed the stimulation of MAPK phosphorylation, downregulation of SIRT3 mRNA and reduction of the superoxide dismutase 2 and isocitrate dehydrogenase 2 expression which were induced by H2O2. H2S also increased activator protein 1 (AP-1) binding activity with SIRT3 promoter and this effect was absent in the presence of the specific AP-1 inhibitor, SR11302 or curcumin. Paraquat administration to mice induced a defected endothelium-dependent aortic vasodilatation and increased oxidative stress in both mouse aorta and small mesenteric artery, which were alleviated by GYY4137 treatment. This vasoprotective effect of H2S was absent in SIRT3 knockout mice.

INNOVATION

The present results highlight a novel role for SIRT3 in the protective effect of H2S against oxidant damage in the endothelium both in vitro and in vivo.

CONCLUSION

H2S enhances AP-1 binding activity with the SIRT3 promoter, thereby upregulating SIRT3 expression and ultimately reducing oxidant-provoked vascular endothelial dysfunction. Antioxid. Redox Signal. 24, 329-343.

Molecular Regulation of Toll-like Receptors in Asthma and COPD

Asthma and chronic obstructive pulmonary disease (COPD) have both been historically associated with significant morbidity and financial burden. These diseases can be induced by several exogenous factors, such as pathogen-associated molecular patterns (PAMPs) (e.g., allergens and microbes). Endogenous factors, including reactive oxygen species, and damage-associated molecular patterns (DAMPs) recognized by toll-like receptors (TLRs), can also result in airway inflammation. Asthma is characterized by the dominant presence of eosinophils, mast cells, and clusters of differentiation (CD)4⁺ T cells in the airways, while COPD typically results in the excessive formation of neutrophils, macrophages, and CD8⁺ T cells in the airways. In both asthma and COPD, in the respiratory tract, TLRs are the primary proteins of interest associated with the innate and adaptive immune responses; hence, multiple treatment options targeting TLRs are being explored in an effort to reduce the severity of the symptoms of these disorders. TLR-mediated pathways for both COPD and asthma have their similarities and differences with regards to cell types and the pro-inflammatory cytotoxins present in the airway. Because of the complex TLR cascade, a variety of treatments have been used to minimize airway hypersensitivity and promote bronchodilation. Although unsuccessful at completely alleviating COPD and severe asthmatic symptoms, new studies are focused on possible targets within the TLR cascade to ameliorate airway inflammation.

Panax Notoginseng Saponins Ameliorates Coxsackievirus B3-Induced Myocarditis by Activating the Cystathionine-γ-Lyase/Hydrogen Sulfide Pathway

This study is to determine the therapeutic effects of Panax notoginseng saponins (PNSs) on coxsackievirus B3 (CVB3)-induced myocarditis, and whether cystathionine-γ-lyase (CSE)/hydrogen sulfide (H2S) pathway is involved. Mouse model of myocarditis was induced by CVB3 infection, and the mice were subjected to vehicle (saline) or drug treatments (sodium bisulfide (NaHS), propargylglycine (PAG), or PNSs). The results showed that there were inflammatory cell infiltrations, interstitial edemas, and elevated inflammatory cytokines, in CVB3-induced myocarditis. PAG administration increased, whereas NaHS treatment decreased the severity of the myocarditis. PNS treatment dramatically alleviated these myocardial injuries and decreased the viral messenger RNA (mRNA) expression by the enhanced expression of CSE/H2S pathway. Moreover, the therapeutic effects of PNSs on myocarditis were stronger than those of NaHS. Finally, the effect of PNSs on CSE/H2S pathway and cardiac cell protection were verified in cultured cardiac cells. PNSs may be a promising medication for viral myocarditis therapy.

Hydrogen sulfide attenuates cytokine production through the modulation of chromatin remodeling

Hydrogen sulfide (H2S) is an endogenous gaseous biological mediator, which regulates, among others, the oxidative balance of cells under normal physiological conditions, as well as in various diseases. Several previous studies have reported that H2S attenuates inflammatory mediator production. In this study, we investigated the role of H2S in chromatin modulation in an in vitro model of lipopolysaccharide (LPS)-induced inflammation and evaluated its effects on inflammatory cytokine production. Tamm-Horsfall protein 1 (THP-1) differentiated macrophages were pre-treated with sodium hydrosulfide (NaHS) (an H2S donor) at 0.01, 0.1, 0.5 or 1 mM for 30 min. To stimulate cytokine production, the cells were challenged with bacterial LPS (1 µg/ml) for 1, 4, 8 or 24 h. Histone H3 acetylation was analyzed by chromatin immunoprecipitation (ChIP), cytokine production was measured by ELISA and histone deacetylase (HDAC) activity was analyzed using a standard biochemical assay. H2S inhibited the production of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in a concentration-dependent manner; it was most effective at the two highest concentrations used. This effect was associated with a decrease in histone H3 acetylation at the IL-6 and TNF-α promoters in the cells exposed to H2S or H2S + LPS. The findings of the present study suggest that H2S suppresses histone acetylation, which, in turn, inhibits chromatin openness, leading to a decrease in the gene transcription of various pro-inflammatory cytokines. Therefore, this mechanism may contribute to the previously demonstrated anti-inflammatory effects of H2S and various H2S donors.

Characterization of zofenoprilat as an inducer of functional angiogenesis through increased H2 S availability

BACKGROUND AND PURPOSE

Hydrogen sulfide (H2 S), an endogenous volatile mediator with pleiotropic functions, promotes vasorelaxation, exerts anti-inflammatory actions and regulates angiogenesis. Previously, the SH-containing angiotensin-converting enzyme inhibitor (ACEI), zofenopril, was identified as being effective in preserving endothelial function and inducing angiogenesis among ACEIs. Based on the H2 S donor property of its active metabolite zofenoprilat, the objective of this study was to evaluate whether zofenoprilat-induced angiogenesis was due to increased H2 S availability.

EXPERIMENTAL APPROACH

HUVECs were used for in vitro studies of angiogenesis, whereas the Matrigel plug assay was used for in vivo assessments.

KEY RESULTS

Zofenoprilat-treated HUVECs showed an increase in all functional features of the angiogenic process in vitro. As zofenoprilat induced the expression of CSE (cystathionine-γ-lyase) and the continuous production of H2 S, CSE inhibition or silencing blocked the ability of zofenoprilat to induce angiogenesis, both in vitro and in vivo. The molecular mechanisms underlying H2 S/zofenoprilat-induced angiogenesis were dependent on Akt, eNOS and ERK1/2 cascades. ATP-sensitive potassium (KATP ) channels, the molecular target that mediates part of the vascular functions of H2 S, were shown to be involved in the upstream activation of Akt and ERK1/2. Moreover, the up-regulation of fibroblast growth factor-2 was dependent on CSE-derived H2 S response to H2 S and KATP activation.

CONCLUSIONS AND IMPLICATIONS

Zofenoprilat induced a constant production of H2 S that stimulated the angiogenic process through a KATP channel/Akt/eNOS/ERK1/2 pathway. Thus, zofenopril can be considered as a pro-angiogenic drug acting through H2 S release and production, useful in cardiovascular pathologies where vascular functions need to be re-established and functional angiogenesis induced.

Sputum-to-serum hydrogen sulfide ratio in COPD

OBJECTIVES

Hydrogen sulfide (H₂S) is a gas produced by respiratory cells including smooth muscle cells and may play a role as a cellular gasotransmitter. We evaluated whether H₂S levels in serum or sputum could represent a new biomarker of COPD in a cross-sectional study.

METHODS

H₂S levels in sputum and serum samples were measured using a sulfide-sensitive electrode in 64 patients with stable COPD (S-COPD), 29 COPD subjects during acute exacerbation (AE-COPD), 14 healthy smokers and 21 healthy non-smokers.

RESULTS

Sputum H₂S levels in AE-COPD subjects were higher than those in S-COPD, healthy smoking and non-smoking subjects (p<0.001), but serum H₂S levels in AE-COPD were lower than those in S-COPD (p<0.001). Thus, the sputum-to-serum ratio of H₂S (H₂S ratio) in AE-COPD subjects were higher than those in stable COPD, healthy smoking and non-smoking subjects (p<0.001). In 14 COPD subjects whose H₂S ratios were measured during and after an exacerbation, the mean ratio was increased during exacerbation (p<0.05). H₂S ratio was positively correlated with St. George's Respiratory Questionnaire score, sputum neutrophils and IL-6 and IL-8 levels in sputum and serum (p<0.01) but inversely correlated with sputum macrophages (%), FEV₁%predicted and FEV₁/FVC (p<0.01). The cut-off level of H₂S ratio to indicate an exacerbation was ≥0.44 (sensitivity of 93.1% and specificity of 84.5%).

CONCLUSIONS

The ratio of sputum-to-serum levels of H₂S may provide a useful marker of COPD indicative of obstructive neutrophilic inflammation and of potential ongoing exacerbation.

Exogenous hydrogen sulfide (H2S) protects alveolar growth in experimental O2-induced neonatal lung injury

Background

Bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, remains a major health problem. BPD is characterized by impaired alveolar development and complicated by pulmonary hypertension (PHT). Currently there is no specific treatment for BPD. Hydrogen sulfide (H₂S), carbon monoxide and nitric oxide (NO), belong to a class of endogenously synthesized gaseous molecules referred to as gasotransmitters. While inhaled NO is already used for the treatment of neonatal PHT and currently tested for the prevention of BPD, H₂S has until recently been regarded exclusively as a toxic gas. Recent evidence suggests that endogenous H₂S exerts beneficial biological effects, including cytoprotection and vasodilatation. We hypothesized that H₂S preserves normal alveolar development and prevents PHT in experimental BPD.

Methods

We took advantage of a recently described slow-releasing H₂S donor, GYY4137 (morpholin-4-ium-4-methoxyphenyl(morpholino) phosphinodithioate) to study its lung protective potential in vitro and in vivo.

Results

In vitro, GYY4137 promoted capillary-like network formation, viability and reduced reactive oxygen species in hyperoxia-exposed human pulmonary artery endothelial cells. GYY4137 also protected mitochondrial function in alveolar epithelial cells. In vivo, GYY4137 preserved and restored normal alveolar growth in rat pups exposed from birth for 2 weeks to hyperoxia. GYY4137 also attenuated PHT as determined by improved pulmonary arterial acceleration time on echo-Doppler, pulmonary artery remodeling and right ventricular hypertrophy. GYY4137 also prevented pulmonary artery smooth muscle cell proliferation.

Conclusions

H₂S protects from impaired alveolar growth and PHT in experimental O₂-induced lung injury. H₂S warrants further investigation as a new therapeutic target for alveolar damage and PHT.

Hydrogen sulfide as a potential biomarker of asthma

Hydrogen sulfide (H2S), a gas characterized by the odor of rotten eggs, is produced by many cells in the airways and lungs, and may regulate physiologic and pathophysiologic processes. It plays a role in cellular signaling, and represents the third gasotransmitter after nitric oxide and carbon monoxide. Endogenous and exogenous H₂S have anti-inflammatory and anti-proliferative effects, with inhibitory effects in models of lung inflammation and fibrosis. Under certain conditions, H₂S may also be proinflammatory. It is generally a vasodilator and relaxant of airway and vascular smooth muscle cells. It acts as a reducing agent, being able to scavenge superoxide and peroxynitrite. H₂S is detectable in serum and in sputum supernatants with raised levels observed in asthmatics. The sputum levels correlated inversely with lung function. H₂S may play a role in the pathogenesis of asthma.

Hydrogen sulfide decreases collagen Ⅰ and collagen Ⅲ expression in the liver of rats with experimental hepatic fibrosis

AIM: To investigate the effect of hydrogen sulfide on collagen Ⅰ and collagen Ⅲ expression in the liver of rats with experimental hepatic fibrosis.

METHODS: Thirty-two female SD rats were randomly divided into three groups: normal control group, hepatic fibrosis group, and hydrogen sulfide group. Rats in the hepatic fibrosis group and hydrogen sulfide group were subcutaneously injected with carbon tetrachloride to induce hepatic fibrosis. Rats in the hydrogen sulfide group were intraperitoneally injected with sodium hydrosulfide (56 μmol/kg•d; the donor of hydrogen sulfide). Fibrosis was staged using histopathological methods. The expression of collagen Ⅰ and collagen Ⅲ was detected by immunohistochemistry and RT-PCR.

RESULTS: Compared to the normal control group, the stage of fibrosis was elevated (P < 0.01) and the expression of collagen Ⅰ and collagen Ⅲ was increased (both P < 0.01) in the hepatic fibrosis group. Compared to the hepatic fibrosis group, the stage of fibrosis declined (P < 0.05) and the expression of collagen Ⅰ and collagen Ⅲ was decreased (both P < 0.01) in the hydrogen sulfide group.

CONCLUSION: Hydrogen sulfide can decrease the expression of collagen Ⅰ and collagen Ⅲ and inhibit the progression of hepatic fibrosis in rats.