Effect of hydrogen sulphide on beta-amyloid-induced damage in PC12 cells

Mitochondrial Targeting against Alzheimer's Disease: Lessons from Hibernation

Alzheimer's disease (AD) is the most common cause of dementia worldwide and yet remains without effective therapy. Amongst the many proposed causes of AD, the mitochondrial cascade hypothesis is gaining attention. Accumulating evidence shows that mitochondrial dysfunction is a driving force behind synaptic dysfunction and cognitive decline in AD patients. However, therapies targeting the mitochondria in AD have proven unsuccessful so far, and out-of-the-box options, such as hibernation-derived mitochondrial mechanisms, may provide valuable new insights. Hibernators uniquely and rapidly alternate between suppression and re-activation of the mitochondria while maintaining a sufficient energy supply and without acquiring ROS damage. Here, we briefly give an overview of mitochondrial dysfunction in AD, how it affects synaptic function, and why mitochondrial targeting in AD has remained unsuccessful so far. We then discuss mitochondria in hibernation and daily torpor in mice, covering current advancements in hibernation-derived mitochondrial targeting strategies. We conclude with new ideas on how hibernation-derived dual mitochondrial targeting of both the ATP and ROS pathways may boost mitochondrial health and induce local synaptic protein translation to increase synaptic function and plasticity. Further exploration of these mechanisms may provide more effective treatment options for AD in the future.

Hydrogen sulfide signalling in neurodegenerative diseases

The gaseous neurotransmitter hydrogen sulfide (H2 S) exerts neuroprotective efficacy in the brain via post-translational modification of cysteine residues by sulfhydration, also known as persulfidation. This process is comparable in biological impact to phosphorylation and mediates a variety of signalling events. Unlike conventional neurotransmitters, H2 S cannot be stored in vesicles due to its gaseous nature. Instead, it is either locally synthesized or released from endogenous stores. Sulfhydration affords both specific and general neuroprotective effects and is critically diminished in several neurodegenerative disorders. Conversely, some forms of neurodegenerative disease are linked to excessive cellular H2 S. Here, we review the signalling roles of H2 S across the spectrum of neurodegenerative diseases, including Huntington's disease, Parkinson's disease, Alzheimer's disease, Down syndrome, traumatic brain injury, the ataxias, and amyotrophic lateral sclerosis, as well as neurodegeneration generally associated with ageing.

Progress and perspective on hydrogen sulfide donors and their biomedical applications

Following the discovery of nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H₂ S) has been identified as the third gasotransmitter in humans. Increasing evidence have shown that H₂ S is of preventive or therapeutic effects on diverse pathological complications. As a consequence, it is of great significance to develop suitable approaches of H₂ S-based therapeutics for biomedical applications. H₂ S-releasing agents (H₂ S donors) play important roles in exploring and understanding the physiological functions of H₂ S. More importantly, accumulating studies have validated the theranostic potential of H₂ S donors in extensive repertoires of in vitro and in vivo disease models. Thus, it is imperative to summarize and update the literatures in this field. In this review, first, the background of H₂ S on its chemical and biological aspects is concisely introduced. Second, the studies regarding the H₂ S-releasing compounds are categorized and described, and accordingly, their H₂ S-donating mechanisms, biological applications, and therapeutic values are also comprehensively delineated and discussed. Necessary comparisons between related H₂ S donors are presented, and the drawbacks of many typical H₂ S donors are analyzed and revealed. Finally, several critical challenges encountered in the development of multifunctional H₂ S donors are discussed, and the direction of their future development as well as their biomedical applications is proposed. We expect that this review will reach extensive audiences across multiple disciplines and promote the innovation of H₂ S biomedicine.

Research progress of hydrogen sulfide in Alzheimer's disease from laboratory to hospital: a narrative review

Alzheimer's disease is a neurodegenerative disease that mainly occurs in old age and early stages. Its main manifestations are memory impairment, aphasia, apraxia, loss of identity, abstract thinking and impairment of computing power, personality and behavior changes, etc. At present, the treatment of Alzheimer's disease only stays on reducing the disease and delaying the development, which is also a difficult problem to overcome in clinical practice. Hydrogen sulfide, as a third gaseous signal molecule after carbon monoxide and nitrogen monoxide, has become very popular in recent years. It shows very promising prospects in the Alzheimer's disease model. It can protect the nerve function and prevent the progress of the disease by affecting the amyloid precursor protein metabolism, anti-apoptosis, anti-inflammatory, and antioxidant pathways. Therefore, this article summarizes the relevant basic and clinical research of hydrogen sulfide in Alzheimer's disease, and discusses its progress and findings and mechanism characteristics.

Sulfur-containing therapeutics in the treatment of Alzheimer's disease

Sulfur is widely existent in natural products and synthetic organic compounds as organosulfur, which are often associated with a multitude of biological activities. OBenzothiazole, in which benzene ring is fused to the 4,5-positions of the thiazolerganosulfur compounds continue to garner increasing amounts of attention in the field of medicinal chemistry, especially in the development of therapeutic agents for Alzheimer's disease (AD). AD is a fatal neurodegenerative disease and the primary cause of age-related dementia posing severe societal and economic burdens. Unfortunately, there is no cure for AD. A lot of research has been conducted on sulfur-containing compounds in the context of AD due to their innate antioxidant potential and some are currently being evaluated in clinical trials. In this review, we have described emerging trends in the field, particularly the concept of multi-targeting and formulation of disease-modifying strategies. SAR, pharmacological targets, in vitro/vivo ADMET, efficacy in AD animal models, and applications in clinical trials of such sulfur compounds have also been discussed. This article provides a comprehensive review of organosulfur-based AD therapeutic agents and provides insights into their future development.

Protecting the aging eye with hydrogen sulfide

Research demonstrates that senescence is associated with tissue and organ dysfunction, and the eye is no exception. Sequelae arising from aging have been well defined as distinct clinical entities and vision impairment has significant psychosocial consequences. Retina and adjacent tissues like retinal pigmented epithelium and choroid are the key structures that are required for visual perception. Any structural and functional changes in retinal layers and blood retinal barrier could lead to age-related macular degeneration, diabetic retinopathy, and glaucoma. Further, there are significant oxygen gradients in the eye that can lead to excessive reactive oxygen species, resulting in endoplasmic reticulum and mitochondrial stress response. These radicals are source of functional and morphological impairment in retinal pigmented epithelium and retinal ganglion cells. Therefore, ocular diseases could be summarized as disturbance in the redox homeostasis. Hyperhomocysteinemia is a risk factor and causes vascular occlusive disease of the retina. Interestingly, hydrogen sulfide (H₂S) has been proven to be an effective antioxidant agent, and it can help treat diseases by alleviating stress and inflammation. Concurrent glutamate excitotoxicity, endoplasmic reticulum stress, and microglia activation are also linked to stress; thus, H₂S may offer additional interventional strategy. A refined understanding of the aging eye along with H₂S biology and pharmacology may help guide newer therapies for the eye.

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 and Endoplasmic Reticulum Stress: A Potential Therapeutic Target for Central Nervous System Degeneration Diseases

There are three members of the endogenous gas transmitter family. The first two are nitric oxide and carbon monoxide, and the third newly added member is hydrogen sulfide (H₂S). They all have similar functions: relaxing blood vessels, smoothing muscles, and getting involved in the regulation of neuronal excitation, learning, and memory. The cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfur transferase acts together with cysteine aminotransferase (3-MST/CAT), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfur transferase with D-amino acid oxidase (3-MST/DAO) pathways are involved in the enzymatic production of H₂S. More and more researches focus on the role of H₂S in the central nervous system (CNS), and H₂S plays a significant function in neuroprotection processes, regulating the function of the nervous system as a signaling molecule in the CNS. Endoplasmic reticulum stress (ERS) and protein misfolding in its mechanism are related to neurodegenerative diseases. H₂S exhibits a wide variety of cytoprotective and physiological functions in the CNS degenerative diseases by regulating ERS. This review summarized on the neuroprotective effect of H₂S for ERS played in several CNS diseases including Alzheimer’s disease, Parkinson’s disease, and depression disorder, and discussed the corresponding possible signaling pathways or mechanisms as well.

GYY4137 Promotes Mice Feeding Behavior via Arcuate Nucleus Sulfur-Sulfhydrylation and AMPK Activation

Hydrogen sulfide (H₂S) is an endogenous gaseous molecule and plays important biological and neurochemical roles in many processes such as the neural activity and immunity. The arcuate nucleus (ARC) of hypothalamus is a control center for appetite and energy metabolism. AMPK is a gage kinase in the monitoring of energy status and regulation of energy metabolism, and it can be activated by H₂S via CaMKKβ/AMPK pathway. But the role of H₂S in ARC and appetite has not been reported. Here we studied the orexigenic effect of H₂S and the mechanisms by means of GYY4137, a water soluble and slow-releasing donor of H₂S, and protein sulfur-sulfhydrylation analysis. We demonstrated that GYY4137-derived H₂S increased food intake of mice, augmented the production of neuropeptide Y (NPY), and elevated the protein sulfur-sulfhydrylation level and the activation of AMPK and CaMKKβ in ARC. Blocking sulfur-sulfhydrylation with DTT eliminated GYY4137-induced activation of AMPK and CaMKKβ. DTT and preventing AMPK activation in ARC with Compound C and Ara-A could both attenuate the orexigenic effect of GYY4137. These findings suggest that H₂S enhances appetite through protein sulfur-sulfhydrylation and the activation of AMPK and NPY function in ARC.

Neuroprotective Effect of Hydrogen Sulfide in Hyperhomocysteinemia Is Mediated Through Antioxidant Action Involving Nrf2

Homocysteine (Hcy) is a sulfur-containing amino acid derived from methionine metabolism. Elevated plasma Hcy levels (> 15 µM) result in a condition called hyperhomocysteinemia (HHcy), which is an independent risk factor in the development of various neurodegenerative disorders. Reactive oxygen species (ROS) produced by auto-oxidation of Hcy have been implicated in HHcy-associated neurological conditions. Hydrogen sulfide (H₂S) is emerging as a potent neuroprotective and neuromodulator molecule. The present study was aimed to evaluate the ability of NaHS (a source of H₂S) to attenuate Hcy-induced oxidative stress and altered antioxidant status in animals subjected to HHcy. Impaired cognitive functions assessed by Y-maze and elevated plus maze in Hcy-treated animals were reversed on NaHS administration. Increased levels of ROS, lipid peroxidation, protein carbonyls, and 4-hydroxynonenal (4-HNE)-modified proteins were observed in the cortex and hippocampus of Hcy-treated animals suggesting accentuated oxidative stress. This increase in Hcy-induced oxidative stress was reversed following NaHS supplementation. GSH/GSSG ratio, activity of antioxidant enzymes viz; superoxide dismutase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were decreased in Hcy-treated animals. NaHS supplementation, on the otherhand, restored redox ratio and activity of antioxidant enzymes in the brains of animals with HHcy. Further, NaHS administration normalized nuclear factor erythroid 2-related factor 2 expression and acetylcholinesterase (AChE) activity in the brain of Hcy-treated animals. Histopathological studies using cresyl violet indicated higher number of pyknotic neurons in the cortex and hippocampus of HHcy animals, which were reversed by NaHS administration. The results clearly demonstrate that NaHS treatment significantly ameliorates Hcy-induced cognitive impairment by attenuating oxidative stress, improving antioxidant status, and modulating AChE activity thereby suggesting potential of H₂S as a therapeutic molecule.

Activation of autophagic flux and the Nrf2/ARE signaling pathway by hydrogen sulfide protects against acrylonitrile-induced neurotoxicity in primary rat astrocytes

Hydrogen sulfide (H₂S), the third gasotransmitter, has been shown to act as a neuroprotective factor in numerous pathological processes; however, its underlying mechanism(s) of action remain unclear. It is widely accepted that activation of moderate autophagy and the Nrf2/ARE signaling pathway play important roles in the biological self-defense systems. In the present study, we investigated whether exogenous H₂S protects against the cytotoxicity of acrylonitrile (AN), a neurotoxin, in primary rat astrocytes. We found that pretreatment for 1 h with sodium hydrosulfide (NaHS), a donor of H₂S (200-800 µM), significantly attenuated the AN-induced decrease in cell viability, increase in lactate dehydrogenase release and morphological changes. Furthermore, NaHS significantly attenuated AN-induced oxidative stress by reducing reactive oxygen species (ROS) levels and increasing glutathione (GSH) concentration. Moreover, NaHS activated the autophagic flux, detectable as a change in autophagy-related proteins (Beclin-1, Atg5 and p62), the formation of acidic vesicular organelles and LC3B aggregation, confirmed by adenoviral expression of mRFP-GFP-LC3. Additionally, NaHS stimulated translocation of Nrf2 into the nucleus and increased expression of heme oxygenase-1 and γ-glutamylcysteine synthetase, downstream targets of Nrf2. Notably, the autophagy inhibitor 3-methyladenine and Beclin-1, or Nrf2-targeted siRNA, significantly attenuated the neuroprotective effects of NaHS against AN-induced neurotoxicity. In conclusion, we identified a crucial role of  autophagy and the Nrf2/ARE signaling pathway in H₂S-mediated neuroprotection against AN-induced toxicity in primary rat astrocytes. Our findings provide novel insights into the mechanisms of H₂S-mediated neuroprotection, and suggest that H₂S-based donors may serve as potential new candidate drugs to treat AN-induced neurotoxicity.

Hydrogen sulfide, nitric oxide, and neurodegenerative disorders

Hydrogen Sulfide (H2S) and Nitric Oxide (NO) have become recognized as important gaseous signaling molecules with enormous pharmacological effects, therapeutic value, and central physiological roles. NO is one of the most important regulators of the pathophysiological condition in central nervous system (CNS). It is critical in the various functioning of the brain; however, beyond certain concentration/level, it is toxic. H2S was regarded as toxic gas with the smell like rotten egg. But, it is now regarded as emerging neuroprotectant and neuromodulator. Recently, the use of donors and inhibitors of these signaling molecules have helped us to identify their accurate and precise biological effects. The most abundant neurotransmitter of CNS (glutamate) is the initiator of the reaction that forms NO, and H2S is highly expressed in brain. These molecules are shedding light on the pathogenesis of various neurological disorders. This review is mainly focused on the importance of H2S and NO for normal functioning of CNS.

Recent Development of Hydrogen Sulfide Releasing/Stimulating Reagents and Their Potential Applications in Cancer and Glycometabolic Disorders

As an important endogenous gaseous signaling molecule, hydrogen sulfide (H₂S) exerts various effects in the body. A variety of pathological changes, such as cancer, glycometabolic disorders, and diabetes, are associated with altered endogenous levels of H₂S, especially decreased. Therefore, the supplement of H₂S is of great significance for the treatment of diseases containing the above pathological changes. At present, many efforts have been made to increase the in vivo levels of H₂S by administration of gaseous H₂S, simple inorganic sulfide salts, sophisticated synthetic slow-releasing controllable H₂S donors or materials, and using H₂S stimulating agents. In this article, we reviewed the recent development of H₂S releasing/stimulating reagents and their potential applications in two common pathological processes including cancer and glycometabolic disorders.

Hydrogen sulfide modulates eukaryotic translation initiation factor 2α (eIF2α) phosphorylation status in the integrated stress-response pathway

Hydrogen sulfide (H₂S) regulates various physiological processes, including neuronal activity, vascular tone, inflammation, and energy metabolism. Moreover, H₂S elicits cytoprotective effects against stressors in various cellular models of injury. However, the mechanism of the signaling pathways mediating the cytoprotective functions of H₂S is not well understood. We previously uncovered a heme-dependent metabolic switch for transient induction of H₂S production in the trans-sulfuration pathway. Here, we demonstrate that increased endogenous H₂S production or its exogenous administration modulates major components of the integrated stress response promoting a metabolic state primed for stress response. We show that H₂S transiently increases phosphorylation of eukaryotic translation initiation factor 2 (eIF2α) resulting in inhibition of general protein synthesis. The H₂S-induced increase in eIF2α phosphorylation was mediated at least in part by inhibition of protein phosphatase-1 (PP1c) via persulfidation at Cys-127. Overexpression of a PP1c cysteine mutant (C127S-PP1c) abrogated the H₂S effect on eIF2α phosphorylation. Our data support a model in which H₂S exerts its cytoprotective effect on ISR signaling by inducing a transient adaptive reprogramming of global mRNA translation. Although a transient increase in endogenous H₂S production provides cytoprotection, its chronic increase such as in cystathionine β-synthase deficiency may pose a problem.

Hydrogen Sulfide Ameliorates Homocysteine-Induced Cognitive Dysfunction by Inhibition of Reactive Aldehydes Involving Upregulation of ALDH2

BACKGROUND

Homocysteine, a risk factor for Alzheimer's disease, induces cognitive dysfunction. Reactive aldehydes play an important role in cognitive dysfunction. Aldehyde-dehydrogenase 2 detoxifies reactive aldehydes. Hydrogen sulfide, a novel neuromodulator, has neuroprotective effects and regulates learning and memory. Our previous work confirmed that the disturbance of hydrogen sulfide synthesis is invovled in homocysteine-induced defects in learning and memory. Therefore, the present work was to explore whether hydrogen sulfide ameliorates homocysteine-generated cognitive dysfunction and to investigate whether its underlying mechanism is related to attenuating accumulation of reactive aldehydes by upregulation of aldehyde-dehydrogenase 2.

METHODS

The cognitive function of rats was assessed by the Morris water maze test and the novel object recognition test. The levels of malondialdehyde, 4-hydroxynonenal, and glutathione as well as the activity of aldehyde-dehydrogenase 2 were determined by enzyme linked immunosorbent assay; the expression of aldehyde-dehydrogenase 2 was detected by western blot.

RESULTS

The behavior experiments, Morris water maze test and novel objects recognition test, showed that homocysteine induced deficiency in learning and memory in rats, and this deficiency was reversed by treatment of NaHS (a donor of hydrogen sulfide). We demonstrated that NaHS inhibited homocysteine-induced increases in generations of MDA and 4-HNE in the hippocampus of rats and that hydrogen sulfide reversed homocysteine-induced decreases in the level of glutathione as well as the activity and expression of aldehyde-dehydrogenase 2 in the hippocampus of rats.

CONCLUSION

Hydrogen sulfide ameliorates homocysteine-induced impairment in cognitive function by decreasing accumulation of reactive aldehydes as a result of upregulations of glutathione and aldehyde-dehydrogenase 2.

AP39, a Mitochondria-Targeted Hydrogen Sulfide Donor, Supports Cellular Bioenergetics and Protects against Alzheimer's Disease by Preserving Mitochondrial Function in APP/PS1 Mice and Neurons

Increasing evidence suggests that mitochondrial functions are altered in AD and play an important role in AD pathogenesis. It has been established that H₂S homeostasis is balanced in AD. The emerging mitochondrial roles of H₂S include antioxidation, antiapoptosis, and the modulation of cellular bioenergetics. Here, using primary neurons from the well-characterized APP/PS1 transgenic mouse model, we studied the effects of AP39 (a newly synthesized mitochondrially targeted H₂S donor) on mitochondrial function. AP39 increased intracellular H₂S levels, mainly in mitochondrial regions. AP39 exerted dose-dependent effects on mitochondrial activity in APP/PS1 neurons, including increased cellular bioenergy metabolism and cell viability at low concentrations (25–100 nM) and decreased energy production and cell viability at a high concentration (250 nM). Furthermore, AP39 (100 nM) increased ATP levels, protected mitochondrial DNA, and decreased ROS generation. AP39 regulated mitochondrial dynamics, shifting from fission toward fusion. After 6 weeks, AP39 administration to APP/PS1 mice significantly ameliorated their spatial memory deficits in the Morris water maze and NORT and reduced Aβ deposition in their brains. Additionally, AP39 inhibited brain atrophy in APP/PS1 mice. Based on these results, AP39 was proposed as a promising drug candidate for AD treatment, and its anti-AD mechanism may involve protection against mitochondrial damage.

Hydrogen Sulfide Selectively Inhibits γ-Secretase Activity and Decreases Mitochondrial Aβ Production in Neurons from APP/PS1 Transgenic Mice

Hydrogen sulfide (H2S) is now considered to be a gasotransmitter and may be involved in the pathological process of Alzheimer's disease (AD). A majority of APP is associated with mitochondria and is a substrate for the mitochondrial γ-secretase. The mitochondria-associated APP metabolism where APP intracellular domains (AICD) and Aβ are generated locally and may contribute to mitochondrial dysfunction in AD. Here, we aimed to investigate the ability of H2S to mediate APP processing in mitochondria and assessed the possible mechanisms underlying H2S-mediated AD development. We treated neurons from APP/PS1 transgenic mice with a range of sodium hydrosulfide (NaHS) concentrations. NaHS attenuated APP processing and decreased Aβ production in mitochondria. Meanwhile, NaHS did not changed BACE-1 and ADAM10 (a disintegrin and metalloprotease 10) protein levels, but NaHS (30 μM) significantly increased the levels of presenilin 1(PS1), PEN-2, and NCT, as well as improved the γ-secretase activity, while NaHS (50 μM) exhibits the opposing effects. Furthermore, the intracellular ATP and the COX IV activity of APP/PS1 neurons were increased after 30 μM NaHS treatment, while the ROS level was decreased and the MMP was stabilized. The effect of NaHS differs from DAPT (a non-selective γ-secretase inhibitor), and it selectively inhibited γ-secretase in vitro, without interacting with Notch and modulating its cleavage. The results indicated that NaHS decreases Aβ accumulation in mitochondria by selectively inhibiting γ-secretase. Thus, we provide a mechanistic view of NaHS is a potential anti-AD drug candidate and it may decrease Aβ deposition in mitochondria by selectively inhibiting γ-secretase activity and therefore protecting the mitochondrial function during AD conditions.

The Neuroprotective Effects of Decursin Isolated from Angelica gigas Nakai Against Amyloid β-Protein-Induced Apoptosis in PC 12 Cells via a Mitochondria-Related Caspase Pathway

Decursin, purified from Angelica gigas Nakai, has been proven to exert neuroprotective property. Previous study revealed decursin protected the PC12 cells from Aβ25-35-induced oxidative cytotoxicity. The present study aimed to investigate whether decursin could protect PC12 cells from apoptosis caused by Aβ. Our results indicated that pretreatment of PC12 cells with decursin significantly inhibited Aβ25-35-induced cytotoxicity and apoptosis. The mechanism of action is likely to reverse Aβ25-35-induced mitochondrial dysfunction, including the reduction of mitochondrial membrane potential, the inhibition of reactive oxygen species production, and the decrease of mitochondrial release of cytochrome c in PC12 cells. In addition, decursin significantly suppressed the activity of caspase-3 and moderated the ratio of Bcl-2/Bax induced by Aβ25-35. These findings indicate that decursin exerts a neuroprotective effect against Aβ25-35-induced neurotoxicity in PC12 cells, at least in part, via suppressing the mitochondrial pathway of cellular apoptosis.

Hydrogen Sulfide Prevents Advanced Glycation End-Products Induced Activation of the Epithelial Sodium Channel

Advanced glycation end-products (AGEs) are complex and heterogeneous compounds implicated in diabetes. Sodium reabsorption through the epithelial sodium channel (ENaC) at the distal nephron plays an important role in diabetic hypertension. Here, we report that H₂S antagonizes AGEs-induced ENaC activation in A6 cells. ENaC open probability (P_O) in A6 cells was significantly increased by exogenous AGEs and that this AGEs-induced ENaC activity was abolished by NaHS (a donor of H₂S) and TEMPOL. Incubating A6 cells with the catalase inhibitor 3-aminotriazole (3-AT) mimicked the effects of AGEs on ENaC activity, but did not induce any additive effect. We found that the expression levels of catalase were significantly reduced by AGEs and both AGEs and 3-AT facilitated ROS uptake in A6 cells, which were significantly inhibited by NaHS. The specific PTEN and PI3K inhibitors, BPV_(pic) and LY294002, influence ENaC activity in AGEs-pretreated A6 cells. Moreover, after removal of AGEs from AGEs-pretreated A6 cells for 72 hours, ENaC P_O remained at a high level, suggesting that an AGEs-related “metabolic memory” may be involved in sodium homeostasis. Our data, for the first time, show that H₂S prevents AGEs-induced ENaC activation by targeting the ROS/PI3K/PTEN pathway.

Cystathionine β-synthase inhibition is a potential therapeutic approach to treatment of ischemic injury

Hydrogen sulfide (H2S) has been reported to exacerbate stroke outcome in experimental models. Cystathionine β-synthase (CBS) has been implicated as the predominant H2S-producing enzyme in central nervous system. When SH-SY5Y cells were transfected to overexpress CBS, these cells were able to synthesize H2S when exposed to high levels of enzyme substrates but not substrate concentrations that may reflect normal physiological conditions. At the same time, these cells demonstrated exacerbated cell death when subjected to oxygen and glucose deprivation (OGD) together with high substrate concentrations, indicating that H2S production has a detrimental effect on cell survival. This effect could be abolished by CBS inhibition. The same effect was observed with primary astrocytes exposed to OGD and high substrates or sodium hydrosulfide. In addition, CBS was upregulated and activated by truncation in primary astrocytes subjected to OGD. When rats were subjected to permanent middle cerebral artery occlusion, CBS activation was also observed. These results imply that in acute ischemic conditions, CBS is upregulated and activated by truncation causing an increased production of H2S, which exacerbate the ischemic injuries. Therefore, CBS inhibition may be a viable approach to stroke treatment.

Hydrogen sulfide-based therapeutics: exploiting a unique but ubiquitous gasotransmitter

Hydrogen sulfide (H2S) has become recognized as an important signalling molecule throughout the body, contributing to many physiological and pathological processes. In recent years, improved methods for measuring H2S levels and the availability of a wider range of H2S donors and more selective inhibitors of H2S synthesis have helped to more accurately identify the many biological effects of this highly reactive gaseous mediator. Animal studies of several H2S-releasing drugs have demonstrated considerable promise for the safe treatment of a wide range of disorders. Several such drugs are now in clinical trials.

Hydrogen sulfide inhibits homocysteine-induced endoplasmic reticulum stress and neuronal apoptosis in rat hippocampus via upregulation of the BDNF-TrkB pathway

AIM

Homocysteine (Hcy) can elicit neuronal cell death, and hyperhomocysteinemia is a strong independent risk factor for Alzheimer's disease. The aim of this study was to examine the effects of hydrogen sulfide (H2S) on Hcy-induced endoplasmic reticulum (ER) stress and neuronal apoptosis in rat hippocampus.

METHODS

Adult male SD rats were intracerebroventricularly (icv) injected with Hcy (0.6 μmol/d) for 7 d. Before Hcy injection, the rats were treated with NaHS (30 or 100 μmol·kg(-1)·d(-1), ip) and/or k252a (1 μg/d, icv) for 2 d. The apoptotic neurons were detected in hippocampal coronal slices with TUNEL staining. The expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cleaved caspase-12, and BDNF in the hippocampus were examined using Western blotting assays. The generation of H2S in the hippocampus was measured with the NNDPD method.

RESULTS

Hcy markedly inhibited the production of endogenous H2S and increased apoptotic neurons in the hippocampus. Furthermore, Hcy induced ER stress responses in the hippocampus, as indicated by the upregulation of GRP78, CHOP, and cleaved caspase-12. Treatment with the H2S donor NaHS increased the endogenous H2S production and BDNF expression in a dose-dependent manner, and significantly reduced Hcy-induced neuronal apoptosis and ER stress responses in the hippocampus. Treatment with k252a, a specific inhibitor of TrkB (the receptor of BDNF), abolished the protective effects of NaHS against Hcy-induced ER stress in the hippocampus.

CONCLUSION

H2S attenuates ER stress and neuronal apoptosis in the hippocampus of Hcy-treated rats via upregulating the BDNF-TrkB pathway.

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 [corrected] increases survival during sepsis: protective effect of CHOP inhibition

Sepsis is a major cause of mortality, and dysregulation of the immune response plays a central role in this syndrome. H2S, a recently discovered gaso-transmitter, is endogenously generated by many cell types, regulating a number of physiologic processes and pathophysiologic conditions. We report that H2S increased survival after experimental sepsis induced by cecal ligation and puncture (CLP) in mice. Exogenous H2S decreased the systemic inflammatory response, reduced apoptosis in the spleen, and accelerated bacterial eradication. We found that C/EBP homologous protein 10 (CHOP), a mediator of the endoplasmic reticulum stress response, was elevated in several organs after CLP, and its expression was inhibited by H2S treatment. Using CHOP-knockout (KO) mice, we demonstrated for the first time, to our knowledge, that genetic deletion of Chop increased survival after LPS injection or CLP. CHOP-KO mice displayed diminished splenic caspase-3 activation and apoptosis, decreased cytokine production, and augmented bacterial clearance. Furthermore, septic CHOP-KO mice treated with H2S showed no additive survival benefit compared with septic CHOP-KO mice. Finally, we showed that H2S inhibited CHOP expression in macrophages by a mechanism involving Nrf2 activation. In conclusion, our findings show a protective effect of H2S treatment afforded, at least partially, by inhibition of CHOP expression. The data reveal a major negative role for the transcription factor CHOP in overall survival during sepsis and suggest a new target for clinical intervention, as well potential strategies for treatment.

Aggravation of seizure-like events by hydrogen sulfide: involvement of multiple targets that control neuronal excitability

AIMS

Epileptic seizures are well-known neurological complications following stroke, occurring in 3% of patients. However, the intrinsic correlation of seizures with stroke remains largely unknown. Hydrogen sulfide (H2 S) is a gas transmitter that may mediate cerebral ischemic injury. But the role of H2 S in seizures has not been understood yet. We examined the effect of H2 S on seizure-like events (SLEs) and underlying mechanisms.

METHODS AND RESULTS

Pentylenetetrazole (PTZ)- and pilocarpine-induced rat epileptic seizure models were tested. Low-Mg(2+) /high-K(+) - and 4-aminopyridine (4-AP)-induced epileptic seizure models were examined using patch-clamp recordings in brain slices. It was found that NaHS aggravated both PTZ- and pilocarpine-induced SLEs in rats, while both low-Mg(2+) /high-K(+) - and 4-AP-induced SLEs were also exacerbated by NaHS in brain slices, which may be due to its regulation on the voltage-gated sodium channel, N-methyl-D-aspartic acid receptor (NMDAR), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function. Furthermore, these effects were reversed by blocking voltage-gated sodium channel, NMDAR, and AMPAR.

CONCLUSIONS

These results suggest a pathological role of increased H2 S level in SLEs in vivo and in vitro. Enzymes that control H2 S biosynthesis could be interesting targets for antiepileptic strategies in poststroke epilepsy treatment.

Sodium/calcium exchanger is upregulated by sulfide signaling, forms complex with the β1 and β3 but not β2 adrenergic receptors, and induces apoptosis

Hydrogen sulfide (H2S) as a novel gasotransmitter regulates variety of processes, including calcium transport systems. Sodium calcium exchanger (NCX) is one of the key players in a regulation calcium homeostasis. Thus, the aims of our work were to determine effect of sulfide signaling on the NCX type 1 (NCX1) expression and function in HeLa cells, to investigate the relationship of β-adrenergic receptors with the NCX1 in the presence and/or absence of H2S, and to determine physiological importance of this potential communication. As a H2S donor, we used morpholin-4-ium-4-methoxyphenyl(morpholino) phosphinodithioate-GYY4137. We observed increased levels of the NCX1 mRNA, protein, and activity after 24 h of GYY4137 treatment. This increase was accompanied by elevated cAMP due to the GYY4137 treatment, which was completely abolished, when NCX1 was silenced. Increased cAMP levels would point to upregulation of β-adrenergic receptors. Indeed, GYY4137 increased expression of β1 and β3 (but not β2) adrenergic receptors. These receptors co-precipitated, co-localized with the NCX1, and induced apoptosis in the presence of H2S. Our results suggest that sulfide signaling plays a role in regulation of the NCX1, β1 and β3 adrenergic receptors, their co-localization, and stimulation of apoptosis, which might be of a potential importance in cancer treatment.

Hydrogen sulfide prevents hydrogen peroxide-induced activation of epithelial sodium channel through a PTEN/PI(3,4,5)P3 dependent pathway

Sodium reabsorption through the epithelial sodium channel (ENaC) at the distal segment of the kidney plays an important role in salt-sensitive hypertension. We reported previously that hydrogen peroxide (H₂O₂) stimulates ENaC in A6 distal nephron cells via elevation of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P₃) in the apical membrane. Here we report that H₂S can antagonize H₂O₂-induced activation of ENaC in A6 cells. Our cell-attached patch-clamp data show that ENaC open probability (P_O) was significantly increased by exogenous H₂O₂, which is consistent with our previous finding. The aberrant activation of ENaC induced by exogenous H₂O₂ was completely abolished by H₂S (0.1 mM NaHS). Pre-treatment of A6 cells with H₂S slightly decreased ENaC P_O; however, in these cells H₂O₂ failed to elevate ENaC P_O. Confocal microscopy data show that application of exogenous H₂O₂ to A6 cells significantly increased intracellular reactive oxygen species (ROS) level and induced accumulation of PI(3,4,5)P₃ in the apical compartment of the cell membrane. These effects of exogenous H₂O₂ on intracellular ROS levels and on apical PI(3,4,5)P₃ levels were almost completely abolished by treatment of A6 cells with H₂S. In addition, H₂S significantly inhibited H₂O₂-induced oxidative inactivation of the tumor suppressor phosphatase and tensin homolog (PTEN) which is a negative regulator of PI(3,4,5)P_3. Moreover, BPV_(pic), a specific inhibitor of PTEN, elevated PI(3,4,5)P₃ and ENaC activity in a manner similar to that of H₂O₂ in A6 cells. Our data show, for the first time, that H₂S prevents H₂O₂-induced activation of ENaC through a PTEN-PI(3,4,5)P₃ dependent pathway.

A novel mechanism of formaldehyde neurotoxicity: inhibition of hydrogen sulfide generation by promoting overproduction of nitric oxide

Background

Formaldehyde (FA) induces neurotoxicity by overproduction of intracellular reactive oxygen species (ROS). Increasing studies have shown that hydrogen sulfide (H₂S), an endogenous gastransmitter, protects nerve cells against oxidative stress by its antioxidant effect. It has been shown that overproduction of nitric oxide (NO) inhibits the activity of cystathionine-beta-synthase (CBS), the predominant H₂S-generating enzyme in the central nervous system.

Objective

We hypothesize that FA-caused neurotoxicity involves the deficiency of this endogenous protective antioxidant gas, which results from excessive generation of NO. The aim of this study is to evaluate whether FA disturbs H₂S synthesis in PC12 cells, and whether this disturbance is associated with overproduction of NO.

Principal Findings

We showed that exposure of PC12 cells to FA causes reduction of viability, inhibition of CBS expression, decrease of endogenous H₂S production, and NO production. CBS silencing deteriorates FA-induced decreases in endogenous H₂S generation, neurotoxicity, and intracellular ROS accumulation in PC12 cells; while ADMA, a specific inhibitor of NOS significantly attenuates FA-induced decreases in endogenous H₂S generation, neurotoxicity, and intracellular ROS accumulation in PC12 cells.

Conclusion/Significance

Our data indicate that FA induces neurotoxicity by inhibiting the generation of H₂S through excess of NO and suggest that strategies to manipulate endogenous H₂S could open a suitable novel therapeutic avenue for FA-induced neurotoxicity.

Formaldehyde impairs learning and memory involving the disturbance of hydrogen sulfide generation in the hippocampus of rats

Formaldehyde (FA), a well-known indoor and outdoor pollutant, has been implicated as the responsible agent in the development of neurocognitive disorders. Hydrogen sulfide (H(2)S), the third gasotransimitter, is an endogenous neuromodulator, which facilitates the induction of hippocampal long-term potentiation, involving the functions of learning and memory. In the present study, we analyzed the effects of intracerebroventricular injection of FA on the formation of learning and memory and the generation of endogenous H(2)S in the hippocampus of rats. We found that the intracerebroventricular injection of FA in rats impairs the function of learning and memory in the Morris water maze and novel object recognition test and increases the formation of apoptosis and lipid peroxidation in the hippocampus. We also showed that FA exposure inhibits the expression of cystathionine β-synthase, the major enzyme responsible for endogenous H(2)S generation in hippocampus and decreases the production of endogenous H(2)S in hippocampus in rats. These results suggested that FA-disturbed generation of endogenous H(2)S in hippocampus leads to the oxidative stress-mediated neuron damage, ultimately impairing the function of learning and memory. Our findings imply that the disturbance of endogenous H(2)S generation in hippocampus is a potential contributing mechanism underling FA-caused learning and memory impairment.

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

Exposure to particulate air pollution is associated with increased cardiopulmonary morbidity and mortality, although the pathogenic mechanisms are poorly understood. We previously demonstrated that particulate matter (PM) exposure triggers massive oxidative stress in vascular endothelial cells (ECs), resulting in the loss of EC integrity and lung vascular hyperpermeability. We investigated the protective role of hydrogen sulfide (H(2)S), an endogenous gaseous molecule present in the circulation, on PM-induced human lung EC barrier disruption and pulmonary inflammation. Alterations in EC monolayer permeability, as reflected by transendothelial electrical resistance (TER), the generation of reactive oxygen species (ROS), and murine pulmonary inflammatory responses, were studied after exposures to PM and NaSH, an H(2)S donor. Similar to N-acetyl cysteine (5 mM), NaSH (10 μM) significantly scavenged PM-induced EC ROS and inhibited the oxidative activation of p38 mitogen-activated protein kinase. Concurrent with these events, NaSH (10 μM) activated Akt, which helps maintain endothelial integrity. Both of these pathways contribute to the protective effect of H(2)S against PM-induced endothelial barrier dysfunction. Furthermore, NaSH (20 mg/kg) reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in bronchoalveolar lavage fluids in a murine model of PM-induced lung inflammation. These data suggest a potentially protective role for H(2)S in PM-induced inflammatory lung injury and vascular hyperpermeability.

Hydrogen sulfide protects against chemical hypoxia-induced injury by inhibiting ROS-activated ERK1/2 and p38MAPK signaling pathways in PC12 cells

Hydrogen sulfide (H(2)S) has been proposed as a novel neuromodulator and neuroprotective agent. Cobalt chloride (CoCl(2)) is a well-known hypoxia mimetic agent. We have demonstrated that H(2)S protects against CoCl(2)-induced injuries in PC12 cells. However, whether the members of mitogen-activated protein kinases (MAPK), in particular, extracellular signal-regulated kinase1/2(ERK1/2) and p38MAPK are involved in the neuroprotection of H(2)S against chemical hypoxia-induced injuries of PC12 cells is not understood. We observed that CoCl(2) induced expression of transcriptional factor hypoxia-inducible factor-1 alpha (HIF-1α), decreased cystathionine-β synthase (CBS, a synthase of H(2)S) expression, and increased generation of reactive oxygen species (ROS), leading to injuries of the cells, evidenced by decrease in cell viability, dissipation of mitochondrial membrane potential (MMP) , caspase-3 activation and apoptosis, which were attenuated by pretreatment with NaHS (a donor of H(2)S) or N-acetyl-L cystein (NAC), a ROS scavenger. CoCl(2) rapidly activated ERK1/2, p38MAPK and C-Jun N-terminal kinase (JNK). Inhibition of ERK1/2 or p38MAPK or JNK with kinase inhibitors (U0126 or SB203580 or SP600125, respectively) or genetic silencing of ERK1/2 or p38MAPK by RNAi (Si-ERK1/2 or Si-p38MAPK) significantly prevented CoCl(2)-induced injuries. Pretreatment with NaHS or NAC inhibited not only CoCl(2)-induced ROS production, but also phosphorylation of ERK1/2 and p38MAPK. Thus, we demonstrated that a concurrent activation of ERK1/2, p38MAPK and JNK participates in CoCl(2)-induced injuries and that H(2)S protects PC12 cells against chemical hypoxia-induced injuries by inhibition of ROS-activated ERK1/2 and p38MAPK pathways. Our results suggest that inhibitors of ERK1/2, p38MAPK and JNK or antioxidants may be useful for preventing and treating hypoxia-induced neuronal injury.

ACS6, a Hydrogen sulfide-donating derivative of sildenafil, inhibits homocysteine-induced apoptosis by preservation of mitochondrial function

BACKGROUND

The hydrogen sulfide-releasing sildenafil, ACS6, has been demonstrated to inhibit superoxide formation through donating hydrogen sulfide (H2S). We have found that H2S antagonizes homocysteine-induced oxidative stress and neurotoxicity. The aim of the present study is to explore the protection of ACS6 against homocysteine-triggered cytotoxicity and apoptosis and the molecular mechanisms underlying in PC12 cells.

METHODS

Cell viability was determined by Cell Counting Kit-8 assay. Cell apoptosis was observed using the chromatin dye Hoechst 33258 and analyzed by Flow Cytometry after propidium iodide staining. Mitochondrial membrane potential was monitored using the fluorescent dye Rh123. Intracellular reactive oxygen species were determined by oxidative conversion of cell permeable 2',7'-dichlorfluorescein-diacetate to fluorescent 2',7'-dichlorfluorescein. The expression of cleaved caspase-3 and bcl-2 and the accumulation of cytosolic cytochrome c were analyzed by Western blot.

RESULTS

We show that ACS6 protects PC12 cells against cytotoxicity and apoptosis induced by homocysteine and blocks homocysteine-triggered cytochrome c release and caspase-3 activation. ACS6 treatment results in not only prevention of homocysteine-caused mitochondrial membrane potential (Δψ) loss and reactive oxygen species (ROS) overproduction but also reversal of Bcl-2 down-expression.

CONCLUSIONS

These results indicate that ACS6 protects PC12 cells against homocysteine-induced cytotoxicity and apoptosis by preservation of mitochondrial function though inhibiting both loss of Δψ and accumulation of ROS as well as modulating the expression of Bcl-2. Our study provides evidence both for a neuroprotective effect of ACS6 and for further evaluation of ACS6 as novel neuroprotectants for Alzheimer's disease associated with homocysteine.

Inhibition of endogenous hydrogen sulfide generation is associated with homocysteine-induced neurotoxicity: role of ERK1/2 activation

Both elevated homocysteine and decreased hydrogen sulfide (H(2)S) are observed in the brains of Alzheimer's disease (AD) patients. Reactive oxygen species (ROS) overproduction contributes to the neurotoxicity of homocysteine; however, H(2)S is an endogenous antioxidant gas. Therefore, the aim of this study was to investigate whether the imbalance of proportion to this endogenous protective antioxidant gas is involved in homocysteine-caused neurotoxicity. We show that homocysteine inhibits the generation of endogenous H(2)S and the expression and activity of cystathionine-β-synthetase (CBS), the main enzyme responsible for the generation of H(2)S in PC12 cells. S-Adenosylmethionine, an activator of CBS, not only prevents homocysteine-induced inhibition of endogenous H(2)S production but also attenuates homocysteine-triggered cytotoxicity and accumulation of ROS. We find that activation of ERK1/2 occurs in homocysteine-treated PC12 cells and blockade of ERK1/2 with U0126 abolished the homocysteine-induced cytotoxicity and inhibitory effect on endogenous H(2)S generation. These results indicate that homocysteine neurotoxicity involves reduction of H(2)S production, which is caused by inhibition of CBS and mediated by activation of ERK1/2. Our study suggests a promising future of H(2)S-based therapies for neurodegenerative diseases such as AD.

Beneficial effect of a hydrogen sulphide donor (sodium sulphide) in an ovine model of burn- and smoke-induced acute lung injury

BACKGROUND AND PURPOSE

The present study investigated whether the pathophysiological changes induced by burn and smoke inhalation are modulated by parenteral administration of Na(2)S, a H(2)S donor.

EXPERIMENTAL APPROACH

The study used a total of 16 chronically instrumented, adult female sheep. Na(2)S was administered 1 h post injury, as a bolus injection at a dose of 0.5 mg.kg(-1) and subsequently, as a continuous infusion at a rate of 0.2 mg.kg(-1).h(-1) for 24 h. Cardiopulmonary variables (mean arterial and pulmonary arterial blood pressure, cardiac output, ventricular stroke work index, vascular resistance) and arterial and mixed venous blood gases were measured. Lung wet-to-dry ratio and myeloperoxidase content and protein oxidation and nitration were also measured. In addition, lung inducible nitric oxide synthase expression and cytochrome c were measured in lung homogenates via Western blotting and enzyme-linked immunosorbent assay (elisa) respectively.

KEY RESULTS

The H(2)S donor decreased mortality during the 96 h experimental period, improved pulmonary gas exchange and lowered further increase in inspiratory pressure and fluid accumulation associated with burn- and smoke-induced acute lung injury. Further, the H(2)S donor treatment reduced the presence of protein oxidation and 3-nitrotyrosine formation following burn and smoke inhalation injury.

CONCLUSIONS AND IMPLICATIONS

Parenteral administration of the H(2)S donor ameliorated the pulmonary pathophysiological changes associated with burn- and smoke-induced acute lung injury. Based on the effect of H(2)S observed in this clinically relevant model of disease, we propose that treatment with H(2)S or its donors may represent a potential therapeutic strategy in managing patients with acute lung injury.