H2S releasing aspirin protects amyloid beta induced cell toxicity in BV-2 microglial cells

Association between aspirin use and risk of dementia: a systematic review and meta-analysis

PURPOSE

Dementia and Alzheimer's disease (AD) pose significant challenges to public health globally with no effective treatment strategies available. Therefore, the research focuses on developing effective prophylaxis to prevent the onset of these diseases. Recent studies have suggested that low-dose aspirin may help reduce the risk of dementia. Nonetheless, evidence regarding the correlation between aspirin consumption and the onset of dementia and AD is limited. This review aims to provide an up-to-date summary of the existing evidence and evaluate the association between aspirin and the onset of dementia and Alzheimer's disease.

METHODS

A systematic search of PubMed, Embase, Web of Science, PsycINFO, and CINAHL databases was conducted to find eligible studies published until April 2023. A random-effects meta-analysis of the eligible studies was then performed to assess the link between aspirin use and the onset of dementia and Alzheimer's disease. Additionally, we conducted subgroup analyses to evaluate the overall effect of low-dose (75-100 mg) aspirin consumption on the onset of dementia and AD.

RESULTS

A total of 875 studies were identified, with only 22 meeting the inclusion criteria. There was no statistically significant impact of aspirin consumption on the onset of dementia (HR 1.13, 11 studies) or Alzheimer's disease (HR 0.91, 3 studies). Additionally, subgroup analysis showed that taking low doses of aspirin (75-100 mg) did not significantly affect the onset of either dementia (HR 0.96, 13 studies) or Alzheimer's disease (HR 0.85, 2 studies).

CONCLUSIONS

Aspirin use does not decrease the risk of dementia or AD, even when taken in low doses. However, the quality of the studies analyzed was inadequate, with only three randomized controlled trials included in the review. Future high-quality studies are needed to assess the effect of aspirin consumption on these diseases. These findings may assist clinicians in selecting appropriate prophylactic strategies for patients at risk of developing dementia and AD.

Hydrogen Sulfide (H2S) Signaling as a Protective Mechanism against Endogenous and Exogenous Neurotoxicants

In view of the significant role of H₂S in brain functioning, it is proposed that H₂S may also possess protective effects against adverse effects of neurotoxicants. Therefore, the objective of the present review is to discuss the neuroprotective effects of H₂S against toxicity of a wide spectrum of endogenous and exogenous agents involved in the pathogenesis of neurological diseases as etiological factors or key players in disease pathogenesis. Generally, the existing data demonstrate that H₂S possesses neuroprotective effects upon exposure to endogenous (amyloid β, glucose, and advanced-glycation end-products, homocysteine, lipopolysaccharide, and ammonia) and exogenous (alcohol, formaldehyde, acrylonitrile, metals, 6-hydroxydopamine, as well as 1-methyl-4-phenyl- 1,2,3,6- tetrahydropyridine (MPTP) and its metabolite 1-methyl-4-phenyl pyridine ion (MPP)) neurotoxicants. On the one hand, neuroprotective effects are mediated by S-sulfhydration of key regulators of antioxidant (Sirt1, Nrf2) and inflammatory response (NF-κB), resulting in the modulation of the downstream signaling, such as SIRT1/TORC1/CREB/BDNF-TrkB, Nrf2/ARE/HO-1, or other pathways. On the other hand, H₂S appears to possess a direct detoxicative effect by binding endogenous (ROS, AGEs, Aβ) and exogenous (MeHg) neurotoxicants, thus reducing their toxicity. Moreover, the alteration of H₂S metabolism through the inhibition of H₂S-synthetizing enzymes in the brain (CBS, 3-MST) may be considered a significant mechanism of neurotoxicity. Taken together, the existing data indicate that the modulation of cerebral H₂S metabolism may be used as a neuroprotective strategy to counteract neurotoxicity of a wide spectrum of endogenous and exogenous neurotoxicants associated with neurodegeneration (Alzheimer's and Parkinson's disease), fetal alcohol syndrome, hepatic encephalopathy, environmental neurotoxicant exposure, etc. In this particular case, modulation of H₂S-synthetizing enzymes or the use of H₂S-releasing drugs should be considered as the potential tools, although the particular efficiency and safety of such interventions are to be addressed in further studies.

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.

Combined application of H2S and a plant growth promoting strain JIL321 regulates photosynthetic efficacy, soil enzyme activity and growth-promotion in rice under salt stress

Salinity stress is one of the most harmful abiotic stresses that inhibit crop growth and grain yield. In this study, a salt-tolerant bacterium was isolated from the soil of the rice rhizosphere and named Myroides sp. JIL321, based on the results of the phylogenetic tree analysis. The strain JIL321 tolerated up to 1, 283.37 mM of NaCl and exhibited positive plant growth-promoting traits, such as the production of indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Therefore, the effects of JIL321 on rice (Oryza sativa L.) under salinity stress were determined. The inoculation of strain JIL321 significantly increased the chlorophyll content and the accumulation of osmotic adjustment substances, such as proline and soluble sugars, in rice expose to salt stress. Additionally, strain JIL321 inoculation significantly enhanced the activities of some enzymes commonly found in soil, such as urease, invertase and catalase. Moreover, the production of hydrogen sulfide (H₂S), a pivotal signaling molecule, was also induced in rice by salt stress. Treatment with sodium hydrogen sulfide (NaHS, H₂S donor) improved salt stress tolerance of the rice, while treatment with hypotaurine (HT, H₂S scavenger) significantly suppressed it. Interestingly, NaHS treatment also improved the production of IAA and ACC deaminase in strain JIL321 under 0 mM and 150 mM salt concentrations. The combined treatment of JIL321 and NaHS could further improve the growth of salt-stressed rice seedlings, most likely due to the interaction effect between H₂S and strain JIL321. To our knowledge, this study is the first to demonstrate that the combined use of H₂S and plant growth-promoting bacteria could alleviate the adverse effects of salt stress on rice plants, and further verifies the novel role of H₂S as a signaling molecule that enhance the tolerance of plant to abiotic stresses.

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.

Hydrogen sulfide: An endogenous regulator of the immune system

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

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

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

Hemoglobin-Improved Protection in Cultured Cerebral Cortical Astroglial Cells: Inhibition of Oxidative Stress and Caspase Activation

Oxidative stress plays a major role in triggering astroglial cell death in diverse neuropathological conditions such as ischemia and neurodegenerative diseases. Numerous studies indicate that hemoglobin (Hb) is expressed in both resting and reactive glia cells, but nothing is known regarding a possible role of Hb on astroglial cell survival. Thus, the purpose of the present study was to investigate the potential glioprotective effect of Hb on hydrogen peroxide (H₂O₂)-induced oxidative stress and apoptosis in cultured rat astrocytes. Our study demonstrates that administration of graded concentrations of Hb (10^-12 to 10^-6 M) to H₂O₂-treated astrocytes reduces cell death in a concentration-dependent manner. H₂O₂ treatment induces the accumulation of reactive oxygen species (ROS) and nitric oxide (NO), a drop of the mitochondrial membrane potential, and a stimulation of caspase-3/7 activity. Exposure of H₂O₂-treated cells to Hb was accompanied by marked attenuations of ROS and NO surproductions, mitochondrial membrane potential reduction, and caspase-3/7 activity increase. The protective action of Hb was blocked by the protein kinase A (PKA) inhibitor H89, the protein kinase C (PKC) inhibitor chelerythrine, and the mitogen-activated protein (MAP)-kinase kinase (MEK) inhibitor U0126. Taken together, these data demonstrate for the first time that Hb is a glioprotective factor that protects astrocytes from apoptosis induced by oxidative stress and suggest that Hb may confer neuroprotection in neurodegenerative diseases. The anti-apoptotic activity of Hb on astrocytes is mediated through the PKA, PKC, and MAPK transduction pathways and can be accounted for by inhibition of oxidative stress-induced mitochondrial dysfunctions and caspase activation.

Nonsteroidal Anti-Inflammatory Therapy: A Journey Toward Safety

The efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) against inflammation, pain, and fever has been supporting their worldwide use in the treatment of painful conditions and chronic inflammatory diseases until today. However, the long-term therapy with NSAIDs was soon associated with high incidences of adverse events in the gastrointestinal tract. Therefore, the search for novel drugs with improved safety has begun with COX-2 selective inhibitors (coxibs) being straightaway developed and commercialized. Nevertheless, the excitement has fast turned to disappointment when diverse coxibs were withdrawn from the market due to cardiovascular toxicity. Such events have once again triggered the emergence of different strategies to overcome NSAIDs toxicity. Here, an integrative review is provided to address the breakthroughs of two main approaches: (i) the association of NSAIDs with protective mediators and (ii) the design of novel compounds to target downstream and/or multiple enzymes of the arachidonic acid cascade. To date, just one phosphatidylcholine-associated NSAID has already been approved for commercialization. Nevertheless, the preclinical and clinical data obtained so far indicate that both strategies may improve the safety of nonsteroidal anti-inflammatory therapy.

Paeoniflorin attenuates Aβ1-42-induced inflammation and chemotaxis of microglia in vitro and inhibits NF-κB- and VEGF/Flt-1 signaling pathways

Alzheimer׳s disease (AD) is a neurodegenerative disease with elusive pathogenesis, which accounts for most cases of dementia in the aged population. It has been reported that persistent inflammatory responses and excessive chemotaxis of microglia stimulated by beta-amyloid (Aβ) oligomers in the brain may accelerate the progression of AD. The present study was conducted to explore whether paeoniflorin (PF), a water-soluble monoterpene glycoside isolated from the root of Paeonia lactiflora Pallas, could attenuate Aβ1-42-induced toxic effects on primary and BV-2 microglial cells in vitro. Our data showed that PF pretreatment inhibited Aβ1-42-induced production of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 in rodent microglia. Also, the nuclear translocation of nuclear factor kappa B (NF-κB) subunit p65 and the phosphorylation of NF-κB inhibitor alpha (IκBα) in Aβ1-42-stimulated microglial cells were suppressed by PF administration. Moreover, PF treatment reduced the release of chemokine (C-X-C motif) ligand 1 (CXCL1) and chemokine (C-C motif) ligand 2 (CCL-2) from Aβ1-42-stimulated microglia. Additionally, application of PF inhibited the increases in vascular endothelial growth factor (VEGF) and VEGF receptor 1 (Flt-1) triggered by Aβ1-42, and resulted in a concomitant reduction in microglial chemotaxis. Restoration of VEGF was noted to counteract the inhibitory effect of PF, suggesting that PF mitigated Aβ1-42-elicited microglial migration at least partly by suppressing the VEGF/Flt-1 axis. In summary, in presence of Aβ1-42, PF pretreatment inhibited the excessive microglial activation and chemotaxis.

Puerarin protects against β-amyloid-induced microglia apoptosis via a PI3K-dependent signaling pathway

Puerarin extracted from Radix puerariae is well-known for its anti-oxidative and neuroprotective activities. In this study, we investigated the protective effect of puerarin on amyloid-β protein (Aβ)-induced cytotoxicity and its potential mechanisms in BV-2 and primary microglial cells. We found that pretreatment with puerarin afforded protection against Aβ-induced cytotoxicity through inhibiting apoptosis in BV-2 and primary microglial cells. This result was also confirmed by the activated caspase-3 assay. Phospho-Akt and Bcl-2 expression increased after pretreatment with puerarin in BV-2 and primary microglial cells exposed to Aβ, whereas Bax expression and cytochrome c release decreased. In addition, puerarin treatment prevented the loss of mitochondrial membrane potential and reactive oxygen species production. Interestingly, these effects of puerarin against Aβ insult were abolished by LY294002, an inhibitor of PI3K phosphorylation. Taken together, these findings suggest that puerarin prevents Aβ-induced microglial apoptosis via the activation of PI3K/Akt signaling pathway, and might be a potential preventive or therapeutic agent for Alzheimer's disease.

Hydrogen sulfide donors in research and drug development

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

Role of hydrogen sulfide in secondary neuronal injury

In acute neuronal insult events, such as stroke, traumatic brain injury, and spinal cord injury, pathological processes of secondary neuronal injury play a key role in the severity of insult and clinical prognosis. Along with nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H2S) is regarded as the third gasotransmitter and endogenous neuromodulator and plays multiple roles in the central nervous system under physiological and pathological states, especially in secondary neuronal injury. The endogenous level of H2S in the brain is significantly higher than that in peripheral tissues, and is mainly formed by cystathionine β-synthase (CBS) in astrocytes and released in response to neuronal excitation. The mechanism of secondary neuronal injury exacerbating the damage caused by the initial insult includes microcirculation failure, glutamate-mediated excitotoxicity, oxidative stress, inflammatory responses, neuronal apoptosis and calcium overload. H2S dilates cerebral vessels by activating smooth muscle cell plasma membrane ATP-sensitive K channels (KATP channels). This modification occurs on specific cysteine residues of the KATP channel proteins which are S-sulfhydrated. H2S counteracts glutamate-mediated excitotoxicity by inducing astrocytes to intake more glutamate from the extracellular space and thus increasing glutathione in neurons. In addition, H2S protects neurons from secondary neuronal injury by functioning as an anti-oxidant, anti-inflammatory and anti-apoptotic mediator. However, there are still some reports suggest that H2S elevates neuronal Ca(2+) concentration and may contribute to the formation of calcium overload in secondary neuronal injury. H2S also elicits calcium waves in primary cultures of astrocytes and may mediate signals between neurons and glia. Consequently, further exploration of the molecular mechanisms of H2S in secondary neuronal injury will provide important insights into its potential therapeutic uses for the treatment of acute neuronal insult events.

Inhibition of mitochondrial fission attenuates Aβ-induced microglia apoptosis

Mitochondrial division inhibitor 1 (mdivi-1), a selective inhibitor of mitochondrial fission protein dynamin-related protein 1 (Drp1), has been reported to display neuroprotective properties in different animal models. In the present study, we investigated the protective effect of mdivi-1 on β-amyloid protein (Aβ)-induced cytotoxicity and its potential mechanisms in BV-2 and primary microglial cells. We found that mitochondrial fission was increased in Aβ treatment and inhibition of mitochondrial fission by mdivi-1 significantly reduced Aβ-induced expression of CD11b (a marker of microglial activation), viability loss and apoptotic rate increase in BV-2 and primary microglial cells. Moreover, we also found that mdivi-1 treatment markedly reversed mitochondrial membrane potential loss, cytochrome c (CytC) release and caspase-3 activation. Altogether, our data suggested that mdivi-1 exerts neuroprotective effects against Aβ-induced microglial apoptosis, and the underlying mechanism may be through inhibiting mitochondrial membrane potential loss, CytC release and suppression of the mitochondrial apoptosis pathway.

Biology and therapeutic potential of hydrogen sulfide and hydrogen sulfide-releasing chimeras

Hydrogen sulfide, H2S, is a colorless gas with a strong odor that until recently was only considered to be a toxic environmental pollutant with little or no physiological significance. However, the past few years have demonstrated its role in many biological systems and it is becoming increasingly clear that H2S is likely to join nitric oxide (NO) and carbon monoxide (CO) as a major player in mammalian biology. In this review, we have provided an overview of the chemistry and biology of H2S and have summarized the chemistry and biological activity of some natural and synthetic H2S-donating compounds. The naturally occurring compounds discussed include, garlic, sulforaphane, erucin, and iberin. The synthetic H2S donors reviewed include, GYY4137; cysteine analogs; S-propyl cysteine, S-allyl cysteine, S-propargyl cysteine, and N-acetyl cysteine. Dithiolethione and its NSAID and other chimeras such as, L-DOPA, sildenafil, aspirin, diclofenac, naproxen, ibuprofen, indomethacin, and mesalamine have also been reviewed in detail. The newly reported NOSH-aspirin that releases both NO and H2S has also been discussed.

A novel hydrogen sulfide-releasing N-methyl-D-aspartate receptor antagonist prevents ischemic neuronal death

Physiological levels of H(2)S exert neuroprotective effects, whereas high concentrations of H(2)S may cause neurotoxicity in part via activation of NMDAR. To characterize the neuroprotective effects of combination of exogenous H(2)S and NMDAR antagonism, we synthesized a novel H(2)S-releasing NMDAR antagonist N-((1r,3R,5S,7r)-3,5-dimethyladamantan-1-yl)-4-(3-thioxo-3H-1,2-dithiol-4-yl)-benzamide (S-memantine) and examined its effects in vitro and in vivo. S-memantine was synthesized by chemically combining a slow releasing H(2)S donor 4-(3-thioxo-3H-1,2-dithiol-4-yl)-benzoic acid (ACS48) with a NMDAR antagonist memantine. S-memantine increased intracellular sulfide levels in human neuroblastoma cells (SH-SY5Y) 10-fold as high as that was achieved by ACS48. Incubation with S-memantine after reoxygenation following oxygen and glucose deprivation (OGD) protected SH-SY5Y cells and murine primary cortical neurons more markedly than did ACS48 or memantine. Glutamate-induced intracellular calcium accumulation in primary cortical neurons were aggravated by sodium sulfide (Na(2)S) or ACS48, but suppressed by memantine and S-memantine. S-memantine prevented glutamate-induced glutathione depletion in SH-SY5Y cells more markedly than did Na(2)S or ACS48. Administration of S-memantine after global cerebral ischemia and reperfusion more robustly decreased cerebral infarct volume and improved survival and neurological function of mice than did ACS48 or memantine. These results suggest that an H(2)S-releasing NMDAR antagonist derivative S-memantine prevents ischemic neuronal death, providing a novel therapeutic strategy for ischemic brain injury.

H2S-Induced sulfhydration of the phosphatase PTP1B and its role in the endoplasmic reticulum stress response

Although originally considered toxic, hydrogen sulfide (H(2)S) has been implicated in mediating various biological processes. Nevertheless, its cellular targets and mode of action are not well understood. Protein tyrosine phosphatases (PTPs), which regulate numerous signal transduction pathways, use an essential cysteine residue at the active site, which is characterized by a low pK(a) and is susceptible to reversible oxidation. Here, we report that PTP1B was reversibly inactivated by H(2)S, in vitro and in cells, through sulfhydration of the active-site cysteine residue. Unlike oxidized PTP1B, the sulfhydrated enzyme was preferentially reduced in vitro by thioredoxin, compared to glutathione or dithiothreitol. Sulfhydration of PTP1B in cells required the presence of cystathionine γ-lyase (CSE), a critical enzyme in H(2)S production, and resulted in inhibition of phosphatase activity. Suppression of CSE decreased H(2)S production and decreased the phosphorylation of tyrosine-619 in PERK [protein kinase-like endoplasmic reticulum (ER) kinase], thus reducing its activation in response to ER stress. PERK, which phosphorylates the eukaryotic translational initiation factor 2, leading to attenuation of protein translation, was a direct substrate of PTP1B. In addition, CSE knockdown led to activation of the nonreceptor tyrosine kinase SRC, previously shown to be mediated by PTP1B. These effects of suppressing H(2)S production on the response to ER stress were abrogated by a small-molecule inhibitor of PTP1B. Together, these data define a signaling function for H(2)S in inhibiting PTP1B activity and thereby promoting PERK activity during the response to ER stress.